An ultra-high vacuum(UHV) compatible electron spectrometer employing a double toroidal analyzer has been developed. It is designed to be combined with a custom-made scanning tunneling microscope(STM) to study the spatially localized electron energy spectrum on a surface. A tip–sample system composed of a piezo-driven field-emission tungsten tip and a sample of highly ordered pyrolytic graphite(HOPG) is employed to test the performance of the spectrometer.Two-dimensional images of the energy-resolved and angle-dispersed electrons backscattered from the surface of HOPG are obtained, the performance is optimized and the spectrometer is calibrated. A complete electron energy loss spectrum covering the elastic peak to the secondary electron peaks for the HOPG surface, acquired at a tip voltage of-140 V and a sample current of 0.5 pA, is presented, demonstrating the viability of the spectrometer.
The Compton profile of molecular hydrogen has been determined at an incident photon energy of 20 ke V based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved at p z = 0. Different theoretical methods, i.e., the density functional method, and the Hartree–Fock method, were used to calculate the Compton profiles of hydrogen with different basis sets, and the theoretical calculations are in agreement with the experimental observation in the whole p z region. Compared with the HF calculation, the DFT-B3 LYP ones are in better agreement with the present experiment, which indicates the electron correlation effect is very important to describe the wavefunction in the ground state of hydrogen.
The decay pathways of the structured ionization region of oxygen at different momentum transfers,i.e.,0,0.23 a.u.(atomic unit),and 0.91 a.u.,are studied by measuring the ion and the scattered electron coincidently.It is found that the dipole-forbidden superexcited states of(2σu)-1(c4Σu-)npσu 3Σg-← X3Σg-decay into different channels according to the principal quantum number n.The broad ridge above 35 eV,which may be due to inner-valence excited states of(2σg)-1nλ or multiply excited states,is observed both at small and large momentum transfers,and its decay channel of O++ O is dominant.
With potential applications in various fields, gold related catalysts have received intensive attentions. In the past decade, mechanisms of gold catalysis for low-temperature CO oxidation, NOx oxidation/reduction, selective oxidation of alcohols have been investigated both experimentally and theoretically based on model catalysts using free or supported gold nanoparticles and single crystal gold surfaces. In this short review, we summarize recent theoretical studies on molecular oxygen activation process, water or hydroxyl involved oxidation reaction, and also the effect of local structure on the reactivity and selectivity.
The dissociative ionization of CO2 induced by 5 keV electrons in two-body and three-body dissociative channels of CO2+2and CO3+2is identified by the ion–ion coincidence- method using a momentum imaging spectrometer. The partial ionization cross sections(PICSs) of different ionic fragments are measured and the results generally agree with the calculations made by a semi-empirical approach. Furthermore, the PICSs of the dissociative channels are also obtained by carefully considering the detection efficiency of the micro-channel plates and the total transmission efficiency of the time of flight system.
