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Nitric oxide adsorption, decomposition, and desorption were studied on Rh(100) in the temperature range from 88 to 1100 K using electron energy loss spectroscopy (EELS) and temperature programmed desorption (TPD). The EEL spectrometer was equipped with a multichannel detector for fast data acquisition. There are two adsorption states of NO on Rh(100), designated α1NO and α2NO, characterized by vibrational modes at 114 and 196 meV, respectively, and assigned to a lying down or highly inclined species and a vertically adsorbed species. The populations of the two states as functions of the total NO coverage were measured on the clean surface and with coadsorbed oxygen and CO. These coadsorbed species, whether adsorbed before or after the NO, increase the α2 population at the expense of α1. A model that includes an adsorbate–adsorbate interaction (rangeapprox. 7 Å) which converts α1NO to α2NO and which permits adsorbing NO to diffuse so as to favor α1 adsorption fits the measured populations of the two species on the clean surface and produces a saturation coverage of 0.62 ML (1 ML=1.39×1015 molecule/cm2), in good agreement with the published result. Decomposition and desorption of NO at temperatures >90 K were studied by a series of temperature programmed EELS (TP-EELS) experiments at heating rates from 0.048 to 5.25 K/s and by TPD. At saturation, 62% of the NO decomposes as evidenced by the extent of N2 desorption in TPD peaks at 460 and 770 K. The remaining NO desorbs molecularly near 430 K with an activation energy Ea=28±3 kcal/mol and first order preexponential v=1014±1 s-1, as determined by TP-EELS. The decomposition of α1NO occurs near 170 K with Ea=10.5±0.7 kcal/mol and v=1011.8±0.7 s-1. The extent of the α2NO decomposition and its activation energy are strongly coverage dependent. The temperature at which its decomposition rate is a maximum approaches that of α1NO at low... [ABSTRACT FROM AUTHOR]

The CO adsorption site occupations on Fe(111) have been determined as a function of coverage and temperature using temperature programmed desorption (TPD) and time-resolved electron energy loss spectroscopy (TREELS). CO does not adsorb in a thermally equilibrated distribution among the four adsorption sites at 100 K; selective adsorption occurs due to different coverage and temperature dependent sticking probabilities. Upon heating, the nonequilibrium distribution relaxes via CO site changes. At approx. 250 K and moderate coverage, CO adsorbed in the on-top site changes to the bridge-like shallow hollow site. A heating rate variation analysis yielded an activation barrier E=4.5±0.5 kcal mol-1 and effective first order preexponential ν1=101.5±0.5 s-1 for this process. A similar site change from the deep hollow to the shallow hollow occurs at low coverage near 160 K. Dissociation occurs at approx. 300 K when all CO are adsorbed in the shallow hollow site. With low coverages the dissociation reaction occurs with E=20±5 kcal mol-1 and ν1=1011±2 s-1. The resulting adsorbed atomic C and O recombinatively desorb at approx. 760 K with Eapprox. 48 kcal mol-1 and ν2approx. 0.1 cm2 s-1. At higher coverages, in addition to dissociation, some of the CO in the shallow hollow desorb, with Eapprox. 32 kcal mol-1 and ν1approx. 1017 s-1. [ABSTRACT FROM AUTHOR]

The intensities of the stretch modes of CO adsorbed in bridge and top sites on Rh(100) are presented as a function of coverage, temperature, and during reaction with O. Following adsorption at 90 K, the top site is predominantly occupied at low coverages, and at 0.5 atomic monolayers (ML) only the top site is occupied and a c(2×2) low energy electron diffraction (LEED) pattern is observed. With higher coverages the bridge site is increasingly occupied, and at saturation a p(4(2)1/2×(2)1/2)R45° LEED pattern is observed. The occupations of bridge and top sites at a fixed (0.5 ML) total coverage are observed to vary reversibly when the temperature is linearly ramped from 87 to 371 K and back down to 90 K; the difference in the binding enthalpy of bridge and top sites is determined to be 1.10±0.06 kcal mol-1. The enthalpy difference between bridge and top sites is also obtained from temperature programmed EELS (TP-EELS) which follows the site occupations as the temperature is increased past desorption. Surface order is found to have a significant effect on the normalized intensities of CO in conventional EEL spectra. The normalized intensities in angle integrated spectra, obtained by modulating the voltage difference applied to the two halves of the split analyzer input lenses, are insensitive to changes in the degree of surface order. The effect of low frequency frustrated rocking motions of diatomic molecules on the temperature dependence of the intensities observed in electron energy loss spectroscopy (EELS) is discussed. TP-EELS of coadsorbed CO and O allows the direct observation of the changes in the occupation of CO binding sites during reaction, and the results are correlated with LEED and temperature programmed reaction spectroscopy (TPRS) measurements of the reaction. Segregation of the reactants during the reaction is important. [ABSTRACT FROM AUTHOR]

The magnitudes of the challenges facing electron-based metrology for post-CMOS technology are reviewed. Directed self-assembly, nanophotonics/plasmonics, and resistive switches and selectors are examined as exemplars of important post-CMOS technologies. Materials, devices, and architectures emerging from these technologies pose new metrology requirements: defect detection, possibly subsurface, in soft materials, accurate measurement of size, shape, and roughness of structures for nanophotonic devices, contamination-free measurement of surface-sensitive structures, and identification of subtle structural, chemical, or electronic changes of state associated with switching in non-volatile memory elements. Electron-beam techniques are examined in the light of these emerging requirements. The strong electron-matter interaction provides measurable signals from small sample features, rendering electron-beam methods more suitable than most for nanometer-scale metrology, but as is to be expected, solutions to many of the measurement challenges are yet to be demonstrated. The seeds of possible solutions are identified when they are available. [ABSTRACT FROM AUTHOR]

The design, construction, and operation of a high-resolution electron energy-loss spectrometer incorporating a multidetector of 96 discrete anodes are described. In conjunction with temperature and pressure perturbations, this fast data-acquisition spectrometer allows studies of surface kinetics and reaction mechanisms by accumulating spectra in as fast as 2 ms. A comprehensive hardware and software system has been developed that permits experimental control and data acquisition with an LSI 11/23 microcomputer. A routine increase in data-acquisition speed of ≊10, when compared to a conventional electron energy-loss apparatus, has been achieved when the spectrometer is operated with 10–20-meV resolution. [ABSTRACT FROM AUTHOR]