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Enhancing photoluminescence (PL) in single-layer transition metal dichalcogenides has garnered significant interest, particularly for advancing high-performance 2D electronics and optoelectronics. The combination of surface engineering and contemporary growth methods has provided a platform for investigating optical signals. In this study, we present variations in PL and Raman signals of single-layer MoS2 flakes grown conformally using the glass-assisted CVD method on square-patterned surfaces with varying well depths. PL spectroscopy revealed a systematic and pronounced enhancement in intensities as the valley thickness decreased from 285 nm to 225 nm. Conversely, for the hill regions of the samples, the PL intensity initially increased with decreasing valley thickness and then decreased, despite the hill regions having a constant thickness of 300 nm. On the other hand, PL maps did not exhibit a systematic dependence of intensities on the hill-valley thickness distinction, contrary to expected results based on literature data for similar materials on flat surfaces. The origin of the intensity oscillations was attributed to possible mechanisms, including thickness-dependent interference and strain-related exciton funneling effects. Additionally, Raman measurements revealed irregular variations in intensity in hill regions, dependent on the thicknesses of the underlying SiO2 layers. Furthermore, we observed that the sizes of the flakes increased as the well depths of the underlying patterned surface decreased. This phenomenon might be attributed to alterations in the carrier gas flow pattern and varying temperature gradients between the hills and valleys. These results hold substantial potential to open new avenues for the integration of 2D transition metal dichalcogenides into on-chip electronic and optoelectronic devices.

In the rapidly developing field of optoelectronics, the utilization of transition-metal dichalcogenides with adjustable band gaps holds great promise. MoS2, in particular, has garnered considerable attention owing to its versatility. However, a persistent challenge is to establish a simple, reliable and scalable method for large-scale synthesis of continuous monolayer films. In this study, we report the growth of continuous large-area monolayer MoS2 films using a glass-assisted chemical vapor deposition (CVD) process. High-quality monolayer films were achieved by precisely controlling carrier gas flow and sulfur vaporization with a customized CVD system. Additionally, we explored the impact of chemical treatment using lithium bistrifluoromethylsulfonylamine (Li-TFSI) salt on the optical properties of monolayer MoS2 crystals. To investigate the evolution of excitonic characteristics, we conditionally grew monolayer MoS2 flakes by controlling sulfur evaporation. We reported two scenarios on MoS2 films and flakes based on substrate-related strain and defect density. Our findings revealed that high-quality monolayer MoS2 films exhibited lower treatment efficiency due to substrate-induced surface strain. whereas defective monolayer MoS2 flakes demonstrated a higher treatment sensitivity due to the p-doping effect. The Li-TFSI-induced changes in exciton density were elucidated through photoluminescence, Raman, and x-ray photoelectron spectroscopy results. Furthermore, we demonstrated treatment-related healing in flakes under variable laser excitation power. The advancements highlighted in our study carry significant implications for the scalable fabrication of diverse optoelectronic devices, potentially paving the way for widespread real-world applications., Scientific and Technological Research Council of Turkiye (TUEBIdot;TAK); [TUEBIdot;TAK 121M601]; [TUEBIdot;TAK 118C524]; [TUEBIdot;TAK 120N885]; [TUEBIdot;TAK 123M134], This work was supported by Scientific and Technological Research Council of Turkiye (TUEB ; Idot;TAK) (Project Numbers: TUEBITAK 121M601, TUEB ; Idot;TAK 118C524, TUEB ; Idot;TAK 120N885, TUEB ; Idot;TAK 123M134). Authors sincerely thank Professor Dr ; Scedil;efik Suezer for the ARXPS holder.

