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Intracortical neural stimulation with untethered, ultrasmall carbon fiber electrodes mediated by the photoelectric effect
摘要： Objective: Neural stimulation with tethered, electrically activated probes is damaging to neural tissue and lacks good spatial selectivity and stable chronic performance. The photoelectric effect, which converts incident light into electric potential and heat, provides an opportunity for a tetherless stimulation method. We propose a novel stimulation paradigm that relies on the photoelectric effect to stimulate neurons around a free-floating, ultrasmall (7-8μm diameter) carbon fiber probe. Methods: A 2-photon microscope induced photo-stimulation with a laser. Chronoamperometry and chronopotentiometry were used to characterize the electrochemical properties of photo-stimulation, while the fluorescence of Rhodamine-B was used to quantify temperature changes. Results: Photo-stimulation caused a local cathodic potential pulse with minimal leakage current. Stimulation induced voltage deflections of 0.05 - 0.4V in vitro, varying linearly with the power of the laser source (5 – 40 mW). Temperature increases in the immediate vicinity of the electrode were limited to 2.5°C, suggesting that this stimulation modality can be used without inducing heat damage. Successful stimulation was supported in vivo by increased calcium fluorescence in local neurons at stimulation onset in a transgenic GCaMP-3 mouse model. Furthermore, cells activated by photo-stimulation were closer to the electrode than in electrical stimulation under similar conditions, indicating increased spatial precision. Conclusion: Our results support the hypothesis that the proposed photoelectric method is effective for neural stimulation. Significance: Photoelectric stimulation is precise and avoids the need for a potentially destructive tether, making it a promising alternative to electrical stimulation.
关键词： GCaMP,electrochemistry,neuromodulation,photovoltaic effect,2-photon microscopy,temperature-dependent,fluorescence
更新于2025-09-23 15:23:52
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Local photo-excitation of shift current in noncentrosymmetric systems
摘要： Photocurrent in solids is an important phenomenon with many applications including the solar cells. In conventional photoconductors, the electrons and holes created by light irradiation are separated by the external electric field, resulting in a current flowing into electrodes. Shift current in noncentrosymmetric systems is distinct from this conventional photocurrent in the sense that no external electric field is needed and, more remarkably, is driven by the Berry phase inherent to the Bloch wavefunction. It is analogous to the polarization current in the ground state but is a dc current continuously supported by the nonequilibrium steady state under the pumping by light. Here we show theoretically, by employing Keldysh–Floquet formalism applied to a simple one-dimensional model, that the local photo excitation can induce the shift current which is independent of the position and width of the excited region and also the length of the system. This feature is in stark contrast to the conventional photocurrent, which is suppressed when the sample is excited locally at the middle and increases towards the electrodes. This finding reveals the unconventional nature of shift current and will pave a way to design a highly efficient photovoltaic effect in solids.
关键词： nonequilibrium Green’s function method,shift current,photovoltaic effect
更新于2025-09-23 15:21:21
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Photovoltaic effect generated by spin-orbit interactions
摘要： An AC electric ?eld applied to a junction comprising two spin-orbit coupled weak links connecting a quantum dot to two electronic terminals is proposed to induce a DC current and to generate a voltage drop over the junction if it is a part of an open circuit. This photovoltaic effect requires a junction in which mirror re?ection symmetry is broken. Its origin lies in the different ways inelastic processes modify the re?ection of electrons from the junction back into the two terminals, which leads to uncompensated DC transport. The effect can be detected by measuring the voltage drop that is built up due to that DC current. This voltage is an even function of the frequency of the AC electric ?eld.
