arXiv subjects

J. R. Manson

Publications and source records attributed to J. R. Manson.

12 recordsLinked to original sources

arXiv2020

The Electron-Phonon Coupling Constant for Single-Layer Graphene on Metal Substrates Determined from He Atom Scattering

Recent theory has demonstrated that the value of the electron-phonon coupling strength $λ$ can be extracted directly from the thermal attenuation (Debye-Waller factor) of Helium atom scattering reflectivity. This theory is here extended to multivalley semimetal systems and applied to the case of graphene on different metal substrates and graphite. It is shown that $λ$ rapidly increases for decreasing graphene-substrate binding strength. Two different calculational models are considered which produce qualitatively similar results for the dependence of $λ$ on binding strength. These models predict, respectively, values of $λ_{HAS} = 0.89$ and 0.32 for a hypothetical flat free-standing single-layer graphene with cyclic boundary conditions. The method is suitable for analysis and characterization of not only the graphene overlayers considered here, but also other layered systems such as twisted graphene bilayers.

cond-mat.mtrl-sci↗

arXiv2020

The Electron-Phonon Interaction of Low-Dimensional and Multi-Dimensional Materials from He Atom Scattering

Atom scattering is becoming recognized as a sensitive probe of the electron-phonon interaction parameter $λ$ at metal and metal-overlayer surfaces. Here, the theory is developed linking $λ$ to the thermal attenuation of atom scattering spectra (in particular, the Debye-Waller factor), to conducting materials of different dimensions, from quasi-one dimensional systems such as W(110):H(1$\times$1) and Bi(114), to quasi-two dimensional layered chalcogenides and high-dimensional surfaces such as quasicrystalline 2ML-Ba(0001)/Cu(001) and d-AlNiCo(00001). Values of $λ$ obtained using He atoms compare favorably with known values for the bulk materials. The corresponding analysis indicates in addition the number of layers contributing to the electron-phonon interaction that is measured in an atom surface collision.

cond-mat.supr-con↗

arXiv2020

Origin of the Electron-Phonon Interaction of Topological Semimetal Surfaces Measured with Helium Atom Scattering

He atom scattering has been demonstrated to be a sensitive probe of the electron-phonon interaction parameter $λ$ at metal and metal-overlayer surfaces. Here it is shown that the theory linking $λ$ to the thermal attenuation of atom scattering spectra (the Debye-Waller factor), can be applied to topological semimetal surfaces, like the quasi-one dimensional charge-density-wave system Bi(114) and the layered pnictogen chalcogenides.

cond-mat.mtrl-sci↗

arXiv2017

Electron-Phonon Coupling Constant of Metallic Overlayers from Specular He-Atom Scattering

He atom scattering has been shown to be a sensitive probe of electron-phonon interaction properties at surfaces. Here it is shown that measurements of the thermal attenuation of the specular He atom diffraction peak (the Debye-Waller effect) can determine the electron-phonon coupling constant $λ$ for ultrathin films of metal overlayers on various close-packed metal substrates. Values of $λ$ obtained for single and multiple monolayers of alkali metals, and for Pb layers on Cu(111), extrapolated to large thicknesses, agree favorably with known bulk values. This demonstrates that He atom scattering can measure the electron-phonon coupling strength as a function of film thickness on a layer-by-layer basis.

cond-mat.supr-con↗

arXiv2016

The electron-phonon coupling strength at metal surfaces directly determined from the Helium atom scattering Debye-Waller factor

A new quantum-theoretical derivation of the elastic and inelastic scattering probability of He atoms from a metal surface, where the energy and momentum exchange with the phonon gas can only occur through the mediation of the surface free-electron density, shows that the Debye-Waller exponent is directly proportional to the electron-phonon mass coupling constant $λ$. The comparison between the values of $λ$ extracted from existing data on the Debye-Waller factor for various metal surfaces and the $λ$ values known from literature indicates a substantial agreement, which opens the possibility of directly extracting the electron-phonon coupling strength in quasi-2D conducting systems from the temperature or incident energy dependence of the elastic Helium atom scattering intensities.

cond-mat.mtrl-sci↗

arXiv2015

Temperature Dependence in Rainbow Scattering of Hyperthermal Ar Atoms from LiF(001)

