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Unformatted text preview: Simultaneous determination of thickness and optical constants of polymer thin film by analyzing transmittance Changsoo Jung and Bum Ku Rhee We present a novel method for determining both the thickness and the optical constants of a weakly absorbing thin film upon a nearly transparent substrate through analysis of transmittance measured at various incident angles with coherent light. We demonstrate this method for a polymer thin film. The refractive indices and extinction coefficients of poly ~ DRI-anthranilic acid ! at wavelengths of 1064, 632.8, and 532 nm were determined for the first time to our knowledge. We also confirmed the validity of our method with a polystyrene thin film whose optical constant was known. It was found that a thickness of a few hundred nanometers can easily be measured and that this method offers simplicity as well as the capability of in situ measurement. 2002 Optical Society of America OCIS codes: 120.4530, 120.5240, 120.7000, 310.6860. 1. Introduction A number of polymer materials have been investi- gated intensively for their potential applications in linear and nonlinear optical devices. Most polymer films under study were deposited by the spinning technique upon glass substrates of plane-parallel plates. For the optical study or application of a poly- mer thin film, information on thickness and optical constants ~ refractive index and extinction coefficient ! is essential, but making simultaneous measurements of these three parameters is not a trivial undertak- ing. 1,2 For these measurements, the prism coupling method, ellipsometry, and photometry have been widely used. The first method permits the simulta- neous determination of refractive index and thick- ness by measuring only the angle of incidence, but it has the following disadvantages: Not only can the extinction coefficient not be measured 3 but also films should be thick enough to allow more than two modes to be guided for accurate measurement. 4 Besides, films might sometimes be damaged because a film must be attached to a prism as closely as possible. With respect to ellipsometry, although an accurate refractive index can be extracted even for a single atomic or molecular layer such as a Langmuir Blodgett film, 1,2,5,6 a special substrate that is espe- cially thick or strongly absorbing is required so the problem of reflection from the back side can be elim- inated. 7 Thus in situ measurement of optical con- stants of a thin film deposited upon a glass substrate of a plane-parallel plate is not possible. This prob- lem disappears in photometry, 3,69 in which the re- flectance and transmittance are measured and analyzed. However, photometry requires relatively lengthy analysis and complex experimental appara- tus including a monochromator because white light is used to avoid a possible interference effect in the substrate....
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This note was uploaded on 03/15/2011 for the course FISICA 101 taught by Professor Chavez during the Spring '11 term at ASU.
- Spring '11