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Keda Jin, Tobias Wichmann, Sabine Wenzel, Tomas Samuely, Oleksander Onufriienko, Pavol Szabó, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Jiaqiang Yan, F. Stefan Tautz, Felix Lüpke, Markus Ternes, Jose Martinez‐Castro

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[Assembly of Arbitrary Designer Heterostructures with Atomically Clean Interfaces](https://mdr.nims.go.jp/datasets/029b87dd-f1a8-404b-9e4f-cebf8b528b2f)

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Assembly of Arbitrary Designer Heterostructures with Atomically Clean InterfacesRESEARCH ARTICLEwww.advmatinterfaces.deAssembly of Arbitrary Designer Heterostructures withAtomically Clean InterfacesKeda Jin, Tobias Wichmann, Sabine Wenzel, Tomas Samuely, Oleksander Onufriienko,Pavol Szabó, Kenji Watanabe, Takashi Taniguchi, Jiaqiang Yan, F. Stefan Tautz,Felix Lüpke, Markus Ternes, and Jose Martinez-Castro*Van der Waals heterostructures are an excellent platform for studyingintriguing interface phenomena, such as moiré and proximity effects.Many of these phenomena occurring in such heterostructures’ interfaces andsurfaces have so far been hampered because of their high sensitivity todisorder and interface contamination. Here, it reports a dry polymer-basedassembly technique to fabricate arbitrary designer van der Waalsheterostructures with atomically clean surfaces. The key features of thesuspended dry pick-up and flip-over assembly technique are: 1) theheterostructure surface never comes into contact with polymers, 2) theassemble is entirely solvent-free, 3) it is entirely performed in a glovebox,and 4) it only requires temperatures below 130 °C. By performing ambientatomic force microscopy and atomically-resolved scanning tunnelingmicroscopy on example heterostructures, it demonstrates the fabrication ofair-sensitive heterostructures with ultra-clean interfaces and surfaces. Itenvisions that, due to the avoidance of polymer melting, this technique ispotentially compatible with heterostructure assembly under ultra-highvacuum conditions, which promises ultimate heterostructurequality.K. Jin, T. Wichmann, S. Wenzel, F. S. Tautz, F. Lüpke, M. Ternes,J. Martinez-CastroPeter Grünberg Institut (PGI-3)Forschungszentrum Jülich52425 Jülich, GermanyE-mail: j.martinez@fz-juelich.deK. Jin, T. Wichmann, S. Wenzel, F. S. Tautz, F. Lüpke, M. Ternes, J. Martinez-CastroJülich Aachen Research AllianceFundamentals of Future Information Technology52425 Jülich, GermanyK. Jin, M. Ternes, J. Martinez-CastroInstitute for Experimental Physics II BRWTH Aachen52074 Aachen, GermanyThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/admi.202300658© 2023 The Authors. Advanced Materials Interfaces published byWiley-VCH GmbH. This is an open access article under the terms of theCreative Commons Attribution License, which permits use, distributionand reproduction in any medium, provided the original work is properlycited.DOI: 10.1002/admi.2023006581. IntroductionThe mechanical assembly of van derWaals (vdW) heterostructures[1] is a keytechnology for studying the emergingphenomena occurring at interfaces be-tween 2D materials.[2,3] The popularityof this method is based on the easeand speed with which heterostructurescan be built in a virtually infinite num-ber of possible combinations. The con-stant demand for cleaner and better de-vices has driven the successive refine-ment of the assembly techniques, withthe aim to meet the criteria of reliabil-ity, cleanliness, and interface quality toan ever greater extent, despite the si-multaneous increase in the complexityof the structures. Currently, the dry pick-up assembly of 2D materials[4] and re-lated techniques[5–8] are the most widelyused ones in this regard as they offergreat versatility and yield high-qualityT. Wichmann, F. S. TautzInstitute for Experimental Physics IV ARWTH Aachen52074 Aachen, GermanyT. Samuely, O. Onufriienko, P. SzabóCentre of Low Temperature Physics, Faculty of SciencePavol Jozef Šafárik University & Institute of Experimental Physics, SlovakAcademy of Sciences04001 Košice, SlovakiaK. WatanabeResearch Center for Electronic and Optical MaterialsNational Institute for Materials Science 1-1 NamikiTsukuba 305-0044, JapanT. TaniguchiResearch Center for Materials