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5411. Chemisorption on plasma-grown aluminium oxide: a study using inelastic electron tunnelling spectroscopy
Classified abstracts 5404-5412 roughness, the silicide surface roughness, and the corrosion behaviour of the silicidelayer. The formation of PtSi is more sensitive to the presence of oxide than Pd2Si and may even be suppressed. Remnants of the oxide are identified within the silicide using Auger sputter profiling technique. They can be interpreted as diffusing markers and provide information about the diffusing atomic species. Results of such marker experiments for formation of Pd2Si and PtSi are discussed. H F611 and P S Ho, J Appl Phys, 52 (9), 1981, 5510-5516. 37
5404. New wide angle, high transmission energy analyzer for secondary ion mass spectrometry. (USA) A conically tapered resistive disc with a single conducting hemisphere is used to effect the same energy selection as a pair of concentric hemispheres. The combination of this energy filter with a quadrupole mass spectrometer produces a secondary ion mass spectrometry (SIMS) instrument with a high total transmission attributable to its open geometry and lack of restricting apertures. An approximate form for the energy filter-mass spectrometer combined transmission function is constructed for operating conditions pertaining experimentally, and the theory and experiment are shown to be in good agreement. For a primary beam spot large compared with the electrical entrance aperture of the quadrupole, the energy bandwidth increases linearly with the spot diameter, and the transmission increases quadratically with the mass bandwidth and inverse quadratically with the spot diameter. The overall transmission (absolute 'sensitivity) is typically on the order of 5 x 10 -+ in the static mode, and would be much higher ( ~ 12% for typical applications) in the dynamic mode with small spot rastering. Static mode ion transmissions are measured for Cu +, AI +, Si + and Ni + at the peak of the kinetic energy distribution with an energy bandwidth of less than 3 eV. The instrument is used to study the copper surface in the static mode at current densities as low as 1.5 × 10 -9 A gm 2, using 90 ° incidence for the primary ions, with energies as low as 500 eV. The kinetic distribution of Cu + ions is only weakly dependent upon primary ion energy over the range 500 eV to 3 keV. The Cu + distributions show a 13-eV balfwidth and a maximum at 10 eV, while the Cu~ ion kinetic energy distribution has a 10-eV balfwidth and a maximum at 7 eV. Molecular ions ejected from a copper surface after a plasma oxidation are CuOH +, .CU2 O+ Cu2OH + and Cu2(C2H2)+. These ions have kinetic energy distributions with ~ 7 eV half-widths and peaks at ~ 5 eV. The aforementioned measurements are made with an energy resolutaon ofless than 3 eV, wh,ch is compatible with a mass resolution equal to the mass number of at least 250 ainu. M W Siegel and M J Vssil, Rev Sci lnstrum, 52 (11), 1981, 1603-1615~ 37 5405. Application of dynamic emittanee matching to secondary ion mass spectrometry. (USA) The implementation of the dynamic emittance matching (DEM) concept into our secondary ion mass spectrometer is described. The importance of this feature is presented in terms of increased ion transmission when operating at low primary ion beam fluxes, that is, the static secondary ion mass spectrometry (SIMS) or molecular SIMS mode. A discussion of the principle and the design of the DEM electronics in the system is given. Experimental comparisons are presented and discussed which contrast DEM and conventional results with respect to viewing area, ion transmission and imaging capability. J E Campuna et al, Rev Sci Instrum, 52 (10), 1981, 1517-1520. 37 5406. Field emission thermal resorption spectroscopy. (USA) Thermal desorption spectra from single crystal planes of a field emitter are obtained with the technique described. The specimen temperature is varied linearly and the field emission current from the face of interest is recorded vs temperature. Heating current and temperature measurements are transmitted to and from the tip using digital techniques via fibreoptic links to assure the high isolation necessary. A microcomputer is used to control the entire system, produce the linear temperature sweep, and acquire and treat the data. The desorption of hydrogen from the (111) plane of field-evaporated tungsten is presented as a test of the technique; a comparison between our spectra and the data reported in the literature shows a good correlation between the field emission and the classical thermal desorption spectroscopy. A good facet selectivity is obtained as proved by a result concerning H 2 on W (210). (Belgium) J M Deroehette, Rev Sci lnstrum, 53 (1), 1982, 34-37. 37 5407. A calibration technique for s computer-controlled photoelectron
