Method for mechanically creating van der waals heterostructures, and set of stamps

Abstract

The present invention relates to a method for mechanically creating van der Waals heterostructures and to a set of stamps which is designed for mechanically creating van der Waals heterostructures and in particular for carrying out the method.

Description

[0001] DESCRIPTION

[0002] Method for the mechanical construction of van der Waals heterostructures and stamp set

[0003] The present invention relates to a method for the mechanical construction of van der Waals heterostructures. Furthermore, the invention relates to a stamping set designed for the mechanical construction of van der Waals heterostructures, in particular for carrying out a method according to the invention.

[0004] The mechanical assembly of van der Waals heterostructures is a key technology for investigating new phenomena that occur at the interfaces between different 2D materials. The popularity of this method is based on the simplicity and speed with which heterostructures can be constructed in a virtually infinite number of possible combinations. The constant demand for cleaner and better devices has driven the successive refinement of assembly techniques, with the goal of meeting the criteria of reliability, cleanliness, and quality of the interfaces to an ever greater extent, even as the complexity of the structures increases. Currently, the assembly process of 2D materials known as "deterministic dry pick-up assembly" and related techniques are the most widely used assembly methods in this field. They offer great versatility and yield high-quality heterostructures.

[0005] In the assembly process known as deterministic dry pick-up assembly, a polydimethylsiloxane (PDMS) stamp covered with a polymer film is used to pick up a peeled or exfoliated 2D crystal. While the polymer of the polymer film exhibits strong adhesion within a certain temperature range, the PDMS is soft and thus prevents the picked-up 2D material from breaking. The heterostructure is then incorporated into the final stack from top to bottom, starting with the material that will ultimately form the uppermost layer. In the final step, the heterostructure is released by contact with the target substrate and melting of the polymer of the polymer film. Alternatively, a polymer whose thermoplastic properties allow for melt-free release can be used.

[0006] Critically, the assembly process, known as deterministic dry pick-up assembly, requires full contact between the polymer of the polymer film and the heterostructure surface, which inevitably leads to polymer residues on the heterostructure surface. Therefore, if the heterostructure surface is made of a reactive material, contact with the polymer will attack its surface. One strategy to circumvent this problem is to use a protective layer in the form of an inert material sandwiched between the polymer and the reactive material. In this case, the polymer residues can be removed from the protective layer using a combination of solvents such as chloroform, acetone, or isopropanol and AFM-based cleaning methods. The combination of these cleaning methods has shown that contamination-sensitive surface science techniques can be successfully applied.However, due to their limited thickness, protective layers can limit the accessibility of the underlying material. An alternative way to avoid contact of the polymer with the heterostructure surface is to build the van der Waals heterostructure in reverse order and flip it after the stacking process. This method is called the "dry transfer-flip" technique. In this case, the van der Waals heterostructure is released by melting the polymer layer used in the assembly (polypropylene carbonate, PPC), leaving a thick PPC layer beneath the finished heterostructure. The PPC is then removed by heating at 250 °C in a vacuum.

[0007] Unfortunately, the dry-transfer-flip technique also has some disadvantages. The assembled heterostructure must be heated for several hours under high vacuum to remove the PPC layer remaining beneath the heterostructure, which can cause atomic defects on the surface of the heterostructure. Furthermore, the required temperature of 250 °C is incompatible with 2D materials that decompose at this temperature. Finally, the large amount of PPC that must be sublimed from the underside of the heterostructure is incompatible with ultrahigh vacuum (UHV).

[0008] Based on this prior art, it is an object of the present invention to provide a stamp set and a method of the type mentioned at the outset, which at least partially overcome the aforementioned disadvantages.

