This PDF file contains the front matter associated with SPIE Proceedings Volume 11089, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The coherent backlight unit (C-BLU) using a diffractive optical element (DOE) for full-color flat-panel holographic display is proposed. The coherent backlight unit is composed of two diffractive optical elements (DOEs) that are imprinted on the same glass substrate. The illumination area of the backlight is 250 mm x 130 mm and the thickness is 2.2 mm, which is slim compared to other conventional coherent backlight units for holographic display systems. In experiments, the total efficiency is measured as 0.8% at red (638 nm), 3.9% at green (520nm), and 3.4% of blue (473 nm). As a result, we could get the 10 inch full color holographic display with 4k resolution.

Infrared rectennas often use metal-insulator-insulator-metal (MIIM) diodes since their femtosecond scale tunneling is fast enough to rectify terahertz signals. Many factors threaten to degrade the rectenna performance, such as impedance matching with the antenna and material losses at frequency, but the most challenging limitation is the diode’s rectification efficiency. Geometric diodes, planar conductors with a geometric asymmetry that imposes a preferred current direction, offer several advantages over MIIM diodes including negligible capacitance and greater tolerance to high input powers. For carriers to experience the geometric features that promote current asymmetry, their mean-free-path length must be on the order of, or greater than, critical device dimensions. Graphene, with long carrier mean-free-path lengths, is therefore a choice material. By optimizing the geometry of these diodes, their current-voltage characteristics can be made to exhibit large current asymmetries, which is crucial for efficient rectification. The challenge is tuning the geometry to achieve large asymmetries at sufficiently low voltages for efficient operation in rectennas. A Monte Carlo simulator tracked the motion of electrons under an applied bias to determine the current-voltage characteristics for geometric diodes of a specified shape, and various geometries were analyzed to deduce important diode parameters. The current-voltage characteristics were then used in a rectifier circuit simulator to assess attainable rectification efficiencies, and compare them to those of the best projected MIIM diode from a quantum tunneling simulator. The results suggest that geometric diodes may offer improved rectification efficiencies over MIIM diodes for high input powers.

Perfect light absorption (PLA) in nanophotonics has a wide range of applications from solar-thermal based applications to radiative cooling. However, most of the proposed platforms require intense lithography which makes them of minor practical relevance. On the other hand, thin-film light absorbers are lithographically free and can be deposited cheaply on large area based on matured technologies. However, thin-film light absorbers were thought to have major limitation and cannot be tailored compared to metamaterials. Here, we show how to design PLA using thin-films in terms of wavelength range, bandwidth, spatial profile of optical losses, directionality and iridescence. We also show that iridescent free, PLA can occur by simply heating metallic thin-films when the metal is of low reflectance and its oxide is of high refractive index. We theoretically and experimentally demonstrate Generalized Brewster angle effect in thin film light absorbers. In addition, we demonstrate hydrogen sensing using three different PLA strategies showing record sensitivity and figure of merit. Furthermore, we show various strategies to create ultra-pure structural colors. Finally, we demonstrate different solar-thermal applications for novel thin-film PLA designs.

This report reviews progress in capillary-force-directed self-assembly fabrication methods together with applications of the suspended structures as fiber-based optical components, cells scaffolds for tissue regeneration, and as templates for suspended microfluidic networks and nanomaterials. Capillary forces can direct polymeric solutions, melts and nanocomposites to form near constant diameter fibers, not just over long distances, as in electrospinning, but over micron to centimeter distances typical of integrated circuits and MEMS. Crude hand-brushing of polymeric solutions over micropillar arrays has produced, in a matter of seconds, uniform arrays of near identical nanofibers and trampolinelike membranes suspended between the micropillars. Direct point-to-point writing has also been accomplished with AFM tips, capillary syringes and electrospinning jets. The brush-on method, while fast, does not produce arbitrary patterns. The direct-write method, while producing arbitrary patterns, is slow. Recently, fast arbitrary patterning has been demonstrated by photopatterning holes through thin suspended polymer films, followed by thermal annealing which causes holes, driven by capillary force, to expand, form threads and thin into fibers. For an ablation threshold of polystyrene of 10 mJ/cm² at 193 nm there are many adequately intense excimer lasers that could be incorporated into roll-to-roll systems. At a hole exposure threshold of ~1 mJ/cm² , even current 193 nm wafer stepping projection printers could pattern wafers with arbitrary suspended structures at economically sustainable production rates of greater than 50 wafers per hour. A new method of extending this fabrication method to three-dimensions is also described, that additionally overcomes the need for prefabricated micropillar arrays.

Surface enhanced Raman scattering (SERS) is a vibrational spectroscopy method that enables the quantification of the concentration of small molecules. SERS sensing has been demonstrated in a wide variety of applications, from explosive and drug detection, to monitoring of bacteria growth. Underpinning SERS sensing are the sensor surfaces that are composed of vast quantities of metal nanostructures which confine light into small gaps called “hotspots”, enhancing Raman scattering. While these surfaces are essential for increasing Raman scattering intensity so that analyte signal may be observed in small concentrations, they introduce signal variations due to spatial distributions of Raman enhancement and hotspot volume. In this work, we introduce a convolutional neural network model that improves concentration regressions in SERS sensors by learning the distributions of sensor surface dependent latent variables. We demonstrate that this model significantly improves predictions compared to a traditional multilayer perceptron approach, and that the model uses analyte spectral information and is capable of reasonable interpolations.

We show a fully integrated, coherently combined laser system in the InP-Si₃N₄ hybrid platform. Coherent combining of two InP-based gain chips is obtained with a combining efficiency of ~92%. Besides, we demonstrate narrow-linewidth, tunable diode lasers in InP/GaAs-Si₃N₄ platform. The Si₃N₄ photonic integrated circuit performs as a tunable external cavity for both InP and GaAs gain chips simultaneously. Single frequency lasing at 1.55 and 1 um is simultaneously obtained on a single chip with the spectral linewidths of 18-kHz and 70-kHz respectively. We also obtain wide-angle beam steering by using the wide wavelength tuning range provided by dual-band diode lasers.

