bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) 2D Semiconductor Electronics: Advances, Challenges and Opportunities
Authors: Javey Ali 
Published: February 2020

Two-dimensional (2-D) semiconductors exhibit excellent device characteristics, as well as novel optical, electrical, and optoelectronic characteristics. In this talk, I will present our recent advancements in defect passivation, contact engineering, surface charge transfer doping, and heterostructure devices of layered chalcogenides. We have developed a defect repair/passivation technique that allows for observation of near-unity quantum yield in monolayer MoS2. The work presents the first demonstration of an optoelectronically perfect monolayer. Forming Ohmic contacts for both electrons and holes is necessary in order to exploit the performance limits of enabled devices while shedding light on the intrinsic properties of a material system. In this regard, we have developed different strategies, including the use of surface charge transfer doping at the contacts to thin down the Schottky barriers, thereby, enabling efficient injection of electrons or holes. We have been able to show high performance n- and p-FETs with various 2D materials. Additionally, I will discuss the use of layered chalcogenides for various heterostructure device applications, exploiting charge transfer at the van der Waals heterointerfaces. I will also present progress towards achieving tunnel transistors using layered semiconductors.
(Invited) Phosphorene Transistors - a Brief Review
Authors: Xiong Kuanchen , Luo Xi , Hwang James C. M. 
Published: February 2020

Phosphorene, despite its instability when directly exposed to ambient oxygen or water, has been successfully processed into stable field-effect transistors (FETs). This paper reviews the emergence and progress of phosphorene FETs, all in little over a year. In such a short time, back-gated FETs evolved into front-gated FETs, gate length was reduced to the sub-micron range, passivation by high-k dielectrics or hexagonal boron nitride was demonstrated with temporal, thermal and mechanical stability, ohmic contact was achieved down to cryogenic temperatures, and cutoff frequencies was pushed above 10 GHz. These and other attractive characteristics promise the phosphorene FET to be a viable candidate for current-generation thin-film electronics, as well as future-generation ultra-thin-body low-power-consumption high-speed and high-frequency transistors.
Table I lists chronologically the pioneering papers on phosphorene FETs, which experimentally demonstrated promising performance characteristics, despite crude construction so that the top surface of the phosphorene channel was either exposed or protected only by polymer. Additionally, although the carrier mobility, current capacity, and on/off ratio were adequate, further improvement in the subthreshold slope was needed to improve the energy efficiency of these devices. To passivate the phosphorene surface, atomic-layer deposited aluminum oxide and exfoliated hexagonal boron nitride (hBN) have been used to demonstrate phosphorene FETs that were stable under ambient conditions up to several months and over a temperature range of −263 °C to 150 °C as listed in Table II. Longer-term stability could not be assessed because phosphorene FETs exist for just little over a year.
The attractive characteristics of phosphorene FETs demonstrated to date, such as carrier mobility, current capacity, on/off ratio, cut-off frequencies, temporal, thermal and mechanical stabilities indicate that they are viable candidates for thin-film flexible electronics operating in the gigahertz frequency range. However, for higher-speed and higher-frequency applications, they need to be further improved especially in reducing the interface state density to the 1011-cm−2 range and the gate length to the 10-nm range. For such an ultrathin-body low-power consumption nano-FET, not only the gate stack, but also the entire stack from the front gate, gate insulator, phosphorene channel, back insulator, back gate, to substrate needs to be optimized together, in addition to optimization of ohmic contacts and proper scaling of all other dimensions. This daunting task may be accomplished in much shorter time than the decades it took to develop Si or III-V FETs, judging from the extremely rapid development of phosphorene FETs to date. Ultimately, the same as for all 2D devices, uniform, reproducible and large-area growth or synthesis of phosphorene will be required for low-cost high-yield manufacture.

