Search

Within the field of archeology, textile research is of growing interest because of its potential to provide relevant information regarding either the development or the technological advancement of ancient populations or the socio-economic and religious purposes of textile production. It is of paramount importance in cultural heritage research to use non-destructive techniques. Therefore, dye analyses were performed using two non-destructive methods: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and Fourier transform infrared spectroscopy (FT-IR). In order to build a database, standard samples of dyed silk were prepared using several natural dye compounds; these samples were then analyzed with FT-IR and TOF-SIMS. Afterwards, spectroscopic analyses were carried out on five textile fragments coming from the 16th to the 18th century Korean tombs. FT-IR and TOF-SIMS spectra allowed the identification of fiber of the archeological textiles, making it possible to distinguish between the cotton and silk fibers. Furthermore, it was possible to identify indigo in three blue fabrics and to show its presence in a green textile. The results suggest that FT-IR and TOF-SIMS are two efficient and very helpful techniques for the characterization of excavated fabrics. Copyright © 2011 John Wiley & Sons, Ltd.

The fabrication process of semiconductor is more and more difficult as scaling down. Especially, the via profile formation is one of the main challenges which is suffering from making stable device process because ArF photo resist (PR) itself can not provide proper etch selectivity to sub-layers. Recently, many researches have been studied for the via process in terms of photo property, etch property and process compatibility using bi-layer resist process (BLR), tri-layer resist process (TLR), and multi-layer resist (MLR) process. In this paper, we proposed and demonstrated for beyond 90nm scaled logic via process consisting of high-k inter metal dielectric (IMD) using multi-layer resist (MLR) organic hard mask. Based on the test results described in this paper, the results show the higher etching selectivity to each layer and also helped to easily control the anisotropic profiles.

We studied the durability of the previously reported low mass loaded, highly efficient electrospray deposited Pt film as a cathode and Ni mesh as anode electrode in PV assisted water electrolysis system for 1000 h. This assembly showed no detectable decline in performance for initial 200 h, but thereafter it started to decline with time and showed 18% decline after 1000 h. For conclusion, we analyzed the electrode surfaces by different analyzing techniques. Results showed that Pt film was detaching from the surface and there was a deposition of passive layer of Fe2O3 on edge side of cathode surface. The iron derivative might be come from the corrosion of the stainless steel connectors that we used in PV assisted water electrolysis system. The etching and oxidation of anode surface was also observed but it might not be responsible for deterioration of performance.

The morphology from symmetric diblock copolymers of poly(styrene-b-propylmethacrylate) (PS-PPrMA), where polystyrene (PS) block was perdeuterated near the copolymer/air and copolymer/substrate interfaces and in the bulk, was characterized by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Elemental depth profiles measured in the negative ion mode by a Cs + primary ion beam demonstrate variations in hydrogen, deuterium, carbon, oxygen and hydrocarbons within the diblock copolymer according to the depth. The annealed deuterated poly(styrene-b-propy[methacrylate) (dPS-PPrMA) copolymer samples showed a decrease in the deuterated PS secondary ion peak intensity as compared to the as-cast samples. TOF-SIMS depth profiling was obtained for the lamellar morphology of dPS-PPrMA which is found to orient parallel to the surface of the substrate. This preferential orientation resulted in a periodic variation in the composition of each block that continued through the entire copolymer film with thickness of 700 and 2100A. Temperature-dependent annealing studies on dPS-PPrMA thin film on the silicon substrates were performed to investigate the lower critical ordering transition (LCOT) properties of diblock copolymers.

