ABSTRACT
A novel IR method for measuring the kinetics of N(2)O photodecomposition has been devised and used to calibrate the flux of Lyman-alpha (10.2 eV) radiation from a H(2)/Ar microwave discharge lamp. The photodecomposition of N(2)O occurs with a weak pressure dependence due to the operation of a wall effect consuming some photogenerated active oxygen species. This effect is removed by working at high N(2)O pressures. The Lyman-alpha flux from the lamp is 1.28 +/- 0.36 x 10(15) photons cm(-2) s(-1).
ABSTRACT
The dynamics of electron-induced reactions in condensed trifluoroiodomethane (CF3I) were studied under ultrahigh vacuum conditions. Seven CF3I radiolysis products (C2F6, C2F5I, C2F3I, CF2I2, C2F4I2, CFI3 and C2F3I3) were identified using temperature-programmed desorption experiments conducted after irradiation with 4 eV electrons. Although C2F6 formation at energies above 4 eV is ascribed to electron-induced electronic excitation followed by prompt dissociation of the C-I bond to form [Formula: see text] radicals that dimerize, the formation of the other six radiolysis products at low sub-ionization incident electron energies is attributed to dissociative electron attachment (DEA) because of the observed resonance peaks in the radiolysis product yields as functions of incident electron energy (â¼2 to â¼ 7 eV). All seven CF3I electron-induced reaction products were also identified following irradiation with 500 eV electrons. While dissociative electron attachment and/or electron impact excitation may play an important role in the high-energy radiation-induced synthesis of the high-yield product C2F6, a dramatic enhancement of up to â¼ 2 × 10(4) in product yield per electron at 500 eV relative to that at 4 eV for some products suggests, however, that DEA is not the dominant mechanism for the high-energy radiation-induced synthesis of those products.
ABSTRACT
This article reviews recent research using a low-energy electron microscope, built by Tromp at IBM, and equipped with an accelerator that permits in situ irradiation with a beam of self-ions. The available ion energies of 20 eV to 5 keV span the range from epitaxial growth by a hyperthermal beam to sputtering at the level of approximately 10 atoms per incident ion. The design criteria and instrument calibration are described. The research described is surface science that requires a vacuum maintained below 10(-10) Torr, with all components contained in the same vacuum. Two general categories of applications are sketched. Experiments that accurately measure important physical quantities include surface mass diffusion over an extended temperature range; determining the critical chemical potential at which island nucleation occurs; observation and explanation of the universal evolution by which adatom and advacancy islands both grow and shrink by beam-driven processes; and the study of sublimation (regarded as negative ion beam intensity). Experiments described here with other goals include beam-assisted synthesis first of large pans and mesas for isolating surface experiments (e.g., nucleation) from the surrounding crystal, and second of Fourier waves on steps, for studies of diffusive relaxation. Operation of exotic structures including Bardeen-Herring sources and Frank growth spirals deformed by crystal anisotropy are also described.
