Fabric illumination

The science of color measurement has been explored by various authors (127,128). AATCC evaluation procedure no. 6 describes a method for instmmental measurement of color of a textile fabric. AATCC evaluation procedure no. 7 may be used to determine the color difference between two fabrics of a similar shade. Instmmentation may be either a spectrophotometer for measuring reflectance versus wavelength, or a colorimeter for measuring tristimulus values under specified illumination. If a spectrophotometer is used, however, the instmment must be equipped with tristimulus integrators capable of producing data in terms of CIE X, Y, and Z tristimulus values. 

A prerequisite for all etch-stop techniques discussed so far is an electrical connection to an external power supply. However, if the potential required for passivation in alkaline solutions is below 1 V, it can be generated by an internal galvanic cell, for example by a gold-silicon element [As4, Xil]. An internal galvanic cell can also be realized by a p-n junction illuminated in the etchant, as discussed in the next section. Internal cells eliminate the need for external contacts and make this technique suitable for simple batch fabrication. 

A schematic view of the cold cathode fabrication process is shown in Fig. 10.18. The cold cathode is fabricated by low pressure chemical vapor deposition (LPCVD) of 1.5 pm of non-doped polysilicon on a silicon wafer or a metallized glass substrate. The topmost micrometer of polysilicon is then anodized (10 mA cnT2, 30 s) in ethanoic HF under illumination. This results in a porous layer with inclusions of larger silicon crystallites, due to faster pore formation along grain boundaries. After anodization the porous layer is oxidized (700 °C, 60 min) and a semi-transparent (10 nm) gold film is deposited as a top electrode. 

Spray pyrolysis of ethanolic solutions of Fe(acetylacetone)3 or FeCls between 370°C and 450°C onto a glass substrate are reported for the fabrication of a-Fe20s thin-film photoanodes [75]. Upon illumination by a 150 W Xe lamp samples consistently demonstrate photocurrents of 0.9 mAcm , IPCE values up to 15%, and robust mechanical stability with no signs of photocorrosion for the undoped samples. With simultaneous multiple doping of 1% A1 and 5% Ti, an IPCE of 25% can be reached at 400 nm. Zn doping is known to induce p-type character in Ee20s thin film electrodes [76]. 

Figure 5.38 illustrates the experimental setup for water photoelectrolysis measurements with the nanotuhe arrays used as the photoanodes from which oxygen is evolved. The 1-V characteristics of 400 nm long short titania nanotuhe array electrodes, photocurrent density vs. potential, measured in IM KOH electrolyte as a function of anodization hath temperature under UV (320-400 nm, lOOmW/cm ) illumination are shown in Fig. 5.39. The samples were fabricated using a HF electrolyte. At 1.5V the photocurrent density of the 5°C anodized sample is more than three times the value for the sample anodized at 50°C. The lower anodization temperature also increases the slope of the photocurrent—potential characteristic. On seeing the photoresponse of a 10 V 5°C anodized sample to monochromatic 337 nm 2.7 mW/cm illumination, it was found that at high anodic polarization, greater than IV, the quantum efficiency is larger than 90%.

A 13.4% efficient cell fabricated by close space sublimation of CdTe on CD CdS was reported in 1991 [3], followed by a 14.5% cell a year later by the same gronp [4]. The CdS thickness was between 50 and 150 nm. The cells were illuminated throngh the tin oxide/glass, which was used as the substrate for the CdS deposition, and this geometry has been used ever since for these cells. 

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