bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Atomistic Understanding on the Surface of GaAs By Ab Initio Thermodynamics; From Equilibrium Shape to Growth Shape
Authors: Yeu In Won , Hwang Cheol , Choi Jung-Hae 
Published: December 2020

The III-V semiconductor nanowires (NWs) have attracted substantial attention as an ideal system for the study on the growth mechanism and electronic device applications. For the precise manipulation of the nanowire growth, understanding on the temperature–pressure (T–P) dependent variation in surface energy and reconstruction which governs the anisotropic interaction between vapor sources and crystal solids is crucial. Unfortunately, the quantitative values of the variation in surface energy cannot be obtained only using the conventional electronic structure calculation. To overcome this difficulty, we have developed a reliable ab initio thermodynamic method by which the T–P dependent surface energy is predicted from the atomic-scale calculations on: surface reconstructions of InAs1; equilibrium crystal shapes of GaAs and InAs2; and anisotropic adsorption and growth conditions of GaAs NW3.
In this talk, we present an ab initio thermodynamics approach by combining the atomic-scale calculation with the thermodynamic treatment to take a step forward in the theoretical modeling on the growth of polar GaAs <111> nanowire by calculating the change in Gibbs free energy during the nucleation and growth process. By comparing the nucleation rate between different stacking sequences, the formation probability of stacking fault or wurtzite segment was quantitatively predicted under arbitrary vapor-phase growth conditions. The predicted T–P dependent probability from atomic-scale calculation is directly comparable to the experiments and remarkably consistent with the available results to date, elucidating the fundamental asymmetric growth mechanism. Our ab initio approach is truly independent of any empirical data, bridging to the experimentally controllable variables. This simulation can be applied to various nanomaterials, including two-dimensional materials as well as other III-V and II-VI NWs, where the precise control of the stacking sequence is significant for their properties.
[1] Yeu et al., Sci. Rep., 2017, 7, 10691
[2] Yeu et al., Sci. Rep., 2019, 9, 1127
[3] Yeu et al., Appl. Surf., Sci., 2019, 497, 143740
Tackling the Development of Rechargeable Calcium Batteries: The CARBAT Project
Authors: Palacin M. , Black Ashley , Tchitchekova Deyana S. , Johansson Patrik , Araujo Rafael B. , Aren Fabian , Arroyo-de Dompablo Elena , Torres Arturo , Tortajada José , Luque Javier , Wuersig Andreas , Bremes Hans G 
Published: December 2020

While the cost of the state-of-the-art electrochemical energy storage technology, the Li-ion battery (LIB), has been reduced by 8% at the pack level annually during the last decade (1), it is nowreaching its fundamental limits in terms of energy density. Furthermore, the risk of limited lithium supply and associated cost increases cannot be ignored. Therefore, new sustainable battery chemistries must be developed. Calcium-based rechargeable batteries are proposed to help solving some of the Grand Challenges our modern society is facing: pollution, oil-dependency, and climate change.
Batteries based on Ca have promise of leap-frog increase in energy densities and are especially attractive as Ca is the 5th most abundant element in the Earth’s crust and can indeed be used as a metallic anode with conventional wide potential window electrolytes (2,3). The CARBAT project builds on this breakthrough and its main objective is to achieve proof-of-concept for a Ca anode rechargeable battery. CARBAT combines scientific efforts of computational screening, solid-state and coordination chemistry, materials science, electrochemistry, and battery engineering, and apply these to: (i) develop cathode active materials operating at 4 V and with capacities of 200-300 mAh/g, (ii) optimize electrolyte formulations for fast Ca2+ transport (>1 mS/cm), and finally (iii) assemble a 100 mAh cell demonstrator. All developed materials and cells are validated and benchmarked vs. state-of-the-art LIB technology, both in terms of performance and sustainability indicators.
(1) Nykvist, B.; Nilsson, M. Nat. Clim. Change, 2015, 5, 329.
(2) Muldoon, J. Chem. Rev., 2014, 114, 11683.
(3) Ponrouch, A.; Frontera, C.; Barde, F.; Palacin, M.R. Nat. Mater., 2016, 15, 169.
(Invited) Electrode-Electrolyte Design for Rechargeable Air-Batteries
Authors: Lu Yi-Chun 
Published: December 2020