This study considers a recently proposed topology optimization based approach for designing photonic membrane cavities supporting a dipole cavity mode. Foremost, the study demonstrates that the approach is robust towards the choice of initial guess provided for the optimization problem, in the sense that near identical final designs are obtained for vastly different initial guesses. This finding suggests that the final designs are near-optimal under the given design constraints. Secondarily, by stopping the design procedure after the same fixed number of design iterations for all initial guesses, it shows that the designed photonic cavity is sensitive towards certain small perturbations of their geometry, stressing the need for utilizing robust optimization techniques and imposing fabrication conforming length-scales in the cavity geometries.

Sensing the direction of sounds provides animals clear evolutionary advantage. For large animals in which the distance between the ears is larger or comparable to the audible sound wavelength, directional hearing is simply accomplished by recognizing the intensity and time differences of the wave impinging on the two ears. In small (subwavelength) animals, angle sensing seems instead to rely on coherent coupling of soundwaves from the two ears. Inspired by this natural design, here we present a subwavelength photodetection pixel that can measure both the intensity and the incident angle of light. It consists of two silicon nanowire optical resonators spaced at subwavelength distance that are electrically isolated but optically coupled. We exploit this effect to fabricate a subwavelength angle-sensitive pixels.

The ultra-small size of CdSe quantum dots (US-CdSe), which have both the surface state and band edge emissions, have been paid more attention owing to their unique optical properties. However, the low quantum yield (QY) and poor stability limits their application in solid-state lighting (SSL). In order to solving above problems, the US-CdSe were prepared by adding zinc element and coating with SiO₂ through the colloidal chemistry method. The result shows that the QY of US-CdSe is improved from 18 to 36 % after zinc doped due to enhance the band edge emission intensity as well as the stability also can be improved after zinc doping. Moreover, the band edge and surface state emission peaks for all samples fix at 440 and 540 nm, respectively. The US-CdSe and CdSe:Znx QDs were stored at room temperature for 5 months, and the CdSe:Zn15 has the highest QY enhancement of 5.6%/month. The luminous intensity of CdSe:Znx QDs coated with SiO₂ only decreases between 8 to 18 % depends on Zn concentrations, while the as-prepared US-CdSe decreases more than 18 % at 100 °C, meaning that the SiO₂-coating sample have excellent thermal stability and more potential for SSL application.

The coupling between surface plasmons (SPs) and excitons in 2D transition metal dichalcogenide (TMD) materials has been attracted growing research attention in recent days. Strong electric field confinement and absorption enhancement could be expected, as a result of the SP-excition couping. We prepared exfoliated flakes of MoS2, a representative TMD material, on Au nanogratings fabricated by electron beam lithography. We studied influences of propagating SP on optical properties of the MoS2 flakes on the Au nanogratings, based on both experimental measurements and numerical calculations. Local surface potential maps of the samples suggested that the strain states in the MoS2 flakes and the dipoles formed at the MoS2/ Au interface could cause spatial modulation of the bandgap energies of the MoS2 flakes. The surface potential measurements were carried out using Kelvin probe force microscopy in dark and under TM/TE-mode light illumination. Band diagrams of the MoS2/Au nanogratings were proposed to explain all the experimental results. This study can help us to understand and control the physical characteristics of the TMD/metal nanostructures.

Metallic nitrides are cutting-edge materials for nano plasmonics. The authors focused on a fabrication of subwavelength films with them by pulsed laser deposition at 355 nm. Fortunately an initial stage of the PLD process succeeded in depositing titanium nitride (TiN), aluminum nitride (AlN), silver (Ag), gold (Au), copper (Cu), and aluminum (Al) thin films on glass substrate. Basically the deposition rate depended on each material, laser energy (pulse fluence), and distance between the target and substrate, and the thickness of the PLDed films proportional to pulse number. But the deposition rate or angular distribution of the plume is poorly-reproducible. We have been exploring an improvement in the situation through rotation of target, expansion of the laser spot, and minor addition of argon with QCM deposition monitor.

Recent developments in hybrid electro-optic (EO) systems, in which an organic material with an ultra-large second-order susceptibility is combined with silicon (SOH) or gold (POH) waveguides at the nanoscale. Tight confinement of the optical and RF fields in such devices has enabled operating frequencies > 300 GHz and voltage-length parameters (UπL) < 40 V-μm with existing high-performance organic electro-optic (OEO) materials. However, achieving UπL values on the order of 1 V-μm will require a new generation of OEO materials. The short path lengths within hybrid devices greatly alleviate concerns about optical loss, enabling development of OEO chromophores with extraordinarily large hyperpolarizabilities and refractive indices at telecom wavelengths. However, as device dimensions shrink, chromophore-surface interactions, space-efficiency, and refractive index anisotropy become more critical. Practical device implementations also require materials with high thermal and chemical stability and uncompromising EO performance. We have used a theory-aided design process applying classical and quantum mechanical techniques to design a new generation of OEO materials intended to meet the needs of hybrid devices. We have synthesized these materials, characterized their hyperpolarizability by hyper-Rayleigh scattering, and evaluated their bulk electro-optic behavior and prospects for implementation in nanoscale devices.

Recently femtosecond laser has been proved to shift the resonance in the far-field and enhance the field distribution in the near field by modifying the shape of nanoparticles. Here we estimate the photoluminesence properties of hybrid oligomers integrated with nanodiamonds by examining the near-field distribution and calculating the Purcell factor in 3D orientations.

We design two different compact and low-loss 2D T-junction optical mode demultiplexing by using objective-first inverse design algorithm. These devices are designed for transverse-electric (TE) and transverse magnetic (TM), separately. High device performances were achieved for the specific designs of 1×2, 1×3 mode demultiplexers with fractional footprints at the orders of a few microns. The presented T-junction 1×2, 1×3 devices operate at the C-band; the device has a footprint of 2.8 μm × 2.8 μm and 4.44 μm × 4.44 μm, respectively and splits TE/TM_0,1,2 modes efficiently. The modal efficiencies at the corresponding target wavelength of each vertically or horizontally aligned channels were obtained mostly to be nearunity together with minimal crosstalk ranges of around <-30 dB. The electromagnetic inverse design allowing the implementation of more than three output channels along with the novel functionalities will pave the way for compact and manufacturable 1xN couplers, which is of ultimate significance for integrated photonics.

