Surfaces of undoped and boron doped polycrystalline diamond films influenced by negative DC bias voltage

The hydrogen ion bombardment is performed by applying a negative bias voltage to the substrate during microwave plasma chemical vapor deposition process, using only hydrogen as reactant gas. The size of (001) faces increases after hydrogen ion etching while other grains are etched off. The surfaces of [001]-oriented films after doping boron are investigated by scanning electron microscopy (SEM) and cathodoluminescent (CL) spectra. The absence of the band-A emission in the CL spectra means a low density of dislocation in the films. It is the first time that the peak at 741.5 nm and the broad peak at approximately 575 and 625 nm in the CL spectra were reduced efficiently after boron doping in (001) polycrystalline diamond films and to propose that these phenomena should be explained in simple terms with penetration of the lattice nets of the [001]-oriented faces model.     

Characterization of p–n junction formed at the boundary of facets in cubic-BN using scanning electron microscope

For the application of ultraviolet light emitting diodes, self-organized p–n junctions were formed at the boundaries of facets in cubic boron nitride. The optical and electrical characteristics of these junctions were studied using cathodoluminescence (CL) and electron-beam-induced current (EBIC) in a scanning electron microscope. The p and n regions were clearly distinguished by the variation of CL spectra and monochromatic CL images. A broad band with a peak at 4.0 eV (310 nm) was observed in p-region, but not in n-region. Monochromatic CL image at 4.0 eV showed that the Be impurity distribution in p-region was not uniform. Variation of EBIC profiles indicated the inhomogeneity of diffusion length along p-n junction. The inhomogeneous electroluminescence along the p–n junction under the reverse current condition was clarified by the inhomogeneities revealed by EBIC and CL characterizations.     

Non-linear increases in excitonic emission in synthetic type-IIa diamond

Free-exciton emissions increase non-linearly by cathodoluminescence (CL) above the threshold probe current of 30 μA in high-pressure high-temperature synthetic type-IIa diamond. A droplet of electron-hole liquid (EHL) is also observed by CL for the first time. Furthermore, boron acceptor bound-exciton emission as well as free-exciton emission also increases super-linearly in an unintentionally boron-contaminated area. The threshold probe current of non-linear increase of excitonic emission is in accordance with the emergence of the EHL peak. It is considered that the non-linear increase of excitonic emissions is due to the increase in the radiative recombination rate of free excitons under high exciton density.     

The effect of HPHT treatment on the spectroscopic features of type IIb synthetic diamonds

The effect of high pressure high temperature treatment on the spectroscopic features of boron-doped type IIb synthetic diamonds has been studied. Synthetic HPHT diamond crystals with different concentrations of boron acceptors were annealed at temperatures in the range 1800–2650 °C under a stabilizing pressure of 7–7.5 GPa. Fourier-transform infra-red absorption spectroscopy and cathodoluminescence were applied to study the effect of the annealing. We found that for annealing temperatures up to 2650 °C, the IR absorption features related to neutral boron acceptors did not change in intensity, demonstrating that single substitutional boron was not affected by the treatment. This finding is in good agreement with the recent first-principle calculations of Goss and Briddon (Phys. Rev. B 73 (2006) 085207) predicting very high activation energies for migration of substitutional boron in the diamond lattice. For diamonds with boron concentration of about 1 ppm, it was found that annealing at 2650 °C for 1 h produced an intense CL emission band peaking at 2.85 eV, which is known to be related to dislocations. It was suggested that dislocations in the studied boron-doped diamonds were formed due to plastic deformation occurred during anneals.     

