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Dalga boyundan daha küçük boyuttaki ışık soğurucuları optoelektronik, foton algılama, solar hücre ve sensör alanlarında çok büyük bir potansiyele sahiptir. Cihazın boyutlarını küçültmek yapay ve ileri seviye özellikler kazandırır. Günümüz yarı iletken teknolojisindeki daha küçük boyutta ve daha yüksek performans gösteren cihazların üretilmeye çalışılmasının yükselen bir trend olması bundan dolayıdır. Elektromanyetik dalga soğurucularının performansını ve çalıştığı ışık tayfı bölgesini belirleyen iki temel özellik vardır: malzeme seçimi ve yapının şekli. Mükemmel ışık soğurucuları ışığı yapılarında hapsedebilmek için bir metal, yarı iletken veya herhangi çeşitte soğurma özelliği olan bir katmana ihtiyaç duyar. Geleneksel metaller çoğunlukla birincil olarak tercih edilen malzeme olmasına rağmen hem yitimli bir yapıya sahip olan hem de üretim, entegrasyon ve ayarlanabilirlik gibi daha üstün termal özellikleri olan başka türde malzemeler de mevcuttur.Geleneksel metaller yitimli bir yapıya sahip olmaları sebebiyle harika soğrucu malzemeler olmalarına rağmen aşınma ve oksitlenmeye karşı dayanıklı değillerdir. İlk çalışmamızda, geleneksel metallere alternatif bir malzeme olarak geçiş metali karbürlerinin ve geçiş metali nitrürlerinin ışığın görünür bölgeden (Vis) yakın kızıl ötesi bölgeye (NIR) kadar çok geniş bir frekans aralığında mükemmel bir şekilde soğurulmasındaki eşsiz potansiyelini inceledik. İlk olarak, mükemmel ışık soğurucularının gereksinimleri hakkında bir öngörü sahibi olmak için geçiş matrisi metodu (TMM) olarak adlandırılan sistematik bir modelleme tekniği kullanıldı. Elde edilen modelleme sonuçları geçiş metali karbürlerinin ve nitrürlerinin elektriksel geçirgenlik değerlerinin ideal değerler ile çok iyi örtüştüğünü ispatlamaktadır. Ayrıca bu seramik malzemeler metallere kıyasla daha iyi termal özelliklere ve de aşınma ve oksitlenmeye karşı dayanıklı olduklarından da tercih edilmektedirler. Bu özellikleri sayesinde yüksek verimlilikle çalışan ve uzun süreli stabil olan ışık toplayan sistemlerin dizaynı için bir fırsat sunmaktadırlar. Düzlemsel ve ikizkenar yamuk şeklinde sıralanmış katmanlardan oluşan iki farklı şekil kullanıldı. Numerik simülasyon teknikleri kullanılarak her bir karbür ve nitrür için yapıların optik performansları optimize edildi. Bulunan sonuçlar bu seramik malzemelerin bütün yitimli yapıdaki ve plazmonik özellikteki metallere kıyasla daha geniş aralığı soğurabildiğini göstermektedir. Düzlemsel dizilişte titanyum karbür (TiC) 405 nm-1495 nm aralığı kadar geniş bir bandı 0.9'un (normalize olarak) üzerinde soğurarak en geniş soğurma bandını gerçekleştirmiştir. İkizkenar yamuk dizilişinde ise vanadyum nitrürün (VN) 300 nm ile 2500 nm aralığı kadar geniş bir bant genişliğine sahip olduğu görülmüştür. Bu çalışmanın çıktıları solar buhar üretimi ve termal fotovoltaik gibi hem optik hem de termal gereksinimleri olan alanlar dahil olmak üzere gelecekteki yüksek performanslı enerji dönüşüm cihazlarının dizaynı konusunda bir yol ışığı olabilecek niteliktedir.Mevcut dizaynların büyük bir çoğunluğu üretim aşamasında bir litografi aşaması gerektirmektedir ki bu da yapının büyük boyutlarda üretilmeye uygunluğunu ve tekrar edilebilirliğini engellemektedir. İkinci çalışmamızda, litografisiz üretilebilen, sadece bizmut (Bi) metalinden yapılmış nanoyapılardan oluşan, çift fonksiyon gösteren, görünür ve yakın kızıl ötesi bölgede çok geniş bantlı soğurucu, orta kızıl ötesi bölgede ise çok yüksek kırıcılık indisi hassaslığı olan bir dart bantlı soğurucu olarak davranan bir yapı dizayn ettik, ürettik ve karakterize ettik. Bizmutun geleneksel metallere kıyasla çok daha iyi bir elektriksel geçirgenlik özelliği olduğu geçiş matrisi metodu ve Bruggeman'ın etkin ortam kuramı (EMT) kullanılarak ayrıntılı bir şekilde incelendi ve açıklandı. Yapının litografi kullanılmadan, büyük boyutlarda üretimini mümkün kılacak şekilde üretilmesi için eğik açılı kaplama tekniği kullanılarak çok yoğun biçimde dizilmiş ve rastgele yerleşmiş/yönelmiş Bi nanoyapıları elde edildi. Ayrıca, bu üretim tekniğinin alttan üste işlemleme yaklaşımıyla üretilen yapının yerleşmesinin ve uzunluğunun kontrol edildiği gösterilmiştir. Karakterizasyon sonuçlarına göre yapı görünür ve yakın kızılötesi bölgelerinde 0.8 üzerinde soğurmaya sahipken orta kızılötesi bölgede ise 6.54 µm merkezlenmiş dar bantlı bir soğurma göstermektedir. Bi yapılarının çok yoğun bir biçimde paketlenmesinden ve sıradışı bir geçirgenlik özelliğine sahip olmasından dolayı nanoyapılar, aralarındaki çok küçük boşluklarda güçlü bir şekilde ışığı hapsedebilmektedir ve bu özellikleri algılama uygulamalarında kullanılmaya uygundur. Yapılan incelemede Bi nanoyapılarının 2.151 µm/birim kırıcılık indisi (RIU) kadar yüksek bir hassaslık değerine sahip olduğu ölçülmüştür. Bu değer bilindiği kadarıyla şimdiye kadar deneysel olarak elde edilen en yüksek hassaslık değeridir. Basit ve büyük boyutlarda üretime uygun olan üretim rotasının olması ve bizmutun eşsiz optik özellikleri, bu dizaynı birçok optoelektronik ve sensör uygulamaları için ümit verici kılmaktadır. Subwavelength light absorbers have an enormous potential on applications such as photodetection, optoelectronics, solar cells and sensing. Scaling down the device dimensions provides artificial and advanced properties. That's why achieving higher performance devices with smaller sizes is the main trend in semiconductor technology. Design of an electromagnetic wave absorber has two dominant factors on the performance and spectral operation region: material selection and design configuration. Perfect light absorbers require an absorbing layer, such as a metal, semiconductor or any type of absorbing material, to achieve light confinement. While conventional metals have been mostly the primary choice in designs, there are various material types other than them which can have advantageous thermal properties in fabrication, integration or tunability besides having lossy nature.Although conventional metals are great absorbing materials due to lossy natures, they are not durable against erosion and oxidation. In the first work, we scrutinize unprecedented potential of transition metal carbides (TMCs) and nitrides (TMNs) as optional materials to conventional metals, for realization of light perfect absorption in an ultra-broad frequency range encompassing all of the visible (Vis) and near infrared (NIR) regions. To gain insight on the condition for light perfect absorption, a systematic modeling approach based on transfer matrix method (TMM) is firstly utilized. Our modeling findings prove that the permittivity data of these TMCs and TMNs are closely matched with the ideal data. Thus, they can have stronger and broader absorption behavior compared to metals. Besides, these ceramic materials are preferred to metals due to the fact that they have better thermal properties and higher durability against erosion and oxidation than metals. This could provide the opportunity for design of highly efficient light harvesting systems with long-term stability. Two different configurations which are planar and trapezoidal arrays are employed. Numerical simulations are conducted to optimize the device optical performance for each of the proposed carbides and nitrides. Our findings reveal that these ceramic coatings have the broadest absorption response compared to all lossy and plasmonic metals. In planar configuration, titanium carbide (TiC) has the largest absorption bandwidth (BW) where an absorption above 0.9 is retained over a broad wavelength range of 405 nm-1495 nm. In trapezoid architecture, vanadium nitride (VN) shows the widest BW covering a range from 300 nm to 2500 nm. The results of this study can serve as a beacon for the design of future high performance energy conversion devices including solar vapor generation and thermal photovoltaics where both optical and thermal requirements can be satisfied.Majority of existing designs necessitate a lithography-step during the fabrication, which hinders the repeatability, upscaling and large-scale compatibility of these designs. In the second work, we designed, fabricated and characterized a lithography free, double functional single Bismuth (Bi) metal nanostructure for ultra-broadband absorption in the visible and near-infrared, and narrowband response with ultra-high refractive-index sensitivity in mid-infrared (MIR) range. The superior permittivity data of Bi over conventional metals is comprehensively analyzed and explained using systematic modeling approaches based on TMM and Bruggeman's effective medium theory (EMT). To achieve a large scale fabrication of the design in a lithography-free route, oblique-angle deposition approach is used to obtain densely packed and randomly spaced/oriented Bi nanostructures. It has been shown that this fabrication technique can provide a bottom-up approach to control the length and spacing of the design. Our characterization findings reveal a broadband absorption above 0.8 in Vis and NIR, and a narrowband absorption centered around 6.54 µm. Due to densely packed architecture of the Bi nanostructures and its extraordinary permittivity response, they can provide strong field confinement in their ultra-small gaps and this could be utilized for sensing application. An ultrahigh sensitivity of 2.151 µm/refractive-index-unit (RIU) is acquired for this Bi nanostructured absorber, which is, to the best of our knowledge, the experimentally attained highest sensitivity so far. The simple and large scale compatible fabrication route of the design together with extraordinary optical response of Bi coating, makes this design promising for many optoelectronic and sensing applications. 98

