Search query: NbS2 high pressue

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abstract: Exploring two dimensional (2D) crystals with intrinsic room temperature magnetism is of particular importance to develop practical spintronics applications at the nanoscale. Here, we report the electronic and magnetic properties of a freestanding 2D NbS2 crystal on the basis of first principles calculations. Our results demonstrate that the 2D NbS2 monolayer is a bipolar magnetic semiconductor with a spin bandgap of 0.27 eV by using the screened hybrid density functional HSE06 method. In particular, both electron and hole doping could induce the transition from a bipolar magnetic semiconductor to a half metal in NbS2 nanosheets, where the spin polarization direction of carriers in half metallic NbS2 nanosheets can be tuned with the doping type. The Monte Carlo simulation predicts a Curie temperature of over 141 K in the 2D NbS2 crystal, which can be enhanced up to 273 K by hole doping or applying a biaxial tensile strain. These findings imply the great potential of 2D NbS2 nanosheets in nanoscale spintronics applications.
author_names: Ying-jie Sun

Zhiwen Zhuo

Xiaojun Wu
title: Bipolar magnetism in a two dimensional NbS2 semiconductor with high Curie temperature
year: 2018

abstract: Lithium sulfur batteries practically suffer from short cycling life, low sulfur utilization, and safety concerns, particularly at ultrahigh rates and high sulfur loading. To address these problems, we have designed and synthesized a ternary NbS2@S@IG composite consisting of sandwich type NbS2@S enveloped by iodine doped graphene (IG) The sandwich type structure provides an interconnected conductive network and plane to point intimate contact between layered NbS2 (or IG) and sulfur particles, enabling sulfur species to be efficiently entrapped and utilized at ultrahigh rates, while the structural integrity is well maintained. NbS2@S@IG exhibits prominent high power charge/discharge performances. Reversible capacities of 195, 107, and 74 mA h g 1 (1.05 mg cm 2) have been achieved after 2000 cycles at ultrahigh rates of 20, 30, and 40 C, respectively, and the corresponding average decay rates per cycle are 0.022% 0.031% and 0.033% respectively. When the area sulfur loading is increased to 3.25 mg cm 2, the electrode still maintains a high discharge capacity of 405 mAh g 1 after 600 cycles at 1 C. Three half cells in series assembled with NbS2@S@IG can drive 60 indicators of LED modules after only 18 s of charging. The instantaneous current and power of the device reach 196.9 A g 1 and 1369.7 W g 1, respectively.
author_names: Zhubing Xiao

Zhi Yang

Linjie Zhang

Hui Pan

Ruihu Wang
title: Sandwich Type NbS2@S@I Doped Graphene for High Sulfur Loaded, Ultrahigh Rate, and Long Life Lithium Sulfur Batteries.
venue: ACS nano
year: 2017

abstract: Despite intense efforts on all known quasi two dimensional superconductors, the origin and exact boundary of the electronic orderings, particularly charge density waves and superconductivity, are still attractive problems with several open questions. Here, in order to reveal how the superconducting gap evolves, we report on high quality complementary measurements of magneto optical imaging, specific heat, magnetic susceptibility, resistivity measurements, Andreev spectroscopy, and London penetration depth \ensuremath{\lambda}}_{ab}(T) measurements supplemented with theoretical calculations for $2\mathrm{H}\text{\ensuremath{ \mathrm{Nb}\mathrm{Se}}_{2} and $2\mathrm{H}\text{\ensuremath{ \mathrm{Nb}\mathrm{S}}_{2} single crystals. The temperature dependence of \ensuremath{\lambda}}_{ab}(T) calculated from the lower critical field and Andreev spectroscopy can be well described by using a two band model with $s$ wave like gaps. The effect of pressure on the superconducting gap of both systems illustrates that both bands are practically affected. Upon compression, the Fermi surfaces do not change significantly, and the nesting remains almost unaffected compared to that at ambient condition. However, a strong bending in the upper critical fields {H}_{\mathrm{c}2} curves is obtained under pressure and support the presence of a strong Pauli paramagnetic effect. In \mathrm{Nb}\mathrm{Se}}_{2} using a two band model with $s$ wave like gaps, the temperature dependence {H}_{\mathrm{c}2}(T) can be properly described. In contrast to that, the behavior of {H}_{\mathrm{c}2} for \mathrm{Nb}\mathrm{S}}_{2} is ruled by the spin paramagnetic effect. The estimated values of the penetration depth at $T=0\phantom{\rule{0.16em}{0ex}\mathrm{K} confirm that \mathrm{Nb}\mathrm{Se}}_{2} and \mathrm{Nb}\mathrm{S}}_{2} superconductors depart from a Uemura style relationship between {T}_{\mathrm{c} with \mathbit{\ensuremath{\lambda}}_{ab}\ensuremath{ }2}(T) the in plane superconducting penetration depth.
author_names: Arnab Majumdar

