Showing papers by "Nicholas Winograd published in 1981"

Design and performance of an energy‐ and angle‐resolved secondary ion mass spectrometer

Abstract: The design and performance of an energy‐ and angle‐resolved secondary ion mass spectrometer are described. The instrument incorporates a quadrupole mass filter mounted on a flange which can be rotated under ultrahigh vacuum conditions, allowing variation of the polar collection angle of secondary ions, while rotation of the sample crystal about an axis parallel to the primary ion beam provides azimuthal angle section. Energy analyses are performed in the 0–100 eV range using a 90° spherical electrostatic sector combined with an accelerating/decelerating lens system which provides a variable 1–15 eV bandpass. Low energy electron diffraction provides complementary information on surface and adsorbate geometry. The determination of energy and angular distributions of secondary ions ejected from an ion‐bombarded Ni(001)c(2×2)–CO surface illustrates the capabilities of the system.

Secondary ion mass spectrometry/X‐ray photoelectron spectroscopy study of CO adsorption on Ni and of Fischer–Tropsch synthesis on FeRu alloys

Abstract: The adsorption of CO on a Ni(100) single crystal surface has been investigated by X-ray photoelectron spectroscopy and static secondary ion mass spectrometry. At room temperature CO chemisorbs molecularly on Ni. A saturation coverage of about 0.5 monolayer is reached after 2 L CO exposure. The NiCO+/Ni2CO+ ratio increases from very low values at low coverage to a saturation value of about 4.5. Dynamic studies of Ni+ and NiCO+ yields during exposure to 1.3 × 10−6 to 1.3 × 10−5 Pa of CO show reversible pressure and temperature dependent changes in addition to chemisorption. We ascribe these effects to CO weakly adsorbed on both the clean and CO-covered Ni surface. The interaction of CO and H2 with FeRu alloy surfaces has been studied by XPS and SIMS as well as by kinetic measurements. Fe surface enrichment is observed which explains the catalytic behavior of the alloys in Fischer–Tropsch synthesis (FTS). Ru rich surfaces remain unchanged during FTS but an extensive and rapid carbon build-up is found on the alloy surfaces. Silica supported alloys coke more slowly. The carbon build up on pure Fe is preceded by a carbide formation that coincides with a maximum in hydrocarbon synthesis activity. Potassium promoted Fe exhibits a faster carbon deposition than pure Fe, but the potassium appears to stay on the uppermost surface by diffusing through the carbon layers.