Two kinds of boron and nitrogen co-doped carbon nanotubes (CNTs) dominated by bonded or separated B and N are intentionally prepared, which present distinct oxygen reduction reaction (ORR) performances. The experimental and theoretical results indicate that the bonded case cannot, while the separated one can, turn the inert CNTs into ORR electrocatalysts. This progress demonstrates the crucial role of the doping microstructure on ORR performance, which is of significance in exploring the advanced C-based metal-free electrocatalysts.

Can Boron and Nitrogen Co-doping Improve Oxygen Reduction Reaction Activity of Carbon Nanotubes?

Cubic boron nitride (cBN) has a number of highly desirable mechanical, thermal, electrical, and optical properties. Because of this, there has been an extensive worldwide effort to synthesize thin films of cBN. Film synthesis is difficult in that without significant levels of ion bombardment during growth, only sp2-bonded BN forms, not sp3-bonded cBN. Recently there has been considerable progress in improving the deposition techniques and cBN film quality. In addition, progress has been made in understanding how energetic deposition conditions can lead to cBN formation. However, unanswered questions remain and process improvements are still needed. In this paper we critically and comprehensively review recent developments in cBN film synthesis and characterization. First, the structures and stability of the BN phases and characterization techniques are described. Next, the key experimental parameters controlling cBN film formation and synthesis techniques are discussed. Following a review of microstructure, the proposed mechanisms of cBN formation and the observed mechanical and electrical properties of cBN films are analyzed. We conclude by highlighting the current impediments to the practical realization of cBN-film technology.

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Review of advances in cubic boron nitride film synthesis

The control of BN and BC bonds in BCN films synthesized using pulsed laser deposition

Cubic BN (cBN) has a set of extreme properties similar or even superior to diamond The advance of science and technology of cBN has however been severely hampered by the poor quality of the material available (random orientation, limited film thickness, poor crystallinity and adhesion with substrates due to a non-cubic BN interlayer) This paper reviews the recent progress in the nucleation, growth and characterization techniques of cBN films It describes various successful approaches in interface engineering and growth techniques in increasing film thickness, improving crystallinity and adhesion of cBN films to the substrate, which are the major issues hindering cBN films for both mechanical and electronic applications Based on observations of the surface and interface structures, we further discuss the growth mechanisms of cBN films via physical and chemical routes

https://iopscience.iop.org/article/10.1088/0022-3727/40/20/S03/pdf

Nucleation, growth and characterization of cubic boron nitride (cBN) films

Oxygen reduction and evolution reactions are of immense importance in electrochemical conversion/ storage devices like regenerative/alcohol/hydrogen based fuel cells and metal-air batteries. Here, a rational facile synthesis methodology has been developed to design N-doped carbon nanotubes (N-CNTs) and Fe-Fe3C nanostructures co-embedded in B-doped mesoporous carbon nanostructures (BFNCNTs) as a noble metal-free superior bi-functional electrocatalyst for oxygen evolution/reduction reactions. The incorporation of N and B with negligible/undetectable B-N formation and Fe-Fe3C nanostructures leads to the superior performance by introducing plenty of defects, local heterogeneity and a high specific surface area (similar to 272 m(2) g(-1)). Besides, mesoporous boron-doped carbon acts as a host material for NCNTs and Fe-Fe3C, and it offers good connectivity as well as a protective coating for durable catalysis. Remarkably, more positive onset (-30 mV) and half-wave potentials (-225 mV) with -94% current retention under accelerated stability test and fuel tolerance for the ORR, in combination with lower onset (422 mV) and E-j=10(OER) (562 mV) potentials with high current density (190 mA cm(-2) @ 0.8 V vs. Ag/AgCl) for the OER as compared to commercial state-of-the-art electrocatalysts suggest superior bifunctional behavior of BFNCNTs. The complete oxygen electrochemical activity Delta E = E-j(OER)=10 = E-1/2(ORR) = 0.788 V for BFNCNTs is lower than recently reported various state-of-the-art bifunctional catalysts. Besides, a prototype battery fabrication using BFNCNTs as the cathode electrode for driving a light emitting diode has been demonstrated. Overall, BFNCNTs have potential to serve as a non-precious electrocatalyst for electrochemical energy devices.

