bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Nature and Control of High-k Dielectric/III-V Interfaces
Authors: Cabrera Wilfredo J , Halls Mathew D. , Chabal Yves J 
Published: February 2020

III-V semiconductor surfaces are notoriously difficult to control as their native oxides are not stable. For the growth of high-k dielectric, interface passivation layers have recently been incorporated into InP/high-k dielectric stacks using different approaches, including atomic layer deposition (ALD) to grow thin aluminum silicate layers and deposition of a buffer silicon layer prior to aluminum oxide growth. While beneficial effects have been observed on the interface electrical properties, little is known about the chemical composition and formation mechanisms of these interfacial layers. Futhermore, there is growing evidence that elemental diffusion from the substrate or its oxide may impair electrical properties. There is therefore a need for chemical characterization of surfaces and interfaces under typical processing conditions.
Combined in-situ IR measurements and ab initio calculations of InP(100) surfaces reveal that a mild annealing (~300oC) typically needed for atomic layer deposition leads to marked chemical changes at the surface, with the formation of surface InPO4-species (P=O and P-OH species). The initial interaction of trimethylaluminum with this hydrophosphonated surface is characterized by the formation of P-O-Al and dative bonding between Al and the oxygen atom of neighboring P=O moiety, requiring several cycles to complete this interfacial layer. This chemical interface transformation and subsequent impact on the quality of an ALD-grown Al2O3 layer can be substantially altered by silicon deposition using trisilane exposure. Comparison of several silicon precursors [SiCl4, Si(OCH3)4 and Si3H6] by in-situ spectroscopy reveals that Si3H6 best reacts with the hydrophosphonate-terminated surface and reduces the native oxide by forming a SiOx layer that prevents interaction of TMA with the native oxide, leading to a denser Al2O3 layer. Deposition of a thin aluminum silicate barrier layer by ALD is also investigated, and Al from TMA found to play a key role in activating silicon precursors. However, TMA reaction with Si-modified surfaces leads to efficient methyl transfer to Si, a source of interfacial carbon contamination.
Finally, mass transport is examined in HfO2/In0.53Ga0.47As stacks. Diffusion of indium through HfO2 is observed after post deposition annealing in N2 or forming gas environments by low energy ion scattering and X-ray photo electron spectroscopy, and found to be consistent with changes in interface layer thickness observed by transmission electron microscopy. Prior to post processing, elemental arsenic is detected in the form of arsenic oxide at the surface of ALD-grown HfO2 and is desorbed upon annealing at 350oC. Indium diffusion occurring upon annealing, resulting in a reduction of the interfacial layer thickness and a potential densification of HfO2, is confirmed by an increase in capacitance.
(Invited) Fabrication and Characterization of Silicon Microwire Anodes by Electrochemical Etching Techniques
Authors: Nöhren Sandra , Quiroga-González Enrique , Carstensen Jürgen , Föll Helmut 
Published: February 2020

Silicon with a gravimetrical capacity of 4200 mAh/g for Li storage is optimal for Li ion battery anodes. Unfortunately neither bulk silicon nor silicon micro particles (mixed in pastes together with e.g. carbon black, CNT's) up to now allowed for stable battery anodes. In contrast highly ordered silicon microwire arrays galvanically connected to a Cu electrode shows good cycling stability, combined with nearly optimal gravimetric capacity taking into account the strong expansion of silicon when loaded with Li. In this paper several aspects of the completely (electro-) chemical process sequence of the Si microwire anode will be discussed including macropore ethching with sophisticated pore diameter modulation (cf. Fig. 1), post etching for wire formation and galvanic Cu deposition for optimal embedding of the Si microwires into a Cu foil electrode [1, 2].
FFT impedance (FFT-IS) analysis has been used for the in-situ characterization and optimization as well of the electrochemical process steps as for the performance of the battery anode. Several examples will be presented. Optimal cycling stability has been found for a Li charging up to 75% of the full capacitance while the wire length can be tuned to capacitance per area of the cathode, e.g. microwires with a length of 70 µm ,with an active loading of 1.35 mg/cm2show a stable capacity of 3150 mAh/g for more than 100 cycles [1].
Especially the comparison of FFT-IS data for standard paste electrodes containing silicon particles and for the silicon microwire anodes clearly indicates that the highly symmetric (closed packed) arrangement of the microwires increases the cycling stability: when charging the anode the expansion of hexagonally closed packed silicon wires leads to a mechanical stabilization between the wires. In addition no passive material is forced to move and the electrical contact to the Cu electrode is not affected while the silicon wires enlarge in size. Further improvements for silicon containing anodes will be discussed.
[1] E. Quiroga-González, J. Carstensen, and H. Föll, Electrochim. Acta 101, 93 (2013).
[2] E. Quiroga-González, J. Carstensen, and H. Föll, Materials 6, 626 (2013).

