Thin Films Of BN Research Articles

The Influence of Carbon on Polytype and Growth Stability of Epitaxial Hexagonal Boron Nitride Films

AbstractBoron nitride (BN) is a promising 2D material as well as a potential wide‐bandgap semiconductor. Chemical vapor deposition (CVD) is commonly used to deposit single layers or thin films of BN, but the deposition process is insufficiently understood at an atomic scale. the CVD of BN is studied using two boron precursors, the organoboranes, triethylborane, and trimethylborane. Using high resolution (scanning) transmission electron microscopy and electron energy loss spectroscopy, this study shows that hexagonal‐BN (h‐BN) nucleates and grows epitaxially for ≈4 nm before it either polytype transforms to rhombohedral‐BN (r‐BN), turns to less ordered turbostratic‐BN or is terminated by a layer of amorphous carbon. this study proposes that the carbon in the organoboranes deposits on the epitaxially growing h‐BN surface and this either leads to the polytype transition to r‐BN, the transition to less ordered BN growth, or complete surface poisoning with carbon terminating BN growth. These results question the use of organoboranes in CVD of epitaxial BN films, and the polytype stability of h‐BN growing on graphene.

Thermal stability of thin hexagonal boron nitride grown by MOVPE on epigraphene

Passivating graphene with a layer of hexagonal boron nitride (hBN) is known to protect it from environment effects that degrade its mobility. However, growth of high-quality BN on graphene is challenging because of the lack of surface dangling bonds. Here, we report the growth of thin BN films (down to 10 nm) on monolayer epigraphene grown on silicon carbide single-crystal substrates using metal–organic vapor phase epitaxy (MOVPE). The BN film has continuous coverage on the epigraphene surface, with smooth morphology. Particles consisting of layered BN are also observed on the surface with a higher density at the step edges. High-Resolution Scanning Transmission Electron Microscopy (HRSTEM) reveals high structural quality BN layers, with a clean and abrupt interface with graphene. The BN/epigraphene/SiC heterostructure is stable up to high temperature (1550 °C), and annealing improves its crystallinity. These results show that MOVPE growth technique has a potential for large-scale production of BN fully coated graphene and high-temperature applications.

Novel BN/Pd composite films for stable liquid petroleum gas sensor

Composite films of BN/Pd were synthesized by depositing thin films of BN by pulsed laser deposition technique and evaporating a thin layer of palladium on top of it to form a bi-layer structure. This bi-layer structure was then subjected to rapid thermal annealing for the incorporation of Pd in BN. The films thus obtained were characterized by SEM, XRD and FTIR studies. Liquid petroleum gas (LPG) sensing properties were also investigated critically. Very stable and reproducible LPG sensing properties and comparatively at lower operating temperature of 460K would make this material superior to prevalent oxide based sensors.

ChemInform Abstract: Advances with Ammonia—Borane: Improved Recycling and Use as a Precursor to Atomically Thin BN Films

AbstractReview: 16 refs.

Advances with Ammonia‐Borane: Improved Recycling and Use as a Precursor to Atomically Thin BN Films

Advances with Ammonia‐Borane: Improved Recycling and Use as a Precursor to Atomically Thin BN Films

Initial growth of hexagonal and cubic boron nitride: A theoretical study

Smaller cellular telephones and more energy-efficient windows are just two examples of technological advances which call for new materials. Materials chemists seek to develop new materials, both out of pure curiosity to see which combination of elements and structures can be obtained and in efforts to produce materials, with specific properties. The starting materials (in solid, liquid or gaseous form) can then be combined and prepared in various ways. A chemical method that is gaining more attention for thin-film growth is Atomic Layer Deposition (ALD). This is a sophisticated type of vapor deposition in which the precursor gases are introduced separately into the reaction chamber.Silicon carbide (SiC) and cubic boron nitride (c-BN) are extremely hard diamond-like materials, both with a high potential for application within the modern microelectronics and tool industry. Hexagonal boron nitride (h-BN), with its graphite-like layered structure, is a promising ceramics material.Deposition of thin SiC and BN films from gaseous precursors has been studied by theoretical and experimental methods. The chemical composition and atomic arrangement of a growing surface is important for vapor growth. The surface may be terminated (e.g., by hydrogen atoms) and adopt various geometrical structures. Reconstruction of unterminated SiC(0001) surfaces, as well as H abstraction from the corresponding H-terminated surfaces, were studied using quantum mechanical calculations. Elementary reactions for vapor growth of SiC and BN, and in situ incorporation of dopant and contaminant species into these surfaces were also investigated theoretically. Moreover, thin films of BN were deposited by means of laser-assisted ALD. The general goal has been to predict and/or explain experimental results by investigating growth mechanisms.

