Grazing angle reflectance spectroscopy of organic monolayers on nanocrystalline diamond films ☆ Z. Remes ⁎, H. Kozak, O. Babchenko, S. Potocky, E. Ukraintsev, B. Rezek, A. Kromka Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, CZ-162 53 Praha 6, Czech Republic abstract article info Available online xxxx Keywords: Nanocrystalline diamond Infrared spectroscopy Functionalization Grazing angle Brewster angle The nanocrystalline diamond (NCD) layers were grown by the large area (linear plasma) MWCVD on polished silicon substrates with and without intermediate mirror-like metallic coatings. The optical reflectance and Raman spectroscopy in the ultraviolet, visible and near infrared region (UV–VIS–NIR) reveals the thickness and the optical quality of NCD layers. The modified grazing angle reflectance (GAR) spectroscopy is applied in the mid infrared region 800–4000/cm to detect the molecular vibrations (functional groups) at the functionalized NCD surface. The optical absorbance of functionalized NCD surface is evaluated from p-polarized reflectance spectra measured at Brewster angle of incidence (BAR) to eliminate the interference fringes. We report a significant enhancement of sensitivity of BAR using NCD growth on metal mirrors. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Various special properties, for example chemical stability, large electrochemical potential window, high transparency in wide optical range and good biocompatibility make diamond particularly suitable for bio-applications [1]. Surface functionalization by organic layers enhances the usability of diamond by many new properties, including tunable electrical conductivity, wettability as well as selective affinity for organic adhesion [2]. The strength of the chemical or electrostatic bonds at the diamond/organic interface [3] provides an important advantage over widely used glass or metal substrates where the stability of the protein monolayers has been proved to be poor [4]. Nano-crystalline diamond (NCD) deposited on non-diamond substrates provides economical alternative to single crystal diamond showing most of the diamond excellent properties [5]. Our high quality NCD layer consists of a closely packed polycrystalline material with typical crystalline sp 3 bonded carbon grain size around 100 nm and some sp 2 bonded carbon located at grain boundaries [6]. We have shown recently that the non-diamond content in NCD films can be significantly reduced by deposition of NCD under the optimized growth conditions on carefully selected substrates followed by the post-growth etching and cleaning [7]. The experiments done on photochemically functionalized NCD surface demonstrated the repeatability of DNA hybridization and denaturation after covalent immobilization of DNA [8]. Proteins have been attached covalently to NCD thin film and it has been shown that, although the proteins are immobilized at the surface, they are still fully functional and active [9]. NCD surface has been also functionalized by grafting the NCD surface with several nm thick organosilane coatings [10]. The information about NCD surface is typically obtained from XPS [11], UV elipsometry [12], fluorescence imaging [13] and wetting experiments [14]. The infrared absorbance spectroscopy of molecular vibrations provides direct evidence for the appearance and disap- pearance of the specific functional groups chemically bonded or adsorbed to the surface of the biofunctionalized nanodiamonds [15]. Recently we reported IR absorbance spectra of a linker molecule monolayer (10-undecenoic acid) covalently bonded to the NCD surface with and without DNA fragments coupled to it, and IR spectra of the ultra-thin organosilane layer deposited on NCD by the spin coating technology [16]. We proposed the Brewster angle reflectance (BAR) as a new method of detecting functional groups attached to NCD thin film surfaces. However, the BAR sensitivity was rather low due to the low reflectivity of NCD/silicon interface. In this paper we report on a significant improvement of BAR using newly developed technology of NCD growth on metal mirror. The technology of highly transparent NCD films deposited on metal coatings was recently developed by our group using substrates made of one side polished silicon wafers coated by the metallic films [17]. 2. Experimental The polished silicon wafers coated by about 100 nm Al films were nucleated using spin coating of polymer enriched with fine grained diamond powder (NanoAmando, New Metals and Chemicals Corp. Ltd., Kyobashi) [18] to prevent scratching of Al film. NCD films were grown for 5 hours in the large area linear antenna MW CVD reactor (modified Diamond & Related Materials 20 (2011) 882–885 ☆ Authorship Statement: Submission of the article has been approved by author/ co-author(s). The article is the author's original work, and has not been published or submitted simultaneously elsewhere. ⁎ Corresponding author. Tel.: + 420 220 318 111; fax: + 420 233 343 184. E-mail address: remes@fzu.cz (Z. Remes). 0925-9635/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2011.04.001 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond