Dye films

K Kudo, M Yamashina, and T Morizumi, Field effect measurement of organic dye films, Jpn. J. Appl. Phys., 23 130, 1984. 

Reflectivity, a crucial property, is related directly to the refractive iudex of a dye film, which itself is fuudameutally related to the molar absorptiou coefficieut of the dye. It... 

Experimental results of an extensive study on the photoconductivity of solid dye films seemed to prove the existence of such an unstable addition product (A02) (triplet).45... 

Whereas in good-conducting doped or polymeric dyes ft-or -type conductivity can be explained without difficulty by analogy with inorganic semiconductors, the p- and -type photoconductivity in insulating (intrinsic) dye films cannot be explained in this manner. It is necessary to take into consideration the existence of defect states (lattice defects, dislocations, impurities etc.) distributed at different depths in the forbidden zone between valence and conduction band these defect states are able to trap electrons and holes, respectively, with different probability 10,11,88),... 

Quantitatively, it should be possible to describe the p- and -type conductivity of dye films with known densities of empty and filled centers pr, nT) by capture cross-sections of these centers for free electrons and free holes (s , Sj,), because the free-carrier lifetime (rn, rv) of electrons and holes is given by... 

Fig. 14. Scheme of the vidicon tube. (1) Scanning beam (cathode potential F = 0 volt) (2) gauze (3) dye film (4) transparent supporting electrode (potential +30 volt) (5) amplifier (6) galvanometer... 

Figure 15. Influence of the Polyester Yellow dye film absorbance and polymer binder material on the marking threshold energy. PnBMA = poly(n-butyl methacrylate) PiBMA = poly(isobutyl methacrylate) PS = polystyrene PsBMA = poly (sec-butyl methacrylate) PVB = polyvinylbutyl PMMA = polymethyl methacrylate PVAC = polyvinylacetate, S-iBMA = poly(styrene-co-isobutyl methacrylate), PC = polycarbonate S-AN — poly(styrene-co-...

Although measurements of the photoelectron emission from organic solids began about 1910, and the first measurements of the external photoeffect from dye films date from the 1930 s,39 precise measurements... 

The excitation of an SEW using a single prism is seen as a dip in the reflectivity from the prism base (see Fig. 8) when the angle of incidence satisfies Eq. (8). The location in angle of the minimum in reflectivity, the depth of the minimum and its width are very sensitive to the presence of an overlayer on the metal substrate. Pockrand, et al.— have pointed out that this technique is considerably more sensitive than ellipsometry for measuring the optical properties of thin films. They also discuss the problems due to the fact that the dye films are really anistropic. 

A photoresist pattern was deposited on a nonlinear diazo dye film and then oxygen etched to form a line of nonlinear and linear sections with a 32 pm QPM period. The upper surface was then planarized with a UV cured resin. A raised QPM +/0 channel waveguide was then formed with three more processing steps [104]. Despite the complexity of the fabrication, losses were below 3 dB cm 1 at 1.59 pm and a maximum SHG figure of merit of 4x10 % W 1 cm 2 was obtained [105,106]. 

The exciton migration within aggregates of cyanine dyes and the possibility of oxygen diffusion into the porous dye film result in a bulk generation of photocurrent [80]. Photoholes produced due to the oxidation of excitons by molecular oxygen diffuse to the back contact. The diffusion coefficient of charge carriers in dye layer (Dc) can be evaluated from the potential-step chronoamperometric measurements in the indifferent electrolyte. Considering dye film as a thin-layer cell, the current vs. time dependence can be described as follows [81] ... 

The photoelectrochemical activity inherent in thin films of aggregated cyanine dyes permits them to act as the spectral sensitizers of wide bandgap semiconductors [69]. It is seen from Fig. 4.14 that the photoelectrochemical behaviour of semiconductor/dye film heterojunctions fabricated by deposition of 200 nm-thick films of cyanine dyes on the surface of TiC>2 and WO3 electrodes, bears close similarity to that of semiconductor electrodes sensitized by the adsorption of dye aggregates. Thus, both anodic and cathodic photocurrents can be generated under actinic illumination, the efficiency of the photoanodic and photocathodic processes and the potential at which photocurrent changes its direction being dependent on dye and semiconductor substrate [69]. 

Mortazavi, M. A., Knoesen, A., Kowel, S. T., Higgins, B. G., and Dienes, A. Second-harmonic generation and absorption studies of polymer-dye films oriented by corona-onset poling at elevated temperatures. Journal of the Optical Society of America B Optical Physics), vol. 6, (no. 4), April 1989, pp. 733-741. 

An electrode covered with several molecular layers of dye could be made to adsorb all of the visible light, and obviate the need for the multielectrode stack. Very thick dye layers have tended not to be conductive or highly photoconductive so that their photoelectrochemical efficiencies are no better and perhaps worse than those seen on electrodes modified with very thin dye films. Molecular disorder of the dye appears to be the dominant reason for lack of conductivity in thick films of fluorescein-type, cyanine-type, and phthalocyanine-type dyes (12). It has been shown however that ordered molecular systems (mainly conjugated, highly unsaturated hydrocarbons) have considerable potential as conductive media, and that these ordered systems may be used to chemically modify electrode surfaces (12, 15). 

Our attention has been directed to modifying Sn02 electrodes and later, metal electrodes with very thin films (10-100 molecular layers) of phthalocyanines which appear to aggregate when sublimed. The oriented phthalocyanine phase or phases sensitize the response of the Sn02 electrodes with efficiencies many times greater than monomolecular layers of covalently attached chromophores or randomly oriented multilayer dye films (9). Our initial studies have been conducted with phthalocya-nines which we expected would orient in a linear "pancake-stack," by virtue of the interaction between the central metal atoms — either a covalent bond or a strong electrostatic interaction. 

The problems with organic solid-state photovoltaic devices are well known the localized nature of the optical excitations in most cases and the high density of charge-carrier traps in polycrystalline dye films limit the efficiency of charge-carrier generation and separation. Nevertheless, Chamberlain et have... 

It should be noted that the experimental spectra are not corrected for double passage of light through the sample. Losses of light to double reflection and absorption of dye film must be considered in order to obtain the true value of the optical density in our optical setup. For this, the reflectance spectrum of J-aggregated PIC 2-18 film was measured (Fig. 25). The corrected optical density of J-aggregated film D(Xcor)=log [Io/(fo--A-R)] was calculated by solving the quadratic equation for the absorption coefficient obtained from the formula for the measured optical density D(A) ... 

He J A, et al. 2000b. Surface relief gratings from electrostatically layered azo dye films. Appl Phys Lett 76(22) 3233 3235. 

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