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Hexagonal boron nitride, as a solid material, has incredible application potential in optics, biology and health sciences

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Author : TRUNNANO
Update time : 2021-12-07 15:18:18
What is Hexagonal boron nitride?
Hexagonal boron nitride (H-BN) ceramics are important microwave communication materials in the aerospace field. However, H-BN is a covalent bond compound with a low self-diffusion coefficient at high temperatures and difficult sintering. It is usually prepared by a hot pressing sintering process. Without proper additives, hot pressing sintering temperature and pressure are very high, and the hot pressing sintering process is difficult to produce ceramic products with complex shapes. At present, reaction sintering and high-pressure gas-solid combustion are also used, but it is difficult to obtain sintered products with satisfactory shape and size. The use of mechanochemical activation with hexagonal boron nitride powder was followed by press-free sintering of H-BN ceramics to obtain 70% of the relative density of AlN ceramics used.
Characteristics and application of hexagonal boron nitride
Hexagonal boron nitride, as a solid material, has incredible application potential in optics, biology and health sciences, attracting more and more attention worldwide. Professor Bernard Gil (National Centre for Scientific Research) and Professor Guillaume Cassabois (University of Montpellier) made groundbreaking contributions to the physics of this interesting material and to the development of its ability to interact with and control electromagnetic radiation. They are collaborating with Professor James H. Edgar of Kansas State University in the United States to investigate the application of hexagonal boron nitride to emerging quantum information technologies. Professor Edgar has been developing advanced technologies for high purity boron nitride crystals.
Hexagonal boron nitride (hBN) is a versatile solid material that plays a central role in many traditional applications, from lubrication to cosmetic powder formulation, thermal control and neutron detection. HBN, first synthesized in 1842 as a fragile powder, exhibits a layered crystal structure that differs from that of graphite: tightly bound B and N atoms arranged in a network plane of weak interactions superimposed on each other. In a similar manner, graphene can be derived from graphite and monolayer hBN can be obtained. In fact, hBN sits at the intersection of two worlds, widely used in shortwave solid-state light sources, and layered semiconductors such as graphene and transition metal halogens. However, hBN shows a number of distinct properties from these two classes of materials, making it a unique and potentially widely used candidate material.
HBN crystal growth
With the development of new techniques for the growth of large (about 110.2 mm3) hBN single crystal, the research and application of hBN has entered a new stage since 2004. Professor Edgar and his team at Kansas State University have played a key role in this field. They examined in detail the factors that determine and control the growth process, the eventual crystal size and quality, as well as the effects of doping impurities and changing the boron isotope ratio in the sample. HBN crystals are grown from solutions of molten metals, such as chromium and nickel or iron and chromium, and have the ability to dissolve boron and nitrogen. Professor Edgar and his collaborators have shown that crystals obtained from pure boron are of better quality than those obtained from hBN powder. They also investigated the effects of gas composition, metal-solvent selection and crucible type on the growth process.
The research team also developed unique techniques for growing isotopically pure hBN crystals. Natural boron is a mixture of two isotopes boron-10 (20%) and boron-11 (80%), which differ in nuclear mass but share the same chemical properties and yield an indistinguishable hBN crystal structure. However, the isotope fraction in the LATTICE of hBN has a profound effect on its vibration modes, also known as phonons. Crystals containing only boron-10 (h10BN) or boron-11 (h11BN) have longer phonon lifetimes. The random distribution of boron isotopes in the crystal structure causes phonon modes to disperse more frequently and reduces their lifetime. When hBN contains only a single boron isotope, phonon scattering is reduced and phonon lifetime is prolonged. This improves the thermal conductivity of the hBN, making it more efficient at dissipating heat. Its optical properties are also of great significance, particularly for its application in the field of nanophotonics, the study of light compressed to dimensions below free-space wavelengths. In this case, in the case of h10BN, the wavelength of light is reduced by a factor of 150.
HBN and Quantum information technology
The ability to generate and manipulate individual photons is at the heart of modern quantum technology. Unlike traditional thermal sources (such as incandescent lamps) and coherent sources (lasers), single-photon sources emit light in the form of single quantum particles (photons) that interact with other individual photons and can be used to store or generate new information in quantum computing. Defects in crystal structures, such as those caused by the incorporation of impurity atoms, can act as single-photon sources in some cases. In the case of hBN, the potential high-density defect, combined with a large bandgap, provides an opportunity to create an ideal supporting single-photon source. Unlike nanophotonics applications, which require extreme sample purity, quantum applications exhibit significantly enhanced spectral characteristics at 4.1 eV light energy relative to pure hBN.
Photoluminescence experiments on hBN samples containing C, Si and Mg impurities show that the spectral characteristics of hBN are significantly enhanced at 4.1 eV light energy compared with pure hBN. Recent cathode luminescence experiments (in which phonon emission is induced by an electron beam) have reported single-photon emission at this frequency, but this has not been observed in the case of laser-induced emission (photoluminescence). Many spectral lines below 4 eV have also been observed in photoluminescence experiments, which may correspond to single-photon emission defects in this energy range. However, the origin of these defects remains widely debated. Although studying the phenomenon of single-photon emission of hBN is complex, the work of Professors Edgar, Gil and Cassabois has provided solid evidence of the extraordinary potential of this material in the field of quantum technology.
Hexagonal Boron Nitride supplier
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