Gas-phase multiphoton polymerisation method and use

Abstract

The invention relates to a gas-phase multiphoton polymerisation method with a reactor having at least one light source (4) and a substrate deposition area having at least the steps: - adding a gas flow of radical initiators and monomers (3) to a reactor containing a substrate (6) at a defined pressure and temperature, wherein monomers (3) adsorb on the substrate (6); focusing a point on the substrate surface (6) with the at least one light source (4) and splitting and / or breaking up the radical initiators in the focus volume (5) of the at least one light source (4) to form free radicals (2) by multiphoton absorption, whereby a radical polymerisation of the monomers (3) with the free radicals (2) formed is started in the area of the substrate surface (6) having free radicals (2), and a local polymer thin film is formed on the substrate (6). The invention also relates to a use of the gas-phase multiphoton polymerisation method.

Description

[0001] Gas-phase multiphoton polymerization process and use

[0002] The invention relates to a gas-phase multiphoton polymerization process with a reactor having a light source and a region for substrate deposition and an associated use.

[0003] In the following, the term “multiphoton” means that the energy of two photons or more is applied to excite an initiator molecule and form free radicals.

[0004] The initiated chemical vapor deposition (iCVD) process is a process in which a thin polymer layer is created through free radical polymerization. The process takes place under vacuum conditions (typically with a process pressure of 40-50 Pa). One or more monomers and an initiator are usually fed into a reactor in the form of vapors. To prevent condensation on the reactor walls, the reactor and all inlet and outlet lines are heated to approximately 90-130 °C (depending on the monomer used). To start the process, a filament located above the substrate holder is heated (-250-400 °C), which causes the initiator molecules to decompose into free radicals. The monomer molecules do not decompose and adsorb onto the substrate holder. For the monomer molecules to adsorb, the substrate holder must be cooled to 20-35 °C.The free radicals collide with the adsorbed monomer molecules and initiate free radical polymerization on the cooled substrate holder. The process is typically carried out in a flow-through process. New (co)monomer and initiator molecules are continuously added to the reactor, while byproducts and unreacted molecules are simultaneously pumped out. This is also possible in a batch process.

[0005] Two-photon (3D) printing is a process in which, for example, focused light sources are used to generate radicals extremely locally. Using a focused laser, initiators are excited with the energy of two photons only at the focal point to generate radicals. This allows for extremely high-precision 3D printing from a resin (a mixture of monomers, initiator, and solvent).

[0006] According to the state of the art, the local polymerization of polymer thin films is currently carried out in several steps, such as by applying masks.

[0007] The publications EP 2 905 121 B1 and EP 2 569 140 B1 disclose a device and a method for producing three-dimensional structures, such as bodies or surface structures, from a material to be solidified, in particular from an organopolysiloxane-containing material, by site-selective solidification of the material as a result of light-induced organic crosslinking. Qiu, Mingjun, et al., in "Recent progress in non-photolithographic patterning of polymer thin films," Progress in Polymer Science^ 42 (2023): 101688, demonstrate that the problem of structuring thin-film surfaces is currently highly relevant.

[0008] In "Gas-Phase 3D Printing of Functional Materials," Advanced Materials Technologies 5.12 (2020): 2000657, de la Huerta, Cesar Arturo Masse, et al. demonstrate the principle of spatial atomic layer deposition (SALD) as a new way to print functional materials and devices with spatial and topological control. This expands the potential of SALD and ALD in general and opens a new avenue in the field of area-selective deposition of functional materials.

[0009] Furthermore, Schäfer, Katherine J., et al., in "Two-photon absorption cross-sections of common photoinitiators." Journal of Photochemistry and Photobiology A: Chemistry 162.2-3 (2004): 497-502, investigate the two-photon absorption properties of commercially available photoinitiators typically used in conventional radiation curing and frequently used in two-photon absorption-based polymerizations.

[0010] The problems with the current state of the art are essentially that processes for the local deposition of polymer thin films require complex and labor-intensive systems. The known systems, such as diblock copolymerization, result in specific surface patterns that cannot be individually adjusted. Other systems use specially structured substrates.

[0011] In addition, the currently known systems have several combined process steps.

