Ultrananocrystalline diamond (UNCD) films are deposited using microwave plasma enhanced chemical vapor deposition system. Depositions of films are carried out at low pressure 25 mbar, low temperature 400 ºC and at low microwave power (800 - 1000 Watt). Diamond thin films were characterized using Raman spectroscopy, AFM, field emission scanning electron microscopy and optical contact angle measurements. In-situ diagnosis of the plasma composition is carried out using optical emission spectroscopy (OES). OES spectra show intense peak at 516.5nm corresponding to C2 dimer. Peaks at 387.0nm, 405.3nm, 431.5nm, 486.1nm, and 656.1nm have also been observed. Effect of horizontal position of plasma ball with respect to substrate position has been critically analyzed. Relation between the horizontal positioning and plasma ball along with the emission spectra of different gas species are studied which are very much crucial to predict the uniformity and morphology of the films deposited. Dependence of film wetability with the plasma ball positioning and relative intensity of carbon dimer has been studied C2 dimer plays an important role not only in the nucleation and growth of UNCD films but also on the surface modification .