formulation

Abstract

The present invention relates to a formulation comprising at least; i) a 1st metal oxide nanoparticle; ii) a 2nd metal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1st metal oxide nanoparticle; and iii) a solvent. The formulation may exhibit at least one of properties as an advanced material or as a high-performance material. The formulation may be used in the nanotechnology process to make semiconductor device / display device application, for example semiconductor chip, or a Liquid crystal display (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot display (QLED), AR display, VR display, MR display, plasma (PDP) display, electroluminescent (ELD) display fabricated on a substrate controlled by semiconductors.

Description

[0001] Foreignfiling text P24-196

[0002] - 1 -

[0003] Formulation

[0004] The present application relates to a formulation preferably to be used for forming an optical medium comprising metal oxide nanoparticles, use of a 5 formulation, methods for preparing an optical layer, optical layers, method for preparing a formulation, method for fabricating an optical medium, an optical medium, optical device, and a display device.

[0005] Background of the Invention

[0006] Metal oxide nanoparticles have found application as modifiers as well as rigid building blocks for nanostructures made by nanoimprint lithography. [DOI: 10.1051 / epjap / 2012120166; 10.1038 / s41467-020-16136- 5]

[0007] 15 A typical nanoimprint procedure involves dispensing a metal oxide (or other type of) nanoparticle containing ink onto a substrate via, e.g., spin coating or inkjet printing and bringing the resulting thin liquid film in contact with a mold. The action of capillary forces allows the ink to fill the mold’s nanosized cavities. The following curing step causes a change in colloidal 20 stability of the nanoparticle ink through different mechanisms that result in interparticle crosslinking while the solvent can be removed by gradual diffusion and evaporation provided the mold is made from a porous material. The curing process is driven either thermally or preferentially by continuous or pulsed high intensity ultraviolet irradiation, preferentially at a wavelength of 365 nm.

[0008] The mechanisms of nanoparticle crosslinking include i) direct sintering resulting from the complete or partial breakdown of capping ligands at the nanoparticle surface that is caused by highly energetic and redox reactive 30 electron-hole pair states populated by UV absorption of the metal oxide particle core, ii) crosslinking through capping ligands that typically contain olefinic functional groups and / or, iii) chemical conversion of an added Foreignfiling text P24-196

[0009] -2 -

[0010] bonding agent to form a homogenous and amorphous inorganic material acting as a glue. The bonding agent can also comprise precursors used for metal oxide nanoparticle synthesis (US 2014072720 A2), (US 2019243237 A2). Notably, pathways ii and iii can also start from reactive excited states 5 populated through the absorption of UV light by the metal oxide nanoparticle core.

[0011] Titanium dioxide, TiCh, has found widespread use as a material for direct photocuring in the prior art, for its bandgap allows electronic absorption in the 365 nm region and the excited state lifetime matches the timescale of the chemical reactions that underly afore described three pathways toward interparticle bonding. Notably, the deposition of thin and dense films comprising TiCh in form of at least one of the known crystal morphologies was pointed out as a prerequisite for achieving effective photocuring activity 15 (US 2007267764 A2).

[0012] The use of thin titania films has been claimed for UV light driven self- and pre-cleaning of substrate or mold surfaces, with TiCh acting as an antisticking layer in the latter case (US 2010109205 A2).

[0013] 20

[0014] TiO2 films have been deposited via gas phase deposition and sol-gel approaches that require an elevated temperature curing step for conversion into anatase (500°C) or rutile (700°C) forms (US 2015322286 A2). Another remarkable approach uses commercial colloids of crystalline, surface modified TiCh nanoparticles as building blocks for direct UV nanoimprinting of several types of meta-surfaces (US 2019243237 A2).

[0015] While the latter strategy may be generalized to any nanomaterial showing electronic absorption at 365 nm and effective excited state reactivity, 30 photocorrosion to adjacent layers of organic material is a severe downside that can cause device failure. This shortcoming has been overcome by means of surface modification of high band gap metal oxide, e.g., ZrCh, Foreignfiling text P24-196

[0016] - 3 -

[0017] nanoparticles with bonding / coupling agents comprising olefinic or other types of organic functional groups that crosslink effectively in the presence of radicals generated from exposure to UV light (LIS2013078796 A2).

[0018] 5 Patent Literature

[0019] 1. US 2014072720 A2

[0020] 2. US 2019243237 A2

[0021] 3. US 2007267764 A2

[0022] 4. US 2010109205 A2

[0023] 5. US 2015322286 A2

[0024] 6. US 2019243237 A2

[0025] 7. US2013078796 A2

[0026] Non-Patent Literature

[0027] 15 8. DOI: 10.1051 / epjap / 2012120166; 10.1038 / s41467-020-16136-5

[0028] Summary of the invention

[0029] The inventors newly have found that there are still one or more of considerable problems for which improvement is desired, as listed below: 20 providing a new formulation to provide reduced or no photocorrosion with keeping good UV photocuring properties, preferably at around 365nm light wavelength of UV light;

[0030] preventing aggregation of 1stand / or 2ndmetal oxide nanoparticle(s) in the formulation, allow processing in form of colloids in the formulation, in an organic solvent, polymer matrix material and / or polymerizable organic monomer(s); effectively detaching I removing capping ligand(s) from the surface of said1stand / or 2ndmetal oxide nanoparticle(s) by UV photocuring or decomposed by UV photocuring, preferably at around 365nm light wavelength of UV light photocuring; providing a suitable ink formulation for 30 UV-NIL process, without or less causing aggregation of the 1stand the 2ndmetal oxide nanoparticles, with keeping good UV photocuring properties, Foreignfiling text P24-196

[0031] - 4 -

[0032] leading less or no UV photocorrosion problems namely at 365nm light wavelength.

[0033] The inventors aimed to solve one or more of the above-mentioned

[0034] 5 problems.

[0035] Then, the present inventors have surprisingly found that one or more of the above-described technical problems can be solved by the features as defined in the claims.

[0036] Namely, it is found a new formulation comprising at least, essentially consisting of or consisting of;

[0037] i) a 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified metal oxide nanoparticle or colloidally stable metal oxide nanoparticle;

[0038] 15 ii) a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified or colloidally stable metal oxide nanoparticle; and

[0039] iii) a solvent;

[0040] 20 - wherein said 1stmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 12 elements, group 14 elements of the periodic table, preferably said group 4 element is Ti, said group 12 element is Zn, said group 14 element is Sn; and

[0041] - said 2ndmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 5 elements of the periodic table. Preferably said group 4 element is Zr or Hf, said group 5 element is Nb or Ta.

[0042] Preferably said formulation to be used for forming an optical medium 30 containing metal oxide nanoparticles. Foreignfiling text P24-196

[0043] - 5 -

[0044] In another aspect, the invention further relates to a new formulation comprising at least, essentially consisting of or consisting of;

[0045] i) a 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified metal oxide nanoparticle or colloidally stable metal oxide 5 nanoparticle;

[0046] ii) a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified or colloidally stable metal oxide nanoparticle; and

[0047] iii) a solvent;

[0048] - wherein the photocuring at 365nm wavelength of light effectively causes aggregation and solidification of said 1stmetal oxide nanoparticle whereas photocuring is ineffective for said 2ndmetal oxide nanoparticle, which still may be removed by a solvent rinse or gentle rubbing.

