bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fabrication and Characterization of Crystalline Thin Film MoS2 Prepared By RF Magnetron Sputtering
Authors: Gustavsen Kim R , Wang Kaiying 
Published: February 2020

Thin film molybdenum disulfide (MoS2) exhibits unique physical and electrochemical properties. Most notably MoS2 has shown itself to be a viable candidate as an earth abundant catalyst for the hydrogen evolution reaction (HER) [1-3]. However, preparation of quality MoS2 thin films often involves complex synthesis techniques not capable of large-scale production. In this paper we present a study of thin film MoS2 prepared by radio frequency (RF) magnetron sputtering, which is an industrial large-scale thin film fabrication method. Substrate temperature during deposition and its effect on the morphology, electrical – and optical properties of the sputtered MoS2 thin films will be investigated.

The MoS2 thin films were deposited at room temperature (RT) and 400°C using an Argon atmosphere with a pressure of 5.9 mTorr, and RF power of 150W. Following deposition the samples were annealed at 550°C for three hours. A visual representation of the thin film MoS2 on quartz substrate after the annealing process is seen in Figure 1. Visually the MoS2 films have a gold brown color, where the sample deposited at room temperature is slightly darker. The absorbance spectra (250-850 nm) show that the film deposited at room temperature display no peaks associated with MoS2, while the thin film deposited at 400°C show a small 'C' transition peak at ~418 nm (Figure 2). Post annealing absorbance spectra of both films indicate the four transition peaks characteristic of MoS2. The 'A' and 'B' peaks are direct transitions related to the band-edge excitons, whereas the 'C' and 'D' absorbance peaks arise from van Hove singularities in the electronic density of states associated with layered MoS2 [4,5]. X-ray diffraction (XRD) was performed using a Si substrate and the existence of the (002) plane indicates that the thin films are crystalline (Figure 3).
In conclusion, we have determined the effect of substrate temperature during deposition and post annealing on the properties of the MoS2 thin films. Additionally, preparation of crystalline MoS2 has been demonstrated using a large-scale thin film production technique. The morphology, optical – and electrical properties have been studied on ITO glass and quartz substrates.

References

Wang, D.; Zhang, X.; Bao, S.; Zhang, Z.; Fei, H. & Wu, Z. J. Mater. Chem. A, The Royal Society of Chemistry, 2017, 5, 2681-2688

Hong Li, C. T., Ai Leen Koh, Lili Cai, Alex W. Contryman, Alex H. Fragapane, Jiheng Zhao, Hyun Soo Han, Hari C. Manoharan, Frank Abild-Pedersen, Jenk K. Nørskov, and Xiaolin Zheng (2016). Nature Materials 15

Haotian Wang, C. T., Desheng Kong, Karen Chan, Frank Nano Reasearch 8: 566-575.

Mak, C. Lee, J. Hone, J. Shan, and T. Heinz, Phys. Rev. Lett. 105, 136805 (2010).

Britnell et al., Science 340, 1311 (2013).

Figure 1
(Battery Division Research Award) Forming Interphases
Authors: Xu Kang 
Published: February 2020

Solid electrolyte interphases (SEI) enable the battery chemistries to maximize energy density by operating beyond the thermodynamic stability limits of non-aqueous electrolytes 1
,2. The chemical building blocks of SEI come from the decomposition of either solvents or salt anion, depending on a host of interwoven parameters such as the HOMO/LUMO energy levels of these components (reduction/oxidation stability) as well as their interactions (solvation sheath structures). Designing electrolytes for new battery chemistries requires understanding of interphasial chemistries and the ability to manipulate them. This talk summarizes our efforts in interfacing various electrode chemistries to electrolytes of non-aqueous, aqueous and hybrid natures.

Reference
s
:

[1] K. Xu, Chem. Rev.,
2004, 104, 4303
[2] K. Xu, Chem. Rev.,
20
1
4, 1
1
4, 11503
(Battery Division Postdoctoral Associate Research Award Sponsored by MTI Corporation and the Jiang Family Foundation) Stable Li Metal Anode through Designed Solution Chemistry and Electrode Architecture
Authors: Liu Haodong , Liu Ping 
Published: February 2020

