Starting in March 2000, we will highlight user applications as a way to illustrate new uses and to provide for communication between users. Most postings will probably be from universities and research centers, but welcome any interesting data. Our plans are to show the data, provide method information, and then links to researchers web site or email.
Our first contributor is from Professor R. Superfine's Group at the University of North Carolina at Chapel Hill. Their focus was to clean the substrates for work related to carbon nanotubes. The substrates are Si wafers and are described below. In the images shown on the left below, the thin, linear objects on the surface that are 1.5 microns or less in length and less than 100 nm in height/width are carbon nanotubes. The larger, irregularly shaped objects on the surface are particles of amorphous carbon.
In this image set, the removal of micron and submicron particles from the exact same areas on the substrates is clearly seen. The CO2 cleaning process did not remove the gold layers, but removed all of the amorphous carbon particles and the nanotubes. Subsequent work has been done to attempt to selectively remove the amorphous carbon.
Samples were approximately 1 cm x 2 cm, and were held with tweezers during the CO2 cleaning process, and the nozzle-sample distance was about 0.75 in. No precautions for moisture condesation were taken.
Dr. Superfine's research group can be reached at: http://www.physics.unc.edu/~rsuper/research
At the 1999 Boston MRS show, there was a poster session by a group associated with them, and in the higher magnification images presented there, the carbon nanotubes were clearly visible and research on their properties was discussed.
a) AFM image of multi-walled nanotubes (MWNT) and amorphus carbon deposited on a Au pattern (bright) on Si substrate (dark), before any CO2 snow jet cleaning. This sample has been UV-cleaned and rinsed with deionized water.
b) AFM image of same sample in image a AFTER three fifteen-second intervals of CO2 snow jet cleaning with a nozzle-sample distance of about 3/4".
c) AFM image of another sample with MWNT's and amporphus carbon on a Au/Si patterned surface prior to any CO2 snow jet cleaning.
d) AFM image of sample in image c after three fifteen-second intervals of CO2 snow jet cleaning with a nozzle-sample distance of about 3/4".
Another research group at NRL under Dr. Snow developed a method to clean substrates and still have the nanotubes remain. They coated the substrate and then etched the regions they wanted cleaned. Next, they CO2 Snow Cleaned those areas. Then they removed the protective layer exposing the remaining nanotubes.
