Charged Particle Beams
Tandem Ion Accelerator
Many aspects of the research in Professor Golovchenko's group involve the use of charged particle beams of various sorts to probe and modify materials. For example many research projects take advantage of the Tandem Ion Accelerator Facility. Here ion beams with millions of electron volts of kinetic energy impinge on targets that can be studied in great detail by taking advantage of a broad range particle-solid interaction phenomena. A great deal of research has focused on understanding the fundamental physics involved in these interactions. As a result properties like scattering kinematics, scattering cross-sections, multiple scattering, stopping power, and particle excitation of inner shell x-rays has led to analysis techniques that can often provide unique insights into fundamental properties of targets under study.
Many of the thesis projects in Professor Golovchenko's group have involve the use the Harvard Tandem Ion Accelerator. Students have used Rutherford Backscattering Analysis (RBS) to evaluate materials compositions and thin film properties like thickness and homogeniety, Ion Channeling to establish the crystalline quality of molecular beam epitaxially grown surface layers, and Proton Induced X-ray emission, for very sensitive elemental analysis of various target materials. A new application of the very energetic ion beams available from the Tandem Accelerator is to assist in the creation of nanostructures using various excitation processes to influence and induce extremely small scale atomic flows in bombarded target materials.
The tandem accelerator has been used to study problems as diverse as delta doping of silicon crystals during metal mediated molecular beam epitaxy, to the variation thermal vibration amplitudes of atoms in high temperature superconductors near the transition temperature.
Focused Ion Beam Machine
A new facility recently installed near the Tandem Accelerator is the Focused Ion Beam (FIB) machine. This, state of the art, instrument provides 50 kilovolt gallium ions in a beam that can be focused down to 5 nanometers and scanned in complex partterns over a target surface. The ions from the FIB can be used to create complex structures in materials on the micrometer and even nanometer length scales. Current research with the FIB involves the generation of nanopores through sputtering and surface atomics scale flows, ion beam modification of carbon nanotubes and ion beam induced quantum dots.
A many fundamental and applied physics studies have been in the Golovchenko group aver the years. Perusal of the titles in the Charged Particle Reference list will give a brief sense of the scale of possible studies.