Built-in Field Research Articles

Carrier density dependent Auger recombination in c-plane (In,Ga)N/GaN quantum wells: insights from atomistic calculations

Understanding Auger recombination in (In,Ga)N-based quantum wells is of central importance to unravelling the experimentally observed efficiency ‘droop’ in modern (In,Ga)N light emitting diodes (LEDs). While there have been conflicting results in the literature about the importance of non-radiative Auger recombination processes for the droop phenomenon, it has been discussed that alloy fluctuations strongly enhance the Auger rate. However, these studies were often focused on bulk systems, not quantum wells, which lie at the heart of (In,Ga)N-based LEDs. In this study, we present an atomistic analysis of the carrier density dependence of the Auger recombination coefficients in (In,Ga)N/GaN quantum wells. The model accounts for random alloy fluctuations, the connected carrier localisation effects, and carrier density dependent screening of the built-in polarisation fields. Our studies reveal that at low temperatures and low carrier densities the calculated Auger coefficients are strongly dependent on the alloy microstructure. However, at elevated temperatures and carrier densities, where the localised states are starting to be saturated, the different alloy configurations studied give (very) similar Auger coefficients. We find that over the range of carrier densities investigated, the contribution of the electron-electron–hole related Auger process is of secondary importance compared to the hole-hole-electron process. Overall, for higher temperatures and carrier densities, our calculated total Auger coefficients are in excess of 10−31 cm6 s−1 and may reach 10−30 cm6 s−1, which, based on current understanding in the literature, is sufficient to result in a significant efficiency droop. Thus, our results are indicative of Auger recombination being an important contributor to the efficiency droop in (In,Ga)N-based light emitters even without defect-assisted processes.

A Novel Spinel Ferrite-Hexagonal Ferrite Composite for Enhanced Magneto-Electric Coupling in a Bilayer with PZT.

The magnetoelectric effect (ME) is an important strain mediated-phenomenon in a ferromagnetic-piezoelectric composite for a variety of sensors and signal processing devices. A bias magnetic field, in general, is essential to realize a strong ME coupling in most composites. Magnetic phases with (i) high magnetostriction for strong piezomagnetic coupling and (ii) large anisotropy field that acts as a built-in bias field are preferred so that miniature, ME composite-based devices can operate without the need for an external magnetic field. We are able to realize such a magnetic phase with a composite of (i) barium hexaferrite (BaM) with high magnetocrystalline anisotropy field and (ii) nickel ferrite (NFO) with high magnetostriction. The BNx composites, with (100 - x) wt.% of BaM and x wt.% NFO, for x = 0-100, were prepared. X-ray diffraction analysis shows that the composites did not contain any impurity phases. Scanning electron microscopy images revealed that, with an increase in NFO content, hexagonal BaM grains become prominent, leading to a large anisotropy field. The room temperature saturation magnetization showed a general increase with increasing BaM content in the composites. NFO rich composites with x ≥ 60 were found to have a large magnetostriction value of around -23 ppm, comparable to pure NFO. The anisotropy field HA of the composites, determined from magnetization and ferromagnetic resonance (FMR) measurements, increased with increasing NFO content and reached a maximum of 7.77 kOe for x = 75. The BNx composite was cut into rectangular platelets and bonded with PZT to form the bilayers. ME voltage coefficient (MEVC) measurements at low frequencies and at mechanical resonance showed strong coupling at zero bias for samples with x ≥ 33. This large in-plane HA acted as a built-in field for strong ME effects under zero external bias in the bilayers. The highest zero-bias MEVC of ~22 mV/cm Oe was obtained for BN75-PZT bilayers wherein BN75 also has the highest HA. The Bilayer of BN95-PZT showed a maximum MEVC ~992 mV/cm Oe at electromechanical resonance at 59 kHz. The use of hexaferrite-spinel ferrite composite to achieve strong zero-bias ME coupling in bilayers with PZT is significant for applications related to energy harvesting, sensors, and high frequency devices.

