Preparation of atomically clean and flat Si(1 0 0) surfaces by low-energy ion sputtering and low-temperature annealing

Si(1 0 0) surfaces were prepared by wet-chemical etching followed by 0.3–1.5 keV Ar ion sputtering, either at elevated or room temperature (RT). After a brief anneal under ultrahigh vacuum (UHV) conditions, the resulting surfaces were examined by scanning tunneling microscopy. We find that wet-chemical etching alone cannot produce a clean and flat Si(1 0 0) surface. However, subsequent 300 eV Ar ion sputtering at room temperature followed by a 700 °C anneal yields atomically clean and flat Si(1 0 0) surfaces suitable for nanoscale device fabrication.     

The initial oxidation of aluminum thin films at room temperature

Thin film and ultra-high-vacuum techniques have been utilized in fabricating uncontaminated, atomically clean, aluminum surfaces in order to characterize the initial low temperature, low pressure oxidation kinetics of aluminum. The kinetics were followed gravimetrically by the quartz crystal microbalance technique and the aluminum-aluminum oxide surface was examined by utilizing electron microscopy and scanning electron microscopy techniques.     

Decomposition of carbon monoxide on a (110) nickel surface

New investigations of the (110) nickel/carbon monoxide system have been made using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), mass spectroscopy and work function measurements. Room temperature adsorption of CO on the surface was reversible with the CO easily removable by heating in vacuum to 450°K. The CO formed a double-spaced structure on the surface which, however, was unstable at room temperature for CO pressures less than 1×10^?7 torr. Work function changes greater than + 1.3 eV accompany this reversible CO adsorption. Irreversible processes leading to the build-up of carbon, and under certain circumstances oxygen, on the surface were the primary concern of the measurements reported here. These processes could be stimulated by the electron beams used in LEED and AES, or by heating the clean surface in CO. The results of AES investigations of this carbon (and oxygen) build-up, together with CO desorption results could be explained on the basis of two surface reactions. The primary reaction was the dissociation of chemisorbed CO leaving carbon and oxygen atomically dispersed on the surface. The second reaction was the reduction of the surface oxygen by CO from the gas phase. The significance of the dissociation reaction to COdesorption studies is discussed.     

Study of the structural and magnetic characteristics of epitaxial Fe3Si/Si(111) films

The results of the structural and magnetic studies of the epitaxial structure prepared during the simultaneous evaporation from two iron and silicon sources on an atomically pure Si(111)7 × 7 surface at a substrate temperature of 150°C have been presented. The epitaxial structure has been identified as a single-crystal Fe₃Si silicide film with the orientation Si[111]‖Fe₃Si[111] using methods of the X-ray structural analysis, transmission electron microscopy, and reflection high-energy electron diffraction. It has been established that the epitaxial Fe₃Si film at room temperature has magnetic uniaxial anisotropy (H _a = 26 Oe) and a relatively narrow uniform ferromagnetic resonance line (ΔH = 11.57 Oe) measured at a pump frequency of 2.274 GHz.     

Application of high energy ion channeling to GaAs(110), Au-GaAs(110) and Pd-GaAs(110)

The first application of high energy ion channeling to the atomically clean GaAs(110) surface and metal-GaAs interfaces is reported. Questions of sample preparation, background correction and computer simulation are addressed. It is found that the Ga and As atoms at the clean surface are laterally displaced ? 0.1 Å from the ideal bulk-like sites. The implications of this result to current LEED models are discussed. Au overlayers, deposited at room temperature, do not seem to produce lateral displacements of the substrate for coverages below ≈ 5 monolayer (ML). However, ≈ 0.9 ML of the substrate are expanded or contracted upon Au deposition; this process is completed at a coverage of 0.5 ML. Neither an indication of any order in the Au film is found, nor seems a significant (? 5%) fraction of Au atoms to occupy substitutional sites. In contrast, room-temperature deposition of Pd disorders the substrate substantially, without threshold coverage, even at very small film thicknesses.     

