Professors Marco Rolandi and Scott Dunham of the University of Washington are receiving an award from the Macromolecular, Supramolecular and Nanochemistry Program to explore both experimentally and computationally the synthesis of nanomaterials spatially confined in the region around the tip of an atomic force microscope (AFM). Accurate placement control during nanomaterial synthesis is critical for device integration and applications in electronics and optoelectronics. The region between the tip of an AFM and a sample constitutes a unique nanoscale environment where highly localized zeptomolar chemical reactions occur. A recent approach involves applying a moderate (~10 V) bias across the tip-sample gap containing ad-hoc liquid precursors. Tip sample proximity exposes the precursor molecules to electric fields in excess of 109 V/m, as well as tip field emitted electrons with current densities as high as 107 A/m2. This strategy has already demonstrated the spatially confined synthesis of carbon and semiconductor nanowires, but a clear understanding of the nanoscale chemical reactions leading to these nanomaterials is still lacking. The awarded project focuses on understanding the fundamental processes occurring near the tip/sample gap during nanomaterials synthesis by creating physically based models of the system. In this integrated approach, the modeling and experimental efforts proceed synergistically, with the measured behavior suggesting possible models and the resulting models used for refining the characterization. Results from this work are expected to lay the foundations for a strategy, broadly applicable to spatially controlled nanomaterial synthesis, that enables novel nanodevices design.
Lack of spatial control in synthesis processes is a recognized bottleneck in the investigation of nanomaterials and structures at the nanometer scale. The facile nano-confined chemistry of this project is applicable to a broad range of materials, thus impacting nanoscale science and the development of nanomaterials technological applications. From the environmental standpoint, this novel approach does not require use of abundant quantities of polymer based sacrificial layers, nor the contamination of gallons of water for photoresist processing, as is the case in the widely adopted radiation-based lithography. Educational efforts in this project include making nanoscale science and computer modeling accessible to a broader scientific community including undergraduate institutions, community colleges, middle and high schools. The latest experimental results and modeling tools are projected to be included in courses at both the undergraduate and graduate levels. High school teachers and undergraduate students are routinely hosted at the Center for Nanotechnology laboratories, as part of the RET and REU existing programs.
Intellectual Merit: Researchers have developed a novel approach for the localized synthesis of silicon and germanium nanostructures with deterministic placement and geometry control. Potential applications of these semiconductor nanostructures include electronic circuits and photovoltaics.This synthesis occurs through the reaction of organometallic precursors at the interface of the biased tip (< 10 nm radius) of an atomic force microscope and the sample. The tip is translated with nanometer precision to create desired geometries, which include lines, dots, and gratings ranging from a few nanometers to several microns. This strategy is also coupled with an inexpensive stamping method for large area fabrication. This method uses a soft conducting stamp made of silicone polymer that is pressed onto the substrate with a clamp, or for wafer scale fabrication with a reporpused mask aligner. The results from this research include a deeper understanding of the kind of chemical reactions occuring during this lithography process to allow for better use of this process and expand the materials libray to other inorganic semiconductors including doped materials. Broader Inpacts: Current nanoscale fabrication often involves top-down processes that effectively chisel the nanocomponents. During this process the majority of the material is disposed of and goes to waste. This strategy builds nanoscale components from the bottom-up with precise geometry control. Only the required precursor is used in the synthesis process, the rest can be recycled. In this fashion, nanostructure fabrication with low energy consumption and low waste disposal can be developed.
