DE102014203488B4 - Device with switchable optical properties, method for producing a device and use of a device - Google Patents

Abstract

Device (1) with switchable optical properties, the device (1) having a nanostructured surface (3) with at least one nanostructure (5), the nanostructure (5) having a characteristic dimension of at least 100 nm, and the nanostructure ( 5) has a material (15) which, in a first hydration state, exhibits a plasmonic resonance in a wavelength range dependent on the characteristic dimension, the plasmonic resonance being at least attenuated in a second hydride state of the material (15), the material (15) is reversibly switchable from the first to the second hydration state.

Description

The invention relates to a device with switchable optical properties according to claim 1, a method for producing a device with switchable optical properties according to claim 12, and the use of a device with switchable optical properties according to claim 16.

Devices with switchable optical properties are known. For example, there are rotatable interference filters in which a reflected or transmitted wavelength range can be shifted with respect to its position in the electromagnetic spectrum by rotating the filter. Expanding foils provided with gold nano-antennas are also known which have an absorption in a specific wavelength range which can be shifted by stretching the foil. The disadvantage of these approaches is on the one hand the difficulty of selecting a certain, optically switchable wavelength range with a certain bandwidth and producing a device accordingly, and on the other hand the fact that the wavelength range to be switched is only shifted within the electromagnetic spectrum. As a result, there is always the risk that a flank of a shifted absorption or reflection band will still protrude into the area under consideration, so that, in principle, a particularly good switching contrast cannot be achieved. In addition, the optical properties of the devices mentioned here by way of example are switched mechanically, for example by turning or stretching. This causes wear and thus a reduction in the service life of the devices.

Phase change materials are also known which either function as plasmonic nano-antennas themselves or are used in combination with nano-antennas made of other materials, for example gold. Such phase change materials are, for example, vanadium dioxide (VO ₂ ), germanium antimony telluride (GST, Ge ₂ Sb ₂ Te ₅ ), and gallium lanthanum sulfide (GLS). Such phase change materials are typically switchable electrically, by laser pulses or, in particular, thermally. However, since the phase change takes place at a certain critical temperature, such materials can only be used under certain, appropriate environmental conditions. Furthermore, the phase change materials themselves have only a low quality, in particular poor electrical conductivity and thus high attenuation, so that they have very poor optical properties. They are therefore seldom used alone, but rather in hybrid plasmonic systems, for example combined with nano antennas made of gold or other metals with low plasmonic attenuation. If a phase change is then carried out in the phase change material, the dielectric environment of the actual nano-antenna changes, so that its plasmonic response is changed. However, this results in an extremely low switching contrast, because it is not the properties of the antenna itself that are changed, but only its dielectric environment.

Out US 8 077 276 B2 discloses a display system that includes a dimming device that is capable of being switched between a light-reflecting state and a light-transmitting state. The dimming device has a layer structure with a first layer and a second layer, the first layer comprising a first material whose optical properties change as a function of a hydrogen concentration. The second layer comprises a second material that can release or absorb hydrogen upon external stimulation. The first material can be yttrium, lanthanum, or an Mg ₂ Ni alloy. In particular, the first layer consists of a matrix in which microparticles of the first material are embedded. The surface of such a layer is planar and has no structure. The dimming device does not have any specific tuning to a specific wavelength range. It therefore only has a non-specific, wavelength-independent dimming property.

Out Strohfeldt, N. [et al.]: Long-term stability of capped and buffered palladium-nickel thin films and nanostructures for plasmonic hydrogen sensing applications. In: OPTICAL MATERIALS EXPRESS, Vol. 3, No. 2, 2013, pp. 194-204 , a nanostructure emerges from palladium nanodiscs, which has the function of a hydrogen sensor.

The invention is therefore based on the object of creating a device which does not have the disadvantages mentioned. Accordingly, it is the object of the invention to provide a method for producing such a device and uses thereof.

The object is achieved in that a device with the features of claim 1 is created. This has a nanostructured surface with at least one nanostructure, the nanostructure having a characteristic dimension of at least 100 nm, preferably of at least 200 nm. The nanostructure has a material which, in a first hydration state, exhibits a plasmonic resonance in a wavelength range dependent on the characteristic dimension, the plasmonic resonance being at least attenuated in a second hydride state of the material. Preferably the plasmonic resonance disappears completely in the second hydration state of the material. The material can be reversibly switched from the first to the second hydration state. Because the plasmonic resonance is at least attenuated in the second hydration state of the material, whereby it preferably disappears, the optical properties of the device change, such as its transmission, reflection and / or absorption in the spectral range of the plasmonic resonance when the nanostructure is converted from the first hydration state to the second hydration state or back. The nanostructured surface preferably has a multiplicity of nanostructures. Because the wavelength range of the plasmonic resonance depends on the characteristic dimensions of the nanostructure, it is easily possible to select a suitable wavelength range, in particular to match the intended use of the device, and to match the nanostructure with regard to its characteristic dimensions. The device can be adapted to a large number of possible uses and to a large number of desired wavelength ranges. It can also be used independently of external environmental conditions and in particular in different temperature ranges. Because the plasmonic resonance depends on the hydration state of the material of the nanostructure, whereby it preferably disappears completely in the second hydration state, a high switching contrast can be achieved for the device. The reversibility of the conversion of the material from the first to the second hydration state and back ensures that the device can be used without restriction over a long service life with consistent properties without wear and without aging.

The first state of hydration differs from the second state of hydration in that the material in the first state of hydration has a lower hydrogen content than in the second state of hydration. It is possible here for the material to have no hydrogen in the first hydration state, it being possible, for example, to be in elemental form, in which case it has hydrogen in the second hydration state, in particular as a hydrogen compound. Alternatively, it is preferably possible that the material is present in the first hydration state as a hydrogen compound with a lower stoichiometric hydrogen content, it being present in the second hydration state as a hydrogen compound with a higher stoichiometric hydrogen content.

A maximum of the switchable plasmonic resonance band is preferably in a range that extends from the near infrared (wavelength at least 800 nm) to the terahertz range (wavelength <1 mm). The characteristic dimension of the nanostructure is always smaller than the wavelength range to be switched. In particular, the characteristic dimension is preferably at most 20 μm, particularly preferably at most 15 μm.

The term “nanostructured” refers to a structure of the surface, the characteristic dimension of which is in a size range in which a plasmonic resonance occurs in the first hydration state. Accordingly, the characteristic dimension of the nanostructure is in particular at most so large that a plasmonic resonance can still be observed.

The term “characteristic dimension” is to be understood as a dimension of the nanostructure on which the spectral position of the plasmonic resonance depends. For example, the characteristic dimension is a length of the nanostructure along a direction in which a dipole oscillation is excited within the scope of the plasmonic resonance, the resonance frequency depending on the length. If a nanostructure has different dimensions in different directions, a dimension in one of the directions is typically decisive for the spectral position of the plasmonic resonance. If, for example, a rod-shaped nanostructure is considered, the length of the rod-shaped nanostructure is typically decisive for the spectral position of the plasmonic resonance, while a width and height play at most a subordinate role for this. Therefore, in this example, the length of the rod-shaped nanostructure is to be regarded as a characteristic dimension.

