FIELD OF THE INVENTION

[0001] The present invention relates to a lithographic process that permits the simultaneous (for the purpose of this application, the term "simultaneous" is meant to describe events that are triggered by the same thermomechanical process, whether they happen at the same time or not) writing, application, or forming of surface relief structures and fluorescent patterns that are superimposed into suitably responsive materials. The process uses materials that can be deformed by thermomechanical treatment and at the same time undergo a change of their fluorescence properties. This permits the creation of superimposed patterns or markings with feature dimensions that range to the sub-micrometer level and which are useful in a variety of applications that range from anti-counterfeiting features to the rapid location of small surface relief features by optical means. Products produced by the process are also disclosed.

BACKGROUND OF THE INVENTION

[0002] There are many applications known in which the surface of a material is structured with features with dimensions that range from the nm to the cm length scale. A broad variety of processes is known to create such structures, ranging from classic thermoplastic processing such as injection molding to the manipulation with atomic force microscopes or thermal probes, i.e., controlled silicon cantilevers with a heatable sharp tip. There are also many uses for structured fluorescent features, i.e., fluorescent patterns with a laterally changing emission color and/or intensity. Such features can also produced by a variety of processes that range from printing fluorescent inks to localized bleaching of fluorescent substrates. Interestingly, there are no processes, which permit the simultaneous writing of surface relief structures and fluorescent patterns that are superimposed.

[0003] Accordingly, one problem of the present invention was to create a process which permits the simultaneous writing, application or forming of surface relief structures and fluorescent patterns or markings that are superimposed. SUMMARY OF THE INVENTION

[0004] The present invention provides a process, which permits the simultaneous writing, application or forming of surface relief structures and fluorescent patterns or markings that are superimposed into a suitable responsive material. By virtue of the process, products are disclosed including the disclosed materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The invention will be better understood and other features and advantages will become apparent by reading the detailed description of the invention, taken together with the drawings, wherein:

[0006] Figure 1 illustrates the chemical structure UPy-OPV-UPy, an example of a suitable responsive material.

[0007] Figure 2 provides a schematic representation of one embodiment of the Dual Write Process according to the present invention. Thermomechanical treatment (for example with a NanoFrazor) changes the surface structure and fluorescence color of a suitable responsive material, such as for example UPy- OPV-UPy, simultaneously.

[0008] Figure 3 provides another schematic representation of one embodiment of the Dual Write Process according to the present invention. In a first writing step (left) the thermomechanical treatment (for example with a NanoFrazor) changes the surface structure and fluorescence color of a suitable responsive material, such as for example UPy-OPV-UPy, simultaneously. Applying the same treatment to a previously treated area permits further changing the surface structure, while the emission color is not further changed.

[0009] Figure 4 provides another schematic representation of one embodiment of the Dual Write Process with additional color control. Changing the time/temperature profile used in the thermomechanical treatment (for example with a NanoFrazor) allows one to tailor the fluorescence color of a suitable responsive material, such as for example UPy-OPV-UPy, at the locations of writing.

[0010] Figure 5 illustrates an example of a surface relief structure and a fluorescent pattern that are superimposed. AFM image (a) and fluorescence microscopy image (b) of a structure written with a silicon cantilever with a heatable sharp tip into UPy-OPV-UPy. The images show that the writing process results in a relief pattern (a) that is superpositioned with a fluorescence microscopy image. The scale bar in (b) is approximate. [0011] Figure 6 illustrates an example of a surface relief structure and a fluorescent pattern that are superimposed, including an AFM image (a) and a fluorescence microscopy image (b) of a structure written with a silicon cantilever with a heatable sharp tip into UPy-OPV-UPy. The images show that the writing process results in a relief pattern (a) that is superpositioned with a fluorescence microscopy image. The scale bar in (b) is approximate.

[0012] Figure 7 illustrates the result of the repeated application of the Dual write approach, including AFM images (a,b) and a fluorescence microscopy image (c) of structures written with a silicon cantilever with a heatable sharp tip into UPy-OPV-UPy. The QR code was written as a first pattern (a). The logo "ami" was subsequently written into an area that had been written over in the first step. The logo is clearly visible as a relief pattern (b) but it does not further change the fluorescence color (c) and is therefore invisible in the fluorescence microscopy image.

[0013] Figure 8 illustrates schematically the self-assembly of UPy-OPV-UPy, an example of a suitable responsive material, into a red-orange light emitting supramolecular polymer and the thermomechanical transformation into a state with a different fluorescence color.

[0014] Figure 9 shows fluorescence microscopy images of a pristine film of UPy-OPV-UPy and samples that were either locally heated or mechanically treated. The images clearly show the localized change of the fluorescence color from red to yellow-green.