[0049] 15 In other words, the resulting film is not mechanically persistent after photocuring.

[0050] In another aspect, the invention also relates to use of the formulation of any one of preceding claims for forming an optical medium comprising metal 20 oxide nanoparticles, preferably for fabricating optical grating structures of an optical waveguide by nanoimprint lithography, preferably by UV nanoimprint lithography (UV-NIL), or thermal nanoimprint lithography (TNIL) or by a combination of UV-NIL and TNIL.

[0051] In another aspect, the invention relates to a method for preparing the formulation of the present invention comprising at least, essentially consisting of or consisting of, following step (A):

[0052] (A) mixing at least a 1stmetal oxide nanoparticle,

[0053] a 2ndmetal oxide nanoparticle that is a different type of metal oxide

[0054] 30 nanoparticle to said 1stmetal oxide nanoparticle, preferably said 1stand 2ndmetal oxide nanoparticles are each independently selected from a surface- modified Foreignfiling text P24-196

[0055] - 6 -

[0056] or colloidally stable metal oxide nanoparticle, and

[0057] iii) a solvent;

[0058] - wherein said a 1stmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic 5 table, group 12 elements, group 14 elements of the periodic table, preferably said group 4 element is Ti, said group 12 element is Zn, said group 14 element is Sn; and

[0059] - said a 2ndmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 5 elements of the periodic table. Preferably said group 4 element is Zr or Hf, said group 5 element is Nb or Ta.

[0060] In another aspect, the invention relates to a method for preparing the formulation of the present invention comprising at least, essentially

[0061] 15 consisting of or consisting of, following step (A):

[0062] (A) mixing at least a 1stmetal oxide nanoparticle,

[0063] a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said 1stand 2ndmetal oxide nanoparticles are each independently selected from a surface- 20 modified

[0064] or colloidally stable metal oxide nanoparticle, and

[0065] iii) a solvent;

[0066] - wherein the photocuring at 365nm wavelength of light effectively causes aggregation and solidification of said 1stmetal oxide nanoparticle whereas photocuring is ineffective for said 2ndmetal oxide nanoparticle, which still may be removed by a solvent rinse or gentle rubbing. .

[0067] In other words, the resulting film is not mechanically persistent after photocuring.

[0068] 30 In another aspect, the invention furthermore relates to a method for preparing an optical medium comprising metal oxide nanoparticles, preferably for fabricating optical grating structures of an optical waveguide Foreignfiling text P24-196

[0069] - 7 -

[0070] by nanoimprint lithography; comprising, essentially consisting of or consisting of, the following steps (a) to (d), preferably the steps (a) to (d) are executed in this order:

[0071] (a) providing the formulation of any one of claims 1 to 11 onto a surface of 5 a substrate to form a curable composite, preferably by wet deposition process, more preferably by spin-coating or ink-jetting, even more preferably by ink-jetting; and

[0072] (b) pressing a mold against said curable composite formed on the substrate;

[0073] (c) irradiating the curable composite with UV light, preferably at around 365nm to form a cured composite; and

[0074] (d) optionally applying a thermal treatment to remove any organic component.

[0075] 15 In another aspect, the invention furthermore relates to an optical layer obtained by providing the formulation of the present invention, preferably said optical layer to be used for nanoimprint lithography, more preferably to be used for direct UV nanoimprint lithography, wherein the thickness of the optical layer is in the range from 1 to 900nm, preferably from 3 to 600nm, 20 more preferably 5 to 500nm, very preferably 7 to 400nm.

[0076] In another aspect, the invention furthermore relates to an optical device comprising one or more of optical mediums made by the method of the present invention.

[0077] In another aspect, the invention furthermore relates to a display device comprising at least one functional medium configured to direct and modulate a light or configured to emit light; and the optical medium of the present invention, or the optical device of the present invention.

[0078] 30

[0079] Technical effects of the invention

[0080] The present invention may provide one or more of following effects; Foreignfiling text P24-196

[0081] - 8 -

[0082] providing a new formulation to exhibit reduced or no photocorrosion induced by the deposited optical layer while keeping good UV photocuring properties of said layer, preferably by irradiation at around 365 nm.; preventing aggregation of 1stand / or 2ndmetal oxide nanoparticle(s) in the 5 formulation, allow processing in form of transparent colloids in the formulation, in an organic solvent, polymer matrix material and / or polymerizable organic monomer(s); effectively detach I remove any capping ligand(s) from the surface of said1stand / or 2ndmetal oxide nanoparticle(s) by UV photocuring or UV induced decomposition, preferably at around 365nm light wavelength of UV light photocuring; effectively change the colloidal stability of said1stand / or 2ndmetal oxide nanoparticle(s) by UV photocuring, preferably at around 365nm light wavelength of UV light photocuring; providing a suitable ink formulation for UV-NIL process, without or less causing aggregation of the 1stand the 2ndmetal oxide 15 nanoparticles, with keeping good UV photocuring properties, leading less or no UV photocorrosion problems namely at 365nm light wavelength.

[0083] Brief description of the figures

[0084] Figure 1: SEM image of imprints in material NIL1 (20.000x magnification) 20 Figure 2: SEM image of imprints in material NIL1 (50.000x magnification) Figure 3: SEM image of imprints in material NIL2 (20.000x magnification) Figure 4: SEM image of imprints in material NIL2 (50.000x magnification)

[0085] Definition of the terms

[0086] In the context of the present invention, the term “ligand” as used herein, refers to an ion or molecule attached to a metal atom by

[0087] coordinate bonding.

[0088] The term “surfactant” as used herein, refers to an additive that reduces the 30 surface tension of a given formulation. Foreignfiling text P24-196

[0089] - 9 -

[0090] The term “wetting and dispersion agent” as used herein, refers to an additive that increases the spreading and filling properties of a given formulation. In this way, the tendency of the molecules to adhere to each other is reduced.

[0091] 5

[0092] The term “adhesion promoter” as used herein, refers to an additive that increases the adhesion of a given formulation.

[0093] The term “optical layer” as used herein, refers to a layer of an intermediate. Nanostructure may be preferably formed by pressing a mold onto said layer as the method of the present invention.

[0094] The term “optical medium” is a nanostructure or nanostructures including nanosized optical gratings, or any other patterned or random nano-sized 15 uneven structures fabricated on a substrate, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. In other words, optical medium of the present invention may be a nanostructure or nanostructures of an optical device of the present invention and it is a part of an optical device of the present invention.

[0095] 20

[0096] The term “optical device” as used herein, relates to a device containing one or more optical components for forming a light beam including, but not limited to, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. Preferred optical device in the context of the present invention is a waveguide for augmented reality (AR) device, for virtual reality (VR) device and / or for mixed reality (MR) device, or preferred optical devices are augmented reality (AR) glasses, virtual reality (VR) glasses and / or mixed reality (MR) glasses.

