Нанокомпозит на основе сульфида мышьяка в пористом стекле: фотоиндуцированные эффекты и влияние наночастиц золота тема диссертации и автореферата по ВАК РФ 00.00.00, кандидат наук Альхалил Джордж

• Альхалил Джордж
• кандидат наук
• 2023

Оглавление диссертации кандидат наук Альхалил Джордж

Реферат

Synopsis

Introduction

Chapter 1. Chalcogenide glasses - Photoinduced phenomena

1.1. Introduction to Chalcogenide glasses

1.1.1. The Structure of Chalcogenide Glasses

1.1.2. Optical properties

1.1.3. Photoinduced Phenomena

1.2. Photoinduced Phenomena classified by their mechanism

1.2.1. Photodecomposition

1.2.2. Photocrystallization or (amorphization)

1.2.3. Photopolymerization

1.2.4. Photovaporization

1.3. Photoinduced Phenomena classified by their observed effect

1.3.1. Photoinduced volume changes (contraction or expansion)

1.3.2. Photo-Induced Anisotropy

1.3.3. Photodarkening and Photobleaching

1.4. Photoinduced phenomena of materials at the nanoscale

1.5. Theories of photoinduced phase transition

1.6. Conclusion

Chapter 2. Experimental section

2.1. Materials

2.2. Synthetic methods

2.2.1. Porous glasses fabrication

2.2.2. As2S3 doped in porous glasses

2.2.3. As2S3-Au doped in porous glasses

2.3. Method for investigating the As2S3-Au complex formation

2.4. Methods for investigating the structure and composition of the samples

2.5. Methods for investigating the photoinduced phenomena of the samples

2.6. Quantum chemical calculations

Chapter 3. Synthesis and characterization of As2S3-Au impregnated in porous glasses

3.1. Introduction

3.2. Porous glass structure

3.3. As2S3-Au complex formation

3.4. Synthesis of As2S3 and As2S3-Au doped in porous glasses

3.5. Compositional analysis of As2S3 and As2S3-Au doped in porous glasses

3.6. Conclusion

Chapter 4. Photoinduced phenomena observed in As2S3 impregnated in porous glasses

4.1. Introduction

4.2. Bandgap energy dependence on the annealing temperature

4.3. Refractive index measurement

4.4. Characterization and Comparison of As2S3-doped Porous Glass and Thin Films

4.5. Specifics of Photobleaching in As2S3-PG

4.5.1. Dependence on the As2S3 concentration

4.5.2. Reversibility of the phase transition

4.5.3. Dynamics of phase transition

4.6. Arrhenius activation energy of the thermal induced transition

4.7. Anisotropic photoinduced changes

4.8. Photoluminescence of Arsenic Sulfide Impregnated in Porous Glasses

4.8.1. PL spectra of As2S3-PG

4.8.2. Effects of Gold Nanoparticles and Laser Irradiation

4.9. Optical recording on As2S3-PG

4.10. Conclusion

Chapter 5. Structural Transformations: Experimental and Quantum Chemical Modeling Study

5.1. Introduction

5.2. Structural investigation using Raman spectroscopy

5.3. Quantum chemical modeling-computational methodology

5.4. Raman spectra for over-stoichiometric As-rich molecules

5.5. Network to cage-like molecules photoinduced transformations

5.6. Conclusion

Conclusions

Acknowledgment

List of abbreviations

References

Appendix A. Texts of author's main publications

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Общая характеристика диссертации

Введение диссертации (часть автореферата) на тему «Нанокомпозит на основе сульфида мышьяка в пористом стекле: фотоиндуцированные эффекты и влияние наночастиц золота»

Актуальность темы работы

Халькогенидные стекла становятся все более важным классом материалов благодаря своим перспективным физическим и оптическим свойствам [1]. Среди халькогенидных материалов особенно уникальным является сульфид мышьяка (Аб28з), который привлек множество применений, таких как генерация суперконтинуума, инфракрасные оптические волокна и среда для оптической записи. [2-4]. Аб28з также использовался для других применений, таких как генерация второй гармоники в термополированных стеклах, генерация коррелированных пар фотонов в планарных волноводах и широкополосное каскадное четырехволновое смешение [57]. Кроме того, двумерные (2D) слои Аб23з продемонстрировали высокоанизотропные механические и оптические свойства, с удлинением, превышающей удлинение графена [8].

Фотоиндуцированные эффекты (ФЭ) в Аб28з были широко исследованы и представляют значительный интерес [9-12]. Хотя ФЭ являются преимущественным свойством в определенных областях применений, таких как оптическая запись фотонных структур, они могут быть нежелательным атрибутом в других областях, требующих стабильного материала, например, в оптических волокнах. На ФЭ в Аб28з могут влиять несколько факторов, включая состав (АбхЗш-х), термическую историю, метод приготовления и длину волны облучения. [12-16]. Кроме того, ФЭ, возникающие в материале, могут отличаться в зависимости от размера материала, например, объемное стекло, тонкие пленки и нанослои [17,18].

Развитие нанофотонных технологий требует понимания свойств материалов в наноразмерном состоянии. На данном масштабе материалы проявляют уникальные физические, химические, механические и оптические свойства, вызывающие привлекательность в различных областях применений.

Танака и др. первыми изучали и наблюдали аномальные фотоиндуцированные эффекты, проявляющиеся в нано размерном состоянии [19]. В частности, данные исследователи изучали влияние толщины пленки на фотопотемнение в аморфных пленках As-S и As-Se. Авторы показывали, что фотопотемнение уменьшается с уменьшением толщины пленки, полностью исчезая при толщине пленки менее 50 нм. Предлагается два варианта для интерпретации представленного наблюдения. Первый — структура пленок зависит от их толщины. Второй —фотопотемнение на поверхности пленки отличается от основной ее массы. В более позднем исследовании Хаяши и Мицуиши подтвердили наблюдаемое явление и приписали его напряжению, вызванному несоответствием решеток между пленкой и подложкой. Данное напряжение может стать более значительным в нанослоях материала и может потенциально привести к изменениям в структуре и в свойствах пленки. [20]. В обеих упомянутых работах изучалось фотоиндуцированное поведение пленок с минимальной толщиной около 30 нм, однако не рассматривалось поведении пленок меньшего размера. Данное ограничение послужило первым мотивом для настоящего исследования, в котором основное внимание уделяется изучению оптических свойств нанокомпозита на основе As2S3 с размером меньше 30 нм.

Допирование сульфида мышьяка другими материалами изучалось как метод воздействия на его ФЭ. Предыдущие эксперименты были посвящены влиянию легирования серебром на ФЭ As2Sз, которое, как было показано, увеличивает стабильность системы за счет уменьшения ее общей свободной энергии [21,22]. Сравнение стабильности структур Ag-As2Sз и Cu-As2Sз показало, что первая структура является более стабильной [21]. Кроме того, ранние исследования показывали, что при внедрении слоя наночастиц золота (AuNPs) под тонкие пленки As2Sз или (AgзAsSз)o.6(As2Sз)o.4 обнаруживается усиление их ФЭ [23,24]. Однако влияние AuNPs на оптические свойства As2S3 было изучено в тонких пленках, в наночастицах As2Sз оно не исследовалось.

Актуальность данной диссертации заключается в синтезе, характеризации и исследовании изменения оптических свойств нанокомпозита на основе сульфида мышьяка, что может расширить наши знания об оптических свойствах данного уникального материала в нано размерном состоянии. В настоящей работе исследуется фотоиндуцированный эффект сульфида мышьяка, импрегнированного в нанопористое стекло, и его влияние на оптические свойства материала. Также исследуется влияние введения наночастиц золота на оптические свойства материала. Предлагаются области применения, показывающие потенциальную возможность записи фотонной структуры на полученном композите.

Целью данного исследования является разработка физико-химического подхода для изготовления нового нанокомпозита на основе сульфида мышьяка и анализ его оптических свойств, фотоиндуцированных эффектов, а также влияния наночастиц золота на его свойства и структуру.

Для достижения поставленной цели в рамках диссертации были поставлены и решены следующие задачи:

• Разработка методики изготовления нанокомпозитов на основе наночастиц сульфида мышьяка, наночастиц золота, импрегнированных в пористые стекла.

• Оценка взаимодействия между наночастицами сульфида мышьяка и золота в растворах, используемых для изготовления нанокомпозита.

• Изучение состава, оптических свойств, и фотоиндуцированных структурных превращений полученных нанокомпозитных материалов, в том числе при термической обработке; и установление особенностей этих процессов.

• Оценка влияния наночастиц золота на фотоиндуцированные изменения и оптические свойства нанокомпозита.

• Выполнение оптической записи фотонной структуры на полученном нанокомпозите.

• Экспериментальное изучение фотоиндуцированных структурных превращений As-S с помощью спектроскопии комбинационного рассеяния света и теоретическое исследование молекулярной структуры сульфида мышьяка As-S с помощью ab initio квантово-химических расчетов.

Научная новизна диссертации отражена в следующих пунктах:

• Предложена методика изготовления нанокомпозитов сульфида мышьяка и сульфида мышьяка с золотом на основе пористого стекла.

• Установлен механизм образования комплексов между сульфидом мышьяка и наночастицами золота.

• В нанокомпозите сульфида мышьяка обнаружен уникальный эффект фотообесцвечивания. Данный эффект противоположен фотопотемнению, обычно наблюдаемому в объемных стеклах и тонких пленках As2S3. Эффект фотообесцвечивания значителен, и он составляет до 0.47 эВ увеличения энергии запрещенной зоны. Данный эффект характеризуется синим сдвигом в спектре пропускания, и имеет обратимый характер путем термической обработки.

• Изучены особенности фотоиндуцированного эффекта, включая зависимость от концентрации As2S3, температуры отжига, интенсивности облучения, кинетики фазового перехода, обратимости, энергии активации Аррениуса, и влияния введения наночастиц золота. Также исследовано влияние облучения на фотолюминесценцию As^-допированных пористых стекол.

• Предложена модель, основанная на измерениях спектроскопии комбинационного рассеяния и квантово-химических расчетах для объяснения фотоиндуцированных структурных изменений.

Теоретическая значимость проведенного исследования заключается в доказательстве регулируемости оптических свойств нанокомпозита сульфида мышьяка в широком диапазоне (2 - 2.68 эВ) путем облучения и нагревания. Также значимость заключается в доказательстве того, что эффект фотообесцвечивания,

наблюдаемый в сульфиде мышьяка, объясняется переходом от сетевой к молекулярно-подобной структуре, сопровождающимся кристаллизацией.

