Impact Collision Ion Scattering Spectroscopy Research Articles

The structure of the Si(100)-(4 × 3) In surface studied by STM and ICISS

When indium is deposited onto the Si(100)-(2 × 1) surface and annealed at temperatures between 200 and 500°C, scanning tunneling microscopy (STM) images show (4 × 3) reconstruction for coverages from 0.5 to 25 monolayers (ML). Although the STM images of the (4 × 3) geometry are not atom-resolved, an arrangement of atoms with a bow-tie like structure can be postulated. We use impact-collision ion-scattering spectrometry (ICISS) to carry out polar angle scans on the Si(100)-(4 × 3)In surface and perform computer-simulated fits using different atomic models of the bow-tie structure. A best fit to the experimental ICISS polar angle scans is obtained for one of the models tested.

Impact-collision ion-scattering spectrometry studies of the VC0.8(111)-(8 × 1) surface

We use impact-collision ion-scattering spectrometry (ICISS) to verify that the (8 × 1) reconstructed surface of VC0.8(111) arises from the superposition of a rectangular surface vanadium layer on top of the hexagonal bulk, in agreement with a surface structure proposed earlier in a scanning tunneling microscopy (STM) study. However, a major discrepancy with the STM results is the absence of any pronounced buckling within the surface unit cell. The ICISS results suggest that the vanadium layer on the surface is perfectly planar.

Three-dimensional three-atom model for computer simulation of impact-collision ion scattering spectroscopy

A new model for computer simulation of impact-collision ion scattering spectroscopy (ICISS) has been developed. By this model, the scattering cross section of the three target atoms arbitrarily placed in the three-dimensional space can be calculated. This made it possible to interpret ICISS data including shadowing and blocking effects from out-of-plane scattering. The method is also effective in the case that the scattering angle is not 180°. As an example, ICISS data of the NbC(111) surface along the [1̄10] azimuth have been analysed. The result of the calculation is in a good agreement with the experimental data. The computational time is sufficiently short, so this method is useful for a quantitative analysis of ICISS data with arbitrary scattering angle and azimuth.

Path-dependent neutralization of Ne + and Na + scattered from Ag(001)

Recent surface crystallographic studies involving impact collision ion scattering spectroscopy (ICISS) have utilized beams of Ne + ions as the probe and an electrostatic analyzer as the detector. The data were analyzed under the assumption that the path dependent neutralization could be neglected for scattered Ne + ions of at least 4 keV incident kinetic energy. We have investigated this assumption by collecting energy and angle dispersive ICISS distributions with a time-of-flight analyzer while separating the ion and neutral yields by application of a potential to the free flight region. This investigation shows that both 5 and 10 keV Ne + scattered from Ag(001) display considerable path-dependent neutralization, but that of Na + is very small.

Coaxial Impact Collision Ion Scattering Spectroscopy Measurements of As/Si(100) Structure Prepared by Ionized Cluster Beam Method

The surface structure of a Si (100) substrate exposed to an As ionized cluster beam (ICB) prior to epitaxial growth of GaAs was investigated by means of coaxial impact collision ion scattering spectroscopy (CAICISS). As a result of the measurement, first, it was proven that both As and Si dimers were formed after As ICB exposure. Second, both As and Si atoms form double domains of 2×1 and 1×2, and both As and Si areas of one domain are larger than those of the other domain in the case of a 3°-off Si substrate. Furthermore, it is likely that As atoms terminate Si atoms as if the As atoms replace the top Si layer. Third, the Si surface is not damaged by As ICB exposure, and the As ions seem to be implanted to the substitutional sites.

Analysis of the NbC(111)-( sqrt 3 x sqrt 3 )R30 degrees-Al surface structure by impact-collision ion-scattering spectroscopy.