It turns out that, in particular from a characteristic dimension of at least 100 nm, the spectral position of the plasmonic resonance is dependent on the characteristic dimension, so that the device can be matched to desired spectral properties by suitable selection of the characteristic dimension. In contrast, there is a limit value for the characteristic dimension, below which there is no dependence of the spectral position of a plasmonic resonance, then typically interpreted as a Mie resonance, on the value of the characteristic dimension. Below this limit it is therefore no longer possible to spectrally match the nanostructure to a desired application by varying a dimension. The choice of a characteristic dimension of at least 100 nm ensures that the device can be spectrally tuned in the manner described.

A “plasmonic resonance” is understood here to mean a localized electron oscillation in a nanostructure that has delocalized electrons, in particular in a metallic nanostructure, the wavelength of the electron oscillation being in the range of the wavelength of the exciting light. It is possible to influence the plasmonic resonance of a nanostructure, in particular by changing its size, shape and material.

A device is also preferred which is characterized in that the nanostructure is selected from a group consisting of a rod-shaped structure, a disk-shaped or spherical structure, a wire-shaped structure, a lattice-shaped structure, a spiral-shaped structure, a cruciform structure, an oligomeric structure Structure, a curved structure, a three-dimensional arrangement, and a combination of at least two of these structures.

A rod-shaped structure is preferably to be understood as a structure which has a larger dimension in a selected direction than in the other two directions oriented perpendicular thereto. This particular direction is called the longitudinal direction of the nanostructure. The characteristic dimension of the nanostructure is preferably its size measured in the longitudinal direction, hence its length. The device particularly preferably has a rod-shaped nanostructure, the length and thus characteristic dimensions of which is at least 200 nm to at most 500 nm. The characteristic dimension is particularly preferably from at least 290 nm to at most 400 nm. Alternatively or additionally, the rod-shaped nanostructure has a height - measured from a surface on which the nanostructure is arranged - of at least 30 nm to at most 70 nm, preferably 50 nm, on. Alternatively or additionally, the nanostructure preferably has a width, measured perpendicular to the height and the longitudinal direction, which is from at least 140 nm to at most 180 nm, preferably 160 nm.

In a preferred exemplary embodiment of the device, a multiplicity of rod-shaped nanostructures are arranged one behind the other in rows oriented parallel to one another, in particular one behind the other along their longitudinal direction. This results - measured in the longitudinal direction - preferably a periodic structure with a period of at least 200 nm to at most 700 nm, preferably 400 nm, based on a unit cell of the periodic structure, the unit cell having exactly one nanostructure. Alternatively or additionally, the nanostructure has a corresponding period of at least 200 nm to at most 700 nm, preferably also of 400 nm, in a direction that is perpendicular to the longitudinal direction and lies in the nanostructured surface. The optical properties of such a periodic structure can be influenced on the one hand via the characteristic dimensions of the nanostructure and on the other hand via the choice of the period in at least one of the directions mentioned here.

The period is preferably selected essentially so that the different nanostructures do not influence one another, in particular do not interfere with one another. If the individual nanostructures are too close to one another, there may be interactions between the nanostructures, which affect their plasmonic resonances in an undesirable manner. A periodic structure of nanostructures can be produced in a particularly simple manner, it being possible at the same time, without additional, complex measures, to ensure that the individual nanostructures are not arranged too close to one another. Furthermore, a periodic arrangement of the nanostructures has the advantage of enabling a stronger and, in particular, also more homogeneous signal of the entire device than is the case with a random structure.

Alternatively, however, it is also possible for the nanostructures to be arranged in a disordered or random manner, or in quasi-periodic structures. As long as it is ensured here that the nanostructures do not interfere with one another, the plasmonic resonance of the individual devices is not negatively influenced. overall, however, the result is a weaker and less homogeneous signal than in the case of a periodic arrangement, and it is less easy to ensure during the manufacture of the device that the individual nanostructures are not positioned too close to one another.

A structured, in particular periodic arrangement of the nanostructures is preferred overall not only in connection with rod-shaped nanostructures, but also in connection with differently designed nanostructures, for example disc-shaped, spherical, wire-shaped, lattice-shaped, spiral-shaped, cross-shaped, oligomeric, curved or three-dimensional structures. Combinations of these structures are also preferably arranged periodically, resulting in the advantages described.

In the case of a wire-shaped structure, the extension in the longitudinal direction is preferably very much greater than the extension of the structure in the two directions oriented perpendicular thereto.

A lattice-shaped structure can be produced by lattice-shaped superimposition of rod-shaped and / or wire-shaped structures.

In a similar manner, a cross-shaped structure can be generated, for example, by crossing two rod-shaped structures, two wire-shaped structures, or one rod-shaped and one wire-shaped structure.

An oligomeric structure preferably has a plurality of individual nanostructures grouped relative to one another, which are combined to form a superordinate nanostructure through the grouping.

A curved structure preferably has either intrinsically curved nanostructures or else an arrangement of a plurality of nanostructures which are positioned along a curved curve. It is possible that the curvature runs in one plane and therefore two-dimensional. Alternatively, it is possible for the curvature to run in three dimensions, so that a three-dimensional, curved structure is realized.

Finally, a three-dimensional nanostructure or arrangement of nanostructures is also generally preferred. It is possible that the optical properties of the device result precisely from the three-dimensional arrangement of the nanostructure or the various nanostructures arranged three-dimensionally relative to one another.

In a preferred embodiment of the device, all of the nanostructures have the same material. But it is also possible to combine different materials with one another. For example, different neighboring nanostructures can comprise different materials. It is thus possible, for example, to arrange a nanostructure made of gold, in particular a gold antenna, next to a nanostructure made of a material other than gold. It is important, however, that such a different nano-antenna, in particular a gold antenna, is not required for the device to function. Rather, the device also has a high plasmonic quality and a high switching contrast when all nanostructures have the same material.

A device is also preferred which is characterized in that the material of the nanostructure is selected from a group consisting of a hydride of a rare earth element, a hydride of a transition metal, and a hydride of an alloy of a transition metal. In particular, it is possible that a hydride of a transition metal from the fourth group of the periodic table, ie a hydride of one of the elements scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc, is used as the material. In a preferred embodiment of the device it is provided that the material is selected from a hydride of an alloy of a transition metal with magnesium.

The term "rare earths" here refers to the elements of the third period of the periodic table with the exception of actinium, as well as the lanthanides, in total the elements scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, and Lutetium.

If a hydride of an element or an alloy is used as the material, this means that the first hydride state is already present as a hydrogen compound of the element or alloy, the second hydride state preferably being a hydrogen compound of the element or alloy with a higher hydrogen content than the first hydride state represents. Alternatively, however, it is also possible for the first hydration state to correspond to a state before hydration, i.e. a state of the element or alloy not connected to hydrogen, in particular - at least with regard to the connection with hydrogen - to a pure state of the element or alloy.

It is therefore possible to use a rare earth element, a transition metal, in particular from the fourth group of the periodic table, or an alloy of a transition metal, in particular an alloy with magnesium, as material in the device.

It is preferably possible that vanadium or vanadium hydride is used as the material.

