CZ2012168A3 - Method of shaping 2D optical and metaoptical structures on a polymer surface - Google Patents

Abstract

The method of 2D shaping of polymeric nanostructures is that the surface of the polymer is subjected to a periodic thermal treatment of the focused and surface-scanning laser beam with a wavelength corresponding to the maximum absorption of the polymer and with the power to allow the molding polymer to overflow. The absorption properties of the polymer can, if desired, be adjusted by surface or volume doping with a suitable substance. To produce more complex structures (e.g., matrices for optical metamaterials), the process is complemented by the simultaneous mechanical movement of the polymer surface in a plane perpendicular to the scanning laser beam in the scanning direction and then rotated by an angle of 0.1.degree. az 359,9.degree. to the original scan direction with re-scanning the same location in the same plane.

Description

Method for shaping 2D optical and metaoptical structures on polymer surface

Technical field

The method of 2D molding a polymer surface for manufacturing optical and metaoptical components (hereinafter 2D) relates to the production of surface-structured polymeric materials and in particular thin polymer layers as matrices for composite optical metamaterials. Intended applications are in the field of imaging systems for sensors, resonators for nanophotonics and especially in the field of hyper-lenses providing huge resolution and last but not least also in the field of affecting the visibility of objects.

BACKGROUND OF THE INVENTION

Numerous processes are used to form polymer structures. The best known is lithography (L. Ellada, L.W. Shacklette IEEE J. Selec. Topics Quan. Electron. 2000, 6, 54). The disadvantage is the diffraction limitation resulting from the wavelength of the radiation used. In addition, selective etching is required for the production of motifs, which in principle limits their quality. Methods capable of replacing photolithography include exposing the polymer layer to an electron or ion beam. In this way, it is possible to achieve a smaller dimension, ie several tens of nm. Extremely complex equipment with expensive and demanding operation is required for the practical application of these procedures. The throughput and the surface area of structured materials are considerably limited - only 100 pm x 100 pm. (U. K. Chettiar, A. V. Klidishev, Η K. Yuan Optics Letters 2007, 32, 1671; C. Enkrich, F. Perez-Willard,

D. Gerthsen, Advanced Materials 2005, 17, 2547).

Several other non-standard processes have therefore been proposed utilizing the instability of thin polymer films due to thermal or electric field gradient (E. Schaffer,

S. Harkema, M. Roerdink, R. Blossey, U. Steiner, Adv. Mater. 2003, 15, 514,

E. Schaffer, T. Thum-Albrecht, T.P. Russell, U. Steiner, Nature, 2000, 403, 874).

The gradient is introduced using the upper structured mask. At the highest gradient site, the greatest instability and shaping of the polymer occurs. Thus, structures with nanometric dimensions were prepared. The production of the necessary masks also requires electron beam lithography.

Other procedures have been developed in recent years; the most interesting are molding, embossing, printing (W. Wu, E. Kim, E. Ponizovskaya, Applied Physics A: Materials Science & Processing 2007, 87, 143; SW Pang, T. Tamamura , M. Nakao, J. Vac. Sci. Technol. B 1998, 16).

However, these processes are limited by the production of the die itself, but also by the molecular weight of the polymer and its surface properties.

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For polymers having covalently bonded azo groups, the method of forming by exposure to two interfering beams of coherent laser radiation has also been shown. Thus, the spatial periodic structure was shaped to correspond to the spatial distribution of the coherent light intensity. This shaping of the polymer is related to the photomgration and photoorientation of the azo groups (KG Yager, CJ Barrett, Curr. Opin. Solid State Mater. Sci. 2001, 5, 487; C. Hubert, C. FioriniDebuisschert, I. Maurin, J.-M. Nunzi, P. Raimond, Adv. Mater., 2002, 14, 729, K. Takada, B. B. Sun, S. Kawata, Applied Physics Letters 2005, 86, F. Formanek, N. Takeyasu, T. Tanaka, Applied Physics Letters 2006)

In some recent works, the formation of structures using a single laser beam has also been described (C. Hubert, C. Fiorini-Debuisschert, I. Maurin, J.-M. Nunzi, P. Raimond, Adv. Mater. 2002, 14, 729).

In preparing this structure, interference occurs between the incident beam and the beam reflected from the underside of the substrate. The disadvantage is that these methods can only be applied to polymers of the azo-polymer type.

Today, much attention is paid to two other techniques - direct electron beam writing and focusing by focused ion beam (S. Griffith, M. Mondol, D. S. Kong, J. Vac. Sci. Technol. B 2002, 14). Furthermore, both methods, which are very complex and time consuming, have the problem of using suitable materials in sampling and deposition.

In Patent No. 2009-656, a method of modifying a polymeric surface by a scanning laser beam while simultaneously mechanically moving the sample was described. This method will allow the shaping of the surface of various polymers using a temperature gradient applied by the laser beam. The advantage of this method is that the periodicity of the prepared structures does not depend on the wavelength used. This method is very simple, but allows only ID structures, known in the literature as simple diffraction gratings, to be prepared.

