Surface Decontamination of Carbon Nanotubes

Paul Su^a,*, Ashkan Vaziri^b, Syed Hassan^b, William W. Doerr^a, and Babak H. Jahromi^b

^a FM Global, Norwood MA, 02062 USA

^b Department of Mechanical and Industrial Engineering

Northeastern University, Boston MA, 02115 USA

* Corresponding author: pocheng.su@fmglobal.com

The ever increasing production and applications of carbon nanotubes (CNTs) and the emergence of related hazards have created a demand for developing surface decontamination techniques for carbon nanotubes.^1,2 CNTs surface contamination can happen due to accidental release or the gradual accumulation during the processing, transport, or storage of CNTs.^3,4,5 In this presentation, first, we provide an overview of two surface decontamination methods of CNTs: the solvent cleaning method and the UV/ozone cleaning method, and highlight the relative advantages and disadvantages of each technique.⁵ Then, we discuss our experimental results on quantifying the removal efficiency of different solvents for surface decontamination of silicon wafers coated by multi-walled CNTs. In our experiments, first CNTs in the form of pristine liquid solution were deposited on the surface of a silicon wafer.  The CNT deposited wafers were then heated to make sure all solvent molecules are evaporated off the wafer surface (confirmed by SEM imaging). The area concentration of CNTs was measured by post-processing of at least 30 images (per wafer) taken from different parts of the wafer after the coating process. The cleaning process was comprised of two stages: First, a sufficient amount of cleaning media was sprayed on the surface of the wafers and the wafers were given fixed time  to let the cleaning media reach deep into the CNT bundles and the surfactant micelles form. Next, the wafers were manually wiped once with a piece of non-woven polyester/cellulose fabric with known pressure and duration. The cleaned wafers were SEM imaged using an imaging process similar to the imaging performed on the initial wafers to obtain the final areal density of the wafers. The removal efficiency was defined as the difference between the initial and the final CNT area density. The experiments were repeated using dry wipe and different cleaning media, including pure water, two surfactants, and a nature agent. The removal efficiencies of these methods can be quantified. To explore the role of surface micro-topography on the CNT efficiency removal for each solvent, we repeated the experiments for silicon wafers with different patterned surfaces. First, the coarse surface features were created using mask aligner and inductively coupled plasma (ICP). Then, the CNT efficiency removal was characterized for different solvents using the procedure discussed above.

Keywords: Carbon nanotubes, surface decontamination, surfactants.

References:

1. National Institute for Occupational Safety and Health (NIOSH), Department of Health and Human Services, Center for Disease Control and Prevention (CDC),  “Progress Toward Safe Nanotechnology in the Workplace”, November 2009.

1. Technical Report, ISO/TR 12885: 2008(E), “Nanotechnologies – Health and safety practices in occupational settings relevant to nanotechnologies”, First edition, October 2008.

1. “Standard Guide for Handling Unbound Engineered Nanoscale Particles in Occupational Settings”, ASTM Standard E 2535 – 07, 2007, ASTM International, PA, United States.

1. Ma-Hock, L., Treumann, S., Strauss, V., Brill, S., Luizi, F., Mertler, M., Wiench, K., Gamer, A.O., Ravenzwaay, B. V., Landsiedel, R., “Inhalation toxicity of multi-wall carbon nanotubes in rats exposed for three months”,  Toxicological Sciences, 112(2), 468-481, 2009.

1. Su, P., “It’s a Small World”, Reason – Issue 3, September 2010, FM Global Research, Norwood, MA.