Picometer Probes for Defects in Nanostructures

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Nanometer scale wires (nanowires) made out of almost every material has attracted tremendous attention over the past ten years. A major reason is their ease of growth, and the many demonstrations of novel devices and unique properties. Intriguing are the quantum size effects whereby materials with nanoscale dimensions develop different properties compared to their bulk. The increased speed and efficiency of two-dimensional quantum devices made with semiconductors, such as silicon and gallium arsenide, has already been driving progress in the electronics industry for decades. The growth of three-dimensional, semiconductor nanowires, is enabling further developments in novel device and circuit design. Nanowires are too tiny to be seen with an optical microscope and therefore, many of their structural properties have been revealed through various types of electron microscopies. But their most important properties are controlled by their atomic point defects - missing atoms, impurity atoms, or atoms in between the rows of the crystalline matrix. In the research proposed here, we will apply picoscale probes to determine the complete atomic picture of novel semiconductor nanowires. In particular, we will apply the latest in aberration-corrected transmission electron microscopy (new facility at U. Victoria). This machine has a resolution of 35 picometers, capable of peering into the spaces between atoms. We will apply the associated technique, electron holography, to map the electrical activation in nanowires and measure magnetic fields at nanowire ferromagnetic contacts. We will establish a transmission helium ion microscopy facility and use coherent helium atoms to probe bulk and surface defects. Helium ions and neutral atoms are 35 - 90 picometers in diameter, easily capable of passing in between rows of atoms. We will collaborate to access atom probe tomography, a technique that can map the elemental identity of every atom within a nanowire. We will complement these tools with existing macroscopic characterization techniques, including in-situ electrical and optical excitation, scanning tunneling microscopy, and ballistic electron emission microscopy. Seeing point defects and their movements directly in materials is becoming a possible dream. The proposed research program will help confirm theoretical predictions about their presence in novel semiconductor nanowires. Identification is fundamental to the control of nanowire electronic properties. New understanding invariably leads to innovation, engagement with existing Canadian companies, and eventually to the establishment of new industries in Canada. If successful, the novel semiconductor nanostructures investigated in this research will impact the telecommunications, advanced lighting, solar energy, and information technology industries in Canada and elsewhere. Three-dimensional geometries are critical to continued increases in integrated circuit densities a billion dollar industry which Canada plays a roll. The proposed research is internationally cutting edge, an activity that easily attracts new students and post doctoral fellows to the field.