摘要:

Scanning tunneling microscopy (STM) was used to examine the surface structure of supported gold particles. STM images of annealed gold particles showed that particles larger than 150 Å have a polyhedral shape and a relatively smooth surface morphology. However, the surfaces of the particles smaller than 60 Å remained highly corrugated even after long annealing times. We believe that the difference in morphology of large and small particles may have some important implications for supported metal catalysis.

ISSN:0734-2101    

DOI:10.1116/1.576518

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Initial stages of Si molecular beam epitaxy on vicinal Si(001) substrates were investigated using scanning tunneling microscopy. It was found that at temperatures around 750 K first a preferential growth of one type of terrace occurs, leading to the formation of a single‐domain surface. During continued growth both step flow and nucleation of islands occur. Disordered areas can block the step flow and antiphase disorder offers preferential nucleation sites.

ISSN:0734-2101    

DOI:10.1116/1.576519

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We describe a method for measurement of the local density of states on metals with the scanning tunneling microscope and apply it to the study of thesp‐gap surface state on Au(111). Local surface state peak intensity changes are found to correlate with surface features. Spectroscopic images of the surfaces are produced. The surface state intensity is substantially reduced at step edges as compared to the value for large terraces. A change in the intensity by a factor of 2 over the 23×(3)1/2reconstruction unit cell is also observed. These effects are attributed to a spatial variation of the surface state intensity with the local potential. Upward shifts of the surface state energy have also been observed on narrow terraces, however more detailed measurements are necessary to understand this effect.

ISSN:0734-2101    

DOI:10.1116/1.576476

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A new method to obtain high quality Fourier transform infrared reflection absorption spectra (FT‐IRAS) from adsorbates on single crystal surfaces is presented. This new method can effectively cancel absorptions in the spectrometer due to atmospheric gases, and also effectively compensates for long term drifts in the background spectrum. The apparatus design and the background subtraction procedure are shown along with sample FT‐IRAS measurements.

ISSN:0734-2101    

DOI:10.1116/1.576477

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The effect of incremental ion bombardment on the surface layers of an aqua regia etched InP sample was studied by monitoring the components of the In 3d5/2and O 1sx‐ray photoelectron spectroscopy (XPS) lines as the sample was bombarded with low energy (1 keV) Ar+ions. The changes in the stoichiometry of the surface produced large shifts in the position of the In 3dand O 1slines that were not paralleled by shifts in the P 2pline. Analysis of these shifts indicated that the surface was covered with a mixture of indium hydroxide and indium phosphate, with the phosphate closer to the InP substrate. It is proposed that this layer structure is due to differences in the dissolution rates of the oxidation products in the acid etch and the effect of the distilled water rinse. It may be possible to alter the composition of such oxides by carefully tailoring the etch conditions to optimize the kinetics for the particular oxide phase required. The analysis of the XPS lines also showed that the InP substrate was damaged at very low ion doses, and finally decomposed by the ion beam. When the ion ‘‘cleaned’’ sample was exposed to oxygen, a different oxide system was produced which consisted largely of In2O3and InPO4[or In(PO3)x]. This model of the oxidized surface of InP is consistent with other measurements and we conclude that ion milling together with XPS and careful curve fitting can be used to find the nature of the thin oxides on InP.

ISSN:0734-2101    

DOI:10.1116/1.576478

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

According to the two‐minima electron diffusion model of Spicer, James, and Moll [W. E. Spicer, Quant. Rep.9, April (1968); L. W. James and Z. L. Moll, Phys. Rev.183, 740 (1969)] for near threshold photoemission, minority‐carrier diffusion lengthLand escape probabilityPfor a variety of Beryllium doped GaAs(100) epitaxies grown by molecular beam epitaxy, have been obtained. These epitaxies, before being activated with cesium and oxygen by using the two‐stages method described by Stocker and Goldstein [B. J. Stocker, Surf. Sci.47, 501 (1975); B. Goldstein,ibid.47, 143 (1975)], were passivated in two different ways. (i) Chemically, with a 5:1:1 H2O: H2O2: H2SO4solution and (ii) by the deposition of a 700–800 Å thick antimony layer. A better performance of the samples using this last type of passivation is shown. In order to evaluateLandPfrom the electron diffusion model, it is necessary to know the dispersion relation of the absorption coefficient for each sample. They have been obtained from normal‐incidence reflectance measurements by means of a Kramers–Krönig analysis. The electronic diffusion length values obtained ranged from 4.5 to 2.1 μm and the escape probabilities between 8.1% and 20.2% for Be concentrations of 1×1018and 1×1019cm−3, respectively.