NanoarchitectonicsNational Institute for Materials Science1-1 Namiki, Tsukuba 305-0044, JapanJ. YanMaterials Science and Technology DivisionOak Ridge National LaboratoryOak Ridge TN 37831, USAAdv. Mater. Interfaces 2024, 11, 2300658 2300658 (1 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbHhttp://crossmark.crossref.org/dialog/?doi=10.1002%2Fadmi.202300658&domain=pdf&date_stamp=2023-10-27www.advancedsciencenews.com www.advmatinterfaces.deheterostructures. The method of dry pick-up assembly proceedsas follows: A polydimethylsiloxane (PDMS) polymer stamp cov-ered with a sticky polymer film is used to pick up 2D crystalsexfoliated from bulk material onto a substrate, typically Si/SiO2.While the polymer film has a strong adhesion over a certain tem-perature range, the PDMS is soft, allowing a controlled contactto the flakes and protecting them from damage. The heterostruc-ture is then assembled from the top to the bottom, starting withthe material that will eventually form the topmost layer. In thelast step, the heterostructure is released by contacting the tar-get substrate and melting the polymer. Alternatively, a polymerwhose thermoplastic properties allows a melt-free release can beemployed.[7] Crucially, standard dry pick-up assembly techniquesrequire fully contacting the heterostructure surface with the poly-mer, which inevitably leaves polymer residues on the surface andinterface (due to the in-diffusion of molten polymer) of the finalheterostructure.[9] In particular, if the heterostructure surface isformed by a reactive material, the contact with the polymer willdegrade its surface.A strategy to circumvent this problem is the use of a protec-tive layer, i. e., an inert material that is placed as the topmostlayer of the heterostructure to protect (encapsulate) the layersunderneath from degradation.[6,10–12] In this case, the polymerresidues can be removed from the protective layer with a com-bination of solvents such as chloroform, acetone or isopropanol,and the trapped bubbles in the interface can be removed withAFM-based mechanical cleaning methods.[13,14] The combina-tion of inert encapsulation layers with such cleaning methodshas been demonstrated to allow contamination-sensitive surfacescience techniques to be applied successfully.[15,16] Nevertheless,protective layers can pose a limit to the accessibility of the under-lying material due to their finite thickness and electronic proper-ties that can mask those of the underlying materials.An alternative to avoid polymers to come into contact withthe heterostructure surface is to assemble it in reverse order andto flip it over after the assembly process.[17–19] Using such tech-niques, the vdW heterostructure is typically released by meltingthe polymer layer (polypropylene carbonate, PPC) that is usedduring assembly, leaving a thick PPC layer underneath the fin-ished heterostructure. The PPC is then removed by annealingat 250 °C in vacuum. Unfortunately, while the dry-transfer fliptechnique is a huge step forward, it also has its limitations: 1)The assembled heterostructure must be annealed in high vac-uum for several hours to properly remove the residual PPC layerfrom underneath the heterostructure. Such extended annealingcan cause atomic defects on the heterostructure surface.[18] 2)The required annealing temperature of 250 °C is incompatiblewith many 2D materials which degrade at this temperature.[20] 3)The large amount of PPC that must be evaporated makes it in-compatible with ultra-high vacuum (UHV) environments, whichare sensitive to organic contaminants.Here, we present a novel technique for the mechanical as-sembly of ultra-clean vdW heterostructures that overcomes thedrawbacks of existing assembly methods. Our suspended drypick-up and flip-over assembly technique does not require theuse of a protective encapsulation layer, nor does it require addi-tional cleaning by solvents or AFM. Using ambient AFM and low-temperature STM, we demonstrate that atomically clean surfacesand interfaces are achievable for a variety of heterostructures.2. Results and Discussion2.1. Description of the Suspended Dry Pick-Up and Flip-OverAssembly TechniqueWe start by preparing two PDMS stamps. The first one (stamp1) is used to assemble the vdW heterostructure, while the sec-ond one (stamp 