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This paper investigates optoelectronic performance of nanowire (NW) solar cells using GaAs and its alloy GaAs1-xBix for three different mole fractions of Bi e.g., x = 0.01, 0.043, 0.078 using extensive numerical simulation in order to evaluate the potential of the alloy as a solar cell material. Finite-difference time-domain (FDTD) method is used to obtain the optimum geometric dimensions of the nanowire in order to achieve maximum photocurrent. GaAs0.922Bi0.078 NW solar cell of length 2-µm and optimized diameter D = 140 nm with filling ratio (FR) of 0.5, produces a maximum Jsc of 49.31 mA/cm2 which is 23% higher than its GaAs counterpart. Additionally, GaAsBi NW exhibits much higher absorption, and lower reflection as well as transmission coefficients for the incident optical irradiation, due largely to its bandgap bowing property owing to incorporation of Bi, as compared to GaAs NW. Furthermore, we present electric field distribution and optical generation rate profiles under the incident irradiation in NWs to obtain a better insight into the device physics. Various material and transport parameters of the novel alloy material required to carry out electrical simulation using Lumerical 3D charge transport simulator, are presented in detail, and the effect of SRH recombination lifetime on the electrical performance i. e., open circuit voltage Voc and power conversion efficiency (PCE) of the NW solar cells is studied. Our findings reveal that GaAs0.99Bi0.01 NW exhibits the maximum PCE of 34.34% found to be 6.425% larger than that of GaAs NW under AM 1.5G illumination.

Direct bandgap Cu2ZnSnSe4 (CZTSe) material is a promising absorber for thin film photovoltaics due to its affordable production cost and ecofriendly constituents. However, bulk defects, small grain size, short minority carrier lifetime and band bending at CZTSe/Mo (back contact) interface limit the performance of CZTSe solar cells. To overcome these issues, we design a single junction CdS(n)/ (AgxCu1–x)2ZnSnSe4 (p) /Cu2ZnSnSe4 (p + ) solar cell where we use (AgxCu1–x)2ZnSnSe4 (ACZTSe) as the main absorber layer. We have chosen the carrier density of each layer in a such way that ACZTSe becomes depleted and generated minority are collected efficiently. In our design, we utilize CZTSe as the back surface field layer to prevent surface recombination and indium doped tin oxide (ITO) as the back electrode to avoid band bending and increase the open circuit voltage. Additionally, we optimize the thicknesses of different layers and achieve a maximum efficiency of 18.63% including Shockley-Read-Hall, radiative and surface recombination mechanisms. The photo conversion efficiency (PCE) of our designed solar cell is 6 % higher (12.6% vs 18.63%) than that of the best reported selenium rich CZTSe solar cell. The design concept proposed in this work would help in harvesting solar energy efficiently from next generation CZTSe solar cells.

This paper reports unique InGaAs-based ion-sensitive field-effect transistor (ISFET) sensor devices having a sensing gate in addition to the traditional floating gate with different kinds of barrier materials such as no barrier, single barrier (InP) and double barrier (InP and InAlAs), at sub-100 nm technology node. The impact of barrier layers coupled with the modified gate architecture on the sensing performance of the proposed devices has been investigated and compared thoroughly in terms of different performance metrics, e.g., threshold voltage sensitivity, ON-current sensitivity, and ON/OFF-current sensitivity. Interestingly, it has been found that the sensor device with a single barrier exhibits the highest threshold voltage sensitivity of ~ 67 mV/pH and largest ION/IOFF ratio sensitivity of 25/pH, compared to the other devices. Furthermore, it is worth mentioning that the threshold voltage sensitivity of the single-barrier sensor device crosses the conventional Nernst limit of 59 mV/pH at room temperature, by 14%. Critically analyzing the results, it is found that the sensor device with a single barrier has evolved as the most promising device for pH-sensing application, not only from the standpoint of high sensitivity parameters, but also from the fabrication point of view.

This paper reports opto-electronic properties and photo-voltaic performances of non-polar, semi-polar and polar solar cells employing InGaN/GaN multiple quantum wells (MQWs) with and without using AlGaN material as electron and hole blocking layers. In addition, the investigation is conducted for a number of QWs, e. g., 3, 5, 7, and 10. The performance of such devices is evaluated in terms of current density–voltage characteristics, power–voltage characteristics, fill factor, and power conversion efficiency. Our TCAD simulation results show that the InGaN/GaN solar cell featuring non-polar crystal structure, seven QWs alongside AlGaN blocking layers turns out to be the optimised device exhibiting open circuit voltage (Voc) of 1.08 V, short circuit current density (Jsc) of − 7.64 mA/cm2 and power conversion efficiency (η) of 5.36% among all other solar cells. The optimized device exhibits a considerably high value of η compared to earlier findings of nitride based solar cells. Hence our present design for InGaN/GaN MQW solar cells could provide an encouraging guideline for design and development of solar cells utilizing III–V nitride semiconductors in near future.

Exceptional points (EPs) in non-Hermitian systems have recently attracted considerable attention owing to unique state-flipping and peculiar phase accumulation features. The dynamical encirclement ...

