Physical Properties of Nano-size Pore Surfaces and Metal Films on Pore Surfaces of Porous Silicon

在2.0 μ m单晶硅阳极氧化制得的多孔硅中，发现了正电子离子的产率，其寿命为几十纳秒，暴露于氧气后寿命缩短。当温度从300 K降低到85 K时，寿命从33ns延长到45ns，多普勒展宽湮灭辐射的半峰全宽增加，当温度低于85 K时，两者趋于平稳。当温度从300 K下降到外推的0 K时，正电子子的强度从22%下降到15%。温度依赖的正电子湮灭是根据孔隙表面上不成对电子密度的温度依赖来理解的。在以0.02 μ m单晶硅制成的多孔硅中尚未发现正电子离子的形成。没有正电子形成的主要原因是表面密度低。

The yield of ortho-positroniums with a lifetime of a few ten nanosecond, which is shortened upon exposure to oxygen gas, has been found in a porous silicon made by anodization of a silicon single crystal of 2.0OMEGAcm. The lifetime becomes long from 33ns to 45ns, and the full width at half maximum of the Doppler-broadened annihilation radiation increases, as the temperatere is decreases from 300 K to 85 K,and both of them level off at temperatures lower than 85 K.The intensity of ortho-positroniums decreases from 22 % to 15 % as the temperature goes down from 300 K to extrapolated 0 K.Temperature-dependent positronium annihilation is understood in terms of the temperature dependence of unpaired electron density on pore surfaces.The formation of ortho-positroniums has not been found in a porous silicon made with a silicon single crystal of 0.02 OMEGAcm. No positronium formation has been explained mainly on the low surface density.