Photoelectrochemical Imaging Research Articles

Photoelectrochemical visualization in real-time of hydrogen distribution in plastic regions of low-carbon steel

The in-situ scanning photoelectrochemical microscopy is a new technique giving images of hydrogen diffusion in the metals in real time with a good resolution. This paper presents some photoelectrochemical images of hydrogen distribution in a low-carbon steel ahead of a crack tip and in the regions submitted to a high deformation such as in the case of the metal bending.

Photo-electrochemical imaging of hydrogen-induced damage in stainless steel

Blisters and their surrounding crack-tip areas in AISI 304 stainless steel have been imaged by Scanning Photo-Electrochemical Microscopy (SPEM), a technique providing photo-electrochemical images of hydrogen trapping and detrapping into blisters in real time, in situ and in continuous under hydrogen charging. The increased hydrogen concentration has also been imaged in the plastic enclave at the crack tip around a blister during its growth. The images acquired in time sequence can be examined as a single frame or assembled in a 2D or 3D movie, both in grey scale or false colour.

ChemInform Abstract: Photoelectrochemical Imaging of the Etching and Passivation of Silicon in Aqueous KOH.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Photoelectrochemical imaging and microscopic reactivity of oxidised Ti

To clarify the correlation between photoelectrochemical images and surface reactivity, investigations of ellipsometry ( d ox , structure), coulometry ( d), capacitance ( N D ) and i ph were carried out on single grains ( hkl) of passive titanium. The results prove that only the oxide layers on (xxx0) planes grow homogeneously up to 10 V. The observed strong decrease of i ph with increasing d ox is in clear contrast to the Butler-Gaertner model. This is explained by the large recombination rate which can be diminished by an electric field. On more closely packed planes, N D , structure and thickness change simultaneously. Hence, a quantitative interpretation is not possible, but qualitatively it is the same as on (xxx0). Thus, in photoelectrochemical images, an increasing i ph indicates a high field strength and a corresponding high electrochemical reactivity expressed by rate of etr, eg Fe 2+ oxidation or oxygen evolution. Since ionic motions are hindered in tightly packed oxide films, itr changes in the opposite direction.

Photoelectrochemical imaging of the etching and passivation of silicon in aqueous KOH

Anisotropic chemical etchants are used widely to fabricate silicon microstructures; however, the roles of surface heterogeneity and localised chemical effects during the etch process are still unclear. This investigation has employed photoelectrochemical microscopy to resolve spatially the reactivity of p-Si <100> and <111> during etching and passivation in 2.0 M KOH. Potentiodynamic photocurrent measurements demonstrate that the interfaces follow the ideal Gärtner response until an anodic oxide is formed. Examination of the potential-dependent transient photocurrent response indicates that formation of an oxide inhibits charge carrier transfer and pins the Fermi level. Furthermore, the growth and dissolution of the oxide are reversible over a time scale of minutes. In situ optical and subsequent atomic force microscopies show that during the etching process surface roughening occurs preferentially at particular sites, the density of which is greater at <100> oriented samples, and corresponds to regions at which pyramids are formed. Photoelectrochemical microscopy results provide spatial information on the reactivity of interfaces. Both the <111> and <100> orientations exhibit responses which are attributed to lattice defects at the semiconductor surface. These act as recombination centres but do not manifest themselves in the final etch morphology. Examination of the influence of the electrode potential and effect of pre-passivation indicates that the oxide formed is uniform and does not exhibit pinholes as in fluoride-containing media. However, real-time photocurrent imaging of the oxide removal process resulted in quite different behaviour, and an additional photoimage contrast was observed which differed considerably between the two crystal orientations. The origin of this heterogeneity is attributed to the different dissolution kinetics of the oxides formed.