Optoelektronik cihaz performansını Moore yasasının ölçeklendirme sınırlarının ötesine ulaştırmak için yeni malzemelere ve cihaz mimarisine dayalı teknolojilere ihtiyaç vardır. Atomik boyuttaki ince yapıları ve oluşan kuantum hapsetme etkileri sebebiyle iki boyutlu (2B) yarıiletken malzemeler, yüksek yüzey-hacim oranı, geniş optik soğurma bant aralığı ve yüksek yük mobilite değeri gibi önemli yapısal ve elektronik özelliklere sahip olabilmektedir. Tez kapsamında, optoelektronik uygulamalar açısından önemli sonuçlar verme potansiyeline sahip metal halojenür 2B bizmut triiyodür (BiI3) ve geçiş metali dikalkojenit tek katmanlı 2B molibden disülfür (MoS2) malzemelerin yüksek kristallikte ve geniş alanlı üretimleri yapılmıştır. Malzemelerin sentezi aşamasında fiziksel buhar taşınımı, altın katman destekli eksfoliasyon ve kimyasal buhardan biriktirme yöntemleri kullanılmıştır. Malzemelerin ayrıntılı yapısal ve optik incelemeleri optik görüntüleme, taramalı elektron mikroskopisi/enerji dağılımlı X-ışını spektroskopisi, X-ışını difraktometrisi, atomik kuvvet mikroskopisi, 3B lazer taramalı eş odaklı mikroskopi, optik absorpsiyon spektroskopisi, Raman spektroskopisi ve fotolüminesans (PL) spektroskopisi yöntemleri kullanılarak gerçekleştirilmiştir. Her iki malzemenin de yüksek kristallik özelliklerinin ortaya çıkarılmasının yanı sıra dolaylı enerji bant yapısından doğrudan bant yapısına geçtiği PL ve Raman analizleri ile gösterilmiştir. BiI3 nanokristalleri onlarca mikron geniş yanal alanlı, 10 nanometrenin altında kalınlıkta katmanlı yapıda ve kristallik özelliklerini koruyacak şekilde üretilebilmiştir. BiI3 nanokristallerde kalınlığa bağlı olarak 576 nanometreye kadar PL kayması gözlenmiştir. Ayrıca, büyütme basıncı, sıcaklığı ve sürenin kristal büyümesine etkileri incelenerek 25 Torr, 290 oC ve sıfır dakika bekleme süresinin ince kristal oluşumu için optimum koşul olduğu görülmüştür. Diğer taraftan, MoS2 nanokristalleri tek katman kalınlığında (0.64 nm) ve onlarca mikron g, Novel materials and device architecture-based technologies are needed to extend optoelectronic device performance beyond the scaling limits of Moore's law. Two-dimensional (2D) semiconductor materials can have important structural and electronic properties, such as high surface-to-volume ratio, wide optical absorption band gap, and high charge mobility value, due to their atomically fine structures and quantum confinement effects. Within the scope of the thesis, metal halide 2D bismuth triiodide (BiI3) and transition metal dichalcogenide monolayer 2D molybdenum disulfide (MoS2) materials, which have the potential to give important results in terms of optoelectronic applications, have been produced with high crystallinity and large area. During the synthesis of the materials, physical vapor transport, gold layer assisted exfoliation and chemical vapor deposition methods were used. Detailed structural and optical examination of materials has been carried out by using optical imaging, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray diffractometry, atomic force microscopy, 3D laser scanning confocal microscopy, optical absorption spectroscopy, Raman spectroscopy, and photoluminescence (PL) spectroscopy. In addition to revealing the high crystallinity properties of both materials, it has been shown by PL and Raman analyzes that the indirect energy transitions from the band structure to the direct band structure. BiI3 nanocrystals could be produced with a wide lateral area of tens of microns, a layered structure under 10 nanometers thick, and preserving their crystalline properties. Depending on the thickness, PL shifts of up to 576 nanometers were observed in BiI3 nanocrystals. In addition, the effects of growth pressure, temperature and duration on crystal growth were examined and it was found that 25 Torr, 290 oC and zero minutes waiting time were the optimum conditions for ultrathin crystal formation. On the other hand, MoS2 nanocrystals were

The chemical vapor deposition (CVD) technique has been widely used to grow high quality single layer MoS2 crystals. However, there are still issues that need to be clarified in order to determine the appropriate conditions for the repeatable and scalable process. In this study, we experimentally investigated the effect of flow direction on the size distribution and optical signal of monolayer MoS2 flakes grown on microchannel arrayed surfaces. As an important parameter controlling the CVD process, the carrier gas flow was revealed to be highly sensitive to geometric orientation of the patterned surface. The flow direction parallel to the array yielded larger flakes with narrower size distribution, and enhanced photoluminescence (PL) peak intensities compared to the case with flow normal to the array while the Raman intensities for both the cases are almost the same. The size distributions were obtained as 6 +/- 13 and 37 +/- 4 mu m for the perpendicular and parallel cases, respectively. It was also found that the PL peak intensity increased by approximately 1.5 times when switching to parallel configuration. This study presents an experimental approach to understand the influence of the precursor stream reshaped by the growth surface geometry on the structural and optical properties of monolayer MoS2, which has great potential for use in optoelectronic applications., Scientific and Technological Research Council of Turkey [TUEBITAK 121M601, TUEBITAK 118C524], This work was supported by Scientific and Technological Research Council of Turkey. Project Nos. TUEBITAK 121M601 and TUEBITAK 118C524. F G A and A Y sincerely thank Prof Dr Nihan Kosku Perkgoez and Prof Dr Feridun Ay for their valuable supports.