A surface-induced orientation of symmetric, deuterated polystyrene/poly(propyl methacrylate) diblock copolymers, dPS-PPrMA with different molecular weights (Mn = 135 000, 119 600, and 75 300) was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Elemental depth profiles obtained in the negative ion mode by a Cs+ primary ion beam demonstrate variations in hydrogen, deuterium, carbon, oxygen, and hydrocarbons within the diblock copolymer according to the depth. Solution casting films of the copolymers with thicknesses of 700 and 2100 A exhibited no preferential orientation of the microdomain morphology with respect to the surface at room temperature. Annealing the copolymer films at 215 °C for 4 h produced a dramatic orientation of the microdomains parallel to the surface of the film. This preferential alignment provided regular oscillation in the composition of both blocks, which continued through the entire film. The periodicity as determined from a depth profile of TOF-SIMS showed good agreement with the results of small-angle X-ray scattering. Positive and negative ion molecular depth profiles by a C60+ cluster ion beam also provide information pertaining to the lower disorder–order transition (LDOT) behavior of the dPS-PPrMA copolymer. Depth profile results indicate a PPrMA layer preferentially located at the copolymer/silicon substrate interface. The microdomain separation processes of dPS-PPrMA were investigated as a function of the annealing temperature and time. Copyright © 2010 John Wiley & Sons, Ltd.

Nylon 6 fibers are used, for the first time, in dye-sensitized solar cells (DSSCs). The overall energy conversion efficiency obtained with 0.18 M nylon 6 reaches 6.2%, which is comparable to that (6.7%) obtained without adding nylon 6 on the day of cell fabrication. However, it is found that the long-term stability of the DSSCs with nylon 6 is superior to that of a reference electrolyte as a result of the complexation of nylon 6 with I(3)(-). Furthermore, nylon 6 is found to be a corrosion inhibitor for silver metal in the electrolyte containing I(3)(-).

Different fluorocarbon thin films were deposited on Si substrates using a plasma-polymerization method. Fluorine-containing hydrophobic thin films were obtained by inductively coupled plasma (ICP) and pulsed plasma (PP) with a mixture of fluorocarbon precursors C2F6, C3F8, and c-C4F8 and the unsaturated hydrocarbons of C2H2. The influence on the fluorocarbon surfaces of the process parameters for plasma polymerization, including the gas ratio and the plasma power, were investigated under two plasma-polymerized techniques with different fluorocarbon gas precursors. The hydrophobic properties, surface morphologies, and chemical compositions were elucidated using water contact angle measurements, field emission-scanning electron microscope, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In this study, the ICP technique provides coarser grained films and more hydrophobic surfaces as well as a higher deposi...

Plasma-polymerized fluorine-containing thin films were fabricated by five different plasma methods, viz. inductively coupled plasma (ICP), pulsed-plasma (PP), capacitively coupled plasma (CCP), self-ignition plasma (SIP), and plasma source ion implantation/inductively coupled plasma (PSII/ICP). Octafluoropropane (C3F8) was mixed with acetylene (C2H2) to investigate the effect of different plasma techniques on the films. The properties of the plasma polymers, viz. hydrophobic properties, binding structure, deposition rate, and chemical composition, varied considerably depending on the plasma polymerization method. The plasma-polymerized thin films made by the different methods were characterized using surface analytical instruments: field-emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Cross-section images from FE-SEM revealed that the deposition rate of the polymer film in the case of using CCP plasma was higher while that for PSII/ICP and self-ignition plasma, respectively, was lower compared with the deposition rate of the ICP and pulsed-plasma. The water contact angle measurement showed that the ICP and PSII/ICP techniques produced more hydrophobic surfaces. XPS and TOF-SIMS analyses indicated that the ICP and PSII/ICP methods produced more F-containing functional groups, especially CF2 and CF3 groups. Also, the NEXAFS results revealed that the ICP and PSII/ICP techniques provide more fluorine species on the plasma polymer surface compared with other techniques.

