First-principles calculations to investigate electronic structures and magnetic regulation of non-metallic elements doped BP with point defects.

In order to control the magnetic properties and electronic structures of black phosphorene (BP) monolayer, the structures, electronic and magnetic properties of non-metallic elements doped BP monolayer without or with defects including P vacancy (VP) have been studied by density functional theory (DFT). Defective BP appears ferromagnetic metallicity, and the magnetic moment is 0.086 µB. The magnetism mainly comes from the spin polarization of P atoms near the defect point. For non-metallic elements doped intrinsic BP, system doped with B and N shows P-type semiconductor. C doped shows non-magnetic metal properties. Odoped exhibits magnetic P-type semiconductor. Si and S doped shows ferromagnetic metal properties. The magnetism mainly comes from the spin polarization of P atoms near the defect point, and a small part comes from doped atoms. In the case of non-metallic elements doped defective BP, the results show that flaw-b-C and flaw-s-Si exhibit non-magnetic metallic properties. The flaw-b-S shows P-type semiconductor with indirect band gap of 0.712 eV. Other systems exhibit ferromagnetic metallicity, and the magnetism mainly comes from the spin polarization of P atoms near defect point. Non-metallic elements doped BP monolayer without or with point defects can effectively adjust magnetic properties and electronic structures.

Removal of spiral turbulence by virtual electrodes through the use of a circularly polarized electric field.

Heart disease is the leading cause of death and is often accompanied by cardiac fibrillation. Defibrillation using the virtual electrode effects is a promising alternative compared to using the high-voltage electric shock in the clinic. Our earlier works [S. L. Murphy, K. D. Kochanek, J. Xu, and E. Arias, NCHS Data Brief 427 (2021); R. A. Gray, A. M. Pertsov, and J. Jalife, Nature 392, 75-78 (1998); F. X. Witkowski, L. J. Leon, P. A. Penkoske, W. R. Giles, M. L. Spano, W. L. Ditto, and A. T. Winfree, Nature 392, 78-82 (1998); M. Santini, C. Pandozi, G. Altamura, G. Gentilucci, M. Villani, M. C. Scianaro, A. Castro, F. Ammirati, and B. Magris, J. Interv. Card. Electrophysiol. 3, 45-51 (1999).] prove that, compared with other external electric fields, a low voltage circularly polarized electric field is more efficient in turning non-excitable defects in cardiac tissue into virtual electrodes. It, therefore, needs lower voltage to stimulate the excitation waves and causes less harm to reset the spiral turbulence of cardiac excitation for defibrillation. In this paper, we investigate the virtual electrode effect of multiple defects by the circularly polarized electric field for the removal of spiral turbulence. Considering different shapes, sizes, and distributions of multiple defects, we reveal the phase locking of stimulated excitations around multiple virtual electrodes. Furthermore, the circularly polarized electric field parameters are optimized to remove the spiral turbulence.

Manipulation of Subwavelength Periodic Structures Formation on 4H-SiC Surface with Three Temporally Delayed Femtosecond Laser Irradiations.

Controlling laser-induced periodic surface structures on semiconductor materials is of significant importance for micro/nanophotonics. We here demonstrate a new approach to form the unusual structures on 4H-SiC crystal surface under irradiation of three collinear temporally delayed femtosecond laser beams (800 nm wavelength, 50 fs duration, 1 kHz repetition), with orthogonal linear polarizations. Different types of surface structures, two-dimensional arrays of square islands (670 nm periodicity) and one-dimensional ripple structures (678 nm periodicity) are found to uniformly distribute over the laser-exposed areas, both of which are remarkably featured by the low spatial frequency. By altering the time delay among three laser beams, we can flexibly control the transition between the two surface structures. The experimental results are well explained by a physical model of the thermally correlated actions among three laser-material interaction processes. This investigation provides a simple, flexible, and controllable processing approach for the large-scale assembly of complex functional nanostructures on bulk semiconductor materials.

One-step fabrication and electromagnetic wave absorption of graphene/Ag@polyaniline ternary nanocomposites.

Based on in situ intercalation polymerization of aniline, a one-step synthesis of a graphene/Ag@PANI ternary composite is proposed. The results show that together with sunlight exposure, Ag+ induces the polymerization of aniline accompanied by self-reduction to form a Ag@PANI core-shell nanostructure, and consequently, exfoliates the graphite sheet into graphene. Through a PANI shell, Ag@PANI nanoparticles all anchor onto the surface of graphene, forming a stable ternary structure. The performance of graphene/Ag@PANI is closely related to its micro-morphology, which depends on the selected Ag+/aniline ratio during the synthesis. Double-layer absorbers with graphene/Ag@PANI as the absorbing layer present excellent absorption performance. The effective absorbing bandwidths of DB-10, DB-5, and DB-1 all exceed 3 GHz with a thickness of 1 mm and the reflection loss of 1.3 mm DB-10 reaches -44.5 dB at 10.5 GHz. The as-proposed facile and eco-friendly preparation of a graphene-based ternary composite is also of great significance for sensors, supercapacitor electronics, degradation of polymers, and other applications.