Derrick VanGennep

Jeremy Brisbois

Dmitriy A Chareev

Andrey V Sadakov

A S Usoltsev

M Mito

Alejandro V Silhanek

Tapati Sarkar

Abdelwahab Hassan

Olof Karis

Rajeev Ahuja

Mahmoud M Abdel-Hafiez
title: Interplay of charge density wave and multiband superconductivity in layered quasi two dimensional materials: The case of 2H NbS2 and 2H NbSe2
venue: Physical Review Materials
year: 2020

abstract: In all known Group 5 transition metal dichalcogenide monolayers (MLs) the metal centers carry a spin, and their ground state phases are either metallic or semiconducting with indirect band gaps. Here, on grounds of first principles calculations, we report that the Haeckelite polytypes 1S NbX2 (X=S, Se, Te) are diamagnetic direct band gap semiconductors even though the Nb atoms are in the 4+ oxidation state. In contrast, 1S VX2 MLs are antiferromagnetically coupled indirect band gap semiconductors. The 1S phases are thermodynamically and dynamically stable but of slightly higher energy than their 1H and 1T ML counterparts. 1S NbX2 MLs are excellent candidates for optoelectronic applications owing to their small band gaps (between 0.5 and 1 eV) Moreover, 1S NbS2 shows a particularly high hole mobility of 2.68x103 cm2 V 1 s 1 which is significantly higher than that of MoS2 and comparable to that of WSe2
author_names: Yandong Ma

Agnieszka Beata Kuc

Yu Jing

Pierre Herman Theodoor Philipsen

Thomas Heine
title: Two Dimensional Haeckelite NbS2 A Diamagnetic High Mobility Semiconductor with Nb4+ Ions.
venue: Angewandte Chemie
year: 2017

abstract: Two dimensional (2D) heterostructures based on layered transition metal dichalcogenides (TMDs) have attracted increasing attention for the applications of the next generation high performance integrated electronics and optoelectronics. Although various TMD heterostructures have been successfully fabricated, epitaxial growth of such atomically thin metal semiconductor heterostructures with a clean and sharp interface is still challenging. In addition, photodetectors based on such heterostructures have seldom been studied. Here, we report the synthesis of high quality vertical NbS2/MoS2 metallic semiconductor heterostructures. By using NbS2 as the contact electrodes, the field effect mobility and current on off ratio of MoS2 can be improved at least 6 fold and two orders of magnitude compared with the conventional Ti/Au contact, respectively. By using NbS2 as contact, the photodetector performance of MoS2 is much improved with higher responsivity and less response time. Such facile synthesis of atomically thin metal semiconductor heterostructures by a simple chemical vapor deposition strategy and its effectiveness as ultrathin 2D metal contact open the door for the future application of electronics and optoelectronics.
author_names: P Zhang

Ce Bian

Jiafu Ye

Ningyan Cheng

Xiao Wang

Huaning Jiang

Yi Wei

Yiwei Zhang

Yi Du

Lihong Bao

Weida Hu

Yongji Gong
title: Epitaxial growth of metal semiconductor van der Waals heterostructures NbS2/MoS2 with enhanced performance of transistors and photodetectors
venue: Science China Materials
year: 2020

abstract: The relatively high recombination rate of charges remains the most critical limiting factor for solar driven water splitting for hydrogen generation. Herein, a tandem 0D/2D/2D NbS2 quantum dot/Nb2 O5 nanosheet/g C3 N4 flake (NSNOCN) system is designed. Owing to the unique spatial arrangement and elaborate morphology of 0D NbS2 2D Nb2 O5 and 2D g C3 N4 in the newly designed NSNOCN, plenty of spatial charge transfer cascades from g C3 N4 to NbS2 via Nb2 O5 are formed to accelerate separation and transfer of charges significantly, thus contributing to a high photocatalytic H2 generation rate of 13.99 mmol h 1 g 1 (an apparent quantum efficiency of 10.8% at 420 nm) up to 107.6 and 43.7 times by contrast with that of g C3 N4 and Nb2 O5 respectively. This work can provide a new platform in the design of artificial photocatalytic systems with high charge transfer efficiency.
author_names: Bo Lin

Zihao Chen

Pin Song

Haishi Liu

Lixing Kang

Jun Di

Xiao Luo

Longqing Chen

Chao Xue

Bowen Ma

Guidong Yang

Jun Tang

Jiadong Zhou

Zheng Liu

Fucai Liu
title: A Tandem 0D/2D/2D NbS2 Quantum Dot/Nb2 O5 Nanosheet/g C3 N4 Flake System with Spatial Charge Transfer Cascades for Boosting Photocatalytic Hydrogen Evolution.
venue: Small
year: 2020