2) is used to flip and controllably place the vdWheterostructure onto the target substrate. Stamp 1 uses a dome-shaped PDMS, with an approximately 1 × 1 mm2 square depres-sion cut into its center, and is supported on a microscope glassslide (left panel of Figure 1a). Stamp 2 consists of a flat, 5 mmthick PDMS block that has been cut into two pieces with a scalpel,resulting in a trench of approximately 200 μm width (Figure 1aright panel) that exposes the supporting glass slide. For more de-tails on the transfer slide preparation, see Figure S1 (SupportingInformation).Next, we prepare the polymer films that will be used for pick-up, flip-over, and release of the vdW heterostructure. To this end,a commercial poly(vinyl chloride) (PVC) film (RIKEN WRAP,Riken Fabro Corp)[7] is first annealed to 130 °C for one minuteon a hot plate. This step is crucial because it prevents any un-controlled thermal shrinkage of the PVC when mounted on thestamps and heated during subsequent steps (Figure S2, Sup-porting Information). After annealing, we transfer the PVC filmonto a 1 × 1 cm2 square of standard double-sided scotch tape,taking care not to wrinkle the film. The double-sided tape pro-vides support and stability when manipulating the PVC film.Subsequently, we cut the PVC film into two pieces and place oneof them on PDMS stamp 1, the other on PDMS stamp 2 (seeFigure S3, Supporting Information), covering half of the squaredepression and half of the trench as shown in Figure 1a. Notethat, both, the detailed shape of the PDMS stamps as well as thetotal contact area of the PVC films with the PDMS determinethe stiffness of the suspended PVC films. In detail, we have ob-served that stiffer films show stronger adhesion with 2D materi-als. Thus, by placing the PVC on the two stamps such that thesuspended area on stamp 1 is larger than on stamp 2, we pro-mote stronger adhesion between polymer and heterostructureon stamp 2 compared to stamp 1. This crucial feature enablesus to transfer the assembled vdW heterostructure from stamp 1to stamp 2 later in the process, despite them being chemicallyidentical PVC films.Employing the two stamps, we assemble the vdW heterostruc-ture in reverse order using a standard assembly stage (HQgraphene) as described in Figure 1b. We note that the first flaketo be picked up, the base flake, should be thicker than ≈ 40 nmto provide the necessary stiffness and mechanical support for thesubsequently following layers of the heterostructure. We contactthe base flake with stamp 1 at 70 °C by touching roughly halfof the flake with the PVC film (red) and then carefully pullingthe stamp up vertically (panel (i) in Figure 1b; Video S1, Support-ing Information). Subsequently, we pick up subsequent flakes byvdW interaction[5] at 70 °C to assemble the desired heterostruc-ture. For each additional pick-up step, we make sure that theflake does not extend over the edge of the base flake (panel (ii)in Figure 1b; Video S2, Supporting Information).Once the assembly of the vdW heterostructure on stamp 1 iscompleted, we flip the heterostructure using stamp 2. To do this,Adv. Mater. Interfaces 2024, 11, 2300658 2300658 (2 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2024, 1, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/admi.202300658 by National Institute For, Wiley Online Library on [16/04/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deasecond pick-up first pick-upapproachbase flake SiO2base flaketransfer to Stamp 2Au/TiStamp 2release Stamp 1approach pullrelease Stamp 2b ii) iii)base flakeAu/TipullT = 130 °C put down flip i)iv) v) vi)PDMS dome with a holetop viewPDMS trenchtop viewglass slide PVC≈ 1 mm ≈ 200 mFigure 1. Schematic representation of the suspended dry pick-up and flip-over assembly of a WSe2/Graphite heterostructure. a) 3D representations(top view) of stamps 1 and 2, showing in detail how the two PVC films (red) are suspended with the aid of the carved PDMS structures (grey). b) Flowdiagram of the heterostructure assembly. i) Stamp 1 is brought into contact with the base flake (here graphite) at 70 °C by touching the left half of thebase flake (black) with the PVC film (red). The base flake is then picked up by carefully retracting stamp 1 vertically. ii) The van der Waals heterostructureis assembled by