[0097] 30 The term “display device” as used herein, is a kind of an optical device configured to output / present information in visual or tactile form. Examples are Liquid crystal display (LCD), Light emitting diode display (LED display), Foreignfiling text P24-196

[0098] - 10 -

[0099] organic light emitting display (OLED), micro-LED display, quantum dot display (QLED), AR display, VR display, MR display, plasma (PDP) display, electroluminescent (ELD) display. Preferred optical devices in the context of the present invention is AR display, VR display or MR display.

[0100] 5

[0101] Detailed description of the invention

[0102] Hereinafter, embodiments of the present invention are described in detail.

[0103] [Formulation]

[0104] According to the present invention, as one aspect, formulation, preferably to be used for forming an optical medium containing metal oxide nanoparticles, comprises, at least essentially consists of or consists of; i) a 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface modified metal oxide nanoparticle or colloidally stable metal oxide nanoparticle ;

[0105] 15 ii) a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface modified or a colloidally stable metal oxide nanoparticle; and

[0106] iii) a solvent;

[0107] 20 where the 1stmetal oxide nanoparticle and the 2ndmetal oxide nanoparticle of the formulation are defined by A) and / or B):

[0108] A) - wherein said 1stmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 12 elements, group 14 elements of the periodic table, preferably said group 4 element is Ti, said group 12 element is Zn, said group 14 element is Sn; and

[0109] - said 2ndmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 5 30 elements of the periodic table. Preferably said group 4 element is Zr or Hf, said group 5 element is Nb or Ta. Foreignfiling text P24-196

[0110] - 11 -

[0111] B) - wherein the photocuring at 365nm wavelength of light effectively causes aggregation and solidification of said 1stmetal oxide nanoparticle whereas photocuring is ineffective for said 2ndmetal oxide nanoparticle, which still may be removed by a solvent rinse or gentle rubbing. In other 5 words, the resulting film is not mechanically persistent after photocuring.

[0112] It is believed that the formulation of the present invention may lead reduced or no photocorrosion with keeping good UV photocuring properties.

[0113] Preferably, said 1stand 2ndmetal oxide nanoparticles are transparent at visible light wavelengths, namely in the range from 400 to 750nm; more preferably, said 2ndmetal oxide nanoparticles are transparent at or at least weakly absorbing of wavelengths in the 300 to400 nm spectral region.

[0114] 15 [1stmetal oxide nanoparticle]

[0115] Said 1stmetal oxide nanoparticle may consist of an amorphous or crystalline metal oxide core and a protective, hydrolyzed main group metalorganic additive that suppresses aggregation and allows processing the nanoparticles in form of colloids in an organic solvent or liquid coupling 20 agent or polymer matrix material and / or polymerizable organic monomer(s).The protective main group metalorganic additive may or may not form permanent linkage(s) to the metal oxide nanoparticle core to effect colloidal stability of the formulation.

[0116] In a preferred embodiment of the present invention, said 1st metal oxide nanoparticle is a surface modified metal oxide nanoparticle, which may include chemically bonded ligands and / or physically interacting additives or a colloidally stable metal oxide nanoparticle and in case said 1stmetal oxide nanoparticle is a colloidally stable metal oxide nanoparticle, then said 30 formulation further comprises one or more of alkoxysilane as a colloid stabilizer. Furthermore preferably said surface capping ligands are Foreignfiling text P24-196

[0117] - 12 -

[0118] chemically bonded to the nanoparticle surface of the 1stmetal oxide nanoparticle.

[0119] More preferably, said 1stmetal oxide nanoparticle is a surface modified 5 TiCh, ZnO or SnCh nanoparticle having one or more surface capping ligands, which can be either chemically bonded to the nanoparticle surface or function as physically interacting additives to enhance stability and performance.

[0120] Preferably, said TiCh nanoparticle, ZnO nanoparticle, SnO2 nanoparticle are amorphous nanoparticles or crystalline nanoparticles.

[0121] Furthermore preferably, said a surface modified 1stmetal oxide nanoparticle is a surface modified TiO2 nanoparticle having surface capping ligands as a surface modifier.

[0122] 15 It is believed that said 1stmetal oxide nanoparticle may exhibit effective UV photocuring properties of the other material precursors present in the formulation. Namely, when it is mixed with another metal oxide nanoparticle having lower sensitivity to UV for photo curing, said 1stmetal oxide nanoparticle may act like a photo-curing initiator and may effectively 20 improve UV photocuring properties of the materials of the formulation.

[0123] As for said 1stmetal oxide nanoparticle, a publicly known one can be used preferably.

[0124] [2ndmetal oxide nanoparticle]

[0125] In a preferred embodiment of the present invention, said 2ndmetal oxide nanoparticle is a surface modified metal oxide nanoparticle or a colloidally stable metal oxide nanoparticle and in case said 2ndmetal oxide nanoparticle is a colloidally stable metal oxide nanoparticle, then said 30 formulation may further comprise one or more alkoxysilane(s) as hydrolysable main group metalorganic colloid stabilizer. Foreignfiling text P24-196

[0126] - 13 -

[0127] More preferably, said 2ndmetal oxide nanoparticle is a HfCh, Ta2Os, ZrCh or Nb20s nanoparticle, preferably said 2ndmetal oxide nanoparticle has one or more of surface capping ligands as a surface modifier or said formulation contains one or more main group hydrolysable metalorganic additive such 5 as one or more alkoxysilane(s) The protective hydrolysable main group metalorganic additive may or may not sustain permanent linkage(s) to the metal oxide nanoparticle core to effect colloidal stability of the formulation. Preferably said one or more hydrolysable main group metalorganic additive such as alkoxysilane(s) contained in the formulation may stabilize said 2ndmetal oxide nanoparticle in the formulation through ionic and / or dispersive interactions.

[0128] Preferably said nanoparticles are amorphous nanoparticles or crystalline nanoparticles.

[0129] Furthermore preferably, said surface modified 2ndmetal oxide nanoparticle 15 is a Nb20s nanoparticle, and the formulation contains one or more alkoxysilanes to stabilize the nanoparticles.

[0130] It is believed that the hydrolyzed main group metalorganic additive such as an alkoxysilane may interact with said 2ndmetal oxide nanoparticle in the 20 formulation to form a transparent colloid, preferably as micellar colloid.

[0131] In other words, said 2ndmetal oxide nanoparticle may be stabilized through kinetic stabilization through reversible association between metal oxide nanoparticle surface and one or more hydrolysable main group metalorganic additive in the formulation. The term “colloidally stable” means the above mentioned stabilized state.

[0132] It is believed that said 2ndmetal oxide nanoparticle may reduce or prevent photocorrosion problems.

[0133] As for said 2ndmetal oxide nanoparticle, a publicly known one can be used 30 preferably.

[0134] [Alkoxysilane] Foreignfiling text P24-196

[0135] - 14 -

[0136] In a preferred embodiment of the present invention, said alkoxysilane is silane coupling agent or tetraalkoxysilane, more preferably it is a silane coupling agent that contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic hydrocarbon, polyethylene glycol, and / or a 5 fluorocarbon, polymerizable functional group;

[0137] preferably said polymerizable functional group is selected from the group consisting of a vinyl group, (meth)acrylic group, epoxy group, a mercapto group, even more preferably said polymerizable functional group is a (meth)acrylic group.

