Deposition of B4C/BCN/c-BN multilayered thin films by r.f. magnetron sputtering

Thin films of cubic boron nitride (c-BN) and B₄C/BCN/c-BN multilayers, were deposited by r.f. (13.56 MHz) multi-target magnetron sputtering from high-purity (99.99%) h-BN and a (99.5%) B₄C targets, in an Ar (90%)/N₂ (10%) gas mixture. Films were deposited onto silicon substrates with (100) orientations at 300 °C, with r.f. power density near 7 W/cm². In order to obtain the highest fraction of the c-BN phase, an r.f. substrate bias voltage between − 100 and − 300 V was applied during the initial nucleation process and − 50 to − 100 V during the film growth. Additionally, B₄C and BCN films were deposited and analyzed individually. For their deposition, we varied the bias voltage of the B₄C films between − 50 and − 250 V, and for the BCN coatings, the nitrogen gas flow from 3% to 12%. A 300-nm-thick TiN buffer layer was first deposited to improve the adhesion of all samples. X-ray diffraction patterns revealed the presence of c-BN (111) and h-BN phases. FTIR spectroscopy measurements indicate the presence of a peak at 780 cm^− 1 referred to as “out-of-plane” h-BN vibration mode; another peak at 1100 cm^− 1 corresponds to the c-BN TO mode and the “in-plane” vibration mode of the h-BN at 1400 cm^− 1. BN films deposited at 300 °C at a pressure of 4.0 Pa and under − 150 V of nucleation r.f. bias, applied for 35 min, presented the highest c-BN fraction, near 85%. By using 32 layers, it was possible to deposit a 4.6-μm-thick c-BN film with adequate mechanical properties and good adhesion to the substrate.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 100-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal (h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 〈100〉-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal +h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Preparation and characterization of α-Fe2O3 polyhedral nanocrystals via annealing technique

Polyhedral nanocrystals of α-Fe₂O₃ are successfully synthesized by annealing FeCl₃ on silicon substrate at 1000 °C in the presence of H₂ gas diluted with argon (Ar). Uniformly shaped polyhedral nanoparticles (diameter ~ 50-100 nm) are observed at 1000 °C and gases flow rate such as; Ar = 200 ml/min and H₂ = 150 ml/min. Non-uniform shaped nanoparticles (diameter ~ 20-70 nm) are also observed at an annealing temperature of 950 °C with lower gases flow rate (Ar = 100 ml/min and H₂ = 75 ml/min). Nanoparticles are characterized in detail by field-emission electron microscopy (FE-SEM), energy dispersive X-ray (EDX) and high resolution transmission electron microscopy (HRTEM) techniques. HRTEM study shows well resolved (110) fringes corresponding to α-Fe₂O₃, and selected area diffraction pattern (SADP) confirms the crystalline nature of α-Fe₂O₃ polyhedral nanoparticles. It is observed that polyhedral formation of α-Fe₂O₃ nanocrystals depends upon annealing temperature and the surface morphology highly rely on the gas flow rate inside the reaction chamber.     

Facile synthesis of cubic boron nitride nanoparticles from amorphous boron by triple thermal plasma jets at atmospheric pressure

Cubic boron nitride (c-BN) is a superhard material, with hardness value comparable to that of diamond. c-BN is used in a wide range of industrial applications, including tool, abrasives, and refractory. The hardness of c-BN can be improved by decreasing the particle size to the nanoscale; however, the simultaneous application of high pressure (～8 GPa) and temperature (>2,500 K) is required to synthesize the c-BN crystal structure. In this study, we effectively synthesized c-BN nanoparticles from amorphous boron using a triple direct current (DC) thermal plasma jet system at atmospheric pressure. The injection of nitrogen as plasma forming gas generated reactive nitridation species. The average particle size of the synthesized c-BN was 22 nm, and the major crystal structure is the (1 1 1) cubic phase. We carried out a numerical simulation for a thermal fluid, to confirm the high temperature and velocity fields of the plasma jets that formed inside the reactor as the flow rate of plasma forming gas was adjusted. A high production yield of 51% was achieved using amorphous boron at a feed rate of 190 mg/min and the c-BN nanoparticles exhibited high crystallinity without requiring pre-and post-processing.     

Plasma assisted chemical vapour deposition of boron nitride coatings from using BCl3–N2–H2–Ar gas mixture

Boron Nitride coatings have been deposited by plasma-assisted chemical vapour deposition (PACVD) from BCl₃/N₂/H₂/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/H₂ plasma was studied in order to understand the influence of molecular hydrogen in the discharge mixture. Then the two precursors N₂ and BCl₃ 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/N₂ controls the nature of the NH_x (from N to NH₃) 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 H₂ can increase the dissociation rate of the boron precursor BCl₃ 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/H₂ and Ar/Cl₂ 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.     

