Ag growth on Si(111) with an Sb surfactant investigated by scanning tunneling microscopy

We have investigated a room-temperature growth mode of ultrathin Ag films on a Si(111) surface with an Sb surfactant using STM in a UHV system. On the Sb-passivated Si surface, small sized islands were formed up to 1.1 ML. Flat Ag islands were dominant at 2.1 ML, coalescing into larger islands at 3.2 ML. Although the initial growth mode of Ag films on the Sb-terminated Si(111) surface was Volmer-Weber (island growth), the films were much more uniform than Ag growth on clean (Si(111) at the higher coverages. From the analysis of STM images of Ag films grown with and without an Sb surfactant, the uniform growth of Ag films using an Sb surfactant appears to be caused by the kinetic effects of Ag on the preadsorbed Sb layer. Our STM results indicated that Sb suppresses the surface diffusion of Ag atoms and increases the Ag-island density. The increased island density is believed to cause coalescence of Ag islands at higher coverages of Ag, resulting in the growth of atomically flat and uniform Ag islands on the Sb surfactant layer.     

Investigation of the (111) surface of P-doped Si by scanning tunneling microscopy

Received: 27 March 1998     

Correlations between the scanning tunneling microscopy imaged configurations and the electronic structure on stepped Si(111)-( 7x7) surfaces

We have observed the dependence of the scanning tunneling microscopy (STM) imaged atom intensity within the (7x7) unit cell on stepped Si(111) as a function of the tunneling voltage. Pronounced differences from the corresponding atom intensity on the flat surface are observed for the contrast of atoms on the low versus the high side of the step and for the contrast between the faulted versus unfaulted subcells of the (7x7) structure. These differences can be accounted for by changes in the electronic structure within the (7x7) subcells adjacent to the step. Calculations of the local density of states and the STM images using a tight-binding method are in excellent agreement with the experimental results.     

Nature of contrast in Ge/Si(111) layers in scanning tunneling microscopy in the presence of Bi and Sb surfactants

It is known that the use of Bi surfactant (unlike Sb) upon the growth of Ge layers on Si(111) increases the contrast between Ge and Si atoms in a scanning tunneling microscope. This makes it possible to distinguish the Ge and Si surfaces. This effect is studied using computer simulation based on the density functional theory. To explain the observed difference between the Ge and Si layers, both structural and electronic effects are considered. The local density of electronic states, as well as the corresponding decay length to vacuum, has been calculated for each of the surfaces. The simulation results have been compared to the previous scanning tunneling microscopy data.     

Structure of AuSi nanoparticles on Si(111) from reflection high-energy electron diffraction and scanning tunneling microscopy

Gold-rich Au _x Si_1−x particles grown on Si(111)7 × 7 are studied by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). The diffraction patterns reveal that (1) at least two different crystal structures coexist on the substrate; (2) the most prominent data correspond to a rhombohedral or quasi closed-packed structure; and (3) the particles show formation of an unusual contact facet to the substrate. Complete crystal alignment of the particles to the substrate lattice is found with no hints of random orientation. The findings are compared to STM images in terms of their structure, orientation, and morphology.     

Electronic excitation of ice monomers on Au(111) by scanning tunneling microscopy

Scanning tunneling microscopy, inelastic tunneling spectroscopy, and electron induced manipulation are used to investigate electronic excitation of D₂O monomers and small clusters adsorbed at the elbows of the Au(111) reconstruction. Diffusion of molecules, dissociation of clusters, and rearrangement of the reconstruction is induced by electronic excitation. Threshold energies of between 200 and 250 meV and of 446 meV are explained by combined vibrational modes of D₂O molecules. External vibrational modes of D₂O molecules on Au(111) are identified by inelastic tunneling spectroscopy at ≈18, 30, and 41 meV.     

Bistability in scanning tunneling spectroscopy of Ga-terminated Si(111)

Bistable electron transport, a phenomenon usually associated with double-barrier structures, has been observed with a conventional STM junction formed between a metal tip and a Ga-terminated Si(111) surface at 77 K. Large hysteresis loops appear in the current-voltage characteristics when electrons are injected from the tip to the surface. The turn-on bias varies from -3.1 to -4.0 V and shows an inverse dependence on the tip-sample distance, indicating a strong field effect. The turn-off bias, however, is essentially pinned at a conductance threshold of -2.7 V.     

Imaging surface electronic structure of NiAl(110) using low-temperature scanning tunneling microscopy

The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k_). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed.