Stretchable photonic crystal panel

Abstract

The invention relates to a stretchable photonic crystal panel, wherein said panel exhibits a percentage change of the optical resonance wave of less than 0.2%, standardised to the percentage stretch. The stretchable photonic crystal panel comprises a stretchable substrate layer (1) and a nanostructured waveguide layer (2), wherein the waveguide layer (2) comprises polygonal portions (3), which are delimited by stretch channels (4), and wherein the polygonal portions (3) have a size between 2 μm and 1 mm.

Description

[0001] Stretchable photonic crystal plate

[0002] The present invention relates to stretchable photonic crystal slabs (Flexible Photonic Crystal Slab f-PCS), their production and use as flexible sensors for monitoring the human body.

[0003] Flexible photonic crystal slabs (Flexible Photonic Crystal Slab f-PCS) are known from CN101201540A, JP2007193286A, and also from [Karrock, T., Paulsen, M., & Gerken, M. (2017). Flexible photonic crystal membranes with nanoparticle high refractive index nanoparticle layers. Beilstein Journal of Nanotechnology, vol. 8(1), 2017, 203-209. ISSN 2190-4286 (E) DOI: https: / / doi.org / 10.3762 / bjnano.8.22 URL: https: / / www.beilstein-journals.org / bjnano / content / pdf / 2190-4286-8-22.pdf]. Stretching the photonic crystal slabs leads to a change in the optical resonance wave of the photonic crystal.

[0004] US 2022 / 0042905 A1 claims artificial optical devices which exhibit a change in optical properties, particularly in color, when stretched or heated.

[0005] The devices are constructed from a layer of a flexible polymer and several flexible segments located thereon, which contain photonic crystals.

[0006] The Japanese document JP5946052B2 proposes multilayer photonic crystals with a “sublayer” with a lower refractive index to suppress background effects.

[0007] The paper “Flexible integrated photonics: where materials, mechanics and optics meet [Invited]”, Opt. Mater. Express 3, 2013, pp. 1313–1331, provides an overview of the mechanical design principles and materials processing of flexible photonic crystal plates.

[0008] US 11,161,276 B2 describes a 3D printing process for producing one-dimensional flexible photonic crystals for monitoring the human body.

[0009] The described flexible photonic crystal slabs (Flexible Photonic Crystal Slab f-PCS) can be used as sensors. What they have in common is that stretching or increasing the temperature leads to an immediate change in the optical properties by changing the optical resonance wave.

[0010] When monitoring the human body, instantaneous changes in optical properties are disadvantageous, as a certain degree of deformation may be desired without a detectable change in optical properties occurring. This is the case, for example, with "smart" wound dressings or plasters, where the patient or athlete should be allowed a certain degree of freedom of movement without sending a signal too early or being impaired.

[0011] Therefore, the object of the invention is to provide new stretchable photonic crystal slabs (Flexible Photonic Crystal Slab f-PCS).

[0012] In particular, the object of the invention is to provide new stretchable photonic crystal slabs (Flexible Photonic Crystal Slab f-PCS) which largely retain their optical properties at lower stretches.

[0013] In particular, it is an object of the invention to provide novel stretchable photonic crystal slabs (Flexible Photonic Crystal Slab f-PCS) which have a percentage change in the optical resonance wave of less than 0.2% normalized to the percentage strain.

[0014] The object of the invention is achieved by a multilayer stretchable photonic crystal slab (Flexible Photonic Crystal Slab f-PCS) which has a percentage change in the optical resonance wave of less than 0.2%, normalized to the percentage strain, wherein the stretchable photonic crystal slab has a stretchable substrate layer (1) and a nanostructured waveguide layer (2), wherein the waveguide layer consists of slabs (3) which are delimited by strain grooves (4), and wherein the slabs (3) have a size between 2 pm and 1 mm.

[0015] In a particular embodiment, the nanostructured waveguide layer is formed from materials selected from the group titanium dioxide (TiO2), niobium pentoxide (Nb2O5) and / or tantalum pentoxide (Ta2O5).

[0016] In a further particular embodiment, the stretchable substrate layer also has a nanostructure.

[0017] In a preferred embodiment, the stretchable photonic crystal plate comprises one or more sublayers in addition to the stretchable substrate layer and the nanostructured waveguide layer.

[0018] In a further preferred embodiment, the sublayers are low-index layers.

[0019] In a further particular embodiment, the sublayers are formed from the material silicon oxide (SiO2).

[0020] In a further embodiment, the stretchable photonic crystal plate has at least one superlayer (6).

[0021] In a particular embodiment, the material for the superlayers is selected from the group consisting of gold (Au) and / or silicon dioxide (SiO2). The choice of SiO2 as the material for the superlayer offers the advantage of allowing good bonding of silanes. If gold is selected as the material for the superlayer, this offers a good opportunity for bonding of thiols.

[0022] In a further aspect of the invention, the object is achieved by a method which comprises the following steps i. producing the flexible substrate layer by a. pouring a master mold, b. degassing and c. subsequently allowing it to harden ii. optionally applying a sublayer to the flexible substrate layer produced in step i using the cathode sputtering method iii. applying a high-index waveguide layer to the flexible substrate layer produced in step i or in step ii using the cathode sputtering method iv. producing the expansion grooves in the waveguide layer by a. mechanical loading or b. lithographic methods or c. with the aid of masks, wherein in the lithographic methods (iv. b.) or the use of masks (iv. c.) expansion grooves in the range from 0.5 pm to 1 mm can be specifically set.

[0023] The effect of the stable optical properties during stretching can be attributed to the stretch grooves, which absorb a large part of the mechanical deformation so that the floes remain unaffected.

[0024] Figure 4 shows a multilayer stretchable photonic crystal slab (Flexible Photonic Crystal Slab f-PCS) under strain according to the invention. The strain groove (4') widens, thus absorbing the mechanical strain, while the expansion of the slabs (3) remains largely unaffected.

[0025] Table 1 shows the shift of the resonance wavelength with strain for f-PCS according to the invention without a sublayer (sample 1), with a sublayer (sample 2), and for a non-inventive fully flexible photonic crystal (sample 3), as also described in [Karrock, T., Paulsen, M., & Gerken, M. (2017). Flexible photonic crystal membranes with nanoparticle high refractive index nanoparticle layers. Beilstein Journal of Nanotechnology, 8(1), 203- 209. https: / / doi.Org / 10.3762 / bjnano.8.22].

[0026] Table 1 : Measurements of optical properties under strain for f-PCS

[0027] For a fully flexible photonic crystal, a 1% strain is also expected to result in a 1% change in the lattice period L and thus a change in the resonance wavelength Io of approximately 1%. This relationship is demonstrated in [Karrock, T., Paulsen, M., & Gerken, M. (2017). Flexible photonic crystal membranes with nanoparticle high refractive index nanoparticle layers. Beilstein Journal of Nanotechnology, 8(1), 203-209. https: / / doi.org / 10.3762 / bjnano.8.22].

[0028] The f-PCS according to the invention show a significantly lower percentage change in the optical resonance wave - and thus in the optical properties - upon stretching than is the case with sample 3.

[0029] All f-PCS according to the invention show a percentage change of the optical resonance wave of less than 0.2% normalized to the percentage strain.

[0030] The f-PCS with sublayer (Sample 2) according to the invention show the smallest value (0.002) for the strain-normalized percentage change in the resonance wavelength and better noise suppression than the f-PCS without sublayer (Sample 1), also according to the invention. Description of the figures:

[0031] Figure 1 shows the stretchable photonic crystal plate according to the invention with substrate layer (1) and nanostructured waveguide layer (2), wherein the waveguide layer consists of slabs (3) delimited by expansion grooves (4).

[0032] Figure 2 shows the stretchable photonic crystal plate according to the invention, with sublayer (5) between the stretchable substrate layer (1) and the nanostructured waveguide layer (2).

[0033] Figure 3 shows the stretchable photonic crystal plate according to the invention, with superlayer (6) on the nanostructured waveguide layer (2).

[0034] Figure 4 shows a multilayer stretchable photonic crystal slab (Flexible Photonic Crystal Slab f-PCS) under strain according to the invention. The strain groove (4') widens, thus absorbing the mechanical strain, while the expansion of the slabs (3) remains largely unaffected.

[0035] Figure 5 shows the spectral optical properties of f-PCS without a sublayer when stretched perpendicular to the lattice alignment of the one-dimensional periodic nanostructure. The sample was clamped in a strain jig for characterization. A displacement of 0 pm of the micrometer screw corresponds to 0% strain. By turning the micrometer screw, a clamping jaw of the strain jig is moved, stretching the sample. The measured wavelength of the resonance at this strain is shown at the top. The spectra for the unstretched sample and two strain states are shown below. It is clearly evident that the resonance changes only minimally in wavelength.

[0036] Figure 6 shows the spectral optical properties of f-PCS without a sublayer when stretched parallel to the lattice alignment of the one-dimensional periodic nanostructure. The sample was clamped in a strain jig for characterization. A displacement of 0 pm of the micrometer screw corresponds to 0% strain. By turning the micrometer screw, a clamping jaw of the strain jig is moved, stretching the sample. The measured wavelength of the resonance at this strain is shown at the top. The spectra for the unstretched sample and two strain states are shown below. It is clearly evident that the resonance changes only minimally in wavelength.

[0037] Figure 7 shows the clamping device with an f-PCS clamped by two clamping jaws and a micrometer screw for adjusting the strain (left image). In the middle image, the slabs of the f-PCS according to the invention can be seen in the relaxed state. In the image to the right, the surface of the f-PCS according to the invention under strain (in this case 6%) can be seen. Figure 8 shows the spectral optical properties of f-PCS when stretched perpendicular to the lattice alignment of the one-dimensional periodic nanostructure of an f-PCS with a sublayer of 100 nanometers SiC>2. The sample was clamped in a strain device for characterization. 0 pm displacement of the micrometer screw corresponds to 0% strain. By turning the micrometer screw, one clamping jaw of the strain device is moved and the sample is stretched. Spectra for the unstretched sample and two strain states are shown.It is clearly visible that the resonance changes only minimally in wavelength.

[0038] Figure 9 shows the spectral optical properties of f-PCS when stretched parallel to the lattice alignment of the one-dimensional periodic nanostructure of an f-PCS with a 100-nanometer SiO2 sublayer. The sample was clamped in a strain jig for characterization. A displacement of 0 pm of the micrometer screw corresponds to 0% strain. By rotating the micrometer screw, a clamping jaw of the strain jig is moved, stretching the sample. Spectra for the unstretched sample and two strain states are shown. It is clearly evident that the resonance changes only minimally in wavelength.

[0039] Figure 10 shows the surface of an inventive f-PCS with a 100 nanometer SiO2 sublayer. The left image is taken in the relaxed state, and the right image is taken in the stretched state (in this case, 5%).

[0040] Examples are described below without limiting the doctrine in its generality.

