WO2014171995A1 - Systèmes et procédés de fabrication de structures métallisées dans une matrice de support polymère - Google Patents

Systèmes et procédés de fabrication de structures métallisées dans une matrice de support polymère Download PDF

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Publication number
WO2014171995A1
WO2014171995A1 PCT/US2014/014121 US2014014121W WO2014171995A1 WO 2014171995 A1 WO2014171995 A1 WO 2014171995A1 US 2014014121 W US2014014121 W US 2014014121W WO 2014171995 A1 WO2014171995 A1 WO 2014171995A1
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metal
radiation
range
mixture
structures
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PCT/US2014/014121
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English (en)
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Eric Mazur
Kevin L VORA
Seungyeon Kang
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President And Fellows Of Harvard College
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Publication of WO2014171995A1 publication Critical patent/WO2014171995A1/fr

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/105—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern by conversion of non-conductive material on or in the support into conductive material, e.g. by using an energy beam
    • H05K3/106—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern by conversion of non-conductive material on or in the support into conductive material, e.g. by using an energy beam by photographic methods
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/06—Coating on selected surface areas, e.g. using masks
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/08—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of metallic material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/14—Decomposition by irradiation, e.g. photolysis, particle radiation or by mixed irradiation sources
    • C23C18/143—Radiation by light, e.g. photolysis or pyrolysis
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/0042—Photosensitive materials with inorganic or organometallic light-sensitive compounds not otherwise provided for, e.g. inorganic resists
    • G03F7/0043—Chalcogenides; Silicon, germanium, arsenic or derivatives thereof; Metals, oxides or alloys thereof
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/20—Exposure; Apparatus therefor
    • G03F7/2051—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source
    • G03F7/2053—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source using a laser
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/10—Using electric, magnetic and electromagnetic fields; Using laser light
    • H05K2203/107—Using laser light
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/12—Using specific substances
    • H05K2203/125—Inorganic compounds, e.g. silver salt

Definitions

  • the present disclosure relates generally to methods and systems for generating metalized structures (e.g., connected and disconnected micro- and nano-sized structures) in a support matrix, e.g., a polymeric substrate, and to such a metalized support matrix having a plurality of metalized structures distributed therein.
  • a support matrix e.g., a polymeric substrate
  • one conventional method for creating three dimensional (3D) metal structures includes depositing metal on polymer patterns generated by direct laser writing, e.g., by coating 3D polymer structures or by filling contiguous volumetric voids.
  • the types of metal structures that can be created by such an approach are limited. Accordingly, there is a need for methods and systems for fabricating metal structures in substrates, and particularly, there is a need for such methods and systems that allow direct, and fast fabrication of both connected and disconnected three-dimensional metal structures.
  • the present invention provides methods for fabricating metal structures (e.g., silver and gold structures), which can have tunable dimensions.
  • ultrafast laser radiation is employed for direct-writing of such metal structures in a substrate, e.g., a polymeric substrate.
  • nonlinear optical interactions between one or more chemical precursors and femtosecond pulses are utilized to limit photoreduction processes to focused spots, where in some cases the interaction volume can be smaller than the diffraction limit.
  • metal nanostructures can be created in a focal volume, which can be rapidly scanned in three dimensions (3D).
  • 3D three dimensions
  • metal grid and woodpile patterns can be produced, e.g., over hundreds of micrometers in dimensions.
  • the process can be scalable and can have a variety of applications, such as SERS (surface enhanced Raman spectroscopy) and metamaterials.
  • the methods of the invention allow generating metal structures with submicron resolution (e.g., a resolution less than about 300 nm, e.g., in a range of about 100 nm to about 300 nm, e.g., in a range of about 50 nm to about 200 nm).
  • the methods of the invention allow the fabrication of metal (e.g., silver) nanostructures within a polymeric matrix, where the metal nanostructures exhibit a maximum size of 100 nm or less (e.g., in a range of about 80 to about 100 nm).
  • metal (e.g., silver) structures for example, disconnected metal structures, can be generated in 3D at writing speeds greater than about 200 ⁇ /sec (micrometers (microns) per second) (e.g., up to about 400 ⁇ /sec).
  • the metal structures e.g., silver structures
  • the metal features can be generated at a writing speed (e.g., the speed at which the focal volume is scanned) in a range of about 1 to about 400 ⁇ /sec (e.g., in a range of about 1 to about 200 ⁇ /sec).
  • a method for fabricating metal structures includes providing a mixture of at least one compound (e.g., one or more monomers or one or more polymers), at least one metal precursor and at least one solvent, and applying the mixture to a surface of a substrate, where the polymer includes gelatin.
  • the applied mixture can be cured (e.g., via air-drying and/or a heat treatment), e.g., to increase the viscosity of the mixture to generate a cured mixture, e.g., a polymeric matrix in which metal precursor and/or ions associated with the metal precursor are distributed.
  • radiation e.g., radiation pulses
  • the cured mixture can include a plurality of metal ions associated with the metal precursor (e.g., an ionic form of a metal constituent of the metal precursor) and the focused radiation can cause chemical reduction of at least a portion of the metal ions within at least a portion of the location into which the radiation (e.g., radiation pulses) is focused, thereby fabricating a metalized region (structure).
  • the focused radiation can have a sufficiently high intensity within the location into which it is focused so as to undergo non-linear absorption by at least one radiation absorbing constituent of the cured mixture, thereby mediating the reduction of at least a portion of the metal ions in that location.
  • the applied radiation has a wavelength to which the cured mixture (e.g., the polymer layer) is substantially transparent.
  • the cured mixture can exhibit no allowed electronic transitions at the energy of the applied radiation.
  • the radiation wavelength can be in a range from visible to near infrared (e.g., in a range of about 500 nm to about 1500 nm).
  • the curing of the mixture (e.g., by heating the mixture at an elevated temperature, such as a temperature in a range of about 40 °C to about 120 °C) can cause a portion of the metal precursor to form metal nanoparticles, which can function as seed particles for generating metalized structures in the subsequent step of irradiating the cured mixture.
  • the nanoparticles can have a size in each dimension (e.g., in each of x, y, and z Cartesian dimensions) that is in a range of about 2 nm to about 20 nm, and preferably in a range of about 2 nm to about 10 nm, e.g., in a range of about 5 nm to about 10 nm.
  • seed metallic nanoparticles can be added to the mixture to facilitate the formation of the metalized structures in the subsequent steps.
  • the mixture in addition to the metal precursor (e.g., a metal salt), can include metal nanoparticles (e.g., nanoparticles of gold or silver), which can function as seed particles for formation of metalized structures.
  • these seed metal nanoparticles can have a size in each dimension that is in a range of about 2 nm to about 100 nm, and preferably in a range of about 2 nm to about 20 nm, e.g., in a range of about 5 nm to about 20 nm.
  • the focused radiation can have a sufficiently high intensity within at least a portion of the location onto which it is focused so as to be absorbed via non-linear processes (e.g., multi-photon absorption) by one or more constituents (moieties) of the cured mixture, which can be a polymeric layer, thereby mediating the chemical reduction of the metal precursor.
  • constituents (moieties) can be residual solvent, or nanoparticles, or polymer in the mixture, etc.
  • the radiation intensity and/or fluence that can mediate the reduction of metal ions associated with the metal precursor can depend on a variety of factors, such as, the type of the polymer, whether any degradation of the polymeric film has occurred, e.g., due to exposure to ambient light, the presence of seeding nanoparticles, etc.
  • the radiation fluence can be as small as about 20 J/m 2 (e.g., about 20.7 J/m 2 or greater) and/or the pulse energy can be as small as about 0.07 nJ.
  • the radiation intensity at the focal volume associated with radiation pulses applied to the cured mixture can be in a range of about 4xl0 12 W/m 2 to about 2xl0 15 W/m 2 .
