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首页> 外文期刊>Physical review >Formation of nanoscale fine-structured silicon by pulsed laser ablation in hydrogen background gas
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Formation of nanoscale fine-structured silicon by pulsed laser ablation in hydrogen background gas

机译：氢气背景气体中脉冲激光烧蚀形成纳米级细结构硅

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The formation of nanoscale fine structures during pulsed laser ablation of a silicon target in a hydrogen atmosphere has been studied by analyzing the deposited silicon fine structures prepared under different conditions. Transmission electron microscopy, scanning electron microscopy (SEM), Raman scattering, and infrared absorption studies on the deposited samples indicate that silicon nanocrystallites are produced when the background gas pressure is higher than a critical value. The deposited substance is found to show hierarchical structure having surface hydrogenated silicon nanocrystallites as the primary structure and aggregates pf the nanocrystallites as the secondary structure. The secondary structure depends on the hydrogen background gas pressure, while the size of the primary nanocrystallites is 4-5 nm independent of the pressure. These results suggest that the fine structure is formed in two steps; the silicon nanocrystallites having a stable surface are initially formed and they are subsequently aggregated to form the secondary structure. Analysis of surface free energy suggests that the stability is acquired by termination of the surface by creation of Si—H bonds. We carried out fractal analysis of the SEM image of the deposits and found that the secondary structure shows good self-similar structure when deposited at higher background gas pressure. The fractal dimension of aggregated secondary structure varies from 1.7 to more than 2.0 with decreasing background gas pressure. Comparison of these values with reported results for the fractal growth simulation indicates that the region at which aggregation of the nanocrystallites takes place changes from in the plume to on the substrate with decreasing background gas pressure. Effects of the hydrogen background gas on the nanocrystallization process and spatial distribution of formed nanocrystallites in the plume are discussed. The formation of surface stabilized Si nanocrystallites and their spatial confinement by background gas in the first and second steps determine the hierarchical structure of deposited substance.
机译：通过分析在不同条件下制备的沉积的硅精细结构，研究了在氢气氛中脉冲激光烧蚀硅靶期间纳米级精细结构的形成。对沉积样品的透射电子显微镜，扫描电子显微镜（SEM），拉曼散射和红外吸收研究表明，当背景气压高于临界值时会产生硅纳米晶体。发现所沉积的物质显示出具有表面氢化硅纳米晶体作为主要结构并且纳米晶体的聚集体作为二级结构的分层结构。二级结构取决于氢气的背景气压，而一级纳米微晶的大小与压力无关，为4-5 nm。这些结果表明精细结构是分两个步骤形成的。首先形成具有稳定表面的硅纳米晶体，然后将它们聚集以形成二级结构。对表面自由能的分析表明，通过创建Si-H键终止表面可以获得稳定性。我们对沉积物的SEM图像进行了分形分析，发现当在较高的背景气压下沉积时，二级结构显示出良好的自相似结构。随着背景气压的降低，聚集的二级结构的分形维数从1.7变化到大于2.0。将这些值与分形生长模拟的报告结果进行比较，结果表明，随着背景气压的降低，纳米微晶发生聚集的区域从羽状区域变为基底上的区域。讨论了氢气本底气体对羽流中纳米晶化过程和形成的纳米微晶空间分布的影响。在第一步和第二步中，表面稳定的Si纳米微晶的形成以及它们在背景气体中的空间限制决定了沉积物质的分层结构。

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