Electrochemically deposited polycrystalline n-CdSe thin films studied with laterally resolved photoelectrochemistry and SEM

Semiconducting thin films of n-CdSe were electrochemically deposited on Ti substrates with the potential difference as the driving force. By using a photomasking technique different film thicknesses could be obtained on the same substrate. The film electrodes were characterized with photoelectrochemical (PEC) imaging, optical microscopy and scanning electron microscopy (SEM) /energy-dispersive X-ray analysis. PEC imaging is done with a fibre-optical laser scan microscope that allows a laterally resolved mapping of the photoelectrochemical response. The results show that substrate preparation is crucial for the photoelectrochemical performance of the film. At scratches in the substrate the film shows a lower photoresponse. Very thin films give low photoresponse. These films also show a different morphology in the SEM pictures. The films are not homogeneous and have a less ideal composition when they are too thin. We have found PEC imaging a good complement to other methods for characterization of semiconducting thin films.

Combined Raman and photoelectrochemical imaging system. Application to TiO2 films grown anodically on TiAg alloy

Combined Raman and photoelectrochemical imaging system. Application to TiO2 films grown anodically on TiAg alloy

Photoelectrochemistry of silicon-delta-doped GaAs structures

Delta doping with silicon has been used to form a contact of metallic conductivity buried 1 μm below the surface of a GaAs MBE-grown structure. The electrochemistry of the high-purity GaAs above the contact could then be investigated. The interfaces in the structure were located by photoelectrochemical etching; the spatial distribution of defects and also some information concerning their origin within the grown layers was obtained by photoelectrochemical imaging.

Charge recombination imaging at the WSe 2/I − interface

Intensity modulated photocurrent measurements obtained with a focussed laser beam have been used to obtain real video images of surface recombination processes in a photoelectrochemical cell (PEC) with micrometric lateral resolution. We report here, for the first time, photoelectrochemical images of the relaxation time constant for a holes trapped at the illuminated WSe 2/I − interface, which is directly related with the surface recombination rate of electrons and holes. These images convey easyly assimilable information about the influence of the semiconductor topography (crystallographic orientations, micro-defects, etc.) on its photoelectrochemical performance.

Photoelectrochemical imaging—part I. Background and theory

Imaging of spatial variability of electrode processes using signals stimulated by a focused light spot is described. The signals include photovoltage and photocurrent, photoacoustic and photothermal effects, as well as the reflected light intensity. The theory of contrast in the photocurrent image is presented: methods utilizing intensity modulated light are compared with those in which the spot is scanned rapidly without intensity modulation. Effects of variation of intensity modulation frequency and spot scan speed are calculated; blurring, streaking and shadowing effects are explained. For systems which are not photoactive, the feasibility of an imaging procedure based upon the small thermal effect induced by the focused spot on the current for an electrode process is assessed. Methods of imaging utilizing potential variations at constant (usually zero) current are compared with those involving the measurement of current variations at constant potential.

Photoelectrochemical imaging—part II. The passivating oxide film on iron

Photocurrent imaging of passive iron, both of pure metal and of an impure material in which grain boundary segregation was suspected, showed great heterogeneity with NaOH electrolyte, much less heterogeneity with Na 2SO 4 electrolyte. Effects of light intensity and electrode potential were spatially variable: the heterogeneity was such as to counsel caution in the interpretation of results based upon measurements averaged over the entire surface. It is speculated that the passive layer formed in Na 2SO 4 has a duplex morphology, with a uniform overlayer dominating the photoresponse, whereas in NaOH the film comprises a single barrier layer nucleated directly onto the metal.

Photoelectrochemical imaging of sub-monolayer lead deposits on n-GaAs

A scanning laser microscope has been used to obtain a spatially resolved map of the photocurrent distribution around metal particles at the n-GaAs/electrolyte interface. A minority carrier capture zone that is potential dependent is observed around the metal particles. Mechanisms of image contrast are discussed in terms of particle size, scattering phenomena, screening effects and carrier recombination effects.

