1 Introduction

All of the current lithography methods utilize the same basic principle: the exposure of a material to electromagnetic radiation which chemically alters the exposed regions to make them more or less soluble [1]. In optical lithography, the photosensitive material is exposed to ultraviolet (UV) light through a mask. This method, however, is limited by the wavelength of light. Some methods were proposed for optical lithography improvement, including immersion lithography and deep UV lithography [2, 3]. In immersion lithography, the desired liquid medium is introduced between optical system and sample surface. By this way, the resolution is increased by a factor equal to the refractive index value of the introduced liquid [1]. Another technique—extreme ultraviolet lithography (EUV) tends to utilize the photons with smaller wavelength. Application of light with 14.5 nm wavelength is now commonly in the case of EUV. In this case, the resolution in order of 10 nm was expected. However, some problems, related to insufficient reflectance of applied wavelength and power loss in EUV systems exists. As the optics are not used lenses, but multilayer mirrors, with reflection on the basis of interlayer interference. At each reflection about one-third of light intensity is absorbed, so EUV systems must be equipped with powerful light source. In addition, EUV has extremely high requirements on planarity of the masks. The phase shift caused by several nanometers mask flatness deviation is sufficient to produce defects in recording media. Other problems of EUV are associated with secondary electron emission, materials heating and transparency at used wavelength that substantially restricts resolution limits of this technique [1].

An alternative to traditional optical lithography are electron beam patterning and interference lithography techniques. Electron beam lithography is capable of far smaller features, but each feature must be written individually, rather than the parallel exposure that take place in optical lithography [4]. Therefore, electron beam lithography is generally considered to be slow, expensive and low throughput technique. Interference lithography employs the interactions between coherent laser beams to directly pattern the resist on a submicron length scale. Usually, two or more laser beams intersect at the sample surface or in materials bulk. In this way, structures with 3D resolution can be prepared, but the technique is very sensitive to lasers tuning and arrangement vibration instabilities [5]. Some improvement, e.g. application of diffraction mask or prism, seems to be capable to overcome these problems, but only limited quantity of patterns can be prepared in this way [6, 7]. Rather special kind of beam pattering technique is one-beam laser nanopatterning. This unique process does not require multi-beam interference or specific optical equipment. Polarized laser light interferes close to irradiated surface producing inhomogenity in energy distribution and forming self-assembled array of sub-micron features of modified material, i.e. ripples [8, 9].

One alternative and elegant approach for improving the light utilizing patterning methods is near-field optical lithography. Near-field optical lithography, based on a scanning near-field optical microscopy configuration, uses the field-enhancement effect appearing at the extremity of a metallic tip when illuminated with an incident light polarized along the tip axis [10]. The local enhancement of the electromagnetic field strength below the tip’s occurs and which can cause a photoreaction [11]. Obtained patterns depend on a few experimental parameters, such as the polarization state, the illumination mode and the tip’s geometry [12].

One of the most widely used patterning techniques is so-called soft lithography. Soft lithography [13, 14] represents a conceptually different approach to rapid prototyping of various types of both microscale and nanoscale structures, and devices on planar, curved, flexible and soft substrates. The conception of ‘‘soft lithography’’ cannot be referred to one specific method, but rather covers a group of techniques with common features. A large number of patterning techniques, which are essentially based on the printing, molding and embossing with an elastomeric stamp are microcontact printing, replica molding, microtransfer molding, micromolding in capillary, solvent-assisted micromolding, phase-shifting edge lithography, nanotransfer printing, and nanoskiving was be emerged [15–18]. All these techniques use organic and polymeric materials that are referred to as soft matter by physicists.

Nanoimprint lithography (NIL) (a next generation lithography candidate) is a high-resolution, and cost-effective nanopatterning technology based on the mechanical deformation of the thermoplastic polymer under controlled temperature and pressure. Accuracy better than 10 nm has been achieved by applying this technique [19]. This technique also offers the fabrication of three-dimensional structures by a layer-by-layer approach [20]. The imprinting results depend on several parameters, such as Tg of the using different polymers, film thickness, width and height of the features on the substrate, and mechanical properties of the polymers. Example of application of this technique is the air-bridged structures widely used in monolithic microwave integrated circuit and nanoelectromechanical system [21] for manufacturing semiconductor device.