contacting the exfoliated flake b (green, WSe2), initially located on the SiO2 substrate (purple), with the part of the base flake that islocated directly underneath the PVC film. iii) The base flake on stamp 1 is brought into contact with stamp 2 at 130 °C, making sure that each stamptouches roughly half of the base flake (white and red dashed lines). iv) The van der Waals heterostructure is transferred by sliding stamp 1 sidewaysuntil the base flake is only in contact with stamp 2. v) After flipping the heterostructure upside down, stamp 2 with the heterostructure is mounted inthe micro-manipulator stage. Subsequently, stamp 2 is brought into contact with the target substrate Au/Ti (yellow) on SiO2 (purple) at 130 °C. vi) Theheterostructure is finally released from stamp 2 by sliding the latter sideways and retracting it vertically.we place stamp 2 on the transfer stage and raise the tempera-ture to 130 °C. We then carefully bring stamp 1 into contact withstamp 2, making sure that the PVC films on the two stamps onlytouch the base flake on opposite sides and not each other (panel(iii) in Figure 1b). Stamp 1 is then released by gently pressingand sliding it laterally (panel (iv) in Figure 1b; Video S3, Sup-porting Information). Next, stamp 2 is flipped over by mount-ing it into the micro-manipulator. The heterostructure is thenbrought into contact with the target substrate at 130 °C (panel(v) in Figure 1b). Finally, we release the vdW heterostructure byslowly moving stamp 2 laterally (panel (vi) in Figure 1b; Video S4,Supporting Information).2.2. Arbitrary Designer HeterostructuresBy assembling example heterostructures composed of a wide va-riety of different vdW materials, we demonstrate the broad ap-plicability of our suspended dry pick-up and flip-over assem-bly technique. The used base flakes of the heterostructures in-clude common materials typically used for optical, transport, andsurface characterization experiments, such as hexagonal boronnitride (hBN), graphite, or MoS2.[21–23] In addition, we demon-strate that air-sensitive (reactive) materials, such as NbSe2, canalso be used as base flakes, although only the base flake sur-face area, which did not come into contact with the PVC filmis atomically clean. Figure 2 shows a summary of six exampleheterostructures: a) WSe2 on graphite, the former being a tran-sition metal dichalcogenide known to induce strong spin-orbitcoupling into graphene[24]; b) bilayer graphene on hBN, the latterbeing an insulator, which is typically used for gating purposes[25];c) twisted-bilayer graphene on MoS2, assembled from two sepa-rate graphene monolayers that have been sequentially picked upwith a controlled twist angle between them, allowing the simul-taneous study of the strongly correlated physics of twisted-bilayergraphene and the proximity-induced strong spin-orbit couplingby the transition metal dichalcogenide[26]; d) graphene on CrSBr,the latter being a 2D antiferromagnetic semiconductor whoseelectronic interlayer coupling can be magnetically controlled[27];e) WSe2 on MoS2, a semiconductor heterostructure that hasbeen intensively studied for its optoelectronic properties[28]; f )WTe2 on NbSe2, a heterostructure that realizes 1D topologicalsuperconductivity.[18,29].From the successful assembly of the heterostructures demon-strated here, we conclude that the suspended dry pick-up andflip-over assembly technique can be applied to a wide range ofAdv. Mater. Interfaces 2024, 11, 2300658 2300658 (3 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2024, 1, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/admi.202300658 by National Institute For, Wiley Online Library on [16/04/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.decadbfeGr/CrSBr/graphiteWSe2/graphite BLG/hBNWSe2/MoS2 BL-WTe2/NbSe2tBLG/MoS2Figure 2. Exemplary vdW heterostructures. All panels show optical microscopy images of various assembled heterostructures on Au covered SiO2substrates. The flake outlines are indicated as color-coded dashed lines. a) WSe2 on graphite. b) Bilayer graphene (BLG) on hexagonal boron nitride(hBN). c) Twisted-bilayer graphene (tBLG) on MoS2. Inset: optical images of the exfoliated graphene flakes prior to the assembly. d) Graphene (Gr) onCrSBr on graphite. e) WSe2 on MoS2. f) Multilayer WTe2 on