AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP24
Study of High and Low Work Function Surfaces for HyperThermal Surface Ionization using an Absolute Kelvin Probe

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: I.D. Baikie, Robert Gordon University, UK
Authors: I.D. Baikie, Robert Gordon University, UK
U. Petermann, Robert Gordon University, UK
B. Lägel, Robert Gordon University, UK
K. Dirscherl, Robert Gordon University, UK
Correspondent: Click to Email
We have performed a study of high (> 6eV) and low (<3 eV) work function surfaces in order to identify suitable target materials as an ion source for a new type of mass spectrometer technique based upon Hyperthermal Surface Ionization (HSI). In this application a molecular beam of neutral gas molecules is ionized by supersonic collision on a target surface. High work function surfaces produce positive ions (pHSI), low work function surface negative ions (nHSI). Analytical merits of HSI include very high sensitivity, atmospheric pressure inlet and informative mass spectra. As this technique does not use electron impact filaments the amount of cracking products is substantially reduced. The Ultra-High Vacuum Scanning Kelvin probe (SKP) is a technique producing relative work function topographies between a scanning reference tip and sample in a truly non-invasive fashion with high accuracy (1-2 meV). We demonstrate a novel extension of this technique, using photoelectric (PE) determination, which produces absolute work function data even if the tip work function is not known. Using this hybrid probe, together with SEM and AES, we have followed a) work function topographies of clean surfaces in UHV, b) changes in work function with oxidation that are related to surface cleaning processes, c) the temperature dependent (300 -1000 K) oxidation kinetics of polycrystalline metal surfaces (Re, Pt, Mo, W, Pd) for pHSI and d) electron beam evaporation of Ca, Gd and LaB@sub 6@ for nHSI. We will report the optimum parameters for target stability and performance under both pHSI and nHSI operating conditions. We will also illustrate informative mass spectra produced by Time-of-Flight HSI.