[0009] To achieve this object, the present invention provides a method for the mechanical construction of van der Waals heterostructures, comprising the steps of a) arranging a polymer film on a polymer element of a first stamp such that the polymer film covers part of an opening of a depression provided on the upper side of the polymer element, in particular approximately half of the opening of the depression of the polymer element, b) arranging a polymer film on a polymer layer of a second stamp such that the polymer film covers part of an opening of a recess provided on the upper side of the polymer layer, in particular approximately half of the opening of the recess of the polymer layer, c) picking up a base flake arranged on a carrier with the first stamp by moving the first stamp and the base flake towards each other,the polymer film partially covering the opening of the depression is brought into contact with approximately half of the base flake surface, and the first stamp, with the base flake adhering to its polymer film, and the support are moved away from each other; d) picking up a first 2D crystal arranged on a support with the first stamp by moving the first stamp and the crystal toward each other; bringing a portion of the surface of the base flake arranged in alignment with the polymer film in the direction of movement into contact with the surface of the crystal; and then moving the first stamp, with the van der Waals heterostructure held thereon, which comprises the base flake and the crystal adhering thereto, and the support away from each other; e) moving the first stamp and the second stamp toward each other and contacting only the surface of the base flake with the polymer film of the second stamp;f) peeling the polymer film of the first stamp from the base flake by moving the stamps relative to each other in a direction transverse, in particular perpendicular, to the direction in which the stamps were moved in step e), whereupon the van der Waals heterostructure remains on the second stamp, g) rotating the second stamp such that the base flake points towards a target substrate, h) moving the second stamp and the target substrate towards each other until the base flake touches the target substrate, and i) peeling the polymer film of the second stamp from the base flake by moving the stamps relative to each other in a direction transverse, in particular perpendicular, to the direction in which the stamps were moved in step h).

[0010] It should be noted here that the movements of components toward and / or away from each other performed in steps c), d), e), and h) are relative movements that can be brought about by moving both corresponding components, but preferably by moving only one component. These relative movements preferably occur in a vertical direction, advantageously by moving only the upper component.

[0011] The method according to the invention is carried out using two stamps. The first stamp comprises a polymer element, which can be arranged with its underside, for example, on a glass slide, and which is provided with a recess on its upper side. The polymer element is preferably dome-shaped, with the recess then being formed on the upper side of the dome. The recess is advantageously substantially cuboid-shaped and, viewed from above, has, in particular, an opening area of ​​approximately 500 x 500 μm. 2The second stamp comprises a horizontally extending polymer layer, the underside of which can be arranged, for example, on a glass slide. On the upper side, the polymer layer has a recess, in particular in the form of a continuous vertical incision or cut, which divides the polymer layer into two parts, the width of the recess advantageously being approximately 200 μm. The polymer element and the polymer layer are preferably made of a silicone, in particular of polydimethylsiloxane (PDMS).

[0012] The polymer films arranged on the stamps in steps a) and b) serve to hold, tilt, and release the van der Waals heterostructure to be constructed during the subsequent process steps. For example, a commercially available polyvinyl chloride film can be used as the polymer film, which is preferably first heated to 130°C on a hot plate for one minute. This step is advantageous in that uncontrolled thermal shrinkage of the PVC can be reliably prevented during the process according to the invention. The arrangement of the polymer films on the polymer element of the first stamp and on the polymer layer of the second stamp is preferably such that the freely floating area of ​​the polymer layer on the first stamp is larger than on the second stamp, thereby promoting stronger adhesion between the polymer film and the heterostructure on the second stamp compared to the first stamp.

[0013] To manipulate the first stamp and the second stamp, in particular during the execution of steps c) to h), at least one suitable micromanipulator is preferably used.

[0014] The method according to the invention is advantageous over the prior art described above in that it requires neither the use of a protective layer nor other cleaning methods such as solvents or AFM cleaning. This allows van der Waals heterostructures with atomically clean surfaces to be achieved at comparatively low process temperatures.

[0015] Preferably, after carrying out step d), at least one further crystal layer arranged on a horizontally extending substrate is picked up with the first stamp by lowering the first stamp vertically in the direction of the further crystal layer, bringing the surface of the first crystal layer into contact with the surface of the further crystal layer and then moving the first stamp with the van der Waals heterostructure held thereon, which has the base flake, the first crystal layer and the further crystal layer, vertically upwards again.

[0016] Advantageously, steps c) and d) are carried out at a temperature of about 70°C.