Figure 1
(Invited) Strain Engineering in Ultrathin Black Phosphorus
Authors: Li Yanyong , Lau Shu Ping 
Published: February 2020

We report the giant anisotropic strain response in vibrational modes of ultrathin black phosphorus (BP). A modified bending technique was employed to apply precise uniaxial tensile strain to zigzag or armchair directions of the BP flakes. The Raman shift rates of A1
g, B2g and A2
g modes of BP are significantly distinct for strain applied along zigzag or armchair directions. For the applied strain along zigzag direction, the Raman shift rate and the Grüneisen parameter of the B2g mode can reach a remarkable value of ~-11 cm-1/% strain and ~3.7 respectively, which are the largest among all the reported values in two-dimensional materials. The density functional theory calculations were performed to understand the exceptional anisotropic strain response in the vibrational modes of BP. It is found that not only the bond lengths but also the bond angels are changed in BP upon applied strain which lead to giant anisotropic response in mode B2g . Furthermore, we demonstrate a simple method based entirely on the strained BP and conventional Raman spectroscopy to determine the crystallographic orientations of BP without the aid of polarization Raman spectroscopy. This work may pave a way to study the strain-induced anisotropic electrical conductance and the magnetotransport properties of BP.
Simultaneous Intercalation and Oxidant-Free Polymerization of Pyrrole Between 2D Titanium Carbide (MXene) for High Performance Pseudocapacitive Electrodes
Authors: Boota Muhammad , Anasori Babak , Voigt Cooper , Zhao Meng-Qiang , Barsoum Michel W. , Gogotsi Yury 
Published: February 2020

Electrochemically active organic materials which offer pseudocapacitve characteristics are attractive for energy storage applications because they are economical, environmentally benign, lightweight, and their functionalities can be tuned to achieve the required electrochemical properties.1 Despite aforementioned advantages, they tend to degrade upon cycling mainly because of their poor conductivity. One option to improve the cycling and the overall electrochemical performance of the pseudocapacitve organic materials is to deposit/graft them onto conductive carbon particles.2 Two-dimensional carbides and carbonitirides called MXenes, which generally offer metallic conductivity, may become a suitable option to replace carbon in pseudocapacitve electrodes to improve the electrochemical performance of the organic materials.3,4

Here, we report a facile approach to simultaneously align and intercalate heterocyclic organic molecule pyrrole between the Ti3C2Tx MXene layers. On contrary to the conventional approaches, pyrrole monomer was polymerized without addition of any oxidant when mixed with the Ti3C2Tx colloidal solution, which was confirmed by various spectroscopic techniques. When the optimized composition was tested as a pseudocapacitive electrode, it exhibited high volumetric and gravimetric capacitances of 1000 F/cm3 and 416 F/g, respectively, at 5 mV/s. Most important, excellent capacitance retention of 92% was observed after 25,000 cycles at 100 mV/s.
1. M. Boota et al., Adv. Mater. (2015). DOI (10.1002/adma.201504705)
2. M. Boota et al., ChemSusChem, 8, 3576–3581 (2015)
3. M. R. Lukatskaya et al., Science., 341, 1502–1505 (2013)
4. M. Ghidiu, M. R. Lukatskaya, M.-Q. Zhao, Y. Gogotsi, and M. W. Barsoum, Nature, 516, 78–81 (2014)
Electrodeposition and Capacitance of WS2 Thin Films Onto ITO and Glassy Carbon from Aqueous and Non-Aqueous Electrolytes
Authors: Fan Li , Suni Ian Ivar 
Published: February 2020

Two-dimensional (2D) layered materials, including graphene, metal oxides, metal chalcogenides and their composites have shown to be efficient and promising materials for high performance supercapacitor electrodes, with high surface area and large in-plane conductivity. Among the 2D layered supercapacitors, MoS2, MoSe2, WS2, and WSe2 are semiconductors with intriguing electronic, electrochemical and electrocatalytic properties.
We have synthesized WS2 thin films onto both ITO and glassy carbon electrodes by the electro-reduction of (NH4)2WS4 from both aqueous and acetonitrile electrolytes. During cyclic voltammetry, a cathodic peak that overlaps with H2 evolution is observed at at -1.2V vs Ag/AgCl in aqueous solutions. In acetonitrile, no cathodic peak is observed on ITO, but a cathodic peak that overlaps with a background cathodic peak is observed on glassy carbon. The background peak appears to arise form TEA-BF4 reduction, since the current density scales with TEA-BF4 concentration.
The standard reduction potential, effective diffusion coefficient and transfer coefficient for WS2 electrodeposition in acetonitrile are determined are estimated from cyclic voltammetry at different scan rates. Results will also be presented for the specific capacitance of WS2 films deposited atop glassy carbon electrodes (GCE) following application of potential sweep methods for activing GCE.
The ARPA-E REBELS Program: Advances and Challenges after 1.5 Years of Research
Authors: Albertus Paul S. , Soloveichik Grigorii L. , Tuttle John R. , Litzelman Scott Joseph , Pouy Mark J. 
Published: February 2020