spectrometer. (GB) A new method for calibrating the energy scale of photoelectron spectra,
774
using the He + peak at 24.59 eV, is shown to be satisfactory for both the He I and the He II spectra produced by spectrometers fitted with He I/He II photon sources. (Australia) P H Cannington and W Fock, J Phys E: Sci Instrum, 15 (1), 1982, 49-52. 37 5408. Local field effects on voltage contrast in the scanning electron microscope. (GB) The local field effects on voltage contrast in the scanning electron microscope (SEM) mean that local fields generated by a non-uniform potential distribution on the specimen surface cause a variation in the secondary electron (SE) detector current. It causes some errors in the voltage measurement. We shall present a theory to calculate the SE detector current in the presence of the local fields. In the calculation, we assume that the field distribution above the specimen surface (metal electrodes with 8 #m width and 12 ~m separation) is two-dimensional. Analysed models are a conventional SEM detector system (model A), a retarding-field energy analyser with an extraction field (model B) and a high-resolution energy analyser with an extraction field (model C). The results show that the local field effects could not be neglected even in models B and C with strong extraction fields. The calculated values of local field effects in models A and B agree well with the experimental ones. The dependence of local field effects on the electrode geometry is equivalent to that on the extraction field, though this dependency is not so strong. (Japan) K Nsksmse et al, J Phys D; Appl Phys, 14 (1), 1981, 1939-1943. 37 5409. Adsorption of ammonia on Pt{001 }. (GB) Ammonia adsorption on both the clean Pt{001 } metastable (1 x 1) surface and the stable (5 x 20) surfaces has been studied, principally by ARUPS and LEED. Pbotoemission spectra were recorded along the [1 I] azimuth in the plane of incidence over a range of photon incidence and polar collection angles, using a uv resonance lamp line source and a rotatable hemispherical retarding field analyser. Adsorption at ~ 200 K results in a strong attenuation of photoemission peaks on both the (1 x 1) and (5 x 20) surfaces attributed to surface states or resonances. On the (5 × 20) surface, at off-normal emission a small enhancement of a bulk-transition peak at ~ - 4 eV is observed, and new but weak features develop at - 7 . 5 and - 11 eV, assigned as NH3, 3a I and le molecular orbital features. On the (1 x 1) surface at normal emission a peak develops at - 4 eV during NH 3 adsorption, which is associated with enhanced emission from the substrate. The (5 x 20) surface is not converted to (1 x 1) by ammonia adsorption, but exposure to the LEED electron beam causes a rapid conversion, attributed to electron beam cracking of adsorbed ammonia. N R Palmer et al, Vacuum, 31 (10-12), 1981, 679-682. 37 5410. Reactive properties of lead monolayers on copper and silver surfaces. (GB) The interaction of oxygen with Pb overlayers on polycrystalline Cu, Ag and Cu (111 ) surfaces in the coverage range 0.05-1 monolayers has been studied by X-ray photoelectron spectroscopy. Oxygen reacts with the Pb overlayers to produce lead monoxide species for all three surfaces. For Pb/Cu, the oxidation rate decreases linearly with Pb coverage, whereas for Pb/Ag the oxidation rate decreases sharply in the range 0eb = 0.5-0.7. It is concluded that the Pb overlayers on Ag react directly with oxygen from the gas phase and that the change in reactivity accompanies a change in overlayer structure. In contrast, it is shown that for the Pb/Cu system with 0p~ < 1, the dominant oxidation mechanism is probably a spillover process in which an oxygen ad-species migrates from the exposed Cu surface to the Pb islands. D Chadwick et al, Vacuum, 31 (10-12), 1981, 705-709. 37 5411. Chemisorption on plasma-grown sluminium oxide: a study using inelastic electron tunnelling spectroscopy. (GB) Inelastic electron tunnelling (IET) spectra are reported for 2-hydroxycycloheptatrienone (tropolone), 8-hydroxyquinoline (oxine), 1,2-diaminoethane, 1,2-dihydroxyethane and 1-amino-2-hydroxyethane adsorbed from the vapour on to plasma-grown aluminium oxide. The mode of chemisorption of these adsorbates is discussed as are the oxide surface sites involved in the sorption process. Robert J Turner et al, Vacuum, 31 (10-12), 1981, 603-608. 37 5412. The depth resolution of composition-depth profiles obtained by ballcratering and Auger electron spectroscopy. (GB) The provision of accurate composition~lepth profiles to depths > 1 #m is important in the characterization and investigation of thick films, surface
