DE102016007736B4 - Method for local modification of a substrate - Google Patents

Abstract

Method for locally modifying a substrate (10), comprising the steps: - providing a laser arrangement for generating a first laser beam of a first wavelength, a second laser beam of a second wavelength and a third laser beam of a third wavelength different from the first and the second wavelength, wherein each laser beam has a fluence in a common writing area (16) above a predetermined threshold value, - providing a substrate arrangement (100, 110) comprising the substrate (10), the active molecules (12) in the substrate (10) or in the immediate vicinity the substrate (10), which are positioned in the writing area (16) and have the following properties: • the active molecules (12) are photonically transformed into a first energetically increased electronic state by absorbing light of the first wavelength from an electronic ground state (Z) ( Z) can be stimulated, • the active molecules (12) are absorbed rption of light of the second wavelength from its first energetically increased electronic state (Z) can be excited photonically into an energetically higher, that is to say into a second energetically increased electronic state (Z), with a spontaneous, radiationless of the second energetically increased electronic state (Z) Excitation path exists, the efficiency of which is greater than that of any corresponding photonic excitation path, the active molecules (12) can be de-excited from their first energetically increased electronic state (Z) with stimulated emission to their electronic ground state (Z) by absorption of light of the third wavelength, - Generating the first, the second and the third laser beam, the profile of the third laser beam having a sub-area of vanishing intensity and the temporal coordination of the laser beams taking place in such a way that active molecules (12) in the writing area (16) • by absorption of light from the first Laser beam ph are excited otonically into their first energetically increased electronic state (Z), • are stimulated back into their electronic ground state (Z) outside the sub-region of vanishing intensity of the third laser beam under stimulated emission and • within the sub-region of vanishing intensity of the third laser beam photonically into their second energetically increased electronic state (Z) is stimulated and the substrate (10) locally modifying, thermal energy is excited without radiation.

Description

Field of the Invention

The invention relates to a method for locally modifying a substrate, in particular for introducing fine structures into the substrate, in particular for introducing nanoscale fine structures, i.e. Fine structures with structure sizes in the order of magnitude of a few nm to a few 10 nm. Such fine structures are particularly relevant in the area of data storage.

State of the art

From the EP 1 616 344 B1 A method for nanostructuring a substrate is known, in which molecules of the substrate in a writing area are excited by means of a first focused laser beam from a basic state of a first photochromic configuration to an energetically increased electronic state of the same photochromic configuration, from which they are unspecified change to a permanently modified state. In order to push the structure size of the modifications produced in this way below the Abbe diffraction limit, a second laser beam is focused in the writing area, the profile of which has a sub-area of vanishing intensity generated by interference. The substrate molecules have the property of being converted from the ground state of the first photochromic configuration to a ground state of a second photochromic configuration of the molecule by light of the wavelength of the second laser steel. In the second photochromic configuration of the molecule, light of the wavelength of the first laser beam is not suitable for stimulating a transition to an energetically increased electronic state, from which the molecule, like in the first photochromic configuration, could change into the permanently modified state.

The substrate is thus only modified in the overlap area of the first laser beam and the area of the vanishing intensity of the second laser beam. In this way, so-called subdiffraction structures can be created, i.e. Structures with structure sizes below the Abbe diffraction limit.

A disadvantage of the known method is the very special requirements placed on the substrate, which must essentially consist of switchable photochromes, which can be photonically excited in their first configuration and converted to a permanently modified state, and which - in their second configuration - have such a photonic excitation - at least with the same wavelength - do not allow. This severely limits the choice of materials for possible substrates, which are also subject to a large number of additional conditions for practical applications.

From the US 2011/0039213 A1 A lithographic process is known in which the subdiffraction polymerisation of a photoresist is aimed for. The photoresist contains a so-called photoinitializer, which, when excited photonically by a first laser beam, initiates polymerization of the prepolymer surrounding it with little delay. At the same time, it has the property of being able to be converted into an inactive state by the light of a second laser beam. Here, too, the profile of the second laser beam has a region of vanishing intensity within which the polymerization takes place, while in the overlap region of the first laser beam and regions of non-vanishing intensity of the second laser beam there is no polymerisation of the photoresist.

Out Sure, TA. et al .: "Fluorescence microscopy with diffraction resolution barrier broken by stimulated emission", PNAS, Vol 97, No 15, 8206-8210 (2000) the so-called STED microscopy is known. Here, a fluorophore is transferred from its electronic ground state to an energetically increased electronic state, from where it returns to the electronic ground state with the emission of fluorescent light. At the same time, however, the illumination area is illuminated by means of a second laser beam, the so-called STED beam, the profile of which has a sub-area of vanishing intensity and the wavelength of which is suitable for stimulating the fluorophores in the energetically increased electronic state to stimulate emission. The timing of the two laser beams must be such that the fluorophores are first excited from their basic to the energetically elevated state, but before an essentially spontaneous fluorescence emission, ie within the fluorescence lifetime of the excited state, the stimulated de-excitation is carried out by the STED beam, so that only those fluorophores in the overlap region of the first laser beam and partial area of vanishing intensity of the second laser beam spontaneously emit their fluorescence to a considerable extent. This spontaneous fluorescence can be recorded in isolation with suitable timing of an optical detector, so that the creation of subdiffraction-resolved images is possible.

