A detailed structural model for the indium-induced Si(111)-(4×1) surface reconstruction has been determined by analyzing an extensive set of x-ray-diffraction data recorded with monochromatic (hω = 9.1 keV) synchrotron radiation. The reconstruction is quasi-one-dimensional. The main features in the structure are chains of silicon atoms alternating with zigzag chains of indium atoms on top of an essentially unperturbed silicon lattice. The indium coverage corresponds to one monolayer. The structural model consistently explains all previously published experimental data.Considerable interest has focused recently on adsorbate-induced modification of semiconductor surfaces as a technique to create nanoscale quantum structures of high perfection. In this paper we report the formation of quasi-one-dimensional (1d) chains on the (4×1)-reconstructed Si(111) surface induced by the adsorption of indium and present the atomic structure as determined by surface x-ray diffraction (SXRD). In direct 3 and inverse 4 photoemission investigations on single-domain samples and recently in inverse photoemission investigations on a three-domain sample 5 the Si(111)-(4×1)-In reconstruction showed a quasi-1d metallic behavior. Additionally to this interesting electronic property the surface exhibits an image state that also showed quasi-1d behavior in its strongly anisotropic dispersion: Along a certain direction the dispersion is very well described by a free electron parabola whereas in the perpendicular direction the dispersion falls below the free electron parabola. 6 Scanning tunneling microscopy (STM) investigations of the Si(111)-(4×1)-In reconstruction 1,7-11 resolved zig-zag chains running in the 110 directions in the filled-state images and linear chains in the empty-state images. Tunneling data was acquired at bias voltages down to 0.04 V consistent with metallic behavior in agreement with scanning tunneling spectroscopy results. 1 Adsorbed hydrogen was found to displace the indium atoms. 9-11 Filled-state STM images of the hydrogenated substrate show a (4×1) reconstruction with straight chains instead of the broad zigzag chains on the indium-terminated surface. 9-11 From these observations and results found in the literature Saranin et al. 9 proposed a structural model. This model as well as the model derived by Collazo-Davila et al. 12 by applying direct methods to transmission electron diffraction (TED) data are at variance with the x-ray photoelectron spectroscopy (XPS) results of Abukawa et al. 13 Since the core-level spectra did not show peaks corresponding to surface silicon atoms a complex substrate reconstruction can be ruled out.All the inconsistencies between the earlier experimental results are eliminated with our structural model. The determination of the geometric structure lays the foundation for a theoretical investigation of the interesting electronic structure of this system. We used the well established experimental technique SXRD to determine the structure of the Si(111)-(4×1)-In reconstruction. To minimi...

In-vacuum multi-modal monochromator for synchrotron-based hard x-ray micro-imaging AIP Conference Proceedings 1741, 040025 (2016)

The structure of the ͑3 3 1͒ reconstructions of the Si(111) and Ge(111) surfaces induced by adsorption of alkali metals has been determined on the basis of surface x-ray diffraction and low-energy electron diffraction measurements and density functional theory. The ͑3 3 1͒ surface results primarily from the substrate reconstruction and shows a new bonding configuration consisting of consecutive fivefold and sixfold Si (Ge) rings in ͗110͘ projection separated by channels containing the alkali metal atoms. [S0031-9007(98)05973-0] PACS numbers: 61.10.Eq, 61.14. Hg, 68.35.Bs, 71.15.Mb Over the last decade there has been a large effort to understand the structure and properties of reconstructions on elemental semiconductor surfaces. The main driving force behind these reconstructions is the reduction of the number of dangling bonds without introducing too much strain in the surface region. Three structural elements meeting this principle have emerged so far. Particularly important are adatoms which saturate three dangling bonds on (111) surfaces while creating only one unsaturated bond. Adatoms stabilize the clean Ge(111)-c͑2 3 8͒ surface [1] and are also a major stabilizing factor in the dimer-adatom-stacking-fault model of the clean Si͑111͒-͑7 3 7͒ surface [2]. The second structural element that effectively reduces the number of dangling bonds is the dimer frequently found on the (001) surfaces [3]. The third structural element is the p-bonded chain which was first proposed for the clean Si͑111͒-͑2 3 1͒ reconstruction [4]. Yet this simple principle has been of no utility in predicting surface structures as demonstrated by the metal induced ͑3 3 1͒ reconstructions on the (111) surfaces of Si and Ge. Despite the small unit cell, the atomic geometry is still unknown and has been heavily debated over the last ten years [5][6][7][8][9][10][11][12][13]. The mere observation of the symmetry-breaking ͑3 3 1͒ unit cell calls for a unidirectional structural motif and it was, therefore, appealing to introduce p-bonded chains to explain the 3 3 1 periodicity. At present, there are two promising models for the ͑3 3 1͒ reconstruction that have been proposed on the basis of scanning tunneling microscopy (STM) [8], electronic properties [9], and total-energy calculations [10]. The Seiwatz model [see Fig. 1(a)] [7,11,12] consists of parallel p-bonded chains formed by fivefold rings of Si (Ge) atoms in ͗110͘ projection, separated by empty channels, with a top-site adsorbate saturating the surface dangling bonds. The second model is the extended Pandey model [10,13] [see Fig. 1(b)] which consists of a sevenfold ring carrying the p-bonded chain alternating with a five and six-member ring of Si. It is intuitive to describe the ring sequences from these models with the notation 567567 (extended Pandey) and 500500 (Seiwatz model). Unfortunately, neither of these structures is able to explain our surface x-ray diffraction data (SXRD) or low-energy electron diffraction (LEED) data.We determined the structure by using a multipletechnique ...

The imaging beamline (IBL/P05) operated by Helmholtz Zentrum Geesthacht (HZG) at the DESY PETRA III storage ring consists of two experimental stations: A micro tomography and a nano tomography end station.Here an overview of the experimental setups and the data acquisition will be given. In addition some first results out of the wide range of applications using the micro tomography station at P05 will be shown. Furthermore, we present first results of the nano tomography end station. These were obtained with an x-ray microscopy setup, which currently operates at energies of 17.4 and 30 keV using polymer compound refractive lenses (CRLs) and rolled prism lenses. Taken together these results clearly show the high potential of the newly built imaging beamline IBL.

A magnetostriction-induced structural phase transition in a single crystal of TbNi 2 B 2 C has been studied by high resolution x-ray diffraction. On cooling, we have observed a tetragonal-to-orthorhombic distortion below the Néel temperature, 14.3 K, similar to what has been seen in ErNi 2 B 2 C. The mismatch between the a and b lattice parameters increases continuously with decreasing temperature up to a value of a/bϪ1Ϸ0.55% at the lowest temperature measured, Tϭ8.6 K. ͓S0163-1829͑99͒08433-7͔