In 2014, the Advanced Research Projects Agency-Energy (ARPA-E) started the Reliable Electricity Based on ELectrochemical Systems (REBELS) program, focusing on fuel cells utilizing natural gas for stationary power production and value-added products generation. The intent of REBELS was twofold: (1) demonstrate that operating fuel cells in an “intermediate” temperature range of 200-500 oC could reduce system cost compared to polymer electrolyte membrane (PEM) fuel cells and higher temperature solid oxide fuel cells (SOFCs), and (2) create new electrochemical functionality such as charge storage in the stack and liquid fuel production to benefit grid applications. REBELS was enabled by more than 15 years of materials research on new electrolytes, such as solid acids, proton-conducting ceramics, and alternative oxygen-conducting ceramics to yttria-stabilized zirconia. This presentation describes the rationale behind the REBELS program, including changes in the U.S. electrical grid and the evolving opportunities for distributed power generation. Technical barriers to intermediate temperature operation such as methane activation at lower temperatures and reduced power density due to electrode overpotentials and electrolyte resistance will be highlighted.
In the year and a half since the REBELS program began, teams working on a variety of material systems have made progress on several fronts. New anode compositions and microstructures enabled fuel cells to operate directly on methane at 500 oC without coking. New cathode materials mitigated the increase in electrode overpotential as temperature decreased from higher temperature SOFC operation. New electrocatalyst materials and morphologies allowed solid acid fuel cells to operate around 250 oC with reduced platinum loadings. New electrochemical functions have also been demonstrated, such as power production with internal charge storage (no external fuel) and conversion of methane to products such as methanol and ethylene.
This presentation will summarize the performance of technologies within the REBELS program with respect to PEM and SOFCs, and it will revisit the original assumptions that motivated the program. Components of the techno-economic models required to rigorously evaluate the program, such as electrochemical performance, materials cost, stack lifetime, efficiency etc. will be discussed.
Reaction Distribution in Mixed-Conducting SOFC Cathodes Investigated with Patterned Thin Film Electrodes
Authors: Amezawa Koji , Fujimaki Yoshinobu , Shindo Yusuke , Nakamura Takashi , Iguchi Fumitada , Yashiro Keiji , Yugami Hiroo , Kawada Tatsuya , Nitta Kiyofumi , Terada Yasuko 
Published: February 2020

Solid oxide fuel cells (SOFCs) recently attract attentions as one of promising high-efficiency energy-conversion devices. For enhancement of the cell performance or low temperature operation, oxygen reduction kinetics on the cathode should be improved. In a mixed ionic-electronic conducting (MIEC) cathode, such as (La,Sr)CoO3
-

d
and (La,Sr)(Co,Fe)O3
-

d
, reaction area for the oxygen reduction reaction is not limited to only the electrode/electrolyte/gas interface (the triple phase boundary) but also distributes to the oxide surfaces within a certain distance from the electrode/electrolyte interface, i.e. within an effective reaction area. However, there are no reports which directly observe such a reaction distribution by experimental manners, as far as the authors know.
For experimental and quantitative observation of the reaction distribution in an MIEC SOFC electrode, a patterned thin film electrode, which is a kind of the columnar electrode simplifying a porous electrode, was used in this work [1]. As a typical MEIC electrode material, La0.6Sr0.4CoO3-