Out Fischer, J. et al .: "The Materials Challenge in Diffraction-Unlimited Direct-Laser Writing Optical Lithography", Adv.Mater. 2010, 22, 3578-3582 the application of the STED principle is known in photolithography. Active molecules in the photoresist are excited by the first laser beam from their electronic ground state to an energetically increased electronic singlet state. From there, they are transferred back to the basic state by means of the STED beam in the edge region under stimulated emission. In the low-intensity center of the STED beam, however, the active molecules either transition to the ground state either with spontaneous emission or without radiation to a triplet state that is energetically between the ground and the excited singlet state. This serves as an initiator for the localized polymerization of the photoresist.

From the RU 2 510 632 C1 a further development of this method is known. Here, the triplet state is not used directly for polymerizing the photoresist, but rather as an initiator for a photochemical reaction, which is not disclosed in any more detail and with which the silver salt contained in the photoresist is locally reduced to silver nanoparticles. In a subsequent step, a plasmon excitation of these nanoparticles takes place by means of a further laser, which causes a locally narrowly limited polymerization of the photoresist.

The idea of laying a trace of silver nanoparticles and stimulating them plasmonically to initiate a localized polymerization is also used in Stamplecoskie, KG et al .: "Dual-Stage Lithography from a Light-Driven, Plasmon-Assistes Process: A Hierarchical Approach to Subwavelength Features", Langmuir 2012, 28, 10957-10961 picked up. However, it does not mention the use of the STED principle.

From the DE 10 2005 012 739 B4 the verification of a photolithographically generated structure by means of STED microscopy is known.

The DE 10 2015 015 497 A1 gives a general overview of the application of high-resolution microscopy methods in photolithography.

Task

It is the object of the present invention to provide an alternative method for the fine structuring of a substrate, in which the requirements for the molecular properties of the substrate are reduced and therefore the range of substrates accessible to the method is expanded.

Statement of the invention

• - Bereitstellen einer Laseranordnung zur Erzeugung eines ersten Laserstrahls einer ersten Wellenlänge, eines zweiten Laserstrahls einer zweiten Wellenlänge und eines dritten Laserstrahls einer von der ersten und der zweiten Wellenlänge verschiedenen, dritten Wellenlänge, wobei jeder Laserstrahl in einem gemeinsamen Schreibbereich eine Fluenz oberhalb eines vorgegebenen Schwellenwertes aufweist,
• - Bereitstellen einer das Substrat umfassenden Substratanordnung, die Wirkmoleküle in dem Substrat oder in unmittelbarer Nachbarschaft zu dem Substrat aufweist, welche im Schreibbereich positioniert werden und folgende Eigenschaften haben:
  • • die Wirkmoleküle sind durch Absorption von Licht der ersten Wellenlänge von einem elektronischen Grundzustand photonisch in einen ersten energetisch erhöhten elektronischen Zustand anregbar,
  • • die Wirkmoleküle sind durch Absorption von Licht der zweiten Wellenlänge von ihrem ersten energetisch erhöhten elektronischen Zustand photonisch in einen energetisch höheren, zweiten energetisch erhöhten elektronischen Zustand anregbar, wobei von dem zweiten energetisch erhöhten elektronischen Zustand ein spontaner, strahlungsloser Abregungspfad existiert, dessen Effizienz größer ist als diejenige jedes entsprechenden photonischen Abregungspfades,
  • • die Wirkmoleküle sind durch Absorption von Licht der dritten Wellenlänge von ihrem ersten energetisch erhöhten elektronischen Zustand unter stimulierter Emission in ihren elektronischen Grundzustand abregbar,
• - Erzeugen des ersten, des zweiten und des dritten Laserstrahls, wobei das Profil des dritten Laserstrahls einen Teilbereich verschwindender Intensität aufweist und wobei die zeitliche Koordination der Laserstrahlen derart erfolgt, dass Wirkmoleküle im Schreibbereich
  • • durch Absorption von Licht des ersten Laserstrahls photonisch in ihren ersten energetisch erhöhten elektronischen Zustand angeregt werden,
  • • außerhalb des Teilbereichs verschwindender Intensität des dritten Laserstrahls unter stimulierter Emission wieder in ihren elektronischen Grundzustand abgeregt werden und
  • • innerhalb des Teilbereichs verschwindender Intensität des dritten Laserstrahls photonisch in ihren zweiten energetisch erhöhten elektronischen Zustand angeregt und unter Abgabe das Substrat lokal modifizierender, thermischer Energie strahlungslos abgeregt werden.