  • the radiation fluence can be as small as about 0.1 kJ/m 2 (e.g., about 0.6 kJ/m 2 or greater) and/or the pulse energy can be as small as about 0.5 nJ.
  • the radiation intensity at the focal volume associated with a radiation pulse applied to the cured mixture can be in a range of about 1.2xl0 16 W/m 2 to about 3.6xl0 17 W/m 2 .
  • the polymeric layer generated by the curing step can be in the form of a polymeric film having a thickness, e.g., in a range of about 0.5 micrometers (microns) to about 250 micrometers, in a range of about 0.5 micrometers (microns) to about 50 micrometers, in a range of about 0.5 micrometers to about 20 micrometers, in a range of about 1 micrometer to about 250 microns, or in a range of about 100 micrometers to about 160 micrometers.
  • the polymeric layer generated by the curing step can have a thickness in a range of about 250 micrometers to about 3 millimeters.
  • the step of curing the applied mixture can be performed in a variety of ways.
  • the applied mixture can be air-dried at room temperature, for example, or heated at an elevated temperature for a selected duration, e.g., by placing the mixture-coated substrate in an oven.
  • the applied mixture can be cured to form a polymeric matrix by exposing it to a temperature in a range of about 20 °C to about 50 °C (e.g., in a range of about 20 °C to about 30 °C, for a duration in a range of about 30 minutes to about 24 hours).
  • the applied mixture can be cured to form a polymeric matrix, for example, by exposing it to a temperature in a range of about 40 °C to about 150 °C, e.g., in a range of about 50 °C to about 100 °C, for a duration in a range of about 30 minutes to about 24 hours.
  • the applied mixture can be cured at these temperatures to form a more viscous or solid polymeric matrix.
  • one or more locations of the cured mixture can be exposed to radiation (e.g., radiation pulses) to cause chemical reduction of metal ions associated with the metal precursor in at least a portion of those locations.
  • radiation e.g., radiation pulses
  • the applied radiation comprises a plurality of radiation pulses having a pulsewidth, e.g., in a range of about 5 femtoseconds (fs) to about 100 nanoseconds (ns)
  • the radiation pulses can have a pulsewidth in a range of about 10 fs to about 1 picosecond (ps), e.g., in a range of about 10 fs to about 500 fs.
  • the pulses applied to the polymeric matrix can have an energy in a range of about 0.07 nanojoules (nJ) to about 40 nJ (e.g., in a range of about 0.1 nJ to about 10 nJ).
  • the pulses applied to the polymeric matrix can have an energy in a range of about 0.2 nJ to about 40 nJ (e.g., in a range of about 0.4 nJ to about 15 nJ).
  • the number of radiation pulses applied to the location into which the pulses are focused can be in a range of 1 to about 1 million (e.g., in a range of 1 to about 200,000, in range of 1 to about 100,000, in a range of 1 to about 60,000, in a range of 1 to about 10,000, in a range of 1 to about 1000, in a range of 1 to about 500, in a range of about 10 to about 50,000, or in a range from about 3,000 to about 20,000).
  • the radiation can be focused into the cured mixture (e.g., a polymeric layer) with a numerical aperture in a range of about 0.4 to about 1.5, e.g., 0.8.
  • the radiation can have a wavelength (e.g., a central wavelength when the radiation is in the form of pulses) in a range of about 500 nanometers
  • the central wavelength can be in a range of about 500 nm to about 2000 nm, or in a range of about 500 microns to about 1500 microns.
  • polymers can be utilized.
  • the polymer can be, without limitation, gelatin, polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinylcarbazole (PVK),
  • PAA polyacrylic acid
  • PVP polyvinyl pyrrolidone
  • PVA polyvinyl alcohol
  • PVK polyvinylcarbazole
  • PMMA polymethylmethacrylate
  • PS polystyrene
  • the metal precursor can be a metal salt, e.g., nitrate, halide or chlorate salts of metals.
  • a variety of silver salts such as AgNC ⁇ , AgCH 3 COO, AgC10 4 , AgBF 4 , among others, can be utilized to fabricate silver structures.
  • the silver structures are in the form of crystalline silver.
  • HAuCl 4 can be employed to fabricate gold structures.
  • solvents can be employed.
  • suitable solvents include, without limitation, water (e.g., distilled water), an alcohol, e.g., ethanol, and ethylene glycol.
  • the cured mixture can be substantially free of a constituent that can cause reduction of the metal ions associated with metal precursor in absence of the applied radiation.
  • a mixture of a metal precursor, a polymer and a solvent is employed to generate a metal-doped polymeric matrix, e.g., by curing the mixture as discussed above, where the solvent is slow in reducing the metal ions in the metal-doped matrix in regions of the polymeric matrix outside the focal volumes of the applied radiation pulses or is incapable of reducing the metal ions in those regions.
  • the solvent does not cause any significant reduction of the metal ions associated with the metal precursor (e.g., a reduction of at least about 50% of the ions present in the metal-doped polymer) in absence of the applied radiation even after passage of a few days, or a few weeks, or a few months.
  • the solvent is free of any alcohol.
  • the mixture can include a metal precursor (e.g., Ag Os), a polymer (e.g., PVP, gelatin, PAA), and water, while lacking any alcohol constituent.
  • the polymer can be selected so as to modulate the reducing action of the solvent on the metal ions associated with the metal precursor.
  • the polymer can inhibit the growth of metal particles generated via reduction of the metal ions by the solvent in the metal-doped polymer beyond a certain limit.
  • PVP can be employed to modulate the reducing action of the solvent, e.g., water.
  • gelatin can be employed to modulate the reducing action of the solvent, e.g., water.
  • the metalized structures can be in the form of two- dimensional or three-dimensional metalized regions that are separated from one another by unmetalized regions (the unmetalized regions refer to those regions in which the metal precursor and/or ions associated with the metal precursor have not undergone a chemical reduction reaction) of the cured mixture, which can be a polymeric layer.
  • the metallic structures can form interconnected two-dimensional or three-dimensional metal structures.
  • the methods of the invention can be employed to fabricate disconnected three-dimensional metal structures (regions) within a polymeric matrix, where each metal structure has a size in at least one dimension (and in some cases, in each of three dimensions, e.g., x, y, and z Cartesian dimensions) that is less than about 5 micrometers, e.g., in a range of about 100 nm to about 5 micrometers (e.g., in a range of about 150 nm to about 3 micrometers), or in a range of about 300 nm to about 3 micrometers.
  • the methods of the invention can be employed to fabricate disconnected three-dimensional metal structures (regions) within a polymeric matrix, where each metal structure has a size in at least one dimension (and in some cases, in each of three dimensions, e.g., x, y, and z Cartesian dimensions) that is less than about 5 micrometers, e.g., in a range of about 50 nm to about 5 micrometers (e.g., in a range of about 50 nm to about 500 nanometers), or in a range of about 100 nm to about 2 micrometers.
  • the metalized structures are formed within the cured mixture (e.g., a polymeric layer) according to a predefined pattern (e.g., a two-dimensional or a three-dimensional pattern).
  • the substrate on which the polymeric layer is disposed can be mounted on a translation platform that is movable in three dimensions in response to control signals from a controller.
  • the controller can move the platform and consequently the substrate, and can further control the application of the radiation to the cured mixture (e.g., a polymeric layer (film)) so as to ensure that selected locations of the polymeric layer are exposed to the radiation. For example, these locations can be distributed within a two-dimensional or a three-dimensional extent of the polymeric layer.
  • the substrate can be fixed and the radiation can be scanned in two or three dimensions to form a desired pattern.
  • the metal structures can have at least one of their dimensions extended to be as large as 100 micrometers, or 1 millimeter or larger by relative motion of the radiation and the cured mixture (e.g., a polymeric layer), e.g., by
  • a method of generating metal structures comprises generating a polymeric matrix having a plurality of metal ions distributed therein, and focusing at least one radiation pulse (e.g., a laser pulse) onto at least one location of the polymeric matrix so as to cause at least a portion of the metal ions within said location to form one or more metal structures.