Another patterning technique can be applied on block copolymers. A block copolymer consists of two or more polymeric chains (blocks), which are chemically different and covalently attached to each other. If the block copolymers are heated at molten temperature, different parts of macromolecule are driven to segregate into a variety of ordered structures by the repulsion of the immiscible blocks. Because the size of each part is approximately several nanometers, the structure well below 100 nm size can be prepared in this way [22]. In the thin film state, the block copolymer patterning occurs relative to the surfaces of the film. Block copolymer thin films are of particular interest because of the possibility of obtaining two-dimensional patterns with very high registry and regularity. Application of this technique access to a length scale symmetry preparation [23].

Another perspective technique for polymer patterning utilizes the external electric field or temperature gradient [24, 25]. Structures with different sizes and morphology can be prepared in this way [26–28]. These techniques allow both, surface and bulk modification of polymer properties [29, 30]. This relatively new promising technique for polymer patterning is based on the hydrodynamic instabilities of liquid polymer surface enhanced by external electric field or temperature gradient [31–33]. Well-defined polymeric patterns with dimensions ranging from a few tens of nm to a few mm can be prepared by this technique.

In our previous work, we described the new technique for polymer patterning [34]. Like the tradition lithography or direct laser writing we use the laser beam to modify the materials. However, the driving forces and mechanism of polymer modification are rather different. In difference from traditional utilization of light, the polymer flows under temperature gradient introduced by light absorbtion. Prepared structures are not limited by light diffraction limit. In this work, we give more detailed study of observed phenomenon and demonstrate the preparation of more complex structures completed with their possible application in photonics.

2 Experimental

2.1 Materials

Polymethylmethacrylate (M w = 1,459,000 (PMMA 1500K)) of optical purity was supplied from Goodfellow, PMMA 15K (M w = 14,700) was purchased from Sigma-Aldrich. Mesotetraphenyl porphyrine (C44H30N4), 99.7 % grade, was supplied from Frontier Scientific. Solution of epoxy resin (photoresist, Su-8) was purchased from Microchem. All materials were used without further purification. Material properties of used polymers are summarized in Table 1.

Table 1 Properties of the studied polymers (molecular weight M w, glass T g and fluid T f temperature)
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2.2 Sample preparation

Thin polymer films doped by porphyrine were prepared by spin-coating technique. The polymer was dissolved in dichlorethane and doped by porphyrine in two ways. In the case of bulk doping, the polymer solution was mixed with porphyrine, dissolved in dichlorethane. In another case, the layer of pristine polymer was prepared by spin coating and then coated with porphyrine by vacuum evaporation. Vacuum deposition was performed under 10−6 Torr pressure and at 1 A electric current. For preparation of more complex structures, the combination of both methods was used.

The doped polymer films were modified by laser scanning and simultaneous mechanical movement. This technique of polymer modification was recently proposed by our team [34]. Chosen polymer area is scanned by continuous wave laser beam line by line. Laser beam was focused into spot with approximate diameter 0.5 μm. Laser operating at 405 nm wavelength and 0.1 W laser power was applied. Sample mechanical movement is added to the laser scanning. The velocity of sample movement was 2 μm/s. The process is schematically depicted in Fig. 1.

Fig. 1
figure 1

Scheme of laser modification of PMMA doped by porphyrine: a pristine featureless polymer surface, b surface distortion after the laser scanning on motionless sample surface and c laser scanning and simultaneous mechanical movement of sample

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For preparation of more complex structure polymer films doped with porphyrine were modified by laser scanning. Then, in a second step, the porphyrine was deposited on the surface of modified polymer, the sample was turned by 90° regarding to previous orientation and scanned again.

2.3 Methods of sample characterization

Molecular weights of polymers were determined by gel-chromatography method. The heat flow, glass transition (T g) and fluid (T f) temperatures of polymers were measured by the standard calorimetric method using the DSC 2920 technique.

For measurements of UV–Vis spectra 50 nm thick porphyrine layers on to glass substrate were prepared. The absorption spectra were measured in the spectral range 270–800 nm using standard spectrophotometer (Varian Cary 50).

Atomic force microscopy (AFM) was used for sample surface morphology characterization. AFM studies were performed under ambient conditions with Digital Instruments CP II set-up in contact mode. The direct measurement of the polymer surface was done with a scanning electron microscope Tesla BS 340. Additional coating of samples by 50 nm gold layer was used to prevent polymer charging and degradation.

Surface chemistry was characterized by XPS technique. An Omicron Nanotechnology ESCAProbe spectrometer was used. The dimension of the analyzed area was 1 × 1 mm2. The X-ray source was monochromated at 1,486.7 eV. The spectra were measured stepwise with a step in binding energy of 0.05 eV. The data were processed by the CasaXPS program.