Lithium metal is being extensively studied as an anode to replace graphite due to its high capacity and the lowest negative electrochemical potential. Current research focus is to mitigate lithium dendrite growth and to increase coulomb efficiency during electrochemical cycling by using various surface coatings, electrolyte additives. In addition, a 3D host can be beneficial due to the reduced volume change.
We have recently focused on designing interfacial chemistries that enable dendrite free cycling. In this regard, we report the synthesis of lithium methyl carbonate, a known compound in common anode SEI, via a simple one step reaction. This reaction is used to coat Li or Cu with a protection layer of pure LMC, which is supported by the cryo-TEM observations.1 This coating layer is shown to enable dendrite free Li cycling in a symmetric Li||Li cell even at a current density of 3 mA cm-2.2 Moreover, FIB-SEM shows this LMC coating layer loses thickness once it is transferred into EC/DMC, which reveals that it dynamically dissolves into the carbonate electrolyte. In order to enhance the sustainability of the LMC coating layer in commercial electrolytes, LMC powder is used to pre-saturate the organic electrolyte. As a consequence of the two strategies, the Li cycling CE in a commercial carbonate electrolyte is significantly improved from 90.5% to 96.1%. These findings provide new insights on designing effective protection layers and managing sustainable SEI formation for stable Li cycling. Recently, we have extended the one step reaction approach to the formation of a polymer gel electrolyte which enables the Li/Li cell cycled for 1000 hours without increase of resistance at a current density of 5 mA cm−2. Finally, we will discuss recent progress on a novel 3D electrode design that enables dendrite free and high coulombic efficiency of Li metal cycling in carbonate electrolytes.

Acknowledgements

This work was supported by the Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research Program (Battery 500 Consortium) under Contract DE-EE0007764. Part of the work used the UCSD-MTI Battery Fabrication Facility and the UCSD-Arbin Battery Testing Facility.
Synthesis of Ternary Blended Materials of Li1.2Mn0.4Ni0.16Co0.24O2, the Li2MnO3-Stabilized Compound, and Olivine Fluorides (Li2MPO4F) As a High Capacity Cathode Materials for Lithium Ion Batteries
Authors: Agubra Victor Anafo , Moore Todd , Kemp Ricardo , Intekhab Abdullah Farooq 
Published: February 2020

The area of blended cathode materials is still evolving and there are very few research on the subject. The blending parent cathode materials typically involves high capacity electrode materials; layered oxides compounds with spinel cathode compounds that are lower in cost, more environmentally benign and higher operating voltage. These blended cathode materials are expected to be resilient in terms of storage capacity, cycle life, cheaper and environmentally safer. However, chemically, there are exist challenges in pairing a high- operating voltage material and high capacity material and still achieving less resistance, greater storage and cycle life may be difficult to achieve, since high voltages are likely to enable more degradation pathways.
This paper seeks to explore a composite systems made of three different cathode materials involving lithium rich compounds Li1.2Mn0.4Ni0.16Co0.24O2, the Li2MnO3-stabilized compounds, spinel, or Olivine fluorides (Li2MPO4F). This study aims to design a better ternary system that meets the high energy density demand for hybrid electric vehicles and at the same time, minimizes the salient but important material properties like the thermal stability, longer life, high capacity and yet meet bottom line. The paper therefore explores a thorough understanding of the various interaction of each of the compounds so as to tailor their properties to have that synergy, conducting basic scientific analysis of the particle-to particle interaction at the atomic level, as well as the chemical interaction of the constituents in the ternary system to achieve the synergistic effect.
Surface Energy Modulation of PdCu Nanocatalysts Via the Crystal Structure Change for Lithium-Oxygen Battereis
Authors: Park Mihui , Liang Chaoping , Agyeman Daniel Adjei , Cho Kyeongjae , Kang Yong-Mook 
Published: February 2020