  • the radiation pulse(s) can cause reduction of at least a portion of the metal ions so as to form said one or more metal structures.
  • the radiation pulse(s) can be non-linearly absorbed by at least one constituent of the polymeric matrix, thereby mediating the reduction of the metal ions.
  • the metal-doped polymeric matrix can be formed by generating a mixture of a polymer, a metal precursor and a solvent, and curing the mixture, e.g., via heating the mixture.
  • the mixture can be applied to a substrate, such as a glass substrate, and then cured to form a metal-doped polymeric layer.
  • a variety of polymers, metal precursors, and solvents, such as those discussed above, can be employed to form the mixture.
  • Some examples of polymers include, without limitation, gelatin, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl carbazole, polymethylmethacrylate, and polystyrene.
  • the polymeric matrix is free of a constituent capable of reducing said metal ions in absence of the radiation pulses.
  • the polymeric matrix can be formed of PVP and can be free of an alcohol constituent.
  • the radiation pulses can have a pulsewidth in a range of about 5 fs to about 100 ns and a fluence in a range of about 0.5 J/m 2 to about 500 J/m 2 in locations into which the pulses are focused.
  • the radiation pulses can have a central wavelength to which polymeric matrix is substantially transparent in absence of non-linear absorption.
  • the polymeric matrix can be formed of gelatin and can be free of an alcohol constituent.
  • the radiation pulses can have a pulsewidth in a range of about 5 fs to about 1 ns and a fluence in a range of about 0.1 kJ/m 2 to about 15 kJ/m 2 in locations into which the pulses are focused.
  • the radiation pulses can have a central wavelength to which polymeric matrix is substantially transparent in absence of non-linear absorption.
  • a method of generating metal structures comprises applying an aqueous solution of a polymer and a metal precursor to a substrate surface, curing the applied solution so as to generate a polymeric matrix, and focusing one or more pulses of radiation into at least one three-dimensional region of the polymeric matrix so as to metalize at least a portion of said three-dimensional region.
  • the metallization can occur via reduction of metal ions associated with the metal precursor, where the reduction can be mediated via non-linear absorption of the radiation by one or more constituents of the polymeric matrix.
  • the aqueous solution is free of any alcohol.
  • the radiation pulses can have a pulsewidth in a range of about 5 fs to about 100 ns (e.g., in a range of about 5 fs to about 1 ns, in a range of about 5 fs to about 1 ps), and a pulse energy in a range of about 0.05 nJ to about 40 nJ (e.g., in a range of about 0.1 nJ to about 40 nJ).
  • the aqueous solution can be formed by dissolving PVP in water.
  • the aqueous solution can be formed by dissolving gelatin in water. In various embodiments, such an aqueous solution, does not include any alcohol.
  • a method of generating metal structures comprises generating a polymeric matrix over a substrate surface, said polymeric matrix having a metal precursor distributed therein, and focusing radiation onto at least one location of the polymeric matrix so as to cause chemical reduction of at least a portion of ions associated with the metal precursor within at least a portion of said location, thereby generating a metalized structure.
  • the focused radiation can have a sufficiently high intensity at said location so as to undergo non-linear absorption by at least one radiation- absorbing constituent of said polymeric matrix, thereby mediating the chemical reduction of the metal ions.
  • the radiation pulses employed to cause selective reduction of the metal ions in the polymeric matrix can have a pulsewidth in a range of about 5 femtoseconds to about 100 nanoseconds, e.g., in a range of about 5 femtoseconds to about 1 picosecond, or in a range of about 5 femtoseconds to about 500 femtoseconds; an energy in a range of about 0.05 nJ to about 40 nJ, e.g., in a range of about 0.1 nJ to about 20 nJ, or in a range of about 0.1 nJ to about 10 nJ.
  • the radiation pulses can be focused into a focal volume within the polymeric matrix such that the radiation fluence within at least a portion of the focal volume can be in a range of about 0.5 J/m 2 to about 500 J/m 2 , e.g., in a range of about 1 J/m 2 to about 100 J/m 2 , or in a range of about 10 to about 100 J/m 2 .
  • the radiation pulses employed to cause selective reduction of the metal ions in the polymeric matrix can have a pulsewidth in a range of about 5 femtoseconds to about 1 nanosecond, e.g., in a range of about 10 femtoseconds to about 1 picosecond, or in a range of about 10 femtoseconds to about 100 femtoseconds; an energy in a range of about 0.1 nJ to about 40 nJ, e.g., in a range of about 0.4 nJ to about 10 nJ, or in a range of about 0.5 nJ to about 5 nJ.
  • the radiation pulses can be focused into a focal volume within the polymeric matrix such that the radiation fluence within at least a portion of the focal volume can be in a range of about 0.1 kJ/m 2 to about 15 kJ/m 2 , e.g., in a range of about 0.5 kJ/m 2 to about 20 kJ/m 2 , or in a range of about 0.6 to about 15 kJ/m 2 .
  • a metalized substrate in another aspect, includes a polymeric matrix (s-g a flexible polymeric matrix) and a plurality of metalized structures that are distributed, e.g., according to a predefined two-dimensional or three-dimensional pattern, within the matrix.
  • the metalized structures have a maximum size of 100 nm or less.
  • the metalized substrate can comprise a gelatin matrix that can be stretched under a tensile load without breaking.
  • at least one dimension of the metalized substrate can be increased by
  • FIGURE 1 illustrates a flowchart of one exemplary method of generating metallic structures according to various aspects of the applicants' teachings
  • FIGURE 2A is a schematic view of a substrate with a polymeric mixture disposed on a surface thereof in accordance with various aspects of the applicants' teachings;
  • FIGURE 2B is a schematic view of the substrate and polymeric mixture of FIGURE 2A after curing of the mixture, e.g., via a heat treatment, to form a polymeric layer;
  • FIGURE 2C is a schematic view of radiation being applied to selected locations of the polymeric layer shown in FIGURE 2B;
  • FIGURE 3 is a schematic view of a polymeric layer of FIGURE 2B having a plurality of metallic structures distributed therein;
  • FIGURE 4 is a schematic view of a focal volume of a radiation beam focused into the polymeric layer in accordance with various aspects of the applicants' teachings;
  • FIGURE 5 is a perspective schematic view of a polymeric film with a network of interconnected metallic structures formed therein disposed on a substrate in accordance with various aspects of the applicants' teachings;
  • FIGURE 6A is a perspective schematic view of a stand-alone metalized polymeric substrate fabricated in accordance with various aspects of the applicants' teachings;
  • FIGURE 6B is a perspective schematic view of a stand-alone metalized polymeric substrate fabricated in accordance with various aspects of the applicants' teachings, which exhibits mechanical flexibility;
  • FIGURE 7 is a schematic view of one exemplary system for performing metallization methods according to various aspects of the applicants' teachings
  • FIGURE 8 schematically depicts an exemplary system utilized for generating silver structures in a metal-doped polymeric matrix in accordance with an exemplary embodiment of the applicants' teachings
  • FIG. 9 is an SEM image of an array of fabricated silver nanostructures in accordance with an embodiment of the present teachings. The inset shows a closeup view of a single silver nanostructure
  • FIGs. 10A and 10B are, respectively, an in-situ optical image of a square array and a hexagonal array of silver nanostructures that alternate along the z-direction to form a 10- layered 3D pattern of silver within a gelatin matrix in accordance with an embodiment of the present teachings;
  • FIG. IOC is a 3D computer generated image of the silver arrays depicted in FIGs. 10A and 10B;
  • FIG. 1 1 A is an SEM image of a single silver nanostructure fabricated in accordance with an embodiment of the present teachings
  • FIG. 1 IB is an EDS map of elemental silver for the single silver nanostructure shown in FIG. 11 A;
  • FIG. 1 1C is a high resolution energy dispersion x-ray spectroscopy image of the silver nanostructure
  • FIG. 1 ID is a high resolution energy dispersion x-ray spectroscopy image of a neighboring area of the silver nanostructure
  • FIG. 12A shows a transmittance spectrum of an unpatterned gelatin sample formed in accordance with an embodiment of the present teachings, spanning the ultraviolet to terahertz wavelengths of the electromagnetic spectrum (between about 200 nm to about 1500 nm);
  • FIG. 12B shows a high transmission window seen in the transmittance spectrum of FIG. 12A, which spans from the visible to near-IR;
  • FIG. 12C shows another high transmission window seen in the transmittance spectrum of FIG. 12A, which in the terahertz range;
  • FIGURE 13A is an optical microscope image of a polymeric film with metalized regions formed therein produced in accordance with various aspects of the applicants' teachings;
  • FIGURE 13B is an optical microscope image of the same polymeric film as that shown in FIGURE 13 A, but taken with a focal length different than the focal length associated with the image of FIGURE 9A;
  • FIGURE 14 is an energy-dispersive X-ray spectroscopy spectrum of a substrate on which a metalized polymeric layer formed according to various aspects of the applicants' teachings is disposed;
  • FIGURES 15A-15C are 3D renderings of a stack of sequential 2D in-situ bright- field optical images of silver structures formed according to various aspects of the applicants' teachings;
  • FIGURE 16A is a scanning electron microscope image of an array of silver dots fabricated on a glass substrate according to various aspects of the applicants' teachings;
  • FIGURE 16B is a high resolution energy dispersion x-ray spectroscopy image of the array of silver dots shown in FIGURE 16A;
  • FIGURE 16C is a close-up image taken head-on of an individual silver dot formed according to various aspects of the applicants' teachings
  • FIGURE 16D is a close-up image taken at a 61° tilt angle of an individual silver dot formed according to various aspects of the applicants' teachings;
  • FIGURE 17 is a plot of ultraviolet and visible micro-absorption and scattering spectroscopy data showing a silver surface plasmon peak centered around 425 nm;
  • FIGURE 18 is a transmission electron microscopy image of silver nanoparticles formed according to the teachings of the invention.
