bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Two-Dimensional Materials for Electronic Devices: Transition-Metal Dichalcogenides and Topological Insulators
Authors: Vandenberghe William , Laturia Akash , Tiwari Sabyasachi , Sorée Bart , Van de Put Maarten 
Published: February 2020

As scaling of electronic devices has reduced dimensions into the nanoscale regime, investigations towards intrinsically two-dimensional (2D) materials are being pursued. Examples of 2D materials under investigation are monolayers of graphite, transition-metal dichalocogenides (TMDs), tellurium, and 2D topological insulators (TIs). To enable practical applications however, 2D materials must outperform currently employed three-dimensional materials. Properties of interest are mobilities, device drive current, and dielectric response but these properties are not yet fully known and understood in 2D materials.
We present a theoretical investigation of the dielectric response in transition-metal dichalcogenides. We determine a method to define and extract, from first principles, the dielectric constant of a two-dimensional material. We apply this method to calculate the low-frequency and high-frequency dielectric constant of semiconducting TMDs, both those in the hexagonal phase, e.g. MoS2, WSe2, as well as those in the tetragonal phase, e.g. ZrS2 and HfSe2. We find that the in-plane static dielectric constant for the TMDs in the tetragonal phase is very large, which will give rise to large polar-optical phonon scattering and low mobilities in tetragonal TMDs. [1]
We also present a new strategy to deal with both the high concentration of defects found in 2D materials as well as the difficulty of making perfectly straight edges. The strategy proposes to make transistors out of 2D TIs since 2D TI materials host topologically protected edge states that are robust against perturbations. In fact, we show how 2D TI field-effect transistor performance is actually improved in the presence of defects. The high on-current, related to the high electron velocity in these devices gives 2D field-effect transistors a predicted performance that exceeds that of conventional field-effect transistors. [2, 3]
[1] A. Laturia, M. L. Van de Put, and W. G. Vandenberghe, "Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk," npj 2D Materials and Applications, vol. 2, no. 1, p. 6, 2018/03/08 2018.
[2] W. G. Vandenberghe and M. V. Fischetti, "Imperfect two-dimensional topological insulator field-effect transistors," Nature Communications, vol. 8, 2017.
[3] S. Tiwari, M. L. Van de Put, B. Sorée, and W. G. Vandenberghe, "Carrier Transport in a Two-Dimensional Topological Insulator Nanoribbon in the Presence of Vacancy Defects," in 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), 2018, pp. 92-96: IEEE.
(Invited) Ordered Mesoporous Metal Oxide Thin Films: From Room Temperature Ferroelectrics to Tunable Magnetic Materials
Authors: Brezesinski Torsten 
Published: February 2020

Advances in sol-gel processing and polymer templating have enabled the preparation of several important mesostructured materials with different pore symmetries and unprecedented properties. However, especially the synthesis of structurally and compositionally well-defined metal oxides with a crystalline wall structure is challenging for various reasons.
In the first part of this talk, I will describe the preparation of a series of high quality, ordered mesoporous metal oxide films of thickness ≤500 nm by the dip-coating method using a soft-templating process (via coassembly of hydrolyzing salt precursors and an amphiphilic diblock copolymer) and their characterization by advanced imaging, diffraction, and spectroscopic methods. In the second part, I will show that the general idea of combining nanomagnetism and electrochemical energy storage concepts can be applied to mesoporous metal oxide films with spinel and perovskite structures, [1-4] and discuss the structure-property relationships of room temperature ferroelectrics, [5] among others.
[1] C. Reitz, P. M. Leufke, R. Schneider, H. Hahn and T. Brezesinski, Chem. Mater. 26 (2014) 5745.
[2] C. Reitz, C. Suchomski, D. Wang, H. Hahn and T. Brezesinski, J. Mater. Chem. C 4 (2016) 8889.
[3] C. Reitz, D. Wang, D. Stoeckel, A. Beck, T. Leichtweiss, H. Hahn and T. Brezesinski, ACS Appl. Mater. Interfaces 9 (2017) 22799.
[4] L. A. Dubraja, C. Reitz, L. Velasco, R. Witte, R. Kruk, H. Hahn and T. Brezesinski, ACS Appl. Nano Mater. 1 (2018) 65.
[5] L. A. Dubraja, R. Kruk and T. Brezesinski, Adv. Electron. Mater. (2018) https://doi.org/10.1002/aelm.201800287.
(Invited) High-Voltage β-Ga2O3 vertical Power Diodes and Transistors with Fin Channels
Authors: Li Wenshen , Hu Zongyang , Nomoto Kazuki , Jinno Riena , Nakamura Tohru , Jena Debdeep , Xing Huili Grace 
Published: February 2020

