WO2018114590A1 - Process for the production of microstructures - Google Patents

Abstract

The invention relates to a process for the production of microstructures in which a photosensitive material is provided on a substrate and a laser is focused in one or more regions of the material such that, in this region or these regions, the photosensitive material is activated by multi-photon absorption, wherein the laser is reflected on a reflective surface and is modulated by interference with itself in the region or the regions.

Description

 Applicant:

 Leibniz Institute for New Materials non-profit GmbH

 Campus D2 2

 66123 Saarbruecken

Process for the production of microstructures

description

Field of the invention

The invention relates to a process for selective photoactivation, in particular for the production of microstructures.

State of the art

Optical microstructures which act in the manner of photonic crystals have hitherto been produced by different methods. i) multi-film systems, mainly deposited, optionally followed by lateral structuring (by Gasphasenprozes ^¬ se such as PVD, CVD, ALD by conventional lithography imaging exposure or exposure masks ^¬)

ii) By standing waves supported conventional Li ^¬ thographie, wherein a photoresist in the exposed areas, or at the edge thereof by interference an additional vertical structure is imprinted Lateral high-resolution lithography techniques such as multi-beam interference lithography or electron beam lithography

 iv) rapid prototyping in

 Form of laser direct write, especially using two-photon polymerization

(Two-photon lithography)

v) self-assembly of colloidal systems In the drawing, these methods in particular in the structuring ^¬ tion in the vertical direction disadvantages. Due to their production, multifilm systems have only a single, uniform structure in the vertical direction over the entire surface. Here, even with the optional subsequent la--lateral structuring by conventional lithography SämT ^¬ Liche not etched regions retain the same vertical structure. The uniform vertical structure also applies to the convent ionel ^¬ le lithography with support by standing waves.

In addition, the vertical structure is limited to a strict periodicity. Other ^¬ lithography methods such as laser interference lithography or electron beam lithography are not capable of vertical to lateral centering struc ^¬ high resolution. Although conventional two-photon lithography allows a high degree of flexibility due to freely selectable arrangement of the structures in all three spatial directions, it is not significantly lower in the vertical resolution to a depth of focus

Write wavelength limited. Thus, the smallest wavelength at which generated structures in the manner of a photonic crystal can interact with light is significantly larger than the wavelength originally used to create the structure.

The self-assembly of colloidal systems is essentially limited to periodic structures. Disturbances of this Anord ^¬ voltage occur, but most are controllable in their density and not in their specific localization.

From Jeon et al. Small 2014, 10 (8), 1490-1494, Butt et al. Adv. Optical Mater. 2016, 4, 497-504 and Siddique et al. Optical ^¬ Ma terials Express 2015, 5 (5), May 2, 2015, the production of periodic structures is known, which are produced by interference of multiple laser beams or exposure to UV light in connection with a reflection on a substrate. In the case of Jeon et al. For example, a laser previously split into two is reassembled at an angle and this interference pattern is reflected on a reflective surface. Characterized periodic structures on the surface can be obtained wel ^¬ che are structured periodically in the vertical direction by the self-interference of the interference pattern. However, this lateral resolution and vertical resolution of the structural ^¬ structures strictly on the angle of the laser beams are dependent and therefore can not be influenced independently of one another. In the other method, the vertical resolution is achieved flat by a self-interference pattern of a UV lamp in conjunction with a light mask. Therefore, all structures have the same vertical structure and can not be freely varied.

task

The object of the invention is to provide a method which overcomes the disadvantages of the prior art and in particular allows the production of structures with improved structuring in the vertical direction.

solution

This object is achieved by the inventions having the features of the independent claims. Advantageous developments of the inventions are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into the content of this specification. The inventions also include all meaningful and in particular all-mentioned combination Nati ^¬ ones of independent and / or dependent claims.

The object is achieved by a method in which a photosensitive material is provided on a substrate and a laser is focused in one or more regions of the material such that in this region or these regions the photosensitive material is activated by multiphoton absorption, wherein the laser is reflected on a reflective surface and is modulated by interference with itself in the region or regions.

Individual method steps are closer beschrie ^¬ ben. The steps do not necessarily have to be performed in the order given, and the steps to be described

Method may also include other, not mentioned steps.