Практическая значимость проведенного исследования заключается в разработке новой методики синтеза нанокомпозита на основе пористого стекла наночастиц сульфида мышьяка и наночастиц золота с перестраиваемыми оптическими свойствами, управляемыми светом или термической обработкой, и имеющими потенциал для использования в качестве функциональных компонентов при разработке и производстве фотонных устройств и систем. Основные положения, выносимые на защиту:

1. При облучении сульфида мышьяка, импрегнированного в нанопористое стекло, лазерным лучом с длиной волны 532 нм и с интенсивностью 500 мВт/см2 в течение 60 минут сдвигает его край оптического поглощения в сторону более высоких энергий на 0.28-0.47 эВ. Фотоиндуцированный сдвиг края оптического поглощения обратим термической обработкой при 190 °С.

2. Наблюдается анизотропия показателя преломления для облученного сульфида мышьяка, импрегнированного в нанопористое стекло, при этом разница в показателе преломления на длине волны 787 нм составляет 6*10-5. Введение в композит наночастиц золота снижает анизотропный эффект материала на 80%.

3. При взаимодействии наночастиц сульфида мышьяка и наночастиц золота образуются комплекс, в котором из-за перераспределения электронной плотности между двумя материалами происходит подавление локализованного плазмонного резонанса в наночастицах золота и тушение возбужденных состояний в сульфиде мышьяка, что приводит к снижению интенсивности его фотолюминесценции на 40% и 30% для возбуждения при 405 нм и 514 нм, соответственно.

4. Фотоиндуцированные структурные преобразования наночастиц сульфида мышьяка, импрегнированного в пористое стекло, обусловлены как переходом структурных элементов из аморфного в кристаллическое состояние. При этом

образуются кластеры, составы которых обогащены мышьяком, и имеющие

структуру AS4S1, R-AS4S2, Z-AS4S3, P-AS4S4, и R-AS4S4.

Апробация результатов работы

Основные результаты исследований были представлены и обсуждены на следующих конференциях:

XLVIII Scientific and educational conference, ITMO UniverSity, RuSSia (2019); Conference "BaSic ProblemS of OpticS" BPO, ITMO UniverSity, RuSSia (2019); 21St International Conference on Advanced LaSer TechnologieS, Prokhorov General PhySicS InStitute of RuSSian Academy of ScienceS, RuSSia (2021); XI CongreSS of Young ScientiStS (KMU), ITMO UniverSity, RuSSia (2022); XLX Scientific and educational conference, ITMO UniverSity, RuSSia (2022); Smart CompoSiteS International School, Immanuel Kant Baltic Federal UniverSity, RuSSia (2022).

Достоверность полученных результатов обусловлена тем, что в работе использованы надежные и проверяемые синтетические методы, стандартизированные методы определения характеристик материалов, теоретические и вычислительные модели, признанные и принятые научным сообществом. Кроме того, результаты, достигнутые данным исследованием, были подтверждены в ходе их рецензирования по процессу публикации в высокорейтинговых рецензируемых научных журналах.

Личный вклад автора

Личный вклад автора заключается в постановке научных задач и целей исследований. Все теоретические и экспериментальные исследования проведены автором лично или при его определяющем участии. Автор также сыграл главную роль в публикации научных работ, проведенных в данной диссертации.

Структура и объем диссертации

Диссертация состоит из введения, пяти глав, заключения и списка литературы. Объем диссертации составляет 243 страниц, включая библиографию из 167 ссылок. Работа содержит 42 рисунка и 10 таблиц.

Основное содержание работы

Первая глава представляет собой обзор литературы, включающий краткое описание халькогенидных стекол. Приводятся определение, классификация и различные оптические свойства халькогенидных стекол с акцентом на стекло As2S3. В главе освещаются различные фотоиндуцированные эффекты, наблюдаемые в халькогенидных стеклах в целом и As2S3 в частности. Кроме того, в ней обобщены некоторые факторы, которые могут влиять на фотоиндуцированные эффекты As2S3, такие как состав AsxSioo-x, термическая история, метод приготовления, длина волны облучения и легирование другим материалом. В конце главы рассматриваются различные теоретические подходы, предложенные и используемые для описания фотоиндуцированных и термоиндуцированных эффектов.

Во второй главе представлены материалы и методы, использованные для получения необходимых экспериментальных образцов, и для определения их характеристик. В данной главе описаны синтетические методы, использованные для получения пористых стекол, легированных As2S3 и As2S3-Au. Пористые стекла были получены путем подвергания натриево-боросиликатных стекол кислотной обработке с последующей сушкой. Пористые стекла, допированные As2S3, были приготовлены путем растворения As2S3 в пропиламине, добавления в раствор пористых стекол и последующего отжига. Взаимодействие между AuNPs и As2S3 было изучено с помощью спектров поглощения в видимой области и инфракрасного спектра. Поверхность и состав образцов были проанализированы с помощью атомно-силовой микроскопии, сканирующей электронной микроскопии с энергодисперсионной рентгеновской спектроскопией и вторично-нейтральной масс-спектрометрии. Энергия запрещенной зоны образцов была рассчитана с помощью программы PARAV-V2.0. Фотоиндуцированные эффекты в образцах были изучены экспериментально с помощью спектров оптического пропускания и спектроскопии комбинационного рассеяния света, а также теоретически с помощью ab initio

квантово-химического моделирования с использованием программного пакета 0ашв1ап-09.

В третьей главе рассматривается синтез и характеристика пористых стекол, допированных лб283 и наночастицами Аи. Объясняется уникальная структура пористых стекол, их высокая площадь поверхности и средняя пористость. Исследуется образование комплексов АБ23з-Аи. В главе подробно описаны методы синтеза, и методы анализа состава образцов, такие как энергодисперсионная рентгеновская спектроскопия (EDX), и вторичная нейтральная масс-спектрометрия (БКМБ).

Поверхность пористых стекол была исследована с помощью атомно-силового микроскопа (АСМ), а распределение размеров пор было определено путем анализа АСМ-изображения. Результаты показали равномерное распределение пор со средним размером пор в пределах 18-28 нм.

О 5 10 15 20 25 30 35 40 45 50 Роге сНатйсг (пт)

Рисунок 1 - Поверхности пористых стекол. (а) АСМ микрофотография поверхности пористого стекла и (Ь) Распределение размеров пор

Процесс создания композита Лв23з-Ли-РО включал смешивание растворов лб23з и ЛиКРБ, что привело к изменению цвета, которое было вызвано взаимодействием между двумя типами наночастиц [25]. Однако плазмонный пик ЛиКРБ не изменил своего положения, он стал менее отчетливым на коротковолновой стороне при

смешивании с лб283. Данное наблюдение свидетельствует о том, что наночастицы сохранили свой средний размер и не агрегировались.

Подавление плазмонного резонанса обусловлено сильной связью полупроводник-металл между лб283 и Ли. Данная связь приводит к делокализации электронов плазмы и подавлению плазмонного резонанса, что также наблюдалось в других коллоидных нанокомпозитах [26].

516

400 425 450 475 500 52Ъ 550 575 600 525 650 В75 700 725 750 775 \Vavclcngth (шп)

Рисунок 2 - Видимые спектры поглощения ЛБ^з-пропиламина (зеленая кривая), ЛиКРБ, диспергированных в толуоле (синяя кривая) и их смеси непосредственно после смешивания (красная кривая) и после стабилизации цвета (черная кривая)

Для изучения взаимодействия между лб283 и ЛиКРБ были проведены измерения спектров ИК поглощения.

\\'ауспитЬсг (ст )

Рисунок 3 - ИК спектры пропиламина и растворов ЛБ283-пропиламина

Когда лб28з растворяется в пропиламине, атом серы замещается алкиламиновой группой пропиламина. Атом водорода из алкил-аминовой группы мышьяка приводит к образованию группы ККН3+. Данная группа соединяется с отрицательно заряженной атомами серы [27]. Полагается, что при смешивании растворы ЛиКР и лб283 были взаимодействие начинается с электростатического связывания между группой КН3+ из кластеров пропиламина-ЛБ283 и группой С-Б- на поверхности ЛиКР. Данное явление приводит к увеличению числа отрицательно заряженных групп связей Б на поверхности ЛиКР, которые впоследствии ковалентно соединяются с ЛиКР. Сборка кластеров лб283 вокруг ЛиКРБ приводит к значительному увеличению колебания группы КН3+ [28]. ИК спектр смешанного раствора подтверждает данное положение. Схема предполагаемого взаимодействия между лб283 и ЛиКРБ представлена на Рисунок 6.

Рисунок 4 - ИК спектры функционализированного ЛиКРБ

\Vavcnunibcr (ст )

толуольного раствора и додеканэтиол-

3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800

\УауепитЬег (ст )

Рисунок 5 - ИК спектры сухих остатков для толуольного раствора и додеканэтиол-функционализированных ЛиКРБ, растворенных в толуоле после испарения толуола

* = Dodecanethiol ♦ = R-NH34 Рисунок 6 - Схематическая диаграмма As2S3 вытеснения додеканэтиола из AuNPs

SEM_EDX использовался для изучения состава и распределения элементов в различных образцах (AS2S3-PG и AS2S3-AU-PG). Измерения проводились на разных глубинах (на поверхности, на 500 мкм и на 1000 мкм) для определения глубинного профиля атомных соотношений As/S в стекле.

На основании этих измерений была рассчитана концентрация сульфида мышьяка по всей толщине PG путем определения его массы к соотношению массы кремния и кислорода. Распределение концентрации указывает на относительно небольшое изменение в распределении сульфида мышьяка в пористое стекло. Таблица 1 показывает, что отношение As/S выше для образцов, содержащих AuNPs. Кроме того, чем глубже профиль анализа, тем выше отношение As/S в стекле для обоих образцов.

Таблица 1 - Профиль глубины атомного соотношения элементов As/S в стекле

Глубина 0 - 100 цш 400 - 600 цш 900 - 1100 цш Среднее

as2s3-pg as55s46 as56s44 As6lS39 as56s44

AsS/SiO % 2.1 1.7 1.7 1.83

as2s3-au-pg as58s42 as70s30 as75s25 as64s36

AsS/SiO % 2 2 1.6 1.86

В четвертой главе представлены результаты экспериментального исследования. Изучены оптические свойства, а также влияние облучения и отжига на оптические свойства образцов и влияние наночастиц золота на эти свойства.

В полученных нанокомпозитах наблюдался значительный (до 0.47 эВ) и обратимый эффект фотообесцвечивания (синий сдвиг в спектре пропускания, который может быть отменен термической обработкой), что противоположно эффекту, обычно наблюдаемому для объемных стекол и тонких пленок As2S3 (т.е. фотопотемнение) [15].

