Photoluminescence Characteristics of Size-controlled Germanium Nanoparticles-Film

采用流动气体蒸发法，在低He或Ar气体压力下，以高气速从钨热丝中蒸发锗，制备锗纳米颗粒。通过对系统制备的锗纳米粒子的x射线衍射分析，得到了晶体结构和平均粒径的结果。(1)在不同的气体压力和气体速度条件下，形成了非晶态、菱形和四边形三种结构。在He气体条件下，即压力小于0.3Torr，速度大于20m/s，形成了非晶锗纳米颗粒。在He条件下，气体压力在1.0 ~ 2.0Torr之间，气体速度在0.3 ~ 20m/s之间，四方型锗纳米颗粒的形成最为频繁，但在与金刚石结构的混合物中也经常发现四方型结构。在上述He气体条件下，形成了具有普通金刚石结构的锗纳米颗粒。(2)通过x射线衍射测量，确定了四边形结构的晶格参数为a = 0.538nm, c = 0.879nm。这些数值不同于高压形式下已经观察到的数值。与普通气体蒸发法制备的锗纳米颗粒相比，本文制备的纳米颗粒的c参数减小了约3%。认为本研究形成的四方结构是锗的一种新结构。(3)菱形结构和菱形与四边形混合结构的锗纳米粒子的光致发光测量结果表明，两种结构的锗纳米粒子在红外区域具有相似的广谱光谱，峰值在1550nm附近。真正的峰值可能在更长的波长上，由于探测器的弱点，在目前的设置中无法测量。

Germanium nanoparticles were produced by the Flowing Gas Evaporation Method, where Ge was evaporated from the tungsten hot filament in a low He or Ar gas pressure with a high gas velocity. From the X-ray diffraction analysis of the systematically produced Ge-nanoparticles, the following results on crystal structure and the mean particle size were obtained. (1) Three kinds of structure of amorphous, diamond and tetragonal were formed depending on conditions of the gas pressure and the gas velocity. The amorphous Ge-nanoparticles were formed under the He gas conditions, that is, the pressure was below 0.3Torr and the velocity was over 20m/s. The most frequent formation of tetragonal Ge-nanoparticles was under the He conditions, where the gas pressure is from 1,0 to 2.0Torr and the gas velocity is from 0.3 to 20m/s, though the tetragonal structure was always found in the mixture with the diamond structure. Out of the He gas conditions mentioned above, Ge-nanoparticles with the ordinary diamond structure was formed. (2) The lattice parameters of the tetragonal structure was determined to be a = 0.538nm and c = 0.879nm from the X-ray diffraction measurement. These values are different from those of already observed in the high-pressure form. And also the c-parameter in the present case is smaller by about 3% than that of Ge-nanoparticles formed by the ordinary Gas Evaporation Technique. It is considered that the tetragonal structure formed in the present study is a new structure of germanium. (3) Photoluminescence measurements of both specimens of Ge-nanoparticles with diamond structure and with mixed structure of diamond and tetragonal showed the similar broad spectra in infrared region with the peak near 1550nm. The real peak may be in much longer wavelength, where it cannot be measured in the present setup because of the weakness of the detector.