The invention relates to a method of Multiphotonenlithogra- pie. In this method, the wavelength of the excitation laser and the excitation wavelength of the photosensitive ^¬ Ma terials are chosen so that by multiple photon excitation with more activation is triggered. Accordingly, gen the excitation wavelengths mostly in the high frequency range, eg. B. in the UV range, while the laser used in the low-frequency range, z. B. in the infrared range, are. The need for multiple photons requires a very high focus of the laser, which is very high

Spatial resolution of activation allows. Usually, since ^¬ at least twice as great as the excitation wavelength of the photosensitive material at the wavelength of the laser. With multiple absorption, the wavelength can be several times as large as the excitation wavelength.

In multiphoton lithography, the excitation is effected by the absorption of 2 or more photons, preferably 2, 3 or 4 photons, in particular 2 or 3 photons. In the case of exactly 2 photons, the method is also referred to as two-photon ^lithography .

The wavelength of the laser is preferably between 450 nm and 3 μm, in particular between 640 nm and 3 μm.

In the conventional methods, a spatial resolution of 200 nm in the lateral direction is achieved by optical focusing, for example via droplet lenses. In the vertical direction, i. perpendicular to the surface, on the other hand, only a resolution of approx. 600 nm is possible because the laser can only be focused to a limited extent there.

The focusing preferably takes place only in a narrowly limited area of the surface. As a result, the generation of the structures on the surface can be precisely controlled. Preferably, the laser is focused in a lateral direction on a range.

By the reflection of the laser at a surface beispiels-, a reflective substrate, and the therefrom resultie ^¬ leaders interference modulating the intensity of the laser along the optical path through the material. Characterized an area or several areas in which the activation threshold is exceeded ^¬ for the material form. This may be the case in one or more areas, depending on the parameters used. The areas are usually in the form of an ellipsoidal disc, so that the material is activated within such a shaped area. The distance is given by half the write wavelength, di ^¬ vidiert by the refractive index of the material. By carefully setting the parameters, it is possible to actually exceed the activation threshold in only one of these disks, so that structural units with a vertical dimension of less than 200 nm can be realized. Structural units consisting of several (eg 2-12) of these individual disks, however, are also feasible. Similarly, by moving the laser and / or the substrate related activated Be ^¬ rich, such. As line structures are generated. Due to the interference, these individual slices have a spacing of half the write wavelength divided by the refractive index of the material. Within this vertical grid given by the standing waves, the vertical position of these structural units is freely addressable, in contrast to conventional lithography supported by standing waves. Since no restriction of the lateral positioning of the structural units takes place, the full flexibility and control remains. lierbarkeit the multiphoton lithography process obtained, supplemented by a much higher resolution in the vertical direction. Due to the interference, these features have a pitch of half the write wavelength divided by the refractive index of the material. By diffusion of radicals, the activated area can expand. This distance may still change due to shrinkage and swelling of the polymerized areas in later development steps. These steps can therefore also be used specifically to influence the final structure.

Standing waves over a reflecting substrate have been predominantly a disturbing factor in previous lithographic processes and have been exploited only occasionally, in conjunction with masking techniques, to impart a periodic structure to substantially vertical walls.

In a preferred embodiment, it is a pulsed laser. This is understood to mean a laser with a laser-own pulse, which allows Multiphotonenabsorption. Preference is given to a laser having a pulse duration of less than one picosecond, and particularly preferably a pulse peak power of more than 100 watts. The pulse duration and the pulse peak power of the laser are adjusted so that it allows in the desired range a sufficiently strong Multiphotonenaufnähme of the material through the Photoini ^¬ tiator to trigger the desired photoreaction. By appropriate choice of the parameters, the distance of the intensity maximum to the upper ^¬ surface can be precisely controlled in combination with the interference. This allows selective control of certain areas. It can also be pulsed several times to achieve a certain Akti ^¬ vation in one area. Likewise, different areas can be activated one after the other within a photosensitive material. How long a particular area is exposed to one or more pulses depends on the desired structure. By appropriate variations of the parameters, in particular those of successive regions, structures with different vertical distances can be obtained.

