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Relaxation time of an adsorbing 4He film
A54 Surface Science 125 (1983) 291-297 North-Holland Publishing Company RELAXATION
TIME
M. SINVANI
291
OF AN ADSORBING
4He FILM
*
** a n d D . G O O D S T E I N
California Institute of Technology, Pasadena, California 91125, USA Received I June 1982; accepted for publciation 27 June 1982 The readsorption of 4He atoms on a constantan heater surface was studied after flash desorption by the heat pulse technique. The replenishment of the desorbed film after the heat pulse was found to be essentially linear with the time between the pulses, reaching saturation at some critical value, try, which strongly depended on the pressure in the vapor, Pg. With the help of kinetic theory for the flux of atoms striking a surface, the measured value of tr¢ could be calibrated to give P~. We have verified this formula directly and used it to measure pressures down to 10 -9 Torr.
298 PAIRWISE
Surface Science 125 (1983) 298-303 North-Holland Publishing Company CORRELATIONS
SOLID-GAS P. T A R A Z O N A
AND WE'ITING
TRANSITIONS
AT A
INTERFACE and R, EVANS
H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 I T L UK Received 19 May 1982; accepted for publication 14 June 1982 We summarize the main results of our study of the density-density correlation function for Sullivan's model of a gas adsorbed on a solid substrate. In the approach to complete wetting, when a thick film of liquid density is adsorbed at the substrate, long-ranged transverse (parallel to the surface) correlations develop at the edge of the film where the density profile is similar to that of a liquid-gas interface. For a class I wetting situation the range of the transverse correlations increases and ultimately diverges as the bulk gas pressure approaches the saturated vapour pressure. We comment on other situations where long-ranged correlations arise and mention the possibility of observing these in diffraction experiments and in computer simulations. Sullivan's model always predicts a second-order phase transition between class II and class I wetting. By extending his model and allowing the attractive part of the solid-fluid potential to be longer-ranged than the attractive fluid-fluid potential we find that this wetting transition can become a first-order (Cahn) transition.
TIME
M. SINVANI
291
OF AN ADSORBING
4He FILM
*
** a n d D . G O O D S T E I N
California Institute of Technology, Pasadena, California 91125, USA Received I June 1982; accepted for publciation 27 June 1982 The readsorption of 4He atoms on a constantan heater surface was studied after flash desorption by the heat pulse technique. The replenishment of the desorbed film after the heat pulse was found to be essentially linear with the time between the pulses, reaching saturation at some critical value, try, which strongly depended on the pressure in the vapor, Pg. With the help of kinetic theory for the flux of atoms striking a surface, the measured value of tr¢ could be calibrated to give P~. We have verified this formula directly and used it to measure pressures down to 10 -9 Torr.
298 PAIRWISE
Surface Science 125 (1983) 298-303 North-Holland Publishing Company CORRELATIONS
SOLID-GAS P. T A R A Z O N A
AND WE'ITING
TRANSITIONS
AT A
INTERFACE and R, EVANS
H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 I T L UK Received 19 May 1982; accepted for publication 14 June 1982 We summarize the main results of our study of the density-density correlation function for Sullivan's model of a gas adsorbed on a solid substrate. In the approach to complete wetting, when a thick film of liquid density is adsorbed at the substrate, long-ranged transverse (parallel to the surface) correlations develop at the edge of the film where the density profile is similar to that of a liquid-gas interface. For a class I wetting situation the range of the transverse correlations increases and ultimately diverges as the bulk gas pressure approaches the saturated vapour pressure. We comment on other situations where long-ranged correlations arise and mention the possibility of observing these in diffraction experiments and in computer simulations. Sullivan's model always predicts a second-order phase transition between class II and class I wetting. By extending his model and allowing the attractive part of the solid-fluid potential to be longer-ranged than the attractive fluid-fluid potential we find that this wetting transition can become a first-order (Cahn) transition.