The identification of the colorants used on ancient textiles provides a historical pathway to the understanding of the processes associated with one of the oldest of chemical technologies, namely textile dyeing. In this paper, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to detect dyes on textiles avoiding the time-consuming and destructive extraction procedures necessary for the spectrophotometric and chromatographic methods previously used. The plant dyes investigated belong to a variety of chemical groups, which include curcumin, crocin, carthamin, purpurin, alizarin, brazilin, shikonin, and indigo. Reference textile samples were prepared with dye extracts of plants and were characterized by TOF-SIMS. TOF-SIMS spectra for the dyed textiles showed element ions from metallic mordants, specific fragment ions, and molecular ions from organic dyes. Remnant dyes on excavated textiles have also been identified using TOF-SIMS. The ancient textile sample showed the presence of indigo clearly, although the fiber itself had degraded badly. From the results, it was concluded that most of plant dyes can be identified with TOF-SIMS and it is a very promising technique for the archaeology field.

Titanium dioxide (TiO2) film for dye-sensitized solar cells (DSSCs) has surface defects such as oxygen vacancies created during the annealing process. The authors used a plasma treatment technique to reduce defects on TiO2 surfaces. They investigated the influence of different gas plasma treatments of TiO2 film on the photoelectric performance of DSSC. Short-circuit photocurrent density (Jsc), open-circuit photovoltage (Voc), and the amount of adsorbed dye for DSSCs were measured. As a result, the solar-to-electricity conversion efficiencies of the O2- and N2-treated cells increased by 15%–20% compared to untreated cells. On the other hand, solar energy conversion efficiency of CF4-plasma treated cells decreased drastically. The increased amount of adsorbed dye on the TiO2 film was measured by time-of-flight secondary ion mass spectrometry. TiO2 surfaces modified by plasma treatment were characterized using analytical instruments such as x-ray photoelectron spectroscopy and near-edge x-ray absorption fine...

Plasma source ion implantation (PSII) technique was used for the ion implantation and deposition of copper film on the polyimide. In PSII–EIAMAD (energetic ion assisted mixing and deposition) process, a polyimide film was immersed in a plasma, and high negative voltage pulses were applied to accelerate ions into the substrate resulting in the mixing effect of copper atoms with polyimide layers. This method was used to improve the adhesion between Cu layer and polyimide film depending on ion species, ion energy, and treatment time. The adhesion strength was determined by the 90° peel test. The deposited-copper surface was investigated by SEM and AFM, and the interface between Cu film and polyimide was characterized by AES. Enhancement of adhesion for PSII–EIAMAD treated copper film was observed and its interface was very gradient in AES depth profile. The Cu-deposited layers are adherent and reasonably stable after heat treatment of 24 h at 100 °C.

We report successful development of both discrete ultraviolet (UV) photodiodes and UV imagers consisting of 8×8 backside-illuminated AlGaN p-i-n photodiode arrays. The discreteAlGaN p-i-n photodiodes showed a responsivity of 0.1A∕W, a cutoff wavelength of 350nm, an external quantum efficiency of 35%, and a response time of 4.1ns. Then, 8×8 AlGaN p-i-n photodiode arrays were fabricated, followed by hybridizations with readout integrated circuits manufactured using a 0.5μm 2poly-3metal N-well complementary metal-oxide semiconductor process by gold stud bumping. The 8×8 focal plane array UV imagers operated successfully by sensing radiation in the 300–350nm spectral bands.

A new type of hybrid gel electrolyte matrix based on tetraethyl orthosilicate (TEOS) and poly(ethylene glycol) (Mw 200, PEG200) was developed for dye-sensitized solar cells (DSSCs). The quasi-solid-state DSSC containing the hybrid gel electrolyte rendered an open-circuit voltage of 0.74 V, a short-circuit photocurrent density of 9.2 mA cm−2 and a fill factor of 0.61 at 100 mW cm−2, and consequently an overall solar energy conversion efficiency of 4.1%. TiO2 films and gels were characterized by FE-SEM and FT-IR, and the assembled DSSCs by photocurrent density–voltage and incident photon-to-current conversion efficiency measurements.

