Sign flipping of spontaneous polarization in vapour-deposited films of small polar organic molecules.

Films of polar molecules vapour-deposited on sufficiently cold substrates are not only amorphous, but also exhibit charge polarization across their thickness. This is an effect known for 50 years, but it is very poorly understood and no mechanism exists in the literature that can explain and predict it. We investigated this bulk effect for 18 small organic molecules as a function of substrate temperature (30-130 K).

Spontaneous Polarization of Cryo-Deposited Films for Five Normal Saturated Monohydroxy Alcohols, CHOH, = 1-5.

Vapor-deposited films of neutral polar molecules on cold surfaces exhibit spontaneous electric polarization across the faces of the film. We deposited known amounts of the first five members of the normal monohydroxy alcohols at substrate temperatures in the range of 30-130 K. It is known that voltages measured are proportional to film thickness and that the effect is substrate-independent.

Spontaneous polarization of vapor-deposited 1-butanol films and its dependence on temperature.

Films of 1-butanol were vapor deposited under vacuum conditions at cryogenic temperatures on a polycrystalline platinum foil. Kelvin probe measurements showed the generation of a large negative voltage on the vacuum side of the film relative to its back side in contact with the platinum foil. Voltages across vapor deposited films, which are known to require molecules with an electric dipole moment, were confirmed to be proportional to the amount of gas deposited at a given temperature.

The electron affinity of gallium nitride (GaN) and digallium nitride (GaNGa): the importance of the basis set superposition error in strongly bound systems.

The electron affinity of GaN and Ga2N as well as the geometries and the dissociation energies of the ground states of gallium nitrides GaN, GaN(-), Ga2N, and Ga2N(-) were systematically studied by employing the coupled cluster method, RCCSD(T), in conjunction with a series of basis sets, (aug-)cc-pVxZ(-PP), x=D, T, Q, and 5 and cc-pwCVxZ(-PP), x=D, T, and Q. The calculated dissociation energy and the electron affinity of GaN are 2.12 and 1.