Figure 1
(Invited) Investigation of the Si/TiO2/Electrolyte Interface Using Operando Tender X-ray Photoelectron Spectroscopy
Authors: Lichterman Michael Frankston , Richter Matthias Hermann , Hu Shu , Crumlin Ethan J , Axnanda S , Favaro Marco , Drisdell Walter , Hussain Z , Mayer Thomas , Brunschwig Bruce , Lewis Nathan S. , Lewerenz Hans Joachim , Liu Z 
Published: February 2020

Photoelectrochemical (PEC) cells based on semiconductor-liquid interfaces provide a method of converting solar energy to electricity or fuels 1-3. Recently, we have demonstrated operational systems that involved stabilized semiconductor-liquid junctions 4,5.
We have employed operando ambient-pressure X-Ray photoelectron spectroscopy (AP-XPS) on these highly stable semiconductor-liquids junctions to directly characterize the semiconductor-liquid junction at room temperature under real-time electrochemical control 6,7. The escape depth of photoelectrons that originate from tender X-ray synchrotron radiation — 2.3 to 5.2 keV — allows for sampling of the sample simultaneously near the sample surface but through an electrolyte layer as the inelastic mean free path of such photoelectrons is on the order of 5 to 10 nanometers. Accordingly, tender X-ray AP-XPS has enabled simultaneous monitoring of the semiconductor surface, the semiconductor-electrolyte interface, and the bulk electrolyte of a PEC cell as a function of the applied potential, E. Accumulation, depletion and Fermi level pinning were observed. The observed shifts in the core level emission binding energies with respect to the applied potential directly revealed ohmic and rectifying junction behavior on metallized and semiconducting samples, respectively.
1. H. J. Lewerenz et al., Energ. Environ. Sci., 3, 748–760 (2010).
2. H. J. Lewerenz, in Photoelectrochemical Materials and Energy Conversion Processes, R. C. Alkire, D. M. Kolb, J. Lipkowski, and P. N. Ross, Editors, vol. 12, p. 61–181, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany (2010).
3. Z. Huang, C. Xiang, H. J. Lewerenz, and N. S. Lewis, Energ. Environ. Sci., 7, 1207–1211 (2014).
4. S. Hu et al., Science, 344, 1005–1009 (2014).
5. M. F. Lichterman et al., Energy Environ. Sci., 7, 3334–3337 (2014).
6. S. Axnanda et al., Meet. Abstr., MA2013-02, 921–921 (2013).
7. S. Axnanda et al., (2014), submitted.
(Invited) P-Type Transparent Conducting Oxide Protection Layers for Sustainable Photoelectrochemical Water Oxidation
Authors: Chen Le , Yang Jinhui , Lee Lyman , Klaus Shannon , Woods-Robinson Rachel , Lum Yanwei , Cooper Jason K. , Sharp Ian D. , Bell Alexis T. , Ager Joel W. 
Published: February 2020

