Scattering Of Atoms Research Articles

Graphene on Ni(111): Electronic Corrugation and Dynamics from Helium Atom Scattering.

Using helium atom scattering, we have studied the structure and dynamics of a graphene layer prepared in situ on a Ni(111) surface. Graphene/Ni(111) exhibits a helium reflectivity of ∼20% for a thermal helium atom beam and a particularly small surface electron density corrugation ((0.06 ± 0.02) Å peak to peak height). The Debye–Waller attenuation of the elastic diffraction peaks of graphene/Ni(111) and Ni(111) was measured at surface temperatures between 150 and 740 K. A surface Debye temperature of θD = (784 ± 14) K is determined for the graphene/Ni(111) system and θD = (388 ± 7) K for Ni(111), suggesting that the interlayer interaction between graphene and the Ni substrate is intermediary between those for strongly interacting systems like graphene/Ru(0001) and weakly interacting systems like graphene/Pt(111). In addition we present measurements of low frequency surface phonon modes on graphene/Ni(111) where the phonon modes of the Ni(111) substrate can be clearly observed. The similarity of these findings with the graphene/Ru(0001) system indicates that the bonding of graphene to a metal substrate alters the dynamic properties of the graphene surface strongly and is responsible for the high helium reflectivity of these systems.

A Giant Reconstruction of α-quartz (0001) Interpreted as Three Domains of Nano Dauphine Twins.

Silica (SiO2) is one of the most common materials on Earth. The crystalline form α-quartz is the stable silica polymorph at ambient conditions although metastable forms exist. α-quartz is a piezoelectric material, it can be produced artificially and is widely used for example in electronics and the biosciences. Despite the many application areas, the atomic surface structures of silica polymorphs are neither well understood nor well characterized. Here we present measurements of α-quartz (0001). Helium Atom Scattering combined with Atomic Force Microscopy reveals a giant reconstruction consisting of 5.55 ± 0.07 nm wide ribbons, oriented 10.4° ± 0.8° relative to the bulk unit cell. The ribbons, with the aid of atomistic modelling, can be explained as a self-organised pattern of nano Dauphine twins (nano electrical twins).

Surface Structure of Bi(111) from Helium Atom Scattering Measurements. Inelastic Close-Coupling Formalism.

Elastic and inelastic close-coupling (CC) calculations have been used to extract information about the corrugation amplitude and the surface vibrational atomic displacement by fitting to several experimental diffraction patterns. To model the three-dimensional interaction between the He atom and the Bi(111) surface under investigation, a corrugated Morse potential has been assumed. Two different types of calculations are used to obtain theoretical diffraction intensities at three surface temperatures along the two symmetry directions. Type one consists of solving the elastic CC (eCC) and attenuating the corresponding diffraction intensities by a global Debye–Waller (DW) factor. The second one, within a unitary theory, is derived from merely solving the inelastic CC (iCC) equations, where no DW factor is necessary to include. While both methods arrive at similar predictions for the peak-to-peak corrugation value, the variance of the value obtained by the iCC method is much better. Furthermore, the more extensive calculation is better suited to model the temperature induced signal asymmetries and renders the inclusion for a second Debye temperature for the diffraction peaks futile.

Ionic Liquid–Vacuum Interfaces Probed by Reactive Atom Scattering: Influence of Alkyl Chain Length and Anion Volume

The liquid–vacuum interfaces of a series of room-temperature ionic liquids (RTILs) containing the 1-alkyl-3-methylimidazolium cation ([Cnmim]) were investigated by reactive-atom scattering (RAS). The length of the alkyl chain (n = 4, 6, 8, and 12) and the anion type (bis(trifluoromethylsulfonyl)imide ([Tf2N]), trifluoromethanesulfonate ([OTf]), and tetrafluoroborate ([BF4])) were varied systematically to determine their effects on the preferential occupancy of the surface by alkyl chains. The experiments employed collisions with gas-phase, ground-state oxygen atoms, O(3P), generating OH and H2O products that revealed the abundance of abstractable H atoms at the liquid surface. Two complementary approaches with different O atom energies and detection methods were employed: we denote these RAS-laser-induced fluorescence (RAS-LIF) and RAS-mass spectrometry (RAS-MS). [Cnmim][BF4] RTILs were studied by both methods, giving consistent trends of strongly increasing alkyl coverage with chain length. Even for the ...

