1. Aerogels for 3D Integration of Nanoelectronics
Rachel A. Berezik, Mary E. Summers, Thomas H. LaBean
North Carolina State University, Department of Materials Science & Engineering
Introduction
Methods
Conclusion
A long-term goal for DNA nanotechnology is to use DNA to enable self-assembling nanoelectronics with single electron transistors from the bottom up
Our goal is to make an electrically conductive aerogel network out of agarose and carbon nanotubes (CNT’s) for this application
Want to find percolation limit, or the concentration threshold at which there is no more conductivity
Want to make composite aerogels that show even dispersion of CNT’s, durability and other mechanical properties, and conductivity
Agarose Hydrogels:
Not widely used for this application, but proven the best among other gel materials for its economic feasibility and ability to maintain form throughout processing
3% agarose gels and CNT composite hydrogels
Vary CNT concentration around percolation limit while retaining continuous electrical conductivity
Prepared gel solution (agarose powder, water, and CNT’s), poured into mold, and let solution set
Gels were observed to be very rubbery, light-weight, and opaque before undergoing critical point dyer
Ethanol Exchanges:
This step ensures that gels are of pure condition before being placed into critical point dryer
10% ethanol increase every 1.5 hours
After reaching 100% ethanol, the gels were placed in ethanol-acetone solution
Critical Point Dryer:
Creates an aerogel by systematically removing liquid
Ethanol and acetone are standard critical point drying solvents
Resulting gels were success if they maintained size and shape, but were aerated and light weight
Need to tune CNT concentration throughout aerogels and corresponding conductivities
Want to see individual CNT’s and networks of those nanotubes touching (top figure)
Right now, seeing many of them associating with one another (bottom figure)
+ H2O + heat
Microstructure of agarose (Ao, et al.)
EtOH
CO2
Agarose with CNT contact points
Future
Apply DNA self-assembly in aerogel networks
Use single-electron transistor to create a system imbedded into aerogel network
Experiment with dispersing agents
Concentration tuning
SEM, TEM, and cryomicrotoning
air
Results & Discussion
References
Using microwave impedence spectrosopy, can characterize distribution of CNT’s in aerogel
Figure below shows CNT dispersion in aerogel with very good resolution
Individual nanotubes can be seen, but there is still clustering
wt% SWCNT in
3% agarose aerogel
wt% SWCNT in
Ao, G., Khripin, C. Y., & Zheng, M. (2014). DNA-Controlled Partition of Carbon Nanotubes in Polymer Aqueous Two-Phase Systems. Journal of the American Chemical Society, 136(29),
Brown, S., Jesperson, T. S., & Nygard, J. (2008). A Genetic Analysis of Carbon-Nanotube- Binding Proteins. Wiley InterScience, 4(4),
Mao, B., Divoux, T., Snabre P. (2016). Normal Force Controlled Rheology Applied to Agar Gelation. University de Bordeaux.
(Below percolation threshold)
(Above percolation threshold)
Objective
Using the detergent, benzene dodecylsulfonate might not be conducive to dispersion
Develop an electrically conductive CNT aerogel for long range electron transfer
Integrate DNA templated devices to create 3D electronic materials
Need to try other surfacants such as DNA oliqos with CNT affinity and diblock polypeptide, a good gelating domain and CNT-binding domain
Acknowledgements
North Carolina State University College of Engineering, NCSU Department of Materials Science & Engineering, NCSU Office of Undergraduate Research