High‐Temperature Strength of Boron Suboxide Ceramic Consolidated by Spark Plasma Sintering

The spark plasma sintering (SPS) of B₆O ceramics using a highly crystalline boron suboxide powder with a low oxygen deficiency level is reported. The monolithic boron suboxide ceramic exhibited a room‐temperature strength of 300 ± 20 MPa, which is comparable to the strength of monolithic boron carbide. With increasing flexural test temperature, the strength of the boron suboxide ceramics increased to 450 MPa at 1400°C. The increase in strength with the temperature is associated with the unique microstructure of boron suboxide grains, which allows intergranular “brittle” fracture along subgrains even at 1400°C. This suggests that even higher strengths can be achieved.     

Cathodoluminescence and electron field emission of boron-doped a-C:N films

The optical and electrical properties of so-called carbon nitride films (a-C:N) and boron doped so-called carbon nitride films (a-C:N:B) are studied with cathodoluminescence (CL) spectroscopy and electron field emission measurement. The a-C:N films were first deposited on Si by a filtered cathodic arc plasma system, and then boron ions (∼1 × 10¹⁶ cm⁻²) were implanted into the a-C:N films to form a-C:N:B films by a medium current implanter. The structural and morphological properties of a-C:N and a-C:N:B films were then analyzed using secondary ion mass spectrometer, X-ray photoelectron spectroscopy, FT-IR spectra, Raman spectroscopy and atomic force microscopy. The a-C:N film exhibits luminescence of blue light (∼2.67 eV) and red light (∼1.91 eV), and the a-C:N:B film displays luminescence of blue light (∼2.67 eV) in CL spectra measured at 300 K. Furthermore, the incorporated boron atoms change the electron field emission property, which shows a higher turn on field for the a-C:N:B film (3.6 V/μm) than that for the a-C:N film (2.8 V/μm).     

Influence of the thermal process of carbon template removal in the mesoporous boron nitride synthesis

Influence of the thermal process involved in the carbon template elimination during the synthesis of mesoporous boron nitride by using nanocasting process of a mesoporous CMK-3 carbon with a borazinic precursor is presented. The borazinic precursor, the tri(methylamino)borazine (MAB), is converted to boron nitride (BN) inside the mesopores of a CMK-3 mesoporous carbon template by ceramization under nitrogen or under ammonia. The carbon template elimination is carried out by thermal treatment under air or under ammonia. The X-ray diffraction, TEM and pore size analysis are used to study the texture of the boron nitride synthesized from the carbon template. A template elimination performed by hydrogenation with an ammonia treatment allows to obtain an organized porous structure, which is not possible by using an oxidation treatment. In order to preserve the mesoporous organization of boron nitride, a two steps procedure (ceramization followed with template elimination by hydrogenation) is more efficient than a one step procedure (ceramization and template hydrogenation simultaneously).     

Effect of distributed injection of air into the afterburning chamber of a ram-rocket engine on the efficiency of combustion of boron particles

A mathematical model of combustion of boron particles in a ram-rocket engine is developed. The boron combustion efficiency for one-stage and two-stage injection of air into the afterburning chamber is calculated. It is demonstrated that two-stage injection of air sometimes allows the time of complete combustion of boron particles to be significantly reduced (by a factor of 1.5–3); thus, the fuel combustion efficiency in the ram-rocket engine can be increased. The simulated results are consistent with available experimental data.     

Cathodoluminescence of boron-doped heteroepitaxial diamond films on platinum

Cathodoluminescence (CL) spectra of diamond films epitaxially grown on single crystal platinum (111) have been investigated at room temperature and 89 K. It was found that the CL spectra of the heavily boron-doped (>3×10²⁰ cm⁻³) diamond films of more than 16 μm thickness consist only of a near-edge emission at 248±1 nm (5.00±0.02 eV), while any other emissions are absent. It was also found that the temperature dependence of the 248 nm band is very unusual, since its intensity increases as temperature increases. This result is in strong contrast to CL intensities of both the free exciton and the bound exciton, which decrease significantly with temperature. It is concluded that a new electronic band due to heavily-doped boron is the origin of the 248 nm emission.     

