Surface Science 458 (2000) 113–122 www.elsevier.nl/locate/susc
Growth of silicon nanostructures on graphite Paul Scheier 1, Bjo¨rn Marsen, Manuel Lonfat, Wolf-Dieter Schneider 2, Klaus Sattler * Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, HI 96822, USA Received 23 November 1999; accepted for publication 14 February 2000
Abstract Silicon nanostructures such as small clusters, superclusters, and elongated chains, with an average diameter of a few nanometers, have been synthesized by magnetron sputtering on cleaved highly oriented pyrolytic graphite (HOPG). Scanning tunneling microscopy (STM ) reveals that flat, defect-poor areas of the HOPG surface are covered with almost uniformly sized silicon clusters of 0.6±0.2 nm, 5.1±1.2 nm, and 15.4±3 nm diameter. Surface regions with defects such as pits and craters, descending a few layers into the graphite surface, are sparsely covered with silicon. Most of the deposited material, with an average diameter of 2 nm, is found to be attached to the monatomic step edges forming the crater rims. A simulation of the growth process, i.e. deposition of silicon atoms onto a surface with built-in defects, and subsequent surface diffusion and aggregation of the adatoms, convincingly reproduces most of the Si nanostructures observed in the STM topographs. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Clusters; Computer simulations; Growth; Scanning tunneling microscopy; Silicon; Sputter deposition
1. Introduction Clusters deposited on well-defined surfaces allow the construction of new materials with novel properties [1]. The current urge for an ever decreasing size of components in the microelectronics industry renders this particularly relevant for silicon clusters [2]. Their electronic and optical properties are especially sensitive to their size and structure [3–13]. Since the earliest study on silicon * Corresponding author. Tel.: +1-808-956-8941; fax: +1-808-956-7107. E-mail addresses:
[email protected] (P. Scheier),
[email protected] ( K. Sattler) 1 Permanent address: Institut fu¨r Ionenphysik, Universita¨t Innsbruck, A-6020 Innsbruck, Austria. 2 Permanent address: Institut de Physique de la Matie`re Condense´e, Universite´ de Lausanne, CH-1015 Lausanne, Switzerland.
clusters by Honig [14], several experimental investigations on silicon clusters have been performed [15–30], including a few STM studies [23,26–30]. Kuk et al. [23] deposited Si clusters on Au(001) 10 and observed a wide variety of different cluster images, even though size-selected clusters were deposited. McComb et al. [26 ] observed a sitespecific variation in the electronic characteristics of Si clusters, which were deposited without size selection but observed with atomic resolution. Dinh et al. [27,28], in the context of an investigation of the optical properties of passivated Si nanostructures, synthesized Si nanocrystals by laser ablation and by thermal evaporation in an Ar buffer gas, and determined the size distribution of a monolayer of these nanostructures on HOPG with an STM. Size-selected Si and Si clusters 30 39 were imaged with a low-temperature STM on Ag(111) [29]. Manipulation experiments and the
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appearance of the clusters in the images indicated soft-landing of the clusters. Recently, again in an STM study, Marsen and Sattler [30] succeeded in creating fullerene-structured nanowires of silicon by magnetron sputtering on HOPG substrates. The present STM study intends to investigate in more detail the sub-monolayer and monolayer growth regimes of Si nanostructures on defectpoor and defect-rich HOPG surfaces.
2. Experimental The synthesis of Si nanostructures was performed in a high-vacuum chamber with a base
pressure of p