SUMMARY OF THE INVENTION

These disadvantages are overcome by a method of shaping double diffraction grating nanostructures in a polymer matrix by exposing the surface of the polymer or thin polymer layer to a periodic heat treatment of a focused and surface-scanning laser beam of wavelength equal to the wavelength corresponding to maximum absorption of the polymer used. the surface of the polymer or thin polymer layer on the support moves in a plane perpendicular to the scanning laser beam and moves in a scanning direction or perpendicular to the scanning direction, in that the surface of the polymer or thin polymer layer with the formed structure is subsequently rotated in a plane perpendicular to the scanning laser beam at an angle between 0.1 ° and 359.9 ° and subjected again •

at the same location, the periodic thermal action of the focused and surface-scanning laser beam, wherein the surface of the polymer or thin polymer layer on the substrate moves in a plane perpendicular to the scanning laser beam and moves in the scanning direction or perpendicular to the scanning direction.

The scanning of the polymer or thin polymer layer is repeated at the same location at the selected angle for the primary formed structure. Thus, the polymer or thin polymer layer is modified twice at the same site.

To improve the response in subsequent scanning, it is possible to steam a dye enhancing the absorption of the laser beam at a given wavelength onto the polymer or thin polymer layer. Various types of polymers can be formed in the proposed manner, including polymers with chemically bonded chromophores or photoresists, which again increase the absorption of the laser beam at the wavelength used.

This method allows the creation of 2D structures. It is possible to create a system of points, holes or structures of the so-called fishing net. The planar symmetry of these structures can be changed from rectangular patterns (squares and / or rectangles) to rectangular motifs (rhombuses and / or rectangles).

The method was modified using an intermediate step of deposition of an organic dye selected from the group of phthalocyanines, porphyrins, azo dyes for shaping polymers of the photoresist group.

The structures of the fishing net can be selectively plated to obtain microresonators and optical resonators on which the properties of metamaterials are based.

By the method according to the invention, an arrangement of two continuously overlapping grids known as the fishing net structure can be prepared on the polymer surface. Its parameters (periodicity, amplitude, kind of symmetry) are determined by the rate of the laser absorbing substance (0.01 to 10% by weight of the dye in the polymer), the speed of mechanical movement of the polymer or polymer layer (0.01 to 100 pm / s) (0.1 to 1000 mW) and scan speed and method (rectangular and / or angular symmetry structures).

The device for preparing 2D shaped polymer nanostructures according to the invention consists of a movable stage on which a polymer or thin polymer layer with a substrate is placed and a laser focus beam source that allows scanning along the rows of the polymer or thin polymer layer through the focused laser beam. in a plane perpendicular to the scanning laser beam.

The method of 2D surface shaping of polymers or polymer thin films in the nanoscale region of the invention is simple and inexpensive. During the preparation of the fishing net structure and other structures, their geometrical, optical, surface and material parameters can be smoothly changed by simply changing the direction of movement, speed of movement, and laser power.

The novelty of the solution lies in the periodic heating of the polymer surface above the pour point Tf with simultaneous mechanical movement of the polymer with the possibility of overlap of the formed partial structures. This inexpensive technological method, supplemented by selective shadow vapor deposition of silver, is useful for the production of optical metamaterials with the possibility of operatively changing the periodicity and amplitude of structures.

Overview of pictures

Fig. 1a shows an arrangement of a thin polymeric layer 1 doped with porphyrin deposited on a support

2.

Fig. 1b shows the same arrangement after application of the laser beam.

Figure 1c shows the same arrangement after application of the laser beam with simultaneous movement of the stage 4 in the selected direction.

Fig. 1d shows a shaped grid rotated 5 by an angle in the range of 0.1 ° to 359.9 °.

Fig. 1e shows a repetition of step a-c to form a fishing net structure.

Giant. 2 shows the shaped structures of a fishing net according to Example 1.

The invention is illustrated by the following examples:

Examples

He did

A polymethymethacrylate (PMMA) layer of 7% polymer solution in 1,2-dichloroethane, volume doped with porphyrin (mesotetrafenilporphyrin), with a final film thickness of 5000 nm was prepared on a centrifuge at 1500 rpm. Porphyrin is a substance with high efficiency light absorption at a wavelength of ca 400 nm. Further, the polymer layer was exposed to a periodic heat treatment of a focused and surface-scanned laser beam of 400 pW and simultaneously mechanical movement of the polymer layer in the scanning direction (2 µm / s). In the next step, the substrate with the first portion of the desired structure on the polymer layer was rotated 90 ° and the scanning was repeated at 400 pW while simultaneously moving the polymer layer in the scanning direction (2 µm / s). Thus, fishing net structures were prepared with a periodicity of 1.5 µm and an amplitude of 0.5 µm (Fig. 2a, c, d).

