Light-induced Conductance Changes Research Articles

One-Pot Fabrication of Copper-Doped WO3·H2O Opto-Functional Layered Device using Submerged Photosynthesis of Crystallites.

This study introduces a one-pot, submerged photosynthesis of crystallites (SPsC) method for fabricating monohydrate tungstic acid (WO3·H2O) nanoplates directly integrated onto a stainless steel mesh, offering a simplified production and enhanced device stability for optical functional applications. The fabricated devices demonstrate exceptional broadband light absorption across the ultraviolet (UV), visible (Vis), and near-infrared (NIR) ranges. Notably, 1% Cu doping significantly boosts the NIR absorption, yielding a high solar utilization efficiency of 81.40%. In solar water evaporation experiments, the devices exhibit a maximum temperature increase of 13 °C under 1-Sun (100 mW/cm2) illumination, achieving an energy conversion efficiency of 32.5%. Moreover, electrochemical characterization reveals light-induced conductivity changes and enhanced current density, suggesting potential applications in rectifying devices. This versatile and environmentally conscious SPsC fabrication method holds promise for the sustainable development of diverse nanodevices.

Cellular interfaces with hydrogen-bonded organic semiconductor hierarchical nanocrystals

Successful formation of electronic interfaces between living cells and semiconductors hinges on being able to obtain an extremely close and high surface-area contact, which preserves both cell viability and semiconductor performance. To accomplish this, we introduce organic semiconductor assemblies consisting of a hierarchical arrangement of nanocrystals. These are synthesised via a colloidal chemical route that transforms the nontoxic commercial pigment quinacridone into various biomimetic three-dimensional arrangements of nanocrystals. Through a tuning of parameters such as precursor concentration, ligands and additives, we obtain complex size and shape control at room temperature. We elaborate hedgehog-shaped crystals comprising nanoscale needles or daggers that form intimate interfaces with the cell membrane, minimising the cleft with single cells without apparent detriment to viability. Excitation of such interfaces with light leads to effective cellular photostimulation. We find reversible light-induced conductance changes in ion-selective or temperature-gated channels.

Proteorhodopsin characterization based on metal–insulator–metal structure technique

We investigated the light-induced conductivity changes of dry green light absorbing proteorhodopsin (GPR) using a metal–insulator–metal system (MIM). The steady-state and time-dependent current–voltage ( I– V) characteristics were measured as a function of GPR concentration for different illumination conditions. As the photoconductivity of GPR in the dry film was varied due to the incident light intensity and the wavelength, we could directly observe the photoconductivity changes inside the GPR by measuring the I– V of the MIM system. In addition to these steady-state measurements, applied bias-dependent properties were studied. The optical absorption spectrum of the GPR film between 450 nm and 650 nm correlates with the action spectrum of the MIM system. The GPR maintained higher photoactivity under green light illumination, which is correlated with the formation of an M-like intermediate.

Light-induced reversible conductivity changes in silicon-on-insulator nanowires

Silicon-on-insulator (SOI) samples are preferred for extention of the metal-oxide-silicon technology. Here, we report a reversible change in electrical conductivity in dark conditions of a 20-nm-thick SOI layer, induced by illumination. In spite of some similarities with the Staebler–Wronski effect in hydrogenated amorphous silicon, we point out important differences such as the crystalline nature of our silicon film, the lack of hydrogen and a much shorter relaxation time at ambient temperature. This time can even be reduced by application of a vertical electric field. We suggest that interface traps play a major role in this mechanism. Finally, we noticed a conductivity change between ambient light and dark conditions.

Photoresponses and light adaptation of pineal photoreceptors in the trout

The photoresponses of 116 photoreceptors in the excised perfused pineal body of adult trout were intracellularly recorded. Brief flashes produced slower, but otherwise comparable, responses to retinal receptor cells. The absolute sensitivity, as well as the light-induced membrane conductance changes, were also similar to those of retinal cone cells in the same species. Steady illumination decreased the cell sensitivity to superimposed flashes, in accordance with the Weber-Fechner relation, indicating the presence of light adaptation. This conclusion is supported by the non-exponential nature of the amplitude-intensity relation and by the conspicuous shortening of the time-to-peak with increasing flash intensity. The time-dependent response decay typical of retinal photoreceptors was not found, however. The fact that, during constant illumination, the pineal photoresponses maintain the same amplitude set at the initial peak perhaps represents an original mechanism of light adaptation which allows these cells to maintain their voltage-dependent synthesis and secretion of indolamines as a constant relation with daily illumination.