High electron mobility transistors (HEMTs) based on gallium nitride (GaN) with a wide range of application potentials need to be rigorously examined for reliability to take advantage of their intrinsically extraordinary properties. The most vital parameter of the reliability, the hotspot, or Tmax, resides in the two-dimensional electron gas (2DEG) temperature profile inside the device where optical access is often restricted. The device surface temperature can be measured by widespread IR thermography with the limitation of diffraction-based IR transmission losses. However, Tmax on the sub-surface cannot be reached thermographically. Although finite element analysis (FEA)-based thermal simulations can easily reveal the 2DEG temperature profile, accuracy is tightly dependent on the realistic modeling of material/structure parameters. Because these parameters are rather sensitive to fabrication and processing, it is quite difficult to specify them accurately. To overcome these drawbacks, a method integrating both IR thermography and FEA thermal analysis is demonstrated on a fabricated high-power 40 × 360 μm packaged GaN HEMT as a proof-of-concept. Utilizing the simulation and measurement temperature profiles, a correlation algorithm is developed so that accuracy of the FEA thermal simulation is improved by calibrating the parameters specific to fabrication/process conditions by thermographic measurement. Then, it is quantitatively shown that the proposed method is able to find the 2DEG temperature profile and Tmax with an accuracy that best suits the intrinsic and extrinsic characteristics of the device under test. The method sheds light on GaN reliability engineering by providing a feasible and reliable alternative to realistically reveal hotspot information for device lifetime assessments.

