Chemical Analysis and Electronic Structure Studies of Vacancy-Type Defects by Measuring Positron Annihilation Momentum Distribution in Wide Range

我们用正电子湮没辐射二维角相关(2D-ACAR)和符合多普勒展宽(CDB)的正电子湮没技术测量了几种金属和半导体中正电子取样的较宽范围内的电子动量分布。主要研究结果如下：1)含有害铜杂质的核反应堆压力容器(RPV)钢的Fe-Cu模型合金，在无缺陷的铜超细颗粒嵌入铁基中呈现出量子点状的正电子状态。所有正电子的波函数完全被限制在粒子中。在这种状态下的正电子向我们传达了有关粒子的原子和电子结构的有用的和独有的信息。通过对Fe-1.0%Cu单晶的2D-ACAR实验，确定了Fe中体心立方铜超微粒的费米面。费米面几乎是球形的，但在体心立方结构的(110)布里渊面的中心周围有12个颈口。在中子辐照的Fe-Cu模型合金中，我们观察到辐照诱导的微孔洞，其内表面几乎覆盖着铜原子。2)空位-溶质复合体在Al-Cu-℃合金的初始快速时效硬化中的作用。用CDB方法研究发现，淬火空位最初与镁原子结合，而不是与铜原子结合，空位-镁复合体在150℃时容易迁移到空位下沉。在空位下沉的初始1min时效过程中形成空位-镁-铜复合体。位错-溶质相互作用是初始快速硬化的根源。3)石墨和硅中的MGIC数真空团簇。通过正电子湮没实验和第一性原理计算，我们首次观察到共价键材料中的幻数空位：中子辐照后的石墨。

We have measured electron momentum distributions in wider ranges sampled by positrons in several metals and semiconductors using positron annihilation techniques of two dimensional angular correlation of annihilation radiation (2D-ACAR) and coincidence Doppler broadening (CDB). Marked results are as follows.1) Fe-Cu model alloys for nuclear reactor pressure vessel (RPV) steels containing harmful Cu impurities.A quantum-dot-like positron state is demonstrated in the defect-free Cu ultrafine particles embedded in Fe matrix. The wave functions of all positrons are entirely confined in the particles. The positrons in this state convey us usefu and exclusive information about the atomic and electronic structures of the particles. By 2D-ACAR experiments on Fe-1.0%Cu single crystals, we have determined the Fermi surface of BCC Cu ultrafine particles in Fe. The Fermi surface is almost spherical but has 12 necks around the centers of (110) Brillouin faces of the BCC structure.In neutron-irradiated Fe-Cu model alloys, we have observed irradiation-induced microvoids of which inner surfaces are almost coated with Cu atoms. After annealing around 4O0℃, the dissociation of vacancies from the microvoids leads to the formation of Cu ultrafine particles.2) Role of vacancy-solute complex in the initial rapid age hardening in Al-Cu-Mg alloy.Using CDB method, we have found that quenched-in vacancies are bound to Mg atoms rather than Cu atoms initially and the vacancy-Mg complexes easily migrate to vacancy sinks at 150℃. Vacancy-Mg-Cu complexes form during the initial 1 min aging at vacancy sinks. The dislocation-solute interaction is the origin of the initial rapid hardening.3) Mgic number vacanvy clusters in graphite and Si.By combining positron annihilation experiments and first-principles calculation, we firstly observed magic number vacancies in a covalent-bond materials : graphite after neutron irradiation.