[0017] Steps e) to i) are preferably carried out at a temperature of about 130°C.

[0018] The target substrate is preferably made of an alloy comprising Au and Ti.

[0019] Advantageously, the base flake has a thickness of at least 40 nm to ensure the necessary stiffness and mechanical support for the subsequent layers of the heterostructure.

[0020] The material of the base flake and / or the crystal layers comprises in particular graphite and / or NbSe2 and / or MoS2 and / or h-BN.

[0021] Furthermore, the present invention provides a stamp set which is designed for the mechanical construction of van der Waals heterostructures and can be used in particular for carrying out the method according to the invention, comprising two stamps, wherein the first stamp has a polymer element which is provided with a depression on its upper side, and wherein the second stamp has a horizontally extending polymer layer which has a recess on its upper side, in particular in the form of a continuous vertical cut which divides the polymer layer into two parts. According to one embodiment of the present invention, the polymer element of the first stamp is dome-shaped and provided with the depression on the upper side of the dome.

[0022] Preferably, the polymer element of the first stamp and the polymer layer of the second stamp are each arranged on a glass slide.

[0023] The polymer element and the polymer layer are advantageously made of a silicone, in particular polydimethylsiloxane (PDMS).

[0024] According to one embodiment of the present invention, the recess of the polymer element of the first stamp is essentially cuboid-shaped and, viewed from above, has in particular an opening area of ​​approximately 500 x 500 pm 2 on.

[0025] The recess of the polymer layer of the second stamp preferably has a width of about 200 pm.

[0026] Further features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

[0027] Figure 1 is a schematic first sectional view of a first stamp of a stamp set according to an embodiment of the present invention;

[0028] Figure 2 shows a schematic second sectional view of the first stamp shown in Figure 1, wherein the sectional view shown is rotated by 90° compared to Figure 1; Figure 3 shows a schematic first sectional view of a second stamp of the stamp set;

[0029] Figure 4 is a schematic second sectional view of the second punch shown in Figure 3, the sectional view shown being rotated by 90° with respect to Figure 3; and

[0030] Figures 5 to 14 are schematic views showing successive steps of a method according to an embodiment of the present invention using the stamps shown in Figures 1 to 4.

[0031] The same reference numbers refer to the same or similar components.

[0032] Figures 1 to 4 show two stamps 2 and 3 of a stamp set 1 according to an embodiment of the present invention. The first stamp 2 shown in Figures 1 and 2 has a polymer element 4, in this case dome-shaped, which is positioned on a slide 5, in this case a slide made of glass. On its upper side, the polymer element 4 is provided with a recess 6, which in the illustrated case is essentially cuboid-shaped and, viewed from above, has an opening area of ​​approximately 500 x 500 μm. 2The second stamp 3 shown in Figures 3 and 4 comprises a horizontally extending polymer layer 7, which is also positioned on a slide 5 and here has a thickness of 5 mm. On its upper side, the polymer layer 7 is provided with a recess 8, which in the present case has the shape of a continuous vertical cut that divides the polymer layer 7 into two parts. In the illustrated embodiment, the recess 8 of the polymer layer 7 has a width B of approximately 200 μm. The polymer element 4 of the first stamp 2 and the polymer layer 7 of the second stamp 3 are preferably made of a silicone, in this case polydimethylsiloxane (PDMS). The first stamp 2 is used in the method described in more detail below for constructing a van der Waals heterostructure. The second stamp 3 is used to tilt and detach the van der Waals heterostructure onto a target substrate 9.