  • FIGURES 19A and 19B are optical microscopy images at different focal lengths of a sample formed according to various aspects of the applicants' teachings
  • FIGURE 20 is a scanning electron microscope image of an array of silver dots fabricated on a glass substrate according to various aspects of the applicants' teachings; and FIGURES 21(A)- 21(E) depict a scanning electron microscope image of a single silver dot fabricated on a glass substrate according to various aspects of the applicants' teachings and high resolution EDS maps showing the elemental composition of carbon, oxygen, silicon, and silver, respectively.
  • the present disclosure relates generally to methods and systems for generating metalized structures (regions) in a substrate, e.g., a polymeric substrate, and to such substrates having a plurality of metalized structures (regions) distributed therein.
  • a substrate e.g., a polymeric substrate
  • short laser pulses are focused into selected locations within a polymeric substrate having a plurality of metal ions distributed therein so as to cause chemical reduction of at least a portion of the metal ions, thereby generating metalized regions in at least a portion of those locations.
  • the polymeric substrate can be substantially transparent to the wavelength of the applied radiation.
  • the focusing of the radiation into the selected locations can result in a radiation intensity within at least a portion of those locations, e.g., at the focal volume, that is sufficiently high such that the radiation is absorbed via non-linear processes, e.g., via multi-photon absorption, by one or more constituent(s) of the polymeric substrate.
  • non-linear absorption of the radiation can in turn facilitate the chemical reduction of the metal ions, e.g., by facilitating charge transfer from the radiation-absorbing constituent to the metal ions.
  • the metalized structures can be separated from one another by unmetalized portions of the polymeric substrate. In other words, in some cases, the metalized structures can be distributed within the polymeric material as disconnected three-dimensional metalized regions. In other cases, the metal structures can form interconnected metalized regions within the polymeric material.
  • compound is used herein consistent with its common meaning in the art to refer to substance composed of atoms or ions of two or more elements in chemical combination.
  • the atoms or ions can be united by covalent, and/or ionic bonds, or van-der- waals forces.
  • the term "monomer” is used herein consistent with its common meaning in the art to refer to a molecule or compound, usually containing carbon and of relatively low molecule weight, that is capable of conversion to polymers, synthetic resins, or elastomers by combination with itself or other similar molecules or compounds.
  • polymer is used herein consistent with its common meaning in the art to refer to a macromolecule formed by the chemical union of five or more repeating chemical units, e.g., by repeating monomers.
  • nanoparticle is used herein to refer to a material structure whose size in any dimension (e.g., x, y, and z Cartesian dimensions) is less than about 1 micrometer
  • nanoparticle (micron), e.g., less than about 500 nm, or less than about 100 nm, e.g., in a range of about 2 nm to about 20 nm.
  • a nanoparticle can have a variety of geometrical shapes, e.g., spherical, ellipsoidal, etc.
  • the term “nanoparticles” is used as the plural of the term “nanoparticle.”
  • chemical reduction and “reduction” are used herein consistent with the use of these terms in the art to refer to a chemical reaction in which a chemical species decreases its oxidation number, typically by gaining one or more electrons.
  • photoreduction refers to a chemical reduction that is mediated by photons.
  • substantially transparent is intended to mean that the linear absorption coefficient of the material for a radiation wavelength is less than about 25%, and preferably less than about 5%. In other words, radiation having that wavelength can penetrate into the material without much absorption by the material. As discussed below, such radiation can be used, e.g., for fabricating three- dimensional metallic patterns
  • short radiation pulses refers to pulses of electromagnetic radiation having a temporal duration in a range of about 5 femtoseconds (fs) to about a few hundred nanoseconds (ns) (e.g., 500 ns).
  • focal volume is used herein consistent with its common meaning in the art to refer to a volume extended axially about a focal plane, a plane at which a focused radiation beam exhibits a minimum beam waist and a maximum intensity, up to a plane at which the beam exhibits a beam waist that is larger than the minimum beam waist by a factor of about V2.
  • the contact of the metal precursor with the solvent results in generating ionic species associated with the constituents of the metal precursor, including metal ions, where at least a portion of the metal ions remains in the cured mixture to form, e.g., a polymer matrix doped with a plurality of metal ions.
  • a mixture of a polymer, a metal precursor, and a solvent is applied to a surface 12 of a substrate 14 (step A).
  • the mixture can be in the form of a solution or a colloid.
  • the solvent can be water and the mixture can be in the form of an aqueous solution.
  • a variety of techniques known in the art can be employed to apply the mixture to the substrate surface.
  • the mixture can be applied to the substrate surface by pouring the mixture onto the surface or by dipping the substrate into the mixture.
  • spin-casting can be employed to obtain a thin layer of the mixture over the substrate surface.
  • the substrate surface is treated, e.g., via plasma treatment and/or salinization, prior to the application of the mixture thereto.
  • the substrate surface e.g., the surface of a glass substrate
  • substrates can be employed.
  • suitable substrates include, without limitation, glass, polymer or other organics, and semiconductor substrates (e.g., silicon).
  • semiconductor substrates e.g., silicon
  • the substrate surface to which the mixture is applied is preferably flat.
  • the mixture of the polymer, the metal precursor, and the solvent is an aqueous solution formed by dissolving the polymer and the metal precursor in water.
  • the mixture can be formed by dissolving the polymer and the metal precursor in an organic solvent, such as an alcohol.
  • metal salts can be utilized as the metal precursor.
  • a variety of silver salts such as AgNC ⁇ , AgCHsCOO, AgC10 4 , AgBF 4 , among others, can be utilized to generate silver structures.
  • HAuCl 4 can be employed to generate gold structures.
  • polymers can be employed in the practice of the invention.
