Preparation and characterisation of an aligned carbon nanotube array on the silicon (100) surface Jingxian Yu, a Dusan Losic, a Matthew Marshall, a Till Bo ¨cking, bc John Justin Gooding b and Joseph George Shapter* a Received 31st July 2006, Accepted 20th September 2006 First published as an Advance Article on the web 11th October 2006 DOI: 10.1039/b611016a Arrays of aligned carbon nanotubes formed by self-assembly on a Si (100) surface are described. The surface of a Si (100) wafer has been modified by reaction of hydride-terminated Si (100) with ethyl undecylenate to give ethyl undecanoate self-assembled monolayers (SAMs) which were linked by stable silicon–carbon covalent bonds. The ester terminus of the monolayer was converted to an alcohol whereupon shortened carbon nanotubes were covalently attached using carbodiimide coupling. The formation of the SAM and its subsequent modification with nanotubes has been followed using a series of techniques including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), IR spectroscopy and cyclic voltammetry. Introduction For the purpose of nanofabrication, building nanostructures and nanoelectronic devices, self-assembly (SA) is envisaged as an important avenue for fabricating and employing supra- molecular nanostructures with targeting properties. 1,2 The controlled manipulation and approach of molecules to the surface is a key feature in the development of chemical-based nanotechnology. One of the interesting approaches involves the creation of densely packed highly organised monolayers on a solid substrate. Drawing inspiration from nature, building blocks may include a wide variety of molecules such as DNA, polymers, proteins, enzymes, lipids and nanoparticles. 3,4 The most studied and the best-characterised self-assembled monolayers (SAMs) are those formed by alkanethiolates chemisorbed from solution onto gold surfaces. 5–7 They offer numerous advantages such as simple preparation, well-defined organisation, densely-packed structures and the possibility of introducing a vast number of functional groups at the mono- layer surface. 8 These unique characteristics make SAMs an excellent model system for fundamental studies in surface physics, chemistry, biology and surface engineering and offer numerous applications including: optical devices, biotechno- logy and biosurfaces, biosensors, chemical sensors, corrosion prevention, adhesion, tribology and electrochemistry. 1,8–12 Despite the interest in alkanethiols on gold their widespread technological application is uncertain due to issues related to long-term stability of the monolayers. Dynamic studies of alkanethiols on gold surfaces have revealed several serious disadvantages of the thiol–gold chemistry. Particularly of concern is their thermal instability, 13,14 influence of UV photooxidation, 15 evidence of the changing structures over time, 14,15 instability in solution, gold etching and adsorbate– solution interchange. 1,8,16 Critical evidence of the maturation of SAMs has shown that over a period of several months in air, there are dramatic changes in structure and integrity due to the oxidation process. 14,15 Other more stable monolayer systems based on new substrates and non-thiol chemistry need further development. This study will explore the fabrication of monolayers based on covalent bonds as opposed to thiol chemistry based on weaker, pseudocovalent bonds which are reversible with energies of formation of 40 kcal mol 21 . 17 Silicon is the obvious first alternative substrate to be explored where Si–C and Si–O–C bonds are generally quite strong (80–100 kcal mol 21 ) with surface rearrangement unlikely. 17 In view of the importance of silicon as the primary semi- conductor material in modern microelectronic devices, efforts to control its electronic properties and to tailor the chemical and physical characteristics of its surface are of major importance. One approach to this surface modification has been through the use of various siloxane-anchored self- assembled monolayers attached to the native silicon oxide by Si–O–C bonds. 1 A disadvantage of this approach is the presence of an oxidised layer and the low number of func- tionalised siloxanes commercially available. To avoid these disadvantages, recently the preparation of dense alkyl monolayers covalently bonded to silicon surface has been reported. 18,19 The basic approach for monolayer formation on Si substrates is based on surface hydrogenation followed by the reaction with aliphatic alkenes. It has been shown that neat 1-alkenes react efficiently with a hydrogen- terminated silicon surface. The resulting monolayer, which is linked to the surface by very stable covalent Si–C bonds, is densely packed as evidenced from infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry and wetting experi- ments. 18,20 A variety of functionalised monolayers on silicon surfaces with different lengths and functional groups on the a School of Chemistry, Physics and Earth Sciences, Flinders University, Sturt Road, Bedford Park, SA 5042, Australia b School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia c School of Physics, University of New South Wales, Sydney, NSW 2052, Australia PAPER www.rsc.org/softmatter | Soft Matter This journal is ß The Royal Society of Chemistry 2006 Soft Matter, 2006, 2, 1081–1088 | 1081