bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Photoluminescence Properties of CuInS2 and AgInS2 Nanocrystals Synthesized in Aqueous Solutions
Authors: Borkovska L. , Romanyuk A , Strelchuk V. , Polishchuk Yu. , Kladko V. , Stroyuk O. , Raevskaya A. , Kryshtab T. 
Published: February 2020

The CuInS2 and AgInS2 are the low-toxic semiconductor materials with direct band gap and high absorption coefficient in the visible and near-infrared regions. The nanocrystals (NCs) based on these materials demonstrate enhanced photoluminescence (PL) tunable over the whole visible spectral range resulting in growing attention for their application in light-emitting devices, solar cells and bio-markers.
Despite the fact that different strategies have been developed for the synthesis of I-III-VI NCs, it still remains a challenge to develop a facile, general, and inexpensive method for the preparation of I-III-VI NCs with controllable luminescence spectrum.
Herein, we report the results of investigations of the photoluminescent, optical and structural properties of CuInS2 and AgInS2 NCs synthesized in mild conditions in aqueous solutions in the presence of aliphatic mercapoacids. The pristine colloidal solution of the NCs, the powdered NCs as well as the NC embedded in the polymer films of gelatin or polyvinyl alcohol were studied. The X-ray diffraction patterns and the Raman scattering spectra of powdered NCs indicated their tetragonal phase. The average size of the NCs was estimated to be about 4 nm for the AgInS2 and about 2 nm for the CuInS2 ones. The optical absorption spectra of the NCs solution as well as of the nanocomposite films showed the band onset larger than the band gap of the corresponding bulk chalcopyrite materials indicating a quantum confinement effect.
The PL spectra showed a wide band with maximum at about 2.0 eV for the AgInS2 NCs and 1.8 eV for the CuInS2 NCs and a Stokes shift in the range of 0.3-0.7 eV. The PL band is caused by carrier recombination via the levels of defects in the NCs. No exciton emission was observed. As the temperature decreased, the PL intensity increased, the PL band broadened and the PL maximum shifted to the blue on about 0.02 eV for the CuInS2 NCs and on about 0.27 eV for the AgInS2 NCs. It is shown that the PL spectra of the CuInS2 NCs can be well fitted with single Gaussian function, while those for the AgInS2 NCs by two. The PL band spectral position did not change essentially with the excitation power, but varied with the excitation energy (wavelength). The latter is explained by strong dependence of the PL excitation spectra on the emission position in the PL spectrum. For the AgInS2 NCs this dependence was found to be different for two PL components which allowed supposing that these PL components were connected with two different ensembles of the NCs.
It is shown that the PL quantum yield in the NCs studied can reach around 15% that makes them suitable for future optoelectronic and bio-medical applications.
Investigation of Trapezoidal Well for Improving the Light Efficiency in Algainp-Based LEDs
Authors: Oh Hwa Sub 
Published: February 2020

(AlxGa1-x)0.5In0.5P-based LEDs have a small conduction band offset that limits their electron confining potential.1 This weaker electron confinement subsequently leads to electron heterobarrier leakage in AlGaInP heterostructure LEDs, especially in short-wavelength devices, where a fraction of the electrons injected into the active region have a sufficient thermal energy to escape into the cladding layer. To overcome this problem, trapezoidal well structures are introduced in the active region in order to prevent carrier overflow and to gain a higher light output power (Pout). In the field of AlGaInP-based LEDs that emit a short peak wavelength at around 590 nm, however, the effects of the trapezoidal well profile in the active region on LED performance has yet to be systematically studied.
In this study, we investigate the behaviors of optical and electrical characteristics according to their trapezoidal well profile in the active region through the analysis of optical behaviors and device performances.
To investigate the optical behaviors according to the trapezoidal well shape, the sloped barrier (SB) is inserted between well and flat barrier (FB) and the thickness of SB (dSB) is changed from 2.5 nm to 10 nm. And, the FB thickness is adjusted from 15 to 0 nm to maintain the total barrier thickness 20 nm. The schematic diagram of MQW structures of a trapezoidal-shaped well is depicted in Fig. 1(b).
Fig. 2 shows the device performances having different sloped barrier profiles in the MQW LED structures. As the current is increased to 600 mA, the current-voltage (I-V) curves show different behavior according to the SB thickness. In Fig. 1(a) inset, the forward bias voltage at 350 mA decreases from 2.86 V to 2.62 V with an increase in the thickness of SB from 0 to 10 nm. Fig. 1(b) then shows the light output power (Pout)-current characteristics of LEDs on the dSB and the normalized efficacy of the same LEDs at 350 mA operating current is shown in the figure inset. As the dSB between the well and the barrier is increased from 0 to 5.0 nm, the normalized efficacy improves from 1.0 to 1.16 and the maximum Pout increases from 400 to 500 mA, though at a further increase of the dSB to 10 nm, the normalized efficacy degrades to 0.98.
How Predictive Are Reactor-Scale Simulations of Wbg Semiconductor Epitaxy? a Sensibility Analysis of SiC and Nitride Epitaxy Models
Authors: Yanguas-Gil Angel , Shenai Krishna 
Published: February 2020