Влияние температуры отжига на изменение пропускания в образцах нанокомпозита As2S3-PG с концентрацией легирующих элементов 1% было оценено путем измерения спектров пропускания и расчета энергии для запрещенной зоны после отжига при различных температурах вблизи температуры стеклования As2S3 140-250 °С

Энергия запрещенной зоны As2S3-PG уменьшается с увеличением температуры отжига до 190 после чего энергия не меняется. Влияние температуры отжига на энергию запрещенной зоны As2S3-PG объясняется переформированием структуры и, соответственно, изменением в электронных свойствах материала из-за разрыва и реформирования связей и перегруппировки атомов в материале.

Annealing temperature

400 450 500 550 600 650 700 750 800 Wavelength (nm)

И

3 .0 -| 2.92.82.72.62.52.42.32.2-

Temperature (C0)

Рисунок 7 - Спектры пропускания и ширины запрещенной зоны As2S3-PG, отожженных при различных температурах в диапазоне 140-250 ^

70

60

50

40

30

20

10

0

125

150

175

200

225

250

275

Спектроскопическая эллипсометрия была использована для измерения показателя преломления и спектров коэффициента экстинкции чистого пористого стекла, образцов Аб23з-РО и Лв23з-Ли-РО. Результаты показали увеличение показателя преломления как для Аб23з-РО, так и для Лв23з-Ли-РО, причем присутствие ЛиКРБ подтверждается плазмонными особенностями поглощения, наблюдаемыми в спектрах.

Wavelength (nm)

Рисунок 8 - Показатель преломления (сплошные линии) и коэффициент экстинкции (пунктирные линии) чистого PG (черный), AS2S3-PG (красный), AS2S3-AU-PG (зеленый)

Исследовано влияние облучения на спектры оптического пропускания аб28з-допированного пористого стекла (As2Sз-PG) и тонкого слоя аб23з (аб23з-ть). Спектры As2S3-PG и тонкого слоя до и после облучения и отжига, а также спектр чистого пористого стекла были измерены с целью определения энергии запрещенной зоны и энергии Урбаха. Результаты представлены в Таблица 2.

Композит As2S3-PG показал обратимый эффект фотообесцвечивания. Данный эффект отличается от ранее наблюдаемого эффекта фотопотемнения для As2Sз-TL. Фотообесцвечивание ранее наблюдалось в тонких пленках халькогенидов и считалось наноразмерным эффектом из-за увеличенного отношения поверхности к объему.

Размер осажденного материала в данном исследовании был ограничен размером пор, который находится в наноразмерном диапазоне, в связи с этим, наблюдаемое фотообесцвечивание можно объяснить наноразмерным эффектом.

Wavelength (nm)

Рисунок 9 - Спектры оптического пропускания образцов: чистого (недопированного) пористого стекла (1), исходного As2S3-PG (2), облученного As2S3-PG (3), облученного и отожженного As2S3-PG (4), исходного As2S3-TL (5), облученного As2S3-TL (6), облученного и отожженного As2S3-TL (7)

Таблица 2 - Сравнение влияния отжига и освещения на энергию запрещенной зоны и энергию Урбаха для As2S3-PG и As2S3-TL

As2S3-PG As2S3-TL

Eg (эВ) Eu (эВ) Eg (эВ) Eu (эВ)

Первоначальное состояние 2.43 0.313 2.35 0.111

После облучения 2.66 0.304 2.27 0.113

После отжига 2.47 0.322 2.33 0.120

Уменьшение энергии Урбаха, наблюдаемое в As2Sз-PG во время фотоиндуцированных изменений, объясняется уменьшением аморфного состояния и соответствующей плотности локализованных состояний в фазе As2S3 в PG, что

согласуется с изменением ширины запрещенной зоны. Исходное состояние As2S3-PG не было восстановлено после отжига. Следовательно, предполагается, что в фотоиндуцированных превращениях As2S3-PG участвуют обратимые и необратимые изменения.

Для изучения влияния концентрации легирующего элемента As2S3 на фотоиндуцированный сдвиг и влияния наночастиц золота были приготовлены десять образцов с различной концентрацией легирующего элемента As2S3; пять из них содержали AuNPs. Спектры пропускания образцов были измерены до и после облучения лазерным излучением с длиной волны 532 нм в течение 60-90 минут с интенсивностью от 500 до 1000 мВт/см2.

70 60

& 50

ш

о

g 40-Е

ё 30-I-

2010 0

After irradiation

450 500 550 600 650 700 750 800 850 900 950 1000 Wavelength (nm)

Initial

-10

After irradiation --6

--8

--9

--10

450 500 550 600 650 700 750 800 850 900 950 1000

Wavelength (nm)

Рисунок 10 - Спектры оптического пропускания: As2Sз-PG (1-5); (Ь) As2Sз-Au-PG (6-10). До облучения (сплошные кривые); после облучения (пунктирные кривые)

Спектры пропускания были использованы для расчета ширины запрещенной зоны образцов на каждом этапе с помощью метода диаграммы Тауcа. Также для сравнения результатов была построена диаграмма зависимости энергии ширины запрещенной зоны от концентрации легирующего элемента.

Наблюдется меньше энергии запрещенной зоны образцов с допантом As2S3 в пористых стеклах при пропитке AuNPs и As2S3, по сравнению с образцами только с As2S3. Изменение энергии запрещенной зоны увеличивалось с ростом концентрации для образцов без AuNPs, при этом данная зависимость не наблюдалась для образцов

70

60

с AuNPs. Увеличение энергии запрещенной зоны после облучения свидетельствует о структурных преобразованиях упорядоченного типа в молекулах As2S3.

Таблица 3 - Энергии запрещенной зоны As2S3-PG и As2S3-Au-PG

As2S3-PG As2S3-Au-PG

Номер образца 1 2 3 4 5 6 7 8 9 10

Концентрация легирующего элемента % 1.15 1.68 1.9 2 2.45 0.9 1.4 1.75 2.2 2.64

Eg (эВ) Первоначальное состояние 2.4 2.25 2.17 2.11 2 2.45 2.21 2.19 2 2

После облучения 2.68 2.6 2.47 2.48 2.47 2.68 2.61 2.46 2.36 2.4

АЕе (эВ) 0.28 0.35 0.3 0.37 0.47 0.23 0.4 0.27 0.36 0.4

The dopant concentration (%)

Рисунок 11 - Зависимость энергии запрещенной зоны от концентрации легирующего элемента: As2S3-PG (черный); As2S3-Au-PG (красный). До облучения (сплошные линии), после облучения (пунктирные линии)

Обратимость фотоиндуцированных изменений в As2S3-PG была исследована в течение двух циклов облучения и отжига в образцах с AuNPs и без них с концентрацией допанта 1.8%. Спектры пропускания были измерены и использованы для расчета энергии запрещенной зоны, и результаты показали, что

фотоиндуцированные изменения обратимы в течение более чем одного цикла. Обратимость фотоиндуцированных изменений в материале является важным аспектом для потенциального применения в таких областях, как хранение данных и преобразование энергии.

¡п ¡г ап ¡г ап

Process

Рисунок 12 - Энергия запрещенной зоны образцов As2S3-PG и As2S3-Au-PG в течение двух циклов облучения и отжига. "т" - исходный, "к" - облученный и '^п" -отожженный образец

Кинетика фотоиндуцированных изменений была изучена в образцах с AuNPs и без них, концентрация легирующего элемента в обоих случаях составляла 2%. Изменение пропускания со временем измерялось при постоянной мощности облучения для отслеживания временной зависимости фотоиндуцированных изменений. Были использованы три различные мощности облучения 3,5, 2,6 и 1,7 Вт/см2. Результаты представлены на Рисунок 13. Данные показали, что фотообесцвечивание происходило по экспоненциальной схеме, с временной шкалой в несколько минут, что согласуется с предыдущими исследованиями эффектов фотопотемнения [29]. Пропускание сначала резко возрастало, а затем наступала фаза насыщения в течение более длительного времени.

Time (s) Time (s)

Рисунок 13 - Временная зависимость светопропускания As2S3-PG и As2S3-Au-PG (Ь), измеренная при мощностях облучения 3,5 (черный), 2,6 (красный) и 1,7 Вт/см2 (синий), пунктирные линии представляют экспериментальные данные, а сплошные кривые - экспоненциальную подгонку

Сплошные кривые на Рисунок 13 обозначают экспоненциальную аппроксимацию экспериментальных данных для фотоиндуцированных изменений, и описываются (1):

ПО = П«0 -а* ехр (1)

где, a - предэкспоненциальный коэффициент, ^да) - передача после длительного времени облучения, т - характерное время процесса, ив - дробная экспонента.

Таблица 4 - Зависимость времени релаксации от интенсивности облучения, полученная из теоретической подгонки к экспериментальным данным с использованием растянутой экспоненциальной функции с в=0.7

Образец В] ремя релаксации т (s)

3.5 Вт/см2 2.6 Вт/см2 1.7 Вт/см2

As2S3-PG 42 102 240

As2S3-Au-PG 100 170 280

Время релаксации уменьшается с увеличением интенсивности облучения. Образцы с AuNPs имеют более длительное время релаксации. Параметр в является мерой распределения времен релаксации и, как считается, учитывает неоднородность локального окружения. Данный параметр характеризует влияние среды на кинетику реакции при фотоиндуцированных изменениях, и представляет собой распределение высоты потенциального барьера.

Список литературы диссертационного исследования кандидат наук Альхалил Джордж, 2023 год

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26. Khon E. et al. Suppression of the plasmon resonance in Au/CdS colloidal nanocomposites // Nano Lett. American Chemical Society, -2011. -Vol. 11, -№ 4. -P.1792-1799.

27. Johs B., Hale J.S. Dielectric function representation by B-splines // Phys. status solidi. -2008. -Vol. 205, -№ 4. -P. 715-719.

28. Khalkho B.R. et al. Citrate functionalized gold nanoparticles assisted micro extraction of L-cysteine in milk and water samples using Fourier transform infrared spectroscopy // Spectrochim. Acta Part A Mol. Biomol. Spectrosc. -2022. -Vol. 267. -P. 120523.

29. Shimakawa K., Nakagawa N., Itoh T. The origin of stretched exponential function in dynamic response of photodarkening in amorphous chalcogenides // Appl. Phys. Lett. American Institute of PhysicsAIP, -2009. -Vol. 95, -№ 5. -P. 051908.

30. Murayama K., Suzuki H., Ninomiya T. Luminescence and optically detected ESR in a-As2S3 // J. Non. Cryst. Solids. North-Holland, -1980. -Vol. 35-36, -№ PART 2. -P. 915-920.

