Tuning the Photoresponse of Nano-Heterojunction: Pressure-Induced Inverse Photoconductance in Functionalized WO3 Nanocuboids

S.R. and S.S. contributed equally to this work. This work was mainly supported by the Natural Science Foundation of China (Grant No. 11874076), National Science Associated Funding (NSAF, Grant No. U1530402), and Science Challenging Program (Grant No. TZ2016001). D.E. thanks the financial support from Spanish MINECO under Grant No. MAT2016-75586-C4-1-P and from Generalitat Valenciana under Grant Prometeo/2018/123, EFIMAT. The X-ray diffraction measurements were performed at the BL15U1 station, Shanghai Synchrotron Radiation Facility (SSRF) in China. The HP XAS measurements were performed at 20 ID-C, APS, ANL. APS is supported by DOE-BES, under contract no. DE-AC02-06CH11357. The authors gratefully acknowledge Professor T. Irifune for providing the nanodiamonds for the HP XAS measurements, and K. Yang (SSRF), A. G. Li (SSRF), and C. J. Sun (APS) for their support in the in situ HP measurements.Inverse photoconductivity (IPC) is a unique photoresponse behavior that exists in few photoconductors in which electrical conductivity decreases with irradiation, and has great potential applications in the development of photonic devices and nonvolatile memories with low power consumption. However, it is still challenging to design and achieve IPC in most materials of interest. In this study, pressure-driven photoconductivity is investigated in n-type WO3 nanocuboids functionalized with p-type CuO nanoparticles under visible illumination and an interesting pressure-induced IPC accompanying a structural phase transition is found. Native and structural distortion induced oxygen vacancies assist the charge carrier trapping and favor the persistent positive photoconductivity beyond 6.4 GPa. The change in photoconductivity is mainly related to a phase transition and the associated changes in the bandgap, the trapping of charge carriers, the WO6 octahedral distortion, and the electron–hole pair recombination process. A unique reversible transition from positive to inverse photoconductivity is observed during compression and decompression. The origin of the IPC is intimately connected to the depletion of the conduction channels by electron trapping and the chromic property of WO3. This synergistic rationale may afford a simple and powerful method to improve the optomechanical performance of any hybrid material.Natural Science Foundation of China (Grant No. 11874076); National Science Associated Funding (NSAF, Grant No. U1530402); Science Challenging Program (Grant No. TZ2016001); Spanish MINECO MAT2016-75586-C4-1-P; Generalitat Valenciana under Grant Prometeo/2018/123, EFIMAT; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Pressure-induced metallization and robust superconductivity in pristine 1T-HfSe2

The two-dimensional semiconductor 1T-HfSe2 is found to have highly tunable transport properties under pressure including metallization and pressure-driven superconductivity. The temperature-dependent resistivity of the sample suggests that a charge-density wave (CDW) state exists at low pressures in HfSe2, but it is suppressed below 20 GPa. It is further found that metallization takes place at ∼24 GPa followed by the appearance of a superconducting state at 26 GPa with a Tc of 6.7 K. Upon further compression to 33 GPa, the Tc increases monotonically to 7.5 K. Raman spectra, x-ray diffraction, transport measurements, and density-functional theory calculations suggest that the occurrence of the pressure-induced metallization and superconducting transition are intimately linked to a structural phase transition from the trigonal (P 3‾ m1) to a hexagonal structure (P63/mmc). Because of the phase transition, a massive structural reconstruction, and substantial band-structure changes around the Fermi level take place, which are due to the modification of weak van der Waals forces. The pressure-induced manipulation of the transport properties of 1T-HfSe2 could provide crucial information towards its practical applications

High-Pressure X-ray Diffraction and DFT Studies on Spinel FeV₂O₄

We have studied the behaviour of the cubic spinel structure of FeV2O4 under high-pressure by means of powder X-ray diffraction measurements and density-functional theory calculations. The sample was characterized at ambient conditions by energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction experiments. One of the main findings of this work is that spinel FeV2O4 exhibits pressure-induced chemical decomposition into V2O3 and FeO around 12 GPa. Upon pressure release, the pressure-induced chemical decomposition appears to be partially reversible. Additionally, in combination with density-functional theory calculations, we have calculated the pressure dependence of the unit-cell volumes of both the spinel and orthorhombic FeV2O4 crystal structures, whose bulk moduli are B0 = 123(9) and 154(2) GPa, respectively, finding the spinel FeV2O4 to exhibit the lowest bulk modulus amongst the spinel oxides. From experimental results, the same information is herein obtained for the cubic structure only. The Raman modes and elastic constants of spinel FeV2O4 have also obtained the ambient conditions

Biofabrication of Fe₃O₄ Nanoparticles from <i>Spirogyra hyalina</i> and <i>Ajuga bracteosa</i> and Their Antibacterial Applications

Iron oxide nanoparticles (NPs) have attracted substantial interest due to their superparamagnetic features, biocompatibility, and nontoxicity. The latest progress in the biological production of Fe3O4 NPs by green methods has improved their quality and biological applications significantly. In this study, the fabrication of iron oxide NPs from Spirogyra hyalina and Ajuga bracteosa was conducted via an easy, environmentally friendly, and cost-effective process. The fabricated Fe3O4 NPs were characterized using various analytical methods to study their unique properties. UV-Vis absorption peaks were observed in algal and plant-based Fe3O4 NPs at 289 nm and 306 nm, respectively. Fourier transform infrared (FTIR) spectroscopy analyzed diverse bioactive phytochemicals present in algal and plant extracts that functioned as stabilizing and capping agents in the fabrication of algal and plant-based Fe3O4 NPs. X-ray diffraction of NPs revealed the crystalline nature of both biofabricated Fe3O4 NPs and their small size. Scanning electron microscopy (SEM) revealed that algae and plant-based Fe3O4 NPs are spherical and rod-shaped, averaging 52 nm and 75 nm in size. Energy dispersive X-ray spectroscopy showed that the green-synthesized Fe3O4 NPs require a high mass percentage of iron and oxygen to ensure their synthesis. The fabricated plant-based Fe3O4 NPs exhibited stronger antioxidant properties than algal-based Fe3O4 NPs. The algal-based NPs showed efficient antibacterial potential against E. coli, while the plant-based Fe3O4 NPs displayed a higher zone of inhibition against S. aureus. Moreover, plant-based Fe3O4 NPs exhibited superior scavenging and antibacterial potential compared to the algal-based Fe3O4 NPs. This might be due to the greater number of phytochemicals in plants that surround the NPs during their green fabrication. Hence, the capping of bioactive agents over iron oxide NPs improves antibacterial applications