5404. New wide angle, high transmission energy analyzer for secondary ion mass spectrometry. (USA) A conically tapered resistive disc with a single conducting hemisphere is used to effect the same energy selection as a pair of concentric hemispheres. The combination of this energy filter with a quadrupole mass spectrometer produces a secondary ion mass spectrometry (SIMS) instrument with a high total transmission attributable to its open geometry and lack of restricting apertures. An approximate form for the energy filter-mass spectrometer combined transmission function is constructed for operating conditions pertaining experimentally, and the theory and experiment are shown to be in good agreement. For a primary beam spot large compared with the electrical entrance aperture of the quadrupole, the energy bandwidth increases linearly with the spot diameter, and the transmission increases quadratically with the mass bandwidth and inverse quadratically with the spot diameter. The overall transmission (absolute 'sensitivity) is typically on the order of 5 x 10 -+ in the static mode, and would be much higher ( ~ 12% for typical applications) in the dynamic mode with small spot rastering. Static mode ion transmissions are measured for Cu +, AI +, Si + and Ni + at the peak of the kinetic energy distribution with an energy bandwidth of less than 3 eV. The instrument is used to study the copper surface in the static mode at current densities as low as 1.5 × 10 -9 A gm 2, using 90 ° incidence for the primary ions, with energies as low as 500 eV. The kinetic distribution of Cu + ions is only weakly dependent upon primary ion energy over the range 500 eV to 3 keV. The Cu + distributions show a 13-eV balfwidth and a maximum at 10 eV, while the Cu~ ion kinetic energy distribution has a 10-eV balfwidth and a maximum at 7 eV. Molecular ions ejected from a copper surface after a plasma oxidation are CuOH +, .CU2 O+ Cu2OH + and Cu2(C2H2)+. These ions have kinetic energy distributions with ~ 7 eV half-widths and peaks at ~ 5 eV. The aforementioned measurements are made with an energy resolutaon ofless than 3 eV, wh,ch is compatible with a mass resolution equal to the mass number of at least 250 ainu. M W Siegel and M J Vssil, Rev Sci lnstrum, 52 (11), 1981, 1603-1615~ 37 5405. Application of dynamic emittanee matching to secondary ion mass spectrometry. (USA) The implementation of the dynamic emittance matching (DEM) concept into our secondary ion mass spectrometer is described. The importance of this feature is presented in terms of increased ion transmission when operating at low primary ion beam fluxes, that is, the static secondary ion mass spectrometry (SIMS) or molecular SIMS mode. A discussion of the principle and the design of the DEM electronics in the system is given. Experimental comparisons are presented and discussed which contrast DEM and conventional results with respect to viewing area, ion transmission and imaging capability. J E Campuna et al, Rev Sci Instrum, 52 (10), 1981, 1517-1520. 37 5406. Field emission thermal resorption spectroscopy. (USA) Thermal desorption spectra from single crystal planes of a field emitter are obtained with the technique described. The specimen temperature is varied linearly and the field emission current from the face of interest is recorded vs temperature. Heating current and temperature measurements are transmitted to and from the tip using digital techniques via fibreoptic links to assure the high isolation necessary. A microcomputer is used to control the entire system, produce the linear temperature sweep, and acquire and treat the data. The desorption of hydrogen from the (111) plane of field-evaporated tungsten is presented as a test of the technique; a comparison between our spectra and the data reported in the literature shows a good correlation between the field emission and the classical thermal desorption spectroscopy. A good facet selectivity is obtained as proved by a result concerning H 2 on W (210). (Belgium) J M Deroehette, Rev Sci lnstrum, 53 (1), 1982, 34-37. 37 5407. A calibration technique for s computer-controlled photoelectron
spectrometer. (GB) A new method for calibrating the energy scale of photoelectron spectra,
