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

对于低电子温度等离子体和基片表面自由基的辐照，我们在电感耦合射频氢甲烷等离子体中用孔口将电子温度可控区和沉积区分开。在直径为6 mm的小孔情况下，我们发现在衬底上沉积了纳米晶金刚石。此外，当甲烷在氢气中的稀释率降低到1%以下时，可以生成相当合格的纳米晶金刚石。相反，当孔口直径增大时，会沉积类金刚石碳膜。其原因是血浆中Sp3/Sp2的碳氢自由基比降低。为了将这一特性应用于广域薄膜沉积，我们采用了中空型磁控等离子体源。在静磁场和电场的作用下，可以产生高密度的等离子体。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出由规则四面体组成的多面体表面的纳米粒子。另一方面，在高电子温度等离子体中，可以沉积由石墨膜制成的纳米墙。这种差异可以用背景胶片中SP2/SP3成分的局部变化来解释。在低电子温度等离子体中，SP3/SP2的比例变大，形成了具有钻石状SP3结构的纳米粒子。在低电子温度等离子体中，通过促进反应物在表面的迁移，生成具有多面体结构的纳米粒子，也可以减少高能离子撞击衬底对成核和生长的损害，这样，在低电子温度等离子体中控制自由基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.