Dane Aykutlu, Demirok U Korcan, Aydinli Atilla, Suzer Sefik
Bilkent University, Physics Department, 06800 Ankara, Turkey.
J Phys Chem B. 2006 Jan 26;110(3):1137-40. doi: 10.1021/jp0545748.
We investigated silicon nanoclusters Si(nc) in a SiO2 matrix prepared by the plasma-enhanced chemical vapor deposition technique, using X-ray photoelectron spectroscopy (XPS) with external voltage stimuli in both static and pulsed modes. This method enables us to induce an additional charging shift of 0.8 eV between the Si2p peaks of the oxide and the underlying silicon, both in static and time-resolved modes, for a silicon sample containing a 6 nm oxide layer. In the case of the sample containing silicon nanoclusters, both Si2p peaks of Si(nc) and host SiO2 undergo a charging shift that is 1 order of magnitude larger (>15 eV), with no measurable difference between them (i.e., no differential charging between the silicon nanoclusters and the oxide matrix could be detected). By use of a measured Auger parameter, we estimate the relaxation energy of the Si(nc) in the SiO2 matrix as -0.4 eV, which yields a -0.6 eV shift in the binding energy of the Si(nc) with respect to that of bulk Si in the opposite direction of the expected quantum size effect. This must be related to the residual differential charging between the silicon nanoclusters and the oxide host. Therefore, differential charging is still the biggest obstacle for extracting size-dependent binding energy shifts with XPS when one uses the oxide peak as the reference.
我们使用X射线光电子能谱（XPS），在静态和脉冲模式下施加外部电压刺激，研究了通过等离子体增强化学气相沉积技术制备的SiO₂基质中的硅纳米团簇Si(nc)。对于含有6 nm氧化层的硅样品，该方法使我们能够在静态和时间分辨模式下，在氧化物的Si2p峰与下层硅之间诱导出0.8 eV的额外电荷偏移。对于含有硅纳米团簇的样品，Si(nc)和主体SiO₂的Si2p峰都会发生电荷偏移，且偏移量要大1个数量级（>15 eV），两者之间没有可测量的差异（即未检测到硅纳米团簇与氧化物基质之间的差异电荷）。通过使用测量的俄歇参数，我们估计SiO₂基质中Si(nc)的弛豫能量为-0.4 eV，这使得Si(nc)的结合能相对于块状Si的结合能在与预期量子尺寸效应相反的方向上偏移了-0.6 eV。这一定与硅纳米团簇和氧化物主体之间的残余差异电荷有关。因此，当使用氧化物峰作为参考时，差异电荷仍然是用XPS提取尺寸依赖性结合能偏移的最大障碍。
