Recrystallization of MBE‐Grown MoS2 Monolayers Induced by Annealing in a Chemical Vapor Deposition Furnace

A systematic study of MoS2 grown by a combination of physical vapor deposition and post-growth annealing treatment has been conducted. Hereby, MoS2 thin films with thicknesses between 1 and 2 layers are first grown on sapphire by molecular beam epitaxy at different growth temperatures and then transferred to S environment inside a tube furnace for an annealing process. Depending on the growth temperature, the as-grown layers are either amorphous or form a crystalline structure composed of closely packed nanometer-size grains. The annealing process leads to recrystallization of these layers significantly increasing the size of the MoS2 crystalline domains to the range of 50–100 nm. While the originally amorphous layer displays rotational domains after annealing, recrystallization of samples grown at high temperatures yields single crystalline layers. All samples display an increase of the crystallite dimension, which is accompanied by the disappearance of the defect-related peaks in the Raman spectra, sharpening of the excitonic signatures in absorption, and strong enhancement of the photoluminescence yield. The results represent a promising way to combine advantages of physical vapor deposition and a post-growth annealing in a chemical vapor deposition furnace toward fabrication of wafer-scale single crystalline transition metal dichalcogenide mono- and multilayer films on non-van der Waals substrates.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

GNN-SL: Sequence Labeling Based on Nearest Examples via GNN

To better handle long-tail cases in the sequence labeling (SL) task, in this work, we introduce graph neural networks sequence labeling (GNN-SL), which augments the vanilla SL model output with similar tagging examples retrieved from the whole training set. Since not all the retrieved tagging examples benefit the model prediction, we construct a heterogeneous graph, and leverage graph neural networks (GNNs) to transfer information between the retrieved tagging examples and the input word sequence. The augmented node which aggregates information from neighbors is used to do prediction. This strategy enables the model to directly acquire similar tagging examples and improves the general quality of predictions. We conduct a variety of experiments on three typical sequence labeling tasks: Named Entity Recognition (NER), Part of Speech Tagging (POS), and Chinese Word Segmentation (CWS) to show the significant performance of our GNN-SL. Notably, GNN-SL achieves SOTA results of 96.9 (+0.2) on PKU, 98.3 (+0.4) on CITYU, 98.5 (+0.2) on MSR, and 96.9 (+0.2) on AS for the CWS task, and results comparable to SOTA performances on NER datasets, and POS datasets.Comment: preprin

Y‐Stabilized ZrO2 as a Promising Wafer Material for the Epitaxial Growth of Transition Metal Dichalcogenides

Y-stabilized ZrO2 (YSZ) as a promising single-crystal wafer material for the epitaxial growth of transition metal dichalcogenides applicable for both physical (PVD) and chemical vapor deposition (CVD) processes is used. MoS2 layers grown on YSZ (111) exhibit sixfold symmetry and in-plane epitaxial relationship with the wafer of (1010) MoS2 || (211) YSZ. The PVD-grown submonolayer thin films show nucleation of MoS2 islands with a lateral size of up to 100 nm and a preferential alignment along the substrate step edges. The layers exhibit a strong photoluminescence yield as expected for the 2H-phase of MoS2 in a single monolayer limit. The CVD-grown samples are composed of triangular islands of several micrometers in size in the presence of antiparallel domains. The results represent a promising route toward fabrication of wafer-scale single-crystalline transition metal dichalcogenide layers with a tunable layer thickness on commercially available wafers.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Interreg http://dx.doi.org/10.13039/100013276Peer Reviewe

Atomic Layer Deposition of MoS2 Decorated TiO2 Nanotubes for Photoelectrochemical Water Splitting

