Dynamic control of piezoelectricity enhancement via modulation of the bulk photovoltaic effect in a BiFeO 3 thin film

Piezoelectricity, which is an electromechanical effect induced by conversion between mechanical and electrical energy, is one of the key functionalities in ferroelectric oxides. Traditionally, structural engineering in synthesis via a variety of processing control parameters has been a well-established route to host so-called morphotropic phase boundaries for enhancing piezoelectricity. However, this involves dealing with synthetical complexity and difficulties of strictly controlling structures and defects. Instead, for simple and in situ control, here, a critical pathway for light-induced piezoelectricity enhancement and its dynamic control is unveiled in a BiFeO3/DyScO3 thin film by implementing an in-plane geometry operation, allowing for modulation of the bulk photovoltaic effect. A series of in-plane length-dependent piezoresponse force microscopy and conductive atomic force microscopy-based measurements under illumination reveals its strong influence on the photocurrent and photovoltage, consequently revealing a maximum of eightfold increase of the effective piezoelectric coefficient, dzz. Light polarization dependent measurements show sinusoidal behavior of piezoelectricity closely linked to photocurrent variations, leading to a further threefold increase of dzz. Temporal decay measurements reveal persistent behavior of enhanced piezoelectricity after removal of illumination, associated with reemission of photocarriers trapped in sub-levels. These results pave the way for light-induced piezoelectricity enhancement compatible with the photovoltaic effect in ferroelectric thin films for multifunctional nano-optoelectronics

The effects of point defect type, location, and density on the Schottky barrier height of Au/MoS2 hetero-junction: A first-principles study

Using DFT calculations, we investigate the effects of the type, location, and density of point defects in monolayer MoS2 on electronic structures and Schottky barrier heights (SBH) of Au/MoS2 heterojunction. Three types of point defects in monolayer MoS2, that is, S monovacancy, S divacancy and MoS (Mo substitution at S site) antisite defects, are considered. The following findings are revealed: (1) The SBH for the monolayer MoS2 with defects is universally higher than that for its defect-free counterpart. (2) S divacancy and MoS antisite defects increase the SBH to a larger extent than S monovacancy. (3) A defect located in the inner sublayer of MoS2, which is adjacent to Au substrate, increases the SBH to a larger extent than that in the outer sublayer of MoS2. (4) An increase in defect density increases the SBH. These findings indicate a large variation of SBH with the defect type, location, and concentration. We also compare our results with previously experimentally measured SBH for Au/MoS2 contact and postulate possible reasons for the large differences among existing experimental measurements and between experimental measurements and theoretical predictions. The findings and insights revealed here may provide practice guidelines for modulation and optimization of SBH in Au/MoS2 and similar heterojunctions via defect engineering.Comment: 20 pages, 8 figure

Reactive oxygen species may be involved in the distinctive biological effects of different doses of 12C6+ ion beams on Arabidopsis

IntroductionHeavy ion beam is a novel approach for crop mutagenesis with the advantage of high energy transfer line density and low repair effect after injury, however, little investigation on the biological effect on plant was performed. 50 Gy irradiation significantly stimulated the growth of Arabidopsis seedlings, as indicated by an increase in root and biomass, while 200 Gy irradiation significantly inhibited the growth of seedlings, causing a visible decrease in plant growth.MethodsThe Arabidopsis seeds were irradiated by 12C6+. Monte Carlo simulations were used to calculate the damage to seeds and particle trajectories by ion implantation. The seed epidermis received SEM detection and changes in its organic composition were detected using FTIR. Evidence of ROS and antioxidant systems were analyzed. RNA-seq and qPCR were used to detect changes in seedling transcript levels.Results and discussionMonte Carlo simulations revealed that high-dose irradiation causes various damage. Evidence of ROS and antioxidant systems implies that the emergence of phenotypes in plant cells may be associated with oxidative stress. Transcriptomic analysis of the seedlings demonstrated that 170 DEGs were present in the 50 Gy and 200 Gy groups and GO enrichment indicated that they were mainly associated with stress resistance and cell wall homeostasis. Further GO enrichment of DEGs unique to 50 Gy and 200 Gy revealed 58 50Gy-exclusive DEGs were enriched in response to oxidative stress and jasmonic acid entries, while 435 200 Gy-exclusive DEGs were enriched in relation to oxidative stress, organic cyclic compounds, and salicylic acid. This investigation advances our insight into the biological effects of heavy ion irradiation and the underlying mechanisms

Mechanical-force-induced non-local collective ferroelastic switching in epitaxial lead-titanate thin films.

