The metallic 1T phase of WS2 (1T‐WS2), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution ...reaction (HER). As the semiconductor 2H phase of WS2 (2H‐WS2) is inherently stable, methods for synthesizing 1T‐WS2 are limited and complicated. Herein, a uniform wafer‐scale 1T‐WS2 film is prepared using a plasma‐enhanced chemical vapor deposition (PE‐CVD) system. The growth temperature is maintained at 150 °C enabling the direct synthesis of 1T‐WS2 films on both rigid dielectric and flexible polymer substrates. Both the crystallinity and number of layers of the as‐grown 1T‐WS2 are verified by various spectroscopic and microscopic analyses. A distorted 1T structure with a 2a0 × a0 superlattice is observed using scanning transmission electron microscopy. An electrochemical analysis of the 1T‐WS2 film demonstrates its similar catalytic activity and high durability as compared to those of previously reported untreated and planar 1T‐WS2 films synthesized with CVD and hydrothermal methods. The 1T‐WS2 does not transform to stable 2H‐WS2, even after a 700 h exposure to harsh catalytic conditions and 1000 cycles of HERs. This synthetic strategy can provide a facile method to synthesize uniform 1T‐phase 2D materials for electrocatalysis applications.
A highly uniform and stable 1T phase of WS2 on the 4 in wafer‐scale is presented, which is still a great challenge due to the metastable nature of 1T phase as well as the lack of suitable growth/fabrication methods. In this way, the 1T‐WS2 is utilized as an electrocatalyst for the hydrogen evolution reaction and exhibits efficient catalytic activity and high durability.
An unconventional phase‐change memory (PCM) made of In2Se3, which utilizes reversible phase changes between a low‐resistance crystalline β phase and a high‐resistance crystalline γ phase is reported ...for the first time. Using a PCM with a layered crystalline film exfoliated from In2Se3 crystals on a graphene bottom electrode, it is shown that SET/RESET programmed states form via the formation/annihilation of periodic van der Waals' (vdW) gaps (i.e., virtual vacancy layers) in the stack of atomic layers and the concurrent reconfiguration of In and Se atoms across the layers. From density functional theory calculations, β and γ phases, characterized by octahedral bonding with vdW gaps and tetrahedral bonding without vdW gaps, respectively, are shown to have energy bandgap value of 0.78 and 1.86 eV, consistent with a metal‐to‐insulator transition accompanying the β‐to‐γ phase change. The monolithic In2Se3 layered film reported here provides a novel means to achieving a PCM based on melting‐free, low‐entropy phase changes in contrast with the GeTe–Sb2Te3 superlattice film adopted in interfacial phase‐change memory.
Reversible crystalline–crystalline phase‐change memories are developed by stacking In2Se3 on the bottom graphene electrode. This shows SET and RESET programmed states via formation and annihilation of periodic van der Waals' gaps. The reversible transition of monolithic In2Se3 layered film demonstrates the potential of melting‐free and low‐entropy phase‐change memories.
The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based ...on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.
Plants monitor seasonal cues to optimize reproductive success by tuning onset of reproduction and inflorescence architecture. TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS T (FT) and their orthologs ...antagonistically regulate these life history traits, yet their mechanism of action, antagonism and targets remain poorly understood. Here, we show that TFL1 is recruited to thousands of loci by the bZIP transcription factor FD. We identify the master regulator of floral fate, LEAFY (LFY) as a target under dual opposite regulation by TFL1 and FT and uncover a pivotal role of FT in promoting flower fate via LFY upregulation. We provide evidence that the antagonism between FT and TFL1 relies on competition for chromatin-bound FD at shared target loci. Direct TFL1-FD regulated target genes identify this complex as a hub for repressing both master regulators of reproductive development and endogenous signalling pathways. Our data provide mechanistic insight into how TFL1-FD sculpt inflorescence architecture, a trait important for reproductive success, plant architecture and yield.
Herein, a high‐quality gate stack (native HfO2 formed on 2D HfSe2) fabricated via plasma oxidation is reported, realizing an atomically sharp interface with a suppressed interface trap density (Dit ≈ ...5 × 1010 cm−2 eV−1). The chemically converted HfO2 exhibits dielectric constant, κ ≈ 23, resulting in low gate leakage current (≈10−3 A cm−2) at equivalent oxide thickness ≈0.5 nm. Density functional calculations indicate that the atomistic mechanism for achieving a high‐quality interface is the possibility of O atoms replacing the Se atoms of the interfacial HfSe2 layer without a substitution energy barrier, allowing layer‐by‐layer oxidation to proceed. The field‐effect‐transistor‐fabricated HfO2/HfSe2 gate stack demonstrates an almost ideal subthreshold slope (SS) of ≈61 mV dec−1 (over four orders of IDS) at room temperature (300 K), along with a high Ion/Ioff ratio of ≈108 and a small hysteresis of ≈10 mV. Furthermore, by utilizing a device architecture with separately controlled HfO2/HfSe2 gate stack and channel structures, an impact ionization field‐effect transistor is fabricated that exhibits n‐type steep‐switching characteristics with a SS value of 3.43 mV dec−1 at room temperature, overcoming the Boltzmann limit. These results provide a significant step toward the realization of post‐Si semiconducting devices for future energy‐efficient data‐centric computing electronics.