Nanocrystalline diamond growth on different substrates

Nanocomposite films consisting of diamond nanoparticles of 3-5 nm diameter embedded in an amorphous carbon matrix have been deposited by means of microwave plasma chemical vapour deposition (MWCVD) from CH₄/N₂ gas mixtures. Si wafers, Si coated with TiN, polycrystalline diamond (PCD) and cubic boron nitride films, and Ti-6Al-4V alloy have been used as substrates. Some of the substrates have been pretreated ultrasonically with diamond powder in order to enhance the nucleation density n_nuc. It turned out that n_nuc depends critically on the chemical nature of the substrate, its smoothness and the pretreatment applied. No differences to the nucleation behaviour of CVD PCD films were observed. On the other hand, the growth process seems to be not affected by the substrate material. The crystallinity (studied by X-ray diffraction) and the bonding environment (investigated by Raman spectroscopy) show no significant differences for the various substrates. The mechanical and tribological properties, finally, reflect again the influence of the substrate material: on TiN, a lower hardness was measured as compared to Si, PCD and c-BN, whereas the adhesion of c-BN/nanocrystalline diamond (NCD) system was determined by that of the c-BN film on the underlying Si substrate.     

Structural evolution of boron nitride films grown on diamond buffer-layers

Boron nitride films on diamond buffer layers of varying grain size, surface roughness and crystallinity are deposited by the reaction of B₂H₆ and NH₃ in a mixture of H₂ and Ar via microwave plasma-assisted chemical vapor deposition. Various forms of boron nitride, including amorphous α-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurzitic w-BN and cubic c-BN, are detected in the BN films grown on different diamond buffer layers at varying distances from the interface of diamond and BN layers. The c-BN content in the BN films is inversely proportional to the surface roughness of the diamond buffer layers. Cubic boron nitride can directly grow on smooth nanocrystalline diamond films, while precursor layers consisting of various sp²-bonded BN phases are formed prior to the growth of c-BN film on rough microcrystalline diamond films.     

Parameter spaces for the nucleation and the subsequent growth of cubic boron nitride films

The data existing in the literature about the deposition of cubic boron nitride thin films were reviewed critically in order to establish the parameter spaces of c-BN nucleation and growth. The ion energy E_i, the flux ratio F (=incoming ions/incoming boron atoms), the ion mass m_i, (or the ratio Ar/N₂, respectively), and the substrate temperature T_s, had already been identified as the decisive parameters which are, however, interdependent. Earlier data collections on c-BN deposition had shown that, irrespective of the deposition technique used, a well-defined c-BN region exists in the F/E_i parameter space, in which the deposition of c-BN is possible. Similar regions exist in the F/m_i and F/T_s parameter spaces. The present collection extends these older diagrams considerably, especially to the low energy region. From this extention it can be concluded that the momentum transfer concepts proposed in the literature fail to explain the data. Furthermore, the older collections were considered valid for nucleation and growth likewise. However, in recent years data have been published showing that the boundaries of the c-BN regions are different for nucleation and growth. After successful nucleation, subsequent growth can occur either at reduced ion bombardment (either energy or flux ratio or ion mass) and also at reduced temperatures. The existing data for this parameter reduction have been collected in this paper. It will be shown that the growth depends in a similar way as the nucleation on the (interdependent) ion bombardment parameters but no longer on temperature. This means that the nucleation and growth of c-BN are based on different, although in both cases ion-induced, mechanisms.     

Preparation of c-BN films by RF sputtering and the relation of BN phase formation to the substrate bias and temperature

This paper deals with the deposition of cubic boron nitride (c-BN) films by radio frequency (RF) magnetron sputtering. The nearly pure c-BN films have been prepared on Si(100) substrates using hexagonal boron nitride (h-BN) targets. Argon gas mixed with nitrogen gas was used as sputtering gas. The deposited films were characterized by Fourier transform infrared (FTIR) spectroscopy and transmission electron diffraction (TED). A ‘temperature-bias' phase diagram has been worked out. It indicates that the c-BN phase prefers the relative high temperature and negative bias. An opinion was presented that the c-BN nuclei grow discontinuously with every time the ‘thermal spike' coming.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on TiO2 (rutile) layer deposited on Si(111) substrates

GaN nanorods have been synthesized by ammoniating Ga₂O₃ films on a TiO₂ middle layer deposited on Si(111) substrates. The products were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD analysis indicates that the crystallization of GaN film fabricated on TiO₂ middle layer is rather excellent. The FTIR, SEM and HRTEM demonstrate that these nanorods are hexagonal GaN and possess a rough morphology with a diameter ranging from 200 nm to 500 nm and a length less than 10 μm, the growth mechanism of crystalline GaN nanorods is discussed briefly.     

