Illumination Power Research Articles

Quality assessment in light microscopy for routine use through simple tools and robust metrics.

Although there is a need to demonstrate reproducibility in light microscopy acquisitions, the lack of standardized guidelines monitoring microscope health status over time has so far impaired the widespread use of quality control (QC) measurements. As scientists from 10 imaging core facilities who encounter various types of projects, we provide affordable hardware and open source software tools, rigorous protocols, and define reference values to assess QC metrics for the most common fluorescence light microscopy modalities. Seven protocols specify metrics on the microscope resolution, field illumination flatness, chromatic aberrations, illumination power stability, stage drift, positioning repeatability, and spatial-temporal noise of camera sensors. We designed the MetroloJ_QC ImageJ/Fiji Java plugin to incorporate the metrics and automate analysis. Measurements allow us to propose an extensive characterization of the QC procedures that can be used by any seasoned microscope user, from research biologists with a specialized interest in fluorescence light microscopy through to core facility staff, to ensure reproducible and quantifiable microscopy results.

Highly precise AMCW time-of-flight scanning sensor based on parallel-phase demodulation

A novel amplitude-modulated continuous wave (AMCW) time-of-flight (ToF) scanning sensor based on parallel-phase demodulation is proposed and demonstrated. Contrast to the conventional AMCW ToF sensor which utilizes serial-phase demodulation, the proposed sensor processes each different phase shift demodulation independently in parallel manner, so that the proposed sensor can maintain high demodulation contrast and short total integration time. Based on these characteristics of parallel-phase demodulation, the proposed sensor platform can be implemented with 2D laser scanning system with a single photodetector, maintaining a moderate frame rate, high optical SNR, and very high pixel resolution. In the validating demonstration, the proposed AMCW ToF scanning sensor shows extremely low measured distance noise per reference distance of 0.056 % at 1.50 m with only 30 mW illumination power. Additionally, FHD scale (1920 × 1080) highly precise 3D depth map with 800 nsec integration time can be achieved using the proposed AMCW ToF scanning sensor.

Experimental investigation for pulsed laser nitriding of metals

Pulsed laser nitriding of active metals has been regarded as a promising method for performance enhancement of metals. Nevertheless, clarifying the complicated mechanisms of pulsed laser nitriding such as the nitrogen transport and the chemically active state of nitrogen poses challenges due to the rather fast and complex processes. In this work, the in situ momentum measurements, in situ laser-induced breakdown spectroscopy (LIBS) measurements, in situ transient off-axis Digital holography (TODH) measurements and energy dispersive spectroscopy measurements were implemented to investigate the pulsed laser nitriding. It was revealed experimentally that the laser-supported-detonation (LSD) may be the key, and the nitriding process could proceed effectively only when the illumination power density of laser can reach the threshold of generating LSD. The LSD-induced high-speed N+ ions and N atoms flow to the metal surface, which may be the major mechanism for the nitrogen transporting to the metal surface. Moreover, the experimental results of LIBS showed that the chemically active state of nitrogen is N+ ions and their lifetime is at the scale of 102 ns. The lifetime of N+ ions was found to be prolonged as the nitrogen pressure was increased. As indicated by TODH experimental results, the prolonged lifetime of N+ ions may be caused by the smaller shock wave velocity at the higher nitrogen pressure. These experimental findings in this work may clarify the nitrogen transport mechanism and the chemically active state of nitrogen, which may lead to a better understanding of the pulsed laser nitriding and provide the guidance for optimizing the related industrial design in the future.