[0138] In one embodiment, the alkoxysilane may be represented by formula (c1). (R20O)4-m1 — Si — (R21)m1 - (c1)

[0139] wherein ml is 0, 1 , 2 or 3, preferably 1 ;

[0140] 15 R20is a straight-chain alkyl having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, very preferably 1 to 3 carbon atoms; a branched or cyclic structure-containing alkyl having 3 to 15 carbon atoms, preferably 3 to 10 carbon atoms, more preferably 3 to 5 carbon atoms; an aryl having 6 to 20 carbon atoms, preferably 6 to 15 20 carbon atoms, more preferably 6 to 10 carbon atoms, (meth)acrylate group;

[0141] wherein one or more non-adjacent CH2 may be replaced by O, S, CO, CO- O, O-CO, C=O, O-CO-O, CR22=CR23or C^C;

[0142] R22and R23are each independently H, a straight-chain alkyl having 1 to 25 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 1 to 10 carbon atoms; a branched or cyclic structure containing alkyl having 3 to 25 carbon atoms, preferably 3 to 15 carbon atoms, more preferably 3 to 10 carbon atoms; an aryl having 6 to 25 carbon atoms, preferably from 6 to 15 carbon atoms, more preferably 6 to 10 carbon atoms;

[0143] wherein one or more H may be replaced by OH, COOH, a straight-chain 30 alkyl having 1 to 6 carbon atoms, a branched or cyclic structure-containing alkyl having 3 to 6 carbon atoms; Foreignfiling text P24-196

[0144] - 15 -

[0145] wherein R21is a straight-chain alkyl having 1 to 25 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 1 to 10 carbon atoms; a branched or cyclic structure-containing alkyl having 3 to 25 carbon atoms, preferably 3 to 15 carbon atoms, more preferably 3 to 10 carbon atoms; a straight-chain 5 alkenyl having 1 to 25 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 1 to 10 carbon atoms; a branched or cyclic structure-containing alkenyl having 3 to 25 carbon atoms, preferably 3 to 15 carbon atoms, more preferably 3 to 10 carbon atoms; an aryl having 6 to 25 carbon atoms, preferably from 6 to 15 carbon atoms, more preferably 6 to 10 carbon atoms;

[0146] wherein one or more non-adjacent CH2 may be replaced by O, S, CO, CO- O, O-CO, O-CO-O, CR24=CR25, C=CR24R25, or C=C, preferably replaced by O-CO;

[0147] wherein R24and R25are each independently H, a straight-chain alkyl having 15 1 to 25 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 1 to 10 carbon atoms; a branched or cyclic structure containing alkyl having 3 to 25 carbon atoms, preferably 3 to 15 carbon atoms, more preferably 3 to 10 carbon atoms; an aryl having 6 to 25 carbon atoms, preferably 6 to 15 carbon atoms, more preferably 6 to 10 carbon atoms, very preferably R2420 and R25are H;

[0148] wherein one or more H may be replaced by OH, COOH, a straight-chain alkyl having 1 to 6 carbon atoms, a branched or cyclic structure-containing alkyl having 3 to 6 carbon atoms.

[0149] In a preferred embodiment, R21may be straight or branched alkyl group, branched or cyclic structure-containing alkyl group, (meth)acryl group.

[0150] It is believed that such alkoxysilane may prevent aggregation of 1stand / or 2ndmetal oxide nanoparticle(s) in the formulation, allow processing 1stand 30 2ndmetal oxide nanoparticles in form of colloidal formulations, in an organic solvent, polymer matrix material and / or polymerizable organic monomer(s). It is also believed that such alkoxysilane may be effectively Foreignfiling text P24-196

[0151] - 16 -

[0152] detached / removed from the surface of said1stand / or 2ndmetal oxide nanoparticle(s) by UV photocuring and / or decomposed by UV photocuring.

[0153] Thus, in a preferred embodiment of the present invention, said surface 5 modified 1stmetal oxide nanoparticle has or interacts with a hydrolyzed alkoxysilane as a surface capping ligand or surface stabilizing additive, preferably said alkoxysilane is silane coupling agent or tetraalkoxysilane, more preferably it is silane coupling agent contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic hydrocarbon, polyethylene glycol, and / or a fluorocarbon, polymerizable functional group; said surface modified 2ndmetal oxide nanoparticle has an alkoxysilane as a surface capping ligand, preferably said alkoxysilane is silane coupling agent or tetraalkoxysilane, more preferably it is silane coupling agent contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic

[0154] 15 hydrocarbon, polyethylene glycol, and / or a fluorocarbon, polymerizable functional group;

[0155] preferably said polymerizable functional group is selected from the group consisting of a vinyl group, (meth)acrylic group, epoxy group, a mercapto group, even more preferably said polymerizable functional group is a 20 (meth)acrylic group.

[0156] As for such alkoxysilane, publicly available ones like disclosed in US 2013 / 016444A1 can be used preferably, including 3-(trimethoxysilyl)propyl methacrylate and octyltriethoxysilane.

[0157] For examples, said 1stand 2ndmetal oxide nanoparticles with alkoxysilane may be obtained by publicly known method like described in US

[0158] 2013 / 016444A1.

[0159] 30 In a preferred embodiment of the present invention, the relative molar quantities of metal oxide (M) and hydrolysable main group metal element (E) such as Si of the surface capping ligand or stabilizing additive precursor Foreignfiling text P24-196

[0160] - 17 -

[0161] is M:E > 4, more preferably M:E > 200, even more preferably M:E > 400; and preferably it is M:E <1500, more preferably M:E <1200, even more preferably <1200. Thus, preferably said relative molar quantities of metal oxide (M) and Si atom of the surface capping ligand or stabilizing additive 5 precursor (E) M:E is in the range from 4 to 1500. More preferably from 200 to 1200. Even more preferably from 400 to 1000.

[0162] [1stmetal oxide nanoparticle & 2ndmetal oxide nanoparticle]

[0163] In a preferred embodiment of the present invention, the mass ratio of the 1stmetal oxide nanoparticle to the 2ndmetal oxide nanoparticle is within the range from 1 : 1 to 1 :99. Preferably it is within the range from 3:7 to 1 :49, more preferably from 1 :4 to 1 : 19.

[0164] It is believed that this mixing ratio may effectively reduce or prevent issues 15 related to photocorrosion while maintaining good UV photocuring properties of the materials (including 1st and 2nd metal oxide nanoparticles, and optionally matrix materials) in the formulation.

[0165] In a preferred embodiment of the present invention, the average diameter 20 size of said 1stmetal oxide nanoparticle and / or 2ndmetal oxide nanoparticle (excluding capping ligands and any surface-interacting hydrolyzed main group metalorganic additives) is in the range from 1nm to 100nm.

[0166] It is believed that it is preferably for ink jetting or spin coating, it may lead to a good refractive index value such as more than 2.0, and / or it may exhibit more dense film or dense optical grating for an optical waveguide by nanoimprint lithography after curing.