Synergic effect of graphene and core-shells structured Au NR@SiO2@TiO2 in dye-sensitized solar cells.

Graphene and Au nanorods (AuNRs) coated with SiO2@TiO2 double shells (AuNR@SiO2@TiO2) were incorporated to form novel composite photoanodes in dye sensitized solar cells (DSSCs). The performances of the photoanodes and DSSCs are studied systematically. The short circuit current density (J sc) and power conversion efficiency (PCE) of these composited DSSCs were greatly enhanced and the influences of the graphene, AuNRs and the SiO2@TiO2 double shells were revealed. The optimal properties with the maximal J sc of 16.26 mA cm-2 and PCE of 8.08% are obtained in the DSSC co-doped with graphene and AuNR@SiO2@TiO2, significantly higher than those of the conventional DSSC with pure TiO2 photoanode by 37.7% and 32.9%, respectively. These significant enhancements in J sc and PCE are attributed to the synergistic effect of graphene, the local surface plasma resonance of AuNRs, as well as the outer SiO2@TiO2 double shells, which result in the increased specific surface area and dye adsorption, the increased light absorption, the decreased charge transfer resistance R 2 and electron recombination and thus the increased J sc and PCE of the DSSCs.

BrCl+ elimination from Coulomb explosion of 1,2-bromochloroethane induced by intense femtosecond laser fields.

By using a dc-slice imaging technique, photodissociation of 1,2-C2H4BrCl was investigated at 800 nm looking for heteronuclear unimolecular ion elimination of BrCl+ in an 80 fs laser field. The occurrence of fragment ion BrCl+ in the mass spectrum verified the existence of a unimolecular decomposition channel of BrCl+ in this experiment. The relative quantum yield of the BrCl+ channel was measured to be 0.8%. By processing and analyzing the velocity and angular distributions obtained from the corresponding sliced images of BrCl+ and its partner ion C2H4 +, we concluded that BrCl+ came from Coulomb explosion of the 1,2-bromochloroethane dication 1,2-C2H4BrCl2+. With the aid of quantum chemical calculations at the M06-2X/def2-TZVP level, the potential energy surface for BrCl+ detachment from 1,2-C2H4BrCl2+ has been examined in detail. According to the ab initio calculations, two transition state structures tended to correlate with the reactant 1,2-C2H4BrCl2+ and the products BrCl+ + C2H4 +. In this entire dissociation process, the C-Br and C-Cl bond lengths were observed to elongate asymmetrically, that is, the C-Br chemical bond broke firstly, and subsequently a new Br-Cl chemical bond started to emerge while the C-Cl bond continued to exist for a while. Hence, an asynchronous concerted elimination mechanism was favored for BrCl+ detachment.

Theoretical and experimental studies on hydrogen migration in dissociative ionization of the methanol monocation to molecular ions H3 + and H2O.

The dissociative ionization processes of the methanol monocation CH3OH+ to H3 + + CHO and H2O+ + CH2 are studied by ab initio method, and hydrogen migration processes are confirmed in these two dissociation processes. Due to the positive charge assignment in dissociation processes, the fragmentation pathways of CH3OH+ to H3 + CHO+ and CH3OH+ to H2O + CH2 + are also calculated. The calculation results show that a neutral H2 moiety in the methanol monocation CH3OH+ is the origin of the formation of H3 +, and the ejection of fragment ions H3 + and H2O+ is more difficult than CHO+ and CH2 + respectively. Experimentally, by using a dc-slice imaging technique under an 800 nm femtosecond laser field, the velocity distributions of fragment ions H3 +, CHO+, CH2 +, and H2O+ are calculated from their corresponding sliced images. The presence of low-velocity components of these four fragment ions confirms that the formation of these ions is not from the Coulomb explosion of the methanol dication. Hence, the four hydrogen migration pathways from the methanol monocation CH3OH+ to H3 + + CHO, CHO+ + H3, H2O+ + CH2, and CH2 + + H2O are securely confirmed. It can be observed in the time-of-flight mass spectrum of ionization and dissociation of methanol that the ion yields of fragment ions H3 + and H2O+ are lower than CHO+ and CH2 + respectively, which is consistent with the theoretical results according to which dissociation from the methanol monocation to H3 + and H2O+ is more difficult than CHO+ and CH2 + respectively.