Search

Electrospinning is an amazing process that enables the production of primarily nanofiber membranes. Nevertheless, the mechanism underlying the formation of two-dimensional (2D) nonwoven structure remains a fascinating enigma. This paper presents a novel morphology of nanofiber membranes with a cluster structure that bears resemblance to the solar nebula. The mechanism of nanofiber cluster structures in the electrospinning process is elucidated through the geometric potential theory, which begins with a zero-dimensional receptor, progresses to a one-dimensional (1D) receptor, a 2D receptor, and ultimately culminates in a fractal-like lattice receptor. Moreover, a three-dimensional (3D) printing-like novel approach is presented for the manipulation of nanofiber membrane’s shape through the use of a lattice-structured receptor. The fabrication process of the cluster structure nanofiber membranes by electrospinning is presented, and their remarkable potential applications are discussed. [ABSTRACT FROM AUTHOR]

We explored the coupling between magnetic and magneto-transport properties in MnBi2Te4 crystals with Fermi energy EF ranging from 10 to 100 meV in the conduction band. Electrical, magnetic, and magneto-transport measurements reveal distinct behaviors depending on EF. At lower EF values (10 meV), MnBi2Te4 exhibits degenerate-semiconductor-like electrical transport and ferrimagnetism, with weak coupling between magneto-resistance and ferrimagnetism. In contrast, MnBi2Te4 displays metallic transport and antiferromagnetism (AFM) at higher Fermi energies, with magneto-resistance strongly coupled to antiferromagnetism and canted antiferromagnetism under a large external magnetic field. Remarkably, Hall measurements demonstrate a pronounced anomalous Hall resistivity (AHR) when the EF of MnBi2Te4 is 10 meV, larger than that reported for other bulk MnBi2Te4 crystals in the literature. Significant AHR is attributed to the Berry-phase effect in electronic-band structure based on first-principles calculation. The evolution of magnetic and magneto-transport properties in EF shifted MnBi2Te4 can be semi-quantitatively explained by the Ruderman–Kittel–Kasuya–Yosida interaction between neighboring MnTe layers. Our work suggests that the strongly Fermi-energy-sensitive magneto-transport properties observed in MnBi2Te4 may be useful in developing magnetic sensors/detectors. [ABSTRACT FROM AUTHOR]

Layered BiCuXO (X = S, Se, and Te) compounds attract much attention recently because of their superior thermoelectric properties. However, the major shortcoming of these compounds is the relatively large electrical resistance. Exploring the mechanism of electrical scattering of BiCuXO can give some hints on how to optimize their electrical conductivity. Here, we compared electrical and magnetotransport properties of degenerate semiconductor BiCuXO. These compounds show metallic electrical properties, and the in-plane resistivity is linearly dependent on the temperature at the high-temperature regime (>150 K). The magnetoresistance of these compounds is approximately quadratically dependent on the square of magnetic field B, and magnetoresistance decreases from 10%–16% to 0.5% when the temperature is increased from 2 to 300 K. The Hall measurements substantiate that the electrical carriers of BiCuXO are holes, which perhaps come from Bi vacancies. The electron-optical-phonon interaction is the major mechanism of electron scattering when the temperature is higher than 80 K. Analyzing the linear coefficient ρxx-T of BiCuXO (X = S, Se, and Te) suggests that the averaged electron-phonon interaction of BiCuSO is nearly six times larger than that of BiCuSeO/BiCuTeO. Based on the Thomas-Fermi model, compared with BiCuSO, the weak electron-phonon interaction in BiCuSeO/BiCuTeO could be attributed to a highly screened Coulomb interaction between electrons and ions. This work may be useful to optimize the electrical properties of BiCuXO to satisfy the requirement of thermoelectric materials. [ABSTRACT FROM AUTHOR]

Recently the layered oxide semiconductor Bi 2 O 2 Se was hotly explored for its ultrahigh mobility and ultrafast photo-response whose physical origins need to be further explored or elucidated. Here, we have grown halogen (Cl, Br, I) doped and un-doped Bi 2 O 2 Se single crystals by a melt-solidification method. Comparative electrical transport characterizations and detailed data-analysis substantiate that the electron-electron scattering is the major source of resistivity in un-doped Bi 2 O 2 Se crystals; however, in halogen-doped Bi 2 O 2 Se crystals, electron-electron scattering is only effective at low temperature (<60 K) and subsequently electron-phonon-interaction scattering is dominated to resistivity. Hall measurement and analysis show that electron concentration of halogen-doped Bi 2 O 2 Se (∼10 20 cm -3 ) is one-order higher than un-doped one (∼10 19 cm -3 ), but the carrier mobility of halogen-doped Bi 2 O 2 Se at 2 K (∼10 2 cm 2 V -1 s -1 ) is reduced by more than two orders than un-doped ones (∼10 4 cm 2 V -1 s -1 ). Three kinds of relaxation time (due to the impurity scattering, electron-electron scattering and electron-phonon scattering), calculated by linear-response theory and electron-/phonon-dispersion, are in agreement with experimental results quantitatively. The scattering mechanism evolution from sole electron-electron scattering (un-doped Bi 2 O 2 Se) to electron-phonon scattering (doped Bi 2 O 2 Se) at high temperature (>60 K) is attributed to the net effect of decreased screened Coulomb-interaction and increased Fermi energy in halogen-doped Bi 2 O 2 Se. This work may provide clues of physical origins of superior electrical/photoelectrical properties of Bi 2 O 2 Se., (© 2020 IOP Publishing Ltd.)