1,494 research outputs found
Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations
Although many prototype devices based on two-dimensional (2D) MoS2 have been
fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental
nature of 2D MoS2-metal contacts has not been well understood yet. We provide a
comprehensive ab initio study of the interfacial properties of a series of
monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt,
Ni, and Au). A comparison between the calculated and observed Schottky barrier
heights (SBHs) suggests that many-electron effects are strongly suppressed in
channel 2D MoS2 due to a charge transfer. The extensively adopted energy band
calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc
interface. By contrast, an ab initio quantum transport device simulation better
reproduces the observed SBH in the two types of contacts and highlights the
importance of a higher level theoretical approach beyond the energy band
calculation in the interface study. BL MoS2-metal contacts have a reduced SBH
than ML MoS2-metal contacts due to the interlayer coupling and thus have a
higher electron injection efficiency.Comment: 36 pages, 13 figures, 3 table
Mass-Producible 2D-MoS2âImpregnated Screen-Printed Electrodes
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
ACS Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acsami.7b05104Two-dimensional molybdenum disulfide (2D-MoS2) screen-printed electrodes (2D-MoS2-SPEs) have been designed, fabricated, and evaluated toward the electrochemical oxygen reduction reaction (ORR) within acidic aqueous media. A screen-printable ink has been developed that allows for the tailoring of the 2D-MoS2 content/mass used in the fabrication of the 2D-MoS2-SPEs, which critically affects the observed ORR performance. In comparison to the graphite SPEs (G-SPEs), the 2D-MoS2-SPEs are shown to exhibit an electrocatalytic behavior toward the ORR which is found, critically, to be reliant upon the percentage mass incorporation of 2D-MoS2 in the 2D-MoS2-SPEs; a greater percentage mass of 2D-MoS2 incorporated into the 2D-MoS2-SPEs results in a significantly less electronegative ORR onset potential and a greater signal output (current density). Using optimally fabricated 2D-MoS2-SPEs, an ORR onset and a peak current of approximately +0.16 V [vs saturated calomel electrode (SCE)] and â1.62 mA cmâ2, respectively, are observed, which exceeds the â0.53 V (vs SCE) and â635 ÎŒA cmâ2 performance of unmodified G-SPEs, indicating an electrocatalytic response toward the ORR utilizing the 2D-MoS2-SPEs. An investigation of the underlying electrochemical reaction mechanism of the ORR within acidic aqueous solutions reveals that the reaction proceeds via a direct four-electron process for all of the 2D-MoS2-SPE variants studied herein, where oxygen is electrochemically favorably reduced to water. The fabricated 2D-MoS2-SPEs are found to exhibit no degradation in the observed achievable current over the course of 1000 repeat scans. The production of such inks and the resultant mass-producible 2D-MoS2-SPEs mitigates the need to modify post hoc an electrode via the drop-casting technique that has been previously shown to result in a loss of achievable current over the course of 1000 repeat scans. The 2D-MoS2-SPEs designed, fabricated, and tested herein could have commercial viability as electrocatalytic fuel cell electrodes because of being economical as a result of their scales of economy and inherent tailorability. The technique utilized herein to produce the 2D-MoS2-SPEs could be adapted for the incorporation of different 2D nanomaterials, resulting in SPEs with the inherent advantages identified above
2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction
We explore the use of two-dimensional (2D) MoS2 nanosheets as an electro-catalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electro-catalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underling support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrodes individual electron transfer kinetics/properties. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER
Biosensors based on two-dimensional MoS2
The unique properties of two-dimensional molybdenum disulfide (2D MoS2) have so far led to immense research regarding this material's fundamentals, applications, and, more recently, its potential for biosensing. 2D MoS2 has properties that make it of great interest for developing biosensors. These properties include large surface area, tunable energy band diagrams, a comparatively high electron mobility, photoluminescence, liquid media stability, relatively low toxicity, and intercalatable morphologies. In this Review, the current progress on 2D MoS2 based biosensors is presented and the prospects for future possibilities of expanding its applications for a variety of biosensing applications are discussed
Tunable Magnetic Properties of Transition Metal Doped MoS\u3csub\u3e2\u3c/sub\u3e
We report a detailed investigation of the electronic and magnetic properties of the transition metal (TM) doped two-dimensional (2D) MoS2 using ab initio calculations. The doping is achieved by substituting two or more Mo atoms by TM atoms of the 3d series. Additionally, the effect of codoping on the 2D MoS2 by cation-cation and cation-anion pairs is also investigated. Our results demonstrate that the TM doping of 2D MoS2 leads to a significant reduction of the energy gap and the appearance of magnetic features whose major characteristic is the ferromagnetic coupling of the TM dopants. The latter is found to be significantly enhanced by codoping as demonstrated by codoping with (Co,Cu), (Ni,Cu), (Mn,Cu), and (Mn,Sb) codopant pairs