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Synopsis General thesis summary

Relevance of the chosen topic

Chalcogenide glasses are an increasingly important class of materials due to their promising physical and optical properties [1]. Among chalcogenide materials, arsenic sulfide (As2S3) is particularly unique and has found numerous applications, such as supercontinuum generation, infrared optical fibers and media for optical recording [2-4]. As2S3 has also been used for other applications, such as second harmonic generation in thermally poled glasses, correlated photon-pair generation in planar waveguides, and broadband cascaded four-wave mixing [5-7]. Additionally, two-dimensional (2D) As2S3 layers have shown highly anisotropic mechanical and optical properties with stretchability that exceeds that of graphene [8].

The phenomenon of photoinduced changes (PICs) in As2S3 has been extensively investigated due to its applications in photonics and optoelectronics [9-12]. PICs are a desired property for certain applications, such as optical recording of photonic structures. However, for other applications that require a stable material, such as in optical fibers PICs are considered an unappealing property. The PICs in As2S3 can be influenced by several factors, including the composition (AsxSioo-x), thermal history, preparation method, and irradiation wavelength [12-16]. Additionally, the PICs that occur in the material can vary depending on its dimensions: bulk glass, thin films and nanolayers [17,18].

Advances in nanophotonic and nanofabrication technology require an understanding of the properties of materials at the nanoscale. At the nanoscale, materials exhibit unique physical, chemical, mechanical, and optical properties that make them of great interest for various applications.

Tanaka et al. were the first to study and observe an anomalous photoinduced effect that appears in PICs at the nanoscale [19]. Specifically, they studied the photodarkening in amorphous As-S and As-Se films with different thicknesses. They showed that

photodarkening decreased with decreasing film thickness, disappearing entirely when the films were less than 50 nm thick. This suggests that either the structure of the films depends on their thickness or that the photodarkening effect behaves differently at the surface compared to the bulk of the films. Hayashi and Mitsuishi later confirmed this effect and attributed it to the strain induced by the lattice mismatch between the film and the substrate. This strain which can become more significant in nanolayers potentially lead to changes in the film's structure and properties [20]. Both studies investigated the photoinduced behavior of films with a minimum thickness of around 30 nm, but no reports have been made on the behavior at smaller dimensions. This gives the first motivation for this dissertation which focuses on studying the optical properties of As2S3 nanocomposite with As2S3 dimension beyond 30 nm.

Doping arsenic sulfide with other materials has been studied as a method for influencing its PICs. Previous experiments have focused on the effect of silver doping on the PICs of As2S3, which has been shown to increase the stability of the system by decreasing its total free energy [21,22]. Comparisons between the stability of Ag-As2S3 and Cu-As2S3 structures revealed that the former is more stable [21]. Additionally, introducing a layer of gold nanoparticles (AuNPs) under As2S3 or (Ag3AsS3)0.6(As2S3)0.4 thin films was found to enhance their PICs [23,24]. While the effect of AuNPs on the optical properties of As2S3 was studied in thin films, it hasn't been investigated in As2S3 nanoparticles.

The relevance of this dissertation lies in the synthesis, characterization and manipulation of As2S3 nanocomposite, which expands our knowledge of the optical properties of this material at the nanoscale. The study investigates the photoinduced effect of As2S3 impregnated in nanoporous glass and its influence on the material's optical properties. The impact of introducing gold nanoparticles on the optical properties of the samples is also investigated. Finally, areas of application are proposed by showing the potential for optical recording of photonic structures on the obtained composite.

The goal of this research is to develop a physicochemical approach for the fabrication of new As2S3 nanocomposite and to analyze its optical properties, photoinduced effects, as well as the effect of gold nanoparticles on these properties.

In order to achieve the goal in the framework of the thesis, the following objectives have been established:

• Developing synthetic methods for the fabrication of arsenic sulfide and arsenic sulfide-gold nanocomposite impregnated in porous glass.

• Assessing interparticle interactions between arsenic sulfide and gold nanoparticles in colloidal systems used for the fabrication of arsenic sulfide-gold nanocomposite impregnated in porous glass.

• Studying the composition, optical properties, and photoinduced structural transformations of the obtained nanocomposite materials, including those under thermal treatment, and establishing the peculiarities of these processes.

• Evaluating the impact of gold nanoparticles on the photoinduced changes and optical properties of the nanocomposite.

• Performing optical recording of photonic structures on the obtained nanocomposite.

• Experimentally studying the photoinduced structural transformations of As-S using Raman spectroscopy, and theoretically investigating the molecular structure of arsenic sulfide As-S through ab initio quantum chemical calculations.

Novelty of research is reflected in the following:

• A novel physicochemical method for fabricating arsenic sulfide and arsenic sulfidegold nanocomposites using porous glasses has been proposed.

• A mechanism for the formation of complexes between arsenic sulfide and gold nanoparticles has been established.

• A unique photobleaching effect was revealed in arsenic sulfide nanocomposite which is opposite to the photodarkening typically seen in As2S3 bulk glasses and thin films. The photobleaching effect is significant and represent up to 0.47 eV increase in the

bandgap energy. This effect is characterized by a blue shift in the transmission spectrum, which can be reversed through thermal treatment.

• The specificities of the photoinduced effect were studied, including the dependence on As2S3 concentration, annealing temperature, irradiation intensity, kinetics of phase transition, reversibility, Arrhenius activation energy, and the influence of introducing gold nanoparticles. The effect of irradiation on the photoluminescence spectra of As2S3-doped porous glasses was also investigated.

• A model was proposed based on Raman spectroscopy measurements and ab initio quantum chemical calculations to explain the photoinduced structural changes.

The theoretical significance of the conducted research lies in proving the adjustability of the optical properties of arsenic sulfide nanocomposite over a broad range (2 - 2.68 eV) by irradiation and thermal treatment. The significance also lies in proving that the photobleaching effect observed in arsenic sulfide is attributed to the transition from a network to a molecular-like structure accompanied by crystallization.

The practical significance of the conducted research lies in the development of novel physicochemical method for the synthesis of arsenic sulfide and arsenic sulfide-gold nanocomposite with tunable optical properties that can be controlled by light and thermal treatment and have the potential to be used as functional components in the engineering and manufacturing of photonic devices and systems. Assertions that are presented for defense:

1. Irradiating arsenic sulfide impregnated in nanoporous glass by a laser beam at 532 nm with the intensity of 500 mW/cm2 for 60 minutes shifts its optical absorption edge towards the higher energies by 0.28-0.47 eV. The photoinduced shift in the optical absorption edge is reversible by thermal treatment at 190 °C.

2. Photoinduced change in the refractive index of arsenic sulfide impregnated in nanoporous glass is anisotropic and accompanied by 6*10-5 difference in the refractive index at 787 nm between parallel and perpendicular component of polarization

relative to the polarization of laser irradiation. Introducing gold nanoparticles to the composite reduces the anisotropic response of the material by 80%.

3. When mixing solutions of arsenic sulfide and gold nanoparticles they interact and form complexes. The strong metal-semiconductors coupling between the two materials leads to the suppression of the plasmonic resonance in gold nanoparticles and the quenching of excited states in arsenic sulfide. The later decreases the photoluminescence intensity of arsenic sulfide by 40%, 30% for excitation at 405 nm, 514 nm, respectively.

4. Photoinduced structural transformations of arsenic sulfide impregnated in nanoporous glass are attributed to transition from a network to a molecular structure accompanied by crystallization. Irradiation results in the formation of As-rich clusters, As4S1, R-As4S2, Z-As4S3, P-As4S4, and R-As4S4.

Approbation of research results

Key research results were presented and discussed at the following conferences: XLVIII Scientific and educational conference, ITMO University, Russia (2019); Conference "Basic Problems of Optics" BPO, ITMO University, Russia (2019); 21st International Conference on Advanced Laser Technologies, Prokhorov General Physics Institute of Russian Academy of Sciences, Russia (2021); XI Congress of Young Scientists (KMU), ITMO University, Russia (2022); XLX Scientific and educational conference, ITMO University, Russia (2022); Smart Composites International School, Immanuel Kant Baltic Federal University, Russia (2022).

The accuracy of the obtained results is achieved through the use of verifiable and reliable synthetic methods, characterization techniques, and theoretical and computational models that are recognized by and accepted throughout the scientific community. Additionally, the results were validated during the publication process where scientific peers examined, reviewed, and accepted the work that was presented.

Personal contribution of the author

The author's personal contribution lies in the formulation of the research scientific problem and goals. All theoretical and experimental studies were carried out by the author personally or with his decisive participation. The author also played a major role in the publication of the scientific results found in this dissertation.

Thesis structure and number of pages

This thesis consists of an introduction, five chapters, a conclusion, and a list of references. The dissertation is 243 pages, including a bibliography of 167 references. The work contains 42 figures and 10 tables.

Main contents of the work

The first chapter is a literature review that includes a brief summary of chalcogenide glasses. The definition and classification of chalcogenide glasses, in addition to their different optical properties are provided with a focus on As2S3 glass. The chapter highlights the different photoinduced effects observed in chalcogenide glasses in general and in As2S3 in particular. Furthermore, it summarizes the several factors that can influence the photoinduced effects of As2S3, such as the composition AsxS100-x, thermal history, preparation method, irradiation wavelength, and doping with other material. Finally, the different theoretical approaches used to describe the photoinduced and thermally induced effects are explored.

The second chapter presents the materials and methods used to obtain the necessary experimental samples and to determine their characteristics. This chapter describes the synthetic methods used to obtain As2S3 and As2S3-Au doped porous glasses. The porous glasses were prepared by subjecting sodium-borosilicate glasses to an acidic treatment followed by drying. The As2S3 doped porous glasses were prepared by dissolving As2S3 in propylamine and adding the porous glasses to the solution, with a following annealing. The interaction between AuNPs and As2S3 was studied using visible absorption spectra and Fourier transform infrared (FTIR) absorption spectra. The surface and composition of the samples were analyzed using atomic force microscopy, scanning electron microscopy with

energy dispersive X-ray spectroscopy, and secondary neutral mass spectrometry. The bandgap energy of the samples was calculated using PARAV-V2.0 software. The photoinduced phenomena of the samples were studied experimentally using optical transmission spectra and Raman spectroscopy, and theoretically using ab initio quantum chemical modelling via the Gaussian-09 program package.

The third chapter discusses the synthesis and characterization of porous glasses doped with As2S3 and Au nanoparticles. It explains the unique structure of porous glasses, their high surface area and average porosity. The formation of As2S3-Au complexes is explored. The chapter details the synthesis methods and materials used, as well as the used compositional analysis techniques: Energy-dispersive X-ray spectroscopy (EDX), Secondary neutral mass spectrometry (SNMS), etc.