In Situ Synthesis of Bi2S3/BiFeO3 Nanoflower Hybrid Photocatalyst for Enhanced Photocatalytic Degradation of Organic Pollutants.

Photocatalytic degradation of Malachite Green oxalate (MG) in a water body is of significant importance to our health protection, as it could cause various serious diseases. However the photocatalytic activity of most catalysts is still unsatisfactory, due to the poor reactive oxygen species production as a result of sluggish charge separation. Here, innovative nanoflower-shaped Bi2S3/BiFeO3 heterojunctions are prepared via a facile sol-gel method, exhibiting an enhanced reactive oxygen species generation, which leads to the excellent photocatalytic performance toward MG degradation. We verify that interfacing BiFeO3 with Bi2S3 could form a fine junction and offers a built-in field to speed up charge separation at the junction area; as a result, this shows much higher charge separation efficiency. By virtue of the aforementioned advantages, the as-prepared Bi2S3/BiFeO3 heterojunctions exhibit excellent photocatalytic performance toward MG degradation, where more than 99% of MG is removed within 2 h of photocatalysis. The innovative design of nanoflower-like Bi2S3/BiFeO3 heterojunctions may offer new viewpoints in designing highly efficient photocatalysts for environmentally related applications.

Gradient tungsten-doped Bi3TiNbO9 ferroelectric photocatalysts with additional built-in electric field for efficient overall water splitting

Bi3TiNbO9, a layered ferroelectric photocatalyst, exhibits great potential for overall water splitting through efficient intralayer separation of photogenerated carriers motivated by a depolarization field along the in-plane a-axis. However, the poor interlayer transport of carriers along the out-of-plane c-axis, caused by the significant potential barrier between layers, leads to a high probability of carrier recombination and consequently results in low photocatalytic activity. Here, we have developed an efficient photocatalyst consisting of Bi3TiNbO9 nanosheets with a gradient tungsten (W) doping along the c-axis. This results in the generation of an additional electric field along the c-axis and simultaneously enhances the magnitude of depolarization field within the layers along the a-axis due to strengthened structural distortion. The combination of the built-in field along the c-axis and polarization along the a-axis can effectively facilitate the anisotropic migration of photogenerated electrons and holes to the basal {001} surface and lateral {110} surface of the nanosheets, respectively, enabling desirable spatial separation of carriers. Hence, the W-doped Bi3TiNbO9 ferroelectric photocatalyst with Rh/Cr2O3 cocatalyst achieves an efficient and durable overall water splitting feature, thereby providing an effective pathway for designing excellent layered ferroelectric photocatalysts.

Simultaneously realizing high piezoelectricity and thermal stability in BNT-based ceramics via integrating layered diffusion and thermal treatment

An inherent conflict of (Bi0.5Na0.5)TiO3-based (BNT) lead-free piezoelectric ceramics is the optimizing piezoelectric response (d33) with deteriorating depolarization temperature (Td), which severely restricts the further achievements of BNT-based ceramics. A new strategy is proposed in this work to simultaneously realize high piezoelectric property (d33 = 140 pC/N) and thermal stability (Td = 232 °C) in BNT-based ceramics by integrating layered composite structure of 0.89(Bi0.5Na0.5)TiO3-0.11BaTiO3 with high Td and 0.87(Bi0.5Na0.5)TiO3-0.11BaTiO3-0.02(Sm0.5K0.5)TiO3 with large d33 (BNT1/BNT2) and thermal treatment processes. In the layered composite ceramics, the composition difference induces a built-in field (Eb) that promotes the diffusion of ferroelectric-relaxor (FE-RE) phase transition in the ceramics, delaying the Td to 185 °C. In addition, the thermal treatment processes facilitate both the Eb expansion, stabilize the d33 over a wide temperature range, as well as enlarge the grain size to elevate the d33 from 133 pC/N to 145 pC/N. Hence, the strategy we proposed is promising to offer a new paradigm for designing piezoelectric materials with high piezoelectric response over a wide temperature range.