Physical and thermal properties of l‐lactide/ϵ‐caprolactone copolymers: the role of microstructural design

Understanding the underlying role of microstructural design in polymers allows for the manipulation and control of properties for a wide range of specific applications. As such, this work focuses on the study of microstructure–property relationships in l‐ lactide/?‐caprolactone (LL/CL) copolymers. One‐step and two‐step bulk ring‐opening polymerization (ROP) procedures were employed to synthesize LL/CL copolymers of various compositions and chain microstructures. In the one‐step procedure, LL and CL were simultaneously copolymerized to yield P(LL‐stat‐CL) statistical copolymers. In the two‐step procedure, poly(l‐ lactide) (PLL) and poly(?‐caprolactone) (PCL) prepolymers were synthesized in the first step before CL and LL respectively were added in the second step to yield P[LL‐b‐(CL‐stat‐LL)‐b‐LL] and P[CL‐b‐(LL‐stat‐CL)‐b‐CL] block copolymers as the final products. The findings reveal that, in addition to the copolymerization procedure employed, the length and type of the prepolymer play important roles in determining the chain microstructure and thereby the overall properties of the final copolymer. Moreover, control over the degree of crystallinity and the type of crystalline domains, which is controlled during the polymer chemistry process, heavily influences the physical and mechanical properties of the final polymer. In summary, this work describes an interesting approach to the microstructural design of biodegradable copolymers of LL and CL for potential use in biomedical applications. © 2019 Society of Chemical Industry     

Influence of the substrate type on CVD grown homoepitaxial diamond layer quality by cross sectional TEM and CL analysis

To assess diamond-based semiconducting devices, a reduction of point defect levels and an accurate control of doping are required as well as the control of layer thickness. Among the analyses required to improve such parameters, cross sectional studies should take importance in the near future. The present contribution shows how FIB (focused ion beam) preparations followed by electron microscopy related techniques as TEM or CL allowed to perform analysis versus depth in the layer, doping and point defect levels. Three samples grown along the same week in the same machine with identical growth conditions but on different substrates (CVD-IIIa (110) oriented, CVD-optical grade (100) oriented and a HPHT-Ib (100) oriented) are studied. Even though A-band is observed by CL, no dislocation is observed by CTEM. Point defect type and level are shown to substantially change with respect to the substrate type as well as the boron doping levels that vary within an order of magnitude. H3 present in the epilayer grown on HPHT type of substrate is replaced by T1 and NE3 point defects for epilayers grown on the CVD type one. An increase of excitonic transitions through LO phonons is also shown to take place near the surface while only TO ones are detected deeper in the epilayer. Such results highlight the importance of choosing the correct substrate.     

The Effect of Particle Size Distribution on the Microstructure and the Mechanical Properties of Boron Carbide-Based Reaction-Bonded Composites

The presence of unreacted, free silicon lowers the mechanical properties of reaction-bonded boron carbide. The fraction of free silicon can be reduced by increasing the green density of the initial boron carbide performs. The use of multimodal boron carbide mixtures allows attaining 75% green density. After reaction bonding with molten silicon, the composites consist of four phases, namely the original B₄C particles, the B₁₂(B,C,Si)₃ phase, product of the dissolution–precipitation process, β-SiC, and residual Si. The volume fraction of residual Si in the composites is in the 8–10% range. The infiltrated composites display elevated values of the mechanical properties with a high Weibull modulus.     

Local boron doping quantification in homoepitaxial diamond structures

The capability of transmission electron microscopy (TEM) using the high angle annular dark field mode (HAADF, also labelled Z-contrast) to quantify boron concentration, in the high doping range between 10¹⁹ cm^? 3 and 10²¹ cm^? 3, is demonstrated. Thanks to the large relative variation of atomic number Z between carbon and boron, doping concentration maps and profiles are obtained with a nanometer-scale resolution. A novel numerical simulation procedure allows the boron concentration quantification and demonstrates the high sensitivity and spatial resolution of the technique.     

