BN Deposition Research Articles

Highly Efficient Osmotic Energy Harvesting in Charged Boron‐Nitride‐Nanopore Membranes

AbstractRecent studies of the high energy‐conversion efficiency of the nanofluidic platform have revealed the enormous potential for efficient exploitation of electrokinetic phenomena in nanoporous membranes for clean‐energy harvesting from salinity gradients. Here, nanofluidic reverse electrodialysis (NF‐RED) consisting of vertically aligned boron‐nitride‐nanopore (VA‐BNNP) membranes is presented, which can efficiently harness osmotic power. The power density of the VA‐BNNP reaches up to 105 W m−2, which is several orders of magnitude higher than in other nanopores with similar pore sizes, leading to 165 mW m−2 of net power density (i.e., power per membrane area). Low‐pressure chemical vapor deposition technology is employed to uniformly deposit a thin BN layer within 1D anodized alumina pores to prepare a macroscopic VA‐BNNP membrane with a high nanopore density, ≈108 pores cm−2. These membranes can resolve fundamental questions regarding the ion mobility, liquid transport, and power generation in highly charged nanopores. It is shown that the transference number in the VA‐BNNP is almost constant over the entire salt concentration range, which is different from other nanopore systems. Moreover, it is also demonstrated that the BN deposition on the nanopore channels can significantly enhance the diffusio‐osmosis velocity by two orders of magnitude at a high salinity gradient, resulting in a huge increase in power density.

Studying the Growth of Cubic Boron Nitride on Amorphous Tetrahedral Carbon Interlayers

The growth of cubic boron nitride (cBN) films on bare silicon and amorphous tetrahedral carbon (ta-C) layers prepared on silicon substrates was studied. The cBN films were prepared by radio frequency magnetron sputter deposition at approximately 870 degrees C. The original ta-C interlayers were graphitized and restructured under high temperature and possibly under ion bombardment during BN deposition. The majority of graphitic basal planes were nearly perpendicular to the surface of silicon substrates. The BN films grown on these restructured carbon layers were deposited with higher content of cubic phase and did not show delamination signs. Turbostratic BN (tBN) basal planes extended carbon basal planes and their edges served as cBN nucleation sites. The cBN films grown on textured ta-C interlayers were insensitive to the ambient environment. The residual sp(3)-bonded carbon phase confined in the interlayers probably acts as a diffusion barrier preventing the oxidation of dangling bonds near BN interface and thus precludes weakening the interface as a result of volume expansion. The carbon interlayers also improve the crystallinity of the oriented tBN because they are continuation of carbon graphitic basal planes so that the volume fraction of nitrogen-void (N-void) defects in the sp(2)-bonded BN intermediate layers is reduced. The strong sp(3)-bonded carbon matrix could thereto withstand large compressive stress and facilitates deposition of thicker cBN films.

Evaluation of PECVD deposited Boron Nitride as Copper Diffusion Barrier on Porous Low-k Materials

AbstractUltra low dielectric constant (κ) material is needed as the inter-metal dielectrics to reduce RC delay when device dimension is scaled to sub-100nm. Porous dielectric films have been considered as good candidates for the application as inter-metal dielectrics due to their ultra low-k properties. Identifying proper dielectric copper diffusion barrier on the porous low-k films is critical for the low-k/Cu damascene fabrication process. In this study, we have evaluated the compatibility of plasma-deposited amorphous Boron Nitride film as a dielectrics copper diffusion barrier on a MSQ-based porous low-k LKD5109 film (from JSR). Both microwave plasma enhanced CVD (2.45 GHz) and radio-frequency plasma enhanced CVD (13.56 MHz) were applied for the BN deposition in order to evaluate the compatibility of the two plasma processes with the porous film. Growth parameters were optimized to minimize the boron diffusion and carbon depletion in the porous low-k films, which were found to have deleterious effects on the dielectric properties of the low-k films. FTIR and micro-Raman were employed for analyzing the changes in chemical structure of the low-k films after BN growth. Capacitance-voltage measurement was used to characterize the dielectric constants of BN film on Si and the BN-deposited porous low-k film. SIMS characterization was carried out to evaluate the performance of the BN film against copper diffusion.

Diagnostics of the hexagonal boron nitride interface layer by in situ FTIR reflection spectroscopy

Growth of hexagonal boron nitride (h-BN) interface layer between TiN covered steel substrates and cubic boron nitride (c-BN) film was investigated in situ by polarised infrared reflection absorption spectroscopy. The position and form of the Berreman peak in p-polarisation depend strongly on deposition conditions. The influence of the bias voltage as well as of the BN deposition rate on the peak shift was investigated in detail. Data evaluation indicates that at higher film thickness the texture of h-BN could be changed during growth. c-BN nucleation only was achieved if h-BN Berreman absorption peak frequencies was in the range between 1565 and 1575 cm −1. At this condition stable c-BN films in the thickness range of 1.6 μm were obtained.