We report a record high continuous wave (CW) output power of 250 mW for the 780 nm band AlGaAs laser. The selectively buried ridge (SBR) structure was used and each layer of the laser was designed to have the lowest defect density by using the deep level transient spectroscopy (DLTS) analyses. The laser operated at a peak wavelength of 783 nm with a threshold current of 38 mA. The stable fundamental transverse mode was observed at 100 mW, 70 °C for more than 3000 h. The far-field aspect ratio, a ratio of far-field vertical angle over far-field parallel angle to the junction plane, was measured to be 1.8, which is small enough for the high density CD-R system.

The surface resistivity of several polymers such as poly(styrene/butadiene copolymer), modified poly(phenyleneoxide), poly(ethylene terephthalate), and polyimide was improved by the argon gas plasma source ion implantation (Ar-PSII) technique equipped with a mesh-type conducting grid. With the grid, the surface resistivities of the modified polymers decreased up to 11 orders of magnitudes at a high ion dose, and remained nearly at the same values after 3 months. The PSII treated polymer sample with the grid provided more uniformly modified surface and lower surface resistivity than that treated without the grid. The extent of the decrease in surface resistivity depended on the polymer structures and physical properties. However, the surface resistivity was independent of the sample thickness, the grid size, and the grid height. Surface analyses using scanning electron microscopy, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy provided the useful information on modified surfaces.

Poly(methylmethacrylate) (PMMA), poly(2-hydroxyethyl methacrylate (PHEMA), and poly(2-hydroxypropyl methacrylate) (PHPMA) were modified to improve the wettability by two techniques: plasma and plasma source ion implantation. The modified surfaces were characterized to investigate the dependence of the modification and hydrophobic recovery on the polymer structure. The differences obtained under optimal experiment conditions among the polymers were interpreted in terms of their polymer structures including the glass transition temperature. The surface free energy, calculated from the contact angle measurements, revealed that its polar component was a dominant factor in improving the wettability. The PSII treatment created more functional groups on the surface and extensively modified the polymer layer than the plasma treatment.

Visible electroluminescence (EL) from cathodically biased n‐Si in an electrolyte solution containing has been studied. EL from the porous n‐Si samples fabricated by photoelectrochemical etching over a wide range of current densities shows both blueshift and peak broadening with increasing , which can be attributed to the progressive participation of more silicon hydride species, , with larger n in the emitting progress. Based on analysis of spectral changes and resolution of the EL peak into components, a revised mechanism of the EL, where silicon hydrides are considered to donate electrons to sulfate radical anions, is proposed. EL is produced by recombination of the resulting radical, , with an accumulated electron in the conduction band. The radicals would lead to competing reactions that strip off hydrogens from the surface silicon hydrides. with larger n is subject to the earlier EL. © 1999 The Electrochemical Society. All rights reserved.

Electrochromism of nanocrystalline TiO{sub 2} films under cathodic bias in propylene carbonate containing LiClO{sub 4} was studied by time-dependent absorption and fluorescence spectroscopies. The absorption spectra revealed two absorption bands near 700 and 420 nm. The absorption band near 700 nm showed a blue shift and an increase in absorbance with time. The blue shift seemed to be due to the progressive involvement of the trapped electrons in the lower energy levels within the shallow surface states. The newly observed band near 420 nm appeared to have originated from the deep surface states which, lying 1.3--1.8 eV below the conduction band, were gradually filled with electrons in the shallow surface states.

The plasma source ion implantation (PSII) was utilized to improve the wettability and the stability of surface layer formed in the modification of polymeric materials. Polystyrene was treated with different kinds of plasma ions to render the surface more hydrophilic or hydrophobic. Hydrophobic recovery of PSII-treated polystyrene was also observed as a function of aging time, aging temperature, and treatment parameters. Treatment parameters involve kinds of gases, pressure, plasma power, pulse frequency, pulse voltage, etc. To study the effect of inert gas on hydrophobic recovery, polystyrene samples were prepared by helium, argon, or gas-mixture treatment. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to interpret the PSII-treated polystyrene surface and its hydrophobic recovery, with the assistance of x-ray photoelectron spectroscopy and water contact angle measurements. TOF-SIMS spectra of 18O2 PSII-treated samples showed the presence of 18O-containing peaks from the modified ...

