Search query: CrSbS3 monolayer a potential phase

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abstract: Two dimensional intrinsic ferromagnetic semiconductors with controllable magnetic phase transition are highly desirable for spintronics. Nevertheless, reports on their successful experimental realization are still rare. Herein, based on first principles calculations, we propose to achieve such a functional material, namely CrSbS3 monolayer by exfoliating from its bulk crystal. Intrinsic CrSbS3 monolayer is a ferromagnetic half semiconductor with a moderate bandgap of 1.90 eV. It features an intriguing magnetic phase transition from ferromagnetic to antiferromagnetic when applying a small compressive strain ~2% making it ideal for fabricating strain controlled magnetic switches or memories. In addition, the predicted strong anisotropic absorption of visible light and small effective masses make the CrSbS3 monolayer promising for optoelectronic applications.
author_names: Jinlong Yang
title: CrSbS3 monolayer: a potential phase transition ferromagnetic semiconductor.
venue: Nanoscale
year: 2021

abstract: We have used molecular simulation with two intermolecular potential models, TraPPE UA and TraPPE EH, the latter of which accounts for the tetrahedral shape, to study the effects of shape on methane adsorption on graphite. Both models give good descriptions of the vapour liquid equilibria in the bulk phase, but adsorption on graphite is better described by the TraPPE EH model. Molecular configurations in the monolayer, show the variation with temperature of the registry sites for the carbon and hydrogen atoms of the methane molecules. At temperatures below 70 K, the centre of mass (COM) of the molecules is in registry with the centre of the carbon hexagons. For temperatures above 70 K, a commensurate monolayer is initially formed as at low temperatures, then as the loading is increased the first layer remains in registry, but the COM of the methane molecules in the first layer shifts to the top of the graphite carbon atoms with the C H bond pointing to carbon atoms in the second shell of a C hexagon. At temperatures above 93 K, the first adsorbate layer goes through these two commensurate states and then undergoes a transition to an incommensurate solid. Finally, for temperatures greater than 110 K methane behaves like a pseudo spherical molecule.
author_names: Han Zhang

Shiliang Johnathan Tan

Luisa Prasetyo

Duong D Do

David A Nicholson
title: A simulation study of the low temperature phase diagram of the methane monolayer on graphite: a test of potential energy functions.
venue: Physical chemistry chemical physics PCCP
year: 2020

abstract: Transition metal dichalcogenides (TMDs) exist in various crystal structures with semiconducting, semi metallic, and metallic properties. The dynamic control of these phases is of immediate interest for next generation electronics such as phase change memories. Of the binary Mo and W based TMDs, MoTe2 is attractive for electronic applications because it has the lowest energy difference (40 meV) between the semiconducting (2H) and semi metallic (1T' phases, allowing for MoTe2 phase change by electrostatic doping. Here we report phase change between the 2H and 1T' polymorphs of MoTe2 in thicknesses ranging from the monolayer to bulk like case (73 nm) using an ionic liquid electrolyte at room temperature and in air. We find consistent evidence of a partially reversible 2H 1T' transition using in situ Raman spectroscopy where the phase change occurs in the top most layers of the MoTe2 flake. We find a thickness dependent transition voltage where higher voltages are necessary to drive the phase change for thicker flakes. We also show evidence of electrochemical activity during the gating process by observation of Te metal formation. This finding suggests the formation of Te vacancies which have been reported to lower the energy difference between the 2H and 1T' phase, potentially aiding the phase change process. Our discovery that the phase change can be achieved on the surface layer of bulk like materials reveals that this electrochemical mechanism does not require isolation of a single layer and the effect may be more broadly applicable than previously thought.
author_names: Dante Zakhidov

Daniel A Rehn

Evan J Reed

Alberto Salleo
title: Reversible Electrochemical Phase Change in Monolayer to Bulk Like MoTe2 by Ionic Liquid Gating.
venue: ACS nano
year: 2020

abstract: In this paper, we report a simulation study of the effect of the herringbone orientational phase transition on the isosteric heat of adsorption and the heat capacity of the nitrogen adsorption monolayer on graphite surface. We use the previously proposed regression equations of state for phases with the short and long ranged orientational ordering (Ustinov et al. in J Phys Chem C 122:2897 2908, 2018) The proposed approach allows one to give an exhaustive thermodynamic description of the isobaric phase transition without direct estimation of the chemical potential, using only the pVT data obtained in a canonical Monte Carlo simulation. The herringbone orientational phase transition is indicated by a peak in the temperature dependence of the heat capacity. Its height and shape is close to those observed experimentally. In addition, the heat spike is observed on the isosteric heat curves near the transition region. It decreases with increasing temperature and completely disappears at a temperature close to the melting point in the gas crystal system. A combined analysis of the heat capacity and isosteric heat of adsorption demonstrates that the nitrogen monolayer on graphite surface has similar features inherent in a three dimensional system and, therefore, the translational and rotational degrees of freedom normal to the surface are involved in the mechanism of the long to short ranged orientational transition.
author_names: Sergey S Akimenko

