%0 Journal Article
%T Evidence of Carboxyl Modification of Hydrogen-Free Diamond-Like Carbon Films Assisted by Radio Frequency Plasma in Vacuum
%A Yuqi Xue
%A Zixin Wang
%A Jun Wang
%A Changji Hu
%A Fangyan Xie
%A Dihu Chen
%A Zhenhui He
%J ISRN Spectroscopy
%D 2012
%R 10.5402/2012/963298
%X Modification of hydrogen-free diamond-like carbon (DLC) is presented, with acrylic acid (AA) vapor carried into a vacuum chamber by argon and with the in situ assistance of low-power radio frequency (RF) plasma at a temperature below 100¡ãC. Measured by atomic force microscopy (AFM) technique, the roughness ( ) of the DLC was £¿nm. XPS and FT-IR spectra analysis showed that carboxyl groups were immobilized on the surface of the DLC films, with about 40% of carboxyl group area coverage. It was found that the RF plasma and reaction time are important in enhancing the modification rate and efficiency. 1. Introduction Diamond-like carbon (DLC) films, which are hard, stable, inexpensive, and biocompatible, have been widely used in the fields of biosensors and electrochemistry for many years [1, 2]. With the development of modification technology, DNA and protein have been immobilized on DLC films [3, 4]. In the future, DLC films are promising in the applications of electrodes and bioactivity protected films in biosensors. To do so, one challenge is to improve carboxyl or amino modification techniques for the DLC surface to improve protein or DNA immobilization covalently. Recently, a photochemical functionalization technique was carefully studied, which makes possible a functionalized organic monolayer by UV light irradiation immobilization on the hydrogen-terminated surfaces of the nanocrystalline and single-crystal diamond (111), in a thin layer of liquid reactants [5, 6]. However, this technique requires hydrogen-terminated DLC surface at a temperature higher than 800¡ãC (to remove the surface oxygen [7]), which is too high for some applications, such as GMR biosensors, and would damage the GMR elements [8]. Furthermore, the functionalization time was always over 10£¿hrs to obtain a functional group coverage of 10% [6, 9] (for the trifluoroethyl ester of -undecenoic acid (TFU), and the coverage is defined by the ratio of carboxyl group content over that of the carbon monolayer on the surface of the DLC). Ababou-Girard et al. [10] reported a thermal functionalization method to graft ethyl undecylenate molecules onto the hydrogen-terminated amorphous carbon surface. However, this method showed a poor efficiency, with obtained DLC£¿:£¿H rate of merely 4%. Hovis et al. [11] found that vinyl group (C=C) would react with hydrogen-free diamond surface in ultravacuum ( £¿Pa) due to the active sites (dangling bands [12], surface ¦Ð bonds [11], etc.) on the surface of hydrogen-free diamond. However, the reaction rate for vinyl groups is about the order of 10£¿3 on diamond,
%U http://www.hindawi.com/journals/isrn.spectroscopy/2012/963298/