Surface Sensitive Photoelectrochemical Imaging of the Derivatized Surface of TiO2 on Ti

An experimental method of examining surface heterogeneities of films on polycrystalline Ti is presented. Sensitization of the surface with hexacyanoferrate enables the surface properties of the films to be studied photoelectrochemically at subbandgap wavelengths, thereby excluding a response from the oxide interior. The combination of subbandgap photoelectrochemical microscopy of the derivatized surface with suprabandgap photoelectrochemical microscopy reveals significant surface recombination effects on the thin films.

Photocurrent imaging of passive metals

The theory of photoelectrochemical imaging using a scanning laser microscope is presented in outline: the idea of a photocurrent transfer function whose parameters might be spatially variable is introduced and a distinction is made between continuous-scan and step-scan methods of rastering the light spot. In the continuous-scan method interesting blurring, streaking and shadowing effects highlight changes over the surface of different parameters of the photocurrent transfer function. Images of passive copper, bismuth, iron and stainless steel show effects of varying thickness of the passive film and charge carrier recombination rate, effects localised at grain boundaries and around inclusions in the metal and effects showing localised corrosion, inhibition and inhibition breakdown.

Photoelectrochemical Deposition of Metal Patterns on Semiconductors

ABSTRACTMicroscopic metal patterns may be produced on p-type semiconductors using a maskless photoelectrochemical procedure in which electroplating is induced by minority carriers in illuminated portions of a semiconductor electrode. Resolution exceeding l0μ has been achieved for deposits of Au on p-GaAs and Cu on p-Si. “Electroless” imaging and negative photoelectrochemical imaging are also discussed.

ChemInform Abstract: PHOTOELECTROCHROMIC CHARACTERISTICS OF PHOTOELECTROCHEMICAL IMAGING SYSTEM WITH A SEMICONDUCTOR/SOLUTION (METALLIC ION) JUNCTION

Chemischer InformationsdienstVolume 11, Issue 45 Physical Inorganic Chemistry ChemInform Abstract: PHOTOELECTROCHROMIC CHARACTERISTICS OF PHOTOELECTROCHEMICAL IMAGING SYSTEM WITH A SEMICONDUCTOR/SOLUTION (METALLIC ION) JUNCTION T. INOUE, T. INOUESearch for more papers by this authorA. FUJISHIMA, A. FUJISHIMASearch for more papers by this authorK. HONDA, K. HONDASearch for more papers by this author T. INOUE, T. INOUESearch for more papers by this authorA. FUJISHIMA, A. FUJISHIMASearch for more papers by this authorK. HONDA, K. HONDASearch for more papers by this author First published: November 11, 1980 https://doi.org/10.1002/chin.198045011Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue45November 11, 1980 RelatedInformation

Photoelectrochromic Characteristics of Photoelectrochemical Imaging System with a Semiconductor/Solution (Metallic Ion) Junction

Photoelectrochemical reactions at semiconductor electrodes in solutions containing metallic ions have been applied to a reversible imaging system. Clearly visible images were formed on the surfaces of , , and (n‐type) and (p‐type) semiconductor electrodes in solutions with metallic ions such as Tl+, Pb2+, Co2+, and Ag+ as image‐forming agents. Image formation occurs under irradiation with light absorbable by the semiconductors, while semiconductor electrodes are polarized either anodically (for n‐type) or cathodically (for p‐type). Erasing can be accomplished only by polarizing the semiconductor electrodes cathodically (n‐type) or anodically (p‐type), or the image can be held if desired by opening the circuit after the image formation process. For example, a brown image pattern was formed on a sintered n‐type photoelectrode in an aqueous solution containing Tl+when the electrode was anodically polarized (1.0V vs. SCE) under irradiation with absorbable light. The image was stable for more than 20,000 hr in air, but faded immediately when cathodic polarization of −0.5V vs. SCE was applied at a electrode. This imaging process has good reversibility during image formation and erasing. Electrochemical characteristics based on the semiconductor photoelectrode reactions were investigated and discussed focusing on charge transfer across the semiconductor/solution junction.