Masatou Ishihara

Control of preferential orientation of AlN films prepared by the reactive sputtering method

Abstract When aluminum nitride (AlN) thin films are applied to surface acoustic wave devices, (100) orientated films are necessary, because the electromechanical coupling coefficient of the (100) oriented films are superior to that of the (001) oriented films. However, it is hard to prepare the (100) oriented films by sputtering and ion plating. In this study, preferential orientation of AlN films was investigated. It was found that the (100) oriented films were deposited by the reactive DC magnetron sputtering method at a long distance ( L ) between the Al target and substrate (above 120 mm) and at high sputtering pressures (above 0.6 Pa). According to our theory, the relative growth rate of (100)/(001) is varied by changing the deposition unit from atoms to a dimer such as Al–N. Namely, when the mean free path of Al and N is longer than the distance L , Al and N atoms deposit directly on the substrate and the (001) oriented films grow. When it is shorter than the distance L , the collisions of Al and N atoms occur in the space between the target and the substrate and the Al–N dimers are formed and deposit on the substrate. In this case, the (100) orientation is enhanced.

Characterization of cementite films prepared by electron-shower-assisted PVD method.

Abstract It is important to understand the mechanical properties of single phase cementite in order to design the microstructure of advanced steels. Several papers have been published on mechanical properties of cementite embedded in steels or extracted from steels by electrolysis. However, single phase cementite is not documented. The purpose of this study is to prepare cementite films by the PVD method and to characterize their properties. We applied the electron-shower-assisted PVD method in order to produce a single phase cementite film (2.5 μm in thickness) in a C 2 H 2 atmosphere at 523 K. The composition of the film was determined to be 70Fe–28C–2O (at.%). ESCA spectra indicated that the film was not contaminated with other metallic elements. The grain size of the film was revealed to be about 50 nm by AFM. The Vickers hardness was 1230 (under a load of 2.5 g) at room temperature, nearly equal to the value of 1270 of the cementite extracted from carbon steel by electrolysis. Temperature dependence of the hardness was measured up to 673 K. Youngs modulus and Poissons ratio at room temperature were 160 GPa and 0.26, respectively.

Synthesis and Surface Acoustic Wave Property of Aluminum Nitride Thin Films Fabricated on Silicon and Diamond Substrates Using the Sputtering Method

C-axis oriented aluminum nitride (AlN) thin films with a thickness of 1 µm were prepared by reactive DC magnetron sputtering on polycrystalline diamond substrates at a substrate temperature of 623 K. The average surface roughness (Ra) of the AlN thin films was less than 2 nm obtained by locating the diamond substrates at a position of 100 mm from the aluminum target. The full width at half maximum (FWHM) of the rocking curve for the AlN(002) peak determined by X-ray diffraction analysis was about 0.2°. The surface acoustic wave (SAW) structures were completed by the deposition of aluminum electrodes on the as-deposited AlN surfaces. The SAW characteristics of an interdigital transducer (IDT)/AlN/diamond structure were investigated. The phase velocity and coupling coefficient were 10,120 m/s and 0.3%, respectively.

Sidewall modification of single-walled carbon nanotubes using photolysis of perfluoroazooctaneElectronic supplementary information (ESI) available: Fig. S1. UV-vis-NIR spectra of pristine and modified SWNTs. See http://www.rsc.org/suppdata/cc/b4/b402206h/

Photolysis of perfluoroazooctane with single-walled carbon nanotubes led to sidewall modification of the surface with the introduction of perfluorooctyl functional groups, confirmed by means of Raman, XPS, FT-IR, mass, UV-vis-NIR and SEM measurements.

Effect of bias voltage on A1N thin films prepared by electron shower method

Abstract When AlN thin films are applied to surface acoustic wave devices, c-axis- and a-axis-oriented films are necessary for longitudinal and transverse waves respectively. However, it is difficult to prepare a-axis-oriented films by sputtering and ion plating. Nevertheless, a-axis-oriented films have been prepared by the electron shower method, and the films can be changed to c-axis orientation by a negative bias of −200 V. The concentration of O in the films decreases with increasing negative bias voltage. These AlN films contain 20 at.% N, which is independent of the bias voltage.