Adsorption of N-containing species onto SiC(0001) surfaces: A theoretical study

Smaller cellular telephones and more energy-efficient windows are just two examples of technological advances which call for new materials. Materials chemists seek to develop new materials, both out of pure curiosity to see which combination of elements and structures can be obtained and in efforts to produce materials, with specific properties. The starting materials (in solid, liquid or gaseous form) can then be combined and prepared in various ways. A chemical method that is gaining more attention for thin-film growth is Atomic Layer Deposition (ALD). This is a sophisticated type of vapor deposition in which the precursor gases are introduced separately into the reaction chamber.Silicon carbide (SiC) and cubic boron nitride (c-BN) are extremely hard diamond-like materials, both with a high potential for application within the modern microelectronics and tool industry. Hexagonal boron nitride (h-BN), with its graphite-like layered structure, is a promising ceramics material.Deposition of thin SiC and BN films from gaseous precursors has been studied by theoretical and experimental methods. The chemical composition and atomic arrangement of a growing surface is important for vapor growth. The surface may be terminated (e.g., by hydrogen atoms) and adopt various geometrical structures. Reconstruction of unterminated SiC(0001) surfaces, as well as H abstraction from the corresponding H-terminated surfaces, were studied using quantum mechanical calculations. Elementary reactions for vapor growth of SiC and BN, and in situ incorporation of dopant and contaminant species into these surfaces were also investigated theoretically. Moreover, thin films of BN were deposited by means of laser-assisted ALD. The general goal has been to predict and/or explain experimental results by investigating growth mechanisms.

Growth of Boron Nitride Thin Films on Silicon Substrates Using New Organoboron Precursors

Thin films of BN have been deposited on silicon substrates in the temperature range of 600 to 900 °C by supersonic molecular jet epitaxy and plasma-assisted MOCVD using new organoboron precursors such as borane-triethylamine complex (BTEA) and tris(sec-butyl)borane (TSBB). Hydrogen was used as carrier gas, and additional nitrogen and ammonia as reactive gases were supplied by either through nozzle or via remoted plasma. Crack-free, polycrystalline hexagonal BN films with nano-size crystals were successfully grown at temperature as low as 750 °C using BTEA. With increasing substrate temperatures to 900 °C, however, the h-BN films chenged polycrystalline with smoother surface and larger crystals. The changes of relative film quality with deposition temperature and reactive gas have been confirmed with FTIR. Nitrogen plasma enhanced the film quality and the stoichiometry, and removed the surface carbon effectively rather than ammonia and hydrogen plasmas molecular beam. Wide band gaps were calculated using optical transmittance measurements.

Growth of Boron Nitride Thin Films on Silicon Substrates Using New Organoboron Precursors

Thin films of BN have been deposited on silicon substrates in the temperature range of 600 to 900 °C by supersonic molecular jet epitaxy and plasma-assisted MOCVD using new organoboron precursors such as borane-triethylamine complex (BTEA) and tris(sec-butyl)borane (TSBB). Hydrogen was used as carrier gas, and additional nitrogen and ammonia as reactive gases were supplied by either through nozzle or via remoted plasma. Crack-free, polycrystalline hexagonal BN films with nano-size crystals were successfully grown at temperature as low as 750 °C using BTEA. With increasing substrate temperatures to 900 °C, however, the h-BN films chenged polycrystalline with smoother surface and larger crystals. The changes of relative film quality with deposition temperature and reactive gas have been confirmed with FTIR. Nitrogen plasma enhanced the film quality and the stoichiometry, and removed the surface carbon effectively rather than ammonia and hydrogen plasmas molecular beam. Wide band gaps were calculated using optical transmittance measurements.