Controllable Electrocatalytic to Photocatalytic Conversion in Ferroelectric Heterostructures.

Photocatalytic and electrocatalytic reactions to produce value-added chemicals offer promising solutions for addressing the energy crisis and environmental pollution. Photocatalysis is driven by light excitation and charge separation and relies on semiconducting catalysts, while electrocatalysis is driven by external electric current and is mostly based on metallic catalysts with high electrical conductivity. Due to the distinct reaction mechanism, the conversion between the two catalytic types has remained largely unexplored. Herein, by means of density functional theory (DFT) simulations, we demonstrated that the ferroelectric heterostructures Mo-BN@In2Se3 and WSe2@In2Se3 can exhibit semiconducting or metallic features depending on the polarization direction as a result of the built-in field and electron transfer. Using the nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) as examples, the metallic heterostructures act as excellent electrocatalysts for these reactions, while the semiconducting heterostructures serve as the corresponding photocatalysts with improved optical absorption, enhanced charge separation, and low Gibbs free energy change. The findings not only bridge physical phenomena of the electronic phase transition with chemical reactions but also offer a new and feasible approach to significantly improve the catalytic efficiency.

Insight into (Electro)magnetic Interactions within Facet-Engineered BaFe12O19/TiO2 Magnetic Photocatalysts.

A series of facet-engineered TiO2/BaFe12O19 composites were synthesized through hydrothermal growth of both phases and subsequent deposition of the different, faceted TiO2 nanoparticles onto BaFe12O19 microplates. The well-defined geometry of the composite and uniaxial magnetic anisotropy of the ferrite allowed alternate interfaces between both phases and fixed the orientation between the TiO2 crystal structure and the remanent magnetic field within BaFe12O19. The morphology and crystal structure of the composites were confirmed by a combination of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses together with the detailed study of BaFe12O19 electronic and magnetic properties. The photocatalytic activity and magnetic field effect were studied in the reaction of phenol degradation for TiO2/BaFe12O19 and composites of BaFe12O19 covered with a SiO2 protective layer and TiO2. The observed differences in phenol degradation are associated with electron transfer and the contribution of the magnetic field. All obtained magnetic composite materials can be easily separated in an external magnetic field, with efficiencies exceeding 95%, and recycled without significant loss of photocatalytic activity. The highest activity was observed for the composite of BaFe12O19 with TiO2 exposing {1 0 1} facets. However, to prevent electron transfer within the composite structure, this photocatalyst material was additionally coated with a protective SiO2 layer. Furthermore, TiO2 exposing {1 0 0} facets exhibited significant synergy with the BaFe12O19 magnetic field, leading to 2 times higher photocatalytic activity when ferrite was magnetized before the process. The photoluminescence emission study suggests that for this particular combination, the built-in magnetic field of the ferrite suppressed the recombination of the photogenerated charge carriers. Ultimately, possible effects of complex electro/magnetic interactions within the magnetic photocatalyst are shown and discussed for the first time, including the anisotropic properties of both phases.

MoO2-C@MoS2: A unique cocatalyst with LSPR effect for enhanced quasi-full-spectrum photocatalytic hydrogen evolution of CdS

A well-designed cocatalyst structure can improve the light-harvesting and quantum efficiency of photocatalysis. A multidimensional MoO2-C@MoS2 (MOCS) cocatalyst was successfully synthesized by post-sulfidation of MoO2-C nanorods. This controlled sulfidation process effectively inhibits the undesired oxidation of MoO2, stabilizing its metallicity and creating a synergistic effect for H2 evolution. Firstly, the highly dispersed metallic MoO2 nanoparticles induce localized surface plasmon resonance effects, expanding the light-harvesting range and generating abundant hot electrons. Secondly, the build-in electrostatic field and highly conductive carbon framework facilitates efficient interfacial electrons transfer. Thirdly, the amorphous MoOx and fragmented few-layers MoS2 in MOCS provide dual active sites with superior intrinsic activity for H2 evolution. Moreover, the unique multi-interface structure of MOCS optimizes the separation and reaction of charge carriers. As a result, the 20 wt% MOCS/CdS system show an excellent quasi-full-spectrum driven photocatalytic H2 evolution activity of 48.41 mmol/h·g, with 4.03 mmol/h·g in near-infrared region (> 800 nm).