For high voltage and high current applications, vertical power devices are preferred over the lateral counterparts, due to the unaltered footprint with elongated drift region width and the generally higher current density. The development of vertical power devices relies on the ability to epitaxially grow thick drift layers with low defect density and precisely-controlled net doping concentration, often on the order of 1016 cm-3 or lower. One of the unique advantages of β-Ga2O3 over SiC and GaN is the availability of melt-growth methods for the production of high quality single-crystal substrates, which provide excellent platform for homoepitaxy. Recently, high quality thick epitaxial layers grown by halide vapor phase epitaxy (HVPE) have been developed, and β-Ga2O3 vertical power devices have seen rapid developments. In this work, we discuss our recent advancements on high-voltage β-Ga2O3 vertical power diodes and transistors with fin channels.
The ultra-high critical breakdown field of 6-8 MV/cm in β-Ga2O3 is another key advantage of this material. While the high critical field leads to a high projected Baliga’s figure-of-merit, it also brings tremendous challenge to the management of the electric field in power devices, especially with the absence of native p-type doping up till now. One example is the Schottky barrier diodes, in which the electric field at the top surface must be controlled to be much lower than the critical field in order to avoid excessive tunneling current. Another example is the device periphery, where proper edge termination designs are required to avoid premature breakdown due to field crowding. To suppress the electrical field at the surface, we adopted fin channels with metal-insulator-semiconductor (MIS)-based sidewall in Schottky barrier diodes. We show that the charge-coupling effect in these structures allows for effective reduction of the electric field at the top surface, therefore effectively reducing the leakage current due to tunneling. The gated fin channels with sub-micron channel width also allow for the realization of normally-off vertical transistors. A general trend of the electric field peak at the bottom corners of a fin channel is discovered, which provides important guidance for the design of vertical fin channel devices. With the help of field-plating at the device periphery, we show that the breakdown voltage of the fin channel transistors can be much improved. With these field management techniques, we achieved state-of-the-art figure-of-merits in both the fin channel diodes as well as transistors.
(Invited) Thermal Characterization of Ultra-Wide Bandgap Gallium Oxide Electronics
Authors: Choi Sukwon 
Published: February 2020

To extend further the electrical performance envelope of wide bandgap (WBG) power and radio frequency (RF) electronics based on gallium nitride (GaN) and silicon carbide (SiC), device engineers are actively pursuing the development of generation-after-next ultra-wide bandgap (UWBG) devices. At the time being, aluminum gallium nitride (AlGaN), β-gallium oxide (Ga2O3), and diamond are technologically relevant UWBG materials that have bandgaps larger than that for GaN (3.4 eV). In particular, the availability of melt-grown substrates for the Ga2O3 materials system offers a clear economic advantage over SiC and GaN device technologies.
While UWBG Ga2O3 devices are built to operate under higher power densities compared to current state-of-the-art WBG counterparts, the thermal conductivity Ga2O3 is lower than those for GaN and SiC by an order of magnitude. Therefore, self-heating is a major challenge for devices based on this materials system. Electro-thermal interactions that lead to self-heating in Ga2O3 devices need to be accurately assessed and understood to accomplish the successful transition from WBG devices to the UWBG technology.
In this work, we will demonstrate the use of an integrated optical thermography scheme (Raman thermometry, thermoreflectance imaging, and infrared thermography) to study the steady-state and transient thermal characteristics of Ga2O3 Schottky Barrier Diodes (SBD) and lateral Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFET). In addition, we will report our recent progress on the development of a 2-D transducer-assisted Raman thermography technique suitable for Ga2O3 devices, which overcomes limitations associated with current state-of-the-art methods.
(Invited) Limits to Phonon Thermal Boundary Resistance across GaN Interfaces
Authors: Hopkins Patrick 
Published: February 2020