The structure of the NbC(111) clean surface and the aluminum adsorption system at room temperature have been studied by impact-collision ion-scattering spectroscopy, reflection high-energy electron diffraction (RHEED), low-energy electron diffraction, and computer simulation. It has been found that the clean surface exhibits a 1\ifmmode\times\else\texttimes\fi{}1 RHEED pattern and no reconstruction occurs. The outermost layer consists of Nb atoms and relaxes inward by 0.20\ifmmode\pm\else\textpm\fi{}0.05 \AA{}, which is equal to 15.5\ifmmode\pm\else\textpm\fi{}3.9% of the space between the first and second layers of the bulk. The carbon atoms in the second layer also shift inward by 0.05\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. The Al-adsorbed surface has a (\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3)R30\ifmmode^\circ\else\textdegree\fi{} structure with slight modulation. The Al atoms occupy two-thirds of the threefold-hollow sites, under which a Nb atom of the third layer is situated. Adsorbed Al atoms make a honeycomb pattern. The distance between the Al atom and the surface has been determined to be 2.25\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. The Al-Nb bond length is 2.90\ifmmode\pm\else\textpm\fi{}0.05 \AA{}.

Structure of the Si(100)-(2 x 2)In surface.

The question of whether the Si(100)-(2\ifmmode\times\else\texttimes\fi{}2)In reconstruction consists of orthogonal or parallel In ad-dimers was answered by performing studies, using scanning tunneling microscopy and impact-collision ion-scattering spectrometry (ICISS), on low coverages of In adsorbed on a vicinal Si(100) surface. The formation of a predominantly single domain of the (2\ifmmode\times\else\texttimes\fi{}2) phase on the vicinal surface allowed us to use the ICISS experiments to distinguish between the orthogonal and parallel ad-dimer geometries. Our results strongly support the model involving the parallel ad-dimer, in agreement with previous theoretical predictions.

4 x 1 reconstruction of indium deposited on vicinal Si(111) surfaces.

The Si(111)-(4\ifmmode\times\else\texttimes\fi{}1) In reconstruction normally exists in three domains of double-row ridges along three equivalent 〈1\ifmmode\bar\else\textasciimacron\fi{}10〉 directions on a flat Si(111) substrate. Using vicinal Si(111) surfaces as substrates, scanning-tunneling-microscopy images show the existence of only a single domain of the (4\ifmmode\times\else\texttimes\fi{}1) reconstruction with the double rows aligning with the [1\ifmmode\bar\else\textasciimacron\fi{}10] step edges when the surface is misoriented toward the [1\ifmmode\bar\else\textasciimacron\fi{} 1\ifmmode\bar\else\textasciimacron\fi{}2] direction. When the vicinal sample is misoriented toward the opposite, i.e., [112\ifmmode\bar\else\textasciimacron\fi{}], direction, however, all three domains are present. We performed impact-collision ion-scattering spectrometry experiments on the single-domain surface and the results confirm a model in which In adatoms occupy ${\mathit{H}}_{3}$ and ${\mathit{T}}_{4}$ sites with 1/2-monolayer coverage.

Initial stages of the formation of the Au/GaAs(001) interface: A low-energy ion scattering study

Submonolayer coverages of Au on GaAs(001) substrates prepared by various ex situ chemical cleaning procedures using low-energy ion scattering techniques are investigated. This research is compared with previous results for 1 ML of Au deposited on Si(111). A comparison of the energy spectra showed substantial broadening in the Li+ backscattering ion peak from Au deposited on GaAs, as compared to the Au on Si. Li+ impact collision ion scattering spectroscopy (ICISS) results showed that the gold formed an ordered overlayer above the Si surface, which was thermally stable to 500 °C. Even for depositions on room-temperature GaAs(001), shadowing of Au by substrate atoms at low scattering angles showed that Au penetrated below the GaAs surface. The estimate of the average penetration depth into the room-temperature substrate is two to three atomic planes of the GaAs crystal. An ICISS experiment showed that the Au atoms sampled by the ion beam were not ordered on lattice sites, but appeared to occupy multiple and/or random positions within the substrate. Upon annealing to 300 °C, the gold atoms were more ordered, but did not penetrate significantly further into the GaAs. At higher annealing temperatures, the Au either diffused further into the substrate or became incorporated in islands, and occupied favored subsurface sites.