Persistent photoconductance in a-Si: H/a-SiOx:H multilayers

Abstract We report on the existence of a large persistent photoconductance (PPC) effect in multilayers made of alternating layers of glow-discharge deposited hydrogenated amorphous silicon (a-Si: H) and silicon-oxide (a-SiOx: H). The effect consists of a metastable inerease in dark conductivity caused by a brief light exposure. We find that the PPC effect inereases with inereasing oxide sublayer thickness d0, reaching saturation at d0≈ 10nm. The efficiency for the creation of the PPC depends on the oxygen concentration of the oxide used in the multilayers. The magnitude of PPC, measured at room temperature, is independent of the exposure temperature Te between 4 and 100 K, and then inereases with Te up to about Te≈350K. The annealing temperature of the PPC is found to be TEs≈480-485 K independent of Te and the doping of the silicon layers. Using photothermal deflection spectroscopy, we observe that, for a given light exposure, the density of light induced defects (Staebler-Wronski effect) is much larger in a-SiOx: H than in a-Si: H films. Our results suggest that the PPC effect in a-Si: H/a-SiOx: H multilayers is caused by metastable defects created in the defect structure of the oxide layers. These defects are mainly created by light absorbed in the oxide layers. Defects can also be created by hopping injection into the insulating layers of carriers photoexcited in the adjacent silicon layers. Our results indicate that the mechanism proposed for PPC in a-Si:H/a-SiOx:H multilayers is universally valid to explain light-induced conductance changes in multilayers made of alternating layers of a-Si: H and a variety of insulating a-Si: H alloys.

Persistent photoconductance in doping-modulated and compensateda-Si:H

We present experimental results and numerical calculations in support of the following model to explain the origin of the persistent-photoconductivity effect (PPC) in {ital p}-{ital n} multilayers of hydrogenated amorphous silicon ({ital a}-Si:H): Small light exposures create Staebler-Wronski defects in the {ital p}-type regions of the multilayer, making these regions more intrinsic. This brings the equilibrium Fermi level of the multilayer closer to the conduction band in the depletion zones of the {ital n}-type regions, causing an increase in the conductance of the layered structure when the conductance is electron dominated. At large light exposures, the Staebler-Wronski defects created in the {ital n}-type regions pull the Fermi level away from the conduction band, decreasing the conductance of the film. Our experimental results show that, for a given light intensity, the creation rate and annealing kinetics of the PPC in multilayers are correlated with the creation rate and annealing kinetics of the light-induced conductance changes in unlayered {ital p}-type and {ital n}-type {ital a}-Si:H films having the same dopings as the {ital p}-type and {ital n}-type regions in the multilayer. The PPC follows a stretched-exponential time relaxation with the same parameters describing the decays of other metastable conditions in {ital a}-Si:H.more » Our computer calculations can reproduce the dark conductivity and magnitude of the PPC in a multilayer (doped at 100 ppm) as a function of sublayer thickness {ital d}, except for {ital d}{lt}20 nm.« less

A study of light-induced conductivity in bacteriorhodopsin

Measurements have been made of light-induced conductivity changes and the associated kinetics of the relaxation processes in aqueous suspensions and sonicated liposomes containing bacteriorhodopsin (bR). Aqueous suspensions exhibit a single relaxation time of 1 to 2 ms. The addition of D2O to the aqueous suspension slows down the relaxation time, fourfold. Similar behaviour is seen in sonicated liposomes with a relaxation time of 2 to 3 ms. Activation energies of approximately 14 and 6 kJM-1 are obtained for the effect in sonicated liposomes and aqueous suspension containing bR, respectively. These relaxation processes with lifetime of 1 to 2 ms suggest conformational changes in the protein moiety of bR which most probably may be associated with protonation-deprotonation processes or less likely the release and binding of small ions.

Circadian and light-induced conductance changes in putative pacemaker cells of Bulla gouldiana