Palladium-copper (PdCu) alloys have two representative crystal structures; one is body-centered cubic (bcc), the other is face-centered cubic (fcc) even though both Pd and Cu originally have fcc crystal. The fcc PdCu alloys have disordered structure within which Pd and Cu have solid-solution in fcc lattice, whereas the bcc PdCu alloys have ordered structure which consists of alternative layers with either Pd or Cu atoms.
In particular, bcc PdCu alloys have occasionally shown superior performance to fcc PdCu alloys since the unique ordered structure of bcc has isolated Pd on the surface. Most of bcc PdCu alloys have been synthesized for structural transformation by annealing or seed-growth method of fcc PdCu alloys with inevitable grain growth, uneven surface structure and particle size distribution. Despite these limitations, the Pd on the bcc surface which is provided charge flow from Cu serves as an active site for catalytic reaction, which is highly favorable for lithium-oxygen battery. However, the same size of fcc and bcc PdCu alloys is quite difficult to be obtained since the crystallites larger than 20 nm favor the ordered bcc structure with lower symmetry. Thus, bcc PdCu alloys in nanoscale have been rarely reported, consequently fcc and bcc PdCu nanoparticles (NPs) have never been properly compared until now.
In this study, we successfully synthesize fcc and bcc PdCu alloys in nanoscale through precisely adjusting the driving force for reducing organometallic complex. The bcc PdCu NPs with higher surface energy govern the growth thermodynamics of discharge product and greatly improved battery performance based on density functional theory calculation and experimental proof. This study provides critical descriptor on material design in the perspective of modulating surface structure via crystal structure to tune its intrinsic properties.
The Relationship between the Oxygen Vacancies Density with the Electronic and Optical Properties of Hafnium Oxide
Authors: Islamov Damir R. , Gritsenko Vladimir A. , Kruchinin Vladimir N. , Lebedev Mikhail S. 
Published: February 2020

Hafnia-based high-κ dielectrics are widely used in modern MOS devices, perspective RRAM and FRAM cells, dopand of ceramics in teeth prosthetic. The electronic properties of HfO2, such as leakage currents and luminescence, are defined by traps and defects. The presence of traps increases the conductance of dielectric. Electron or hole localization on traps shifts the voltage threshold and leads to device degradation. In active layers of RRAM, traps act as precursors of a filament during the HRS/LRS switch. The trap density ≲1022 cm-3 is a huge for degeneration of devices, but is very low for detecting within chemical analytical techniques. Previously, it was reported that comparison measured J-V dependencies with multiphonon transport models allows extracting the density of oxygen vacancies (VO), which acts as traps, in the HfO2. In the study, we try to get correlations between the trap density and optical properties of hafnia films.
Variation of the trap density in HfO2 was supported by different conditions of film synthesis using ALD technique and different precursors: TEMAH+H2O and Hf(thd)4+O2. The series of samples was annealed in N2-flow for 1 hour at different temperatures. Annealing was performed directly in the reaction chamber at T
ann = 440, 550 and 700 °C for TEMAH+H2O samples and T
ann = 550 and 700 °C for samples deposited from Hf(thd)4+O2 precursor system. Dispersion dependencies of refractive index were measured by spectral and laser ellipsometry. It was found that the refractive index grows as films are depleted by oxygen. The results offer a new in situ technique for quality evaluation of synthesized HfO2 films, namely evaluation of oxygen vacancy density.
The work was supported by the Russian Science Foundation, grant #16-19-00002.
Chain Length Dependence of the Dielectric Constant and Polarizability in Conjugated Organic Thin Films
Authors: Van Dyck Colin Jean-Louis , Marks Tobin , Ratner Mark A 
Published: February 2020

Dielectric materials are ubiquitous in optics, electronics and materials science. Recently, there has been new effort to characterize the dielectric performance of thin-films made of polarizable molecule assemblies, at both theoretical and experimental levels. [1-3] In this context, we will present the relation between the polarizability of the constituting molecule and the film dielectric constant, using periodic Density Functional Theory (DFT) calculations, for conjugated and saturated chains.
We particularly explore the implication of the peculiar chain length dependence of the polarizability for conjugated molecules. We show and explain from DFT calculations and a simple Clausius-Mossotti-like depolarization model how this chain-length dependence is affected by the collective polarization. We show that a high sensitivity of the dielectric constant to the thin-film thickness is expected for conjugated molecules. This latter can increase by a factor of 3-4 at a reasonable coverage, just by extending the molecular length. This significantly limits the decline of the thin-film capacitance with the film thickness.[4]
[1] Heitzer et al, Acc. Chem. Res., 2016, 10.1021/acs.accounts.6b00173
[2] Suchand Sangeeth et al, JACS, 2016, 10.1021/jacs.6b02039
[3] Bergren et al, J. Phys. Chem. C, 2010, 10.1021/jp106362q
[4] Van Dyck et al, ACS Nano, 2017, 10.1021/acsnano.7b01807

Figure 1
(Invited) Epitaxial Growth of 2D Transition Metal Dichalcogenide Monolayers, Alloys and Heterostructures
Authors: Zhang Xiaotian , Chubarov Mikhail , Choudhury Tanushree , Redwing Joan M. 
Published: February 2020