In order to perform logic and memory operation with high speed and accuracy, transistors should have high ON/OFF current ratio and high charge carrier mobility. But it is difficult to achieve both of these criteria in a single transistor. Graphene is considered as one of the most promising candidates due to its high mobility. But graphene field effect transistor (GFET) gives very low ON/OFF current ratio as graphene is a semi-metallic material. In this work, we have modeled strained graphene on silicon FET with high k dielectric material like HfO 2 , TiO 2 and obtained notable improvement in the ON/OFF current ratio along with the drain current. But the structure suffers from significant channel length modulation effect. Finally, we have proposed a cylindrical FET structure with strained graphene layer to minimize the channel length modulation effect while maintaining the high ON/OFF current ratio and high charge carrier mobility.

The authors investigate and physically analyse the effects of the angle of grooving (θ) on various analogues and RF parameters of InAs-channel quantum well MOSFETs with raised source/drain architecture at a 14-nm gate length. Moreover, harmonic distortion analysis is performed to examine the linearity and distortion of common source amplifiers built with such transistors. The findings reveal that the device with θ = 20° exhibits significant improvement in transconductance efficiency (gm/IDS ), output resistance (rd ), and voltage gain (Av ) while showing degradation in transconductance (gm ) compared to the corresponding parameter with θ = 90°. Furthermore, the obtained results manifest that the total harmonic distortion drops to −47 dB for an amplifier built with the device having θ = 90° compared to −22 dB obtained with θ = 20°. Notably, as the angle of grooving increases from 20° to 90°, the gain bandwidth of the amplifier improves by 232% while the peak gain falls by 40%.

Using well-calibrated device simulation, the analogue performance of 20 nm double-gate junctionless transistors (JLTs) is investigated in terms of transconductance (g m), output conductance (g d) for various underlap spacer asymmetricity and dielectric constant (k) values. The spacer length is varied ranging 1–6 nm on both source (L S) and drain sides (L D) while keeping their sum fixed at 12 nm. Obtained results show that for both n- and p-metal-oxide-semiconductor field-effect transistors (FETs), a longer LD increases gm exhibiting weak sensitivity to variations in k while gd increases and decreases with higher and lower k. The present findings reveal that the highest voltage gain of 46.3 and largest gain bandwidth (GBW) of 676 GHz are obtained for complementary metal–oxide–semiconductor (CMOS) amplifiers featuring both n and p transistors with L S = 11 nm, L D = 1 nm and k = 80 and L S = 1 nm, L D = 11 nm and k = 3.9; both figures are quite higher compared with their symmetric counterpart. The studies manifest that such an asymmetric dielectric spacer engineering could be employed in designing high performance nanoscale CMOS amplifiers without increasing hardly any process complexity and cost while providing augmented GBW compared with reported amplifiers based on molybdenum disulphide transistors and tunnel FETs.

Although germanium-tin (GeSn) channel p-MOSFETs exhibit outstanding performance compared to other p-MOS transistors, their accurate analytical model has not yet been reported. In this paper, we present, for the first time, a 2-D surface-potential-based sub-threshold model for GeSn-on-insulator (GeSnOI) MOSFETs taking into account the interface-trapped and fixed-oxide charge densities, and also quantum effects. Unlike most of the earlier models applied to elementary and undoped semiconductor channels, the present model embraces variations in the alloy composition as well as doping concentration in the channel. Furthermore the model neither supports iterations nor involves any fitting parameters throughout the derivation, and hence it is physical, predictive, and applicable to circuit simulators like SPICE. We calculate various device parameters such as threshold voltage Vth, threshold voltage roll-up, drain induced barrier lowering DIBL and subthreshold slope SS related to short channel effects (SCEs) of GeSnOI p-MOSFETs for Sn contents ranging 0–6% and channel thickness from 5 to 10 nm. The obtained results show that the GeSnOI MOSFET with channel thickness of 5 nm yields the lowest value of Vth, DIBL, SS and Vth-shift indicating suppression of SCEs. Our model is verified by comparing analytical results for various device parameters with corresponding numerical simulation results and also with limited experimental data available in the literature.

Transition metal oxides show remarkably diverse quantum functional properties such as high temperature superconductivity, colossal magnetoresistance, multiferroicity, two-dimensional electron gas, and topological insulators. This diversity manifests as a result of many energy scales of similar magnitude competing rather than any particular one dominating in the system. In this regard, growth of atomically controlled epitaxial thin films and heterostructures would allow to control relevant energy scales by imposing various stimuli, such as reduction of dimensionality, introduction of interfaces, modification of the interfacial octahedral tilts, and symmetry breaking; in turn, modified functional properties or completely new phenomena may emerge in epitaxial thin films and heterostructures. Also of exceeding importance is the fact that atomically controlled epitaxial thin films and heterostructures of the multifunctional oxides offer promising potentials for next generation oxide electronics. In this short review, we collect representative examples of quantum correlated phenomena arising in epitaxial films and heterostructures of transition metal oxides and highlight some of the progresses achieved in thin film research of various functional oxides in the last couple of decades.