C-Ti multilayer nanostructures were deposed by Thermionic Vacuum Arc (TVA) technology. The layers consisting of about 100nm Carbon base layer and seven 40nm alternatively T i and C layers were deposed on Silicon substrates. The thickness of such a multilayer structure was up to 500nm. On the other hand, in order to obtain C-Ti multilayer structures with variable thickness and different percentages in C and T i of layers, a 20nm thick C layer was first deposed on Si substrate and then seven T i-C layers, each of these having different thickness of up to 40nm were deposed. To perform the successively layers with various thickness were changed the discharge parameters for C and T i plasma sources to obtain the desirable thickness. By changing of substrate temperature between room temperature and 300°C and on the other hand the bias voltage up to −700V , different batches of samples were obtained for this study. To characterize microstructure properties of as prepared C-Ti multilayer structures were used Electron Microscopy techniques (TEM, SEM, STEM), X-Ray Photoelectron Spectroscopy, Raman Spectroscopy and RBS techniques. The measurements reveal the content of diamond-like sp³ and graphite-like sp² ; the ratio sp³/sp² increases when the bias voltage increases. Also, HRTEM and SAED patterns reveal an increase of amount and size of TiC nanocrystals with the increase of energy of Ti and C ions determined by increase of anode potential. For providing reliable quantitative information regarding the composition and the elements depth profile, RBS studies were performed using the 3MV Tandem Accelerator with specialized RBS spectrum simulation program SIRMA. Raman measurement reveal that peaks appear at around 250, 340, 420, 610, 740, 1340 and 1530−1567cm⁻¹ , suggesting mixtures of TiC, Ti₃C₂O₂ and Ti₃C₂ and at 1340, 1560cm⁻¹ , the characteristic D an G peaks of disordered carbon. The characterstic peaks of Ti₃C₂O₂ and Ti₃C₂ have vibrational modes at 347, 730 and 621cm⁻¹ respectively, peaks at 260 and 420cm⁻¹ correspond to TiC. The shift shown in the spectra of the samples may occurs owing to the mechanical stress. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured, and then the electrical conductivity. Using the Wiedeman-Frantz law was calculated the thermal conductivity, which increase with increase of the temperature, according to the decrease in the proportion of TiC phase.

Passivated, carrier-selective contacts have enabled a recent surge in the efficiency of crystalline silicon solar cells by reducing the Shockley-Read-Hall recombination at the electrical contacts for the cell. They operate by allowing the extraction of only the majority carriers from the absorber, i.e., the c-Si wafer. The molybdenum oxide and nickel stack is known to form an effective hole-selective contact. However, the parasitic optical losses they introduced limit the quantum efficiency and therefore efficiency of solar cells featuring these materials. In this work, we introduce photonic nanostructures with reduced parasitic losses in the contacts and enhancement of light trapping in the active area of the cell. The optimized structure shows its potential for increasing photogenerated current density and efficiency as a result.

The future of optical devices involves manipulation of nanoscale structure. Thus, novel samples that incorporate both photonic crystal (PC) structure and metamaterial properties, known as PC metamaterials, are proposed. First, metamaterials with no PC structure are fabricated as nanorod or nanohelical structures and characterized to extract their optical constants. Then, a computational model for the metamaterial within a PC structure was developed to calculate the photonic bandgap (PBG). These results show that a large PBG with the desired directionality can be achieved with these PC metamaterials.

Metal nanoparticle inks are promising to fabricate conductors for low-cost, printed electronics. Low electrical resistivity can be achieved by nanoparticle sintering. The thermal properties of metal nanoparticle thin films have not been studied extensively but can yield great insights for the optimization of the sintering conditions. For example, in laser sintering, monitoring the changes in thermal conductivity over different stages of the process can help estimating the local temperature as well as the electrical conductivity of the film. In this work, we use frequency-domain thermoreflectance to measure these properties in a silver nanoparticle thin film thermally sintered ex-situ. The film is fabricated by spin coating a commercial printable silver ink with monodispersed 35 nm silver nanoparticles surrounded by a ligand. Using frequencydomain thermoreflectance (FDTR), we measured the thermal conductivity of the thin film by modulating the heat flux over a wide range of frequencies up to 50 MHz. An increase of thermal conductivity with increasing sintering temperature is observed up to a sintering temperature of 155°C, as measured by thermoreflectance or inferred through theWiedemann- Franz Law based on electrical conductivity measurements. The results are corroborated with material characterization by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The thermal and electrical properties are correlated throughout the different stages of sintering. For unsintered films, thermoreflectance gives more accurate values of thermal conductivity because it measures thermal conduction by both electrons and phonons. The Wiedemann- Franz Law underestimates the thermal conductivity by 50% in the unsintered case, which is problematic for modeling and optimization of the sintering process. In the sintered state, thermoreflectance and electrical conductivity measurements are in good agreement, as the contribution to heat transport is dominated by electrons. The thermoreflectance metrology can be used as a non-contact method to determine film conductivity, both thermal and electrical, during manufacturing processes involving nanoparticle inks.

The goal of this work is to achieve an ultra-miniature spectrometer that has a footprint of less than 1mm x 1mm. The design is based on a novel technique known as Fourier spectral filtering. The sensor consists of a group of photodetectors integrated with different Fourier filters. Each filter, combined with the intrinsic spectral response of the silicon photodetector, was designed to have a unique sinusoidal transmission function. By utilizing multiple sinusoids and collecting the data from all of the detectors, a Fourier transform can be performed and the spectral content of the signal can be extracted.