[0033] In the next step, a polymer film 10 is produced, which is to be used for picking up, tilting, and releasing a van der Waals heterostructure. For this purpose, for example, a commercially available polyvinyl chloride (PVC) film (RIKEN WRAP, Riken Fabro Corp) is first heated on a hot plate for one minute to 130 °C. This heat treatment serves to prevent uncontrolled thermal shrinkage of the polymer film during subsequent process steps. After the heat treatment, the polymer film 10 is rolled up to a 1 x 1 cm 2A large square of double-sided adhesive tape is transferred, taking care not to crumple the polymer film 10. The double-sided adhesive tape provides grip and stability when handling the polymer film 10. Next, the polymer film 10 is cut into two pieces. One piece is transferred to the polymer element 4 of the first stamp 2, and the other to the polymer layer 7 of the second stamp 3, covering approximately half of the depression 6 and approximately half of the recess 8, as shown in Figures 1 to 4. It has been found that stiffer polymer films 10 have stronger adhesion, enabling the transfer of van der Waals heterostructures between chemically identical polymer films 10.By arranging the polymer films 10 on the two stamps 2 and 3 such that the suspended area on the first stamp 2 is larger than on the second stamp 3, a stronger adhesion between polymer and heterostructure is promoted on the second stamp 3 compared to the first stamp 2.

[0034] The construction of a van der Waals heterostructure 11 using a method according to an embodiment of the present invention using the stamps 2 and 3 shown in Figures 1 to 4, each provided with a polymer film 10, is described below with reference to Figures 5 to 14.

[0035] In a first step, a base flake 12 is provided on a carrier 13, in this case a SiC^2 carrier, heated to 70°C. The base flake 12 consists of a van der Waals material. For example, it can be a graphite flake. The thickness D of the base flake 12 should be at least 40 nm to ensure the necessary rigidity and mechanical support for the subsequent layers of the heterostructure 11. The first stamp 2 is positioned above the base flake 12 such that the polymer element 4 with the polymer film 10 arranged thereon points toward the base flake 12, see Figure 5.

[0036] Subsequently, the first stamp 2 is lowered in the direction of the arrow 14 using a micromanipulator such that the region of the polymer film 10 of the first stamp 2 projecting horizontally into the recess 6 touches approximately half of the base flake 12, as shown in Figure 6, whereupon the first stamp 2 is again carefully moved vertically upwards.

[0037] In a further step, the first stamp 2, with the base flake 12 held thereon, is positioned, as shown in Figure 7, above a peeled 2D crystal 15 made of a van der Waals material, which is arranged on a support 13 heated to 70°C, in this case an SiO2 support. The peeled crystal 15 can be an NbSe2, an M0S2, and / or an h-BN crystal, to name a few examples. The thickness of the crystal 15 can, in principle, be freely selected.

[0038] The second stamp 3, with the base flake 12 leading, is now moved downwards toward the crystal 15, as indicated by the arrow 16 in Figure 7, such that the portion of the base flake 12 disposed beneath the polymer film 10 touches the crystal 15 without the crystal 15 protruding laterally beyond the base flake 12, see Figure 8. The crystal is then picked up by van der Waals interaction, thereby forming the desired heterostructure 11. However, it should be understood that further crystals can be arranged on the crystal 15 of the now-produced heterostructure 11 by repeating the steps illustrated in Figures 7 and 8.

[0039] After the van der Waals heterostructure 11 has been formed on the first stamp 2, the heterostructure is reversed using the second stamp 3. For this purpose, the temperature is increased to 130°C, and the first stamp 2 is positioned above the second stamp 3 such that the polymer element 4 of the first stamp 2 and the polymer layer 7 of the second stamp 3 face each other, as shown in Figure 9.

[0040] Subsequently, the van der Waals heterostructure 11 is brought into contact with the polymer film 10 of the second stamp 3 by lowering the first stamp 2 in the direction of the arrow 17, taking care that only the free surface of the base flake 12 touches the polymer film 10 of the second stamp 3, see Figure 10. The heterostructure 11 is then transferred to the second stamp 3 by carefully pressing the first stamp 2 as shown in Figure 11 and moving it horizontally sideways in the direction of the arrow 18, so that the polymer film 10 of the first stamp 2 is peeled off the heterostructure 11.

[0041] Subsequently, the second stamp 3 is rotated in the direction of the arrows 19 in Figure 11 and positioned with the micromanipulator above the target substrate 9 such that the heterostructure 11 points toward the target substrate 9, as shown in Figure 12. In this case, the target substrate 9 is an Au / Ti layer positioned on a carrier 13, for example, a SiC^ carrier heated to 130°C.