Two dimensional (2D) organometal halide perovskites (OHPs) have attracted intensive interest for their diverse optoelectronic applications. However, a practical and controllable solution-based way particularly for the synthesis of pure BA2MAPb2I7 and heterostructured BA2PbI4/BA2MAPb2I7 single crystals, which are of great importance for high performance photodetectors, is still lacking. In this study, we report the efficient synthesis route of large-area high-quality BA2MAPb2I7 and BA2PbI4/BA2MAPb2I7 single crystals. We show that the combined method of solution temperature lowering and limiting reagent approaches yields rapid and controllable synthesis. In addition, the correct determination of the BAI:MAI:PbI2 molarity ratios in the synthesis process was revealed to be highly significant. These results provide fundamental insight and useful guideline for obtaining the presented 2D OHPs with regard to high practicality and controllability.

Transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics owing to their unique optical and electronic functionalities. Although atomically thin flat TMD layers have been investigated in various device applications, pattern-mediated growth serves great promise for revealing novel properties and application opportunities of TMDs. Herein, controlled size distribution of CVD-grown monolayer MoS2 flakes by varying the distance between surface pattern features and the effects of patterning on the optical properties of MoS2 domains is reported. Larger flakes and higher uniformity in size distribution are obtained via patterning in comparison with the results from bare surface. Superior photoluminescence (PL) performances are observed for the 2D MoS2 grown on the pattern valleys when compared with the sample on the hill regions and the bare surface. The results demonstrate the notable potential of 2D TMDs for applications in electronics and optoelectronics., This work was supported by Scientific and Technological Research Council of Turkey project numbers TUEBITAK 121M601 and TUEBITAK 118C524., Scientific and Technological Research Council of Turkey [TUEBITAK 121M601, TUEBITAK 118C524]

Transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics owing to their unique optical and electronic functionalities. Although atomically thin flat TMD layers have been investigated in various device applications, pattern-mediated growth serves great promise for revealing novel properties and application opportunities of TMDs. Herein, controlled size distribution of CVD-grown monolayer MoS2 flakes by varying the distance between surface pattern features and the effects of patterning on the optical properties of MoS2 domains is reported. Larger flakes and higher uniformity in size distribution are obtained via patterning in comparison with the results from bare surface. Superior photoluminescence (PL) performances are observed for the 2D MoS2 grown on the pattern valleys when compared with the sample on the hill regions and the bare surface. The results demonstrate the notable potential of 2D TMDs for applications in electronics and optoelectronics., This work was supported by Scientific and Technological Research Council of Turkey project numbers TUEBITAK 121M601 and TUEBITAK 118C524., Scientific and Technological Research Council of Turkey [TUEBITAK 121M601, TUEBITAK 118C524]

Transition metal dichalcogenide (TMD) monolayers have recently garnered significant attention owing to their favorable electronic and optoelectronic properties. To date, chemical vapor deposition (CVD) growth of molybdenum di-sulfide, -selenide, and -telluride (MoS2, MoSe2, and MoTe2, respectively), and tungsten di-sulfide, -selenide, and -telluride (WS2, WSe2, and WTe2, respectively) has been widely investigated as the most promising two-dimensional (2D) TMDs. However, scalable and controllable growth of high-quality TMD monolayers remains a challenge. This review highlights the advances of CVD technique by focusing on the aspects of growth promoters, surface energy assistance and site selectivity, which are of great significance for the growth of monolayer TMDs. The challenges for high-performance applications are discussed at the end with a brief outlook on future work. © 2022 Elsevier Ltd, Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, TÜBITAK: 118C524, 118E996, 121M601, 20AG001, 20AG025, This work was supported by The Scientific and Technological Research Council of Turkey , Research Project Numbers: TÜBİTAK 121M601 , TÜBİTAK 118C524 , TÜBİTAK 118E996 , TÜBİTAK 20AG025 , TÜBİTAK 20AG001 .

