bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic Level Simulation of Ridge Reconstruction and Passivation in GaAs Nanopillars
Authors: Yu Ted H. , Ratsch Christian 
Published: February 2020

State-of-the-art semiconductor nanopillars are an exciting new topic, due to their unique properties that can be used in a number of microelectronic applications. Nanopillars can be grown into microarrays that can maximize surface to volume ratio, ideal for photo-voltaics1, 2. Recently, it was shown that sulfur passivation with sulfur, improved GaAs nanopillar conversion efficiency 2-3 times2. A theoretical understanding on how sulfur can remove mid-gap states in GaAs nanopillar is needed to further improve this process.
In this work, we report our density functional theory (DFT) modeling3 result of 18 different hexagonal shaped GaAs nanopillar that is periodic in the vertical direction. Our model examines energetics and band gaps of the pillars to form a theory on the chemical mechanism for sulfur passivation on nanopillars. Three different stacking are studied, wurtzite, zinc blende, and polytype (ABCB) which contains 50% wurtzite and 50% zinc blende. The nanopillars also differ by their diameter and the way they terminate at the ridges. We theorize that sulfur passivation is mostly effective on the ridges of the nanopillars and that stacking faults play a role in the mid-gap states that exist before passivation.
Further study of our electronic structures, looking at the density of states, show mid-gap states inherent in GaAs ridges passivated by the presence of sulfur. This is because there are dangling bonds along the ridges of the nanopillar that exists when there are stacking faults. We look at many different ways sulfur can react with the ridges. The energetically favorable configuration satisfies the octet rule and eliminates most of the midgap states.

Figure 1: Geometry and density of State for polytype (ABCB) nanopillar before and after sulfur passivation.
References:
1. G. Mariani, A. C. Scofield, C. H. Hung and D. L. Huffaker, Nat. Commun. 4 (1497), doi: 10.1038/ncomms2509 (2013).
2. G. Mariani, R. B. Laghumavarapu, B. T. de Villers, J. Shapiro, P. Senanayake, A. Lin, B. J. Schwartz and D. L. Huffaker, Appl Phys Lett 97 (1), 013107 (2010).
3. T. H. Yu, L. Yan, W. You, R. B. Laghumavarapu, D. L. Huffaker and C. Ratsch, Appl Phys Lett 103, 173902 (2013).

Figure 1
Template-directed Synthesis of Ag2S-Fe2O3 Heterostructures
Authors: Chen Yingjie , Liu Shiben , Zhao Mei , Yu Liyan , Dong Hongzhou , Dong Lifeng 
Published: February 2020

Controlled synthesis of optical-magnetic nanostructures has attracted more and more interest due to their simultaneous optical properties and magnetic manipulating. Ag2S nanocrystals, with a low (~1.0 eV) band gap at room temperature, have become one of the most commonly studied semiconductor nanocrystals. Due to their excellent photoelectric and thermoelectric properties, Ag2S nanocrystals have been widely used in photocatalysis, near-infrared fluorescence imaging, and photoconductive cells. In addition, Fe2O3 nanoparticles with or without interior voids have both magnetic and photocatalytic properties. Thus, the integration of Ag2S and Fe2O3 nanoparticles may lead to further improvements of their optical performance. However, it still remains a difﬁcult task to prepare these desired hybrids in a controllable fashion.
Herein, we demonstrated the synthesis of nanocomposites containing silver sulfide and iron oxide materials by the sulfidation of silver-iron oxide nanotemplates with elemental sulfur as sulfur resource. In the presence of oleylamine, the sulfidation of silver-iron oxide heteromers retained similar nanostructures as templates, indicating an in-situ sulfidation of silver. TEM images, UV-Vis absorption spectra and XRD patterns of as-prepared Ag-Fe2O3 and Ag2S-Fe2O3 nanoparticles synthesized by sulfidation with elemental sulfur were shown in this paper. These investigations would help us to understand the sulfidation and growth process of nanomaterials and control their synthesis for a given application.
Metallization Reliability and Defectivity in Compound Semiconductors
Authors: Kilgore Steve 
Published: February 2020

