Structure of Cleaved (001) USb 2 Single Crystal
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1184-HH02-02
Structure of Cleaved (001) USb2 Single Crystal Shao-Ping Chen1, Marilyn Hawley1, Phil B. Van Stockum2, Hari C Manoharan2 and Eric D Bauer1 1 Los Alamos National Laboratory, Los Alamos, New Mexico; 2Department of Physics and Stanford Institute for Materials and Energy Sciences, Stanford University, Stanford, California ABSTRACT We have achieved what we believe to be the first atomic resolution STM images for a uranium compound taken at room temperature. The a, b, and c lattice parameters in the images confirm that the USb2 crystals cleave on the (001) basal plane as expected. The a and b dimensions were equal, with the atoms arranged in a cubic pattern. Our calculations indicate a symmetric cut between Sb planes to be the most favorable cleavage plane and U atoms to be responsible for most of the DOS measured by STM. Some strange features observed in the STM will be discussed in conjunction with ab initio calculations. INTRODUCTION The purpose of this work is to demonstrate the power of scanning tunneling microscopy (STM) techniques combined with a theoretical underpinning to determine the surface atomic structure and properties of actinide materials, such as the quasi 2-dimensional uranium dipnictide USb2 single crystal, thereby contributing to the understanding of their surface structural and electronic properties. The members of this interesting UX2 (X=P, As, Sb, Bi) series of compounds display dual localized and itinerant 5f electron behavior within the same compound due to the hybridization of the 5f orbitals with the conduction band [1]. With the exception of UO2, which has to be studied at elevated temperature to generate enough carriers for STM imaging [2,3,4], STM techniques have not been applied successfully to the characterization of the surface atomic structure of any other single crystal actinide compound, to the best of our knowledge. However, STM has been used to a limited extent for the study of some cerium compounds [5]. STM probes electronic properties at the atomic level and can directly provide information about the local density of filled and empty states (LDOS) states simultaneously. A STM topograph provides the local atomic arrangement and spacing of the atoms on the surface, local defect structures (e.g. steps, vacancies, and kink sites), and the presence of contaminants, all of which are averaged over when probed in photoemission studies. The quasi two-dimensional USb2 has a layered tetragonal structure that is easily cleaved and has been extensively studied by a number of different techniques, such as resistivity [6], Hall effect measurements [7], photoemission [8] and angle-resolved photoemission spectroscopy [9,10], de Haas-van Alphen [11-13], neutron diffraction [14], nuclear magnetic resonance [15], and U238 Mossbauer spectroscopy [16] techniques. Here, we provide local information about the surfaces of this interesting compound, which we find to contain a high density of defects.
EXPERIMENT Single crystals of USb2 were grown in Sb flux growth [17]. The crystals were prep
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