One of the most intriguing topological features of open systems is exhibiting exceptional point (EP) singularities. Apart from the widely explored second-order EPs (EP2s), the explorations of higher-order EPs in any system requires more complex topology, which is still a challenge. Here, we encounter a third-order EP (EP3) for the first time in a simple fabrication feasible gain-loss assisted optical microcavity. Using scattering-matrix formalism, we study the simultaneous interactions between three successive coupled states around two EP2s, which yield an EP3. Following an adiabatic parametric variation around the identified EP3, we present a robust successive-state-conversion mechanism among three coupled states. The proposed scheme indeed opens a unique platform to manipulate light in integrated devices., Comment: 6 pages, 4 figures

We report a novel GaN/InGaN LED endowed with rectangular shaped multiple quantum wells and gradual narrowing of the bandgap of electron blocking layer (EBL) towards the anode side and subsequently analyze the obtained results through well-calibrated numerical simulation in APSYS. The results show that the droop in internal quantum efficiency (IQE) for the proposed LED decreases to 11% as compared to 54%, obtained in conventional structure. Additionally, while operated at 150 mA the proposed LED provides an output power that is enhanced by 80% more than what is obtained in conventional LED. The analysis reveals that the gradual change in Al content of EBL layer helps scale down the electric field produced in this region due to polarization which in turn imposes strong blocking on the electrons that try to escape out the active region and move to EBL layer. Moreover, due to less amount of downward valence band bending better hole injection takes place in the active region. Consequently the proposed structure allows increased electron and hole concentrations in the multiple quantum wells thereby enhancing its internal quantum efficiency while a large current flows through the device.

We propose a phosphor-free dual wavelength monolithic white LED comprising a tunnel junction that separates a yellow light-emitting InGaN/GaN multiple quantum well (MQW) structure without an electron blocking layer (EBL) from a blue light-emitting MQW structure. Using a well-calibrated APSYS simulation software we investigate its performance in terms of output power, wall plug efficiency, and CIE plot of the emitted light and analyze its operation on the basis of band diagram, carrier distribution, EL spectra and radiative recombination rate taking into account the carrier confinement and carrier reuse effects due to removal of an EBL and incorporation of a tunnel junction, respectively. At the injection current density of 250 A/cm2, our proposed white LED exhibits 232% improvement in output power as compared to a conventional blue LED and only 40% droop reduction of wall plug efficiency as opposed to 56% in a reported white LED. The Commission Internationale de l'Eclairage (CIE) coordinates of the emitted light from the proposed white LED structure are found to be (0.310, 0.309) at 100 A/cm2 which signify a good quality white light emission.

We develop a 2D analytical subthreshold model for nanoscale double-gate junctionless transistors (DGJLTs) with gate-source/drain underlap. The model is validated using well-calibrated TCAD simulation deck obtained by comparing experimental data in the literature. To analyze and control short-channel effects, we calculate the threshold voltage, drain induced barrier lowering (DIBL) and subthreshold swing of DGJLTs using our model and compare them with corresponding simulation value at channel length of 20 nm with channel thickness tSi ranging 5–10 nm, gate-source/drain underlap (LSD) values 0–7 nm and source/drain doping concentrations (NSD) ranging 5–12 × 1018 cm−3. As tSi reduces from 10 to 5 nm DIBL drops down from 42.5 to 0.42 mV/V at NSD = 1019 cm−3 and LSD = 5 nm in contrast to decrement from 71 to 4.57 mV/V without underlap. For a lower tSi DIBL increases marginally with increasing NSD. The subthreshold swing reduces more rapidly with thinning of channel thickness rather than increasing LSD or decreasing NSD.

We study the phenomenon of deliberate inter-modal interactions in a specially designed index guided Microstructured Optical Fiber (MOF) by exploiting multipole expansion method (White et al. 2002). The MOF is designed in such a way that the first layer of holes is judiciously filled with a material having refractive index slightly greater than the background material or core and remaining holes are filled with air. Accordingly, we find an interesting phenomenon of mode crossing between the fundamental mode and a targeted defect mode while tuning the wavelength. Exploring this transition wavelength of the mode crossing, we propose a design of a fiber optic sensor for refractive index measurement (Silva et al. 2014) with enhanced sensitivity.

In this work, we propose and investigate numerically InGaN/GaN based multiple quantum well (QW) blue light-emitting diodes (LEDs) with step quantum well (InGaN)/barrier (GaN) structures. We design four LED structures—(LED-A) InGaN/GaN rectangular quantum well, (LED-B) one down step in the middle of the QW created using sharp increase in In contents, (LED-C) one down step in the middle of the QW and the other down step in the right barrier away from QW and (LED-D) similar to LED-C barring one down step in the left barrier facing the QW. Using well-calibrated APSYS simulation program we compare the variation of output power and internal quantum efficiency of LEDs with input injection current and analyze them in the light of energy band diagram, electric field distribution, carrier concentration and radiative recombination rate. The proposed LED-D exhibits significant improvement in optical output power ~ 180.7% compared to conventional LED-A. Furthermore unlike other three LED structures, LED-D shows a very low internal quantum efficiency droop of 5.1% only at injection current of 120 mA.

We design and evaluate the performance of three InGaN/GaN multiple quantum well blue LEDs – A. rectangular quantum wells with a fixed barrier width, B. trapezoidal quantum wells with a fixed barrier width, and C. trapezoidal quantum wells with a decreasing barrier width towards the anode end – in terms of efficiency droop and power output. We obtain band diagram, electric field, emission spectra and carrier concentration using well calibrated APSYS simulation. Use of trapezoidal quantum wells increases better overlapping between electron and hole wavefunctions thereby increasing radiative recombination events. Furthermore decreasing barrier width from n- to p- regions shortens hole transport path which results in better hole transport and distribution in the wells and hence larger radiative recombination rate. Our proposed structure C exhibits efficiency droop reduction of 2.1% and enhancement of optical power of 236.7% compared to conventional rectangular quantum well structure at injection current of 120 mA.