关键词： quantum dot,photovoltaic effect,spin-orbit interactions,DC current,voltage drop
更新于2025-09-23 15:21:01
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Enhanced Ferroelectric Photovoltaic Effect in Semiconducting Single-Wall Carbon Nanotubes/BiFeO <sub/>3</sub> Heterostructure Enabled by Wide-Range Light Absorption and Efficient Charge Separation
摘要： The interfacial electronic band structures of photovoltaic heterostructure devices greatly affect their light absorption and charge-transport properties and thus their photovoltaic performance. In this work, we report an enhanced ferroelectric photovoltaic effect in a semiconducting single-walled carbon nanotube (S-SWCNTs)/ferroelectric BiFeO3 (BFO) heterostructure. A wide range of light absorption was possible in this structure owing to the low bandgaps of the S-SWCNTs (0.2–2.1 eV) and BFO (2.2–2.7 eV). The heterostructure also enabled efficient charge separation owing to the strong built-in electric field resulting from the synergic effect of the formation of p–f–n junctions (p-type S-SWCNTs/ferroelectric (f) BFO/n-type Nb:SrTiO3) and the introduction of a polarization-mediated internal field in the ferroelectric BFO layer. Compared with a single-layer device (Pt/BFO/Nb:SrTiO3), the heterostructure device (Pt/S-SWCNTs/BFO/Nb:SrTiO3) exhibited substantial enhancement of the photovoltaic performance. The open-circuit photovoltage and short-circuit photocurrent density reached up to 0.23 V and ?7.52 mA cm?2 (corresponding to a photo-conversion efficiency of 4.40%) under one-sun illumination, respectively, after optimization of the ferroelectric layer thickness and appropriate interfacial band alignment. Moreover, by applying switchable electric polarization, this heterostructure could be tuned, enabling the development of controllable photovoltaic devices. Our findings demonstrate that the synergistic integration of materials with different functionalities is a promising approach for the design of photovoltaic devices with tunable performance.
关键词： BiFeO3,light absorption,single-walled carbon nanotube,heterostructure,charge separation,ferroelectric photovoltaic effect
更新于2025-09-23 15:21:01
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One-Structure-Based Multi-Effects Coupled Nanogenerators for Flexible and Self-Powered Multi-Functional Coupled Sensor Systems
摘要： The simultaneous monitoring of multi-physical signals is essential for future sensor systems, but is currently only realized by integrating a variety of sensor types into a single device. However, the ability to use a single sensor structure that shares common electrodes can provide a route to multi-functional sensing while also decreasing device size and increasing spatial resolution. Here we report a ferroelectric barium titanate film-based multi-effect coupled nanogenerator for scavenging light, mechanical, and thermal energies to realize a self-powered multi-functional coupled sensor system without using any external power source. The coupled nanogenerator exhibits a strong coupling enhancement with detection sensitivities of 0.42 nA/(mW/cm2) during illumination by 405 nm light, 1.43 nA/kPa for pressure detection, and -8.85 nA/K for temperature sensing, where both the light and pressure sensing performances have the highest sensitivities during a cooling temperature variation of ~19.5 K and the largest temperature detection sensitivity can be achieved during strong light illumination of 83.2 mW/cm2. Moreover, the coupled nanogenerator array can be integrated into flexible forms for tactile pressure, temperature, and light sensors, and enabling coupled sensing for the development of electronic skins.
关键词： photovoltaic effect,pyroelectric effect,piezoelectric effect,electronic skin
更新于2025-09-23 15:19:57
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Compact Graphene Plasmonic Slot Photodetector on Silicon-on-insulator with High Responsivity
摘要： Graphene has extraordinary electro-optic properties and is therefore a promising candidate for monolithic photonic devices such as photodetectors. However, the integration of this atom-thin layer material with bulky photonic components usually results in a weak light-graphene interaction leading to large device lengths, limiting electro-optic performance. In contrast, here we demonstrate a plasmonic slot graphene photodetector on silicon-on-insulator platform with high responsivity of 0.7 A/W given a just 5 μm-short device length. We observe that the maximum photocurrent, and hence the highest responsivity, scales inversely with the slot width. Using a dual-lithography step, we realize 15 nm narrow slots that show a 30-times higher responsivity per unit device-length compared to photonic graphene photodetectors. Furthermore, we reveal that the back-gated electrostatics is overshadowed by channel-doping contributions induced by the contacts of this ultra-short channel graphene photodetector. This leads to quasi charge neutrality, which explains both the previously-unseen offset between the maximum photovoltaic-based photocurrent relative to graphene’s Dirac point and the observed non-ambipolar transport. Such micrometer compact and absorption-efficient photodetectors allow for short-carrier pathways in next-generation photonic components, while being an ideal testbed to study short-channel carrier physics in graphene optoelectronics.