[0167] In a preferred embodiment of the present invention, said surface modified 30 1stmetal oxide nanoparticle has an alkoxysilane as a surface capping ligand, which may include both chemically bonded ligands and physically interacting additives to enhance stability and performance, or hydrolysable Foreignfiling text P24-196

[0168] - 18 -

[0169] main group metalorganic additive, preferably said alkoxysilane is silane coupling agent or tetraalkoxysilane, more preferably it is silane coupling agent contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic hydrocarbon, polyethylene glycol, and / or a fluorocarbon,

[0170] 5 polymerizable functional group;

[0171] said surface modified 2ndmetal oxide nanoparticle is colloidally stabilized by means of a hydrolysable main group metalorganic additive or a surface capping ligand, preferably an alkoxysilane, said alkoxysilane is silane coupling agent or tetraalkoxysilane, more preferably it is silane coupling agent contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic hydrocarbon, polyethylene glycol, and / or a fluorocarbon, polymerizable functional group;

[0172] preferably said polymerizable functional group is selected from the group consisting of a vinyl group, (meth)acrylic group, epoxy group, a mercapto 15 group, even more preferably said polymerizable functional group is a (meth)acrylic group.

[0173] According to the present invention, as a preferable embodiment, the 1stmetal oxide nanoparticle and the 2ndmetal oxide nanoparticle constitute 0.1 20 w% to 50 w% of the formulation, preferably it is from 1wt.% to 30wt.%, more preferably from 5 to 20wt.%.

[0174] It is believed that it enables to provide a suitable ink formulation for UV-NIL process, without or less causing aggregation of the 1stand the 2ndmetal oxide nanoparticles, with keeping good UV photocuring properties, leading less or no UV photocorrosion problems namely at 365nm light wavelength.

[0175] [Solvent]

[0176] In a preferred embodiment of the present invention, the solvent is an 30 organic solvent. Preferably said organic solvent is selected from one or more members of the group consisting of alcohols, glycols, ethers, ketones, esters, hydrocarbons, aromatic hydrocarbons, amides and sulfones. More Foreignfiling text P24-196

[0177] - 19 -

[0178] preferably said organic solvent is selected from one or more members of the group consisting of ethylene glycol monoalkyl ethers, preferably it is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether and / or ethylene glycol monobutyl ether; 5 diethylene glycol dialkyl ethers, preferably it is diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether and / or diethylene glycol dibutyl ether; propylene glycol monoalkyl ethers, preferably it is propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether and / or propylene glycol monopropyl ether; ethylene glycol alkyl ether acetates, preferably it is methyl cellosolve acetate and / or ethyl cellosolve acetate; propylene glycol alkyl ether acetates, preferably it is propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate and / or propylene glycol monopropyl ether acetate; 2-(2-butoxyethoxy)ethyl acetate; ketones, 15 preferably it is methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone and / or cyclohexanone; alcohols, preferably it is ethanol, propanol, 1 ,3-dimethoxy-2-propanol, butanol, hexanol, cyclo hexanol, ethylene glycol, propylene glycol, triethylene glycol, glycerin, pentanols, preferably it is 1 -pentanol, 2-pentnol, 3-pentanol, 3-ethyl-3-pentanol, 2,4- 20 dimethyl-3-pentanol; esters, preferably it is ethyl 3-ethoxypropionate, methyl 3-methoxypropionate and / or ethyl lactate; and cyclic esters, preferably it is gamma-butyro-lactone; preferably said solvent is selected from propylene glycol alkyl ether acetates, ethylene glycol monoalkyl ethers, propylene glycol and propylene glycol monoalkyl ethers, 1 -pentanol, 2-pentnol, 3-pentanol, 3-ethyl-3-pentanol, 2,4-dimethyl-3-pentanol 1,3- dimethoxy-2-propanol or a mixture of any one of them.

[0179] It is believed that these are preferable for wet printing process e.g. inkjetting or spin coating also suitable for NIL process including UV nanoimprint 30 lithography (UV-NIL), thermal nanoimprint lithography (TNIL) and a combination of UV-NIL and TNIL. Preferably it is suitable for at least UV- NIL process. Foreignfiling text P24-196

[0180] - 20 -

[0181] [Matrix material]

[0182] In a preferred embodiment of the present invention, said formulation may further comprises a matrix material selected from one or more members of 5 the group consisting of a silicone resin, an acrylic resin, an epoxy resin, an olefin resin, a polysulfide resin, a polythiol-urethane resin, polycarbonate resin, a polyamide resin, a polyester resin, a polyphenylene ether resin and a polyarylene sulfide resin. Preferably said matrix material is transparent in visible light wavelength.

[0183] Preferably said matrix material is an acrylate resin, an epoxy resin or a mixture of an acrylate resin and an epoxy resin. It is believed that these are transparent in visible light wavelength and preferable for fabricating an optical medium such as optical gratings for waveguide. Namely these are preferable for wet printing process e.g. inkjetting or spin coating also 15 suitable for NIL process including UV nanoimprint lithography (UV-NIL), thermal nanoimprint lithography (TNIL) and a combination of UV-NIL and TNIL. Preferably it is suitable for at least UV-NIL process.

[0184] [Use]

[0185] 20 In another aspect, the present invention relates to use of the formulation of the present invention for forming an optical medium comprising metal oxide nanoparticles, preferably for fabricating optical grating of an optical waveguide by nanoimprint lithography(NIL), preferably by UV nanoimprint lithography (UV-NIL), or thermal nanoimprint lithography (TNIL) or by a combination of UV-NIL and TNIL, wherein the surface-modified particles exhibit properties from both chemically bonded ligands and physically interacting additives to optimize performance in various applications..

[0186] [Method for preparing the formulation]

[0187] 30 In another aspect, the present invention also relates to a method for preparing the formulation of the present invention, comprising at least, essentially consisting of or consisting of, following step (A): Foreignfiling text P24-196

[0188] - 21 -

[0189] (A) Mixing at least a 1stmetal oxide nanoparticle,

[0190] a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said 1stand 2ndmetal oxide nanoparticles are each independently selected from a surface- 5 modified

[0191] or colloidally stable metal oxide nanoparticle, and

[0192] iii) a solvent;

[0193] where the 1stmetal oxide nanoparticle and the 2ndmetal oxide nanoparticle of the formulation are defined by A) and / or B):

[0194] A) - wherein said 1stmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 12 elements, group 14 elements of the periodic table, preferably said group 4 element is Ti, said group 12 element is Zn, said 15 group 14 element is Sn; and

[0195] - said 2ndmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 5 elements of the periodic table. Preferably said group 4 element is Zr or Hf, said group 5 element is Nb or Ta.

[0196] 20

[0197] B) wherein the photocuring at 365nm wavelength of light effectively causes aggregation and solidification of said 1stmetal oxide nanoparticle whereas photocuring is ineffective for said 2ndmetal oxide nanoparticle, which still may be removed by a solvent rinse or gentle rubbing. In other words, the resulting film is not mechanically persistent after photocuring.

