Devaraj A, Colby R, Hess W P, Perea D E, Thevuthasan S
†Environmental Molecular Sciences Laboratory and ‡Physical Sciences Division, Pacific Northwest National Laboratory, P.O Box 999, Richland, Washington 99352, United States.
J Phys Chem Lett. 2013 Mar 21;4(6):993-8. doi: 10.1021/jz400015h. Epub 2013 Mar 11.
The addition of pulsed lasers to atom probe tomography (APT) extends its high spatial and mass resolution capability to nonconducting materials, such as oxides. For a prototypical metal oxide, MgO, the measured stoichiometry depends strongly on the laser pulse energy and applied voltage. Very low laser energies (0.02 pJ) and high electric fields yield optimal stoichiometric accuracy. Correlated APT and aberration-corrected transmission electron microscopy (TEM) are used to establish the high density of corner and terrace sites on MgO sample surfaces before and after APT. For MgO, long-lifetime photoexcited holes localized at oxygen corner sites can assist in the creation of oxygen neutrals that may spontaneously desorb either as atomic O or as molecular O2. The observed trends are best explained by the relative field-dependent ionization of photodesorbed O or O2 neutrals. These results emphasize the importance of considering electronic excitations in APT analysis of oxide materials.
将脉冲激光添加到原子探针断层扫描（APT）中，可将其高空间分辨率和质量分辨率能力扩展到非导电材料，如氧化物。对于典型的金属氧化物氧化镁（MgO），测量的化学计量比强烈依赖于激光脉冲能量和施加电压。非常低的激光能量（0.02 pJ）和高电场可产生最佳的化学计量精度。相关的APT和像差校正透射电子显微镜（TEM）用于在APT前后确定MgO样品表面角位和平台位的高密度。对于MgO，位于氧角位的长寿命光激发空穴可协助产生氧中性原子，这些氧中性原子可能会以原子O或分子O2的形式自发解吸。观察到的趋势最好用光电离的O或O2中性原子的相对场致电离来解释。这些结果强调了在氧化物材料的APT分析中考虑电子激发的重要性。