Optical properties were examined using laser emitting at 632 nm. Laser light was used for diffraction experiments and for coupling of light into planar waveguide. For diffraction measurement, the sample was oriented perpendicularly to incident laser beam. For coupling of light into waveguide, the sample was placed on to goniometer and rotated relative to angle of light incident with the aim to achieve maximum coupling efficiency.

3 Results and discussion

3.1 Surface patterning

Figure 2 gives the typical structure prepared by laser scanning and simultaneous sample movement. Thin polymer film doped by porphyrine in bulk was exposed to focused beam of laser light in confocal microscope. The laser light of applied wavelength is expected to be absorbed by porphyrine molecules. Figure 2a corresponds to application of laser scanning line along a line on the defined area of motionless sample. Figure 2b and c shows the optical image of surface modified by laser scanning with simultaneous sample movement. After the laser modification the polymer tends to form two protruding surface structures on the boundary of scanned area (Fig. 2a). Surface distortion at the boundaries of the exposed area becomes well visible after achievement a threshold value of intensity of laser light. It should be noted that appearance of the structure occurs only in the direction of laser scanning (left and right sides of image). Formation of the structure in perpendicular direction (top and bottom sides of image) was never observed. It could be assumed that polymer tends to flow in the direction of more pronounced temperature gradient. When the simultaneous mechanical movement of sample is added, the periodical structure is formed (see Fig. 2b). Prepared structure exhibits the system of well-ordered surface maximum and minimum peaks. In other words, the surface profile represents periodical array of lines along which the polymer mass was pulled above the initial flat surface. Proposed mechanism of the structure formative consists in polymer mass re-distribution governed by surface tension gradient (so-called Marangoni effect [35]). The classical mechanism of the Marangoni effect expressed in the formation of surface structures at the interface of two phases is the non-uniformity of surface tension due to temperature gradient [35]. In our experiments, absorption of light during the scanning generates spatial variability of surface tension, usually responsible for Marangoni effect. To our opinion in the first step, the polymer matrix is melted. At the next step, periodical temperature gradient and the surface tensions gradient are created. As can be predicted by Marangoni phenomenon, the polymer tends to flow from the region with smaller surface tension to the region with higher surface tension. On the boundaries of scanned region, the polymer flow must be stopped because the materials outside this region is not in molten state. When continual mechanical movement of sample is added to the laser scanning, processes of polymer melting, flow and stopping achieves equilibriums and 2D periodical structure is created. The driving force for the structure formation is the magnitude of thermal gradient and related inhomogeneity in the surface tension. The initiation and propagation of this process at “stationary conditions” is well described in several works [36, 37] from the theoretical point of view. Nevertheless, in the present case, we deal with non-equilibrium conditions because of continuous sample movement.

Fig. 2
figure 2

Optical and AFM images of modified surface of PMMA doped by porphyrine in bulk a image obtained from optical microscope after applying of laser scanning, b image from optical microscope after applying of laser scanning and simultaneous mechanical movement of sample and c AFM image of modified surface

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3.2 Parameters of the patterns

For verification of proposed mechanism, some additional experiments were performed. The formation of surface patterns can arise not only due to the local heating of the polymer surface, but also due to local heat release in chemical and physico-chemical processes in the laser irradiated polymer. With the aim to estimate the possible changes in surface chemistry, the XPS analysis was used. XPS was performed on PMMA samples doped on surface and in bulk. Relative element concentrations before and after surface modification are given in Table 2. In the case of bulk doped PMMA, the slight decrease in C concentration and increase in N and O concentrations were found. This result indicates the absence of sufficient changes in polymer surface chemistry. Observed changes in element concentrations can be attributed to redistribution of polymer and dopant molecules in fused state. In the case of surface doped PMMA, the considerably smaller concentration of O on the pristine surface was found, in comparison with that doped in bulk. This result could be expected, because the top layer of porphyrine screens the polymer molecules. Similarly, as well as in the case of bulk doped samples, only minor alterations in surface chemistry after the laser modification were found. Small increase in C concentration and small decrease in N concentration can be explained in terms of polymer flow and mixing of porphyrine/polymer layer.

