RESUMEN
Due to the low atomic number of B, hexagonal boron nitride (hBN) has a large neutron scattering cross section and, therefore, is an ideal material for the realization of solid-state neutron detector. Here we apply the THz time-domain spectroscopy to study the effect of neutron irradiation on electronic properties of pyrolytic (PBN) and hot-pressed boron nitride (HBN). The key electronic parameters of these samples, such as the static dielectric constant ε b, the effective carrier density N*, the carrier relaxation time τ, and the electronic localization factor α, are determined optically, and their dependences upon the neutron irradiation fluence (NIF) are examined. We find that for hBN,N* and ε b decrease while τ and |α| increase with increasing NIF. These results can be used to further understand the neutron irradiation effects on the basic physical properties of hBN material. We believe that the results obtained from this work can benefit to the design and application of hBN material for neutron detectors.
RESUMEN
We demonstrate for the first time, to the best of our knowledge, that the optical Hall effect (OHE) can be observed in p-type monolayer (ML) hexagonal boron nitride (hBN) on a fused silica substrate by applying linearly polarized terahertz (THz) irradiation. When ML hBN is placed on fused silica, in which the incident pulsed THz field can create local and transient electromagnetic dipoles, proximity-induced interactions can be presented. The Rashba spin-orbit coupling can be enhanced, and the in-plane spin component can be induced, along with the lifting of valley degeneracy. Thus, in the presence of linearly polarized THz radiation, the nonzero transverse optical conductivity (or Hall conductivity) can be observed. We measure the THz transmission through ML hBN/fused silica in the temperature range from 80 to 280 K by using THz time-domain spectroscopy in combination with an optical polarization examination. The Faraday ellipticity and rotation angle, together with the complex longitudinal and transverse conductivities, are obtained. The temperature dependence of these quantities is examined. The results obtained from this work indicate that ML hBN is a valleytronic material, and proximity-induced interactions can lead to the observation of OHE in the absence of an external magnetic field.
RESUMEN
Sonoluminescence (SL) occurs when acoustically induced oscillating bubbles in a liquid collapse. The SL from pure water normally generates ultraviolet to blue emission which is related to hydroxyl plasma formed in and around the bubbles. It is known that carbon nano-dots (CNDs) can serve as free radical captors, where the C-bonds can couple strongly with free radicals and form C-based functional groups. In this work, a SL experiment is conducted via placing CND aqueous solution (CNDAS) in the focal area of the SL apparatus. Unexpectedly and dramatically, it is found that the color of SL now turns orange, which is so bright that it can be seen even by the naked eye. By examining the CNDAS before and after the SL experiment, it is observed that the influence of CNDs on optical absorption, photoluminescence and SL is mainly achieved via coupling between the C-bonds in the CNDs and the free hydroxyl radicals generated during the processes of acoustically driven cavitation and SL. The interesting and important findings from this work demonstrate that the CNDs in water can modify significantly the SL effect. Thus, CNDs can provide a new test medium for studying and revealing the microscopic mechanism of the SL phenomenon.
RESUMEN
Sonoluminescence (SL) is an interesting physical effect which can convert acoustic energy into light pulses. Up to now, the microscopic mechanism of the SL has not yet been fully clear. It is known that hydroxyl radicals play the important role for SL from water. In this work, we take advantage of carbon nano-dots (CNDs) as free radical captors to modulate the hydroxyl radicals (OH) in SL effect. Through studying the single bubble SL (SBSL) from CND aqueous solution (CNDAS) with trace amount of CNDs, we find that the color of SBSL is tuned dramatically from blue in water to green in CNDAS. Two different SL mechanisms can be identified from emission spectrum. One comes from blackbody-like radiation and another is attributed from the characteristic emission with identified peaks. The decrease in the yield of H2O2 in the presence of CNDs suggests the modulation effect on SL via OH interacting with CNDs. By comparison of the CNDs before and after sonication, it is found that hydroxyl radicals generated during SL can take part in the chain-like oxidation of the chemical groups attached to the CNDs to form larger amount of carboxyl groups. The blackbody temperature of blackbody-like radiation decreases from 15,600 K in water to 11,300 K in CNDAS. Moreover, the emission from hydroxyl radicals and two new luminescent centers related to carboxyl groups are introduced in SL from CNDAS. These important and interesting findings indicate that by adding trace amount of CNDs in water, the effect of SBSL can be significantly modulated, which can provide a macroscopic phenomenon for gaining an insight into the microscopic mechanism of the SL effect.