Quebec and Canadian Studies at Vanderbilt University

The collaborative effort of the Hertel group at Vanderbilt with the Martel group at the University of Montreal aims at the fabrication of thin transparent films made of semiconducting or metallic single-wall carbon nanotubes (SWNTs) with enhanced optical and electronic properties. The electronic behavior of SWNTs has captured the imagination of researchers over the last 15 years owing to their potential for a variety of technologies, from the fabrication of molecular field effect transistors and light emitting devices over composite materials with unique mechanical and electrical properties, to host materials for a number of applications such as Li-ion batteries or supercapacitors and fuel cell membranes. Some of the most promising envisioned applications of carbon nanotubes draw on their unique electronic properties inherited from their parent material graphene, making SWNTs either semiconducting or metallic depending on tube chirality and diameter. However, currently available synthesis schemes produce a more or less polydisperse mixture of metallic and semiconducting carbon nanotubes. The separation of such samples into purely semiconducting and purely metallic fractions is thus been one of the grand unresolved challenges in the field of carbon nanotube research. 
Success in this direction has only been made recently using electrophoresis or ion exchange chromatography. Unfortunately these techniques are either prohibitively expensive or don’t lend themselves to larger scale purification. However, we have recently implemented a new technique for isolation of specific types of semiconducting tubes as well as for the isolation of semiconducting tubes from polydisperse samples in cooperation with collaborators from northwestern University. This technique employs protocols normally used for separation of proteins. More specifically, we use preparative ultra-centrifugation of surfactant stabilized SWNT suspensions in density gradients for the separation of SWNTs by buoyancy. Co-surfactant competition for adsorption sites can also be used to separate highly polarizable metallic tubes from semiconducting ones. 
Within the planned collaboration we intend to combine our expertise with the fabrication of structurally and metallicity sorted SWNT suspensions with the expertise of the Montreal group in making transparent thin films from such suspensions. The combination of the two is expected to facilitate the fabrication of SWNT based thin film transistors as well as the fabrication of films for transparent conducting substrates with equivalent electro-optical but superior mechanical properties if compared with today’s most frequently used commercial ITO substrates. 
The proposed collaboration will be carried out in three stages: a) a 2 month visit of a Vanderbilt graduate student with the Martel group in Montreal during which he will transfer know-how on the fabrication of metallic and chirality enriched nanotube suspensions. At the same time he will learn from the Montreal group how to make transparent thin films from these suspensions. b) in the second stage of this collaboration both groups will be in close contact regarding the experimental characterization of the films fabricated during the two month graduate student visit. The optical characterization will be done mostly at Vanderbilt University using CW and time-resolved optical spectroscopy from the UV to NIR range of the spectrum. The electrical properties of these films will be characterized by the Montreal group. The films will also be used for the fabrication of light emitting devices. c) the third stage is dedicated to dissemination of the results. To this end Prof. Hertel will use some of his sabbatical in the spring of 2008 for two or more one week visits to Montreal for final discussions and the writing of joint publication(s).
If successful we foresee that the collaboration will spin off a number of further research projects with emphasis on applied aspects of the fabrication of transparent conductive or semiconducting thin films from SWNTs for future nano-electronic devices.