abstract: There is an urgent need to develop efficient and nonprecious electrode materials for practical electrocatalyst hydrogen evolution reaction (HER) application to restrain the depletion of fossil fuels. In the present work, we report an efficient and cost effective electrode with high stability for binder free water electrolysis under all ranges of pH from 0 to 14. Herein, a two dimensional (2D) heterostructure of NbS2/MoS2 ultrathin vertical nanosheets was grown on carbon nanofiber with a high aspect ratio by the one step chemical vapor deposition approach. The resultant hybrid catalyst demonstrates superlative HER performance with a small onset potential (41 mV 0 pH, 22 mV 7 pH and 32 mV 14 pH) and a very low overpotential (0.23 V 0 pH, 0.21 V 7 pH and 0.33 V 14 pH to reach 50 mA/cm2) vs reversible hydrogen electrode (RHE) Besides, the fabricated NbS2/MoS2 CNF displays excellent chronoamperometry stability for more than 50 h in all pH ranges. The proposed heterostructure holds the vital prerequisites for being a significant electrode material owing to multiple HER active edge and planar sulfur sites, excellent barrier free charge transfer ability toward the electrolyte, and impressive endurance. Overall, the 2D/one dimensional (1D) hybrid heterostructure appeared to be a precious metal free flexible electrode for excellent HER performance under wide ranges of pH for water splitting applications.
author_names: Paulraj Gnanasekar

Kugalur Shanmugam Ranjith

Palanisamy Manivel

Young-Kyu Han

Jeganathan Kulandaivel
title: Hierarchical NbS2/MoS2 Carbon Nanofiber Electrode for Highly Efficient and Stable Hydrogen Evolution Reaction at All Ranges of pH
year: 2020

abstract: We present magnetic torque, specific heat and thermal expansion measurements combined with a piezo rotary positioner of the bulk transition metal dichalcogenide (TMD) superconductor NbS2 in high magnetic fields applied strictly parallel to its layer structure. The upper critical field of superconducting TMDs in the 2D form is known to be dramatically enhanced by a special form of Ising spin orbit coupling. This Ising superconductivity is very robust against the Pauli limit for superconductivity. We find that superconductivity beyond the Pauli limit still exists in bulk single crystals of NbS2. However, the comparison of our upper critical field transition line with numerical simulations rather points to the development of a Fulde Ferrell Larkin Ovchinnikov state above the Pauli limit as a cause. This is also consistent with the observation of a magnetic field driven phase transition in the thermodynamic quantities within the superconducting state near the Pauli limit.
author_names: Chang-Woo Cho

Jian Lyu

Cheuk Yin Ng

James Jun He

T A Abdel-Baset

Mahmoud M Abdel-Hafiez

Rolf Lortz
title: Superconductivity beyond Pauli's limit in bulk NbS2: Evidence for the Fulde Ferrell Larkin Ovchinnikov state
year: 2020

abstract: The understanding of the nonlinear optical (NLO) properties of photonic materials is relevant and necessary for basic studies and technological developments. Among the materials with high optical n.
author_names: Melissa Maldonado

Manoel L da Silva Neto

Pilar Gregory Vianna

Henrique B Ribeiro

Vanessa Orsi Gordo

Isabel C S Carvalho

Leonardo de S Menezes

Cid B de Araujo

Christiano J S de Matos

Leandro Seixas

Ali Jawaid

Robert Busch

Allyson J Ritter

Richard A Vaia

Anderson S L Gomes
title: Femtosecond Nonlinear Optical Properties of 2D Metallic NbS2 in the Near Infrared
year: 2020

abstract: In recent days, 2 dimensional (2D) niobium disulphide (NbS2) with the near zero Gibbs free energy and superlative acid electrolyte stability has provoked a great deal of interest towards hydrogen evolution reaction (HER) electrocata lyst due to its active basal and edge sulphur sites. Here in, we developed a single step method for the direct deposition of 2D NbS2 on high aspect ratio topographies of silicon nanowires (NWs) by chemical vapor deposition for the appli cations in HER electrocatalyst. The resultant 2D NbS2 electrocatalyst demonstrates the HER overpotential of ~74mV vs. RHE (reversible hydrogen electrode) 1 mA/cm2 under acidic conditions and stable for more than 20 hours. More importantly, we developed the Si NWs array based photoelectrochemical water splitting system with the direct deposi tion of 2D NbS2 as HER catalyst. The resultant 2D NbS2 Si NWs photocathode system demonstrates improved charge transfer characteristics at the Si NbS2 interfaces that leads to an enhanced turn on potential (from 0.06 V to 0.34 V vs. RHE) with the current density of 28 mA/cm2 at the 0 V vs. RHE. The results evidence the synergistic effect of 2D NbS2 electrocatalysts that addresses poor surface kinetics of Si towards solar water electrolysis. Our comprehensive studies reveal that NbS2 as a new class of photoelectrochemical co catalyst for efficient solar HER performance by promoting the charge transfer process with prolonged acid stability.
author_names: Paulraj Gnanasekar

Dharmaraj Periyanagounder

Purushothaman Varadhan

Jr-hau He

Jeganathan Kulandaivel
title: Highly efficient and stable photoelectrochemical hydrogen evolution with 2D NbS2 /Si nanowire heterojunction.
venue: ACS applied materials interfaces
year: 2019