Mikio Noda

Diamond structure in films deposited at relatively low substrate temperature

Diamond films with strong features of diamond crystal have been prepared on Si substrates by DC plasma chemical vapor deposition (CVD), and the structural differences as a function of discharge current (Id) and substrate temperature (Ts) were investigated by scanning electron microscopy, reflection electron diffraction (RED) and Raman spectroscopy. When I d and decrease, the growth rate of the films as well as the size of the diamond grains decreases, and an amorphous second phase grows in relative amount. These results suggest that both the thermal and electron excitation of the reactive species on the substrate are important for the deposition of diamond, and that the increases in atomic hydrogen and electron impinging on the diamond surface are effective in the formation of diamond with a clear-cut crystal surface. It has been confirmed that the formation of diamond films is possible even at Ts around 400 °C when Id sufficiently large.

Formation of Diamond Films by Intermittent Discharge Plasma Chemical Vapor Deposition.

Formation of diamond film by DC plasma chemical vapor deposition (CVD), wherein the waveform of the power supply is half-wave-rectified (HWR), has been investigated. When HWR voltage is applied to the electrodes, the waveforms of the discharge voltage (V d) and current (I d) are intermittent and show a large peak at the beginning of the discharge. The films deposited by intermittent discharge (ID) are superior in crystalline quality compared with that by conventional continuous discharge (CD). The average value of electron temperature (T e) in ID, measured by a Langmuir probe (LP) in the plasma of hydrogen gas, is higher than that of CD. The LP current shows a very high peak at the beginning of the ID process, and the value of T e and density of electrons (N e) at this peak are very large. These rises in T e by ID are effective in enhancing the dissociation of the source gas by electron collision. It has been concluded from the present study that ID is an effectual method to obtain high-quality diamond film.

Microstructures and Hydrogen Bonding Environments of a-Si: H Films Prepared by RF Sputtering in Pure Hydrogen

Microstructures and correlated hydrogen bonding environments of a-Si: H films prepared by RF sputtering in pure hydrogen are investigated by TEM, FT-IR and optical absorption measurements. The films are more homogeneous than those prepared in an Ar/H2 mixture; they are composed of fine grains and tend to have a microcrystalline structure with increasing gas pressure. Configurations of SiH2 and SiH3 increase with increasing voids, indicating that these are formed in the void regions on the surface of the grains. From these results, the roles of argon and hydrogen correlated to the microstructure of the films are discussed.

Deposition of Diamond onto an Aluminum Substrate by DC Plasma CVD

Diamond films are deposited on an aluminum substrate under a constant high discharge current (Id=700 mA) and a methane concentration of about 2% by DC plasma CVD, and their structural characteristics resulting from the difference in substrate temperature (Ts: 140–480°C) are investigated. Many diamond particles with an average size of 0.3 µm and having a clear crystal habit are formed at Ts about 480°C. When Ts is decreased, the deposited films tend to contain hydrogenated amorphous components as well as amorphous carbon phases. The films deposited at extremely low Ts, such as 140°C, are composed of submicron grains like pebbles, in which nanocrystalline diamond crystals and amorphous phases having C–C and C–H bonds aggregate to form these submicron grains. It has been found that diamond films with different grain morphology are deposited on the Al substrate.

Microstructures of hydrogenated silicon films prepared by ion plating

Hydrogenated Si are prepared by ion plating in a pure hydrogen atmosphere and their microstructures are investigated by using a transmission electron microscope and a Fourier-transform infrared spectrometer. The structures of such films change from amorphous to microcrystalline when the RF input power is increased or when the bias voltage of substrates is increased from a negative to a positive value. The structures are also affected by the electrical conductivity of the substrates. When insulating substrates are used, the films tend to have the microcrystalline-type structures due to an accumulation of positive charge. Mass and optical emission spectroscopy suggest that such trends regarding crystallization occur due to an increase in H radicals and a decrease in ionic species impinging onto a substrate during deposition.

Effects of discharge current and substrate temperature on the microstructure of diamond films deposited by DC plasma CVD

Abstract Structural differences of the diamond films deposited on Al substrates by DC plasma chemical vapor deposition as a function of discharge current ( I d ) and substrate temperature ( T s ) has been investigated by SEM, TEM and EELS. The film deposited at T s =300°C and I d =0.7 A / cm 2 are composed of ball-like grains containing microcrystalline diamond crystals. When T s i increases to 450°C, or I d increases to 1 A/cm 2 , diamond which constitutes the film becomes grains with clear crystal habit. These results suggest that the formation of the diamond single crystal structure is possible at low T s of 300°C when I d is sufficiently large.

Microstructures and Hydrogen Bonding Environments of Sputter-Deposited a-Si:H Films

Microstructures and correlated hydrogen bonding environments of a-Si:H films prepared by RF sputtering have been investigated by means of transmission electron microscope and Fourier transform infrared spectrometer. The uniform film formed at low gas pressure during the deposition shows only two strong IR peaks due to SiH configuration. These peaks decrease, and both the peaks due to SiH2 configuration and voids in the films increase consistently with increasing gas pressure, indicating that the uniform portion surrounded by the voids included only SiH constituent and that this SiH2 constituent is formed on the surface of the uniform portion.

Formation of Graphene-Containing Porous Carbon Film for Electric Double-Layer Capacitor by Pulsed Plasma Chemical Vapor Deposition

Porous carbon films (PCFs) containing nanographene were deposited from a gas mixture of H2, CH4, and CO2 by pulsed discharge (PD) plasma-enhanced chemical vapor deposition (CVD) using a Ni catalytic layer, and their capacitance and conductance as an electrochemical double layer capacitor (EDLC) were investigated. The morphological study showed fiberlike structure formation with a 50-nm-thick Ni catalyst film. Nanographene-containing PCFs were deposited with a 100-nm-thick Ni film. When the Ni film thickness increased from 50 to 100 nm, the capacitance increased from 13 to 152 µF/cm2 and the conductance increased from 2.1 to 6.8 mS/cm2. These results show that graphene-containing PCFs are very much suitable as electrode materials of EDLCs.

Hydrogen-etching effect of substrate on deposition of diamond films by DC plasma chemical vapor deposition

The effect of hydrogen plasma etching (HPE) of a Si substrate on the morphology and the quality of the diamond films deposited by DC plasma chemical vapor deposition in CH4-H2 mixture gas have been studied. It has been found that the HPE treatment before diamond deposition results in the modification of the substrate surface through the removal of the Si oxide layer and the formation of an uneven surface, and enhances the nucleation and growth of diamond. The amorphous component contained within the deposited films decreases through the use of the etched substrate, especially when the CH4 concentration is higher than 3%.

EFFECT OF DISCHARGE CURRENT ON THE MICROSTRUCTURE OF DIAMOND FILMS DEPOSITED ON ALUMINUM SUBSTRATE AT LOW SUBSTRATE TEMPERATURE BY DC PLASMA CVD

The effect of discharge current (Id) on the diamond structure has been investigated. The films deposited on Al substrate at a low substrate temperature (Ts) of about 200°C by DC plasma CVD are composed of ball-like grains containing microcrystalline diamond crystals with a hydrogenated amorphous component. When Id increases, the growth rate of the grains and the size of the diamond crystals increase, and the amorphous component decreases. These results show that the increase of Id enhances the diamond structure formation, in addition to the Ts factors well known effect on the formation of a definite diamond film.