Method for producing structured surfaces

Abstract

A process for producing a structured surface, in which a composition comprising nanowires is applied to a surface and structured, especially by partial displacement of the composition. When the solvent is removed, the nanowires aggregate to form structures. These may be transparent and also conductive.

Claims

1. A process for producing metallic structures, comprising: (a) providing a composition comprising metallic nanowires and at least one solvent; (b) structuring the composition on a surface of a substrate by contacting a structure template with a surface of the substrate before or after applying the composition to the surface; and (c) at least partly removing the at least one solvent while the structure template is contacted with the surface of the substrate, thereby resulting in aggregation of the metallic nanowires on the surface of the substrate and forming metallic structures on the surface of the substrate, wherein the metallic nanowires form bundles parallel to the surface of the substrate following recesses of the structure template in a longitudinal direction.

2. The process as claimed in claim 1, comprising applying the composition to a substrate and subsequently applying the structure template to the substrate with partial displacement of the composition.

3. The process as claimed in claim 1, wherein the applying and the structuring are effected by applying the composition into a structured mask.

4. The process as claimed in claim 1, wherein at least 50% by weight of the metallic nanowires have a length exceeding 1 m.

5. The process as claimed in claim 1, wherein at least 50% of the metallic nanowires have an aspect ratio of length to diameter of at least 500:1.

6. The process as claimed in claim 1, wherein the metallic nanowires have a mean diameter below 15 nm.

7. The process as claimed in claim 1, wherein the metallic nanowires have a mean diameter below 5 nm.

8. The process as claimed in claim 1, further comprising subjecting the structures obtained to thermal treatment or plasma treatment.

9. The process as claimed in claim 1, wherein the substrate has a surface comprising at least one hydrolysable silane having at least one nonhydrolyzable group comprising at least one fluorine atom.

10. The process as claimed in claim 9, wherein the metallic nanowires have a mean diameter below 100 nm.

11. The process as claimed in claim 1, wherein the metallic nanowires aggregate to form bundles on the substrate between projections that are formed by the structure template.

12. The process as claimed in claim 1, wherein the metallic structures are in the form of a grid.

13. A process for producing metallic structures, comprising: contacting a structure template having projections with a surface of a substrate and with a composition comprising metallic nanowires and at least one solvent on the surface of the substrate; at least partly removing the at least one solvent while the structure template is in contact with the surface of the substrate; and aggregating the metallic nanowires on the surface of the substrate between the projections of the structure template thereby forming metallic structures comprising bundles parallel to the surface of the substrate following recesses of the structure template in a longitudinal direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 a) TEM image of gold nanowires; b) TEM image of gold nanowires; c) SEM image of the stamp used.

(2) FIG. 2 schematic flow diagram of the process of the invention with nanowires;

(3) FIG. 3 schematic diagram of a sequence of the process of the invention with nanowires;

(4) FIG. 4 schematic diagram of a sequence of the process of the invention with nanowires;

(5) FIG. 5 SEM images of two structured coatings obtained; a) with an average thickness of 15 nm; b) with an average thickness of 45 nm; the small figures show an enlarged detail of the respective SEM image;

(6) FIG. 6 a) transmission spectra of structured coatings obtained (NM-15 nm: structure from FIG. 4a; nm-45 nm: structure from 4b); b) conductivity measurements (NM-15 nm: structure from FIG. 4a; nm-45 nm: structure from 4b);

(7) FIG. 7 measured change in the resistance of a grid of the invention (AuNM) and of a commercial grid of ITO (ITO on PET) on bending of the substrate;

(8) FIG. 8 TEM image of a bent gold nanowire;

(9) FIG. 9 schematic diagram of a process of the invention with an inert surface;

(10) FIG. 10 schematic diagram of a process of the invention with an inert surface;

(11) FIG. 11 schematic diagram of a further embodiment of a process of the invention with an inert surface;