Example 2

The experimental setup and sample preparation was the same as in Example 1. The speed of mechanical movement was varied. The periodicity of the prepared structure was proportional to the speed of movement. In this way, a periodicity of from 700 nm to 2 µm was achieved. It was possible to change the periodicity immediately during preparation and thus to realize the spatially modulated structure of the fishing net with a square and / or rectangular pattern.

Example 3

The experimental setup and sample preparation were the same as in Example 1. The concentration of the porphyrin solution was varied from 2 to 4% and thus the amount of absorbing substance on the polymer surface. In particular, the amplitude of the prepared fishing net structures from 100 nm to 1 µm was affected in this way.

Example 4

The experimental setup and sample preparation was the same as in Example 1. The laser power varied from 250 to 500 pW. In this way it was possible to vary the amplitude of the individual parts of the fishing nets from 100 nm to 1 µm immediately during preparation.

Example 5

The experimental setup and sample preparation was the same as in Example 1. In the next step, the washer with the first portion of the desired structure on the polymer layer was rotated by 45 ° and scanning at slightly lower power was repeated while simultaneously moving the polymer layer in the scanning direction. Thus, angular symmetry fishing net structures were prepared with a periodicity of 0.7 to 2 µm and an amplitude of 0.3 to 1 µm.

Example 6

A polymethymethacrylate (PMMA) layer of 7% polymer in 1,2-dichloroethane (film thickness 5000 nm) was prepared on a centrifuge at 1500 rpm. Porphyrin was then vacuum-vaporized (approx. 50 nm thick) onto the polymer layer. Porphyrin is a substance with high light absorption at a wavelength of ca 400 nm. In addition, the polymer layer was subjected to a periodic heat treatment of a focused and surface-scanned laser beam having a power of 250 to 500 pW and simultaneous mechanical movement of the polymer layer in the scanning direction. In the next step, the washer with the first portion of the desired structure on the polymer layer was rotated 90 °, and the scan at slightly lower power was repeated while simultaneously moving the polymer layer in the scanning direction. Thus, fishing net structures were prepared with a periodicity of 0.7 to 2 µm and an amplitude of 0.3 to 1 µm (Fig. 2b).

Example 7

The experimental setup and sample preparation were the same as in Example 1. Vacuum vapor deposition of the porphyrin to the already formed structure (at a thickness of about 50 nm) followed. In the next step, the washer with the first portion of the desired structure on the polymer layer was rotated 90 ° and the scanning at slightly lower power was repeated while simultaneously moving the polymer layer in the scanning direction. Thus, fishing net structures were prepared with a periodicity of 0.7 to 2 µm and an amplitude of 0.3 to 1 µm (Fig. 2a, c, d).

Industrial applicability

The invention is applicable to the production of surface-structured polymeric materials and especially thin polymeric layers. Intended applications are in the field of imaging systems for sensors, optical metamaterials, resonator for nanophotonics, especially in the field of hyper-lenses providing huge resolution and last but not least also in the field of affecting the visibility of objects.

Claims (7)

Patent claims A method for forming nanostructures of a double diffraction grating in a polymer matrix by exposing the surface of the polymer or thin polymer layer to a periodic heat treatment of a focused and surface scanning laser beam of wavelength equal to the wavelength corresponding to maximum absorption of the polymer used and the surface of the polymer or thin polymer layer on the substrate moves in a plane perpendicular to the scanning laser beam and moves in a scanning direction or perpendicular to the scanning direction, characterized in that the surface of the polymer or thin polymer layer with the formed structure is subsequently rotated in a plane perpendicular the scanning laser beam at an angle in the range of 0.1 ° to 359.9 ° and subjected again to the same point of periodic heat treatment of the focused and surface scanning laser beam, the surface of the polymer or thin polymer layer on the substrate moves in a plane perpendicular to the scanning laser beam and moves in the scanning direction or perpendicular to the scanning direction. The method according to claim 1, characterized in that the scanning of the polymer or thin polymer layer is repeated at the same location at a selected angle to the primary formed structure and / or after rotation by an angle in the range of 0.1 ° to 359.9 °. Method according to claims 1 and 2, characterized in that the polymer or the thin polymer layer is doped with a laser-absorbing substance before shaping, unless the polymer itself absorbs the laser radiation. A method according to claim 1 or 2, characterized in that a laser radiation absorbing layer is deposited on the surface of the polymer or on the surface of the polymer thin film prior to shaping, unless the polymer itself absorbs the laser radiation. A method according to claim 3 or 4, wherein the laser absorbing agent is a chromophor selected from the group consisting of porphyrins, nitro-, nitroso-, carbonyl compounds and the like. Method according to one of Claims 1 to 4, characterized in that the resulting structure, after rotation by an angle, is in the range of 0.1? up to 359.9 ° re-scanned at the same location in the same plane with the intermediate step of dye deposition and / or changing the applied laser beam intensity to form a fishing net structure and / or more complex surface structures. Method according to the preceding claims, characterized in that the resulting structures are selectively metallized.