High Resolution Inverse Photoemission System with Polarization Analysis

为了探测费米能级附近的电子态，人们迫切需要具有偏振分析能力和高分辨率的逆光发射光谱。一个系统，满足这些要求的开发和部分测试。利用在两个不同温度下用SrF_2低通滤波器测量的两个IPES谱之间的差谱实现了带通探测器的高能量分辨率。激子吸收边引起的Urbach尾的能量移动使得人们能够测量具有不同带通特性的IPES光谱。采用负电子亲和势（NEA）GaAs阴极，并在阴极上沉积Cs和O_2，可以减小激发电子束的能带宽度。为此，不仅真空Ar轰击清洗而且预先的化学清洗是非常重要的。为了使NEA阴极获得良好的真空度，我们安装了NEG（非蒸发吸气剂泵）和一台高抽速离子泵。电子透镜的透过率提高到50- 80%。最终获得了超过10 A的光电子流，寿命超过10小时，并安装了3个LEED（低能电子衍射）栅和俄歇光学系统。研制了用于磁化铁磁样品的脉冲磁铁系统。这是用来测量铁磁材料的极化相关谱。

The inverse photomission(IPES) spectroscopy with capabilities of polarization analysis and very high resolution is strongly required to probe the electronic states very near the Fermi level. A system which satisfies such requirements is developed and partly tested. The high energy resolution of the band pass detector is realized by use of the difference spectrum between two IPES spectra measured with a SrF_2 low pass filter set at two different temperatures. The energy shift of the Urbach tail due to the excitonic absorption edge enables one to measure the IPES spectrum with different band pass characteristics. So the difference spectrum realizes a resolution better than 0.25 eV.The energy band width of the excitation electron beam can be reduced by use of the negative electron affinity(NEA) GaAs cathode with use of Cs and O_2 deposition. For this purpose, not only an in-vacuum Ar bombard cleaning but also a preceding chemical cleaning is very important. In order to realize a good vacuum for NEA cathode, we installed NEG(non evaporating getter pump) and a high pumping speed ion pump. The transmittance of the electron lens is improved up to 50-80%. We finally got photoelectron current of more than 10 A with a life time of more than 10 hours.In addition, 3 grids LEED(low energy electron diffraction) and Auger optics are installed. Pulse magnet system to magnetize ferromagnetic samples is also developed. This is used to measure the polarization dependence spectrum of ferromagntic materials.