Coaxial Impact Collision Ion Scattering Spectroscopy Research Articles

Oxygen adsorption on wet-chemically cleaned GaN(0001) surface studied by coaxial impact collision ion scattering spectroscopy

Oxygen adsorption on wet-chemically cleaned GaN(0001) surface has been studied by coaxial impact collision ion scattering spectroscopy (CAICISS). The intensity variation of time-of-flight spectra obtained by CAICISS was compared with simulation results. The CAICISS analysis showed that oxygen is adsorbed at the top of Ga atoms at the surface. The Ga–O bond distance was estimated to be between 1.80 and 1.85 Å. The estimated bond distance is consistent with the Ga–O tetrahedral bond distance in β-Ga2O3.

Surface termination structure of α-Ga2O3 film grown by mist chemical vapor deposition

The surface structure of α-Ga2O3(0001) grown on an α-Al2O3(0001) substrate by mist chemical vapor deposition was studied by coaxial impact-collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). The minimum step height observed in the AFM image was 0.21 ± 0.01 nm, coinciding with the height of three atomic layers of α-Ga2O3(0001). It was revealed by CAICISS analysis that the surface of α-Ga2O3(0001) is terminated by a Ga layer followed by an O layer, which is consistent with the surface termination of α-Al2O3(0001). A structural model taking surface relaxation into account was also constructed by fitting the simulated curve for the azimuth angle dependence of the Ga intensity to the experimental dependence. The resultant structural model is similar to the model of an α-Al2O3(0001) surface, which indicates analogous behavior in corundum crystals.

Surface structure of GaP(110): Ion scattering and density functional theory study

The structure of the GaP(110) surface has been investigated using coaxial impact collision ion scattering spectroscopy (CAICISS) and density functional theory (DFT). CAICISS simulations based on structural parameter values of the well known buckled dimer model obtained in quantitative low energy electron diffraction studies in the 1980s were found to fit well with experimental data measured in the $[\overline{1}10]$ azimuth, but offered a relatively poor fit in all other incident geometries. A new surface structure derived from DFT calculations, involving small changes to bond angles and interlayer spacings, was optimized during the analysis of CAICISS data, until good fits of the data were obtained for all three azimuths ($[\overline{1}10]$, $[001]$, and $[\overline{1}11]$). The key feature of the new structure found to be required for this improved agreement with experiment is the inclusion of relaxations both parallel and perpendicular to the surface between the second and third layers.

Structural analysis of the Cu(100)–p(3[formula omitted])R45°–Sn surface using low and medium energy ion scattering spectroscopies

The atomic structure of the Cu(100)–p(32×2)R45°–Sn surface has been studied using medium energy ion scattering (MEIS), co-axial impact collision ion scattering spectroscopy (CAICISS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The p(32×2)R45° reconstruction was observed with LEED following the deposition of 0.42ML of Sn from a Knudsen cell on to the clean Cu(100) surface. The existence of sub-surface Sn atoms was immediately ruled out by the lack of blocking dips in the MEIS Sn scattered yield. Previously reported Sn overlayer and Cu–Sn surface layer alloy models were tested against the medium and low energy ion scattering data, with the best fit realised following structural optimization of the surface alloy model proposed by Pussi [K. Pussi et al., Surf. Sci. 549 (2004) 24]. Different out-of-plane shifts were observed for Sn atoms depending on their proximity to the missing Cu row.

Analysis of the interactions between He + ions and transition metal surfaces using co-axial impact collision ion scattering spectroscopy

The interactions between low energy He + ions and a series of transition metal surfaces have been studied using co-axial impact collision ion scattering spectroscopy (CAICISS). Experimental data were collected from the Ni(110), Cu(100), Pd(111), Pt(111) and Au(111) surfaces using ion beams with primary energies between 1.5 keV and 4.0 keV. The shadow cone radii deduced from the experimental surface peak positions were found to closely match theoretical predictions. Data analysis was performed using both the FAN and Kalypso simulation codes, revealing a consistent requirement for a reduction of 0.252 in the screening length correction in the Molière approximation within the Thomas–Fermi (TFM) interaction potential. The adjustments of the screening length in the TFM potential, predicted by O'Connor, and the uncorrected Ziegler–Biersack–Littmark (ZBL) potential both yielded inaccurate results for all of the surfaces and incident energies studied. We also provide evidence that, despite their different computational methodologies, the FAN and Kalypso simulation codes generate similar results given identical input parameters for the analysis of 180° backscattering spectra.

