Control of Nucleation and Growth of Nanocrystal Diamond by Irradiation of Radical Low-Temperature Plasma

针对低电子温度等离子体和自由基对衬底表面的辐照，在电感耦合射频氢-甲烷等离子体中，利用小孔将电子温度可控区和沉积区分开。在孔径为6 mm的小孔中，我们发现纳米金刚石沉积在基底上。此外，当甲烷在氢气中的稀释率降低到小于1%时，产生相当合格的纳米晶金刚石。相反，当小孔直径增大时，沉积类金刚石膜。它被解释为减少的碳氢化合物自由基的比例sp3/sp2在等离子体中。为了将这种特性应用于大面积薄膜沉积，我们采用了中空型磁控等离子体源。高密度等离子体可以通过静磁场和静电场的作用产生。通过降低等离子体源区的电子温度，可以降低sp2自由基密度。我们发现，在低电子温度等离子体中生长的纳米粒子具有正四面体组成的多面体表面。另一方面，在高电子温度等离子体中，沉积由石墨膜制成的微球。这种差异可以用背景膜中sp2/sp3分量的局部变化来解释。在低电子温度等离子体中，sp3/sp2的比率变大，这导致形成具有sp3结构的纳米颗粒，如金刚石。在低电子温度等离子体中，由于高能离子撞击在基底上，促进了反应物在基底表面的迁移，生成多面体结构的纳米粒子，从而减少了对成核和生长的破坏，因此，低电子温度等离子体中自由基的控制对纳米结构的成核和生长是非常有效的。

For irradiation of low-electron temperature plasma and radicals on the substrate surface, we separate electron-temperature controllable region from deposition region by orifice in inductively-coupled radio-frequency hydrogen-methane plasma. In case of 6-mm-diamter orifice, we find that nanocrystalline diamond is deposited on the substrate. Further, when the dilution ratio of methane in hydrogen is reduced to be less than 1 %, rather qualified nanocrystalline diamond is created. On the contrary, when the orifice diameter is enlarged, diamond-like carbon film is deposited. It is interpreted by a decrease in the hydrocarbon radical ratio of sp3/sp2 in the plasma. In order to apply this property on wide area film deposition, we employ a hollow-typed magnetron plasma source. A high density plasma can be produced by the effect of static magnetic and electric fields. By reducing the electron-temperature in the plasma source region, the sp2 radical density can de decreased. We find that nanoparticles with polyhedron surfaces composed by regular tetrahedron are grown in the low-electron temperature plasma. On the other hand, in high electron-temperature plasma, nanowalls made of graphite films are deposited. Such difference can be explained by the local change of sp2/sp3 components in the background film. In the low-electron temperature plasma, the ratio of sp3/sp2 becomes large, which results in the formation of nanoparticles with sp3 structure like a diamond. Damage to nucleation and growth due to energetic ions impinging on the substrate can be also reduced in the low-electron temperature plasma, where migration of reactants on the surface is promoted to produce nanoparticles with polyhedron structures.In this way, the control of radicals in low-electron temperature plasma is quite effective for nucleation and growth of nanostructures.