A thermal atomic layer deposition (ALD) process to fabricate MoS2 thin films is successfully demonstrated by using cycloheptatriene molybdenum tricarbonyl (C7H8Mo(CO)3) and H2S as precursors at an ALD temperature below 300 °C. The process is systematically investigated, showing a typical self‐limiting characteristic within an ALD temperature window of 225–285 °C and a high growth‐per‐cycle of 0.11 nm. The as‐deposited films are amorphous while they can be crystallized in situ by sulfurization with H2S at a low temperature of 300 °C. A prototypical application of the developed ALD process is demonstrated by constructing a MoS2/TiO2 heterostructure through depositing MoS2 onto anodized TiO2 nanotubes for photoelectrochemical water splitting. The MoS2/TiO2 heterostructures exhibit approximately three times superior photoelectrochemical performance than the pristine TiO2 nanotubes. This is attributed to an enhanced visible light‐harvesting ability of MoS2 and an improved separation of the photo‐generated charge carriers at the heterostructure interface, which is affirmed by a staggering gap (type II) between MoS2 and TiO2 as probed by ultraviolet photoelectron spectroscopy.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Correlating Heteroatoms Doping, Electronic Structures, and Photocatalytic Activities of Single‐Atom‐Doped Ag25(SR)18 Nanoclusters

Atomic‐level manipulation of catalysts is important for both fundamental studies and practical applications. Here, the central metal atom in an atomically precise Ag25 nanocluster (NC) is replaced with a single Pd, Pt, and Au atom, respectively, and employed as a model system to study the structure–property–activity relationship at the atomic level. While the geometric structures are well‐preserved after doping, the electronic structures of Ag25 NCs are significantly altered. The combination of Ag25 and TiO2 enhances the charge separation at the interface, exhibiting a 10 times higher hydrogen production rate in photocatalytic hydrogen evolution reaction compared to bare TiO2. Further results show that heteroatoms doping has a negative impact on performance, particularly in the cases of Pd and Au doping. Ultraviolet photoelectron spectroscopy measurements and density functional theory calculations suggest that the lower activities are due to an energy mismatch between the levels of doped NCs and TiO2. These findings not only reveal the impact of heteroatoms doping on the electronic properties and photocatalytic activities of NCs, but can also guide the design of heterometallic NCs for photocatalytic applications

Incidence and risk factors for AIDS-related mortality in HIV patients in China: a cross-sectional study

BACKGROUND: To estimate the incidence and risk factors for mortality in HIV-1-infected patients in China. METHODS: Information on AIDS-related deaths was collected from the Chinese Center for Disease Control and Prevention’s Disease Surveillance Information Reporting System and AIDS Prevention and Control Information System. RESULTS: A total of 379,348 HIV cases were recorded in the databases from 2006. Among those, 138,288 patients were reported as having developed AIDS and 72,616 (19%) died of AIDS after data was extracted from the databases in January 2011. Mortality was higher among those patients aged 50 years old or older (AOR: 3.41, CI: 1.47-7.91) who had been infected by intravenous drug use (AOR: 1.65, CI: 1.28-2.14) or blood transfusion/donation (AOR: 2.18: 1.18-3.99). Compared to patients who had not initiated highly active antiretroviral therapy (HAART), those who had initiated HAART were more likely to have a long interval of time between infection confirmation and AIDS-related death. CONCLUSIONS: The effective reduction of AIDS mortality could be improved through timely treatment

Microstructural Evolution in Chroming Coatings Friction Pairs under Dry Sliding Test Conditions

The microstructures of subsurface layers of 20CrMnTi steel pins against chroming and nonchroming T10 under dry sliding tests were studied by means of OM (optical microscopy), XRD (X-ray diffraction), and SEM (scanning electron microscopy). Results showed that the chroming coating strengthened the disc surface and significantly affected microstructural evolution. Three layers—the matrix, deformation layer (DL), and surface layer (SL)—formed in 20CrMnTi for the chroming T10. The matrix and deformation layer (DL) formed in 20CrMnTi for the nonchroming T10. The formation of the microstructure was considered as a result of the shear deformation

Correlating Heteroatoms Doping, Electronic Structures, and Photocatalytic Activities of Single‐Atom‐Doped Ag25(SR)18 Nanoclusters