Particularly preferred is an embodiment of the device in which the material is selected from a group consisting of yttrium dihydride (YH ₂ ), scandium dihydride (ScH ₂ ), lanthanum dihydride (LaH ₂ ), gadolinium dihydride (GdH ₂ ) and promethium dihydride (PmH ₂ ). The first hydration state of the materials mentioned here corresponds in each case to the specified dihydride compound. Due to the high negative enthalpy of reaction between the elements and hydrogen, this is stable and does not spontaneously transform into the unhydrogenated elements. By supplying hydrogen it is possible to convert the materials mentioned into the second hydration state, with, under preferred conditions, namely a hydrogen partial pressure of less than 1 bar up to 1 bar a temperature of about 25 ° C, no complete conversion into the trihydride state, i.e. to MeH ₃ with Me = Y, Sc, La, Gd or Pm, can be achieved. Rather, when hydrogen is supplied as the second hydration state, a final state is reached which is described by the formula MeH _3-x , where Me = Y, Sc, La, Gd or Pm, and x is from at least 0.1 to at most 0.3. Under a high hydrogen partial pressure it is also possible to achieve a composition in which x = 0.01. For the sake of simpler representation, the second hydration state is always referred to below in connection with the elements specifically mentioned here as the trihydride state (MeH ₃ ). This shows that the conversion from the first hydride state, here the dihydride state, to the second hydride state, here the trihydride state, takes place completely reversibly, with the dihydride state being converted into the trihydride state with the supply of hydrogen, which is returned again after the hydrogen supply is interrupted is converted to the dihydride state. A strong and completely reversible conversion of the dielectric properties of the material takes place. The material is metallic in the first hydration state, that is to say as a dihydride, while in the second hydration state, that is to say as a trihydride, it is present as a dielectric or transparent semiconductor. A plasmonic resonance present in the metallic state disappears completely when the material is in the second hydration state, in this case as a trihydride. When converting back to the first hydration state, the plasmonic resonance is completely restored.

Alternatively, an embodiment of the device is preferred in which the material is selected from a group consisting of a hydride of a magnesium alloy of yttrium, a hydride of a magnesium alloy of lanthanum, a hydride of a magnesium alloy of scandium, a hydride of a magnesium alloy of gadolinium, a hydride of a Magnesium alloy of promethium, and a hydride of an alloy of the form Mg ₂ MeH _x with Me = Ni, Co, or Fe. These materials are characterized by a particularly rapid reaction from the first to the second hydration state and back. In addition, they have a particularly high switching contrast - right up to complete absorption in the first hydration state - between the two states.

It is also advantageous that with the materials mentioned here it is possible to use the device under normal pressure and in particular under atmospheric conditions without the properties of the device being impaired. It is therefore not necessary to keep the device under vacuum, nor does a protective gas have to be used. Nevertheless, the use of a protective gas is preferred from the point of view of the risk of explosion due to an oxyhydrogen reaction. However, it is emphasized that even the presence of oxygen does not impair the functionality of the device with regard to its switchable optical properties.

A device is particularly preferred which is characterized in that yttrium dihydride (YH ₂ ) is used as the material. The first state of hydration corresponds to this dihydride compound, the second state of hydration under the preferred conditions described above typically not reaching the stoichiometric trihydride state, but rather a final state which corresponds to the forms YH _3-x given above, where x is at least 0, 1 to a maximum of 0.3. However, as already stated above, it is possible under high hydrogen partial pressure to achieve a value of 0.01 for x. For the sake of simplicity, especially in connection with this material, the second hydration state is hereinafter referred to as yttrium trihydride (YH ₃ ).

Yttrium is not a typical plasmonic material. Rather, it is surprising that precisely yttrium is suitable for the device proposed here. As such, yttrium has a comparatively low electrical conductivity and thus high plasmonic attenuation, so that it is usually assumed that this material is not very suitable for plasmonic nanostructures. In contrast, within the scope of the invention - in particular through numerical simulations of the dielectric functions of yttrium and yttrium dihydride - it has been recognized that suitable plasmonic resonances are formed and that yttrium is a particularly suitable material for the device proposed here.

For yttrium it is shown in particular that the dihydride, which is metallic, has a higher electrical conductivity than elemental yttrium. As a result, a plasmonic resonance in the dihydride state is more pronounced than in the elemental state of yttrium. In addition, it is shown that the dihydride state of yttrium is extremely stable due to the strongly negative enthalpy of reaction of the hydration reaction of yttrium with hydrogen, whereby the yttrium dihydride does not spontaneously convert into elemental yttrium and hydrogen under normal conditions. In contrast, the reaction of yttrium dihydride to yttrium trihydride is reversible. Thus, with the supply of hydrogen, the conversion of the first hydride state (dihydride) into the second hydride state (trihydride) takes place, while the second Hydridation state is again completely converted into the first hydration state after interruption of the hydrogen supply. Yttrium trihydride is a dielectric, especially a transparent semiconductor. A metal-insulator transition therefore takes place from the first hydration state to the second hydration state, due to which the plasmonic resonance present in the first hydration state disappears completely in the second hydration state. This results in a very high switching contrast between the first and second hydration states. By simply switching a hydrogen supply on and off, a switchover between the two hydridization states can be effected completely wear-free and reversibly.

Use of the device at atmospheric pressure and under atmospheric conditions is readily possible without the need to use a protective gas or a vacuum. Rather, the device can also be used in the presence of oxygen, although a reduction in the oxygen partial pressure or even exclusion of the presence of oxygen is preferred in order to prevent the risk of an oxyhydrogen reaction with the hydrogen used to switch the optical properties of the device.

An exemplary embodiment of the device is also preferred which is characterized in that the nanostructure is arranged on a substrate. The substrate has a dielectric or consists of a dielectric. It is possible for the substrate to have a plurality of layers, in particular to consist of a plurality of layers, at least one upper layer on which the nanostructure is arranged directly having a dielectric or consisting of a dielectric. In particular, an embodiment is possible in which the substrate has a first, metallic layer, which preferably comprises gold or consists of gold, wherein the substrate has a second layer arranged on the first layer, which consists of a dielectric, preferably magnesium fluoride ( MgF ₂ ). In this case, the nanostructure is arranged on the second, dielectric layer.

The substrate preferably has a transparent dielectric or consists of a transparent dielectric. This is particularly preferred when the device is to have switchable optical properties which are measured in transmission. Alternatively, it is possible that the substrate has a non-transparent dielectric or consists of a non-transparent dielectric. This is preferably provided when the device has switchable optical properties that are measured in reflection. It is also possible for the substrate to have both a transparent and a non-transparent dielectric, for example in the form of different layers. Finally, it is possible for the substrate to have a switchable dielectric, the properties of which can be switched from transparent to non-transparent and preferably also back.

In this context, the term “transparent” in the context of the invention means in particular that transparency is given at least in the wavelength range in which the plasmonic resonance band is arranged in the first hydration state. There can also be transparency in other wavelength ranges, but it is also possible that there is no or at least not complete transparency there. In any case, the transparency in the wavelength range of the plasmonic resonance of the first hydration state is of particular interest for the invention. The term “non-transparent” is to be understood accordingly in the context of the invention, that is to say as a counter-term or complementary term to the previously explained term “transparent”.

In a preferred embodiment of the device, the substrate has glass, preferably quartz glass. The substrate particularly preferably consists of glass, in particular of quartz glass.