In carrying out the method, the exposure can also be interrupted by interrupting the beam path, for example, when a certain activation has been achieved for a certain range. The exposure can also be interrupted during writing of the structures, for example in order to control specific areas in the photosensitive material, in order to sequentially expose separate areas or to change the parameters of the exposure.

In combination with the interference of the laser by itself, it is possible, the intensity of the laser in such a way to concentrating ^¬ reindeer, that the activation threshold for multi-photon absorption in a range of less than 300 nm in the vertical direction, aeration vorzugt below 200 nm in the vertical direction, is fallen short of. A range of less than 600 nm is preferred in the lateral direction and below 300 nm in the vertical direction, preferably below 400 nm in the lateral direction and below 200 nm in the vertical direction. The information relates to the maximum extent of the activated area. These specifications apply in particular to Akti ^¬ vation with laser pulses. For continuous writing method, z. B. when activating along a linear area, z. B. For fence-like structures, areas with an extent in the vertical direction of less than 200 nm, preferably less than 100 nm, in particular less than 50 nm, preferably in each case in ^combination with a minimum extent in the lateral direction of less than 200 nm, preferably less than 100 nm , in particular below 50 nm, are activated.

With a suitable choice of the parameters, several adjoining areas in the vertical direction can be activated due to the interference, for example, if the energy of the intensity maxima of the interference pattern is also sufficient for ^exceeding the activation threshold.

In the method according to the invention, only an area with a certain vertical spacing is preferably activated during an exposure.

Preferably, step b) is carried out several times, wherein the laser activates a different area of the photosensitive material in at least one repetition.

In a preferred embodiment of the invention, only one laser with a wavelength is used for activation. The laser preferably meets perpendicular to the substrate.

The selective activation can be used differently depending on the photosensitive material. For example, spatially resolved fluorene emission or chemical functionalization can be produced. In a further preferred embodiment of the invention, the photosensitive material in the inactivated state is liquid or highly viscous. It is preferably in the to be exposed Be ^¬ reaching a homogeneous layer on the substrate.

In a preferred embodiment of the invention, the method is used to form a structure in the photosensitive material by the photoactivation. The photosensitive material is preferably a photosensitive resist (photoresist) whose solubility is changed by the photopolymerization. With a negative varnish, a free-standing structure is created after removal of the unexposed material. In the case of a positive varnish, voids are formed after removal of the exposed material.

Such a photosensitive material in this case preferably comprises at least one suitable photoinitiator and at least one photoreactive substance which is activated via the photoinitiator. This can, for example, lead to a change in the solubility.

Via a suitable photoinitiator, the absorption wavelength can be adjusted depending on the wavelength of the laser. It must be selected for multi-photon lithography so is that no suggestion he ^¬ follows at the wavelength of the laser, but only in multiphoton absorption. The photoinitiator are preferably compounds which, upon excitation, lead to the formation of radicals or ions. This can be done for example by the decomposition of the photoinitiator. Preference is given to the formation of radicals. Accordingly, the photo ^¬ paint in this case also comprises at least one radically polymerizable Group. These are, for example, non-aromatic C =C double bonds such as allyl or vinyl groups, particularly preferably double bonds which are accessible to Michael addition, very particularly preferably acrylate and methacrylate radicals.

Examples of negative coatings are SU-8, hybrid polymers, acrylic-based photoresists such as IP-L or IP-G. It may play acrylates or ^¬ lacquers on the basis of (meth) act epoxy resin. It may be necessary to thermally treat the paint before exposure to strengthen it, for example. It is also possible to use sol-gel systems or organopolysiloxanes.

Examples of coatings are paints comprising poly (meth) acrylates having 2, 3, 4, 5 or 6 methacrylate or acrylate groups such as pentaerythritol triacrylate (PETA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETTA), trimethylolpropane trimethacrylate (TMPTMA), poly (ethylene glycol) diacrylate (PEG-DA, avg. M _n 700), dipentaerythritol pentaacrylate

(DPEPA), 2- (hydroxymethyl) 2- [[(1-okoallyl) oxyl] methyl] -1,3-propanediyl diacrylate. 9H-fluorene-9,9-diylbis (4, 1-phenyleneoxyethane-2, 1-diyl) bis-acrylate. The coatings can include still zusätz ^¬ Lich compounds having a (meth) acrylate such as polyethylene glycol-o- phenylphenyletheracrylat.

