Optical transmittance, measurement

CEL solutions were obtained by dissolving poly(N-vinyl pyrrolidone) and a diazoniun salt (D2, D3 or D4) in aqueous acetic acid. The solutions were spin-coated on a conventional photoresist layer formed on a silicon wafer. CEL layers on quartz substrate were used for optical transmittance measurements. 

Figure 9.41. (a) The optical transmittance measured at 40 C and at different frequencies for polyimide SP550 (600 A) with and without the insulating layer, (b) The temperature-dependence of the optical response measured at 1 Hz frequency for the cells with and without the insulating layer [103]. 

Other detection methods are based on optical transmittance [228-231], Alcohol sulfates have been determined by spectrophotometric titration with barium chloride in aqueous acetone at pH 3 and an indicator [232] or by titration with Septonex (carbethoxypentadecyltrimethylammonium bromide) and neutral red as indicator at pH 8.2-8.4 and 540 nm [233]. In a modified two-phase back-titration method, the anionic surfactant solution is treated with hyamine solution, methylene blue, and chloroform and then titrated with standard sodium dodecyl sulfate. The chloroform passing through a porous PTFE membrane is circulated through a spectrometer and the surfactant is analyzed by determining the absorbance at 655 nm [234]. The use of a stirred titration vessel combined with spectrophotometric measurement has also been suggested [235]. Alternative endpoint detections are based on physical methods, such as stalag-mometry [236] and nonfaradaic potentiometry [237]. 

The transmittance T of a sample is a quantitative measure of how much of the light entering a sample is absorbed. (Transmittance is also called optical transmittance, which means the same thing.)... 

The measurement of an optical transmittance is only accurate if I and I0 are both determined at the same, invariant wavelength. We say the light source is monochromatic. 

Optical Microscopy and Transmittance Measurement. A microscope equipped with polarizing optics and thermostatted stage was used in certain studies described below. Transmittance measurements were made by use of a power meter (Lexel model 504) positioned close to the cell, on the optic axis of the incident beam. The cell was mounted on the light scattering stage for these measurements, and the transmittance was determined for light with wavelength 647 nm. 

The fabrication process of vanadium oxide (VO2) has also been studied using RBS/C. Since optieal and electrical properties of VO2 are dramatically changed at 68°C due to phase transition, VO2 is regarded as one of the candidates for thermally activated electronic or optical switching devices for optieal fibers or sensors. To obtain the desired properties, the development of the fabrication process for very thin films, without crystalline defects on various substrates, is required. Single-crystalline VO2 thin films on (0001) plane of a sapphire substrate have been synthesized by a laser ablation method. The quality of VO2 was examined by X-ray diffraction and RBS/C method. The eleetrieal resistanee and the optical transmittance of the VO2 film were measured under inereasing and deereasing temperatures. At a temperature of 68 °C, an abrupt transition of resistanee from metal to... 

Another kind of effective or average optical constants involves mixtures of different particles such as atmospheric aerosols or soils. Effective optical constants for compacted samples of these mixtures might be inferred from reflectance and transmittance measurements as if the samples were homogeneous. But scattering or extinction calculations based on these optical constants would not necessarily be correct. 

The fundamental elements of an ultraviolet-absorption analyzer include (a) a radiation source (b) suitable optical filters (c) a sample cell and (d) an output meter. A transmittance measurement is made by calculating the ratio of the reading of the output with die sample in the cell to die reading widi the cell empty (of ultraviolet-absorbing materials). The concentration can be calculated from the known absorptivity of the substances as previously demonstrated by the equations or it may be determined by comparison with known samples. 

CPs of copolymers can be determined using the optical transmittance method (Chung et al., 1999), and even using a visual observation method (Pandya et al., 1993). Optical transmittance of aqueous polymer solutions at various temperatures can be measured using a UV/visible spectrometer. Sample and reference cells are thermostated with a circular water jacket, and the sample is monitored for the onset of turbidity. For the visual observation method, copolymer solutions at different concentrations are measured by heating them in glass tubes immersed in a well-stirred heating bath. The temperature of Lrst appearance of turbidity is taken as the CP. For both methods, the samples must be well-stirred. 

Despite the fact that direct absorbance/transmittance measurements are well established in analytical chemistry owing to the simplicity of the instrumentation and their broad applicability and versatility towards a large number of analytes, most of the reported miniaturized optical devices are based on the measurement of variations of the real part of the refractive index, such as SPR sensors [84,109-111] or interferometric sensors [94,112]. 

Optical transmittance, T, is a measure of how much light that enters a sample is absorbed. 

For the majority of bioanalytical applications, measures of absorbance will be made at defined wavelengths, and the absorbance reading is sometimes referred to as the optical density (OD) reading. The absorbance is calculated from the transmittance measure using the logarithmic relationship described by the following equation ... 

Fig. 3. Electrical resistivity (measurements were performed at room temperature in vacuum using thermally evaporated aluminum contacts on stabilized samples) and average optical transmittance, versus rf power density.

This is also confirmed by a decrease on the optical transmittance, especially for rf power densities lower than 5 W/cm. For the films with lower resistivity (< 10 Qcm), we measured Hall mobilities of about 2 cm A s and a carrier concentration of 3xl0 cm (n-type). For these undoped films an excess of interstitial Zn ions or/and oxygen vacancies can contribute with free electrons to the electrical conduction. Concerning the ZnO films used for the TFTs, due to the high value of the electrical resistivity ( 10 Qcm) it was not possible to measure the Hall. 

This was developed by Aerometrics in 1983, in collaboration with Lewis Research center, for research into pollution reduction from gas turbines. It is particularly relevent to measurements of small, spherical particles such as are found in fuel injection systems, medical nebulizers and bubbles in water. Aerometrics was later acquired by TSI who currently produce the TSI/Aerometrics PDPA 2D System. This instrument measures sizes in the 0.5 to 10,000 pm range using various optical configurations. The optical transmitter and receiver can be traversed together to move the location of the optical probe for spatial mapping of the flow field and the particle size distributions. 

As several researchers have shown empirically, the use of —log(reflectance) can provide, analogous to a transmittance measurement, a linear relationship between the transformed reflectance and concentration, if the matrix is not strongly absorbing as can be found for many samples studied by near-infrared spectroscopy. This issue is presented in detail below. A different approach based on a physical model was considered for UV/VIS measurements and later also applied within the mid-infrared. A theory was derived by Kubelka and Munk for a simple, onedimensional, two-flux model, although it must be noted that Arthur Schuster (1905) had already come up with a reflectance function for isotropic scattering. A detailed description of theoretical and practical aspects was given by Korttim. The optical absorption... 

Optical transmittance (7) of the samples was measured with a Cary 500 Scan spectrophotometer in the spectral range 190-3000 nm. Optical absorption (OA) spectra (Fig. 1), were calculated on the basis of transmittance and were used to... 

Fig. 11. Optical transmittance at a depth of 1 m measured along the track shown in profile below. Resuspension of sediment from the bottom bv waves results in lowered transmittance in shallow wafer... 

The samples have been prepared by e-beam evaporation of a dielectric layer followed by thermal evaporation of the silver fraction, which builds the island film, while the sandwich is completed by a further dielectric film. In every sample, intentionally the same amount of silver (corresponding to an average thickness of 4 nm, as recorded by quartz monitoring) has been embedded in a 6 nm thick dielectric film, formed from either Mgp2, LaFs, Si02, or AI2O3. The optical transmittance T and reflectance R of all films have been measured by a Perkin Elmer Lambda 19 spectrophotometer. To correlate the optical properties with the sample morphology, transmission electron microscopy (TEM) has been applied. 

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