Stoichiometry, contamination and microstructure of MnSb(0 0 0 1) surfaces

The stoichiometry, microstructure and surface composition of MnSb have been investigated using X-ray photoelectron spectroscopy, electron diffraction and microscopy. Epitaxially grown samples were exposed to ambient air for several weeks and methods for preparing clean, stoichiometric and smooth surfaces were investigated. Air-stored sample surfaces are chemically stratified but dominated by Mn oxides 4-5 nm thick. These oxides are difficult to remove by ion bombardment and annealing (IBA), but a brief etch in HCl removes them very efficiently. It leaves the surface Sb-rich, and clean, smooth and stoichiometric surfaces are then readily recovered by IBA. These surfaces exhibit a (2 × 2) surface reconstruction with atomically flat terraces. This reconstruction can be reversibly changed to a (1 × 1) by Sb deposition and annealing.     

FMR in surface oxidized iron single crystals

Ferromagnetic resonance absorption has been observed at room temperature in iron single crystals of whisker type (grown along [100] direction). The surface of the samples has been oxidized in air at 760 Torr at approx. 350 °C for periods up to 240 min. With the increasing degree of oxidation the resonance linewidth broadens and the resonance field shifts to lower values. Moreover, in oxidized samples an additional resonance peak situated above, the main resonance occurs, with intensity, position and linewidth depending on the period of oxidation. The ferrimagnetic resonance absorption in the iron oxide surface layer could be responsible for the occurence of this peak.     

Influence of the surface conditions on rf plasma characteristics

The secondary electron emission is a surface dependent phenomenon, more influenced by surface preparation than by the material itself. The present paper deals with the effect of the electrode surface conditions: clean (atomically clean) and contaminated electrodes (standard conditions even after mechanical and chemicals cleaning) on the characteristics of an asymmetric discharge by PIC/MCC simulations. In the arrangement with one clean and one contaminated electrode the discharge characteristics strongly depend upon which electrode is powered. The obtained PIC/MCC simulation results indicate that contamination of electrodes and variations of the secondary electron emission coefficients can lead to more or less significant changes in properties of rf plasmas.     

Formation of a passive layer in surface oxidation of Gd: A leed and AES study

The surface oxidation of epitaxial and polycrystalline Gd samples grown in ultrahigh vacuum on W(110) substrates has been investigated using Auger-electron spectroscopy (AES) and low energy electron diffraction (LEED). The surface crystallography of clean epitaxial films monitored by LEED is hcp(0001) and remains unchanged even after 300 L oxygen exposure at room temperature. The LEED pattern of bulk Gd₂O₃ in Mn₂O₃ structure is observed only when oxygen is exposed at an elevated substrate temperature of about 500°C. AES clearly reveals various stages of oxidation as a function of the oxygen exposure for epitaxial as well as polycrystalline films. It is found that the oxidation does not proceed beyond one monolayer of the Gd surface.     

An electron energy loss study of aluminum single crystals exposed to carbon monoxide

Aluminum single crystals of orientations {111}, {110}, and {100} were exposed at room temperature to carbon monoxide. The electron energy loss spectra of the exposed surfaces (> 20000 L) were essentially the same as those of clean surfaces. Since such spectra are very sensitive to small amounts of absorbate (e.g., 0.001 to 0.01 monolayer of oxygen), it is inferred that carbon monoxide does not adsorb on these clean low-order faces at room temperature. Similar results were obtained on polycrystalline and evaporated film samples. This finding contrasts with previous work on aluminum exposed to carbon monoxide.     