Analysis of polar direction of AlN grown on (0001) sapphire and 6H‐SiC substrates by high‐temperature metal‐organic vapor phase epitaxy using coaxial impact collision ion scattering spectroscopy

AbstractHigh‐crystalline quality AlN layers with an atomically flat surface are grown on (0001) sapphire and 6H‐SiC substrates by metal‐organic vapor phase epitaxy at 1400 °C without low‐temperature buffer layer. The polar direction of AlN layers is investigated by coaxial impact‐collision ion scattering spectroscopy (CAICISS). For AlN growth on sapphire substrate, trimethylaluminum (TMAl) is supplied for 10 sec before introducing ammonia (NH3). For AlN growth on SiC substrate, TMAl and NH3 are supplied at the same time. The CAICISS spectrum of AlN layers is analyzed by measuring the dependence of the Al atoms signal intensity on the angle of ion beam incidence considering the shadowing and focusing effects for determining the polar direction of AlN layers. The CAICISS spectra clearly indicate the polar direction of AlN layers and both AlN layers are found to be had the Al‐polarity. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comment on “Computer Simulation of Coaxial Impact-Collision Ion Scattering Spectroscopy Spectra of Clean Pt(111) Surface and Pt(111)–p(2×2)-O Surface”

The clean Pt(111) and Pt(111)-p(2×2)-O surfaces have been investigated using the computer simulation of coaxial impact-collision ion scattering spectroscopy (CAICISS). The computer simulations employing the atomic collisions in a crystalline target (ACOCT) program code, which treats the atomic collisions three-dimensionally and is based on the binary collision approximation (BCA), were carried out for the case of 3 keV He+ ions incident along the [211] azimuth of the clean Pt(111) and Pt(111)-p(2×2)-O surfaces. The comparisons between ACOCT results and experimental CAICISS data show that the experimental results on the clean Pt(111) surface are relatively well reproduced by the ACOCT simulations for no surface relaxation, and that the ACOCT simulations for the Pt(111)-p(2×2)-O surface appear the oxygen occupancy in the fcc-hollow sites over the hcp-hollow sites. The ACOCT results for the clean Pt(111) and Pt(111)-p(2×2)-O surfaces are consistent with the analyzed results of low-energy electron diffraction (LEED).

Reply to “Comment on `Computer Simulation of Coaxial Impact-Collision Ion Scattering Spectroscopy Spectra of Clean Pt(111) Surface and Pt(111)–p(2×2)-O Surface' ”

Reply to “Comment on `Computer Simulation of Coaxial Impact-Collision Ion Scattering Spectroscopy Spectra of Clean Pt(111) Surface and Pt(111)–p(2×2)-O Surface' ”

Computer simulation of CAICISS spectra of clean Cu(1 0 0) surface and Cu(1 0 0) surface by Pt deposition

The clean Cu(100) surface and Pt/Cu(100) surface by Pt deposition at room temperature have been investigated using the computer simulation of coaxial impact-collision ion scattering spectroscopy (CAICISS). The computer simulations employing the ACOCT program code, which treats the atomic collisions three-dimensionally and is based on the binary collision approximation (BCA), were carried out for the case of 3keV He+ ions incident along the 〈100〉 and 〈110〉 azimuths of the clean Cu(100) and Pt/Cu(100) surfaces. The comparisons between ACOCT results and experimental CAICISS data show that the experimental results on the clean Cu(100) surface are relatively well reproduced by the ACOCT simulations including the inward relaxation of 1.2% in the first interlayer spacing and the outward relaxation of 1.6% in the second interlayer spacing, and that the ACOCT simulations for the Pt deposition with coverages of 2.35ML and 2.75ML on the Cu(100) surface appear the concentrations of 0.24ML of Pt sitting 2.3Å and 0.25ML of Pt sitting 2.5Å above the outermost atomic layer, respectively.

Growth process and surface structure of MnSi on Si(1 1 1)

The solid-phase epitaxial growth process and surface structure of MnSi on Si(111) were investigated by coaxial impact-collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). For the Si(111) sample deposited with 30 monolayers (ML) of Mn at room temperature, the intermixing of Mn and Si gradually started at 100°C and reached equilibrium at approximately 400°C. At this equilibrium state, the Mn atoms were transformed into crystalline MnSi film. Further annealing caused the desorption of Mn atoms. We identified the structure of MnSi as cubic B20 and the crystallographic orientation relationships as Si(111)//MnSi(111) and Si[1¯21¯]//MnSi[1¯10]. The MnSi(111) surface was found to have a dense Si terminating layer on its topmost surface. On the other hand, 3ML of Mn deposited on Si(111) reacted with Si even at room temperature and formed a pseudomorphic structure. This structure was transformed into MnSi after annealing. A filmlike morphology with protrusions was observed for the sample with 30ML of Mn, while island growth occurred for the sample with 3ML of Mn.