Process modeling can be the perfect complement to process development: in addition to offering a cost-effective way of exploring the parameter space of a given process or new reactor configurations, models are able to provide information regarding details of surface and gas phase chemistry that is not readily available experimentally. This information can be extremely useful in helping us rationalize trends in yield, epitaxial quality and defect concentration, or why a particular set of experimental conditions leads to the highest quality materials.
In the case of physical vapor and chemical vapor epitaxy, the fundamental aspects of reactor-scale simulations are well established. However, it is our knowledge of homogeneous and heterogeneous processes what limits the predictive nature of our models. Every reactor rate and transport coefficient comes with an associated error that propagates into the model solution. In addition to this, the complexity of the overall kinetics of the growth process complicates our ability to identify rate limiting processes exclusively based on experimental trends of growth rates as a function of experimental parameters. Consequently, knowing how sensitive our model is to the different assumptions will help us both better understand the margin of error of model predictions and identify the key steps in the growth process.
In this talk I will summarize the sensitivity analysis studies that we have carried out on the heterogeneous and homogeneous processes during SiC, GaN, and AlN epitaxy. Using datasets compiled from different models available in the literature, we will compare the predicted results in both 0.5D and simplified 1D and 2D models that will allow both local and non-local sensitivity studies. The advantage of 0.5D models is that they can be used as a first order approximation to simulate epitaxy on planetary systems where wafer to wafer variability is lower than in-wafer variability. We will use these models to identify both the key steps and the main sources of error as a function of the experimental conditions. Finally, we will study the impact that reduction on complexity has on model predictions.
(Invited) Developing Periodically Oriented Gallium Nitride for Frequency Conversion
Authors: Hite Jennifer K , Freitas Jaime A. , Mastro Michael A , Vurgaftman Igor , Meyer Jerry R. , Brown Christopher G. , Kub Francis J , Bowman Steven R. , Eddy Charles R. 
Published: February 2020

