Delivered by Ingenta to: Purdue University Libraries IP: 95.181.176.123 On: Wed, 08 Jun 2016 11:36:49 Copyright: American Scientific Publishers RESEARCH ARTICLE Copyright © 2008 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 8, 3526–3531, 2008 Morphological Observation of Y and T Junctions in Nanostructured Boron Nitride Thin Films Sushil Kumar 1 ∗ , A. Parashar 1 , C. M. S. Rauthan 1 , S. K. Singhal 2 , P. N. Dixit 1 , B. P. Singh 2 , and R. Bhattacharyya 1 1 Plasma Processed Materials Group, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India 2 High Pressure Physics Group, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India Formations of Y and T nano junctions have been observed in boron nitride films deposited on sil- icon substrates by plasma chemical reaction of diborane (B 2 H 6 diluted in hydrogen) and ammonia (NH 3 ) gases using dual frequency (microwave/radio) plasma enhanced chemical vapor deposi- tion technique without any intentional heating of the substrates. It has been observed that these nano junctions form at a critical feed gas ratio of ammonia and diborane. We have investigated the effect of gas feed ratio R (=NH 3 /B 2 H 6 ) in the plasma reaction chamber, keeping all other deposition parameters constant, on the morphology of boron nitride films. The deposited films are characterized by SEM, AFM, TEM and Laser Raman. For gas feed ratio, R< 100, octahe- dron and cubic morphologies have been observed in BN films and on increasing R to >100, size of the crystallites reduces to nanometer level. In some of our BN samples deposited at a crit- ical value of gas ratio (R = 400), uniform Y and T junctions having bamboo like morphologies, in nanometer level, have been observed, which we wish to emphasis here as an interesting and newer observation in boron nitride films deposited by the dual frequency PECVD technique. This change in morphology exhibited by varying gas feed ratio is mainly due to excess nitrogen ions in the plasma. Keywords: Boron Nitride, Y and T Junctions, PECVD, Nanostructures, Morphology. 1. INTRODUCTION For last about one and half decades numerous research findings have been reported on new physical phenomena of materials in the nanoscale size, synthesis and its advanced properties. These properties of nanosize materials have emerged as a future leader in areas, such as electronics, optoelectronics, photonics, information communications, medicine, environment, energy etc. As new material prop- erties of carbon nanostructures have been much talked since the observation of hollow nanostructures, in gen- eral and nanotubes 1–2 and nanocages like C 60 ,C 70 etc. 3 in particular. Similar structures have also been proposed for other compound materials such as boron nitride (BN). 4 Such structures are normally formed at high temperature by deposition, 4 chemical reaction from a vapor phase 5 or by a reactive ball-milling process. 6 These BN nano- structures could be seen as building blocks of nanoelec- tronics, where nano carbon structures lack, particularly where high temperatures and high bandgap materials are ∗ Author to whom correspondence should be addressed. required. Recently, there is a review article appeared in a materials journal which cover the latest advances related to the synthesis of pure and doped boron nitride nanotubes. 7 Boron nitride (BN) is a well known III-V compound with extraordinary mechanical, thermal, electrical, opti- cal and chemical properties when it is made with reason- ably high cubic content and thus finds significant potential applications. 8–12 After first success in synthesizing cubic boron nitride (c-BN) using high pressure and high tem- perature by Wentorf, Jr., 13 many low pressure techniques have been exploited to grow c-BN films. These techniques are based on physical vapour deposition 14–17 and chem- ical vapour deposition. 18–20 In most of the cases mixed phases of BN have been achieved. In both type of deposi- tion techniques, energetic ions bombardment plays a major role in the formation of c-BN films. In ion assisted mode of deposition there is an energy threshold of bombard- ing ions for nucleation of c-BN crystallites. 21 Matsumoto et al. 22 have been able to develop c-BN films having high cubic phase and thickness over 20 micron at compara- tively high temperatures (∼1100  C) and 50 torr pressure using Ar-N 2 -BF 3 -H 2 gaseous mixture in a DC jet CVD and 3526 J. Nanosci. Nanotechnol. 2008, Vol. 8, No. 7 1533-4880/2008/8/3526/006 doi:10.1166/jnn.2008.167