Toshiaki Fujino

Surface hydroxyl formation on vacuum-annealed TiO2(110)

The change in surface composition and structure of a rutile TiO2(110) surface during thermal annealing in an ultrahigh vacuum was studied by coaxial impact–collision ion scattering spectroscopy and time-of-flight elastic recoil detection analysis. When the clean TiO2(110) surface with a 1×1 bridging-oxygen-rows structure was obtained by annealing at 730 °C, about one monolayer of hydrogen atoms still resided on the surface. These hydrogen atoms were assigned to surface hydroxyls as an ingredient of the TiO2(110)1×1 structure, which was formed in the self-restoration process of surface oxygen vacancy defects by dissociative adsorption of water molecules during thermal annealing.

Structural Analysis of 6H–SiC(0001)√3×√3 Reconstructed Surface

Using coaxial impact-collision ion scattering spectroscopy (CAICISS), the structure of the 6H–SiC(0001)√3×√3 reconstructed surface was investigated. As a result of composition analysis, the topmost layer of this surface was found to be covered with Si adatoms. Moreover, from the incidence angle dependence of the scattering intensity due to C atoms, it was found that the √3×√3 periodicity was formed by a one-third monolayer of Si adatoms occupying T4 sites, and the height of the Si adatoms from the first substrate layer was determined to be 1.5±0.2 A.

Adsorption of H on the Ge/Si(001) Surface as Studied by Time-of-Flight Elastic Recoil Detection Analysis and Coaxial Impact Collision Ion Scattering Spectroscopy

We have used time-of-flight elastic recoil detection analysis (TOF-ERDA) and coaxial impact-collision ion scattering spectroscopy (CAICISS) to investigate the structural changes of the Ge/Si(100) surface caused by atomic hydrogen adsorption. The following conclusions have been reached. (1) When the Ge(1 ML)/Si(001) surface is exposed to atomic hydrogen at room temperature, the saturation coverage of hydrogen is slightly less than that for a clean Si(001) surface. (2) The desorption curve of hydrogen for this surface showed that the topmost layer of the surface is covered by about 0.45 ML of Ge atoms intermixed with Si atoms, and the rest of the 1 ML of Ge atoms are incorporated in the bulk Si layer. (3) Upon initial adsorption of hydrogen, the asymmetry of the Ge dimer is removed, forming the symmetric Ge dimer with a slightly expanded intradimer bond length.

Influence of Hydrogen-Surfactant Coverage on Ge/Si(001) Heteroepitaxy

The growth of Ge on Si(001) at 300°C with dynamically supplied atomic hydrogen (H) as a surfactant has been monitored in real time using coaxial impact-collision ion scattering spectroscopy and time-of-flight elastic recoil detection analysis feasible in a gas phase atmosphere. It has been revealed that (1) a submonolayer of H atoms readily acts as a surfactant, (2) the intermixing of Ge and Si occurs at the initial stage of Ge growth in the presence of H-surfactant, and (3) beyond optimal H coverage of about 0.6 monolayer, the roughening of Ge films occurs even though a monohydride phase is maintained at the growth front.

Coaxial Impact-Collision Ion Scattering Spectroscopy and Time-of-Flight Elastic Recoil Detection Analysis for In Situ Monitoring of Surface Processes in Gas Phase Atmosphere

Based on conventional coaxial impact-collision ion scattering spectroscopy (CAICISS) and time-of-flight elastic recoil detection analysis (TOF-ERDA), we have developed a novel ion scattering and recoiling spectrometer equipped with a differential pumping system for in situ monitoring of surface processes in gas phase atmosphere in the pressure regime up to 10-4 Torr. In order to demonstrate the performance of this apparatus, we have applied it to real-time monitoring of Ge thin film growth on a Si(001) surface in atomic hydrogen (H) atmosphere. The morphology of Ge thin films and H coverage on the growth front during the growth in H atmosphere were successfully observed.

Ge thin film growth on Si(111) surface using hydrogen surfactant

Abstract We have investigated the atomic hydrogen (H)-surfactant mediated growth of Ge on Si(111) surface, using coaxial impact-collision ion scattering spectroscopy (CAICISS), time-of-flight elastic recoil detection analysis (TOF-ERDA) and scanning electron microscopy (SEM). It has been found that the Ge thin film on the Si(111)1×1-H surface is flattened by the H-surfactant, whilst on the Si(111)7×7 surface the flatness does not change in spite of supplying H. These results indicate that the flatness of the Ge thin film is strongly influenced by the structure of the Si(111) substrate surface at the initial stage of Ge thin film growth.

Influence of Mn Incorporation on Molecular Beam Epitaxial Growth of GaMnN Film

To clarify the origin of ferromagnetic behavior at room temperature in wurtzite GaMnN{0001} film grown by molecular beam epitaxy on an N-polar GaN(0001) based layer on sapphire(0001) substrates, we have investigated the surface structure, composition and lattice polarity of GaMnN films using coaxial impact-collision ion scattering spectroscopy. It was found that (1) incorporation of Mn atoms into GaN film suppresses the inversion of lattice polarity at the initial stage of GaMnN growth, (2) Mn atoms occupy substitutional sites of Ga atoms in the wurtzite GaN crystal, and (3) no notable surface segregation of Mn atoms occurs.

Hydrogen Segregation and Its Detrimental Effect in Epitaxial Growth of Ge Thin Film on Hydrogen-Terminated Si(001) Surface

We have performed real-time monitoring of Ge thin film growth on a hydrogen-terminated Si(001) surface at growth temperatures ranging from room temperature to 350°C, to clarify the influence of hydrogen atoms on Ge/Si(001) heteroepitaxy. Hydrogen atoms segregated to the surface and a portion of them desorbed from the growth front during Ge deposition, depending on the growth temperature. The existence of hydrogen atoms on the growth front increased the growth temperature for Ge/Si(001) heteroepitaxy, while the flatness of the deposited Ge thin film was improved, indicating that hydrogen atoms suppress the surface migration of deposited Ge atoms.

Thermal Stability in the Morphology of Ge Films on Si(001) Grown by Hydrogen-Surfactant-Mediated Epitaxy

The change in the morphology of flat Ge films on Si(001) fabricated by hydrogen-surfactant-mediated epitaxy during thermal annealing has been monitored in real time using coaxial impact-collision ion scattering spectroscopy. The temperature at the onset of roughening is found to increase with the film thickness, which improves the thermal stability in retaining smooth morphology. Flat Ge films of over 40 monolayers exhibit a rapid transition to a large island structure upon the onset of roughening. The thickness dependence of film roughening can be correlated with strain relaxation at the surface of the initial film.

Atomic-hydrogen-induced self-organization of Si(111)√3×√3-In surface phase studied by CAICISS and STM

Abstract Using coaxial impact collision ion scattering spectroscopy (CAICISS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) techniques, we have investigated the interaction of atomic hydrogen with the Si(111)√3×√3-In surface phase at elevated temperatures and structural behavior of In clusters induced by the interaction. Upon atomic hydrogen interaction, SiIn bonds are broken and replaced by SiH bonds. As a result, the √3×√3 reconstruction is destroyed and small In clusters are formed on hydrogen-terminated Si(111)1×1 surface. Using STM, we also have found that the size of the In cluster increases with increasing substrate temperature during hydrogen exposure of the √3×√3-In surface phase. From CAICISS experimental results, we have found that atomic-hydrogen-induced In clusters for Si(111)√3×√3-In surface phase have an In(100) crystalline structure, while those for Si(001)4×3-In surface phase are polycrystalline. In conclusion, we have found that structural differences of surface give rise to different atomic-hydrogen-induced self-organization.