We report a numerical study on formation and stability of parabolic pulses during their propagation through highly nonlinear specialty optical fibers. Here, we have formed a parabolic pulse at wavelength of 2.1 μm from a Gaussian input pulse with 1.9 ps FWHM and 75 W peak power after traveling through only 20 cm length from the input end of a 1 m long chalcogenide glass based microstructured optical fiber (MOF). Dependence on input pulse shapes towards most efficient conversion into self-similar states is reported. The stability in terms of any deviation from dissipative self-similar nature of such pulses has been analyzed by introducing a variable longitudinal loss profile within the spectral loss window of the MOF, and detailed pulse shapes are captured. Moreover, three different dispersion regimes of propagation have been considered to study the suitability to support most stable propagation of the pulse.

Ultra-low power logic applications at advanced CMOS technology nodes have been extensively investigated nowadays to increase packing density in Integrated Circuits at a lower cost. Junctionless (JL) transistors have emerged as promising alternatives to conventional MOSFETs because of their relatively easy fabrication steps and extreme scalability. We perform a detailed numerical study to evaluate the effects of channel doping concentration, dielectric constant of underlap spacers, source/drain resistance on logic performance of 20 nm gate length JL MOSFETs in terms of ON-current at a given OFF-current, subthreshold swing, gate capacitance and intrinsic delay for supply voltages ranging 0.4–0.75 V. In comparison with the reported experimental data for inversion-mode device, our optimized JL device exhibits enhancement of I ON by 15.6%, reduction of drain-induced barrier lowering (DIBL) by 22.5% while preserving equally low SS of 61.5 mV/decade at channel length of 34 nm and supply voltage of 0.75 V.

We investigate the impact of sidewall spacers on the analog/RF performance of double gate junctionless transistors at channel length of 30 nm using extensive numerical device simulation. Furthermore, we report the performance of a common source amplifier built employing such devices. The simulation deck is calibrated with experimental results published elsewhere. The influence of spacer layers is analyzed in terms of the dielectric constant and spacer layer thickness. Our findings reveal that peak transconductance and peak intrinsic gain increase by 5.2 and 71.3 % for spacer dielectric constant k = 30 as compared to the respective value for k = 3.9 while peak unity gain cut-off frequency and maximum frequency of oscillations increase by 37 and 83.3 % for k = 3.9 compared with the value for k = 30. It is evident from our studies that peak transconductance, peak transconductance generation factor, peak gain and peak cut-off frequency increase by 13, 10, 27 and 20 %, respectively, for spacer length of 5 nm compared with the corresponding value for spacer length of 15 nm. Additionally, our analysis shows that the peak gain of a common source amplifier increases with higher value of load resistance and spacer dielectric constant while it reduces with a larger spacer length. Moreover, we present a comparison of various device parameters of JLTs associated with analog/RF performance and gain of the common source amplifier with the corresponding parameter obtained with undoped inversion mode transistors.

We have developed an algorithm which utilizes model equations for MOSFETs to extract BSIM3v3.2.2 MOSFET model parameters of Ge-channel transistors. The model represents the entire transfer characteristics from sub-threshold to strong inversion regions and the output characteristics from linear to saturation regions thus capturing all the operating bias conditions of gate to source voltage VGS and drain to source voltage VDS. For extraction of various BSIM parameters, the model equations are fitted with reported experimental characteristics, and some with TCAD simulation data of Ge MOSFETs for various geometrical dimensions over a wide range of bias conditions. The algorithm used for extracting BSIM3V3.2.2 parameters by fitting BSIM3v3.2.2 model equations with experimental or simulation data is written in MATLAB code. The extracted BSIM model parameters are employed in ADS circuit simulator to reproduce the transfer characteristics of Ge MOSFETs with the same channel length and channel width of 80 nm for both high and low body bias conditions. The characteristics obtained from ADS match well with those obtained from TCAD simulation using SILVACOATLAS thereby ensuring the accuracy of our extraction methodology. The extracted set of BSIM3V3.2.2 parameters is used to generate transfer and output characteristics of Ge channel pMOSFETs at channel length of 70 nm. The extracted value of threshold voltage, bulk mobility and saturation velocity are −0.2 V, 0.18 m2/V.s and 1.2 × 106 m/s, respectively. Our study reveals that various device parameters such as transconductance, intrinsic voltage gain, and cut-off frequency show a maximum value of 677 μS/μm, 2.7, and 63 GHz, respectively.

Effects of a Ge interface control layer on the electrical properties of RF sputter-deposited TaYOx on n-GaAs substrates are studied in detail. It is found that the incorporation of an ultrathin Ge layer in between TaYOx and GaAs substrate improve various electrical parameters such as interface state density, border trap density, frequency dispersion, leakage current density and flat-band shift thereby improving capacitor performance. The trapping of charge carriers in GaAs MOS capacitors during constant voltage stress has also been studied and the increase in gate leakage current observed during electrical stress is estimated and explained by taking into account the build up of trap charges and stress induced trap generation. The cross-section of traps is also estimated to be in the range of 10ź18 cm2. Such a small value for the capture cross-section implies that the generated traps are neutral centers which are probably responsible for trap-assisted tunneling during voltage stressing.