The surface of porous glasses was examined using an atomic force microscope (AFM), and the distribution of pore sizes was determined through analysis of the AFM image. The results showed a uniform pore distribution pattern with an average pore size between 18-28 nm.

Pore diameter (nm)

Figure 1 - Surfaces of the porous glasses. (a) AFM micrograph of the PG surface and (b) PG pore size distribution

The process of creating an As2S3-Au-PG composite involved mixing solutions of As2S3 and AuNPs, which resulted in a color change. This change is assumingly attributed to an interaction between the two types of nanoparticles [25]. The plasmonic peak of the AuNPs

did not change position but became less distinct on the short wavelength side when mixed with As2S3, suggesting that the nanoparticles retained their average size and did not aggregate.

Wavelength (nm)

Figure 2 - Visible absorption spectra of As2S3-propylamine (green curve), AuNPs dispersed in toluene (blue curve), and their mixture directly after mixing (red curve), and after colour stabilization (black curve)

The suppression of the plasmonic resonance is due to the strong semiconductor-metal coupling between As2S3 and AuNPs. This coupling leads to the delocalization of plasma electrons and the suppression of the plasmonic resonance. It has also been observed in other colloidal nanocomposites [26].

FTIR absorption spectra measurements were conducted to study the interaction between As2S3 and AuNPs. When As2S3 is dissolved in propylamine, a sulfur atom is replaced by the alkyl amine group of propylamine. The extra hydrogen from the arsenic alkyl ammonium group leads to the formation of an RNH3+ group, which then bonds to the negatively charged dangling sulfur bond [27]. When the AuNP and As2S3 solutions are mixed, it is believed that the interaction starts with electrostatic binding between the NH3+ group from propylamine-As2S3 clusters and the C-S- group on the AuNP surface. This leads to an increase in the number of negatively charged S dangling bonds on the AuNP surface,

which later covalently bond to AuNPs. The assembly of As2S3 clusters around the AuNPs results in a significant increase in NH3+ resonance light scattering [28]. The FTIR spectrum of the mixed solution supports this hypothesis. A schematic diagram of the suggested interaction between As2S3 and AuNPs is presented in Figure 6.

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Figure 3 - FTIR spectra of propylamine and As2S3-propylamine solutions

Wavenumber (cm )

Figure 4 - FTIR spectra of toluene solution and dodecanethiol-functionalized AuNPs

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Wavenumber (cm1)

Figure 5 - FTIR spectra of toluene solution and dodecanethiol-functionalized AuNs dissolved in toluene after toluene evaporation

* - Dodecanethiol ♦ = R-NH3+ Figure 6 - Schematic diagram of As2S3 displacing dodecanethiol from AuNPs

SEM_EDX was used to examine the composition and the distribution of elements in different samples (As2S3-PG and As2S3-Au-PG). Measurements were taken at different depths (at the surface, at 500 ^m, at 1000 ^m) to determine the depth profile of As/S atomic ratios in the glass.

Based on these measurements, the concentration of arsenic sulfide was calculated throughout the thickness of PG by determining the ratio of its mass to silicon and oxygen mass. This indicates a relatively small variation in the distribution of arsenic sulfide in the porous glass. Table 1 shows that the As/S ratio is higher for samples containing AuNPs.

Additionally, the deeper the analysis profile, the higher the As/S ratio in the glass for both samples.

Table 1 - Atomic ratio depth profile of As/S elements in the glass

Depth 0 - 100 ^m 400 - 600 ^m 900 - 1100 ^m Average

As2S3-PG As55S46 As56S44 As61S39 As56S44

AsS/SiO % 2.1 1.7 1.7 1.83

As2S3-Au-PG As58S42 As70S30 As75S25 As64S36

AsS/SiO % 2 2 1.6 1.86

The fourth chapter presents the results of the experimental study. The optical properties as well as the effect of irradiation and annealing on the optical properties of the samples and the effect of gold nanoparticles on these properties are studied.

In the obtained nanocomposites a significant (up to 0.47 eV) and a reversable photobleaching effect (a blue shift in the transmission spectrum that can be reversed by thermal treatment) was observed. This is opposite to the effect usually observed for As2S3 bulk glasses and thin films (i.e., photodarkening.) [15].

The effect of annealing temperature on the bandgap energy of as-prepared As2S3-PG with a 1% dopant concentration was evaluated. The transmission spectrum was measured and the bandgap energy was calculated after annealing at different temperatures near the glass transition temperature of As2S3 140-250 °C. The bandgap energy of As2S3 decreases with increasing annealing temperature up to 190 °C, and after that it remains constant. This change in the bandgap is attributed to changes in the structure and electronic properties of the material, which take place due to the breaking and reforming of bonds and the rearrangement of atoms in the material.

Annealing temperaturi

3.0 -1 2.9 2.82.7 2.62.5 2.42.32.2

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Wavelength (nm)

Temperature (C0)

Figure 7 - The transmission spectra and the band gap energies of as-prepared As2S3-PG annealed at different temperatures in the range 140-250 °C

Spectroscopic ellipsometry was used to measure the refractive index and extinction coefficient spectra of pure porous glass, As2S3-PG, and As2S3-Au-PG samples. The results showed an increase in the refractive index for both As2S3-PG and As2S3-Au-PG. The presence of AuNPs was confirmed by plasmonic absorption features observed in the spectra.

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-PG-As2S3 -PG-As2SrAu

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Figure 8 - Refractive index (solid lines), and extinction coefficient (dotted lines) of pure PG (black), As2S3-PG (red), As2S3-Au-PG (green)

The effect of irradiation on the optical transmission spectra of As2S3-doped porous glass (As2S3-PG) and As2S3 thin layer (As2S3-TL) was investigated. The spectra of As2S3-PG and the thin layer before and after irradiation and annealing, as well as the spectrum of pure PG were measured and utilized to determine the bandgap energy and Urbach energy. The results are presented in Table 2.

Wavelength (nm)

Figure 9 - Optical transmission spectra of the samples: pure (undoped) porous glass (1), initial As2S3-PG (2), irradiated As2S3-PG (3), irradiated and annealed As2S3-PG (4), initial As2S3-TL (5), irradiated As2S3-TL (6), irradiated and annealed As2S3-TL (7)

Table 2 - Comparison of the influence of annealing and illumination on the bandgap energy and Urbach energy of As2S3-PG and As2S3-TL

AS2S3-PG AS2S3-TL

Eg (eV) Eu (eV) Eg (eV) Eu (eV)

Initial 2.43 0.313 2.35 0.111

After irradiation 2.66 0.304 2.27 0.113

After annealing 2.47 0.322 2.33 0.120

The As2S3-PG composite showed a reversible photobleaching effect (PB). This effect is different from the previously observed photo-darkening effect for As2S3-TL. The PB effect was previously observed in chalcogenide thin films and was thought to be a nanoscale effect

due to the increased surface-to-volume ratio. The size of the deposited material in this study was limited to the size of the pores, which is in the nanometer range, and this may explain the observed reversible PB effect as a nanoscale effect.

The decrease in Urbach energy observed in As2S3-PG during photoinduced changes is attributed to a decrease in amorphous state and in related density of localized states within the As2S3 phase in PG. The initial state of As2S3-PG could not be restored after annealing which suggests that both reversible and irreversible changes are involved in the photoinduced transformations of As2S3-PG.

Ten samples with varying As2S3 dopant concentrations (five of them containing AuNPs) were prepared to explore the effect of As2S3 dopant concentration on the photoinduced shift and the influence of introducing gold nanoparticles. The transmission spectra of the samples were measured before and after irradiation with laser light of 532 nm wavelength for 60 to 90 minutes with intensity ranging from 500 to 1000 mW/cm2.

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Figure 10 - Optical transmission spectra of: (a) As2S3-PG (1-5); (b) As2S3-PG -Au (6-10). Before irradiation (solid curves); after irradiation (dashed curves)

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The transmission spectra were used to calculate the bandgap energies of the samples at each stage using the Tauc plot method. The bandgap energy was plotted as a function of the dopant concentration to compare the results.

Table 3 - AS2S3-PG and AS2S3-AU-PG bandgap energies

AS2S3-PG AS2S3-AU-PG

Sample number 1 2 3 4 5 6 7 8 9 10

The dopant concentration % 1.15 1.68 1.9 2 2.45 0.9 1.4 1.75 2.2 2.64

Eg (eV) Initial 2.4 2.25 2.17 2.11 2 2.45 2.21 2.19 2 2

After irradiation 2.68 2.6 2.47 2.48 2.47 2.68 2.61 2.46 2.36 2.4

AEg (eV) 0.28 0.35 0.3 0.37 0.47 0.23 0.4 0.27 0.36 0.4

The dopant concentration (%)

Figure 11 - Bandgap energy versus dopant concentration of: AS2S3-PG (black); AS2S3-AU-PG (red). Before irradiation (solid lines), after irradiation (dashed lines)

The bandgap energy of samples with As2S3 dopant in PG was smaller when impregnated with both AuNPs and As2S, compared to samples with only As2S3. The change in bandgap energy increased with higher concentrations for samples without AuNPs, but this dependence was not observed in samples with AuNPs. The increase in bandgap energy after irradiation suggests ordering-type structural transformations in the As2S3 molecules.

The reversibility of photoinduced changes in As2S3-PG was investigated over two cycles of irradiation and annealing in samples with and without AuNPs with a dopant concentration of 1.8%. The transmission spectra were measured and used to calculate the bandgap energy. The results showed that the photoinduced changes are reversible for more

than one cycle. The reversibility of the photoinduced changes in the material is an important aspect for potential applications in fields such as data storage and energy conversion.

in ir an ir an

Process

Figure 12 - The bandgap energy of AS2S3-PG and AS2S3-AU-PG samples during two cycles of irradiation and annealing. "in" represents initial, "ir" irradiated and "an" annealed sample

The kinetics of photoinduced changes were studied in samples with and without AuNPs, both having a dopant concentration of 2%. The transmittance change over time was measured at a constant irradiation power to monitor the time dependence of the photoinduced changes. Three different irradiation powers of 3.5, 2.6, and 1.7 W/cm2 were employed (the results are presented in Figure 13). The data revealed that PB occurred in an exponentiallike pattern with a time scale of several minutes. This is consistent with previous studies on photodarkening effects [29]. The transmittance increased abruptly at first, followed by a saturation phase at longer times.