Dense MoS2 MicroâFlowers Planting on BiomassâDerived Carbon Fiber Network for Multifunctional Sulfur Cathodes
The significant challenge in lithiumâsulfur batteries (LSBs) arises from low conductivity of sulfur cathode, loss of active sulfur species due to less anchoring sites and sluggish redox kinetics of lithium polysulfides (LPSs). Herein, the dense MoS2 microâflowers assembled by crossâlinked 2D MoS2 nanoflakes planting on biomassâderived carbon fiber (CF) network (MoS2/CFs) are fabricated as multifunctional sulfur cathodes of LSBs. The 2D MoS2 nanoflakes supported on CF provide abundant anchoring sites for strong adsorption, while the 3D flowerlike structure prevents lamellar aggregation of 2D MoS2 nanoflakes. Importantly, the dense MoS2 microâflowers planting on the network weaved by biomassâderived CFs ensures the high electronic conductivity of the MoS2/CFs composite, sufficient electrode/electrolyte interaction, fast electron and Li+ transportation. Moreover, the CF network weaved from costâeffective tissue paper reduces the cost of LSBs. Thus, the SâMoS2/CFs cathode exhibits a high rate capability (1149 and 608â
mA h gâ1 are obtained at 0.2â
C and 4â
C, respectively), excellent cyclic performance with âŒ75% capacity retention and 99% Coulombic efficiency at 2â
C after 500 cycles, corresponding to âŒ0.05% capacity fading per cycle only, as well as structure integrity during the discharge/charge process.800 Dong Chuan Road, Minhang District, Shanghai 200240, ChinaA novel, costâeffective, dense 3 D MoS2 microâflowers assembled by crossâlinked 2D MoS2 nanoflakes planting on biomassâderived carbon fiber (CF) network (MoS2/CFs) are fabricated as multifunctional sulfur cathodes of LSBs. The 2D MoS2 nanoflakes provide abundant anchoring sites for strong adsorption, while the 3D flowerlike structure prevents lamellar aggregation of 2D MoS2 nanoflakes. Significantly, the dense MoS2 microâflowers supported on carbon fibers ensures the high electronic conductivity of the MoS2/CFs composite, sufficient electrode/electrolyte interaction, fast electron and Li+ transportation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155938/1/slct202001729-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155938/2/slct202001729_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155938/3/slct202001729.pd
Broadband and Tunable Light Harvesting in Nanorippled MoS2 Ultrathin Films
Nanofabrication of flat optic silica gratings conformally layered with two-dimensional (2D) MoS2 is demonstrated over large area (cm2), achieving a strong amplification of the photon absorption in the active 2D layer. The anisotropic subwavelength silica gratings induce a highly ordered periodic modulation of the MoS2 layer, promoting the excitation of Guided Mode Anomalies (GMA) at the interfaces of the 2D layer. We show the capability to achieve a broadband tuning of these lattice modes from the visible (VIS) to the near-infrared (NIR) by simply tailoring the illumination conditions and/or the period of the lattice. Remarkably, we demonstrate the possibility to strongly confine resonant and nonresonant light into the 2D MoS2 layers via GMA excitation, leading to a strong absorption enhancement as high as 240% relative to a flat continuous MoS2 film. Due to their broadband and tunable photon harvesting capabilities, these large area 2D MoS2 metastructures represent an ideal scalable platform for new generation devices in nanophotonics, photo- detection and -conversion, and quantum technologies
Acoustic phonon limited mobility in two-dimensional semiconductors: Deformation potential and piezoelectric scattering in monolayer MoS2 from first principles
We theoretically study the acoustic phonon limited mobility in n-doped
two-dimensional MoS2 for temperatures T < 100 K and high carrier densities
using the Boltzmann equation and first-principles calculations of the acoustic
electron-phonon (el-ph) interaction. In combination with a continuum elastic
model, analytic expressions and the coupling strengths for the deformation
potential and piezoelectric interactions are established. We furthermore show
that the deformation potential interaction has contributions from both normal
and umklapp processes and that the latter contribution is only weakly affected
by carrier screening. Consequently, the calculated mobilities show a transition
from a high-temperature \mu T^{-1} behavior to a stronger \mu T^{-4} behavior
in the low-temperature Bloch-Gruneisen regime characteristic of unscreened
deformation potential scattering. Intrinsic mobilities in excess of 10^5 cm^2
V^{-1} s^{-1} are predicted at T 10^{11}
cm^{-2}). At 100 K, the mobility does not exceed ~7 x 10^3 cm2 V^{-1} s^{-1}.
Our findings provide new and important understanding of the acoustic el-ph
interaction and its screening by free carriers, and is of high relevance for
the understanding of acoustic phonon limited mobilities in general.Comment: Substantially revised version. 17 pages, 11 figure
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