ZnTiO3 cubic nanomaterials were synthesized hydrothermally under surfactant free conditions, in presence of the inexpensive material urea. Calcination at 6000C yields highly crystalline hexagonal stoichiometric ZnTiO3 phase (as confirmed from powder X-ray diffraction, X-ray photoelectron spectra and Raman studies). This is in contrast to earlier reports, which said that ZnTiO3 can be synthesized at much higher temperature i.e. 9450C. Distinct signatures of Zn-O and Ti-O vibrations were manifested in the IR spectra with concomitant decrease in intensity of -NH and -CO stretching frequencies of urea. Thus urea plays a critical role in formation and stabilization of the ZnTiO 3 phase. The ZnTiO3 nanomaterials showed much superior photo catalytic efficiency than TiO2 nanomaterials due to enhanced electron–hole separation in the former because electrons can easily get transferred from the conduction band (CB) of Ti to CB of Zn. Surface studies indicate larger pore volume and pore diameter of the ZnTiO3 nanomaterials. The ZnTiO3 nanomaterials also get effectively sensitized by a porphyrin dye (PHy) synthesized with hydantoin anchoring groups. Electron injection rate from PHy to ZnTiO3 is much higher than from PHy to TiO2 implying the prospect of using the titanate nanomaterials as photoanode materials in dye sensitized solar cells (DSCs) .

Using extensive numerical device simulation, we investigate the influence of sidewall spacers on the analog/RF performance of double-gate junctionless transistors at channel length of 30 nm. Our findings reveal that peak transconductance and peak intrinsic gain increase by 5.2 and 71.3% for spacer dielectric constant k = 30 as compared to the respective values for k = 3.9, while peak unity gain cut-off frequency increases by 37% for k = 3.9 compared with the value for k = 30. The transconductance generation factor is found to be less sensitive to the variation in k. With increasing k the output conductance becomes less for low gate overdrive voltage V GT while it shows a reverse trend for higher V GT. It is evident from our studies that peak transconductance, peak transconductance generation factor, peak gain, and peak cut-off frequency increase by 13, 10, 27, and 20%, respectively, for spacer length of 5 nm compared with the corresponding values for spacer length of 15 nm. However, with a larger spacer length, the output conductance exhibits reduced value for lower V GT, while it becomes comparable with the values for smaller spacer lengths as V GT increases.

In this study, sunlight was used for in situ preparation of gel-based various nanohybrid systems. A naturally occurring amino acid, l-phenylalanine derivative formed a hydrogel with graphene oxide (GO)/reduced graphene oxide (rGO) at physiological pH. This hydrogel was then used in the presence of silver ions and diffuse sunlight to form initially a tri-nanohybrid system consisting of six atom silver nanoclusters, nanosheets, and nanofibers. Interestingly, a time-dependent morphological transformation occurs in this nanohybrid system to form one tri-nanohybrid to another tri-nanohybrid with the appearance of a novel, nanoscopic intermediate tetra-nanohybrid system consisting of four distinctly different nanomaterials (nanofibers, nanosheets, nanospheres, and nanoparticles). UV-Vis and fluorescence spectroscopic analyses, transmission electron microscopic, X-ray photo electron spectroscopic and MALDI-TOF mass spectral analyses with time were applied to characterise these morphological transformations in gel based nanohybrids. Time-dependent X-ray photo electron spectroscopic (XPS) analysis was used to uncover the mechanism for the transformation of silver nanoclusters to silver nanoparticles in the hydrogel matrix. Sunlight was used to trigger time-dependent structural transformation in the nanohybrid systems. Interestingly, one of these tri-nanohybrid systems (silver nanoparticles containing rGO based hydrogel) shows a catalytic property of reducing nitroarenes to aminoarenes and the catalytic efficiency can be modulated by changing the size of the silver nanoparticles with time in diffuse sunlight. The mechanism for different catalytic activities for different hybrids with varying size of silver nanoparticles has also been deciphered.

With NASA funding, the Deep Space Optical Communication (DSOC) Project at JPL is planning a system level technology demonstration of optical communications from deep space. A 22 cm diameter flight laser transceiver (FLT) is being developed for space flight. The FLT will be designed to transmit an average laser power of 4W at 1550 nm and receive a weak 1064 nm laser signal (> 100 femtowatts). Use of the Hale telescope at Palomar Mountain, CA, retrofitted with a photon-counting receiver to detect the downlink from space, is planned. The Optical Communication Telescope Laboratory (OCTL) at Table Mountain, CA will transmit a 1064 nm laser beacon to serve as a pointing reference for the FLT and support low-rate uplink data-rates. The DSOC FLT is part of the baseline payload for the Psyche mission spacecraft recently selected for flight by NASA, providing link demonstration opportunities during the mission cruise phase. Link demonstration opportunities at distances of approximately 0.1 to 2 astronomical units (AU) are expected. The DSOC system is being designed to support downlink data-rates of 0.2 to > 200 Mb/s and uplink data rates of approximately 1.6 kb/s. A status update of DSOC Project activities on flight and ground development will be summarized in this paper.

Recent developments for laser communication on CubeSats across interplanetary distances will be presented. A binary polarization-shift-keyed modulation scheme using dual gain-switched diode lasers is developed and demonstrated within an end-to-end link testbed to achieve signal acquisition under extremely poor signal-to-noise conditions (-43.5 dB average signal-to-noise power ratio at a 1-MHz symbol rate) to simulate direct-to-Earth links, while simultaneously targeting a limited SWaP footprint (1.5U envelope). Additional system design and constraints for the compact laser transmitter will be discussed.