Two-dimensional (2D) transition metal dichalcogenides (TMDs) comprise a compelling class of new materials with intriguing properties that arise from their ultra-thin form, thickness-dependent bandstructure, large exciton binding energies and unusual spin and valley polarization physics. The majority of the research that has been carried out thus far employs ultra-thin TMD flakes exfoliated from bulk crystals but future device development requires the ability to synthesize large area single crystal films and heterostructures. Our research is aimed at the development of an epitaxial growth technology for TMDs and related layered chalcogenides based on gas source/metalorganic chemical vapor deposition (CVD/MOCVD) to enable monolayer growth over large substrate areas and layer-by-layer growth of heterostructures.
Our recent studies have focused on the epitaxial growth of WSe2 and (Mo,W)S2 monolayer films, alloys and heterostructures using metal hexacarbonyl and hydride chalcogen precursors on substrates including sapphire and hexagonal boron nitride (hBN). A multi-step precursor modulation growth method was developed to independently control nucleation density and the lateral growth rate of TMD domains on the substrate. This approach also enables an estimation of metal-species surface diffusivity and domain growth rate as a function of growth conditions providing insight into the fundamental mechanisms of monolayer growth. Using the multi-step growth process, coalesced monolayer and few-layer TMD films were obtained on sapphire substrates up to 2” in diameter at growth rates on the order of ~ 1 monolayer/hour. In-plane X-ray diffraction demonstrates that the films are epitaxially oriented with respect to the sapphire resulting from a merging of 0o and 60o oriented domains. Room temperature photoluminescence (PL) measurements demonstrate strong emission peaks in the range of ~1.6 eV for WSe2 and ~2.0 eV for WS2 monolayers with lateral variations that may arise from residual strain in the films. (Mo,W)S2 alloy growth using simultaneous flows of Mo and W hexacarbonyl precursors reveals evidence of atomic scale ordering of Mo and W atoms within the monolayer. Growth and characterization of MoS2/WS2 and WSe2/WS2 vertical heterostructures will also be discussed.
(Invited) Bottom-up Grown Nanowire Quantum Devices
Authors: Bakkers Erik P.A.M. 
Published: February 2020

The main challenge for the development of a quantum computer is to solve decoherence. The promise of topological quantum computation is that local noise does not affect and destroy the quantum state, and therefore long coherence times are expected. In a topological system the quantum information is encoded in quasi particles, called Majorana Zero Modes (MZM).
First signatures of MZM have been obtained in InSb nanowires [1]. Recently, different schemes for performing logical operations and uncovering the properties of Majorana states are proposed. For such a universal computational architecture the realization of a near-perfect nanowire network assembly is needed in which Majorana states are coherently coupled.
Here, we demonstrate a generic process by which we can design any proposed braiding device by manipulating an InP substrate and thereby the nanowire growth position and orientation [2]. Our method leads to highly controlled growth of InSb nanowire networks with single crystalline wire-wire junctions. Additionally, nanowire “hashtag” structures are grown with a high yield and contacted. In these devices, the Aharonov–Bohm (AB) effect is observed, demonstrating phase coherent transport. These measurements reveal the high quality of these structures. Furthermore, this platform is used for in-situ epitaxial shadow growth of a superconductor on the nanowire facets, resulting in transport contacts. With this new generation devices we have observed quantized MZM [3].

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Zhang et al. Nature
2018
, accepted
Structural and Charging Stability of Metal Nanodot Memory in SiO2; First-Principles Study
Authors: Nakayama Takashi , Yamazaki Shota , Shiraishi Yuto 
Published: February 2020

