bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab Initio Molecular Dynamics Simulations of Amorphous Metal-Polysulfides as Cathode Materials for Lithium-Ion Batteries
Authors: Si Jinkai , Ma Ying
Published: September 2023

Lithium-sulfur batteries offer a few advantages, including high energy density and low cost, compared to our current battery technology. However, various polysulfide intermediates formed during charging and discharging lead to the polysulfide shuttle effect, which hinders their commercial application. It has been shown that amorphous metal sulfides can reduce the formation of polysulfides, although a fundamental understanding is lacking. In this research, amorphous molybdenum and titanium sulfides with different sulfur concentrations were generated by the simulated melt-quench process using ab initio molecular dynamics simulations. Different numbers of lithium ions were added at the cathode/electrolyte interface to simulate the electrochemical conversion process in these materials. It is observed that the behavior of amorphous metal sulfides is different from that of sulfur, and the formation and diffusion of lithium polysulfides have been greatly reduced. Insights obtained from this work could help to develop new strategies to effectively inhibit the polysulfide shuttle effect.
Removing the Two-Phase Region in Spinel LiMn2O4 Towards High-Rate, High-Energy Density Partially Disordered Spinels
Authors: Chen Tina , Yang Julia , Barroso-Luque Luis , Ceder Gerbrand
Published: September 2023

Resource constraints have become critical for the Li-ion industry. Spinel LiMn2O4 presents a cheaper, more sustainable alternative to traditional layered Li-ion cathodes, but its capacity is constrained by a two-phase transition at ~3V associated with a large, inhomogeneous volume change that leads to particle cracking and poor cycling stability. In contrast, the partially disordered spinels (PDS) have more sloping, solid-solution-like behavior, resulting in better rate capability and more homogeneous volume change. In this talk, we demonstrate that PDS achieves this by introducing cation disorder, which can shrink, and even fully remove, the two-phase region. By analyzing samples from cluster expansion-based Monte Carlo simulations, we identify the mechanisms that increase Li solubility in the LiMn2O4 phase and lead to this shortened ~3V plateau. These results provide guidance on the optimal level of disorder in spinels to achieve both solid-solution behavior and good Li mobility and also highlight more generally how disorder can be utilized to reduce the effects of problematic phase transformations in ordered frameworks.
Phase-Field Modeling of Dead Lithium Formation during Charge/Discharge Cycles
Authors: Zhang Jin , Chadwick Alexander F. , Voorhees Peter W.
Published: September 2023

The formation of inactive or "dead" lithium is one of the main reasons for performance decay in lithium batteries, but recent studies find that modified charging protocols can revive this inactive portion of lithium. Thus, the ability to simulate events that lead to the disconnection and reconnection of lithium under experimental conditions can provide a fundamental understanding of the evolution of dead lithium during the charge/discharge cycle. Here, we apply a recently developed quantitative electrochemical phase-field model to study the morphological and topological evolution of lithium during battery operation. We simulate the charge/discharge behavior of lithium metal anodes from the scale of individual dendrites to anodes of relevant experimental size with realistic materials parameters to examine the pathways leading to disconnection and reconnection. Additionally, we quantify the amount of inactive lithium formed during cycling. We discuss the effect of various factors like electrolyte properties, discharge rate, and the assumed reaction kinetics (i.e., Butler-Volmer versus Marcus-Hush) on dead lithium formation. The presented simulation tool can be employed to explore battery design; thus, we will discuss possible ways to optimize the charge and discharge cycles to minimize the amount of dead lithium. Beyond the present application to lithium, the model can also be extended to other metal-anode batteries.
Lithium Ion Battery Electrode Calendering Study By Combining X-Ray Computed Tomography and 3D-Resolved Physical Process Models
Authors: Xu Jiahui , Zapata Dominguez Diana , Demortiere Arnaud , Franco Alejandro A.
Published: September 2023

Significant amount of research has been done recently on how to increase energy densities while maintaining or lowering costs in response to the growing demand for lithium-ion batteries (LIBs). In order to achieve optimization of the manufacturing process of batteries, it is essential to understand the influence of each process stage on the architectures of the electrodes, which affects the energy, power, lifetime and safety of the LIB cells. Our ERC-funded ARTISTIC project1 develops a digital twin that enables predicting the electrode architectures and their electrochemical performances from parameters at each stage of the LIBs manufacturing process.

In this work, we present our most recent research, which studies the manufacturing process of LiNixMnyCo1-x-yO2 (NMC)-based cathodes and especially focuses on the electrode calendering stage2. Our methodology encompasses coarse-grained molecular dynamics and discrete element method to simulate the calendering process of electrodes that are virtually produced after the drying and slurry simulations. In this new work, we account in our model for non-spherical NMC secondary particles with realistic 3D shapes derived by X-ray computed tomography (XCT), together with spherical particles representing the carbon binder domain. An in situ compressing micro-XCT experiment is carried out on the NMC electrode to monitor the change of the electrode morphology upon the calendering process. The findings from the simulation are validated by comparing our predicted electrode architectures with the experimental ones. Our approach captures the alterations in orientation of the secondary particles throughout the calendering processes and the relaxation process, as well as their possible deformation and spring back effect brought on by the pressure. Additionally, we discuss the comparison of variations in porosity, tortuosity factor, conductivity, different phases distribution and pore size distribution during the calendering process.

