Dr. Bruce Kay and his colleagues are applying and extending molecular-beam surface scattering techniques to ice surfaces to examine the chemical kinetics and reaction dynamics of molecular processes occurring both on the surface and within the bulk of amorphous and crystalline ice films. We use these “chemically tailored” nanoscale films as model systems to elucidate the mechanistic details of the complex physiochemical processes that take place in aqueous solutions, deeply super-cooled liquids, astrophysical dust and comets, and at the aqueous-mineral geochemical interface. In related experiments, we are examining hydrophobic and hydrophilic interactions between water and various other materials using thermal desorption and surface spectroscopic techniques to probe interphase transport and phase separation. Elucidation of these processes will further our understanding of solvation and reactions in multi-phase, multi-component solutions and in determining reaction mechanisms in heterogeneous systems. These molecular-level studies are germane to Department of Energy programs in environmental restoration, waste processing, and contaminant fate and transport.
We are also using molecular beam scattering instrumentation to study physisorption and chemisorption on oxide surfaces. Recently, we have shown that physisorption of weakly bound gases can be used to titrate small concentrations of surface defects and to determine their binding energies on magnesium oxide(100). Currently, we are also engaged in adsorption studies on the surfaces of nanoporous thin MgO films. This work was initiated by our discovery of the deposition angle dependent porosity of amorphous solid water films grown under ballistic deposition (BD) conditions. We have found that the MgO films created under reactive BD conditions are composed of a tilted array of porous nanoscale crystalline filaments with high porosity (~ 90%) and high-surface area (~ 1000 m2/g). These films have chemical binding sites analogous to those on MgO(100). However the fraction of chemically active, high energy binding sites is greatly enhanced on the nanoporous film. This unique collection of properties makes these materials attractive candidates for chemical applications such as sensors and heterogeneous catalysts.