Table 2 Surface concentration of elements (C(1s), O(1s) and N(1s)) in bulk and surface doped PMMA before and after the laser modification determined from XPS analysis
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Because the chemical changes of the polymer surface initiated by the laser irradiation are not substantive one can conclude that the surface patterning is mostly due to classical temperature effects. Standard procedure for theoretical analysis of surface pattern in thin polymer films under temperature gradient is linear stability analysis [38, 39] according which the formation of surface structures is governed by the surface tension and material redistribution ratio due to heat transfer, where the temperature gradient once again destabilizes the situation, while the viscous drag damps disturbances. There are several cases, which can lead to periodical structure appearance under temperature gradient: (1) non-uniform density distribution over the layer of viscous liquid heated from one side—so-called gravitational instability [40], (2) so-called concentration instability appears in multicomponent system due to difference in component concentration [41] and (3) surface tension instability corresponds to differences in surface tension of homogeneous thin film due to temperature gradient, presented in these films [42].

In case of gravitational instability, stability of thin films limit is determined by the value of the Rayleigh dimensionless criterion and does not depends on the forces of surface tension. Rayleigh dimensionless criterion is strongly related to thickness of treated film. For verification of this mechanism, the series of samples with different layer thickness were prepared and examined in the same way. Dependence of amplitude of prepared periodical structure on the sample thickness is given in Fig. 3. In Fig. 3, the dependence for PMMA with two different molecular weights is shown. Samples were prepared with the same porphyrine concentrations and modified at the same laser light intensity. From Fig. 3, it is evident that the amplitude of the patterns increases linearly with increasing sample thickness up to the threshold thickness of about 2,100 nm in both investigated cases. Above the threshold thickness, the increase rate slows down considerably. Appearance of threshold thickness and linear character of amplitude increase leads us to the conclusion that the polymer flow is not governed by gravitational instability. Rising part of curves can be explained by the amount of absorbed light energy increasing with the film thickness. The upper part of the curves can be attributed to limited light penetration–absorption in polymer when only thin surface layer of the polymer is affected.

Fig. 3
figure 3

Dependences of resulted amplitude of prepared lattices on initial thickness of PMMA film (with different molecular weight 1500K and 15K)

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Surface instability may also be attributed to non-uniform concentrations in multicomponent system. In our experiments, where we used ether the pristine films or films with homogeneous concentration of dopant, this mechanism can be excluded.

Another reason for outbreak of surface instability may be the presence of surface tension gradients due to non-uniform temperature field of a system on the upper free surface. This mechanism seems to be more reasonable in the present case. In this case, the structure formation must depend on the surface tension and viscous damp. With the aim to investigate the viscous damp influence, two kinds of PMMA with different molecular weights were examined since it is well known that viscous damp of polymer is strongly related to their molecular weight. Linear polymer with the larger molecular weight will have greater value of viscous damp than its low-molecular homolog. The resulted surface pattern of films with the same thickness and concentration of dopant are given in Fig. 4. It is evident that at lower molecular weight sufficiently sharper structure with higher amplitude is formed. One can say that utilizing of polymers with different molecular weight can result in differences in surface tension too. It should, however, be noted that surface tension of thin films is much more dependent on the chemistry of macromolecules rather than on molecular weight [43].

Fig. 4
figure 4

AFM images of bulk doped PMMA modified by laser scanning and simultaneous sample movement (film thickness 700 nm, dopant concentration 3 %): a, b Surface of PMMA with different molecular weight (1500K and 15K)

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3.3 Preparation of structure on photoresist

From the practical point of view it seems to be interesting to choose the polymer based negative photoresist as recording media for patterning. In this case, the prepared pattern can be fixed by cross-linking. One of examples is the application of soft lithography techniques for patterning of commonly used photoresist—Su-8 with following strengthening by polymer cross-linking during UV illumination [44, 45]. Our first experiments, performed by bulk doping of Su-8, and subsequent patterning and UV exposition, were not successful because the presence of porphyrine prevents the polymer cross-linking. To overcome this problem, another technique of material doping was proposed—high vacuum evaporation of chromophore on the top of pristine polymer layer. In this case, the Su-8 films not contain dye and can be easy cross-linked.

First, maintaining the structure of porphyrine during vacuum deposition was verified. Figure 5 shows absorption spectra of porphyrine, deposited on to glass substrate by vacuum evaporation and, for comparison, by deep-coating method from solution (3 % porphyrine concentration in chloroforme). The strong absorption peak near 400 nm is attributed to so-called Soret band and is typical for porphyrine and porphyrine derivatives. This peak appears on both vacuum deposited and deep-coating deposited porphyrine spectra. From the presence of Soret band in spectrum of vacuum deposited porphyrine film is evident that the structure of porphyrine macrocycle is conserved during deposition. Broadening of the Soret band and additional peak at 330 nm can correspond to formation of dimers, trimers and organization of porphyrine molecules into crystal structures [46].