Studying the x- ray atomic Scattering form Factor and Nuclear Magnetic Shielding Constant for Be atom in its Excited state (1s2 2s 3s) and the Be - like ions

The division partitioning technique has been used to analyze the four electron systems into six-pairs electronic wave functions for ( for the Beryllium atom in its excited state (1s2 2s 3s ) and like ions ( B+1 ,C+2 ) using Hartree-Fock wave functions . The aim of this work is to study atomic scattering form factor f(s) for and nuclear magnetic shielding constant. The results are obtained numerically by using the computer software (Mathcad).

Studying the x- ray atomic Scattering form Factor and Nuclear Magnetic Shielding Constant for Be atom in its Excited state (1s2 2s 3s) and the Be - like ions

The division partitioning technique has been used to analyze the four electron systems into six-pairs electronic wave functions for ( for the Beryllium atom in its excited state (1s2 2s 3s ) and like ions ( B+1 ,C+2 ) using Hartree-Fock wave functions . The aim of this work is to study atomic scattering form factor f(s) for and nuclear magnetic shielding constant. The results are obtained numerically by using the computer software (Mathcad).

Aggrecan: Unusual Polyelectrolyte Biophysics and Interactions Conferred by the Bottlebrush Structure

Aggrecan is a negatively-charged proteoglycan with a bottlebrush structure present in the cartilage matrix. Its chief function is to maintain a self-repelling charged atmosphere within the cartilage matrix that attracts waters and exerts a swelling pressure (Chandran and Horkay, 2011). In this study we use Atomic Force Spectroscopy and Dynamic Light Scattering in complementary ways to study the polyelectrolyte biophysics of the aggrecan bottlebrush. We describe how the bottlebrush dynamics and interactions depart from that of linear polyelectrolytes, and discuss the implications for cartilage diseases and tissue-engineering solutions.

Atomic Scattering Polarization. Observations, Modeling, Predictions

AbstractThis paper highlights very recent advances concerning the identification of new mechanisms that introduce polarization in spectral lines, which turn out to be key for understanding some of the most enigmatic scattering polarization signals of the solar visible spectrum. We also show a radiative transfer prediction on the scattering polarization pattern across the Mg iih & k lines, whose radiation can only be observed from space.

Characterization of early growth stages of Pb/Ge(001)

Early stages of thin Pb film growth on Ge(001) substrate, exhibiting quantum size effects (QSE), are characterized by means of Photoelectron Diffraction and Helium Atom Scattering. Pb is found to form a commensurate first monolayer, while an ordered layer-by-layer growth only sets in after deposition of 4 monolayers. In the intermediate coverage range no long range order of the overlayer is established and we find that uncorrelated islands of preferred four-layer thickness are formed. Continuous Pb film with long range order emerges through islands coalescence close to a coverage of 4 monolayers, upon which a more regular layer-by-layer growth mode sets in.

Scattering of fast atoms and ions from surfaces under channeling conditions

Scattering of fast atoms and ions from surfaces under glancing angles of incidence proceeds in the regime of ‘surface channeling’ where projectiles are steered in terms of small angle collisions by atoms of the topmost layer of the surface. Collisions with the solid under these conditions are characterized by defined trajectories for the ensemble of scattered projectiles that is the basis for a detailed model description of the interaction mechanisms. An overview will be presented concerning the different aspects and techniques that demonstrate the substantial potential of surface channeling for studies on the ion–surface interactions and on the structure of surfaces. As examples will be discussed, studies on charge transfer, electron emission phenomena, interactions with insulators, investigation of growth, and structure of ultrathin films, as well as the recently discovered fast atom diffraction. Copyright © 2014 John Wiley & Sons, Ltd.

