Evaporation rate during film formation

Blistering due to phase separation duringjUm formation This phenomenon may occur when there are two volatile components of different evaporation rates. Water may diffuse into the voids left by one of the solvents, generating blisters. This is therefore an early blistering, since it occurs during film formation [77]. 

The following subsections examine the interplay between physical and chemical phenomena in rapidly concentrating systems during film formation. We present examples of how the structure of the precursors and the rates of condensation, evaporation, and shear during deposition affect the structure of the depositing film. 

Relative humidity can have a significant impact on drying behavior and film quahty. Water-based formulations that perform weU when apphed under dry conditions may be deficient under high humidity apphcation conditions. The rate of water evaporation is much slower at high humidity, but solvent evaporation continues. This results in solvent depletion during the critical phases of film formation and consequent poor film development. 

For ideal solutions, the partial pressure of a component is directly proportional to the mole fraction of that component in solution and depends on the temperature and the vapor pressure of the pure component. The situation with group III-V systems is somewhat more complicated because of polymerization reactions in the gas phase (e.g., the formation of P2 or P4). Maximum evaporation rates can become comparable with deposition rates (0.01-0.1 xm/min) when the partial pressure is in the order of 0.01-1.0 Pa, a situation sometimes encountered in LPE. This problem is analogous to the problem of solute loss during bakeout, and the concentration variation in the melt is given by equation 1, with l replaced by the distance below the gas-liquid interface and z taken from equation 19. The concentration variation will penetrate the liquid solution from the top surface to a depth that is nearly independent of zlDx and comparable with the penetration depth produced by film growth. As result of solute loss at each boundary, the variation in solute concentration will show a maximum located in the melt. The density will show an extremum, and the system could be unstable with respect to natural convection. 

Two series of growth experiments were earried out 1) AES-EELS investigation of Yb/Si(lll) film growth process and 2) in situ Hall measurements [4] at room temperature for the Yb/Si(lll) system during its formation. P-type (lOQ cm) Si(lll) wafers were used as substrates. A thoroughly degassed Ta-cell heated by direct current was used to evaporate Ytterbium (99.99%) onto the Si(l 11)7x7 surface at room temperature in the UHV chamber. The deposition rate was calibrated with a quartz sensor before the experiments and checked again after that. In both our experiments new portions of Yb were added onto the same sample... 

Thin films of polymers are formed by dropping a small amount of a solution of a polymer onto the carrier electrode, and then spinning it at several thousands r.p.m. As in the case of A1 or A2, the redox-active compound is added to the polymer solution or diffused afterwards from a solution. During centrifugal spinning the evaporation of the solution leads to an increase of the concentration of the polymer causing an increased viscosity and the formation of a solid film. Only in the case of Newtonian fluids does the solution of the hydrodynamic equations lead asymptotically to a uniform layer thickness that is independent of the liquid profile at the start of the rotation The thickness of the films depends on the rotation speed, the evaporation rate and the initial viscosity... 

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