Fig. 5
figure 5

Absorbance of porphyrine deposited on to glass substrate. The solid and dash lines correspond to evaporated and bulk doped films

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In the next step, Su-8 layers covered by porphyrine were exposed to laser scanning with simultaneous sample movement, like in the case of bulk doping of PMMA. Figure 6a shows the structure obtained after polymer modification. It is evident that prepared structure shows some tendency to be “periodical”, but the quality of this periodicity is “bad” (Fig. 6a). In the next step, additional laser illumination of prepared pattern was performed. The next laser illumination results in material redistribution and sufficient improvement of the structure quality. Figure 6b gives the surface profile of prepared structure after two stages of polymer modification. The differences between Figs. 6a and b are evident, but the nature of observed phenomenon, the driving forces for material flow and structure improvements during the second stage, are not clear now. In the next step, prepared structures were fixed by UV light illumination and developed in dichlorethane. As can be expected, cross-linked Su-8 is not soluble and only top layers of porphyrine are dissolved. Typical surface profile of prepared structure is given in Fig. 6c.

Fig. 6
figure 6

AFM images of surface of Su-8 with doped with porphyrine after modification by laser scanning and simultaneous mechanical movement: a surface after application of laser scanning and sample movement, b surface after subsequent laser illumination and c surface of modified film exposed to UV light and treated in dichlorethane

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Proposed technique opens-up a possibility to utilize wider range of materials as dopant, regardless of their solubility and miscibility with polymer. As an example—class of phthalocyanines (materials with “bad” solubility in common solvents) can be used instead of porphyrine different dyes, deposited on the top of polymer can serve as light absorber for patterning process and as “active” material in next utilization of prepared structures, e.g. in sensor application. Properties of polymer matrix remain invariable, which may be important in some specific applications. In addition, deposition of dyes on to formerly patterned polymer surface opens-up new way for more complex 2D polymer surface patterning (see below).

3.4 Complex structure preparation

2D polymer surface patterning was performed in several steps. After polymer doping and patterning, the additional layer of porphyrine was deposited on to the top of modified sample. Then, the sample was turned on 90° regarding to previous orientation and sample scanning was performed again, perpendicularly to previous scanning direction. Optical images of prepared structure are given in Fig. 7. Figure 7a shows image taken from optical microscope and Fig. 7b gives 3D image evaluated from reflected laser light. In the case of 3D image, the region between singly- and doubly modified areas is given for best comparison. From Fig. 7 is evident that the surface modification occurs during both scans. On the sites subjected to first and second modifications, the apparent change in the surface morphology occurs. Because it is difficult from only optical image to make a definitive conclusion about the sample topography, additional analysis by SEM and AFM were performed. Figure 8 gives the result obtained from SEM analysis. It is clearly visible that prepared structure represents a system of ordered squares, like chequered paper in writing book. The chequered paper nature could be expected as a result of superposition of two linear lattice patterns. Typical AFM image is shown in Fig. 9. In general, expected character of pattern was also confirmed by AFM imaging. Modified surface represents the “chequered” structure. However, it is apparent that the amplitudes of intersected lattices are different. Difference in the lattice amplitude can be explained in the terms of surface–tip interaction which can be influenced by mutual orientation of pattern and scan direction (AFM scan was performed line by line from the top of the sample to the bottom). It should be noted that not only square-law symmetry of prepared structures can be obtained. By the choice of suitable angle between two superposed pattern, different structures with diamond-shared symmetry can be prepared.

Fig. 7
figure 7

Optical image of prepared cross section of two laser scans. First scan was applied on the doped PMMA (vertical orientation of lattice lines). Then, the additional layer of porphyrine was deposited on to prepared lattice and laser scanning with simultaneous sample movement was applied in perpendicular direction: a image from optical microscope, b 3D image of prepared structure evaluated from reflected laser light

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Fig. 8
figure 8

SEM image of prepared complex pattern on PMMA (1500K) doped by 3 % porphyrine

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Fig. 9
figure 9

AFM image of prepared complex pattern on PMMA (1500K) doped by 3 % porphyrine

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Prepared 2D structures seem to be interesting for wide range of application. For example, system of micro-rings can found their application in photonics, as wavelength sensitive components [47–49], 2D photonic crystal [50] or optical metamaterial [51]. They can serve as substrate for next metal or semiconductor depositions. Selectively coating of prepared structure [52, 53] by metal opens-up a way for preparation of materials with negative refractive index, permittivity or permeability [51].