[0012] Furthermore, state-of-the-art polymer iCVD coatings are homogeneous and cannot be applied locally on a substrate.

[0013] 3D printing from the gas phase is currently only known, as previously described, through the principle of spatial atomic layer deposition, which, however, is a complex process that is only suitable for flat surfaces.

[0014] Wet-chemical 3D printing using two-photon polymerization is mature and widely used in science and industry. However, this method is limited to a single polymer "resin" and does not allow for free modification of the chemical functionalities through the structure. Furthermore, the resins must have certain viscosities and may require solvents. A large amount of unreacted liquid also remains.

[0015] The present invention is based on several objects.

[0016] The aim is to provide a simple and versatile process for the local deposition of polymer thin films. Furthermore, the proposed process should enable deposition from the vapor phase, thus allowing for more precise application, obtaining polymers with significantly fewer defects than the wet-chemical approach, and also enabling greater variation in the monomers.

[0017] These tasks are solved with a gas-phase multiphoton polymerization process according to the main claim.

[0018] The gas-phase multiphoton polymerization process with a reactor having at least one light source and a substrate deposition area comprises at least the following steps:

[0019] - Addition of a gas flow consisting of radical initiators and monomers into a reactor containing a substrate at a defined pressure and temperature, whereby monomers adsorb onto the substrate;

[0020] - Focusing a point on the substrate surface with the at least one light source and splitting and / or breaking up the radical initiators in the focus volume of the at least one light source into free radicals by multiphoton absorption, whereby a radical polymerization of the monomers with the free radicals formed is initiated in the region of the substrate surface containing free radicals and a local polymer thin film is formed on the substrate.

[0021] The area of ​​the substrate surface containing free radicals in which the radical polymerization is started also includes the gas volume above and below.

[0022] In a preferred embodiment, a laser or an ultrafast pulsed laser with a pulse duration between 1 attosecond and 15 picoseconds can be used as the light source.

[0023] The radical initiators can be formed, in particular, from initiators and / or monomers or dimers. When using monomers or dimers as radical initiators, a pulse can be combined with an off-time for polymerization before another pulse is applied.

[0024] The reactor can be operated in vacuum or at atmospheric pressure or at higher pressure.

[0025] In addition, the substrate surface can be cooled partially or completely.

[0026] The reactor can be operated in flow or batch mode.

[0027] The gas flow of radical initiators and monomer molecules can also be varied over time in terms of its composition and / or volume flow. In particular, several local polymer thin film layers can be stacked on the substrate surface to form multilayers during the process.

[0028] The at least one light source can successively focus one and / or more focus volumes on the substrate surface.

[0029] In addition to the at least one light source, further light sources for focusing may be present in order to increase the number of focus volumes.

[0030] Several light sources can also work together locally to generate the necessary energy.

[0031] Furthermore, the size of the local polymer thin film can be determined in particular by the focus volume of the light source and the larger volume of the polymers formed by the ongoing polymerization.

[0032] In addition, the local polymer thin film can be formed in a continuous or discontinuous manner according to the process.

[0033] The local polymer thin film can also be formed with or without a gradient in the composition.

[0034] If several polymer thin film layers are present, the individual polymer thin film layers may or may not differ in their composition, at least partially.

[0035] In addition, in the case of a discontinuous local polymer thin film, the individual polymer thin film sections may or may not differ in their composition, at least partially.

[0036] The procedure may additionally include the following step:

[0037] Addition of an inhibitor to the reactor, wherein the addition of the inhibitor takes place simultaneously with the gas flow of monomers and radical initiators into the reactor or sequentially. The inhibitor is added to stop the polymerization. Preferably, the inhibitor is deactivated locally by the at least one light source, for example, in the focal volume, in order to limit the polymerization to the focal volume and prevent polymerization outside it.

[0038] The method may also additionally comprise a chemical processing of the locally formed polymer thin film by an added liquid and / or an added gas independently of or in combination with the at least one light source.

[0039] Furthermore, the process may additionally include the use of a plasma in the reactor at atmospheric pressure or in a vacuum to enhance the gas-phase multiphoton polymerization process. The gas-phase multiphoton polymerization process may be used to produce a locally formed polymer thin film or a locally formed polymer thin film multilayer on a substrate surface.