Achieving stable operation of high efficiency photoanodes used as components of solar water splitting devices is critical to realizing the promise of this renewable energy technology. Here, we show that a p-type transparent conducting oxide (p-TCO) can function as a selective hole conduct and corrosion protection layer on photoanodes used for light-driven water oxidation. We selected NiCo2O4 with the inverse spinel structure was used as the p-TCO and show that this material, when integrated with Si-based photoanodes, has the requisite electronic structure, stability, transparency, and hole conductivity to achieve sustained and efficient solar water oxidation.
NiCo2O4 was deposited on n-Si (100) and np-Si (100) by reactive sputtering at a substrate temperature of 70-100 °C. The film structure was amorphous, as shown by the lack of XRD and Raman features. P-type conductivity was confirmed by measurement of a positive Seebeck coefficient. Light transparency of >70% (l > 400 nm) was achieved with a NiCo2O4 thickness of 40 nm. The hole conductivity was 50-60 S/cm and, as expected, p-NiCo2O4 forms a rectifying contact to n-Si.
Photoelectrochemical (PEC) evaluation was performed in aqueous 1M NaOH (pH 14) with simulated AM1.5 illumination; these conditions would rapidly corrode the n-Si photoanodes in the absence of a protection layer. PEC performance of the np-Si/p-NiCo2O4 structures is excellent, particularly when a thin NiFe oxygen evolving catalyst is applied. An onset potential of 0.95 V vs. RHE is observed, which is one of the lowest reported for a Si-based photoanode. The current density at the reversible potential for water oxidation (+1.23 V vs. RHE) is >25 mA cm-2, and the current rises to a limiting value of 30 mA cm-2 at more anodic potentials, which demonstrates the attractive combination of transparency and low-resistance hole conductivity in the NiCo2O4. Long-term testing indicates multi-day stability with minimal decrease in performance or observable corrosion of the Si photoanode. In depth characterization of both the solid-solid interfaces between NiCo2O4 and light absorber/catalyst and of the solid/electrolyte interface will be discussed.
This work demonstrates that p-TCOs are promising as corrosion protection layers for stable water oxidation photoanodes.
This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.
(Invited) Investigations into the Formation of Germanene Using Electrochemical Atomic Layer Deposition (E-ALD)
Authors: Ledina Maria , Liang Xuehai , Kim Youn-Geun , Jung Jin , Perdue Brian , Tsang Chu , Soriaga Manuel , Stickney John Lewellen 
Published: February 2020

Germanene would be the Ge analogue of Graphene. A number of ab-initio calculations in the literature suggest that Germanene sheets would display unique properties, similar to those observed in Graphene. Those reports indicate the deposits should have a buckled structure, where half the atoms are about 0.7 nm higher than the other half. MicroRaman, electrochemistry and in-situ scanning tunnelling microscopy (EC-STM) have been used to better understand the electrochemical growth of Ge from aqueous solutions, from the first atomic layers on Au(111). The studies to be discussed have resulted in some interesting, though not clearly understood results, such as why only about 3 ML of Ge can be formed by direct electrodeposition on Au, depending on the pH. Subsequent deposition, under those aqueous conditions, simply stopped after three ML. Reports in the literature indicate that thicker deposits of Ge can be formed on other electrode surfaces, though it is not clear why growth on Au is different. In-situ STM studies of the first atomic layers of Ge have shown a number of processes which are not yet well understood, such as the formation of nanoscopic atomically flat chips on the surface. There are suggestions that Germanene is being formed. In addition, there is clear evidence of the formation of a surface alloy with the Au substrate, though the phase diagram suggests no significant alloying at room temperature, used in these studies. Further, though Au(111) displays the expected reconstructed (√3X23) “herringbone” structure expected, incorporation of Ge into the this structure occurs very slowly by reduction at relatively high potentials, starting at defects and step edges. Previous work by this group, lead to development of an electrochemical ALD cycle for the growth of thicker Ge films. That cycle is being further investigated, as some spots in early deposits displayed a Raman spectrum indicative of the presence of germanene.
A Study on the Seed Step-Coverage Enhancement Process (SSEP) of through Silicon Via (TSV) Using Electrophoretic Deposition (EPD) of Pd/PVP Colloids
Authors: Lee Dongryul , Lee Yujin , Cho Hyungkoun , Lee Min Hyung 
Published: February 2020

The seed step-coverage enhancement process (SSEP) using Pd/PVP (Polyvinylpyrrolidone) colloids were investigated for the filling of through silicon via (TSV) without void. TEM analysis showed that the Pd nano-particles were well dispersed in aqueous colloidal solution with average diameter of 5.67 nm. These Pd nano-particles were uniformly deposited on the substrate of Si/SiO2/Ti wafer by electrophoresis with high frequency alternating current (AC). After electroless Cu deposition on the substrate treated with Pd/PVP colloids, the adhesive property between deposited Cu layer and substrate was evaluated. As a result of that, the Cu deposit showed superior adhesion property in comparison with that on treated substrate by the existing Pd ion catalyst. Finally, by implementing the SSEP using Pd/PVP colloids in TSV, we achieved 700% improvement of step coverage of Cu seed layer compared to PVD process, resulting in void-free fillng in high aspect ratio TSV.
Mechanistic Transition of Electron Transfer Kinetics from Quantum Electron Tunneling to Trap-Facilitated Hopping through TiO2 Films Grown By Atomic Layer Deposition on SnO2 Electrodes
Authors: Avila Jason Ryan , Katz Michael Jacob , Farha Omar K. , Hupp Joseph T. 
Published: February 2020