Spectral shifts of visible electroluminescence (EL) from cathodically biased n-Si in electrolyte solution containing persulfate ions are described. The electrochemically etched n-Si cathodes exhibit a blue shift of the EL with the increase of applied potential. It is explained that the blue shift is caused by the formation of an accumulation layer and the Fermi level pinning in the porous Si. A study of the EL as a function of time at a constant potential shows a red shift, which can be attributed to the bandgap lowering caused by the conversion of the predominant surface bonds Si-H to Si-Si. Electro-polymerization of aniline on the porous Si surface enhanced the stability of the EL possibly due to the strengthening of the surface bonds.

Current-voltage (J-V) curves of n-GaAs/KOH(aq)-Se{sub 2}{sup 2{minus}}/Se{sup 2{minus}} and n-Si/acetone-LiClO{sub 4}-Fc{sup +/0} (ferrocenium ion/ferrocene) solar cells exhibit sigmoidal shapes near the open-circuit potential. J-V and flatband potential measurements indicate that the deviation of the J-V curves from the ideal square-like shape to S shape is due to the light-induced displacement of the bandedges. Analytical expression describing the dependence of light-induced bandedge shifts on the anodic photocurrent, the density of surface states, and the interfacial charge-transfer velocity are derived and verified experimentally. Application of the expressions to J-V data yields quantitative information on the kinetics of interfacial charge transfer.

The luminescence properties of PSMA-Ln(III) (Ln = Sm, Dy, Tb, Gd, Yb, Eu) in aqueous solution were investigated. Upon excitation of the styrene subunit, energy migrates from the PSMA polymer to Ln 3+ ions, and luminescence enhancements of Tb 3+ , Eu 3+ , Sm 3+ and Dy 3+ were observed. In PSMA-Eu 3+ , the effect of environment around the metal ion largely contributes to the luminescence enhancement. Fluorescence from PSMA in PSMA-Ln 3+ complexes was also measured. PSMA fluorescence intensity was enhanced upon coordination to Ln(III) (Ln = Sm, Dy, Tb, Gd), and λ em,max was blue-shifted due to Ln(III) association to the polymer chain and the reduced chain mobility of PSMA. In the presence of Eu 3+ and Yb 3+ , however, PSMA luminescence intensity was decreased. Compared to Tb 3+ , the unlikely low efficiency of energy transfer from styryl moieties in PSMA−Eu 3+ and diminished PSMA fluorescence intensities are attributed to the possibility of a deactivating charge transfer state due to the low reduction potentials of Eu 3+ and Yb 3+ .

The open-circuit photovoltage (V[sub oc]) of semiconductor/liquid junction solar cells is a critical parameter in determining the energy conversion efficiency. A simple, quantitative relationship between the semiconductor surface recombination velocity (S[sub r]) and the open-circuit photovoltage (V[sub oc]) of photoelectrochemical systems was derived and verified experimentally. Experimental results obtained for the n-Si/acetone-FeCp[sub 2][sup +/0]-LiClO[sub 4] junction indicate that V[sub oc] is controlled by surface recombination. Quantitative analysis of the results using the derived expression yields values of the barrier height and S[sub r] that compare favorably with published data. Application of the equation to other semiconductor/liquid junction cells suggests that the expression may be important in evaluating and understanding the behavior of a wide range of photoelectrochemical systems.