[0040] In particular, the locally formed polymer thin film or the locally formed polymer thin film multilayer can be used to structure the substrate.

[0041] In a particularly preferred embodiment, the gas-phase multiphoton polymerization process can be carried out using a vacuum reactor comprising at least one light source and an area for substrate deposition comprising the steps:

[0042] - Addition of a gas flow comprising initiators and monomers into a vacuum reactor containing a substrate at a defined vacuum and defined temperature, whereby monomers adsorb onto the substrate;

[0043] - Focusing a point on the substrate surface with the at least one light source and splitting the initiators in the focus volume of the light source into free radicals by multiphoton absorption, whereby a radical polymerization of the monomers with the free radicals formed in the region of the free radicals

[0044] substrate surface (and the gas volume above and below) and a local polymer thin film is formed on the substrate.

[0045] The same or different monomers can be used as monomers and the same or different radical initiators can also be used as initiators.

[0046] The gas-phase multiphoton polymerization process can be used as a simple, well-controllable method for local polymerization from the gas phase. With excellent process control, it is possible to use the process for gas-phase 3D printing.

[0047] The process according to the invention combines multi-photon 3D printing and gas-phase polymerization.

[0048] Various monomers and initiators, which are already known from iCVD processes, can be used.

[0049] Known multi-photon initiators and multi-photon absorption mechanisms are deeply understood by science and can be optimized for the gas-phase multi-photon polymerization process.

[0050] Previous polymer vapor-phase coatings are homogeneous and cannot be applied locally to a substrate. However, the process according to the invention makes it possible to generate free radicals locally. According to the state of the art, radicals in the iCVD process are not generated directly on the surface / interface in the vacuum chamber, but rather reach the entire substrate surface through transport through the vapor phase. By generating free radicals directly above the substrate surface, polymerization starts locally. The resolution then depends only on the polymerization length, which is usually longer than the laser focus. The process according to the invention makes it possible to apply on-demand patterns on a small scale in polymer thin films from the vapor phase.

[0051] The invention enables the local and extremely precise application of polymer thin films. The precision is determined in particular by the focus of the light source and the coil radius of the macromolecules, which is approximately 10 nm.

[0052] Previous processes with many steps, including masking, which are used in industry, can be eliminated by the method according to the invention.

[0053] In addition, greater precision can be achieved than with the conventional wet chemical process.

[0054] By introducing gases one after the other, it is possible to produce thin films of different polymers or polymer layers in a single process step. Monomers can be used and combined in the gas phase that are not possible in wet chemistry, since the process is solvent-free.

[0055] Furthermore, the variable gas flows allow different polymers to be combined as desired, thus creating much more complex (chemically and precision-engineered) structures.

[0056] This is particularly interesting for the field of microelectronics and also for biomedical applications.

[0057] With the structured thin films / 3D prints produced, it becomes possible to address completely new problems in science and industry.

[0058] The process according to the invention is based on the principle of multiphoton initiation in the gas phase. Since the monomers in the reactor, especially in a vacuum reactor, adsorb onto the substrate and the initiators are excited there, a local polymer layer forms.

[0059] Typical initiators of iCVD processes are, for example, perfluorobutanesulfonyl fluoride (PFBSF) and di-tert-butyl peroxide (DTBP / also called TBPO).

[0060] Alternatively, other known initiators from wet-chemical 2-photon polymerization can be used, for example, if the vapor pressures are suitable for the vacuum process. The invention is described below with reference to the attached figure in

[0061] The description of the figures is intended to illustrate the invention and is not to be considered limiting. They show:

[0062] Figure 1 is an exemplary schematic representation of a first variant of the gas-phase multiphoton polymerization process according to the invention,

[0063] Figure 2 shows an exemplary schematic representation of multilayers of polymers deposited by the gas-phase multiphoton polymerization process according to the invention,

[0064] Figure 3 shows an exemplary schematic plan view of a structured polymer film after local deposition by the gas-phase multiphoton polymerization process according to the invention,