Epitaxy of cubic boron nitride on (001)-oriented diamond

Cubic boron nitride (c-BN), although offering a number of highly attractive properties comparable to diamond, like hardness, chemical inertness and a large electronic bandgap, up to now has not found the attention it deserves. This mostly has to do with preparational problems, with easy chemical routes not available and, instead, the necessity to apply ion-bombardment-assisted methods. Hence, most of the c-BN samples prepared as thin films have been nanocrystalline, making the prospect of using this material for high-temperature electronic applications an illusion. Although heteroepitaxial nucleation of c-BN on diamond substrates has been demonstrated using the high-pressure-high-temperature technique, none of the low-pressure methods ever succeeded in the epitaxial growth of c-BN on any substrate. Here, we demonstrate that heteroepitaxial c-BN films can be prepared at 900 degrees C on highly (001)-oriented diamond films, formed by chemical vapour deposition, using ion-beam-assisted deposition as a low-pressure technique. The orientation relationship was found to be c-BN(001)[100]||diamond(001)[100]. High-resolution transmission electron microscopy additionally proved that epitaxy can be achieved without an intermediate hexagonal BN layer that is commonly observed on various substrates.     

Photoluminescence properties of the In2O3 octahedrons synthesized by carbothermal reduction method

In₂O₃ octahedrons were synthesized by carbothermal reduction method. The products were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction analysis (SAED) and room-temperature photoluminescence (PL) spectra. The results show that the products are single-crystalline In₂O₃ octahedrons with the arrises length in the range of 400-3000 nm. The PL spectra displays blue and green emission peaks which can be indexed to default and oxygen vacancies; blue-shift and intensity decrease was observed when excitation wavelength decreases from 380 nm to 325 nm. The growth mechanism of the In₂O₃ octahedrons is discussed.     

Effects of oxygen partial pressures on microstructures and compositions of BaO-SrO-ZnO-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films by RF-sputtering method

Ceramic thin films have been deposited by radio frequency magnetron sputtering method, using a mixture of 1 mol (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ and 1 mol ZnO as target. The effects of oxygen partial pressures on crystallization and morphologies of thin films have been investigated in detail by X-ray diffraction, scanning electron microscope (SEM), and atomic force microscope. X-ray photoelectron spectroscopy (XPS) analysis was carried out to identify the composition and chemical state near the films’ surface. It is observed that the diffraction intensity of (001) peak increases dramatically when a small amount of oxygen is added to Ar atmosphere. The cross-sectional SEM images verify that the growth rate decreases sharply due to existence of oxygen, because the thickness decreases from 3.10 μm (pure Ar) to 1.38 μm (O₂/Ar ratio of 0.2:1). The morphologies indicate that the thin films are crackfree with perfect crystallization and all the particles are uniform in size when the O₂/Ar flow ratios are 0.2:1 and 0.4:1. The ceramics thin films grown at O₂/Ar flow ratio of 0.2:1 does not contain adsorbed oxygen, which is confirmed by XPS.     

SnO2/α-Fe2O3 hierarchical nanostructure: Hydrothermal preparation and formation mechanism

In this paper, we reported a simple solution method to assemble SnO₂ nanorods hierarchically on the surface of α-Fe₂O₃ nanosheets using Fe₃O₄ nanosheets as precursor. The product was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). Our experimental results show that the lattice mismatch at the interface of SnO₂ nanorods with α-Fe₂O₃ nanosheets played an important role in determining the growth direction of SnO₂ nanorods. The interface prefers to take the least lattice mismatch and thus the preferential growth direction of SnO₂ nanorods was along [1 0 1] direction. The result may have important impact on the understanding of the nucleation growth process in a heterogeneous system.     

Synthesis of vertically aligned boron nitride nanosheets using CVD method

Boron nitride nanosheets (BNNSs) protruding from boron nitride (BN) films were synthesized on silicon substrates by chemical vapor deposition technique from a gas mixture of BCl₃–NH₃–H₂–N₂. Parts of the as-grown nanosheets were vertically aligned on the BN films. The morphology and structure of the synthesized BNNSs were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transformation infrared spectroscopy. The chemical composition was studied by energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Cathodoluminescence spectra revealed that the product emitted strong UV light with a broad band ranging from 250 to 400 nm. Field-emission characteristic of the product shows a low turn-on field of 6.5 V μm^?1.     