Direct Transfer of Kinetic Data from a Microbalance into a Tube Reactor for CVD BN on SiC Fabrics

BN deposition from B,B′,B″-trichloroborazine/Ar gas mixtures is investigated in a microbalance system with a parallel flow arrangement, and in a tube reactor for the deposition on the fiber surface of SiC fiber fabrics. The deposition rates, rdep, in the microbalance system were simulated by numerical solution of all differential equations necessary for the description of the hydrodynamic problem (computer code Fluent). The molar deposition rate, rdep, was described by a Langmuir–Hinshelwood type formula rdep = krKc/(1+Kc), in which kr [mol m–2 s–1] = 4.66 × 109 exp(–E1a/(RT)), E1a = 299 kJ mol–1; K [m3 mol–1] = 2.22 × 10–3 exp(E2a/(RT)), E2a = 130.2 kJ mol–1. The evaporation rate of the precursor was also simulated. The experiments were carried out in the deposition range: total pressure p = 250–1000 Pa, deposition temperature Tdep = 1050–1233 K, concentration of the precursor c = 10–4–10–3 mol m–3. The deposition on fabrics was carried out in a tube reactor under similar deposition conditions. The deposition was simulated with the data obtained in the microbalance system. Characteristic numbers are derived where, in the case of the Langmuir–Hinshelwood formula, a constant deposition rate can be reached.

Plasma assisted chemical vapour deposition of boron nitride coatings from using BCl 3–N 2–H 2–Ar gas mixture

Boron Nitride coatings have been deposited by plasma-assisted chemical vapour deposition (PACVD) from BCl 3/N 2/H 2/Ar gas mixtures in a hot wall capacitively coupled radio-frequency (13.56 MHz) reactor. The nature of active species in the plasma during deposition was determined by Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS). The plasma characterisation was performed as follows: first, an Ar/H 2 plasma was studied in order to understand the influence of molecular hydrogen in the discharge mixture. Then the two precursors N 2 and BCl 3 were added and the new gas mixture studied. Finally the deposition plasma was investigated. These characterisations were correlated to the microstructure and c-BN concentrations determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR). The study demonstrates the major role of atomic hydrogen on the possible mechanisms leading to BN deposition: —the introduction of hydrogen in Ar/N 2 controls the nature of the NH x (from N to NH 3) species in the gas phase. These results are correlated to the relative amount of NH groups in the films, —by a modification of the excitation state of the plasma (n e, T e) the introduction of H 2 can increase the dissociation rate of the boron precursor BCl 3 and, reacting with chlorine, leads to the formation of HCl. This corresponds to an increase in the growth rate of the coatings. Finally, BN samples containing 5% of cubic phase were treated by Ar, Ar/H 2 and Ar/Cl 2 plasmas. These post treatments demonstrated that ion assisted preferential etching of h-BN by H or Cl atoms could be used to obtain large concentrations of c-BN coatings and possibly offer a new route for deposition of low stress cubic boron nitride.

Plasma diagnostics of r.f. PACVD of boron nitride using a BCl 3−N 2−H 2−Ar gas mixture

Boron nitride coatings have been synthesised by plasma-assisted chemical vapour deposition (PACVD) from a BCl 3/N 2/H 2/Ar gas mixture in a hot wall capacitively coupled r.f. (13.56 MHz) system. The influence of the gas composition has been investigated in terms of the nature of active species in the plasma phase using optical emission spectroscopy and mass spectrometry. These characterisations have been correlated with microstructure, and the type of bonding in the deposited films was determined by scanning electron microscopy and Fourier transformed infrared spectroscopy. The study is focused on the major role of hydrogen on the possible mechanisms leading to BN deposition from this complex mixture. The characterisation was performed by steps. First, an Ar/H 2 plasma was studied in order to understand the influence of molecular hydrogen content. To this discharge were then added separately the two precursors N 2 and BCl 3. Finally the deposition plasma was investigated. These characterisations have shown that: (a) a maximum of H atom density is obtained for a 15–30% H 2 in the Ar/H 2 plasma mixture; (b) the introduction of hydrogen in Ar/N 2 controls the nature of the NH x (from N to NH 3) species in the gas phase. These results are correlated with the relative amount of NH bonding in the films; (c) by a modification of the excitation state of the plasma ( ▪) the introduction of H 2 can increase the dissociation rate of the boron precursor BCl 3, and, reacting with chlorine, leads to the formation of HCl. This corresponds to an increase of the growth rate of the coatings. A high content of H 2 in the discharge (H 2>30%) is, however, detrimental to their quality; (d) we were also able to propose possible mechanisms leading to BN formation.