Evidence for a build-in remnant field in symmetrically contacted MAPbBr3 x-ray detectors

Millimeter-thick methylammonium lead tribromide (MAPbBr3) single crystal x-ray detectors have recently raised attention due to their high x-ray attenuation efficiency and good charge transport properties. However, an intriguing feature of the photocurrent response of MAPbBr3 detectors has been largely overlooked in the literature. After biasing, transient sensitivity is measured under x rays at short-circuit (bias = 0 V), thus revealing a large remnant electric field that builds up under bias. Here, we exploit the x-ray sensitivity of MAPbBr3 detectors at zero-bias in order to probe the internal built-in field, as well as to investigate the charge transport properties of the perovskite material. Our model derived from the Hecht equation is able to fully rationalize the response of the detectors both at short-circuit and under moderate applied bias. Moreover, we provide a method for the estimation of the internal electric field, and for the sum of the electrons and holes mobility–lifetime products μeτe+μhτh. This general method could extend to any perovskite-based x-ray detector exhibiting transient sensitivity at zero-bias.

Field-Assisted Regulation Induced by Cobalt-Doped ZnO for Dendrite-Free Lithium Metal Anodes.

Lithium metal batteries are deemed as an optimal candidate for the next generation of durable energy storage devices. However, the growth of lithium dendrite and significant volume expansion pose as obstacles that impede the application of lithium metal batteries. In this work, a functional copper current collector was designed by coating it with Co-doped ZnO (Co/ZnO) to enhance the lithiophilicity through local electric fields and built-in magnetic fields induced by the ferromagnetic material. The incorporation of Co not only induces a local electric field and thus accelerating electron transfer, but also imparts the ferromagnetic behavior to ZnO, resulting in an internal magnetic field to regulate the dynamic trajectory. Profiting from the above advantages, the symmetric cells have excellent cycle stability in 1 mA cm-2 and 1 mAh cm-2 , maintaining ultra-low voltage for over 2000 h. This study provides a realizable pathway for next-generation current collector of copper modification.

Field-free magnetization switching through modulation of zero-field spin–orbit torque efficacy

To make spin–orbit torque magnetic random access memory (SOT-MRAM) practical, current-induced magnetization switching without an external bias field is essential. Given that the CoFeB/MgO structure has already been used in typical spin-transfer torque-MRAM for its high tunneling magnetoresistance, leveraging a similar material system to achieve field-free SOT switching is of great importance. In this work, we systematically investigate the field-free switching mechanism in CoFeB/W/CoFeB T-type structures, where the two CoFeB layers are in-plane and perpendicularly magnetized, respectively. Initial SOT characterization shows a sizable zero-field SOT efficacy (χHx=0) for such T-type devices. Furthermore, field-free angle-dependent SOT measurement confirms the parallel relationship between the built-in bias field and the magnetization of the in-plane magnetized CoFeB. Based on thorough verification and exclusion of other potential mechanisms, the Néel orange-peel effect emerges as the dominant origin for such a built-in bias field, where a positive correlation between the deposited film surface roughness and χHx=0 is found. Based on this discovery, the field-free switching efficacy in T-type structures is further optimized via film roughness tuning and examined with pillar-shaped devices. Our results provide insights into the tentative approach to improve field-free switching using T-type devices and the feasibility of downscaling.

