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Applications
Published in Pramod K. Naik, Vacuum, 2018
Solar cells and solar modules directly convert the solar radiation into electricity. A photovoltaic absorber material is required for the solar cell. The material needs to absorb the incoming light efficiently and produce mobile charge carriers, electrons and holes that are separated at the terminals of the device without significant loss of energy. A thin-film solar cell is made by depositing one or more thin layers of photovoltaic material on a substrate, such as glass, plastic or metal. Thin film cells are flexible and lightweight. Rigid thin film solar panels that are sandwiched between two panes of glass are employed in some photovoltaic power stations. Cadmium telluride (CdTe) is mainly used as the semiconducting material in thin film photovoltaics. It is sandwiched with cadmium sulfide to form a p–n junction solar photovoltaic cell. Some of the world's largest photovoltaic power stations employ CdTe photovoltaics. Other materials used for solar cells include copper indium gallium selenide and amorphous silicon. Sharma et al24 have discussed the subject in their review article. Thin-film interference is the optical phenomenon responsible for the coloured reflections that we observe. It occurs in structures composed of one or more transparent thin films, having typical thickness similar to the wavelength of light. Thin films are used for decorative applications. Reflection and refraction occurs at the top interface for the light incident on a single transparent thin film. Light transmitted into the film travels till it reaches the bottom interface, where a part is reflected and a part is transmitted. This process repeats as several times. Due to the wave nature of light, each portion of it can be imagined as a partial wave with its own wavelength, amplitude and phase. The manner in which the partial waves interfere determines the wavelengths that are transmitted and those reflected. The amount of the optical phase accumulated by a partial wave during the transit through the film depends on 'optical thickness' which is governed by the thickness of the layer, the incidence angle and the refractive index, thus giving rise to the destructive and constructive interference condition and to the emerging colours. In the compact disc (CD) manufacturing process, the developed glass master is deposited with a thin film of nickel up to a typical thickness of around 400 nm. In the computer hard disc manufacturing process, the developed glass master is coated with a thin film of nickel of thickness about 400 nm in vacuum. During the replication
Producing a thin coloured film on stainless steels – a review. Part 2: non-electrochemical and laser processes
Published in Transactions of the IMF, 2023
G. T. Alliott, R. L. Higginson, G. D. Wilcox
It has been reported that when stainless steel is exposed to high temperatures, such as the heat of a furnace or welding equipment, colour appears on the surface of the steel.7,18–22 The colour is formed by the progressive thickening of the surface oxide layer. The thickening of the oxide layer by exposure to heat to produce colour is called thermal tinting or temper colouring.7,23 The colour produced is a result of thin film interference. Figure 3,24 shows a thermal tinted stainless steel motorbike exhaust manifold following exposure to hot exhaust gases.