The solid curves in Figure 13 show a stretched exponential fit of the experimental data for photoinduced changes. This exponential fit is described by formula (1):

T(t) = 7-(«0 -a* exp (- (1)

where, a is pre-exponential factor, T(^) is the transmission after a long irradiation time, t is characteristic time of the process, and P is fractional exponent.

Time (s) Time (s)

Figure 13 - The time dependence of light transmission of As2S3-PG (a) and As2S3-Au-PG (b) measured with different irradiation powers 3.5 (black), 2.6 (red) and 1.7 W/cm2 (blue), dashed lines represent the experimental data and solid curves the exponential fit

Table 4 - The relaxation time dependence on the irradiation intensity obtained from the theoretical fit to the experimental data using stretched exponential function with P=0.7

Sample Relaxation time r (s)

3.5 W/cm2 2.6 W/cm2 1.7 W/cm2

As2S3-PG 42 102 240

As2S3-Au-PG 100 170 280

The relaxation time decreases with increasing irradiation intensity, and samples with AuNPs have longer relaxation times. The exponent P is a measure of the distribution of relaxation times and is considered to account for the inhomogeneity of the local environments. This suggests dispersive reaction kinetics in photoinduced changes, which can be attributed to the exponential distribution of potential barrier height.

The Arrhenius activation energy is a parameter that describes the temperature dependence of a process in materials science, including chemical reactions and phase transitions in glasses. It is a measure of the energy barrier that must be overcome for the

process to occur. It is determined by measuring the temperature dependence of a property that is sensitive to the relaxation process. The Arrhenius equation shows that the activation energy is a function of temperature, and the higher the activation energy, the slower the reaction rate, and vice versa. The Arrhenius equation has the following form:

where t is the Arrhenius relaxation time, t0 is the relaxation time at a very high temperature, k is Boltzmann constant, T temperature, and AEa is the activation energy which can determine the energy barrier for the thermal transition.

The Arrhenius activation energy was determined by measuring the transmittance of samples, with and without AuNPs, with a dopant concentration of 2% while annealing at 190 °C. A low-intensity green light laser (532 nm) with low intensity to prevent any photoinduced transformations, was used to track changes in transmission.

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Figure 14 - The time dependence of light transmission of As2S3-PG (black) and As2S3-Au-PG (red) measured upon annealing the samples at 190 °C

Figure 14 illustrates that the AS2S3-AU-PG sample had a faster relaxation time of approximately 63 s, compared to that of As2S3-PG — around 135 s. Using formula (2), the Arrhenius activation energy for As2S3-PG and As2S3-Au-PG was calculated. It was found to be 0.18 eV and 0.15 eV, respectively.

The lower Arrhenius activation energy for samples with AuNPs suggests that the addition of AuNPs can improve the structural transformation process in As2S3 glasses during annealing. The presence of AuNPs as catalytic centers facilitates the formation of new heteropolar bonds in the As2S3-Au-PG sample, providing nucleation sites for the transformation process to occur. As a result, the As2S3-Au-PG sample has a faster relaxation time than the As2S3-PG sample.

Cross polarization method was used to investigate the photoinduced birefringence, which involves measuring the light transmission through polarizers arranged either in parallel or crossed orientations [128].

Figure 15 - Scheme of the optical system that was used for measuring the birefringence effect

Figure 16 shows the measurement of the refractive index variation at different angles of incident polarization on samples with and without AuNPs in the irradiated regions. It worths mentioning that no birefringence is observed in the unirradiated areas. The largest refractive index change, indicative of birefringence, was observed at a 45-degree angle relative to the polarization of irradiation. This anisotropic response is attributed to the material's response to irradiation, which results in the formation of nanocrystals with a nonzero dipole moment oriented in the direction of the irradiating laser beam. Addition of

AuNPs reduced the anisotropic response by around 80%, possibly due to scattering effects leading to a more isotropic response.

Angle (degree)

Figure 16 - The refractive index changes for samples with and without AuNPs at different angles of incident polarization

The photoluminescence (PL) spectra of the As2S3-PG samples were measured under excitation with 405 nm and 532 nm lasers. Due to the presence of multiple Gaussian peaks in the PL spectra deconvolution was performed to obtain more detailed information about the PL centers. The peaks obtained from the deconvolution process and the PL spectra are shown in Figure 17. The results indicate the presence of a broad and intense band at 511 nm when excited with a wavelength of 405 nm (Figure 17 (a)). The PL spectrum, excited with 532 nm, is dominated by a broad emission band centered around 596 nm with shoulder around 630 nm.

The PL observed in the As2S3-PG samples investigated in this research does not conform to the established Epl ~ Eg/2 rule that typically characterizes the intrinsic properties of chalcogenide glasses [30]. This could be attributed to the fact that the observed PL emission is originating from arsenic sulfide nanoparticles rather than its bulk form [31,32].

Wavelength (nm) Wavelength (nm)

Figure 17 - Deconvoluted experimental PL spectra of AS2S3-PG when excited with (a) 405 nm laser and (b) 532 nm laser. Deconvoluted spectra are represented by curves P1, P2, P3, and P4. The resulted sum of the deconvoluted spectra is represented by curve fit envelope

The effect of AuNPs on the PL emission of As2S3-PG samples was investigated using confocal luminescent scanning microscopy. Samples with and without AuNPs, having the same concentrations, were analyzed. The results showed that the presence of AuNPs led to a decrease in the PL emission intensity of As2S3-PG by 40%, 30% for excitation at 405 nm, 514 nm, respectively. This effect is attributed to the strong semiconductor-metal coupling between As2S3 and Au, which resulted in the suppression of the plasmonic resonance of AuNPs and the quenching of excited states in As2S3. The observed effect is similar to what has been previously observed in Au/CdS colloidal nanocomposites [26].

425 450 475 500 525 550 575 600 625 650 675 700 Wavelength (nm)

Figure 18 - Experimental PL spectra of As2S3-PG (black curves) and As2S3-Au-PG (red curves) when excited at 405 nm and 514 nm

The effect of irradiation with different photon energies on the PL emission of the samples was investigated. Under excitation with a 514 nm laser beam, the PL intensity of the samples decreased by 58% and 64% after irradiation with 405 nm and 514 nm lasers, respectively. Irradiation with a 405 nm laser beam resulted in a decrease in PL intensity in the irradiated region by 83% with the same laser. The increase was by 39% in regions irradiated with 514 nm. This effect is attributed to photoinduced structural transformations that are dependent on the laser wavelength. The decrease in PL intensity at 514 nm after irradiation can be explained by an increase in the bandgap energy of the samples caused by the irradiation. Increasing the bandgap energy brings the excitation wavelength at 405 nm closer to the resonant absorption-reemission wavelength, which results in an increase in PL intensity. The formed nanocrystals have a relatively wide bandgap energy and exhibit PL emission in the 490 nm range.

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As2S3-PG (Iex=514nm) -Initial

-PL after 405nm irradiation

PL after 514nm irradiation

425 450 475 500 525 550 575 600 625 650 675 700 Wavelength (nm)

Wavelength (nm)

0

525

550

575

600

625

650

675

700

Figure 19 - Experimental PL spectra of PG- AS2S3 when excited at (a) 405 nm and (b) 514 nm. The initial PL spectra (black curves), the PL spectra after irradiation with 405 nm laser (blue curves) and with 514 nm laser (green curves)

Figure 20 - Confocal microscope image of the recorded TEM grating in the reflected mode, when excited at (left) 514 nm and (right) 405 nm

The composite material was shown to be effective in utilizing photoinduced changes for optical recording of photonic structures, which makes it suitable for applications in sensing and detection. The composite combines the properties of photonic crystals and

luminescent materials, allowing for both optical recording and luminescence emission, making it versatile for a range of sensing applications. Taking into consideration the strong luminescence emission and high nonlinearity of arsenic sulfide, this composite material holds promise for various applications in photonic crystals and nonlinear optics.

The fifth chapter discusses the use of Raman spectroscopy and quantum chemical calculations in studying the photoinduced structural transformations of As-S. The chapter aims to gain insights into the structural transformations of As-S that occurs under irradiation.

To study the reversible photoinduced structural transformations, the Raman spectra of two samples, As2S3-PG and As2S3-Au-PG, were measured at different stages: initial sample, after irradiation, after annealing at 190 °C for 1 hour. In the initial sample, there is a broad band centered at 350 cm-1 corresponding to AsS3 pyramidal units and homopolar bonds SS at 149 cm-1 and 218 cm-1. After irradiation, the homopolar S-S bonds break, and new peaks appear at 176 cm-1, 189 cm-1, 216 cm-1, 235 cm-1, and 368 cm-1, indicating the formation of various As-S molecules. The peaks at 189 cm-1, 216 cm-1, 235 cm-1, and 368 cm-1 are usually attributed to As-As bonds and appear in the Raman spectra of P-realgar-like molecules.

236

Raman shift (cm-1)

Figure 21 - Raman spectrum of As2S3-PG sample: annealed (black), after irradiation (red), and after irradiation and annealing (blue)

After irradiation, the sample was annealed. The resulting spectrum (blue curve in Figure 21) is similar to the spectrum before irradiation, indicating that most of the irradiation-induced transformations are erased upon annealing.

182 252 435 485

Figure 22 - Raman spectrum of As2S3-Au-PG sample: annealed (black), after irradiation (red), and after irradiation and annealing (blue)

The Raman spectra of As2S3-Au-PG show significant differences from those of As2S3-PG. The spectrum is dominated by gold and gold-sulfur bond vibrations with peaks at 182, 252 cm-1 and in the region 400-500 cm-1 assigned to radial Au-S stretching modes. The peak at 363 cm-1 corresponds to the pyramidal units of AsS3 with two shoulders at 319 cm-1 and 387 cm-1 attributed to the symmetric and asymmetric vibrations of the As-S-As bridges. Additionally, the bands at 183 cm-1 and 255 cm-1 can be assigned to As-As stretching vibrations, and the strong bands at 436 cm-1 and 484 cm-1 are attributed to S-S bond stretching vibrations.

The appearance of several peaks in the Raman spectra after irradiation in the range 180-255 cm-1 led to the assumption that the irradiation results in the formation of As-rich molecules. Therefore, Raman spectra of various As-rich molecules, starting from realgar As4S4 to duranusite As4S1 were calculated. Namely, they included: two molecular configurations of As4S4 composition, realgar-type and pararealgar-type molecules, three

molecular configurations of the As4S3 composition, two molecular configurations of As4S2 and As4S1.

To identify the most effective quantum chemical method for calculating, 14 distinct ab initio quantum chemical methods were employed to study four molecules with known geometries: dimorphite, realgar, pararealgar, and uzonite. The calculated and optimized molecular geometries were compared with experimental data. It was found that the HF method produced molecular geometries that were the closest to those acquired via X-ray diffraction analysis. Consequently, all calculations in this study employed the HF method with the 6-311 G(d) basis set.