Rechargeable metal-air batteries have attracted intensive research attentions owing to their high gravimetric energy density. However, they suffer from poor cycle life, low round-trip efficiency and low practical energy density. The development of stable and reversible metal-air chemistries requires fundamental understanding on how solvent and salt/additives affect the reaction mechanism and mediation processes. In this presentation, we combine in situ/operando spectroscopy/analytical techniques (online electrochemical mass spectrometry, isotopic labeling and UV-Vis spectroscopy) to reveal the reaction and degradation mechanism of oxygen reduction and oxygen evolution reactions in rechargeable metal-oxygen batteries. We will discuss the role of redox mediator, electrolyte structure-function relationship, and materials design strategies in addressing air-battery degradation.
Acknowledgment. This work is supported by a grant from Research Grants Council (RGC) of the Hong Kong Special Administrative Region under CUHK14307919.
Role of Discharge-Product Morphology and Formation Rates in Li–O2 Battery Performance
Authors: Torayev Amangeldi , Monroe Charles W. 
Published: December 2020

Lithium–oxygen batteries have unprecedented theoretical capacity. Achieving the theoretical capacity in practice remains a challenge – even during low-power operation – because of higher-order phenomena that accompany the formation of discharge products, such as surface passivation and clogging of the cathode’s pores. In the last few years, Li–O2 battery research has moved towards systems that preferentially form large discharge-product particles, which can be achieved by using high-donicity electrolytes and including mediators as additives.1 In this study we examine the implications of discharge-product growth and morphology on performance using numerical simulations.
A continuum model is developed which incorporates multicomponent mass transfer2 described by Onsager-Stefan-Maxwell laws. Including more details about liquid-phase transport is particularly important when modelling solution-mediated discharge processes, because the diffusion of soluble reaction intermediates can control the battery’s apparent discharge capacity. Detailed reaction models, which include precipitation and film-growth kinetics are also necessary, to elucidate the competition between discharge-product formation pathways3: thin-film formation can slow interfacial reaction kinetics, whereas pore clogging raises overpotentials by hindering the transport of reactive species.
Large discharge products form through a solution-phase mechanism, which is favoured by electrolytes that sustain the presence of an LiO2 intermediate for a relatively long time. These intermediate forms the final Li2O2 discharge product either by electrochemically reacting with a lithium ion or by chemically disproportionating, thereby contributing to discharge-product-particle growth. When LiO2 reaction intermediates are long-lived, they can build up in the electrolyte, particularly near the electrode/electrolyte interface. Thus, the system is locally pushed from the dilute into the concentrated regime, and pairwise interactions between species can become significant to device performance.
(1) Torayev, A.; Magusin, P. C. M. M.; Grey, C. P.; Merlet, C.; Franco, A. A. Text Mining Assisted Review of the Literature on Li-O2 Batteries . J. Phys. Mater.
2019, 2, 044004.
(2) Liu, J.; Khaleghi Rahimian, S.; Monroe, C. W. Capacity-Limiting Mechanisms in Li/O2 batteries. Phys. Chem. Chem. Phys.
2016, 18, 22840–22851.
(3) Yin, Y.; Torayev, A.; Gaya, C.; Mammeri, Y.; Franco, A. A. Linking the Performances of Li–O2 Batteries to Discharge Rate and Electrode and Electrolyte Properties through the Nucleation Mechanism of Li 2 O 2. J. Phys. Chem. C
2017, 121, 19577–19585.
Liquid Metal Coating for Improving Li-Anode Cyclability
Authors: Koul Supriya , Morita Yoshiyuki , Ogasa Hiroshi , Fujiwara Yoshiya , Kushima Akihiro 
Published: December 2020

