Deposition of hydrogenated amorphous carbon films with enhanced sp 3 -C bonding on nanocrystalline palladium interlayer M. Roy a , Kunal Mali b , Niraj Joshi c , D.S. Misra d , S.K. Kulshreshtha a, ⁎ a Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India b Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India c Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai-400085, India d Department of Physics, Indian Institute of Technology Bombay, Mumbai-400076, India Abstract The present study deals with the deposition of hydrogenated amorphous carbon (a-C:H) films on Si (100) substrates with and without an interlayer of nanocrystalline palladium (nc-Pd ) on them, by high-voltage electro-dissociation of N,N-dimethyl formamide (DMF). Significant improvement in the sp 3 carbon content has been observed for a-C:H films grown on nc-Pd interlayer as revealed by Fourier transformed infrared (FTIR), Raman, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopic techniques. It is inferred that H 2 activation on palladium sites leads to the stabilization of sp 3 -C bonding, thereby improving the quality of the deposits grown on them. Keywords: a-C:H; Nanocrystalline palladium; Interlayer; Electro-deposition; Raman; XPS 1. Introduction Since the beginning of the last decade, thin films of amorphous carbon have attracted considerable interest [1–8] due to their properties akin to diamond that make them quite promising for the coating technology. These amorphous carbon films encompass a broad class of carbon materials comprising of different combinations of diamond, graphite and polymeric bonding in an intimately mixed amorphous structure and hence describe a wide range of material properties. Depending on their structure they can have a maximum of 90% of the carbon atoms in sp 3 hybridized tetrahedral bonding configuration, similar to that in diamond [3–6], on which the diamond-like properties in these materials such as hardness, electrical resistivity, transpar- ency in the IR region, etc. depend [1–3,9–11]. However it is not easy to grow amorphous carbon films with very high fraction of carbon atoms in sp 3 hybridized tetrahedral bonding configura- tion. Of late high-voltage electro-dissociation of common organic solvents [12–16] has provided with a simple and inexpensive technique for depositing hard amorphous carbon films at around room temperature, practically on any conducting substrate. But the quality (i.e. excellent material properties, exhibited by the films with high sp 3 -C content) of the deposits still remains a major concern. So, it will be of tremendous practical significance if one can improve upon the content of sp 3 -C in these electro-deposited films. It is known from the existing literature [13] that the hydrogen evolved during electro- dissociation of the protic solvents, upon activation, can participate in the process of bond breaking and bond making, thereby modifying the carbon linkages within the films. It is also known that palladium films can adsorb and activate H 2 even at room temperature (RT) [17] and the process of activation commences through its surface adsorption, especially at the grain boundaries [18]. Maximum efficiency is therefore expected when the grain size of palladium is in the nanometer scale. Hence the natural question arises if nanocrystalline palladium-induced in-situ activation of evolved H 2 could improve the sp 3 -C content of the electro-deposited amorphous carbon films. To find an answer to this question, we deposited amorphous carbon films on both bare and nanocrystalline palladium coated silicon substrates by high-voltage electro- dissociation of N,N-dimethyl formamide (DMF). To discrimi- nate the effect due to variation in current density, all samples