ERC Artistic : Home Artistic. http://www.erc-artistic.eu/.

Xu, J., Ngandjong, A.C., Liu, C., Zanotto, F.M., Arcelus, O., Demortière, A., and Franco, A.A. (2023). Lithium ion battery electrode manufacturing model accounting for 3D realistic shapes of active material particles. Journal of Power Sources 554, 232294. 10.1016/j.jpowsour.2022.232294.
Modelling Air Cooling in a Module of Prismatic Li-Ion Cells
Authors: Zatta Nicolò , Trovo Andrea , Guarnieri Massimo
Published: September 2023

The control of temperature in lithium-ion stacks is of increasing industrial importance. In fact, an efficient thermal conditioning system ensures a homogeneous temperature distribution among the cells, preventing conditions which could hinder performance or led to temperature runaway and so a disruptive failure of the module. CFD models for thermal analysis can be useful in the design phase to optimize the module layout and to size the cooling system, as well as to support experimental campaigns in the definition of reduced-order thermal models to be implemented into the Battery Management System (BMS) for in-operation temperature prediction. The present work presents the development of a computational model of a 48V-20Ah 20-cell Li-ion module and its air-cooling system based on COMSOL Multiphysics software. Unlike most papers available in the literature, the individual cells are modelled by considering an internal ohmic heat generation term as a function of both state of charge, cell temperature and sign of the applied current (charge or discharge), exploiting experimentally validated data provided by the manufacturer in temperature-controlled conditions. In addition, the reversible thermal generation term due to entropic phenomena, which is often ignored in the literature, was computed alongside an irreversible term accounting for cell overpotentials. The entropic contribution, which was estimated experimentally and optimised computationally, resulted non-negligible when the module is cycled at ≤ 1C. To take into account the effect of the fan cooling system, the motion field was solved in COMSOL using a turbulent k-ε model. To ensure model accuracy, only minor geometrical simplifications were introduced to the fluid volume. The resulting geometrical complexity, made of manifold and narrow channels, called for special attention in the computational resolution. Assuming a decoupled behaviour, namely that the thermal evolution does not affect the flow field, allowed to use the stationary fluid-dynamic solution as the starting point for the time-dependent thermal simulation. The model was run under different experimental current profiles and the validation was performed on the entire module under effective operating conditions and not on a single cell under natural convection condition with the external environment, as is usually found in the literature. The computational data were found to be in good agreement with experimental measurements for all the cells even after charge-discharge cycles lasting more than two hours. The simulations provided insights to improve the positions of thermal sensors inside the module and to optimize the efficiency of the cooling system, that could not be done based on thermal measurements only.

Figure 1
(Invited) From Material Discovery Towards a Prototype Hydrogen Generator
Authors: Vaes Jan , Vereecken Philippe M.
Published: September 2023

This contribution illustrates the approach that has been taken to develop a pre-commercial prototype of a water electrolyzer. The aim has been to develop and integrate novel nanostructured materials for both electrodes and membranes, demonstrating their upscaling potential by integrating them together in a water electrolysis cell with an active surface are of 50 cm² in order to proof their potential for further advancing the state of the art of green hydrogen generation.

Based on industrial experience with medium flow hydrogen generators, the boundary conditions for the new electrode and membrane components were set, safeguarding their integration potential in a scalable stack. A nano-porous intrinsically conductive membrane material has been developed, that allows to drastically reduce the thickness of the separator, reducing ohmic losses without compromising gas separation quality during operation at elevated pressures (up to 20 barg). This was combined with nanostructured electrodes of 4-10 μm thickness on both sides of the membrane. Given the vast range of dimensional scales, from 10-8 to 10-1
m, special attention was needed for the interconnections of the materials to establish the required electronic and ionic coupling together with adequate mechanical robustness. Two phase fluid flow modelling was done do have an optimal reactant distribution and gas evacuation from the electrode surfaces. Aspects like contact resistance, elasticity, stiffness, and overall electric field distribution inside the cell were considered. To characterize the cell in operation, a dedicated balance of plant has been built (Fig.1). The installation is automated and takes care of the electrolyte solution conditions and of the process window settings in terms of applied current, electrolyte flow and operational temperature at a pre-set pressure. The resulting cell potential, the gas purity of both oxygen and hydrogen streams and the differential pressure between anolyte and catholyte chambers are continuously monitored. The upscaled cell demonstrates a high hydrogen generation efficiency of 85% (HHV) that outperforms currently installed alkaline systems in terms of productivity and gas purity when operated at an elevated pressure 20 bar. The cell robustness, documented over 800 hours, reveals further areas of improvement for both the internal construction of the stack and the control logic of the balance of plant.