NbSe2 where the bulk and bilayer (BL) areas are marked with yellow and red dashed lines,respectively. The scale bars are 20 μm in all panels.materials including most of the common materials used for op-tics, electronic transport, and surface science studies. We notethat, if there are any additional principal limitations at all, theywill most likely be found in the vdW heterostructure assemblyprocess itself: A too strong interaction between the exfoliatedflakes and the SiO2 substrate might prevent the pick-up by thebase flake or previously picked-up layers on top of the base flake.2.3. Surface and Interface QualityTo assess the quality of our assembled vdW heterostructures, wecharacterize the resulting surface and internal interface quality.To this end, we inspect the assembled vdW heterostructures withambient condition contact-mode AFM (c-AFM), focusing here onthose with top layers of either monolayer graphene (Figure 3a,b)or twisted bilayer graphene (Figure 3c,d), because compared tothe thicker 2D materials, graphene is more prone to wrinkle andfold. Less-than-optimal transfer methods tend to produce moretrapped blisters and wrinkles in the graphene, allowing a di-rect comparison between different mechanical assembly meth-ods. We assess three different criteria: 1) The number and areaof trapped blisters at the interface, 2) possible damage of the top-most layer, such as ruptures, 3) the amount of residue left onthe surface. In comparison to standard dry-transfer techniques,we find that a reverse assembly of vdW heterostructures gener-ally results in a lower number of trapped blisters and protectsthe topmost surface from rupturing in agreement with earlierreports.[30] Furthermore, the overall higher stiffness of the het-erostructure provided by the base flake contributes to better inter-faces, because it avoids inhomogeneities and stress arising fromflexing of the polymer film. Lastly, we do not observe any tracesof residue or damage on the topmost graphene layer whatsoever.In fact, the only visible residues are located in the contact frontbetween the PVC and the base flake (see Figure S4, SupportingInformation).To further compare the surface quality achieved with our sus-pended dry pick-up and flip-over assembly technique to standarddry-transfer methods, we assembled a heterostructure followingRef. [7], where the heterostructure surface comes in full contactwith the PVC polymer, i.e., without flip. The surface of the re-sulting Gr/NbSe2/graphite heterostructure (Figure S5, Support-ing Information) exhibits substantial polymer residue as well asdamaged regions where the graphene is partially ruptured. Addi-tionally, the graphene/NbSe2 interface shows a multitude of blis-ters, a signature of trapped polymer residues at the interface.[9]Adv. Mater. Interfaces 2024, 11, 2300658 2300658 (4 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2024, 1, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/admi.202300658 by National Institute For, Wiley Online Library on [16/04/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.de0.4 mtBLG/MoS20443 m69Gr/CrSBr/graphite0480 0.2 0.4 0.6 0.8 1.08.5 nmdistance ( m)height (nm) Gr/CrSBrGr/graphiteMoS2bottom Grtop Gr044height (nm)height (nm)3 m0.4 m0.0 0.2 0.4 0.6 0.8distance ( m)01 0.66 nm0.64 nmMoS2bottom Grtop GrGr/graphiteGr/CrSBrabcdFigure 3. Atomic force microscopy on assembled vdW heterostructures. a) AFM topography of graphene on CrSBr on graphite. b) Zoom into the regionhighlighted by the white rectangle in panel a and topography cross-section along the white arrow. The thicknesses of the CrSBr steps are indicated.c) AFM topography of twisted-bilayer graphene on MoS2. d) Zoom into the region highlighted by the white rectangle in panel (c), showing MoS2 andthe two graphene layers and topography cross-section along the white arrow. The thicknesses of the steps correspond to that of the graphene layers.In contrast, the vdW heterostructures assembled with our sus-pended assembly technique do not show damage or surface con-tamination. Moreover, these heterostructures exhibit a reducednumber of blisters, which also have a smaller radius. A detailedanalysis of the AFM topographies in Figure 3b,d shows thattheir roughness is smaller than the noise of the c-AFM (RMS= 0.74 nm), demonstrating