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ABSTRACT: A lithographic method to generate reactive thiol groups on functionalized synthetic diamond for biosensor and molecular electronic applications is developed. We demonstrate that ultrananocrystalline diamond (UNCD) thin films covalently functionalized with surface-generated thiol groups allow controlled thiol-disulfide exchange surface hybridization processes. The generation of the thiol functional head groups was obtained by irradiating phenylsulfonic acid (PSA) monolayers on UNCD surfaces. The conversion of the functional headgroup of the self-assembled monolayer was verified by using X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and fluorescence microscopy. Our findings indicate the selective generation of reactive thiol surface groups. Furthermore, we demonstrate the grafting of yeast cytochrome c to the thiol-modified diamond surface and the electron transfer between protein and electrode.
Langmuir 10/2010; 26(20):15895-900. · 4.19 Impact Factor
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ABSTRACT: We have characterized ultrananocrystalline diamond films with different surface terminations by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The surface terminations were performed by plasma functionalization in atmospheres of hydrogen, fluorine, and oxygen. XPS proves the dense monolayer coverage of the surface functionalization. AFM and STM show low impact of the plasma treatment on the surface morphology. STS has been used to investigate the surface electronic properties, for H-terminated surfaces the electronic structure is dominated by the sp3 carbon phase of the grain surfaces; for O- and F-terminated surfaces, however, sp2 carbon from the grain boundaries seems to determine the surface band gap.
Applied Physics Letters 03/2010; 96(9):092109-092109-3. · 3.84 Impact Factor
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ABSTRACT: Reaction of disperse ultrananocrystalline diamond (UNCD) and mixtures of UNCD containing 10%–20% nanoboron carbide ( B <sub>4</sub> C ) with methane gas at temperatures near 1200 K results in mechanically rigid compacts called nanocarbon ensembles (NCE) and boron-doped NCE, respectively. Seebeck coefficient and electrical conductivity results lead to strongly temperature dependent power factors that increase 30–40 fold for boron containing ensembles compared to undoped material. It is likely that boron substitutional doping of nanographite crystallites results in a multiplicity of electronic states within a narrow energy band around the Fermi level leading to an increase in configurational electronic entropy.
Applied Physics Letters 05/2008; · 3.84 Impact Factor
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ABSTRACT: In this work, a facile method for the preparation of structured and functional polymer grafts on diamond surfaces is described. Uniform poly(styrene) (PS) grafts with a thickness of approximately 110 nm were created directly onto oxidized ultrananocrystalline diamond (UNCD) surfaces by the self-initiated photografting and photopolymerization of bulk styrene with UV irradiation. The stable covalent bonding of the PS grafts allows polymer analogue reactions with drastic reaction conditions without noticeable detachment of the polymer coating. Thus, various functionalities, such as nitro, sulfonic, and aminomethyl groups have been successfully incorporated to the polymer grafts. Furthermore, the reactivity contrast between hydrogenated and oxidized UNCD surfaces allows for the preparation of structured polymer grafts. Finally, we have demonstrated the good reactivity and accessibility of the incorporated pendant functional groups.
Journal of the American Chemical Society 01/2008; 129(50):15655-61. · 9.91 Impact Factor
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ABSTRACT: We have investigated the formation of self-assembled monolayers (SAMs) of 4'-nitro-1,1-biphenyl-4-diazonium tetrafluoroborate (NBD) onto ultrananocrystalline diamond (UNCD) thin films. In contrast to the common approach to modify diamond and diamond-like substrates by electrografting, the SAM was formed from the saturated solution of NBD in acetonitrile by pure chemical grafting. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and near edge X-ray absorption fine structure spectroscopy (NEXAFS) have been used to verify the direct covalent attachment of the 4'-nitro-1,1-biphenyl (NB) SAM on the diamond substrate via stable C-C bonds and to estimate the monolayer packing density. The results confirm the presence of a very stable, homogeneous and dense monolayer. Additionally, the terminal nitro group of the NB SAM can be readily converted into an amino group by X-ray irradiation as well as electrochemistry. This opens the possibility of in situ electrochemical modification as well as the creation of chemical patterns (chemical lithography) in the SAM on UNCD substrates and enables a variety of consecutive chemical functionalization for sensing and molecular electronics applications.
Journal of the American Chemical Society 01/2007; 128(51):16884-91. · 9.91 Impact Factor
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ABSTRACT: We have studied the electrochemical impedance spectroscopy of conductive ultrananocrystalline diamond (UNCD) modified by either oxidation or hydrogenation surface treatments. The impedance was measured in the frequency range from 0.1 Hz to 40 kHz at different DC voltages and the results fitted to an equivalent electrical circuit. Despite the complexity of the conductive UNCD surface, composed of sp3-bonded grains and grain boundaries with a high content of sp2-bonded carbon atoms, a Randles circuit with a constant phase element (CPE) for the capacitive element provided a reasonable model for both terminations. However, the parameters of the CPE were very different for each termination. Taking into account the results obtained, we propose that the interfacial impedance of oxidized UNCD is dominated by the oxidized sp2-bonded carbon atoms present at the grain boundaries, and the interfacial impedance of hydrogen-terminated UNCD is governed by both the grain boundaries and the grains.
Electrochimica Acta. 54(6):1909-1915.