A multi-beam beacon was transmitted from the Optical Communication Telescope Laboratory (OCTL) located at Table Mountain, CA to the Lunar Laser Space Terminal (LLST), on-board the Lunar Atmospheric Dust and Environment Explorer (LADEE) spacecraft, during NASA’s recent Lunar Laser Communication Demonstration (LLCD). The laser beacon (1568±0.1 nm) was square wave modulated and sensed by a quadrant sensor on LLST. While link acquisition and tracking proceeded with the sensed signal, on-board processing extracted power incident on the quadrant sensor and telemetered it down over the optical downlink. Subsequently, post-processing of the codewords received at OCTL retrieved the power time series recorded at LLST. Analysis comparing measured and predicted mean irradiance delivered to LLST consistently agreed to within < 1 decibel (dB). Irradiance fluctuations detected at LLST were reconciled with an uplink wave-propagation simulation model using Kolmogorov phase screens.

Using APSYS simulation program, we investigate the optical performance of InGaN/GaN multiple quantum well (MQW) blue light-emitting diodes (LEDs) with a W-shaped well structure with respect to optical output power and internal quantum efficiency with variation in injection current. The concept of W-shaped quantum well is proposed to lower the polarization field and to obtain better overlapping between the peaks of electron and hole concentrations. Our proposed LED with W-shaped quantum wells exhibits 91% improvement in output power as compared to a rectangular quantum well LED. Furthermore, our proposed LED shows 20% efficiency drooping in contrast to 49% with a conventional LED at an input current = 120 mA. Moreover, we analyze our results with the help of band diagram, electron and hole concentrations, and also radiative recombination rate in the wells obtained from numerical simulation program.

This work analyzes the effect of incorporating a shallow first well and a two-step electron-blocking layer (EBL) on the performance of an InGaN/GaN rectangular multiple quantum well LED using well-calibrated numerical simulator SILVACOATLAS. The results show 78% improvement in output power of the proposed LED structure in comparison with the conventional structure at 150 mA injection current. In addition, the droop in internal quantum efficiency (IQE) for the proposed LED structure reduces to 29% from 54% which is observed in conventional structure. The simulation study reveals that the shallow first well facilitates to reduce the effective blocking provided by the preceding GaN layer to the injected electrons, thereby increasing the electron injection. In addition, the stepped electron-blocking layer raises the energy barrier for electrons at the EBL causing better confinement of electrons compared to conventional structure. The stepped EBL also decreases the effective energy barrier for holes significantly, thereby aiding better injection of holes into the multiple quantum well light-emitting region. Consequently, carrier concentrations in the active region of the proposed structure increase, thereby enhancing its output power at high input current.

New graphene oxide (GO)- based hydrogels that contain vita- min B2/B12 and vitamin C (ascorbic acid) have been synthesized in water (at neutral pH value). These gel-based soft materials have been used to syn- thesize various metal nanoparticles, in- cluding Au, Ag, and Pd nanoparticles, as well as nanoparticle-containing re- duced graphene oxide (RGO)-based nanohybrid systems. This result indi- cates that GO-based gels can be used as versatile reactors for the synthesis of different nanomaterials and hybrid sys- tems on the nanoscale. Moreover, the RGO-based nanohybrid hydrogel with Pd nanoparticles was used as an effi- cient catalyst for CC bond-formation reactions with good yields and showed high recyclability in Suzuki-Miyaura coupling reactions.

Two types of nano-materials (nanotubes and graphene) were incorporated at different concentrations into a bio-compatible polymer matrix, and the mechanical properties of the composite films were studied. Although both nanomaterials improved the mechanical attributes of the polymer, it was found that the composites containing the nanotube–graphene mixture exhibited significantly superior elasto-plastic properties. This work presents a facile technique of fabricating nano-composites that could be scaled up and applied to various types of polymers. These multi-component films have the potential to be used in a wide range of applications including bio-medicine and photovoltaics, as well as the military and automotive industry.

Spacecraft carrying optical communication lasers can be treated as artificial stars, whose relative astrometry to Gaia reference stars provides spacecraft positions in the plane-of-sky for optical navigation. To be comparable to current Deep Space Network delta-Differential One-way Ranging measurements, thus sufficient for navigation, nanoradian optical astrometry is required. Here we describe our error budget, techniques for achieving nanoradian level ground-base astrometry, and preliminary results from a 1 m telescope. We discuss also how these spacecraft may serve as artificial reference stars for adaptive optics, high precision astrometry to detect exoplanets, and tying reference frames defined by radio and optical measurements.

Current and near-term Mars relay telecommunications services are provided by a set of NASA and ESA Mars science orbiters equipped with UHF relay communication payloads employing operationally simple low-gain antennas. These have been extremely successful in supporting a series of landed Mars mission, greatly increasing data return relative to direct-to-Earth lander links. Yet their relay services are fundamentally constrained by the short contact times available from the selected science orbits. Future Mars areostationary orbiters, flying in circular, equatorial, 1-sol orbits, offer the potential for continuous coverage of Mars landers and rovers, radically changing the relay support paradigm. Achieving high rates on the longer slant ranges to areostationary altitude will require steered, high-gain links. Both RF and optical options exist for achieving data rates in excess of 100 Mb/s. Several point designs offer a measure of potential user burden, in terms of mass, volume, power, and pointing requirements for user relay payloads, as a function of desired proximity link performance.

Rapidly varying but of nearly-mean-zero longitudinal dispersion profile has been adopted to achieve self-similar propagation of parabolic optical pulses through a chalcogenide glass based and segmented highly-nonlinear bandgap optical fiber at 2.8 µm.