As material length scales decrease below typical vibrational heat carrier (e.g., phonon) mean free paths, the thermal boundary resistances (TBR) at heterogeneous material interfaces become the dominant thermal resistances that dictate temperature rises, thermal runaway, and power density at failure in a wide array of devices. In this work, I will discuss the phonon scattering processes that dictate the thermal boundary conductance (TBC, the inverse of TBR, so TBC = 1/TBR) across GaN-based interfaces, including the maximum limits to TBC at GaN interfaces and the roles of point defect scattering and interfacial layers on GaN TBC. I will first present experimental measurements of the TBC from 78−500 K across isolated heteroepitaxially grown ZnO films on GaN substrates. This data provides an assessment of the underlying assumptions driving phonon gas-based models, such as the diffuse mismatch model (DMM), and atomistic Green’s function (AGF) formalisms used to predict TBC. Our measurements, when compared to previous experimental data, suggest that TBC can be influenced by long wavelength, zone center modes in a material on one side of the interface as opposed to the “vibrational mismatch” concept assumed in the DMM; this disagreement is pronounced at high temperatures. At room temperature, we measure the ZnO/GaN TBC as 490[+150,−110] MW m-2 K-1. The disagreement among the DMM and AGF, and the experimental data at elevated temperatures, suggests a non-negligible contribution from other types of modes that are not accounted for in the fundamental assumptions of these harmonic based formalisms, which may rely on anharmonicity. Given the high quality of these ZnO/GaN interfaces, these results provide an invaluable, critical, and quantitative assessment of the accuracy of assumptions in the current state of the art computational approaches used to predict phonon TBC across interfaces. I will then turn my discussion to focus on the role that interfacial imperfections, such as point defects and continuous films at the interface, have on GaN TBC. These results demonstrate the large variability that can occur in TBC at GaN-based interfaces based on interfacial non-idealities.
1. J. T. Gaskins, et al. "Thermal boundary conductance across heteroepitaxial zno/gan interfaces: Assessment of the phonon gas model," Nano Letters, 18, 7469–7477 (2018).
2. B. F. Donovan, et al. "Thermal boundary conductance across metal-gallium nitride interfaces from 80 - 450 K," Applied Physics Letters, 105, 203502 (2014).
(Invited) Design and Energy Application of Piezoelectric Biomaterials
Authors: Yang Rusen 
Published: February 2020

Multifunctional materials have received increasing attention in recent years. Owing to their inherent biological nature as well as piezoelectric properties, piezoelectric biomaterials are considered as promising candidates for application in fields ranging from electrochemical energy storage to biological systems. Rational material design is important to enhance their piezoelectric and biological activity. Herein, recent advancements to piezoelectric biomaterials like peptide-based micro/nanostructures are provided. Synthetic methods, morphological features, and piezoelectric performance of piezoelectric biomaterials are presented. The effect of growth direction, phase and structure of piezoelectric biomaterials on their piezoelectric activity are discussed. The applications of piezoelectric biomaterials in the field of nanogenerators are provided at the end.
Reference:

Yuan, T. Lei, Y. Qin, R. Yang, Flexible electronic skins based on nanogenerators and piezotronics, Nano Energy, submitted

Nguyen, S. Kelly, R. Yang, Piezoelectric peptide-based nanogenerator enhanced by single-electrode triboelectric nanogenerator, APL Materials
5, 074108 (2017)

Nguyen, R. Zhu, K. Jenkins, R. Yang, Self-assembly of diphenylalanine peptide with controlled polarization for power generation, Nature Communications
7, 13566 (2016)