Gallium nitride is a semiconductor widely used in both optical and electronic devices. The polarity of GaN (+/- c-direction) influences many properties of the resultant material, including chemical reactivity and electric field in these ‘spontaneously polarized’ materials. By engineering inversion layers, we have demonstrated control of GaN polarity on both polar faces of GaN. By employing a selective growth method to deposit the IL, the lateral polarity of the GaN can be alternated, thus enabling structures referred to as periodically oriented (PO) GaN.
On N-polar substrates, we demonstrated that optimization of the MOCVD growth rates resulted in sharp, vertical interfaces and smooth surfaces. This work has moved the technology substantially closer to practical non-linear optic emitters by using HVPE to extend the PO GaN templates on N-polar substrates to total thicknesses of up to 500 mm, while faithfully maintaining the pattern of alternating polarity. Additionally, cross-sectional cathode-luminescence (CL) imaging of such an extension shows that the large initial dislocation densities occurring in the original inversion layers greatly decreased after about 25 mm of regrowth.
For growth on Ga-polar substrates, we have demonstrated that inversion layers can be created using atomic layer deposition (ALD) of Al2O3. This new capability is especially relevant because Ga-polar films are more prominent in devices, as they result in lower impurities, higher quality and smoother films. In this case, GaN grown over the inversion layer is N-polar. This inversion layer was used to form laterally-patterned stripes of alternating Ga- and N-polar films. We find that annealing the ALD films crystallizes the Al2O3, thereby allowing N-polar GaN to be grown over the new sapphire-like surface. Transmission electron microscopy shows that the inversion layer in a PO GaN structure is crystalline, a-plane oriented, and a-phase. TEM characterization further indicates that the GaN layers, both above and below the Al2O3 inversion layer, are c-oriented without any rotation between them. The optimization of this process has enhanced the surface smoothness.
These methods of GaN polarity inversion offer the promise of engineered materials with custom lateral and vertical polarity variations for applications in novel electronic and optoelectronic devices, a subset of which are expected to be suitable for non-linear optics.
Weak Quantum Confinement and Polaritons in ZnO and ZnO Cu Nanocrystals Prepared by Electrochemical Method
Authors: Torchynska Tetyana V. , El Filali Brahim , Díaz Cano Aaron Israel , Shcherbyna Lyudmula V. 
Published: February 2020

Photoluminescence (PL), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman scattering have been used for the optical and structural characterization of ZnO nanocrystals (NCs) of various sizes. The samples prepared by an electrochemical method have a size of NCs from the range 60 to 600 nm after a heat treatment for 2 hours at 400 oC in ambient air. The Raman scattering technique presents the several active modes including the surface phonon mode. The Raman intensity increases with decreasing NC size and the Raman spectrum shifts to low energy. Simultaneously the X-ray diffraction diagrams present a small shift of XRD peaks that testifies on a change in the lattice parameters in ZnO NCs with decreasing NC size.
Photoluminescence spectra show a free exciton and defect-related emission. The intensity stimulation of exciton-related PL bands with NC size decreasing up to 60 nm is attributed to the realization of the week confinement and the exciton-light coupling with the formation of polariton in small size of ZnO NCs. The numerical calculation of recombination times in the frame of this model has confirmed the presented explanation.
Development of Wide Bandgap Multifunctional NiO Nanostructures and Thin Films for Sensing Applications
Authors: Tomar Monika , Tyagi Manisha , Sharma Anjali , Gupta Vinay 
Published: February 2020

Realizations of transparent pn homo-junction have become more important for the development of transparent electronics for the next-generation optoelectronic devices. The tunability of the electrical conductivity of NiO thin ﬁlms with both P-type and N-type conduction by varying growth kinetics using RF sputtering technique with good optical and properties in the visible region have been demonstrated. The pn homo-junction of NiO thin ﬁlms has been fabricated. The room-temperature conductivities for n-type and p-type NiO thin ﬁlms have been studied using Hall measurement. Glancing angle deposition (GLAD) configuration of rf sputtering technique is utilized to fabricate the array of vertically align nanorods of NiO and are exploited for the development of homojunction devices. The fabricated homo-junction exhibits good rectifying behaviour with efficient ultra-violet (UV) photodiode characteristics, and providing suitable solution for the development of low-cost UV photo-detectors with enhanced response characteristics. The obtained results on the developed UV photo-detector will be elaborated.
Further, Nickel oxide (NiO) nanoparticles (NiO-NPs) have been synthesized by a simple chemical route and exploited successfully for the fabrication of urea biosensors. A thin layer of NiO nanoparticles deposited on indium tin oxide (ITO) coated glass serves as efficient platform for the immobilisation of Urease (Ur) biomolecules for the detection of Urea. The array of NiO nanorods prepared by GLAD was also used as a matrix for making bio-electrode for the efficient detection of Urea using electrochemical techniques. The prepared amperometric bio-electrodes based on NiO nanostructures (Ur/NiO/ITO/glass) exhibits a high sensitivity of about 21.0 mA/(mM-cm2) and good linearity over a wide range (up to 16.65 Mm) of urea concentration.
(Invited) Analytic Methods for Benchmarking Hydrogen and Fuel Cell Technologies
Authors: Melaina Marc , Saur Genevieve , Ramsden Todd , Eichman Joshua 
Published: February 2020

