Brown University Students Earn Inaugural Outstanding Journal of the SID Student Paper of the Year Designation

Four years of work results in an award-winning paper on the development of carbon nano-structures fabricated using liquid-crystalline materials as a carbon precursor.

by Matthew Sousa, Sylvain Cloutier, Kengqing Jian, Christopher Chan, and Bevan Weissman

AT the heart of every academic research team is a core group of students and advisors driving the research forward. The most effective teams are those strengthened by a constituency with diverse strengths, backgrounds, and levels of experience. Such was the case with an interdisciplinary team at Brown University, led by Professors Gregory Crawford and Robert Hurt, which collaborated on a project involving the synthesis of carbon nanostructures using liquid-crystalline materials. Their key asset was their student team: electrical-engineering graduate students Matthew Sousa and Sylvain Cloutier, chemistry graduate student Kengqing Jian, and chemical-engineering undergraduate students Christopher Chan and Bevan Weissman (Fig. 1). Their work culminated in the development of carbon nanostructures fabricated using liquid-crystalline materials as a carbon precursor. The results of their efforts were published in an article entitled "Pen-Writable Nanocarbon Arrays Fabricated Using Liquid Crystalline Materials for Potential Use in Displays," which appeared in the September 2005 issue of the Journal of the Society for Information Display (JSID). The work has culminated in the awarding of the inaugural Outstanding JSID Student Paper of the Year to the student authors.

The initial seeds of the project began in 2001 as a collaboration between Professors Crawford and Hurt at Brown University, experts in their respective fields of liquid crystals and materials. Their initial studies focused on the fabrication of nanomaterials using viscous carbon mesophase pitch materials. Jian led the initial experimental work. Difficulties were encountered with the pitch materials as the researchers struggled to overcome the materials' high viscosities and melting temperatures. Pursuing similar materials, Chan joined the research effort and began investigating discotic liquid-crystalline materials originally designed for the fabrication of liquid-crystalline polarizers demonstrated by Optiva, Inc.¹ Working together, the two students successfully fabricated carbon nano-tubes using these materials in nanochannel templates.

The initial work on these materials, as well as discussions between Professors Crawford and Hurt, resulted in Sousa, a graduate student in Brown's Display and Photonics Lab, joining the research team. Sousa's efforts stemmed from his interest in field emitters for display applications; following discussions with Professors Crawford and Hurt, all involved had high hopes for these nanotubes as a potential material for this application. Because the material they were using was liquid crystalline at room temperature, it could easily be printed in patterns in a nanochannel template, similar to ink from a pen on a piece of paper. Figure 2 shows the process, where an ink-jet printer or fluid dispenser locally infiltrates the nanochannel templates and the aqueous solution evaporates, leaving behind a thin layer of the dried precursor on the walls of the templates. The materials are then carbonized at 700°C, and the template is subsequently etched away, leaving patterned arrays of nanotubes, also shown in Fig. 2. Sousa began working with Jian to fabricate various patterned nanotube arrays using a variety of discotic liquid-crystalline precursors.

Largely due to the alignment of the precursor at the template wall, the initial tubes fabricated displayed poor electrical properties, greatly diminishing their potential effectiveness as field emitters. But they presented interesting physical results warranting further investigation. Initial analysis of the structures by TEM (conducted by Nancy Yang at Sandia National Laboratories) revealed that the graphene layer orientation of the nanotubes was significantly different from the orientation of the graphene layers in a typical nano-tube fabricated using more conventional methods, such as chemical vapor deposition.

In conversations with fellow electrical-engineering graduate students regarding the characterization of carbon nanotubes, the group enlisted the expertise of Cloutier, whose research focused on Raman spectroscopy of nanotubes. The group began examining their samples and collected spectra similar to those of more conventional carbon nanotubes, indicating the presence of nano-tube-like structures containing highly disordered graphene planes. At the same time, Weissman began working with the group as they began focusing on methods to alter the alignment of the graphene planes of the nanotubes and obtain a more conventional graphene orientation, targeting better electrical performance for device applications. They were able to use a combination of discotic liquid-crystalline precursors – a lyotropic liquid-crystal dye was used as an alignment layer for discotic pitch molecules. Molecular interactions between these two materials "flipped" the orientation of the graphene planes so they were parallel to the long axis of the structure. Further examination by TEM and Raman spectroscopy confirmed the expected results. Currently, the group is further investigating the electrical properties of these modified nanostructures for field-emitter applications.

This research effort, pushed to success by collaboration among the outstanding student researchers, represents the power of the academic-research environment. The collective knowledge, strengths, and expertise of all academicians involved, as well as the fresh ideas and approaches provided by graduate students, are what feed the university research enterprise. The Outstanding Student Paper of the Year designation was created by the Society for Information Display (SID) to recognize exemplary research efforts by students at both the graduate and undergraduate levels. The Brown University team has already demonstrated their worth in this regard and earned their place as the inaugural recipients of this award. Their continued research efforts along this vein of interest, as well as many others they might pursue, will be invaluable to the display industry and scientific community.

The student researchers are now off furthering their career: Matthew Sousa has taken a position as a postdoctoral research fellow at Case Western Reserve University; Sylvain Cloutier has taken a position as an assistant professor of electrical engineering at the University of Delaware; Kengqing Jian is working as a postdoctoral research fellow at Brown University; Christopher Chan now attends graduate school at the University of Pennsylvania; and Bevan Weissman is finishing his undergraduate degree in chemical engineering at Brown.

References

¹T. Fiske, L. Ignatov, P. Lazarev, V. Nazarov, and M. Paukshto, SID Symposium Digest Tech Papers 33, 866 (2002).
²S. Remizow, A. Krivoshchepov, V. Nazarov, and A. Grodsky, Mol. Mater. 14, 179 (2001). •

Fig. 2: (a) A schematic illustration of the process used to pattern the liquid-crystal precursor on top of the anopore templates. (b) SEM image of nanotubes patterned using the liquid-crystal precursor. The inset is an optical microscope image of a patterned array of nanotubes.