中性原子在NaCl纳米立方体角上的荷电诱导发射
Charging Induced Emission of Neutral Atoms from NaCl Nanocube Corners
摘要：
中性阳离子/阴离子从固体碱金属卤化物的分离原则上可以通过向碱金属卤化物晶体的表面提供/减去电子来引起，但通常构成非常吸热的过程。然而，发射所需的能量对于位于不太有利的位置的原子来说较小，例如表面台阶和扭结。对于碱金属卤化物立方体中的角离子，结合是最弱的，因此一旦它被中和，应该更容易去除该原子。我们进行了第一性原理密度泛函计算和模拟的中性和带电的NaCl纳米立方体，建立提取的中性角离子的能量学。空穴捐赠（电子去除）后，我们发现，分离的中性Cl角原子将需要一个有限的能量约0.8 eV。相反，在向立方体捐赠过量电子之后，可以以约0.6 eV的较低成本从角落提取中性Na原子。由于立方体电子亲合能级（接近NaCl（100）表面态，我们也确定）估计位于真空以下约1.8 eV，因此从真空向纳米立方体捐赠零能量电子时的总能量平衡将是放热的。作为副产物，获得并分析了NaCl（100）表面以及纳米立方体Na和Cl角空位的原子和电子结构。
英文摘要：
Detachment of neutral cations/anions from solid alkali halides can in principle be provoked by donating/subtracting electrons to the surface of alkali halide crystals, but generally constitutes a very endothermic process. However, the amount of energy required for emission is smaller for atoms located in less favorable positions, such as surface steps and kinks. For a corner ion in an alkali halide cube the binding is the weakest, so it should be easier to remove that atom, once it is neutralized. We carried out first principles density functional calculations and simulations of neutral and charged NaCl nanocubes, to establish the energetics of extraction of neutralized corner ions. Following hole donation (electron removal) we find that detachment of neutral Cl corner atoms will require a limited energy of about 0.8 eV. Conversely, following the donation of an excess electron to the cube, a neutral Na atom is extractable from the corner at the lower cost of about 0.6 eV. Since the cube electron affinity level (close to that a NaCl(100) surface state, which we also determine) is estimated to lie about 1.8 eV below vacuum, the overall energy balance upon donation to the nanocube of a zero energy electron from vacuum will be exothermic. The atomic and electronic structure of the NaCl(100) surface, and of the nanocube Na and Cl corner vacancies are obtained and analyzed as a byproduct.
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