[0041] The f-PCS without a sublayer are produced as follows. Polydimethylsiloxane (PDMS, manufacturer Dow Chemical, product name Sylgard 184) is mixed in a ratio of eight to one (elastomer to hardener) for twenty minutes. An ULTRA_TURRAX Tube Drive mixer from IKA is used for mixing. After twenty minutes of stirring, the PDMS is degassed. To do this, the PDMS is subjected to a vacuum for twenty minutes until no more bubbles form and a clear liquid is visible. This liquid is then deposited onto a nanostructured master. The master was produced by AMO GmbH using interference lithography. The nanostructure of the master has a period of 370 nm and a grating depth of 30 nm, 45 nm, or 60 nm. This master is placed in a basin with the nanostructure facing upwards. The PDMS is tilted onto this master until the master is completely covered. The master and the PDMS are then baked for 30 minutes at 130°C.The Heraeus T6060 furnace is used for this purpose. After baking, the now-cured PDMS is cooled for one hour. After cooling, the master and the PDMS are cut from the tank with a scalpel and carefully separated. The PDMS is now imprinted with the negative mold of the nanostructure. In the next step, the nanostructured PDMS is attached to a holder for the sputtering system using Kapton tape and installed in the sputtering system. The sputtering system is a model nano36 from Kurt J. Lesker. It can be equipped with up to three targets. After evacuating the sputtering system, a high-index layer of Nb2Ü5 (Kurt J. Lesker, EJUNBOX353TK 4) or TiO2>2 (Kurt J. Lesker, EJUTIO2403TK4) is applied to the PDMS using RF sputtering. The layer thickness is between 60 nm and 100 nm. After the sputtering process, the PDMS substrates are removed from the sputtering system.The slabs are then created by fractures of the high-index layer under mechanical stress.

[0042] The f-PCS with sublayer are produced as follows. Polydimethylsiloxane (PDMS, manufacturer Dow Chemical, product name Sylgard 184) is mixed in a ratio of eight to one (elastomer to hardener) for twenty minutes. An ULTRA_TURRAX Tube Drive mixer from IKA is used for mixing. After twenty minutes of stirring, the PDMS is degassed. To do this, the PDMS is subjected to a vacuum for twenty minutes until no more bubbles form and a clear liquid is visible. This liquid is then deposited onto a nanostructured master. The master was produced by AMO GmbH using interference lithography. The nanostructure of the master has a period of 370 nm and a grating depth of 30 nm, 45 nm, or 60 nm. This master is placed in a basin with the nanostructure facing upwards. The PDMS is tilted onto this master until the master is completely covered. The master and the PDMS are then baked for 30 minutes at 130°C.The Heraeus T6060 furnace is used for this purpose. After baking, the now-cured PDMS is cooled for one hour. After cooling, the master and the PDMS are cut from the tank with a scalpel and carefully separated. The PDMS is now imprinted with the negative mold of the nanostructure. In the next step, the nanostructured PDMS is attached to a holder for the sputtering system using Kapton adhesive tape and installed in the sputtering system. The sputtering system is a model nano36 from Kurt J. Lesker. It can accommodate up to three targets. After evacuating the sputtering system, a low-index SiO2 layer (company: Kurt J. Lesker, EJUSIO2453TK4) is first applied using RF sputtering. The high-index layer of Nb2O5 (Kurt J. Lesker, EJUNBOX353TK4) or TiO2 (Kurt J. Lesker, EJUTIO2403TK4) is then applied to the low-index layer using RF sputtering. The layer thickness is between 60 nm and 100 nm.After the sputtering process, the PDMS substrates are removed from the sputtering system. The slabs are then created by fractures of the high-index layer under mechanical stress. The measurement of the samples is the same for both f-PCS variants. The f-PCS is mounted on a strain holder between two clamping jaws. One of the clamping jaws is movable and can be moved using a micrometer screw (Mitutoyo, 102-301). The holder is positioned on a transmitted-light microscope (Nikon Eclipse Ti-ll) and illuminated with white light (Nikon D-LH / LC). The strain holder is located between two linear polarizing filters that suppress the excitation light and transmit only the resonance of the f-PCS. The resonance of the f-PCS is then directed either to a spectrometer or to a Nikon camera (Nikon Digital Camera D5100). Now the f-PCS is stretched in defined steps by further turning the micrometer screw (e.g. in 100 pm steps).After each step, a spectrum and an image are recorded. The spectra are subsequently evaluated by tracking the change in the resonance peak position relative to the strain using fitting algorithms. The images provide information about the extent of the lateral displacement of the floes due to the strain.