Lifespan Extension of Podospora anserina Mic60-Subcomplex Mutants Depends on Cardiolipin Remodeling

Function of mitochondria largely depends on a characteristic ultrastructure with typical invaginations, namely the cristae of the inner mitochondrial membrane. The mitochondrial signature phospholipid cardiolipin (CL), the F₁F_o-ATP-synthase, and the ‘mitochondrial contact site and cristae organizing system’ (MICOS) complex are involved in this process. Previous studies with Podospora anserina demonstrated that manipulation of MICOS leads to altered cristae structure and prolongs lifespan. While longevity of Mic10-subcomplex mutants is induced by mitohormesis, the underlying mechanism in the Mic60-subcomplex deletion mutants was unclear. Since several studies indicated a connection between MICOS and phospholipid composition, we now analyzed the impact of MICOS on mitochondrial phospholipid metabolism. Data from lipidomic analysis identified alterations in phospholipid profile and acyl composition of CL in Mic60-subcomplex mutants. These changes appear to have beneficial effects on membrane properties and promote longevity. Impairments of CL remodeling in a PaMIC60 ablated mutant lead to a complete abrogation of longevity. This effect is reversed by supplementation of the growth medium with linoleic acid, a fatty acid which allows the formation of tetra-octadecanoyl CL. In the PaMic60 deletion mutant, this CL species appears to lead to longevity. Overall, our data demonstrate a tight connection between MICOS, the regulation of mitochondrial phospholipid homeostasis, and aging of P. anserina.     

Direct pyrolysis mass spectrometry analyses of polyamide‐6 containing melamine and boron compounds

In this work, the thermal degradation characteristics of polyamide 6 (PA6) containing melamine (Me) and a boron‐containing additive, borophosphate (BPO₄), zinc borate (ZnB) or a boron and silicon‐containing oligomer (BSi) are investigated systematically via direct pyrolysis mass spectrometry. In the presence of boron compounds, not only the release of melamine and its degradation products but also thermal characteristics of PA6 are affected significantly and the interactions between melamine and PA6 are enhanced. For the composite involving BPO₄, sublimation of melamine and degradation of PA6 are slightly shifted to high temperatures. Whereas, for the composites involving ZnB and BSi, sublimation of melamine is depressed due to the glassy surface formed by ZnB and BSi and release of thermal degradation products of PA6 are shifted to lower temperatures noticeably. The glassy surface generated by ZnB allows the release of degradation products of melamine to a certain extent. Conversely, for the composite involving BSi, reduction in the yields of degradation products of melamine is also noted. The trap of degradation products of melamine in the polymer matrix causes significant decrease in the the temperature region where thermal degradation products of PA6 are recorded. POLYM. COMPOS. 34:1389–1395, 2013. © 2013 Society of Plastics Engineers     

Extraction of boron and silicon in hydrodifluoride processing of a datolite concentrate

The composition of volatile products upon heating of a datolite concentrate that was fluorinated with ammonium hydrodifluoride were studied; the temperature parameters of the transition of the boron and silicon compounds to the gaseous phase were determined and it was established that the difference of the volatilities of the boron and silicon fluoroammoium salts allows selective extraction of these products. A closed technical scheme for processing datolite concentrate by ammonium hydrodifluoride to produce commercial products, viz., ammonium fluoborate, boric acid, amorphous silica, and fluorite, was proposed.     

Multiphysics modeling of proton exchange membrane water electrolysis: From steady to dynamic behavior

Proton exchange membrane water electrolysis (PEMWE) is currently developed for the design of mature industrial-scale manufactures with commercialization. It needs reducing hydrogen production cost by lowering material cost and increasing operating current density. In engineering perspectives, the study of electrolytic performance during dynamic operation is crucial for PEMWE system management and process control. However, there is few multiphysics models of PEMWE considering transient behavior. The one-dimensional (1D) comprehensive dynamic multiphysics model allows to explore temporal transport phenomena in the PEMWE, and predict electrolytic performance. The 1D model is endorsed by the spatially lumped model from the literature. Changing values of structural and physical properties of porous transport layers (PTLs) and catalyst layers (CLs) allows the observation of their effects on the electrolytic performance and transport phenomena in two-phase flow regime. It suggests that the appropriate PTL properties, and CL fabrication method can lower the cost and remain high electrolytic performance.     