the flatness of the vdW heterostruc-tures’ interfaces assembled with this method.2.4. Scanning Tunneling MicroscopyFinally, we analyze the surface quality and thus the compatibil-ity of our suspended dry pick-up and flip-over assembly tech-nique with contamination-sensitive surface science techniqueslike STM. For this, we inspect the WTe2/NbSe2 vdW heterostruc-ture shown in Figure 2f. Since both NbSe2 and WTe2 are air-sensitive, the heterostructure was assembled in an argon-filledglovebox and transferred from there to the UHV chamber host-ing the STM in a vacuum suitcase. For a detailed atomic-levelevaluation of the surface cleanliness, measurements at three dis-tinct sites were conducted: bulk NbSe2, bulk WTe2 and bilayerWTe2. Figure 4a shows an atomically resolved image of NbSe2—without any surface contaminants—and its 3 × 3 charge densitywave, which emerges below TCDW = 32 K and is known to be verysensitive to external perturbations.[31] In the same way, we wereable to obtain atomically resolved images of the bilayer WTe2 sit-uated on the NbSe2, again showing only single atomic defects(Figure 4b) and in different areas of the bilayer as well as on topof trapped blisters WTe2 (Figure S6, Supporting Information).We also analyzed the amount of polymer residue on the sur-face and the edge of bulk WTe2 on NbSe2. For this purpose, wemeasured a 2 × 2 μm2 STM image topography corresponding tothe maximum scanning range at 4 K (Figure S7a, Supporting In-formation), which points to the absence of polymer residue at themicrometer scale.As a reference, we use PDMS to dry-transfer a bulk WTe2 flakeand examine its surface with STM. Figure S8 (Supporting Infor-mation) reveals a substantial PDMS residue on its surface, serv-ing as a counter-example that shows the limitations of transfertechniques requiring full polymer contact.3. ConclusionThe suspended dry pick-up and flip-over assembly techniqueallows the mechanical assembly of arbitrary designer vdWAdv. Mater. Interfaces 2024, 11, 2300658 2300658 (5 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2024, 1, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/admi.202300658 by National Institute For, Wiley Online Library on [16/04/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.dea 5 nm0 85b0 100topo (pm)topo (pm) 10 nmFigure 4. Scanning tunneling microscopy on a BL WTe2/NbSe2 heterostructure. a) Atomic resolution STM topography on bulk NbSe2 showing its 3 ×3 charge density wave (sample bias Vbias = 90 mV and tunneling current Iset = 100 pA). b) Atomic resolution STM topography on bilayer WTe2 on bulkNbSe2 (Vbias = 100 mV, Iset = 100 pA). Only a few single-atomic defects are observed on both surfaces, their abundance is close to the material’s bulkdefect concentration.heterostructures with ultra-clean surfaces and interfaces. No-tably, the method is suitable for heterostructure assembly in aglovebox and thus can be used for air-sensitive materials. Thehigh quality of the resulting vdW heterostructures enables de-tailed surface studies, such as STM with atomic resolution evenon air-sensitive materials, without requiring a protective layer.The reported assembly technique can be readily applied to thebroad variety of available vdW materials and therefore can be ap-plied in various research areas such as optics, electronic trans-port, and surface science. Because it does not require polymermelting nor chemical solvents, it also constitutes a potentialvenue towards the all-UHV fabrication of vdW heterostructures.4. Experimental SectionPDMS Stamp Preparation: It used a commercial PDMS elastomer kit(SYLGARD®184), mixing a polymeric base and curing agent at a 10:1(w/w) ratio in a Petri dish. To prepare the dome-shaped PDMS for stamp1, the Petri dish was placed upside down for several days, allowing themixed liquid to slowly form a droplet and cure simultaneously.Sample Preparation: It exfoliated flakes from bulk crystals onto 285 nmSiO2/Si substrates. Before the exfoliation, the SiO2/Si substrates wereultrasonically cleaned by acetone and 2-propanol, followed by 30 s UV–Ozone treatment.