Ordered nanostructured crystals of thin perovskites films are of great interest to researchers because of the dimensional-dependence of their photoelectronic properties for developing the perovskites with novel properties. In this presentation, both top-down and bottom-up approaches for fabricating nanostructured perovskite films are demonstrated. First, a variety of micro/nanopatterns of a perovskite film are fabricated by either microimprinting or transfer-printing a thin spin-coated precursor film in soft-gel state with a topographically pre-patterned polymer mold, followed by thermal treatment for complete conversion of the precursor film to a perovskite one. Second, we also demonstrate a simple and robust route, involving the controlled crystallization of the perovskites templated with a self-assembled block copolymer (BCP), for fabricating nanopatterned perovskite films with various shapes and nanodomain sizes. When the precursor ion solution of a perovskite and poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) was spin-coated on the substrate, a nanostructured BCP was developed by microphase separation. Spontaneous crystallization of the precursor ions preferentially coordinated with the P2VP domains yielded ordered nanocrystals with various nanostructures. The nanopatterned perovskites showed significantly enhanced photoluminescence (PL) with high resistance to both humidity and heat due to geometrically confining crystals in and passivation with the P2VP chains. The self-assembled perovskite films with high PL performance provided a facile control of color coordinates by color conversion layers in blue-emitting devices for cool-white emission.

Ambient energy harvesting is a promising route to achieve self-powered electronic devices. A nanogenerator scavenges mechanical energy from surrounding and converts it into electrical energy to supply power to a self-powered system. Using piezoelectric, thermoelectric, and triboelectric effects, several nanogenerators have been developed. Piezoelectric nanogenerators harvest kinetic energy to provide power for portable and small electronics. The kinetic energy generated from human body motions is an excellent energy source to power wearable devices. Biocompatibility, flexibility, high efficiency, and small volume are the main attributes for applications related to the human body. Piezoelectric nanogenerators based on thin films are desirable for their ability to scavenge irregular mechanical energies from bending. The power generation mechanism of a thin film based piezoelectric nanogenerator is determined by the coupled piezoelectric and semiconducting properties of the thin film. ZnO is an appealing material for piezoelectric nanogenerators thanks to its coupling effect of semiconducting and piezoelectrical properties, extremely high elasticity, high power density, low-cost and controlled growth, and biocompatibility. Herein, a flexible piezoelectric nanogenerator with ZnO nanoflakes-polyethylene terephthalate (PET) is reported. The direct synthesis of ZnO nanoflakes on flexible PET substrate was achieved via a simple, fast, low-temperature, low-cost, highly stable, and reproducible sonochemical method. The synthesized ZnO thin films were characterized in detail. The results show that ZnO nanoflakes were grown with high purity and highly crystallinity along [0001] direction. Our piezoelectric device generated a peak voltage of 62 mV with great reproducibility (p-value of 0.0212). The fabrication of ZnO nanoflakes-PET piezoelectric nanogenerators helps us to develop more flexible and bio-compatible nanogenerators particularly self-powered wearable electronics.

Plasmonic structures have a wide variety of sensing applications because of their high field localization effect that leads to high sensitivity at lower powers. Specifically, plasmonic nanohole arrays are attractive platforms for sensing because of their easy alignment and measurement. In terms of fabricating these sensors, usually an adhesion layer is needed to ensure firm contact between the plasmonic metal layer and the substrate. Most fabrication efforts rely on titanium or chromium based metallic adhesion layers. However, the presence of the adhesion layer may hinder the plasmonic resonance by broadening the resonance and reducing the plasmonic field enhancement. This leads to degradation of sensing capabilities. We investigate the effect of tantalum, chromium, and titanium adhesion layers on plasmonic sensors made of nanohole arrays. Using the bulk refractive index data for metallic adhesion layers, we show that tantalum has the potential to show less damping effect compared to commonly used chromium and titanium. However, it still causes significant damping because of its high absorption, which becomes even larger for tantalum thin film according to our ellipsometry measurement results. We also propose here to use MgO dielectric adhesion layers to avoid the damping effect. Our investigation on MgO adhesion layers shows strong adhesion properties without scarifying sensor performance. Moreover, we will present an alternate sensor geometry that is less prone to damping by the adhesion layer and that can enhance the plasmonic resonance even if there is a metallic adhesion layer.

The demand for an ultrabroad optical material with a bandgap tunable from zero to at least 1–2 eV has been one of the driving forces for exploring new 2D materials since the emergence of graphene, transition metal dichalcogenides, and black phosphorus. As an ultra-broadband 2D material with energy bandgap ranging from 0 to 1.2 eV, layered PtSe₂ shows much better air stability than its analogue, black phosphorous. In this work, high quality of centimeter scale PtSe₂ films with controllable thicknesses were prepared through thermally assisted conversion method. The linear and nonlinear optical performance and ultrafast dynamics of layered PtSe₂, and signatures of the transition from semiconductor to semimetal have been systematically studied experimentally and theoretically. Combining with rate equations, first-principles calculation, and electrical measurements, a comprehensive understanding about the evolution of nonlinear absorption and carrier dynamics with increasing layer thickness is provided, indicating its promising potential in nanophotonic devices such as infrared detectors, optical switches, and saturable absorbers.

MoS2 has attracted substantial attention due to its atomic thickness and outstanding electronic and mechanical properties. As one of the thinnest semiconductors in the world, MoS2 is promising to build flexible electronics that can be integrated with objects with arbitrary shapes and inspires a vision of distributed ubiquitous electronics. Despite recent advances in two-dimensional materials-based electronics (e.g. 2D materials-based transistors, memory devices and sensors), an efficient and flexible energy harvesting solution is necessary, but still missing, to enable a self-powered system. At the same time, the electromagnetic (EM) radiation in the Wi-Fi band (2.4 GHz and 5.9 GHz) is becoming increasingly ubiquitous and it would be beneficial to be able to wirelessly harvest it to power future distributed electronics. However, the rectennas (i.e. RF energy harvesters) based on flexible semiconductors have not been fast enough to cover the Wi-Fi band due to their limited transport properties. Here we present a unique MoS2 semiconducting-metallic phase heterojunction, which enables a flexible and high-speed Schottky diode with a cutoff frequency of 10 GHz. Due to a novel lateral architecture and self-aligned phase engineering, our MoS2 Schottky diode exhibits significantly reduced parasitic capacitance and series resistance. By integrating the MoS2 rectifier with a flexible Wi-Fi band antenna, we successfully fabricate a fully flexible rectenna that demonstrates direct energy harvesting of EM radiation in the Wi-Fi band with zero external bias (battery-free). Moreover, taking advantage of the nonlinearity of the MoS2 Schottky diode, a frequency mixing in the gigahertz range is also successfully demonstrated on flexible substrates.

