Topmost Region Research Articles

Near-edge x-ray absorption fine structure and x-ray photoemission spectroscopy study of the InN epilayers on sapphire (0001) substrate

A polarization-dependent near-edge x-ray absorption fine structure (NEXAFS) study was performed on InN films epitaxially grown on sapphire (0001) substrates, in order to investigate the change in structure and crystallographic orientation of the film as a function of film thickness. For thin films, the N K-edge NEXAFS spectra showed a strong polarization-dependent spectral feature. The polarization dependence decreased with increasing film thickness and disappeared at a thickness of about 3000 Å. Chemical configuration in InN films was investigated using high-resolution x-ray photoemission spectroscopy (XPS). XPS analysis on the In 3d peak and the N 1s main peak at 396.4 eV suggested that indium and nitrogen are bound in the form of InN in all of the samples. An additional peak observed at 397.4 eV in the N 1s photoelectrons is believed to originate from the formation of oxynitrides at the topmost region of the film.

Characterization of Co-Al-O magnetic thin films by combined use of XPS, XRD and EPMA

Several Co–Al–O alloy thin films with different physical properties were prepared by reactive r.f. sputtering of Co85Al15 and Co70Al30 alloy targets in Ar + O2 atmospheres and were characterized by XPS, x-ray diffraction (XRD) and electron probe microanalysis (EPMA). The alloy films contained metallic Co, mainly of hexagonal phase, and also CoO. The Al oxide in the Co–Al–O thin films did not give any detectable diffraction peaks. The EPMA results showed that [Al]/([Co] + [Al]) ratios, where [M] denotes molar fraction of element M in the alloy, were almost the same as the compositions of the targets used for sputtering. However, quantitative XPS analysis resulted in much higher values of [Al]/([Co] + [Al]) ratios in comparison with the bulk values, suggesting enrichment of Al in the surface region. Aluminium detected by XPS was all in the oxidized state, and was in the form of hydroxide in the top surface region. Cobalt in the topmost region was in the form of oxyhydroxide, which was easily reduced to the metallic state by Ar+ etching. By taking the XPS, XRD and EPMA results into consideration, the difference of Co–Al–O alloys in electric resistance was explained qualitatively by the difference in microstructure of the alloy films, i.e. the difference in thickness of the oxide films on nanoscale particles of metallic Co embedded in an oxidized Al matrix together with the clearance between the nanoscale Co particles. Copyright © 1999 John Wiley & Sons, Ltd.

Properties of ruthenium aluminide prepared by plasma activated sintering

Surface region of a series of Cu-Ta alloys prepared by sputter-deposition were characterized by XRD, XPS and AES. Just after preparation, Ta was enriched in the topmost region as an oxide film while Cu was enriched under the surface film. The surface film thickness on alloys increased by a 5 h air-exposure. The surface film thickness after 5 h exposure to air plotted against alloy composition had a large maximum at 22 at.% Ta. The surface films consisted of (Cu, Ta)Ox(OH)y·nH2O type compound where Cu and Ta were enriched in low and high Ta alloys, respectively, after 5 h exposure although just Ta was enriched in the surface film on as-prepared alloys. Enrichment of Cu in the metallic state under the surface film was observed on all the alloys. When the oxidation proceeds on low Ta alloys, enriched metallic Cu under the surface film diffuses through the surface film to the top surface to form copper oxide film. On high Ta alloys, however, the Ta-rich surface oxide film on high Ta alloys is protective enough to prevent diffusion of Cu through the surface film. The composition dependence of the oxidation behavior of Cu-Ta alloys in air is largely related to the protectiveness of the initial oxide film.