Performance of laser ablated, laser annealed BN emitters deposited on polycrystalline diamond

Thin BN films of about 100 nm were deposited on 25 μm thick n-type polycrystalline diamond by laser ablation and annealed with a 25 ns pulse from an excimer laser at 0.1 J. Current densities of about 2 A/cm2 were obtained with an extraction electrode probe area of 2×10−3 cm2 (500 μm diameter). Emission is governed by a Fowler–Nordheim-type behavior with some deviation at higher currents due to the voltage dependency of the BN resistance. From present experiments it cannot be deduced if the films exhibit negative electron affinity. Emission currents are stable and independent of pressure to about 10−4 Torr. The magnitude of the current fluctuations are similar to Spindt-type devices. Compared to Mo and Si emitters, no careful high vacuum conditioning procedure is needed prior to operation. At current densities above 1 A/cm2, restructuring of the emission area took place at some locations of the 0.5 cm × 1 cm sample, leaving craters in the diamond substrate. After restructuring, emission still took place with modified current–voltage characteristics. Based on these results, carbon-doped BN has the potential for creating very rugged, low noise, high current density cold electron sources.

Correlation of boron and nitrogen contents with the flux of energetic Ar+ ions at the substrate during the deposition of BN coatings by RF magnetron sputtering

Thin films of BN x O y have been deposited by RF magnetron sputtering from a BN target in Ar plasma (1 Pa) at different substrate RF bias conditions. The possibility of obtaining high-quality BN coatings at a target–substrate distance greater than the mean free path of B and N atoms has been investigated. The discharge characteristics have been measured by means of an electrostatic probe of the Langmuir type. The flux and energy of the Ar + ions have been determined and correlated to the net contents of boron and nitrogen as measured by means of the N(d,p) and 11 B(p,α) nuclear reactions. The results deduced by XRD, FTIR and nanohardness measurements show that under the experimental conditions used, the flux of Ar + ions at the substrates is insufficient to promote the formation of crystalline BN films.

A study of deuterium permeation through thin BN films

Stainless steel membranes have been coated by using the ion beam assisted deposition technique with BN thin films: some deposited films exhibit the cubic microcrystalline structure (c-BN) while others exhibit the hexagonal one (h-BN). The samples have been submitted to deuterium permeation tests and in a second step they have been analysed by elastic recoil detection (ERD). It was observed that the permeation flux transient is sensible to the structure of the deposited layers as suggested by the different shape of the permeation curves pertinent to the h-BN or to the c-BN coated samples. These different shapes have been attributed to deuterium trapping processes in the BN layers with the hexagonal structure: the higher deuterium content in the h-BN than in the c-BN, after permeation, as revealed by ERD analysis, is consistent with the previous observation.

Thin BN films obtained by dual-ion-beam sputtering: an FT-IR and spectroscopic ellipsometry characterization

Thin BN films (100–250 nm) have been deposited on Si(100) substrates in a double-ion-beam sputtering system from a h-BN target. The films have been characterized by FT-IR spectroscopy and spectroscopic phase-modulated ellipsometry as a function of the deposition and irradiation parameters. Assistance with Ar + ions result in boron rich films with refraction indexes above 2 or even higher as the deposited energy of the assisting ions increases. N 2 +-bombardment causes stoichiometric and even nitrogen-rich BN films characterized by refraction indexes around 1.85. The stability of the films is enhanced when the deposited energy of the N 2 + ions is above 30 eV/atom and/or the deposition is performed on substrates at temperatures above 100°C.

Observation of a negative electron affinity for boron nitride

This study reports UV-photoemission (UPS) measurements made on boron nitride crystals and thin films. The materials examined are commercial grade c-BN powder and thin films of BN deposited with ion beam assisted e-beam evaporation and laser ablation. The thin film samples examined exhibited varying amounts of sp3 (cubic) and sp2 (hexagonal, amorphous) bonding as determined by FTIR measurements. The UPS measurements displayed the spectral distribution of the low energy photoemitted electrons and the total energy width of the spectra. These characteristics can be related to the electron affinity. The measurements on several of the BN powder and thin film samples revealed features in the emission spectra which are indicative of a negative electron affinity (NEA) surface.