(12) FIG. 12 schematic diagram of a further embodiment of a process of the invention with an inert surface;

(13) FIG. 13 schematic diagram of a further embodiment of a process of the invention with an inert surface;

(14) FIG. 14 schematic diagram of a further embodiment of a process of the invention with an inert surface;

(15) FIG. 15 measurement of the transmission of various samples (1: grid structure, variant 1; 2: grid structure, variant 2; 3: nanowires, flat; 4: nanowires, flat and densely packed);

(16) FIG. 16 SEM image of the grid structure obtained according to variant 1 (a) overall image; b) structure in greater resolution; structure width 18.68 m+/0.98 m);

(17) FIG. 17 SEM image of the grid structure obtained according to variant 2 (structure width 30.59 m+/3.8 m);

(18) FIG. 18 SEM image of the silver nanowires, flat;

(19) FIG. 19 SEM image of commercially available silver nanowires after structuring (comparative example);

(20) FIG. 20 SEM image of commercially available silver nanowires after structuring (comparative example).

DETAILED DESCRIPTION OF INVENTION

(21) I. Structuring by Aggregation

(22) FIG. 1 shows TEM images of gold nanowires. The nanowires, with a length below 2 nm, have a length of well above 500 nm. It is readily apparent in a) and b) how the nanowires combine to form bundles of their own accord. FIG. 1 c) shows one of the stamps used.

(23) FIG. 2 shows a schematic diagram of the sequence of a process of the invention. This firstly involves applying the composition to the surface (200). Thereafter, the nanowires in the composition are structured (210). This is preferably accomplished by applying a structure template with partial displacement of the composition. Thereafter, the solvent is at least partly removed (220).

(24) FIG. 3 shows an inventive embodiment of the process. As shown in FIG. 3 a), after the application of the composition, the nanowires 300 are arranged randomly on the surface of the substrate 310. They are still dispersed here in a solvent. Thereafter, a structure template, preferably in the form of a stamp 320, is applied to the surface 310 (FIG. 3 b)). In this case, the stamp comprises cylindrical projections with planar end faces (similarly to FIG. 1 c)). These form a contact face with the surface of the substrate 310. As a result, the composition is displaced in these regions. As a result, the nanowires are transferred into the interstices between the projections. Then the solvent is at least partly removed. This can be assured, for example, by virtue of the projections of the stamp being higher than the thickness of the composition applied. This results in formation of a cavity above the composition through which the solvent can evaporate. The local increase in the concentration of the nanowires results in formation of bundles of nanowires 330. These preferably aggregate between the projections 320 on the substrate 310 (FIG. 3 c)). After the structure template has been removed, what remains on the surface of the substrate 310 is a structure 340 formed from the nanowires (FIG. 3 d)). In some cases, it may be necessary to remove the organic constituents of the structure by an aftertreatment; this can be accomplished, for example, by a plasma treatment.

(25) FIG. 4 shows the sequences of the process shown in FIG. 3 as a representation in vertical cross section. FIG. 4 a) shows the situation of FIG. 3 b) in vertical cross section. The composition applied is arranged between the two projections 320 that are in contact with the surface of the substrate 310. This composition in this case comprises a solvent 305 and the nanowires 300 dispersed therein, which are shown here as a round cross section. The representation does not mean that the nanowires are fully dispersed. It may quite possibly be the case that they are already in partly aggregated form in the dispersion and have thus already formed the first bundles. In the next step, the solvent 305 is removed. The nanowires 330 in the interstitial space between the projections 310 now combine to form bundles on the surface 310. This is also promoted by the fact that the nanowires are very long and flexible.

(26) After the stamp has been removed, it is still possible to conduct a sintering step (FIG. 4c)). In this case, for example, a plasma treatment removes the organic shell of the nanowires and the density of the bundle of the nanowires is increased further. This can increase the conductivity of the nanowires bundles 350.

(27) FIGS. 9, 10, 11, 12, 13 and 14 show further embodiments of the invention.