An electrospun membrane was prepared from a 16 wt % solution of poly(vinylidenefluoride- co-hexafluoropropylene) (PVdF-HFP) in a mixture of acetone/ N, N-dimethylacetamide (7:3 wt %) at an applied voltage of 12 kV. It was then activated by immersing it in 0.6 M 1-hexyl-2,3-dimethylimidazolium iodide, 0.1 M LiI, 0.05 M I 2, and 0.5 M 4- tert-butylpyridine in ethylene carbonate/propylene carbonate (1:1 wt %) to obtain the corresponding membrane electrolyte with an ionic conductivity of 10 (-5) S cm (-1) at 25 degrees C. On the basis of this electrospun membrane electrolyte, quasi-solid-state dye-sensitized solar cells were fabricated, which showed an open-circuit voltage ( V oc) of 0.76 V, a fill factor of 0.62, and a short-circuit current density ( J sc) of 15.57 mA cm (-2) at an incident light intensity of 100 mW cm (-2). This yields a light-to-electricity conversion efficiency of 7.3%. Moreover, this cell possessed better long-term stability than that fabricated with conventional liquid electrolyte.

Effects of incorporation of acid-treated single-wall carbon nanotubes (a-SWCNs) in TiO(2) film and of anchorage of dye-linked, a-SWCNs (hereafter dye-SWCNs) to the TiO(2)/electrolyte interface on photocurrent-voltage characteristics of dye-sensitized solar cells were studied. Compared with an unmodified cell, the modified cell with the a-SWCNs in TiO(2) film showed a 25% increase in short-circuit photocurrent (J(sc)). The J(sc) increase is correlated with improved connectivity between the a-SWCNs and the TiO(2) particles and with enhanced light scattering by TiO(2) clusters formed in the presence of the a-SWCNs. In the case of anchoring dye-SWCNs to the TiO(2)/electrolyte interface, the open-circuit voltage (V(oc)) increased by as much as 0.1 V, possibly due to the basicity of the TiO(2) surface from NH groups of ethylenediamine moieties of the anchored dye-SWCNs.

In a hybrid photovoltaic device of ITO/TiO 2 /polymer/Au, the photocurrent was characterized with different temperature by using regio-random (P3HT) and regular (RP3HT) poly(3-hexyl thiophene)s. RP3HT showed a constant photocurrent at temperatures higher than 195 K. On the other hand, the photocurrent of the P3HT device decreased gradually below room temperature. The drift charge mobility of both types of devices was calculated by the space charge limited current (SCLC) theory using dark J-V characteristics. The phtotocurrent began to decrease below a critical mobility range of 10 -5 cm 2 /V.s.

We studied the photovoltaic device with the heterojunction hybrid structure of n-type semiconductor TiO 2 and p-type conducting polymer. poly(2-methoxy, 5-(2'-ethyl-hexoxy)-1,4-phenylenevinylene) (MEHPPV). The polymer layer has both light sensitizing and charge transporting functions. PEDOT layer inserted in the structure of [TO/TiO 2 /MEHPPV/PEDOT/Au improved the fill factor as well as the conversion efficiency The PEDOT modified device showed that the J sc , V oc , FF and η ρ were 0.64 mA/cm 2 , 0.75 V. 0.54 and 0.49%. repectively, under the illumination of 50 mW/cm 2 (AM1.5).

Beneficial effects of in situ photopolymerized poly[di-(ethylene glycol)-2-ethyl hexyl ether acrylate] (PDEA) in the pores of dye-coated TiO 2 film on the photovoltaic characteristics of dye-sensitized solar cells (DSSCs)are reported. We have found remarkable enhancements of short-circuit photocurrent (J s c ) by 39% and of open-circuit voltage (V O C ) by 40 mV for the PDEA-modified DSSC compared with those of a conventional DSSC. This led to an enhancement in the overall solar energy conversion efficiency of 4.9% for the modified cell over 4.0% for a cell without PDEA at 100 mW/cm 2 . Moreover, the PDEA modification has led to improved long-term stability of the DSSC. Analyses of optical absorption and transient photocurrent of the cells suggest that the increased concentration of photo-injected electrons as a result of blocking of trap states in TiO 2 contributes to the enhancement in the J S C of PDEA-modified DSSCs. The V O C increase is attributed to an improved screening of the conduction band electrons from I 3 - ions in the presence of PDEA adhered to TiO 2 particles.

