Effect of kinetic and vibrational energy of molecular beam on surfase reactions

为了研究气态分子与固体表面的反应机理，我们构建了一种新型的多表面分析系统分子束装置。本文主要研究了硅表面的碳化和氮化。用乙烯束照射清洁和加热的硅表面进行碳化。反应结束后，用低能电子差（LEED）和x射线光电子能谱（XPS）对反应表面进行了分析。反应发生在600℃以上。当温度达到675ºC时，反应速率随温度升高而升高，但高于温度时反应速率降低。在反应的初始阶段，观察到LEED模式的变化，这意味着沉积的C原子有规则地排列在Si（100）表面。反应性C和Si原子分别由乙烯束和Si原子在衬底的外扩散提供给生长的碳化物层。在低于675℃的温度下，Si的外扩散是碳化物层生长的速率决定步骤。在较高的温度下，C供应的速率是速率决定步骤。由于在675℃时碳化物层的停留时间基本一致，C的供给率随温度的升高而降低，说明在该温度下碳化物层和碳化物层的供给达到了平衡。对于氮化，我们使用了能量在100到1000eV之间的N_2^+离子束。用XPS研究了辐照过程中材料表层的化学变化。在100-200eV较低的能量下，形成了一层极薄的接近化学计量的化合物Si_3N_4，但在较高的能量下，氮化层含有许多缺陷。通过退火使缺陷部分消失。

For study of reaction mechanisms of gaseous molecule and solid surface, we have constructed a new molecular beam apparatus which is attached to a multi-surface analysis system. In the present work, carbonization and nitridation of Si surface have been investigated.For the carbonization an ethylene beam was irradiated on the clean and heated Si surfaces. After the reaction the surfaces were analyzed by low energy electron differaction (LEED) and X-ray photoelectron spectroscopy (XPS). The reaction occured above 600ﾟC.The reaction rate increacsed with temperature up to 675ﾟC,but it decreased above the temperature. In an initial stage of the reaction a change of the LEED patern was observed, which means that the deposited C atoms were regularly arranged on the Si (100) surface. The reactive C and Si atoms were supplied on the growing carbide layr by the ethlene beam and the outdiffusion of Si atoms in the substrate, respectively. At the lower temperatures than 675ﾟC the outdiffusion of Si is the rate-determining step of the carbide layr growth. At the higher temperatures, the rate of the C supply is the rate determing step. The C supply rate may decrease with the temperatre due to the residence time the carbide layr was nearly unity at 675ﾟC,which suggests that the both supplies were balanced at the temperature.For the nitridation we have used a N_2^+ ion beam of energy between 100 and 1000eV.The chemical change of the surface layr during the beam irradiation was studied by XPS.At the lower energies of 100-200eV a very thin film of a nearly stoichimetric compound Si_3N_4 was formed, but at the higher energies the nitride layrs contained many defects. The defects were partially dimished by annealing.