Akihito Matsumuro

Preparation of carbon nitride thin films by ion beam assisted deposition and their mechanical properties

Abstract Carbon nitride films have been prepared by ion beam assisted deposition, in which carbon was evaporated by electron beam and nitrogen ions were simultaneously bombarded onto silicon substrates. The ion bombardment energies and the deposition temperatures are varied to promote the C–N cluster formation and to improve the mechanical properties of the films. N 1s peaks in XPS spectra indicate the existence of two different N 1s bonding states, one attributed to nitrogen inserted into the graphitic ring structure, and the other attributed to nitrogen surrounded by three carbons in the C–N network. The formation of the C–N cluster similar to the disordered turbostratic structure is enhanced at high deposition temperature, whereas bonding states are not affected by the ion bombardment energy. Nano-indentation studies show that the increase of deposition temperature leads the hardness of the film up to 20 GPa. The films prepared under appropriate conditions have low friction coefficient of 0.2 against SiC and steel balls in an ambient environment.

Effect of substrate bias on AlN thin film preparation in shielded reactive vacuum arc deposition

Abstract Aluminum nitride (AlN) thin films were prepared using reactive cathodic vacuum arc deposition in conjunction with a macrodroplet shield plate. Various bias conditions, such as no bias (floating), 0-V bias (same potential as anode), DC bias of −10 to −30 V, and RF power of 25–200 W, were applied to the substrate table. For floating bias, a -axis-oriented film was obtained. For 0-V bias, the films prepared on molybdenum substrate showed no preferential orientation, although the film prepared on silicon and borosilicate glass showed a -axis-orientation. For RF bias, the orientation changed from the a - to the c -axis as the RF power increased. The hardest (27 GPa) film was obtained for 0-V bias, and the hardness of the other films ranged from 19 to 24 GPa. The refractive index of the film prepared on quartz substrate was approximately 2.0 over the visual and infrared regions for all films. The extinction coefficient was less than 0.01 over the visual and infrared regions, with the exception of the film prepared under the 0-V bias condition, which showed a higher value.

Influence of Deposition Temperatures on Bonding State and Microstructure of Carbon Nitride Thin Films Prepared by Ion-Beam-Assisted Deposition

The influences of the deposition temperature on bonding states and microstructures of carbon nitride films prepared by ion-beam-assisted deposition are analyzed by Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). FT-IR absorption spectra exhibit a peak corresponding to the C≡N bond and its population decreases with the deposition temperature. N 1s peaks in XPS spectra indicate the existence of two different N 1s bonding states, one attributed to nitrogen inserted into the graphitic ring structure, and the other attributed to nitrogen surrounded by three carbons in the C–N network. The increase of the deposition temperature leads to the formation of the C–N cluster similar to the highly disordered turbostratic structure. In C–N film growth, however, the sequential phase transformation from sp2-bonded phases to sp3-bonded phase frequently observed in BN film deposition is not found in TEM analyses.

Wear resistance of carbon nitride thin films formed by ion beam assisted deposition

Abstract Carbon nitride (CNx) thin films were synthesized by ion beam assisted deposition (IBAD) with electron beam evaporation of C and simultaneous irradiation of N ion beams. The (111)- and (200)-oriented TiN thin films and Si (100) wafer were used for substrates. The N/C content ratios of CNx films were determined to be up to 0.44. The friction coefficients against SiC and steel balls were 0.2–0.3, irrespective of the substrate materials, in both air and a vacuum of 1.3×10–4 Pa. The films prepared with a N/C transport ratio of one on the TiN(200) substrate showed good wear resistance in comparison with those prepared on the Si substrate. The wear rate of this sample was 0.25 times lower than that of a-C:H films. The difference in this wear behavior was attributed to higher adhesive strength due to the chemical bonding between the film and the TiN substrate.

