Channamallappa Lingaraju Nagendra

Publications (15) View all

• Article: Effect of high-energy electron-beam irradiation on the optical properties of ion-beam-sputtered silicon oxynitride thin films.

  Shivaprasad Karanth, Ganesh H Shanbhogue, C L Nagendra
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  ABSTRACT: Silicon oxynitride thin films are prepared by ion-beam sputtering, and the optical properties and surface chemical composition are studied by spectrophotometric and x-ray photoelectron spectroscopy, respectively. It is seen that the films sputtered by use of nitrogen alone as the sputtering species from a silicon nitride target are completely transparent (k < 0.005) and have a refractive-index dispersion from 1.85 to 1.71 over the visible and near-infrared spectral regions, and the films show distinct spectral lines that are due to silicon, Si(2s), nitrogen, N(1s), and oxygen, O(1s). Sputter deposition of argon and of argon and nitrogen produces silicon-rich silicon oxynitride films that are absorbent and have high refractive indices. These films have a direct electronic transition, with a threshold energy of 1.75 eV. Electron irradiation transforms optically transparent silicon oxynitride films into silicon-rich silicon oxynitride films that have higher refractive indices and are optically absorbing owing to the presence of nonsaturated silicon in the irradiated films. The degradation in current responsivity of silicon photodetectors, under electron irradiation, is within 3% over the wavelength region from 450 to 750 nm, which is entirely due to the degradation of optical properties of silicon oxynitride antireflection coatings.
  Applied Optics 10/2005; 44(29):6186-92. · 1.41 Impact Factor
• Article: Multilayer antireflection coatings for the visible and near-infrared regions.

  H G Shanbhogue, C L Nagendra, M N Annapurna, S A Kumar, G K Thutupalli
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  ABSTRACT: With a high-refractive-index mixed-oxide dielectric material of ZrTiO(4) and ZrO(2) [Substance H2 (Sub2) from E. Merck, Darmstadt, Germany], in combination with magnesium flouride (MgF(2)), design optimization and experimental production of low-loss antireflection (AR) coatings are carried out. Design-optimization studies that make use of these materials as constituents of a seven-layer coating system demonstrate that when the useful bandwidth of an AR coating is extended to cover a wider spectral range, the designs are in general found to have increased integrated reflection loss, higher ripple, and increased spectral instability. The experimental studies on Sub2 material show that the films have excellent optical performance over a wider process window, the advantage of which is demonstrated in the production of different AR coatings on a variety of glasses with refractive indices that range from 1.45 to 1.784 and different mechanical, thermal, and chemical properties. The manufacturing process of AR coatings shows a consistency better than 99% with respect to optical properties and durability.
  Applied Optics 10/1997; 36(25):6339-51. · 1.41 Impact Factor
• Article: Low-reflection-loss attenuator optical coatings: theory and experiment.

  S A Kumar, C L Nagendra, G K Thutupalli
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  ABSTRACT: Following the optical admittance matching approach, we have derived explicit equations to evaluate the refractive index and thickness of the matching dielectric layer deposited on an attenuator layer to obtain zero or near-zero reflection loss at one or more than one wavelength. With these equations a new family of optical coatings that can not only attenuate the input optical radiation to a required level but can also show a very low reflection loss (less than 0.1%) within a specified band is successfully designed and developed. Typical coatings, produced by electron-beam evaporation, have an average reflection loss of less than 1% and transmittance of 0.42 and 0.64 ± 0.02 over visible and near-IR spectral regions, respectively.
  Applied Optics 06/1996; 35(16):3047-51. · 1.41 Impact Factor
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  Article: Optical properties of semiconductor-metal composite thin films in the infrared region.

  C L Nagendra, J L Lamb
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  ABSTRACT: Germanium:silver (Ge:Ag) composite thin films having different concentrations of Ag, ranging from 7% to 40%, have been prepared by dc cosputtering of Ge and Ag. The films' surface morphology and optical properties have been characterized using transmission electron microscopy and infrared spectrophotometry. It is seen that, although the films that contain lower concentrations of Ag have islandlike morphology (i.e., Ag particles distributed in a Ge matrix), the higher metallic concentration films tend to have a symmetric distribution of Ag and Ge. The optical constants (i.e., refractive index n and absorption index k) derived from the measured optical properties show a semiconductor behavior even as high as 40% of Ag concentration, beyond which the metallic properties dominate over the entire infrared spectrum. Comparison of the n and k data with the two well-known effective medium theories, namely, the Maxwell-Garnett theory and the Bruggeman theory, shows that both theories have limited scope in predicting the optical properties of semiconductor-metal composite films in the infrared region. However, an empirical polynomial equation can simulate the experimental data at all wave numbers of the IR spectrum.
  Applied Optics 07/1995; 34(19):3702-10. · 1.41 Impact Factor
• Article: Thin Semiconductor/Metal Films For Infrared Devices

  James L. Lamb, Channamallappa L. Nagendra
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  ABSTRACT: Spectral responses of absorbers and reflectors tailored. Thin cermet films composites of metals and semiconductors undergoing development for use as broadband infrared reflectors and absorbers. Development extends concepts of semiconductor and dielectric films used as interference filters for infrared light and visible light. Composite films offer advantages over semiconductor films. Addition of metal particles contributes additional thermal conductivity, reducing thermal gradients and associated thermal stresses, with resultant enhancements of thermal stability. Because values of n in composite films made large, same optical effects achieved with lesser thicknesses. By decreasing thicknesses of films, one not only decreases weights but also contributes further to reductions of thermal stresses.
  07/1995;