[0198] The details of said 1stmetal oxide nanoparticle and said 2ndmetal oxide nanoparticle are described in the section of [1stmetal oxide nanoparticle] and [2ndmetal oxide nanoparticle] above.

[0199] 30

[0200] In another aspect, the present invention also relates to a method for fabricating an optical medium or an optical device of the present invention, Foreignfiling text P24-196

[0201] - 22 -

[0202] preferably for fabricating optical grating of an optical waveguide by nanoimprint lithography; comprising, essentially consisting of or consisting of, the following steps (a) to (d), preferably the steps (a) to (d) are executed in this order:

[0203] 5 (a) providing the formulation of the present invention, onto a surface of a substrate to form a curable composite, preferably by wet deposition process, more preferably by spin-coating or ink-jetting, even more preferably by ink-jetting; and

[0204] (b) pressing a mold against said curable composite formed on the substrate;

[0205] (c) irradiating the curable composite with UV light, preferably at around 365nm to form a cured composite; and

[0206] (d) optionally applying a thermal treatment to remove any organic component.

[0207] 15

[0208] In a preferred embodiment of the present invention, wherein in step (d), the temperature at the range from 50 to 650 °C, preferably it is from 200 to 600°C, more preferably from 250 to 500°C, is applied. Preferably, in step(d), a UV cured composite obtained by step (c) is heated from the room 20 temperature to the temperature in the range from 200 to 600°C.

[0209] Preferably, the method further comprises step (o) before step (a);

[0210] (o) substituting the solvent of the formulation of the present invention with another solvent or a solvent mixture.

[0211] [Optical layer]

[0212] In another aspect, the present invention also relates to an optical layer, preferably a particle-free optical layer, preferably to be used for nanoimprint lithography, more preferably to be used for direct UV nanoimprint

[0213] 30 lithography produced by the method of the present invention. Foreignfiling text P24-196

[0214] - 23 -

[0215] The thickness of the optical layer is in the range from 1 to 700nm, preferably from 3 to 600nm, more preferably 5 to 500nm, very preferably 7 to 400nm.

[0216] 5 - Optical medium

[0217] The present invention further relates to an optical medium fabricated by the method for fabricating an optical medium of the present invention.

[0218] Preferably, said optical medium is a nanostructure or nanostructures including nanosized optical gratings, or any other patterned or random nano-sized uneven structures fabricated on a substrate, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. In other words, optical medium of the present invention may be a nanostructure or nanostructures of an optical device of the present invention and it is a part of an optical device of the 15 present invention.

[0219] - Optical device

[0220] The present invention further relates to an optical device comprising one or more of optical mediums made by the method of the present invention. 20 Preferably said optical device is an optical waveguide. Preferably said optical medium is an optical grading.

[0221] It is preferred that the optical device is a device containing one or more optical components for forming a light beam including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. Preferred optical devices in the context of the present invention are waveguides for augmented reality (AR) device, for virtual reality (VR) device and / or for mixed reality (MR) device, or preferred optical devices are augmented 30 reality (AR) glasses, virtual reality (VR) glasses and / or mixed reality (MR) glasses. Foreignfiling text P24-196

[0222] - 24 -

[0223] - Display device

[0224] Finally, the present invention relates to a display device comprising at least one functional medium configured to modulate a light or configured to emit light; and the composite, or an optical device of the present invention.

[0225] 5

[0226] Examples of said display device is selected from a Liquid crystal display (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot display (QLED), Augmented Reality (AR) hardware, Virtual Reality (VR) hardware, Mixed Reality (MR) hardware, plasma (PDP) display and an electroluminescent (ELD) display. Said AR, VR and MR hardware are also called as AR, VR and MR display. Preferably said display device is AR hardware, VR hardware or MR hardware.

[0227] 15 Thus, the term “functional medium” of the optical device may be LCD, LED, OLED, micro-LED, PDP, ELD layer, array, or display included in said display device.

[0228] The present invention is further illustrated by the examples following herein20 after which shall in no way be construed as limiting. The skilled person will acknowledge that various modifications, additions and alternations may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

[0229] [Working examples]

[0230] Analytics and measurement methods

[0231] Ellipsometry is used to determine layer thickness, refractive index (n) and absorption index (k) of a metal oxide layer. Measurements are performed using an ellipsometer M2000 from J. A. Woolam and three different angles 30 of incidence (65°, 70° and 75°). The measurement data is analyzed with software CompleteEase from J. A. Woolam, applying a Gen-Osc fitting Foreignfiling text P24-196

[0232] model for obtaining refractive index (n) as well as absorption index (k). The optical constants are averaged from five measured points on each wafer.

[0233] All chemicals for synthesis described are purchased from Sigma Aldrich 5 and used without further purification, unless differently mentioned elsewhere.

[0234] UV / vis measurements are performed using a Cary 7000 spectrometer from Agilent. UV LED irradiation is performed by an in-house built 365 LED source.

[0235] Preparation example 1: preparation of 1stmetal oxide nanoparticle Heating plate, 2000ml multi-neck flask with magnetic core, cooler under argon atmosphere is prepared.

[0236] 15

[0237] 98% 3-(Trimethoxysilyl)propyl methacrylate (2.425ml; 10.00 mmol;

[0238] 12.500mol%) is dissolved in 1-methoxypropan-2-ol (1000.000 ml; 10208.50 mmol; 12760.622 mol%) and 2M of hydrochloric acid (HCI) (7760.000 n I; 253.27 mmol; 316.594 mol%) is added. Then obtained solution A is stirred 20 for 2hours at 80°C and allowed to cool back to room temperature.

[0239]

[0240] 30 Preparation example 2: preparation of 2ndmetal oxide nanoparticle Foreignfiling text P24-196

[0241] - 26 -

[0242] A mixture of Nb2Os nanoparticle and hydrolyzed R-Si(0R’)3 is prepared based on the procedure of US2013 / 0164444. Namely based on the following procedure of US2013 / 0164444.

[0243] “1.55 mL of 3-(trimethoxysilyl)propyl methacrylate were added to 650 mL of 5 PGME in a 1 L round bottom flask. 5 mL of 2 M HCI are added and the solution is stirred at room temperature for 20 h. After this, 11.65 mL of niobium ethoxide are added and the solution is heated to 80 °C for 2 h while stirring.

[0244] The resulting solution is concentrated by rotor evaporation to 30% w / w.

[0245] Example 1

[0246] A 9:1 (Nb2Os nanoparticles : TiCh nanoparticles by volume (from preparation examples 1 and 2)) mixture is obtained by mixing the Nb2Os and TiO2 metal oxide nanoparticle colloids prepared in 1 -m ethoxy-2 - 15 propanol as shown in table 1.

[0247] Nb2Os nanoparticle colloid: Nb2Os with R-SiOs in 1-methoxy-2-propanol where R = prop-3-yl methacrylate, in 1-methoxy-2-propanol

[0248] TiO2 nanoparticle colloid: TiCh with R-SiOs in 1-methoxy-2-propanol 20 wherein R is prop-3-yl methacrylate.

