Formation of Gold Nanowires on MgO Surfaces
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Formation of Gold Nanowires on MgO Surfaces Akira Ueda1, Richard R. Mu1, Vanessa Saunders1, Thurston Livingston1, Marvin H. Wu1, Vera L. Arantes2, and Don O. Henderson1 1 Chemical Physics Laboratory, Department of Physics, Fisk University, Nashville, TN 37208, U.S.A. 2 FEAU-Universidade do Vale do Paraiba, Sao Jose Campos, SP, Brazil ABSTRACT Gold nanowires were fabricated on the stepped MgO (100) surfaces. The stepped MgO (100) surfaces were produced by polishing (100) surfaces at an inclined angle ~1º toward a  direction. An atomic force microscope image indicates that gold nanowires have grown at the steps on MgO (100) surface with a height of ~ 2 nm and a width of ~60 nm. INTRODUCTION Recently nano-size materials have been paid attentions due to their diverse potentials in the fields of laser, optics, computer, electronics, biomedical science, and so on. Moreover, the nano-size materials provide the fields to study fundamental physics such as the quantized conductivity and the quantum Hall effect . Regardless of any actual applications at this stage, the gold nanowire formation on MgO (100) surfaces was attempted. As shown later in the experimental results section, we have observed that the annealing single crystalline MgO (100) surface at high temperature in an oxidizing atmosphere can cause the step formation along two possible  directions on the (100) surface. By tilt-polishing the surface toward one of  directions by an angle of ~1o, we may depress the step formation of the other of two possible  directions, as shown in Fig.1.
(b) tilt-polished 0] [11 g n alo pe o l s
Figure 1 Schematic model of the regulated steps for the tilt-polished MgO surface. (a) Two possible  directional step edges can be formed on an as-received MgO (100) surface. (b) One-directional step edges can be formed on the tilt-polished MgO surface.
Once we obtain such regulated steps, we may fabricate gold nanowires by depositing gold and by a suitable annealing recipe. We expect that gold atoms have the tendency to accommodate at the step sites, and the accumulation of the gold atoms leads to the formation of gold nanowires. During this research, we have come across a series of recent publications by Himpsel’s group  in which the step arrays of Si were formed on a Si (111) 7x7 reconstructed surface by miscutting a Si substrate and special annealing procedures. They also deposited CaF2 to make some patterns for the formation of nanowires or quantum dots, which is similar to the way of the lithographic procedures. Their method on Si has been established and the applications are also in a process. For our case, the substrate is a single crystalline MgO that is transparent in visible-near IR range, and it may have an advantage for the optical applications. EXPERIMENTAL The substrates were purchased from Princeton Scientific Corp. (Princeton, NJ) and were cut into smaller pieces suitable for the optical transmission measurements and the atomic force micro