Self-powered photosensor based on curcumin:reduced graphene oxide (CU:rGO)/n-Si heterojunction in visible and UV regions

This study proposes a novel photosensor that uses curcumin:reduced graphene oxide/silicon (CU:rGO)/ n -Si heterojunction, prepared at different molar ratios of rGO with CU. The CU:rGO was deposited on an n-Si by electrochemically. The EDX, XRD, SEM and absorbance analyses of CU:rGO film were investigated. From the I-V measurements, the all CU:rGO/ n -Si devices showed excellent rectification characteristics both in the dark and under various illumination intensities. The device with higher rGO ratio (labelled D1) had better performance overall having the rectification ratio of 86094, the ideality factor of 2.15 and photosensitivity of 198 (at 150 mW/cm 2 ), which was attributed to the extraordinary electro-optical properties of rGO. Hence, the electrical and optical properties of D1 device were analyzed in detailed. The typical I-V measurements were conducted both in dark and under AM 1.5 G illumination of various light intensities. The intensity of the incident light varied from 10 to 150 mW/cm 2 . The photocurrent exhibited a strong dependence on the light intensity. The I-V measurements of another device (labelled D4) prepared under the same conditions were achieved at 365 nm and 395 nm wavelengths and it showed good sensitivity to light even in the UV region. Furthermore, both D1 and D4 devices operated in self-powered mode in visible and UV light without the need for any external voltage. According to the experimental results, the produced CU:rGO/n-Si devices can be potential devices for photosensor applications in a wide spectral region. • A curcumin:reduced graphene oxide(CU:rGO/n-Si heterojunction photosensor, prepared at different molar ratios of rGO with CU. • The EDX, XRD, SEM and absorbance analyses of CU:rGO film were investigated. • The CU:rGO/ n -Si device showed excellent rectification characteristics both under visible and UV light illumination. • Both under visible light and at 365 nm and 395 nm, the device showed self-powered mode. • The photosensitivity reached to 1.0 × 10 5 at the zero biased point for 150 mW/cm 2 illumination power.

Fabrication and photoresponsive characteristics of ZnO film for ultraviolet ZnO/porous Si photodetector: The effect of post-processing treatment

This article demonstrates a well-designed fabrication process of ultraviolet (UV) ZnO/porous Si photodetector as a function of post-processing temperature. The structural and optical features of the deposited ZnO layers were thoroughly elucidated through which a robust correlation between the post-processing temperature and the addressed characteristics were established. Particularly, a decrease in the attained energy bandgap from 3.3 eV to 3.22 eV was obtained upon increasing the treatment temperature from 600 °C to 800 °C; the morphological analysis revealed the occurrence of average nanoparticle diameters of 69 nm and 64 nm, respectively. Continuously, the fabricated devices also demonstrated a well-established relation with the applied post-processing temperature wherein relatively high photoresponsivity and specific detectivity were attained at high temperature. Specifically, the photoresponsivity and specific detectivity values were observed to be 5.6 (μA/mW) and 1.8×1011 Jones at 25mW/cm2 illumination power using treatment temperature of 800 °C, respectively. In the meanwhile, the response time of the proposed device was estimated to be ∼300ms.

Sensitive MoS2 photodetector cell with high air-stability for multifunctional in-sensor computing

With the development of artificial intelligence and the Internet of Things, the number of sensory nodes is growing rapidly, leading to the exchange of large quantities of redundant data between sensors and computing units. In-sensor computing schemes, which integrate sensing and processing, have provided a promising route to addressing the sensing/processing bottleneck by reducing power consumption, time delay and hardware redundancy. In this study, an in-sensor computing architecture involving a photoelectronic cell based on a wafer-scale two-dimensional MoS2 thin film was demonstrated. The MoS2 photodetector cell used a top-gate device structure with indium tin oxide (ITO) as the transparent gate electrode, which exhibited high air-stability and a high photoresponsivity (R) up to 555.8 A W–1 at an illumination power density (Pin) of 16.0 µW cm–2 (λ = 500 nm). Additionally, a MoS2 photodetector array with uniform photoresponsive characteristics was achieved. Furthermore, logic gates, including inverter, NAND, and NOR, were achieved based on MoS2 photodetector cells. Such multifunctional and robust in-sensor computing was ascribed to the uniform wafer-scale MoS2 film grown by atomic layer deposition (ALD) and the unique device structure. Because the detection of optical signals and logic operations were achieved through MoS2 photodetector cells with area efficiency, the proposed in-sensor computing device paves the way for potential applications in high-performance, integrated sensing and processing systems.

