Image processing for grazing incidence fast atom diffraction

Grazing incidence fast atom diffraction (GIFAD, or FAD) has developed as a surface sensitive technique. GIFAD is less sensitive to thermal decoherence but more demanding in terms of surface coherence, the mean distance between defects. Such high quality surfaces can be obtained from freshly cleaved crystals or in a molecular beam epitaxy (MBE) chamber where a GIFAD setup has been installed allowing in situ operation. Based on recent publications by Atkinson et al. and Debiossac et al, the paper describes in detail the basic steps needed to measure the relative intensities of the diffraction spots. Care is taken to outline the underlying physical assumptions.Comment: IISC-21 International Workshop on Inelastic Ion-Surface Collisions, Dosnostia Sept. 2015. Elsevier, NIM-B (2016

Elastic and inelastic diffraction of fast atoms,\linebreak Debye-Waller factor and M\"{o}ssbauer-Lamb-Dicke regime

The diffraction of fast atoms at crystal surfaces is ideal for a detailed investigation of the surface electronic density. However, instead of sharp diffraction spots, most experiments show elongated streaks characteristic of inelastic diffraction. This paper describes these inelastic profiles in terms of individual inelastic collisions with surface atoms taking place along the projectile trajectory and leading to vibrational excitation of the local Debye oscillator. A quasi-elastic regime where only one inelastic event contributes is identified as well as a mixed quantum-classical regime were several inelastic collision are involved. These regimes describe a smooth evolution of the scattering profiles from sharp spots to elongated streaks merging progressively into the classical diffusion regime

Refraction of fast Ne atoms in the attractive well of LiF(001) surface

Ne atoms with energies up to 3 keV are diffracted under grazing angles of incidence from a LiF(001) surface. For a small momentum component of the incident beam perpendicular to the surface, we observe an increase of the elastic rainbow angle together with a broadening of the inelastic scattering profile. We interpret these two effects as the refraction of the atomic wave in the attractive part of the surface potential. We use a fast, rigorous dynamical diffraction calculation to find a projectile-surface potential model that enables a quantitative reproduction of the experimental data for up to ten diffraction orders. This allows us to extract an attractive potential well depth of 10.4 meV. Our results set a benchmark for more refined surface potential models which include the weak Van der Waals region, a long-standing challenge in the study of atom-surface interactions

Energy loss and inelastic diffraction of fast atoms at grazing incidence

The diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD) was first interpreted only in terms of elastic diffraction from a perfectly periodic rigid surface with atoms fixed at equilibrium position. Recently, a new approach have been proposed, referred here as the quantum binary collision model (QBCM). The QBCM takes into account both the elastic and inelastic momentum transfer via the Lamb-Dicke probability. It suggests that the shape of the inelastic diffraction profiles are log-normal distributions with a variance proportional to the nuclear energy loss deposited on the surface. For keV Neon atoms impinging the LiF surface, the predictions of the QBCM in its analytic version are compared with numerical trajectory simulations. Some of the assumptions such as the planar continuous form, the possibility to neglect the role of lithium atoms and the influence of temperature are investigated. A specific energy loss dependence $\Delta E\propto\theta^7$ is identified in the quasi-elastic regime merging progressively to the classical onset $\Delta E\propto\theta^3$. The ratio of these two predictions highlight the role of quantum effects in the energy loss.Comment: 9 pages 8 figures paper prepared for IISC-2

Elastic and inelastic diffraction of fast neon atoms on a LiF surface

Grazing incidence fast atom diffraction has mainly been investigated with helium atoms, considered as the best possible choice for surface analysis. This article presents experimental diffraction profiles recorded with neon projectile, between 300 eV and 4 keV kinetic energy with incidence angles $\theta_i$ between 0.3$^\circ$ and 1.5$^\circ$ along three different directions of a LiF(001) crystal surface. These correspond to perpendicular energy ranging from a few meV up to almost 1 eV. A careful analysis of the scattering profile allows us to extract the diffracted intensities even when inelastic effects become so large that most quantum signatures have disappeared. The relevance of this approach is discussed in terms of surface topology.Comment: 9 page

Nonequilibrium control of thermal and mechanical changes in a levitated system

Fluctuation theorems are fundamental extensions of the second law of thermodynamics for small nonequilibrium systems. While work and heat are equally important forms of energy exchange, fluctuation relations have not been experimentally assessed for the generic situation of simultaneous mechanical and thermal changes. Thermal driving is indeed generally slow and more difficult to realize than mechanical driving. We here use feedback cooling techniques to implement fast and controlled temperature variations of an underdamped levitated microparticle that are one order of magnitude faster than the equilibration time. Combining mechanical and thermal control, we verify the validity of a fluctuation theorem that accounts for both contributions, well beyond the range of linear response theory. Our system allows the investigation of general far-from-equilibrium processes in microscopic systems that involve fast mechanical and thermal changes at the same time

Coherent diffraction of hydrogen through the 246 pm lattice of graphene

International audienceWe study the diffraction of neutral hydrogen atoms through suspended single-layer graphene using molecular dynamics simulations based on density functional theory. Although the atoms have to overcome a transmission barrier, we find that the de Broglie wave function for H at 80 eV has a high probability to be coherently transmitted through about 18% of the graphene area, contrary to the case of He. We propose an experiment to realize the diffraction of atoms at the natural hexagon lattice period of 246 pm, leading to a more than 400-fold increase in beam separation of the coherently split atomic wave function compared to diffraction experiments at state-of-the art nano-machined masks. We expect this unusual wide coherent beam splitting to give rise to novel applications in atom interferometry

Selective photodissociation of tailored molecular tags as a tool for quantum optics

Recent progress in synthetic chemistry and molecular quantum optics has enabled demonstrations of the quantum mechanical wave–particle duality for complex particles, with masses exceeding 10 kDa. Future experiments with even larger objects will require new optical preparation and manipulation methods that shall profit from the possibility to cleave a well-defined molecular tag from a larger parent molecule. Here we present the design and synthesis of two model compounds as well as evidence for the photoinduced beam depletion in high vacuum in one case