Examples of photoinitiators are α-hydroxyketones, acylphosphine oxides, α-aminoketones, benzophenones, phenylglyoxylates, Irgacure 819, Irgacure 369, Darocur TPO, 7-diethylamino-3-thenoylcoumarin (DETC), 2-isopropylthioxanthone (ITX). The material may also include other adjuvants, such as radical scavengers, wetting aids.

The material may also include at least one solvent.

The photosensitive material onto a substrate aufgetra ^¬ gen. This can be done for example by spinning, drop, printing, brushing, roller coating, knife coating, dipping card or similar.

The structure is created by triggering the activation within the photosensitive material. The composition may include other ingredients.

Examples include dyes, fluorescent or phospho ^¬ reszierende compounds, nanoparticles, especially conductive nanoparticles, graphenes. These components can be used to provide the structures produced with further properties, such as fluorescence or conductivity.

As substrates different substrates are suitable. It can be directly to a, the laser reflecting surface han ^¬ spindles. Alternatively, it may also be a material permeable to the laser light under which the reflective surface is arranged. Such a layer is preferably less than 10 μm thick.

The substrate may have a coating which reflects the wavelength used. This can be for example

Metal or semi-metal such as silver, gold, aluminum, steel, gold, platinum, nickel, nickel titanium, silicon, copper. It is not necessary that the surface reflects the wavelength of completeness, ^¬ dig. Partial reflection is also sufficient if adequate energy for multiphoton absorption is still achieved in the area of the modulation. In principle, a sufficiently large difference in refractive index contrast between substrate and photosensitive composition is enough.

The surface may be modified prior to application of the photosensitive composition with compounds which enhance the bonding of the photosensitive compositions, in particular the polymerized composition, by means of so-called adhesion promoters. These may be, for example, compounds which contain at least one group which can participate in the activation reaction and at least one group which can bind to the surface. This bond can only be coordinative. Examples of such compounds are, for example, silanes having at least one acrylate or methacylate group or an epoxide group. To produce a structure of the photosensitive mate rial ^¬ exposed at one or more points, this can be done by multiple activation of the material in different distances from the surface. By moving the laser and / or the photosensitive material, or the substrate on which it is arranged, different areas of the material are exposed and the desired structure is produced.

This is repeated until the desired structure has been keeping it ^¬.

The photosensitive material is preferably exposed in what is known as the "dip-in" conformation same side of the substrate as the lens for exposure. The lens is additionally immersed in a drop of the photosensitive material. The photosensitive material and the objective have the same refractive index. The refractive index of the substrate is different. For this method, the refractive index of the photosensitive material must match the objective. These methods avoid loss of resolution by refraction. In addition, an autofocus effect of the system can be used. This takes place by a reflection dependent pattern the substrate surface and thus enabling the light ^¬ attaching the structure to the substrate. Without this function, variations in the vertical positioning of the laser within the monomer are possible, which can lead to a loss of the structures in the development step. The surface is found where there is a relatively large difference in the refractive indices, that is usually between one optically thinner to a visually denser material. For interference with only one laser, the dip-in method is preferred.

It is also possible to expose through the substrate with the photosensitive material on the other side of the substrate. The reflective surface is just ^¬ if arranged underneath.

The method may include further steps. Thus, it may be necessary, after application of the photosensitive material, solvent, for example by heating to entfer ^¬ NEN.

After the process it may be necessary to remove the unexposed material. The necessary steps depend on the photosensitive material used. These steps may include washing, further exposures and / or heat treatments.

The inventive method säu ^¬ lenförmige or elongated protrusions may be formed on the substrate, for example. These can be arranged arbitrarily. Due to the interference, these structures preferably have structural features in a vertical direction with an extent of less than 400 nm, in particular less than 300 nm, very particularly less than 200 nm. A structural feature may be, for example, the vertical extent of an ellipsoidal disk or the vertical extent of a corresponding projection or a freely suspended, fixed on at least one side element. Such elements are possible because the polymerization takes place within the photoresist and can be triggered there highly selectively.