An exemplary embodiment is also possible in which the substrate has an expansion film, consists of an expansion film or is designed as an expansion film. The at least one nanostructure is arranged on the stretch film. If a large number of nanostructures are arranged on the stretch film, it is possible to vary a distance between the individual nanostructures by preferably elastic stretching of the stretch film. This allows the optical properties of the device to be influenced in addition to its switchability. For example, it is thus possible to shift the spectral position of the plasmonic resonance in the first hydration state.

Also preferred is an embodiment of the device which has a source for atomic hydrogen or protons. The source is arranged and designed in such a way that atomic hydrogen or protons can be supplied through it to the nanostructure. It is possible that the material of the nanostructure does not react with molecular hydrogen, but rather only with atomic hydrogen or with protons in order to move from the first hydration state to the second hydration state. It is also possible that the material reacts with molecular hydrogen, with a reaction rate for a reaction with atomic hydrogen or with protons is much greater than a reaction rate with molecular hydrogen. If yttrium dihydride is used as material, it only reacts with atomic hydrogen or with protons. In this case, the source for atomic hydrogen or protons ensures that atomic hydrogen or protons can be supplied to the nanostructure for switching the optical properties of the device.

An exemplary embodiment of the device is also preferred which is characterized in that the source for atomic hydrogen or protons has a catalyst material which can catalytically convert molecular hydrogen into atomic hydrogen or into protons. Preferably the source consists of the catalyst material. The source is preferably arranged on the at least one nanostructure. In particular, it is possible for the nanostructure to be coated with the catalyst material of the source. Alternatively, it is possible that the catalyst material is arranged in the vicinity of the at least one nanostructure. The term “in the vicinity” preferably refers to a distance on the nanostructured surface that is selected in such a way that the atomic hydrogen or the protons provided by the source during a typical diffusion time that is necessary for the distance from the source to to travel to the nanostructure, do not recombine with each other to form molecular hydrogen. Depending on the specific design of the device, a different, characteristic migration time can also be addressed here instead of a diffusion time if other transport mechanisms exist from the source to the nanostructure, for example because a flow from the source to the nanostructure is specified. In such a case, too, the phrase “nearby” means that the distance is selected in such a way that the hydrogen atoms or protons do not recombine with one another to any relevant extent on their way from the source to the nanostructure. Thus, depending on the specific transport mechanism, the source can ultimately be arranged closer to the nanostructure or further away from it. An exemplary embodiment is possible in which a global source is provided for all nanostructures of the nanostructured surface. For example, it is possible for the source to be integrated into a hydrogen supply to the device, for example in the form of a filter or grid coated with catalyst material. Alternatively it is possible for several sources to be arranged on the nanostructured surface. In particular, it is possible for a source to be assigned to each nanostructure. This is particularly the case when the nanostructure is coated with the catalyst material of the source.

Alternatively or additionally, an embodiment of the device is preferred in which an electrochemical source for atomic hydrogen or protons is provided. For example, it is possible for the device to have an electrochemical cell which is designed in such a way that, when an electrical voltage is applied, hydrogen is generated in the area of the nanostructured surface, preferably in statu nascendi. An electrode of the electrochemical cell at which hydrogen is generated - in particular in statu nascendi - is particularly preferably arranged in the immediate vicinity of the at least one nanostructure. It is then possible that the atomic hydrogen formed on the electrode combines with the material of the nanostructure before it can react to form molecular hydrogen. In one embodiment of the device, it is possible for the nanostructured surface to be arranged on an electrode of an electrochemical cell on which hydrogen is generated.

In an embodiment in which an electrochemical source for atomic hydrogen or protons is provided, it is easily possible to reverse this formation reaction, in particular by reversing the polarity of the electrochemical cell. In this way, after switching the device to the second hydration state, polarity reversal can be carried out, as a result of which hydrogen is then actively broken down at the electrode, so that the device returns from the second hydration state to the first hydration state. In this way, very simple switching of the device is possible, and neither a supply line for hydrogen nor a discharge line for the same is required. Rather, electrical feeds to the device are sufficient, as a result of which it can be embodied completely encapsulated. This is particularly advantageous with regard to miniaturization of the device, for example when used as an optical spectacle filter, because an external hydrogen supply could be perceived as disruptive here.

Of course, an embodiment is possible in which an electrochemical source is combined with a source which has catalyst material which is suitable for converting molecular hydrogen into atomic hydrogen or protons. For example, it is then possible that the hydrogen generated by the electrochemical source does not react in statu nascendi with the material of the nanostructure, but rather is initially formed as molecular hydrogen, which is then split up in a further step by the catalyst material.

It is also preferred an embodiment of the device, which thereby is characterized by the fact that the nanostructure has a top layer. In one embodiment it is possible that the cover layer serves to protect the nanostructure, namely in particular as protection against oxidation and / or as mechanical protection. In a preferred embodiment, the cover layer is arranged only on a nanostructure surface of the nanostructure facing away from the substrate. It has been recognized that this is sufficient for effective protection against oxidation. In this case, side surfaces of the nanostructure are preferably free from the cover layer. Accordingly, an oxide of the material of the nanostructure can form on these side surfaces when oxygen is supplied. However, this does not impair the function of the device.

The cover layer preferably has platinum or palladium. The cover layer is preferably made of platinum or palladium. The cover layer particularly preferably has platinum or consists of platinum. It has been recognized that platinum is much more stable to degradation than palladium and is therefore more durable, the overall durability of the device increasing if platinum is used for the cover layer instead of palladium. Both platinum and palladium have catalytic properties, due to which molecular hydrogen is catalytically converted into atomic hydrogen, so that a top layer made of these materials not only provides protection against oxidation and mechanical damage, but also serves as a source of atomic hydrogen. As already indicated above, it is possible to additionally provide an electrochemical source for atomic hydrogen or protons.

If the cover layer is only to serve as a catalyst for converting molecular hydrogen into atomic hydrogen or into protons, it is sufficient if it is arranged in the form of islands, in particular in the form of islands spaced apart, on the substrate surface or on the nanostructure surface . In particular, there is no need for a closed layer for the catalytic effect of the cover layer. On the other hand, if the cover layer is to provide additional protection against oxidation, in particular in the area of the nanostructure surface, a closed cover layer is preferably provided.

The cover layer preferably has a thickness of at least 2 nm to at most 15 nm, preferably from at least 5 nm to at most 7 nm, particularly preferably 6 nm. A cover layer with a thickness in this range interferes with the formation of a plasmonic resonance in the nanostructure not, the cover layer on the other hand being thick enough to ensure effective protection of the nanostructure against oxidation and mechanical damage. At the same time, sufficient catalytic activity is provided to provide atomic hydrogen or protons. Thicker cover layers, in particular in the range of 20 nm thickness, interfere with the development of the plasmonic resonance in the nanostructure. Thinner cover layers, on the other hand, may no longer guarantee adequate protection of the nanostructure, and at the same time their catalytic activity may be inadequate.