Lithium metal is a promising anode material for Li-ion batteries because of its high specific capacity and negative electrochemical potential. However, there are two major challenges that need to be overcome before it can be used in practical applications: 1) electrolyte consumption and 2) dendrite. Lithium being thermodynamically reactive, it decomposes the electrolyte in contact. The dendrite causes short circuit in the battery creating safety issues, and the detachment of the dendrite from the electrode leads to irreversible capacity loss. The exposure of fresh lithium surface associated with the chipping action leads to the further decomposition of the electrolyte.
In this work, we propose a liquid metal (LM) as a semi-solid liquid interface (SSLI) layer to uniformly deposit Li and protect it from direct contact with the electrolyte. Ga-Sn-In alloy, which is in a liquid state at room temperature, was dispersed on a Li metal or directly on a copper current collector as a SSLI layer. Elements in the LM alloy with Li to form a “solid” layer. It is energetically favorable for Li to alloy with these elements than to plate on the film. This high “wettability” of the film against Li promote the uniform deposition and suppresses the nucleation of the dendrites. It will also prevent Li from directly contacting the electrolyte to mitigate undesired chemical reactions.
The effect of LM coating was verified using a Li-Li symmetric cell. The cells without LM failed only after few cycles. The huge increase in the voltage corresponds to significant growth of SEI on the lithium electrode. On the other hand, the cell with LM coating was able to cycle for 100 cycles. A full-cell test using LiNi1/3Co1/3Mn1/3O2 cathode with copper current collector without excess Li was also tested. The result showed much improvement in the cycle lifetime with the LM coating. Scanning Electron Microscopy analysis of the coating layer was performed after the battery cycle test to confirm the ability of the LM coating to reduce the formation of dendrite at the surface.

Figure caption
: SEM micrographs of (A) Cu current collector and (B) the surface after battery cycle test for with and without LM coating. Smooth LM coating was achieved to reduce the surface roughness on the Cu film, and the Li dendrite formation on the surface was reduced by the LM coating.

Figure 1
What Happens to Repeatable Low TCE Copper with Annealing
Authors: Kondo Kazuo , Dinh V Quy 
Published: December 2020

1. Introduction

Since the Copper resistivity is second lowest next to the Silver, the Copper electrodeposits have been very intensively used in the wiring for the semiconductor and the printed circuit board (PCB). The Copper problem is the thermal coefficient of expansion(TCE). The TCE of Silicon is 2x10-6(1/K) and the TCE of Copper is 18x10-6(1/K). If the composite of the Silicon and the Copper warpage, protrusion or delamination occurs. This discussion is focused on the low TCE Copper with repeatable annealing.

2. Results

1) Figure 1 shows the TCE comparison with our repeatable low TCE Copper and the conventional Copper. X-axis is the expansion length and y-axis is the temperature. For the conventional Copper, the TCE is 18x10-6(1/K) and the expansion length is linear with the temperature. However, for our repeatable low TCE Copper, the TCE is 6x10-6(1/K) and 1/3 of the conventional Copper. The TCE of 6x10-6(1/K) repeats three times. This TCE of 6x10-6(1/K) starts after two times pre-annealing.
2) Also we have run 200 cycles of -40℃ to 200℃ heat cycle test and measured the TCE and the resistivity. These TCE and the resistivity have been measured after 50,100,150 and 200 cycles.
The TCE up to 300℃ for 50, 100 and 150 cycles show constant value and the TCE is lower with 200 cycles. The resistivities of 50,100,150 and 200 cycles become even lower than as deposit of zero cycle.
The repeatable low TCE mechanism will be discussed at the meeting.

Reference

V. Q. Dinh and K. Kondo, ECS J.Solid State Sci. Technol., 6, P566-P569 (2017)

Figure 1
Understanding the Role of Electrochemically Inactive Substituent in Layered Oxide Cathode Materials for Advanced Sodium Ion Batteries
Authors: Yang Junghoon , Bak Seongmin , Teeter Glenn , Han Sang-Don 
Published: December 2020

The importance of electrochemical energy storage systems for large-scale application has been growing increasingly over the last decades. Due to high cost, limited source and several technical barriers of the lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) are considered as one of promising candidates for large-scale energy storage systems based on their cost-effective, earth abundant and recyclable characteristics.[1] As promising cathode materials for SIBs, P2-type sodium iron manganese oxide with layered structures (Na
x
Mn
y
Fe1-y
O2, 0.5 < x < 0.8) demonstrates similar high energy density analogous to the LiBs.[2] However, the capacity retention of the cell with layered structure cathode is not optimized especially when it is charged and discharged with wide voltage window to obtain higher capacity. The major reason for this is a phase transition induced by gliding of transition metal slabs, which causes irreversible structural changes gradually during cycling.[3]
To address this phase transition issue, we introduce electrochemically inactive component (e.g., Mg2+) in the material. The introduction of the Mg2+ by substituting with existing transition metal(s) is able to provide improved capacity retention due to their enhanced structural stability. We systematically analyzed the capacity fading trends at high and low voltage regions, where each different transition metal dominantly contributes to the redox reactions, which provides mechanistic understanding of the structural degradation of P2-type NaxMnyFe1-yO2 and the effect of Mg2+ on transition metal redox behaviors. In addtion, by tracing the structural changes in the cathode, we demonstrated that the introduction of Mg2+ effectively abbreviates the unwanted phase transitions. The results can provide the insights of the phase transition mechanism and redox behaviors of layered type cathode materials and the strategies to stabilize the structure by employing electrochemically inactive substituent(s), thus enabling rational design of new cathode materials for the development of next generation SIBs.
[1] M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Adv. Funct. Mater. 23 (2013) 947-958.
[2] C. Delmas, C. Fouassier, P. Hagenuller, Physica B+C 99 (1980) 81-85.
[3] E. Talaie, V. Duffort, H. L. Smith, B. Fultz, L. F. Nazar, Energy Environ. Sci., 5 (2015) 2512.

