Effect Of White Light Illumination Research Articles

Effect of Light Illumination on the Corrosion Behavior of Mg-RE Alloy EV31A in Chloride-Alkaline Solutions

The effect of white light illumination on the corrosion behavior of a Mg - Rare Earth (RE) alloy EV31A specimens in peak aged condition was investigated in 0.1 M NaOH solution containing 0, 80, 100 and 200 ppm chloride ions at room temperature. The passivation current density decreased upon illumination in the 0.1 NaOH solution without chloride addition. On the other hand, increased passive current densities were observed in the chloride containing solutions upon illumination. The white light illumination did not affect the open circuit potential of the EV31A. This result indicated that alloying additions did not significantly alter the bandgap of the passive layer or induce bandgap states in the passive layer in order to harvest the longer wave lengths of the white light. The incubation time for passivity perturbation decreased with illumination. The charge carrier density increased significantly upon illumination. The exchange current density for hydrogen evolution increased under the illuminated conditions. The Mott-Schottky results pointed out that light illumination induced surface defects of n-type character. These defects could have been potential sites for chloride adsorption that decreased the stability of the passive film. The white light illumination did not result in induced photo potential due to wide bandgap of the passive layer. Since the band bending was not altered, the electric field remained the same in both illuminated and non-illuminated condition. Overall, illumination of white light did not offer significant benefit to the localized corrosion resistance of the Mg-RE alloy in alkaline-chloride solutions.

Effect of Light Illumination on the Corrosion Behavior of Mg-RE Alloy EV31A in Chloride-Alkaline Solutions

Mg-RE alloy EV31A is a Mg-Zn-Gd-Nd-Zr alloy used in aerospace and high performance automobile applications where creep and corrosion resistance are required. These alloys can also be used in Mg-air batteries as possible anode materials in alkaline electrolytes in order to minimize the negative difference effect. EV31A is an age hardenable alloy. The precipitation reactions occurring during the aging process follow the sequence of a-Mg →β'' → β' → β (Mg3RE) → Mg41RE5. The alloy showed excellent passivity in the 0.1 M NaOH solution. More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition. Peak aging at 200 °C for 16 h imparted better resistance for localized corrosion than the solution treated or over aged conditions[1]. Light illumination has been reported to increase the resistance to passivity breakdown of various metals and alloys such as iron[2], copper[3], aluminum[4], and stainless steel. During illumination, the band bending of the passive layer is modified by the electron-hole pair generation and the electric field that drives the transport of point defects across the passive layer is considerably decreased. This quenched electric field is considered to improve the localized corrosion resistance of the material. Light illumination also modifies the electronic properties of the passive film. The effect of white light illumination on the corrosion behavior of peak aged EV31A specimens was investigated in 0.1 M NaOH solution containing 0, 80, 100 and 200 ppm chloride ions at room temperature. The passivation current density decreased upon illumination in the 0.1 NaOH solution without chloride addition. On the other hand, increased passive current densities were observed in the chloride containing solutions upon illumination. The white light illumination did not affect the open circuit potential of the EV31A. This result indicated that alloying additions did not significantly alter the band gap of the passive layer or induce band gap states in the passive layer in order to harvest the longer wave lengths of the white light. The incubation time for passivity perturbation decreased with illumination. The charge carrier density increased significantly upon illumination. The exchange current density for hydrogen evolution increased under the illuminated conditions. The Mott-Schottky results pointed out that light illumination induced surface defects of n-type character, possibly oxygen vacancies. These defects could have been potential sites for chloride adsorption that decreased the corrosion resistance. The white light illumination did not result in induced photo potential due to wide band gap of the passive layer. Since the band bending was not altered, the electric field remained the same in both illuminated and non-illuminated condition. Overall, illumination of white light was not beneficial to the localized corrosion resistance of the Mg-RE alloy in alkaline-chloride solutions. [1] J. Ninlachart, K.S. Raja, Acta Metallurgica Sinica (English Letters), 2017, 30(4), 352–366 [2] P. Schmuki, H. Bohni, Electrochimica Acta, Vol. 40, No. 6, pp. 775-783, 1995 [3] C. B. Breslin, D. D. Macdonald, Electrochimica Acta 44 (1998) 643±651 [4] M. A. Amin, Electrochimica Acta 56 (2011) 2518–2531

Graphene Oxide/Poly(3-hexylthiophene) Nanocomposite Thin-Film Phototransistor for Logic Circuit Applications