Oxidation behavior of sputter-deposited Cu-Ta alloys in air

Surface region of a series of Cu-Ta alloys prepared by sputter-deposition were characterized by XRD, XPS and AES. Just after preparation, Ta was enriched in the topmost region as an oxide film while Cu was enriched under the surface film. The surface film thickness on alloys increased by a 5 h air-exposure. The surface film thickness after 5 h exposure to air plotted against alloy composition had a large maximum at 22 at.% Ta. The surface films consisted of (Cu, Ta)O x (OH) y · nH 2O type compound where Cu and Ta were enriched in low and high Ta alloys, respectively, after 5 h exposure although just Ta was enriched in the surface film on as-prepared alloys. Enrichment of Cu in the metallic state under the surface film was observed on all the alloys. When the oxidation proceeds on low Ta alloys, enriched metallic Cu under the surface film diffuses through the surface film to the top surface to form copper oxide film. On high Ta alloys, however, the Ta-rich surface oxide film on high Ta alloys is protective enough to prevent diffusion of Cu through the surface film. The composition dependence of the oxidation behavior of Cu-Ta alloys in air is largely related to the protectiveness of the initial oxide film.

An auger electron spectroscopic study of the corrosion behavior of an amorphous Zr 40Cu 60 alloy

The corrosion behavior of an amorphous Zr 40Cu 60 alloy in laboratory air (RH = 60 ± 10%) at room temperature was studied by grazing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES) combined with Ar ion sputter-etching. In general, the corrosion behavior of the roll-side of the specimen which was in contact with the chilling roll during quenching was different from that of the freely solidified surface (top-side). The GIXRD data suggested that monoclinic ZrO 2 ( m-ZrO 2) and tetragonal ZrO 2 ( t-ZrO 2) were formed under a surface layer of metallic copper which was also formed by corrosion of alloy. The t-ZrO 2 was distributed more deeply than the m-ZrO 2. By AES, it was clarified that a metallic copper layer covered with a very thin ZrO 2 was placed in the topmost region, and that, under the copper layer on the roll-side surface, a sandwich structure of ZrO 2 and metallic copper was formed, i.e. the corroded region consisted of several layers of ZrO 2-rich and copper-rich layers distributed alternatively. On the top side, however, the oxidized layer did not develop significantly and the sandwiched structure of ZrO 2 and metallic copper was not observed.

Tantalum deposition on and reaction with the hydrogen terminated diamond (100) surface studied by Auger electron and electron energy loss spectroscopy

The evolution of the tantalum/diamond interface upon room-temperature Ta deposition on the (100) surface of a boron doped, synthetically grown diamond single crystal was monitored by Auger electron spectroscopy (AES), ionization loss spectroscopy (ILS), and electron energy loss spectroscopy (ELS). Characteristic loss peaks indicate carbide formation at the interface from very low coverages on, reflecting the strong interaction between tantalum and carbon. Thicker layers of TaC are formed during subsequent thermal annealing by diffusion of carbon into the tantalum film, at the same time the topmost diamond region is transformed into poorly ordered graphitic carbon.

Collimated magnetron sputter deposition with grazing angle ion bombardment

Collimated magnetron sputter deposition with concurrent grazing angle ion bombardment has been developed as a technique for enhancing the ability to deposit films into trenches and vias. The collimated sputtering technique uses a conventional magnetron cathode operating at low pressure (mTorr) and a physical collimator or directional filter mounted between the cathode/discharge plasma and the sample position. The collimator serves to limit the directionality of the transmitted, sputtered atoms to near-normal incidence. A broad-beam Kaufman-type ion source is mounted on the sample side of the collimator such that the ion beam impacts the sample surface at grazing (5°–15°) incidence. This serves to resputter the depositing film selectively from the topmost regions of the sample surface, while lower areas, such as trenches and vias, are geometrically shielded.

Mössbauer study of boron-implanted materials: Armco-iron, carbide-rich steel X90CrMoV18 and austenitic steel X10CrNiTi189

Boron implantation was used to modify the phase composition at the surface of three different steels. Conversion electron Mossbauer spectra reveal the modification of the existing phases by the implanted boron. Furthermore, a thin amorphous layer is formed in the topmost region of all three materials.

