Session C01: CMP + Materials 1: Materials Growth Techniques

Synthesis of Platinum Nanoparticles and the Catalyzed Production of Hydrogen

With the recent excitement to find alternatives to fossil fuels, hydrogen fuel cells have been considered as a possibility. Yet hydrogen fuel cells are not yet a very good option, due in part to hydrogen most commonly and easily being produced in connection with fossil fuel use. This has spurred research, including our own, into finding novel ways to produce hydrogen gas that doesn't involve fossil fuels. We are investigating a system for hydrogen production that utilizes Ferritin, an iron storing protein found in all animals, and methyl viologen, an herbicide. In a light catalyzed reaction with Ferritin acting as a semi-conductor, platinum ions are reduced to form small, roughly 2 nm in diameter, platinum nanoparticles. We've successfully synthesized, separated, characterized, and imaged platinum nanoparticles using this process. To produce hydrogen gas, we have attempted, unsuccessfully, to reduce methyl viologen and use reduced methyl viologen to reduce hydrogen gas with platinum nanoparticles acting as catalyst. This part of our system is being investigated and refined.   

A chemical vapor deposition growth study to grow 700+ um Carbon Nanotube-based neural probes.

A new approach to neural probe arrays using Carbon Nanotube (CNT) Templated Microfabrication produces probes that would be smaller and more compliant than existing technologies. Tall probes on the order of one to two mm are essential to effectively communicate with the brain. My research has involved a CVD CNT growth study to ensure consistently tall probes. I used a fractional factorial method and a SAS program called JMP to test the effects of four different factors on CNT growth height. Over a 100+ man hours, I tested the effect of gas flow rate, Fe catalyst thickness, H2/C2H4 ratio, and temperature on CNT forest height. By statistical analysis, we determined that gas flow rate and Fe thickness have the largest effect on CNT forest growth. We are now able to consistently grow neural probe samples at 700 um and higher, which are sufficient for our needs at this time.   

An Investigation of MPCVD Synthesis of Boron-rich BN

Boron-rich Boron Nitride (BN) is a material with high hardness that has often been synthesized by methods that involve high pressure and high temperature. Microwave Plasma Chemical Vapor Deposition (MPCVD) was utilized to nitride a deposited Boron layer on a Silicon substrate using Hydrogen (𝐻2), Diborane (𝐵2𝐻6), and Ammonia (𝑁𝐻3) at pressure and power of 60 Torr and 800 W respectively. By analyzing the Optical Emission Spectra of the process at fixed conditions, it is found that a low flow rate of Ammonia (≤1 𝑠𝑐𝑐𝑚 𝑁𝐻3), along with a high flow rate of Diborane (≥2 𝑠𝑐𝑐𝑚 𝐵2𝐻6), would be helpful in synthesizing Boron-rich thin films. Characterization of different films synthesized found a maximum hardness of 25 GPa from nanoindentation and similar patterns in the substrate shown by optical microscopy, AFM, and SEM. By utilizing OES and characterization results, conditions for Boron-rich BN have been investigated. It is suggest that a five stage process to deposit the Boron layer and nitride it to complete the deposition of BN would be the most effective to maximize the B/N ratio at a starting temperature of 1250° C.   

Tungsten Atomic Layer Deposition on Vertically Aligned Carbon Nanotubes

Vertically Aligned Carbon Nanotubes (VACNTs) can be grown from two-dimensional patterns into three-dimensional structures using lithographic and chemical vapor deposition techniques. These porous, low-density structures can then be filled, or infiltrated, with other materials to impart unique properties to the structure. Depending on the filler material, the resulting composite structure may have many applications such as metal MEMS devices. Many of the challenges of infiltration into nano-porous materials can potentially be overcome through Atomic Layer Deposition (ALD) processes. Tungsten, with its conductivity, high thermal resistance, and high density, is of special interest to us. Tungsten ALD, using Silane and Tungsten Hexafluoride precursors, is used to fill VACNT structures. In contrast to near ideal ALD processes, the tungsten film deposited with each cycle becomes non-self-limiting at large precursor exposures, leading to a larger growth-per-cycle [>5 Å per cycle] than many other ALD processes. The precursor transport and surface reactions occur in the diffusion-limited regime, leading to non-uniform deposition at shorter dose times. With appropriate tuning of three-dimensional feature size and dose times, a near solid structure can be formed.