774
using the He + peak at 24.59 eV, is shown to be satisfactory for both the He I and the He II spectra produced by spectrometers fitted with He I/He II photon sources. (Australia) P H Cannington and W Fock, J Phys E: Sci Instrum, 15 (1), 1982, 49-52. 37 5408. Local field effects on voltage contrast in the scanning electron microscope. (GB) The local field effects on voltage contrast in the scanning electron microscope (SEM) mean that local fields generated by a non-uniform potential distribution on the specimen surface cause a variation in the secondary electron (SE) detector current. It causes some errors in the voltage measurement. We shall present a theory to calculate the SE detector current in the presence of the local fields. In the calculation, we assume that the field distribution above the specimen surface (metal electrodes with 8 #m width and 12 ~m separation) is two-dimensional. Analysed models are a conventional SEM detector system (model A), a retarding-field energy analyser with an extraction field (model B) and a high-resolution energy analyser with an extraction field (model C). The results show that the local field effects could not be neglected even in models B and C with strong extraction fields. The calculated values of local field effects in models A and B agree well with the experimental ones. The dependence of local field effects on the electrode geometry is equivalent to that on the extraction field, though this dependency is not so strong. (Japan) K Nsksmse et al, J Phys D; Appl Phys, 14 (1), 1981, 1939-1943. 37 5409. Adsorption of ammonia on Pt{001 }. (GB) Ammonia adsorption on both the clean Pt{001 } metastable (1 x 1) surface and the stable (5 x 20) surfaces has been studied, principally by ARUPS and LEED. Pbotoemission spectra were recorded along the [1 I] azimuth in the plane of incidence over a range of photon incidence and polar collection angles, using a uv resonance lamp line source and a rotatable hemispherical retarding field analyser. Adsorption at ~ 200 K results in a strong attenuation of photoemission peaks on both the (1 x 1) and (5 x 20) surfaces attributed to surface states or resonances. On the (5 × 20) surface, at off-normal emission a small enhancement of a bulk-transition peak at ~ - 4 eV is observed, and new but weak features develop at - 7 . 5 and - 11 eV, assigned as NH3, 3a I and le molecular orbital features. On the (1 x 1) surface at normal emission a peak develops at - 4 eV during NH 3 adsorption, which is associated with enhanced emission from the substrate. The (5 x 20) surface is not converted to (1 x 1) by ammonia adsorption, but exposure to the LEED electron beam causes a rapid conversion, attributed to electron beam cracking of adsorbed ammonia. N R Palmer et al, Vacuum, 31 (10-12), 1981, 679-682. 37 5410. Reactive properties of lead monolayers on copper and silver surfaces. (GB) The interaction of oxygen with Pb overlayers on polycrystalline Cu, Ag and Cu (111 ) surfaces in the coverage range 0.05-1 monolayers has been studied by X-ray photoelectron spectroscopy. Oxygen reacts with the Pb overlayers to produce lead monoxide species for all three surfaces. For Pb/Cu, the oxidation rate decreases linearly with Pb coverage, whereas for Pb/Ag the oxidation rate decreases sharply in the range 0eb = 0.5-0.7. It is concluded that the Pb overlayers on Ag react directly with oxygen from the gas phase and that the change in reactivity accompanies a change in overlayer structure. In contrast, it is shown that for the Pb/Cu system with 0p~ < 1, the dominant oxidation mechanism is probably a spillover process in which an oxygen ad-species migrates from the exposed Cu surface to the Pb islands. D Chadwick et al, Vacuum, 31 (10-12), 1981, 705-709. 37 5411. Chemisorption on plasma-grown sluminium oxide: a study using inelastic electron tunnelling spectroscopy. (GB) Inelastic electron tunnelling (IET) spectra are reported for 2-hydroxycycloheptatrienone (tropolone), 8-hydroxyquinoline (oxine), 1,2-diaminoethane, 1,2-dihydroxyethane and 1-amino-2-hydroxyethane adsorbed from the vapour on to plasma-grown aluminium oxide. The mode of chemisorption of these adsorbates is discussed as are the oxide surface sites involved in the sorption process. Robert J Turner et al, Vacuum, 31 (10-12), 1981, 603-608. 37 5412. The depth resolution of composition-depth profiles obtained by ballcratering and Auger electron spectroscopy. (GB) The provision of accurate composition~lepth profiles to depths > 1 #m is important in the characterization and investigation of thick films, surface