Passive radiative cooling (PasRadCool), which emits thermal energy from objects to deep cold space through atmospheric transparency, offers complementary and alternative green energy solutions for passive cooling of buildings, clothing, and renewable energy harvesting. Depending on the spectral emissive/absorptive properties of the unit under test (UUT), radiative heat exchanges occur between the UUT, atmosphere, and sun, while at the same time non-radiative heat exchange occurs. The performance of the PasRadCool is determined by the combined thermal and thermodynamic effects of both exchange mechanisms. Although the non-radiative heat exchange, which consists of conductive and convective processes to the outer surfaces of the UUT and the surrounding air fluid, is very sensitive to environmental changes, the actual performance is not fully determined since this feature is considered statically in many studies. Herein, we propose a method that reveals the non-radiative thermal characteristics of the PasRadCool under real operating conditions. With a photonic radiative cooler structure, which we manufacture as a proof of concept, we perform nighttime field test measurements in varying non-radiative thermal conditions. The proposed method extracts the time-dependent non-radiative heat transfer coefficient of the UUT as accurately as possible. We also confirm that our experimental result shows good agreement with both numerical and analytical methods. The proposed approach, which highlights the realistic thermal management of PasRadCool, is not specific to the circumstances of our study and can be applied to all PasRadCool situations with different geometry, material, and environmental conditions.