Figure 23 - Optimized molecular geometries of (a) D-As4S3, (b) R-As4S4, (c) P-As4S4, (d) As4S5 and their bond length. S and As atoms are represented by yellow and red balls, respectively

Figure 24 - The simulated Raman spectra of arsenic sulfide molecules ranging from As4S4 to As4S1

The calculated spectra were analyzed and compared to the experimental spectrum obtained after irradiating the sample. The results showed that the irradiation led to the formation of several clusters, such as As4S1, R-As4S2, Z-As4S3, R-As4S4, and P-As4S4. A spectrum resulted from composing these clusters. This spectrum was added to the spectrum of As2S3. The similarity between the resulting spectrum (As4S1, R-As4S2, Z-As4S3, R-As4S4, P-As4S4, As2S3) and the experimental spectrum is illustrated in Figure 25.

The dipole moment for all modulated clusters was also obtained. Notably, three of the clusters suggested to form after irradiation, namely P-As4S4 (1.605), Z-As4S3 (1.16), and As4S1 (1.488), exhibit relatively high dipole moments. These clusters can account for the observed anisotropic changes in the form of birefringence.

Figure 25 - Comparison between the experimental spectrum (red curve) and the sum of the spectra (black curve) for the clusters As4S1, R-As4S2, Z-As4S3, R-As4S4, P-As4S4, and As2S3

Table 5 - Calculated electric dipole moments (D) of different arsenic sulfide clusters

As4S5 R-As4S4 P-As4S4 Z-As4S3 D-As4S3 S-As4S3 R-As4S2 P-As4S2 As4S1

0.953 0.000 1.605 1.161 1.270 2.511 0.000 1.696 1.488

After identifying the formation of As-rich molecular clusters through the Raman spectra, the study further investigated this phenomenon by calculating the formation energies of these clusters and comparing them to the formation energies of fragments in continuous network structure. The network-like fragments were generated by breaking one bond in each molecule at various positions.

Figure 26 - Optimized geometries of five molecules (a) As4S1, (b) R-As4S2, (c) Z-As4S3, (d) P-As4S4, (e) R-As4S4 and their corresponding H-terminated molecular fragments, from which they may have been formed. S and As atoms are represented by yellow and red balls, respectively, while the terminated H atoms are coloured in grey. The figure also includes the formation energies Ef in Hartree

To simplify the analysis, the results of the formation energies for the modulated clusters and their fragments are shown in Table 6. In addition, the formation energy of each

fragment is calculated relative to the formation energy of the corresponding molecule.

Table 6 - The formation energies Ef for the modulated clusters As4Sx and the difference in the formation energy between the fragments and the corresponding molecule AEf presented in eV

As4S1-0 As4S1-1 As4S1-2 As4S1-3

Ef -0.556229 -0.549136 -0.697307 -0.6988

AEf (eV) 0.193 -3.838 -3.879

R-As4S2-0 R-As4S2-1 R-As4S2-2

Ef -0.68414 -0.698796 -0.833562

AEf (eV) -0.398 -4.065

Z-As4S3-0 Z-As4S3-1 Z-As4S3-2 Z-As4S3-3

Ef -0.852927 -0.999619 -0.833562 -0.99057

AEf (eV) -3.991 0.526 -3.745

R-As4S4-0 R-As4S4-1 R-As4S4-2

Ef -1.00786 -1.133065 -1.004656

AEf (eV) -3.4 0.087

P-As4S4-0 P-As4S4-1 P-As4S4-2 P-As4S4-3 P-As4S4-4

Ef -1.003456 -0.99057 -0.977327 -1.12235 -0.993403

AEf (eV) 0.35 0.711 -3.235 0.273

The stability of fragments and their potential for transformation into molecular structures under irradiation are estimated by comparing the difference in formation energies (AEf) between each fragment and corresponding molecule. Fragments with a positive and high AEf (>3 eV) are considered stable, while fragments with small and negative AEf are thought to be able to transform into molecular structures.

The obtained difference in formation energy of approximately 0.35 eV is noteworthy because it is similar to the measured Arrhenius activation energy of approximately 0.18 eV, providing additional evidence for the proposed mechanism of the photoinduced structural transformations.

Figure 27 - Potential energy landscape demonstrating the possible photoinduced transitions from network-like structures to molecular structures for five molecules: As4S1, R-As4S2, Z-As4S3, P-As4S4, and R-As4S4. The network clusters are displayed are formed by breaking a bond in the corresponding molecule-type clusters. Their cluster-forming energies (Ef) are shown relative to the corresponding molecule

Summary of the main results

This research is designed to study the synthesis, characterization, and manipulation the optical properties of a new nanocomposite composed of arsenic sulfide (As2S3) and gold nanoparticles (AuNPs). The nanocomposite was created using a chemical deposition method that involved dissolving As2S3 powder in propylamine and impregnating porous glass (PG) pieces in solutions with and without the addition of AuNPs. This method is simple and inexpensive for studying materials at the nanoscale.

The nanocomposite synthesized by combining arsenic sulfide and gold nanoparticles showed a reversible photobleaching effect, which is opposite to the photodarkening effect observed in As2S3 bulk glasses and thin films. The bandgap energy of the nanocomposite varied depending on the concentration of As2S3 in the glass. It was possible to tune this bandgap over a wide range of 2 to 2.68 eV by irradiation.

The impact of As2S3 dopant concentration and the presence of AuNPs on the photoinduced absorption edge shift were studied. It was observed that when the dopant concentration increases, the bandgap energy decreases. Furthermore, samples with both As2S3 and AuNPs have a smaller bandgap compared to those with only As2S3, which is attributed to an excess of As-As bonds in the As2S3-Au-PG samples.

The kinetics of photoinduced changes in samples with and without AuNPs were measured by monitoring changes in transmittance over time during irradiation with varying powers. Photobleaching occurred exponentially over a few minutes, and the relaxation time decreased with increasing irradiation intensity, with longer relaxation times observed in samples without AuNPs. The kinetics of thermally induced changes were also monitored by measuring changes in transmittance over time during annealing, with As2S3-Au-PG samples showing a faster relaxation time than As2S3-PG samples. The Arrhenius activation energy found to be lower for As2S3-Au-PG samples, suggesting that the presence of AuNPs facilitated the formation of new heteropolar bonds and resulted in a faster relaxation time.

The nanocomposite was found to exhibit photoinduced birefringence due to its anisotropic response to irradiation and the formation of nanocrystals with nonzero dipole

moment. AuNPs were found to decrease the anisotropic response by approximately 80%, which can be attributed to their scattering properties.

The photoluminescence spectra of the samples revealed strong emission with various emission peaks between 446 and 660 nm. The effect of irradiation on the photoluminescence emission intensity was also investigated. A wavelength-dependent photoinduced transformation was observed. The presence of AuNPs reduced the photoluminescence emission intensity of As2S3-PG, which was attributed to strong coupling between As2S3 and Au resulting in the quenching of excited states.

Raman spectroscopy and ab initio quantum chemical calculations were employed to study the photoinduced structural changes in As-S. The Raman measurements showed the appearance of several peaks associated with As-As homopolar bonds after irradiation, including signatures of P-realgar-like molecules. Annealing the samples largely reversed the irradiation-induced changes.

Quantum chemical calculations were conducted to determine the Raman spectra of various As-rich molecules. The calculated spectra were compared to the experimental spectrum obtained after irradiating the sample, revealing the formation of several clusters, As4S1, R-As4S2, Z-As4S3, R-As4S4, and P-As4S4. Notably, three of these clusters have relatively high dipole moments, which may explain the observed photoinduced birefringence in the composite material. Quantum chemical calculations were also used to investigate the network to molecular transition in the composite material. The formation energy of various potential network-like fragments was calculated by breaking one bond in each molecule at different positions. The results identified the potential network-like fragments involved in the transition. The difference in formation energy between those molecules and their corresponding fragments is around 0.35 eV, which is similar to the measured Arrhenius activation energy of approximately 0.18 eV. This supports the proposed mechanism for the photoinduced structural transformations.

The photoinduced changes in the composite material have potential applications in optical recording of photonic structures. The material's strong luminescence emission along

with its ability for optical recording, make it promising for a range of applications in photonic crystals and optical sensors.

Publications

The key results detailing the primary research findings were published in high impact international journals indexed in Scopus and Web of Science.

1. Alkhalil, G., Burunkova, J.A., Csik, A., Donczo, B., Szarka, M., Petrik, P., Kokenyesi, S. and Saadaldin, N. Photoinduced structural transformations of Au-As2S3 nanocomposite impregnated in silica porous glass matrix. Journal of Non-Crystalline Solids, 610, p.122324. (2023)

2. Alkhalil, G., Burunkova, J. A., Stepanova, M., Veniaminov, A., Donczo, B., Szarka, M., & Kokenyesi, S. Photoluminescence emission in arsenic sulfide nanocomposite. Journal of Non-Crystalline Solids: X, 100174. (2023)

3. Burunkova, J. A., Alkhalil, G., Veniaminov, A. V., Csarnovics, I., Molnar, S., & Kokenyesi, S. Arsenic trisulfide-doped silica-based porous glass. Optics & Laser Technology, 147, 107658. (2022).

4. Burunkova J, Alkhalil G, Tcypkin A, Putilin S, Ismagilov A, Molnar S, Daroczi L, Kokenyesi S. Laser Light Durability and Nonlinear Optical Properties of Acrylate Polymer- Chalcogenide Glass- Gold Nanocomposites. physica status solidi (a). (2022).

5. J. Burunkova, S. Molnar, V. Sitnikova, D. Shaimadiyeva, G. Alkhalil, R. Bohdan, J. Bako, F. Kolotaev, A. Bonyar, S. Kokenyesi. Polymer-chalcogenide glass nanocomposites for amplitude-phase modulated optical relief recording// Journal of Materials Science: Materials in Electronics, Vol. 30, Issue 10, pp 9742-9750. (2019).

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Introduction

Relevance of the topic

Due to their promising physical and optical properties, chalcogenide glasses (ChGs) represent an important and growing class of materials [1]. Arsenic sulfide (AS2S3), a chalcogenide material, possesses several unique properties [2]. Recently, As2S3 has found numerous applications ranging from nonlinear effects such as supercontinuum generation [3], to passive devices like optical fibers for the infrared spectral region [4], and media for optical recording [1]. As2S3 photonic crystal fiber was used for ultra-broadband infrared supercontinuum generation extending from 2.5 to 15 ^m [3]. In another example, second harmonic generation was observed in thermally poled As2S3 glasses [5]. As2S3 planar waveguides were used for correlated photon-pair generation [6], and in other works for broadband cascaded four-wave mixing [7]. Two-dimensional (2D) As2S3 layers were shown to exhibit highly anisotropic mechanical and optical properties. It was found that the stretchability of As2S3 can exceed that of graphene [8].