Figure 1
Driving Commercial Advancements in PEM Electrolysis – from Lab to Plant Floor
Authors: Ayers Katherine E. , Capuano Christopher , Carmo Marcelo
Published: September 2023

Proton exchange membrane (PEM) electrolysis has advanced significantly in the last 10 years, scaling from units in the sub 100 kW range to installed systems at 10 megawatts and greater. This technology, among others, is likely to play a major role in decarbonizing the industry, transportation, and energy sectors, as both the cost of electrolyzer technology and the renewable energy to power it have decreased. Still, the capital cost of electrolysis needs to be further reduced to economically replace hydrogen from steam methane reforming in very large applications, especially as capacity factor goes down to take advantage of the lowest cost electricity. There is also significant potential to decrease cost, as electrolyzer manufacturing is still relatively undeveloped.

PEM electrolysis has been developed for many decades and is proven as a reliable, scalable technology. However, electrodes are overdesigned due to the manual methods used to produce them, as well as the aerospace legacy of these systems. Many advancements such as reductions in catalyst loadings, use of thinner membranes, novel porous transport layers, and alternate cell configurations have been shown to be feasible in the lab, but have been slow to transition to commercial products.

There are many factors in this lag, including the need to often change manufacturing methods when moving from the lab to a product environment. While this effort is sometimes viewed as “just engineering”, there is significant fundamental understanding required to translate a slow, manual process where finished parts can be individually scrutinized, to a fast, automated process that has to include automated inspection as well. For example, a catalyst ink that is hand painted onto a substrate will need different properties and formulation to deposit the catalyst by spray printing, or yet different properties for other methods such as slot die or gravure printing. Determining acceptability of the resulting parts can no longer rely on human judgment but must be well enough understood that the most important properties can be quickly measured and analyzed in real time. In addition, the scale over which high quality needs to be achieved increases by orders of magnitude when moving from lab scale to product scale. This talk will discuss these types of challenges and approaches to solve them.
(Invited) Capacitive Deionization (CDI) – an Industrial Research Perspective
Authors: Mazumder Prantik , StClair Todd , Bourcier Roy
Published: September 2023

As the demand for freshwater keeps increasing due to industrialization and population growth, the world is progressively interested in desalination for sourcing potable water. While membrane-based reverse osmosis (RO) and thermal-based evaporation/distillation are proven technologies for desalination, they are also expensive. Capacitive deionization (CDI) - introduced in the 1970s - where the positive and negative ions are separated by the application of an electric field across pairs of high surface area electrodes, has been considered as a potentially cheaper technology. In the mid-2000s, Corning carried out a research project on developing CDI. The workstreams involved developing novel materials for electrodes, new device architecture, predictive theoretical models at electrode and device scales, and eventually a plant-level cost analysis that connected the electrode and device-level parameters to the final cost of water desalination, in $/gallon, which is the ultimate arbiter for techno-economic feasibility. We made significant progress in: (a) developing thin all-carbon electrodes which were electrochemically inert, highly conductive, and possessed high specific capacitance (F/cc) (b) designing a flow-past device architecture based on stacked planar electrodes with a small footprint (c) developing user-friendly simplified theoretical models, and (d) formulating two high-level figures of merit (FOM), namely, volumetric efficiency (VE) and recovery ratio (RR) – both of which need to be maximized to compete against incumbent technologies such as RO, especially in the high-throughput brackish water market sector. Our prototype achieved an equivalent VE of ~40 kg/ft3/day of salt removal. However, the plant-level cost analysis suggested that there is not much room for improving the overall cost structure compared to RO even with such high device level performance for high throughput desalination markets. In this talk we will present our experience with the development of CDI technology. We will cover all aspects of the project - electrode materials development, device architecture, theoretical models, and cost analysis – and will also offer an industrial perspective on CDI technology development, particularly when it comes to competing against well-established and entrenched technologies. We will also highlight how systems-level thinking and analyses are extremely important for such technology assessments and point out that only focusing on lab-scale performance metrics can be misleading.
Optimization Strategies of Photovoltaics-Powered Green Hydrogen Production
Authors: Wang Xuanjie , Liu Xinyue , Zhang Lenan
Published: September 2023

Green hydrogen production powered by photovoltaics provides a clean solution for energy conversion and storage. The key parameter of photovoltaic electrolysis (PV-EC) system is the solar-to-hydrogen (STH) efficiency. Previous studies have been mostly focused on improving the efficiency of each system individually using multi-junction PV materials, catalysts and electrolytes. However, the coupling between photovoltaic and electrochemical devices is still elusive to achieve high STH efficiency in a system level. In our study, the optimization strategies of PV-EC systems are demonstrated to approach thermodynamic limit (26.6%) for green hydrogen production. First, we list three design parameters for modeling, namely number of PV, number of EC and the area ratio between PV and EC. Then we model the crystalline silicon PV coupled with a real EC system. The STH efficiency varies under different PV and EC combinations. The STH efficiency map clearly defines three regions indicating the engineering space for PV-EC coupling, Tafel slope and area ratio. The optimization strategies presented in this study can lead to further advancements in coupled PV-EC systems with well-controlled performance for different conditions.
Boundary-Directed Epitaxy of Block Copolymers Toward Sub-10 nm Fabrication
Authors: Su Katherine Anna , Jacobberger Robert , Stan Liliana , Arnold Michael Scott
Published: September 2023