We present the successful design and synthesis of few-layer graphenes over an Au/MgO catalytic system by chemical vapor deposition with methane as the carbon source. The resulting structures were composed of a few graphitic layers, and the highest synthesis yield was found to be 62% when the methane flow rate was 120 mL/min. The dimension of the in-plane crystallites was found to increase with the reaction time. A simple purification step was used to remove the MgO support that resulted in graphene sheets decorated with Au nanoparticles. Such an approach makes it possible to synthesize high purity Au–graphene nanostructured composites by using a single reaction step and without the need for additional functionalization or attachment.

Radio frequency sputtering system is employed to fabricate metal oxide semiconductor (MOS) capacitors using an ultra-thin layer of HfAlO x dielectric deposited on n-GaAs substrates with and without a Si interface control layer incorporated in between the dielectric and the semiconductor. Measurements are performed to obtain capacitance voltage ( C – V ) and current voltage ( I – V ) characteristics for GaAs/Si/HfAlO x and GaAs/HfAlO x capacitors under different constant voltage and constant current stress conditions. The variation of different electrical parameters such as change in interface trap density, hysteresis voltage with various values of constant voltage stress and the dependence of flat band voltage, fractional change in gate leakage current density, etc. with stress time are extracted from the C – V and I – V data for capacitors with and without a Si interlayer. Further the trap charge density and the movement of trap centroid are investigated for various injected influences. The dielectric breakdown and reliability properties of the dielectric films are studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t bd ⩾ 1350 s) is observed for HfAlO x gate dielectric with a silicon inter-layer under the high constant voltage stress at 8 V. Compared to capacitors without a Si interlayer, MOS capacitors with a Si interlayer exhibit improved electrical and breakdown characteristics, and excellent interface and reliability properties.

In the presence of a small amount of a proteinous amino acid (arginine/tryptophan/histidine) or a nucleoside (adenosine/guanosine/cytidine), graphene oxide (GO) forms supramolecular stable hydrogels. These hydrogels have been characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) analysis, Raman spectroscopy, and rheology. The morphology of the hydrogel reveals the presence of nanofibers and nanosheets. This suggests the supramolecular aggregation of GO in the presence of an amino acid/nucleoside. Rheological studies of arginine containing a GO-based hydrogel show a very high G' value (6.058 × 10(4) Pa), indicating the rigid, solid-like behavior of this gel. One of these hydrogels (GO-tryptophan) has been successfully utilized for the in situ synthesis and stabilization of Au nanoparticles (Au NPs) within the hydrogel matrix without the presence of any other external reducing and stabilizing agents to make Au NPs containing the GO-based nanohybrid material. The Au NPs containing the hybrid hydrogel has been characterized by using UV/vis spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). In this study, gold salt (Au(3+)) has been bioreduced by the tryptophan within the hydrogel. This is a facile "green chemical" method of preparing the GO-based nanohybrid material within the hydrogel matrix. The significance of this method is the in situ reduction of gold salt within the gel phase, and this helps to decorate the nascently formed Au NPs almost homogeneously and uniformly on the surface of the GO nanosheets within the gel matrix.

The concept of deep-space optical communications was formulated shortly after the invention of lasers. The promise of laser communications, high data rate delivery with significantly reduced aperture size for the flight terminal, led to the pursuit of several successful experiments from Earth orbit and provided the incentive for further demonstrations to extend the range to deep space. This paper is aimed at presenting an overview of the current status of optical communications with an emphasis on deep space. Future perspectives and applications of optical communications related to near-Earth and interplanetary communications are also addressed.

We report the photo-thermal properties of single and double wall carbon nanotubes (CNT) dispersed in various solvents with different concentrations when exposed to near infrared nm laser irradiations. All these studies were correlated to the dispersivity of CNT in various solvents. The observed temperature increase of the various nanotube solutions was found to be determined by the concentration of the optically active nanotubes, as determined from their Raman scattering spectra, which are resonant in the spectral range of the laser excitation. Such findings could significantly improve the understanding of the optically active CNT species, their overall laser induced-heating levels, and thus reducing the amount of the CNT required for bio-medical photothermal applications to limit the possible undesired cytotoxic effects that occur at high nanotube concentrations. Our studies open up the possibility of using selective species of CNT as effective low-toxic photo thermal agents for cancer targeting and ablation.

Metal–oxide–semiconductor (MOS) capacitors fabricated by depositing yttrium oxide (Y 2 O 3 ) using radio frequency sputtering system on top of n-GaAs substrates have been investigated. To study the interface properties, charge trapping behavior and breakdown characteristics of Y 2 O 3 gate dielectric, the MOS capacitors were subjected to constant current stress, high pulse voltage stress and high constant voltage stress. The average value of the cross section of generated traps during electrical stress has been determined from our experimental data. Further the trap charge density, its distribution and location have been investigated by measurements on application and subsequent withdrawal of high pulse voltage stress. Additionally, stress induced leakage current density and time dependent dielectric breakdown characteristics have been obtained and time-to-breakdown exceeding 840 s is observed for Y 2 O 3 gate dielectrics directly deposited on n-GaAs. Our experimental results have been analyzed with simple analytical formulae available in the literature.