Coverage Analysis of Molecularly Thin Lubricant Films Using Molecular Dynamics Simulations and CAICISS Measurements

In order to examine the coverage of molecularly thin lubricant films on magnetic recording media, a method using coaxial impact collision ion scattering spectroscopy (CAICISS) is proposed. In this method, it is presumed that if a lubricant film of perfluoropolyether completely covers the surface, the fluorine-to-carbon atomic ratio (F/C ratio) of the surface should become 2. In this paper, we reproduce molecularly thin lubricant films on a carbon overcoat by full-atom molecular dynamics simulations, and calculate their coverage and F/C ratios. assuming the CAICISS measurement, the F/C ratios were computed considering the shadow cones formed behind the surface atoms. By comparing the F/C ratios with the coverage, we conclude that the coverage measurement method using CAICISS can accurately evaluate the coverage of molecularly thin lubricant films.

Surface Characterization of GaN(0001) Grown by Liquid Phase Epitaxy Using Coaxial Impact-Collision Ion Scattering Spectroscopy

We characterized the surface cleanliness, structure, and composition of GaN(0001) grown by liquid phase epitaxy (LPE) using coaxial impact-collision ion scattering spectroscopy (CAICISS). Contamination on the as-received LPE-GaN(0001) was removed by annealing at 900 °C, but annealing was unable to remove the O atoms from the as-grown surface, indicating that the as-grown sample incorporated O atoms. Although the as-grown sample contained O atoms, its structural perfection was maintained. These facts were explained by localization of O atoms near dislocations. The etched surface exhibited high crystalline quality, which was comparable to that of the sample grown by vapor phase epitaxy (VPE).

Computer Simulation of Coaxial Impact-Collision Ion Scattering Spectroscopy Spectra of Clean Pt(111) Surface and Pt(111)-p(2×2)-O Surface

The clean Pt(111) and Pt(111)-p(2×2)-O surfaces have been investigated using the computer simulation of coaxial impact-collision ion scattering spectroscopy (CAICISS). The computer simulations employing the atomic collisions in a crystalline target (ACOCT) program code, which treats the atomic collisions three-dimensionally and is based on the binary collision approximation (BCA), were carried out for the case of 3 keV He+ ions incident along the [211] azimuth of the clean Pt(111) and Pt(111)-p(2×2)-O surfaces. The comparisons between ACOCT results and experimental CAICISS data show that the experimental results on the clean Pt(111) surface are relatively well reproduced by the ACOCT simulations for no surface relaxation, and that the ACOCT simulations for the Pt(111)-p(2×2)-O surface appear the oxygen occupancy in the fcc-hollow sites over the hcp-hollow sites. The ACOCT results for the clean Pt(111) and Pt(111)-p(2×2)-O surfaces are consistent with the analyzed results of low-energy electron diffraction (LEED).

CAICISS and STM study of [formula omitted] and [formula omitted] tin phases on Si(1 0 0)

Tin (Sn) adsorption on Si(100) surface has been studied by scanning tunneling microscopy (STM) and co-axial impact collision ion scattering spectroscopy (CAICISS). The c(8×4) and (5×1) phases were analyzed to reveal their atomic structure. It has been confirmed that the c(8×4) structure consists of buckled Sn dimers. The (5×1) structure has been found to be partially irregular along (5×1) rows and to consist of double Sn layer. The Sn atoms in the first layer are undimerised while those in second layer form asymmetric dimers.

New method of evaluation for interatomic interaction potential in LEIS with large-angle scattering using the two-atom scattering model

The interaction potential between an incident ion and a target atom in impact-collision ion scattering spectroscopy (ICISS), which is a specialization of low energy ion scattering (LEIS) and its variants, i.e. ICISS with detection of neutrals (NICISS), coaxial ICISS (CAICISS) and impact-collision atom scattering spectroscopy with detection of neutrals (NICASS), has been evaluated by the new method using the dependence of the total scattering angle on the impact parameter for the first collision in the numerical calculations based on the two-atom scattering model (TWASM). From the comparison of determined values of scaling factor for the Firsov screening length by three-dimensional computer simulations with calculated ones by TWASM, it became obviously that the interatomic potentials for the various combinations of an incident ion and a target atom in LEIS are suitably given by the Moliere potential with the reduced Firsov screening length employing the scaling factor obtained in TWASM calculations.