The directed self-assembly (DSA) of block copolymers (BCPs) can be used to produce nanometer-scale patterns without the cost and process complexity of state-of-the-art optical nanolithography. Thus, DSA is of potential use in a wide variety of semiconductor technologies, such as finFETs and biosensors. To control the position and orientation of BCP domains and create technologically useful patterns, conventional DSA mechanisms often rely on topographically complex structures or high-resolution chemical patterns that are difficult to fabricate. In comparison, a newly discovered mechanism for the DSA of BCPs – termed “boundary-directed epitaxy” – utilizes the chemical contrast at the boundaries between a substrate and relatively wide chemical stripe.[1] As a result, aligned and high density-multiplied BCP nanopatterns with half-pitch of 6.4 nm have been created using stripes as wide as 100 nm. By obviating the need for high-resolution chemical patterns, boundary-directed epitaxy offers exciting opportunities for the fabrication of sub-10 nm nanostructures.

[1] Boundary-directed epitaxy of block copolymers. R.M. Jacobberger, V. Thapar, G.-P. Wu, T.-H. Chang, V. Saraswat, A.J. Way, K.R. Jinkins, Z. Ma, P.F. Nealey, S.-M. Hur, S. Xiong, M.S. Arnold,
Nature Communications
11, 4151 (2020), 10.1038/s41467-020-17938-3.

Figure 1
A Ferroelectric Property Tailoring Method of Al0.7Sc0.3n Films by Sputter-Deposition Pressure
Authors: Tokita Yukimura , Tsutsui Kazuo , Kakushima Kuniyuki , Wakabayashi Hitoshi , Hoshii Takuya
Published: September 2023

New ferroelectric materials have been extensively studied for scaled non-volatile memory [1]. Among materials, Al1-x
Sc
x
N (ASN) films are attracting attention owing to their high remnant polarization (Pr
) of over 100 µC/cm2 [2]. Although the material is started to be characterized, a high coercive field (E
c) with a relatively high leakage current has been an issue. As reactive sputtering used to deposit nitrides is known to be influenced by the condition, in this study, we have changed the sputtering pressure for ASN deposition and characterized the ferroelectric properties. The composition of the ASN films is Al0.7Sc0.3N.

Metal-insulator-metal (MIM) capacitors with 50-nm-thick ASN film capacitors with TiN electrodes were fabricated by a reactive sputtering process. We varied the sputtering pressure from 0.76 to 1.1 Pa. Figure 1 shows the leakage current (J-V) of the capacitors. The capacitor with a low-pressure ASN film shows a relatively low leakage current and a breakdown field (E
BD) of 8 MV/cm which is high considering the bandgap of the ASN film to be 3.2 eV. On the other hand, the capacitor with a high-pressure ASN film showed a high leakage current with a reduced E
BD of 5.2 MV/cm. As the leakage current is determined by the interface, stacking the ASN layers may result in reducing the leakage current while maintaining a high E
BD. The leakage current of a capacitor with a 5-nm-thick low-pressure ASN at each interface and a 40-nm-thick high-pressure ASN film is also shown in fig. 1. We see a slight suppression in the leakage current and improvement in the E
BD to be 6.2 MV/cm.

P
r of the capacitors were obtained by positive-up-negative-down (PUND) measurements. The pulse-height dependent P
r is shown in fig. 2. The capacitor with a low-pressure ASN film revealed a high E
c of 3.8 MV/cm, while the one with a high-pressure ASN film was 3.4 MV/cm. The capacitor with stacked ASN films showed the same E
c of 3.4 MV/cm. The capacitors with single film showed a gradual change in the P
r on the electric field. In the stacked one, in contrast, a sharp change in the electric field with a constant P
r of 100 μC/cm2 was obtained.

In conclusion, stacked ASN films deposited by different sputter pressures show reduced leakage current with a high breakdown field. Although the physical change by the pressure is still unknown, tailoring the interface and bulk regions has a possibility to further improve the ferroelectric properties.

References

[1] H. A. Hsain, et al., J. Vac. Sci. Technol., A 40, 010803 (2022). [2] S. Fichtner, et al., J. Appl. Phys.,
125, 114103 (2019).

Figure 1
Thickness-Dependent Flat-Band Voltage of Ferroelectric Al0.7Sc0.3n Films on SiO2/Si Substrate
Authors: Nonaka Ryusei , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki
Published: September 2023

Ferroelectric films have a high potential for random access memory (RAM) thanks to the switching speed with low power consumption. Along with the advent of ferroelectric HfO2 films, various materials have been reported to show high remnant polarization (P
r) with thickness scalability. Although its high P
r can be utilized for data storage, and charge trapping in addition to the depolarization field to compensate the P
r has been the issue for ferroelectric/paraelectric stacked structure. It was recently reported that Al1-x
Sc
x
N (ASN) films have a high P
r of above 100 µC/cm2 and are expected for high-density RAM applications [1]. However, the charge trapping behavior at AlScN/paraelectric interface is not characterized yet. In this work, we fabricated Al0.7Sc0.3N(1~50nm)/SiO2(27nm)/nSi MOS capacitors to measure the surface potential change induced by the thickness of the ASN films.