[0065] Figure 4 is an exemplary schematic representation of a second variant of the gas-phase multiphoton polymerization process according to the invention with several light sources,

[0066] Figure 5 is an exemplary schematic representation of the second variant of the gas-phase multiphoton polymerization process according to the invention with several light sources according to Fig. 4 with overlap of the light sources,

[0067] Figure 6 is an exemplary schematic representation of the first variant of the gas-phase multiphoton polymerization process according to the invention according to Fig. 1, wherein the volume of the light source provides enough photons for a 2-photon polymerization,

[0068] Figure 7 is a plan view of the exemplary schematic representation of the first variant of the gas phase multiphoton polymerization process according to the invention according to Fig. 6 and

[0069] Figure 8 shows an exemplary schematic representation of the required light source volume for a 1-photon excitation with one light source (left), for a 2-photon excitation with one light source (middle) and for a 2-photon excitation by light volume overlap with two light sources (right) in the gas phase multiphoton polymerization process according to the invention.

[0070] Fig. 1 shows an exemplary schematic representation of the gas-phase multiphoton polymerization process according to the invention. Initiator molecules 1 and monomer molecules 3 are present in the gas phase in a vacuum reactor. A light source 4, particularly in the form of a laser, is focused onto a point on a substrate surface 6, which is optionally cooled to improve adhesion, so that multiphoton absorption occurs in the focal volume of the light source 5 and initiators 1 are split into free radicals 2. This initiates a radical polymerization, and a local polymer thin film 7 is formed in the region of the substrate surface 6 located in the focal volume of the light source 5.

[0071] Fig. 2 shows an exemplary schematic representation of multilayers of polymers deposited by the inventive gas-phase multiphoton polymerization process. Several layers of a locally deposited polymer film 8 are located on a substrate surface 6. A light source 4 is focused on a point of the polymer film 8 already locally deposited on the substrate surface 6, so that multiphoton absorption occurs in the focal volume of the light source 5, and a locally formed polymer thin film 7 is formed.

[0072] In addition, Figure 3 shows an exemplary schematic top view of a structured polymer film after local deposition using the gas-phase multiphoton polymerization process according to the invention. The exemplary polymer film structures formed on a substrate surface 6 are visible.

[0073] Fig. 4 shows an exemplary schematic representation of a second variant of the inventive gas-phase multiphoton polymerization process with multiple light sources 4. By focusing the light sources 4 on the substrate surface 6, each light source 4 forms a locally formed polymer thin film 7. The volume of the polymerization 10 is determined by the light sources 4.

[0074] Figure 5 shows an exemplary schematic representation of the second variant of the inventive gas-phase multiphoton polymerization process with multiple light sources 4 according to Figure 4, with overlapping light sources 4. By focusing the light sources 4 on the substrate surface 6, a common / individual locally formed polymer thin film 7 is formed by the overlap of the light sources 4. The volume of the polymerization 10 is determined by the overlap of the light sources 4.

[0075] Fig. 6 shows an exemplary schematic representation of the first variant of the gas phase multiphoton polymerization process according to the invention as shown in Fig. 1, wherein the volume of the light source 5 provides enough photons for a 2-photon polymerization. Shown are the light source 4 focused onto a substrate surface 6 and the polymer thin film 7 formed locally by the 2-photon polymerization, the focus volume for excitation of the 2-photon polymerization 9 of the light source 4 and the polymerization volume 10. Fig. 7 shows a top view of the exemplary schematic representation of the first variant of the gas phase multiphoton polymerization process according to the invention as shown in Fig. 6. The focus volume for excitation of the 2-photon polymerization 9 of the light source 4 and the polymerization volume 10 can be seen. Fig.Figure 8 shows an exemplary schematic representation of the required light source volume for 1-photon excitation with a single light source 4 (left), for 2-photon excitation with a single light source 4 (center), and for 2-photon excitation through light volume overlap with two light sources 4 (right) in the gas-phase multiphoton polymerization process according to the invention. The focus volume for excitation by 1 photon 11 (left), the focus volume for excitation by 2 photons 9 (center), and the focus volume / volume for excitation by 2 photons through overlap of two light sources 12 are shown.