The ocular circadian rhythm of compound action potential frequency in Bulla gouldiana is driven by rhythmic changes in the membrane potential of putative circadian pacemaker cells. Changes in the membrane potential of these neurons is required for light-induced phase shifts of the rhythm. We have tested the proposition that these changes in membrane potential reflect underlying changes in ionic conductances. We have found that: 1. Membrane conductance in the dark is highest during the subjective night when the cells are hyperpolarized, decreases as the cells depolarize spontaneously near projected dawn and is lowest during the subjective day. The changes in membrane potential and conductance follow a similar time course. 2. Long pulses of light delivered to eyes during their subjective night produce a characteristic response: There is initially a large, phasic depolarization accompanied by a burst of CAPs; this is followed by a repolarizing phase during which CAP activity is reduced to zero; and finally a tonic depolarization develops that is accompanied by a resumption of CAP activity at a steady rate. 3. During the subjective night, the tonic depolarization is accompanied by a decrease in conductance compared to the previous dark value. However, light pulses of similar duration delivered to eyes during their subjective day causes tonic depolarizations and increased CAP activity, but no measurable change in conductance. 4. Membrane responses to light are sensitive to agents that reduce Ca2+ flux. Light pulses during the subjective night produce a phasic depolarization, but the repolarization phase is eliminated in low Ca2+/EGTA seawater and is reduced in 5 mM Ni2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Light-induced conductivity changes in phosphorus-doped hydrogenated amorphous silicon

In this study we have investigated the temperature dependence of light-induced conductivity changes in phosphorus-doped hydrogenated amorphous silicon(a-Si:H). At certain temperatures, the transition of the dark conductivity change after illumination from normal to abnormal(inverse) Staebler-Wronski(SW) effects have been observed. This transition temperature decreases with increasing doping concentration. On the other hand, the light-induced photoconductivity change shows the normal SW effects in all temperatures but the magnitude of change decreases drastically above transition temperature. Possible mechanism for these effects is discussed.

Towards understanding persistent photoconductance in doping modulated amorphous silicon

Abstract We present a simple model to explain the origin of the persistent photoconductance (PPC) in p–n–p–n multilayers made of hydrogenated amorphous silicon: brief light exposures create metastable Staebler-Wronski defects in the p-type material, making it more intrinsic. This in turn pushes the Fermi level of the whole multilayer closer to the conduction band, thus causing the observed metastable increase of the electron dominated coplanar conductance of the multilayer. Much longer light exposures are needed to shift the Fermi level towards midgap due to Staebler-Wronski defects in the n-type layers, leading to a consequent decrease in the PPC effect. In support of our model we present experimental results on the creation rate and annealing kinetics of the light-induced metastable conductance changes in a multilayer and in p-type and n-type single layers.

Light-induced effects on the rapidly cooled state in hydrogenated amorphous silicon.

We have investigated the effects of light-induced conductivity changes on the thermal quenched state in phosphorus-doped hydrogenated amorphous silicon (a-Si:H). It was observed that the dark conductivity change strongly depends on cooling history, but the photoconductivity change is independent of that. The results will be discussed on the basis of the existing models for thermal equilibrium processes.

Light-induced conductivity changes of purple membrane suspensions in strong electrolytes.

Measurements have been made of the modulated light-induced changes in conductivity and the associated relaxation times of bacteriorhodopsin in a variety of strong electrolytes, both unbuffered and buffered. The effects of pH and temperature variation have been studied as well as the effect of adding valinomycin. Two relaxation times can be distinguished: a fast lifetime associated with protonation-deprotonation, and a slow lifetime associated with ion binding. The ion-binding effects appear to be cation specific.

Light-induced conductivity changes in hydrogenated amorphous silicon films prepared in cascaded glow discharge reactors

Light-induced changes in the conductivity, photoconductivity and activation energy of dark conductivity (Staebler-Wronski effect) were studied in hydrogenated amorphous silicon films prepared in cascaded glow discharge reactors. It was found that the films grown upstream are prone to such effects (although not as strongly as reported in the literature), whereas the films grown downstream are almost unaffected even after prolonged illumination and are stable in light. These changes were investigated further by applying an external electric field during illumination. It was found that under these conditions the change in conductivity decreased as the electric field gradually increased and vanished when the field approached 10 4–10 5 V cm -1 which is comparable with the built-in field in a solar cell.

Photoinduced metastable surface effects in boron-doped hydrogenated amorphous silicon films

We observed metastable light-induced conductance changes in p-type hydrogenated amorphous silicon films which are different from those discovered by Staebler and Wronski. In contrast to the large metastable decrease in the dark conductance after prolonged exposure to band-gap light (Staebler–Wronski effect) we observed an increase in the dark conductance by more than a factor of 30 at room temperature. This light-induced increase can be reversed by annealing. The anomalous conductance increase is associated with the presence of a surface oxide layer because it disappears after etching the sample. We find that the enhanced conductance is due to an increase of a hole accumulation layer in the sample caused by a light-induced metastable change in the surface oxide.