Fabrication of a Counter-Directional Pump/Signal Combiner with Built-In Mode Field Adapter

This article introduces a novel counter-directional pump/signal combiner with a built-in mode field adapter. This combiner offers additional functionality to address the problem of mode field mismatch between the gain fiber and delivery fiber, which occurs when using a large-core (50 μm) signal fiber to suppress stimulated Raman scattering. The combiner exhibits negligible degradation in beam quality as a result of implementing mode field matching and employing an effective feedback alignment technique. The beam quality of the mode field adapter integrated in the combiner is improved by 10%, compared to the conventional approach, thanks to the reduction in splicing points and the prevention of fusion loss caused by tapering-induced cladding diameter mismatch. The combiner demonstrates an average pump coupling efficiency of 98.5% and a temperature rise coefficient of less than 10 °C/kW without active cooling. Furthermore, an integrated device based on the combiner is fabricated to shorten the length of delivery fiber, therefore mitigating the effects of stimulated Raman scattering. All those techniques mentioned above are utilized in a narrow linewidth laser system, resulting in an output of approximately 5840 W with a nearly single-mode characteristic.

Reversible charge injection-controlled resistance switching in BiFeO3 ferrodiodes

The ferroelectric diode effect is a promising candidate for resistive memory applications, but the precise role of defects in the current switching mechanism remains unclear. Here, we investigated ferroelectric SrRuO3/BiFeO3/SrRuO3 capacitors and observed strong diode current. The capacitors exhibited preferred polarization orientation toward the bottom electrode in the presence of an imprint field, as evidenced by poor polarization retention of upward polarizations at a bias voltage of 1 V. Interfacial defect-mediated charge injection and trapping enabled by negative voltage poling reduced the built-in field and improved the retention property at the expense of reduced diode current. This phenomenon can be reversed by long-time positive voltage poling, allowing the deeply trapped charges to be expelled out of the trap for the rejuvenation of the diode current. Our study provides experimental evidence that interfacial defects modify the diode current in a manner opposite to that of the switched polarization.

Back-surface electric field passivation of CdTe solar cells using sputter-deposited CdSe

CdTe back-surface passivation is one of the effective ways to enhance device performance. In recent years, the role of Se passivation in high performance CdSeTe thin film solar cell device has received increasing attention. However, current high-efficiency devices only have a considerable concentration of Se at the very front of the device, while most of the area on the back side of the absorber layer is not passivated by Se. This means that further efficiency improvements may be possible if more defects on the back surface of the absorber layer are passivated by Se, while maintaining the built-in field. Here, based on the magnetron sputtering process, chemical passivation and electric field passivation can be achieved when a small amount of CdSe is deposited on the CdTe back surface. When the CdSe thickness is ∼20 nm (Before annealing), the optimal cell current was increased from 23.8 mA/cm2 to 26 mA/cm2 and the efficiency was increased from 13.1% to 15.5%. External quantum efficiency and impedance spectroscopy measurements indicate that the performance improvement is due to the reduction of the interfacial recombination current on the back surface.

Wake-Up Free Ultrathin Ferroelectric Hf0.5Zr0.5O2 Films.

The development of the new generation of non-volatile high-density ferroelectric memory requires the utilization of ultrathin ferroelectric films. The most promising candidates are polycrystalline-doped HfO2 films because of their perfect compatibility with silicon technology and excellent ferroelectric properties. However, the remanent polarization of HfO2 films is known to degrade when their thickness is reduced to a few nanometers. One of the reasons for this phenomenon is the wake-up effect, which is more pronounced in the thinner the film. For the ultrathin HfO2 films, it can be so long-lasting that degradation occurs even before the wake-up procedure is completed. In this work, an approach to suppress the wake-up in ultrathin Hf0.5Zr0.5O2 films is elucidated. By engineering internal built-in fields in an as-prepared structure, a stable ferroelectricity without a wake-up effect is induced in 4.5 nm thick Hf0.5Zr0.5O2 film. By analysis of the functional characteristics of ferroelectric structures with a different pattern of internal built-in fields and their comparison with the results of in situ piezoresponse force microscopy and synchrotron X-ray micro-diffraction, the important role of built-in fields in ferroelectricity of ultrathin Hf0.5Zr0.5O2 films as well as the origin of stable ferroelectric properties is revealed.