Nguyen, K. Jenkins, R. Yang, Epitaxial growth of vertically aligned piezoelectric diphenylalanine peptide microrods with uniform polarization, Nano Energy
17, 323 (2015)
(Invited) Electrolyte Oxidation Limits the Life of Alkaline Membrane Water Electrolyzer
Authors: Kim Yu Seung , Li Dongguo , Matanovic Ivana , Lee Albert S , Chung Hoon T 
Published: February 2020

Alkaline anion exchange membrane (AEM) water electrolyzers paid significant attention due to the cost benefits over proton exchange membrane electrolyzers. The durability of AEM electrolyzers is one of the critical requirements for the commercially viable systems. We have investigated that the possible performance loss over time is related to the oxidation of polymeric binders used for AEM electrolyzers. In this presentation, the oxidative degradation of the phenyl group is reported using the commercial Pt/C, IrO2 and house-made perovskite oxide catalyst.
Rotating disk electrode experiments exhibited that the oxidation of phenyl group on the oxygen evolution reaction (OER) catalysts is pronounced: The oxidation rate of commercial Pt/C and IrO2 catalysts was > 11% at 1.6 V vs. RHE over the 5-hour chronoamperometric test, while the house-made LA0.85Sr0.15CoO3 catalyst perovskite oxide catalyst exhibited 4.1%. Density functional theory calculations show that the adsorption of the phenyl on the perovskite oxide catalyst is significantly smaller, suggesting that the electrolyte oxidation is related to the adsorption properties of the phenyl group.
Hierarchical Carbon Nanofiber/Birnessite-MnO2 Nanosheets Cathode for High Performance and Low-Cost Aqueous Rechargeable Zinc Ion Battery
Authors: Chen Xiujuan , Li Wei , Liu Xingbo 
Published: February 2020

Abundant and safe charge carrying feedstock with high energy density have made aqueous zinc-ion batteries (ZIBs), specifically the Zn/MnO2 system, a highly promising candidate for large-scale energy storage device. The traditional alkaline Zn/MnO2 batteries have become dominant in primary battery chemistry. Great efforts have been devoted to developing rechargeable alkaline Zn/MnO2 batteries, however, they are plagued by poor cycling stability. Very recently, the Zn/MnO2 systems in near neutral electrolyte have emerged to demonstrate improved capacities, cyclability and rechargeability. However, the commonly used tunnel-type MnO2 cathode with low conductivity usually undergoes phase transition to layered structure upon discharge-charge cycles, leading to collapse of framework and thus poor cycling and rate performance. To address these issues, it is proposed that directly using birnessite-MnO2 with layered structure as a cathode may minimize the “sacrificial capacity” induced by phase transition and integrating birnessite-MnO2 with a conductive substrate may enhance the conductivity.
In this work, the hierarchical core-shell carbon nanofiber@MnO2 (CNF@MnO2) cathode was prepared by a facile wet-chemistry method, where vertically aligned birnessite-MnO2 nanosheets were in situ grown on the surface of carbon nanofibers. The self-supported CNF@MnO2 cathode showed excellent electrochemical performance for Zn-ion batteries in a near neutral electrolyte due to its structural stability and enhanced conductivity. A high discharge capacity of 306 mA h g−1 has been reached after 100 cycles at current density of 300 mA g−1. Even at a high rate of 1.5 A g−1, CNF@MnO2 still maintained a high capacity of 258 mA h g-1 upon 100 cycles. Such remarkable performance is attributed to the unique core-shell structure and intimate contact between CNF and layered MnO2, in which the conductive CNF core facilitates the electron transfer and layered MnO2 minimizes the structural collapse and promotes the kinetics for co-insertion and extraction of Zn2+/H+ ions. Given the simplicity of preparation, exceptional electrochemical performance and low cost, CNF@MnO2 cathode holds substantial promise for aqueous rechargeable Zn-ion batteries.

Figure 1. Scanning electron microscopy image of carbon nanofiber@MnO2 (CNF@MnO2) cathode for aqueous rechargeable Zn-ion batteries in near neutral electrolyte.