This object is achieved by a method having the features of claim 1, ie by a method for locally modifying a substrate, comprising the steps:

• - Providing a laser arrangement for generating a first laser beam of a first wavelength, a second laser beam of a second wavelength and a third laser beam of a third wavelength different from the first and the second wavelength, each laser beam having a fluence in a common writing range above a predetermined threshold value ,
• Providing a substrate arrangement comprising the substrate, which has active molecules in the substrate or in the immediate vicinity of the substrate, which are positioned in the writing area and have the following properties:
  • The active molecules can be excited photonically from an electronic ground state into a first energetically increased electronic state by absorption of light of the first wavelength,
  • • The active molecules can be excited photonically by absorption of light of the second wavelength from their first energetically increased electronic state into an energetically higher, second energetically increased electronic state, with the second energetically increased electronic state a spontaneous, radiationless de-excitation path exists, the efficiency of which is greater than that of any corresponding photonic de-excitation path,
  • The active molecules can be de-excited from their first energetically increased electronic state with stimulated emission into their electronic ground state by absorption of light of the third wavelength,
• - Generation of the first, the second and the third laser beam, the profile of the third laser beam having a partial area of vanishing intensity and the time coordination of the laser beams taking place in such a way that active molecules in the writing area
  • Are photonically excited into their first energetically increased electronic state by absorption of light from the first laser beam,
  • Outside the sub-region of vanishing intensity of the third laser beam are stimulated back into their electronic ground state under stimulated emission and
  • • within the sub-region of vanishing intensity of the third laser beam, are excited photonically into their second energetically increased electronic state and are released without radiation, giving off locally modifying, thermal energy.

Preferred embodiments of the invention are the subject of the dependent claims.

In contrast to the known methods, in the method according to the invention the modification of substrate molecules does not take place on the way of the photonic excitation of the substrate molecules themselves, but rather by photonic excitation of auxiliary molecules, referred to here as active molecules, which have a highly efficient radiation-free excitation path (e.g. by inter- and / or intramolecular) Vibrations, rotations, collisions, etc.) from their excited state, so that the radiation-free de-excitation in the immediate vicinity of the active molecule leads to a strong, local temperature increase, which in turn produces the desired modification of the substrate molecule. This modification can be a thermally induced ablation, a thermally induced polymerization or another indirectly or directly thermally induced reaction.

The basic principle of the invention consists initially in a two-stage excitation of the active molecules in the writing area.

The writing area can be predetermined by a common focal area of the laser beams used. However, it is also possible, e.g. by means of interference techniques to create a region of increased fluence common to the laser beams used, within which (and outside of which precisely not) the occurring fluences are sufficiently high to trigger the reactions explained here. The term "writing area" is to be understood in this broad sense.

By means of the first laser beam, ie by means of light of the first wavelength, a photonic excitation of an active molecule takes place in the writing area from an electronic ground state Z ₀ to a first excited, ie energetically increased electronic state Z ₁ . From here, further excitation into a higher, second electronic state Z ₂ takes place by means of a second laser beam, ie by means of light of a second wavelength.

The electronic ground state Z ₀ can (and usually does, but does not necessarily have to) coincide with the spectroscopic ground state S _{0 of} the active molecule. The term “basic state” is to be understood in the context of the present description in the sense of an initial state from which the reaction triggered according to the invention originates. Analogously, the excited, ie energetically increased, electronic states Z ₁ and Z _{2 can} coincide with the spectroscopic states S ₁ and S _n , in particular S ₂ . However, this is not absolutely necessary and in fact is not the case in many embodiments of the invention. In particular, one or more spectroscopic states S _{1 can be} skipped in the excitation and de-excitation processes triggered according to the invention. As will be clarified further below using an example, the term “excited state” or “energetically increased electronic state” can also encompass several spectroscopic states. Where necessary, the abbreviation S ₁ for spectroscopic states in the narrower sense and the designation Z _n for states in the above sense are used to differentiate. In any case, the term “state” - since the invention takes place in the molecular and not in the idealized, atomic range - does not mean a sharp energy level, but rather a more or less wide energy range, such as that in the range of emission and absorption -Peaks reflected.

An essential feature of the invention is that a highly efficient, radiation-free de-excitation path exists from the second excited state Z ₂ . This means that the spontaneous de-excitation from the excited state Z ₂ takes place predominantly without radiation and thereby thermally induces the desired modification of the substrate.