(28) FIG. 9 shows a substrate 500, on the surface of which an inert layer 510 has been applied. The composition 520 comprising nanowires has been arranged thereon. A structure template in the form of a stamp 530 is applied to this surface. The operations here are shown in FIG. 10. The composition 520 is displaced by the projections of the structure template 530 into the interstices between the projections (upper part of the figure). This is promoted by the inert surface 510 on the substrate 500. When the projections of the structure template 530 have come into contact with the substrate 500, or with the inert surface 510, the entire composition 520 is arranged in the depressions of the structure template (FIG. 10, lower part of the figure).

(29) FIGS. 11 to 14 show another embodiment of the invention. For this purpose, the composition comprising the nanowires 620 is applied to a structure template 610 which may be arranged on a carrier 600 (FIG. 11). A coating bar 630 is used to force the composition into the depressions of the structure template. The filled structure template 610 obtained as a result, in which the depressions have been filled with composition 620, is shown in FIG. 12. The structure template may have been arranged on a carrier 600.

(30) As shown in FIG. 13, this filled structure template 610 with the composition 620 in the interstices can then be brought into contact with an inert surface 640 on a substrate 650 (lower part of the figure).

(31) In order to produce the structure on the inert surface, the structure template together with the inert surface is rotated, such that the inert surface is arranged at the bottom. In this way, the nanowires can aggregate on the inert surface.

(32) In principle, the same arrangement as shown in the lower part of FIG. 10 is obtained.

(33) Irrespective of the manner of preparation of the arrangement, the solvent in the composition is now at least partly removed in this arrangement. In this way, the aggregation of the nanowires on the inert surface can be promoted.

(34) Thereafter, as shown in FIG. 14, the structure template 610 is removed. This affords a metallic structure 660 on the inert surface 640.

I.1. Examples

(35) The TEM images were recorded with a JEM 2010 (JEOL, Germany) at 200 kV. The SEM images were recorded with a Quanta 400 ESEM (FEI, Germany). Optical measurements were recorded with a Cary 5000 (Varian). The spectrum of the glass substrate was recorded as the baseline. The current/voltage measurements were conducted with a Keithley 2450 Sourcemeter.

(36) The gold nanowires were produced analogously to H. Feng, Y. Yang, Y. You, G. Li, J. Guo, T. Yu, Z. Shen, T. Wu, B. Xing, Chem. Commun. 2009, 1984 and J. H. M. Maurer, L. Gonzalez-Garcia, B. Reiser, I. Kanelidis, T. Kraus, ACS Appl. Mater. Interfaces 2015, 7, 7838.

(37) For this purpose, 30 mg of HAuCl.sub.4H.sub.2O were dissolved in a mixture of 5.8 mL of n-hexane (99%, ABCR, Germany) and 1.7 mL of oleylamine ((Z)-octadec-9-enylamine technical grade, 70%, Sigma-Aldrich, Steinheim, Germany). 1.5 mL of triisopropylsilane (98%, ABCR, Germany) were added and the solution was left to stand at room temperature overnight. The nanowires were precipitated by the addition of ethanol. The supernatant was removed and the nanowires were redispersed in n-hexane. The wash step was repeated and the nanowires were then redispersed in cyclohexane, in order to obtain solutions having a gold concentration of 4 mg/mL or 8 mg/mL.

(38) 30 L of a composition of gold nanowires dispersed in cyclohexane (4 mg/mL, 8 mg/mL) were applied to a substrate. Thereafter, a structured stamp made of PDMS was pressed immediately onto the substrate. The composition is forced into the depressions of the stamp as a result. The stamp comprised a hexagonal arrangement of cylindrical projections of diameter 4 m and a distance between the projections of 5 m (center to center). The height of the projections was 5 m. When the solvent was evaporated, bundles of the gold nanowires which recreate the structure of the depressions were formed in the depressions. After the stamp had been removed, the structure was treated with a hydrogen plasma (mixture of 5% hydrogen in argon) at room temperature for 15 minutes (RF PICO plasma system (Diener electronic, Ebhausen, Germany) 0.3 mbar, 100 W).