  • suitable polymers include, without limitation, gelatin, polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinylcarbazole (PVK), polymethylmethacrylate (PMMA), polystyrene (PS), among others.
  • PPA polyacrylic acid
  • PVP polyvinyl pyrrolidone
  • PVA polyvinyl alcohol
  • PVK polyvinylcarbazole
  • PMMA polymethylmethacrylate
  • PS polystyrene
  • solvents can be utilized to form the mixture.
  • suitable solvents include, without limitation, water (e.g., distilled water), ethanol, and ethylene glycol.
  • the choice of solvent can be based on the effect of the solvent on the metal precursor.
  • some alcohols can facilitate chemical reduction of metal ions associated with the metal precursor and hence speed up the metallization process. While in some applications, it might be desirable to utilize such alcohols as a solvent to speed up the metallization process, in other applications it might more desirable to use a solvent that does not substantially affect the chemical reduction of the precursor in absence of the applied radiation.
  • the applied mixture can then be cured, e.g., via an air-drying step and/or a heat treatment, to form a polymeric layer 16 through which the metal ions are distributed (step B).
  • exemplary mixtures containing gelatin that are applied to the substrate surface can be air-dried at room temperature for a time duration in a range of about 12 hours to about 24 hours.
  • mixtures applied to the substrate surface can be cured by heating the mixture to an elevated temperature, e.g., by placing the substrate in an oven, for a selected time.
  • the mixture can be heated to a temperature in a range of about 40 °C to about 150 °C, e.g., in a range of about 50 °C to about 100 °C, for a time duration in a range of about 30 minutes to about 2 hours.
  • the curing can cause the mixture to form a more viscous polymeric layer (e.g., a solid polymeric matrix) through which the metal ions are distributed.
  • the cured polymeric matrix 16 can be in the form of a film covering at least a portion of the substrate surface.
  • the film can exhibit a variety of thicknesses.
  • the film 16 can have a thickness in a range of about 0.5 microns to about 20 microns, e.g., 14 microns.
  • the film 16 can have a thickness in a range of about 0.5 microns to about 250 microns, e.g., about 160 microns, and even greater.
  • a film 16 containing gelatin for example, can have a thickness in a range of about 250 microns to about 3 millimeters.
  • the film 16 is shown as having a substantially uniform thickness, in other cases the film can have a non-uniform thickness. Further, in other cases, rather than forming a continuous film, the cured polymeric layer can be in the form of a plurality of separated polymeric portions disposed on the substrate surface (not shown).
  • a plurality of radiation pulses at a wavelength to which the polymeric film 16 is substantially transparent can be focused into a plurality of three-dimensional locations 18 within the polymeric film 16 to selectively cause chemical reduction of the metal ions in at least a portion of those locations (step C).
  • the reduction of the metal ions associated with the metal precursor generates metalized regions within those locations, as shown schematically by the regions 20 in FIG. 3.
  • short laser pulses can be tightly focused into a focal volume of the cured mixture (e.g., a polymeric matrix) such that multiple photons converge in time and space to collectively bridge an electronic energy gap of at least one constituent of the cured mixture to cause reduction of at least a portion of the metal ions.
  • a focal volume of the cured mixture e.g., a polymeric matrix
  • the focusing of the radiation causes the radiation intensity to be sufficiently high within at least a portion of each of the locations 18 (e.g., corresponding to the focal volume of the focused radiation) such that non-linear absorption of the radiation by one or more constituents of the polymeric film can occur.
  • non-linear absorption can include multi-photon (e.g., two-photon, three-photon, or four- photon) absorption of the radiation, e.g., at the focal volume.
  • the radiation fluence at the focal volume can be as small as about 20.7 J/m 2 , or smaller (e.g., 0.5 J/m 2 ). In some aspects, for example, the radiation fluence can be as small as about 0.1 kJ/m 2 (e.g., about 0.6 kJ/m 2 or greater).
  • the non-linear absorption of the radiation by one or more constituents of the polymeric film can mediate the chemical reduction of the metal precursor.
  • multi-photon absorption of the radiation by the solvent or a moiety of the polymeric mixture can cause electronic excitation of the solvent or that moiety into one or more excited electronic states.
  • a charge transfer between one or more of these excited electronic states and the metal precursor can cause chemical reduction of the metal precursor.
  • FIG. 4 schematically shows that, in some
  • a focused radiation beam penetrates the polymeric film, its beam waist continues to decrease until it reaches a minimum diameter (d m izie) in a focal plane (fp).
  • the intensity of the radiation within a volume (e.g., focal volume 22) surrounding the focal plane can be sufficiently high so as to lead to the non-linear absorption of the radiation in that volume, thereby resulting in the chemical reduction of the metal ions in that volume.
  • This allows selectively metalizing desired three-dimensional portions of the polymeric film.
  • the metal precursor is silver nitrate (AgNC ⁇ )
  • the reducing reaction can lead to formation of silver structures (e.g., crystalline silver regions), e.g., within the focal volume of the focused radiation.
  • the three-dimensional metalized structures can be separated from one another, i.e., they can be in the form of disconnected metalized regions 20 as shown schematically in FIG. 3.
  • the polymeric matrix can exhibit sufficient structural stability to maintain the disconnected metal structures (voxels) in place. Further, in many cases, the polymeric matrix can exhibit a high degree of chemical stability to significantly slow down sample degradation with time.
  • such metalized structures (regions) can have a size in at least one dimension, and in some cases in each of three dimensions (e.g., x, y, z Cartesian dimensions), that is less than about 2 microns, e.g., in a range of about 150 nm to about 1 micron.
  • the metalized regions can have a partial overlap with one another to collectively generate interconnected structures (e.g., by scanning a radiation beam (radiation pulses) over an extent of the polymeric film).
  • a network 24 of interconnected metalized regions can be formed by practicing the methods of the invention, as shown schematically in FIG. 5.
  • the polymeric matrix having one or more metallic structures 20 distributed therein can be removed from the underlying substrate 14 to provide a stand-alone metalized polymeric substrate 26, as shown schematically in FIG. 6A.
  • a polymeric substrate having a plurality of metallic structures distributed therein can exhibit mechanical flexibility, e.g., as shown schematically in FIG. 6B by the bent substrate 28.
  • Such mechanical flexibility can be useful in a variety of applications.
  • the polymeric matrix can exhibit elastic material properties that can increase the flexibility of the metalized polymeric substrate.
  • a metalized gelatin substrate can be configured to stretch when subject to a tensile load.
  • At least one dimension of the metalized gelatin substrate can be increased by 10% when placed under a tensile load without breaking.
  • such flexible metalized polymeric matrix can be employed to fabricate flexible biological sensors, flexible photovoltaics, flexible chemical sensors, flexible integrated optical devices, flexible metamaterials, and flexible integrated electrical devices.
  • a layer of silane can be deposited on the substrate surface to facilitate subsequent removal of the polymeric matrix from the substrate.
  • the wetting properties of the substrate can be selected such that the polymer matrix formed during the curing step separates from the substrate surface.
  • a polymeric mixture can also be used in conjunction with a substrate that does not wet with the solvent (or solution) used in the mixture.
  • a polymeric substrate e.g., a polymeric film
  • a polymeric substrate e.g., a polymeric film
  • they allow selective metallization of three-dimensional volumes (voxels) within the polymeric film.
  • the metallization occurs selectively in volume portions in which the intensity of the applied radiation is sufficiently high to result in non-linear absorption.
  • the methods of invention for fabricating metalized structures can find a variety of applications.
  • Some examples of such applications include, without limitation, metamaterials, metal materials, antennae, biological sensors, chemical sensors,
  • the methods of the invention utilize a mixture of chemical reagents that allow generating a support matrix, e.g., a polymer matrix, for the metal structures to be generated via application of the laser pulses while ensuring that reduction of the metal ions in regions of the support matrix not illuminated by the laser pulses does not occur, or at least occurs very slowly, for example, over a period of weeks, months or years.