Interaction of oxygen, carbon monoxide and nitrogen with (001) and (110) faces of molybdenum

A combination of low-energy electron diffraction and retarding potential measurements was employed to study gaseous adsorption on atomically clean (001) and (110) Mo single crystal surfaces. Adsorption of oxygen on the (001) surface at room temperature occurred with a sticking coefficient close to unity and produced a large increase in work function and appreciable changes in the intensity distributions of the integral order diffraction beams, without the appearance of any new diffraction beams. These results indicate that a surface monolayer of oxygen was formed with a unit mesh having the same dimensions as that of the underlying molybdenum surface. Exposures above 6 × 10⁻³ Torr-sec produced a uniform decrease in intensities, thus indicating a second monolayer with amorphous structure. On heating, two additional surface structures were observed, characterized by one-half and one-third order beams, respectively. A clean surface was obtained by heating above 1100 °C. An exposure of 1 to 7 × 10⁻⁷ Torr-sec of oxygen for the (110) face resulted in two types of patterns characteristic of lattices with one-quarter and one-half the surface density of the (110) Mo face, with an increased work function accompanying the latter pattern. Exposure of the clean surface at 400 to 800 °C produced similar patterns of enhanced intensities with no increase in work function. Possible models are discussed. It is concluded that place exchange models account for these results, as well as the one-half and one-third order structures on the (001) face, in a more satisfactory manner than adsorption above the surface. An exposure to 10⁻⁵ Torr-sec produced a monolayer coverage with a unit mesh similar to that of the molybdenum substrate. Additional exposure resulted in further amorphous adsorption. Adsorption of CO produced changes in the intensity distributions, with the appearance of no new maxima, for both (001) and (110) Mo surfaces. Nitrogen, at an exposure of 3 × 10⁻³ Torr-min did not adsorb on either the (001) or (110) Mo surface, but when dissociated by electron impact it adsorbed on both Mo surfaces with the same dimensions of unit mesh as those of the Mo substrates and with an increase in work function of 1.05 eV for the (001) and 0.05 eV for the (110) surface.     

Synchrotron radiation photoemission study of interface formation between MgO and the atomically clean In0.53Ga0.47As surface

The evolution of interface formation between MgO and the atomically clean In_0.53Ga_0.47As is studied by synchrotron radiation based photoemission. The deposition of MgO in a step wise fashion on the decapped In_0.53Ga_0.47As surface at room temperature results in the growth of an ultrathin interfacial oxide layer. Subsequent thermal annealing at 400 °C led to the reduction of the As and In oxides and the appearance of a Ga oxide component. The deposition of metallic Mg resulted in the further removal of the interfacial oxide and the out diffusion of In into the overlayer indicating severe disruption of the interface. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Layer-by-layer intercalation of potassium into the graphite (0 0 0 1) surface

Exposure of an atomically clean but high step density (0 0 0 1) graphite surface to a hot potassium beam results in intercalation of the potassium into the graphite. It has been determined by low energy electron diffraction (LEED) that the single crystal surface has undergone shear displacement at the surface of the top layers to form an K|A|K|A|K… stacking with the surface localized potassium in a disordered state. The intercalation is observed to proceed in a layer-by-layer manner as a function of potassium beam exposures.     

Growth and morphology of the epitaxial Fe(1 1 0)/MgO(1 1 1)/Fe(1 1 0) Trilayers

Growth and surface morphology of epitaxial Fe(1 1 0)/MgO(1 1 1)/Fe(1 1 0) trilayers constituting a magnetic tunnel junction were investigated by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). STM reveals a grain-like growth mode of MgO on Fe(1 1 0) resulting in dense MgO(1 1 1) films at room temperature as well as at 250 °C. As observed by STM, initial deposition of MgO leads to a partial oxidation of the Fe(1 1 0) surface which is confirmed by Auger electron spectroscopy. The top Fe layer deposited on MgO(1 1 1) at room temperature is relatively rough consisting of clusters which can be transformed by annealing to an atomically flat epitaxial Fe(1 1 0) film.     