Vitaly A Gorbunov

Eugene A Ustinov
title: Heat capacity and heat of adsorption at orientational phase transition in nitrogen monolayer on graphite
venue: Adsorption
year: 2019

abstract: In this work a vapor phase assisted approach for the synthesis of monolayer MoS2 is demonstrated, based on the sulfurization of thin MoO3 x precursor films in an H2S atmosphere. We discuss the co existence of various possible growth mechanisms, involving solid gas and vapor gas reactions. Different sequences were applied in order to control the growth mechanism and to obtain monolayer films. These variations include the sample temperature and a time delay for the injection of H2S into the reaction chamber. The optimized combination allows for tuning the process route towards the potentially more favorable vapor gas reactions, leading to an improved material distribution on the substrate surface. Raman and photoluminescence (PL) spectroscopy confirm the formation of ultrathin MoS2 films on SiO2/Si substrates with a narrow thickness distribution in the monolayer range on length scales of a few millimeters. Best results are achieved in a temperature range of 950 1000 degC showing improved uniformity in terms of Raman and PL line shapes. The obtained films exhibit a PL yield similar to mechanically exfoliated monolayer flakes, demonstrating the high optical quality of the prepared layers.
author_names: Devendra Pareek

Marco A Gonzalez

Jannik Zohrabian

Mohamed Hassan Sayed

Volker Steenhoff

Colleen Lattyak

Martin Vehse

Carsten Agert

Jurgen Parisi

Sascha Schafer

Levent Gutay
title: A vapor phase assisted growth route for large scale uniform deposition of MoS2 monolayer films
year: 2019

abstract: An integrated approach is applied to reveal fine changes in the surface normal structure of 1,2 dimyristoyl sn glycero 3 phospho l serine (DMPS) monolayers at the air lipid water interface occurring in a liquid expanded (LE) liquid condensed (LC) transition. The combination of the Langmuir monolayer technique, X ray reflectometry, and molecular dynamics (MD) modeling provides new insight into the molecular nature of electrostatic phenomena in different stages of lipid compression. A homemade setup with a laboratory X ray source (l 1.54 A) offers a nondestructive way to reveal the structural difference between the LE and LC phases of the lipid. The electron density profile in the direction normal to the interface is recovered from the X ray reflectivity data with the use of both model independent and model based approaches. MD simulations of the DMPS monolayer are performed for several areas per lipid using the all atom force field. Using the conventional theory of capillary waves, a comparison is made b.
author_names: Yury A Ermakov

Viktor E Asadchikov

B S Roschin

Yu O Volkov

Daria A Khomich

Alexey Nesterenko

A M Tikhonov
title: Comprehensive Study of the Liquid Expanded Liquid Condensed Phase Transition in 1,2 Dimyristoyl sn glycero 3 phospho l serine Monolayers: Surface Pressure, Volta Potential, X ray Reflectivity, and Molecular Dynamics Modeling
venue: Langmuir
year: 2019

abstract: An integrated approach is applied to reveal fine changes in the surface normal structure of dimyristoylphosphatidylserine (DMPS) monolayers at the air/lipid/water interface occurring in a liquid expanded (LE) liquid condensed (LC) transition. The combination of the Langmuir monolayer technique, X ray reflectometry and molecular dynamics (MD) modeling provides new insight into the molecular nature of electrostatic phenomena in different stages of lipid compression. A homemade setup with a laboratory X ray source (l=1.54 A) offers a nondestructive way to reveal the structural difference between the LE and LC phases of the lipid. The electron density profile in the direction normal to the interface is recovered from the X ray reflectivity data with the use of both model independent and model based approaches. MD simulations of the DMPS monolayer are performed for several areas per lipid using the all atom force field. Using the conventional theory of capillary waves, a comparison is made between the electron density profiles reconstructed from the X ray data and those calculated directly from MD modeling, which demonstrates remarkable agreement between the experiment and simulations for all selected lipid densities. This confirms the validity of the simulations and allows an analysis of the contributions of the hydrophobic tails and hydrated polar groups to the electron density profile and to the dipole component of the electric field at the interface. According to the MD data, the dependence of the Volta potential on the area per lipid in the monolayer has a different molecular nature below and above the phase transition. In the LE state of the monolayer, the potential is determined mostly by the oriented water molecules in the polar region of the lipid. In the LE LC transition, these molecules are displaced to the bulk, and their effect on the Volta potential becomes insignificant compared with the contribution of the hydrophobic tails. The hydrophobic tails are highly ordered in the state of the liquid crystal so that their dipole moments entirely determine the growth of the potential upon compression up to the monolayer collapse.
author_names: E A