If the device has a large number of nanostructures, these are preferably designed to be identical in particular with regard to their characteristic dimensions, particularly preferably with regard to all dimensions and geometric features and / or with regard to their material. However, an exemplary embodiment of the device is also possible in which different nanostructures, in particular with different characteristic dimensions, with different orientations, and / or with different materials are combined with one another. This makes it possible to adapt the optical properties of the device even more flexibly to different wavelengths and / or polarizations. Different, complex combinations of nanostructures can also be realized in order to realize different functionalities, such as narrower wavelength bands or other specific optical properties.

The object is also achieved in that a method for producing a device with switchable optical properties having the features of claim 12 is created. In particular, a device according to one of the exemplary embodiments described above is produced as part of the method. Within the scope of the method, a nanostructured surface with at least one nanostructure is produced on a substrate, the nanostructure having a material which, in a first hydration state, exhibits a plasmonic resonance in a wavelength range dependent on a characteristic dimension of the nanostructure, the plasmonic resonance in a second hydride state of the material is at least damped, and wherein the material is reversibly switchable from the first into the second hydride state. The material is preferably selected such that the plasmonic resonance completely disappears in the second hydration state. In connection with the method there are the advantages that have already been described in connection with the device.

A wavelength range to be switched is preferably selected as part of the method. The term of the wavelength range to be switched speaks one Wavelength range in which the plasmonic resonance to be switched or in any case the wavelength at the maximum of the band of plasmonic resonance is arranged. In a next step, a material suitable for the wavelength range to be switched is preferably determined. Furthermore, a suitable geometry for a nanostructure is preferably selected from the material. In particular, the characteristic dimensions of the nanostructure are preferably established. It is possible, through the choice of the material and the geometry and size of the nanostructure, to flexibly select a switchable wavelength range specifically for the application, and to design the device appropriately for the specific application required. According to what has been said above, it is evident that the wavelength range to be switched can be flexibly and suitably adapted or matched to the desired application over a wide range. It is therefore possible, in a simple manner, to produce a precisely fitting device with use-adapted, switchable optical properties.

In the context of the method, an arrangement and / or combination for a plurality of nanostructures is preferably also selected in order to flexibly adjust the optical properties of the device. It is particularly possible that with regard to their characteristic dimensions, their other dimensions and / or their geometry, their orientation and / or their material, different nanostructures are combined with one another and arranged relative to one another in such a way that certain optical properties are realized. Here, for example, different wavelengths and / or polarizations can be achieved for the device. In particular, various complex combinations of nanostructures are possible in order to realize certain functionalities such as narrower wavelength bands. Of course, within the scope of the method it is also possible to provide an arrangement of a large number of nanostructures that are identical in terms of their characteristic dimensions, their other dimensions and / or their geometry, and / or in terms of their material.

An embodiment of the method is also preferred which is characterized in that a mask is applied to the substrate. The mask is structured as a negative form of the nanostructure to be produced. The material or a starting material for the nanostructure is then introduced into the structured mask. In this case, in particular, recessed areas or recesses previously formed during the structuring of the mask are filled with the material or the starting material. The mask is then removed. The positive shape of the material or of the starting material then remains on the substrate, whereby the nanostructured surface is formed.

If the material is introduced into the structured mask, this indicates in particular that it is already introduced into the mask in the first hydration state. As an alternative, it is possible for a starting material for the nanostructure to be introduced into the structured mask, the starting material not yet being in the first hydration state but, for example, in the elemental state. The starting material is then later brought into the first hydration state. A mask made of polymethyl methacrylate, or PMMA for short, is preferably applied to the substrate, the mask being structured as a negative form of the nanostructure to be produced by electron beam lithography and subsequent development. This procedure is known as such, so it will not be discussed further here. It is emphasized, however, that the development of the mask, which is preferably carried out using a wet chemical process, does not have any negative influence on the functionality of the device. This shows that the device functions very stably even under poorly clean production conditions, with the type of production proposed here allowing a comparatively high concentration of impurities to get onto the nanostructured surface and also into the material of the nanostructure itself. However, the device proposed here is not sensitive to this, so that no particularly clean conditions, in particular no manufacture under vacuum or a protective gas atmosphere, are required for its manufacture.

It turns out that the removal of the mask is also preferably carried out wet-chemically, the functionality of the device not being impaired by this either.

An embodiment of the method is preferred which is characterized in that a starting material for the nanostructure is introduced into the structured mask, the starting material then - preferably after removal of the mask - being converted into the first hydration state. For example, it is possible that hydrogen is supplied to the starting material in order to convert it into the first hydration state. Elemental yttrium is particularly preferably introduced into the structured mask as the starting material, the yttrium - preferably after removal of the mask - being converted into the material in its first hydration state, namely yttrium dihydride, by adding hydrogen. The elemental yttrium is preferred for conversion to yttrium dihydride with a mixture of 4% by volume of hydrogen in Nitrogen applied for 10 min. Of course, a mixture of hydrogen with another protective gas, for example a noble gas, in particular argon, another inert gas, for example carbon dioxide, or a mixture of hydrogen with air is also possible. Exclusion of oxygen is only preferred for reasons of the risk of explosion.

The material or the starting material are preferably converted into the vapor phase by electron beam-assisted evaporation and thus evaporated onto the structured mask. Alternatively or in addition, it is possible for the material or the starting material to be converted into the vapor phase by thermal evaporation, by sputtering or in another suitable manner and thus to be evaporated onto the structured mask.

An embodiment of the method is also preferred which is characterized in that a cover layer is applied to the material or the starting material. The cover layer is preferably vapor-deposited, in particular by means of electron-beam-assisted vaporization. A platinum cover layer is particularly preferably applied. The cover layer is preferably applied after the material or the starting material has been applied and before the mask is removed, in particular without breaking the vacuum required for the preceding steps.

An embodiment of the method is preferred in which a mask made of PMMA is first arranged on a quartz glass substrate, the PMMA mask then being structured and developed by electron beam lithography. Then yttrium is evaporated onto the structured mask by means of electron beam-assisted evaporation. Platinum is then preferably vapor-deposited so that a platinum layer is formed on the yttrium. Finally, the mask is removed and the elemental yttrium is exposed to hydrogen in order to convert it to the first hydration state so that it is then present as yttrium dihydride.

Finally, the object is also achieved by using a device with optically switchable properties with the features of claim 16. The use relates in particular to a device according to one of the exemplary embodiments described above, or a device which is produced in a method according to one of the embodiments described above. The advantages that have already been described in connection with the device and the method are thereby realized.

One use of a device provides that it is used as a switchable optical filter. In particular, it is possible for the device to be used as a switchable infrared filter. A particularly preferred use provides that the device is used as a glasses filter, in particular as a military glasses filter, for example for use in night vision devices or otherwise for filtering IR radiation. It is particularly advantageous if the device is miniaturized, for which purpose an electrochemical source can be provided as a source for atomic hydrogen or protons. It is then also unnecessary to carry a hydrogen-containing gas bottle; rather, the device must be connected exclusively to a voltage source, for which a battery can be provided, for example.

The plasmonic resonance of the at least one nanostructure leads to a concentration of electromagnetic energy in the immediate vicinity of the nanostructure when irradiated with a wavelength tuned to the plasmonic resonance. This energy can be used to trigger local chemical reactions, in particular by providing local activation energy in the form of concentrated electromagnetic radiation. For this reason, it is also preferred to use the device in a locally controllable chemical reactor in which the optical properties of the device can be switched as required in order to either start the reaction locally by plasmonic resonance and an associated energy concentration, or start the To stop the reaction locally by preventing or switching off the plasmonic resonance or by preventing a sufficient supply of energy to start the reaction.