Analysis of the HfC(111) surface structure by impact collision ion scattering spectroscopy (ICISS)

The structure of the HfC(111) clean surface and the O 2, D 2 adsorption systems at room temperature have been studied by impact collision ion scattering spectroscopy (ICISS). The clean surface exhibits a 1 × 1 low energy electron diffraction (LEED) pattern and no reconstruction occurs. The outermost layer consists of Hf atoms and the space between the first and second layer contracts by 0.18 ± 0.05 A ̊ , which is equal to (13.4 ± 3.7)% of the corresponding bulk value. The oxygen-adsorbed surface has a 1 × 1 structure and the O atom is located on the threefold hollow site, under which a Hf atom of third layer exists. By comparing the ICISS spectra with computer simulations, the distance between the O atom and the surface has been determined at 0.90 ± 0.05 A ̊ (O-Hf bond length = 2.10 ± 0.07 A ̊ ). In case of deuterium, D, the atom is adsorbed on the same site as oxygen and the distance from the surface is 1.36 ± 0.07 A ̊ (D-Hf bond length = 2.33 ± 0.10 A ̊ ). Judging from the distance between the Hf atom and the adsorbates, the Hf-O bond seems to be rather ionic and the Hf-D bond seems covalent.

Analysis of the HfC(111) surface structure by impact collision ion scattering spectroscopy (ICISS)

Analysis of the HfC(111) surface structure by impact collision ion scattering spectroscopy (ICISS)

Si(111)–(2√3×2√3)Sn reconstruction studied by ion scattering spectrometry and scanning tunneling microscopy

The techniques of impact collision ion scattering spectrometry (ICISS) and scanning tunneling microscopy (STM) were used to study the (2√3×2√3)R30° reconstruction of Sn on the Si(111) surface. Our STM results show that the 2√3×2√3 structure has three equivalent orientations and that the electronic structure is onefold symmetric. ICISS polar-angle scans, using lithium ions (Li+) backscattered from Sn, establish that Sn atoms are located on top of the Si(111) surface. These scans, which reflect the relative positions of the Sn atoms with respect to each other, are compared with computer simulations of two models of the surface. Reasonable agreement is obtained with a model which contains two layers of Sn atoms.

Surface reconstructions of the Sn/Si(111) system investigated by ion-scattering spectrometry and scanning tunneling microscopy

We report the use of impact-collision ion scattering spectrometry (ICISS) and scanning tunneling microscopy (STM) to study the in-plane geometry of both the √3 × √3 and 2√3 × 2√3 reconstructions of Sn on Si(111). For the √3 × √3 reconstruction the Sn atoms are thought to sit in fourfold atop (T 4 ) sites, or threefold hollow (H 3 ) sites. ICISS polar angle scans show a definite agreement with computer simulations of the T 4 model. The ICISS scans also determine the spacing between Sn and Si layers. Previous STM work reported a twofold symmetric structure for the 2√3 × 2√3 reconstruction with three possible orientations. We use ICISS and STM to provide information on both the geometry and registration of atoms on the surface in order to solve the structure of this particular surface.

Ag thin film growth on hydrogen-terminated Si(100) surface studied by TOF-ICISS

Using time-of-flight (TOF) type low-energy impact-collision ion scattering spectroscopy (ICISS) and elastic recoil detection analysis (ERDA), we have investigated (1) the effect of the saturation of surface dangling bonds of Si(100) surfaces with atomic hydrogen upon Ag thin film growth, and (2) the effect of hydrogen adsorption onto Ag thin films (∼ 1 ML coverage) on the clean surfaces. We find that (1) epitaxial growth of Ag films is promoted by the hydrogen atoms residing at the film/substrate interface and (2) adsorption of hydrogen onto Ag monolayer deposited on Si(100) surfaces transforms the Ag monolayer into very small crystallites of Ag(100) grown epitaxially on the Si(100) substrate.