ASN films were sputter deposited on a thermally oxidized 27-nm-thick SiO2. The thickness of the ASN films was changed from 1 to 50 nm. TiN films were in-situ deposited atop, and patterned to be the gate electrodes. Finally, annealing at 420oC in forming gas was conducted. The ASN films used in this study have a coercive field of 5.3 MV/cm and are already up-polarized [2]. Therefore, no ferroelectric switching is involved during the capacitance-voltage (C-V) measurements.

Fig. 1 shows the obtained C-V curves of the MOS capacitors, where we can see a strong thickness-dependent shift in the C-V curves. No apparent hysteresis nor SiO2/Si interface degradation was observed. Fig. 2 shows the summary of the extracted V
fb on equivalent oxide thickness (EOT). In the thin layer region, V
fb shifts to a positive direction and saturates with a shift by 0.27 V. Further increase in the thickness shifts back to the negative direction, and again gradually to the positive direction. Although the physical origin of the complicated V
fb shift behavior is not clear, we anticipate that the thickness-dependent stain to induce an inverse piezoelectric effect with charge trapping is the origin of the behavior.

In conclusion, we measured the V
fb shift of ASN films on the SiO2/Si substrate. The thickness-dependent V
fb shift showed complicated behavior with a thickness that can be attributed to the piezoelectric property of ASN films.

References

[1] S. Fichtner, et al., J. Appl. Phys.,
125, 114103 (2019). [2] S.-M. Chen, et al., Jpn. J. Appl. Phys., 61, SH1007 (2022).

Figure 1
(Best Paper Award) Aluminum Josephson Junction Formation on 200mm Wafers Using Different Oxidation Techniques
Authors: Lang Simon , Schewski Alexandra , Eisele Ignaz , Kutter Christoph , Lerch Wilfried
Published: September 2023

For superconducting quantum circuits with a large number of Qubits, reproducible components are crucial for reducing entanglement decoherence. Particularly for reliable industrial manufacturing on full-scale 200 mm' wafers, a very high uniformity level is required to ensure sufficient coherence times. In the present work the special focus was put on manufacturing Al/AlOx/Al
Josephson junctions (JJ), which are the most important component of many quantum circuit. Fully Al-based CMOS-compatible JJ’s were produced using a double dry etch process. After patterning the first Al metallization several oxidation processes have been investigated.

Static oxidation has been performed by first removing the native AlOx in a multi-chamber system with Ar milling. The final tunneling oxide was controlled by applying a specific pressure in the chamber under a pure O2 atmosphere. Afterwards, without breaking the vacuum, the second Al metallization has been deposited by sputtering. Oxide thicknesses between 1 and 2.5 nm were achieved. A full mapping of the process homogeneity will be given.

On the other hand, a dynamic recipe controlled plasma oxidation process was performed, where the native AlOx
was first removed by a H2
plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm. The second Al metallization was again deposited by sputtering.

Both oxidation processes were carefully studied to understand the initial oxidation process of the aluminum surface. Special attention was devoted to the non-destructive removal of the native AlOx with respect to the Al interface. Because the oxide thicknesses varied between 1 and 10 nm, the transition between direct and Fowler-Nordheim tunneling could be investigated. The process-stability on full scale 200 mm wafers and on chip size could be determined via test structures as well as the resistance variation of the Josephson junctions. Furthermore, the electrical properties of the different oxides could be measured and analyzed on wafer level. These studies provide insight into the structure and composition of the aluminum oxides and the applicability for Qubits.
(Invited) (Photo-)Electrochemical Reactions on Semiconductor Surfaces:Si and III-V Surfaces – Atomic and Electronic Structure
Authors: Jaegermann Wolfram
Published: September 2023

Semiconductor/electrolyte interfaces are used in many application areas where strong non linear variations in the electric performance depending on applied potential or due to illumination play a decisive role. Often a simplified explanation on charge redistribution across the semiconductor/electrolyte junctions is applied considering only the charge redistribution involving the bulk and the electrolyte following an idealized semiconductor /metal Schottky barrier model. But as will be addressed in our contribution strong deviations are usually observed in real devices which are due to Fermi level pinning effects and adsorbate related double layer potential shifts of the band edges. This is especially true for photoelectrochemical cells used in water splitting devices. For this reason we will present detailed surface science studies on the properties of Si and III-V surfaces espcially by applying photoelectron spectroscopy.

In so-called model experiments the effect of surface states found on differently doped Si(111) and (100) surfaces is investigated in relation to the resulting surface electronic structure after appying different surface preparation and processing procedures. Additionally the reactivity and the changes in electronic structure following a „frozen electrolyte“ junction formation will be presented after water exposure at low sample temperature. The results are compared to photoelectrochemical cells based on Si single crystals as well as thin film multiabsorber cells used as photocathodes.