[0249] Table 1

[0250]

[0251] 30 Spin coating and UV illumination Foreignfiling text P24-196

[0252] - 27 -

[0253] PGME solutions of the nanoparticles are obtained by diluting the solutions to the target concentration. Mixtures of Nanoparticles are prepared from the high concentration solutions and then diluted to the final concentration.

[0254] 5 Spin coated films are prepared on cleaned two-inch silicon wafers (cleaning procedure: cleaning with 2-propanol, rinsing with deionized water, drying on a hotplate at 100°C for 10 minutes, plasma cleaning in an oxygen plasma (Diener electronic Femto-SR-PC-c) for 10 minutes) by spin coating 250 pl of a 12 wt% solution of nanoparticles in PGME at 2,000 rpm for 25 seconds with an acceleration of 1 ,500 rpm / s. The films are soft-baked at 60°C for 1 minute and illuminated with a UV lamp. After illumination with 365 nm light for 15 minutes (525 mW / cm2), the films are measured with an ellipsometer to determine the refractive index. The results are summarized in the table 2.

[0255] Table 2: Refractive index and film thickness of the films prepared from nanoparticle solutions.

[0256]

[0257] By replacing TiO2 nanoparticles with Nb2Os nanoparticles as the main metal 30 oxide nanoparticles, the issues of photocorrosion associated with TiO2 can be reduced or eliminated. Furthermore, by incorporating a small amount of Foreignfiling text P24-196

[0258] - 28 -

[0259] TiO2 nanoparticles, excellent UV photocuring properties can be achieved while allowing for the effective detachment or removal of capping ligands, resulting in the formation of high-quality films with a higher refractive index value.

[0260] 5

[0261] NIL imprint tests

[0262] Formulations for NIL test imprints are prepared by adding ethyl lactate to the high concentration NP solutions in PGME and then removing the PGME under vacuum. The concentration of the NP solution in ethyl lactate is calculated to match the concentrations in PGME.

[0263] The high concentration nanoparticle solutions are either diluted with ethyl lactate to the target concentration or the solutions are mixed and the additive (3-(trimethoxysilyl)propyl methacrylate) added and the mixture diluted as a last step to the target concentration.

[0264] The composition of the formulations used for NIL imprint tests is shown in table 3.

[0265] Table 3: Composition of the solutions for nanoimprint tests.

[0266]

[0267] Thin films for imprint tests are obtained by spin coating the solutions on cleaned two-inch wafers at 1,000 rpm and letting them dry at room temperature for 10 minutes.

[0268] Test structures are imprinted into the films using a commercial NIL tool (NIL 30 Technology CNI v3.0) with a self-made stamp (Ormostamp® on quartz, coated with a Profactor BGL-GZ-96 antisticking layer). Imprints are made by applying reduced pressure to the imprint stack (20 mbar) and applying 4 Foreignfiling text P24-196

[0269] - 29 -

[0270] bar pressure onto the stamp. After a hold time of 4 minutes, the imprints are illuminated at 365 nm for 5 minutes in the tool, followed by an illumination at 365 nm for 15 minutes (525 mW / cm2) outside of the imprint tool. To facilitate SEM analysis, the samples are additionally hardbaked at 300°C 5 for 5 minutes.

[0271] As can be seen from the SEM images (Figure 1 to figure 4), the imprints in NIL 1 have much less cracks and delamination (Figure 1 and Figure 2). This is due to a better fixation during the UV illumination step and leads to less defects during the hard baking step. NIL 2 shows significant delamination (Figure 3) and stronger cracking (Figure 4) during the hard baking step.

[0272] 15

[0273] 20

[0274] 30

Claims

Foreignfiling text P24-196- 30 -Claims1. Formulation, preferably to be used for forming an optical medium comprising metal oxide nanoparticles, comprising at least;5 i) a 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified metal oxide nanoparticle or colloidally stable metal oxide nanoparticle;ii) a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified or colloidally stable metal oxide nanoparticle; andiii) a solvent;- wherein said 1stmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic 15 table, group 12 elements, group 14 elements of the periodic table, preferably said group 4 element is Ti, said group 12 element is Zn, said group 14 element is Sn; and- said 2ndmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 5 20 elements of the periodic table., optionally said group 4 element is Zr or Hf, said group 5 element is Nb or Ta.

2. Formulation, preferably to be used for forming an optical medium comprising metal oxide nanoparticles, comprising at least;i) a 1stmetal oxide nanoparticle, preferably said metal oxide nanoparticle is a surface-modified metal oxide nanoparticle or colloidally stable metal oxide nanoparticle,ii) a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said metal 30 oxide nanoparticle is a surface-modified or colloidally stable metal oxide nanoparticle; andiii) a solvent;Foreignfiling text P24-196- 31 -wherein the photocuring at 365nm wavelength of light effectively causes aggregation and solidification of said 1stmetal oxide nanoparticle whereas photocuring is ineffective for said 2ndmetal oxide nanoparticle, which still may be removed by a solvent rinse or gentle rubbing.

53. Formulation of claim 1 or 2, wherein said 1stmetal oxide nanoparticle is a surface modified metal oxide nanoparticle, which may include chemically bonded ligands and / or physically interacting additives or a colloidally stable metal oxide nanoparticle and in case said 1stmetal oxide nanoparticle is a colloidally stable metal oxide nanoparticle, then said formulation further comprises one or more of alkoxysilane as a colloid stabilizer.

4. Formulation of any one of claims 1 to 3, wherein said 1st metal oxide nanoparticle is a surface modified metal oxide nanoparticle, which may 15 include chemically bonded ligands and / or physically interacting additives said 1stmetal oxide nanoparticle is a surface modified TiCh, ZnO or SnCh nanoparticle having one or more surface capping ligands, which can be either chemically bonded to the nanoparticle surface or function as physically interacting additives to enhance stability and performance.20 Said TiO2 nanoparticle, ZnO nanoparticle, SnO2 nanoparticle are amorphous nanoparticles or crystalline nanoparticles, preferably said a surface modified 1stmetal oxide nanoparticle is a surface modified TiO2 nanoparticle having surface capping ligands as a surface modifier.

5. Formulation of any one of claims 1 to 4, wherein said 2ndmetal oxide nanoparticle is a surface modified metal oxide nanoparticle or a colloidally stable metal oxide nanoparticle and in case said 2ndmetal oxide nanoparticle is a colloidally stable metal oxide nanoparticle, then said formulation further comprises one or more of alkoxysilane as a colloid 30 stabilizer.Foreignfiling text P24-196- 32 -6. Formulation of any one of claims 1 to 5, wherein said 2ndmetal oxide nanoparticle is a HfCh, Ta2Os, ZrCh or Nb2Os nanoparticle, preferably said 2ndmetal oxide nanoparticle has one or more of surface capping ligands as a surface modifier or said formulation contains one or more of alkoxysilane, 5 preferably said one or more alkoxysilane contained in the formulation may stabilize said 2ndmetal oxide nanoparticle in the formulation through ionic and / or dispersive interactions, preferably said nanoparticles are amorphous nanoparticles or crystalline nanoparticles, preferably said surface modified 2ndmetal oxide nanoparticle is a Nb20s nanoparticle and the formulation contains one or more of alkoxysilanes.