Compound semiconductor devices are in mass volume production yet our understanding of reliability and defectivity of III-V materials is still evolving. Process-induced defects in electroplated Au interconnect metallization on GaAs devices were detected during the course of reliability testing. Abnormally high lognormal sigmas (σ > 0.7) indicated the existence of a bi-modal failure mechanism. A distinct early lifetime failure mode was observed along with the intrinsic electromigration metallization wear-out failure mode. Increased temperature stress showed only a slight acceleration on the early failure mechanism but selection of a higher resistance degradation failure percentage criterion reduced the extent of these early failures. Physical characterization of the electroplated Au film revealed as-deposited nanoscale voids. Elimination of these voids through process improvement as well as suggested mechanisms for the early failures is discussed.
(Invited) Neutron Irradiation Effect on GaN-Based Materials
Authors: Zhang Ming-lan , Yang R X , Wang X L , Liu S F 
Published: February 2020

For the predominant property, GaN becomes a promising material for ultraviolet/ blue light-emitting diode, solar blind ultraviolet photodetector, radiation resistant particle detectors, and high power high temperature electronic devices. Because of the radiation hardness of GaN, those devices have the potential to be used in outer space and other radiation environment. Irradiation induced defects play the main role in the reliability of GaN based devices. Recently, a strong effort by several groups was devoted to the analyses of electrical and optical properties of defects and their interaction by irradiating GaN with electrons, ions, neutrons and protons [1–4], which is very important for the devices operating at extreme harsh environment.
Positron annihilation spectroscopy (PAS) with a slow-positron beam is an efficient tool for the investigation of open-volume defects such as vacancies in semiconductors, at which they get trapped. In a vacancy the electron density is decreased which makes the positron lifetime longer and narrows the positron-electron momentum distribution. The latter can be observed by recording the Doppler broadening of the energy spectrum of the annihilation radiation. Especially the momentum distribution of the core electrons is sensitive to the chemical environment of an annihilation site. However, in the case of light elements such as O or N the annihilation probability with the core electrons is negligible.
The samples used in the present work were grown on C-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD) with unintentionally doped and Si doped. A 20 nm low temperature GaN nucleation layer was initially grown, and 4 μm GaN film grown at 1050°C was followed. The sample was cut into small pieces with an area of about 10×10 mm2, and irradiated with 2MeV proton from heavy ion accelerator. The incident fluence is 1014, 1015, or 1016 cm-2, respectively. Positron annihilation spectroscopy, XRD, and Raman spectra were measured.
Irradiation induced defect is vacancies which increased with incident proton. XRD result shows that the crystal-order was kept after proton irradiation. Raman spectra of the Si doped sample shows a “carrier removal” effect but there is not any change in the other spectra.
References:

Look D C, Reynolds D C, Hemsky J W, et al. Defect Donor and Acceptor in GaN, J. Phys. Rev. Lett., 1997, 79: 2273-2276.

Fang Z Q, Hemsky J W, Look D C, et al. Electron-irradiation-induced deep level in n-type GaN, Appl. Phys. Lett., 1998, 72: 448-449.

Auret F D, Goodmann S A, Koschnick F K, et al. Effect of heating rate on positive-temperature-coefficient-of-resistivity behavior of conductive composite thin films, Appl. Phys. Lett., 1998, 73: 3742-3744.

Auret F D, Goodmann S A, Koschnick F K, et al. Proton bombardment-induced electron traps in epitaxially grown n-GaN, Appl. Phys. Lett., 1999, 74: 407-409.
Effect of Rising Edge in Dynamic Stress with Various Duty Ratio in Amorphous Ingazno Thin Film Transistor
Authors: Lee Yeol-hyeong , Seok Su-jeong , Kim Byeong-Koo , Kim Sung-Ho , Lee Tae-Kuen , Kim Ohyun 
Published: February 2020

Recently, many research explains the positive threshold voltage (V

th
) shift of oxide TFT as charge trapping at gate dielectric or interface of gate dielectric and channel layer. But mechanism of degradation of rising edge of dynamic stress has not been explained exactly.
During all stresses, gate stress of 1 Hz with 50%, 20%, 10% and 1% duty ratio was applied at 120 ℃ and both drain voltage and source voltage were grounded. Gate voltage (VG
) was on-voltage (Von
) of 20 V and off-voltage (Voff
) of 0 V in unipolar positive stress, Von
of 0 V and Voff of -20 V in unipolar negative stress, and Von
of 20 V and Voff
of -20 V in bipolar stress (Fig.1). During illumination, samples were illuminated using a top LED. We defined Vth
as gate voltage at 1 nA of drain current ID
at VDS
of 15V. We defined effective time as sum of Von
time in all stress including illumination
Fig. 2 shows the ΔVth as function of time with 50%, 20% 10% and 1% duty ratio. In dark, positive unipolar gate stress was applied in fig. 2(a) and bipolar gate stress was applied in fig. 2(b). In illumination, positive unipolar gate stress was applied in fig. 2(c) and bipolar gate stress was applied in fig. 2(d). Fig. 3 shows the ΔVth at effective time of 2000s as reciprocal function of duty ratio for positive unipolar gate stress and bipolar gate stress. At same effective stress time, ΔVth was increase with decreasing duty ratio and ΔVth was larger in bipolar gate stress than in unipolar positive gate stress. Fig. 4 shows ΔVth at effective time of 2000s as reciprocal function of duty ratio under positive unipolar gate stress for illumination and dark. In dark, higher ΔVth was observed compared with illumination.
In this study, we investigated relationship of ΔVth with various bias stress condition including positive unipolar, negative unipolar and bipolar gate stress and ambient including dark and illumination. We will explain positive bias temperature stress based on charge trapping and introduce new mechanism of additional positive ΔVth on rising edge of dynamic stress.