Designing N-doped carbon nanotubes and Fe–Fe3C nanostructures co-embedded in B-doped mesoporous carbon as an enduring cathode electrocatalyst for metal–air batteries

We report on the growth of cubic boron nitride films on {100} silicon using a low density, supersonic plasma jet generated by a direct‐current arc discharge expanded to low pressures. The arc discharge was operated on source gas mixtures of nitrogen and argon, with boron trichloride injected downstream of the expansion nozzle. The films were analyzed by infrared absorption and x‐ray photoelectron spectroscopy. Phase selectivity was obtained by the application of a negative bias to the substrate so as to bombard the surface with energetic ions during deposition. The deposition process was found to be highly sensitive to substrate temperature and substrate bias voltage.

Cubic boron nitride synthesis in low‐density supersonic plasma flows

This paper describes the growth and analysis of cubic boron nitride films in a low-density, supersonic nitrogen/argon plasma flow into which boron trichloride gas was injected. Both hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN) were synthesized using this apparatus. Phase selectivity is obtained by applying a relatively low negative bias voltage to the substrate. All of the films described in this paper were grown on {100} silicon wafers at substrate temperatures varying from 400–700 °C. Boron nitride films with greater than 90% cubic phase were successfully synthesized with this method. The films were analyzed using infrared spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. The volumetric percentages of the hexagonal and cubic phases were determined from model fits to the infrared transmission spectra of the films. X-ray photoelectron spectroscopy provided qualitative evidence for the presence and/or lack of sp2 bonding through the identification of a π-plasmon feature in the spectra. Infrared reflectance spectra are used to provide insight into the growth mechanisms leading to c-BN formation and have revealed features which are not present in the transmission spectra, specifically the 1305 cm−1 LO mode of c-BN and the 1610 cm−1 LO mode of h-BN. The mean ion energies involved with this bias-enhanced chemical vapor deposition (CVD) process are much lower than the ion energies in traditional physical vapor deposition (PVD) processes; however, the ion fluxes (currents) used in this CVD process are at least an order of magnitude higher, resulting in a total momentum transfer to the deposited atoms through ion bombardment that is at least equal to or greater than that reported for many ion-enhanced PVD processes.

Low energy ion impact-enhanced growth of cubic boron nitride in a supersonic nitrogen/argon plasma flow

Near-edge X-ray absorption fine structure spectroscopy of arcjet-deposited cubic boron nitride

: An experimental study of the measurement of cathode temperature, current distribution, and near-cathode electron number density in a high power hydrogen arcjet is presented. This study is motivated by the desire to better understand arc-electrode interactions in arcjet thrusters, which in many cases, is the main determinate of arcjet lifetime. Measurements such as these may also provide the needed boundary conditions for numerical arcjet simulations, presently under development. We describe in this paper the application of a non-intrusive in-situ measurement technique for on-axis, spectral imaging of the electrode region of arcjets, and the application of this technique to the measurement of the cathode and anode temperatures, cathode spot size, and current distribution in a 30kW hydrogen arcjet thruster. A relatively large field of view (twice the throat diameter) and high spatial resolution (9 micrometers) are achieved.

Darren Berns

Papers

Cubic boron nitride synthesis in low‐density supersonic plasma flows

Low energy ion impact-enhanced growth of cubic boron nitride in a supersonic nitrogen/argon plasma flow

Near-edge X-ray absorption fine structure spectroscopy of arcjet-deposited cubic boron nitride

Plasma and Cathode Emission from a High Power Hydrogen Arcjet Thruster

Spectral imaging of the arcjet electrode region