Graphene is a sheet-structured material that lacks a forbidden band, being a good candidate for use in radiofrequency applications. We have elaborated graphene-oxide-doped poly(3-hexylthiophene) nanocomposite to increase the interlayer distance and thereby open a large bandgap for use in the field of logic circuits. Graphene oxide/poly(3-hexylthiophene) (GO/P3HT) nanocomposite thin-film transistors (TFTs) were fabricated on silicon oxide substrate by spin coating method. The current–voltage (I–V) characteristics of TFTs with various P3HT compositions were studied in the dark and under light illumination. The photocurrent, charge carrier mobility, subthreshold voltage, density of interface states, density of occupied states, and ION/IOFF ratio of the devices strongly depended on the P3HT weight ratio in the composite. The effects of white-light illumination on the electrical parameters of the transistors were investigated. The results indicated that GO/P3HT nanocomposite thin-film transistors have high potential for use in radiofrequency applications, and their feasibility for use in digital applications has been demonstrated.

Impact of White Light Illumination on the Electronic and Chemical Structures of Mixed Halide and Single Crystal Perovskites

This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH3NH3PbI3−xClx) thin films and CH3NH3PbI3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n‐type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb0) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n‐type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb0 is found, which induces strong Fermi‐level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light‐induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite‐based devices.

Rifampicin adsorbed onto magnetite nanoparticle: SERS study and insight on the molecular arrangement and light effect

In this study, the surface‐enhanced Raman spectroscopy (SERS) technique was used to asses key information regarding the surface adsorption of Rifampicin (RIF) onto magnetite nanoparticle previously dressed with a bilayer of lauric acid (LA). The effects of white light illumination on the physicochemical properties of the RIF molecule were also investigated. Transmission electron microscopy, dynamic light scattering, zeta‐potential, and Fourier transform infrared spectroscopy were also employed to characterize the investigated materials. Vibrational mode assignments for the SERS spectra and comparison between the data recorded from the free and adsorbed RIF provided insights for the adsorption of this biomolecule onto the LA‐bilayer dressed magnetite nanoparticle. The results suggested that the species binding to the outer carboxylate group of the LA‐bilayer is more likely the piperazine nitrogen adjacent to the imine nitrogen. The SERS data also revealed the enhancement of the RIF molecule stability to white light irradiation while adsorbed onto the magnetite nanoparticle. Copyright © 2015 John Wiley & Sons, Ltd.

Characterization and modeling of TIPS-pentacene-poly(3-hexyl) thiophene blend organic thin film transistor

Thin film transistor based on the blend of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) and the poly(3-hexylthiophene) (P3HT) was made on SiO2 insulator layers by spin coating method. The blend of TIPS-pentacene and P3HT was prepared for molar ratio of TIPS:P3HT=1:0.4ml. Electrical characteristics of the blend of TIPS-pentacene and P3HT transistors under dark and white light illuminations were analyzed. We have exploited the experimental curves current–voltage of our TFT to extract electrical parameters such us mobility, threshold voltage, sub-threshold voltage and trapped density under dark and white light illumination. Finally we have studied the effect of white light illumination on threshold voltage of the organic thin film transistor based on the blend of TIPS-pentacene and P3HT.

An analysis of the effect of illumination to the reverse and forward bias current transport mechanisms in an efficient n-ZnO/n-CdS/p-Cu(In,Ga)Se2 solar cell

Temperature dependent current–voltage measurements are used to determine the effect of white light illumination on the dominant current transport mechanism in an efficient n-ZnO/n-CdS/p-Cu(In,Ga)Se2 heterojunction solar cell. The forward J–V characteristics are modelled by double exponential expression. In the dark, the forward current transport is mainly dominated by recombination at interfacial regions with pronounced tunnelling effect. Nevertheless, approximately above 200K, the thermal dependence of the diode parameters in the second junction interface can be explained in terms of properly increasing contribution of pure depletion region recombination mechanism. Under white light illumination, the forward current is still dominated by the tunnelling enhanced interface recombination mechanism with considerably enhanced tunnelling contribution. The presence of a significant distortion observed below 180K is attributed to the shift of Fermi level at junction interface and recharge distribution in the junction region due to metastable nature of the defect states. Below and above than 230K, the reverse bias current transport in the dark is described by using space charge limited current and a thermally activated behaviour, respectively. Under illumination the variation of temperature dependent reverse current with voltage suggests that either the SCL current in the velocity saturation regime or tunnelling dominates the current transport.