[0042] In a further step, the heterostructure 11 is brought into contact with the target substrate 9 by lowering the second stamp 3 in the direction of the arrow 20 shown in Figure 12, see Figure 13.

[0043] In a final step, the polymer film 10 of the second stamp 3 is detached from the heterostructure 11 by slowly moving the second stamp 3 horizontally sideways in the direction of the arrow 21 shown in Figure 13, as shown in Figure 14.

[0044] The method according to the invention is advantageous in that it requires neither the use of a protective layer nor other cleaning methods such as solvents or AFM cleaning. This allows van der Waals heterostructures with atomically clean surfaces to be achieved at comparatively low process temperatures.

[0045] Thanks to the possibility of constructing heterostructures from different materials, the inventive method has a broad applicability. Examples of heterostructures constructed on common substrates for optical, transport, and surface characterization experiments are hexagonal boron nitride (h-BN), graphite, or M0S2. Furthermore, investigations have shown that materials with a reactive surface, such as NbSe2, can also be used as substrates, although only the area of ​​the surface that did not come into contact with the polymer film is atomically clean. Further experiments showed that the constructed ultraclean van der Waals heterostructures consist of a variety of different van der Waals materials, which facilitates the investigation of

[0046] (i) WSe2 on graphite, a transition metal dichalcognide known to induce strong spin-orbit coupling in graphene;

[0047] (ii) bilayer graphene on h-BN

[0048] (iii) twisted bilayer graphene on M0S2, which contains two single graphene monolayers sequentially grown with a controlled twist angle between them, allowing the simultaneous investigation of the strongly correlated physics of twisted bilayer graphene and the strong spin-orbit coupling induced by the transition metal dichalcogenide;

[0049] (iv) graphene on CrSBr, the latter being a 2D antiferromagnetic semiconductor whose interlayer electronic coupling can be magnetically controlled;

[0050] (v) WSe2 on M0S2, a semiconductor heterostructure that has been intensively studied for its optoelectronic properties; and

[0051] (vi) WTe2 on NbSe2, a heterostructure exhibiting one-dimensional topological superconductivity.

[0052] From the successful assembly of all these very different heterostructures, it can be concluded that the inventive method is suitable for a wide range of material combinations. To assess the quality of the interfaces of the van der Waals heterostructures experimentally assembled using the inventive method, both the surface and interlayer quality were considered. For this purpose, the assembled van der Waals heterostructures were examined using contact AFM (c-AFM), focusing on those with capping layers of either single-layer graphene or twisted bilayer graphene. This is because graphene, as an atomically thin 2D material, is more prone to wrinkles and creases than thicker 2D materials. Less optimal assembly methods lead to more trapped bubbles and wrinkles in graphene, allowing different mechanical assembly methods to be compared.Three different criteria were evaluated: the amount of residue remaining on the surface, the number and area of ​​trapped bubbles at the interface, and potential damage to the top layer, for example, in the form of cracks. It was found that inverted stacking of van der Waals heterostructures protects the top surface, preventing fracture and resulting in fewer trapped bubbles. Furthermore, the increased stiffness of the base flakes contributes to better interfaces by avoiding inhomogeneities due to the elasticity of the polymer film. Importantly, no traces of residue or damage were detected on the top graphene layer. In fact, the surface residues are mainly located at the contact front between the polymer film and the base flake.

[0053] To compare the surface quality achieved with the inventive method with other assembly methods, a heterostructure was assembled in a regular stacking sequence and with filling contact between the heterostructure surface and the polymer film, using the method described above, referred to as "deterministic dry pick-up assembly." The surface of the assembled Gr / NbSe2 / graphite heterostructure exhibited significant polymer residues as well as damaged areas where the graphene was partially fractured. In contrast, the van der Waals heterostructures assembled according to the invention exhibited a roughness that is smaller than the c-AFM noise (RMS = 0.74 nm), which demonstrates the flatness of the van der Waals heterostructures assembled according to the invention.