(39) Depending on the concentration of the gold nanowires in the composition, it was possible to control the thickness of the structures obtained. When a concentration of 4 mg/mL was used, a structure having an average thickness of 15 nm was obtained. The minimum width was 250 nm (FIG. 5 a)). When 8 mg/mL was used, it was possible to obtain a structure having an average thickness of 45 nm and a minimum width of 600 nm (FIG. 5 b)). The minimum width corresponds to the minimum width of the structure found in the SEM range.

(40) FIG. 6 a) shows transmission spectra of the grids obtained. The grid from FIG. 5 a) shows high transmission over the entire visible region (upper line). The grid from FIG. 5 b) also shows high transmission of up to 68% (lower line). The values are in good agreement with calculated values for a grid having the same coverage. The haze value measured was 1.6% (FIG. 5a) and 2.7% (FIG. 5b). This is below the value typically required for displays (<3%).

(41) FIG. 6 b) shows the corresponding voltage/current diagrams. The thinner grid showed a resistance of 227 /sq, the thicker grid a resistance of 29 /sq. These are higher than the calculated values for grids of pure gold (32.5 /sq for d=5 m, w=250 nm, h=15 nm, and 4.5 /sq for d=5 m, w=600 nm, h=45 nm with a resistivity for gold of 2.4410.sup.8 m). However, this can be attributed to irregularities in the grid, for example resulting from particle boundaries after sintering, and unconnected grid elements.

(42) FIG. 7 shows the results of bending tests. In the figure, the change in the resistance versus the initial resistance ((RR.sub.0)/R.sub.0) is plotted against the number of bending cycles. The samples were bent under tension with a bending radius of 5 mm. For the experiments, 10 inventive grids on PET were used with an initial average resistance of 100 /sq (AuNM). A comparative experiment used was a commercially available grid of ITO on PET having a resistance of 100 /sq (ITO on PET, Sigma-Aldrich, R.sub.0=100 /sq). The resistance of the comparative sample rose by several orders of magnitude after a few cycles. For the grids of the invention, the rise within the first 50 cycles was below one order of magnitude, followed by an asymptotic trend toward (RR.sub.0)R.sub.0=0.056 after 450 cycles. The grids of the invention are accordingly also suitable for flexible substrates.

(43) FIG. 8 shows an example of the flexibility of the thin gold nanowires. The R values indicate the radii of the circles fitted to the bending. It was possible to observe bending radii of up to 20 nm without causing the wires to break.

I.2. Production of the Stamp

(44) The PDMS stamp was produced with a silicone template. The prepolymer and the crosslinker of the PDMS kit (Sylgard 184, Dow Corning) were mixed in a ratio of 10:1 (by weight) and degassed. The mixture was introduced into the template which had been silanized beforehand with trichloro(octadecyl)silane (Sigma-Aldrich, St. Louis, Mo., USA), and hardened at 70 C. Thereafter, the stamp was removed from the template.

I.3. Comparative Examples

(45) Compositions comprising commercially available silver nanowires (Seashell Technology; diameter 130 nm+/10 nm; length 35 m+/15 m) were produced and applied to surfaces analogously to the examples. It is found that there is no aggregation. Nor can the nanowires be displaced by applying a stamp, and so there is no formation of a structure.

(46) FIG. 19 shows the analogous performance of the process of the invention with the same stamp. It is found that there is no structuring.

(47) Nor does a larger stamp (diameter 25 m of the column-shaped projections with centers separated by 50 m) lead to structuring (FIG. 20).

