Modification of infrared reflectivity using silicon dioxide thin films derived from silsesquixane resins

Abstract

Changes in the infrared reflection spectrum of a thin film of silica-like resinous material sandwiched between metal electrodes can be induced by applying an electric potential to a top electrode which is semitransparent. Characteristic infrared absorption lines change in proportion to a small electric current flowing through the material. These changes occur with response times of the order of seconds, and show time constants of the order of minutes to reach stationary values.

1 . A method of varying the infrared spectrum of a silicon dioxide thin film derived from a silsesquioxane resin comprising 
 (i) directing a beam of infrared radiation to a metal-insulator-metal device containing a silicon dioxide thin film derived from a hydrogen silsesquioxane resin, an alkyl silsesquioxane resin, or an aryl silsesquioxane resin,    (ii) applying an electric potential difference across the metal-insulator-metal device containing the thin film, and    (iii) monitoring the variation in the infrared reflection or transmission spectrum of the thin film in response to the electric current flowing through the thin film.    
     
     
         2 . A method according to  claim 1  in which the thin film is arranged in the metal-insulator-metal device between an upper layer of metal and a lower layer of metal, the metal of each layer being selected from the group consisting of gold, palladium, platinum, silver, chromium, aluminum, copper, nickel, titanium, and tin; and alloys such as titanium-tungsten, titanium nitride, nickel-chromium, indium tin oxide, and gallium arsenide.  
     
     
         3 . A method according to  claim 2  in which the upper layer of metal has a thickness such that it is transparent or semitransparent to the passage of a beam of infrared radiation, and the lower layer of metal has a thickness such that the beam of infrared radiation can be reflected, whereby when the beam of infrared radiation is directed at the metal-insulator-metal device, the beam of infrared radiation is able to pass through the upper layer of metal and be reflected back by the lower layer of metal.  
     
     
         4 . A method according to  claim 3  in which the upper layer of metal has a thickness in the range of about 0.005 μm to 0.080 μm (5 to 80 nanometer); the thin film has a thickness in the range of about 0.1 μm (100 nanometer) to 1.5 μm (1,500 nanometer); and the lower layer of metal has a thickness of at least about 0.15 μm (150 nanometer).  
     
     
         5 . A method according to  claim 1  in which the beam of infrared radiation has a wavelength in the range of about 2.5 μm to 25 μm.  
     
     
         6 . A method according to  claim 5  in which the beam of infrared radiation is essentially monochromatic.  
     
     
         7 . A method of modifying the spectral signature of a surface coating of an object which is subject to remote observation and is identifiable by its spectral reflectance comprising: 
 (i) mounting on the surface of the object a metal-insulator-metal device containing a silicon dioxide thin film derived from a hydrogen silsesquioxane resin, an alkyl silsesquioxane resin, or an aryl silsesquioxane resin,    (ii) applying an electric potential difference across the metal-insulator-metal device containing the thin film, and    (iii) varying the infrared reflection spectrum of the thin film in response to the electric current flowing through the thin film.    
     
     
         8 . A method according to  claim 7  in which the object is an aircraft or a watercraft.  
     
     
         9 . In the processing or transmission of data in a communication or computational device containing an optical switch, the improvement comprising an optical switch which is a metal-insulator-metal device containing a silicon dioxide thin film derived from a hydrogen silsesquioxane resin, an alkyl silsesquioxane resin, or an aryl silsesquioxane resin, the metal-insulator-metal device being so constructed and arranged whereby 
 (i) a beam of infrared radiation can be directed to the metal-insulator-metal device containing the thin film, so that when    (ii) an electric potential is applied to the metal-insulator-metal device containing the thin film, (iii) the infrared reflection spectrum of the thin film is varied in response to the electric current flowing through the thin film.    
     
     
         10 . An optical switch according to  claim 9  in which the beam of infrared radiation is a monochromatic beam having a wavelength which coincides with a vibrational absorption of the thin film.  
     
     
         11 . A coating for an object exposed to a beam of infrared radiation comprising a metal-insulator-metal device containing a silicon dioxide thin film derived from a hydrogen silsesquioxane resin, an alkyl silsesquioxane resin, or an aryl silsesquioxane resin, means for applying an electric potential difference to the metal-insulator-metal device for varying the infrared reflection spectrum of the thin film in response to electric current flowing through the thin film, the metal-insulator-metal device including an upper layer of metal having a thickness such that it is transparent or semitransparent to the passage of a beam of infrared radiation, and a lower layer of metal having a thickness such that a beam of infrared radiation can be reflected, whereby when a beam of infrared radiation is directed at the metal-insulator-metal device, the beam of infrared radiation is able to pass through the upper layer of metal and be reflected back by the lower layer of metal.  
     
     
         12 . A coating according to  claim 11  in which the upper layer of metal has a thickness in the range of about 0.005 μm to 0.080 μm (5 to 80 nanometer), the thin film has a thickness in the range of about 0.1 μm (100 nanometer) to 1.5 μm (1,500 nanometer), and the lower layer of metal has a thickness of at least about 0.15 μm (150 nanometer).  
     
     
         13 . A coating according to  claim 11  in which the object is a window pane.