Deep-tissue two-photon microscopy with a frequency-doubled all-fiber mode-locked laser at 937 nm

In two-photon microscopy, low illumination powers on samples and a high signal-to-noise ratio (SNR) of the excitation laser are highly desired for alleviating the problems of photobleaching and phototoxicity, as well as providing clean backgrounds for images. However, the high-repetition-rate Ti:sapphire laser and the low-SNR Raman-shift lasers fall short of meeting these demands, especially when used for deep penetrations. Here, we demonstrate a 937-nm laser frequency-doubled from an all-fiber mode-locked laser at 1.8 μm with a low repetition rate of ∼9 MHz and a high SNR of 74 dB. We showcase two-photon excitations with low illumination powers on multiple types of biological tissues, including fluorescence imaging of mouse brain neurons labeled with green and yellow fluorescence proteins (GFP and YFP), DiI-stained and GFP-labeled blood vessels, Alexa Fluor 488/568-stained mouse kidney, and second-harmonic-generation imaging of the mouse skull, leg, and tail. We achieve a penetration depth in mouse brain tissues up to 620 μm with an illumination power as low as ∼10 mW, and, even for the DiI dye with an extremely low excitation efficiency of 3.3%, the penetration depth is still up to 530 μm, indicating that the low-repetition-rate source works efficiently for a wide range of dyes with a fixed excitation wavelength. The low-repetition-rate and high-SNR excitation source holds great potential for biological investigations, such as in vivo deep-tissue imaging.

Light-Induced Raman Spectra Oscillations and Macroscopic Propulsion of Graphene Bubbles

Atomically thin graphene bubbles can form on a flat substrate due to trapped substances between graphene and the substrate, providing an impressive case to study the intriguing properties of graphene with a nanoscale curvature. The energy balance between the van der Waals interaction of graphene to the substrate and the elastic energy required to deform graphene determines the shape, size, and internal pressure of the graphene bubble. In this work, light interference-induced Newton rings were clearly resolved not only in optical microscopy images but also in Raman spectroscopy maps of the graphene bubble, which originated from the optical standing waves formed in the graphene/SiO2/Si microcavity. Importantly, for the first time, such optical standing waves were directly visualized by imaging the spatial temperature distribution of laser-irradiated graphene bubbles through Raman scan mapping. Raman spectra oscillations can be explained by the laser-induced local heating effect and nonuniform temperature on the surface of the graphene bubble. Furthermore, with a higher laser power of illumination, a direct light propulsion of the bubble was observed on a macroscopic scale. The trajectory of the graphene bubble movement can be effectively manipulated by controlling the position and travel direction of the laser beam. These results offer an exciting opportunity to tune the optoelectronic properties of graphene and other two-dimensional materials at nanoscale confinement and to achieve the direct light manipulation of matter.

Efficacy assessment of metalloporphyrins as functional materials for photodetection applications: role of central tetrapyrrole metal ions

Despite the continued research, it is still not entirely clear how important characteristics of metalloporphyrins are exploited for optoelectronic applications. Consequently, the stimulant aim for this work is to design and implement organic/inorganic heterojunctions based on metalloporphyrins (CuTPP, NiTPP, FeTPPCl, and MnTPPCl)/n-Si and evolve their photodetection performance. To evaluate the performance variation of variously manufactured photodetectors, structural characterizations using XRD, Raman spectroscopy, XPS, and AFM are combined with optical absorption and photoluminescence. Core level emissions are used to unveil the deposited films’ electronic and structural features. The estimated energy gap values are found to be 2.4, 2.53, 2.49, and 2.43 eV for CuTPP. NiTPP. FeTPPCl, and MnTPPCl, respectively. The fabricated devices’ PL-spectra are analyzed, where CuTPP exhibited the lowest value of excitonic binding energy. The photodetection performance is evaluated via the J–V relation under dark and various radiant illumination power. The microelectronic parameters of the manufactured heterojunctions are estimated. Ultimately, the photodetectors' figures of merit are estimated for all the fabricated devices, where CuTPP/n-Si heterojunction achieved the best performance and highest values of R = 11.95 mA/W, D* = 8.7 × 109 Jones, LDR = 46.18 dB, SNR = 203.4, and trise/tfall = 51.32/54.29 ms. Consequently, MTPP-based photoreceptors would play an active role as a powerful tool for light detection soon.Graphical abstract