(48) II. Structurizing with an Inert Surface

(49) II.1. Production of a PDMS stamp

(50) There follows a description of the production of an embossing stamp from PDMS (silicone rubber) as casting made from a nickel master:

(51) II.1.A. Description of the Nickel Master and the Casting Mold

(52) The nickel master is an electrolytically produced nickel foil, for example of dimensions 100 mm100 mm, to which a microstructure (regularly arranged cylindrical columns having a diameter of more than 1 m) has been applied. This nickel foil is adhesive-bonded to the base of a casting mold produced from aluminum or similar material or mounted by means of ferromagnetic bonding film. It should be noted here that the nickel master has to be applied in an absolutely planar manner since any unevenness will be reflected in the later stamp.

(53) Moreover, the casting mold has to be placed in as horizontal a position as possible in order that the embossing stamp will later have a uniform thickness.

(54) II.1.B. Mixing of the Silicone Rubber and Mold Casting

(55) The base material and hardener of a polydimethyl-siloxane (PDMS) (e.g. Sylgard 184 from Dow Corning) are in a suitable ratio (e.g. 10:1) brought together and the two components are mixed by stirring. The amount to be made up is guided by the desired thickness of the embossing stamp (typical stamp thickness: 2 to 4 mm). The mixing vessel should have a capacity of 3 times the volume of the mixture in order to prevent overflow in the subsequent degassing operation.

(56) For removal of the air bubbles mixed in in the course of stirring, the mixture is introduced into a vacuum drying cabinet (at room temperature) and evacuated until all the air bubbles have been removed.

(57) The degassed PDMS mixture is then poured into the casting mold and the mixture is left to harden. In most cases, it is advisable to accelerate the hardening by heat treatment of the casting mold. Typically, heating of the casting mold to 70 C. for one hour leads to complete hardening of the PDMS.

(58) II.1.C. Demolding Operation

(59) The demolding of the PDMS stamp is accomplished by using a scalpel or another sharp blade to cut the PDMS away from the vertical wall of the casting mold around the entire circumference and then lifting it away from the edge with a flat and blunt tool (e.g. a flat spatula) and then cautiously detaching it from the nickel master. Irregularities at the edge can then be cut off with a sharp blade (e.g. carpet knife).

(60) II.2. Functionalization of the substrate surface:

(61) There follows a description of the production of the antiadhesive coating material (hydrophobic):

(62) II.2.A. Varnish Production

(63) Amounts Used:

(64) TABLE-US-00001 267.8 g methyltriethoxysilane (MTEOS) 84.8 g tetraethoxysilane (TEOS) 150.0 g Levasil 300/30 3.0 g conc. (37%) hydrochloric acid 13.35 g perfluorooctyltriethoxysilane (Dynasylan F 8261) 518.95 g isopropanol
Procedure:

(65) A 2 L reactor (jacketed vessel with connected cooling) with an internal thermometer is charged with the amounts of MTEOS and TEOS weighed out. The amount of Levasil weighed out is added and the mixture is left to stir vigorously for 2-3 min. Then the amount of concentrated hydrochloric acid weighed out is added and the mixture is left to stir further. The reaction solution and the internal temperature on the thermometer are observed and the observation is written down. The temperature within the reactor should not exceed 60 C. in this time. After stirring for 10-15 min, the amount of perfluorooctyltriethoxysilane weighed out is added and the mixture is left to stir for a further 30 min. Then the amount of isopropanol weighed out is added and the mixture is left to stir for 15 min. The material is dispensed into a 2 L glass bottle and then filtered with the aid of a pressure filtration (prefilter+0.45 m filter). The finished varnish is dispensed into a 2 L Schott glass bottle and stored in a refrigerator until further use.

(66) II.2.B. Layer Production

(67) The varnish was applied by means of spin-coating (1000 rpm/min, 30 sec) and baked in an oven (air atmosphere; heat up to 100 C. within 30 min; hold for 30 min, heat up to 250 C. within 240 min, hold for 1 h, cool down).

