激光作用磷化铟所产生的负离子质谱及其分析

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

MASS SPECTROMETRY OF LASER GENERATED NEGATIVE InP CLUSTER IONS

Both positive and negative InP cluster ions were generated on a self-built laser probe time-of-flight mass spectrometer. The negative mass spectra showed an alternation of the cluster ion intensities with the odd/even total number of atoms in the clusters. This result is attributed to that all the valence electrons in the clusters of odd atom number are paired, thus stable. It is proposed that, based on the above result, the stability of such cluster ions depends more on their electronic structures than on their geometric structures. Further studies on both theoritical computation and experimentation are being carried on