Hiroshi Makita

Low Temperature Fabrication of Diamond Films with Nanocrystal Seeding

Well-faceted diamond films have heen fabricated at 200° C on the silicon substrate by the magnetoactive microwave plasma chemical vapor deposition (CVD) method. The substrate was seeded with nanocrystal diamond about 5 nm in diameter synthesized by the explosion process. The nanocrystal seeding brought about the improvement in quality of the fabricated films and the decrease in the time required for diamond nucleation. It took about 5 h to seed the scratched Si substrate at temperatures below 300° C.

Fabrication of Diamond Films at Low Pressure and Low-Temperature by Magneto-Active Microwave Plasma Chemical Vapor Deposition.

We succeeded in fabrication of diamond films at substrate temperature of 80° C by using the magneto-active microwave plasma chemical vapor deposition (CVD) method at low pressure (0.1 Torr) with forced substrate cooling. The magneto-active microwave discharge enables us to use high-density microwave plasma under low pressure. High-density plasma-enhanced CVD under low-pressure is advantageous for low-temperature synthesis of diamond films because of decrease in thermal flux to the substrates from neutral gases heated in the plasma. Deposited films were investigated by scanning electron microscopy (SEM), Raman scattering spectroscopy, thin-film X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The fabricated films are randomly oriented polycrystalline diamond of fine crystallite size (below 100 A). The deposition rate of the diamond films decreased with decreasing substrate temperature in the range below 400° C.

Characterization of N-doped diamond films by transmission electron microscopy

The N-doped diamond films have been investigated by transmission electron microscopy (TEM). TEM images clearly reveal that both the density and distribution of the planar defects are greatly affected by the N/C ratio (the ratio of N atoms to C atoms in the source gas). As the N/C ratio increases, much more planar defects are formed. Moreover, the phenomenon that a heavily nitrogen doping leads to the generation of the amorphous domains in diamond lattice is directly confirmed by TEM images for the first time, and the average size of these amorphous domains is on the order of nanometers. Based on the TEM observation results, the nitrogen doping effects on the crystallinity variation of chemical-vapor-deposited diamonds are discussed.

Electron Microscopic Study on the Initial Stages of (111)-Oriented Diamonds Grown on Pt Substrates

The initial stages of (111)-oriented diamonds grown on Pt substrates have been studied by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM images clearly reveal that scratching pretreatment strongly damages the surfaces of (111)-Pt substrates. After pretreatment, the column like polycrystalline damage layers are observed to form on the Pt surfaces for the first time, the average thickness of which is about 400 to 500 nm. During the subsequent deposition process, these surface damage layers gradually recrystallized into the single-crystalline state. The nucleation and initial growth of diamond particles are, in fact, accompanied by the Pt surface recrystallization process, and the formation of the (111)-oriented diamond grains is discussed in regard to the Pt surface recrystallization process.