Based on the first principles calculation, this paper systematically studies the adsorption of three gases on the wurtzite GaAs nanowires (100) surface. Compared with CH₄ and H₂, the surface absorbed with H₂O has the lowest adsorption energy, thus it is the easiest to adsorb on the surface. The gas adsorption will result in the increase of band gaps, work functions and surface electron affinity, especially H₂O adsorption system with the largest band gap of 1.34eV. The adsorption of these gases produces a dipole moment pointing from the GaAs nanowires to the residual gas molecules. For H₂O molecular adsorption, which impedes the electron emission and decrease electrons emission capacity. The surface structures also reconstruct with different degrees. The residual gas adsorption can greatly affect the optical properties of the surface and undermine the performance of GaAs nanowire, particularly H2O adsorption. This work can help to understand the fading mechanism of the performance of optoelectronic devices based on GaAs nanowires.

Disordered photonic systems as observed in iridescent insects and flowers introduces new pathways for realizing cost-effective and scalable structural colors. In this work, we present a fast-colorimetric humidity sensor derived from a disordered arrangement of polydisperse nanoporous titania microspheres. The sensor relies on changes in the total scattering of the microspheres upon variations in the surrounding humidity. The incoherent scattering from each particle allows the sum of the individual cross sections to determine the total scattering cross section, which converts the individual noisy spectra to a smoothly varying spectrum that gives rise to a saturated color.[1] We show that because the titania microspheres is highly porous with 1~2 nm-sized nanopores, water can diffuse into the particle interior via intracrystalline dynamics, thereby changing the effective permittivity and consequently the scattered color at ultra-fast speeds (sub 50ms). Our results provide a practical route toward achieving cheap, simple, scalable, ultrafast colorimetric humidity sensors using structural colors from disordered nanoporous microspheres [2]. [1] Alam, A-M; Baek K; Son J; Pei Y-R; Kim D-H; Choy J-H; and Hyun J-K. Generating Color from Polydisperse, Near Micron-Sized TiO2 Particles, ACS Appl. Mater. Interfaces, 2017, 9 (28), 23941– 23948 [2] M-Noor, S; Jang, H ; Baek K; Pei Y-R; Alam, A-M; Kim,Y.H; Kim, I.S; Choy, J.H and Hyun J-K. Ultrafast humidity-responsive structural colors from disordered nanoporous titania microspheres. Submitted (2019)

The current multi-touch interactions are mainly relying on the contact between objects and diplay screens, which is restricted in a two dimensional plane. To expand the dimension of human-machine interaction, we propose a kind of remote multi-point optical 'touch' technology in which users can control the displays from distant laser pens. The touching system consists of a laser pen used as touching light, double layered transparent optical films with sub-wavelength gratings, and photodetector arrays set around the sidewalls of the optical films. The working mechanism is: when the incident light hits the optical films, it will be converted to waveguide light propagating along the films by the gratings on the films and eventually reaches detectors on the sidewalls for position detection. In this work, touch time response up to millisecond level is superior to conventional optical touch technologies. The design overcomes the problem that the touch point caused by direct contact technology is beyond the reach of human body under the touch of large screen. Optical touch based on sub-wavelength grating couplers will make touch more intelligent and natural.

This paper reports a novel optoelectronic sub-7nm CMOS transistor, which can be fabricated with a multiple quantum well (MQW) laser or tunnel light emitting diode (TLED) in the drain region, and an underlying avalanche breakdown photo diode (APD). The CMOS, photonic device, and APD are integrated as one transistor. The methods described in this report are fully compatible with a conventional CMOS process flow, including the FINFET technology, and scalable for future sub-10nm technology nodes. The Ion/Ioff ratio may surpass 10nm CMOS with these additional optoelectronic components.

A 355-nm solid state laser was irradiated onto 55-nm thick amorphous Si on a glass substrate using a spot beam steering method. After irradiation with a single pulse of Gaussian beam of varying laser energies, the Si surfaces were examined using Nomarski optical images. The images were composed of several color regions including pink, orange, dark red, and yellow. The energy fluences were 30-40 mJ/cm² (pink), 40-70 mJ/cm² (orange), 70-110 mJ/cm² (dark red), and over 110 mJ/cm² (yellow). Within the pink to dark-red area, as the fluence increases, the surface roughness and Si crystallinity also increase. However, in the yellow region, the Si surface is partially ablated due to the excess laser intensity. The laser beam, not exceeding the peak fluence of 110 mJ/cm2 , was scanned in the horizontal direction with beam overlap number of 20-100. The result revealed that high stain was observed in 20 pulses (scan pitch of 8.0 μm) caused by the difference in energy density from pulse to pulse. However, in 100 pulses (scan pitch of 1.6 μm), the Si surface was smooth and uniform with a roughness of 22 nm.

In this paper, the authors have propounded a pragmatic solution to circumvent the problem of inherent n-type conductivity of Zinc Oxide (ZnO), which remains the major obstacle to superior device performance. The proposed method employs the concept of carrier confinement in heterojunction thin film transistors that offers a prospective alternative to intruding into lesser known materials and their associated complexities. Carrier confinement is achieved in the low band-gap Cadmium Zinc Oxide (CdZnO) channel shielded by high band-gap Magnesium Zinc Oxide (MgZnO) on one side and gate dielectric SiO₂ on the other, which has been further corroborated by Energy Band diagram of the confined region that manifests the formation of two dimensional electron gas (2-DEG) at the CdZnO-SiO₂ interface. The device exhibits almost ideal transfer characteristics with a very narrow transition region between the ON and OFF states. The sub-threshold region is characterized by a high I_ON/I_OFF ratio (10¹¹) and near ideal sub-threshold swing (74mV/decade). Although a slight compromise in field effect mobility is incurred owing to the carrier transport mechanisms in confined regions, the benefits of carrier confinement in the low potential well far outweigh its detriments to emerge as a promising method for improving device performance.