Transition metal dichalcogenide (TMD) monolayers have recently garnered significant attention owing to their favorable electronic and optoelectronic properties. To date, chemical vapor deposition (CVD) growth of molybdenum di-sulfide, -selenide, and -telluride (MoS2, MoSe2, and MoTe2, respectively), and tungsten di-sulfide, -selenide, and -telluride (WS2, WSe2, and WTe2, respectively) has been widely investigated as the most promising two-dimensional (2D) TMDs. However, scalable and controllable growth of high-quality TMD monolayers remains a challenge. This review highlights the advances of CVD technique by focusing on the aspects of growth promoters, surface energy assistance and site selectivity, which are of great significance for the growth of monolayer TMDs. The challenges for high-performance applications are discussed at the end with a brief outlook on future work. © 2022 Elsevier Ltd, Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, TÜBITAK: 118C524, 118E996, 121M601, 20AG001, 20AG025, This work was supported by The Scientific and Technological Research Council of Turkey , Research Project Numbers: TÜBİTAK 121M601 , TÜBİTAK 118C524 , TÜBİTAK 118E996 , TÜBİTAK 20AG025 , TÜBİTAK 20AG001 .

We propose and demonstrate photonic crystals (PCs) providing backward-directional propagation of surface slow waves, which is significant for potential PC-based photonic applications. An effective pathway for backward directing of surface slow light along with the modification of other important characteristics is presented via implementing surface morphological diversity in PCs. With the surface orientation angle varying from 900 to 300, the newly appearing bands inside the band gap shift to higher frequencies, and negative group indices up to -100 are observed as the strong indication of backward propagation. Furthermore, dependence of the propagation direction on the surface corrugation angle has been verified via detailed time-domain analyses and microwave experiments using dipole source. As obtained from both the numerical and experimental results, for instance, the structure with 600 provides a well-defined backward propagation. In addition, normalized-delay-bandwidth-product can easily be modified by varying the surface orientation angle in the proposed structures according to the necessities of the application. Furthermore, the group velocity dispersion spectra extracted for each periodic structure exhibit considerably high-range near-zero values as 0.139 ps(2)/m at 900 for the range of 495.54-501.25 nm and 0.176 ps(2)/m at 850 for the range of 495.66-501.25 nm. Third order dispersion spectra also obtained for the proposed PCs show near-zero values as 0.098 ps(3)/m at 900 and 0.113 ps(3)/m at 850 in the corresponding frequency regimes. Facile control of the key characteristics such as backward-directed surface wave propagation in the periodic dielectric structures having morphological diversity serves a great potential for next-generation photonic applications.

We demonstrate efficient and compact lxN wavelength-demultiplexing by using objective-first inverse design algorithm. Ultra-high device performances were achieved for the certain designs of 1x2, 1x3, and 1x4 demultiplexers with very small footprints at the orders of a few microns. The presented 1x2, 1x3, and 1x4 devices operate at the wavelength sets of 1.31 mu m, 1.55 mu m; 1.31 mu m, 1.47 mu m, 1.55 mu m, and; 1.31 mu m, 1.39 mu m, 1.47 mu m, 1.55 mu m, respectively. The transmission efficiencies at the corresponding target wavelengths of each vertically or horizontally aligned channels were obtained mostly to be near-unity together with very small crosstalk ranges of around 0.01% - 1.2%. The inverse design approach allowing the implementation of more than four output channels together with the novel functionalities will pave the way for compact and manufacturable lxN couplers, which is of ultimate significance for integrated photonics.

In this paper, we propose efficient and compact 2D T-junction 1 x N in-plane-incidence wavelength demul-tiplexers by using recently developed objective-first inverse design algorithm. Ultra-high device performance was achieved for the specific designs of 1 x 2, 1 x 4, and 1 x 6 wavelength (de)multiplexers with small footprints 2.80 mu m x 2.80 mu m, 4.60 mu m x 2.80 mu m, 6.95 mu m x 2.80 mu m, respectively. We used two approaches to binarize - epsilon threshold and binarization-cost - to obtain silicon wavelength demultiplexer considering fabrication constraints. For instance, the transmission efficiency of binarization-cost 1 x 2 demultiplexer was -0.30 dB for 1.31 mu m and -0.54 dB at 1.55 mu m while crosstalks at the operating wavelengths are negligibly small, i.e., -17.80 and -15.29 dB, respectively. Moreover, for the binarization-cost 1x4 demultiplexer, the transmission efficiency values were approximately -1.90 dB at 1.31,1.39,1.47, and 1.55 mu m as the crosstalk was approximately -13 dB. Furthermore, the objective-first algorithm was used to employ our demultiplexers as multiplexers, which means the ports that were once used as inputs in demultiplexers are designed to be used as outputs. We envision that the devices are compact, reliable, and T-shaped that is useful for optical communication systems. These rudimentary results are also relevant to the burgeoning field of nanophotonics.