Preferably, the structure produced in the vertical direction has at least 1, 2, 3, 4, 5, 6 or 7 structural features with the above-mentioned extent. It can be up to 12 structural features.

The structures may be arranged periodically or not periodically. Because each structural feature is separated by a separate

Writing process is generated, different arrangements and / or structures can be produced in a manufacturing process. For example, the arrangement of the structures on the substrate in the lateral and vertical directions can be varied. The structures can also be arranged randomly. In a preferred embodiment of the invention, the structure comprises at least one freestanding structural feature. This is understood to mean a structural feature which bridges at least two structures arranged on the surface, ie, in particular, has no vertical connection to the surface. So there is a cavity below the freestanding structure. By way of example, the freestanding structures can form the structure of a lattice or of one or more fissured structures by bridging a plurality of columnar structures on the surface. The free-standing structural feature preferably has a minimum extension in the vertical direction of less than 200 nm, preferably less than 100 nm, in particular less than 50 nm, preferably in each case in combination with a minimum extension in the lateral direction of less than 200 nm, preferably less than 100 nm, in particular less than 50 nm, up.

By structuring in the vertical direction structures can be obtained in a simple manner, which the structures on butterfly wings such. B. of Morpho rhetenor, same. These are vertically layered structures which have an at least partially angle-independent color impression.

By avoiding lateral periodicity, strongly angularly dependent color effects, which are caused by diffraction at the lateral arrangement, can be reduced. Thus, a substantially angle-independent structural color is achieved, which is determined prior al ^¬ lem through the vertical arrangement. This can be achieved, for example, by creating a vertically ordered structure. This determines the ^wavelength , which is mainly reflected by the structure. This respectively ordered in the vertical direction, or periodi ^¬ cal structure is then not periodically arranged on the surface. By this arrangement, the Bragg reflection, which can cover the color impression of the entire structure, can be suppressed.

Freestanding structures increase the angular resistance of the entire structure by preventing a large change in the paths in the material from changing the angle. This would inevitably lead to a color change. By a tapered shape of the individual structure of the effect is stabilized. The individual structures are placed at a variable distance from each other. Preferably, the distance varies by about +/- 30% of the average distance, in each case based on the centers of the freestanding structures. By varying the distance a similar effect is achieved as the gewell ^¬ th lines in the butterfly.

In another embodiment, the structures are so combined that they merge with each other, wherein there is also a vertical structuring. This can beispielswei ^¬ se be achieved that overlapping areas are exposed in the lateral direction. Thereby, the reflection of a certain wavelength can be maintained. Since the structure next to the stratification furthermore has cavities and pores, the wavelength of the reflection and thus the color of the structure can change depending on compounds adsorbed on the surface of the structure. These structures are distinguished, for example, by the fact that they at the same distance to the surface of a structure features at ^¬ game as cavities or bulges having. The invention also relates to structures produced by the process.

The invention also relates to the use of the structures produced in optical applications, sensors, structured surfaces, for example for influencing the wetting behavior or for self-cleaning surfaces. These may be, for example, holograms, diffractors, photonic crystals, sensors, security elements. They may also be structures which have been produced by molding from the structures according to the invention.

For use, the structures can be further treated. For example, it is possible for absorbent metal or ink layers to be deposited on the structures.

Particularly preferred is the use as a security feature. The structures can also be used as masters for molding an embossing tool. As a result, the structures produced can be duplicated in a simple manner.

Further details and features will become apparent from the following description of preferred embodiments

Connection with the subclaims. In this case, the respective features can be implemented on their own or in combination with one another. The possibilities to solve the problem are not limited to the embodiments. For example, area information always includes all - not mentioned - intermediate values and all imaginable subintervals. The embodiments are schematically Darge ^¬ up in the figures. The same reference numerals in the individual figures designate the same or functionally identical or with respect to their functions corresponding elements. In detail shows:

Fig. 1 Schematic representation of the conventional writing method (a)) and with the aid of interference (b));

 Fig. 2 SEM image of an inventively prepared

 Structure;

3 shows SEM images of structures according to the invention;

 Fig. 4 Schematic representation of a manufactured sample

 (Number 1);

 Fig. 5 Schematic representation of a manufactured sample

 (No. 2);

Fig. 6 Schematic representation of a manufactured sample

 (# 3);

 7 shows an impression of a structure according to the invention; Left SEM images of the corresponding intermediate steps; Right: schematic representation of the process;

Fig. 8 Schematic representation of a manufactured sample

 (No. 4);

 9 shows a SEM image of a structure according to the invention;

Fig. 10 A sensor manufactured according to the invention;

Fig. 11 SEM image of an inventively prepared

 Structure;

 FIG. 12 shows a TEM image of a structure produced by the method according to the invention; FIG.