Recent experiments have reported measurements of rainbow scattering features in the angular distributions of hyperthermal Ar colliding with LiF(001) [Kondo et al., J. Chem. Phys. 122, 244713 (2005)]. A semiclassical theory of atom-surface collisions recently developed by the authors that includes multiphonon energy transfers is used to explain the temperature dependence of the measured scattered angular distribution spectra.

physics.chem-ph↗

arXiv2012

Modifying molecular scattering from rough solid surfaces using ultrashort laser pulses

We consider solid surface scattering of molecules that were subject to strong non-resonant ultrashort laser pulses just before hitting the surface. The pulses modify the rotational states of the molecules, causing their field free alignment, or a rotation with a preferred sense. We show that field-free laser-induced molecular alignment leads to correlations between the scattering angle and the sense of rotation of the scattered molecules. Moreover, by controlling the sense of laser induced unidirectional molecular rotation, one may affect the scattering angle of the molecules. This provides a new means for separation of mixtures of molecules (such as isotopes and nuclear-spin isomers) by laser controlled surface scattering.

physics.chem-ph↗

arXiv2011

Modifying molecule-surface scattering by ultrashort laser pulses

In recent years it became possible to align molecules in free space using ultrashort laser pulses. Here we explore two schemes for controlling molecule-surface scattering process, which are based on the laser-induced molecular alignment. In the first scheme, a single ultrashort non-resonant laser pulse is applied to a molecular beam hitting the surface. This pulse modifies the angular distribution of the incident molecules, and causes the scattered molecules to rotate with a preferred sense of rotation (clockwise or counter-clockwise). In the second scheme, two properly delayed laser pulses are applied to a molecular beam composed of two chemically close molecular species (isotopes, or nuclear spin isomers). As the result of the double pulse excitation, these species are selectively scattered to different angles after the collision with the surface. These effects may provide new means for the analysis and separation of molecular mixtures.

physics.chem-ph↗

arXiv2008

Diffraction of fast atoms and molecules from surfaces

Prompted by recent experimental developments, a theory of surface scattering of fast atoms at grazing incidence is developed. The theory gives rise to a quantum mechanical limit for ordered surfaces that describes coherent diffraction peaks whose thermal attenuation is governed by a Debye-Waller factor, however, this Debye-Waller factor has values much larger than would be calculated using simple models. A classical limit for incoherent scattering is obtained for high energies and temperatures. Between these limiting classical and quantum cases is another regime in which diffraction features appear that are broadened by the motion in the fast direction of the scattered beam but whose intensity is not governed by a Debye-Waller factor. All of these limits appear to be accessible within the range of currently available experimental conditions.

physics.atom-ph↗

arXiv2008

Calculations of Trapping and Desorption in Heavy Atom Collisions with Surfaces

Calculations are carried out for the scattering of heavy rare gas atoms with surfaces using a recently developed classical theory that can track particles trapped in the physisorption potential well and follow them until ultimate desorption. Comparisons are made with recent experimental data for xenon scattering from molten gallium and indium, systems for which the rare gas is heavier than the surface atoms. The good agreement with the data obtained for both time-of-flight energy-resolved spectra and for total scattered angular distributions yields an estimate of the physisorption well depths for the two systems.

physics.class-ph↗

arXiv2008

Calculations of the Energy Accommodation Coefficient for Gas-Surface Interactions

Calculations are carried out for the energy accommodation coefficient at a gas-surface interface using a recently developed classical mechanical theory of atom-surface collisions that includes both direct scattering and trapping-desorption processes in the physisorption well of the interaction potential. Full three-dimensional calculations are compared with the available data for the accommodation of rare gases at a tungsten surface and good agreement is found for the heavier gases for which classical physics is expected to be valid at all measured temperatures.

physics.class-ph↗

arXiv2008

Theory of Direct Scattering, Trapping and Desorption in Atom-Surface Collisions

When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features due to direct scattering and to trapping in the physisorption well with subsequent desorption. James Clerk Maxwell is credited with being the first to describe this situation by invoking the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that exchanges no energy and specularly reflects and another part that equilibrates or accommodates completely and then desorbs with an equilibrium distribution. In this paper a scattering theory is developed, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped fraction of particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of recent experimental measurements which exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra.

physics.class-ph↗