  • a support matrix e.g., a polymer matrix
  • a nonlinear interaction inside a gelatin matrix doped with silver ions can lead to the growth of silver nanostructures embedded and fixed inside a dielectric matrix.
  • the gelatin can provide a matrix for supporting the silver nanostructures.
  • FIG. 7 schematically depicts an exemplary system 30 that can be employed to perform metallization methods according to various aspects of the present teachings.
  • the exemplary system 30 includes a translation platform 32 on which a substrate, e.g., the above substrate 14 on which the polymeric film 16 is disposed, can be mounted.
  • the translation platform 32 can be moved in three orthogonal directions (e.g., x, y, z Cartesian directions) so as to allow delivering radiation to selected portions of the polymeric film.
  • the system 30 further includes a radiation source 34, which in this implementation can be a laser.
  • the radiation source can be an unamplified Ti: Sapphire laser system that can generate laser pulses with a pulse width, e.g., in a range of about 50 fs to about 800 fs, a pulse energy, e.g., in a range of about 5 nJ to about 100 nJ, at a central wavelength of 800 nm.
  • the Ti: Sapphire laser system can generate laser pulses at a repetition rate in a range of about 1 MHz to about 90 MHz, e.g., 11 MHz (as discussed below, in many embodiments, a modulator is employed to apply pulses to the polymeric layer at a lower repetition rate).
  • the radiation pulses generated by the source can be attenuated (e.g., by employing a neutral density filter (not shown)) such that the energy of the pulses applied to the polymeric matrix is in a range of about 0.05 nJ to about 40 nJ, e.g., in a range of about 0.07 nJ to about 20 nJ.
  • the radiation pulses generated by the source can be attenuated such that the energy of the pulses applied to the polymeric matrix is in a range of about 0.1 nJ to about 40 nJ, e.g., in a range of about 0.5 nJ to about 15 nJ.
  • a radiation modulator 36 receives the radiation generated by the radiation source 34, e.g., the radiation pulses generated by the Ti: Sapphire laser.
  • the radiation modulator 36 can function as a shutter under the control of a controller 38 to ensure that selected locations within the polymeric film 16 are exposed to the radiation.
  • the repetition rate of the pulses leaving the modulator to be applied to the polymeric matrix can be in a range of about 1 kHz to about 1 MHz, e.g., about 500 kHz.
  • the controller 38 can move the platform 32, and consequently the substrate 14 mounted thereon based on, e.g., a set of predetermined coordinates 40 identifying a plurality of locations within the polymeric film 16. Further, the controller 38 can provide control signals to the radiation source 34 (e.g., to trigger the radiation source to generate radiation pulses - though such triggering is not always needed) and to the radiation modulator 36 to ensure that radiation is directed to the selected locations within the polymeric film 16. For example, the controller 38 can control the light modulator 36 so that each selected location would receive a desired number of radiation pulses.
  • the radiation leaving the modulator 36 is reflected by a mirror 42 (which can comprise multiple mirrors and other optical elements known in the art) to focusing optics 44, which in turn focuses the radiation onto the selected locations within the polymeric film
  • the focusing optics 44 can include one or more refractive and/or reflective elements, such as a compound objective lens, an aspheric lens, a parabolic reflector, and other suitable optical elements known in the art.
  • the focusing optics 44 provide sufficient focusing of the radiation (e.g., characterized by the numerical aperture of the focused radiation) such that the laser intensity at the selected locations (which typically encompass the focal volume of the focused radiation) is sufficiently high to cause non-linear absorption of the radiation by one or more constituents of the polymeric film 16.
  • the system can also include a microscope (not shown) for in-situ monitoring of the polymeric film during laser processing.
  • such non-linear absorption of the radiation in each location can facilitate chemical reduction of the metal precursor (e.g., by facilitating charge transfer processes) so as to form a metalized region (e.g., a region containing crystalline form of the metal) within at least a portion of that location.
  • a metalized region e.g., a region containing crystalline form of the metal
  • the selected locations can be separated from one another so as to form disjointed metalized regions (that is, metalized regions that are separated from one another by portions of the polymeric film that are not treated by the radiation).
  • the locations onto which the radiation is focused are chosen such that at least some of the metalized regions are overlapping, e.g., to form an extended structure, such as a line.
  • the methods of the invention for patterning metals at the micro- and nano-scales find a variety of applications from microelectronics to optics to biosensors, to name a few.
  • the methods of the invention allow fabricating 3D disconnected metal nanostructures in a dielectric matrix via multiphoton absorption of short laser pulses, which can find a variety of applications.
  • a solution was prepared by dissolving 0.8 g of gelatin in 4 mL of deionized water in a vial. The two components were mixed using a vortex mixer and then the sample vial was heated in a 55 °C water bath to dissolve the gelatin. This heating of the sample vial was continued until all the gelatin has fully dissolved. Next, 0.105g of AgNC>3 was added to the vial and the above mixing step was repeated until all the AgN(3 ⁇ 4 was completely dissolved. The prepared solution was drop cast onto a glass slide. Lastly, the sample was air-dried at room temperature overnight. The resulting sample included a thick gelatin film doped with silver ions on a glass substrate.
  • a Tksapphire laser centered at 795 nm with an 11-MHz repetition rate, and 50-fs pulse length was used for the radiative processing of the sample.
  • the laser fabrication setup was similar to that shown in FIG. 8.
  • the laser exposure was limited to individual voxels where the focal volume had a full-width half-max diameter of 1 ⁇ .
  • the numerical aperture (NA) of the objective was 0.8, and the working distance was 3mm.
  • Three dimensional (3D) structures were created by focusing the laser pulses inside the bulk of the gelatin matrix; layers were patterned sequentially starting from the layer closest to the substrate and moving towards the air interface. This was a single step process and did not require any further processing.
  • the feature size of the silver structures was measured to be as small as 80 nm. Further, the inspection of the processed samples showed the feasibility of fabricating 3D structures with more than 16 layers with this single step laser writing procedure.
  • Figure 9 shows a scanning electron microscopy (SEM) image of an array of silver dots, which exhibit some size variability, with the smallest structures being sub-100-nm in diameter, which is smaller than any other previously reported direct metal writing results. There are no visible domain separations in these nanoparticles, indicating a low defect structure.
  • the dots were fabricated with exposures of 79,000 pulses with 0.2 nJ per pulse and translation speeds of 10 ⁇ /s.
  • the silver structures in 3D were fabricated by irradiating layers sequentially. Since the background matrix is solid and provides mechanical support, it is possible to create silver structures that are disconnected in the z-direction.
  • FIG. 10A and 10B show two in-situ optical images taken from a 10-layer pattern of dots of two samples and FIG. IOC shows a graphic illustration of that structure.
  • the pattern includes alternating layers of silver dots arranged in square (FIG. 10A) and pseudo- hexagonal arrays (FIG. 10B). These optical images are representative of the full structure, which is shown schematically in FIG. IOC, and which can be seen in a video created from an image stack of the whole structure.
  • FIG. 1 1A shows an SEM image of one of the fabricated silver dots
  • FIG. 1 IB shows its corresponding energy dispersion spectroscopy (EDS) map
  • FIG. 1 1C shows its corresponding EDS spectrum.
  • FIG. 1 ID is a spectrum collected from an area next to the silver nanodot.
  • the spectra shown in FIG. 1 1C and FIG. 1 IB indicate that the nanodot is composed of silver and the other non-patterned areas are free of silver. Furthermore, the SEM image shows a lower surface roughness and a strong Ag signal.
  • FIG. 12A, 12B, and 12C show transmission spectra of the doped gelatin matrix previous to laser patterning over a range of 200 nm - 1500 microns ( ⁇ ).