A futuristic thin-film transistor based on a double-well heterostructure exploiting the band-gap tailoring property of Zinc Oxide (ZnO) has been proposed. Effects of carrier confinement in the MgZnO/CdZnO heterojunction have been studied by employing an additional MgZnO barrier in the CdZnO channel to create two potential wells. Carrier transport and device operation have been explained with the help of energy band diagrams extracted at different operating voltages. The optimised double-well structure yields an unprecedented I_ON/I_OFF=10¹⁵, simultaneously achieving a sub-threshold swing=74mV/decade, thereby indicating high switching speed. A high value of field-effect mobility, (μ_FE, max=32cm² /V-s) over a wide range of gate bias, manifests its ability to overcome the carrier scattering problem due to confinement, making it a promising candidate for high resolution and fast response optical display applications.

The development of flexible organic photovoltaic solar cells, using an optically transparent substrate material and organic semiconductor materials, has been widely utilized by the electronic industry when producing new technological products. The flexible organic photovoltaic solar cells are the base Poly (3,4-ethylenedioxythiophene), PEDOT, Poly(3- hexyl thiophene, P3HT, Phenyl-C61-butyric acid methyl ester, PCBM and Polyaniline, PANI, were deposited in Indium Tin Oxide, ITO, and characterized by Electrical Measurements and Scanning Electron Microscopy (SEM). In addition, the thin film obtained by the deposition of PANI, prepared in perchloric acid solution, was identified through PANI-X1. The result obtained by electrical Measurements has demonstrated that the PET/ITO/PEDOT/P3HT:PCBM Blend/PANIX1 layer presents the characteristic curve of standard solar cell after spin-coating and electrodeposition. The Thin film obtained by electrodeposition of PANI-X1 on P3HT/PCBM Blend was prepared in perchloric acid solution. These flexible organic photovoltaic solar cells presented power conversion efficiency of 12%. The inclusion of the PANI-X1 layer reduced the effects of degradation these organic photovoltaic panels induced for solar irradiation. In Scanning Electron Microscopy (SEM) these studies reveal that the surface of PANI-X1 layers is strongly conditioned by the surface morphology of the dielectric. The flexible organic photovoltaic solar cells developed in this work were applied in the educational platform Arduino, where tests demonstrated their efficient capacity to keep the platform in operation during exposure of the organic solar cells to the illumination with 100 mW/cm2.

The development of Flexible Optoelectronic Organic Sensor (FOOS), using an optically transparent substrate material and organic semiconductor materials, has been widely utilized by the electronic industry when producing new technological products. The greatest interest in studying organic semiconductor materials has been connected to its already known potential applications, such as: batteries, organic solar cells, flexible organic solar cells, organic light emitting diodes, organic sensors and others. Phototherapy makes use of different radiation sources, and the treatment of hyperbilirubinemia the most common therapeutic intervention occurs in the neonatal period. In this work we developed an organic optoelectronic sensor capable of detecting and determining the radiation dose rate emitted by the radiation source of neonatal phototherapy equipment. The sensors were developed using optically transparent substrate with Nanostructured thin film layers of Poly(9-Vinylcarbazole) covered by a layer of Poly(P-Phenylene Vinylene). The samples were characterized by UV-Vis Spectroscopy, Electrical Measurements and SEM. With the results obtained from this study can be developed dosimeters organics to the neonatal phototherapy equipment.

Whispering gallery mode resonators (WGMRs) are very interesting for sensing because a resonance shift could be caused by any perturbation of the surrounding environment. Additionally such a resonator is coated with nanomaterials to tailor and enhance the sensitivity for a specific purpose. WGMR were fabricated using standard telecommunication fiber and a hydrogen flame, characterized using the scan method to obtain the quality factors and then coated with gold nanoparticles (Au NPs) using dip coating method and characterized again for comparison. Au NPs were chosen because their positive impact on microresonator sensitivity has been mentioned before and the surface can later be functionalized. The deposited layer was investigated and new properties no over-coupling due to Van der Waals forces and suppression of higher order modes were observed after coating the resonator. To observe the localized surface plasmon resonance a glucose sensor test was performed using the WGMRs coated with Au NPs and glucose oxidase. Comparing the results with control measurements, the resonance shifted more for samples with Au NPs.

A sensitive optical magnetic field sensor was experimentally demonstrated using Ni-subwavelength grating (SWG) combined with a SiO₂/Ag plasmonic structure. We fabricated the Ni-SWG structure on the Ag/SiO₂ structure using electron beam lithography and a liftoff process. As a result, a dip in the reflection spectra with normal incidence was obtained at a wavelength of 530 nm. The reflectivity at the dip position significantly decreased with the intensity of the magnetic field applied to the structure. When a magnetic field of 43 mT was applied, the change in reflection reached approximately 4% of that without magnetic field. The experimental results indicate that our sensor achieves millitesla order of sensitivity for the magnetic field. The electromagnetic field distribution around the Ni-SWG/SiO₂/Ag calculated using the finite-difference time-domain method clarified the reason for the high sensitivity of our sensor.

In this study, the doping of boron in cuprous oxide as p-type material and its application for optoelectronic device is presented. Thin films are fabricated using metallic targets of Copper and Boron by rf magnetron co-sputtering in the Ar and O₂ ambient. The X-ray diffraction spectra of the doped samples matched with cubic Cu₂O phase, with no significant peak shift compared to intrinsic Cu₂O film. Raman analysis confirmed the Cu₂O phase in both doped and un-doped films. For doped thin films optical transparency was enhanced compared to intrinsic cuprous oxide. Band gap of doped and undoped Cu₂O were 2.67 eV and 2.47 eV respectively. Heterojunction is fabricated with n-Si and the electrical properties were studied.

