Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as low as 150 x q eV, we find first unambiguous experimental evidence that potential energy alone is sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF(2) single crystal. Our investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock formation which can be linked to a solid-liquid phase transition.

Scattering of fast neutral atoms with keV kinetic energies at alkali-halide surfaces under grazing angles displays intriguing diffraction patterns. The surprisingly strong persistence of quantum coherence despite the impulsive interaction with an environment at solid state density and elevated temperatures raises fundamental questions such as to the suppression of decoherence and of the quantum-to-classical crossover. We present an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the h110i direction and compare with recent experimental diffraction data. From the quantitative reconstruction of diffraction images the vertical LiF-surface reconstruction, or buckling, can be determined. DOI: 10.1103/PhysRevLett.101.253201 PACS numbers: 34.35.+a, 61.85.+p, 68.49.Bc, 79.20.Rf Diffraction of massive particles scattered at surfaces was one of the key experiments establishing the quantum wave nature. Coherent atom and molecule optics was initiated when Estermann and Stern [1] observed interference patterns of slow (''thermal'') helium atoms and H 2 molecules scattered off alkali-halide surfaces. Thermal atom scattering (TAS) [2,3] as well as low-energy electron diffraction (LEED) [4] are nowadays routinely employed to accurately probe properties of surfaces. These techniques exploit the fact that the de Broglie wavelength dB of the beam particles is comparable to the lattice constant a. More recently, probing the wave nature of massive objects has taken center stage in exploring the quantum-toclassical crossover [5,6]. One ingredient of the quantumto-classical transition is the limit of small de Broglie wave length dB ! 0, the other the ubiquitous presence of unobserved environmental degrees of freedom within the framework of decoherence theory [1], or alternatively, elements beyond standard unitary quantum dynamics, including the frequently involved ''collapse'' of the wave functions [7,8]. In matter-wave interferometry of large and complex biomolecules, de Broglie wavelengths as small as few picometer (10 À12 m) have been reached [6].Even shorter wavelengths have been accessed by recent fast-atom scattering studies at surfaces [9-11] with dB as small as % 200 femtometers. Persistence of quantum diffraction and the apparent suppression of decoherence is all the more remarkable, as thermal fluctuation amplitudes of the surface atoms are much larger than dB and, moreover, collisions with keV projectile energies would strongly suggest the dominance of dissipative and decohering processes. In this Letter we present an ab initio simulation of fast helium atom diffraction ( 4 He) at a LiF (100) surface. We analyze the suppression of decoherence in grazingincidence scattering within an open quantum system (OQS) approach and quantitatively reconstruct experimental diffraction images [9,10] in considerable detail. Fastatom diffraction has the potential to become a powerful tool to interrogate structural and dynamical properties of surfaces.Fast-atom scattering at surfaces under s...

First time-resolved photoemission experiments employing attosecond streaking of electrons emitted by an XUV pump pulse and probed by a few-cycle NIR pulse found a time delay of about 100 attoseconds between photoelectrons from the conduction band and those from the 4f core level of tungsten. We present a microscopic simulation of the emission time and energy spectra employing a classical transport theory. Emission spectra and streaking images are well reproduced. Different contributions to the delayed emission of core electrons are identified: larger emission depth, slowing down by inelastic scattering processes, and possibly, energy dependent deviations from the free-electron dispersion. We find delay times near the lower bound of the experimental data.

Quantum diffraction of fast atoms scattered from the topmost layer of surfaces under grazing angles of incidence can be employed for the analysis of detailed structural properties of insulator surfaces. From comparison of measured and calculated diffraction patterns we deduce the rumpling of the topmost surface layer of LiF(001) (i.e., an inward shift of Li + ions with respect to F − ions). The effect of thermal vibrations on the measurement of rumpling is accounted for by ab initio calculations of the mean-square vibrational amplitudes of surface ions. At room temperature this leads to a reduction of the apparent rumpling by 0.008Å. We then obtain a rumpling of (0.05 ± 0.04)Å, which improves its accuracy achieved in previous work.

We simulate the electron transmission through insulating Mylar (polyethylene terephthalate, or PET) capillaries. We show that the mechanisms underlying the recently discovered electron guiding are fundamentally different from those for ion guiding. Quantum reflection and multiple near-forward scattering rather than the self-organized charge up are key to the transmission along the capillary axis irrespective of the angle of incidence. We find surprisingly good agreement with recent data. Our simulation suggests that electron guiding should also be observable for metallic capillaries.