A high‐quality gate stack (native HfO2 on 2D HfSe2) is proposed for future low‐power computing applications. The proposed gate stack exhibits atomically sharp interface with suppressed gate leakage ensuring ideal operation (subthreshold slope (SS) ≈ 60 mV dec−1). Furthermore, steep‐switching operation (SS ≈ 3.43 mV dec−1) overcoming the fundamental Boltzmann limit is demonstrated at room temperature with gated‐region‐controlled structure.
The Third East‐Asia Microscopy Conference (EAMC3) Rhyu, Im Joo; Yang, Cheol‐Woong; Lee, Zonghoon
Microscopy research and technique,
January 2019, 2019-Jan, 2019-01-00, 20190101, Letnik:
82, Številka:
1
Journal Article
Abstract
Nd
2
Fe
14
B and Nd
2−x
Dy
x
Fe
14
B (x = 0.25, 0.50) particles were prepared by the modified co-precipitation followed by reduction–diffusion process. Bright field scanning transmission ...electron microscope (BF-STEM) image revealed the formation of Nd–Fe–B trigonal prisms in − 101 viewing zone axis, confirming the formation of Nd
2
Fe
14
B/Nd
2−x
Dy
x
Fe
14
B. Accurate site for the Dy substitution in Nd
2
Fe
14
B crystal structure was determined as “f” site by using high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It was found that all the “g” sites are occupied by the Nd, meanwhile Dy occupied only the “f” site. Anti-ferromagnetic coupling at “f” site decreased the magnetic moment values for Nd
1.75
Dy
0.25
Fe
14
B (23.48 μB) and Nd
1.5
Dy
0.5
Fe
14
B (21.03 μB) as compared to Nd
2
Fe
14
B (25.50 μB). Reduction of magnetic moment increased the squareness ratio, coercivity and energy product. Analysis of magnetic anisotropy at constant magnetic field confirmed that “f” site substitution did not change the patterns of the anisotropy. Furthermore, magnetic moment of Nd
2
Fe
14
B, Nd
2−x
Dy
x
Fe
14
B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0° and 180°.
Face masks will be used to prevent pandemic recurrence and outbreaks of mutant SARS-CoV-2 strains until mass immunity is confirmed. The polypropylene (PP) filter is a representative disposable mask ...material that traps virus-containing bioaerosols, preventing secondary transmission. In this study, a copper thin film (20 nm) was deposited via vacuum coating on a spunbond PP filter surrounding a KF94 face mask to provide additional protection and lower the risk of secondary transmission. Film adhesion was improved using oxygen ion beam pretreatment, resulting in cuprous oxide formation on the PP fiber without structural deformation. The copper-coated mask exhibited filtration efficiencies of 95.1 ± 1.32% and 91.6 ± 0.83% for NaCl and paraffin oil particles, respectively. SARS-CoV-2 inactivation was evaluated by transferring virus-containing media onto the copper-coated PP filters and subsequently adding Vero cells. Infection was verified using real-time polymerase chain reaction and immunochemical staining. Vero cells added after contact with the copper-coated mask did not express the RNA-dependent RNA polymerase and envelope genes of SARS-CoV-2. The SARS-CoV-2 nucleocapsid immunofluorescence results indicated a reduction in the amount of virus of more than 75%. Therefore, copper-coated antiviral PP filters could be key materials in personal protective equipment, as well as in air-conditioning systems.
The room-temperature charge carrier mobility and excitation–emission properties of metal halide perovskites are governed by their electronic band structures and intrinsic lattice phonon scattering ...mechanisms. Establishing how charge carriers interact within this scenario will have far-reaching consequences for developing high-efficiency materials for optoelectronic applications. Herein we evaluate the charge carrier scattering properties and conduction band environment of the double perovskite Cs2AgBiBr6 via a combinatorial approach; single crystal X-ray diffraction, optical excitation and temperature-dependent emission spectroscopy, resonant and nonresonant Raman scattering, further supported by first-principles calculations. We identify deep conduction band energy levels and that scattering from longitudinal optical phononsvia the Fröhlich interactiondominates electron scattering at room temperature, manifesting within the nominally nonresonant Raman spectrum as multiphonon processes up to the fourth order. A Fröhlich coupling constant nearing 230 meV is inferred from a temperature-dependent emission line width analysis and is found to be extremely large compared to popular lead halide perovskites (between 40 and 60 meV), highlighting the fundamentally different nature of the two “single” and “double” perovskite materials branches.
Graphite oxide (GO) samples were prepared by a simplified Brodie method. Hydroxyl, epoxide, carboxyl, and some alkyl functional groups are present in the GO, as identified by solid-state 13C NMR, ...Fourier-transform infrared spectroscopy, and X-ray photoemission spectroscopy. Starting with pyrolytic graphite (interlayer separation 3.36 Å), the average interlayer distance after 1 h of reaction, as determined by X-ray diffraction, increased to 5.62 Å and then increased with further oxidation to 7.37 Å after 24 h. A smaller signal in 13C CPMAS NMR compared to that in 13C NMR suggests that carboxyl and alkyl groups are at the edges of the flakes of graphite oxide. Other aspects of the chemical bonding were assessed from the NMR and XPS data and are discussed. AB stacking of the layers in the GO was inferred from an electron diffraction study. The elemental composition of GO prepared using this simplified Brodie method is further discussed.
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