Nonlinear nanoelectrodynamics of a Weyl metal

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe4. As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their “symmetry fingerprints” in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe4 single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

Electrochemical Synthesis of Reduced Graphene Oxide‐Wrapped Polyaniline Nanorods As An Active Nanocomposite For Improved Photocurrent Generation And Photocatalytic And Antibacterial Activities

This study depicts the electrochemical synthesis of nanocomposites basede on Polyaniline nanorods wrap with reduced graphene oxide (PANI-rGO) on ITO substrates. Synthesis of PANI-rGO nanocomposites was elaborated by the incorporation of rGO in PANI thin films during electropolymerization in the presence of sulfuric acid. The synthesis of reduced graphene oxide was by modification on the well-known Hammer's method. The thin films nanocomposites were characterized by X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (FESEM), UV–Visible and electrochemical photocurrent spectroscopy. FESEM revealed the formation of PANI nanorods with diameters between 50 and 150 nm. The XPS was employed to confirm the compositions of PANI-rGO nanocomposites. From photoelectrochemical results, the generated photocurrent was improved in the presence of rGO in PANI Nanorods. Whereas, experimental findings show that the introduction of rGO into PANI improved the photo response from 7 µA.cm-2 to 13 µA.cm-2. Integration of 3D rGO in PANI results in better photocatalytic performance for the degradation of Congo Red. The enhanced photocatalytic activity with presence of rGO revealed the good potential of PANI-GO nanocomposites for dye degradation. The effective removal of congo red up to 90% has been observed in acidic medium and is acceptable results compared to the surface area of the substrate. At optimum conditions, also the nature of the antibacterial activities has been investigated by ITO/PANI and ITO/PANI-rGO thin films, and the results have showed exhibited antibacterial activity against the growth of E.coli gram-negative bacteria.

Are solution processed CsPbI3 perovskite nanocrystalline films similar to traditional crystalline semiconductors?

We use ultrafast photocurrent spectroscopy with a sub-25 picosecond resolution to address a long-standing question in emergent perovskite materials: are solution-processed CsPbI3 perovskites nanocrystal films similar to their counterparts semiconductors including GaAs and Si? Prior to carrier trapping, all semiconductors show similar transition of transport mechanism from the band-like transport due to the longitudinal optical (LO) phonon scattering in the higher temperature region to a combination of band-like and hopping transport mechanisms in the lower temperature region. The critical difference is that CsPbI3 demonstrate the strongest carrier-LO phonon interaction among all semiconductors, most likely due to the unique cation-halogen bond arrangements within the highly symmetric lattice structure. This ultrafast dynamics work establish a foundation of fundamental carrier transport understating for perovskite optoelectronics.

Boosting Piezo/Photo-Induced Charge Transfer of CNT/Bi4O5I2 Catalyst for Efficient Ultrasound-Assisted Degradation of Rhodamine B

Strain-induced internal electric fields present a significant path to boosting the separation of photoinduced electrons and holes. In addition, piezo-induced positive/negative pairs could be released smoothly, taking advantage of the excellent electroconductibility of some conductors. Herein, the hybrid piezo-photocatalysis is constructed by combining debut piezoelectric nanosheets (Bi4O5I2) and typical conductor multiwalled carbon nanotubes (CNT). The photocatalytic degradation efficiency that the hybrid CNT/Bi4O5I2 exhibits was remarkably increased by more than 2.3 times under ultrasonic vibration, due to the piezo-generated internal electric field. In addition, the transient photocurrent spectroscopy and electrochemical impedance measurement reveal that the CNT coating on Bi4O5I2 enhances the piezo-induced positive/negative migration. Therefore, the piezocatalytic activity of CNT/Bi4O5I2 could be improved by three times, compared with pure Bi4O5I2 nanosheets. Our results may offer promising approaches to sketching efficient piezo-photocatalysis for the full utilization of solar energy or mechanical vibration.