# US 4,396,643 A · Radiation absorbing surfaces > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,396,643 A - Document ID: US4396643A - Status: Granted - Kind: A - Application number: 06/278,979 - Filed: 1981-06-29 - Granted: 1983-08-02 - Earliest claimed: 1981-06-29 - Assignees: Minnesota Mining and Manufacturing Company - Inventors: Robert D. Kuehn; Valdis Mikelsons; Gary L. Dorer - Web page: https://patentgrep.com/patent/US4396643A ## CPC - F24S 70/25: Coatings made of metallic material - F24S 70/225: for spectrally selective absorption - Y02E 10/40: Solar thermal energy, e.g. solar towers - Y10S 126/908: Particular chemical - F24S: SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS (for producing mechanical power from solar energy F03G6/00) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract A substantially radiation absorbing layer of metal having a microstructured surface characterized by a plurality of randomly positioned discrete protuberances of varying heights and shapes, which protuberances have a height of not less than 20 nanometers nor more than 1500 nm, and the bases of which contact the bases of substantially all adjacent protuberances is disclosed. The metal layer, which may be a coating on a variety of substrates, is useful as a radiation absorber (particularly solar). A method is disclosed for producing such layers. ## Claims ### Claim 1 A substantially radiation absorbing layer of metal having a microstructured surface characterized by a plurality of randomly positioned discrete protuberances of varying heights and shapes, which protuberances have a height of not less than 20 nanometers nor more than 1500 nm, and the bases of which contact the bases of substantially all adjacent protuberances. ### Claim 2 (depends on 1) The layer according to claim 1 wherein said metal is selected from chromium, aluminum, copper, gold, and nickel. ### Claim 3 (depends on 1) The layer according to claim 1 wherein the tips of said protuberances are spaced apart a distance in the range of 3 to 500 nm. ### Claim 4 (depends on 3) The layer according to claim 3 wherein the average spacing between the tips of said protuberances is in the range of 1/10 to 1/4 the average height of the protuberances. ### Claim 5 (depends on 1) A selective solar absorber comprising the layer according to claim 1. ### Claim 6 (depends on 1) A flat plate solar collector comprising the layer according to claim 1. ### Claim 7 A substantially radiation absorbing composite surface, comprising: (a) a replicated microstructured layer characterized by a plurality of randomly positioned discrete protuberances of varying heights and shapes, which protuberances have a height of not less than 20 nanometers nor more than 1500 nm, and the bases of which contact the bases of substantially all adjacent protuberances, and (b) an overcoating of a thin film of at least one metal having a thickness in the range of 40 to 200 nanometers. ### Claim 8 (depends on 7) The composite surface according to claim 7 which is a selective absorbing surface. ### Claim 9 (depends on 7) The composite surface according to claim 7 wherein said thin film of metal is selected from chromium, aluminum, copper, gold, and nickel. ### Claim 10 (depends on 7) The surface according to claim 7 wherein said replicated microstructured layer is an embossable or castable material selected from metal, nonmetal, and plastic materials. ### Claim 11 (depends on 7) A selective solar absorber comprising the composite surface according to claim 7. ### Claim 12 (depends on 7) A silverless graphics art film comprising the composite structure according to claim 7. ### Claim 13 (depends on 7) A flat plate solar collector comprising the composite surface according to claim 7. ### Claim 14 An article having a substantially radiation absorbing surface, said article comprising: a substrate having on at least one surface thereof, (a) a layer of an oxide or hydroxyoxide of a metal, selected from the group consisting of aluminum, magnesium and zinc or alloys thereof, which layer is a substantially complete conversion of a thin-film of said metal, the thickness of said thin-film prior to conversion being at least 5 nanometers and exhibiting a surface after said conversion characterized by a plurality of randomly positioned discrete protuberances of varying heights and shapes, which protuberances extend from said substrate surface a distance of not less than 20 nanometers nor more than 1500 nm, and the bases of which contact the bases of substantially all adjacent protuberances, and (b) an overcoating upon said oxide or hydroxyoxide layer, which overcoating is a contiguous connected thin layer of at least one metal having a thickness in the range of 40 to 200 nanometers. ### Claim 15 (depends on 14) The article according to claim 14 wherein said substrate is selected from aluminum, stainless steel, glass, and polyester. ### Claim 16 (depends on 14) The article according to claim 14 wherein the absorbance over the total solar range of said article is within the range of 70 percent to 98 percent. ### Claim 17 (depends on 14) The article according to claim 14 wherein said metal overcoating is selected from chromium, aluminum, copper, gold, and nickel. ### Claim 18 (depends on 14) The article according to claim 14 wherein said overcoating is absorbing. ### Claim 19 (depends on 14) The article according to claim 14 wherein said overcoating is of chromium. ### Claim 20 (depends on 14) The article according to claim 14 wherein said overcoating is deposited by vacuum deposition, sputtering, electroless plating, or chemical vapor deposition. ### Claim 21 (depends on 14) A selective solar absorber comprising the article according to claim 14. ### Claim 22 (depends on 14) A silverless graphics art film comprising the article according to claim 14. ### Claim 23 (depends on 14) A flat plate solar collector comprising the article according to claim 14. ### Claim 24 A process for preparing a substantially radiation absorbing composite surface, said process comprising the steps of: (a) providing a replicated microstructured layer characterized by a plurality of randomly positioned discrete protuberances of varying heights and shapes, which protuberances have a height of not less than 20 nanometers nor more than 1500 nm, and the bases of which contact the bases of substantially all adjacent protuberances, and (b) overcoating said microstructured layer with a contiguous connected thin layer of metal having a thickness in the range of 40 to 200 nanometers. ### Claim 25 (depends on 24) The process according to claim 24 wherein said replicated microstructured layer is an embossable or castable material selected from metal, nonmetal, and organic materials. ### Claim 26 (depends on 24) The process according to claim 24 wherein said metal overcoating is selected from chromium, aluminum, copper, gold, and nickel. ### Claim 27 The process of preparing a substantially radiation absorbing surface, said process comprising (a) providing a substrate having on at least one surface thereof a layer of an oxide or hydroxyoxide of a metal, selected from the group consisting of aluminum, magnesium and zinc or alloys thereof, which layer is a substantially complete conversion of a thin-film of said metal, the thickness of said thin-film prior to conversion being at least 5 nanometers and exhibiting a surface after said conversion characterized by a plurality of randomly positioned discrete protuberances of varying heights and shapes, which protuberances extend from said substrate surface a distance of not less than 20 nanometers nor more than 1500 nm, and the bases of which contact the bases of substantially all adjacent protuberances, and (b) overcoating upon said oxide layer a contiguous connected thin layer of at least one metal having a thickness in the range of 40 to 200 nanometers. ### Claim 28 (depends on 27) The process according to claim 27 wherein said substrate is selected from aluminum, stainless steel, glass, and polyester. ### Claim 29 (depends on 27) The process according to claim 27 wherein said thin layer of metal is selected from chromium, aluminum, copper, gold, and nickel.