Distribution of pulmonary blood flow in conscious resting rats

The pattern of pulmonary blood flow (PBF) distribution was determined in the rat, in which lung gravitational forces are minimal. Microspheres were infused into the inferior vena cava of 15 conscious, and 5 anesthezided rats. Relative scatter of specific PBF [(sample activity/sample weight)/(total activity/total weight)] in 28 lung samples was calculated. In 5 of the conscious rats, consecutive determinations were made 30 min apart. In 5 anaesthetized rats, PBF was determined in prone and supine positions. Relative scatter of specific PBF varied from 0.84 to 1.12, with PBF being distributed preferentially to the hilar, central regions. There was a high correlation between consecutive measurements: y=0.88 × + 0.11 ( n=140, r=0.92). By changing from prone to supine position, PBF to the topmost regions, increased, and that to the lowermost regions decreased, by only 3 percent. The results indicate that in the conscious resting rat, PBF has a small but significant preferential distribution to the hilar, central regions, with lower blood flow to the peripheral regions of the lung.

A Surface Spectroscopic and Wettability Study of a Segmented Block Copolymer Poly(Etherurethane)

In this study, a multitechnique surface analytical approach is used to provide comprehensive surface molecular, structural, and thermodynamic information of a segmented Poly(etherurethane) (PEU) block copolymer (Texin-985). Through sample preparation methods described in this paper, a clean stable PEU material is provided. Subsequent analysis employing Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance Fourier Transform Infrared (ATR/FT-IR), and Comprehensive Wettability Profiling provides a comprehensive molecular structure of the topmost interfacial region, ranging through a bulk analysis probing depths in the micron range. Also featured in this paper are results obtained through the implementation of a higher-energy x-radiation source for ESCA analysis. Through the use of angle-dependent ESCA utilizing Mg K α x-radiation, used in conjunction with a Ti K α x-radiation source, a hard- and soft-component depth profile expanded from a conventional profile of ∼20 Å to 100 Å (using a Mg anode source) to ∼20 Å to 200 Å is obtained. Due to the greater depth of analysis, we also obtain atomic ratios (using calculated sensitivity factors) which are closer to true bulk atomic percentages of Texin-985 (PEU).

INTERMIXING OF ION-IMLANTED AlGaAs/GaAs SUPERLATTICES

AbstractCross-sectional Transmission Electron Microscopy, Sputter-Auger spectroscopy, and Raman spectroscopy have been used to study intermixing and residual damage in annealed ion-implanted Al0.3Ga0.7As/GaAs superlattices. Several implant species were studied Nse, Si, Mg, Be). Three different regions can be distinguished in the annealed ionimplanted superlattice samples. The topmost region contains a dense network of stacking faults and microtwins, residual damage from an implantation-amorphized region which has recrystallized during annealing. In the second region, which is relatively defect-free, either total, or at least appreciable intermixing of the GaAs and Al0.3Ga0.7As layers occurs. For fixed annealing conditions, the degree of intermixing varies with the mass of the implanted species. The third region contains many small dislocation loops which form by the agglomeration of point defects during implantation or the subsequent annealing process. Raman spectroscopy is used to compare the degree of intermixing and residual damage between AlGaAs alloys generated by superlattice disordering and uniform “as-grown” alloys of the same composition which have undergone identical implant and anneal treatments.

Chromosomal protein poly(ADP-ribosyl)ation in pancreatic nucleosomes.

When pancreatic chromatin fragments were prepared and resolved in the presence of 80 mM NaCl, endogenous poly(ADP-ribose) polymerase activity was found to be maximal in nucleosome periodicities of four to five units and did not respond to any further increases in nucleosomal architecture. Furthermore, in nucleosome complexities spanning 1 through 14 and over unit lengths, polyacrylamide gel electrophoresis on acid-urea and acid-urea-Triton gels has shown pancreatic histone H1 to be the only actively ADP-ribosylated histone species. The extent of ADP-ribosylation of histone H1 was also demonstrated to retard the protein's mobility in acid-urea, acid-urea-Triton, and lithium dodecyl sulfate polyacrylamide gels and to consist of at least 12 distinct ADP-ribosylated species extractable in all nucleosome complexities studied. Finally, extraction and subsequent electrophoresis of total chromosomal proteins in the presence of lithium dodecyl sulfate also evidenced heavy ADP-ribosylation at the level of nonhistone chromosomal proteins of the high mobility group comigrating in the core histone region, as well as in the topmost region of the gels where poly(ADP-ribose) polymerase was found to form a poly(ADP-ribosyl)ated aggregate.