Growth and characterization of boron nitride thin films and nanostructures using atomic layer deposition = Bor nitrür ince filmlerin ve nanoyapıların atomik katman biriktirme yöntemi ile büyütülmesi ve karakterizasyonu

Abstract

Being a member of III-nitride family, boron nitride (BN) and its nanostructures have recently attracted a lot of attention, mainly due to their distinctive and superior material properties, including wide band gap, high-temperature stability, high oxidation and corrosion resistance, as well as high thermal conductivity. This versatile material has found applications in UV emission, lubrication, composite reinforcement, gas adsorption, cosmetics, and thermal management. For modern electronic applications, it is imperative to obtain high quality BN films on large area substrates with a controlled thickness in order to fulfill the entire spectrum of hBN applications. Also, a facile method such as atomic layer deposition (ALD) using non halide precursors is necessary to obtain BN films at low temperatures compliant with the standards in terms of having nontoxic byproducts. ALD is a special case of chemical vapor deposition (CVD), in which two or more precursors are sequentially exposed to substrate surface separated by purging periods. In comparison with other thin film growth methods, hall mark of ALD is self limiting growth mechanism which enables deposition of highly uniform and conformal thin films with sub-angstrom thickness control. The precise and conformal layer by layer growth of ALD can be exploited to achieve growth of BN hollow nanofibers (HNFs) on high aspect ratio electrospun polymer nanofibrous templates. BN HNFs fabricated by combination of ALD and electrospinning can be utilized to address and solve important constraints associated with previous methods of fabrication such as severe preparation conditions, limited control over morphology, and low purity of the resulting BN HNFs. In this thesis, we report on the controlled deposition of BN films and its nanostructures with the use of a hollow-cathode plasma source integrated (HCPA-ALD) reactor and present detailed materials characterization results of deposited thin films and fabricated nanostructures. Depositions are carried out at low substrate temperatures (less than 450 °C) using sequential injection of nonhalide triethylboron (TEB) and N2/H2 plasma as boron and nitrogen precursors, respectively. The deposition process parameters such as pulse length of TEB and substrate temperature, as well as the influence of post-deposition annealing are studied. Moreover, another nonhalide alternative precursor named tris(dimethyl)amidoboron (TDMAB) was studied for deposition of BN films. Initial experiments were performed using TDMAB and N2/H2 plasma as boron and nitrogen precursor. In addition to BN thin film growth studies, we report on electrospun polymeric nanofibrous template-based fabrication and characterization of AlN/BN bishell HNFs. Synthesized AlN/BN bishell HNFs were found to be polycrystalline with a hexagonal structure along with lowimpurity content.