Carbon Thin Films from Plant-Derived Precursors Pravin Jagadale and Maheshwar Sharon Nanotech Research Center (NTRC), Birla College, Kalyan, MS, India Madhuri Sharon Monad Nano Tech Pvt. Ltd., Adishankaracharya Marg, Powai, Mumbai, India Golap Kalita Chubu University, Kasugai, Aichi, Japan Thin films of nanocrystalline diamond-like carbon thin film are synthesized by the thermal flash vapor deposition technique using turpentine oil. Effect of applied voltage and substrate temperature on the formation of thin film of carbon is discussed. It is observed that at substrate temperature (7508C), semiconducting Nanocrys- talline diamond-like carbon thin films with prominent (111) phase and band gap 1.04 eV can be prepared by flash evaporation tech- niques in less than 3 minutes. XRD, Rocking Curve analysis, SEM and Raman studies were carried out to confirm the structure of film prepared by this method. Electrical conductivity and optical band gap analysis were done to find out the electrical properties and band gap of the film. Keywords nanodiamond, turpentine oil, crystalline nanodiamond- like carbon, thermal flash evaporation INTRODUCTION For the development of homojunction carbon solar cells, a process for synthesizing low band gap semiconducting carbon is necessary. Sharon et al. [1 – 3] developed homojunction carbon solar cell from semiconducting carbon obtained from soot of camphor by electron beam evaporation technique. Later Dillip et al. [4] tried to synthesize semiconducting carbon from the camphor soot using pulse laser deposition technique. They achieved semiconducting carbon with a band gap lower than 1.0 eV. Sharon’s group [5] has reported that by suitable control of deposition condition of pyrolysis, it is possible to make semiconducting carbon with band gap in the range of 0.25 eV to 5.5 eV. As an extension of their work; it was thought of using the flash evaporation technique to synthesize carbon thin film of band gap around 1.0 eV. In the flash evaporation technique, precursor to be pyrolysed is kept in a boat. Over the boat tungsten coil is wrapped. Above the coil, a substrate is kept whose temperature can be con- trolled externally. This entire assembly is kept in a container that can be evaporated. When suitable electrical power is given to the tungsten coil, precursor due to sudden high temp- erature gets evaporated and pyrolysed simultaneously. This pyrolysed product gets deposited on the substrate. By control- ling the electrical power to the coil, the substrate temperature and the vacuum, it is possible to get a desired thin film of carbon. In this paper the result of our efforts to synthesize semi- conducting carbon using turpentine oil with flash evaporation technique is discussed. RESULTS AND DISCUSSION Effect of Voltage Applied to the Tungsten Coil Carbon thin films deposited on quartz plates were used to measure their resistivity at different temperatures by the two- probe method. The temperature coefficient resistance (TCR) showed negative TCR, which signifies the semi conducting behavior of the carbon. The activation energy for the conduc- tivity of the thin film was calculated from the slope of the linear plot of 1/T Vs Ln (1/R). The variation in activation energy with the applied voltage (i.e., to the tungsten coil) is shown in Figure 1. From the trend shown in figure, it appears that lower than 190 V should be applied to the tungsten coil to get a carbon film of band gap around 1.0 eV. But it was observed that at voltage less the 190 V no carbon film could be obtained. Therefore, in second set of experiments, different temperature of the substrate by adjusting the distance between the substrate and filament Received 27 November 2006; accepted 3 April 2007. One of us (GK) is thankful to Ministry of Non-Conventional Energy to provide a fellowship to carry out this work. We are also thankful to Excel Instruments for providing the flash evaporation unit free of charge for carrying out this work. Address correspondence to Pravin Jagadale, NTRC, Birla College, Kalyan, MS, India. E-mail: pravinjagadale@gmail.com Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 37:467–471, 2007 Copyright # 2007 Taylor & Francis Group, LLC ISSN: 1553-3174 print /1553-3182 online DOI: 10.1080/15533170701471588 467