Diamond Surface Modifications with Diazonium Salt
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0956-J11-04
Diamond Surface Modifications with Diazonium Salt Hiroshi Uetsuka, Dongchan Shin, Norio Tokuda, Kazuhiko Saeki, and Christoph E. Nebel National Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8568, Japan
ABSTRACT The growth of covalently bonded nitrophenyl layers on atomically smooth boron-doped single crystalline diamond surfaces is characterized, using cyclic voltammetric attachment and constant potential grafting by electrochemical reduction of aryl diazonium salts. We apply atomic force microscopy (AFM) to characterize nitrophenyl layer-growth and thickness. Angleresolved X-ray photoelectron spectroscopy is applied to reveal bonding arrangement of phenyl molecules and transient current measurements during the grafting is used to investigate the dynamics of chemical bonding. Nitrophenyl groups at an initial stage of attachment grown threedimensional forming layers with varying heights and densities. Layer thicknesses of up to 80 Å are detected for cyclic voltammetry attachment after 5 cycles, whereas the layer becomes denser and only about 25 Å thick in case of constant potential attachment. No monomolecular closed layer could be detected. The data are discussed taking into account established growth models.
INTRODUCTION Bio-sensor devices based on diamond attract increasing attention as diamond is known to be biocompatibility, chemical inert, shows excellent electrochemical properties and long term chemical stability of bio-molecules bonded to it [1]. To realize such devices, covalently bonded linker molecular layers are required. Grafting of a variety of substrate materials by aryl groups using the reduction of diazonium salts is a rather popular electrochemical technique [2]. Modification of metal surfaces [3], of silicon [4,5], and of many carbon materials [2,6-12] have meanwhile been performed. A few studies discuss attachment to polycrystalline boron-doped diamond [13], to ultra-nano-crystalline diamond (UNCD) [14,15], and to nanocrystalline diamond [16]. These surfaces are all relative rough and do not allow characterization on nanoscale dimensions. This is however required as the growth of phenyl layers is fast, complex and can result in multilayer formation as reported on hydrogen terminated silicon [5]. In this study, we apply cyclic voltammetric and constant potential attachment experiments to grow electrochemically nitrophenyl films on atomically smooth metallically doped single crystalline diamond. The growth is characterized using cyclic voltammograms, transient attachment currents, atomic force microscopy (AFM) in contact and tapping mode and angleresolved X-ray photoelectron spectroscopy (XPS) to reveal the detailed growth and formation properties of nitrophenyl on atomically smooth diamond surface.
EXPERIMENTAL DETAILS Boron-doped single-crystalline diamond films have been grown homoepitaxially on synthetic (100) Ib diamond substrates with 4 mm × 4 mm × 0.4 mm size, using microwave plasma-assisted chemical vapor deposition (CVD). The surface of these films i
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