在气压为10 Pa的惰性气体Ar环境下,采用XeCl准分子激光器(波长308 nm),调整激光单脉冲能量密度为4 J/cm2,激光烧蚀电阻率为3000 Ω·cm的高纯单晶Si靶,在玻璃或Si衬底上沉积制备了纳米Si晶薄膜。实验中靶和衬底间距离保持为3 cm,对衬底既没有加温也没有冷却。拉曼(Raman)谱测量结果表明,所制备的薄膜中已有纳米Si晶粒形成。保持脉冲总数不变,分别取激光脉冲频率为1 Hz,3 Hz,10 Hz和20 Hz,相应沉积时间约为10 min,3.3 min,1 min和0.5 min,采用扫描电子显微镜(SEM)观察所得样品的表面形貌,不同脉冲频率下的结果比较显示,脉冲频率越大,制备的纳米Si晶薄膜的平均晶粒尺寸就越小,晶粒尺寸分布也越均匀。沉积动力学过程的非线性是导致实验出现该结果的原因。

Nanocrystalline silicon films were prepared by pulsed laser ablation at an ambient pressure of 10 Pa of pure Ar gas. The output of a XeCl excimer laser (wavelength: 308 nm, pulse duration: 15 ns, laser fluence: 4 J/cm2) was focused on the surface of a single crystalline Si target (resistivity: 3000 Ω·cm) and the silicon or glass substrate was located at a distance of 3 cm from the Si target. The substrates were not heated or cooled during deposition. The Raman spectra indicate that the films are composed of Si nanoparticles. The scan electron microscopy (SEM) images of the samples obtained at pulse repetition rate of 1 Hz, 3 Hz, 10 Hz and 20 Hz are compared under the same number of laser pulses. The result shows that the higher pulse repetition rate leads to the smaller Si nanoparticles and more uniform size distribution. It is the nonlinear dynamic process to lead to the experimental result.