Figure 1
Electrochemical Energy Storage with Mediator-Ion Solid Electrolytes
Authors: Yu Xingwen , Manthiram Arumugam 
Published: February 2020

From an electrochemical point of view, many liquid-phase or gas-phase materials exhibiting a high operating voltage and a high intrinsic capacity can potentially be used as electrodes for the development of high energy, low-cost aqueous batteries. However, under the traditional battery operating principle with a porous separator, there is a tendency of shuttling of liquid or gaseous electrodes through the porous separator, which strictly limits the application of liquid-phase or gaseous-phase materials for the development of energy storage systems.1

We have recently developed a new mediator-ion battery concept with alkali-metal-ion (Li+-ion or Na+-ion) solid-electrolyte separators.2 The anode and cathode reactions of the redox couples can be maintained by a shuttling of the alkali-metal ion through the solid-state electrolyte between the catholyte and the anolyte. This unique battery-development strategy can not only eliminate the chemical-crossover problem of the liquid or gaseous reactants, but also circumvent the metal-dendrite problem.3 Based on the unique features, the “mediator-ion” battery concept offers a versatile approach for the development of a broad range of new battery systems.
This presentation will first introduce the basic concept and operating principle of the mediator-ion battery. Then a sequence of mediator-ion batteries with a variety of redox couples we recently developed will be demonstrated.4-8 These novel mediator-ion batteries can be classified into four categories including, (1) meatal anode – inorganic liquid cathode batteries (zinc – bromine, zinc – Ferricynide, and zinc – polysulfide batteries), (2) meatal anode – organic liquid cathode batteries (zinc – quinone batteries), (3) meatal anode – gaseous cathode batteries (zinc – air and iron – air batteries), and (4) organic liquid anode – gaseous cathode batteries (quinone – air and methyl viologen – air batteries). At the end of this presentation, future prospects of this novel battery development strategy will be discussed.

References

Manthiram, X. Yu and S. Wang, Nat Rev Mater, 2017, 2, 16103.

W. Yu and A. Manthiram, Joule, 2017, 1, 453-462.

W. Yu, M. M. Gross, S. F. Wang and A. Manthiram, Adv Energy Mater, 2017, 7, 1602454.

W. Yu and A. Manthiram, ACS Appl. Energy Mater, 2018, 1, 273−277.

W. Yu and A. Manthiram, ACS Energy Letters, 2017, 2, 1050-1055.

W. Yu and A. Manthiram, Advanced Sustainable Systems, 2017, 1, 1700082.

W. Yu and A. Manthiram, Sustain Energ Fuels, 2018, 2, 1452-1457.

W. Yu and A. Manthiram, ACS Appl. Energy Mater, 2018, 1, 2424–2428.
(Invited) TiO2 Nanotube Arrays: Photoelectrochemical and Photocatalytic Applications
Authors: Schmuki Patrik , Liu Ning , Altomare Marco 
Published: February 2020

TiO2nanomaterials have over the last 30 years attracted tremendous scientific and technological interest. Main research direction using TiO2in functional applications are still the use in photocatalysis e.g. for the direct splitting of water into H2and O2to generate the potential fuel of the future, hydrogen, or the use in Grätzel type solar cells. In order to achieve a maximum turn-over rate (by creating a high surface area), usually nanoparticles are used either suspended or compacted to a photoelectrode. Over the past decades various 1D and highly defined TiO2 morphologies were explored for the replacement of nanoparticle networks and were found in many cases superior to nanoparticles. Nanotubes or wires can be grown by hydrothermal or template methods, or even more elegantly, by self-organizing anodic oxidation. The latter is not limited to TiO2but to a full range of other functional oxide structures on various metals and alloys can be formed. These advanced and doped morphologies can be grown on conductive substrates as ordered layers and therefore can be directly used as functional electrodes (e.g. photo-anodes). The presentation will focus on these highly ordered nanotube arrays of TiO2and discuss most recent progress in synthesis and modification for photocatalytic and photoelectrochemical for H2generation.
Literature: (reviews):

- P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904

- K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385