DETAILED DESCRIPTION OF THE INVENTION

[0015] This invention pertains to a process that permits the thermomechanical modification of a suitable, stimuli-responsive material so that topological features and fluorescence characteristics of the material are changed simultaneously so that the process leads to simultaneous writing, application or forming of surface relief structures and fluorescent patterns or markings that are superimposed.

[0016] The invention also pertains to products produced by the processes described herein. That is, products or constructions are disclosed having a surface comprising a stimuli-responsive material, wherein the surface includes at least one relief structure and at least one portion that exhibits a first fluorescence and at least one second portion that exhibits a second fluorescence, wherein the first fluorescence is different than the second fluorescence. The invention also encompasses various objects formed with or including the products or constructions. [0017] Thermomechanical modification of a surface can be achieved by a broad variety of techniques in which the surface of an object formed by the material is deformed as a result of the process. For the purpose of describing this invention, any combination of time/temperature/and force that is capable of imparting a surface relief structure shall be deemed suitable to achieve the "thermomechanical modification" sought by this invention. Processes can include, but are not limited to hot-embossing tools, mechanical treatment with a sharp tip such as a silicon cantilever, which may or may not have a heatable sharp tip, such as in an atomic force microscope (AFM) or a nanolithographic devices such as the commercially available NanoFrazor (Pires, D. et al. Nanoscale Three-Dimensional Patterning of Molecular Resists by Scanning Probes. Science 328, 732-735, doi: 10.1126/science.1187851 (2010)).

[0018] On the other hand, we have previously reported a range of materials, which change their fluorescence properties upon thermomechanical treatment on account of reversible or irreversible changes of the aggregation state of fluorescent dye molecules, which were optionally embedded in a polymer matrix (Lott, J.; Ryan, C; Valle, B.; Johnson, J.; Schiraldi, D.A.; Shan, J.; Singer, K.D.; Weder, C; Two-Photon 3D Optical Data Storage via Aggregate Switching of Excimer-Forming Dyes; Adv. Mater. 2011, 23, 2425-2429. Sing, C.E.; Kunzelman, J.; Weder, C; Temperature Indicators for High Temperature Applications; J. Mater. Chem. 2009, 19, 104-110. Crenshaw, B.; Kunzelman, J.; Sing, S.; Ander, C; Weder, C; Threshold Temperature Sensors with Tunable Properties; Macromol. Chem. Phys. 2007, 208, 572-580.). While a broad range of materials that display fluorescence color changes and the generation of fluorescent patterns in response to thermal or mechanical treatment have been reported, the prior art does neither disclose a material nor a process in which a thermomechanical treatment changes simultaneously both: the surface structure and the fluorescence colour.

[0019] We surmised that simultaneous writing, application or forming of surface relief structures and fluorescent patterns or markings that are superimposed could be achieved by applying a thermomechanical treatment to a suitable responsive material, which is capable of changing both, the surface structure (by way of deformation) and the fluorescent color, simultaneously. Indeed, we demonstrate that this is, for example, possible with a supramolecular polymer whose shape and fluorescence properties change upon thermomechanical modification. We show that patterns can be drawn or stamped or embossed into its surface, thereby realizing a high-resolution topographical modification that is aligned with a substantially identical fluorescent pattern that is generated at the same time. In preferred embodiments of the present invention submicrometer patterning is achieved; that is, both the fluorescence and topological patterns have features with characteristic dimensions of 1 μπι or less. Examples demonstrated here as embodiments of the present invention demonstrate that the features generated by the process according to the invention can be read-out by AFM and fluorescence microscopy, but those skilled in the art will appreciate that other techniques may also be suitable, and may change depending on the length scale and optical characteristics of the features written. Examples shown here demonstrated that repeated thermomechanical treatment can be used to achieve topological modifications at locations whose topology and fluorescence characteristics had already been modified, by previous thermomechanical treatment; this repeated process allows, under certain circumstances, to further change the surface topology, while no further altering the fluorescence characteristics, thereby creating a topological pattern that is different from the underlying fluorescence pattern.

[0020] The process according to the present invention is useful for many technological problems. The hitherto unachieved creation of superimposed patterns with feature dimensions that range to the sub-micrometer level is for example useful in anti-counterfeiting features. Other embodiments include the use as alignment mark, and a feature that permits the rapid, easy, and reliably location of small surface features by optical means.

