Nanoscale Electric-Field Material Transfer
An ultra-high-vacuum (UHV) scanning-tunneling -microscope (STM) designed for high-stability has been developed for microscopy, spectroscopy and lithography. Construction of this instrument has included design and fabrication of all the mechanical and electrical systems necessary for a UHV STM with the unique capabilities of nanoscale surface modification and characterization. These unique features, combined with complete computer control of all microscope functions, result in an instrument with a high degree of reliability, stability, control and measurement capabilities. During the course of this project, unique measurements on an inertial positioning system were made and a new technique for rapidly determining the critical voltage for nanoscale mound formation was developed. Additionally, new and more flexible techniques for fabricating craters and controlling the size of deposited mounds with the STM under vacuum were developed. The instrument has been used to make the first quantitative characterization of nanoscale mound formation under UHV conditions. Results indicate that mound formation under vacuum with negative pulses is broadly similar to mound formation under ambient conditions. Measurements indicate that the rise-time of the pulse plays a role in the process with the results for atmosphere and vacuum somewhat contradictory. Mound formation with positive pulses is largely unsuccessful under UHV conditions, which is in marked contrast to the ambient results. Unique transient measurements of the photon emission from the tunneling junction under ambient conditions have also been made. These results are consistent with a critical electric-field initiated process that results in transfer of material between the tip and sample. The future direction of this work and its implications for device fabrication are discussed.
- Pub Date:
- MOUND FORMATION;
- SCANNING TUNNELING MICROSCOPE;
- Physics: Condensed Matter; Engineering: Materials Science