7. Formulation of any one of claims 1 to 6, wherein the mass ratio of the 1stmetal oxide nanoparticle to the 2ndmetal oxide nanoparticle is within the range from 1:1 to 1 :99, preferably it is within the range from 3:7 to 1 :49, 15 more preferably from 1 :4 to 1 :

198. Formulation of any one of claims 1 to 7, wherein said surface modified 1stmetal oxide nanoparticle has an alkoxysilane as a surface capping ligand, preferably said alkoxysilane is silane coupling agent or tetraalkoxysilane, 20 more preferably it is silane coupling agent contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic hydrocarbon, polyethylene glycol, and / or a fluorocarbon, polymerizable functional group; said surface modified 2ndmetal oxide nanoparticle has an alkoxysilane as a surface capping ligand, preferably said alkoxysilane is silane coupling agent or tetraalkoxysilane, more preferably it is silane coupling agent contains an aliphatic hydrocarbon having at least 4 carbon atoms or aromatic hydrocarbon, polyethylene glycol, and / or a fluorocarbon, polymerizable functional group;preferably said polymerizable functional group is selected from the group 30 consisting of a vinyl group, (meth)acrylic group, epoxy group, a mercapto group, even more preferably said polymerizable functional group is a (meth)acrylic group.Foreignfiling text P24-196- 33 -9. Formulation of any one of claims 1 to 8, wherein the solvent is an organic solvent, preferably said organic solvent is selected from one or more members of the group consisting of alcohols, glycols, ethers, ketones, 5 esters, hydrocarbons, aromatic hydrocarbons, amides and sulfones. More preferably said organic solvent is selected from one or more members of the group consisting of ethylene glycol monoalkyl ethers, preferably it is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether and / or ethylene glycol monobutyl ether; diethylene glycol dialkyl ethers, preferably it is diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether and / or diethylene glycol dibutyl ether; propylene glycol monoalkyl ethers, preferably it is propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether and / or propylene glycol monopropyl ether; ethylene 15 glycol alkyl ether acetates, preferably it is methyl cellosolve acetate and / or ethyl cellosolve acetate; propylene glycol alkyl ether acetates, preferably it is propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate and / or propylene glycol monopropyl ether acetate; 2-(2-butoxyethoxy)ethyl acetate; ketones, 20 preferably it is methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone and / or cyclohexanone; alcohols, preferably it is ethanol, propanol, 1 ,3-dimethoxy-2-propanol, butanol, hexanol, cyclo hexanol, ethylene glycol, propylene glycol, triethylene glycol, glycerin, pentanols, preferably it is 1 -pentanol, 2-pentnol, 3-pentanol, 3-ethyl-3-pentanol, 2,4- dimethyl-3-pentanol; esters, preferably it is ethyl 3-ethoxypropionate, methyl 3-methoxypropionate and / or ethyl lactate; and cyclic esters, preferably it is gamma-butyro-lactone; preferably said solvent is selected from propylene glycol alkyl ether acetates, ethylene glycol monoalkyl ethers, propylene glycol and propylene glycol monoalkyl ethers, 1 -pentanol, 30 2-pentnol, 3-pentanol, 3-ethyl-3-pentanol, 2,4-dimethyl-3-pentanol 1,3- dimethoxy-2-propanol or a mixture of any one of them.Foreignfiling text P24-196- 34 -10. Formulation of any one of claims 1 to 9, further comprises a matrix material selected from one or more members of the group consisting of a silicone resin, an acrylic resin, an epoxy resin, an olefin resin, a polysulfide resin, a polythiol-urethane resin, polycarbonate resin, a polyamide resin, a 5 polyester resin, a polyphenylene ether resin and a polyarylene sulfide resin.Preferably said matrix material is transparent in visible light wavelength. Preferably said matrix material is an acrylate resin, an epoxy resin or a mixture of an acrylate resin and an epoxy resin.

11. Formulation of any one of preceding claims, wherein the 1stmetal oxide nanoparticle and the 2ndmetal oxide nanoparticle constitute 0.1 w% to 50 w% of the formulation, preferably it is from 1wt.% to 30wt.%, more preferably from 5 to 20wt.%.15 12. Method for preparing the formulation of any one of claims 1 to 11 , comprising at least following step (A):(A) mixing at least a 1stmetal oxide nanoparticle,a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, preferably said 1stand 2nd20 metal oxide nanoparticles are each independently selected from a surface- modifiedor colloidally stable metal oxide nanoparticle, andiii) a solvent;- wherein said a 1stmetal oxide nanoparticle comprises a metal element selected from the group consisting of group 4 elements of the periodic table, group 12 elements, group 14 elements of the periodic table, preferably said group 4 element is Ti, said group 12 element is Zn, said group 14 element is Sn; and- said a 2ndmetal oxide nanoparticle comprises a metal element selected 30 from the group consisting of group 4 elements of the periodic table, group 5 elements of the periodic table, preferably said group 4 element is Zr or Hf, said group 5 element is Nb or Ta.Foreignfiling text P24-196- 35 -13. Method for preparing the formulation of any one of claims 1 to 11 , comprising at least following step (A):(A) mixing at least a 1stmetal oxide nanoparticle,5 a 2ndmetal oxide nanoparticle that is a different type of metal oxide nanoparticle to said 1stmetal oxide nanoparticle, andiii) a solvent;- wherein the photocuring at 365nm wavelength of light effectively causes aggregation and solidification of said 1stmetal oxide nanoparticle whereas this is not the case for said 2ndmetal oxide nanoparticle which still can be removed by a solvent rinse or gentle rubbing.

14. Method for fabricating an optical medium comprising metal oxide nanoparticles, preferably for fabricating optical grating of an optical15 waveguide by nanoimprint lithography; comprising the following steps (a) to (d), preferably the steps (a) to (d) are executed in this order:(a) providing the formulation of any one of claims 1 to 11 onto a surface of a substrate to form a curable composite, preferably by wet deposition process, more preferably by spin-coating or ink-jetting, even more 20 preferably by ink-jetting; and(b) pressing a mold against said curable composite formed on the substrate;(c) irradiating the curable composite with UV light, preferably at around 365nm to form a cured composite; and(d) optionally applying a thermal treatment to remove any organic component,and optionally in step (d), the temperature of the thermal treatment in the range from 50 to 650 °C, preferably it is from 200 to 600°C, more preferably from 250 to 500°C, is applied, optionally, in step(d), a UV cured composite 30 obtained by step (c) is heated from the room temperature to the temperature in the range from 200 to 600°C.Foreignfiling text P24-196- 36 -15. Method according to any one of claim 14, further comprises step (o) before step (a);(o) substituting the solvent of the formulation of any one of claims 1 to 11 with another solvent or a solvent mixture.

516. An optical device comprising one or more of optical mediums made by the method of any one of claims 14 or 15, preferably said optical device is an optical waveguide, preferably said optical medium is an optical grading, and optionally said optical device is at least partly filled with a metal oxide.

17. A display device comprising at least one functional medium configured to direct and modulate a light or configured to emit light; and the optical device of claim 16.152030

Images