Electrochemical reactivity at graphitic micro-domains on polycrystalline boron doped diamond thin-films electrodes

This paper deals with the electrochemical reactivity of boron doped diamond (BDD) electrodes. A comparative study has been carried out to show the influence of the presence of graphitic micro-domains upon the surface of these films. Those graphitic domains are sometimes present on as-grown boron doped diamond electrodes. The effect of doping a pure Csp³ diamond electrode is established by highly oriented pyrolytic graphite (HOPG) abrasion onto the diamond surface. In order to establish the effect of doping on a pure Csp³ diamond electrode, the amount of graphitic domains was increased by means of HOPG crystals grafted onto the BDD surface. Indeed that method allows the enrichment of the Csp² contribution of the electrode.The presence of graphitic domains can be correlatively associated with the presence of kinetically active redox sites. The electrochemical reactivity of boron doped diamond electrodes shows a distribution of kinetic constants on the whole surface of the electrode corresponding to different active sites. In this paper, we have studied by cyclic voltammetry and electrochemical impedance spectroscopy the kinetics parameters of the ferri/ferrocyanide redox couple in KCl electrolyte. A method is proposed to diagnose the presence of graphitic domains on diamond electrodes, and an electrochemical “pulse cleaning” procedure is proposed to remove them.     

Borcalein: a Carborane-Based Analogue of Baicalein with 12-Lipoxygenase-Independent Toxicity

12-Lipoxygenase is crucial for tumour angiogenesis. 5,6,7-Trihydroxy-2-phenyl-4H-1-benzopyran-4-one (baicalein) is a suitable inhibitor for this enzyme but is rapidly metabolised in vivo. Thus, an improvement of the metabolic stability is necessary to enhance the therapeutic efficiency. An emerging approach to enhance metabolic stability of carbon-based pharmaceuticals is the use of metabolically stable, non-toxic boron clusters, such as dicarba-closo-dodecaborane(12)s (carboranes) as phenyl mimetics. Therefore, the unsubstituted phenyl ring of baicalein was replaced by meta-carborane, resulting in borcalein, the carborane analogue of baicalein. This substitution resulted in a decreased inhibitory activity toward 12-lipoxygenase, but led to increased toxicity in melanoma (A375, B16, B16F10) and colon cancer cell lines (SW480, HCT116, CT26CL25) with decreased tumour selectivity in comparison to baicalein. Surprisingly, borcalein displays a different mechanism of cytotoxicity with increased intracellular production of reactive oxygen species (ROS), reactive nitrogen species (RNS) and nitric oxide (NO).     

A quantitative study of the boron acceptor in diamond by Fourier-transform photocurrent spectroscopy

Fourier-transform photocurrent spectroscopy (FTPS) was used as a sensitive spectroscopic method to study boron doping in diamond layers, deposited by microwave plasma enhanced chemical vapor deposition (CVD). Results were compared to boron doped single crystals, synthesized at high pressure and high temperature. Introduction of boron increases the photosensitivity of diamond; the measured spectrum of excited states of the boron acceptor depends both on the crystal perfection and the boron concentration. The spectrum of excited states is a clear fingerprint of the presence of substitutional boron (up to 31 absorption lines have been identified). A quantitative assessment of the substitutional boron concentration is possible and the sensitivity of FTPS in combination with photothermal ionization spectroscopy (PTIS) for boron detection in diamond is estimated to be better then 1 part per billion (ppb).