Ferroelastic switching in ferroelectric/multiferroic oxides plays a crucial role in determining their dielectric, piezoelectric, and magnetoelectric properties. In thin films of these materials, however, substrate clamping is generally thought to limit the electric-field- or mechanical-force-driven responses to the local scale. Here, we report mechanical-force-induced large-area, non-local, collective ferroelastic domain switching in PbTiO3 epitaxial thin films by tuning the misfit-strain to be near a phase boundary wherein c/a and a1/a2 nanodomains coexist. Phenomenological models suggest that the collective, c-a-c-a ferroelastic switching arises from the small potential barrier between the degenerate domain structures, and the large anisotropy of a and c domains, which collectively generates much larger response and large-area domain propagation. Large-area, non-local response under small stimuli, unlike traditional local response to external field, provides an opportunity of unique response to local stimuli, which has potential for use in high-sensitivity pressure sensors and switches

Wireless, battery-free optoelectronic systems as subdermal implants for local tissue oximetry

Monitoring regional tissue oxygenation in animal models and potentially in human subjects can yield insights into the underlying mechanisms of local O2-mediated physiological processes and provide diagnostic and therapeutic guidance for relevant disease states. Existing technologies for tissue oxygenation assessments involve some combination of disadvantages in requirements for physical tethers, anesthetics, and special apparatus, often with confounding effects on the natural behaviors of test subjects. This work introduces an entirely wireless and fully implantable platform incorporating (i) microscale optoelectronics for continuous sensing of local hemoglobin dynamics and (ii) advanced designs in continuous, wireless power delivery and data output for tether-free operation. These features support in vivo, highly localized tissue oximetry at sites of interest, including deep brain regions of mice, on untethered, awake animal models. The results create many opportunities for studying various O2-mediated processes in naturally behaving subjects, with implications in biomedical research and clinical practice.Center for Bio-Integrated Electronics at Northwestern University; Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF) [ECCS-1542205]; Materials Research Science and Engineering Center [DMR-1720139]; State of Illinois; Northwestern University; Developmental Therapeutics Core at Northwestern University; Robert H. Lurie Comprehensive Cancer Center [NCI CA060553]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Three-dimensional, multifunctional neural interfaces for cortical spheroids and engineered assembloids.

Three-dimensional (3D), submillimeter-scale constructs of neural cells, known as cortical spheroids, are of rapidly growing importance in biological research because these systems reproduce complex features of the brain in vitro. Despite their great potential for studies of neurodevelopment and neurological disease modeling, 3D living objects cannot be studied easily using conventional approaches to neuromodulation, sensing, and manipulation. Here, we introduce classes of microfabricated 3D frameworks as compliant, multifunctional neural interfaces to spheroids and to assembloids. Electrical, optical, chemical, and thermal interfaces to cortical spheroids demonstrate some of the capabilities. Complex architectures and high-resolution features highlight the design versatility. Detailed studies of the spreading of coordinated bursting events across the surface of an isolated cortical spheroid and of the cascade of processes associated with formation and regrowth of bridging tissues across a pair of such spheroids represent two of the many opportunities in basic neuroscience research enabled by these platforms

Optoelectronic properties of ferroelectric semiconductors

The optoelectronic properties, such as bulk photovoltaic effect and photoconductivity, of ferroelectric semiconductors have been attracting enormous attention, due to their promising application in solar cells and other multi-functional devices. These exciting findings, such as the highly-conductive domain walls and flexo-photovoltaic effect, reveal the fact that there might be other undiscovered and fascinating phenomena in the field of optoelectronics. The emergence of important physical properties of a semiconductor could be from the defects, including structural defects and point defects that naturally exist in the system or are artificially introduced. For example, defects could increase/decrease the carrier density and modify the electronic structure, thus changing the carrier transport properties. With this being the background, we first focused our study on the bulk photovoltaic effect of the ferroelectric domain walls. We showed that the domain wall can largely enhance the photovoltaic current via an interaction with the defects. We further investigated the effect of the heterointerface of a thin film, as the interface usually shows unexpected physical properties. We started by comparing the optoelectronic properties of bismuth ferrite thin films grown on different substrates and found that the strontium titanate could provide a highly conductive path at its surface with bismuth ferrite. We proved that this is due to the significant defect density and high carrier mobility of strontium titanate. Inspired by this exciting result, we further investigated the physical properties of strontium titanate in its heterostructures. Results showed that the interface between strontium titanate and other oxides is polar when the temperature is down to the onset of the quantum paraelectric phase of strontium titanate. We demonstrate that the principle of the emergence of the polar interface is due to the generic band bending at the interface of two dissimilar materials. In the last part of the thesis, we investigate the magneto-photocurrent effect in bismuth ferrite. This has not been ever studied but is urgently needed, because spin-current and ferromagnetism-tuned physical properties are critical for studies of spin-charge conversion systems. We demonstrate that an unprecedented hysteretic magneto-photocurrent behaviour exists in the bismuth ferrite-terbium scandate system, due to the potential ferromagnetism texture at the interface. We purpose a plausible model that is based on the spin galvanic effect and Hanle spin precession, and successfully explains the ferromagnetism-related spin scattering behaviours