Hess’s research interest is the experimental study of the properties of layers of simple molecules adsorbed on a uniform surface at low temperatures. Phenomena of interest include wetting (that is, growth of a uniform film to macroscopic thickness) or non-wetting by liquid and solid adsorbates; layer-by-layer versus continuous growth, which is related to roughening of the adsorbate free surface; preroughening, which is associated with disordering of the outermost layer; melting or other phase transitions within individual layers; and particularly phase separation in binary films of one or two molecular layers.
A current interest is binary mixture films. There are questions relating to such phenomena as the extent of 2-D solubility or segregation of components between layers, and displacement of a preadsorbed monolayer of one component by one or more layers of the other component. The infrared technique is particularly valuable for mixtures, provided suitable molecules are chosen.
Other interests include superfluid properties of liquid helium.