It is also preferred to use the device as an optical switching element, in particular for an integrated circuit, very particularly an integrated nano circuit. Such a switching element can preferably be used in the telecommunications sector and generally in optical communication.

Use of the device as a device with switchable plasmonically induced transparency (switchable plasmonically induced transparency - EIT) is also preferred. A plurality of nanostructures are preferably arranged relative to one another in such a way that a dipole couples with a quadrupole. For example, it is possible that three rod-shaped nanostructures are arranged relative to one another on the nanostructured surface in such a way that two nanostructures are aligned parallel to one another, while a third nanostructure is arranged perpendicular to and frontally in front of the two parallel nanostructures, so that a quasi U-shaped structure - albeit with spaced apart nanostructures - is created. In the event of electromagnetic excitation, the two nanostructures oriented parallel to one another form a quadrupole, while the nanostructure oriented perpendicular to this forms a dipole, the dipole coupling with the quadrupole. This results in a retardation for electromagnetic waves in the spectral range of the plasmonic excitation of the nanostructure arrangement. Such a switchable nanoplasmonic retarder - also referred to as a phase plate - is particularly suitable for use in telecommunications applications. An absorber based on the switchable plasmonic, electromagnetically induced transparency can also be designed in an analogous manner.

Such a device can have nanostructures which are all formed from the same material or have the same material. But it is also possible to combine different materials with one another. For example, it is possible for both the two rod-shaped nanostructures, which are oriented parallel to one another, and the nanostructure, which is oriented perpendicular thereto, to have yttrium or yttrium dihydride as material. However, it is also possible that the vertical nanostructure or the two parallel nanostructures have gold, while the other nanostructure or the other nanostructures in each case have yttrium or yttrium dihydride.

In this sense, use of the device as an optical retardation plate or optical retarder is also preferred, as described above. Use of the device as a phase shifter is also preferred. Use of the device as an optical modulator is also preferred.

As indicated, the device is preferably used in telecommunications applications. Typical wavelengths used for telecommunications are between 1.2 µm and 1.7 µm. The optical properties of the device can easily be adapted to this wavelength range, in particular by appropriate design of the characteristic dimensions of the nanostructure.

Use of the device as an optical absorber, in particular as a perfect, switchable optical absorber, is also preferred. A perfect absorber is characterized by an absorption of almost 100% for a specific wavelength. The device designed or used as a perfect, switchable optical absorber preferably has an absorption of at least 95%, particularly preferably of at least 99%. A preferred embodiment of such a perfect absorber has a two-layer substrate which has a first, reflective layer, preferably made of metal, a second, dielectric layer being arranged on the first layer. The nanostructured surface with the at least one nanostructure is arranged on the dielectric layer. The first layer preferably consists of gold, with the second layer consisting of magnesium fluoride (MgF ₂ ). Yttrium dihydride is preferably used as the material for the at least one nanostructure. The wavelength for which the perfect absorber has almost 100% absorption can be set on the one hand by the geometry of the at least one nanostructure and on the other hand by varying the thickness of the second, dielectric layer. The perfect absorber can be switched because it actually only absorbs in the first hydration state of the material of the nanostructure, while in the second hydration state it preferably has reflective properties due to the first, metallic layer of the substrate.

Use of the device as a nano-optical component is very generally preferred.

Finally, use of the device as a hydrogen detector is also preferred. The presence of hydrogen can easily be determined by the disappearance of the plasmonic resonance. If no hydrogen is present, the material of the nanostructure is in the first state of hydration, so that the plasmonic resonance can be observed. Under the influence of hydrogen, the material is converted into the second hydration state, so that no plasmonic resonance can be observed. In this way, hydrogen can be detected safely and reliably with high accuracy.

The description of the device, the method and the use are to be understood as complementary to one another. In particular, method steps that have been described in connection with the device or the use are steps of a preferred embodiment of the method. Device features which have been described in connection with the method and the use are features of a preferred exemplary embodiment of the device. The device is preferably characterized by at least one feature which is caused by at least one step of the method or by a feature of the use. Conversely, one embodiment of the method is preferably characterized by at least one method step due to a feature of the device.

Last but not least, within the scope of the invention, a switchable optical filter, in particular a switchable glasses filter, is preferred which has an exemplary embodiment of the device. Alternatively, the device is preferably designed as a switchable optical filter, in particular as a switchable glasses filter. Accordingly, a locally controllable chemical reactor, a switching element, in particular for an integrated circuit, a switchable plasmonic device with electromagnetically induced transparency, an optical retarder, an optical absorber, in particular a perfect, switchable optical absorber, and a hydrogen detector are also used as embodiments of the device prefers.

• 1 eine schematische Teildarstellung eines Ausführungsbeispiels einer Vorrichtung mit schaltbaren optischen Eigenschaften in Seitenansicht;
• 2 eine schematische Draufsicht auf die Vorrichtung;
• 3 eine diagrammatische Darstellung eines Extinktionsspektrums in dem ersten Hydridisierungszustand und in dem zweiten Hydridisierungszustand der Vorrichtung, und
• 4 eine diagrammatische Darstellung einer Abhängigkeit des Maximums einer plasmonischen Resonanzbande von einer charakteristischen Abmessung der Vorrichtung.

The invention is explained in more detail below with reference to the drawing. Show:

• 1 a schematic partial representation of an embodiment of a device with switchable optical properties in side view;
• 2 a schematic plan view of the device;
• 3 a diagrammatic representation of an extinction spectrum in the first hydration state and in the second hydration state of the device, and
• 4th a diagrammatic representation of a dependence of the maximum of a plasmonic resonance band on a characteristic dimension of the device.

1 shows a schematic partial representation of an embodiment of a device 1 with switchable optical properties in side view. The device 1 has a nano-structured surface 3 on, which in turn has a nanostructure 5 , preferably a multitude of such nanostructures 5 having. The nanostructure 5 is here rod-shaped, in particular cuboid. It has a characteristic dimension, which here is the length I of the cuboid nanostructure 5 is.

The nanostructure 5 is on a substrate 7th arranged, here specifically on a substrate surface 9 of the substrate 7th .

The nanostructure 5 has a height h _NS above the substrate surface 9 as well as one only in 2 width b shown, the width b being measured perpendicular to the direction of the length I and the height h _NS .

The characteristic dimension, here the length I, is at least 100 nm, preferably at least 200 nm. In a preferred exemplary embodiment of the device, the width b of the nanostructure is 160 nm, the height h _{NS being} 50 nm. The length I is in particular from at least 100 nm to at most 500 nm, preferably from at least 290 nm to at most 400 nm. Preferably, the length I is 290 nm, 320 nm, 335 nm, 355 nm, or 385 nm Width and height of the nanostructure 5 by varying the length I as the characteristic dimension, the spectral position of a maximum of a plasmonic resonance band, which in particular can be matched in this way to a desired use of the device. The device exhibits a variety of nanostructures 5 on, these are preferably formed identically, in particular having identical dimensions and particularly preferably periodically on the substrate surface 9 are arranged distributed. However, it is also possible for various nanostructures to be grouped together to form a superordinate nanostructure, with a plurality of such superordinate nanostructures then preferably being arranged - in particular periodically - on the substrate surface. A periodic arrangement of the nanostructures is not absolutely necessary, as long as it is ensured that the individual nanostructures do not mutually influence each other, in particular interference and / or a shift in the spectral position of the maximum of the plasmonic resonance band should / should be avoided. To that extent is the arrangement of the various nanostructures 5 each other preferably controlled. A periodic arrangement is particularly easy to produce, with a distance between the various nanostructures being able to be controlled in a particularly simple manner. In addition, a periodic arrangement ensures a particularly homogeneous and strong signal for the device 1 .