Physical and water aging of glass fiber-reinforced plastic pipes

Physical and water aging of glass/epoxy composite — GFRE — pipes used for oil transport were investigated with special emphasis on their effect on the flexural and impact behavior. Different aging conditions were selected in order to simulate in-service environments trying to obtain reliable results from accelerated laboratory tests. In water uptake experiments at 80°C, the mass increases continuously, suggesting that an irreversible process occurs. In addition, samples aged in air at 80°C exhibit a DSC endothermic peak that can be related to physical aging. The calorimetric curve for specimens water aged at 80°C shows combined effects of water absorption and physical aging. On the other hand, while the independent effect of temperature and water aging on the composites mechanical response is only moderate, their combined effect seems to be dramatic. This result is mostly attributed to the weakening of the fiber–matrix interface induced by the water ging at high temperature, which consequently affects flexural and impact properties. SEM observations confirm the irreversible damage observed in water uptake experiments. Good interfacial adhesion between fiber glass and epoxy resin is observed for unaged specimens, whereas completely clean fibers are seen for specimens water aged at 80°C, indicating that the fiber–matrix interface is completely removed as a result of this aging condition.     

Fabrication of nc-Si/SiO2 structure by thermal oxidation method and its luminescence characteristics

Nano-crystalline silicon/silicon oxide （nc-Si/SiO2） structures have been prepared from amorphous silicon films on both silicon and quartz substrates by using electron-beam evaporation approach and annealing at temperatures about 600 ℃ in air. As a thermal oxidation procedure, the annealing treatment is not only a crystallization process but also an oxidation process. Scanning electron microscopy is employed to characterize the surface morphology of the nc-Si/SiO2 layers. Transmission electron microscopy study shows the sizes of nc-Si grains on the two different substrates. The nc-Si/SiO2 structures exhibit visible luminescence at room temperature as confirmed by photoluminescence spectroscopy. Comparing the photoluminescence spectra of different samples, our results agree with the quantum confinement-luminescence center model.     

Surface magnetism of Fe(110) from polarized electron scattering

Exchange- and spin—orbit-induced scattering asymmetry spectra of polarized slow electrons from the ferromagnetic Fe(110) surface have been calculated by dynamical theory and found to agree with recent experimental data taken at room temperature. Comparison of exchange asymmetry spectra, obtained for various interaction and layer-dependent magnetization models, with the data implies firstly an enhancement of the surface magnetization by about 30% with respect to the bulk, and secondly the importance of spin-dependent localized inelastic electron—electron scattering processes.     

Influence of the deformation type and medium on the mechanodynamic penetration of nitrogen molecules into surface layers of armco iron

The extraction of nitrogen molecules from deformed samples of armco iron with different initial structures (annealed and subjected to equal-channel angular pressing) and different deformation prehistories (deformation in liquid nitrogen at 77 K, rolling in air at room temperature, and their combination) has been studied. It has been shown that the preliminary deformation in liquid nitrogen increases its concentration in the surface layer of the material and shifts the principal peak of its release toward low temperatures during heating. The results are associated with the existence of different types of nitrogen traps in annealed and nanostructured armco iron and with their changes during subsequent deformation.     

镍清洁表面制备中去除碳的一种简便方法

单用氩离子剥离很难完全去掉镍表面上的碳。在10^-8—10^-9托下用电子轰击加速氧的吸附,使残留着碳的镍表面吸附一定的氧;再将这个表面加热到360℃保温45分钟,获得了一个无碳的原子级清洁表面。讨论了利用氧去除碳的条件和机制。 关键词：     

Chemisorption of pyridine and pyrrole on iron oxide surfaces studied by XPS

Adsorption of pyridine and pyrrole on model iron oxide surfaces has been studied by X-ray photoelectron spectroscopy. At room temperature both molecules adsorb with their molecular identity intact. Upon heating above 320 K pyridine decomposes on the surface whereas pyrrole desorbs intact at 345 K. The bonding of pyridine and pyrrole to the surface at room temperature is studied by monitoring the change in measured N(1s) and C(1s) binding energies between gas-phase molecules and the monolayer phase at room temperature. The results suggest that pyridine bonds via electron donation from the non-bonding nitrogen lone pair to the surface while pyrrole bonds via electron donation from a π-bonding orbital to the surface. The differences in surface bonding are interpreted in the context of the concept of Lewis acids and bases applied to surfaces.