Exchanges between Si and Pb adatoms on Si(111)

Real-time observation by high-temperature scanning tunneling microscopy of exchanges between Si and Pb atoms on a Si(111)-√3 × √3 surface is reported. The exchange rate is obtained as a function of the temperature. The activation energy of the exchange is about 1.2 eV, and the prefactor, shown to depend on the Pb coverage, is from 2 × 10¹⁰ to 8 × 10¹¹ s⁻¹. This prefactor is much larger than that for the exchange between Pb and Ge adatoms on a Ge(111)-c(2 × 8) surface, indicating that the adatom arrangement greatly influences the exchange mechanism. We also report that metastable 9 × 9 reconstruction appears during Pb desorption.     

Surface electronic structure of polar NiO(111) films

The surface and electronic structure of polar NiO(111) films with or without facets, prepared on a Mo(110) substrate, were in situ studied using various surface analytical techniques. A new surface state located at 0.8–1.8 eV measured by electron energy loss spectroscopy was observed on faceted NiO(111) films, which is originated from surface Ni vacancies. This surface state is decreased by annealing or deposition of Ni atoms. The experimental results indicate that the charge transfer occurs between surface and bulk of the faceted NiO(111) films. Present work provides a model surface with polarity and facets, which can be used for further investigation on chemical adsorption of atoms or molecules as well as selective reaction.     

Conductivity of ultrathin Pb films during growth on Si(111) at low temperatures

The dipole modes of non-parabolic quantum dots are studied by means of their current and density patterns as well as with their local absorption distribution. The anticrossing of the so-called Bernstein modes originates from the coupling with electron-hole excitations of the two Landau bands which are occupied at the corresponding magnetic fields. Non-quadratic terms in the potential cause an energy separation between bulk and edge current modes in the anticrossing region. On a local scale the fragmented peaks absorb energy in complementary spatial regions which evolve with the magnetic field. Received 3 December 2001 / Received in final form 5 April 2002 Published online 9 July 2002     

Temperature dependence of surface electronic structure of Si(111) surface

Temperature dependence of angle-resolved ultraviolet photoelectron spectra has been obtained for Si(111) surfaces starting with a thermally quenched “1 × 1” surface and ending with a high temperature “1 × 1” surface. it has been found that the surface state at 0.8 eV below the Fermi level exhibits degradation with the increase in temperature, which explains the difference of surface electronic structures between a quenched “1 × 1” surface and a high temperature “1 × 1” surface. Electron correlation effect in a dangling-bond derived surface state is postulated as a cause for the phenomenon.     

Initial stages of praseodymium growth on Si(111): morphology and electronic structure

An STM study of the Pr---Si(111)-(7 × 7) interface reveals a much more heterogeneous growth morphology than is suggested by diffraction techniques and spectroscopies which average over the surface. Deposition of 1 ML followed by annealing at 650°C gives the most orderly growth, but this falls short of 2D epitaxy. At high temperatures (> 1000°C), the small amount of rare earth remaining on the surface stabilises some novel Si(111) surface reconstructions.     

Nucleation and growth of Si on Pb monolayer covered Si(111) surfaces

With a scanning tunneling microscope (STM), we study the initial stage of nucleation and growth of Si on Pb monolayer covered Si(111) surfaces. The Pb monolayer can work as a good surfactant for growth of smooth Si thin films on the Si(111) substrate. We have found that nucleation of two-dimensional (2D) Pb-covered Si islands occurs only when the substrate temperature is high enough and the Si deposition coverage is above a certain coverage. At low deposition coverages or low substrate temperatures, deposited Si atoms tend to self-assemble into a certain type of Si atomic wires, which are immobile and stable against annealing to ~ 200 °C. The Si atomic wires always appear as a double bright-line structure with a separation of ~ 9 Å between the two lines. After annealing to ~ 200 °C for a period of time, some sections of Si atomic wires may decompose, meanwhile the existing 2D Pb-covered Si islands grow laterally in size. The self-assembly of Si atomic wires indicate that single Si adatoms are mobile at the Pb-covered Si(111) surface even at room temperature. Further study of this system may reveal the detailed atomic mechanism in surfactant-mediated epitaxy.     

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 414–418 (10 March 1997)     

Characteristics of low-temperature-grown GaN films on Si(111)

In this paper, we report on the characteristics of GaN films grown on Si(111) at a low temperature (200 °C) by electron cyclotron resonance (ECR) plasma-assisted metalorganic chemical vapor deposition (PA-MOCVD). Structural analysis of the GaN films was performed by using scanning electron microscopy (SEM), atomic force miscroscopy (AFM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), and Rutherford backscattering spectrometry (RBS). Post deposition analysis revealed high quality crystalline GaN was obtained at this low temperature. Electrical analysis of the GaN films was done by using current-voltage (I-V) measurements where electrical characterizations were carried on GaN/Si heterojunction and Schottky barrier diodes. Rectification behaviour was observed for the isotype GaN/Si (n-n) heterojunction. Ideality factors and Schottky barrier heights for Ni and Cr Schottky barriers on GaN, were deduced to be 1.4 and 1.7; and 0.62 and 0.64 eV, respectively.     

Growth of Ag on Pb Island with Si(111) Substrate

We study the growth of Ag on Pb island surface with low temperature scanning tunnelling microscopy.Two growth modes,the subsurface island mode and the surface alloy mode,are observed on tie substrate at room temperature and at 100 K,respectively.In the surface alloy mode,the perfect alloy AgPb_2 is formed on the Pb island surface after annealing.The two growth modes at different substrate temperatures are attributed to the existence of an exchange barrier of Ag atoms on the Pb island surface.The modulation of the exchange barrier by the quantum well states is also observed on the Pb island.     

Electronic structure of Si(111) surfaces

We report on new angle-resolved photoemission studies of Si(111) 2 × 1 and 7 × 7 surfaces. The emission from the 2 × 1 surface shows much structure. For normal emission the energy positions are insensitive to the photon energy in the range 19–27 eV. The emission has been interpreted as a probe of the surface density of states, SDOS, including both surface states, resonances and bulk-like states. The SDOS was also calculated as a function of parallel momentum k_∥ for a model of the Si(111) 2 × 1 surface obtained from energy minimization considerations. We identify emission from the dangling bond band, which has a positive dispersion of 0.6 eV, and also emission from surface resonances which have some character of the compressed and stretched back bonds. There are also other predicted surface resonances that correspond to experimental peaks which have not been identified in previous work. Except for the dangling bond band, the surface resonances are limited in k_∥ space, so that it is not possible to follow these resonance bands over all angles. Maximum intensity for the normal emission from the dangling bond is obtained at 23 eV, while the emission from the lowest s-like states monotonically increases towards 30 eV photon energy. When annealing the cleaved 2 × 1 surface to the 7 × 7 reconstructed surface, the spectra broaden significantly. The intensity of the dangling bond decreases and we see a very small metallic edge.