Multi-functionally ferroelectric polymer promotes highly-efficient large-area organic solar cells with excellent comprehensive performance

Developing high-performance active layer with excellent comprehensive performance is very crucial for the commercialization of organic solar cells (OSCs). Here, we demonstrate the multi-function of ferroelectric polymer polyvinylidene fluoride (PVDF) in improving the device comprehensive performance including device efficiency, stability, green-solvent large-area printing and mechanical property. Addition of PVDF not only enhances the build-in field to promote charge kinetics, but also develops robust network through strong interaction and chain entanglement between polymer donor and PVDF. Importantly, such robust network effectively protects the active layer from excessive flushing/swelling between D/A component to optimize layer-by-layer (LBL) deposition, induce a favorable vertical phase distribution and prolong the film-forming process, consequently facilitating green-solvent blade-coating printing, improving device efficiency and stability, and enhancing device mechanical flexibility. Due to the multiple advantages of PVDF, the PM6/BTP-eC9 obtains an excellent efficiency of 18.35% for BTP-eC9-based LBL devices. By blade-coating printing with green solvent, one of the highest efficiencies of 16.40% is achieved for large-area (1.21 cm2) binary device. Particularly, toughness is used to comprehensively evaluate mechanical property of OSCs, showing significant improvement with simultaneously enhanced fracture strength and tensile strain, and enabling small molecule-based system even have comparable mechanical flexibility and comprehensive performance to the all-polymer system.

Enhancing polarization retention in BiFeO3 domain wall nanodevices through controlled space charge redistribution

Ferroelectric thin films with binary switchable polarization offer promising applications in domain wall (DW) memory. However, achieving reliable polarization retention in size-reduced devices remains challenging. In this study, we present a planar ferroelectric BiFeO3 DW nanodevice demonstrating stable polarization retention through electrical cycling. By precisely controlling the device size, including the width and gap of planar Pt electrodes, we observed a back-switching process in switched polarization within 20 min, as characterized by ex-situ piezoresponse force microscopy (PFM). To overcome this issue, long-time alternating voltage pulse cycling effectively suppressed the back-switching behavior, leading to symmetrized polarization coercive voltages of the device. PFM characterization further confirmed the persistence of the artificially created DW between the electrode pair. This improved polarization retention was attributed to the migration of mobile charged defects, such as oxygen vacancies, at the domain boundary. The presence of these defects generated a local built-in field, which screened the net polarization induced by the charged DW. Upon erasing the DW, the local built-in field gradually dissipated during opposite voltage poling, resulting in restored poor polarization retention and asymmetric coercive voltage in the nanodevices. This work presents a promising approach to utilize defect redistribution for stabilizing the switched polarization in the development of high-density ferroelectric DW memory.

Fabricating the ternary CeO2@CNTs/CdSe composite with synchronously enhanced adsorption and photocatalytic activity toward water-soluble pollutants removal

Constructing heterogeneous catalyst with different bandgaps is a prospect way to realize efficient charge transfer of catalytic redox reaction. Semiconductor-based catalyst as a prospective material can effectively solve sewage issues under light irradiation, but the efficiency is greatly influenced by the recombination rate of photoelectrons and holes. In this work, cerium dioxide (CeO2) nanoparticles (NPs) were grown in-situ on carbon nanotubes (CNTs), which can maintain the pollutant removal efficiency of pure CeO2 NPs and enhance the adsorption intensity under visible light for CeO2@CNTs composite. Furthermore, the introduction of cadmium selenide (CdSe) was conducive to establish built-in electronic field in the ternary CeO2@CNTs/CdSe catalyst, which effectively enhanced the catalytic activity of CeO2@CNTs/CdSe. In comparison to CNTs, CdSe, CeO2 and CeO2@CNTs composite, the ternary CeO2@CNTs/CdSe catalyst exhibited higher photocurrent intensity, lower recombination of photoelectrons and holes (e-/h+) pairs, indicating much better photocatalytic activity. CeO2@CNTs/CdSe as photocatalyst displayed excellent adsorption ability for Congo red (CR), which contributed to increase the transparency of reaction solution and improve the utilization rate to light, the evaluated degradation efficiency of CR achieved 83.58 % and the reduction ratio of Cr(VI) was nearly 100 %. This work confirms that CeO2@CNTs/CdSe composite with excellent adsorption and photocatalytic ability is a promising photocatalyst material in wastewater treatment.

