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

我们利用二维角相关湮灭辐射（2D-ACAR）和重合多普勒展宽（CDB）的正电子湮灭技术测量了几种金属和半导体中正电子采样的更宽范围内的电子动量分布。标记结果如下：1)含有害Cu杂质的核反应堆压力容器（RPV）钢用Fe-Cu模型合金。在铁基体中嵌入无缺陷的Cu超细粒子中发现了类似量子点的正电子态。所有正电子的波函数完全局限在粒子中。处于这种状态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和专有的信息。通过对Fe-1.0%Cu单晶的2D-ACAR实验，确定了BCC Cu超细颗粒在Fe中的费米表面。费米面几乎是球形的，但在BCC结构的（110）布里渊面中心周围有12个颈。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，其内表面几乎被Cu原子包裹。在400℃左右退火后，微孔中空位的解离导致Cu超细颗粒的形成。2)空位溶质复合物在Al-Cu-Mg合金初始快速时效硬化中的作用。利用CDB方法，我们发现在150℃时，淬灭的空位最初与Mg原子结合，而不是Cu原子，空位-Mg配合物很容易迁移到空位汇。空位- mg - cu配合物在空位汇的初始1分钟老化过程中形成。位错-溶质相互作用是初始快速硬化的原因。石墨和硅中的幻数空穴团簇。利用正电子湮没实验和第一性原理计算相结合的方法，首次观察到中子辐照后共价键材料石墨中的幻数空位。

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.