Changxin Zhu

Observation of Initial Growth of In on Silicon(100) Surface

The initial growth of In on a Si(100) surface as a function of the coverage has been investigated using scanning tunneling microscopy (STM). In(2×2) is a frequently observed phase at coverages below 0.5 monolayer (ML), the In(2×1) phase appears at the coverage above 0.5 ML, and the coexistence of the In(2×2) and In(2×1) reconstructions becomes a dominant phase at the coverage between 0.5 ML and 1.0 ML. Further deposition of In above 1.0 ML gives rise to the onset of three-dimensional island nucleation and growth associated with layer-by-layer growth. The island is highly oriented with major axes along the directions. The island is located on the terrace adjacent to the step edge, suggesting that the step edge should be a preferred site for island nucleation.

Large area dimer vacancy array on the Si(100) surface studied by scanning tunneling microscope

Abstract Large area dimer vacancy arrays can be formed on the Si(100) surface when Si atoms are deposited on the Si(100)-2×1 surface followed by quenching from 1200°C. The dimer vacancy lines (DVLs) of the dimer vacancy array run perpendicular to the dimer rows and the basic building cells of the DVLs are: (i) a cluster of two missing dimers; (ii) a complex of one missing dimer and a cluster of two missing dimers. Small isolated islands with DVLs like that of the Si(100) surface are observed on the surface. The precursors of the islands are investigated. The formation mechanism of the island is that the interaction between the stress field of the dimers on the Si(100) surface and that of the island causes the dimer vacancies in the dimer rows of the island and the attraction between the dimer vacancies in adjacent dimer rows aligns the dimer vacancies.

Initial stage of aluminum thin film growth on Si(100) surfaces as observed by scanning tunneling microscopy

Abstract The phases of aluminum (Al) adsorbed on Si(100)-2 × 1 surfaces were investigated by using scanning tunneling microscopy (STM). The changes were observed as a function of the Al coverage over the range from 0.5 to 9 monolayers (ML). The STM images revealed that once a well-ordered Al-2 × 2 adlayer is completed at 0.5 ML, further deposition of aluminum results in surface roughness and disappearance of the Al-2 × 2 phase. This is due to the formation of Al clusters that absorb the Al ad-dimers without disruption of the Si-2 × 1 structure. The structure of the Al-2 × 1 phase was not observed at coverages above 0.5 ML. As the growth proceeds, the pseudomorphic layer relaxes to form islands at 2 ML. These islands are highly oriented and have a prominent epitaxial relationship between Al(110) and Si(100). This indicates that the Si-2 × 1 structure has a strong effect on the epitaxial growth of the Al islands.

Growth kinetics of aluminum on the Si(100) surface studied by scanning tunneling microscopy

Abstract The kinetic processes at the initial stage of Al on Si(100) were investigated as a function of the substrate temperatures by using scanning tunneling microscopy (STM). The experimental relationship between the island number density and the substrate temperature was obtained. It was found that there was a transition temperature T0 at which the island number density had a minimum value. The existence of the transition temperature was interpreted in terms of the competition between the reevaporation and capture of adatoms. Experimental results were quantitatively discussed through establishing the theoretical dependences of the island number density on the substrate temperatures below and above T0 by using probability analysis method. Then the adsorption energy Ea and the activation energy for surface diffusion, Ed, were determined.

STRUCTURES OF AL/SI(100) SURFACES AS DETERMINED BY SCANNING TUNNELING MICROSCOPY

The structures of Al/Si(100) surfaces with coverages below 0.5 monolayer have been determined using scanning tunneling microscopy (STM). Through careful STM measurements, Al dimers are atomically resolved, where the Al dimer bond is intuitively demonstrated to be parallel to the Si dimer bond. The atomic arrangements at the ends of Al dimer rows have been discussed on the basis of the interpretation of dual‐bias STM images. Two possible structures at the end of an Al dimer row are a single atom termination and a dimer termination, depending on whether the Al dimer row ends at a surface defect, respectively.

Formation and atomic structures of double-layer steps on Si(100) surfaces studied by scanning tunneling microscope

Abstract In this paper, we used an ultra-high-vacuum scanning tunneling microscope (STM) to study the step structures of the Si(100) surfaces and found that double-layer steps can exist even at a low miscut angle (∼0.5°) from the (100) direction. The double-layer B steps are caused by the shrinkage of the span of the single-layer steps, and basically run in a zigzag manner with many kinks. The second layer atoms are rebonded at the step edges, and the rebonded atoms form asymmetric dimers that make the outmost dimers on the upper terrace brighter. The asymmetric dimers propagate from the kink site and form local c-4×2 structures. Their related atomic structure models are discussed.

Atomic structures of kinks at double-layer steps on Si(100) surfaces

We studied the kink structures at double-layer step by scanning tunneling microscopy and catalogued the kinks into two types: complex kinks (composed of minus kinks and plus kinks) and simple kinks (only minus or plus kinks). Both of the kinks create a local A terrace. The dimers in the local A terrace are buckled. For a complex kink, the buckling of the dimers in the local A terrace is determined by the interaction of the buckled dimers propagated from minus kinks and plus kinks. For a simple kink, the buckling of the dimers in the local A terrace is determined by the buckling of the rebonded dimers at step edges. The directions of the buckled dimers are determined by the tensile stress between dimer rows. The brightness of the outermost dimers in an upper terrace is caused by the buckling of the dimers and the charge transfer between the two atoms of the dimers.