Thermal effects of white light illumination during microsurgery: clinical pilot study on the application safety of surgical microscopes

Modern operating microscopes offer high power illumination to ensure optimal visualization, but can also cause thermal damage. The aim of our study is to quantify the thermal effects in vivo and discuss conditions for safe use. In a pilot study on volunteers, we measured the temperature at the skin surface during microscope illumination, including the influence of anaesthesia and the effects of staining, draping, or moistening of the skin. Irradiation within the limit given by safety regulations (200 mW/cm(2)) results in skin surface temperature of 43 degrees C. Higher intensities (forearm 335 mW/cm(2), back 250 mW/cm(2)) are tolerated, resulting in reversible hyperaemia. At a very high illumination intensity (750 mW/cm(2)), pain occurs within 30 s at temperatures of 46 degrees C+/-1 degrees C (hand and forearm), and 43 degrees C+/-2 degrees C (back), respectively. Anaesthesia has no distinct effect on the temperature, whereas staining and drapes result in much higher temperatures (>100 degrees C). Moistening at practicable flow rates can reduce temperature efficiently when combined with a light absorbing and water absorbent drape. In conclusion, surgeons must be aware that surgical microscope illumination without protective means can cause skin temperatures to rise much above pain threshold, which in our study serves as a (conservative) benchmark for potential damage.

A new pathway of photoinactivation of photosystem II. Irreversible photoreduction of pheophytin causes loss of photochemical activity of isolated D1-D2-cytochrome b559 complex.

A new pathway of photoinactivation of photosystem II (PS II) connected with irreversible photoaccumulation of reduced pheophytin (Ph) in isolated D1-D2-cytochrome b559 complexes of reaction center (RC) of PS II was discovered. The inhibitory effects of white light illumination on photochemical activity of D1-D2-cytochrome b559 complexes of RCs of photosystem II, isolated from pea chloroplasts, have been compared under anaerobic conditions in the absence and in the presence of sodium dithionite, electron transfer from which to the oxidized primary electron donor P680+ results in the photoaccumulation of anion-radical of the primary electron acceptor, Ph(-.). In both cases, prolonged illumination (1-5 min, 120 W/m(2)) led to a pronounced loss of the photochemical activity as it was monitored by measuring the amplitude of the reversible photoinduced absorbance changes at 682 nm related to the photoreduction of Ph. The extent of the photoinactivation depended on the illumination time and pH of the medium. At pH 8.0, the presence of dithionite during photoinactivation brought about a protective effect compared to that in a control sample. In contrast, lowering pH to 6.0 increased the sensitivity to photoinactivation in the dithionite-containing samples. For 5 min irradiation, the photochemical activity in the absence and in the presence of dithionite decreased by 35 and 72%, respectively (this was accompanied by an irreversible bleaching of the pheophytin Q(x) absorption band at 542 nm). Degradation of the D1 and D2 proteins was not observed under these conditions. A subsequent addition of an electron acceptor, potassium ferricyanide, to the illuminated samples restored neither the amplitude of the signal at 682 nm nor absorption at 542 nm. It is suggested that at pH. 7.0 the photoaccumulated Ph(-.) is irreversibly converted into a secondary, most probably protonated form, that does not lead to destruction of the RCs but prevents the photoformation of the primary radical pair [P680+Ph(-.)]. A possible application of this effect to photoinactivation of PS II in vivo is discussed.

Light-assisted deposition of CdS thin films

The effects of white light illumination during the deposition of CdS thin films in aquasi-closed volume on the structural, photoelectrical and optical propertiesareinvestigated. The films were highly c-axis oriented with an increasing intensity of (002)reflection as the illumination increases. The room temperature resistivity values of the CdS filmsdecreased in the range of 107-104 Ω cm. The photosensitivity in the fundamental absorptionregion and the transparency in the transmission region considerably increased as theillumination increased. Under 100 mW cm-2 insolation, the efficiencies of the CdS/CdTe solarcells based on CdS window materials which were deposited: (1) in the dark; and (2) under anillumination of 150 mW cm-2; were found to be 1.8% and 7.3%, respectively.