N-type conductivity in c-BN films deposited by microwave plasma-assisted chemical vapour deposition

n-type conductivity was observed in thin films of BN deposited by microwave plasma-assisted chemical vapour deposition using a single-source organometallic precursor. The depositions were carried out on various substrates using N2 as the carrier gas. These films were characterized by FTIR, XRD and SEM which revealed the presence of crystallites of boron nitride. The deposition conditions were optimized to obtain the maximum concentration of c-BN in the thin films of boron nitride. Seebeck studies indicate that electrons are the majority charge carriers. I-V studies of the p-n junction between p-Si and n-BN indicate typical behaviour of diode characteristics.

Elemental composition of thin c-BN layers

Some experiments on the growth of cubic boron nitride (c-BN) show that the content of c-BN in BN films depends on the film thickness. Non-cubic phases, such as amorphous and hexagonal BN, can be identified, particularly near the substrate. To understand these phase variations, elemental depth profiles of thin BN films were measured by high resolution elastic recoil detection (ERD). BN films have been prepared by r.f. glow discharge ( r . f = 13.56 MHz ) from a mixture of B 2 H 6 (10% in argon) and N 2 . Layers 48 nm and 90 nm thick have been deposited on crystalline silicon with integrated portions of the cubic phase of 55% and 67% respectively. ERD measurements showed that the integrated boron-to-nitrogen ratio is close to unity for the thicker film, but significant enhancements of boron are found near the interface with the silicon substrate and at the surface. These enhancements are coupled with a decrease in the hydrogen content, which is about 9% on average. The elemental fluctuations will be correlated with the occurrence of different BN phases and improvements for c-BN deposition will be suggested.

Growth of BN by hot filament assisted electron beam deposition

Thin films of BN were deposited using an electron beam for evaporating boron and a hot filament for activating N2. The IR spectrum of the deposited film on Si substrates showed a strong absorption at 1097 cm-1 clearly indicating a cubic structure. Scanning electron micrograph and X-ray diffraction patterns confirm the polycrystalline nature of the films. Raman spectra of the films showed peaks at 1056 and 1304 cm-1, which are the characteristic Raman lines for cubic boron nitride.

Deposition of wear-resistant BN coatings by r.f. plasma-assisted chemical vapour deposition

Thin films of BN have been deposited by r.f. plasma-assisted chemical vapour deposition using B 2H 6N 2H 2 gas mixtures. The deposited layers were characterized mainly by IR reflection spectroscopy. On the anode, stoichiometric films could only be obtained when a large excess of N 2 was present in the gas phase. For films grown at the r.f. plate, the mixing of B 2H 6 and N 2 was less critical. The films were amorphous and had a hexagonal-like short-range order (turbostratic structure). Hardness values up to 9GPa have been obtained for films grown on stainless steel substrates.

Intermediate layers for the deposition of polycrystalline diamond films

Thin films of BN, hard carbon, a-C:H, and SiC have been deposited onto ZnS or (100)-silicon as precursors to the growth of polycrystalline diamond films. These layers must protect the substrate from chemical attack at the deposition temperatures used in microwave plasma chemical vapor deposition (CVD) and also promote the nucleation of crystalline diamond. The thermal stability, the optical properties of these coatings, and their ability to nucleate diamond growth are investigated. BN thin films appear to be the best interlayer for both protection and nucleation enhancement. Hard carbon and a-C:H interlayers provide no real benefit in themselves. Silicon carbide was identified at the interface between one type of hard carbon film and the silicon substrate using x-ray photoelectron spectroscopy (XPS). Si–C islands may provide nucleation sites for CVD diamond. Silicon carbide can provide both protection and nucleation enhancement if the crystallinity and texture are optimized.

Growth of Stoichiometric Bn Films by Pulsed Laser Evaporation

AbstractThe feasibility of growing stoichiometric thin films of BN by pulsed laser evaporation has been investigated. Films grown under high vacuum conditions were N-deficient. This result is consistent with thermodynamic calculations, which indicate that B metal formation, with concomitant N2 desorption, is energetically favored over BN formation. Stoichiometric films were grown in NH3 with substrate temperatures of 400, 500, and 1000ºC. Analysis of films grown under these conditions by grazing incidence x-ray diffraction indicates the films to be highly oriented, hexagonal BN.