Imaging quantum and other small-size effects at nanostructure contacts Jon Pelz and Steve Ringel, DMR-0076362, DMR-0505165 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). AlG aAs AlG aA s A u film AlG aAs AlG aA s A u film G aA sQ W d (nm ) 0 2 4 6 8 10 12 14 16 B H (eV ) 0.90 1.00 1.05 1.10 m odel AlG aAs m easured d (nm ) 0 2 4 6 8 10 12 14 16 B H (eV ) 0.90 1.00 1.05 1.10 1D Q W m odel W ith pinning effects AlG aAs G aA s m easured Q W width d (nm) (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. 100 nm (a) 100 nm (b) (a ) (b ) (c ) (d ) Prob e Tip Phys. Rev. Lett 94, 206803 (2005).