Thermal oxidation of single crystal aluminum nitride — A high resolution transmission electron microscopy study

The impact of the oxidation time on the structures of thermal oxides formed on AlN was determined by high resolution transmission electron microscopy (HRTEM). Oxidation of AlN single crystals was performed for 2 to 6 h at 1000 °C. Oxidation for 2 h produced mostly amorphous oxide layers whereas oxidation for both 4 and 6 h produced partially crystalline oxide layers. The oxide layer thickness varied from 205 to 600 nm for oxidation times of 2 and 6 h respectively. The crystalline oxide was mostly single phase α-Al₂O₃ except at the surface where it was a mixture of γ-Al₂O₃ and α-Al₂O₃. Based on the different structures produced for different oxidation times, we speculate that the oxide formed changes with thickness: first an amorphous oxide, then γ-Al₂O₃, and finally α-Al₂O₃ as the oxide thickness increases. The AlN crystal was nearly defect- and oxygen-free for oxidation at 1000 °C. This could be due to the rapid diffusion of the nitrogen and aluminum interstitials at a high temperature leading to a point-defect equilibrium throughout the nitride. A faceted interface between Al₂O₃ and AlN could be attributed to the surface diffusion to minimize energy.     

Atmospheric pressure PECVD of SiO2 thin film at a low temperature using HMDS/O2/He/Ar

SiO₂-like thin films were deposited at a low temperature (< 50 °C) by a remote-type, atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) using a pin-to-plate-type, dielectric barrier discharge with gas mixtures containing hexamethyldisilazane (HMDS)/O₂/He/Ar. The film characteristics were investigated according to the HMDS and O₂ flow rates. To obtain a more SiO₂-like thin film, an adequate combination of HMDS and oxygen flow rates was required to remove the -(CH₃)_x bonding in the HMDS and to oxidize the Si in HMDS effectively. At the optimized flow rates, the surface roughness of the SiO₂-like thin film was also the lowest. By using HMDS (50 sccm) and O₂ (500 sccm) flow rates in the gas mixture of HMDS/O₂/He (2 slm)/Ar (600 sccm), SiO₂-like thin films with a low impurity (< 6.35% C) were obtained at a deposition rate of approximately 10.7 nm/min.     

RF magnetron sputtered aluminium oxide coatings on iridium

The effects of process parameters on the microstructural morphology of aluminium oxide (Al₂O₃) coatings on Ir have been studied. Al₂O₃ coatings were deposited on Ir-coated isotropic graphite (IG) substrates at substrate temperatures of room temperature (RT)-1073 K, RF power of 200–600 W in an Ar, or Ar+1–10% O₂, sputtering gas atmosphere by RF magnetron sputtering. Al₂O₃ coatings which were deposited at high substrate temperatures and high RF powers in an Ar, or an Ar+O₂, sputtering gas atmosphere were found to contain a dense, fine columnar structure with a -Al₂O₃ phase, low Ar content and a relatively high hardness value of ca. 1050 H _v. Furthermore, high resolution transmission electron microscopy (HRTEM) results revealed the epitaxial growth of Al₂O₃ coatings on Ir-coated IG substrate. It was found that the interface between Al₂O₃ and Ir coatings was sharp and Al₂O₃ coatings remained intact with the Ir-coated IG substrate.     

Interface characterization by TEM,AES and SIMS in tough SiC (ex-PCS) fibre-SiC (CVI) matrix composites with a BN interphase

The fibre-matrix interfacial zone formed during the isothermal/isobaric chemical vapour infiltration processing of SiC fibres (ex-polycarbosilane)/boron nitride/SiC matrix composites has been analysed by TEM/electron energy loss spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy. In the composites, the boron nitride interphase (deposited from BF₃-NH₃) is made of turbostratic boron nitride, almost stoichiometric but containing some oxygen (less than 5 at %). The boron nitride layer stacks are randomly orientated except in the very vicinity of the fibre surface where they lie almost parallel to the substrate. The long chemical vapour infiltration treatment at 1000 °C used to infiltrate the SiC matrix acts as an annealing treatment for the metastable ex-polycarbosilane fibres which gives rise to the growth of an SiO₂/carbon amorphous double layer at the boron nitride/fibre interface. Deflection of microcracks arising from the failure of the brittle SiC-matrix occurs at the boron nitride/SiO₂ interface considered to be the weaker link in the matrix/boron nitride interphase/SiO₂/carbon/fibre sequence. It is suggested that the combination of the boron nitride layered interphase and SiO₂/carbon fibre decomposition products might play an important role in determining the propagation path of microcracks in the fibre/matrix interfacial zones and could be responsible, at least to some extent, for the non-brittle behaviour of such composites.