自偏压作用下纳米碳管的定向生长

以玻璃为基板材料, 在550 ℃的低温条件下利用微波等离子体化学气相沉积法合成了定向纳米碳管.结果表明, 在利用微波等离子体化学气相沉积法合成纳米碳管时, 因等离子体作用存在于基板表面的自偏压对纳米碳管的定向生长起着非常重要的作用.自偏压的作用总是使纳米碳管的生长垂直于基板表面.     

MWPCVD低温合成纳米碳管的生长机理

The synthesis of carbon nanotubes (CNTs) at low temperature has received a great deal of attention and be-comes a challenging issue. But few model which accounts for the growth of CNTs is suited for the synthesis of CNTs by microwave plasma chemical vapor deposition (MWPCVD) at low temperature because most researchers conclude that the growth mechanism is determined by the catalyst-supporter interaction while ignored the diffusion of carbon in the catalyst. In this paper, under the catalytic effect of cobalt supported by SiO₂ and Al₂O₃, CNTs are synthe-sized by MWPCVD at about 500℃, and tip-growth, the model which accounts for the catalytic growth of CNTs is outlined. It is the temperature difference between the upper and bottom of the catalytic particle that results in the diffusion of carbon atoms from upper to the bottom, and precipitation of saturated carbon on the bottom surface to form CNTs.     

金刚石薄膜负偏压形核的边缘效应

 在微波等离子体化学气相沉积装置中，研究了金刚石薄膜在Si (100)面上的负偏压形核行为，结果表明，偏压大小对金刚石的形核均匀性有显著影响，而甲烷浓度主要影响形核时间，对金刚石的最大核密度影响不大。在硅片尺寸小于钼支撑架时，形核行为存在明显的边缘效应，即在偏压值低于-150 V时，硅片边缘金刚石核密度急剧降低，远低于硅片中央；在甲烷浓度比较低时，硅片边缘核密度要高于中间。研究表明，造成这种现象的主要原因是硅片下的钼支撑架发射电子所致，过量的原子H对金刚石的形核是不利的。     

Ar对微波等离子体CVD单晶金刚石生长的影响

采用自主研发的5 kW不锈钢谐振腔式MPCVD设备,在Ar/H2/CH4气氛下,保持总气压与CH4气流量不变,研究了不同Ar/H2比例对单晶金刚石生长速度和晶体质量的影响.通过拉曼光谱与高分辨率XRD摇摆曲线,从生长速度与生长质量两点对所得样品进行分析.结果表明,适量Ar的存在能够显著提高单晶金刚石的生长速度,并且不损害金刚石的晶体质量.当Ar/H2=30;时,生长速度最高,为35 μm/h.随着Ar/H2比例的进一步增加,单晶金刚石的结晶质量会有所下降,Ar/H2比例过高则会严重破坏单晶金刚石的生长.