Cesium ion bombardment of metal surfaces

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6845705

Tompa, G S

The steady state cesium coverage due to cesium ion bombardment of molybdenum and tungsten was studied for the incident energy range below 500 eV. When a sample is exposed to a positive ion beam, the work function decreases until steady state is reached with a total dose of less than approx. =10/sup 16/ ions/cm/sup 2/, for both tungsten and molybdenum. A steady state minimum work function surface is produced at an incident energy of approx. =100 eV for molybdenum and at an incident energy of approx. =45 eV for tungsten. Increasing the incident energy results in an increase in the work function corresponding to a decrease in the surface coverage of cesium. At incident energies less than that giving the minimum work function, the work function approaches that of cesium metal. At a given bombarding energy the cesium coverage of tungsten is uniformly less than that of molybdenum. Effects of hydrogen gas coadsorption were also examined. Hydrogen coadsorption does not have a large effect on the steady state work functions. The largest shifts in the work function due to the coadsorption of hydrogen occur on the samples when there is no cesium present. A theory describing the steady-state coverage was developed is used to make predictions for other materials. A simple sticking and sputtering relationship, not including implantation, cannot account for the steady state coverage. At low concentrations, cesium coverage of a target is proportional to the ratio of (1 - ..beta..)/..gamma.. where ..beta.. is the reflection coefficient and ..gamma.. is the sputter yield. High coverages are produced on molybdenum due to implantation and low backscattering, because molybdenum is lighter than cesium. For tungsten the high backscattering and low implantation result in low coverages.

• Research Organization: Stevens Inst. of Tech., Hoboken, NJ (USA)
• OSTI ID: 6845705
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ADSORPTION
CATIONS
CESIUM IONS
CHARGED PARTICLES
COLLISIONS
ELEMENTS
ENERGY RANGE
EV RANGE
EV RANGE 100-1000
FUNCTIONS
HYDROGEN
ION COLLISIONS
IONS
METALS
MOLYBDENUM
NONMETALS
SORPTION
SURFACES
TRANSITION ELEMENTS
TUNGSTEN
WORK FUNCTIONS