Atomic‐level manipulation of catalysts is important for both fundamental studies and practical applications. Here, the central metal atom in an atomically precise Ag25 nanocluster (NC) is replaced with a single Pd, Pt, and Au atom, respectively, and employed as a model system to study the structure–property–activity relationship at the atomic level. While the geometric structures are well‐preserved after doping, the electronic structures of Ag25 NCs are significantly altered. The combination of Ag25 and TiO2 enhances the charge separation at the interface, exhibiting a 10 times higher hydrogen production rate in photocatalytic hydrogen evolution reaction compared to bare TiO2. Further results show that heteroatoms doping has a negative impact on performance, particularly in the cases of Pd and Au doping. Ultraviolet photoelectron spectroscopy measurements and density functional theory calculations suggest that the lower activities are due to an energy mismatch between the levels of doped NCs and TiO2. These findings not only reveal the impact of heteroatoms doping on the electronic properties and photocatalytic activities of NCs, but can also guide the design of heterometallic NCs for photocatalytic applications.Heteroatoms doping alters the electronic structures of Ag25 nanoclusters (NCs), while keeping the geometric structures unchanged. In this way, the geometrical effects and the electronic effects are clearly distinguished. The photocatalytic activities of as‐prepared NCs deposited onto TiO2 are investigated. The performances follow the order of Ag25 ≥ PtAg24 > PdAg24 ≥ AuAg24. image © 2023 WILEY‐VCH GmbHDFG http://dx.doi.org/10.13039/501100001659China Scholarship Council http://dx.doi.org/10.13039/501100004543Peer Reviewe

GPT-NER: Named Entity Recognition via Large Language Models

Despite the fact that large-scale Language Models (LLM) have achieved SOTA performances on a variety of NLP tasks, its performance on NER is still significantly below supervised baselines. This is due to the gap between the two tasks the NER and LLMs: the former is a sequence labeling task in nature while the latter is a text-generation model. In this paper, we propose GPT-NER to resolve this issue. GPT-NER bridges the gap by transforming the sequence labeling task to a generation task that can be easily adapted by LLMs e.g., the task of finding location entities in the input text "Columbus is a city" is transformed to generate the text sequence "@@Columbus## is a city", where special tokens @@## marks the entity to extract. To efficiently address the "hallucination" issue of LLMs, where LLMs have a strong inclination to over-confidently label NULL inputs as entities, we propose a self-verification strategy by prompting LLMs to ask itself whether the extracted entities belong to a labeled entity tag. We conduct experiments on five widely adopted NER datasets, and GPT-NER achieves comparable performances to fully supervised baselines, which is the first time as far as we are concerned. More importantly, we find that GPT-NER exhibits a greater ability in the low-resource and few-shot setups, when the amount of training data is extremely scarce, GPT-NER performs significantly better than supervised models. This demonstrates the capabilities of GPT-NER in real-world NER applications where the number of labeled examples is limited

Laser-Like Emission from a Sandwiched MoTe2 Heterostructure on a Silicon Single-Mode Resonator

Molybdenum ditelluride (MoTe2) has recently shown promise as a gain material for silicon photonics. Reliable single-mode operation and material stability remain two of the major issues that need to be addressed to advance this exciting technology, however. Here, laser-like emission from a sandwiched MoTe2 heterostructure on a silicon single-mode resonator is reported. The heterostructure consists of a layer of MoTe2 sandwiched between thin films of hexagonal boron nitride. It is known that tellurium compounds are sensitive to oxygen exposure, which leads to rapid degradation of the exposed layers in air. By encapsulating the MoTe2 gain material, much improved environmental stability is observed. Using a recently introduced single-mode resonator design, better control over the mode spectrum of the cavity is exercised and single-mode operation with a wide free spectral range is demonstrated. At room temperature, a Q-factor of 4500 and a threshold of 4.2 kW cm−2 at 1319 nm wavelength are achieved. These results lend further support to the paradigm of 2D material-based integrated light sources on the silicon platform