Low energy ion scattering analysis of the surface compositional change of Au 3Cu(001) induced by oxygen chemisorption

The change of the surface composition of Au 3Cu(001) induced by oxygen chemisorption was investigated by means of impact collision ion-scattering spectroscopy (ICISS) of time of flight version using 180° scattering of 3 keV Ne + ions. For the clean surface, the topmost layer was found to be occupied almost completely by Au atoms (∼95%) and the second layer by Cu atoms (∼95%). Oxygen chemisorption was performed by exposing the crystal surface to atomic oxygen produced on hot-W filament. With the oxygen adsorption, Au in the topmost layer was replaced with Cu and Cu in the second layer with Au, respectively. Almost complete replacement of elements in the first layer was found at high coverages. At low coverages, at least two Cu atoms were induced by one oxygen atom. From the analysis of the polar scans of the ICISS signals, the oxygen was suggested to be located deeply in the 4-fold hollow site.

Surface Structure Analysis of MoS2 by Coaxial Impact-Collision Ion Scattering Spectroscopy(CAICISS).

Natural MoS2 (001) surface structure was investigated by coaxial impact-collision ion scattering Spectroscopy (CAICISS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) under ultra high vacuum. It was found that the surface reconstruction of MoS2 (001) does not occur. There is the same stacking sequence (2H structure) in the bulk. However, we found the contractions of 3.6±0.4% at the top surface interlayer (d12) and of 0∼2% at the subsequent interlayer (d23).

In SituCharacterization of the Initial Growth Stage of GaAs on Si by Coaxial Impact-Collision Ion Scattering Spectroscopy

The initial growth stage of GaAs on Si has been characterized in situ by coaxial impact-collision ion scattering spectroscopy (CAICISS). The behavior of As atoms on the Si surface and at the step sites is analyzed. The results of analysis on the initial growth stage strongly suggest that the three-dimensional island growth of GaAs on Si occurs even in 1-monolayer (ML) GaAs growth.

Structure Analysis of the CaF2/Si(111) Interface in Its Initial Stage of Formation by Coaxial Impact-Collision Ion Scattering Spectroscopy (CAICISS)

The structure of the CaF2/Si(111) interface in its initial stage of formation has been analyzed with a coaxial impact-collision ion scattering spectroscopy (CAICISS), in which an ion source and a time-of-flight energy analyzer are arranged coaxially so as to take the experimental scattering angle at 180°. It has been found that in the initial stage of the formation of the CaF2/Si(111) interface, a monolayer of CaF rather than CaF2 is formed on Si(111). The arrangement of the Ca and F atoms in the monolayer of CaF with reference to Si(111) is B-type, the Ca atoms being situated at the T4. site just above the second-layer Si atoms. The interlayer distance between the topmost F layer and the underlaying Ca layer is estimated to be 0.64 ± 0.05 A.

Si(111)-(4 x 1)In surface reconstruction studied by impact-collision ion-scattering spectrometry.

The technique of impact-collision ion-scattering spectrometry (ICISS) was used to study the 4\ifmmode\times\else\texttimes\fi{}1 reconstruction of In on the Si(111) surface. The top layer of adatoms is arranged in double-row ridges, with three equivalent orientations running in 〈1\ifmmode\bar\else\textasciimacron\fi{}10〉 directions. Several models have been simulated for both 1/2-monolayer (ML) and 1-ML coverage of the surface. Our ICISS polar-angle scans do not agree with models containing substitutional In in the first Si layer. Instead, a 1/2-ML model with In adatoms sitting in inequivalent sites provides the closest agreement with experiment. The vertical displacement between the In adatoms and the first Si layer has been determined experimentally to be 1.15\ifmmode\pm\else\textpm\fi{}0.15 \AA{}.

TOF-ICISS study of surface damage formed by Ar ion bombardment on Si(100)

The surface damage formed on a clean Si(100)-2 × 1 surface by low-energy Ar ion bombardment has been studied in situ using the impact collision ion scattering spectroscopy (ICISS) method and the time-of-flight (TOF) technique. The Ar ion energy was 1 keV and the ion doses were in the range of 10 14-10 15ions/cm 2. Channeling and focusing effects were observed very clearly on a clean and well-ordered surface. With the increase of the Ar ion dose, such channeling and focusing effects gradually disappear. The annealing process of the surface damage was also investigated.