Electrical characterization of graphene films synthesized by low-temperature microwave plasma chemical vapor deposition

In this Letter, we discuss the results of Hall effect measurements to examine the electrical properties of the graphene films synthesized by low-temperature microwave plasma chemical vapor deposition. Van der Pauw devices with sizes of 50–100 μm were fabricated, for which we observed p-type conduction and mobility from 10 to 100 cm2/V s. To investigate the mobility dispersion, we performed Raman mapping to quantify the number of defects and the disorder in graphene films. The results suggest that the D-band/G-band intensity ratio is correlated with the mobility. Moreover, we discuss the factors controlling the mobility and how to improve the quality of the graphene films by reducing the number of defects.

Effect of Laser Wavelength for Surface Morphology of Aluminum Nitride Thin Films by Nitrogen Radical-Assisted Pulsed Laser Deposition

AlN thin films were prepared on Si(100) substrates by the nitrogen radical-assisted pulsed laser deposition method at a low substrate temperature (200°C) as a function of the laser wavelength (1064, 532 and 266 nm). At the laser wavelength of 1064 nm, Al-rich AlN films were deposited and granular crystals with a diameter of 50 nm were observed on the film surface. The surface roughness (Ra) was 15 nm. At the laser wavelength of 266 nm, c-axis-oriented AlN thin films with smooth surfaces (Ra=5 nm) were obtained and the atomic ratio of N/Al was stoichiometric. The full width at half maximum (FWHM) value of the diffraction profile in the 2θ/θ scan mode was 0.55°. It was found that the use of an ultraviolet laser was more effective for preparing the c-axis-oriented AlN films with a stoichiometric concentration and smooth surfaces.

Zinc-nickel alloy whiskers electrodeposited from a sulfate bath

Abstract Zn Ni alloy whiskers (20–50 μm) were grown from a sulfate bath by electrodeposition. The current density was 20–40 mA cm −2 and the pH was above 2. The structure of the whiskers was h.c.p. η-phase or cubic γ-phase. The Ni content in the whiskers was 2–7 wt.%, which was below that of the bath solution (8.5 wt.%), and anomalous co-deposition occurred. ZnO films covered the surface of the whiskers, but Zn(OH) 2 films did not. When the oxide film disappeared, tip growth of the whiskers ceased, and granular particles (10–30 wt.% Ni) composed of η + γ phases deposited onto the surface of the whiskers; the electrodeposition mechanism changed from anomalous to normal co-deposition. When Ni 2+ ions were not added to the sulfate solution, neither ZnO films nor whiskers were formed, and only Zn(OH) 2 films grew. In order to grow Zn Ni whiskers, ZnO films were necessary.

Low Temperature Graphene Synthesis from Poly(methyl methacrylate) Using Microwave Plasma Treatment

A graphene film having low sheet resistance (600 Ω/sq.) was synthesized at low temperatures of 280 °C. Utilizing microwave plasma treatment, graphene films were synthesized from a solid phase on a copper surface. The full width at half maximum of the 2D-band in the Raman spectrum indicated that a high quality graphene film was formed. Cross-sectional transmission electron microscopy observation revealed that the deposited graphene films consisted of single- or double-layer graphene flakes of nanometer order on the Cu surface, which agrees with the estimated number of layers from an average optical transmittance of 96%.

Effects of the power of electron shower and substrate bias on the synthesis of cementite films

We have succeeded in preparing single-phase cementite films using an electron-shower-assisted PVD method. This paper reports the effects of the power of electron shower and substrate bias on the synthesis of the cementite films. Single-phase cementite films were synthesized using the power of electron shower over 0.3 kW. When the substrate bias was -300 V, oxygen atoms were not detected in the film using EPMA. We obtained a cementite film with a composition of Fe : C : O = 77 : 23 : 0 at - -400 V, which is very similar to the stoichiometry of cementite. Electron diffraction patterns showed that the cementite film was single-phase. XPS spectra revealed that the binding energies of Fe 2p 3/2 and C Is s for the cementite were 707.3 and 283.5 eV, respectively, and an oxygen peak was not observed clearly.