Epitaxial growth of Bi thin films on Ge(111)

AIP Conference Proceedings, 2003

Growth of thin metal films on semiconductors has long been subjected to extensive experimental and theoretical studies. As the applicability of well-ordered structures in electronic, optical or magnetic devices depends significantly on their size and distribution, it is necessary to understand the processes governing the growth of such structures. In this paper we present results of an investigation of room temperature growth of Bi on Si(111). We clarified that rotationally disordered, pseudo-cubic, Bi{012} islands with uniform height are formed in the initial stages of Bi film growth. With increasing of the amount of Bi on the surface, islands interconnect maintaining their uniform height. This process is further accompanied by the unique and unexpected structural phase transition of the {012} film into a hexagonal Bi(001) film.

Journal of Surface Engineered Materials and Advanced Technology, 2013

The epitaxial growth of Ge on Si(111) covered with the 0.3 nm thick SiO 2 film is studied by scanning tunneling microscopy. Nanoareas of bare Si in the SiO 2 film are prepared by Ge deposition at a temperature in the range of 570˚C-650˚C due to the formation of volatile SiO and GeO molecules. The surface morphology of Ge layers grown further at 360˚C-500˚C is composed of facets and large flat areas with the Ge(111)-c(2 × 8) reconstruction which is typical of unstrained Ge. Orientations of the facets, which depend on the growth temperature, are identified. The growth at 250˚C-300˚C produces continuous epitaxial Ge layers on Si(111). A comparison of the surface morphology of Ge layers grown on bare and SiO 2-film covered Si(111) surfaces shows a significantly lower Ge-Si intermixing in the latter case due to a reduction in the lattice strain. The found approach to reduce the strain suggests the opportunity of the thin continuous epitaxial Ge layer formation on Si(111).

Nanotechnology, 2017

Here we demonstrate the controlled growth of Bi(110) and Bi(111) films on an (insulating) α-Al 2 O 3 (0001) substrate by surface X-ray diffraction and X-ray reflectivity using synchrotron radiation. At temperatures as low as 40 K, unanticipated pseudo-cubic Bi(110) films are grown having a thickness ranging from a few to tens of nanometers. The roughness at the film-vacuum as well as at the film-substrate interface, can be reduced by mild heating, where a crystallographic orientation transition of Bi(110) towards Bi(111) is observed at 400 K. From 450 K onwards high quality and ultrasmooth Bi(111) films are formed. Growth around the transition temperature results in the growth of competing Bi(110) and Bi(111) thin film domains.

Physical Review B, 2009

Acta Physica Polonica A

P r oceedi ng s o f t h e 3rd I n t ern at io n al Sy m p osi u m on Scan ni n g Pr o b e Sp ect rosc opy , SPS '0 3

1997

The growth of bismuth on Ge(001) has been studied using scanning tunneling microscopy. Deposition of one-monolayer (ML) Bi at room temperature and subsequent annealing at 500 K results in the formation of a well-ordered (2 x n) vacancy line network oriented perpendicular to the dimer rows. Deposition of two-monolayer Bi under the same conditions results in the formation of square-shaped pits with depths up to 10 ML. The edges of these pits run along the two dimer row directions. Careful analysis of these pits reveal that they mainly consist of (111) and (113) facets. We argue that the morphological transition from the vacancy line network to the square shaped pits pattern is driven by a modification of the surface strain tensor.

Journal of Synchrotron Radiation, 1995

The two-dimensional electronic band structure of monolayer Bi on GaP(ll0) has been mapped using angle-resolved UV photoelectron spectroscopy (ARUPS) with synchrotron radiation. Surface photovoltage effects are corrected for by simultaneous second-order core spectroscopy. From valenceband spectra along the four symmetry directions of the surface Brillouin zone at three photon energies it is possible to distinguish three states as surface related. The topmost band is found to be inside the fundamental band gap, at ca 0.75 eV above the bulk valence-band maximum. Comparison with other V/III-V(110) systems shows that this system is not significantly different, despite the relatively large size of the Bi atoms with respect to the GaP lattice; in a selective comparison with InP and GaAs it would appear that Bi-substrate anion bonding is a more important factor than strain.

Surface Science, 1998

We have followed by scanning tunneling microscopy (STM ) the growth of thin Ge films obtained by reactive deposition epitaxy on Si(111) substrates kept at 500°C. For a Ge coverage less than 0.45 ML, STM images show large 7×7 flat areas without any protrusion. For increasing coverage, flat, triangular 5×5 islands start nucleating while the Si substrate retains the 7×7 reconstruction. The islands' evolution, up to the completion of the wetting layer, is described in the framework of a statistical model of growth. At 3 ML, the composition and ordering of the wetting layer are investigated by Current Imaging Tunneling Spectroscopy (CITS ) measurements, revealing small differences in the atomic corrugations. The analysis of topographic and current images supports an elemental composition for the topmost layer. At coverages larger than 3 ML, thick Ge islands nucleate according to the Stranski-Krastanov mechanism of growth. We analyze the evolution of the lattice strain up to 15 ML coverage. A clear expansion of the lattice parameter as a function of coverage is found both on the islands' top and on the wetting layer.

Physical Review B, 2015

By combining scanning tunneling microscopy with density functional theory it is shown that the Bi(111) surface provides a well-defined incorporation site in the first bilayer that traps highly coordinating atoms such as transition metals (TMs) or noble metals. All deposited atoms assume exactly the same specific sevenfold coordinated subsurface interstitial site while the surface topography remains nearly unchanged. Notably, 3d TMs show a barrier-free incorporation. The observed surface modification by barrier-free subsorption helps to suppress aggregation in clusters. It allows a tuning of the electronic properties not only for the pure Bi surface, but may also be observed for topological insulators formed by substrate-stabilized Bi bilayers.

The Journal of Physical Chemistry C

Defects introduced to the surface of Bi(111) break the translational symmetry and modify the surface states locally. We present a theoretical and experimental study of the 2D defects on the surface of Bi(111) and the states that they induce. Bi crystals cleaved in ultrahigh vacuum (UHV) at low temperature (110 K) and the resulting ion-etched surface are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) as well as spectroscopy (STS) techniques in combination with density functional theory (DFT) calculations. STS measurements of cleaved Bi(111) reveal that a commonly observed bilayer step edge has a lower density of states (DOS) around the Fermi level as compared to the atomic-flat terrace. Following ion bombardment, the Bi(111) surface reveals anomalous behavior at both 110 and 300 K: Surface periodicity is observed by LEED, and a significant increase in the number of bilayer step edges and energetically unfavorable monolayer steps is observed by STM. It is suggested that the newly exposed monolayer steps and the type A bilayer step edges result in an increase to the surface Fermi density as evidenced by UPS measurements and the Kohn−Sham DOS. These states appear to be thermodynamically stable under UHV conditions.