Due to the high charge-retention power, nanometer-scale metal dots are promising systems for near-future memory devices when they are embedded in insulating oxides such as SiO2. However, there exist serious issues of charge-retention degradation [1]; during the repeated charge injection, a metal nanodot is broken by the dissociation of metal atoms from the nanodot surface into insulator under the charge-induced electric field. In addition, the charge leakage from the metal nanodot to dissociated metal atoms decreases the charge-retention power of the metal nanodot. However, there have been no microscopic studies on how the metal nanodot is broken (structural stability) and how the charge-retention power decreases (charging stability). In this work, by the first-principles calculations, we answer these questions and clarify what kind of metal is suitable for a metal nanodot memory in SiO2.
Twenty kinds of metals are considered as candidate elements of metal nanodots. We calculate the dissociation energy of a metal atom from nanodot surface into amorphous SiO2 (a-SiO2) and clarify the structural stability [2]. On the other hand, the charge-retention power is estimated using the ionization energy of a dissociated metal atom in a-SiO2 [3]. Atomic and electronic structures of various metal atoms in a-SiO2 are calculated by the standard first-principles method using VASP code in the density-functional theory.
Main results are summarized as follows: (1) we found that the structural stability is determined by the competition between the metal-metal and metal-SiO2 interactions (bondings). For example, the Au and Ti nanodots are unstable because the Au-Au bonding is basically weak and the Ti-Ti bonding is weaker than Ti-SiO2 interaction, while the W nanodot is stable because the W-W bonding is much stronger than W-SiO2 bonding. It is shown that such strength of bonding reflects both the electron occupancy of d-orbital states and the electron negativity of metal atoms. (2) The degradation of charge-retention power occurs by the charge leakage from a metal nanodot to dissociated metal atoms. It is interesting to note that Ti and W dissociated atoms are difficult to be ionized positively although they have small electron negativity compared to Au. This is because these atoms are electronically bounded strongly to surrounding O and Si atoms in a-SiO2. As a result, the W and Ti nanodots show little charge-retention degradation. (3) From these considerations, we found that the W nanodot has the highest structural and charging stability, thus being suitable for a metal-nanodot memory usage.
These results are discussed in details, together with reviewing recent experiments and considering other degradation processes.
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[1] M. S. Lee et al., Jpn. J. Appl. Phys. 46 (2007) 6202.
[2] R. Nagasawa, T.Nakayama et al., Jpn. J. Appl. Phys. 57 (2018) 04FB05.
[3] M. Y. Yang, T. Nakayama et al, J. Appl. Phys. 114 (2013) 063701.

Figure 1
(Invited) Unconventional Computing with Memristive Devices and Arrays
Authors: Li Can , Wang Zhongrui , Joshi Saumil , Upadhyay Navnidhi K. , Midya Rivu , Rao Mingyi , Xia Qiangfei , Yang J. Joshua 
Published: February 2020

Memristive devices1 have become a promising candidate for unconventional computing2. In this talk, I will present some of our recent work on unconventional computing experimentally implemented by using memristive devices or crossbar arrays.
Using traditional non-volatile memristors with 64 stable analog resistance levels, we have built a dot-product engine based on a 128 x 64 1T1R crossbar array3. Accurate image compression and filtering have been demonstrated with such analog computing accelerator3. In addition, we have demonstrated efficient and self-adaptive in-situ learning in a two-layer neural networks using such memristive arrays4, which is expected to significantly improve the speed and energy efficiency of deep neural networks.
Using our newly developed diffusive memristors5 with diffusion dynamics that is critical for neuromorphic functions, we have developed artificial synapses6 and neurons7 to more faithfully emulate their bio-counterparts and more efficiently perform spiking neural network functions. We have further integrated these artificial synapses and neurons into a small neural network, with which pattern classification and unsupervised learning have been demonstrated7. Moreover, the diffusive memristors can be used as true random number generators8 for cybersecurity applications and artificial nociceptors for robotics applications9.
1. Yang, J. J. et al. Memristive switching mechanism for metal/oxide/metal nanodevices. Nature Nanotechnology
3, 429 (2008).
2. Yang, J. J., Strukov, D. B. & Stewart, D. R. Memristive devices for computing. Nature Nanotechnology
8, 13 (2013).
3. Li, C. et al. Analogue signal and image processing with large memristor crossbars. Nature Electronics
1, 52 (2018).
4. Li, C. et al. Efficient and self-adaptive in-situ learning in multilayer memristive neural networks. Nature communications, under revision (2018).
5. Midya, R. et al. Anatomy of Ag/Hafnia-Based Selectors with 1E10 Nonlinearity. Advanced Materials
29, 1604457 (2017).
6. Wang, Z. et al. Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing. Nature Materials
16, 101-108 (2017).
7. Wang, Z. et al. Fully memristive neural networks for pattern classification with unsupervised learning. Nature Electronics
1, 137 (2018).
8. Jiang, H. et al. A Novel True Random Number Generator Based on a Stochastic Diffusive Memristor. Nature communications
8, 882 (2017).
9. Yoon, J. H. et al. An artificial nociceptor based on a diffusive memristor. Nature Communications
9, 417 (2018).