Large-Scale Multilayer MoS2 Nanosheets Grown by Atomic Layer Deposition for Sensitive Photodetectors

Two-dimensional (2D) transition-metal dichalcogenides have promising optoelectronic applications. However, most reported MoS2-based photodetectors are based on MoS2 flakes, dozens of microns in size, prepared by mechanical exfoliation or chemical vapor deposition, which limits their practical applications. In this study, a wafer-scale, continuous, and uniform multilayer MoS2 nanosheet was grown on an insulating single-crystal sapphire substrate by atomic layer deposition (ALD), with MoCl5 and hexamethyldisilathiane as precursors, because of the smaller lattice mismatch between crystalline sapphire and hexagonally arranged MoS2 compared with polycrystalline substrates. Then, large-area MoS2 nanosheets with high uniformity and homogeneity were obtained on Al2O3/Si and SiO2/Si substrates via large-scale peeling and vacuum stacking transfer. Subsequently, MoS2 photodetectors were fabricated on both substrates with ALD-MoS2 as a photosensitive channel material and high-k Al2O3 or SiO2 as a dielectric layer, which resulted in gate control with relatively low and high voltages, respectively. A high photoresponsivity (R) of 577.4 A W–1 was achieved for the MoS2 photodetector fabricated on the Al2O3/Si substrate at an illumination power density (Pin) of 5.01 μW cm–2 (λ = 500 nm). In addition, the MoS2 photodetectors exhibited a light response over a wide wavelength range (400–700 nm). Moreover, a MoS2 photodetector array containing 4 × 3 photodetectors with a uniform photoelectric response was demonstrated. These results will facilitate future applications of 2D materials in large-scale, high-performance photoelectronic devices and circuits.

Ultrathin Layered Hyperbolic Metamaterial-Assisted Illumination Nanoscopy.

Metamaterial-assisted illumination nanoscopy (MAIN) has been proven to be a promising approach for super-resolution microscopy with up to a 7-fold improvement in imaging resolution. Further resolution enhancement is possible in principle, however, has not yet been demonstrated due to the lack of high-quality ultrathin layered hyperbolic metamaterials (HMMs) used in the MAIN. Here, we fabricate a low-loss composite HMM consisting of high-quality bilayers of Al-doped Ag and MgO with a nominal thickness of 2.5 nm, and then use it to demonstrate an ultrathin layered hyperbolic metamaterial-assisted illumination nanoscopy (ULH-MAIN) with a 14-fold imaging resolution improvement. This improvement of resolution is achieved in fluorescent beads super-resolution experiments and verified with scanning electron microscopy. The ULH-MAIN presents a simple super-resolution imaging approach that offers distinct benefits such as low illumination power, low cost, and a broad spectrum of selectable probes, making it ideal for dynamic imaging of life science samples.

Enhancement in the photovoltaic efficiency of dye-sensitized solar cell by doping TiO2 with MIL-101 MOF structure