The feasibility of employing yttrium oxide (Y2O3) as high-k gate dielectrics for GaAs metal-oxide-semiconductor (MOS) devices has been investigated. MOS capacitors were fabricated using RF-sputtered deposited Y2O3 films on NH4OH treated n-GaAs substrate. Indeed high-k (Y2O3)/GaAs MOS capacitors exhibiting fairly good electrical characteristics, for instance, especially low leakage current density, low hysteresis and allowable density of interface states, have been achieved. The effects of several annealing treatments on Y2O3-gated GaAs MOS capacitors have been investigated in order to optimize the process conditions. A decrease in accumulation capacitance (Cacc) following PDA effectively increases the equivalent oxide thickness (EOT), which is predicted to be correlated with the growth and continuous increase in the physical thickness of a lower-k inter-layer sandwiched between Y2O3 and GaAs. However, leakage currents and interface trap densities are reduced with higher values of annealing temperature. The variation of current density with an equivalent oxide thickness (EOT) has also been investigated.

Large area and few to multi-layer graphene sheets were synthesized on a bimetallic catalyst system via radio-frequency chemical vapor deposition (RF-CVD). Synthesis conditions were varied and their effects on the morphological properties of the graphene structures were observed. As the flow rate of the hydrocarbon was varied, the diameter of the graphene structures increased from a few hundred nanometers to a few micrometers. The number of graphene layers was also found to be dependent on the hydrocarbon concentration. This method shows great potential for the synthesis of large area few-layer graphene sheets, which can be used in various electronic applications.

Background and Objectives Effective postoperative analgesia may enhance early rehabilitation after orthopedic surgery. This randomized double-blind trial investigates the relative contributions of adductor canal block and low-dose intrathecal morphine (ITM) to postoperative analgesia and functional recovery after total knee arthroplasty. Methods Two-hundred one patients undergoing elective unilateral total knee arthroplasty under spinal anesthesia were randomized to 3 groups. All patients received standardized intraoperative local infiltration analgesia and postoperative oral analgesics. Patients in group 1 received a “sham” adductor canal block with 30 mL of normal saline. Patients in group 2 received an adductor canal block with 30 mL of ropivacaine 0.5% with 1:400,000 epinephrine, whereas patients in group 3 received the adductor canal block with the active drug and 100 μg of ITM. The primary outcome measure was the Timed Up and Go (TUG) test on the second postoperative day. Secondary outcomes included postoperative pain scores and opioid requirements, distance walked, time to hospital discharge, and self-reported functional outcomes at 3 months. Results All 3 groups had similar values of TUG test on postoperative day (POD) 2 (46 [36–62], 45 [33–61], and 52 [41–69]; P = 0.166) as well as other short-term and 3-month functional outcomes. Patients in group 3 showed a favorable analgesic profile as evidenced by 3 positive secondary outcomes. These positive outcomes were lower pain scores 12 hours postoperatively both at rest (4 [2–6.3], 4 [2.3–6], and 3 [1–4]; P = 0.007) and on movement (6 [4–8], 6 [3–8], and 4 [2–6]; P = 0.002), a lower incidence of “rescue” intravenous patient-controlled analgesia (42%, 34%, and 20%; P = 0.031), and the lowest cumulative opioid requirements for the first 48 hours postoperatively (86 ± 71, 68 ± 46, and 59 ± 39; P Conclusions Our data suggest that there is no difference in either the primary outcome of TUG test on POD 2, other immediate functional secondary outcomes, or in global functional outcome at 3 months postoperatively across all 3 groups. Our data also suggest an improved analgesic profile in the first 48 hours postoperatively when both adductor canal block and low-dose ITM (100 μg) are added to local infiltration analgesia as evidenced by several positive secondary outcomes of lower pain scores and opioid requirements. Clinical Trial Registration This study was registered at ClinicalTrials.gov, identifier NCT02411149.

Significant technological advances were made toward utilizing the Hale telescope for receiving the faint laser communication signals transmitted from an optical transceiver on a spacecraft orbiting Mars. The so-called Palomar receive terminal design, which would have supported nominal downlink data rates of 1-30 Mbps, is described. Testing to validate technologies for near-Sun (3deg from edge of solar disc) daytime operations is also discussed. Finally, a laboratory end-to-end link utilizing a 64-ary pulse-position modulated photon-counting receiver and decoder that achieved predicted near-capacity (within 1.4 dB) performance is described.

This paper provides an overview of Optical Payload for Lasercomm Science (OPALS) activities and lessons learned during mission operations. Activities described cover the periods of commissioning, prime, and extended mission operations, during which primary and secondary mission objectives were achieved for demonstrating space-to-ground optical communications. Lessons learned cover Mission Operations System topics in areas of: architecture verification and validation, staffing, mission support area, workstations, workstation tools, interfaces with support services, supporting ground stations, team training, procedures, flight software upgrades, post-processing tools, and public outreach.

The Optical PAyload for Lasercomm Science (OPALS) experiment was installed on the International Space Station (ISS) in April 2014. Developed as a technology demonstration, its objective was to experiment with space-to-ground optical communications transmissions from Low Earth Orbit. More than a dozen successful optical links were established between a Wrightwood, California–based ground telescope and the OPALS flight terminal from June 2014 to September 2014. Each transmission required precise bi-directional pointing to be maintained between the space-based transmitter and ground-based receiver. This was accomplished by acquiring and tracking a laser beacon signal transmitted from the ground telescope to the OPALS flight terminal on the ISS. OPALS demonstrated the ability to nominally acquire the beacon within three seconds at 25° elevation and maintain lock within 140 μrad (3σ) for the full 150-second transmission duration while slewing at rates up to 1°/sec. Additional acquisition attempts in low elevation and weather-challenged conditions provided valuable insight on the optical link robustness under off-nominal operational conditions.