The nanostructure 5 points to the in 1 illustrated embodiment only on one of the substrate surface 9 facing away from the nanostructure surface 11 a top layer 13 on which the nanostructure 5 in the area of the nanostructure surface 11 on the one hand against oxidation and on the other hand against mechanical damage. Side faces of the nanostructure 5 that is inclined, in particular perpendicular to the substrate surface 9 are oriented do not have a cover layer here, but rather are free of the cover layer 13 . Here is some material on that 15th the nanostructure 5 exposed.

The material 15th has, in a first hydration state, a plasmonic resonance in a wavelength range that is dependent on the characteristic dimension, here length I, this plasmonic resonance in a second State of hydration of the material 15th is at least attenuated, preferably disappears completely. The material 15th is reversibly switchable from the first to the second hydration state. The material in the second hydration state has a higher hydrogen content than in the first hydration state, it being possible that the material 15th has no hydrogen in the first hydration state.

The exemplary embodiment of the device shown here preferably has 1 Yttrium dihydride (YH ₂ ) as a material 15th on. This corresponds to the first hydration state. When hydrogen is supplied, yttrium dihydride reacts to yttrium trihydride (YH _3-x with x = 0.01 to 0.3), this state being referred to as the trihydride state (YH ₃ ) for the sake of simplicity.

Preferably the in 1 illustrated embodiment as a cover layer 13 Platinum on. A height h _{DS of} the top layer 13 over the nanostructure surface 11 is preferably 6 nm.

The substrate 7th consists preferably of glass, in particular of quartz glass.

Passes the top layer 13 made of platinum, it is also designed as a source of atomic hydrogen, with platinum being a catalyst material which catalyzes the conversion of molecular hydrogen into atomic hydrogen. Hence the top layer 13 suitable in the vicinity of the nanostructure 5 present to convert molecular hydrogen into atomic hydrogen, which is then finally with the material 15th reacts so that this is converted in the presence of hydrogen from the first hydride state to the second hydride state. This conversion is completely reversible, so that in the absence of hydrogen, for example by switching off the hydrogen supply or also by actively removing the hydrogen, for example by pumping out or by (electro) chemical degradation, in particular in an electrochemical cell, the material 15th in turn is converted from the second hydration state to the first hydration state.

The ones not with the top layer 13 provided side surfaces of the nanostructure 5 are typically oxidized under the influence of oxygen. An oxide layer a few nanometers thick, for example with a thickness of 3 nm, is preferably formed. In the preferred exemplary embodiment discussed here, the oxide layer preferably has the empirical formula Y ₂ O ₃ .

2 shows a schematic representation of the device 1 in plan view. Identical and functionally identical elements are provided with the same reference symbols, so that in this respect reference is made to the preceding description. It turns out that here a large number of identical nanostructures 5 periodically in the form of a two-dimensional grid on the substrate surface 9 is arranged distributed. For the sake of clarity, there is only one of the nanostructures 5 with the reference number 5 marked. The lattice structure of the nanostructures 5 on the substrate surface 9 preferably settles over the entire substrate surface 9 periodically continued. Alternatively, however, there is also a quasi-periodic or otherwise controlled arrangement of the nanostructures 5 possible.

The top left is in 2 schematically a unit cell by dotted borders 17th the two-dimensional lattice structure is drawn, which is exactly one nanostructure 5 having. In the usual way, the entire periodic structure can be created by translation of the unit cell 17th along the horizontal as well as the vertical in 2 can be obtained. This shows that the lattice structure has a period P _x in the horizontal direction, referred to here as the x-direction, and a period P _y in the vertical direction, referred to here as the y-direction, in the image plane of 2 having. A value for at least one of the periods P _x and P _y is preferably at least 200 nm. A preferred range for the period P _x and / or the period P _y is from at least 400 nm to at most 700 nm. In a preferred exemplary embodiment, the periods are P _x and P _{y are the} same, particularly preferably they are both 400 nm. However, an exemplary embodiment is also possible in which the period P _{x is} 700 nm, the period P _{y being} 400 nm.

If the characteristic dimension, here the length I, is varied while the periods P _x and P _{y are} fixed, a filling factor of the nanostructured surface increases 3 , being the nanostructures 5 a larger proportion of the substrate surface 9 to complete. In addition to the variation of the characteristic dimension, this effect can lead to a shift in the plasmonic resonance of the nanostructures 5 contribute or be used specifically for this purpose.

3 shows a diagrammatic representation of the measured with the polarization of the exciting light aligned parallel to the length I extinction E of the embodiment of the device 1 according to 2 plotted against the excitation wavelength λ, with a solid line 19th the absorbance of the device 1 with the material 15th of nanostructures 5 represents in the first hydration state, with a dashed line 21st represents the absorbance observed when the material 15th is in the second hydration state. In the preferred embodiment, the solid line represents 19th therefore the represents plasmonic resonance of the yttrium dihydride exhibiting nanostructures, the dashed line 21st represents the extinction of the yttrium trihydride containing nanostructures, which is shown in 3 is indicated.

It turns out that the nanostructures 5 containing yttrium dihydride show a pronounced plasmonic resonance. This is because yttrium dihydride is a metal with good electrical conductivity, so that the plasmonic resonance experiences little attenuation. The top layer is effective here 13 slightly attenuating the plasmonic resonance, but this is not a relevant restriction due to its comparatively small height h _DS . The spectral position of a band maximum λ _{p of} the plasmonic resonance depends in particular on the characteristic dimensions of the nanostructure 5 , hence here from the length I. In addition, the position of the band maximum λ _{p is} also particularly influenced by the period P _x . Finally, the period P _{y also has} an - albeit smaller - influence on the position of the band maximum λ _p .

In a preferred use of the device 1 this is a mixture of hydrogen and nitrogen at a pressure of 1 bar, therefore at atmospheric pressure, fed, the mixture 5 Has vol .-% hydrogen. It is of course possible to use another protective gas, for example a noble gas, in particular argon, or another inert gas, for example carbon dioxide, instead of nitrogen. Furthermore, it is also possible to use a gas mixture of hydrogen and air. Exclusion of oxygen is only preferred for reasons of explosion protection. The supplied, molecular hydrogen is passed through the catalytically active cover layer 13 converted into atomic hydrogen by the material 15th is absorbed, which thereby reacts from the first hydration state to the second hydration state. In the case of metallic yttrium dihydride, there is a metal-insulator transition to dielectric yttrium trihydride, which is transparent. Is also the substrate 7th transparent, is in this hydration state of the material 15th the entire device 1 transparent. Correspondingly, the plasmonic band in the extinction spectrum disappears here, which is shown in 3 on the dashed line 21st is recognizable. This only rises towards small wavelengths λ because an extension of an electronic band of yttrium is observed here, which has its band maximum at 400 nm. In contrast, the band maximum λ _{p is} in an embodiment of the device in which the nanostructure made of yttrium dihydride has a height h _NS of 50 nm, a width b of 160 nm and a length I of 290 nm with a thickness of the top layer h _DS of 6 nm platinum and a periodicity P _x of 400 nm with an identical periodicity in the Y direction, at 1580 nm.