The National Renewable Energy Laboratory (NREL) is involved in a number of low carbon energy conversion projects for transportation and stationary applications. The overall focus is on sustainable, economic solutions that also provide lower carbon emissions for the environment. The range of projects provide cross application insight into transforming how we think about and use energy.
NREL has worked on low carbon energy projects from renewable hydrogen production to integration of hydrogen technologies with electricity markets to end-use applications in the transportation and stationary fuel cell markets. Several different analysis tools and studies have focused on energy resource potential, costs, emissions, and logistical requirements for deployment. These projects bridge traditional market boundaries by integrating electricity services, energy storage, and transportation applications that also can lower the carbon footprint of these energy sectors. In this presentation we will review four types of crosscutting metrics to used to benchmark low-carbon technologies: (1) resource potential, (2) greenhouse gas emissions, (3) cost of delivered energy, including the impacts of different control strategies, and (4) influence of revenue streams from electrolysis units providing grid services. The results of these various analytic approaches highlight the complexity and interdisciplinary nature of efforts to benchmark low-carbon hydrogen and fuel cell technologies.
(Invited) Benchmarking a Metal Oxide-Based Thermochemical Cycle for Solar Hydrogen Production
Authors: McDaniel Anthony H. , Ermanoski Ivan 
Published: February 2020

It is estimated that growth in global population and continued industrialization of developing countries will double world energy consumption by 20351. This rising demand for energy will be largely met by burning fossil fuels, thereby increasing anthropogenic carbon in the atmosphere and fuelling the socioeconomic strife associated with climate change. Developing transformational energy technologies that efficiently and cost-effectively convert solar energy into simple chemical fuels is therefore necessary in order to realize a carbon-neutral, sustainable energy future.
In this talk we will critically assess a two-step, high temperature thermochemical water splitting (WS) cycle powered by concentrated solar energy. This conceptually simple technology, outlined in Figure 1, can theoretically achieve greater solar-to-hydrogen (STH) conversion efficiency than alternative WS routes such as photosynthesis (natural or artificial) or photovoltaic-driven electrolysis2. However, many engineering and material science challenges must be overcome to demonstrate economic viability at large scales.
Cost and scalability issues for solar thermal hydrogen production will be addressed within the context of a particle-based solar receiver reactor concept3–5developed at Sandia through a multi-year research initiative sponsored by the US Department of Energy. Key design principles will be reviewed and create a framework for discussing the synergistic interplay of materials chemistry, reactor design, and system operation necessary for this technology to achieve optimal STH conversion efficiency. The successful implementation of this solar energy conversion technology is predicated on meeting stringent requirements for cost and scalability that are deeply rooted in STH efficiency.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
(1) International Energy Outlook 2011; DOE/EIA-0484(2011); U.S. Energy Information Administration, DOE/EIA-0484(2011) | September, 2011.
(2) Siegel, N. P.; Miller, J. E.; Ermanoski, I.; Diver, R. B.; Stechel, E. B. Ind. Eng. Chem. Res.
2013, 52, 3276–3286.
(3) Ermanoski, I.; Siegel, N. P.; Stechel, E. B. J. Sol. Energy Eng.
2013, 135, 031002.
(4) Ermanoski, I.; Miller, J. E.; Allendorf, M. D. Phys. Chem. Chem. Phys.
2014, 16, 8418.
(5) Ermanoski, I. Int. J. Hydrog. Energy
2014, 39, 13114–13117.

