Materials Science and Engineering B 177 (2012) 1243–1247 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Short communication Cyclic voltammetry response of an undoped CVD diamond electrodes K. Fabisiak a,∗ , R. Torz-Piotrowska b,1 , E. Staryga c , M. Szybowicz d , K. Paprocki a , P. Popielarski a , F. Bylicki a , A. Wrzyszczy ´ nski c a Institute of Physics, Kazimierz Wielki University, Powsta´ nców Wielkopolskich 2, 85-090 Bydgoszcz, Poland b Faculty of Chemical Technology and Engineering, UTLS Seminaryjna 3, 85-326 Bydgoszcz, Poland c Institute of Physics, Technical University of Lód´ z, Wólcza´ nska 219, 90-924 Lód´ z, Poland d Faculty of Technical Physics, Poznan University of Technology, Nieszawska 13A, 60-965 Pozna´ n, Poland article info Article history: Received 10 November 2011 Received in revised form 1 February 2012 Accepted 3 March 2012 Available online 20 March 2012 Keywords: HF CVD Diamond electrode XRD Raman spectroscopy abstract The polycrystalline undoped diamond layers were deposited on tungsten wire substrates by using hot fil- ament chemical vapor deposition (HFCVD) technique. As a working gas the mixture of methanol in excess of hydrogen was used. The morphologies and quality of as-deposited films were monitored by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy respectively. The electrochemical activity of the obtained diamond layers was monitored by using cyclic voltammetry mea- surements. Analysis of the ferrocyanide–ferricyanide couple at undoped diamond electrode suggests that electrochemical reaction at diamond electrode has a quasireversibile character. The ratio of the anodic and cathodic peak currents was always close to unity. In this work we showed that the amorphous carbon admixture in the CVD diamond layer has a crucial influence on its electrochemical performance. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Although diamond is basically an insulating material, the control of conductivity by doping opens up the field for electronic appli- cations. The feasibility of these applications is based not only on the bulk properties but also on the unique surface properties of diamond. The use of diamond films in electrochemistry is relatively a new field of research. The first article in this field was published in 1983 by Iwaki et al. [1], but the field was really initiated by the important article of Pleskov et al. [2]. Usually diamond layers were doped in order to make them conducting but the doping of dia- mond is not a unique way to get sufficient conductivity for many applications. The hydrogen termination of diamond is important in terms of stabilizing the surface structure and generating negative electron affinity (cold cathode applications) [3]. The concentration of hydro- gen in diamond layer is directly proportional to the concentration of sp 2 hybridized carbon phase. As-grown CVD diamond film is always hydrogen terminated [4]. Hydrogen termination generates p-type conductivity which is restricted to the surface region (10 nm) [5] on grain boundaries and gives possibility to use the diamond layer as electrode material in electrochemistry. The amorphous carbon ∗ Corresponding author. Tel.: +48 601200421. E-mail address: kfab@ukw.edu.pl (K. Fabisiak). 1 Deceased. admixture and hydrogen terminated diamond grains are responsi- ble for an electrical contact not only between diamond’s grains but also between the diamond layer and the substrate. The microcrystalline diamond (MCD) structures have the elec- trical conductance caused by some structural defects, and also due to continuous network formed by the amorphous carbons that are incorporated in the intercrystallite boundaries during the diamond growth process [6]. Gruen [6] has observed that when the crys- talline size is reduced, the percentage of the amorphous carbon phase located at grain boundaries increases drastically. Clearly, the electrical properties of diamond layers will be gov- erned by the fraction of amorphous carbon residing at the grain boundaries and the electrical conduction can occur via  states [6]. The aim of the present work is to show that: (a) diamond doping is not neccessary condition using this material for electrochemical applications, (b) there is direct correlation between the diamond quality and its electrochemical sensing properties. 2. Experimental The polycrystalline diamond films were deposited on tungsten wire, 0.5 mm in diameter, as a substrate by Hot Filament Chemical Vapor Deposition (HF CVD) technique. The hot filament has a shape of coil with a length of 30 mm composed of 20 turns and placed about 6 mm above the substrate. The cross-section of the hot fila- ment coil was 5 mm and its temperature was kept at 2300 ± 50 K, as measured by a two-colour pyrometer. 0921-5107/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2012.03.014