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The cubic boron nitride is the second most important superhard materials. To date, the effect of crystallographic anisotropy of the {111} plane on the Knoop microhardness of cubic boron nitride single crystals has not been experimentally obtained. Herein, we measure the detailed Knoop hardness and Vickers hardness for the {111} plane of the amber cubic boron nitride. We find that the crystal orientation dependence of Knoop hardness for amber samples is remarkable and has an obvious regular pattern. The Knoop hardness for amber samples shows a minima about 5° from ⟨110⟩ directions, which is different from the traditional viewpoint that the minimum hardness is on ⟨110⟩ directions. Raman spectra of cubic boron nitrides are measured and help us to explain the hardening of samples. [ABSTRACT FROM AUTHOR]

Cubic boron nitride (c-BN) is a synthetic ultra-wide bandgap semiconductor with attractive application prospects in electronics and optoelectronics. At present, the size of c-BN single crystals obtained by hot pressing method is generally less than 1 mm extremely unfavorable to extracting its carrier concentration through Hall effect measurement. For c-BN crystals, the longitudinal optical phonon-plasma coupling (LOPC) mode which is produced by the coupling of longitudinal optical phonons and free carriers can be observed in mid-infrared reflectance spectrum. Thus, in this work, the mid-infrared reflectance spectrum of the black c-BN crystal grown by hot pressing method is measured. Based on classical dielectric function theory, the carrier concentration of that c-BN sample is finally extracted as 7.14 × 1017 cm−3. Combining electrical measurements, its mobility is also obtained as 11.91 cm2·V-1·s-1. • The highlights of our work is as follows. • This is the first time to extract carrier concentration by fitting LOPC + mode in the mid-infrared reflectance spectrum of the black c-BN crystal, which provides a practical method to obtain the electrical properties without any contact for tiny samples. • The reliability of carrier concentration extracted from mid-infrared reflectance spectrum is confirmed through theoretical simulation. [ABSTRACT FROM AUTHOR]