Asymmetric intermixing in a Co–Al thin film system: An investigation using coaxial impact collision ion scattering spectroscopy

Surface structure evolution during atomic deposition in a Co–Al system was investigated using coaxial impact collision ion scattering spectroscopy (CAICISS). Half monolayer of Al and Co atoms were deposited on Co(0001) and Al(001) single crystal surfaces, respectively, in an ultrahigh-vacuum environment. CAICISS analysis of the deposited surface revealed an asymmetric interfacial reaction, as predicted by previous molecular dynamics simulations. Al atoms deposited on a Co substrate are placed on the surface with no interatomic intermixing. In contrast, significant surface intermixing with the deposited Co atoms occurs on the Al(001) substrate, resulting in the formation of a CoAl intermetallic surface layer of B2 structure. These asymmetric features would be important to the understanding of the structural evolution of thin film multilayers.

Crystallinity and Polarity of Indium Nitride Films Grown on the c-face of Zinc Oxide

Indium nitride (InN) films were grown on the c-face of zinc oxide (ZnO) single crystals by molecular beam epitaxy, and their interfacial structure and crystalline polarity were examined. The c-parameter and the crystallinity of the films strongly depended on the substrate polarity and growth temperature. In particular, the low-temperature-grown films on the oxygen terminated c(-)-face of ZnO (c(-)-ZnO) were single crystalline films with a shorter c-axis than that of bulk InN, while the films grown on the zinc terminated c (+) -face of ZnO (c(+)-ZnO) and the high-temperature-grown films had low crystallinity. Coaxial impact-collision ion scattering spectroscopy (CAICISS) revealed that the low-temperature-grown films on c(-)-ZnO had (0001) In-faces, namely c (+) -polarity (c (+) -InN), and TEM observations suggested the existence of an interfacial layer a few atomic thick in the c (+) -InN/c (-) -ZnO heterostructure. These results on the lattice restriction and the polarity of InN films are discussed in terms of the interfacial structure at the InN/ZnO boundary.

Sulfur passivation of Ge (0 0 1) surfaces and its effects on Schottky barrier contact

The structure of a passivating sulfide layer on Ge (0 0 1) substrates treated in an aqueous sulfide solution is investigated using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and coaxial impact-collision ion scattering spectroscopy (CAICISS). It is found from XPS analysis that the contribution from twofold co-ordinated Ge atoms is dominant in the S-treated Ge surface. The incident and azimuth angle dependencies of the Ge signal intensity are compared between the S-passivated and clean Ge surfaces in CAICISS measurements. The azimuth angle dependence exhibits clear 4-fold symmetry in both the S-passivated and the clean surfaces. From the incident angle dependence along [1 0 0] direction, almost the same shadowing and focusing effects are observed in both the surfaces. These results suggest that Ge surface is passivated by S atoms occupying bridge positions between adjacent surface Ge atoms. In order to examine the effect of S-passivation of Ge surfaces on the interface electrical properties, we perform I–V measurements of Au/S-passivated Ge Schottky diodes. It is found that the S-passivation is effective for obtaining uniform diode characteristics.

Initial growth of platinum on oxygen-covered Ni(1 1 0) surfaces

The initial growth of Pt on the Ni(1 1 0)–(3 × 1)-O and NiO(1 1 0) surfaces has been studied by coaxial impact collision ion scattering spectroscopy (CAICISS), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). Prior to Pt deposition, the atomic structure of the near-surface regions of the Ni(1 1 0)–(3 × 1)-O and NiO(1 1 0) structures were studied using CAICISS, finding changes to the interlayer spacings due to the adsorption of oxygen. Deposition of Pt on the Ni(1 1 0)–(3 × 1)-O surface led to a random substitutional alloy in the near-surface region at Pt coverages both below and in excess of 1 ML. In contrast, when the surface was treated with 1800 L of atomic oxygen in order to form a NiO(1 1 0) surface, a thin Pt layer was formed upon room temperature Pt deposition. XPS and LEED data are presented throughout to support the CAICISS observations.

Determination of a correction factor for the interaction potential of He+ ions backscattered from a Cu(1 0 0) surface

We have used coaxial impact collision ion scattering spectroscopy (CAICISS) data collected from 3keV He+ ions backscattered from a Cu(100) surface in different azimuthal orientations to investigate the influence of the screening length on CAICISS polar angle scans. We have compared the experimental data to computer simulations generated with the FAN code and found that for our experimental conditions an exceptionally low value of 0.53 was required for the correction factor to the Firsov screening length used with the Thomas–Fermi–Moliere potential. In addition we found that the Ziegler–Biersack–Littmark potential is not applicable, resulting in incorrect peak positions in the CAICISS polar angle plots.