A E

Roschin Boris S

V O

K A

N M

Aleksey M Tikhonov
title: Comprehensive study of the LE LC phase transition in DMPS monolayers: surface pressure, Volta potential, X ray reflectivity and MD modeling.
venue: Langmuir the ACS journal of surfaces and colloids
year: 2019

abstract: Structural phase change materials are of great importance for applications in information storage devices. Thermally driven structural phase transitions are employed in phase change memory to achieve lower programming voltages and potentially lower energy consumption than mainstream nonvolatile memory technologies. However, the waste heat generated by such thermal mechanisms is often not optimized, and could present a limiting factor to widespread use. The potential for electrostatically driven structural phase transitions has recently been predicted and subsequently reported in some two dimensional materials, providing an athermal mechanism to dynamically control properties of these materials in a nonvolatile fashion while achieving potentially lower energy consumption. In this work, we employ DFT based calculations to make theoretical comparisons of the energy required to drive electrostatically induced and thermally induced phase transitions. Determining theoretical limits in monolayer MoTe2 and thin films of Ge2Sb2Te5, we find that the energy consumption per unit volume of the electrostatically driven phase transition in monolayer MoTe2 at room temperature is 9% of the adiabatic lower limit of the thermally driven phase transition in Ge2Sb2Te5. Furthermore, experimentally reported phase change energy consumption of Ge2Sb2Te5 is 100 10,000 times larger than the adiabatic lower limit due to waste heat flow out of the material, leaving the possibility for energy consumption in monolayer MoTe2 based devices to be orders of magnitude smaller than Ge2Sb2Te5 based devices.Phase change materials: less is moreTheoretical calculations reveal that the electrostatically driven phase transition of monolayer MoTe2 is accompanied by little heat waste. Phase change materials have enormous potential for thermal and information storage applications, as they can switch between different phases (and properties) with external stimuli. The amount of heat dissipated during these transitions can however limit the operation and further miniaturization of devices. A team from Stanford University has now modeled heat dissipation during the phase transition in electrostatically driven MoTe2 and thermally driven Ge2Sb2Te5: MoTe2 could consume 100 10,000 times less energy per unit volume than Ge2Sb2Te5, as in the latter case most of the energy becomes heat waste. The small amount of heat that enters and leaves the system in the case of MoTe2 makes it very promising for low energy and low dimension devices.
author_names: Daniel A Rehn

Y Li

Eric Pop

Evan J Reed
title: Theoretical potential for low energy consumption phase change memory utilizing electrostatically induced structural phase transitions in 2D materials
venue: npj Computational Materials
year: 2018

abstract: Thermally or chemically active colloids generate thermodynamic gradients in the solution in which they are immersed and thereby induce hydrodynamic flows that affect their dynamical evolution. Here we study a mean field model for the many body dynamics of a monolayer of spherically symmetric active particles located at a fluid fluid interface. Due to the spherical symmetry, the particles do not self propel. Instead, the dynamics is driven by the long ranged Marangoni flows, due to the response of the interface to the activity of the particles, which compete with the direct interaction between particles. We demonstrate analytically that, in spite of the intrinsic out of equilibrium character of the system, the monolayer evolves to a "pseudoequilibrium" state, in which the Marangoni flows force the coexistence of the thermodynamic phases associated to the direct interaction. In particular, we study the most interesting case of a r 3 soft repulsion that models electrostatic or magnetic interparticle forces. For a sufficiently large average density, two dimensional phase transitions (freezing from liquid to hexatic, and melting from solid to hexatic) should be observable in a radially stratified, "onion like" structure within the monolayer. Furthermore, the analysis allows us to conclude that, while the activity may be too weak to allow direct detection of such induced Marangoni flows, it is relevant as a collective effect in the emergence of the experimentally observable spatial structure of phase coexistences noted above. Finally, the relevance of these results for potential experimental realizations is critically discussed.
author_names: Alvaro Dominguez

Mihail N Popescu
title: Phase coexistence in a monolayer of active particles induced by Marangoni flows.
venue: Soft matter
year: 2018

abstract: A theoretical analysis of the characteristics of the hybrid surface plasmon of a monolayer graphene wrapped metamaterial filled cylindrical waveguide is performed. The dispersion relations for different configurations of metamaterials [double positive (DPS) graphene DPS, DPS graphene double negative (DNG) DNG graphene DPS, and DNG graphene DNG] are simulated by solving Maxwell's equations for cylindrical symmetry and implementing impedance boundary conditions at the interface. The electromagnetic response of graphene is modeled using Kubo's formalism. The influence of the geometrical parameters of the waveguide structure, the chemical potential of graphene and the parameters of partnering materials on the dispersion curve, the effective mode index, and the phase velocity is presented. It is observed that the existence of graphene along with metamaterials provides better control and tuning of the propagation of the surface waves. The backward surface waves, forward surface waves, and slow surface waves for the fundamental mode are studied for different waveguide configurations. The results are found to be in accordance with the published literature. These results may have potential applications in tuning surface waves, waveguide technology, modulators, backward wave amplifiers, traveling wave masers, frequency selectors, circular polarizers, switching and phase compensation, and graphene based slow light devices.
author_names: Maryam Saeed

Abdul Ghaffar

Majeed A S Alkanhal

Ali H Alqahtani

Yasin Khan

Sajjad ur Rehman
title: Plasmon modes supported by metamaterial filled monolayer graphene cylindrical waveguides
year: 2020