For III-V semiconductors at first the surface properties of etched InP, GaP and GaInP (100) surfaces will be compared and further modified by subsequent vacuum based processing steps as heating and sputtering. The best surfaces are in their surface composition very close to samples prepared by MOCVD. Also for the III-V materials the interaction with H2O was investigated. In all cases Fermi level pinning close to the valence band maximum was observed and compared to the resulting band diagrams of photoelectrochemical devices used for HER.

In combining photoelectrochemical studies with surface science investigations on the electrode properties using directly contacted but also buried junction photoelectrodes it can be shown that defect levels related to remaining dangling bond states play a dominant role for the performance of the devices. The concentration of the remaining defect states influence the obtained performance in dependence of the interfacial contact composition preferring the formation of buried junctions. In conclusion we suggest that surface science studies of photoelectrodes before and after electrochemical studies are essential and need to be further developed for in operando experiments with special emphasis also in the valence band regime to obtain improved insights into semiconductor/electrolyte junction properties.
Reversible Redox Probes to Determine the Band Edge Locations for Nano-TiO2
Authors: Khurana Divyansh Anil , Plankensteiner Nina , Vereecken Philippe M.
Published: September 2023

Semiconductor (photo-)electrocatalysts show immense promise in answering the difficulties faced in CO2 electrolysis in relation to the reduction product selectivity. We thus see materials like ZnO[1], Cu2-xSe[2], MoS2
[3], TiO2
[4] and their numerous composites being frequently investigated for their catalytic properties in CO2 (photo-)electroreduction. These catalysts are fabricated via varying techniques and can assume very different thicknesses and morphologies. Although the nano-semiconductors may behave differently, often only the bulk properties are considered when proposing possible reaction pathways. Determining band edge locations of semiconductors in solutions is one such case, where Mott-Schottky (MS) measurements are a widely accepted strategy. The measurement of the potential dependence of the capacitance of the semiconductor space-charge layer under depletion indeed forms an elegant method to determine the flat-band potential and hence the band edge positions for bulk semiconductors in solution. However, the MS method cannot be used for nano-structured semiconductor electrodes in the form of thin films, nanorods or nanoparticles coated on conducting substrates, as their nano-dimensions are typically much smaller than that of a semiconductor depletion layer.

In this work, we explored an alternate strategy to determine band edge positions of nano-semiconductors using reversible redox probes. A model thin film system comprised of 30nm anatase TiO2 is used to demonstrate the feasibility of the strategy in aqueous electrolyte solutions. Fe, Ru and Cr based reversible redox species were used as electrochemical probes in cyclic voltammetry experiments with varying solution pH. Based on the presence/absence of the reversible behavior of these probes, we can deduce the TiO2 band edge locations. The procedure also allows us to draw parallels between semiconductor-metal and semiconductor-solution interfaces to gain new insights into the CO2 reduction mechanism on such semiconductor electrodes.

Figure 1
Factors Controlling the High Oxidative Activities of Layered Manganese Oxides
Authors: Wang Chenying , Chakrapani Vidhya
Published: September 2023

The two-dimensional layered birnessite mineral is a powerful natural oxidant and an important model compound in the development of bioinspired electrocatalysts for the water oxidation reaction (OER). The aim of this work was to study the factors controlling their unusually high oxidative activities of natural and synthetic samples for both spontaneous and potential-induced oxidation reactions. The results of the study1 of various cation-exchanged birnessites for spontaneous Cr(III) to Cr(VI) oxidation reactions show that the oxidative activity of birnessite, which decreases in order Mg > Cs = K > Na > Ca > Li > H, is due to its unusually high electron affinity of ∼5.9 eV, which is the highest among all known functional oxides and sulphides in aqueous solution. Both the band gap (Cs > Mg > K > Na > Ca > Li > H) and the electron affinity (Na > Cs > K > Mg > Ca > Li > H) are seen to be strongly affected by the nature of the interlayer cations and their coordinating water molecules. Analysis shows that the band gap scales with the interlayer spacing, while the electron affinity scales with the relative Mn(III)/Mn(II) concentration.

In another study2, the performance of birnessite as an electrocatalytic water oxidation catalyst and the mechanism of key Mn(III) intermediate formation were evaluated through the study of the effects of various electrolyte anions and cations on the catalytic efficiency. In situ spectroelectrochemical measurements show that the activity is controlled by a dynamic dissolution-oxidation process, wherein Mn(III) is formed through the oxidation of labile uncomplexed Mn(II) that shuttles between the crystal lattice and the electrolyte. The role of electrolyte anions is to control the extent of deprotonation of complexed Mn(II) in the lattice while the electrolyte cations control the interlayer spacing. Both in turn govern the shuttling efficiency of uncomplexed Mn(II) and its subsequent electrooxidation to Mn(III). The high electron affinity values put the band edges of birnessite-type structures well below the redox potential of most thermodynamically stable cations and water, enabling their spontaneous oxidation. The high electron affinity is another example of the unusual features of Mn compounds, which Nature uses for its many biogeochemical functions.

C. Wang; N. Smieszek; V. Chakrapani, Unusually High Electron Affinity Enables the High Oxidising Power of Layered Birnessite Chem. Mater.
2021,
33 (19), 7805-7817.