The understanding of electron transfer (ET) phenomenon across semi-conductor interfaces is crucial for applications in photovoltaic systems and electrochemical heterogeneous catalysis . In order to probe ET mechanisms, we exploit atomic layer deposition (ALD) to conformally coat ultrathin films of TiO2 onto a lower conduction band (CB) SnO2 electrode. Between TiO2 film thicknesses of 1 to 10 Å, quantum tunneling through the insulating TiO2 layer is the kinetically preferred ET pathway. At films thicker than 10 Å, there is little change to the ET rate as a function of TiO2 thickness. To our surprise, annealing a 55 Å layer of TiO2 on SnO2, a 10x reduction in ET rate was observed compared to the as deposited TiO2. At potentials near the CB edge of SnO2, electrochemical impedance spectroscopy of nominally flat amorphous TiO2 indicated the presence of nearly double the density of states (DOS) with respect to their crystalline counterpart; the relationship between ET and DOS was studied in depth. These findings show the first observation of change in ET mechanism across semi-conductor interfaces, and demonstrates the ineffectiveness of thick layers films grown by ALD at completely shutting off electron transfer without annealing post film growth.
Experimental and Theoretical Characterization of Electrode Materials That Undergo Large Volume Changes and Application to the Lithium-Silicon System
Authors: Verbrugge Mark W , Baker Daniel R. , Xiao Xingcheng , Zhang Qinglin , Cheng Yang-Tse 
Published: February 2020

The life and performance of lithium-ion batteries is related to the mechanical expansion and contraction of the active materials, particularly for silicon-enhanced negative electrodes. In this work, we develop a theory and commensurate equations to describe how lithium diffuses within lithiated silicon, and we include the influence of active material expansion (upon lithiation) and contraction (upon delithiation). We employ thin-films of vapor-deposited Si to construct our electrodes. This allows us to isolate our analysis to the active material and avoids the necessity of treating binders, conductive diluents, and complicated geometries associated with conventional porous electrodes used in most practical lithium-ion batteries and in the construction and modeling of a Li-Si porous electrode. The model is shown to compare favorably with experimental results.
We have derived an equation system for the treatment of electrode materials that undergo large volume changes during operation. The approach is applied to a thin-film Li-Si system, wherein a volume change of about 270% is observed relative to pure Si and Li3.75Si. Good agreement is obtained when the model calculations are compared with experimental data obtained from Li-Si thin film electrodes (67-nm thickness) subjected to linear-sweep voltammetry experiments over current and potential ranges of interest for many applications, including electrified vehicles.
We ignore the influence of stress on the thermodynamics and transport of the Li-Si thin films. Instead, we use a one-dimensional model which assumes that stress does not impact the chemical potential, because the stresses are negligible within the infinitely thin film that is unconstrained at its interface with the electrolyte. However, the local expansion and contraction of the film, as a function of lithium content, is taken into consideration, and this leads to a moving boundary value problem, where the position of the film surface must be calculated.
Silicon/Carbon Nano-Composite Based Anodes for Advanced Lithium-Ion Batteries
Authors: Dobrowolny Sascha , Mahlendorf Falko , Heinzel Angelika 
Published: February 2020