Strong Interface Interaction of ZnO Nanosheets and MnSx Nanoparticles Triggered by Light over Wide Ranges of Wavelength to Enhance Their Removal of VOCs

The characteristics of the surface and interface of nanocomposites are important for exerting multi-functional properties and widening interdisciplinary applications. These properties are mainly depending on the electronic structures of materials. Some key factors, such as the surface, interface, grain boundaries, and defects take vital roles in the contribution of desired properties. Due to the excellent sensitivity of the QCM (quartz crystal microbalance) device, the surface and interface features of the nanocomposite were studied with the aid of the gas-response of the sensors (Sensor’s Gas-Sensitivity) in this work. To make full use of the visible light and part of NIR, a ZnO/MnSx nanocomposite was constructed using hydrothermal synthesis for narrowing the bandgap width of wide bandgap materials. The results indicated that the absorbance of the resulting nanocomposite was extended to part of the NIR range due to the introduction of impurity level or defect level, although ZnO and MnS belonged to wide bandgap semiconductor materials. To explore the physical mechanism of light activities, the photoconductive responses to weak visible light (650 nm, etc.) and NIR (near-infrared) (808 nm, 980 nm, and 1064 nm, etc.) were studied based on interdigital electrodes of Au on flexible PET (polyethylene terephthalate) film substrate with the casting method. The results showed that the on/off ratio of ZnO/MnSx nanocomposite to weak visible light and part of NIR light were changed by about one to five orders of magnitude, with changes varying with the amount of MnSx nanoparticle loading due to defect-assisted photoconductive behavior. It illustrated that the ZnO/MnSx nanocomposite easily produced photo-induced free charges, effectively avoiding the recombination of electrons/holes because of the formation of strong built-in electrical fields. To examine the surface and interface properties of nanocomposites, chemical prototype sensor arrays were constructed based on ZnO, ZnO/MnSx nanocomposite, and QCM arrays. The adsorption response behaviors of the sensor arrays to some typical volatile compounds were examined under a similar micro-environment. The results exhibited that in comparison to ZnO nanosheets, the ZnO nanosheets/MnSx nanocomposite increased adsorption properties to some typical organic volatile compounds significantly. It would have good potential applications in photo-catalysts, self-cleaning films, multi-functional coatings, and organic pollutants treatment (VOCs) of environmental fields for sustainable development. It provided some reference value to explore the physical mechanism of materials physics and photophysics for photo-active functional nanocomposites.

Coupling photothermal and piezoelectric effect in Bi4Ti3O12 for enhanced photodegradation of tetracycline hydrochloride

Semiconductor photocatalysis is an effective way to remove antibiotic pollution. However, recombination of photogenerated carriers limits the efficiency of photocatalytic degradation of antibiotic. In this work, Bi4Ti3O12 (BTO) with micro-hollow spheres (HS-BTO) was successfully self-assembled by BTO nano-sheets. The microstructure of HS-BTO can serve as a guarantee for its good adsorption capability. Assisted by photothermal effect, HS-BTO shows efficient photodegradation of tetracycline hydrochloride (TC) solution. This work reveals that heat can effectively reduce the charge transfer resistance, accelerate the charge transfer, thus promoting the charge separation and improving the photocatalytic performance. In addition, through ultrasound vibration, polarization charges and built-in polarization fields may be generated in HS-BTO. They can accelerate photogenerated charge carriers separation and greatly suppress recombination rate of electron/hole pairs, and is helpful to achieve piezoelectric catalytic degradation of TC. Consequently, a developed photocatalytic degradation of TC assisted by photothermal and piezoelectric effect is achieved. Thus, this work proposes an innovative approach to coupling optical, photothermal and mechanical energy to advance photocatalysis.