We have investigated the structure of Ag/Sb/Cu(111) surfaces by using time-of-flight impact collision ion scattering spectroscopy. Also, scanning tunneling microscopy measurements were used in studies of the topmost layers of thin film heteroepitaxy systems at room temperature. It was found that on a surface pre-covered with a 0.2 and 0.4 ML of deposited Sb, the (1) Ag(111)[112̄]//Cu(111)[112̄] versus (2) Ag(111) [1̄1̄2]//Cu(111)[112̄] modes of Ag layers become 50% versus 50%. These ratios are much different from deposition of Ag on clean Cu(111) surfaces. Furthermore, for 0.4 ML of Sb pre-covered Cu(111), the outermost first-layer of Ag atoms shift from fcc- to hcp-sites (only the top layer of Ag atoms occupies hcp-sites). In addition, for this case, a Ag(111)(√3×√3)R30°-Sb surface forms on top of the first Ag layer. For both 0.2 and 0.4 ML coverages, Sb atoms are transported to the next growing Ag layer during subsequent Ag deposition. Sb atoms displace up to 1/3 of the first-layer of Ag atoms and are incorporated into first-layer Ag atom sites with an outward displacement of 0.2 Å with respect to Ag atoms in the first layer. With a pre-coverage of Sb atoms, Ag(111) planes prefer to grow as type (2) mode between 300 and 633 K. This growth behavior of Ag(111) planes is different from that shown previously without Sb pre-coverage on Cu(111).

Barium silicides formed on the Si(100) surface have been investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The structure of the silicide surface depends on the preparation procedure; three kinds of silicide phases coexist on the surface when 2 monolayers (MLs) of Ba are deposited on Si(I 00) at the specimen temperature. of 850 K, while two of the three phases appear when 2 MLs of Ba are deposited on Si(100) at room temperature, followed by annealing at 850 K. The STS result indicates that all the phases show semiconducting behavior with a band gap of similar to 1.3 eV and that one of the three phases has local density of states (LDOS) at 2.5 eV below the Fermi energy, which coincides with the reported results of metastable de-excitation spectroscopy (MDS) and ultraviolet photoelectron spectroscopy (UPS).

Abstract Adsorbed structures of Ba on Si(1 1 1) surfaces have been investigated by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We compared the vicinal substrate surface toward [1 2 1] direction with the flat substrate surface of which the inclination from the (1 1 1) plane is small in order to confirm whether the step arrangement is caused by the cooperation of the superstructure on the surface and the proper miscut angle of substrate. On the vicinal Si(1 1 1) surface, one-dimensional step arrangement of 10-times the unit length terraces with a double-layer step height has been observed by STM after annealing at about 1220 K. On the flat Si(1 1 1) surface, three domains of 5×1 have been observed in the same temperature range by LEED and STM.

We investigated the strain relaxation process of GaP1-xNx/GaP and GaAs1-xNx/GaAs in order to clarify their mechanical characteristics by adding nitrogen atoms. It was observed by transmission electron microscopy (TEM) that the critical thicknesses were greater and the generation rates of the misfit dislocations were slower in the GaP1-xNx and GaAs1-xNx layers than those in the GaP layer with a similar lattice mismatch. The critical thickness of the GaAs1-xNx layer was greater than that of the GaP1-xNx layer for the same nitrogen composition of 2%. The direction of higher crack density was orthogonal to that of the higher misfit dislocation density. These results indicate that the propagation of dislocations is prevented in III–V–N alloys such as GaP1-xNx and GaAs1-xNx, so that these alloys are harder than III–V compounds that lack nitrogen atoms. This feature could be attributed to the dislocation pinning and alloy hardening effects due to nitrogen atoms.

Adsorbed structures of Ba on Si (111) surfaces have been investigated by LEED (Low Energy Electron Diffraction) and STM (Scanning Tunneling Microscopy). We compared the vicinal substrate surface with the flat substrate surface of which the inclination from the (111) plane is small in order to confirm whether the step arrangement is caused by the proper miscut angle of substrate. On the vicinal Si (111) surface, one-dimensional 10×1 structure was observed by LEED and the step arrangement of 10-times the unit length terraces with a double-layer step height has been observed by STM after annealing at about 950°C. On the flat Si (111) surface, 3 domains of 5×1 have been observed in the same temperature range by LEED and STM. It was confirmed that the step arrangement was caused by a cooperation of a proper miscut angle of the substrate and the superstructure on the terrace.

We have studied the "1 x 2" structure on 1/2 ML Ba/Si(100) by scanning tunneling microscopy (STM). This phase has two mirror symmetric unit cells, (4,0) x ( 1,2) and (4,0) X (1,- 2). Their combination leads a wavy structure in STM images. We discuss the structure in comparison with previous low-energy electron-diffraction studies, and propose a model of the ''1 x 2" structure where buckled Ba dimers locate on the second Si layer reconstructed into a dimerized ''1 x 2" phase.

Adsorbed structures of Ba on Si(111) surfaces have been investigated by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We compared the vicinal substrate surface toward [12̄1] direction with the flat substrate surface of which the inclination from the (111) plane is small in order to confirm whether the step arrangement is caused by the cooperation of the superstructure on the surface and the proper miscut angle of substrate. On the vicinal Si(111) surface, one-dimensional step arrangement of 10-times the unit length terraces with a double-layer step height has been observed by STM after annealing at about 1220 K. On the flat Si(111) surface, three domains of 5×1 have been observed in the same temperature range by LEED and STM.