However, this alone would lead to fine structuring of the substrate with diffraction-limited feature sizes. The writing area as such is in fact subject to this size limitation. To overcome Abbe's diffraction limit, the invention therefore uses the STED principle mentioned at the beginning in the context of fluorescence microscopy. By means of a so-called STED beam, that is to say by means of the third laser beam, depopulation of the first excited state Z ₁ is effected in regions by stimulated emission, so that in these regions the basis for further excitation according to Z ₂ and thus the radiationless de-excitation from Z _{2 is} withdrawn becomes. Only in those areas in which the sub-area of vanishing intensity of the STED beam and the first laser beam overlap, there are excited active molecules in Z ₁ , which can be converted into the further increased energetic state Z ₂ by the second laser beam.

For the sake of easier understanding, the first laser beam, which excites the active molecules from the basic state Z ₀ into the first energetically increased electronic state Z ₁ , is referred to below as the “preparation steel” and the corresponding wavelength as the “preparation wavelength”. The laser beam used to further excite the active molecules from the first energetically increased electronic state Z ₁ into the second energetically increased electronic state Z _{2 will} be referred to below as the “excitation beam” and the corresponding wavelength as the “excitation wavelength”. The beam used to trigger the stimulated emission of the active molecules excited in Z _{1 will be} referred to below as the “STED beam” and the corresponding wavelength as the “STED wavelength”.

In a preferred embodiment of the invention, the photonic excitation and radiationless de-excitation of the second energetically elevated state takes place cyclically. This is particularly the case when the highly efficient, radiationless de-excitation path leads from the second energetically increased electronic state Z ₂ to the first energetically increased electronic state Z ₁ . Then the molecules returning from Z ₂ to Z ₁ can be immediately excited again to Z ₂ by the excitation beam. However, it is also conceivable to use other materials in which the highly efficient, radiationless de-excitation path leads, for example, directly to Z ₀ . The thermal energy given off to the substrate is higher when viewed in terms of single molecules; overall, however, the process can be less efficient due to the lack of cyclical excitation and de-excitation between Z ₁ and Z ₂ .

The above mention of three laser beams and three wavelengths is intended to facilitate understanding of the invention and is to be understood purely functionally. In practice, however, it is entirely possible that the first and the second wavelength, ie the preparation wavelength and the excitation wavelength, are identical. In particular, it is possible that the first and the second laser beam, ie the preparation beam and the excitation beam, are identical, in particular as one and the same beam with the same wavelength, intensity, beam profile, pulse duration and time and beam path come from the same laser source. This is possible in particular if the active molecules have their state Z _{2 at} approximately the same energetic distance from Z ₁ in which Z ₁ lies above Z ₀ . Then light of the same wavelength can be used to excite both Z ₀ to Z ₁ and Z ₁ to Z ₂ .

Because of the natural width of each energetic state explained above, the third wavelength, ie the STED wavelength, should preferably be longer than the first wavelength, ie the preparation wavelength. The excitation from Z ₀ to Z ₁ during the preparation typically takes place from a lower vibronic sub-level of Z ₀ to a higher vibronic sub-level of Z ₁ . There is a quasi-instantaneous vibronic relaxation within the vibronic sub-levels. However, the stimulated emission to be excited with the STED wavelength has to lead from this lower sub-level of Z ₁ to a vibronic sub-level which is higher within Z ₀ . This is taken into account with the explained red shift of the STED beam compared to the preparation beam.

The sub-region of vanishing intensity is preferably a closed region lying in the center of the profile of the third laser beam, ie the STED beam. In other words, an STED beam with the typical “donut” profile is preferably used. In an alternative embodiment, however, the sub-region of vanishing intensity is a line-like region that divides the profile of the third laser beam, ie the STED beam, centrally. These descriptions are to be understood purely two-dimensionally on the beam profile in the sense of the intensity distribution in the beam cross section. The extension of the sub-area vanishing intensity in the direction of beam propagation can also be varied. All in all, of course, the area has a three-dimensional extent. The specific choice of the sub-area form depends on the form of the desired substrate modification and can largely be chosen freely by the person skilled in the art. The person skilled in the art is familiar with the techniques for producing different STED profiles, which typically involve the use of phase masks in the laser beam.

The second laser beam is preferably a short-pulse laser beam. The first and especially the third laser beam, which may also be pulsed, preferably short-pulse laser beams, can also be designed as continuous wave beams. The pulsed nature of the second laser beam, ie the excitation beam, is of particular advantage for the present invention. For the preparation beam and the STED beam, the Timinig is largely uncritical, since the effects of both beams essentially cancel each other out in their overlapping area. The active molecules intended for further excitation are made available in the Z ₁ state only in the region of vanishing intensity. “Collecting” and jointly stimulating by means of a short pulse leads to a very short-term, but intensive, extremely localized temperature increase in the subsequent, radiation-free de-excitation, which is broken down very quickly due to the instantaneous heat dissipation into the surrounding substrate - albeit with thermal modification of the neighboring one Substrate molecules. A process extended without the use of a short-pulse laser as an excitation laser could lead to heat conduction in a spatially larger area, which would run counter to the intention of modifying the substrate as small as possible.