[0076] List of reference symbols:

[0077] 1 initiators

[0078] 2 Free radicals

[0079] 3 monomers

[0080] 4 Light source, laser

[0081] 5 Focus volume / volume of the light source

[0082] 6 Substrate, substrate surface

[0083] 7 Locally formed polymer thin film

[0084] 8 Locally deposited polymer thin film

[0085] 9 Focus volume / volume for excitation of 2-photon polymerization

[0086] 10 volumes of polymerization

[0087] 11 Focus volume / volume for excitation by 1 photon

[0088] 12 focus volumes / volumes for excitation by 2 photons by overlapping 2 light sources

Claims

CLAIMS 1. Gas-phase multiphoton polymerization process with a reactor having at least one light source (4) and a substrate deposition area having at least the steps: - adding a gas flow of radical initiators and monomers (3) into a reactor containing a substrate (6) at a defined pressure and a defined temperature, wherein monomers (3) adsorb on the substrate (6); - Focusing a point on the substrate surface (6) with the at least one light source (4) and splitting and / or breaking up the radical initiators in the focus volume (5) of the at least one light source (4) to form free radicals (2) by multiphoton absorption, whereby a radical polymerization of the monomers (3) with the free radicals (2) formed is started in the region of the substrate surface (6) containing free radicals (2) and a local polymer thin film (8) is formed on the substrate (6).

2. Process according to claim 1, characterized in that the radical initiators are - Initiators and / or - monomers or dimers are formed.

3. A process according to claim 1 or claim 2, characterized in that the reactor is operated in a vacuum or at atmospheric pressure or at higher pressure.

4. Method according to one of the preceding claims, characterized in that the light source (4) - a laser or - an ultrafast pulsed laser with a pulse duration between 1 attosecond and 15 picoseconds is used.

5. Method according to one of the preceding claims, characterized in that the substrate surface (6) is partially or completely cooled.

6. Process according to one of the preceding claims, characterized in that the reactor is operated in a flow process or batch process.

7. Method according to one of the preceding claims, characterized in that the gas flow of radical initiators and monomer molecules (3) is changed over time in its composition and / or its volume flow.

8. Method according to one of the preceding claims, characterized in that during the implementation of the method, several local polymer thin film layers are stacked on the substrate surface (6) to form multilayers.

9. Method according to one of the preceding claims, characterized in that - the at least one light source (4) successively emits one and / or more Focus volume (5) focused on the substrate surface (6) and / or - in addition to the at least one light source (4), further light sources are provided for focusing and / or - several light sources work together locally to generate the necessary energy.

10. Method according to one of the preceding claims, characterized in that - the size of the local polymer thin film (8) by the focus volume of the light source (5) and the larger volume of the polymers (10) formed by the ongoing polymerization is predetermined and / or - the local polymer thin film (8) is formed in a continuous or discontinuous manner according to the method and / or - the local polymer thin film (8) is formed with or without a gradient in the composition and / or - in the case of several polymer thin film layers, the individual polymer thin film layers differ at least partially in their composition or do not differ and / or - in the case of a discontinuously formed local polymer thin film (8), the individual polymer thin film sections differ or do not differ at least partially in their composition.

11. Method according to one of the preceding claims, characterized in that the method additionally comprises the following step: Addition of an inhibitor into the reactor, whereby the addition of the inhibitor takes place simultaneously with the gas flow of monomers and radical initiators into the reactor or sequentially.

12. Method according to one of the preceding claims, characterized in that the method additionally comprises a chemical processing of the locally formed polymer thin film (8) by an added liquid and / or an added gas independently of or in combination with the at least one light source (4).

13. The method according to any one of the preceding claims, characterized in that the method additionally includes the use of a plasma in the reactor at atmospheric pressure or in a vacuum.

14. Use of the gas-phase multiphoton polymerization method according to any one of the preceding claims for producing a locally formed polymer thin film (8) or a locally formed polymer thin film multilayer on a substrate surface (6).

15. Use according to the preceding claim, wherein the locally formed polymer thin film (8) or the locally formed polymer thin film multilayer comprises the Substrate (6) structured.

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