In this paper, we scrutinize unprecedented potential of transition metal carbides (TMCs) and nitrides (TMNs) for realization of light perfect absorption in an ultra-broad frequency range encompassing all of the visible (Vis) and near infrared (NIR) regions. For this purpose, two different configurations which are planar and trapezoidal array are employed. To gain insight on the condition for light perfect absorption, a systematic modeling approach based on transfer matrix method (TMM) is firstly utilized. Our modeling findings prove that the permittivity data of these TMCs and TMNs are closely matched with the ideal data. Thus, they can have stronger and broader absorption behavior compared to metals. Besides, these ceramic materials are preferred to metals due to the fact that they have better thermal properties and higher durability against erosion and oxidation than metals. This could provide the opportunity for design of highly efficient light harvesting systems with long-term stability. Numerical simulations are conducted to optimize the device optical performance for each of the proposed carbides and nitrides. Our findings reveal that these ceramic coatings have the broadest absorption response compared to all lossy and plasmonic metals. In planar configuration, titanium carbide (TiC) has the largest absorption bandwidth (BW) where an absorption above 0.9 is retained over a broad wavelength range of 405–1495 nm. In trapezoid architecture, vanadium nitride (VN) shows the widest BW covering a range from 300 to 2500 nm. The results of this study can serve as a beacon for the design of future high-performance energy conversion devices including solar vapor generation and thermal photovoltaics where both optical and thermal requirements can be satisfied. TÜBİTAK

In this Letter, we demonstrate strong light emission from defective hexagonal boron nitride (hBN) defect centers upon their coupling with disorder near-touching plasmonic units. Based on numerical simulations and characterization results, the plasmonic design at thin layer thicknesses of 20 nm can provide above 2 orders of magnitude enhancement in photoluminescence (PL) spectra. Moreover, this plasmonic platform shortens the luminescence lifetime of the emitters. The proposed design can be easily extended to other plasmonic-emitter combinations where strong light-matter interaction can be achieved using large-scale compatible routes. (C) 2021 Optical Society of America

In this Letter, we numerically propose the one-way perfect absorption of near-infrared radiation in a tunable spectral range with high transmission in the neighboring spectral ranges. This functionality is obtained by using a two-dimensional, guided-mode resonance-based grating-waveguide metasurface that acts as a frequency-selective reflector, a spacer dielectric, and an absorbing oxide layer. Within the bandwidth of the excited guided-mode resonance excited at 1.82 mu m (with a full-width at half-maximum of 19 nm), we confirmed perfect absorption when light was incident from one of the two opposite directions, whereas in the other direction, perfect reflection was observed. The forward-to-backward absorption ratio reached as high as 60, while the thickness of the entire structure was on the order of the operating wavelength. In addition to the spectral tunability of the excited resonances and their bandwidths, our proposed device supports transparency windows with 65% transmission in the adjacent frequency bands. Our 2D grating is also verified to enable near-absolute insensitivity to the polarization state of incident light. Geometrical parameter modification also gives our design great tunability, as we also designed a device with a 300 nm absorption/reflection linewidth. (C) 2020 Optical Society of America