关键词： plasmonics,photovoltaic effect,graphene,photodetector,bolometric effect,Silicon photonics
更新于2025-09-23 15:19:57
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A surface photovoltaic effect-related high-performance photodetector based on a single CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> micro/nanowire
摘要： With the decrease of materials to the nanoscale, their surface states will play a crucial role in their performance. Here, an individual CH3NH3PbI3 micro/nanowire-based photodetector can show excellent sensitivity and responsivity to light with a wide wavelength range from 200 to 850 nm. A surface state-related photovoltaic effect associated with a surface barrier can be formed due to a depletion of majority carriers (holes) in the surface space charge region. At a low operation voltage, the photodetector can exhibit a low dark current. Upon illuminating near the end connected to the positive electrode, the light-induced decrease of the surface barrier leads to enhanced conduction, showing a large photocurrent. At zero bias, additionally, the photodetector can show a relatively large photogenerated voltage and current when only the vicinity of one end is illuminated. Based on the CH3NH3PbI3 micro/nanostructure performance herein, surface photovoltaic-controlled photodetectors with superior performance will have important applications in new-generation optoelectronic devices.
关键词： CH3NH3PbI3,optoelectronic devices,photodetector,surface photovoltaic effect,micro/nanowire
更新于2025-09-23 15:19:57
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Successive redox-mediated visible-light ferrophotovoltaics
摘要： Titanium oxide materials have multiple functions such as photocatalytic and photovoltaic effects. Ferroelectrics provide access to light energy conversion that delivers above-bandgap voltages arising from spatial inversion symmetry breaking, whereas their wide bandgap leads to poor absorption of visible light. Bandgap narrowing offers a potential solution, but this material modification suppresses spontaneous polarization and, hence, sacrifices photo-voltages. Here, we report successive-redox mediated ferrophotovoltaics that exhibit a robust visible-light response. Our single-crystal experiments and ab initio calculations, along with photo-luminescence analysis, demonstrate that divalent Fe2+ and trivalent Fe3+ coexisted in a prototypical ferroelectric barium titanate BaTiO3 introduce donor and acceptor levels, respectively, and that two sequential Fe3+/Fe2+ redox reactions enhance the photogenerated power not only under visible light but also at photon energies greater than the bandgap. Our approach opens a promising route to the visible-light activation of photovoltaics and, potentially, of photocatalysts.
关键词： ferrophotovoltaics,redox reactions,barium titanate,photovoltaic effect,visible-light response
更新于2025-09-23 15:19:57
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Tailoring the photovoltaic effect in (1a??1a??1) oriented BiFeO <sub/>3</sub> /LaFeO <sub/>3</sub> superlattices
摘要： Ferroelectric and photovoltaic properties of (BiFeO3)(1?x)Λ/(LaFeO3)xΛ superlattices grown by pulsed laser deposition have been investigated (Λ being the bilayer thickness). For a high concentration of BiFeO3 a ferroelectric state is observed simultaneously with a switchable photovoltaic response. In contrast for certain concentration of LaFeO3 a non-switchable photovoltaic effect is evidenced. Such modulation of the PV response in the superlattices is attributed to the ferroelectric to paraelectric phase transition which is controlled with the increase of x. Remarkably, concomitant to this change of PV mechanism, a change of the conduction mechanism also seems to take place from a bulk-limited to an interface-limited transport as x increases.
关键词： photovoltaic effect,ferroelectrics,complex oxides,superlattices,multiferroics
更新于2025-09-23 15:19:57
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Improved Photovoltaic Effect of <i>pa??ia??n</i> Structured BiFeO <sub/>3</sub> Film Deposited by Radio-Frequency Magnetron Sputtering
摘要： Pure phase polycrystalline BiFeO3 ?lm was deposited onto FTO substrate by RF magnetron sputtering method. SEM result shows that BiFeO3 ?lm has the obvious porosity and large clusters which lead to the poor ferroelectric and photovoltaic properties in FTO/BiFeO3/Ag device. However, these properties are improved in p–i–n structured FTO/TiO2/BiFeO3/HTM/Ag device by incorporating the electron and hole transport materials. The hysteresis loop measurement demonstrates the excellent ferroelectric property with large remnant polarization (2Pr = 180 (cid:2)C/cm2) and low leakage current. The J–V curve shows the short-circuit current density is dozens of times larger than that of FTO/BiFeO3/Ag device. Moreover, the photovoltaic output depends on the poling ?eld where the positive poling improves the short-circuit current density to ?85 (cid:2)A/cm2 and the negative poling reduces both the photocurrent and photovoltage. It is believed that the ferroelectric polarization plays a dominant role in the photovoltaic effect.
关键词： BiFeO3 Film,Sputtering,Photovoltaic Effect
更新于2025-09-23 15:19:57