UNS: Nanowire Growth on inductively heated metal films: new reaction diagnostic and pathways towards roll-to-roll processing

Cornell University, Ithaca NY

Investigators

Abstract

1510024 (Hanrath) Semiconductor nano wires (NWs) are essential building blocks of many emerging nanotechnologies. The technological impact of NWs ranges from energy technologies, optoelectronics, and new applications emerging at the intersection of nano- and biotechnology. In the case of energy storage technologies, silicon nano wires (Si NWs) present one of the most attractive electrode materials for high-capacity lithium ion batteries (LIB). Si NWs are also poised to play a key role in emerging solar energy technologies and have garnered significant interest as electrodes in next-generation photoelectrochemical cells. Beyond energy technologies, NWs also have potential as components in a range of emerging optoelectronic and nanobiotechnologies. Multicolor light emitting diodes (LEDs) have been made possible by controlling the composition of the NW, for example, GaN, CdS, and CdSe, for ultraviolet, visible, and near-infrared emission. Precise control over the NW surface functionalization has enabled the fabrication of NW-based chemical and biosensors, including multiplexed electrical detection of cancer markers and detection of single viruses. Vertical Si NW electrode arrays have also been demonstrated as a promising platform to interface with nerve cells to enable neural prosthetics and studies of neuronal circuits in vivo. To meet the growing expectations generated by the rapid progress with NW prototypes, attention in the field is now shifting to the design of scalable and cost-effective processing methodologies. The scale-up challenge is particularly prominent in battery applications requiring high production volumes; e.g.; a 85 kWh battery for en electric vehicle would require approximately 40 kg of Si NWs for the anode. The approach to fabricate NW devices introduced in this proposal is aimed at advancing that goal. Aside from the technical considerations of NW growth mechanism and fabrication methods, there are also important environmental and health aspects to consider. Due to their small size and high mobility NWs and nanotubes have raised concerns about asbestos-like effects. The NW processing technology developed in this project grows NW directly on the current collector metal; this eliminates separate processing of the NW raw material and mitigates potential exposure steps and facilitates the direct integration into the desired device structure. Intellectual Merit: The proposed research is based on recent discoveries in the PI's lab that Si and Ge NWs can be fabricated on resistively and inductively heated metal surfaces submersed in a fluid precursor environment. This approach provides an opportunity to study outstanding fundamental scientific questions concerning the mechanism and rate-determining step of NW growth. The focus on Si NW growth on Cu films as a model systems is motivated by the technological importance of Si NWs and the prospect of advancing NW processing technique to address outstanding challenges concerning scalable fabrication and device integration. The main objective is to establish the fundamental engineering principles for NW growth on flexible substrates and to enable their processing via roll-to-roll processes. The proposed research is structured along three main aims: to (i) establish the fundamental growth mechanism of NWs grown on heated metal films, (ii) understand the complex interplay between reaction kinetics and precursor transport phenomena and (iii) analyze, design and demonstrate NW growth integrated into a roll-to-roll process. The innovative character of the proposed work is in applying resistive and inductive heating of bulk metal foils as a precisely programmable activation technique to initiate NW growth. The fast dynamic response of the reactor system presents an opportunity to gain new insights into the fundamental thermodynamics and kinetics of NW nucleation and growth. The current-voltage and temperature transients of the heated metal will be investigated as a diagnostic tool to study the dynamics of NW growth. The versatility of the reactor design could provide a foundation to spur advances in other areas of nanostructure formation at heated surfaces. Broader Impacts : The technology in this project could have far-reaching industrial applicability as well as use in medical applications. In addition,the PI will leverage established connections to K-12 programs to develop interactive learning modules. The engagement of high school teachers should have effects in illustrating nano fabrication opportunities and challenges to the next generation of scientists and engineers. The PI will work with the learning lending library of the Cornell Center for Materials Research to make the module freely available to be used in high school science classes nationwide. The educational activities will integrate scientific discoveries into the undergraduate and graduate classrooms by creating a new interdisciplinary design course; this module will provide students with the required skills to conceive, design, and evaluate the feasibility of new fabrication processes and chemical products.