THEORY OF POSITRONIUM FORMATION AND POSITRON EMISSION AT METAL-SURFACES
THEORY OF POSITRONIUM FORMATION AND POSITRON EMISSION AT METAL-SURFACES
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DOI：
10.1103/physrevb.22.2226
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发表时间：
1980-09
期刊：
影响因子：
--
通讯作者：
R. Nieminen;J. Oliva
中科院分区：
文献类型：
--
作者：
R. Nieminen;J. Oliva
本文用一个大大超出以往计算的模型，计算了入射到金属表面的正电子（e/sup +/）要么转化成离开表面的正电子素原子（Ps），要么作为裸电子素再发射的概率。Ps转换和e/sup +/发射过程分三个阶段进行：注入，从特征停止距离到表面的热扩散，以及电子捕获与裸e/sup +/逃逸。停止距离和均方根偏差的计算现在包括弹性正电子-离子芯散射的影响（除了非弹性e/sup +/-导电电子和e/sup +/-声子散射）和有限的温度修正的e/sup +/-声子散射。给定表面附近的热e/sup +/，我们研究以下过程的概率：直接e/sup +/. -->.。Ps转换（在简单的“共振能级”模型中计算），e/sup +/捕获到图像电势诱导的表面态，直接e/sup +/逃逸到真空中（微扰理论），以及通过e/sup +/从表面态脱陷形成Ps。通过求解适当的扩散方程来计算总转化和发射效率，其中边界条件由上述表面过程的分支比设定。最终Ps转换和e/sup +/发射效率的温度和入射能量的依赖性，我们的结果与实验进行了比较。«少
The probability for a positron (e/sup +/) incident upon a metal surface either to be converted into a positronium atom (Ps) which leaves the surface or to be reemitted as a bare e/sup +/ is calculated using a model which goes considerably beyond that used in a previous calculation. The Ps conversion and e/sup +/ emission process proceeds in three stages: implantation, thermal diffusion from the characteristic stopping distance to the surface, and electron capture with bare e/sup +/ escape. The stopping distance and its rms deviation are calculated now including both the effect of elastic positron--ion-core scattering (in addition to inelastic e/sup +/-- conduction-electron and e/sup +/-phonon scattering) and finite temperature corrections in the e/sup +/-phonon scattering. Given a thermal e/sup +/ near the surface, we examine the probabilities of the following processes: direct e/sup +/ ..-->.. Ps conversion (calculated within a simple ''resonant-level'' model), e/sup +/ trapping into the image potential induced surface state, direct e/sup +/ escape into vacuum (perturbation theory), and Ps formation via e/sup +/ detrapping from the surface state. Overall conversion and emission efficiencies are calculated by solving an appropriate diffusion equation with boundary conditions set by the branching ratios for the above surfacemore » processes. The temperature and incident energy dependence of our results for final Ps conversion and e/sup +/ emission efficiency are compared with experiment.« less