Mass spectra of some substituted methylcyclosiloxanes

The mass spectra of the substituted methylcyclosiloxanes [Formula: see text] where X = H (n = 4, 5 and 6), X = C6H5 (n = 3 and 4), X = Br (n = 3 and 4), X = Co(CO)4 (n = 4 and 5) have been measured. The compounds X = H fragment by the same kinds of substituent loss and ring contraction mechanisms as previously reported for the compounds X = CH3 but also by the loss of methylhydrogensilanone. The compounds X = Ph fragment by loss of benzene from an intramolecularly bridging benzenonium ion, formed from [M − CH3]+• and by losses of the phenylmethylsilanone fragments. The compounds X = Br only undergo substituent loss without ring fragmentation. The compounds X = Co(CO)4 show stepwise loss of all CO groups from [M]+•, [M − Co(CO)4]+, and [M]++.

Automatic determination of the optical constants of inhomogeneous thin films

The refractive index of a layer is a sensitive function of the preparation conditions. Normal incidence measurement of the optical properties can reveal possible inhomogeneity of index. We propose a method of automatic determination of the complex refractive index and thickness of a layer which includes systematic measurement of the degree of inhomogeneity which is represented by a simple model. The usefulness of the technique is demonstrated by examples that form part of an experimental study of a number of useful optical materials including Y(2)O(3), TiO(2), MgF(2), HfO(2), and SiO(2). The dispersions of the refractive index, the extinction coefficient, and of the inhomogeneity are represented by Cauchy formulas with accurately determined coefficients. The results can therefore be readily used in computing the optical properties of thin-film multilayers.

Inhomogeneity in films: limitation of the accuracy of optical monitoring of thin films

With present-day refinements, thin film multilayers can be designed theoretically to meet virtually any reasonable filtering requirements. Often, when the optical properties are specified over very wide spectral regions the thicknesses of the various layers are not related in any simple way. The manufacture of such multilayers presents many difficulties. The tolerances on layer thickness and refractive indices in some designs are often very narrow. We have developed an optical method for the accurate control of layer thickness that involves the measurement of transmittance over a wide spectral region (400-1000 mm). This measurement is performed continuously during deposition by a rapid scanning monochromator. The accuracy of such a system depends on a precise knowledge of the indices of refraction that are produced during the multilayer deposition. In addition the structure of many optical thin films used for hard coatings departs considerably from the simple method that is traditionally used in optical coating designs. In the method we have developed to compensate for such discrepancies, optical inhomogeneity is included by assuming a linear refractive-index profile, determined by analyzing experimental results. These results are in agreement with other studies of structure.

Nonquarterwave multilayer filters: optical monitoring with a minicomputer allowing correction of thickness errors

Many spectral filtering problems require assemblies of layers having thicknesses that bear no obvious relationship to one another. After a brief review of the optical methods used to monitor deposition of multilayers containing nonintegral thicknesses, we show that the performance of monitoring systems can be improved further by including the real-time calculation of any necessary layer thickness changes that may be required to compensate any errors that might still occur. The apparatus described consists of a minicomputer coupled to a rapid-scanning spectrometer. Such a procedure working in real time avoids the cumulative effects of successive errors. The technique is demonstrated in the production of a beam splitter.

Wideband optical monitoring of nonquarterwave multilayer filters

The construction of optical filters, which are required to have optical properties well defined over wide spectral regions, demands the use of multilayer designs in which there are no simple relationships between the thicknesses of the layers. There are considerable difficulties in the manufacture of such multilayers. First, we must be able to reproduce, sufficiently accurately, the indices of refraction that have been used in the theoretical design. Then we must be able to control the optical thicknesses of each layer, which necessitates measurement of the optical properties of the multilayer during deposition. The apparatus described consists of a minicomputer coupled to a rapid-scanning spectrometer that continuously measures the spectral profile during deposition of each layer. The precise measurement of the evolution of the optical properties during actual construction of a filter allows us to control layer thickness with very good accuracy. The technique is demonstrated in the monitoring of a beam splitter made of a few layers.

Optical monitoring of nonquarterwave multilayer filters

Many spectral filtering problems require the use of assemblies of layers having thicknesses which bear no obvious relationship to each other. Successful production of these multilayers requires films with thicknesses approximating theoretical values. We show that the optical methods currently used in the production of film assemblies of quarterwave layer thicknesses, which are based on the use of just one single wavelength, are poorly adapted to monitoring the deposition of nonintegral thickness multilayers. In contrast we show that with an optical control system utilizing a broad spectral bandwidth, thickness errors can be reduced. Transmittance measurements with the precision necessary to achieve this improved thickness control are attainable with existing instrumentation. This result is established by a computer simulation of the construction of a specific multilayer and remains valid for other nonquarterwave multilayer filters.