Antimony Cluster Manipulation on the Si(001) Surface by Means of STM
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ABSTRACT. We present results of the manipulation of antimony clusters on Si(001) by means of a scanning tunneling microscope. By adjusting tip-sample separation and pulse voltage, an antimony cluster can be removed from the sample surface without damaging it. The success rate of the removed-cluster redeposition from the tip back onto the surface is 30%. In the remainder of the attempts a square shaped structure is created that had a hillock in the center. The hillock exhibits a metallic-like I-V curve. Such a structure cannot be created without an Sb cluster previously removed from the surface and located on the tip.
TNTRODUCTION. The ability to create atomic-scale structures with the scanning tunneling microscope (STM) plays an important role in the development of nanoscale technology. For the investigation of nanoscale test structures and the development of practical nanoscale devices, it is desirable to produce atomically ordered and clean structures of any geometry. By using atomic manipulation with an STM, one can modify an already well ordered surface under conditions of UHV cleanliness. In the STM, strong chemical forces can be exerted on sample atoms and enormous current densities and electric fields can be achieved using relatively small voltages and currents. These interactions have been utilized to create isolated nanoscale structures by a number of methods. mechanically scribing a surface [1-3], creating an etch mask [4-8], decomposing precursor molecules [9-13], and manipulating atoms [14-38]. Basically there are three modes of atomic manipulation: lateral motion, deposition, and removal. Reproducible atomic manipulation and atomic-scale fabrication of general structures was demonstrated by Eigler at al. [15-17], who utilized an STM to move adsorbed atoms on a metal surface at cryogenic temperatures. Other nanoscale structures were created by moving islands of Cs atoms [23] on GaAs(1 10) to make larger island complexes and by accumulating Si atoms under the tip to create nanocolumns [24], crystalline nanoscale pyramids [25], and nanoneedles [26]. Additional examples of lateral motion include displacing adsorbed atoms of Si on Si(l 11) [18] and Cl on Si(0O1) [19], rotating dimers of Sb on Si(OO1) [20], and moving vacancies on GaP(l 10) [21,22]. Deposition of a single Ge atom onto Ge(1 11) surface from the STM tip was demonstrated in 1987 [14]. In 1990, clusters of atoms from a gold tip were reliably deposited onto various surfaces [27,28]. Individual atoms of hydrogen were deposited onto Si(l 11) surfaces from a PtIr tip supplied with hydrogen molecules from an ambient gas [29]. Recently, the assembly of atomic-scale 205 Mat. Res. Soc. Symp. Proc. Vol. 448 © 1997 Materials Research Society
structures was accomplished at room temperature by depositing silicon atoms from a W tip onto the Si(1 11) surface [30]. The atoms were placed onto the tip by first extracting them from the surface.
EXPERIMENTAL. Our experiments were conducted using a custom made STM in ultrahigh vacuum (UHV) with STM tips prepare
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