[0054] Finally, the surface quality and thus the compatibility of the inventive method with impurity-sensitive surface science techniques such as STM was tested. For this purpose, a BL WTe2 / NbSe2 van der Waals heterostructure was investigated. The heterostructure was assembled in an argon atmosphere in a glove box and transported to the low-temperature STM ("scanning tunneling microscopy") in a vacuum case under UHV conditions. The result was NbSe2 without any surface impurities and with a 3 x 3 charge density wave modulation, which occurs below Tcow = 32 K and is known to be very sensitive to external disturbances. In the same way, atomically resolved images of the WTe2 bilayer on NbSe2 were obtained, which again showed only single atomic defects.

[0055] The tests were carried out under the following conditions:

[0056] To produce the stamps, a polymer base and a curing agent were mixed in a Petri dish at a ratio of 10:1 (w / w) using a commercial PDMS elastomer kit (SYLGARD 184). To create the dome-shaped polymer element for the first stamp, the Petri dish was turned upside down for several days so that the mixed liquid slowly formed a droplet and simultaneously hardened. The depression was then created. To create the recess for the polymer layer of the second stamp, the polymer layer positioned on the slide was cut into two parts with a scalpel such that the resulting recess exposed the slide.

[0057] To prepare the samples, 2D crystals were deposited on 285 nm SiO2 / Si substrates. The assembled van der Waals heterostructures were deposited either on a 285 nm SiO2 / Si substrate or, alternatively, on pre-evaporated 100 nm / 10 nm Au / Ti wires on a 285 nm SiO2 / Si substrate and mounted on a standard STM sample plate for STM measurements. All samples were prepared in an argon-filled glove box.

[0058] Atomic force microscopy (AFM) experiments were performed using a Bruker Innova instrument under ambient conditions. The AFM was operated in contact mode with a set force of ~6.2 nN and a scan speed of 20 pm s. 1 The probe tips used in the experiments were Bruker RESPA-20, with a nominal tip radius of 8 nm and a spring constant of 0.9 Nm- 1 .

[0059] The scanning tunneling data were acquired at the Center for Low Temperature Physics in Kosice under ultrahigh vacuum at a base pressure of ~1 x 10-10 mbar and a base temperature of 1.14 K using a mechanically cut Au tip.

[0060] As a result, the inventive method creates a transfer technique that enables the construction of van der Waals heterostructures with ultra-clean surfaces and interfaces. The method is suitable for the construction of heterostructures in a glove box and can therefore also be used for reactive materials. The high quality of the resulting van der Waals heterostructures enables detailed surface studies, such as STM measurements, with atomically resolved images, even on air-sensitive materials without a protective layer. Since the method can be applied to a wide range of materials, it is of great interest in various research areas such as optics, electronic transport, and surface and interface research.Since the process according to the invention requires neither the melting of polymers nor chemical solvents, it also represents an important step towards the production of van der Waals heterostructures under UV conditions.

[0061] It should be understood that the foregoing description of preferred embodiments is not intended to be limiting. Rather, modifications and additions are possible without departing from the scope of the present invention as defined by the appended claims.

