Variable temperature scanning tunneling microscopy

Variable temperature STM/STS was used over the 4.2 - 400 K temperature range to study CDW formation and spatial variations of the superconducting energy gap in Pb films. Topographic variations of the superconducting energy gap in Pb films show an intriguing transition from superconducting to normal behavior over distances much less than the bulk coherence length. More recently, efforts were focused on the development of a multi-chamber UHV-STM system that will couple a wide range of STM/STS capability with sample and tip preparation and characterization facilities. The first chamber of this system is fully functional and is being used to study and modify semiconductor surfaces. Other chambers will be specialized for STM nanolithography and cryogenic UHV-STM. This system accommodates UHV sample and tip transfer between chambers in addition to independent chamber operation modes. STM modification of H-passivated silicon surfaces was accomplished using techniques developed at NIST. A unique STM lateral coarse translation system was developed and used to locate and modify SiMOSFET structures fabricated for this project. Gratings written by STM within the gate region are being evaluated for the creation of finished devices that will exhibit quantum interference effects at higher temperatures than previously observed. Work is also underway to fabricate planar tunnel junction structures that utilize coulomb charging effects to realize logic functions.