高氮含量金属掺杂氮原子簇的液氮冷却-激光溅射生成研究

为了研究激光溅射-超声分子束冷却离子源结构对金属掺杂氮原子簇形成的影响,通过增加液氮冷却、缩小脉冲阀喷气孔与激光轰击靶点的距离,对常规离子源进行了改进,并研究了碱金属和第一过渡系金属掺杂的氮原子簇的生成。通过飞行时间质谱发现了锂氮簇LiN_n~+(n=6,8,1 0,1 2,1 4,1 6,18)和Li_2N_n~+(n=8,1 0,12)、钠氮簇NaN_n~+(n=2-27)、钒氮簇VM_n+(n=6,8,9,1 0,1 1,13,15)和V_2N_n~+(n=17,1 9,21)、铬氮簇CrN_n~+(n=2,4,6,8,9,11)和Cr_2N_n~+(n=9,1 0,11)。实验结果表明,改进后的离子源能显著增加生成的金属掺杂氮原子簇的数量,并明显提高产物的含氮质量分数;掺杂金属的种类对所形成原子簇的组成有很大的影响,各类金属掺杂氮原子簇中丰度最高的分别为LiN_8~+、NaN_(12)~+、VN_(11)~+和CrN_8~+。

Generation of Metal-doped Nitrogen Clusters with High Nitrogen Content by Liquid Nitrogen Cooling-laser Ablation

To investigate the effect of the ion source structure on the formation of doped nitrogen clusters with high nitrogen content, the conventional laser ablation ion source was improved by adding liquid nitrogen cooling and reducing the distance between nozzle of pulse valve and laser ablation spot, and nitrogen clusters doped by alkali metals and first transition metals were studied. LiN_n⁺ (n=6,8,10,12,14,16,18), Li₂N_n⁺ (n=8,10,12), NaN_n⁺ (n=2~27), VN_n⁺ (n=6,8,9,10,11,13,15), V₂N_n⁺ (n=17,19,21), CrN_n⁺ (n=2,4,6,8,9,11) and Cr₂N_n⁺ (n=9,10,11) were observed by time of flight mass spectrometer (TOF-MS). Results indicate that the improved ion source can significantly increase the number of generated doped nitrogen clusters and their nitrogen content. In addition, the type of doped metals has a great influence on the composition of generated clusters. In each type of metal-doped nitrogen clusters, the most abundant clusters are LiN₈⁺, NaN₁₂⁺, VN₁₁⁺ and CrN₈⁺, respectively.