d
was chosen and deposited on a Ce0.9Gd0.1O1.95 electrolyte. In an MEIC cathode, it is believed the oxygen chemical potential decreases in the area where the electrochemical oxygen reduction reaction takes place. Thus, reaction distribution can be understood if the distribution of oxygen potential is revealed. In this work, operando micro X-ray absorption spectroscopy (XAS) technique was applied to evaluate the oxygen potential was evaluated as a function of the distance from the electrode/electrolyte interface. In this operando technique, X-ray absorption spectra could be obtained with a spatial resolution higher than 1 mm at elevated temperature (~1073 K) while controlling atmospheric condition and passing the electronic current through the cell. The effective reaction area could be estimated, for instance, 20 mm from the electrode/electrolyte interface in the case of the La0.6Sr0.4CoO3-

d
patterned thin film electrode having a thickness of 400 nm at 973 K under 1 bar of p(O2) and -220 mV of cathodic overpotential. The effective reaction area tended to expand with decreasing ambient p(O2) and increasing cathodic overpotential.
References
[1] K. Amezawa, Y. Fujimaki, T. Nakamura, K. D. Bagarinao, K. Yamaji, K. Nitta, Y. Terada, F. Iguchi, K. Yashiro, H. Yugami, T. Kawada, Electrochem. Soc. Trans., 66(2), 129 (2015).
Tailoring Electrode Materials for Proton-Conducting Solid Oxide Fuel/Electrolysis Cells with Chemically Stable BaZrO3 Electrolyte
Authors: Bi Lei , Traversa Enrico 
Published: February 2020

Proton-conducting oxides offer an alternative solution for solid oxide cells with its unique advantages, such as low activation energy, high ionic conductivity at intermediate temperatures (1, 2). In the community, it is generally realized that the use of chemically stable electrolyte material BaZrO3 is the most promising way for the development of proton-conducting solid oxide cells. Although the use of BaZrO3 has been achieved with desirable fuel cell performance (2), the design of its air electrode is still a challenge, especially for the proton-conducting solid oxide electrolysis cells. In this presentation, we report our recent work on the tailor of the air electrode materials for proton-conducting solid oxide cell, including the use of traditional Sr-doped LaMnO3 (LSM) cathode for BaZrO3-based fuel cells with desirable cell performance and the design of mixed proton-electronic mixing conducing air electrode for proton-conducting electrolysis cells.
LSM, which is one of the most classical air electrode materials for solid oxide cells, is regarded can be only used above 700 oC due to its poor catalytic activity at intermediate temperatures (around 600 oC). In our study, we successfully employed the inkjet printing technique, enabling LSM work properly as the air electrode for proton-conducting solid oxide fuel cells with BaZrO3 electrolyte. After the optimization, the fuel cell performance reached 200 mW cm-2 at 600 oC, which is encouraging considering the air electrode material is LSM. A further improvement of fuel cell performance was achieved by using mixed electronic-oxygen conductor air electrode material, reaching the highest power output for the BaZrO3-based cells up to now.
In addition to the work on fuel cells, research on the air electrode material for solid oxide electrolysis cells was also carried out. Following to our previous work using proton-electronic mixed conductor for proton-conducting fuel cells (3, 4), a similar strategy was proposed for electrolysis cells. Coupling BaZr0.5Pr0.3Y0.2O3 (BZPY30, a mixed protonic-electronic conductor) with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) as the air electrode, the cell showed a dramatic electrolysis cell improvement compared with the LSCF- BaZr0.7Pr0.1Y0.2O3 (BZPY10, a pure protonic conductor). This result suggests the extension of proton conduction at the air electrode is critical for the transportation of proton at air electrode side and thus facilitates the electrochemical reactions for the proton-conducting electrolysis cells.

References

1. L. Bi, S. Boulfrad and E. Traversa, Chem. Soc. Rev., 43, 8255 (2014).
2. E. Fabbri, L. Bi, D. Pergolesi and E. Traversa, Adv. Mater., 24, 195 (2012).
3. E. Fabbri, I. Markus, L. Bi, D. Pergolesi and E. Traversa, Solid State Ionics, 202, 30 (2011).
4. E. Fabbri, L. Bi, D. Pergolesi and E. Traversa, Energ. Environ. Sci., 4, 4984 (2011).
Ba0.5Sr0.5Co0.8Fe0.2O3 Cathode for Intermediate Temperature Proton-Conducting Solid Oxide Fuel Cells
Authors: Sun Shichen , Cheng Zhe 
Published: February 2020