[0043] List of illustrations

[0044] Fig. 1 Stretchable photonic crystal plate according to the invention;

[0045] Fig. 2 Stretchable photonic crystal plate with sublayer according to the invention;

[0046] Fig. 3 Stretchable photonic crystal plate with superlayer according to the invention;

[0047] Fig. 4 Stretchable photonic crystal plate according to the invention with widened

[0048] expansion groove;

[0049] Fig. 5 Illustration of the optical stability of f-PCS without a sublayer when stretched perpendicular to the grating orientation. The top panel shows the resonance shift when stretched horizontally. The bottom panel shows the spectral response.

[0050] Fig. 6 Illustration of the optical stability of f-PCS without a sublayer when stretched parallel to the grating alignment. The resonance shift upon parallel stretching is shown at the top. The spectral response is shown at the bottom.

[0051] Fig. 7 The left image shows the expansion holder (clamping device) with an f-PCS. The middle image shows the floe structure on the f-PCS in a relaxed state. The right image shows the floe structure under expansion (in this case 6%).

[0052] Fig. 8 Illustration of the spectral behavior during strain perpendicular to the lattice alignment of f-PCS with a sublayer of 100 nanometers SiO2;

[0053] Fig. 9 Representation of the spectral response when strained parallel to the lattice alignment for f-PCS with a sublayer of 100 nanometers SiO2;

[0054] Fig. 10 Illustration of the surface of an f-PCS with a 100-nanometer SiO2 sublayer. The left image is in the relaxed state, and the right image is in the stretched state (in this case, 5%).

[0055] List of reference symbols

[0056] 1 substrate layer

[0057] 2 nanostructured waveguide layer

[0058] 3 waveguide layer floe

[0059] 4 expansion groove

[0060] 5 Sublayer

[0061] 6 Supershift

Claims

CLAIMS Stretchable photonic crystal plate, wherein said plate has a percentage change in the optical resonance wave of less than 0.2%, normalized to the percentage strain, characterized in that the stretchable photonic crystal plate has a stretchable substrate layer (1) and a nanostructured waveguide layer (2), wherein the waveguide layer (2) has slabs (3) delimited by strain grooves (4), and wherein the slabs (3) have a size between 2 pm and 1 mm. Stretchable photonic crystal plate according to claim 1, characterized in that the nanostructured waveguide layer (2) is formed from materials selected from the group titanium dioxide (TiO2), niobium pentoxide (Nb2O5) and / or tantalum pentoxide (Ta2O5). Stretchable photonic crystal plate according to claim 1 or 2, characterized in that the stretchable substrate layer (1) also has a nanostructure.The stretchable photonic crystal plate according to claim 1, 2, or 3, characterized in that, in addition to the stretchable substrate layer (1) and the nanostructured waveguide layer (2), the stretchable photonic crystal plate also has at least one sublayer (5). The stretchable photonic crystal plate according to claim 4, characterized in that the at least one sublayer (5) is a low-index layer. The stretchable photonic crystal plate according to claim 4 or 5, characterized in that the sublayer (5) is formed from the material silicon dioxide (SiO2). The stretchable photonic crystal plate according to one of the preceding claims, characterized in that the stretchable photonic crystal plate has at least one superlayer (6).

8. Stretchable photonic crystal plate according to claim 7, characterized in that the material for the superlayers is selected from the group gold (Au) and / or silicon dioxide (SiO2).

9. A method for producing a stretchable photonic crystal plate according to one of the preceding claims, comprising the following steps: i. producing the flexible substrate layer by: a. casting a master mold, b. degassing, and c. subsequently allowing it to harden; ii. optionally applying a sublayer to the flexible substrate layer produced in step i. using the cathode sputtering method; iii. applying a high-index waveguide layer to the flexible substrate layer produced in step i. or in step ii. using the cathode sputtering method; iv. producing the expansion grooves in the waveguide layer a. by mechanical loading or b. by lithographic methods or c. with the aid of masks, wherein in the lithographic methods (iv. b.) or the use of masks (iv.c.) Expansion grooves in the range of 0.5 pm to 1 mm can be specifically adjusted.

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