# US 9,435,050 B2 · Method of making a porous TiO2 photonic film > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,435,050 B2 - Document ID: US9435050B2 - Status: Granted - Kind: B2 - Application number: 12/715,789 - Filed: 2010-03-02 - Published: 2011-09-08 - Granted: 2016-09-06 - Earliest claimed: 2010-03-02 - Assignees: City University of Hong Kong - Applicants: Yang Yang Li; Jianwen Cheng; Chun Kwan Tsang; Zhengtao Xu - Inventors: Yang Yang Li; Jianwen Cheng; Chun Kwan Tsang; Zhengtao Xu - Web page: https://patentgrep.com/patent/US9435050B2 ## CPC - C25D 11/26: of refractory metals or alloys based thereon - C01G 23/047: Titanium dioxide - C25D 11/024: {Anodisation under pulsed or modulated current or potential} - C25F 3/02: Etching - C25F 3/08: of refractory metals - C25F 3/26: of refractory metals - C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR - C01G: COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts or peroxyacids C01B15/00; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium, or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds containing nitrogen, other non-metals and metal C01B21/082}; metal amides C01B21/092; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanamide C01C3/16; thiocyanates C01C3/20) - C25F: PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR ## Abstract A porous titanium dioxide film having photonic properties is made by etching a titanium substrate in an electrolyte solution in the presence of an electric field. The electrolyte solution can be an organic electrolyte solution. Etching involves providing an electrolyte solution in contact with a pair of electrodes and passing an electric current through the electrolyte solution. The titanium substrate can be one of the pair of electrodes. The current has a wave profile selected from a group consisting of a periodic square profile, a sine wave, a linear profile, or a quintic profile, and is provided either parallel to or perpendicular to a plane of the substrate. ## Claims ### Claim 1 A method of making a porous titanium dioxide structure having a photonic color, the method comprising: providing a pair of electrodes in contact with an electrolyte solution; anodizing a titanium substrate in the electrolyte solution, by passing an electric current having a voltage or current profile through the electrolyte solution and the pair of electrodes in the presence of a first electric field, thereby forming a layer of dense titanium dioxide from the titanium substrate, wherein the first electric field is applied in a first field direction that is transverse to the titanium substrate; etching part of the layer of dense titanium dioxide in the electrolyte solution, by passing an electric current having the voltage or current profile through the electrolyte solution and the pair of electrodes, in the presence of a second electric field, thereby forming a layer of porous titanium dioxide within part of the layer of dense titanium dioxide and that includes pores extending to an outer surface of the layer of porous titanium dioxide, wherein the second electric field is applied in a second field direction that is parallel to the titanium substrate; and adjusting the voltage or current profile and duration of the voltage or current profile while anodizing the titanium substrate and while etching the layer of dense titanium dioxide, thereby controlling the photonic color of the porous titanium dioxide structure. ### Claim 2 (depends on 1) The method of claim 1 wherein the electrolyte solution is an organic electrolyte solution. ### Claim 3 (depends on 2) The method of claim 2 wherein the organic electrolyte solution includes an organic solvent. ### Claim 4 (depends on 1) The method of claim 1 wherein the electrolyte solution is a fluoride solution. ### Claim 5 (depends on 1) The method of claim 1, wherein the electric current has a profile selected from the group consisting of a periodic square profile, a periodic pulsed profile, a sine wave, a linear profile, and a quintic profile. ### Claim 6 (depends on 1) The method of claim 1 wherein the titanium substrate is one electrode of the pair of electrodes. ### Claim 7 (depends on 1) The method of claim 1 wherein anodizing and etching in the electrolyte solution in the presence of the first and second electric fields comprises varying electric field strengths. ### Claim 8 (depends on 1) The method of claim 1 further comprising, after the etching, removing the layer of porous titanium dioxide from the titanium substrate as a free standing porous titanium dioxide structure. ### Claim 9 (depends on 8) The method of claim 8 including removing the layer of porous titanium dioxide from the titanium substrate by one of mechanical force and electropolishing. ### Claim 10 (depends on 1) The method of claim 1 further comprising, after the etching, treating the layer of porous titanium dioxide to change chemical composition or structural features of the layer of porous titanium dioxide. ### Claim 11 (depends on 10) The method of claim 10, wherein treating the layer of porous titanium dioxide comprises chemically treating the layer of porous titanium dioxide. ### Claim 12 (depends on 11) The method of claim 11, wherein chemically treating the layer of porous titanium dioxide comprises partially or fully filling the pores in the layer of porous titanium dioxide with a compound selected from the group consisting of organic molecules, inorganic materials, and biomolecules. ### Claim 13 (depends on 11) The method of claim 11, wherein treating the layer of porous titanium dioxide comprises heating the layer of porous titanium dioxide to create a surface coating on the layer of porous titanium dioxide. ### Claim 14 (depends on 1) The method of claim 1, further comprising, after the etching of the layer of dense titanium dioxide in the electrolyte solution and forming the layer of porous titanium dioxide, anodizing the layer of porous titanium dioxide in the electrolyte solution in the presence of an electric field having the first field direction that is transverse to the titanium substrate. ### Claim 15 A method of making a porous titanium dioxide structure having a photonic color, the method comprising: applying a periodic voltage or current having a period across a titanium substrate, as a first electrode, in an electrolyte solution, and a second electrode in the electrolyte solution, in the presence of a first electric field, thereby anodizing the titanium substrate and forming a layer of dense titanium dioxide from the titanium substrate, wherein the first electric field is applied in a first field direction that is transverse to the titanium substrate; applying a periodic voltage or current across the titanium substrate in the electrolyte solution and the second electrode, in the electrolyte solution, in the presence of a second electric field, thereby etching part of the layer of dense titanium dioxide in the electrolyte solution and forming a layer of porous titanium dioxide within part of the layer of dense titanium dioxide and that includes pores extending to an outer surface of the layer of porous titanium dioxide, wherein the second electric field is applied in a second field direction that is parallel to the titanium substrate; and controlling profile of the periodic voltage or current and duration of application of the periodic voltage or current to the first and second electrodes, thereby controlling thickness of the layer of porous titanium dioxide and the photonic color of the porous titanium dioxide structure. ### Claim 16 (depends on 15) The method of claim 15, including controlling the duration of the application of the periodic voltage or current and thereby controlling the thickness and the photonic color of the layer of porous titanium dioxide by stopping application of the periodic voltage or current after a fixed number of periods of the application of the voltage or current across the first and second electrodes. ### Claim 17 (depends on 15) The method of claim 15, wherein the periodic voltage or current has a profile selected from the group consisting of a periodic square profile, a periodic pulsed profile, and a sine wave profile.