With regard to the choice of material for the substrate or the active molecules, a wide range is available to the person skilled in the art. In a preferred embodiment of the method according to the invention, the substrate arrangement comprises as the substrate a solid body doped with active molecules and transparent to light of the first, second and third wavelength. The active molecules are thus incorporated into the substrate material as auxiliary substances. This can e.g. in the form of single molecules, as a copolymer or in the form of multimolecular substance islands in the substrate matrix. A purely exemplary production method is the provision of substrate and active molecules in a common solution and evaporation of the solvent. The provision of a mixture of a prepolymer and the active molecules with subsequent polymerization can also lead to a doped substrate in the present sense. Since at least the thermal modification of the substrate represents a threshold-prone reaction, there is no fear of an undesired modification of the substrate outside the writing range of the laser beams. This also applies to the preferred, coaxial introduction of the laser beams.

In an alternative application of the invention it is provided that the substrate arrangement comprises as substrate a solid body transparent to light of the first, second and third wavelengths and as the active liquid a liquid containing the active molecules in contact with a surface of the substrate, the writing area at the contact surface between the substrate and the active liquid. With this approach, the processes explained in detail above are not carried out in the substrate itself, but in the neighboring liquid. However, the thermal effect of these processes influences and modifies the adjacent surface of the substrate, so that the desired fine structure modification of the substrate is achieved. The actual modification reaction in the substrate can be of a direct thermal nature or a reaction caused indirectly by the local temperature increase in the active liquid. For example, the short-term and locally restricted temperature increase in the active liquid can lead to considerable local pressure fluctuations, which in turn contribute to ablation on the substrate surface.

The contact between the substrate and the active liquid is preferably direct and the contact surface is a real interface between the substrate and the active liquid. However, it is also a thin coating of the substrate, e.g. for the purpose of protection against an aggressive active liquid, and thus an indirect contact between the substrate and the active liquid is conceivable. The coating must of course be so thin that the desired thermally induced modification of the substrate is not significantly hindered.

Of course, it is also possible to replace the active liquid with an active substance of another state of matter, for example an active solid, an active gas or an active gel which contains the active molecules. The explanations given above in the context of an active liquid apply accordingly. However, due to the high process efficiency found, the use of an active liquid is preferred.

As explained above, it is an advantage of the invention that the range of materials that can be used is expanded compared to the prior art. As a particularly advantageous material for the solid - Whether as a substrate arrangement doped with active molecules or as a substrate itself in surface contact with an active medium - polymers and glass have been proven. This is particularly due to the low modification threshold with regard to thermal and ablative modification on the one hand and with regard to its transparency in the wavelength range of economically available lasers. The concept of transparency is to be interpreted in a function-oriented manner in the context of the present description. A 100% transparency, ie a transmissivity of the solid of 1 for all wavelengths used will hardly be possible in practice and is in particular not necessary. “Transparent” in the sense of the present description is a substance if the absorption or scattering of the wavelengths used is sufficiently small, that there is no undesired modification of the material and that the laser beams used are not weakened in such a way that the above-described, desired processes in the writing area no longer occur come about to a practically relevant degree.

Organic dyes, some of which show the properties relevant to the invention, have proven particularly effective as active molecules - be it for doping a solid or as active molecules within an active medium in surface contact with a solid substrate. A solution of the active molecules in organic solvent has proven to be an effective liquid.

Particularly preferred embodiments see a solid made of PMMA (polymethyl methacrylate) as a substrate in surface contact with a solution of Rhodamine 6G in ethanol, a solid made of glass as a substrate in surface contact with a solution of pyrene in acetone or a pyrene-doped solid made of PVA (polyvinyl acetate) in front.

The person skilled in the art has to choose the wavelengths to be used in practice in view of the special spectroscopic properties of the substances used. However, this should be possible without difficulty on the basis of the known or easily detectable properties of any candidate substances.

Preferred embodiments are the subject of the dependent claims.

Further features and advantages of the invention result from the following special description and the drawings.

Figure list

• 1: ein Termschema einer ersten bevorzugten Ausführungsform der Erfindung,
• 2: ein Termschema einer zweiten bevorzugten Ausführungsform der Erfindung,
• 3: ein Termschema einer Variante der Ausführungsform von 1,
• 4: ein Termschema einer Variante der Ausführungsform von 2,
• 5: ein Termschema einer dritten Ausführungsform der Erfindung,
• 6 ein prinzipieller Aufbau einer ersten Anwendungsform der Erfindung und
• 7 ein prinzipieller Aufbau einer zweiten Anwendungsform der Erfindung.

Show it:

• 1 1 shows a term diagram of a first preferred embodiment of the invention,
• 2nd FIG. 2: a term diagram of a second preferred embodiment of the invention,
• 3rd : a term scheme of a variant of the embodiment of 1 ,
• 4th : a term scheme of a variant of the embodiment of 2nd ,
• 5 FIG. 2: a term diagram of a third embodiment of the invention,
• 6 a basic structure of a first embodiment of the invention and
• 7 a basic structure of a second application of the invention.