Acknowledgement

J. Yang and S.-D. Han acknowledge funding support by the Laboratory Directed Research and Development (LDRD) program at National Renewable Energy Laboratory (NREL).
The work done at Brookhaven National Laboratory was supported by Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. DOE, through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704.
A Simulation Study on the Transient Leakage Current Analysis of a GaN Epitaxial Layer
Authors: Nishida Hirofumi , Kataoka Hiroaki , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki 
Published: December 2020

GaN epitaxial layers on Si substrate are being used as semiconductors for power devices owing to its wide bandgap, a high breakdown voltage with low on-resistance [1]. Due to the presence of crystal defect both in energy and its depth profile, a transient behavior is commonly observed in the channel current. Some of characterization methods, including deep level transient spectroscopy (DLTS), can extract the energy levels with its depth profile, by adopting a Schottky electrode to the epitaxial layer. Therefore, the extracted profile is limited to the surface of the GaN layers. In this work, we conducted a simulation study to extract the defect density profile from a direct current obtained from a GaN epitaxial layer on Si substrate with an Ohmic contact electrode to the surface. While applying a step voltage to the electrode, the transient current was measured and characterized.
The proposed defect extraction method can be analytically expressed by the change in the depletion capacitance (ΔC) in the epitaxial layer upon a voltage of V applied to the electrode at t=0 as shown in equation (1).
Here, ε, Wo
d , W∞
d

,
q, N
d and N
t are the permittivity, depletion width at t=0, depletion width at steady state, doping density of the GaN layer and the trap density, respectively. The change in the charge accumulated to the electrode (ΔQ) can be written as the equation (2). Therefore, by the integral of the transient current, one can obtain the relationship between V and N
t, which can be transformed into the defect density depth profile of the epitaxial layer.
The simulated model is shown in fig. 1(a), where two GaN layers of each N
d=1016 /cm3 are stacked with in two metal electrodes. The area of the electrode is 0.1 mm2. Defect levels of E3 and E7 with a density of N
t,E3 and N
t,E7 are introduced in the top and bottom GaN layers, respectively. By applying a positive V to the Ohmic top electrode, the depletion width increases from the Schottky bottom electrode, depending on the N
d
. By the presence of E3 and E7, a transient current with a time constant depending on the defect levels is obtained as is shown in fig. 2(b). By obtaining the relationship between the ΔQ and the V, as shown in fig. (2), firstly we can extract the N
d of each layer from the change in the slope. The extract N
d values showed a nice agreement to the values set in the simulations. Also, from the ΔQ itself, we can deduce the N
t of each layer.
In conclusions, we have made a simulation of the transient current response of a stacked GaN layers with different defect levels. From the transient current integral, we can extract the doping density and the defect density of each layer.

References

[1] B. J. Baliga, Semicon. Sci. Tech., 28, 074011 (2013). [2] D.V. Lang, Journal of Applied Physics., 45, 3023 (1974)

Figure 1
Towards Tm2+ in Sialon Thin Films Using the Gradient Deposition Method
Authors: Bosco Giacomo , van der Kolk Erik 
Published: December 2020