Fig. 13 SEM image of an inventively prepared

 Structure;

Fig. 14 SEM image of an inventively prepared

Structure; Fig. 15 Schematic representation of an intensity distribution by self-interference;

Fig. 16 The influence of the vertical structuring on the

 Wavelength;

FIG. 1 shows a schematic representation of the advantages of the method according to the invention. In the conventional writing method (Figure 1 a)), the exposure is not vertical struc ^¬ riert. If, for example, a structure is carried out by exposure to three pulses with an intensity maximum at different distances from the substrate. Thus, due to the intensity distribution in the vertical direction, a vertically even projection (FIG. 1a) on the right is obtained. When using a reflective substrate, the laser is reflected by the substrate and interferes with itself. This form in verti ^¬ Kaler towards areas of high and low intensity for each pulse. As a result, the intensity in the vertical direction is much more concentrated and structured. This leads to the formation of a vertically structured elevation (FIG. 1 b) on the right). The intensity can be precisely controlled at a distance to the substrate. Figure 15 shows a schemati cal ^¬ representation of an intensity distribution in the vertical direction by self-interference. In the area beyond the dashed line, the activation threshold is exceeded.

Examples

The arrangement of the experimental setup during the writing process in the stereolithography system (Photonic Professional

GT, Nanoscribe, Karlsruhe, Germany) was a treated silicon wafer as a reflective substrate, a methacrylate Photoresist (IP-Dip, Nanoscribe, Karlsruhe, Germany) and a 63x objective (Plan-Apochromat 63x / 1.40 oil DIC M27, Zeiss, Germany). The used titanium: Sapphire fiber laser had the following parameters: wavelength 780nm, power> 140mW, pulse length> 100fs. The dose of exposure was varied for the individual application examples and is given in the respective Be ^¬ game. The exposure areas that should be polymerized by the modu ^¬ profiled lasers, using a programmed script of stereolithography native software defined (DeScribe, Nanoscribe, Charles ^¬ serenity, Germany). These regions are called patterns ^λ in the examples described and are shown schematically in Figure 4-6. As shown in Fig. 4, the pattern No. 1 comprises a structure of a plurality of patterning units of different sizes. 1 shows in this figure a linear

Structure (length 20 ym, width 200 nm, height 1.5 ym). The lines are vertically structured according to the invention. These form a small square (2) with an extension of 20 ym x 20 ym, which consists of 20 parallel single lines, nine small squares (2) form a middle square (3). Several of these middle squares (3) form a large square (4). This entire structure forms the pattern No. 1. For the lines, the laser was moved by 20 ym (by changing the entrance angle into the lens by Galvoscanner), while for a different lines, the substrate was respectively moved accordingly. Figure 5 shows the pattern No. 2. The smallest unit there bil ^¬ det a selective exposure. (1; 500 nm diameter, height 1.5 ym). Such an exposure usually leads to a columnar like structure with appropriately controllable vertical structuring. The distance between the geometric centers of the

Structures 1 to each other varies between 580 nm and 1360 nm. The mean distance is 1001 +/- 290 nm. The structures 1 form a small square 2 with an extension of 20 ym x 20 ym, consisting of several structures 1). The small squares 2 form a middle square 3 consisting of several small squares. The middle squares 3 form a large square 4.

Figure 6 shows the pattern No. 3. The smallest unit is flat ^¬ if a selective exposure. (1; 500 nm diameter, height 1.5 ym, distance of 1000 nm). The structures 1 form a small square 2 with an extension of 20 ym x 20 ym, consisting of several structures 1). The small squares 2 form a middle square 3 consisting of several small squares. The middle squares 3 form a large square 4.