The device 1 thus has a very high switching contrast between the two hydration states, namely from almost complete transparency to an extinction of more than 40% in the metallic state. Differences in the relative extinction between the two hydration states of approximately 70% can be achieved without any particular effort, with absolute changes in the transmittance of 23% being achievable, which are readily observable with the naked eye. It is easily possible by varying the specific design of the device 1 to achieve even better switching contrasts right up to a perfect absorber that can be switched from almost complete transparency to almost complete absorption.

Will the device 1 If no more hydrogen is supplied or if the hydrogen is actively removed, the trihydride state of the material changes 15th completely reversibly back into the dihydride state, with the plasmonic resonance fully recovering. The change between the two hydration states is preferably diffusion-limited.

It is possible to accelerate the reactions from the first to the second hydration state and back by increasing the temperature of the device. Furthermore, the top layer 13 be made thinner or - depending on the ambient conditions and any other source of atomic hydrogen or protons that may be present - they can be omitted entirely. As a result, the - in particular through the diffusion through the cover layer 13 limited - reaction speeds increased. It also shows that the presence of oxygen - especially when the top layer 13 Has platinum or palladium -, accelerates the reaction from the second hydration state into the first hydration state. This is because that in the vicinity of the top layer 13 the reaction of the top layer 13 escaping hydrogen is accelerated with the oxygen to water, whereby the hydrogen is efficiently discharged. Finally, in particular the reaction from the second hydration state into the first hydration state can also be accelerated by flushing the device and thus expelling the released hydrogen.

4th shows a diagrammatic representation of the dependence of the band maximum λ _p plotted against the characteristic dimension, namely here the length I, of the nanostructure 5 . It is found that in the embodiment of the device discussed here 1 an essentially linear relationship between the length l of the nanostructures 5 and the wavelength of the band maximum λ _p exists, the wavelength of the band maximum λ _p with increasing length I of the nanostructures 5 increases.

In detail it can be seen that not only the wavelength of the band maximum λ _p , but also the extinction with the length I of the nanostructures 5 increases. This is essentially due to the increasing volume of the nanostructures 5 increasing dipole strength.

It is thus possible to determine the wavelength to be switched or the wavelength range of the switchable optical properties of the device 1 to be specifically tailored to a specific use of the same, in particular by adding the characteristic dimension, here namely the length l of the nanostructures 5 , is tuned to the desired target wavelength for the band maximum of the plasmonic resonance λ _p .

Overall, it can be seen that the device 1 a wear-free, completely reversible switchability that can be adapted to a large number of possible uses, in particular the absorption of the device 1 with high switching contrast.

Claims (16)

Device (1) with switchable optical properties, the device (1) having a nanostructured surface (3) with at least one nanostructure (5), the nanostructure (5) having a characteristic dimension of at least 100 nm, and the nanostructure ( 5) has a material (15) which, in a first hydration state, exhibits a plasmonic resonance in a wavelength range dependent on the characteristic dimension, the plasmonic resonance being at least attenuated in a second hydride state of the material (15), the material (15) is reversibly switchable from the first to the second hydration state. Device (1) according to Claim 1 , characterized in that the nanostructure (5) is selected from a group consisting of a rod-shaped structure, a disk-shaped or spherical structure, a wire-shaped structure, a lattice-shaped structure, a spiral structure, a cross-shaped structure, an oligomeric structure, a curved structure , a three-dimensional arrangement, and a combination of at least two of these structures. Device (1) according to one of the preceding claims, characterized in that the material (15) is selected from a group consisting of a hydride of a rare earth element, a hydride of a transition metal, and a hydride of an alloy of a transition metal. Device (1) according to one of the preceding claims, characterized in that the material (15) is selected from a group consisting of yttrium dihydride, scandium dihydride, lanthanum dihydride, gadolinium dihydride and promethium dihydride, or that the material (15) is selected from a group consisting of a hydride of a magnesium alloy of yttrium, a hydride of a magnesium alloy of lanthanum, a hydride of a magnesium alloy of scandium, a hydride of a magnesium alloy of gadolinium, a hydride of a magnesium alloy of promethium and a hydride of an alloy of the formula Mg ₂ MeH _x with Me = Ni, Co, or Fe. Device (1) according to one of the preceding claims, characterized in that the material (15) is yttrium dihydride (YH2). Device (1) according to one of the preceding claims, characterized in that the nanostructure (5) is arranged on a substrate (7), the substrate (7) having a dielectric or consisting of a dielectric. Device (1) according to one of the preceding claims, characterized in that the device (1) has a source for atomic hydrogen or protons, the source being arranged and designed such that atomic hydrogen or protons can be fed through it to the nanostructure (5) is / are. Device (1) according to Claim 7 , characterized in that the source has a catalyst material suitable for converting molecular hydrogen into atomic hydrogen. Device (1) according to one of the Claims 7 and 8th , characterized in that the device (1) has an electrochemical source for atomic hydrogen or protons. Device (1) according to one of the preceding claims, characterized in that the nanostructure (5) has a cover layer (13), wherein the cover layer (13) comprises platinum or palladium, or consists of platinum or palladium. Device (1) according to Claim 10 , characterized in that the cover layer (13) has a thickness of at least 2 nm to at most 10 nm. Method for producing a device (1) with switchable optical properties, wherein a nanostructured surface (3) with at least one nanostructure (5) is produced on a substrate (7) which has a material (15) which in a first hydration state has a shows plasmonic resonance in a wavelength range dependent on a characteristic dimension of the nanostructure (5), the plasmonic resonance being at least attenuated in a second hydration state of the material (15), and wherein the material (15) can be reversibly switched from the first to the second hydration state is. Procedure according to Claim 12 , characterized in that - a mask is applied to the substrate (7), wherein - the mask is structured as a negative form of the nanostructure (5) to be produced, wherein - the material (15) or a starting material for the nanostructure (5) in the structured mask is introduced, and wherein - the mask is removed. Procedure according to Claim 13 , characterized in that a starting material for the nanostructure (5) is introduced into the structured mask, the starting material then being converted into the material (15) in its first hydration state. Method according to one of the Claims 12 to 14th , characterized in that a cover layer (13) is applied to the nanostructure (5). Use of a device (1) with switchable optical properties, namely a device (1) according to one of the Claims 1 to 11 , or a device (1) produced by a method according to one of the Claims 12 to 15th , the device (1) being used - as a switchable optical filter, - in a locally controllable chemical reactor, - as a switching element, - as a device (1) with switchable plasmonically induced transparency, - as an optical retardation plate, - as a phase shifter, - as optical modulator, - as an optical absorber, and / or as - hydrogen detector.

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