  • the transmission spectra show two transparency windows that can allow for the possibility of creating electromagnetic metamaterial devices: one ranges from the visible to near-IR (e.g., in a range of about 500 nm to about 2000 nm) and one in the THz range (e.g., in a range of about 500 microns to 1500 microns).
  • gelatin matrix can exhibit a significantly lower amount of defects compared to other matrices, which helps slow down the sample degradation time.
  • gelatin undergoes the gelation process during the air-drying procedure during which the abundant oxygen and hydrogen in the long protein strands of gelatin form weak hydrogen bonds to generate a tangled network. Water can remain captured between these hydrophilic strands that allows gelatin to have hydro-gel like (or elastomer like) behaviors. The increased viscosity allows forming samples that are thicker than 200 ⁇ .
  • tensile measurements with an Instron tensile test machine show a stretchability of approximately 10%.
  • the Bloom test is known in the art for measuring the strength of a gel or gelatin based on a weight (e.g., in grams) that would be required by a probe (typically with a diameter of 0.5 inch) to deflect the surface of a gel by 4mm without breaking the gel.
  • Typical Bloom grades of gelatins range from about 50 to about 300.
  • a gelatin with a Bloom grade of 75 can be employed to fabricate flexible substrates according to the present teachings.
  • the gelatin-silver matrix can be fabricated over 16 layers or more, which allows for the realization of various metal dielectric composite metamaterial structures.
  • the system schematically shown in FIG. 8 was employed to selectively induce metal-ion photoreduction in the metal-doped polymer matrix.
  • An objective with a numerical aperture (NA) of 0.8 was used to focus a plurality of laser pulses from a
  • Tksapphire laser (795-nm center wavelength, 1 1-MHz repetition rate, 50-fs pulse duration) into the polymer matrix.
  • the exposure was controlled by an acousto-optic modulator.
  • a high-precision translation stage was employed to select the region that was exposed to the laser pulses.
  • aqueous polymeric solution of PVP, AgN0 3 was prepared in a vial by dissolving 0.206 grams (g) of PVP into 8 milliliters (ml) of distilled water followed by adding 0.21 g of Ag 0 3. Care was taken (via aluminum foil shielding) to prevent ambient UV light from initiating a chemical reduction reaction in the polymeric solution.
  • the polymeric solution was kept in a refrigerator for use in the subsequent stages discussed below. The refrigerator advantageously inhibits the chemical reduction of the solution.
  • a plasma-treated surface of a glass substrate was silanized with APMS (Acryloxy propyl methoxy silane).
  • APMS Acryloxy propyl methoxy silane
  • the polymeric solution was removed from the refrigerator and one milliliter of the solution was poured onto the silanized glass surface to generate a polymeric film having a thickness of about 1.5 mm.
  • the glass substrate coated with the polymeric solution was then cured (baked) by placing it in an oven and maintaining it at a temperature of about 55° C for about 2 hours.
  • the curing step causes a reduction of the thickness of the film to tens of micrometers.
  • a Ti: Sapphire laser was employed to produce laser pulses having a 50 fs pulsewidth, a central wavelength of 800 nm, and the laser pulses were focused into selected locations of the polymeric film.
  • a numerical aperture ( A) of 0.8 was employed for focusing the laser beam onto the film.
  • An acousto-optic modulator was utilized to "shutter" the laser beam on and off using software and hardware control.
  • the acousto-optic modulator was employed to control the number of laser pulses applied to the polymeric film and to control the energy deposition into the film.
  • Pulse trains composed of pulses separated by approximately 91 ns, that were 2 microseconds long and temporally separated by about 4 microseconds were applied to the polymeric film. That is, the modulator had a repetition rate of 166 kHz and a duty cycle of 2 microseconds.
  • the energy of each pulse was about 0.3 nJ and it was focused over an area of approximately 2 microns in diameter at the focal plane.
  • the AOM was used to adjust the number of pulses arriving at the polymeric film.
  • the polymeric-coated substrate was translated at a rate of 10 micrometer/second during laser exposure.
  • the depth adjustment was achieved by moving the translation stage in a direction perpendicular to the plane of the polymer film (z-direction).
  • FIGS. 13A and 13B depict optical microscope images of the film showing metalized (darker) regions.
  • the images shown in FIGS. 13A and 13B were taken with different focal lengths, illustrating disconnected metalized regions in different planes in a direction normal to the film. From the leftmost side of the pattern to the rightmost side of the pattern, the distance is about 50 micrometers in each image.
  • the feature sizes of the metallic structures are estimated to be submicron.
  • EDS Energy-dispersive X-ray spectroscopy
  • EDX Energy-dispersive X-ray spectroscopy
  • a sample is exposed to a high energy beam of charged particles (e.g., electrons or protons).
  • the incident beam can cause electronic excitation of various elements of the sample, e.g., by exciting electrons from an inner shell to create a hole in that shell.
  • An electron from an outer shell can then fill the hole and release X-ray energy equal to the energy difference between the two shells.
  • the energy of the emitted X- ray depends on the energy difference between the two shells, which is a characteristic of a particular element.
  • the energy spectrum of the emitted X-ray radiation can be analyzed to determine elemental composition of the sample.
  • the spectrometer employed was Zeiss EVO 55 Environmental SEM with EDAX EDS detector.
  • FIG. 14 shows an EDS spectrum of the above polymeric-coated substrate after its exposure to the laser pulses.
  • the polymer was washed off to perform two-dimensional (2D) analysis of the sample.
  • the Ag peak indicates that silver structures were generated within the polymeric film.
  • the Si peak is from the glass substrate.
  • the other peaks are from various trace dopants in the glass substrate.
  • the carbon peak can be from a glass dopant or a trace amount left over from the polymer.
  • a solution of Ag 0 3 , PVP and H 2 0 was coated onto a glass substrate, whose surface was silanized with Mercapto Propyl Trimethoxy Silane, through a drop casting technique and the coated substrate was baked to create a polymer matrix doped with silver ions.
  • the exemplary system shown in FIG. 8 was employed to selectively induce metal-ion photoreduction in the metal-doped polymer matrix.
  • An objective with a numerical aperture (NA) of 0.8 was used to focus a plurality of laser pulses from a Tksapphire laser (795-nm center wavelength, 1 1-MHz repetition rate, 50-fs pulse duration) into the polymer matrix. The exposure was controlled by an acousto-optic modulator.
  • a high-precision translation stage was employed to select the region that was exposed to the laser pulses. Without being limited to a particular theory, at the focus, nonlinear light-matter interactions induce metal- ion photoreduction processes in a volume smaller than the diffraction-limited focal spot, initiating silver nanoparticle growth.
  • FIGS. 15A - 15C show 3D renderings of a stack of sequential 2D in-situ bright- field optical images of such generated silver structures. The images highlight the disclosed methods allow direct-writing silver structures that are disconnected in 3D inside a polymer.
  • nanostructures is approximately two orders of magnitude faster than other 3D direct- write techniques with similar resolution.
  • a write-speed of 100 ⁇ /s can be achieved using an 1 1-MHz laser.
  • FIG. 16A shows SEM images of an array of silver dots fabricated on a glass substrate
  • FIG. 16B shows the fabricated array and its corresponding high-resolution EDS silver elemental map, confirming that the fabricated dots contain silver
  • FIG. 16C shows a close-up view of an individual silver dot head-on
  • FIG. 12D shows a close-up view of an individual silver dot at a 61° tilt angle.
  • the broad extinction spectrum indicated polydispersity of the silver nanoparticle size.
  • TEM transmission electron microscopy
  • the depicted exemplary system was employed to selectively induce metal-ion photoreduction in a metal-doped polymer matrix.
  • An objective with a numerical aperture (NA) of 0.8 was used to focus a plurality of laser pulses from a
  • Tksapphire laser (795-nm center wavelength, 1 1-MHz repetition rate, 50-fs pulse duration) into the polymer matrix.
