Size-dependent lattice parameters of microstructure-controlled Sn nanowires
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Jae Yong Songa) and Hyun Min Park Division of Industrial Metrology, Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea; and University of Science and Technology, Daejeon 305-333, Republic of Korea (Received 4 March 2011; accepted 23 June 2011)
The size dependence of the lattice parameter of nanosolids has extensively been studied because lattice strain engineering is important in controlling the physical properties of nanowires (NWs), such as band gap, carrier transport, mechanical strength, etc. We have investigated the sizedependent lattice behavior of microstructure-controlled Sn NWs with radii of 7–35 nm. The NW microstructures were controlled as single-crystal, granular, and bamboo structures in the longitudinal direction. Results showed that the a-axis lattice parameter in the [100]-longitudinal direction of NWs can be controlled within 1% by varying the wire microstructure for the same wire radius because it is strongly dependent on the microstructure and the wire radius. Moreover, as the randomness of the grain orientation in the microstructure-controlled NWs increases, by which the anisotropy of surface stress is effectively reduced, the lattice strain of the NW can be compressive or tensile as a function of the wire radius. The longitudinal lattice parameters of microstructure-controlled Sn NWs can be tailored by reducing the effective anisotropy of surface stresses under a dimension confinement in the nanometer scale.
I. INTRODUCTION
Crystallinity, e.g., lattice strain, is important in tailoring the functional properties of nanowires (NWs) and can be controlled by modifying surface stresses.1 Thus, exploration in the field of surface stress engineering can advance the development of NW-based devices; in the advanced thin-film transistor, compressive or tensile stresses have been used to enhance electron or hole mobilities, respectively.2,3 Because the surface layers are relaxed and sometimes reconstructed with the spill-out of surface electrons and changes in surface chemical bondings,4–6 the size-dependent properties of nanoscale materials are seriously influenced by the surfaces and are more effectively affected with the surface-to-volume ratio increasing. So far, through experiments and theoretical analyses, it has been demonstrated that lattice deformations in nanoparticles and NWs are induced by surface stresses and can result in phase transformation.7,8 Surface stresses are caused by imperfections of the coordination number at the surfaces. The bond-order-length-strength model, which is based on such imperfections, has successfully described the sizedependent properties of nanoscale materials, such as lattice contraction, cohesive energy, and strengthening.9 Lattice a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.218 J. Mater. Res., Vol. 26, No. 16, Aug 28, 2011
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contractions in various metal nanoparticles and NWs were experimentally observed10–16 and theoretical
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