Proposed technique opens a way for simple polymer patterning. However, some disadvantages of the technique should be noted. The full patterning of polymer film has never been achieved. Decreasing of initial films thickness reduces pattern amplitude and a residual polymer layers occur in all cases, similarly as in nanoimprint method. In nanoimprint method, however, there are several ways to remove residual polymer layer e.g. by reactive ion etching. The use of pressurized imprinting and a more fluidic imprint resin are very helpful for the residual layer removal. Other approaches consist of reducing the initial volume of resist or using high pressure to squeeze excess of polymer out from the space between the mold and the substrate. The high fidelity transfer of various patterns with no residual layer was successfully demonstrated by controlling the initial resin thickness at the imprint pressure of 15 atm [54]. In our case, we try to decrease thickness of residual polymer layer by application of chemical linking between dye and polymer backbone. It is expected that the linking with dye will lead to more pronounced material redistribution and to decrease thickness of residual polymer layer.

Described method of polymer patterning based on the temperature-induced surface tension gradient and following deformation of polymer films, can achieve resolutions beyond the light diffraction limitations. However, when compared with so-called LIGA method [55], developed for preparation structures that are much taller than wide, the structures with high aspect ratio cannot be prepared by the present method. At the other hand, present method does require less production steps for manufacture the mold, X-ray source or X-ray mask.

4 Optical properties

Uniformly sized and shaped nano- and micro-domains formed on the polymer films can found their application in high-density information storage media, waveguide coupler and filters, temperature, pressure or chemical sensors. Examination of optical properties of prepared structure with the aim to evaluate their possible application in photonics was performed. First, diffraction of light through the lattice was estimated. Because the spot of applied laser possesses the sizes of an order of square millimeters, system of lattices deposited abreast was prepared for diffraction experiments. The areas of 1 × 1 cm2 were patterned on the sample surface. Optical image of prepared structures is given in Fig. 10. When considering difficulties in precise positioning of each lattice, some disagreement in their mutual orientation is observed. The diffraction intensity of light passing through prepared structure was observed and photographed. Obtained image is shown in Fig. 11. From Fig. 11, it is evident that prepared structure exhibits satisfactory diffractive properties. However, some illegibility and vagueness in diffraction intensity maxima is observed. This discrepancy in diffraction can be attributed to disagreement in mutual ordering of lattices.

Fig. 10
figure 10

Optical image of system of lattices, prepared abreast on PMMA (1500K) doped by 3 % porphyrine

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Fig. 11
figure 11

Diffraction pattern of laser light (633 nm) passed through a system of lattices deposited abreast on PMMA (1500K) doped by 3 % porphyrine. Presented process is schematically depicted in the inset

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One of the possible applications of prepared structure is coupling of light into waveguide. Example of utilization of prepared structure as waveguide coupler is given in Fig. 12. The sample with patterned surface (1 × 1 cm2 patterned area) was deposited on to rotation stage and the optimal angle of laser beam incident was founded. This angle corresponds to the most effective light coupling into planar waveguide. From Fig. 12, it is apparent that a part of laser energy was trapped by lattices and travelled along a waveguide. Schematically, this process is depicted in Fig. 12 insert. The prepared profile of a surface pattern had sinusoidal character. From literature, it is well known that for light coupling the rectangular structure profile is more effective [56]. However, for laboratory purposes, the light coupling exhibits sufficient efficiency.

Fig. 12
figure 12

Coupling of light in planar waveguide through system of lattices deposited abreast on PMMA (1500K) doped by 3 % porphyrine. Presented process is schematically depicted in the inset

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5 Conclusion

In this work, we suggested and experimentally examined method for polymer surface patterning by scanning with laser beam combined with sample mechanical movement. Structures with different parameters and symmetry were prepared and analyzed by XPS, SEM, AFM studies. For surface modification, we used PMMA with different molecular weight and polymer photoresist. Mechanism of structure creation was analysed and found to be dependent on surface tension gradient introduced by laser light scanning. Applications of prepared structures in photonics as diffraction elements or waveguide coupler are also given.

There is a considerable technological significance in the experiments we performed. It was shown that a non-tactile non-ablative method without wet chemistry is able to create surface structures of interesting properties. The polymer patterning step can take place in ambient air and can be strongly modulated by change of speed of polymer sample movement, molecular weight of polymer and dopant concentration.