THE EFFECT OF ANNEALING AND ILLUMINATION ON THE FIELD EFFECT CONDUCTANCE OF AMORPHOUS SILICON

We have measured the effect of white light illumination and annealing to 180°C on the field effect conductance of glow discharge a-Si:H. Annealing produces a change in the off conductance by up to a factor of 30, and moves the threshold field by 2 x lo4 ~cm-l. These changes are reproducibly reversed upon illuminating with white light. A major part of the effect of illumination is most likely due to a movement of the Fermi level in the bulk of the material. Annealing to 180°C reverses this effect. Furthermore excess electrons can be trapped at the amorphous siliconsilicon nitride interface by a field assisted trapping mechanism and these are also de-trapped upon annealing to 180°C. Reversible changes in the dark,conductance of thin films of glow discharge amorphous silicon, due to annealing at T > 150°C and illumination with white light, have been reported by a number of groups. These have been interpreted as due to metastable changes in the density or occupancy of defect states which cause a movement of the bulk Fermi level (1)-(3) or conversely as due to the creation and elimination of space charge regions at one or other of the two surfaces of the film (4),(5). We have performed similar measurements on field effect devices, where one surface of a 0.5 um film of a-Si:H is separated from a gate electrode by a 0.5 pm layer of plasma deposited silicon nitride and the other surface is covered by a 0.5 um plasma deposited Si02 layer, but has no gate electrode (6). Such devices are currently of considerable interest as thin film transistors (TFTs) for matrix addressing of displays (7). In our devices, annealing to 180°C (with zero gate volts) produces a room temperature conductance between 5 and 30 times the room tempera?-ure conductance after illuminating the sample with white light from a 50 Watt quaftz-halogen lamp for 90 minutes. Figure 1, shows an example where a conductance change of 30 is observed. Subsequent re-illumination reproduces the initial condition (indicated by the vertical arrow in figure 1) and further cycles of annealing and illumination reproduce the same results. Although the magnitude of the effect in our samples is much smaller than originally reported by Staebler and Wronski (I), it is very comparable with results observed in other laboratories (5). In figure 2 we show the field effect conductance (at 4O0C) in each of the two states. State A is after annealing the sample to 180°C and state B after illumination. The field effect conductance is also reproducible on repetitive cycles of annealin and illumination. In this figure the ordinate is the sheet conductance f G( $210)and the abscissa is the surface field in the semiconductor at the amorphous silicon-silicon nitride interface, given by F = E ~ ~ ~ V ~ / E ~ ~ ~ ~ . V is the gate voltage, tins the dielectric constant and dins the thickness of the insulator and E the dielectric constant of the semiconductor. In figure 2, we plot the same results on both a log and a linear scale. In both states, the field effect conductance shows little change with negative gate voltages, but for increasing positive gate voltages the conductance first increases approximately exponentially, then at higher gate voltages increases approximately linearly. The onset of the linear region occurs at a threshold field Ft. Clearly the cycle of annealing and illumination has two effects, to change the threshold field Ft and to change the off-conductance Go (the approximately constant Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981481 C4-380 JOURNAL DE PHYSIQUE Fig 1. Temperature dependence of Fig 2 . Field effect conductance a t 4 0 ' ~ the dark conductance of a 0.5pm after annealing to 1 8 0 ~ ~ (state A ) conductance at negative gate voltages). These two parameters Go and Ft are of paramount importance in the characterisation of TFTs, and changes in these quantities represent instabilities which are highly'undesirable for device applications. Although the changes are brought about by conditions which are well outside the normal operating conditions of TFTs, an understanding of the origin of the effects is of considerable interest.

Photopotentials on Copper and Copper Alloy Electrodes

The effect of white light illumination on the current‐potential relationships of pure copper and of Cu‐Ni and Cu‐Al alloys in neutral solutions was examined, both under galvanostatic and potentiostatic conditions. The results obtained show that the photoresponse is only weakly affected by the addition of alloying elements to copper, but that it is influenced by the method of formation of the oxide film on the metal surface. Depending on whether or not the film was formed by reaction with a copper solution, the amplitude of the signal response could be strongly affected and the sign of the photopotential at open circuit reversed, indicating a change in the nature of the majority carriers. Polarization of the electrode can also vary the photoresponse, but its rapid following of the potential does not support the view that the structure of the oxide film is altered. Impedance measurements on electrodes under illumination and in the dark indicate that the charge‐transfer reactions, rather than the resistivity of the oxide film, are affected by light.

Diffusion, electric transport, and effect of a silver impurity on the electrical and optical properties of As2Se3

The diffusion and electric transport of silver in glassy As2Se3 was studied in the range 110 to 160 °C with the radioactive tracer 110mAg. It is shown, that the temperature dependence of the silver diffusivity can be described by the formula D = 5.9 × 10−6 exp (−0.41/kT), and that the effective mobility of the silver ions in the range 134 to 155 °C vary within (1.7 to 5.0) × 10−9 cm2/Vs. At temperatures below 134 °C silver is found to migrate in glass in the form of positive ions with an effective charge qeff ≧ + 1, the experimentally measured charge above 134 °C is qeff ≧ +2. This anomalous increase of qeff with temperature is shown to be associated with the formation of inclusions of a second phase (apparently Ag2Se, Ag3AsSe3, or AgAsSe2) in the course of the electric transport at T > 134 °C. A discussion based on the experimental data obtained is made of the mechanism of silver diffusion involving the migration of arsenic selenide through the interlayer space. Further an effect of white light illumination on the concentration profile of silver introduced by diffusion in As2Se3 is revealed. The results obtained are considered on the basis of photochemical reactions occurring at the silver–As2Se3 interface. A study is also made of the effect of silver impurities introduced by diffusion in As2Se3 glasses on the electrical and optical properties of this material. [Russian Text Ignored]