Kazumasa Narumi

Molybdenum substitutional doping and its effects on phase transition properties in single crystalline vanadium dioxide thin film

Molybdenum (Mo) doped vanadium dioxide thin films were synthesized using a Mo striped vanadium (V) target during pulsed laser ablation process. The film structure was characterized by high resolution x-ray diffraction, x-ray rocking curve and Rutherford backscattering/channeling measurements. The results show that the full width at half magnitude of the x-ray rocking curve is as narrow as 0.0074°, comparable to that of the (0001) sapphire substrate, 0.0042°, in this study. The ratio of the aligned-to-random backscattered yield reaches 5%, implying that the growth is that of the single crystalline epitaxy. The result of angular scans for both V and Mo atomic channelings reveals that Mo atoms successfully take sites of the V sublattice as a substitutional dopant. It has been noted that the degradation of the phase transition properties of the film upon doping is closely related to the conductivity in the semiconductor phase.

Pattern formation induced by co-deposition of Ni and C60 on MgO(100)

We report on the unusual phenomenon of pattern formation in the thin film of Ni+C60 mixture deposited on the MgO(100) substrate. Under certain deposition kinetics a periodic system of stripe domains was formed. The domains consist of sub-half-micrometer large droplets encompassed with a thin C60—based rind with a possible polymeric structure. The stripes are embedded in the double-layer platform falling into the epitaxial Ni and amorphous-C (a-C) thin films. During co-deposition the C60 molecules partly disintegrate and transform towards a-C. Due to the accumulation of a-C (with limited solubility in Ni) thermodynamic instability arises in the system and reaching a certain level, it triggers spontaneous partitioning (and self-organization) of the deposited material. As a principal mechanism of the pattern formation, a sequential drift and coordinate release of the thermodynamic instability is proposed.

X-ray and Fourier transformed infrared investigation of beta-SiC growth by ion implantation

Crystalline -SiC layers have been synthesized by low-temperature carbon ion implantation into Si (001) and post annealing at temperatures 800-1200 °C. The crystal structure and the crystalline quality of the -SiC layers was identified and examined by x-ray diffraction and a Fourier transformed infrared spectrometer and x-ray pole figure measurements, respectively. It was found that with this technique of ion implantation, the -SiC layer was grown epitaxially at a temperature of 800 °C and that the crystalline quality of the -SiC layer was much improved at higher annealing temperatures. In a sample annealed at 1000 °C, the -SiC buried layer had a near-perfect orientation relationship with the substrate.

Characterization of epitaxially grown Cu/Nb multilayer on α-Al2O3 with RBS/channeling technique

Abstract Epitaxial growth of Cu/Nb multilayer on α -Al 2 O 3 was realized under UHV electron beam evaporation by controlling the substrate temperature at each stage of multilayer growth. The typical thicknesses of Cu and Nb layers are in the range of 50 to 260 nm. The crystal quality except the interface boundary is shown to be high with RBS/channeling and XRD analyses. It has been found that the deposited Cu and Nb layers are single-crystalline over the sample size far beyond the TEM scale. The orientation relationship between Cu and Nb layers is as follows: Cu(111)/Nb(110) on α -Al 2 O 3 a -plane, Cu(001)/Nb(001) on α -Al 2 O 3 r -plane and textured Cu(111)/Nb(111) on α -Al 2 O 3 c -plane. The suitable temperature for single-crystalline Nb growth is 750°C in common with three different α -Al 2 O 3 substrate and those for single-crystalline Cu growth on Nb(110) and Nb(001) layers are 200°C and RT, respectively. It is concluded that Cu(111)/Nb(110) with Cu[110]//Nb[001] is crystallographically consistent stacking in a hetero-epitaxial manner.

