Microscopic and electronic structure of semimetallic Sb and Semiconducting AlSb fabricated by nanoscale electrodeposition: An in situ scanning probe investigation.

The nanoscale electrocrystallization of pure Sb and the compound semiconductor AlSb on Au(111) has been studied by in situ scanning probe techniques (STM and STS) employing an ionic liquid electrolyte, {AlCl3-[C4mim]+Cl-} (1:1) containing SbCl3. The characteristic changes of the electronic structures with varying potentials have been probed for the first time by normalized differential conductance spectra, (dI/dU)/(I/U). In the underpotential deposition range of Sb the formation of two layers is observed. For the first monolayer a (square root 3 x square root 3)R30 degrees structure is determined from atomically resolved STM images. During the deposition and dissolution of the Sb monolayers characteristic wormlike or spinodal structures appear indicating surface alloying of antimony with the gold substrate. Under overpotential conditions two different Sb structures have been observed. If the deposition potential is continuously stepped to -0.1 V, Sb nanostripes form. On the other hand, randomly dispersed small clusters occur if the potential is jumped from 0.0 to -0.3 V vs Al/Al(III). Both modifications exhibit typical semimetallic behavior as shown by the STS spectra. At -1.1 V the cyclic voltammogram shows a clear reduction wave that is assigned to AlSb compound formation. Deposits in this potential range are characterized by a homogeneous distribution of clusters with diameters of approximately 20 nm. Conductance spectra of these clusters exhibit the main features of the electronic structure of the bulk semiconductor AlSb, with a band gap of 2.0 +/- 0.2 eV. Electrodeposition experiments on both sides of the compound deposition potential show a strong doping effect that is manifest in the corresponding conductance spectra.