In-situ Observation of Atomic Layr Epitaxy by Photoelectron Oscillation

在Si_2H_6气源分子束外延法（GSMBE）中，利用同步辐射对Si（100）表面的Si外延生长过程进行了实时紫外光电子能谱（UPS）测量，发现Si(100)2x1表面态的光电子发射强度周期性振荡。我们将这种光电子强度振荡（PIO）解释为由于硅的逐层生长，并展示了通过PIO监测外延生长过程的可能性。本研究的目的是阐明PIO的起源。所得结果如下：1。用蒙特卡罗方法模拟了反射高能电子衍射振荡和反射高能电子衍射振荡。在生长过程中，假设2x1和1x2表面重构之间交替的模型可以很好地再现PIO。仿真结果还表明，与RHEED振荡相比，在较宽的温度范围和生长速率范围内都能产生PIO。结果1中的模型表明，振荡周期对应于两个单层的生长。为了证实这种关系，在与PIO观测相同的生长条件下，在GSMBE期间测量了RHEED振荡。在不同Si_2H_6压力下，半阶衍射点的振荡周期与PIO的振荡周期吻合较好，为上述对PIO起源的解释提供了直接支持。通过实时UPS研究了在Si（100）上的第一个单分子膜内干氧的初始热氧化过程。在350 ~ 600℃的氧化温度下，o2p态强度随时间的变化呈现langmuir型吸附行为，o2p态强度是表征氧化产物数量的良好指标。当温度高于700ºC时，该过程可以用二维岛生长模型很好地描述。考虑到在较高温度区域存在氧化物分解过程，对氧化动力学的这种差异给出了统一的解释。少

Recently, we carried out real-time ultraviolet photoelectron spectroscopy (UPS) measurements using synchrotron radiation during Si epitaxial growth on a Si(100) surface by Si_2H_6 gas-source molecular-beam epitaxy (GSMBE), and observed that the normal emission intensity of the photoelectrons from the serface states on Si(100)2x1 oscillates periodically. We interpreted this photoelectron-intensity oscillation (PIO) as due to Si layr-by-layr growth, and showed a possibility of monitoring the epitaxial growth process by PIO.The purpose of this study is to elucidate the origin of PIO.The obtained results are described as follows.1.PIO and reflection high-energy electron diffraction (RHEED) oscillation were simulated by the Monte Carlo technique. PIO was reproduced well by a model assuming an alternation between the 2x1 and the 1x2 surface reconstructions during growth. The results of the simulation also showed that PIO appears under wide ranges of the temperature and of the growth rate com … More pared with those for RHEED oscillation.2.The model in result 1 consequently suggests that the period of the oscillations correspond to two monolayr growth. To confirm this relation, RHEED oscillation were measured during GSMBE,under identical growth conditions with those used for PIO observations. The oscillation period at the half-order diffraction spots agreed well with that of PIO at various Si_2H_6 pressures, providing a direct support for the above interpretation for the origin of PIO.3.Initial thermal oxidation processes by dry oxygen within the first monolaver on Si(100) have been investigated by real-time UPS.For oxidation temperatures at 350-600ﾟC the time evolution of the O 2p state intensity, a good measure for the amount of the formed oxide, presented a Langmuir-type adsorption behavior. For temperatures above 700ﾟC, the evolution was well described by a model assuming a twodimensional island growth. A unified explanation is given for this difference in the oxidation kinetics by considering the presence of the oxide decomposition process in the higher temperature region. Less