9625749 Nunes This award provides support for the development of an ultrafast scanning tunneling microscope capable of investigating a wide variety of surface phenomena. In order to ensure stable and reproducible surface and tip conditions for tunneling, the microscope will be operated in ultra-high vacuum using a standard high-vacuum chamber system with a full complement of surface analysis and preparation tools. The microscope will achieve resolution on picosecond time scales using the technique of tunnel junction mixing. In this technique, the intrinsic nonlinearity of the tunnel junction between the sample and microscope in combination with an optically-launched high-speed electrical pulse, allows the detection and measurement of fast processes on the sample surface. Efforts to maximize the time resolution available with this technique, and to push towards femtosecond time scales, will require the use of nano- fabricated tunneling tips with integral photoconductive switches. Research on the design and development of these tips will be carried out as part of a collaborative effort with the University of Alberta and the Alberta Microelectronics Centre. The effort at the University of Alberta will also include the assembly of a 100 fs pulse width Ti:sapphire laser system which will first be used in the testing and evaluation of the microfabricated tips under ambient conditions, and later combined with the ultra-high vacuum tunneling microscope. The development of this instrument will open up a new dimension in scanning tunneling microscopy: The opportunity to probe systems on atomic time scales as well as atomic length scales. This capability will allow the study of a wide variety of systems, including the dynamics of defects in semiconductors and heterostructures, the nonequilibrium response of superconductors, and the dynamics of structural reconfigurations and charge transfer in optically excited molecules. The ability to carry out such stu dies will make the scanning tunneling microscope a high-resolution probe in all four (space-time) dimensions.