Figure 1
(Invited) Life-Cycle Net Energy Assessment of Large-Scale Hydrogen Production Via Photoelectrochemical Water Splitting
Authors: Greenblatt Jeffery Buyers , Sathre Roger , Sharp Ian D. , Ager Joel W. , Houle Frances A 
Published: February 2020

The Joint Center for Artificial Photosynthesis (JCAP) aims to find a cost-effective method to produce fuels for transportation and feedstocks using only sunlight, water, and carbon dioxide as inputs. Development of such a technology offers the possibility of widespread sources of environmentally benign, energy rich chemicals across the globe. Although still at an early stage, solar-driven water splitting to produce hydrogen is the most mature artificial solar-to-fuel conversion approach. Moreover, there is sufficient information from photoelectrochemical (PEC) water-splitting prototypes designed and developed by JCAP and others to perform an assessment of whether large scale application of this approach would be advantageous from a net energy production point of view.
Here we report a prospective life-cycle net energy assessment of a hypothetical large-scale PEC-based hydrogen production facility, assuming energy output equivalent to 1 GW continuous annual average (610 metric tons of H2per day) [1]. We determine essential mass and energy flows required to support such production [2], and use heuristic methods to conduct a preliminary engineering design of the facility. We then develop and apply a parametric model describing system-wide energy flows associated with the production, utilization, and decommissioning of the facility. Based on these flows, we calculate and interpret life-cycle net energy metrics for the facility. We find that under base-case conditions (10% solar-to-hydrogen (STH) conversion and 10 year PEC cell life span) the energy payback time is 8.1 years, the energy return on energy invested (EROEI) is 1.7, and the life-cycle primary energy balance over the 40 years projected service life of the facility is +500 PJ. The most important model parameters affecting the net energy metrics are the STH conversion efficiency, the life span of the PEC cells, and the embodied energy of several components of the PEC cell. We discuss the sensitivities of these and other parameters, and highlight recent work indicating promising ways to improve the net energy metrics. Results suggest that a strong program of research into improved materials and methods to process the materials will have a high impact on the feasibility of this technology.
References:

R. Sathre, C. D. Scown, W. R. Morrow, J. C. Stevens, I. D. Sharp, J. W. Ager, K. Walczak, F. A. Houle, and J. B. Greenblatt, Energy Environ. Sci. 7, 3264 (2014).

P. Zhai, S. Haussener, J. Ager, R. Sathre, K. Walczak, J. Greenblatt, and T. McKone, Energy Environ. Sci. 6, 2380 (2013).

Figure 1
Electrodes for Protonic-Ceramic Membranes Used in Natural Gas-to-Chemicals Processing
Authors: Ricote Sandrine , Manerbino Anthony , Sullivan Neal P , Coors Grover 
Published: February 2020