Detailed description of preferred embodiments

The same reference numerals in the figures indicate the same or analog elements.

1 shows in a highly abstracted form a term diagram of the excitation and de-excitation processes within the active molecules in a first embodiment of the present invention. The illustration only shows the transition paths relevant to the invention, the efficiency of which is a criterion for the sensible selection of the substances to be used for the practical implementation of the invention. The person skilled in the art will understand that further transition paths of lower efficiency are possible and will generally also be given.

At the beginning of the process, the active molecules are in the ground state Z ₀ . The active molecules are excited from the basic state Z ₀ into the first excited state Z ₁ by means of a laser beam, referred to here as the preparation beam, as indicated by the excitation arrow 1 indicated. Typically, the excitation occurs at a higher, vibronic sub-level of Z ₁ , from which an instantaneous Relaxation to a lower vibronic sub-level of Z ₁ takes place. The active molecules are excited further into the second excited state Z ₂ by means of a further laser beam, referred to here as the excitation beam, as by the further excitation arrow 2nd indicated. Here too, the excitation typically takes place in a higher vibronic sub-level, from which an instantaneous relaxation takes place within Z ₂ . The different hatching of both excitation arrows 1 , 2nd indicates that these have different wavelengths and possibly other different beam properties in the embodiment shown. The described excitation from Z ₁ to Z ₂ by means of the excitation beam, however, only takes place in those areas of the writing area in which the active molecules in the first excited state Z ₁ have not previously been converted back to the basic state Z ₀ by means of a STED beam with emission of stimulated emission were. As with the de-energizing arrow 3rd indicated, the stimulated transition from Z ₁ to Z _{0 takes place} from a lower-lying vibronic sub-level from Z ₁ to a higher-lying vibronic sub-level within Z ₀ . The “energetic distance” between Z ₁ and Z ₀ for the stimulated de-excitation is therefore smaller than for the excitation by means of the preparatory beam, which is reflected in particular in the choice of a longer wavelength for the STED beam compared to the preparatory beam. Only those active molecules that lie within a sub-area of vanishing intensity of the STED beam in the writing area experience the aforementioned excitation from Z ₁ to Z ₂ . There is a by the de-excitement arrow 4th indicated, radiationless de-excitation path back to Z ₁ open. Its efficiency is greater than that of any radiation-affected transition from Z ₂ to Z ₁ or to Z ₀ . The radiationless transition will therefore be the dominant de-excitation process. The heat released in the process leads to a considerable jump in temperature, the spatial extent of which is limited to the sub-area of vanishing intensity of the STED beam within the writing area. If the temperature jump or the secondary effects dependent thereon, such as pressure jumps, exceed a threshold value required for permanent modification of the substrate, the substrate is modified in a locally extremely restricted manner, ie the creation of a fine structure with structure sizes below the diffraction limit.

The dashed lines in 1 (as well as in the 2-5 ), indicate that the states Z _n , which in the embodiment of 1 correspond to spectroscopic states S ₁ , do not necessarily have to be immediately adjacent, but rather that spectroscopic states can be skipped in the described excitation and de-excitation processes.

2nd shows a term diagram of a second embodiment of the method according to the invention. As with the uniform hatching of the excitation arrows 1 , 2nd indicated from Z ₀ to Z ₁ and from Z ₁ to Z ₂ , the preparation and the excitation beam have the same wavelength here. In particular, both transitions are preferably excited by means of the same laser beam. The basic molecular principle in this embodiment is the same as that in FIG 1 shown embodiment. In practical use, however, the main difference is that it saves a laser. For the rest, reference can be made to the above explanations.

Both embodiments have in common that the radiation-free de-excitation takes place from Z ₂ back to Z ₁ . This enables cyclic excitation and de-excitation between the states Z ₁ and Z ₂ , which brings about a particular efficiency of these embodiments of the method according to the invention.

The variants acc. the 3rd and 4th differ in this respect from the embodiments of FIG 1 and 2nd . Here, the radiation-free de-excitation of Z ₂ takes place in a state which is lower in energy than Z ₁ , in the illustrated embodiments in particular back to the basic state Z ₀ . In this variant, the heat emission associated with the individual radiationless transition is greater than in the embodiments of FIG 1 and 2nd ; Cyclic excitation and de-excitation between states Z ₁ and Z ₂ takes place in the variants of 3rd and 4th However not. For the rest, reference can be made to the above explanation.