The open-circuit voltage increases substantially and stability of dye-sensitized TiO 2 solar cells is improved when polymer gel containing poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) in N-methyl-2-pyrrolidone replaces commonly used solvents such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN). The energy conversion efficiency of the cell with 6 wt % PVdF-HFP is comparable to that obtainable in ACN and in MPN. The promising effect of PVdF-HFP as a gelator is attributed to its interaction with Li + ions.

The influence of a buffer layer of a TiO 2 -WO 3 composite material located between a TCO substrate and a TiO 2 (P25) layer on photocurrent-voltage characteristics of dye-sensitized solar cells was compared. The buffer layer effectively isolated dye molecules and electrolytes from directly contacting the conducting substrate. In the presence of the buffer layer having 15-75 mol % WO 3 , both open-circuit photovoltage (V oc ) and short-circuit photocurrent (J sc ) were enhanced. Analyses of scanning electron microscopy data and bandedge positions of the TiO 2 -WO 3 films indicate that the V oc and J sc increases are correlated with favorable energy levels for the electron injection from the P25 layer, and with improved interparticle electrical contacts at both the TCO/TiO 2 -WO 3 and the TiO 2 -WO 3 /P25 junctions.

The effect of electrodepositing polypyrrole (PPy) onto dye-coated TiO 2 surface on the photocurrent-voltage (J-V) characteristics of dye-sensitized solar cells was studied. It is observed that both open-circuit voltage (V oc ) and short-circuit photocurrent (J sc ) of PPy-anchored TiO 2 (PPy/TiO 2 ) solar cells increase, compared to those of a TiO 2 cell. Furthermore, the stability of the J-V characteristics is enhanced with the modification. The combined effects of reduced back-electron-transfer to I 3 ions and negative shift of flatband potential explain the V oc increase. Analyses of electrochromic measurements suggest that the J sc increase is related to the enrichment of conduction band electrons in the PPy/TiO 2 electrode.

Time-dependent changes in the mass of nanocrystalline TiO 2 thin film electrodes coupled with absorbance and current-voltage variations were monitored in propylene carbonate containing LiClO 4 . The onset potential for the absorbance at 800 nm lagged behind that for the mass increase by about 0.3 V, which is related to the energy required to desolvate Li + ions adsorbed on the TiO 2 surface prior to intercalation into the TiO 2 lattice. The intercalated Li + ions can accumulate in TiO 2 by repetitive scanning between 0.0 V and an intercalation-occurring potential. Absorption of UV light by TiO 2 affected both the Li + ion desorption from the electrode and possibly the chemical nature of the TiO 2 surface. The potential dependence on the irreversible mass decrease under UV illumination is linked to the flatband potential.

The spectral shifts of visible electroluminescence from chemically modified porous Si under cathodic bias in an electrolyte containing S 2 O 2- 8 have been studied by luminescence and Fourier transform infrared measurements. Modification of porous Si with soluble polyaniline and silane compounds results in blueshifts, whereas redshifts are observed with H + and O + ion implantations. Based on a recently proposed mechanism that silicon hydride acts as an electron injector to sulfate radical anion, the blueshift is linked to the lowering of the energy levels of silicon hydrides on the porous Si surface with the bandedges being invariant with the chemical modifications. The redshift is seen as a result of the conversion of silicon dihydride to silicon monohydride, with the energy levels of silicon monohydride lying higher than silicon dihydride.

The variation of photoelectrochemical behavior in the early stage of a Ru(II)‐dye‐sensitized solar cell with the addition of carboxylic acid in acetonitrile solution is described. In the presence of carboxylic acid, photocurrent‐voltage curves exhibit dramatic enhancement in stability, increase in photocurrent, and decrease in photovoltage compared with those in the absence of carboxylic acid. The changes were studied by measurements of flatband potential, UV‐visible absorption and reflectance spectra, and ac impedance spectra. The measurements revealed that adsorption of carboxylic acid on the surface plays a major role in variations of the photocurrent‐voltage characteristics. © 2000 The Electrochemical Society. All rights reserved.