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(Invited) Renewable Hydrogen Evolution on Nickel Phosphide Electrocatalysts: A Comparative Study of Efficiency and Tolerance to Corrosion
Authors: Dismukes G. Charles , Laursen Anders , Liu Bin , Patraju Kelly , Greenblatt Martha 
Published: February 2020

The intermittent nature of renewable energy sources like photovoltaics and wind mills requires storage of large quantities of energy. Renewable hydrogen produced by electrochemically water splitting into its elements pose an unlimited resource for energy storage. Gaseous hydrogen is not only a carbon-free energy carrier which could replace fossil fuels, but also an important bulk chemical of which ~108 ton/year is produced from natural gas. Platinum and nickel (or alloys thereof) are the electrocatalysts used today for hydrogen evolution in acidic and alkaline solution, respectively. However, the scarcity of platinum and the low efficiency of nickel, have greatly restricted the development of renewable hydrogen from water splitting. Since 2013 the number of reports on the use of transition metal phosphides as a replacement for Pt for hydrogen evolution have virtually exploded. Ni3P and Ni2P were the first phases shown to be highly electrochemically active for hydrogen evolution. Ni2P was unfortunately was shown to deactivate in acid and alkali. We recently reported, that another crystalline phase of the nickel phosphide family, Ni5P4, outlperforms Ni2P and Ni3P and is comparable to platinum on a geometric basis in its electrical efficiency at hydrogen evolution (kinetics and intrinsic overpotential). Moreover, unlike Ni2P this catalyst is corrosion resistant, being stable in both strong acid and alkali during electrocatalysis. Here, we will present our most recent work on multiple nickel phosphides as well a structural basis for the unusually high catalytic activity and corrosion resistance. The work was supported by AFOSR, the NSF and NATCO Pharma.

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Fabrication of a Novel BaCe0.8Y0.2O3-δ - Cu Ceramic-Metallic Composite Membrane for Hydrogen Separation
Authors: Rosensteel Wade A , Sullivan Neal P 
Published: February 2020

This presentation details the first report of a dense BaCe0.8Y0.2O3-δ–Cu (BCY-Cu) ceramic-metallic (cermet) membrane for high-temperature hydrogen separation. Such a composite may have applications in catalytic partial oxidation of methane (CPOX), steam reforming of methane, the gasification of carbonaceous materials, and methane dehydroaromatization (MDA). BCY serves as the proton conductor, while Cu provides electronic conductivity for electronic-charge compensation. A novel molten-copper infiltration technique is used to form a dense cermet membrane by infiltrating a porous BCY skeleton.
The BCY skeleton fabrication begins with mixing appropriate amounts of BaCO3, CeO2, and Y2O3 powders with a mortar and pestle, followed by calcination in air. The phase-purity of the resulting powder is verified by X-ray diffraction spectroscopy. Binder is added to the powder via wet-milling with water, followed by pan drying. The powder is crushed with a mortar and pestle, and sieved to achieve a uniform particle size distribution. Pellets are formed by uniaxial dry-pressing, and subsequently sintered at 1600 °C in air, creating a skeleton with approximately 50 % open porosity (Figure 1a).
This porous BCY skeleton is then infiltrated with copper. Cu and CuO powders are mixed with a mortar and pestle to form a powder containing 8 at.% O. This powder is uniaxially pressed into pellets, which are placed on top of the BCY skeleton. The skeleton and Cu-CuO pellet are placed into a controlled-atmosphere furnace, and heated to 1200 °C in a 330-ppm-oxygen environment (balance argon). Under these conditions, the liquid Cu spontaneously infiltrates the BCY skeleton. While dwelling at 1200 °C, the gas environment is changed to a 10 mol.% hydrogen environment (balance argon), and the sample is cooled.
Cu will not wet, nor infiltrate, a BCY skeleton in a reducing environment, which necessitates the initial heating in the oxidizing environment. Once the Cu-CuO alloy infiltrates the BCY skeleton at high temperature, the environment can be switched to a reducing environment without the Cu-CuO alloy defiltrating the BCY skeleton, due to capillary pressure. The reducing environment removes the O from the alloy, leaving pure Cu metal. An electron micrograph of a polished-cross section of the resulting membrane (Figure 1b) reveals that the cermet is nearly fully dense. Our current efforts focus on hydrogen permeation measurements through these novel cermets.
Figure 1: (a.) Scanning electron micrograph of BCY skeleton after sintering, and (b.) scanning electron micrograph of BCY-Cu membrane, in which the dark phase is Cu and the light phase is BCY.

Figure 1