5 shows the term scheme of a third embodiment of the present invention. This illustrates in particular the broad understanding of the energetic states Z ₁ on which this is based, in comparison to the spectroscopic states S _n in the narrower sense. In particular, in this embodiment two spectroscopic states are to be understood together as the first excited state Z ₁ . In this embodiment, stimulated by the preparation beam, there is first a transition from the basic state Z ₀ to a higher spectroscopic state which is not immediately adjacent to it. There is an (whatever type) de-excitation path - indicated by the de-excitation arrow 5 - in a deeper, but also above Z ₀ , further spectroscopic state. Only from this, depending on the positioning of the specific active molecule, either the excitation into the second excited state Z ₂ or the stimulated de-excitation back to Z _{0 takes place} . The two mentioned Spectroscopic states thus together form the first excited state Z ₁ in the sense of the present description. In the embodiment shown, the radiation-free de-excitation of Z ₂ takes place specifically in the lower of the two spectroscopic states of Z ₁ . Of course, this is not mandatory. Any other goal of this radiationless transition is also conceivable, whereby mutatis mutandum to the corresponding explanations of the difference between the variants of 1 and 3rd on the one hand and 2 and 4 on the other hand.

6 shows in a highly schematic representation the experimental setup of a first application of the present invention. Here is the matrix of a transparent solid 10th with active molecules 12th endowed. This substrate arrangement 100 is made up of a coaxial bundle 14 from three laser beams, namely the preparatory steel, the excitation beam and the STED beam. The laser beam 14 forms a beam waist in which, due to the focusing, the fluences of the individual beams are so large that the threshold values required for the above-described processes according to the invention, at least the threshold value for the thermally induced substrate modification, are exceeded. There is therefore a writing area 16 in which the processes described above take effect. Outside the writing area 16 the fluences are too low to trigger the processes according to the invention, at least the threshold value for the thermally induced substrate modification.

7 shows an alternative substrate arrangement 110 . Here is an undoped, transparent solid 12th in surface contact with one of the active molecules 12th containing active liquid 18th . The bundle of rays 14 Preparation beam, excitation beam and STED beam shine through the transparent solid 10th and has its beam waist in the area of the contact surface between the solid 10th and the active liquid 18th . The processes according to the invention therefore take place in the active liquid 18th in close proximity to the surface of the solid on the liquid side 10th from. This surface is therefore structured by the thermally induced modifications explained.

The table below is intended to provide a purely exemplary overview of experimental constellations for realizing different embodiments of the method according to the invention. Substrate / active molecule Liquid / active molecule First laser beam (λ1) Second laser beam (λ2) Third laser beam (λ3) Δt (1.3) Δt (1.2) PMMA / - (polymethyl methacrylate) Ethanol / Rh6G (0.05 mol / l) 530 nm 440 nm 625 nm 300 ps 600 ps 300 ps 300 ps 300 ps 1.5 mJ / cm ² 75 mJ / cm ² 800 mJ / cm ² PMMA / - (polymethyl methacrylate) Ethanol / Rh6G (0.08 mol / l) 440 nm 625 nm 0 ps - 50 ps 50 ps 250 mJ / cm ² 2000 mJ / cm ² Glass / - Acetone / pyrene (0.4 mol / l) 308 nm 488 nm 0 ps - 1 ns 1 ns 500 mJ / cm ² 2000 mJ / cm ² PVA / pyrene (polyvinyl acetate) (0.4 mol / l) - / - 308 nm 488 nm 0 ps - 1 ns 1 ns 190 mJ / cm ² 760 mJ / cm ²

The application examples listed in the first three lines of the table correspond to an experimental setup acc. 7 . That in line 4th the application example listed in the table corresponds to an experimental setup acc. 6

The constellation acc. The first line of the table further corresponds to the embodiment of FIG 1 . A solid made of PMMA (polymethyl methacrylate) is used as the substrate to be processed. The active liquid is a 0.05 molar solution of rhodamine 6G in ethanol. A laser with a wavelength of 530 nm, a pulse duration of 30 ps and a fluence of 1.5 mJ / cm ^{2 is used} as the preparation laser in the writing area. A laser with a wavelength of 440 nm, a pulse duration of 300 ps and a fluence of 75 mJ / cm ² in the writing area is used as the excitation laser with a time offset of 600 ps. Of the 300 The ps long pulse of the STED laser, which has a wavelength of 625 nm and a fluence of 800 mJ / cm ² in the write area, occurs 300 ps after the preparation pulse.

A similar substance system made of PMMA and a 0.08 molar rhodamine 6G in ethanol has been found in row 2nd the table also for the implementation of the embodiment of 2nd proven. As a (functional) first and second laser, ie (functional) preparation and (functional) excitation laser, a short pulse laser with 50 ps pulse length at a wavelength of 440 nm and a fluence of 250 mJ / cm ^{2 is used} in the writing area. A laser with a wavelength of 625 nm and a fluence of 2,000 mJ / cm ^{2 is used} in the writing area as the STED laser, which pulses simultaneously with the preparation and excitation laser.

