摘要:

Novel structural and chemical properties of Cr monolayer, bilayer, and multilayer films on W(110) have been identified using temperature programmed desorption, low‐energy electron diffraction, and Auger electron spectroscopy. A pseudomorphic (1×1) Cr monolayer forms atT>100 K which is stable up to desorption at ∼1290 K despite a ∼9% lattice mismatch. The second monolayer forms a metastable (2×2) structure in the 500 K

ISSN:0734-2101    

DOI:10.1116/1.575175

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

In recent literature, diverse views have been expressed regarding the nature (ionic versus covalent) of bonding between alkali metals and the Si(001)‐(2×1) surface. Also unsettled is the issue as to whether the metallicity upon K adsorption is due to the partial occupancy of the dangling bonds or due to the metallic K chain. The resolution of these outstanding problems is sought by performing electronic structure total energy calculations using cluster as well as slab models. The cluster model calculations have used anabinitioself‐consistent field Hartree–Fock technique, whereas the slab model has employed pseudopotentials within the density functional formalism. Using a variety of criteria, we conclude that the bond is strong and ionic with negligible covalent effects. At the monolayer coverage, the charge from the adsorbed potassium atoms is transferred into the empty, antibonding dangling bond surface states resulting in the metallization of the Si(001) substrate surface. The presence of the dangling bond states prevents the alkali monolayer from metallization.

ISSN:0734-2101    

DOI:10.1116/1.575176

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have combined the techniques of reflection high‐energy electron diffraction and photoemission in order to study crystal growth of Ge by molecular‐beam epitaxy. Intensity oscillations in the reflected electron beam for deposition on both (001) and (111) surfaces at 20 °C indicate that the growth is essentially layer by layer. The evolution of valence bands and core levels as a function of deposition reveals that in the case of Ge(001) the Ge bulk band structure remains present, indicating crystalline growth. For Ge(111) the bulk band structure disappears and finally resembles the band structure of amorphous Ge, indicating a completely disordered film. At 200 °C, however, the crystalline band structure remains present.

ISSN:0734-2101    

DOI:10.1116/1.575177

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

For the reconstructions present during epitaxial growth, the diffraction experiment of choice is reflection high‐energy electron diffraction (RHEED). In the RHEED geometry, the momentum transfer normal to the surface is small and can be varied by changing the angle of incidence at constant incident energy. The resulting rocking curve, or diffracted intensity versus angle of incidence, is comparable to a low‐energy electron diffractionIVprofile. We present rocking curve results for the 〈001〉 and 〈11̄0〉 principle azimuths for 10‐keV diffraction experiments from GaAs(110). This known surface structure is the best tested structure to develop the analysis. The measurements are compared to a fully convergent dynamicalN‐beam RHEED calculation which includes as many propagating and evanescent beams as needed. An important issue is to determine what extent the diffraction is dominated by bulk features and single‐layer resonances. This is addressed by selectively eliminating beams in the analysis and comparing beam emergence predictions to experimental observations.

ISSN:0734-2101    

DOI:10.1116/1.575178

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have used the dynamical theory of low‐energy electron diffraction to analyze data of the Si(111)7×7 surface and determined the atomic structure. The method includes the use of symmetrized wave functions in real and reciprocal spaces. Individual atomic coordinates for the first five atomic planes (containing 200 atoms) are determined. The low‐energy electron diffraction optimized structure shows an oscillatory relaxation: atomic planes with stretched bonds followed by planes with compressed bonds. Geometric displacements from the bulk dimer–adatom–stacking fault model are presented.

ISSN:0734-2101    

DOI:10.1116/1.575179

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The surface crystallography of arsenic covered Si(001) has been analyzed by low‐energy neutral impact collision ion scattering spectroscopy (NICISS). The 170° backscattered He neutrals and ions have been detected by a time‐of‐flight technique. The measured data show two well‐time‐resolved lines for He scattered at Si and As atoms, respectively. Hence NICISS angular pattern for Si and As could be measured simultaneously. Adsorption of arsenic lifts the original 1×2 reconstruction of the Si(001) substrate and forms itself a 1×2 As overlayer. The As overlayer is well described by a dimer arrangement with an interatomic distance of 2.55 Å of the As dimers. From the ion scattering experiment considerable thermal vibrations of the As atoms in the overlayer have been concluded. Best agreement with Monte Carlo trajectory calculations is obtained for a Debye temperature of 120 K.

ISSN:0734-2101    

DOI:10.1116/1.575180

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-2101    

DOI:10.1116/1.575181

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-2101    

DOI:10.1116/1.575182

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-2101    

DOI:10.1116/1.575183

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-2101    

DOI:10.1116/1.575184

出版商:American Vacuum Society    

年代:1988

数据来源: AIP