We have investigated the growth of 3 monolayers (ML) of Ag on Cu(111) for substrate temperatures from 170 through 640 K by using time of flight-impact collision ion scattering spectroscopy (TOF-ICISS). Also, scanning tunneling microscopy (STM) topographs were taken after the deposition of 0.8 ML of Ag atoms at room temperature (RT). We observed that for deposition of Ag at substrate temperatures above 300 K, two different types of epitaxial growth exist: Ag[11 (2) over bar]parallel to Cu[11 (2) over bar] (type-n) and Ag[(11) over bar2]parallel to Cu[11 (2) over bar] (type-r). The growth modes of the Ag thin films on Cu(111) surfaces depend strongly on the temperature during deposition with the Ag(111) planes having a preferred orientation of either type-n growth mode or type-r growth mode as a function of the Cu substrate temperature. A part of the first-layer Cu atoms (20% of the surface) is displaced at low Ag coverage, where the stacking changes abruptly from fcc to hcp sites because of the Ag atom deposition at 603 K. The STM image of the Ag coverage of 0.8 ML showed a periodic array of triangular misfit dislocation loops at the deposition temperature of RT. The triangular shape in a localized region where the stacking {Ag-Cu (A)-Cu (B)-Cu (C)} is replaced by {Ag-Cu (C)-Cu (B)-Cu (C)} in the first substrate plane. At 603 K, surface alloying of the Ag-Cu. system was confirmed for Ag coverage below 0.15 ML. The experimental results concerning Ag/Cu(111) show many similarities to those in the previous study of Au/Ni(111). This would suggest that observed oscillations in the growth mode, dependent on the substrate temperature during deposition, may be a general phenomenon on solid surfaces, in cases of large misfit since it has now been seen for both Au/Ni(111) and Ag/Cu(111) systems. Furthermore, Cu atoms deposited on the Ag/Cu(111) system form islands with the same orientation of Ag(111) planes. The Cu atoms undergo surface diffusion at room temperature in the direction of type-n . domains for both type-r and type-n modes Ag substrates.

The effect of hydrogen termination on Ba reaction on the Si(100) surface at the initial stage of Ba adsorption was investigated by means of scanning tunneling microscopy (STM). On the bare Si(100) surface, Ba atoms form chain-shaped structures of Ba coverage up to 1/3 monolayer (ML), which extend perpendicular to the Si dimer row. The chain-shaped structure can change its shape because of the movement of Ba atom along the dimer row. On the other hand, in the case of Ba adsorption on a monohydrogenated Si(100)2×1 surface, Ba atoms make clusters, particularly at defect sites. In addition, Ba clusters can move across the dimer row.

Barium induced 2×3 and c(2×6) structures on Si(100), which appear at the Ba coverage below 1/3 ML, have been studied by scanning tunneling microscopy (STM). It is revealed that the 2×3 structure has only one adsorption phase, being independent of Ba coverage. Based on high resolution filled-state STM images where four protrusions are resolved in a unit cell, a model of 2×3 structure is proposed where the building unit consists of a Ba dimer and two Si dimers. It is also found that the c(2×6) structure always coexists with the 2×3 structure and has the same building block. The c(2×6) is realized when adjacent rows of building blocks are out of phase.

We investigated the 2x3 structure on Ba-deposited Si(100) surface by means of scanning tunneling microscopy (STM). The 2x3 structure has a lattice vector with the length of 3a(0) along the Si dimer row of original (100) plane. It is found that STM images of the 20 structure have sample bias voltage dependence, especially in empty-state images. At higher voltage than 1.5 V, only one protrusion is observed in a unit cell. On the other hand, at lower voltage than 1.5 V, an additional protrusion is observed. In comparison of empty-state images with filled-state images, it is found that the protrusion observed at high voltage is due to a Ba dimer and the additional one is due to Si dangling bonds.

Oxidation of a polycrystalline Zr surface is studied by a time-of-flight electron-stimulated desorption (TOF-ESD) method and Auger electron spectroscopy (AES). An S-segregated Zr surface is obtained after heat treatment at 1100 K for 15 min in an ultrahigh-vacuum (UHV) chamber. Several cycles of Ar+ bombardment at 925 K and heating at 1000 K remove sulfur layers, resulting in a nearly clean Zr surface. Although oxygen molecules in dissociative states adsorb onto both types of sample surfaces, the sticking coefficient of the oxygen atoms is considerably decreased on the S-segregated surface. Three different sites for the adsorption of oxygen atoms are noted, namely, the subsurface sites, the hollow sites, and the on-top sites. The S atoms segregate to the Zr surface to occupy the hollow or the on-top site, resulting in the observed decrease of the sticking coefficient of the O atoms. (C) 2000 Published by Elsevier Science B.V.

The adsorption process of oxygen on a Zr surface was studied by a time-of-flight electron-stimulated desorption (TOF-ESD) method. Oxygen adsorption induced hydrogen segregation on the Zr surface. It was revealed that the increase in H+ yield following O2 exposure is not caused by adsorption from the gas phase but by the diffusion of H from the bulk of Zr. In addition, H atoms formed ZrH bonds rather than hydroxyl species. From the analysis of the experimental results, it is suggested that O atoms penetrating into the Zr sample substitute for H atoms at tetrahedral sites, causing the diffusion of H atoms.

The system of Ba overlayers deposited on a deuterium-terminated Si(100) surface was investigated by means of MDS (metastable de-excitation spectroscopy) and TDS (thermal desorption spectroscopy). Deposition of Ba overlayers caused the reduction of SiD bond strength because of charge donation to Si substrate from Ba atoms. As a result, about half of preadsorbed D atoms was released from the sample surface at 1 ML Ba deposition. The other half reacted with adsorbed Ba atoms entirely to form BaD bonds. Therefore, all the SiD bonds were lost, which is quite different from the alkali/D/Si(100) system. More Ba deposition did not induce the desorption of D atoms. The formed BaD bonds are considered to stay between the first and the second layer.