Single- and double-slit collimating effects on fast-atom diffraction spectra

Gravielle, M. S.; Miraglia, J. E.

doi:10.1016/j.nimb.2016.03.042

Cited by 11 publications

(25 citation statements)

References 23 publications

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“…In such integrations, the random − → R os values are derived from a Gaussian distribution covering an area S equal to 2 or 3 reduced unit cells, while the Ω o values are obtained from a Gaussian distribution encompassing an angular region determined by the Heisenberg uncertainty relation. In this aspect, it should be mentioned that the − → R os and Ω o distributions are in principle defined by the profile of a coherent wave packet associated with the impinging particle, which depends on the collimation of the incident beam [30,32,33]. Here we have considered standard sizes of the − → R os and Ω o distributions because reported experimental data [5,8,[22][23][24][25] lack information about collimating parameters.…”

Section: A Scattering Processmentioning

confidence: 99%

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van der Waals effects on grazing-incidence fast-atom diffraction for H on LiF(001)

2016

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We theoretically address grazing incidence fast atom diffraction (GIFAD) for H atoms impinging on a LiF(001) surface. Our model combines a description of the H-LiF(001) interaction obtained from Density Functional Theory calculations with a semi-quantum treatment of the dynamics. We analyze simulated diffraction patterns in terms of the incidence channel, the impact energy associated with the motion normal to the surface, and the relevance of Van der Waals (VdW) interactions. We then contrast our simulations with experimental patterns for different incidence conditions. Our most important finding is that, for normal energies lower than 0.5 eV and incidence along the 100 channel, the inclusion of Van der Waals interactions in our potential energy surface yields a greatly improved accord between simulations and experiments. This agreement strongly suggests a non-negligible role of Van der Waals interactions in H/LiF(001) GIFAD in the low-to-intermediate normal energy regime.

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Section: A Scattering Processmentioning

confidence: 99%

“…Since the θ f -length of GIFAD patterns is affected by the collimating conditions of the incident beam [30,33], not given in Ref. [8], the polar angle is here plotted in arbitrary units.…”

Section: Incidence Along the 110 Channelmentioning

confidence: 99%

van der Waals effects on grazing-incidence fast-atom diffraction for H on LiF(001)

2016

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“…In Refs. [3,16,17] it was shown that the experimental collimating scheme noticeably affects GIFAD distributions, allowing one to examine two different interference mechanisms-inter-channel or intra-channel interferences-by varying the size of the collimating aperture. This behavior is related to the transverse length of the surface area that is coherently illuminated by the incident beam, whose determination is indispensable for an appropriate description of the experimental spectra.…”

Section: Introductionmentioning

confidence: 99%

Coherence-Length Effects in Fast Atom Diffraction at Grazing Incidence

Gravielle

Miraglia

Frisco

2018

Atoms

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Coherence properties of projectiles, found relevant in ion-atom collisions, are investigated by analyzing the influence of the degree of coherence of the atomic beam on interference patterns produced by grazing-incidence fast-atom diffraction (GIFAD or FAD). The transverse coherence length of the projectiles, which depends on the incidence conditions and the collimating setup, determines the overall characteristics of GIFAD distributions. We show that for atoms scattered from a LiF(001) surface after a given collimation, we can modify the interference signatures of the angular spectra by varying the total impact energy, while keeping the normal energy as a constant. Also, the role played by the geometry of the collimating aperture is analyzed, comparing results for square and circular openings. Furthermore, we study the spot-beam effect, which is due to different focus points of the impinging particles. We show that when a region narrower than a single crystallographic channel is coherently illuminated by the atomic beam, the spot-beam contribution strongly affects the visibility of the interference structures, contributing to the gradual quantum-classical transition of the projectile distributions.

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“…Over the past decade, the field has been reinvigorated due to newer, higher-energy helium sources that have allowed observation of diffraction peaks [8] from both insulator [9] (e.g., lithium fluoride) and metallic [10] (e.g., silver) surfaces. In the literature, the phrase coherent scattering has been attached to this process and strides have been made in understanding the different regimes of scattering [11] and the specifics of the outgoing diffraction pattern [12]. Seifert et al [13] alluded to the notion of a Feynman-style [14] which-way measurement process caused by the scatterer-surface interaction, which we explore in more detail here in a gedanken experiment to clarify the notion of coherence (or loss thereof due to surface lattice excitations) in atom-surface scattering.…”

Section: Introductionmentioning

confidence: 99%

Approach to coherent interference fringes in helium-surface scattering

Schram

Heller

2018

Phys. Rev. A

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The conventional notion of elastic, coherent atom-surface scattering originates from the scattering particles acting as a quantum-mechanical matter wave, which coherently interfere to produce distinct Bragg peaks which persist at finite temperature. If we introduce inelastic scattering to this scenario, the result is that the surface particles become displaced by the scattering atoms, resulting in emission or absorption of phonons that shift the final energy and momentum of the scatterer. As the lowest-lying phonons are gapless excitations, the ability to measure these phonons is very difficult and this difficulty is exacerbated by the roughly 1-eV resolution found in high-energy helium scattering experiments. Even though the surface has in effect measured the presence of the scatterer which decoheres the particle, we retain the diffraction spots which are referred to as coherent scattering. How do we reconcile these disparate viewpoints? We propose an experiment to more precisely examine the question of coherence in atom-surface scattering. We begin with an initially coherent superposition of helium particles with equal probabilities of interacting with the surface or not interacting with the surface. The beams are directed so that after the scattering event, the atoms are recombined so that we can observe the resulting interference pattern. The degree to which phonons are excited in the lattice by the scattering process dictates the fringe contrast of the interference pattern of the resulting beams. We use semiclassical techniques to simulate and test the viability of this experiment and show that for a wide range of conditions, despite the massive change in the momentum perpendicular to the surface, we can still expect to have coherent (in the superposition sense) scattering.

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Single- and double-slit collimating effects on fast-atom diffraction spectra

Abstract: Appendix: Complex degree of coherence for an atomic beam passing through a collimating aperture Here we extend the Van Cittert-Zernike theorem [12] to evaluate the complex degree of coherence for two points

Cited by 11 publications

References 23 publications

van der Waals effects on grazing-incidence fast-atom diffraction for H on LiF(001)

van der Waals effects on grazing-incidence fast-atom diffraction for H on LiF(001)

Coherence-Length Effects in Fast Atom Diffraction at Grazing Incidence

Approach to coherent interference fringes in helium-surface scattering

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