[32] The assembled vdW heterostructures were placed ei-ther onto a 285 nm SiO2/Si substrate or alternatively onto pre-evaporated100 nm/10 nm Au/Ti leads on a 285 nm SiO2/Si substrate and mountedto a standard STM sample plate for the STM measurements. All sampleswere fabricated in an argon-filled glovebox.Atomic Force Microscopy: Atomic force microscopy (AFM) experi-ments were conducted using a Bruker Innova instrument under ambientcondition. Contact-mode AFM was used with a setpoint force of ≈6.2 nNand a scan speed of 20 μm s−1. The probing tips used in the experimentswere of type Bruker RESPA-20, with a nominal tip radius of 8 nm and aspring constant of 0.9 N m−1.Scanning Tunneling Microscopy: Scanning tunneling data were ac-quired at the Centre of Low Temperature Physics in Košice in ultra-highvacuum at a base pressure of ≈1 × 10−10 mbar and a base temperature of1.14 K using a mechanically cut Au tip.Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsThe authors thank François C. Bocquet for technical support. Furthermore,the authors are grateful to the Helmholtz Nano Facility for its support re-garding sample fabrication. The authors acknowledge funding from theEuropean Union’s Horizon 2020 Research and Innovation Programmeunder Grant Agreement no 824109 (European Microkelvin Platform).J.M.C., T.W., K.J., M.T., and F.L. acknowledged funding by the DeutscheForschungsgemeinschaft (DFG, German Research Foundation) within thePriority Programme SPP 2244 (project nos. 443416235 and 422707584).J.M.C., F.S.T., and F.L. acknowledge funding from the Bavarian Ministryof Economic Affairs, Regional Development, and Energy within Bavaria’sHigh-Tech Agenda Project “Bausteine für das Quantencomputing auf Ba-sis topologischer Materialien mit experimentellen und theoretischen An-sätzen”. J.M.C. acknowledges funding from the Alexander von HumboldtFoundation. T.S., P.S., and O.O. acknowledge the support of APVV-20-0425, VEGA 2/0058/20, Slovak Academy of Sciences project IMPULZ IM-2021-42, COST action CA21144 (SUPERQUMAP) and EU ERDF (Europeanregional development fund) Grant No. VA SR ITMS2014+ 313011W856.S.W. and F.S.T. acknowledge funding by the DFG through the SFB 1083Structure and Dynamics of Internal Interfaces (project A12). M.T. acknowl-edges support from the Heisenberg Program (Grant No. TE 833/2-1) ofthe German Research Foundation. F.L. acknowledges financial support byGermany’s Excellence Strategy - Cluster of Excellence Matter and Lightfor Quantum Computing (ML4Q) through an Independence Grant. J.Q.Y.was supported by the US Department of Energy, Office of Science, Ba-sic Energy Sciences, Materials Sciences and Engineering Division. K.W.and T.T. acknowledge support from the JSPS KAKENHI (Grant Numbers20H00354, 21H05233, and 23H02052) and World Premier InternationalResearch Center Initiative (WPI), MEXT, Japan.Open access funding enabled and organized by Projekt DEAL.Conflict of InterestThe authors declare no conflict of interest.Adv. Mater. Interfaces 2024, 11, 2300658 2300658 (6 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2024, 1, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/admi.202300658 by National Institute For, Wiley Online Library on [16/04/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deAuthor ContributionsJ.M.C., F.S.T., M.T., and F.L. conceived the research. J.M.C., K.J., T.W., andF.L. designed the experiments. J.Y. grew WTe2 crystals. K.W. and T.T. grewhBN crystals. J.M.C., K.J., and T.W. fabricated the samples. T.S., O.O.,and P.S. set up and provided the STM. J.M.C.and T.W. acquired the STMdata. J.M.C. and K.J. acquired the optical microscope data and AFM data.J.M.C., K.J., F.S.T., and F.L. wrote the paper. All authors commented on themanuscript. J.M.C., F.S.T., M.T., and F.L. supervised the research.Data Availability StatementThe data that supports the findings of this study are available in the sup-plementary material of this article.Keywords2D materials, heterostructures, interfaces, scanning tunneling mi-croscopy, stackingReceived: August 7, 2023Revised: September 28, 2023Published online: October 27, 2023[1] A. Castellanos-Gomez, X. Duan, Z. Fei, H. R. Gutierrez, Y. Huang, X.Huang, J. Quereda, Q. Qian, E. Sutter, P. Sutter, Nat. Rev. MethodsPrimers 2022, 2, 58.[2] Y. Cao, V. Fatemi, S. Fang, K. Watanabe, T. Taniguchi, E. Kaxiras, P.Jarillo-Herrero, Nature 2018, 556, 43.[3] P. Wang, G. 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See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License