Inverse-design algorithms can be used to design compact and high-performance complex photonic structures. In this study, we propose the design of an all-dielectric optical resonator based on the concept of the parallel mirror resonator by using the objective-first inverse design algorithm. Light is strongly confined using a predefined objective function that creates symmetric mirror regions acting as reflective layers for the fundamental transverse-electric polarization mode. Thanks to the flexibility of the algorithm, segments of the cavity and dielectric mirror are designed in a simulation region by choosing a cavity of an appropriate length. A time-domain analysis of the proposed structure was carried out using the two-dimensional finite-difference time-domain method. The proposed structure has a configuration with a footprint of 13.394 x 0.592 mu m(2). The algorithm generates an inverse-designed structure to obtain a resonance peak at the target wavelength without any intuitive scanning of the complete parameter space. As a result, the first-order mode is strongly localized in the region of the cavity for the defined design wavelength. Moreover, the application of the inversely designed resonator as refractive index sensor is examined to show that the proposed structure has the potential for use in integrated photonic devices. Thus, the objective-first inverse design algorithm is promising for use in the design of a variety of photonic structures.

We demonstrate efficient and compact lxN wavelength-demultiplexing by using objective-first inverse design algorithm. Ultra-high device performances were achieved for the certain designs of 1x2, 1x3, and 1x4 demultiplexers with very small footprints at the orders of a few microns. The presented 1x2, 1x3, and 1x4 devices operate at the wavelength sets of 1.31 mu m, 1.55 mu m; 1.31 mu m, 1.47 mu m, 1.55 mu m, and; 1.31 mu m, 1.39 mu m, 1.47 mu m, 1.55 mu m, respectively. The transmission efficiencies at the corresponding target wavelengths of each vertically or horizontally aligned channels were obtained mostly to be near-unity together with very small crosstalk ranges of around 0.01% - 1.2%. The inverse design approach allowing the implementation of more than four output channels together with the novel functionalities will pave the way for compact and manufacturable lxN couplers, which is of ultimate significance for integrated photonics.

Designs of photonic devices have been mainly based on intuitive and brute-force approach. However, there has been increasing demand in photonics to obtain high device performance and improved functionalities along with small footprints. Among the different algorithms developed so far, objective-first inverse design algorithm is one of the greatly utilized methods. In the present work, we apply inverse design algorithm to investigate efficient and compact 1×N (1×2, 1×4) wavelength de-multiplexers for use at telecommunications wavelengths. Besides, we study different photonic structures such as nano-beam cavity and optical filters. Contrary to the forward design method, inverse design approach provides functional and compact photonic devices and it opens new avenues in exploiting the full space of practical structures. © 2019 IEEE., Türkiye Bilimler Akademisi

We propose and demonstrate reduced symmetry photonic surfaces providing highly controlled Bloch wave propagation. The backward and dual directional propagations have been observed in the proposed low-symmetric periodic structures without variation in the unit-cell filling factor. Frequency-domain analyses present group indices up to negative/positive −237∕ 96 as strong indicators of the observed directional controlled surface waves driven by the orientation angle in the range of 20°–90°. Further verification of the index-based propagation direction has been achieved through detailed time-domain analyses and microwave experiments. Smart management of the propagation direction in low-symmetric surfaces has great potential for next-generation photonic applications.

Designs of photonic devices have been mainly based on intuitive and brute-force approach. However, there has been increasing demand in photonics to obtain high device performance and improved functionalities along with small footprints. Among the different algorithms developed so far, objective-first inverse design algorithm is one of the greatly utilized methods. In the present work, we apply inverse design algorithm to investigate efficient and compact 1×N (1×2, 1×4) wavelength de-multiplexers for use at telecommunications wavelengths. Besides, we study different photonic structures such as nano-beam cavity and optical filters. Contrary to the forward design method, inverse design approach provides functional and compact photonic devices and it opens new avenues in exploiting the full space of practical structures. © 2019 IEEE., Türkiye Bilimler Akademisi

We propose and demonstrate reduced symmetry photonic surfaces providing highly controlled Bloch wave propagation. The backward and dual directional propagations have been observed in the proposed low-symmetric periodic structures without variation in the unit-cell filling factor. Frequency-domain analyses present group indices up to negative/positive −237∕ 96 as strong indicators of the observed directional controlled surface waves driven by the orientation angle in the range of 20°–90°. Further verification of the index-based propagation direction has been achieved through detailed time-domain analyses and microwave experiments. Smart management of the propagation direction in low-symmetric surfaces has great potential for next-generation photonic applications.