Self-Assembled structures in Nanodiamond Layer by Spray technique

Diamond powders of various size ranging from few nanometers to tens of micrometers are commonly used to treat the silicon substrate in order to enhance the nucleation process before the growth of thin diamond films by chemical vapor deposition (CVD) techniques[1 and refs. therein]. Recently a great attention is paid to nanodiamond (ND) particles which include stable nitrogen-vacancy (N-V) color centers [2]. In this work we propose the spray technique [3] to directly deposit natural ND layers on silicon substrate using particles of 250 nm. ND particles were dispersed in the apolar solvent 1, 2 - dichloroethano (DCE) by sonication for 30 minutes. Then the dispersion was sprayed on the Si substrate, obtaining the highest ND density in the middle of it. The obtained ND films were analyzed by Raman spectroscopy, atomic force microscopy (AFM) and 3D confocal microscopy. The first technique allows the measurement of the chemical and structural composition and the photoluminescent properties, whereas the other ones measure the topography and morphology of the layers. A careful morphological analysis showed the existence of pillar-like self-assembled structures distributed in an irregular way. The highest pillar density was found far from the center of the sample, where the ND layer is non-uniform. The evolution of the structures were well observed by the 3D image analysis performed by confocal microscopy and AFM. The studyon the formation mechanisms of ND self-assembled structures will be presented and discussed.