Electrodes used in natural gas-to-chemicals processing must demonstrate unique performance attributes in challenging high-temperature, reducing environments. Materials must be stable, have high electronic conductivity, and be chemically inert to methane and other hydrocarbons. Ceramic-metal composites (cermets) made of nickel and the electrolyte material, used as the fuel-side electrodes in protonic ceramic fuel cell, are not suitable as their performance decreases rapidly due to chemical reaction with the natural gas fuel. This leads to carbon-deposit formation, poisoning at the Ni phase and eventual electrode fracture [1]. These issues motivated the development of coke-resistant electrodes and catalysts. The coking rate of copper at 800 °C is reported to be two orders of magnitude lower than that of Ni [2]. This study presents a detailed electrochemical characterization of Cu electrodes on BaCe0.2Zr0.7Y0.1O3-d proton-conducting ceramic electrolyte (BCZY27).
High-quality dense BCZY27 electrolytes with large grains were successfully prepared using solid-state reactive sintering [3-4]. Cu electrodes were deposited by various techniques such as sputtering and screen-printing/painting, resulting in electrodes with different thicknesses and microstructures, making it possible to understand the chemical and electrochemical mechanisms taking place at the electrodes. Impedance spectra were recorded on symmetric cells (electrode/BCZY27/electrode) over a wide temperature range (400 - 700 °C) and in various atmospheres (dry and moist H2, dry methane). Figure 1 displays the ASR of 500 nm sputtered porous Cu electrodes in dry and moist H2. With this electrode architecture, lower ASR are obtained in dry H2, while dense Cu electrodes lead to the opposite trend. Stability tests were also performed to quantify the degradation of the electrodes in hydrogen and methane at 700 °C by using both the ASR and the post-testing micrographs. In this work, the ASR of the various Cu electrodes are compared.
References:
1. C.M. Finnerty, N.J. Coe, R.H. Cunningham, R.M. Ormerod (1998) Catalysis Today
46 137.
2. P.R.S. Jackson, D.J. Young, D.L. Trimm (1986) J. Mater. Science
21 4376.
3 W.G. Coors (2011) “Co-ionic conduction in protonic ceramics of the solid solution, BaCexZr(1-x)Y(y-x)O3-d; part I: fabrication and microstructure, ceramic materials”, Book 3. Intech, Croatia.
4 S. Ricote, N. Bonanos, A. Manerbino, W.G. Coors (2012) Int. J. Hydrogen Energy
37 7954.

Figure 1
(Invited) Reversible Solid Oxide Fuel Cell Development at Versa Power Systems
Authors: Wood Anthony , He Hongpeng , Joia Tahir , Brown Casey Cloudless 
Published: February 2020

Versa Power Systems (VPS) is a developer of Solid Oxide Fuel Cell (SOFC) technology focused on SOFC stack development for commercial applications. In recent years VPS has been developing reversible SOFC (RSOFC) materials systems with a view to future commercial development of RSOFC stacks. VPS has demonstrated significant technical improvements in RSOFC materials technology in a relatively short timeframe, and has begun to test these at the stack level. This paper will provide an update of RSOFC activities including cell and stack testing in both steady-state electrolysis operation and operating with RSOFC cycles (fuel cell and electrolysis cycling).
Hydrogen Permeation through Dense BaCe0.8Y0.2O3-δ - Ce0.8Y0.2O2-δ Composite-Ceramic Membranes
Authors: Rosensteel Wade A , Ricote Sandrine , Sullivan Neal P 
Published: February 2020

This report presents hydrogen permeation measurements through dense composite-ceramic membranes. The high-temperature operation of ceramic hydrogen-separation membranes makes them suitable in many hydrogen-production applications, such as catalytic partial oxidation of methane (CPOX), steam reforming of methane, the gasification of carbonaceous materials, and methane dehydroaromatization (MDA). Hydrogen permeation is measured through BaCe0.8Y0.2O3-δ–Ce0.8Y0.2O2-δ (BCY-YDC) membranes fabricated by solid-state reactive sintering with 1 wt.-% NiO and standard ceramic-processing methods. Hydrogen gas is incorporated into the membrane as protonic defects; proton transport must be compensated by electron transport in order for protons to re-associate into hydrogen gas on the opposite side of the membrane. BCY serves as the proton conductor, and YDC serves as the electronic conductor.
For hydrogen-permeation testing, the composite-ceramic membranes are hermetically sealed inside of a ceramic manifolding assembly utilizing a spring-compression system with vermiculite seals. Hydrogen and helium (for leak detection) are fed to the permeant (feed) side of the membrane using high-precision mass flow controllers, while argon is fed to the permeate (sweep) side of the membrane. All gases are humidified using a room-temperature bubbler, which results in ~3 mol.-% steam. The permeate gas composition is continuously measured using a gas chromatograph calibrated for low levels of hydrogen, helium, nitrogen, and oxygen (balance argon). The hydrogen-permeation rate is quantified through the hydrogen mole fraction measured in the permeate exhaust.
Hydrogen permeation rates are measured as a function of temperature and the hydrogen partial-pressure gradient. The permeation rate is found to increase exponentially with increasing temperature, and linearly with an increasing hydrogen partial-pressure gradient. The hydrogen permeation rate through a BCY-YDC membrane over several days is shown in Figure 1. No degradation in performance is observed at 900 °C and a 0.1 atm hydrogen partial-pressure gradient. However, when the gradient is increased to 0.5 atm, the permeation rate is found to decrease over time. Following testing, grain-boundary fractures and metallic nano-particles are observed in scanning electron micrographs of the membrane. This, in addition to performance degradation, may indicate that the materials are not stable in highly reducing environments. However, X-ray diffraction patterns of the membrane after testing do not reveal the formation of tertiary phases.
Figure 1: Hydrogen permeation through a BCY-YDC membrane at 900 °C with a 0.1 and a 0.5 atm hydrogen partial-pressure gradient.