There are different material candidates for efficient industry compatible luminescence solar concentrators to be used in electricity generating glass applications. Among them, divalent thulium (Tm2+) doping has been shown to have a high potential. It has been reported to have 65% absorption of the solar spectral range when in di-halide hosts, while showing no self-absorption and a relatively neutral color [1]. These characteristics are possible because Tm2+ has a strong absorption from the UV up to about 900 nm. This absorption is generated by intense 4f13 → 4f125d1 electronic transitions and a single emission line at 1140 nm, credited to the 2F5/2 → 2F7/2 transition of the 4f13 configuration. However, this specific oxidation state of thulium is rather anomalous: so far it was only stabilized on di-halide crystals. These crystals are very hygroscopic in nature, therefore not sufficiently attractive for scaling up in industry standard thin film growth techniques. Thus, it is necessary to research on the possible extension in the list of materials able to host such a promising optically active element. However, the intrinsic complex nature of the lanthanide’s electronic structure has prevented a detailed understanding of the valence stability of its elements. Therefore, designing industry compatible hosts ensuring that such exotic ion is stable and capable of efficiently emitting NIR light is a challenging task.
In this work, we show the progress made so far towards unraveling the conditions for stabilization of the Tm2+ in industry compatible thin film materials – more specifically, thin film materials of the SiAlON family. I report recent results on Tm doped SiAlON thin films grown by combinatorial magnetron reactive sputtering. The gradient characterization method [2], developed at the TU Delft’s luminescence materials research group, was used in order to relate position dependent film composition – determined by energy dispersive x-ray spectroscopy – with local transmission, photoluminescence emission and excitation data. This singular approach makes it possible to retrieve a wide composition range in a smaller number of different films. These results are discussed upon the valence stability model of lanthanides of Dorenbos [3], and the model of impurity ionization adopted in solid state statistics.

References

[1] O. M. ten Kate, K. W. Krämer, and E. van der Kolk, “Efficient luminescent solar concentrators based on self-absorption free, Tm2+ doped halides,” Sol. Energy Mater. Sol. Cells, vol. 140, pp. 115–120, Sep. 2015.
[2] E. P. J. Merkx and E. van der Kolk, “Method for the Detailed Characterization of Cosputtered Inorganic Luminescent Material Libraries,” ACS Comb. Sci., vol. 20, no. 11, pp. 595–601, Nov. 2018.
[3] P. Dorenbos, “Valence stability of lanthanide ions in inorganic compounds,” Chem. Mater., vol. 17, no. 25, pp. 6452–6456, Dec. 2005.
High Efficiency Solution-Processed Aluminum-Alloyed Chalcopyrite Thin Film Solar Cells
Authors: Septina Wilman , West Thomas , Giovanelli Anne Curtis , Gaillard Nicolas 
Published: December 2020

CuInGaSe2 (CIGSe) chalcopyrite is one most efficient materials for light conversion to electricity with a record efficiency surpassing all other thin film photovoltaic technologies, achieving 23.4% efficiency. Record efficiencies of CIGSe are typically achieved using 1.16 eV absorbers even though Shockley-Queisser (SQL) limit predicts an optimum bandgap of around 1.4 eV for a single junction solar cell. In theory, higher efficiencies can be expected from wider gap chalcopyrite, however, all attempts to increase efficiency with wide bandgap Ga-rich CIGSe have led to defective materials. Another alternative to increase the band gap of chalcopyrites is by partial replacement of In with other group-V atoms, such as aluminum (Al). The band gap energy of CuInAlSe2 (CIASe) can be tuned from 1.0 eV (CISe) to 2.7 eV (CASe). In addition, Al is also very appealing to reduce the raw materials' cost since it is much more abundant in the earth’s crust than Ga (Al: 82,000 ppm, Ga: 19 ppm) and significantly cheaper (Al: ~$2/kg, Ga: ~$200/kg).
In an attempt to fabricate high-efficiency CIASe devices, we demonstrated an alternative and low cost method by fabricating bandgap tunable Cu(In,Al)(S,Se)2 (CIASSe) utilizing molecular ink consisted of Cu, In, Al, and sulfur containing salts dissolved in methanol. In this study, Cu-In-Al-S containing ink was spin coated into a molybdenum substrate and followed by selenization at high temperature to form selenium-rich CIASSe. We are able to achieve a device with maximum efficiency of 11.6% using CIASSe having relatively low-content of Al (Al/(Al+In)~0.1), significantly higher efficiency than CISSe (no Al) fabricated with the same process (8.3%-efficient). To our understanding, this study is the first demonstration of a relatively high-efficiency Aluminum-alloyed chalcopyrite solar cells through solution-based process. Details of the fabrication process and materials characterization will be discussed.