Also in a two-laser configuration, according to row 3rd Use the table to process a solid body made of glass in surface contact with a 0.4 molar pyrene solution in acetone. The preparation and excitation laser has a pulse duration of 1 ns, a wavelength of 308 nm and a fluence of 500 mJ / cm ² in the writing area. The simultaneously pulsed STED laser has a wavelength of 488 nm and a fluence of 2,000 mJ / cm ² in the writing area.

As an example of an experimental setup acc. 6 points row 4th from the table a solid made of PVA (polyvinyl acetate) doped with pyrene in a concentration of 0.4 mol / l. At the in line 4th The preparation and excitation laser has a pulse duration of 1 ns, a wavelength of 308 nm and a fluence of 190 mJ / cm ² in the writing area. The simultaneously pulsing STED laser has a wavelength of 488 nm and a fluence of 760 mJ / cm ² in the writing area.

Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative exemplary embodiments of the present invention. In the light of the disclosure herein, the person skilled in the art is provided with a broad spectrum of possible variations.

Reference list

1

Suggestion arrow (preparation)

2nd

Suggestion arrow (suggestion)

3rd

De-excitation arrow (stimulated emission)

4th

De-excitation arrow (radiationless transition)

5

Excitement arrow

10th

Substrate

12th

Active molecule

14

Laser beam

16

Writing area

18th

Active liquid

100

Substrate arrangement

110

Substrate arrangement

Claims (12)

Method for local modification of a substrate (10), comprising the steps: - providing a laser arrangement for generating a first laser beam of a first wavelength, a second laser beam of a second wavelength and a third laser beam of a third wavelength different from the first and the second wavelength, wherein each laser beam has a fluence in a common writing area (16) above a predetermined threshold value, - providing a substrate arrangement (100, 110) comprising the substrate (10), the active molecules (12) in the substrate (10) or in the immediate vicinity the substrate (10), which are positioned in the writing area (16) and have the following properties: • The active molecules (12) can be excited photonically from an electronic ground state (Z ₀ ) into a first energetically increased electronic state (Z ₁ ) by absorption of light of the first wavelength, • The active molecules (12) can be excited by absorption of light of the second wavelength can be excited photonically from its first energetically increased electronic state (Z ₁ ) into a higher energetically, ie into a second energetically increased electronic state (Z ₂ ), a spontaneous, radiation-free de-excitation pathway existing from the second energetically increased electronic state (Z ₂ ), whose efficiency is greater than that of each corresponding photonic de-excitation path, • the active molecules (12) can be de-excited from their first energetically increased electronic state (Z ₁ ) with stimulated emission into their electronic ground state (Z ₀ ) by absorption of light of the third wavelength, Generating the first, second and third laser beams, wherein the profile of the third laser beam has a sub-area of vanishing intensity and the temporal coordination of the laser beams takes place in such a way that active molecules (12) in the writing area (16) • photonically by absorption of light from the first laser beam into their first energetically increased electronic state (Z ₁ ) are excited, • outside the sub-region of vanishing intensity of the third laser beam are stimulated back into their electronic basic state (Z ₀ ) under stimulated emission and • within the sub-region of vanishing intensity of the third laser beam are photonically excited into their second energetically increased electronic state (Z ₂ ) and with emission of the substrate (10) locally modifying, thermal energy are excited without radiation. Procedure according to Claim 1 , characterized in that the photonic excitation and radiationless de-excitation of the second energetically increased electronic state (Z ₂ ) takes place cyclically. Method according to one of the preceding claims, characterized in that the third wavelength is longer than the first wavelength. Method according to one of the preceding claims, characterized in that the first and the second wavelength are identical. Method according to one of the preceding claims, characterized in that the partial region of vanishing intensity is a closed region lying in the center of the profile of the third laser beam. Procedure according to one of the Claims 1 to 4th , characterized in that the sub-area of vanishing intensity is a line-like region that divides the profile of the third laser beam centrally. Method according to one of the preceding claims, characterized in that the second laser beam is a short-pulse laser beam. Method according to one of the preceding claims, characterized in that the substrate arrangement (100) comprises as substrate a solid body (10) doped with active molecules (12) and transparent to light of the first, second and third wavelength. Procedure according to one of the Claims 1 to 7 characterized in that the substrate arrangement comprises as substrate a solid (10) which is transparent to light of the first, second and third wavelengths and as active liquid a liquid (18) containing the active molecules (12) in contact with a surface of the substrate (10), wherein the writing area lies on the contact surface between the substrate (10) and the active liquid (18). Method according to one of the preceding claims, characterized in that the solid (10) consists of a polymer or glass. Method according to one of the preceding claims, characterized in that the active molecules (12) are organic dye molecules. Procedure according to one of the Claims 9 or 10th to 11 , as far as related to Claim 9 , characterized in that the active liquid (18) is a solution of the active molecules (12) in an organic solvent.

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