Figure 1
(Invited) Defect-Rich CO2 Reduction Catalysts
Authors: Feng Xiaofeng , Kanan Matthew 
Published: February 2020

The discovery of new structural motifs that promote high electro-reduction activity is essential for the development of electrochemical fuel synthesis. Polycrystalline Au is the most active bulk material for electrochemical CO2 reduction to CO and serves as a useful model system to evaluate new structures [1]. We recently developed a catalyst called oxide-derived Au that has even higher selectivity than bulk Au for CO2 reduction to CO at very low overpotentials [2]. Oxide-derived Au is a nanocrystalline material with a dense grain boundary network. Quantifying the effect of the grain boundaries in oxide-derived Au is challenging because extracting TEM samples from the oxide-derived Au films is inefficient. Here we describe the synthesis of grain-boundary rich Au catalysts by vapor deposition. The catalysts can be directly studied by TEM with minimal sample preparation. We compared the CO2 reduction activity of as-deposited catalysts to catalysts that were annealed at various temperatures. The annealing process has very little impact on the electrochemical surface area or the distribution of Au surface facets, as determined by Cu and Pb underpotential deposition studies. Annealing does, however, reduce the grain boundary density, which is quantified by counting boundaries in a large number of individual particles using TEM. In the low overpotential regime (–0.3 V to –0.4 V vs RHE), there is a linear correlation between grain boundary density and specific current density (surface area normalized) for CO2 reduction to CO. This quantitative correlation between defect density and catalytic activity suggests that grain boundary engineering is a fruitful avenue to explore for the development of practical CO2 reduction catalysts.
References:
(1) Hori, Y. In Modern Aspects of Electrochemistry; Vayenas, C. G., White, R. E., Gamboa-Aldeco, M. E., Eds.; Springer: New York, 2008; Vol. 42, p 89.
(2) Chen, Y.; Li, C. W.; Kanan, M. W. J. Am. Chem. Soc.
2012, 134, 19969−19972.
Cross-linked Anion Exchange Membranes Composed of Imidazolium Salt for Alkaline Fuel Cell
Authors: Song Feifei , Chen Shuli , Gao Ying , Liu Yuyu , Qiao Jinli 
Published: February 2020

The alkaline membrane fuel cells (AMFCs), which use the anion-exchange membranes(AEMs) as electrolytes have attracted considerable attention owing to their higher reaction kinetics, lower fuel crossover, reduced CO poisoning, and use of non-precious metal catalysts. 1 In the development of AMFCs, the AEMs are obviously the key issues to make a breakthrough in AMFC performances. However, the conductivity and stability of AAEMs are still far less than commercial membrane Nafion which has commonly been used to proton-exchange membrane fuel cells (PEMFCs).2

More recently, imidazolium-based AEMs are of interest due to the five-membered heterocyclic ring and π conjugated structure of the imidazolium cation, which is expected to have good stability in alkaline condition.3-4 We here report novel series of alkaline anion-exchange membranes: Chitosan / poly (3-methyl-1-vinylimidazolium chloride)-Co-(1-vinylpyrrolidone) membranes (Cs/PMViC-Co-VP)and PVA/ poly (3-methyl-1-vinylimidazolium chloride)-Co-(1-vinylpyrrolidone) (PVA/PMViC-Co-VP)membranes.
The membranes were prepared by a solution-casting method, where 1g chitosan (degree of deacetylation = 80.0-95.0,supplied by Sinopharm Chemical Reagent Co. Ltd. China) was dissolved in 50 mL of 2% aqueous solution of acetic acid. Meanwhile, PVA (99% hydrolyzed, average molecular weight Mw = 86,000-89,000; Aldrich) was fully dissolved in water to make a 10% solution at 70oC. Then PMViC-Co-VP (supplied by Aldrich) was mixed with the above chitosan solution and PVA solution, respectively. At last, 0.5 mg GA was added in two types of composite solutions for cross-linking reaction. Membranes were obtained with a thickness about 50-120 µm. The The hydroxyl ion conductivity of the obtained membrane is studied using AC impedance technique.