Site-resolved electronic structure of Al nanocluster fabricated on Si(111)7 × 7 surface

Abstract

We have done scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) as well as current imaging tunneling spectroscopy (CITS) of an Al nanocluster periodic array of a submonolayer-Al/Si(111) system. To understand the formation mechanism of this system in detail, a phase diagram of the Al/Si(111) has been carefully produced. Among several structural phases, the nanocluster phase appears for the deposition thickness of 0.24-0.5 ML at a substrate temperature of 550• C. It has been confirmed that these growth conditions should be carefully chosen to produce the well-defined nanocluster. The site-resolved STS spectra of Al nanocluster at 78 K show an insulating energy gap of 3.3 eV. In the CITS images, we have found different features of space-resolved tunneling current for the filled and empty states, which markedly depend on atomic sites and also on inequivalent half-unit cells.

Tip-induced band bending effect and local electronic structure of Al nanoclusters on Si(111)

“…Therefore, the carrier concentration takes minimum around V S = + 4.0 V, and then, actually, the STS spectra of the n0 cluster on the n-type Si ͑111͒ substrate have shown a significant gap of 3.3 V and a structureless feature due to an insufficient current flow from tip to substrate. 12 From the present result, it is important to know the carrier behavior in the probing area for STM/STS on the insulating surface. At least, if one carries out STM/STS experiment to observe fundamental local electronic structure using the insulating surface formed on Si ͑111͒ 7 ϫ 7, a p-type substrate would be preferable.…”

“…It is noted that our former STS results for the same Al nanocluster phase on the n-type Si ͑111͒ substrate are consistent with the present experimental results with the p-type Si substrate in the occupied state. 12 However, the corresponding STS spectra with the n-type Si surface have shown the onset at ϳ + 2.2 V, which is higher by about 1 V compared to the case of the p-type substrate. Besides, the observed sharp peaks in the unoccupied state for the p-type surface have been smeared out for the n-type surface.…”

“…Formerly, we have performed STM/scanning tunneling spectroscopy ͑STS͒ and current imaging tunneling spectroscopy ͑CITS͒ for the Al nanocluster periodic array grown on the n-type Si ͑111͒ substrate, 12 where a significant energy gap of 3.3 eV was observed at 78 K. From these results, the empty-state STS spectra of Si and Al atoms within the cluster on the faulted half unit cell ͑FHUC͒ and the unfaulted half unit cell ͑UFHUC͒ have just shown a structureless feature. As is well known for metal-insulatorsemiconductor ͑MIS͒ system, metal tips definitely induce a band bending on the semiconductor surface.…”