ISSN:0734-2101    

DOI:10.1116/1.576479

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

High resolution x‐ray photoelectron spectroscopy (XPS) has been used to study the interfacial chemistry between vacuum‐deposited silver and poly(ethylene terephthalate) (PET) surfaces. The initial stages of metallization in the subatomic layer regime (∼0.1–1.0 atomic layer of Ag) were monitored. For the untreated PET, the XPS results suggest charge transfer between silver and the carbonyl oxygen in PET in the early stages of metallization. The effect on the untreated PET is small with only about 7% of the PET surface atoms providing reaction sites. Plasma modification with oxygen introduces specific reaction sites resulting in additional chemical bond formation between the vacuum‐deposited silver and the PET surface. The XPS results suggest the primary reaction sites are the plasma‐induced acid groups. The resultant structure is similar to that of a silver carboxylate species. The number of reaction sites is estimated at 3–4 times greater compared to untreated PET. These results are consistent with the significant improvement in adhesion observed for plasma treatment with oxygen.

ISSN:0734-2101    

DOI:10.1116/1.576480

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Reflection high‐energy electron diffraction (RHEED) is an experimentally simple technique, and yet a powerful one for examining the structure of a substrate surface and for monitoring the surface crystal structure and the crystallographic orientation of thin films during their growth. However, it can be difficult to learn to interpret the RHEED patterns of new materials, because a practical and adequately detailed introduction to the technique is not generally available. To address this need, we develop the geometrical principles of RHEED; using the kinematic approximation, we show how a particular point of the sample surface’s reciprocal net gives rise to a diffraction maximum at a particular location on the RHEED viewing screen. We explain the origins of ‘‘reciprocal lattice rods,’’ RHEED streaks, and Laue rings. We show how to calculate the streak spacing, and clarify the basic effect on the RHEED pattern of using a nonzero angle of incidence for the incident beam. Crystalline nets, reciprocal nets, and their RHEED patterns are derived for both (001) and (111) silicon surfaces and are compared to experimentally obtained patterns.

ISSN:0734-2101    

DOI:10.1116/1.576481

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Aluminum and gold coated quartz crystal oscillators were bombarded by 7 keV Ga+and then exposed to fairly low pressures (∼1 mTorr) of dimethyl gold hexafluoroacetylacetonate [denoted Me2Au(hfac) ] at room temperature for several hours. While unirradiated crystals exhibit a mass increase corresponding to approximately one monolayer of Me2Au(hfac), irradiated crystals accumulate significantly more mass. Typically, the accumulated mass on the irradiated surfaces corresponds to a film of gold several hundred angstroms thick. Thus, simple condensation of the organometallic molecules cannot explain the large mass increase. Rather it suggests that spontaneous decomposition of the Me2Au(hfac) is occurring on the irradiated surface. X‐ray photoelectron spectroscopy indicates that the deposited mass is essentially pure gold. Rutherford backscattering spectroscopy indicates that as many as 20 Au atoms are deposited for each implanted Ga atom. Surfaces irradiated with Au ions show much less mass accumulation, but some growth still occurs. These results indicate that two processes contribute to film growth during ion induced deposition: ion decomposition plus the spontaneous decomposition described here.

ISSN:0734-2101    

DOI:10.1116/1.576482

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

This study examines a type of resputtering that attends the deposition of sputtered materials under elementary conditions—sputtering with a single ion beam at pressures below 0.01 Pa. Ne, Ar, Kr, and Xe were employed to sputter nine simple metals ranging in mass from Al to Au. Comparative weight gains on planar and concave substrates revealed the magnitude of resputtering, which varied from about 3.5% for light metals sputtered with heavier ions to over 20% for gold sputtered with neon. The results define a universal curve that appears constant at mass ratios less than unity but increases steeply beyond a mass ratio intercept slightly greater than unity. A theoretical analysis is developed that predicts the striking universality, relates the observed intercept to the existence of finite sputtering threshold energies, and fits the full range of experimental data with one adjustable parameter having a derived value of unity.

ISSN:0734-2101    

DOI:10.1116/1.576483

出版商:American Vacuum Society    

年代:1990

数据来源: AIP