A lithography‐free, double‐functional single bismuth (Bi) metal nanostructure is designed, fabricated, and characterized for ultrabroadband absorption in the visible (vis) and near‐infrared (NIR) ranges, and for a narrowband response with ultrahigh refractive index sensitivity in the mid‐infrared (MIR) range. To achieve a large‐scale fabrication of the design in a lithography‐free route, the oblique‐angle deposition approach is used to obtain densely packed and randomly spaced/oriented Bi nanostructures. It is shown that this fabrication technique can provide a bottom‐up approach to controlling the length and spacing of the design. The characterization findings reveal a broadband absorbance above 0.8 in vis and NIR, and a narrowband absorbance centered around 6.54 µm. Dense architecture and extraordinary permittivity of Bi provide strong field confinement in ultrasmall gaps between nanostructures, and this can be utilized for a sensing application. An ultrahigh sensitivity of 2151 nm refractive‐index unit (RIU–1) is acquired, which is, as far as it is known, the experimentally highest sensitivity attained so far. The simple and large‐scale compatible fabrication route of the design together with the extraordinary optical response of Bi coating makes this design promising for many optoelectronic and sensing applications. Scientific and Technological Research Council of Turkey DPT‐HAMIT. Grant Numbers: 113E331, 114E374, 115F560 Turkish Academy of Sciences Türkiye Bilimsel ve Teknolojik Araştirma Kurumu. Grant Number: 115F560

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO4 ) nanostructures, yielding Au-capped BiVO4 (Au-BiVO4 ). The formation of multiple size/dimension Au capping islands provides strong light-matter interactions at nanoscale dimensions. These plasmonic particles not only enhance light absorption in the bulk BiVO4 (through the excitation of Fabry-Perot (FP) modes) but also contribute to photocurrent generation through the injection of sub-band-gap hot electrons. To substantiate the activity of the photoanodes, the interfacial electron dynamics are significantly improved by using a PBA water oxidation catalyst (WOC) resulting in an Au-BiVO4 /PBA assembly. At 1.23 V (vs. RHE), the photocurrent value for a bare BiVO4 photoanode was obtained as 190 μA cm-2 , whereas it was boosted to 295 μA cm-2 and 1800 μA cm-2 for Au-BiVO4 and Au-BiVO4 /PBA, respectively. Our results suggest that this simple and facial synthetic approach paves the way for plasmonic-based solar water splitting, in which a variety of common metals and semiconductors can be employed in conjunction with catalyst designs., Scientific and Technological Research Council of Turkey (TÜBİTAK); DPT-HAMIT; Turkish Academy of Sciences; TÜBA-GEBİP for Young İnvestigator Award; BAGEP for Young Scientist Award

Date of Conference: 11-15 August 2019 Conference Name: SPIE Nanoscience + Engineering, 2019 Optical Solar Reflectors (OSRs) form the physical interface between the spacecraft and space and they are essential for the stabilization and uniform distribution of temperature throughout the spacecraft. OSRs need to possess a spectrally selective response of broadband and perfect electromagnetic wave absorption in the thermal-infrared spectral range, while strongly reflecting the solar energy input. In this work, we experimentally show that disordered and densely packed ITO nanorod forests can be used as an excellent top-layer metasurface in a metal-insulator-oxide cavity configuration, and a thermal-emissivity of 0.97 is experimentally realized in the spectral range from 2.5 to 25 μm. The low-loss dielectric response of ITO in the solar spectrum, from 300 nm to 2.5 μm range limited the solar absorptivity to an experimental value of 0.167. These make our proposed design highly promising for its application in space missions due to combining high throughput, robustness, low cost with ultra-high performance. The Society of Photo-Optical Instrumentation Engineers (SPIE)

Precise control and stabilization of the operating temperature environment of spacecraft and satellites during their life cycle is of paramount importance to increase device reliabilities and reduce the thermomechanical constraints. Optical solar reflectors are the physical interface between the spacecraft and space, and they are broadband mirrors for the solar spectrum, while having strong thermal emission in the mid-infrared part of the electromagnetic spectrum. Strong light matter interactions in metamaterials and metasurfaces offer significant advantages compared to the conventional methods in performance, weight, launch, and assembly costs. However, the fabrication complexity of these metastructures due to necessitating lithography hinders their upscaling, reproducibility, large-area compatibility, and mass production. In this regard, we propose a facile, lithography-free fabrication route, exploiting oblique deposition to design a metasurface based on disordered and densely packed Indium Tin Oxide (ITO) nanorod forests. The excellent light trapping capability of the nanorod forests, randomness in the geometrical dimensions of these nanorods, combined with the lossy plasmonic nature of ITO in the thermal-infrared range led to strong coupling of thermal radiation to broad plasmonic resonances and, consequently, an experimental emissivity of 0.968, in a very wide range from 2.5 to 25 pm. In the solar spectrum, the low-loss dielectric characteristic of ITO resulted in an experimental solar absorptivity as small as 0.168. Our proposed design with high throughput, robustness, low cost, and high performance, therefore, shows great promise not only for space missions, but also for promoting environmentally friendly passive radiative cooling for our planet and thermal imaging in the field of security labeling.

