Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects
Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects
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DOI：
10.1063/1.4830023
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发表时间：
2013-11-14
影响因子：
3.2
通讯作者：
Brubaker, Matt
中科院分区：
文献类型：
--
作者：
Diercks, David R.;Gorman, Brian P.;Brubaker, Matt
利用两种不同的激光脉冲原子探针层析成像仪（APT）研究了c轴GaN纳米线的场蒸发行为。在原子探针断层扫描分析之前和之后的透射电子显微镜成像被用于协助重建数据并评估所观察到的蒸发行为。结果发现，离子物种表现出优先的位置蒸发相关的GaN的底层晶体结构，从这些位置蒸发的物种是依赖于脉冲激光能量。此外，APT测量的总化学计量与激光脉冲的能量显著相关。在最低的激光能量下，表观组成是富氮的，而较高的激光能量导致测量主要是镓组成。发现这些试样的离子检测（检测效率）的百分比是显着低于所示的其他材料，即使是激光能量产生预期的Ga：N比。表观化学计量变化和低检测效率似乎是在最低激光能量下的激光脉冲之间的Ga离子的蒸发和在较高激光能量下的中性N-2物种的蒸发的结果。所有这些行为都与在所有分析条件下发生的尖端表面上的氮-氮键的形成有关。因此，对于阴离子物质容易形成强双原子键的其他材料，预期具有类似的场蒸发行为。(C)2013 AIP Publishing LLC.
The field evaporation behavior of c-axis GaN nanowires was explored in two different laser-pulsed atom probe tomography (APT) instruments. Transmission electron microscopy imaging before and after atom probe tomography analysis was used to assist in reconstructing the data and assess the observed evaporation behavior. It was found that the ionic species exhibited preferential locations for evaporation related to the underlying crystal structure of the GaN and that the species which evaporated from these locations was dependent on the pulsed laser energy. Additionally, the overall stoichiometry measured by APT was significantly correlated with the energy of the laser pulses. At the lowest laser energies, the apparent composition was nitrogen-rich, while higher laser energies resulted in measurements of predominantly gallium compositions. The percent of ions detected (detection efficiency) for these specimens was found to be considerably below that shown for other materials, even for laser energies which produced the expected Ga:N ratio. The apparent stoichiometry variation and low detection efficiency appear to be a result of evaporation of Ga ions between laser pulses at the lowest laser energies and evaporation of neutral N-2 species at higher laser energies. All of these behaviors are tied to the formation of nitrogen-nitrogen bonds on the tip surface, which occurred under all analysis conditions. Similar field evaporation behaviors are therefore expected for other materials where the anionic species readily form a strong diatomic bond. (C) 2013 AIP Publishing LLC.