Imaging quantum and other small-size effects at nanostructure contacts

1. Imaging quantum and other small-size effects at nanostructure contacts Jon Pelz and Steve Ringel, DMR-0076362, DMR-0505165 100 nm (a) 100 nm (b) Probe Tip (d) (c) (b) (a) (a) Schematic of gold/quantum-well nanocontacts. (b) Image of top gold (Au) surface, showing small gold grains. (c) BEEM image, revealing the buried quantum well contacts. (d) Data points: measured Schottky Barrier Height (SBH) vs. quantum-well width, showing strong size effects. Lines are model predictions. There is great interest in making new kinds of electronic devices using semiconductor nanostructures. Nanometer-sized metal contacts are necessary for most nanostructure devices to function, but little work has been done to measure how small size effects at contacts (such as quantum confinement) affect device behavior. We are developing Ballistic Electron Emission Microscopy (BEEM) to directly image and quantify small-size effects at nanocontacts. This was tested on a cleaved quantum well (QW) heterostructure (see Fig. (a)) which had gold/QW contacts as narrow as 1 nm. Figure (b) shows the measured top surface of a thin gold film (the bumps are small gold grains) while Fig. (c) shows the simultaneously measured BEEM image, revealing the buried gold/QW contacts. BEEM can measure (with nm-scale resolution) the local Schottky energy barrier at the gold/QW contact, which controls how electrons move from the gold film into the QW nanostructure. Fig. (d) shows that this energy barrier increases strongly as the QW width is made narrower. We can understand this increase as a combination of quantum-confinement effects (green line) modified by a small reduction due to nm-scale “pinning” effects (red line). We will next study how the transmission efficiency is affected by small-size effects, and then apply this tool to other nanostructure systems. Phys. Rev. Lett 94, 206803 (2005).

2. Imaging quantum and other small-size effects at nanostructure contacts Jon Pelz and Steve Ringel, DMR-0076362, DMR-0505165 Artwork from 5th student Hannah: Spiked heal, elephant foot, bed of nails, liquid-nitrogen rocket help to understand pressure. “… It’s marvelous how science and technology work together to revolutionize the way we live.” Demonstrating conservation of energy and momen-tum before the 6th grade Science Proficiency test. Education: Three undergraduate REU students (Adam Champion, Sylvia Schaepe, and Corey Campbel) and two graduate students of Jon Pelz (Kibog Park, and Cristian Tivarus) contributed to this work. Sylvia and Corey have both gone on to graduate school, while Adam continues his undergraduate studies. Outreach: In addition to giving lab tours to high school students and other visitors, the PI presents yearly Physics demonstrations in elementary school classrooms (1st – 6th Grade), and has worked with elementary school teachers to help prepare them (and their students) for the Ohio State Proficiency Test. See for example: http://www.physics.ohio-state.edu/ outreach/gallery/Cassingham2-04/index.htm From visit to a 2nd grade classroom. The air in the balloon will soon “shrink” in liquid nitrogen.