Semiconductor microclusters prepared with gas evapolation method in an exited rare gas atomosphere

我们在这里报告了我们在研究半导体(锗)小颗粒和碳纳米管时发现的一些显着的特征1。我们发现用气体蒸发法制备的Ge小颗粒的结构受大气中激发的Ar原子的影响。这些颗粒的拉曼光谱表明，激发气体蒸发法增加了颗粒中的无定形部分。在几托的Ar气氛中，我们观察到了Ar原子、Ge原子/团簇(Ge_2)和Ge离子在Ge的蒸发过程中的发光。无论坩埚是空的还是充满Ge的，都能观察到Ar(I)线。Ar原子是通过放电激发的，电子是由加热坩埚的热钨丝热发射的电子引发的，并被施加在金属丝上的电势加速。当Ar气压和Ge蒸气密度较低时，Ge谱线较强，而Ar气压较高时，Ge_2谱线较强。这说明气体蒸发过程中存在着从Ar到Ge能量转化的原子过程。直径相对较小(通常为d=1.1 nm)的单壁纳米管的拉曼散射光谱表明，与石墨中的E&lt；2g&gt；模相对应的光学声子峰随尺寸发生多次分裂。这一观察结果可以用纳米管的柱状对称性引起的声子随直径变化的色散来解释。在力常数模型的框架下，重新研究了单壁碳纳米管中的声子模。通过与区域折叠模型计算结果的比较，讨论了微管的曲率效应。声子模的直径相关特性对于分析合成样品中单壁碳纳米管的尺寸分布是有用的。

We report here some remarkable features we have found during the study on semiconductor (Germanium) small particles and carbon nanotubes.1. We have found that the structure of Ge small particles prepared with the gas evapolation method is affected by excxited Ar atoms in an atomosphere. Raman spectra of these particles shows the amorphous part in the particle is increased by the excited gas evapolation method.2. We have observed light emission from Ar atoms, Ge atoms/clusters(Ge_2, and Ge ions during the evaporation process of Ge in an Ar-gas atmosphere of a few Torrs. The Ar(I) lines are observed regardless of whether the crucible is empty or filled with Ge. Ar atoms are excited through discharge intiiated by electrons thermionically emitted from the hot W wire heating the crucible and accelerated by the potential applied to the wire. The Ge lines are stronger for lower Ar pressures and for lower Ge vapor density, while the Ge_2 line is stronger for highr Ar pressures. This shows the existence of atomic processes for the energy transformation from Ar to Ge during the gas evapolation.3. Raman scattering spectra of single-walled nanotubes with relative small diameter (typically d = 1.1 nm) show size-dependent multiple splittings of the optical phonon peak corresponding to the E_<2g> mode in graphite. This observation is successfully explained by diameter-dependent dispersions of phonons arising from the cylindrical symmetry of the nanotube.4. Phonon modes in single-walled nanotubes (SWNTs) of carbon are reexamined within the framework of a force constant model. The curvature effect of tubules is discussed by comparing with the results obtained by the zone-folding model. The diameter dependent properties of phonon modes are shown to be useful fo analyzing the size distribution of SWNT in the synthesized samples.