NIRT: Bottom Up Assembly of Metal and Semiconductor Nanowires: Fundamental Forces to Nanoelectronic Circuits

NIRT: Bottom Up Assembly of Metal and Semiconductor Nanowires: Fundamental Forces to Electronic Circuits

Abstract

This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 02-148, category NIRT. The technical goal of this project is to enable bottom-up assembly of nanoparticles by controlling fundamental forces. Compared with top-down nanoparticle assembly, bottom-up assembly provides an inexpensive route to making bulk quantities of nanomaterials, including high-density nanoelectronics. Promising methods have been developed by one of the investigators to produce nanoassemblies using bead templating assembly and DNA-directed bead templating assembly. By engineering the fundamental forces (e.g., van der Waals, solvation, depletion), this proposal seeks to minimize undesired aggregation and control either nondeterministic or deterministic assembly. The principles of fundamental nanoparticle forces learned in this research will be tested in the construction of a functional logic circuit based on quantum mechanical ideas, and the same principles will provide a basis for scaling up production quantities of this circuit.

The logic circuit to be built consists of hexagonal or square arrays of semiconductor nanowires (e.g., silicon, gallium arsenide), with metal (e.g., gold, platinum) gate wires. This project has five objectives. 1) Simple versions of the device will be built with larger wires at the Penn State Nanofab Facility, using electrofluidic techniques. This will enable development of circuit testing procedures required for later tests with the circuit built using directed assembly. 2) A non-deterministic bead templating technique will exploit physical forces (e.g., electrostatics, steric, solvation) to assemble from the bottom up various types of functional nanowires. Essential to this work is the screening of co-solvent/particle systems that aggregate uncontrollably, and this will benefit greatly from phase diagrams simulated with molecular level simulations. 3) Unique sphere-rod interparticle force measurements will synergize with molecular dynamics simulations to produce predictive models and heuristics that will be broadly applicable in stabilizing nanoparticle dispersions, for instance by minimizing van der Waals forces and maximizing the stabilizing solvation forces. 4) Bead templating with DNA-directed assembly will be combined with the heuristics from the third objective to guide assembly while preventing undesired particle interactions as the DNA links the nanowires in the desired configuration. The undesired aggregation has been a critical barrier to otherwise very promising techniques. In both subprojects 2 and 4, the circuits will contain chemical specificity that enables, for instance, metal-semiconductor junctions, facilitating objective 1, because the nanocircuits will need to connect to instrumentation large enough to take useful measurements.

The broader impact resulting from this project will be improved public ability to make 'nano' decisions through hands on experience. Nanotechnology has many new capabilities, some, which will be unfamiliar to even the technologically, educated public. It is imperative that the public have sufficient experience with nanotechnology to make ethical and voting decisions. In order that the public gain 'hands on' experience with nanotechnology, we will conduct semi-annual workshop booths at the 'Central Pennsylvania Festival of the Arts' in State College, Pennsylvania. This event attracts approximately 200 000 participants annually, providing an extremely public forum. The hypothesis to be tested is that as the public participates, their comfort in accepting the technology and voting on decisions will be enhanced.

Another important activity will be to 'teach teachers to teach nano', building the knowledge of State College Pennsylvania k-12 teachers using 'research experience for teachers'-type programs to leverage our own expertise into local students and their parents. For this part of the course, summer lab work with local k-12 instructors will enable the development of interactive modules for use in the classroom.