In this article, a lithography-free multilayer based color filter is realized using a proper series connection of two cavities that shows relatively high efficiency, high color purity, and a wide view angle. The proposed structure is a metal-insulator-metal-insulator-semiconductor (MIMIS) design. To optimize the device performance, at the first step, transfer matrix method (TMM) modeling is utilized to find the right choices of materials for each layer. Simulations are carried out later on to optimize the geometries of the layers to obtain our desired colors. Finally, the optimized devices are fabricated and experimentally characterized to evaluate our modelling findings. The characterization results of the fabricated samples prove the successful formation of efficient and wide view angle color filters. Unlike previously reported FP based designs that act as a band-stop filter in reflection mode (absorbing a narrow frequency range and reflecting the rest of the spectrum), this design generates a specific color by reflecting a narrow spectral range and absorbing the rest of the spectrum. The findings of this work can be extended to other multilayer structures where an efficient connection of cavities in a tandem scheme can propose functionalities that cannot be realized with conventional FP resonators.

Colorimetric detection of target molecules with insensitivity to incident-light polarization has attracted considerable attention in recent years. This resulted from the ability to provide rapid output and reduced assay times as a result of color changes upon altering the environment that are easily distinguishable by the naked eye. In this paper, we propose a highly sensitive refractive-index sensor, utilizing the excitation of guided modes of a novel two-dimensional periodically modulated dielectric grating-waveguide structure. The optimized nanosensor can numerically excite guided-mode resonances with an ultranarrow linewidth (full width at half-maximum) of 0.58 nm. Sensitivity is numerically investigated by considering the deposition of dielectric layers on the structure. For a layer thickness of 30 nm, the maximum sensitivity reached as high as 110 nm/refractive index unit (RIU), resulting in a very high figure of merit of 190. The fabricated devices with 30 nm aluminum oxide and zinc oxide coatings achieved a maximum sensitivity of 235.2 nm/RIU with a linewidth of 19 nm. Colorimetric detection with polarization insensitivity is confirmed practically by a simple optical microscope. Samples with different coatings have been observed to have clearly distinct colors, while the color of each sample is nearly identical upon azimuthal rotation. Excellent agreement is obtained between the numerical and experimental results regarding the spectral position of the resonances and sensitivity. The proposed device is, therefore, highly promising in efficient, highly sensitive, almost lossless, and compact molecular diagnostics in the field of biomedicine with personalized, label-free, early point-of-care diagnosis and field analysis, drug detection, and environmental monitoring.

Materials with a tunable optical response that can be controllably tailored using external stimuli excitation have undergone considerable research effort for the development of active optical devices, such as thermo-optical modulators. Although bismuth (Bi) nanodots, embedded into glass matrices, have been proven to have a thermo-optical response, the recyclability of the structure in solid-liquid phase transitions is a major challenge. Herein, a facile and lithography-free fabrication method is proposed to realize densely packed stand-alone Bi nanorods (NRs), with deep subwavelength gaps and a resonance at the midinfrared range (lambda approximately equal to 4.462 mu m). Owing to these ultrasmall gaps that support lossy Mie-like resonances, strong field confinement is achieved, and the resonance wavelength exhibits great sensitivity to temperature, as the thermal sensitivity reaches as high as 1.0316 nm degrees C-1. This operation is conducted in the moderate temperature interval of 25-85 degrees C, which is far from the melting point of Bi. Overall, our simple, robust, and high-performance device is highly promising for realizing optical switches, thermo-optic modulators, and infrared camouflage.