Deposition of boron nitride on graphite at 1300 K

A method for the deposition of BN onto graphite and other substrates is described. Boron trichloride (BCl3) and ammonia (NH3) diluted with Ar were used as reacting gases. The deposition process was carried out at 1300 K as well as lower temperatures in an open system at pressures of 1 atm. The consequences of the introduction of hydrogen to the system were considered. It was demonstrated that the replacement of argon with hydrogen increases the efficiency of the process as well as the theoretical rate of BN deposition. However, the acceleration of the deposition seems to be unprofitable, because the resulting supersaturation leads to the formation of an amorphous phase. The modification of the experimental conditions were proposed.

The interphase and interface microstructure and chemistry of isothermal/isobaric chemical vapour infiltration SiC/BN/SiC composites: TEM and electron energy loss studies

The boron nitride interphase and its interfaces in two-dimensional-SiC/BN/SiC composites have been analysed by transmission electron microscopy and electron energy loss spectroscopy. BN was deposited by isothermal/isobaric chemical vapour infiltration from BCl3–NH3–H2 mixture at moderate temperature. BN and the fibre/BN interface exhibit different features depending on the nature of the NicalonTM fibre surface, raw or treated prior to the BN deposition. When untreated fibres are used, a carbon-rich layer and silica clusters are formed during the manufacturing of the composite. In that case, the interphase is poorly organized and presents a porous microstructure and a large carbon content. With the treated NicalonTM fibre, no formation of a new interlayer is observed at the fibre–BN interface and the interphase exhibits a better organized turbostratic microstructure with no voids. Additionally, in both types of composites, a carbon-rich layer is formed at the BN–matrix interface during the SiC infiltration step at about 1000 °C.

Phase transformation of BN in the solid state during electrostatic deposition

Experiments on BN deposition were carried out using a new electrostatic accelerator with a cascade electrode arrangement. The most interesting result of the experiment is the solid state phase transformation of boron nitride. Particles built of the hexagonal BN phase, which under the present experimental conditions is thermodynamically stable, formed a coating composed of the E-BN phase, which is metastable.

Kinetic Analysis of Chemical Vapor Deposition of Boron Nitride

BN was deposited on Al2O3 substrates from the BCl3─NH3─Ar reagent system. An impinging jet reactor configuration was used to obtain kinetic data in the temperature range of 800° to 1000°C and in the pressure range of 4 to 20 kPa. The BN deposition could be described by a simple kinetic rate expression with an activation energy of about 39 kcal/mol and a first‐order dependency on BCl3 concentration. The BN deposition rate increased with temperature, pressure, and BCl3 concentration. The microstructure of the BN coatings was not strongly influenced by the process parameters.

Simultaneous Chemical Vapor Deposition of Boron Nitride and Aluminum Nitride

Two chemically different phases, hexagonal BN and AIN, were simultaneously produced by chemical vapor deposition (CVD) using an impinging jet reactor and the BCl3─AlCl3─NH3─Ar reagent system. The microstructure of the BN + AIN composite coatings was strongly dependent on temperature, pressure, and BCl3 and AlCl3 concentrations. The growth characteristics of BN and AIN in the codeposition system were similar to those expected from the single‐phase deposition processes (i.e., BN‐CVD and AIN‐CVD), except the growth of AIN whiskers was accentuated, and competition between BN and AIN deposition in the composites was suspected to be the cause of less‐crystalline deposits. In both BN + AIN‐CVD and AIN‐CVD, the growth of AIN whiskers became more apparent with increasing pressure or temperature. The codeposition behavior observed experimentally was compared with thermodynamic predictions.

XPS study of BN thin films deposited by CVD on SiC plane substrates

AbstractBN films deposited from a BF3NH3 precursor, under chemical vapour infiltration conditions, on plane sintered α‐SiC substrates were analysed by XPS. The films are non‐stoichiometric with an N/B atomic ratio of <1. They also contain significant amounts of oxygen atoms, homogeneously distributed in the film and thought to replace partly the nitrogen atoms in the turbostratic hexagonal network. As a result, ternary BNxOy species are formed locally. Near the BN/SiC interface, the oxygen concentration increases owing to the occurrence of ternary SiNxOy species, thought to be the result of an oxinitriding reaction on the substrate surface with the gas phase containing residual oxygen, at the very beginning of the BN deposition process.