Faculty | Haskell Taub

Angela SpeckHaskell Taub

Professor
office: 312 Physics Building
phone: 573-882-7345
email: taubh@missouri.edu
education: Ph.D., Cornell University, 1971
website

Research Interests

Structure, Phase Transitions, and Dynamics of Adsorbed Films

Several different scattering techniques (elastic and inelastic neutron scattering, x-ray diffraction, and low-energy electron diffraction) are being employed to study the physical properties of films as thin as a single molecular layer. Interest in these quasi two-dimensional (2D) films is based on the premise that phenomena such as crystal growth, structural phase transitions, and changes of state (e.g., melting) will be easier to understand in lower dimensional systems. In some cases, a theory may be easier to formulate conceptually in 2D as in elucidating steps in the melting process. In other cases, it may be easier to implement a model mathematically in 2D rather than 3D. Experimental investigation of these thin films requires some method of holding the sample. In our experiments, the molecules are physically adsorbed on a solid surface. That is, molecules are bound to a substrate by weak van der Waals forces rather than by chemical bonds (chemisorption). These "physisorbed" monolayers can be composed of molecules of various sizes ranging from rare gas atoms and diatomic molecules (e.g., N2) to long-chain hydrocarbons. The condensed phases of these films are in many respects the 2D analogues of the simplest bulk solids, fluids, and gases.X-ray specular reflectivity profiles from xenon films adsorbed on a silver substrate. Our most recent experiments have involved studies of the layer-by-layer structure and growth of physisorbed films. Neutron diffraction experiments with a variety of hydrocarbon films adsorbed on a polycrystalline graphite substrate are being conducted at MURR,. These utilize a diffractometer equipped with a specially designed multidetector-data acquisition system. Synchrotron x- ray sources are sufficiently intense to allow structural studies of films adsorbed on single-crystal substrates. For this purpose, we have developed a unique ultra-high vacuum chamber for use at the National Synchrotron Source at Brookhaven national Laboratory. We are currently investigating the multilayer structure and growth of both rare gas and hydrocarbon films on a Ag(111) substrate.

Read more about the research done in my group.

Publications