In this project a two-tip scanning tunneling microscope (STM) of a new design, never considered before, will be developed. In this design the two tips probe a very thin sample from opposite sides. In addition, another two-tip STM will be designed in which the two tips probe the sample in a more conventional geometry, with both tips on the same side of the sample. Nanotube tips recently developed by the investigator enable these designs. Nanotube tips may be ideal for spin-polarized tunneling, as well as for a host of scientific and practical applications that can benefit from a coherent point source of spin-polarized electrons. The two-tip STM will make possible new experiments that will probe the Green function of the sample material, so that one can get detailed information on semiconducting or metallic samples such as mean free path, the phase and energy dependence of scattering from impurities, details of the band structure, and the transition from the ballistic to diffusive transport. This instrument can also probe the symmetry of the order parameter in a superconductor, so that refinements of the current d-wave picture can be obtained for high temperature superconductivity. Graduate and undergraduate students will participate in this project. They will benefit from training in advanced instrumentation and techniques, in the development of the novel STM instrument, and from using it to probe the behavior of electrons in the most detailed fashion yet available.
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Microscopes with ever increasing ability to probe small details have been major instruments in advancing our understanding of the microscopic structures and behaviors of materials. Scanning tunneling microscopes (STMs) are the latest types of such instruments that now allow the probing of materials at the atomic level of dimensions. In this project, a new type of STM, based on the use of two, rather than one, probe tips will be developed. One version will have the two tips on opposite sides of a very thin sample, a geometry that has never before been even contemplated. A second version of the two-tip STM will be of a more conventional geometry, in which the two tips are on the same side of the sample. Both versions can be realized on the basis of probe tips, which are atomically sharp needles (carbon nanotubes), that were recently developed in the investigator's laboratory. Such two-tip STMs will allow a new set of investigations of the properties of materials, including high temperature superconducting compounds that will result in a better understanding of their structure and behavior. These results will ultimately be of use and benefit to technology. This project will involve the participation of graduate and undergraduate students. They will thereby acquire knowledge and skills in a very active contemporary area of condensed matter physics and materials science. These will enable them to be productive members of the scientific/technological workforce of the next few decades of this century.
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