  • the exposure was controlled by an acousto-optic modulator.
  • a high-precision translation stage was employed to select the region that was exposed to the laser pulses.
  • An aqueous polymeric solution of gelatin, AgN0 3 was prepared in a vial by dissolving 0.8 grams (g) of gelatin into 4 milliliters (ml) of heated distilled water followed by adding 0.105 g of Ag 0 3 . Care was taken (via aluminum foil shielding) to prevent ambient UV light from initiating a chemical reduction reaction in the polymeric solution.
  • the polymeric solution was removed from the refrigerator and one milliliter of the solution was poured onto the silanized glass surface to generate a polymeric film having a thickness of about 1.5 mm.
  • the glass substrate coated with the polymeric solution was then air-dried at room temperature for about a day.
  • the curing step causes a reduction of the thickness of the film to hundreds of micrometers.
  • a Ti: Sapphire laser was employed to produce laser pulses having a 50 fs pulsewidth, a central wavelength of 800 nm, and the laser pulses were focused into selected locations of the polymeric film.
  • a numerical aperture (NA) of 0.8 was employed for focusing the laser beam onto the film.
  • An acousto-optic modulator was utilized to "shutter" the laser beam on and off using software and hardware control.
  • the acousto-optic modulator was employed to control the number of laser pulses applied to the polymeric film and to control the energy deposition into the film. Pulse trains, composed of pulses separated by approximately 91 ns, that were 500 microseconds long were applied to the polymeric film.
  • the energy of each pulse was about 4 nJ and it was focused over an area of approximately 1 micron in diameter at the focal plane.
  • the polymeric-coated substrate was translated at a rate of 100 micrometer/second during laser exposure. The depth adjustment was achieved by moving the translation stage in a direction perpendicular to the plane of the polymer film (z-direction).
  • the process used to generate the silver nanostructures is approximately two orders of magnitude faster than other 3D direct- write techniques with similar resolution. For example, in the exemplary process, a write-speed of 100 ⁇ /s can be achieved using an 11-MHz laser.
  • FIGS. 19A and 19B depict optical microscope images of the film showing metalized (darker) regions in the form of an array of silver dots according to the present example.
  • the depicted array contains 10 layers of silver dots stacked on top of each other.
  • the images shown in FIGS. 19A and 19B were obtained at different focal lengths, to illustrate the disconnected metalized regions in different planes in a direction normal to the film.
  • the two focal lengths show two different layers of the array— one layer is a square lattice (as seen in FIG. 19 A) and the other is offset to approach a hexagonal lattice (as seen in FIG. 19B).
  • the spacing between dots is 2 micrometers, center to center.
  • the feature sizes of the metallic structures are estimated to be submicron.
  • EDS was employed for elemental analysis of the sample using a Zeiss EVO 55 Environmental SEM with EDAX EDS detector. Briefly, the polymer was washed off to perform two-dimensional (2D) analysis of the sample. A strong Ag peak indicated that silver structures were generated within the polymeric film. Thus, a pattern of disconnected 3D metallic structures were observed.
  • a solution of Ag 0 3 , gelatin and H 2 0 was coated onto a glass substrate, through a drop casting technique and the coated substrate was air-dried to create a polymer matrix doped with silver ions.
  • the exemplary system depicted in FIG. 8 was employed to selectively induce metal-ion photoreduction in the metal-doped polymer matrix.
  • An objective with a numerical aperture (NA) of 0.8 was used to focus a plurality of laser pulses from a Tksapphire laser (795-nm center wavelength, 1 1-MHz repetition rate, 50-fs pulse duration) into the polymer matrix. The exposure was controlled by an acousto-optic modulator.
  • a high-precision translation stage was employed to select the region that was exposed to the laser pulses.
  • the size of the resulting silver structures could be adjusted.
  • the structures can be resolved by optical imaging.
  • FIGS. 21A-21E an SEM image of a silver dot having a diameter of approximately 80 nm fabricated on a glass substrate (FIG. 21 A), and corresponding high-resolution EDS elemental maps for carbon (FIG. 2 IB), oxygen (FIG. 21C), silicon (FIG. 2 ID), and silver (FIG. 2 IE) are depicted.
  • the silver element map is in the same shape as the SEM image and indicates that silver structures were generated within the polymeric film.
  • the silicon and oxygen signals are from the glass substrate.
  • the carbon signal could be from a glass dopant or a trace amount left over from the polymer.
  • the data confirms that the fabricated dots contain silver.
  • gelatin was dissolved in H 2 O, minimizing reduction reactions outside the laser- irradiated volume.
  • the use of gelatin with H 2 O in absence of alcohol in the process for generating the silver features discussed in this example can provide both a support matrix and a controlled growth of the silver structures.
  • the omission of the alcohol solvent can significantly decrease, or eliminate, the reduction of Ag + ions in the portions of the polymer that are not exposed to laser radiation, thereby enhancing spatially selective generation of the silver structures.

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Abstract

Selon un aspect, l'invention porte sur un procédé de fabrication de structures métalliques en deux ou trois dimensions, ledit procédé comprenant l'utilisation d'un mélange constitué d'un polymère, d'un précurseur métallique et d'un solvant, ainsi que l'application du mélange sur une surface d'un substrat. Le mélange appliqué peut ensuite être durci de façon à générer une couche polymère (par exemple un film polymère) comportant des ions associés au précurseur métallique distribués à l'intérieur de celle-ci. Ensuite, un rayonnement (par exemple des impulsions de rayonnement), à une longueur d'onde à laquelle la couche polymère est sensiblement transparente, est focalisé sur au moins un emplacement de la couche polymère de façon à provoquer une réduction chimique d'ions métalliques associés au précurseur métallique à l'intérieur d'au moins une partie de cet emplacement, de façon à générer au moins une région métallisée.
PCT/US2014/014121 2013-02-01 2014-01-31 Systèmes et procédés de fabrication de structures métallisées dans une matrice de support polymère WO2014171995A1 (fr)

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CN111352335A (zh) * 2018-12-21 2020-06-30 劳力士有限公司 钟表构件的制造方法
SE1951520A1 (en) * 2019-12-20 2021-06-21 Stora Enso Oyj Method for producing a conductive pattern on a substrate
CN113005433A (zh) * 2019-12-20 2021-06-22 香港中文大学 光致材料沉积方法及相应的设备
WO2021245119A1 (fr) * 2020-06-05 2021-12-09 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Procédé de fabrication d'un dispositif électroconducteur

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Cited By (10)

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Publication number Priority date Publication date Assignee Title
CN111352335A (zh) * 2018-12-21 2020-06-30 劳力士有限公司 钟表构件的制造方法
CN111352335B (zh) * 2018-12-21 2023-10-27 劳力士有限公司 钟表构件的制造方法
SE1951520A1 (en) * 2019-12-20 2021-06-21 Stora Enso Oyj Method for producing a conductive pattern on a substrate
CN113005433A (zh) * 2019-12-20 2021-06-22 香港中文大学 光致材料沉积方法及相应的设备
EP3839628A1 (fr) * 2019-12-20 2021-06-23 The Chinese University Of Hong Kong Procédé de dépôt d'un matériau induit par photons et dispositif associé
WO2021124201A1 (fr) * 2019-12-20 2021-06-24 Stora Enso Oyj Procédé de production d'un motif conducteur sur un substrat
SE545042C2 (en) * 2019-12-20 2023-03-07 Digital Tags Finland Oy Method for producing a conductive pattern on a substrate
EP4079112A4 (fr) * 2019-12-20 2024-01-17 Digital Tags Finland Oy Procédé de production d'un motif conducteur sur un substrat
CN113005433B (zh) * 2019-12-20 2024-02-13 香港中文大学 光致材料沉积方法及相应的设备
WO2021245119A1 (fr) * 2020-06-05 2021-12-09 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Procédé de fabrication d'un dispositif électroconducteur

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