In further support its own Simulationssoft- served would be that simulates the modulation of the laser as a function of genutz ^¬ th substrate, the photoresist, the lens and the positi ^¬ on the focal point in the photoresist. The development of the writing process was carried out as follows: The Sub ^¬ strate with the exposed photoresist was developed in the developer (PEHEMA) for 20 min. Unlike the common ones

To remove the sample from the developer and rinse with isopropanol, this step was modified. This increases the quality and shape of the final structures. In this modified process, most of the developer was removed without drying the sample, with simultaneous addition of isopropanol. This process was repeated twice every other 10 minutes. Thereupon followed a further exposure of the sample, still within the liquid ^¬ speed with a UV lamp for 300 s at 7.3 W / cm ² under N ₂ . The sample was again kept in a very pure isopropanol for purification and dried under the hood at room temperature. A similar process can be used to create structures for

To stabilize etching. In this case, the sample is air-dried with isopropanol after the last washing step, with UV light

15 sec, 7.3 W / cm ² activated under ₂ and then baked at 125 ° C for at least ^¬ 15 min. It shows a significantly increased etch resistance.

As reflective substrates for the writing process, ^treated silicon wafers were used to improve the adhesion of the

To mediate structures on the substrate. For this, the wafer by means of an ultrasonic bath with acetone, isopropanol, ethanol and distilled water, cleaned for 5 min each and subsequently ^¬ ßend dried with compressed air. This was followed by activation of the surface with oxygen plasma for 5 min. The activated sub ^¬ strat were then combined with 20 μΐ adhesive silane, 3- (trichlorosilyl) propyl, placed in a desiccator and maintained under vacuum for a purging with nitrogen for 1 hour at room temperature under exclusion of light. For the application examples such substrates were mainly be ^¬ Wundt.

In the following, three different application examples are shown, which were realized by the described technique: i) butterfly-inspired columnar and line-shaped optical structures, whose example also explains the molding methods; ii) ^λ Fence-like ^λ structures that form a layer of air and material; iii) gas sensors reversibly reacting with isopropanol gas.

Experiments to i)

To write butterfly-like structures, Pattern # 1 and Pattern # 2 were used (Figures 4 and 5). For both patterns, 5 layers were selected with the distance 300 nm for the vertical exposure. The laser power was 19 mW for pattern 1 and 17 mW for pattern 2. The structured area was fixed at 6x6 mm in both cases. The structures of the Mus ^¬ ters 1 showed 1.5 ym height, width 500 nm, and a

Layering of 230 nm very similar dimensions as that of the

Butterfly. The optical properties of this surface were comparable to those of the butterfly, showing anisotropic reflection at the microscopic level, a reflection maximum at 470 nm and a high angular constancy of this wavelength up to an aperture angle of 120 °. Zusätz ^¬ Lich to that described reflection pattern based on the stratification an angle-dependent reflection, hervorge ^¬ call made by the periodic interval of 1000 nm, detected. This angle-dependent reflection and the anisotropic optical properties were reduced in the case of pattern 2 structures, with the angular constancy being retained based on the layering. The color of the surface can be varied by means of the Wel ^¬ lenlänge. This allows the number and the

Diameter of the structural features are controlled. Furthermore, the surface produced using pattern 1 was used to make a

Replication to transfer the structure into another material. The procedure can be Adhesive coating, production of the negative mold, and producing the positive mold with another material (Figure 7 right). For the non-stick coating, the surface stereolithogra ^¬ phisch prepared with oxygen plasma for 1 min was activated, and then after rinsing with nitrogen for 30 min in the presence of 20μ1 anti-adhesive silane, Trichlorfluorsilan (tridecanol cafluor-1, 1,2, 2-tetrahydrooctyl trichlorosilane, AB111444, but GMBH) in a desiccator. This was followed by a baking step at 95 ° C for 45 min. The lithography structure (master strueture) is obtained. Polydimethylsiloxane (PDMS, Sylgard 184, Dow Corning) was mixed 1:10 and applied to the lithography structure, held in vacuo for 10 minutes, and cured at 75 ° C overnight (first molding step). After cooling, the cured PDMS was peeled off to give a negative mold of the structure (First PDMS mold). This was then also anti-adhesion coated as described above, filled with PDMS, and baked (second molding step). The now detached PDMS positive shape (PDMS replica) corresponded to the freestanding master lithograph structure and, like these, also had a layering in the nanometer range.

