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以激光蒸发结合超声分子束膨胀,近年来已成为产生与研究原子簇的一种重要手段。在以这一方式产生的Ga_xAs_y的光电离质谱中,发现含奇数个原子的簇离子的信号强度相对较高。最近我们在自制的装置上,于高真空中直接以脉冲激光作用于GaAs、GaP、InP等多种半导体材料,在所记录的负离子质谱中也都观察到类似的奇强偶弱的现象,其中尤以In_xP_y~-最为显著。实验用的激光离子源飞行时间质谱计的构造已有另文详细介绍。该装置通过朝相反方向分别加速正负离子而可同时记录激光等离子体的正负离子质谱。实验采用Nd~(3+):YAG激光器的调Q倍频输出(532nm),聚焦后作用于样品表面的激光功率密度约为10~8W·cm~(-2)。质谱计的加速电压1kV,正负离子的无场漂移长度约1.15m,数据的模数转换速度为2×10~7s~(-1)。实验所用的磷化铟是片状的高纯度半
In recent years, laser vaporization combined with ultrasonic molecular beam expansion has become an important means of generating and studying atomic clusters. In the photoionization mass spectrum of Ga_xAs_y produced in this way, the cluster ions containing odd number of atoms were found to have relatively high signal intensity. Recently, we have used pulsed lasers directly on a variety of semiconductor materials, such as GaAs, GaP, InP, etc., in home-made devices in a high vacuum. Similar odd and even weak phenomena were observed in the recorded negative ion mass spectra Especially In_xP_y ~ - the most significant. The experimental structure of the laser ion source time-of-flight mass spectrometer is described in detail elsewhere. The device can simultaneously record positive and negative ion mass spectra of the laser plasma by accelerating the positive and negative ions respectively in opposite directions. The Q / Q output (532 nm) of Nd ~ (3 +): YAG laser was used in this experiment. The laser power density after focusing was about 10 ~ 8W · cm ~ (-2) on the sample surface. The accelerating voltage of mass spectrometer is 1kV, the field-free drift length of positive and negative ions is about 1.15m, and the data conversion speed is 2 × 10 ~ 7s -1. The indium phosphide used in the experiment is a plate-like high-purity half