In this work, pure and MIL-101 doped TiO2 films on fluorine doped tinoxide (FTO) were prepared by sol-gel method for dye sensitized solar cell (DSSC) fabrication. MIL-101 metal-organic framework (MOF) structure was synthesized by hydrothermal method and it was used as dopant in TiO2 to enhance an efficiency of DSSC device for the first time. The surface morphology of pure and MIL-101 doped TiO2 films were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), the crystallite size and structural properties of these films were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) techniques, respectively. Ultraviolet–visible spectroscopy (UV–Vis) measurement presents the change in an optical characteristic and the band gap of the film with MIL-101 incorporation owing to its high surface area. The efficiency enhancement in DSSC device with MIL-101 doping was analyzed via current-voltage (I–V) measurement under various power of solar simulator. The results confirm that power conversion efficiency (PCE) can enhance with MIL-101 doping into TiO2. The power conversion efficiency of MIL101@DSSC is 8.687% under 100 mW/cm2 illumination power, which is 1.85 times greater than PCE of undoped DSSC (4.689%). The enhancing efficiency of MIL-101@DSSC can be associated with the energy band alignment, improvement in photoelectron trapping, and increase in dye adsorption owing to pore structure of MIL-101.

(Digital Presentation) Effects of Thermal Convection on Species Transport in Photocatalytic Suspension Reactors

Z-scheme photocatalytic suspension reactors with aqueous redox shuttles present a promising pathway for safe and low cost solar water splitting to produce hydrogen. Soluble redox shuttles act as electron relays between light absorbing particles present in the two compartments. In recent work we have demonstrated a theoretical pathway to attain up to 4% solar-to-hydrogen efficiency with passive diffusion driven species transport [1]. However, to attain larger solar-to-hydrogen efficiencies it is crucial to enhance the rate of species transport between the two reaction compartments. We report on computational and experimental investigations to explore the effects of natural convection on species transport in Z-scheme photocatalytic systems. A transient, two-dimensional fluid flow, heat- and mass-transfer model was developed for a two-compartment system with a porous separator; horizontal and vertical reactor arrangements were considered. Volumetric absorption of visible and infrared components of incident sunlight by the suspension was modeled. Transient species concentration profiles were obtained as a function of the operating solar-to-hydrogen efficiencies, porous separator morphology and the size of the compartments. Model results predict enhanced rates of transport of redox shuttle species between two compartments in the presence of thermal convection in addition to diffusion. At 10% solar-to-hydrogen efficiency, minimum redox shuttle concentration with convection decreases by 80% as compared to passive diffusion alone for a vertically stacked reaction compartment with 2 cm height. Experimental measurements have been also performed on two-compartment prototypes (horizontal and vertical) to probe the effects of natural convection on species mixing. The source of illumination was a xenon-lamp solar simulator (Newport 94023A) with an AM1.5G filter and calibrated such that the incident illumination power at the top of the reactor was 1 sun (1000 W/m2). The reactor was assembled by connecting two polycarbonate tubes (5 cm x 5 cm) with a height of 5 cm and placing a thin separator (Nafion 117 and regenerated cellulose) between the tubes to separate the compartments. A base was 3D-printed and painted black to secure the bottom compartment and maximize absorption of the incident illumination and promote natural convection. Thermocouples (K-type) were placed at various heights within the two compartments to track local temperatures within the fluid, including along the bottom surface of the lower compartment. Over a 3-hour period of 1 sun irradiance, the temperatures were recorded, and a favorable temperature gradient for natural convection was observed (ΔT ~ 2 °C) for vertically-stacked reaction compartments. The flow behavior was visualized through the injection of a colored dye at the bottom surface of the reactor and above the membrane after the 3-hour period. Image processing of the convection video is used to help quantify the rate of mixing within the compartments. Model predictions for flow behavior and temperature profiles were compared to and validated against experimental measurements. Collectively, this study implements a unique approach to predict and evaluate the effect of natural convection on species transport in Z-scheme photocatalytic reactors.[1] Bala Chandran, R., Breen, S., Shao, Y., Ardo, S., & Weber, A. Z. (2018). Evaluating particle-suspension reactor designs for Z-scheme solar water splitting via transport and kinetic modeling. Energy and Environmental Science, 11(1), 115–135. https://doi.org/10.1039/c7ee01360d Figure 1

Interlayer Charge Transfer and Photodetection Efficiency of Graphene–Transition-Metal-Dichalcogenide Heterostructures

