The role of free carbon in the transport and magnetic properties of boron carbide

Bandyopadhyay, Amitava; Beuneu, F.; Zuppiroli, L.; Beauvy, M.

doi:10.1016/0022-3697(84)90120-3

Cited by 43 publications

(17 citation statements)

References 19 publications

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“…The problem with employing such bulk growth techniques for the specialized semiconductor device applications described above is that they require harsh fabrication conditions, demonstrate limited tunability, and tend to yield unfavorable electronic properties such as unacceptably high electrical conductivity. 26,27 It has been demonstrated [28][29][30][31][32][33][34] that the use of thin-film fabrication methods such as chemical vapor deposition or physical vapor deposition can produce B x C thin films that maintain robust mechanical, thermal, and chemical properties, while improving on electrical transport, electronic, and/or optical properties (e.g., resistivity and band gap), without having to resort to the extreme conditions required by traditional bulk growth techniques. In particular, the plasma-enhanced chemical vapor deposition (PECVD) of films from ortho-carborane (o-C 2 B 10 H 12 ), which typically yields amorphous hydrogenated boron carbide (a-B x C:H y ) when lower growth temperatures are used, has been shown to be suitable for producing films for device applications as well as conducive to tuning properties over a wide range.…”

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The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

Nordell

Karki

Nguyen

et al. 2015

Journal of Applied Physics

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Because of its high electrical resistivity, low dielectric constant (j), high thermal neutron capture cross section, and robust chemical, thermal, and mechanical properties, amorphous hydrogenated boron carbide (a-B x C:H y) has garnered interest as a material for low-j dielectric and solid-state neutron detection applications. Herein, we investigate the relationships between chemical structure (atomic concentration B, C, H, and O), physical/mechanical properties (density, porosity, hardness, and Young's modulus), electronic structure [band gap, Urbach energy (E U), and Tauc parameter (B 1/2)], optical/dielectric properties (frequency-dependent dielectric constant), and electrical transport properties (resistivity and leakage current) through the analysis of a large series of a-B x C:H y thin films grown by plasma-enhanced chemical vapor deposition from ortho-carborane. The resulting films exhibit a wide range of properties including H concentration from 10% to 45%, density from 0.9 to 2.3 g/cm 3 , Young's modulus from 10 to 340 GPa, band gap from 1.7 to 3.8 eV, Urbach energy from 0.1 to 0.7 eV, dielectric constant from 3.1 to 7.6, and electrical resistivity from 10 10 to 10 15 X cm. Hydrogen concentration is found to correlate directly with thin-film density, and both are used to map and explain the other material properties. Hardness and Young's modulus exhibit a direct power law relationship with density above $1.3 g/cm 3 (or below $35% H), below which they plateau, providing evidence for a rigidity percolation threshold. An increase in band gap and decrease in dielectric constant with increasing H concentration are explained by a decrease in network connectivity as well as mass/electron density. An increase in disorder, as measured by the parameters E U and B 1/2 , with increasing H concentration is explained by the release of strain in the network and associated decrease in structural disorder. All of these correlations in a-B x C:H y are found to be very similar to those observed in amorphous hydrogenated silicon (a-Si:H), which suggests parallels between the influence of hydrogenation on their material properties and possible avenues for optimization. Finally, an increase in electrical resistivity with increasing H at <35 at. % H concentration is explained, not by disorder as in a-Si:H, but rather by a lower rate of hopping associated with a lower density of sites, assuming a variable range hopping mechanism interpreted in the framework of percolation theory. V

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confidence: 99%

The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

Nordell

Karki

Nguyen

et al. 2015

Journal of Applied Physics

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“…According to the analysis on the composition of the samples and the origin of graphite peak, we deemed that the most possible origin of FM ordering in the Al‐doped B 4 C system was due to the free carbon. Some work by others had investigated the role of free carbon in the form of graphite within the B x C y B C z F system, where x , y , and z represent the atomic percentage of boron, bound carbon, and free carbon, respectively . They claimed that the free carbon would affect the D.C. transport and magnetic properties of boron carbide, and reported that the principal feature of in electron spin resonance lines indicated a dominance of free carbon when its concentration was larger than 3.5%.…”

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confidence: 99%

Magnetic Properties of Al‐doped B₄C and SiC Ceramics

Zhang

2013

J. Am. Ceram. Soc.

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Al-doped B 4 C and Al-doped SiC ceramic compounds were synthesized by high-temperature solid-state sintering. Ferromagnetic (FM) ordering was observed in the doped semiconducting ceramics. The changes in the FM ordering with doping level were different in the two doped systems although they were prepared by similar experimental condition. Our results indicated that some of the C in B 4 C were replaced by the Al atoms, and these displaced C atoms existed in the form of graphite. The synthesized SiC samples, undoped or Al doped, were found to be a mixture consisting of the magnetic and nonmagnetic SiC polytypes. The mechanisms in the generation of the FM ordering due to the dopants in the two ceramics followed different routes.A. Bandyopadhyay-contributing editor Manuscript No. 33091.

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“…Depending on the processing conditions, carbon may come into boron carbide or be present as free carbon forming amorphous carbon or graphite phases. For instance, electric current transport is dominated by the graphite phase when crystalline boron carbide has a free carbon content larger than 5%, which is explained by the much lower graphite resistivity in comparison with that of B 4 C [13]. In a similar way, elastic properties of components determine the elastic behaviour of the whole material, with the typical inconvenience that small amounts of soft compound may worsen the hardness of the system.…”

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Elastic properties of boron carbide films via surface acoustic waves measured by Brillouin light scattering

Salas

Jiménez-Villacorta

Sánchez-Marcos

et al. 2012

Physica Status Solidi (a)

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Surface acoustic wave (SAW) velocity has been determined by high resolution Brillouin light scattering to study the mechano‐elastic properties of boron carbide films prepared by radio frequency (RF) sputtering. The comparison of experimentally observed elastic behaviour with simulations made by considering film composition obtained from elastic recoil detection analysis‐time of flight (ERDA‐ToF) spectroscopy allows establishing that elastic properties are determined by that of crystalline boron carbide with a lessening of the SAW velocity values due to surface oxidation.

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The role of free carbon in the transport and magnetic properties of boron carbide

Cited by 43 publications

References 19 publications

The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

Magnetic Properties of Al‐doped B₄C and SiC Ceramics

Elastic properties of boron carbide films via surface acoustic waves measured by Brillouin light scattering

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The role of free carbon in the transport and magnetic properties of boron carbide

Cited by 43 publications

References 19 publications

The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

Magnetic Properties of Al‐doped B4C and SiC Ceramics

Elastic properties of boron carbide films via surface acoustic waves measured by Brillouin light scattering

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Magnetic Properties of Al‐doped B₄C and SiC Ceramics