Molybdenum disulpihde mono/few layers were deposited by pulsed laser deposition on graphene substrates thereby forming MoS₂ - graphene van der Waal heterostructures. Initially, the optimization of the growth MoS₂ layers were carried out on thermal oxide silicon (Si/SiO₂) substrate by pulsed laser deposition technique. The difference between two Raman peaks A_1g and E1/2_g modes (▵ƒ) was used to determine the number of layers of the grown MoS₂ thin films. The photoluminescence spectra with two excitonic peaks A and B confirmed the formation of mono/ few layered MoS₂ thin films. Similar growth conditions were used to deposit MoS₂ thin films on CVD grown graphene transferred on to thermally oxidized silicon substrate. The formation of MoS₂ - graphene van der Waal heterostructures were confirmed using Raman analysis.

We propose electrically tunable periodically segmented waveguides (PSW) using liquid crystals in their structure. Duty cycles are varied showing that light diffracts and refocuses periodically through the liquid crystal core PSW, when an external voltage is applied on it. The propagation characteristics are analyzed for different values of effective refractive index, duty cycle and external voltage applied. The liquid crystal core PSW performance analyzed presents a device that can works as a polarizer and mode size converter for transversal mode polarization, an important and desired requisite in photonics circuits devices.

Cellular proliferation in lesions may be assessed by imaging the intrinsic fluorescence of the tryptophan amino acid at 345 nm, which may be modified by chronic diseases. Typical image sensors have a limited responsivity, particularly at the UV interval. A fluorescent coating with an absorption peak at the emission wavelength of interest and an emission peak near to the sensor maximum sensitivity may improve the sensor responsivity. In this work, considering our final aim of imaging the intrinsic emission associated to the in-vivo cellular proliferation, fluorescent-thin films of two types of europium-activated phosphors at different concentrations were deposited by the spin-coating technique in a glass substrate and evaluated. The PTG505/F and UKL63/F-U1 phosphors were used for the coatings, these were excited at 345nm, and the quantum efficiency at 515 and 625 nm were assessed, respectively. The results showed that the PTG505/F and UKL63/F-U1 coatings may provide films with a thickness of less than 10 μm, and QE < 130% to sensitize image sensors.

Wide bandgap of 3.37 eV and large exciton binding energy of 60 meV inherited by ZnO has attracted a lot of attention in order to establish it as a potential candidate for the optoelectronic devices. The main challenge encountered for its efficient utilization is default n-type behaviour of ZnO due to the existence of native donor defects. Therefore, achieving p-type behaviour has been a tough job and significant efforts have been made by the research community over the last couple of decades in this direction. Observing the drawbacks shown by the mono-doped samples in achieving p-type ZnO, co-doping has emerged out to be a promising technology with the benefits of increasing dopant solubility and reducing ionization energy. In this report, we have studied the effects of variation in boron implantation dose by varying implantation time to 2 and 4 s on the behaviour of phosphorus implanted (implantation time of 70 s) ZnO thin films, using plasma immersion ion implantation (PIII) technique. Samples were annealed at 800°C for 10 s in oxygen ambient. High resolution X-ray diffraction (HRXRD) showed enhanced phosphorus solubility for 4 s boron co-doped sample. Improved P-O bonding was observed for higher boron co-doped sample from high resolution X-ray photoelectron spectroscopy (HRXPS) measurement. Low temperature photoluminescence (PL) spectra demonstrated donor-acceptor pair (DAP) and free acceptor (FA) peaks at around 3.24 and 3.31 eV, respectively with 4 s boron co-doped sample showing dominant FA peak indicating improved acceptor based optical emission for it.

ZnO, a wide band gap material, has interesting features like high electron mobility, high optical transparency and costeffectiveness. The major drawback of using ZnO as the channel layer is the presence of point defects which affects the carrier concentration. Carrier concentration (n) and interface states of the thin film greatly influence its threshold voltage, thus controlling the intrinsic defects of the film and passivation of interface states is crucial to reduce the threshold voltage variation. UV-Ozone (UV-O) treatment can be used to suppress these defects by supplying reactive oxygen to the film. In this report, we have studied grain boundary, carrier concentration and interface charge effects separately to emulate the effect of UV-O treatment. We have incorporated two distinct defect levels in our model for acceptor-like and donor-like defects in the grain boundary. The electrical parameter extraction was carried out in Silvaco using the TCAD simulator. We have observed an enhancement in corresponding electron mobility from 142.9 to 149.9 cm² /Vs, along with the positive shift in threshold voltage from -0.40 to -0.25 V, with the decrease in number of grain boundaries. With change in carrier concentration, mobility of the device was increased from 44.2 to 150 cm² /Vs. Passivation of interface charge density from 1 x 10¹² to 1 x 10¹⁰ cm^-2 in our model resulted in a significant change in the threshold voltage from 1.25 V to -0.4 V. Authors would like to acknowledge Department of Science and Technology (DST), India and IIT Bombay.

We studied the influence on photoluminescence (PL) spectra of zinc oxide (ZnO) microspheres (MS) via decoration with gold nanoparticles (AuNP). Porous ZnO MSs with various sizes are prepared by hydrothermal method ^[1] . The diameter of MS ranges from 1μm to 4 μm. PL spectra of isolated ZnO MSs pumped with 325 nm laser were measured via a micro-PL setup. Multiple peaks corresponding to whispering gallery modes (WGMs) of various orders with TE and TM polarization were observed in the visible range. Three types of PL emission spectra are found. One has sharp resonant WGM modes similar to those observed for porous ZnO MSs without AuNPs, but with sharper peaks. Another has strong leaky modes with evenly spaced triangle-shape emission peaks. The third also shows a leaky mode pattern but with asymmetric sawtooth like s-lineshapes. Theoretical modeling ^[2] has been performed to simulated the emission pattern of various degrees of AuNP decoration, and the results are compared with experimental data to learn the effect of AuNP decoration on the emission spectra of ZnO MSs. From these studies, we can learn the change of emission spectra of ZnO MSs caused by foreign particles and the technique may find useful application in biosensing.