I. Roy; C. Wang; N. Smieszek; X. Li; L. Tsapatsaris; V. Chakrapani, Formation of the Metastable MnIII Water Oxidation Intermediate in Birnessite is Controlled by a Dissolution-Deposition Process Involving Labile MnII. ChemSusChem
2022,
15 (8), e202200062.

Figure 1
(Invited) Towards a Realistic Modelling of Solid-Liquid Interfaces
Authors: Cucinotta Clotilde S
Published: September 2023

In this talk I will introduce some issues connected with the simulation of electrified interfaces at the nanoscale focusing on simulating the effect of an applied potential to an electrode, using realistic models for the charged electrode electrolyte interface. I will present some recent progress in the simulation of the double layer of fundamental solid liquid interfaces of interest for corrosion and water splitting, and its response to changes of potential applied to the cell [1]; this is obtained applying a general ab initio electrode-charging approach we developed.

[1] R. Khatib, A. Kumar, S. Sanvito, M. Sulpizi and C. S. Cucinotta*, The nanoscale structure of the Pt-water double layer under applied potential revealed, 2021, 391, 138875 In this talk I will introduce some issues connected with the simulation of electrified

interfaces at the nanoscale focusing on simulating the effect of an applied potential to an electrochemical (EC) cell, using realistic models for the charged electrode electrolyte interface. I will present some recent progress in the simulation of the double layer of the fundamental solid liquid interfaces of interest for corrosion and water splitting and its response to changes of potential applied to the cell [1]; this is obtained applying a general ab initio electrode-charging approach we developed.

[1] R. Khatib, A. Kumar, S. Sanvito, M. Sulpizi and C. S. Cucinotta*, The nanoscale structure of the Pt-water double layer under applied potential revealed, 2021, 391, 138875
(Invited) Cations at a Solid-Liquid Interface: A Second Harmonic Generation Investigation
Authors: Suntivich Jin , Xu Pengtao
Published: September 2023

When an electrode contacts an electrolyte, an interfacial electric field forms. This interfacial field can polarize the electrode’s surface and nearby molecules, but its effect can be reversed by applying external potential. One method for quantifying this effect is the phase-sensitive second harmonic generation (PS-SHG) technique. We present our PS-SHG investigation of the Pt/water interface, where we examine the impact of the electrolyte chemistry on the electrical double layer (EDL). We will discuss how switching cations in alkaline electrolytes can affect the solid-liquid interface, in particular, the behavior of interfacial water. Our work provides a tool for quantifying the interfacial electric field at an electrode-electrolyte interface and shows the possibility of how cations can modify the EDL.
Consideration of Improved Adhesion of Direct Copper Seed Layer by Medium-Vacuum Sputtering Using Vacuum Ultraviolet Light
Authors: Endo Shinichi , Shimizu Akihiro , Ueyama Hiroyuki , Fukada Kazuhiro , Kashiwagi Yuta , Takamatsu Hirosuke , Hashimoto Kiyoaki , Takahashi Ryotaro
Published: September 2023

A sputtering method is used to form the seed layer for copper electric plating. In general, copper spatter has weak adhesion to resin, so titanium spatter is combined to increase the adhesion strength. However, etching in the lithography process requires two types of processes, titanium and copper metal. We have reported the improvement of adhesion of copper sputter to glass epoxy resin by medium vacuum sputtering equipment in 242nd ECS meeting. Adhesion strength was improved by performing vacuum ultraviolet treatment as a pretreatment for medium-vacuum sputtering. We discovered the relationship between the hydroxyl groups on the resin surface and the adhesion force by the chemical modification XPS method. Furthermore, by XPS analysis of the peeled copper interface, the adhesion mechanism between the resin and copper due to UV irradiation was estimated. We evaluated the absorption properties in the vacuum ultraviolet region of a thinly processed glass epoxy resin. We investigated the behavior of functional groups at the interface and considered the effect of vacuum ultraviolet rays in the depth direction.
Surface Defect Mediated Interactions of Bacterial Growth Media on Microcrystalline ZnO
Authors: Johnson Dustin , Reeks John , Ali Iman , Caron Alexander , Speights Abagael , McGillivray Shauna , Strzhemechny Yuri
Published: September 2023