Claims

CLAIMS 1. A method for the mechanical construction of van der Waals heterostructures (11), comprising the steps of a) arranging a polymer film (10) on a polymer element (4) of a first die (2) such that the polymer film (10) covers part of an opening of a depression (6) provided on the upper side of the polymer element (4), in particular approximately half of the opening of the depression (6) of the polymer element (4), b) arranging a polymer film (10) on a polymer layer (7) of a second die (3) such that the polymer film (10) covers part of an opening of a recess (8) provided on the upper side of the polymer layer (7), in particular approximately half of the opening of the recess (8) of the polymer layer (7), c) picking up a base flake (12) arranged on a carrier with the first die (2) by moving the first die (2) and the base flake (12) towards each other,the polymer film (10) partially covering the opening of the depression (6) is brought into contact with approximately half of the base flake surface, and the first stamp (2) with the base flake (12) adhering to its polymer film (10) and the carrier are moved away from each other, d) picking up a first 2D crystal (15) arranged on a carrier with the first stamp (2) by moving the first stamp (2) and the crystal (15) towards each other, a part of the surface of the base flake (12) arranged in alignment with the polymer film (10) in the direction of movement is brought into contact with the surface of the crystal (15), and then the first stamp (2) with the van der Waals heterostructure held thereon, (11), which has the base flake (12) and the crystal (15) adhering thereto, and the carrier are moved away from each other, e) moving the first stamp (2) and the second stamp (3) towards each other and contacting only the surface of the base flake (12) with the polymer film (10) of the second stamp (3), f) peeling the polymer film (10) of the first stamp (2) from the base flake (12) by moving the stamps (2, 3) relative to each other in a direction transverse, in particular perpendicular, to the direction in which the stamps (2, 3) were moved in step e), whereupon the van der Waals heterostructure (11) remains on the second stamp (3), g) rotating the second stamp (3) such that the base flake (12) points towards a target substrate (9), h) moving the second stamp (3) and the target substrate (9) towards each other until the base flake (12) touches the target substrate (9), and i) peeling the polymer film (10) of the second stamp from the base flake,by moving the stamps relative to each other in a direction transverse, in particular perpendicular to the direction in which the stamps (2, 3) were moved in step h).

2. The method according to claim 1, characterized in that after carrying out step d) at least one further 2D crystal (15) arranged on a carrier (13) is picked up with the first stamp (2) by moving the first stamp (2) and the further crystal (15) towards one another, bringing the surface of the first crystal (15) into contact with the surface of the further crystal (15) and then moving the first stamp (2) with the Wand-der-Waals heterostructure (11) held on it, which has the base flake (12), the first crystal (15) and the further crystal (15) and the carrier (13) away from one another.

3. Method according to claim 1 or 2, characterized in that the polymer films (10) are made of polyvinyl chloride.

4. Method according to one of the preceding claims, characterized in that the polymer films (10) are heat-treated, in particular at about 130°C, before carrying out steps a) and b).

5. Method according to one of the preceding claims, characterized in that steps c) and d) are carried out at a temperature of about 70°C.

6. Method according to one of the preceding claims, characterized in that steps e) to i) are carried out at a temperature of about 130°C.

7. Method according to one of the preceding claims, characterized in that the target substrate (9) is made of an alloy comprising Au and Ti.

8. Method according to one of the preceding claims, characterized in that the base flake (12) has a thickness (D) of at least 40 nm.

9. Method according to one of the preceding claims, characterized in that the material of the base flake (12) and / or the crystal(s) (15) comprises graphite and / or NbSe2 and / or MoS2 and / or h-BN.

10. Stamp set (1) designed for the mechanical construction of Van der Waals heterostructures (11), in particular for Carrying out a method according to one of the preceding claims, comprising two stamps (2, 3), wherein the first stamp (2) has a polymer element (4) which is provided with a depression (6) on its upper side, and wherein the second stamp (3) has a polymer layer (7), in particular a planar one, which is provided with a recess (8) on its upper side, in particular in the form of a continuous vertical cut which divides the polymer layer into two parts.

11. Stamp set (1) according to claim 10, characterized in that the polymer element (4) of the first stamp (2) is dome-shaped and is provided with the recess (4) on the upper side of the dome.

12. Stamp set (1) according to claim 10 or 11, characterized in that the polymer element (4) of the first stamp (2) and the polymer layer (7) of the second stamp (3) are each arranged on a glass slide (5).

13. Stamp set (1) according to one of claims 10 to 12, characterized in that the polymer element (4) and the polymer layer (7) are made of a silicone, in particular of polydimethylsiloxane (PDMS).

14. Stamp set (1) according to one of claims 10 to 13, characterized in that the recess (6) of the polymer element (4) of the first stamp (2) is substantially cuboid-shaped and, viewed from above, has in particular an opening area of ​​approximately 500 x 500 pm 2 has.

15. Stamp set (1) according to one of claims 10 to 14, characterized in that the recess (8) of the polymer layer (7) of the second stamp (3) has a width (B) of approximately 200 pm. 12 REPLACEMENT SHEET (RULE 26) 3 / 3 Fig. 14

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