Comparing with conventional solid oxide fuel cells (SOFCs) that typically operate at ~750 oC and above, intermediate temperature SOFCs (IT-SOFCs) that operate at temperature of ~400-700 oC offer advantages such as the possibility for the use of lower cost sealing and interconnect materials and the potential for improved reliability and robustness due to the expected slower degradation at reduced temperature. For IT-SOFCs, proton-conducting oxides such as acceptor-doped Ba(Ce, Zr)O3 are often preferred as the electrolyte materials for their high ionic conductivity and low electronic transport number while Ni is almost always used for the anode. In comparison, researchers have not settled on a proper cathode or oxygen electrode, and various materials such as LSCF and SSC have been explored and show different degree of success. Here, we report the use of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as cathode material for proton conducting IT-SOFC with BaZr0.1Ce0.7Y0.1Yb0.1O3 (BZCYYb) electrolyte. In particular, the chemical stability of BSCF cathode subjecting to different atmospheres containing water (H2O) vapor and CO2 and the compatibility of BSCF with BZCYYb electrolyte will be examined. In addition, the impacts of cell operating conditions including cathodic bias voltage, moisture and CO2 on the electrochemical performance of cathode including bulk and interfacial resistance will be reported using cathode symmetrical cells and/or anode-supported button cells. Preliminary results seem to suggest that BSCF cathode displays reasonable stability and compatibility under typical proton conducting IT-SOFC operating conditions, and cathode performance increases in humidified air compared with dry air. Finally, the directions for future design of cathode for proton conducting IT-SOFC will be discussed.
Time Resolved DXAS Study on Micro and Nano NiO/Ce0.9Gd0.1O1.95 Cermets for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Fernandez Zuvich Afra , Larrondo Susana , Saleta Martin , Napolitano Federico , Caneiro Alberto , Troiani Horacio , Lamas Diego German , Arce Mauricio Damian , Serquis Adriana , Soldati Analia 
Published: February 2020

The development of Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFC) as high efficient energy conversion systems requires the optimization of its components: cathode, anode and electrolyte. CeO2-based materials present excellent catalytic properties for the oxidation of H2 and CH4 fuels. Through the incorporation of metals oxides (Gd2O3, Sm2O3, Y2O3) in the CeO2 lattice the ionic conductivity can be significantly improved, becoming good electrolytes, particularly (Ce,Gd)O2-
d (CGO) compound. Furthermore, the addition of metals such as Ni or Cu enhances the material electronic conductivity, thus enabling them as efficient IT-SOFC anodes [1].
It is recognized that the polarization characteristics of Ni-CGO cermet anodes are strongly affected by their preparation conditions, which determine the microstructure and morphology of these materials. For that reason, further exploration of new microstructures has to be done in order to improve anode performance [2]. In a previous work we presented a new modified sol-gel method to incorporate Ni into the precursors solution, which produced a powder with a very homogeneous Ni distribution resulted in smaller particle sizes with narrower distribution than the commercial cermet [3]. In this work, we present a study of the performance of these anodes sintered at different temperatures for the hydrogen oxidation reaction. The electrode polarization resistance is evaluated through Electrochemical Impedance Spectroscopy (EIS) on symmetric cells, while the cell power of Ni-CGO/CGO/LSCF configuration is measured in a home-made equipment. The structural and morphological characterization are analyzed by X-Ray Diffraction and Transmission and Scanning Electron Microscopy, respectively. The study of the oxidation state and coordination of Ce and Ni in these cermets, simulating in-operando conditions, was performed using synchrotron Dispersive X-ray absorption spectroscopy (DXAS) technique. The correlation between the electrochemical behavior, electronic properties and microstructural characteristics will be discussed.
[1] W.C. Chueh, Y. Hao, W. Jung and S.M. Haile, Nature Materials 11 (2012) 155-161.
[2] Z. Liu, B. Liu, D. Ding, M.F. Liu, F.L. Chen, C. R. Xia, Journal of Power Sources 237 (2013) 243-259.
[3] A. Fernandez Zuvich, A. Soldati, S. Larrondo, M. Saleta, D.G. Lamas, L. B. Baqué, A. Caneiro and A. Serquis, ECS Transactions 64 (2014) 233-240.