Figure 2 shows examples of the invention prepared according to structural ^¬ structures with 9 structural features in the vertical direction. Figure 3 shows the present invention to structures produced on un ^¬ terschiedlichen substrates. Glass (a), NiTi (b), Si (c), AuPd thick (thick, d), Au thick (thick, e), Au thin (thin, f). For Glass and NiTi was struc ^¬ riert without pretreatment of the surface. The other metallic layers were applied to a glass surface. FIG. 11 shows fabricated structures after exposure according to pattern No. 2 (FIG. 5).

Figure 16 shows structures created on a substrate with a single write process, each with multiple pulses. The vertical structure could be affected (mittle ^¬ re view) by varying the power and / or wavelength. This affects the reflected wave ^¬ length of the absorbent structure (lower figures), WEL surface consists of many of these columnar structures.

Experiments on ii)

A combination of patterns 1 and 3 at 13 mW was used to make fence-like ^λ structures. For pattern 3, 5 layers were spaced 300 nm apart, and for pattern 1, a 300 nm and 1200 nm layer was used for the vertical exposure. The resulting structures are similar in shape to a fence, with pattern 3 serving as anchor points for the linear pattern 1. With this combination it is accordingly mög ^¬ Lich a layer system to establish a periodic sequence of material and air, or to structure free hanging units of less than 50 nm or 45 nm. For example, the free spaces can now be filled with any other material, which offers great potential for applications in new laser and sensor technologies.

FIGS. 13, 14 show recordings of produced structures. The fence-like structure is clearly visible. In particular, in Figure 13, the two columns are connected only by a thin freestanding structure, with a minimum extension in the vertical and horizontal directions of 45 nm. Experiments on iii)

For these experiments a pattern # 4 was used. Figure 8 shows the pattern No. 4. The smallest unit there forms a punctual exposure (1, diameter 500 nm, height 1.5 ym). The distance between the geometrical centers is chosen to be smaller than the diameter, for example 400 nm. This results in overlapping structures. The structures 1 form a small square 2 with an extension of 20 ym x 20 ym, consisting of several structures 1). The small squares 2 form a middle square 3 consisting of several small squares. The mean squares 3 form a large square 4. Sample 4 with 22 mW power was used to create using the new technology gas sensors that are capable of in the presence of isopropanol in seconds a strong Far ^¬ bumschwung from pink to perform to green. This color change is reversible and has been demonstrated for 10 cycles. The colors can be varied by means of parameters.

FIG. 9 shows a picture of the structure produced. The overlap creates a multi-layered structure with many cavities. The structuring is clearly visible, especially in the vertical direction.

FIG. 10 shows the color change for a structure according to FIG. 9 for the detection of isopropanol. For this, a drop of isopropanol was added to the sample outside the Ge ^¬ visual field, which spreads and then slowly dries. A color change is already visible before the front of the drop the field reached. After evaporation of the isopropanol, the color change disappears again.

FIG. 12 shows the TEM image of a manufactured columnar structure with vertical structuring. By individually addressing the refractive index also can be influenced within the material (light areas: dense + ^¬ height rer refractive index; less bright: less dense + lower refractive index).

Claims

claims A method for selective photoactivation comprising the following steps:  a) providing a photosensitive material on a substrate; b) focusing a laser in one or more regions of the material such that in this region or these regions the photosensitive material is activated by Mehrphotonenab ^¬ sorption,  wherein the laser is reflected at a reflective surface and modulated by interference with itself in the region or regions. 2. The method according to claim 1, characterized in that it is a pulsed laser. 3. The method according to any one of claims 1 or 2, characterized in that step b) is carried out several times, wherein the laser activates at least one repetition, another area of the photosensitive material. 4. The method according to any one of claims 1 to 3, characterized in that the photoactivation leads to the formation of a structure. Structure produced by the method according to claim 6. Structure according to claim 5, characterized in that the structure comprises at least one free-standing structural feature. 7. Use of the structure according to one of claims 5 or 6 in optical applications, sensors and / or structured surfaces.