Oxide removal from Ge(100) surfaces treated by HCl and HF solutions with different concentrations are systematically studied by synchrotron radiation photoelectron spectroscopy (SR-PES). SR-PES results show that clean surfaces without any oxide can be obtained after wet chemical cleaning followed by vacuum annealing with a residual carbon contamination of less than 0.02 monolayer. HF etching leads to a hydrogen terminated Ge surface whose hydrogen coverage is a function of the HF concentration. In contrast, HCl etching yields a chlorine terminated surface. Possible etching mechanisms are discussed. Surface roughness after HF and HCl treatments is also investigated by AFM, which shows that HF treatment leaves a rougher surface than HCl. a) sysun@stanford.edu corresponding author
GaAs based negative electron affinity photocathodes activated with Cs and NF3 are used as polarized electron sources for linear accelerators. It is generally believed that the activation layer consists of CsF. The activation layers of Cs–NF3 on GaAs photocathodes are herein investigated using synchrotron radiation photoelectron spectroscopy. F1s, N1s, and other core levels are recorded at photon energies ranging from 70to820eV. Surprisingly, a significant amount of nitrogen is observed in the activation layers. Two distinct species of nitrogen are observed, one of which decreases along with the fluorine signal as the yield of the photocathode decays with time.
Abstract:The atomic arrangement of Cs oxides in the activation layer of an InP photocathode is investigated using Angle Dependent Photoemission Spectroscopy (ADPES). Two distinct peaks in the O1s core level and in valence band spectra have led to the discovery of two molecular oxygen species incorporated in the thin activation layer: Cs peroxide (Cs 2 O 2 ) and Cs superoxide
SLAC-PUB-12711Submitted to Journal of Applied Physics 2 observation of the peak evolution in the photoemission spectra, and supported by the thermodynamic stability of Cs superoxide as compared to Cs peroxide when there is residual oxygen around.3
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