Work Function Study for the Search of Efficient Target Materials for Use in Hyperthermal Surface Ionization Using a Scanning Kelvin Probe

2000 ◽  
Vol 623 ◽  
Author(s):  
U. Petermann ◽  
I.D. Baikie ◽  
B. Lägel ◽  
K.M. Dirscherl
Keyword(s):  
Work Function ◽  
Surface Ionization ◽  
Kelvin Probe ◽  
Scanning Kelvin Probe ◽  
Flash Annealing ◽  
Function Change ◽  
Work Function Change ◽  
Different Temperatures ◽  
Kinetics Of ◽  
Ongoing Project

AbstractIn order to search for efficient target materials for use in Hyperthermal Surface lonisation (HSI), a new mass spectroscopy ionisation technique, we have performed a study of high and low work function (ø) surfaces as part of an ongoing project. HSI relies on high and low work function surfaces for the production of positive (pHSI) and negative (nHSI) ions, respectively.Using a novel UHV Scanning Kelvin Probe we have followed the oxidation kinetics of polycrystalline Re at different temperatures and examined the effects of oxidation, flash annealing and sputter-anneal cleaning cycles via high resolution work function topographies. Our results indicate that oxidised Re is the best candidate for pHSI in terms of ionisation efficiency and ø change. The peak work function change of 2.05 eV occurred at 900 K to 950K.For the nHSI materials Calcium exhibited the best performance with respect to the ionisation efficiency indicating a wf of 2.9 eV. We will present data in terms of mass fragmentation using an HSI-Time-of-Flight (TOF) system and time stability of the work function.

Work Function Study of Polycrystalline Metals using a UHV Scanning Kelvin Probe

2000 ◽  
Vol 615 ◽  
Author(s):  
U. Petermann ◽  
I.D. Baikie ◽  
B. Lägel ◽  
K.M. Dirscherl
Keyword(s):  
Work Function ◽  
Target Material ◽  
Kelvin Probe ◽  
High Work Function ◽  
Positive Ions ◽  
Polycrystalline Metals ◽  
Scanning Kelvin Probe ◽  
Flash Annealing ◽  
Different Temperatures ◽  
High Work

ABSTRACTWe have undertaken a study of high work function (φ) surfaces as part of an ongoing project searching for efficient target materials for use in Hyperthermal Surface Ionisation (HSI), a new mass spectroscopy ionisation technique. HSI relies on high work function surfaces for the production of positive ions. Polycrystalline metals as Re, W, Mo and Pt are particularly interesting materials in this respect as oxidation substantially increases their φ. We present and discuss the following experimental evidence: a) the magnitude and sign of φ changes in terms of adsorbate induced dipoles, b) the effect of molecular hydrogen exposure on the clean surface, and c) the effect of subsequent oxygen exposure.Using a novel UHV Scanning Kelvin Probe we have followed the oxidation kinetics of polycrystalline metals at different temperatures and examined the effects of oxidation, flash annealing and sputter-anneal cleaning cycles via high-resolution φ topographies. Our results indicate in particular Re as a suitable HSI target material exhibiting a φ increase of 1050 meV at 300 K increasing to 2050 meV at 900 K. Sputter-cleaned surfaces exhibit a dramatic change in the second oxidation phase.We have also examined φ changes associated with N2O and CO2 on Tungsten and Molybdenum. We observe that atomic oxygen gives similar results to O2 but has a much lower initial sticking coefficient. We report that CO2 actually lowers the φ for substrate temperatures under 650 K, the peak work function changes occurs at 850 K and is approximately 1/3 the height of the O2 or O peak.

Very Low Pressure Oxidation of Si and Ge Surfaces

1990 ◽  
Vol 204 ◽  
Author(s):  
Iain D. Baikie
Keyword(s):  
Work Function ◽  
Substantial Reduction ◽  
Second Phase ◽  
Kelvin Probe ◽  
Band Bending ◽  
Effective Electron ◽  
Adsorption Phase ◽  
Dipole Layer ◽  
Function Change ◽  
Work Function Change

ABSTRACTAlthough the oxidation of Si(111) 7×7, Ge(111) 2×8 surfaces are relatively well understood very little work has been performed at sub monolayer coverage. We have utillsed a custom-built high resolution Kelvin probe to follow the changes in work function, and changes in band-bending and surface state occupancy via Surface Photovoltage Spectroscopy (SPV). The Kelvin probe Is an Ideal tool for such analysis due to Its extremely high surface sensitivity, equivalent to 4×1010 molecules/cm2, or 0.01% of the available sites.We observe a very rapid initial adsorption phase, which has not been found by other surface probes, e.g., AES, EELS, etc, corresponding to the formation of an elementary dipole layer. During this phase the Increase In the effective electron affinity with oxygen uptake achieves a maximum of 1V at 0.3 monolayer (ML), on SI(111) at 300 K. We report, for the first time, SPV spectra of SI(111), at 100 K, indicating quenching of a band of surface states centered around the fermi-level, quenching Is completed at the max-Imum of the work function change.The second adsorption phase, involving oxygen penetration through the surface layer and incorporation Into the lattice, commences at 0.25 ML for Si(111) at 300 K. a much earlier stage than previously reported. Further. we find evidence of a metastable SiO2 precursor at coverages below 1 ML. The dipole layer formation (and breakup) is shown to be very sensitive to both temperature and amount of surface Carbon contamination. The second phase also Involves a substantial reduction In band-bending to nearly flat bands at 2 ML, accounting for 20% of the work function change In the case of SI and almost 90% for Ge.

Work function studies of propylene, acetylene, hydrogen and nitrogen chemisorption on molybdenum

1982 ◽  
Vol 47 (11) ◽  
pp. 2996-3003
Author(s):  
Zdeněk Bastl
Keyword(s):  
Work Function ◽  
Surface Topography ◽  
Surface Coverage ◽  
Dissociative Chemisorption ◽  
Complete Coverage ◽  
Surface Sites ◽  
Function Change ◽  
Work Function Change

The work function changes of vacuum deposited molybdenum films caused by the chemisorption of propylene, acetylene, hydrogen and nitrogen were measured using the Kelvin vibrating capacitor method. During the hydrocarbon chemisorption, the work function increased in a low surface coverage region but decreased at the higher surface coverages. The saturation values of the work function changes corresponding to complete coverage of the surface by chemisorbed propylene and acetylene equal -0.08 eV and -0.42 eV, respectively. The observed dependences of the work function change on surface coverage are interpreted by the dissociative chemisorption of hydrocarbons on a limited number of surface sites which are simultaneously the sites of preferred adsorption. The extent of dissociation decreases in the adsorption with the increasing surface coverage. The results of the study of the work function changes induced by the hydrogen and nitrogen chemisorption enabled to draw several conclusions on the surface topography of the used films.

Fundamental studies on SnO2 by means of simultaneous work function change and conduction measurements

2005 ◽  
Vol 490 (1) ◽  
pp. 43-47 ◽  
Author(s):  
T. Sahm ◽  
A. Gurlo ◽  
N. Bârsan ◽  
U. Weimar ◽  
L. Mädler
Keyword(s):  
Work Function ◽  
Function Change ◽  
Work Function Change

scholarly journals THE WORK-FUNCTION CHANGE OF K/Cu(111)

1990 ◽  
Vol 39 (12) ◽  
pp. 1989
Author(s):  
WANG GENG ◽  
LI HAI-YANG ◽  
XU YA-BO
Keyword(s):  
Work Function ◽  
Function Change ◽  
Work Function Change
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