Synthesis of Ti-N thin films prepared by dynamic ion mixing technique and their mechanical properties

Abstract Ti-N thin films were formed on unheated Si(100) substrate with evaporation of Ti by electron beam and simultaneous bombardment of N ion beam in the range of 1–40 keV. The influence of N ion acceleration energies and the content ratios (N/Ti) on microstructures and phases was investigated by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The XRD spectra revealed the formation regions of the single phases and the mixture phases for α-Ti, the stoichometric compounds TiN and Ti2N, at the various ion acceleration energies. The mechanical properties such as hardness, elastic modulus, adhesive strength and friction coefficient were also investigated. Nano-indentation studies showed that the hardness and the elastic moduli for each phase increased with increasing mixing layer thickness in relation to the ion acceleration energy. The single phase TiN and Ti2N films prepared at higher ion energy showed excellent mechanical properties in the hardness and adhesive strength. The relationships between other mechanical properties of the obtained films and their phases were also discussed.

High-Pressure Synthesis of a Bi-Pb-Sr-Ca-Cu-O Superconductor

Nearly perfect high-Tc single-phase powder of Bi-Pb-Sr-Ca-Cu-O was prepared by a modified solid-phase reaction method. This powder was then synthesized under 5.4 GPa to form a high-density block. While the pressed sample exhibited semiconducting behaviour, the post annealed sample showed a superconducting transition with Tc,onset=113 K, Tc,end=105 K and Jc (at 77 K)=508 A/cm2.

Tribological properties of a C60 monolayer film

Abstract The frictional behavior of a C 60 monolayer film between graphite substrates is studied using a homebuilt surface force apparatus. The mean frictional force from the C 60 monolayers is estimated to be approximately 2 mN, which is one-fifth that of C 60 thin films. The C 60 monolayer films exhibit a low frictional force of 2 mN up to 100 scans under a normal stress of 8 MPa, which indicates that the C 60 monolayer film is highly promising for use as a lubricant.

The Use of Sintered Diamond Anvils in the MA8 Type High-pressure Apparatus

A new multi-anvil type high-presure apparatus has been developed using sintered diamond anvils to generate pressures over 30 GPa and temperatures up to about 2000°C. A maximum sample volume of about 1 mm3 is available in this system. The pressure was confirmed by dissociation of forsterite into Mg-perovskite and periclase. The basic techniques and problems in utilizing sintered diamond in the MA8 type high-pressure apparatus are discussed with an emphasis on the future prospect of incorporating simultaneous X-ray diffraction observation.

Elastic and superconducting properties of supersaturated Al-Si and Al-Ge solid-solution alloys treated under a 5.4 GPa pressure

Supersaturated Al-Si and Al-Ge solid solutions having up to a 10 at% solute concentration were treated at 5.4 GPa. The variations in the elastic moduli, superconducting transition temperature Tc and other physical properties were obtained. Using the resonance method the moduli of the solid solutions in both alloy systems decreased with increasing solute concentration, in contrast with those of the two-phase states which increased. The maximum value of Tc was determined as 6.6 K for an Al-15 at% Si solid solution. It was confirmed that the dependence of Tc on the valence electron concentration was remarkably greater than that of other non-transition and noble metal alloys. Using low-temperature specific-heat experiments as a basis, the superconducting properties were discussed in terms of the electronic specific heat coefficient and the Debye temperature in comparison with other metallic superconductors.

Ar Ion Effect on Mechanical Properties of Carbon Nitride Films Prepared by Ion-Beam-Assisted Deposition

Carbon nitride (CN) films have been prepared by ion-beam-assisted deposition. Carbon was evaporated by electron beam and N and Ar ions were bombarded simultaneously from one ion source. To clarify the role of Ar ion bombardment, CN films were prepared on Si(001) substrates. The Ar/N2 ratio was varied between 0 and 2. Mechanical properties were measured in terms of hardness, friction coefficient and wear. The films prepared under Ar/N2 ratio of 1 showed the highest hardness and best wear resistance. The XPS analysis of the CN films showed two distinct bond components that correspond to C–N sp2, and C–N sp3 bond. CN films with Ar/N2 ratio of 1.0 mainly consisted of C–N sp2 bond structure. TEM observation, shows that the simultaneous bombardment of Ar ion promotes two-dimensional network of C–N chemical bonds that are formed similar to stacked graphite-like sheets with a columnar alignment perpendicular to the substrate surface (nanotube-like structure). This is advantageous from the mechanical strength point of view, however, excess bombardment of Ar ion prevents the formation of nanotube-like structure. The variation of the mechanical properties is due to the structural change obtained by simultaneous bombardment of Ar ions.