Photoinduced changes (PICs) of As2S3 are of great importance and have been widely studied [9-12]. The PICs of As2S3 are a desired property for certain applications such as the optical recording of photonic structures. For other applications that require a stable material such as in optical fibers, the PICs of As2S3 are not a desired property. Several factors can influence PICs of As2S3, for example the composition AsxS1oo-x, thermal history, preparation method, irradiation wavelength [12-16]. Furthermore, the material dimension (bulk glass, thin films, and nanolayers) also can affect the type of PICs occurring in the material [17,18].

The advances in nanophotonic, and nanofabrication technology requires a knowledge of the materials properties at the nanoscale, and it revels the unique physical, chemical, mechanical, and optical properties of materials that appear at the nanoscale. Tanaka et al. were the first to observe anomalous photoinduced effects at small dimension, specifically photodarkening in amorphous As-S and As-Se films that depended on the thickness of the film [19]. They found that photodarkening decreased with decreasing film thickness,

disappearing entirely when the films were less than 50 nm thick. Hayashi and Mitsuishi later confirmed this effect and attributed it to strain induced by lattice mismatch between the film and substrate, which can become more significant in nanolayers and potentially lead to changes in the film's structure and properties [20]. Both studies investigated films with a minimum thickness of around 30 nm, but there have been no reports on the behavior at smaller dimensions. This motivates the dissertation to focus on studying the optical properties of As2S3 nanocomposites with dimensions beyond 30 nm.

Doping arsenic sulfide with other material represents another method for influencing its PICs. Numerous experiments have been performed on the effect of silver doping on the PICs of As2S3 [21]. It has been shown that Ag photodoping of As-S sample decreases the total free energy of the system and therefore increases its stability [22]. The stability of the Ag-As2S3 was compared with Cu- As2S3 structure, and it was found to be more stable for Ag-As2S3 [23]. On the other hand, introducing a layer of gold nanoparticles under As2S3 or (Ag3AsS3)0.6(As2S3)0.4 thin films enhanced their PICs [24,25]. Despite these researches on doping As2S3 with silver and introducing gold nanoparticles, there is still a lack of studies investigating the effect of gold nanoparticles on the optical properties of arsenic sulfide.

The relevance of this dissertation lies in the synthesis, characterization, and manipulation of As2S3 nanocomposite, which can enhance our understanding of its optical properties at the nanoscale. The research examines the photoinduced structural changes in As2S3 nanocomposite and how they affect the material's optical properties. Additionally, it investigates the effect of gold nanoparticles on the optical properties of the samples. Moreover, the study proposes potential applications, including optical recording of photonic structures on the resulting composite.

Goal of research

The goal of the thesis is to develop a physicochemical basis for the synthesis of new As2S3 nanocomposite and investigate its optical properties and photoinduced phenomena as well as the effect of gold nanoparticles on these properties.

Research objectives

In order to achieve the goal in the framework of the thesis, the following objectives have been established:

• To develop synthetic methods for the fabrication of arsenic sulfide and arsenic sulfidegold nanocomposite impregnated in porous glasses.

• To assess interparticle interactions between arsenic sulfide and gold nanoparticles in colloidal systems that is used for the fabrication of arsenic sulfide-gold nanocomposite impregnated in porous glasses.

• To study the composition, optical properties, and photoinduced structural transformations of the obtained nanocomposite materials and to establish the peculiarities of these processes, including those under thermal treatment.

• To assess the influence of gold nanoparticles on the photoinduced changes and on the optical properties of the nanocomposite.

• To perform optical recording of photonic structure on the obtained composite material.

• To investigate the photoinduced structural transformations of As-S experimentally using Raman spectroscopy and theoretically by conducting ab initio quantum chemical calculations on the molecular structure of arsenic sulfide As-S.

The novelty of research

New simple physicochemical approach for the fabrication of arsenic sulfide and arsenic sulfide-gold nanocomposite based on porous glasses was suggested.

A mechanism for the displacement of the surface ligands of gold nanoparticles by arsenic sulfide and the complex formation between them is proposed. The strong metal-semiconductors coupling between the two materials leads to the suppression of the plasmonic resonance in gold nanoparticles and the quenching of excited states in arsenic sulfide which decrease its photoluminescence intensity.

It has been shown that arsenic sulfide nanocomposite exhibits a huge (up to ~ 0.47 eV) and reversable photobleaching effect (a shift in the transmission spectrum towards the shorter wavelength that can be reversed by thermal treatment), which is the opposite of the effect usually observed for As2S3 bulk glasses and thin films (i.e., photodarkening.).

The photoinduced changes in the optical properties of the composites, with and without gold nanoparticles, were investigated and characterized.

It was demonstrated that the photoinduced changes in the composite material can be effectively utilized for optical recording of photonic structures.

A model was suggested based on Raman spectroscopy analysis and ab initio quantum chemical calculations to describe the photoinduced structural transformations. Theoretical and practical significance of the research

The theoretical significance of the conducted research lies in the evidence that the optical properties of arsenic sulfide nanocomposite such as the bandgap energy can be tuned over a relatively wide range (2 - 2.68 eV), and that at the nanoscale irradiation leads to network to molecules-like structural transformations which results is in the huge photobleaching effect observed in arsenic sulfide nanocomposite.

The practical significance of the conducted research lies in the development of arsenic sulfide nancomposite that can function as both a sensitive medium for optical recording and a luminescent material, making it useful for a wide range of potential applications from sensing to photonic crystals and nonlinear optics. Assertions that are presented for defense:

1. Irradiating arsenic sulfide impregnated in nanoporous glass by a laser beam at 532 nm with the intensity 500 mW/cm2 for 60 minutes shifts its optical absorption edge towards the higher energies by 0.28-0.47 eV. The photoinduced shift in the optical absorption edge is reversible by thermal treatment at 190 °C.

2. Photoinduced change in the refractive index of arsenic sulfide impregnated in nanoporous glass is anisotropic and accompanied by 6*10-5 difference in the refractive

index at 787 nm between parallel and perpendicular component of polarization relative to the polarization of laser irradiation. Introducing gold nanoparticles to the composite reduces the anisotropic response of the material by 80%.

3. When mixing solutions of arsenic sulfide and gold nanoparticles they interact and form complexes. The strong metal-semiconductors coupling between the two materials leads to the suppression of the plasmonic resonance in gold nanoparticles and the quenching of excited states in arsenic sulfide. The later decreases photoluminescence intensity of arsenic sulfide by 40%, 30% for excitation at 405 nm, 514 nm, respectively.

4. Photoinduced structural transformations of arsenic sulfide impregnated in nanoporous glass are attributed to transition from a network to a molecular structure accompanied by crystallization. Irradiation results in the formation of As-rich clusters, As4S1, R-As4S2, Z-As4S3, P-As4S4, and R-As4S4.

Approbation of research results

Key research results were presented and discussed at the following conferences: XLVIII Scientific and educational conference, ITMO University, Russia (2019); Conference "Basic Problems of Optics" BPO, ITMO University, Russia (2019); 21st International Conference on Advanced Laser Technologies, Prokhorov General Physics Institute of Russian Academy of Sciences, Russia (2021); XI Congress of Young Scientists (KMU), ITMO University, Russia (2022); XLX Scientific and educational conference, ITMO University, Russia (2022); Smart Composites International School, Immanuel Kant Baltic Federal University, Russia (2022).

The accuracy of the obtained results is achieved through the use of verifiable and reliable synthetic methods, characterization techniques, and theoretical and computational models that are recognized by and accepted throughout the scientific community. Additionally, the results were validated during the publication process where scientific peers examined, reviewed, and accepted the work that was presented.

Publications

The key results detailing the primary research findings were published in high impact international journals indexed in Scopus and Web of Science.

1. Alkhalil, G., Burunkova, J.A., Csík, A., Donczo, B., Szarka, M., Petrik, P., Kokenyesi, S. and Saadaldin, N. Photoinduced structural transformations of Au-As2S3 nanocomposite impregnated in silica porous glass matrix. Journal of Non-Crystalline Solids, 610, p.122324. (2023)

2. Alkhalil, G., Burunkova, J. A., Stepanova, M., Veniaminov, A., Donczo, B., Szarka, M., & Kokenyesi, S. Photoluminescence emission in arsenic sulfide nanocomposite. Journal of Non-Crystalline Solids: X, 100174. (2023).

3. Burunkova, J. A., Alkhalil, G., Veniaminov, A. V., Csarnovics, I., Molnar, S., & Kokenyesi, S. Arsenic trisulfide-doped silica-based porous glass. Optics & Laser Technology, 147, 107658. (2022).

4. Burunkova J, Alkhalil G, Tcypkin A, Putilin S, Ismagilov A, Molnar S, Daroczi L, Kokenyesi S. Laser Light Durability and Nonlinear Optical Properties of Acrylate Polymer- Chalcogenide Glass- Gold Nanocomposites. physica status solidi (a). (2022).

5. J. Burunkova, S. Molnar, V. Sitnikova, D. Shaimadiyeva, G. Alkhalil, R. Bohdan, J. Bako, F. Kolotaev, A. Bonyar, S. Kokenyesi. Polymer-chalcogenide glass nanocomposites for amplitude-phase modulated optical relief recording// Journal of Materials Science: Materials in Electronics, Vol. 30, Issue 10, pp 9742-9750. (2019). Thesis structure and number of pages

This thesis consists of an introduction, five chapters, a conclusion, and a list of references. The dissertation is 243 pages, including a bibliography of 167 references. The work contains 42 figures and 10 tables.

Chapter 1. Chalcogenide glasses - Photoinduced phenomena

In this chapter I present a literature review that includes a brief summary of chalcogenide glasses - the class of material to which As2S3 belongs. Here, the definition, classification, and different optical properties of chalcogenide glasses are described with the focus on As2S3 glass. The chapter highlights the different photoinduced effects observed in chalcogenide glasses in general and As2S3 in particular. Furthermore, it summarizes the several factors that can influence the photoinduced effects of As2S3, such as the composition AsxS 100-x, thermal history, preparation method, irradiation wavelength, and doping it with other material. Finally, the different characterization methods, and theoretical approaches suggested and used to describe the photoinduced and thermally induced effect are explored.