Highly sensitive time-of-flight secondary-ion mass spectroscopy for contaminant analysis of semiconductor surface using cluster impact ionization

To compare emission yields of secondary ions from contaminated silicon wafers between cluster and monoatomic ion impacts, pulsed C1+ and C8+ beams are applied to time-of-flight secondary-ion mass spectrometry. C8+ impact of 0.5MeV∕atom provides higher secondary-ion emission yields per incident atom than C1+ impact of 0.5MeV∕atom for organic and metallic contaminants. Higher peak intensities are also observed for a C8+ ion beam with a reduced energy. The enhanced emission yields of secondary ions originating from the contaminants show that mass spectrometry with cluster impact ionization is a powerful analytical tool for highly sensitive detection of the surface contaminants on the silicon wafers.

Morphology evolution of thin Ni film on MgO(100) substrate

Thin Ni films with various thicknesses were deposited onto the MgO(100) single crystal substrate at 400°C. The morphology measured by atomic force microscope shows an apparent correlation with the thickness. The initial 10 A film is composed of small round Ni islands. In the 25 A film, pinholes with narrow size distribution occur, which show local periodic distribution in some regions when the thickness of the film reaches 75 A. The driving force for such a structure is attributed to the elastic strain energy. When the film is about 100 A thick, the pinholes begin to disappear, due to filling by the late-coming atoms and covering of upper islands.

Energy Spectra of Electrons Induced by MeV Atom Clusters

The first observation of the energy distribution of electrons emitted from solids bombarded by MeV atom clusters is reported. In the backward direction, using graphite and Si bombarded by Cn+ and Aln+ (n ≤8), an appreciable suppression of electron emission has been observed at electron energies lower than ~10 eV. Electron yield per atom decreases with increasing n, and becomes less than 50% at n ≥3, relative to the case of n=1. The experimental results cannot be explained in terms of projectile stopping cross sections nor by the clearing-the-way effect. It is probable that the suppressed electron emission is a result of the suppression of the transport or surface transmission of the produced low-energy electrons, rather than of the suppression of ionization.

RBS and SEM analysis of the nickel-fullerene hybrid systems

Abstract Surprising structural variability of the Ni/C 60 /Ni thin film packaging was observed after annealing at elevated temperatures. The thermal processing of the Ni/C 60 /Ni multilayer led to a gradual disruption of the C 60 layer and to the formation of micron-sized octagonal ‘pits’ and rod-type particles. The unusual thermal response points out the complex physiochemical processes incited in the hybrid system by heat treatment. Here, based on the SEM and RBS analysis, the first insight into the microstructural evolution of the Ni/C 60 /Ni multilayer is presented.

Isolation of Co nanoparticles by C60 molecules in co-deposited film

Abstract Mixed Co–C 60 films have been prepared on (0001) α-Al 2 O 3 or (001) NaCl substrates at room temperature (RT) by simultaneous deposition of cobalt and C 60 fullerene. The characterization of these films by atomic force microscopy (AFM) and high-resolution transmission electron microscopy (TEM) reveals a nanocomposite structure of the films with Co nanocrystals dispersed into carbon-based matrix. Electron and X-ray diffraction (XRD) analyses evidence the face-centered cubic (fcc) lattice of Co nanocrystals. Raman experiments confirm the existence of C 60 molecules as the main structure units of the matrix. Some modification in C 60 Raman modes reflects the distortion of C 60 molecules through Co–C 60 bonding within the matrix of the nanocomposite.

Improvement in surface roughness of nitrogen-implanted glassy carbon by hydrogen doping

Abstract We have demonstrated that hydrogen doping (∼30 at.%) improves the surface roughness of N-implanted glassy carbon (GC). Prior to nitrogen implantation, D 2 + molecular ions with energy of 10 keV were implanted in GC to a dose of 6×10 17 D cm −2 . Part of the doped hydrogen atoms is released by 100-keV N 2 + implantation, but hydrogen incorporation occurs simultaneously. Consequently, the concentration of hydrogen in the N-implanted layer exceeds 20 at.% at any N implantation dose. For hydrogen-doped GC, surface roughening due to N implantation was not observed in all cases examined. This indicates that hydrogen incorporation suppresses the surface roughening. A possible mechanism for the surface roughening and its suppression by hydrogen doping is discussed in terms of chemical bonding and structure in the N-implanted layer.