(68) II.3. Silver Nanowire Solution

(69) There follows a description of the preparation of a silver nanowire solution from Cambrios (solvent: ethylene glycol) for layer production:

(70) II.3.A. Purification and Solvent Exchange Via Crossflow Filtration

(71) 200 mL of the silver nanowire solution in ethylene glycol are diluted with 200 mL of pure H.sub.2O (Millipore) and introduced into a large beaker. With the aid of a peristaltic pump (flow rate: 1.2 mL/sec), the solution is pumped through a filter cartridge (material: PES; pore size: 0.5 m; from SpectrumLabs; model: Microkros 30.5 m PES 1.0 mm mLLFLL Dry (4/PK)). The filtrate removed is collected in a collecting vessel. The retentate is guided through a hose back into the large beaker. Filtration is continued until 200 mL of filtrate have been removed.

(72) This process is conducted for a second time in order to remove as many disruptive silver particles as possible. Purity of the nanowire solution>90%.

(73) II.3.B Determination of the Silver Content of the Purified Nanowire Solution in Water

(74) Before the weighing, the sample is agitated manually. The weighings are effected in 50 mL glass flasks, then 2 mL of HNO.sub.3 (65%) are added to the samples and they are made up with ultrapure water. In order to avoid matrix effects, the standards are matched to the acid content of the samples. In order to verify reproducibility, 3 weighings are carried out in parallel.

(75) Standards:

(76) TABLE-US-00002 Element S0 S1 S2 Ag (mg/L) 0.0 5.0 8.0
Instrument Parameters: ICP OES, Horiba Jobin Yvon Ultima 2 Ag determination: clinical nebulizer: pressure: 2.00 bar, flow rate: 0.781/min Ag: =328.068 nm

(77) The determination gave a silver content of 0.295% by weight+/0.002.

(78) II.3.C. Further Solvent Exchange to Obtain a Coating Solution with Different Leveling Properties than the Water-Based Silver Nanowire Solution

(79) 5 mL of the purified silver nanowire solution in water are mixed with 2 mL of 1-amino-2-butanol, 5 L of TODS (3,6,9-trioxadecanoic acid) and 10 mL of acetone, and centrifuged (speed: rcf=2000; duration: 1 min). The resultant supernatant is decanted off and the sediment formed is redispersed in 10 mL of 1-amino-2-butanol.

(80) II.4. Nanoimprint 1

(81) There follows a description of the production (variant 1) of a grid structure of silver nanowires with the aid of a PDMS stamp, in which the silver nanowires are arranged in gridlines:

(82) II.4.A. Description of the Preparation of the Silver Nanowire Solution Shortly Before Sample Production

(83) The sample vessel with the nanowire solution present therein is agitated briefly before the sample production with the aid of a vortexer (from Heidolph, model: Reax control, speed: 2500 rpm), in order to redisperse the sediment.

(84) II.4.B. Coating Operation

(85) A glass substrate (size: 10 cm10 cm0.11 cm), coated with the antiadhesive coating material (see point 11.2), is placed flat on a laboratory bench. A droplet (volume: 20 L) of the nanowire solution prepared is applied in the middle.

(86) A structured PDMS stamp (production described in point 1) is pressed on manually such that the solution is distributed homogeneously under the stamp and excess material is displaced.

(87) In order to evaporate off the excess solvent, the sample (substrate+stamp) is placed onto a hotplate and heated to 50 C. During this process, a metal plate (weight: 800 g) is placed onto the PDMS stamp in order to assure optimal, uniform adhesion of the stamp on the substrate. After 15 min, the sample assembly (substrate.fwdarw.stamp.fwdarw.metal plate) is removed from the hotplate and left to cool on the laboratory bench.

(88) As soon as the sample has cooled down, the metal plate is first removed, one hand is used to stabilize the substrate on the benchtop and the other is used to remove the PDMS stamp by pulling it off.