Nano- and microscale ZnO exhibits significant potential in biomedical applications as an antibacterial agent. This is attributed to the selective toxicity and growth inhibition for a wide range of both Gram-positive and Gram-negative bacteria as well as for microbial strains resistant to traditional antibiotics. Pursuit of novel bactericidal applications, however, is inhibited by uncertainty surrounding the underlying mechanisms of the observed antimicrobial action. The most common suggested mechanisms include generation of various reactive oxygen species, release of Zn ions and surface-surface interactions between the bacterial cell wall and free crystalline surface of ZnO. Recent work has placed an emphasis on the role of the free crystalline surface in bacterial growth inhibition. Additionally, the cytotoxicity of ZnO particles has long been known to be heavily dependent on environmental conditions, yet detailed descriptions of these phenomena are lacking. Herein we investigate the effects of interactions with both bacteria and the bacterial environments on the physicochemical and optoelectronic properties of the free crystalline surface of ZnO microparticles (MPs). This is done to gain insight into the nature of interactions with the bacterial growth media and the influence such interactions have on bacterial growth inhibition. Hereby, we expose hydrothermally grown ZnO MPs to phosphate-buffered saline (PBS) media both with and without the presence of Newman strain S. aureus bacteria. The surface electronic structure and charge dynamics are probed via both time and energy dependent surface photovoltage (SPV) conducted prior to and following minimum inhibitory concentration assays. We demonstrate significant changes in the characteristic timescales of long-lived processes in the SPV transients after exposure to phosphate-rich environments. We also note that the presence of bacteria has an impact on shorter lived processes and suppresses the effect of media at longer timescales. The SPV spectra point to a significant adsorption of phosphate compounds on the crystalline surface. We also demonstrate changes in the electronic structure as a result of exposure to PBS.
Synthesis of Novel Ru Precursors for Atomic Layer Depostion
Authors: Song Young Eun , Chung Taek-Mo
Published: September 2023

Ruthenium (Ru), which has a low bulk resistivity and a high work function, is a well-known metal for electrode materials in various microelectronic applications, such as Dynamic Random Access Memories (DRAM), Ferroelectric Random Access Memories (FRAM), and metal-oxide-semiconductor field-effect transistors (MOSFET). Also, Ru thin films can be used as diffusion barrier layers to improve the electromigration resistance in interconnect systems due to the excellent adhesion characteristics between Ru and Cu. Therefore, research on Ru thin films, that can be deposited by methods such as MOCVD (Metal-Organic Chemical Vapor Deposition) and ALD (Atomic Layer Deposition), is attracting many researchers. To apply these deposition techniques, Ru precursors with volatility and thermal stability are required. In this study, for the synthesis of Ru precursors that can satisfy all conditions, new Ru precursors were designed and prepared by using Ru(η5-Tropone)(η5-CHT) (CHT = Cycloheptatriene) as a starting material, to yield five new ruthenium precursors: Ru(II)(C7H9)(C8H11O) (1), Ru(II)(C7H9)(C9H14O) (2), Ru(II)(C7H9)(C13H14O)(3), Ru(II)(C7H9)(C8H9O) (4), and Ru(II)(C7H9)(C9H11O) (5). These compounds were characterized by 1H-Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), Fourier-transform Infrared Spectroscopy (FT-IR), Elemental Analysis (EA), Thermal Gravimetric Analysis (TGA), and single crystal X-ray diffraction.
(Invited) Sub-Bandgap Thermoreflectance Imaging of Ultra-Wide Bandgap Semiconductors
Authors: Pavlidis Georges , Jamil Muhammad , Bista Bivek
Published: September 2023

Over the past few decades, wide bandgap semiconductors (WBG) have been used to fabricate high power and high frequency devices. Device structures, such as Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs), have begun to be implemented in commercial products such as electrical vehicles and laptop power chargers. With the continuous increase in energy demand, however, extremely high voltage (>10 kV) applications are needed to increase the grid resiliency, storage, and transmission efficiency. Ultra-wide bandgap (UWBG) Semiconductors, with bandgaps >4 eV, could potentially be used to overcome this barrier. Pushing the maximum voltage limit of these devices, however, can lead to significant power dissipation and excessive joule heating.

Unfortunately, the thermal conductivity of some UWBG semiconductors, such as Gallium Oxide, is inherently low and thus requires both device and package level thermal management. Innovative solutions, such as high thermal conductivity substrates, are required to reduce the active channel temperature and extend the device lifetime and reliability. In order to successfully implement these technologies, accurate measurement of the peak temperature and thermal distribution (both vertical and lateral) is necessary. Depth-averaged vertical temperature gradients have been demonstrated via Raman thermometry but this approach can become significantly time consuming if attempting to perform transient or lateral maps. On the other hand, Transient Thermoreflectance Imaging (TTI) has shown the potential to provide high throughput thermal images with high spatial resolution (100 nm) and temporal resolution (50 ns).

Traditionally, TTI has been used to probe the temperature of metals due to their inherent high reflectivity. Nevertheless, recent studies have demonstrated the ability to probe the surface temperature of the semiconductor when using near-bandgap illumination sources. Due to the high bandgap of UWBG semiconductors, the maturity of high transmission UV sources, optics and detectors has not yet been fully developed. This study investigates the applicability of sub-bandgap wavelengths to probe the active channel temperature. The thermal properties of both Gallium Oxide transistors and Transfer Length Method (TLM) structures are investigated using TTI. The accuracy of the channel temperature is assessed by direct comparison to the adjacent metal contact temperature. A finite element model (FEM) is developed to understand the thermal transport in low thermally conductive semiconductors. Finally, a 3D analytical model is used to extract thermal properties such as the thermal conductivity of the thin film layers.

Figure a) Optical CCD Image of Gallium Oxide Transfer Length Method (TLM) Structure b) Transient Thermoreflectance Image (TTI) of Gallium Oxide TLM using sub-bandgap illumination wavelength.

Figure 1