Graphene and transition-metal-dichalcogenide- (TMD) based van der Waals heterostructures in field-effect-transistor (FET) architecture exhibits extremely high sensitivity to optical radiation due to transit and physical separation of the photogenerated carriers across the heterointerface. Both the sensitivity and speed of these detectors depend on the kinetics of charge transfer, but their interdependency at room temperature (T), where these detectors would be most useful, remains largely unexplored. Here we systematically measure the T dependence of the magnitude (gain) and timescale (bandwidth) of photoresponse in graphene-TMD heterostructures well up to the room T. The gain-bandwidth product is found to be strongly dependent on the power of optical illumination and increases with decreasing power (P), becoming as large as $1\phantom{\rule{0.2em}{0ex}}\mathrm{M}\mathrm{Hz}$ in the low-P limit. We find that thermally activated back transfer of charge from graphene to the TMD determines the response time of the detector at higher temperatures under continuous illumination. Our experiment reveals the impact of charge-transfer pathways on the performance in a broad class of graphene-TMD detectors.

Laser Photochemical Nanostructuring of Silicon for Surface Enhanced Raman Spectroscopy

AbstractIn this work, a novel method of fabricating large‐area, low‐cost surface‐enhanced Raman spectroscopy (SERS) substrates is explained which yields nanostructured surface utilizing laser‐induced chemical etching of crystalline silicon (Si) in an hydrofluoric acid solution. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50 nm thick silver (Ag) layer is shown to maximize the SERS performance. The SERS effect is attributed to the electromagnetic field enhancement originating from the nanoscale surface roughness of Si that can be controlled by the illumination power, etch duration, and the spot size of the laser beam. The SERS substrates are found to be capable of detecting a Raman analyte dye molecule down to 10−11 m. SERS performance of the Ag deposited substrates are compared to gold (Au) deposited substrates at 660 and 532 nm excitation. Nanostructured Si surface with Ag exhibits stronger SERS than with Au under 532 nm excitation exhibiting an enhancement factor as high as 109. Raman enhancement factor is calculated both by SERS spectra experimentally, and using finite‐elements simulation of the electric field enhancement. The applicability of the fabricated substrates is examined by adsorbing different analytes.

Precision in iterative modulation enhanced single-molecule localization microscopy

Modulation enhanced single-molecule localization microscopy (meSMLM) methods improve the localization precision by using patterned illumination to encode additional position information. Iterative meSMLM (imeSMLM) methods iteratively generate prior information on emitter positions, used to locally improve the localization precision during subsequent iterations. The Cramér-Rao lower bound cannot incorporate prior information to bound the best achievable localization precision because it requires estimators to be unbiased. By treating estimands as random variables with a known prior distribution, the Van Trees inequality (VTI) can be used to bound the best possible localization precision of imeSMLM methods. An imeSMLM method is considered, where the positions of in-plane standing-wave illumination patterns are controlled over the course of multiple iterations. Using the VTI, we analytically approximate a lower bound on the maximum localization precision of imeSMLM methods that make use of standing-wave illumination patterns. In addition, we evaluate the maximally achievable localization precision for different illumination pattern placement strategies using Monte Carlo simulations. We show that in the absence of background and under perfect modulation, the information content of signal photons increases exponentially as a function of the iteration count. However, the information increase is no longer exponential as a function of the iteration count under non-zero background, imperfect modulation, or limited mechanical resolution of the illumination positioning system. As a result, imeSMLM with two iterations reaches at most a fivefold improvement over SMLM at 8 expected background photons per pixel and 95% modulation contrast. Moreover, the information increase from imeSMLM is balanced by a reduced signal photon rate. Therefore, SMLM outperforms imeSMLM when considering an equal measurement time and illumination power per iteration. Finally, the VTI is an excellent tool for the assessment of the performance of illumination control and is therefore the method of choice for optimal design and control of imeSMLM methods.

High Power Irradiance Dependence of Charge Species Dynamics in Hybrid Perovskites and Kinetic Evidence for Transient Vibrational Stark Effect in Formamidinium.