In this paper, we discuss the setup of a confocal nanoscope in reflection using a super-oscillatory lens (SOL)which offers a sub-diffracted focal spot with an ultra-short depth of focus (≈100 nm). A tolerance of 20 nm defocussing in a 10 μm travel range is thus necessary, translating to an alignment requirement of the stage, with respect to the optical axis, below 2 mrad. We discuss an iterative procedure to fine tune the stage movement to achieve this requirement. We also demonstrate the necessity of the alignment by imaging a 5μm long 1D array of rectangular shaped Au nanostructures with a periodicity of 500 nm

EUV lithography is the main candidate for patterning of future technology nodes. Its successful implementation depends on many aspects, among which the availability of actinic mask metrology tools able to inspect the patterned absorber in order to control and monitor the lithographic process. In this work, we perform a simulation study to assess the performance of coherent diffractive imaging (CDI) and related phase retrieval methods for the reconstruction of non-trivially shaped and a–periodic nanostructures from far field intensity data.

We have investigated a multiple label-free detection method based on Raman spectroscopy and multivariate curve resolution (MCR) analysis to classify breast cancer. Twenty breast tissues collected from five participants during breast surgery were used as biological samples. Ten samples were from malignant tumor mass (cancer core area) and the others were from the safety margin outside of the tumor mass (two sample groups). For each breast tissue sample, twenty Raman spectra were collected using a fiber-optics Raman system consisting of a fiber-optic Raman probe, a low dark current deep-depletion CCD connected to a Czerny-Turner spectrograph and 785-nm laser source. Using MCR analysis iteratively optimized by an alternative least squares (ALS) algorithm, biomarker-dominated spectral data can be obtained from the preprocessed Raman spectra. This allows a more accurate classification between the two sample groups (normal and cancer). We expect that the proposed method based on biomarker analysis using MCR-ALS will more accurately classify breast cancer.

Some semiconducting metal oxides as e.g. tin dioxide (SnO₂), tungsten trioxide (WO₃) or cobalt oxide (Co₃O₄) are well-known for their gas-dependent electrical properties and therefore they are utilized as active components in highly sensitive and cost-efficient resistive type gas sensors. Recently it was shown that it is possible to utilize the correlation of the electrical and the optical properties of these materials to build a new type of optical gas transducer based on metal oxide photonic crystals. However, a detailed theoretical description of the linking mechanism between the optical and the electrical property change was still missing. Utilizing n-type semiconducting WO3 for the detection of hydrogen (H₂) as a model system we have shown, that free carrier absorption plays an important role in understanding the change in optical properties and the complex refractive index of WO₃, respectively. In the presented work we will test this idea on p-type Co₃O₄ for the detection of carbon monoxide. Therefore we synthesized cobalt(II,III) oxide photonic crystals (inverse opals) by a sol-gel based templating method. As expected, a gas induced change in the electrical properties can lead to a shift of the reflection peak due to a change in the refractive index of the material. We show that the characteristics of this optical response (e.g. its magnitude) can be manipulated by photonic band gap engineering, e.g. setting the stop band to the NIR range leads to an increase of the optical response compared to a stop band in the visible regime. The observed behavior is discussed by means of the optical dispersion of the complex refractive index of Co₃O₄ and the Lorentz-Drude model.

Current chemical detection techniques are not feasible in rugged environments where speed of detection, autonomous operation, and compactness are crucial factors. In this study, we investigate the promising photonic crystal structure of porous silicon (pSi) for portable sensing. HF-ethanol electrolyte with Pt/Al electrodes and a sinusoidal current oscillating between 15 mA and 108 mA was used to electrochemically etch p++-type porous silicon optical rugate filters with a 50% porosity. The samples were hydroxylated in ozone gas and functionalized through a ring-opening living polymerization reaction with a heterocyclic silane to retain thermal and alkaline stability. ATR-FTIR spectra and SEM confirmed the ring-opening reaction with grafting via O-Si bonds to the pSi surface. Hydrophobicity was demonstrated by water contact angles of 120-130 degrees. A stable stopband was maintained after varying thermal and alkaline conditions. After confirming pSi stability, a broad range of VOCs were cycled through a pressurized flow chamber and a bifurcated optical fiber CCD spectrometer continuously monitored for changes in the reflected stopband of the sensor. Target library VOCs underwent microcapillary condensation in pSi cavities, changing the composite refractive index and producing predictable optical stopband shifts with a precision within 0.03 nm for pure VOCs and 0.79 nm for complex mixtures and a threshold detection concentration of 1 microgram per cubic meter. With a precision which parallels state-of-theart chemical detection methods, as well as high stability and portability, this nanosensor is viable in chemical detection systems for real-time air quality monitoring, military defense, and forensic analysis.

In this work, TiN uniform thin films and nanostructured thin films were fabricated in a magnetron sputtering system. Two sets of TiN thin films with and without substrate bias were deposited at a nitrogen flow rate varied from 1.2 sccm to 2.0 sccm. The permittivity spectra of TiN films were measured and compared between different deposition conditions. A glancing angle-deposited TiN nanorod array was deposited with substrate bias. The polarization dependent extinction versus wavelength and angle of incidence was measured to discuss the associated transverse and longitudinal plasmonic modes.

We present a novel Memetic optimization algorithm (MA) in conjunction with the frequency domain Finite Element Method (FEM) to design and to optimize 90° bend waveguide. Transmission efficiencies greater than 98% have been achieved for the desired operating wavelength. by using the proposed strategy, opening, new possibilities for photonic devices design and configurations. In the proposed approach, several geometrical conditions and restrictions were considered and imposed on the bending region in order to reduce the bending footprint. Compared with conventional bending schemes, our solution exhibit good fabrication error tolerances and higher transmission efficiency.