Effects of defect structures at surfaces and thin films on grazing scattering of fast ions

Pfandzelter, R.

doi:10.1103/physrevb.57.15496

Cited by 62 publications

(29 citation statements)

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“…The observation is in clear contrast with the assumption of a saturated attractive level shift derived from linear response theory or concepts of classical image charges. Note that the enhanced width for higher E z is dominated by effects caused by thermal vibrations of lattice atoms, whereas charge exchange plays a negligible role in this respect [22].…”

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Energy shift of He groundstate close to an aluminum surface

Wethekam

Winter

2005

Surface Science

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Energy shift of He groundstate close to an aluminum surface

Wethekam

Winter

2005

Surface Science

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“…Growth-induced irregularities such as nucleated islands affect the correlated scattering process and the specularbeam intensity. Thus island densities are deduced from best fits of the measured intensities to computer simulations using classical trajectories [14,15]. We find that the density is saturated and nearly constant in a wide range of coverages between about 0.2 and 0.6 monolayers (ML).…”

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Non-Arrhenius Behavior of the Island Density in Metal Heteroepitaxy: Co on Cu(001)

et al. 2003

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We present a combined theoretical and experimental study of island nucleation and growth in the deposition of Co on Cu(001) -a prototype for understanding heteroepitaxial growth involving intermixing. Experimentally, ion scattering is employed. Using density-functional theory, we obtain energy barriers for the various elementary processes and incorporate these into a kinetic Monte Carlo program to simulate the heteroepitaxial growth. Both the simulations and the experiments show a unique N-shape dependence of the island density on temperature that stems from the interplay and competition of the different processes involved. DOI: 10.1103/PhysRevLett.90.076101 PACS numbers: 68.55.-a, 61.43.Hv, 68.35.Fx, 82.40.Bj Heteroepitaxial metallic structures, such as Co=Cu multilayers represent a new material that has high potential for the development of magnetoelectronic devices. In order to control the interfacial properties it is important to achieve a quantitative understanding of the morphology that develops during growth and its dependence on the growth conditions. A standard model for the initial stages of growth is given by nucleation theory [1], where the island density n x is expressed in terms of the deposition rate F, the adatom hopping rate D D 0 exp ÿE d =k B T , and the binding energy E b of the critical nucleus of size i,The linear dependence of lnn x on 1=T is widely used to deduce quantities such as activation barriers from islanddensity measurements, when adatoms form islands on top of the substrate [2]. However, in heteroepitaxial systems, deposited atoms may incorporate into the substrate displacing substrate atoms into the growing layer [3][4][5][6][7][8][9]. The effect of site exchange is not considered in Eq. (1). A prototypical system where intermixing takes place is Co on Cu(001). A broad [5,6] and bimodal [6] island-size distribution was observed in submonolayer growth studies using scanning-tunnelling microscopy (STM) -in contrast to a Poisson-like distribution anticipated in standard nucleation theory [1]. In addition Nouvertné et al. reported that the island density at 415 K is slightly higher than at 295 K [6], which is at variance with the predictions of Eq. (1). The island composition was found to depend on the growth conditions and to vary from mostly Co to mostly Cu. Moreover, a correlation has been observed between island composition and island size [5,6].From a fundamental standpoint, it is important to extend nucleation theories to account for intermixing. However, to date, only a few studies have attempted this [4,10 -13]. Chambliss and Johnson proposed that substitutional Fe atoms constitute stable nuclei for the growth of Fe on Cu(001) [4]. By accounting for monomer stability [i 0 in Eq. (1)] at substitutional Fe pinning sites, they found that the island density is independent of F=D. Meyer and Behm assumed irreversible pinning of adatoms at substitutional nucleation centers and found that the island density goes through a minimum with increasing temperature -consistent with that...

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“…In practice, structural imperfections like surface steps mediate penetration of some projectiles, leading to a contribution of excited electrons from layers beneath the surface. From computer simulations emulating ion trajectories [23] and an overlayer experiment [21], we infer for scattering of 25 keV protons from our Fe(100) surface a probing depth of λ = (0.5 ± 0.2) ML for electrons of 10 − 20 eV kinetic energy. We note that λ seems to increase for lower electron energies owing to cascade multiplication governed by electron-electron scattering [21].…”

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Layer-dependent magnetization at the surface of a band ferromagnet

Pfandzelter

Potthoff

2001

Phys. Rev. B

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The temperature-dependence of the magnetization near the surface of a band-ferromagnet is measured with monolayer resolution. The simultaneous application of novel highly surface-sensitive techniques enables one to deduce the layer-dependent magnetization curves at a Fe(100) surface. Analysis of data is based on a simple mean-field approach. Implications for modern theories of itinerant-electron ferromagnetism are discussed.A ferromagnetic material is characterized by a spontaneous magnetization m which decreases with increasing temperature T until the paramagnetic state with m = 0 is reached at the Curie point T c . For very low temperatures the form of the magnetization curve m(T ) is governed by spin-wave excitations according to Bloch's law. For temperatures very close to T c critical fluctuations result in a power-law dependence m(T ) ∝ (T c − T ) β with a critical exponent β. In the wide range of intermediate temperatures the form of m(T ) depends on the specific system. In case of a band-ferromagnetic material, such as Fe as a prototype, the detailed form of m(T ) in this intermediate regime must be explained from the underlying electronic structure [1,2].Density-functional theory within the local-spin-density approximation is known to give a quantitatively accurate description of several ground-state properties [3]. For finite temperatures, however, there is no satisfying implementation available. A microscopic theory must account for the existence of local magnetic moments above T c in particular [4]. This requires to deal with correlations among itinerant valence electrons as, for example, within the framework of an orbitally degenerate Hubbard-type model with realistic parameters [5]. The long history of itinerant-electron ferromagnetism shows that this is a demanding task [2]. On the other hand, comparatively simple mean-field approaches based on spin models are known to provide a successful phenomenological description in many cases (see e. g. Ref.[6]). Remarkably, while the Weiss mean-field theory fails to reproduce the known T → 0 and T → T c limits and substantially overestimates T c , the form of the Fe magnetization curve m(T ) at intermediate reduced temperatures T /T c is reasonably well described: For spin-quantum number S = 1/2 there are deviations from the measured bulk magnetization curve of Fe within a few per cent only [7,8].At the surface of a band-ferromagnet the magnetization may be different for different layers α parallel to the surface because of the reduced translational symmetry. Hence, a key quantity that characterizes the surface magnetic structure is the layer-dependent magnetization curve m α (T ). Within the framework of classical spin models, the lowered surface coordination number implies that certain exchange interactions are missing. This directly leads to a reduced magnetic stability at the surface [9]: The top-layer (α = 1) magnetization is substantially reduced as compared with the bulk. However, significant deviations from the bulk magnetization curve are confined t...

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Effects of defect structures at surfaces and thin films on grazing scattering of fast ions

Cited by 62 publications

References 62 publications

Energy shift of He groundstate close to an aluminum surface

Energy shift of He groundstate close to an aluminum surface

Non-Arrhenius Behavior of the Island Density in Metal Heteroepitaxy: Co on Cu(001)

Layer-dependent magnetization at the surface of a band ferromagnet

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