Hybrid halide perovskites materials have the potential for both photovoltaic and light-emitting devices. Relatively little has been reported on the kinetics of charge relaxation upon intense excitation. In order to evaluate the illumination power density dependence on the charge recombination mechanism, we have applied a femtosecond transient mid-IR absorption spectroscopy with strong excitation to directly measure the charge kinetics via electron absorption. The irradiance-dependent relaxation processes of the excited, photo-generated charge pairs were quantified in polycrystalline MAPbI3, MAPbBr3, and (FAPbI3)0.97(MAPbBr3)0.03 thin films that contain either methylamonium (MA) or formamidinium (FA). This report identifies the laser-generated charge species and provides the kinetics of Auger, bimolecular and excitonic decay components. The inter-band electron-hole (bimolecular) recombination was found to dominate over Auger recombination at very high pump irradiances, up to the damage threshold. The kinetic analysis further provides direct evidence for the carrier field origin of the vibrational Stark effect in a formamidinium containing perovskite material. The results suggest that radiative excitonic and bimolecular recombination in MAPbI3 at high excitation densities could support light-emitting applications.

Scalable and low-cost fabrication of flexible WS2 photodetectors on polycarbonate

We present a low-cost and easy-to-implement technique to fabricate large-area WS2 photodetector devices onto transparent and flexible polycarbonate substrates. The method relies on the deposition of large-area (in the cm scale) thin films (~30 nm thick) of WS2 by a recently introduced abrasion-induced method. Interdigitated electrical contacts are then deposited by thermal evaporation through a shadow mask. The photodetectors present well-balanced performances with an good trade-off between responsivity (up to 144 mA/W at a source-drain voltage of 10 V and illumination power of 1 μW) and response time (down to ~70 µs) and a detectivity value of 108 Jones. We found that the devices perform very reversibly upon several illumination and straining cycles and we found a moderate device-to-device variation.

Photodetectors with Buckminsterfullerene Decorated WSe2

In this work, we have studied the interactions of van der Waals (vdWs) hybrid structures composed of two-dimensional tungsten diselenide (WSe2) with zero-dimensional buckminsterfullerene (C60) spheres. The organic-inorganic vdWs heterostructure was fabricated using the spin coated dispersion of C60 over monolayer WSe2 crystallites. The morphology of the spin coated C60 on the surface of monolayer (1L) WSe2 was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Raman and photoluminescence spectroscopy were used to reveal the -type doping of WSe2 by the C60 molecules. Photodetector devices were then fabricated with Ti-contacted electrodes and the photodetector figures of merit for WSe2 and C60-WSe2 hybrids were examined as a function of illumination power and incoming wavelength which showed the C60 decoration of 1L-WSe2 provides an improvement in device performance. Furthermore, the temporal response of the devices was analyzed which showed a reduction in response times by more than two times for the hybrid system. Our results indicate that the C60-WSe2 vdWs hybrid heterostructure appears to be an attractive architecture for enabling charge transfer and high performance photodetection capabilities.

Solid-State Pulsed Time-of-Flight 3-D Range Imaging Using CMOS SPAD Focal Plane Array Receiver and Block-Based Illumination Techniques

Full realization of a solid-state 3-D range imager based on the pulsed time-of-flight method is presented. The system uses block-based segmented illumination in the transmitter realized with a 16-element common anode laser diode bar. The receiver is based on a single chip 2-D SPAD/TDC 0.35 μm CMOS array with 32 × 128 SPAD pixels and 257 TDCs. Segmentation of the illumination improves the SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BG</sub> R in the detection and results in simpler receiver realization than in the commonly used flood-illumination approach. The system is capable of producing cm-accurate 3-D range images within a FOV of 40° × 10° up to a range of 15 m in normal office lighting at a frame rate of ∼30 fps using a low average illumination power of only 2.6 mW. In background illumination of ∼20 klux, 3-D range images were captured at a distance of ∼13 m using the gated SPAD approach at a frame rate of ∼1 fps.