Helium Atom Scattering from Graphene Grown on Rh(111)

Graphene growth on transition-metal surfaces leads to an ordered superlattice that appears as a series of hills and valleys in scanning tunneling microscopy. On Rh(111), the graphene forms an incommensurate epitaxial overlayer; the crystallographic axes of the graphene are closely aligned with the Rh(111) surface lattice vectors, but the Rh and graphene lattice constants are significantly different. Thus, the C atoms sit over different positions of the Rh(111) lattice and their height above the Rh(111) surface varies, but the different binding sites also affect the local electronic structure. Scanning tunneling microscopy is affected by both of these factors. He scattering is more a measure of the geometrical corrugation, the variation of the height of the graphene sheet relative to the Rh(111) surface. We compare the results of He diffraction measurements with those of previous scanning tunneling microscopy measurements to assess the relative geometric and electronic corrugations.

Sandwiching spherical 1,2-dioleoyltrimethylammoniumpropane liposome in gold nanoparticle on solid transducer for electrochemical ultrasensitive DNA detection and transfection

Cationic N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethylammonium propane (DOTAP) liposome is spherically sandwiched in gold nanoparticle (abbreviated as sDOTAP–AuNP) onto a gold electrode surface. The sDOTAP–AuNP is applied for electrochemical label free DNA sensing and Escherichia coli cell transfection for the first time. Complementary target (named as hybridized), non-complementary target (un-hybridized) and single base mismatch target (named as SMM) hybridized surfaces are discriminated sensitively and selectively in presence of [Fe(CN)6]3−/4−. Double strand specific intercalator methylene blue in combination with [Fe(CN)6]3− is used to enhance target detection limit down to femtomolar concentration. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) techniques are used for characterizing DNA sensing. High Resolution Transmission Electron Microscopy (HRTEM), Fourier Transform Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM) and Dynamic Light Scattering (DLS) techniques are used to confirm the spherical nature of the sDOTAP–AuNP–DNA composite in solution and on the solid surface. DNA on the sDOTAP–ssDNA is transferred by potential stripping method (+0.2V (Ag/AgCl)) into buffer solution containing E. coli cells. The transfection is confirmed by the contrast images for the transfected and non-transfected cell from Confocal Laser Scanning Microscopy (CLSM). The results demonstrate effectiveness of the electrochemical DNA transfection method developed and could be applied for other cells.

Scattering and absorption of ultracold atoms by nanotubes

We investigate theoretically how cold atoms, including Bose–Einstein condensates, are scattered from, or absorbed by, nanotubes with a view to analysing recent experiments. In particular, we consider the role of potential strength, quantum reflection, atomic interactions and tube vibrations on atom loss rates. Lifshitz theory calculations deliver a significantly stronger scattering potential than that found in experiment and we discuss possible reasons for this. We found that the scattering potential for dielectric tubes can be calculated to a good approximation using a modified pairwise summation approach, which is efficient and easily extendable to arbitrary geometries. Quantum reflection of atoms from a nanotube may become a significant factor at low temperatures, especially for non-metallic tubes. Interatomic interactions are shown to increase the rate at which atoms are lost to the nanotube and lead to non-trivial dynamics. Thermal nanotube vibrations do not significantly increase loss rates or reduce condensate fractions, but lower frequency oscillations can dramatically heat the cloud.

Scattering and effective interactions of ultracold atoms with spin-orbit coupling

We derive an analytical expression for the scattering amplitude of two ultracold atoms of arbitrary spin and with general spin-orbit (SO) coupling, on the basis of our recent work (Phys. Rev. A \textbf{86}, 053608 (2012)). As an application, we demonstrate that SO coupling can induce scattering resonance in the case with finite scattering length. The same approach can be applied to calculate the two-body bound state of SO-coupled ultracold atoms. For the ultracold spin-1/2 fermi gases in three- or two- dimensional systems with SO coupling, we also obtain the renormalization relation of effective contact interaction with momentum cutoff, as well as the applicability of Huang-Yang pseudo-potential.

