Patterning Polyethylene Oligomers on Carbon Nanotubes Using Physical Vapor Deposition Lingyu Li, ² Yao Yang, ‡ Guoliang Yang, ‡ Xuming Chen, § Benjamin S. Hsiao, § Benjamin Chu, § Jonathan E. Spanier, ² and Christopher Y. Li* ,² A. J. Drexel Nanotechnology Institute and Department of Materials Science and Engineering, Drexel UniVersity, Philadelphia, PennsylVania 19104, Department of Physics, Drexel UniVersity, Philadelphia, PennsylVania 19104, and Department of Chemistry, Stony Brook UniVersity, Stony Brook, New York 11794 Received February 6, 2006; Revised Manuscript Received March 26, 2006 ABSTRACT Periodic patterning on one-dimensional (1D) carbon nanotubes (CNTs) is of great interest from both scientific and technological points of view. In this letter, we report using a facile physical vapor deposition method to achieve periodic polyethylene (PE) oligomer patterning on individual CNTs. Upon heating under vacuum, PE degraded into oligomers and crystallized into rod-shaped single crystals. These PE rods periodically decorate on CNTs with their long axes perpendicular to the CNT axes. The formation mechanism was attributed to “soft epitaxy” growth of PE oligomer crystals on CNTs. Both SWNTs and MWNTs were decorated successfully with PE rods. The intermediate state of this hybrid structure, MWNTs absorbed with a thin layer of PE, was captured successfully by depositing PE vapor on MWNTs detached from the solid substrate, and was observed using high-resolution transmission electron microscopy. Furthermore, this hybrid structure formation depends critically on CNT surface chemistry: alkane-modification of the MWNT surface prohibited the PE single-crystal growth on the CNTs. We anticipate that this work could open a gateway for creating complex CNT-based nanoarchitectures for nanodevice applications. Introduction. Periodic patterning on one-dimensional (1D) carbon nanotubes (CNTs) is of great interest from both scientific and technological points of view. Periodically patterned CNTs could lead directly to controlled two- dimensional (2D) or three-dimensional (3D) CNT supra- structures, an essential step toward building future CNT- based nanodevices. Although both chemical and noncovalent CNT functionalization have attracted extensive attention during the past decades, 1-4 very few efforts have been dedicated to periodically patterning on individual CNTs. Czerw et al. demonstrated regular organization of poly- (propionylethylenimine-co-ethylenimine) (PPEI-EI) on CNTs using scanning tunneling microscopy (STM). 5 CNT elec- tronic structure change upon attachment of polymers was also reported. 6,7 Single-stranded DNA (ssDNA) and proteins have been bound to CNTs, resulting in periodic helical wrapping on the surface of CNTs. 8-10 Helical wrapping SWNT with starch has also been reported. 11,12 Periodic patterning of functionalized SWNTs using Bingle reaction was examined by Worsley et al. using STM, and the occurrence of highly regular (periodicity ∼4.6 nm), long- range patterns was attributed to spatial fluctuation of electron density induced long-range reactivity. 13 Recently, we reported using a controlled polymer solution crystallization method to achieve periodically decorated CNTs and CNFs. 14,15 Polyethylene (PE) and Nylon 6,6 single crystals were controlled to grow on CNTs, forming a unique nanohybrid shish kebab (NHSK) structure. In a NHSK, polymer single crystals are periodically strung along the CNT axis; CNT forms the “shish” while polymer single crystals form the “kebabs”. Periodicity can be controlled easily by tuning crystallization conditions. In a solution-formed NHSK, the 2D lamellar (kebab) normal is parallel to the 1D tubes, rendering a 3D nature of the NHSK. The 3D structure is advantageous for a number of applications such as nano- composites. In other fields such as nanoelectronics, however, a 2D hybrid structure is preferred, which demands the need for an alternative means for fabricating periodic patterns on CNTs. The physical vapor deposition (PVD) technique is used widely for solid surface study. Upon heating under vacuum, metals/polymers decompose into small particles/oligomers and deposit on solid surfaces. 16-24 Gold has long been used as the evaporation source to decorate polymer surfaces to reveal fine surface topography. 16,17 PE has also been used * To whom correspondence should be addressed. E-mail: chrisli@ drexel.edu. Tel: 215-895-2083. Fax: 215-895-6760. ² A. J. Drexel Nanotechnology Institute and Department of Materials Science and Engineering, Drexel University. ‡ Department of Physics, Drexel University. § Stony Brook University. NANO LETTERS 2006 Vol. 6, No. 5 1007-1012 10.1021/nl060276q CCC: $33.50 © 2006 American Chemical Society Published on Web 04/26/2006