(89) II.4.C. Coating Operation, Variant 2

(90) A PDMS stamp with grid structure (production described in point 1, line width 15 m) is placed by its reverse side (unstructured) onto an uncoated glass substrate (size: 5 cm5 cm0.11 cm). A droplet (volume: 20 L) of the nanowire solution prepared is applied to the structured side of the PDMS stamp at the edge.

(91) With the aid of a kind of coating bar (a razor blade here), the droplet of nanowire solution is distributed homogeneously over the structured surface of the PDMS stamp.

(92) Subsequently, a coated glass substrate (size: 5 cm5 cm0.11 cm, coated with antiadhesive coating material) is pressed manually onto the coated side of the PDMS stamp covered with nanowires.

(93) The sample assembly (uncoated glass substrate.fwdarw.PDMS stamp.fwdarw.coated glass substrate) is turned over and dried at 50 C. on a hotplate, weighted down with a metal plate (weight: 800 g). After 1 h, the sample assembly is removed from the hotplate and left to cool on the laboratory bench. As soon as the sample has cooled down, the metal plate is first removed, one hand is used to stabilize the coated substrate and the other is used to remove the PDMS stamp and the uncoated glass substrate by pulling them off.

(94) II.4.D. Characterization

(95) 1. Measurement of Transmission:

(96) Transmission was determined with the aid of a spectrometer (instrument: Ocean Optics QEPro, lamp: DH-2000-BAL).

(97) 2. Determination of Conductivity:

(98) Conductivity was determined with the aid of a 2-point meter (from Keithley, instrument: 2000 Multimeter) on a respective area of 5 mm5 mm, on which contacts were made with conductive silver varnish on two opposite sides.

(99) II.5. Nanoimprint 2

(100) There follows a description of the production (variant 2) of a grid structure from silver nanowires with the aid of a PDMS stamp, in which the silver nanowires are arranged in the square grid areas and these areas are each separated from one another by lines arranged in the form of a grid:

(101) II.5.A. Pretreatment of the Antiadhesively Coated Substrate

(102) A PDMS stamp with grid structure (production described in point 1) is placed onto a glass substrate (size: 10 cm10 cm0.11 cm), coated with the antiadhesive coating material (see point 2). Then the substrate including the stamp placed on is subjected to a plasma treatment in a plasma chamber (duration: 30 min, gas: oxygen). The PDMS stamp is merely placed on and not pressed on, in order thus to hydrophilize the square surfaces of the grid structure of the stamp. And even the actually hydrophobic, coated substrate is hydrophilic after the plasma treatment.

(103) II.5.B. Description of the Preparation of the Silver Nanowires Solution Shortly Before Sample Production

(104) The sample vessel with the nanowire solution present therein is agitated shortly before the sample production with the aid of a vortexer (from Heidolph, model: Reax control, speed: 2500 rpm), in order to redisperse the sediment.

(105) II.5.C. Coating Operation

(106) The hydrophilized substrate is placed flat on to a laboratory bench. A droplet (volume: 20 L) of the nanowire solution prepared is applied in the middle and the hydrophilized PDMS stamp is pressed on manually such that the solution is distributed uniformly under the stamp and excess material is displaced. In order to evaporate the excess solvent, the sample (substrate+stamp) is placed onto a hotplate and heated to 50 C. During this process, a metal plate (weight: 800 g) is placed onto the PDMS stamp. After 15 min, the sample assembly (substrate.fwdarw.stamp.fwdarw.metal plate) is removed from the hotplate and left to cool on the laboratory bench. As soon as the sample has cooled down, the metal plate is first removed, one hand is used to stabilize the substrate on the benchtop and the other is used to remove the PDMS stamp by pulling it off.

LITERATURE CITED

(107) H. Feng, Y. Yang, Y. You, G. Li, J. Guo, T. Yu, Z. Shen, T. Wu, B. Xing, Chem. Commun. 2009, 1984. J. H. M. Maurer, L. Gonzlez-Garcia, B. Reiser, I. Kanelidis, T. Kraus, ACS Appl. Mater. Interfaces 2015, 7, 7838.