Investigation Of The Structure And Properties Of Novel Boron Carbonitride Thin Film Synthesized By Chemical Vapor Deposition

Comparing with boron nitride the BCN materials have much improved electrical conductivity and tailorable band structure with unique advantages in application. In this thesis, boron carbonitride (BCN) thin films composed of nanosheets have been grown by microwave plasma chemical vapor deposition. The BCN films were prepared by introducing CH4 as the carbon source based on the established process of growing hexagonal boron nitride (hBN) films. Due to the importance in application the luminescence properties and field emission properties were investigated for the BCN nanosheet films and the correlation between the above properties and the film structure was established.The effects of the process parameters on the growth of the hBN nanosheet films were investigated and the growth process with controllable structure was well established. It was found that the growth rate is strongly dependant on the reactive pressure. At too low pressure the growth rate is low while at high pressure the crystallinity deteriorates. Normally, the best working pressure was proved to be 6 kPa. The thin films deposited under this working pressure have uniform thickness with large nanosheets sizes. Nucleation time was observed to be between 10 minutes and 30 minutes. With increasing deposition time, hBN films were thicker but with little changes for the single nanosheet.Based on the established process of growing hBN films, the effects of introduced carbon on the morphologies, structures and properties were investigated. The results showed that, two distinct morphologies were observed for the BCN compounds due to different carbon concentration. BCN thin films with lower concentration were composed of vertically aligned BCN nanosheets. The length of the nanosheets is about 300 nm-500 nm, and the thickness is 20 nm-40 nm by SEM analysis. TEM suggests that the sharp edges of the nanosheets are composed of 2 to 20 atomic layers and the interlayer space is 0.331-0.334 nm, close to the interplanar distance of the (002) plane of hBN. Under a typical experimental condition with the flows of He, N2, BF3, H2 and CH4 as 150, 200, 80, 40 and 3 sccm, respectively, the percent content of B, C, and N are determined to be (21.86±2.7)%, (14.40±1.7)% and (63.73±7.7)% respectively by EELS. XPS and FT-IR results suggest that most of the introduced carbon atoms form bonds with nitrogen atoms. The BCN films also exhibit good luminescence properties with the emission peaks at 355, 388 and 506 nm. What is more, due to enhanced conductivity and unique nanosheets structures, electron field emission was observed for the BCN films with the turn-on field at 33.36 V/μm and the maximum current density at 1.542 mA/cm2.At higher carbon concentration, BCN spheres with diameters at the range of 0.3-1.2μm were deposited on silicon substrates. Interestingly, the spheres were also composed of nanosheets with length of 400-500 nm and thickness less than 20 nm. Raman measurements presented the scattering peaks at 1357 cm-1 and 1587 cm-1, corresponding to the first order D band and G band of graphite. The typical composition was determined to be (39.99±4.6)%, (24.75±2.9)% and (35.26±4.1)% for B, C and N respectively by EELS. The PL properties were also measured for the BCN spheres and the emission peaks at around 366 nm and 318 nm were observed, which were attributed to defects that caused by carbon doping.