[0021] One embodiment of a stimulus-responsive supramolecular material according to the present invention is based on a cyano-substituted oligo(phenylene vinylene) dye (UPy-OPV-UPY) that that carries two ureido-4-pyrimidinone (UPy) groups at the termini of peripheral aliphatic groups (Figure 1). The UPy motif, originally developed by Meijer and coworkers (Sijbesma, R. P.; Beijer, F. H.; Brunsveld, L.; Folmer, B. J. B.; Hirschberg, J. H. K. K.; Lange, R. F. M.; Lowe, J. K. L.; Meijer, E. W., Reversible polymers formed from self-complementary monomers using quadruple hydrogen bonding. Science 1997, 278 (5343), 1601-1604), was chosen because it forms strong self-complementary hydrogen-bonded dimers, is easy to synthesize, and its dynamic binding is well investigated. The difunctional UPy-OPV-UPy introduced here was designed to form supramolecular polymers, whose properties are dictated by the supramolecular assemblies formed. The OPV core used is well-known to change its fluorescence color upon aggregation due to the formation of excimers, resulting in a pronounced bathochromic shift of the emission. We further surmised that UPy-OPV-UPy (a) would assemble into a supramolecular polymer, which in a temperature regime that is useful for various application forms a solid material; (b) would be deformable by thermomechanical treatment so that surface relief structures could be imparted; and (c) that the same thermomechanical treatment would result in a detectable change of the materials fluorescence properties, as a result of changing the extent of excimer emission.

[0022] UPy-OPV-UPy was prepared by reacting l,4-bis(cc-cyano-4-(12- hydroxydodecyloxy)styryl)-2,5-dimethoxybenzene with two equivalents of 2-(6- isocyanatohexylaminocarbonylamino)-6-methyl-4[lH]pyrimidinon e using isocyanate chemistry catalyzed by dibutyltin dilaurate (FIG. 1). This simple reaction, which was carried out in hot pyridine to prevent network formation during the reaction, yielded the new monomer in high yield. The precipitation of the reaction mixture into cold acetone afforded the pure product as an orange powder that consists of UPy-OPV-UPy.

[0023] Samples used in the embodiments shown here made by doctor-blading films of UPy- OPV-UPy from the melt at 170°C onto silicon wafers.

[0024] The thermomechanical treatment used here was performed with a silicon cantilevers with a heatable sharp tip on a commercial instrument known in the art as NanoFrazor. The experiments were performed in contact mode and pulsed heating with a temperature at the top of the cantilever between 430 and 460 °C, that correspond to roughly half the value 215-230°C at the tip of the cantilever.

[0025] Surface relief structures were detected with the reader function of the NanoFrazor that simultaneously was operated during thermomechanical treatment.

[0026] Fluorescence patterns were detected using a fluorescence microscope that was equipped with a digital camera under illumination with a mercury lamp.

[0027] Figures 2 - 4 provide schematic representations of embodiments of the Dual Write Process according to the present invention. The simplest embodiment involves a single thermomechanical treatment that simultaneously changes the surface structure and fluorescence color of the responsive material, such as for example UPy-OPV-UPy (Figure 2). This was demonstrated by preparing a thin film of UPy-OPV-UPy on a SI wafer and writing a structure with a silicon cantilever with a heatable sharp tip into this material. This was done with a commercial instrument known in the art as NanoFrazor. The AFM image recorded afterwards (Figure 5a) shows that the writing process results a relief pattern with features that have dimensions of less than 1 μπι. A fluorescence microscopy image of the same sample (Figure 5b) shows that the process has simultaneously created a virtually identical fluorescence image. Figure 6 shows images that result from a similar experiment, but in this case specific information is contained in the images. The example shows that the writing process according to the present invention can be used to write very different types of features, which can contain different types of information, including, but not limited to text, numbers, images, bar codes and quick response (QR) codes, which in turn can provide links to additional information contained elsewhere.

[0028] Figure 3 provides a schematic representation of another embodiment of the Dual Write Process according to the present invention, where in a first writing step (left) the thermomechanical treatment changes the surface structure and fluorescence color of a suitable responsive material, simultaneously. Applying the same treatment to a previously treated area permits further changing the surface structure, while the emission color is not further changed. This embodiment was reduced to practice and the related data are shown in Figure 7. AFM images (a,b) and fluorescence microscopy image (c) of structures written with a silicon cantilever with a heatable sharp tip of the NanoFrazor into UPy-OPV-UPy. The QR code was written as a first pattern (a). The logo "ami" was subsequently written into an area that had been written over in the first step. The logo is clearly visible as a relief pattern (b) but it does not further change the fluorescence color (c) and is therefore invisible in the fluorescence microscopy image.

[0029] Figure 4 finally provides the schematic representation of another embodiment of the Dual Write Process according to the present invention that provides additional color control. Changing the time/temperature profile used in the thermomechanical treatment (for example with a NanoFrazor) allows one to tailor the fluorescence color of a suitable responsive material, such as for example UPy-OPV-UPy, at the locations of writing.

[0030] Those skilled in the art will appreciate that the thermomechanical treatment that was imparted here with the NanoFrazor may be replaced by other techniques that cause similar thermomechanical exposure of the stimuli-responsive material. For example, methods such as hot stamping may be used in applications where a high throughput is needed. Likewise, UPy-OPV- UPy can be replaced by other stimuli-responsive materials that exhibit similar thermomechanical responsiveness.