In the recent years, rechargeable lithium-ion batteries have gained in importance for electronic devices and electric vehicles. Thus, research and development focuses on improving energy and power densities as well as durability of lithium-ion batteries. Especially for high energy and power densities, the electrode materials must possess high specific storage capacities and coulometric efficiencies. However, state-of-the-art anode and cathode electrode materials, e.g. graphite and LiFePO4 exhibit high coulometric efficiencies but rather low theoretical storage capacities (372 and 170 mAh/g, respectively).
In the last decade silicon has become a promising anode material due to its high theoretical specific capacity of 3579 mAh/g at ambient temperature. However, this high specific storage capacity owing to host up to 3.75 lithium atoms per silicon atom leads to extreme volume expansion up to 280 % during lithiation, which results in pulverization and delamination of the electrode material after few cycles. Various approaches have been conducted to overcome these issues e.g. by using nano-sized active material or carbon coated silicon composite material.
In addition to the materials science the electrode structure is of particular importance for the electrochemical performance. Electrode composition, binding mechanism due to the use of suitable binder polymers or particle size distribution of the active material are some exemplary parameters to stabilize the electrode structure and to handle such high mechanical stress during lithiation/delithiation.
Here we present electrochemical investigations of high capacity and high efficiency graphene coated silicon nanocomposite based electrodes prepared by using a wet chemical doctor blade manufacturing process. This active material provides a capacity of >2000 mAh/g with efficiencies >99% over more than 500 cycles. Investigations focus on influence of the stability of the electrode structure by using impedance spectroscopy, scanning electron microscopy, confocal microscopy and estimation of the coating adhesion strength. Cyclic voltammetry and galvanostatic cycling will show the applicability of improved Si/C composite based electrodes compared to conventional graphite based electrodes for lithium-ion batteries both in half cells as well as full cells in combination with commercially available cathode material.
(Invited) A Tale of Spinels: From Li-Ion to Mg Battery Electrodes
Authors: Cabana Jordi 
Published: February 2020

Since the discovery by Thackeray and co-workers of their ability to reversibly intercalate Li, spinel oxides have become a canonical electrode material in battery technologies. Phases with this structure typically present very stable cycle life in the bulk and fast kinetics. When used as positive electrodes, the downside of spinel electrodes is their fairly low capacity and their interfacial instability. In Li-ion batteries, the best performance is obtained with significant amounts of Mn in the structure. Ions of these element, when redox active, are prone to corrosion processes that undermine the cyclability of the electrochemical cell. Further, while full intercalation from M2O4 (M=Mn, Ni, Co...) to Li2M2O4 is possible, it is also poorly reversible. As a result, practical applications limit the utilization to processes between M2O4 and LiM2O4. In other words, this material highlights the barrier of two electron reactivity that is pervasive in battery electrodes based on intercalation reactions.
In this talk, we will overview the strategies we have followed to expand the versatility of spinel oxides as reversible intercalation electrodes. We will discuss our efforts to understand the kinetic limitations of the Mn2O4-Li2Mn2O4 transition using high resolution chemical imaging. We will describe strategies to understand and impart interfacial stability, especially against corrosion processes that damage full battery performance. Finally, we will introduce evidence that this family of oxides could provide a path to explore positive electrodes for emerging multivalent technologies, with emphasis on Mg batteries.
Thermal Study of Reaction Intermediate Stability during Electrochemical Sulfur Reduction in a Lithium-Sulfur Cell
Authors: Seo Jeongwook , Sankarasubramanian Shrihari , Kim Chisu , Zaghib Karim , Prakash Jai 
Published: February 2020

One of the most promising cell chemistries in the quest to surpass Lithium-ion cells in capacity is the Lithium-sulfur cell. The use of Sulfur, due to its high theoretical specific capacity (1675 mAh/g) and natural abundance, is the basis for this future potential. A step towards future development of this cell is the understanding of the complex reactions that occur at the sulfur cathode. The overall mechanism is the electrochemical reduction of octa-sulfur (S8) to Li2S with several intermediate lithium-sulfur composites. Prior research has involved the study of the plateaus and characteristics of the voltage profiles of these cells to try and elucidate the reaction mechanism. Isothermal micro-calorimetry is a versatile tool to study reactions and understand their thermal behavior. Thermodynamic study of these reactions had been reported by the authors elsewhere. Herein we examine the stability of each intermediate by calculating the entropy change of their reaction step.
The entropy change has negative value in the first and second electrochemical reaction stages which generate soluble lithium sulfur (Li2S8 and Li2S4). It changes to positive value when the electrochemical reaction produces insoluble lithium sulfur (Li2S2 and Li2S). The entropy change drops when DOD is 70%. This entropy change pattern exactly corresponds with the voltage profile with various potential plateaus which represents the electrochemical reaction stages. The entropy change values provide a fundamental understanding of the drivers of the electrochemical reaction, can be used to understand the stability of the various intermediates and also predict any new intermediates or reaction steps.