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提出了一种将激光烧蚀制备的纳米Si晶粒按尺寸大小进行分离的新方法。在10 Pa高纯环境气体Ar下,采用波长为308 nm的XeCl准分子激光器,固定激光单脉冲能量密度为3 J/cm2,激光烧蚀电阻率为3000Ω.cm的高纯单晶Si靶,在等离子羽轴线正下方2.0 cm处平行放置一系列单晶Si或玻璃衬底来收集纳米Si晶粒。拉曼(Raman)谱测量结果显示,在距靶平行距离为0.5-2.8 cm范围内,所制备的薄膜中均有纳米Si晶粒形成。利用扫描电子显微镜(SEM)观察了样品的表面形貌,对图中的纳米Si晶粒统计分析表明,随着离靶平行距离的增大,所形成的纳米Si晶粒的平均尺寸逐渐减小。从烧蚀动力学角度对实验结果进行了定性解释,因为不同尺寸的纳米Si晶粒获得了不同的水平速度,所以在重力作用下实现了尺寸的自然分离。
A new method for separating nano-Si grains prepared by laser ablation according to their size was proposed. High-purity single-crystal Si target with a laser single-pulse energy density of 3 J / cm 2 and a laser ablation resistance of 3000 Ω · cm was fixed with a XeCl excimer laser with a wavelength of 308 nm under a high-purity Ar gas of 10 Pa. A series of single crystal Si or glass substrates were placed parallel to each other at 2.0 cm just below the plasma plume axis to collect the nano-Si grains. Raman spectrum measurements showed that nano-Si grains were formed in all the films prepared within a distance of 0.5-2.8 cm from the target. The surface morphology of the samples was observed by scanning electron microscopy (SEM). The statistical analysis of the nano-Si grains in the figure shows that the average size of the formed nano-Si grains gradually decreases as the distance from the target increases . The experimental results are qualitatively explained from the point of view of ablation kinetics. Since the different sizes of nano-Si grains obtain different horizontal velocities, the natural separation of the sizes is achieved under the action of gravity.