Temperature dependent light induced conductivity changes in hydrogenated amorphous silicon

The light induced changes for undoped and phosphorus doped hydrogenated amorphous silicon films deposited by dc glow discharge decomposition have been studied. It is observed that the conductance change after illumination is large for the undoped films deposited near the cathode, and deposited with high silane flow rate. The 0.1%–0.5% phosphorus doped samples show the increase of dark- and photoconductance after illumination. The rate of dark- and photoconductance change are observed to be accelerated as the temperature during the illumination is elevated. The activation energies for the recovery of the conductance changes are observed to be 1.5 and 1.0 eV for undoped and 0.1% phosphorus doped films, respectively. The field effect measurements for 0.1-μm-thick undoped a-Si:H film before and after the illumination show that the gap state density is not changed after illumination. The results are explained on the basis of material heterogeneity. The trapping regions, considered to be contained in tissue, should be assumed to exist in the material to explain the results. The transfer of electrons (or holes for p type samples) between islands and the trapping regions give rise to the light induced changes in conduction.

The contribution of the staebler-wronski effect to gap-state absorption in hydrogenated amorphous silicon

The contribution of light-induced conductivity and luminescence changes to gap-state absorption in a-Si:H was directly measured by photothermal deflection spectroscopy. We show that sample illumination enhances gap-state absorption while annealing restores its magnitude to the original level. Furthermore, we find that doping further enhances this absorption while compensation results in the smallest observed effect. We determine the energy position of the affected states to be 1.2-1.3 eV below the conduction band and tentatively attribute the enhancement to Si dangling bonds created by breaking the SiSi bonds.

Light-induced conductivity changes in purple membrane suspensions.

Small light-induced changes in the conductivity of light-adapted purple membrane suspended in strong electrolyte solutions were detected. The method used involved modulated light and a phase sensitive detector and it allowed us to detect accurately changes as small as 0.0001% in the conductivity of the suspension. The light-induced conductivity changes turned out to be composed of at least two different event: a small fast increase in conductivity (tau approximately 2 ms) followed by a slower and larger decrease in this parameter (tau = 70 ms-80 ms). The effects of pH and temperature on these changes were studied. Both events reached maximal values around neutral pH and approached zero at both high and low pH's. Heating the suspension decreased the photoconductivity change and Arrhenius plots of the data showed breaks around 31 degrees C. It is suggested that the conductivity changes reflect changes in the surface charge of the membrane and can be used to follow the kinetics of the conformational changes occurring in the system.

Nature of light-induced conductance changes in ventral photoreceptors of Limulus.

THE response of invertebrate photoreceptors to light is thought to be composed of small discrete events known as ‘bumps’1–5. The rate of occurrence of these bumps increases and their average size decreases with increasing ambient light intensity (light adaptation)6–10. The mechanisms involved in these processes are unknown. I report here an analysis of the light-induced current fluctuations in the voltage-clamped ventral photoreceptors of Limulus. Results seem to suggest that the conductance change of a bump is due to the opening of discrete channels which have properties similar to those of the discrete channels observed in the vertebrate neuromuscular junction11–14. The data also lead to suggestions of plausible mechanisms for the generation and adaptation of bumps.

Ability to light-induced conductance change of arthropod visual cell membrane, indirectly depending on membrane potential, during depolarization by external potassium or ouabain.

Light responses (ReP) and pre-stimulus membrane potential (PMP) and conductance of photoreceptors of Astacus leptodactylus and Limulus polyphemus (lateral eye) were recorded and changes were observed when the photoreceptor was depolarized by the action of external ouabain of high potassium concentration application. 1 mM/1 ouabain application causes a transient increase of PMP and ReP in Limulus, followed by a decrease which is faster for the ReP (half time time 34 min) than for the PMP (half time 80 min). Irreversible loss of excitability occurs when the PMP is still ca. 40% of the reference value. In both preparations high external potassium concentration leads to total depolarization (beyond zero line to + 10-+ 20 mV) of the PMP and after a time lag of 10 min also to a loss of excitability (intracellular recording). In extracellular recordings (Astacus) the excitability remains at a low level of 15%. The effects are reversible and are similar whether no or 10% external sodium is present. In all experiments the light-induced changes of membrane conductance are about parallel to those of the light response. The fact that the ability of the photosensoric membrane to undergo light-induced conductance changes is membrane potential-dependent is discussed, leading to the explanation that dipolar membrane constituents such as channel forming molecules (probably not rhodopsin) have to be ordered by membrane potential to keep the membrane functional for the photosensoric action.