Atomic Scattering Data and Their Evaluation: Strategies for Obtaining Complete Cross-Section Sets for Electron Collision Processes

We describe the challenges facing, and opportunities for, the scattering community as it attempts to provide complete cross-section databases for the modeling of a variety of important applications in fusion science and low-temperature plasmas. We outline a suggested protocol for how the community might collectively move forward to construct both benchmarked collision systems and ultimately a complete cross-section database for a given species. Some examples of scattering data and techniques that may be useful for benchmarking are provided.

Hybridization of surface waves with organic adlayer librations: a helium atom scattering and density functional perturbation theory study of methyl-Si(111).

The interplay of the librations of a covalently bound organic adlayer with the lattice waves of an underlying semiconductor surface was characterized using helium atom scattering in conjunction with analysis by density functional perturbation theory. The Rayleigh wave dispersion relation of CH3- and CD3-terminated Si(111) surfaces was probed across the entire surface Brillouin zone by the use of inelastic helium atom time-of-flight experiments. The experimentally determined Rayleigh wave dispersion relations were in agreement with those predicted by density functional perturbation theory. The Rayleigh wave for the CH3- and CD3-terminated Si(111) surfaces exhibited a nonsinusoidal line shape, which can be attributed to the hybridization of overlayer librations with the vibrations of the underlying substrate. This combined synthetic, experimental, and theoretical effort clearly demonstrates the impact of hybridization between librations of the overlayer and the substrate lattice waves in determining the overall vibrational band structure of this complex interface.

Компьютерное моделирование дифракции импульсов рентгеновских лучей на нанокристаллах биологических макромолекул с использованием унитарной аппроксимации нестационарных факторов атомного рассеяния

Компьютерное моделирование дифракции импульсов рентгеновских лучей на нанокристаллах биологических макромолекул с использованием унитарной аппроксимации нестационарных факторов атомного рассеяния

Determination of the Surface Corrugation Amplitude from Classical Atom Scattering

The energy landscape of an atomic or molecular projectile interacting with a surface is often described in terms of a corrugation function that gives the classical turning point as a function of position vector parallel to the surface. It is shown here that the relative height variation of the corrugation function for scattering of atoms under classical conditions can be determined by a measurement of the maximum intensity in energy-resolved scattering spectra as a function of surface temperature. This is demonstrated by developing a semiclassical quantum theory of atomic scattering from corrugated surfaces and then extending the theory to the classical limit of large incident energies and high surface temperatures. Comparisons of calculations with available data for Ar atom scattering determine the corrugation amplitude for a molten In surface to be about 29% of the mean interparticle spacing in the bulk liquid.

Publisher’s Note: Competition between Electron and Phonon Excitations in the Scattering of Nitrogen Atoms and Molecules off Tungsten and Silver Metal Surfaces [Phys. Rev. Lett.108, 096101 (2012)

Received 29 February 2012DOI:https://doi.org/10.1103/PhysRevLett.108.139901© 2012 American Physical Society

Competition between Electron and Phonon Excitations in the Scattering of Nitrogen Atoms and Molecules off Tungsten and Silver Metal Surfaces

We investigate the role played by electron-hole pair and phonon excitations in the interaction of reactive gas molecules and atoms with metal surfaces. We present a theoretical framework that allows us to evaluate within a full-dimensional dynamics the combined contribution of both excitation mechanisms while the gas particle-surface interaction is described by an ab initio potential energy surface. The model is applied to study energy dissipation in the scattering of N(2) on W(110) and N on Ag(111). Our results show that phonon excitation is the dominant energy loss channel, whereas electron-hole pair excitations represent a minor contribution. We substantiate that, even when the energy dissipated is quantitatively significant, important aspects of the scattering dynamics are well captured by the adiabatic approximation.