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Yusai Wakafuji, Momoko Onodera, Satoru Masubuchi, Rai Moriya, Yijin Zhang, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Tomoki Machida

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[Evaluation of polyvinyl chloride adhesion to 2D crystal flakes](https://mdr.nims.go.jp/datasets/cf6c56a2-09b1-4742-a5d6-d5bbb34a2bb8)

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Evaluation of polyvinyl chloride adhesion to 2D crystal flakesARTICLE OPENEvaluation of polyvinyl chloride adhesion to 2D crystal flakesYusai Wakafuji1, Momoko Onodera1✉, Satoru Masubuchi 1, Rai Moriya 1, Yijin Zhang1, Kenji Watanabe 2,Takashi Taniguchi 1,3 and Tomoki Machida 1✉We investigated the adhesion of polyvinyl chloride (PVC) to 2D crystal flakes on SiO2/Si substrates. Although the anchoring effectcannot be used to explain adhesion to atomically flat surfaces, PVC is sufficiently strongly adhesive to 2D crystal flake surfaces toallow pickup from SiO2/Si substrates via surface contact alone. Results of the pickup test, whether pickup is possible or impossible,were plotted on a map of contact surface area ratio vs. contact edge length ratio, which allowed us to identify the conditions underwhich flakes can be picked up using PVC and to discuss the adhesion strengths of the surface and edge. This study provides amethod for the evaluation of adhesion forces between polymers and 2D flakes and demonstrates that PVC is a useful polymer fordeterministic transfer and versatile manipulation of 2D flakes.npj 2D Materials and Applications            (2022) 6:44 ; https://doi.org/10.1038/s41699-022-00323-7INTRODUCTIONResearch on 2D materials has been growing rapidly. One of themost fascinating aspects of 2D materials is that they can beassembled into vertical stacks, called van der Waals (vdW)heterostructures1, without the restriction of lattice matching. Thefreedom of choice of material and stacking order means that wehave infinite possibilities in designing vdW heterostructures. Toexplore the field of vdW heterostructures, techniques for stacking2D materials are essential2. Various types of polymers have beenused to facilitate the assembly of 2D materials. The first reported2D material transfer technique used polymethyl methacrylate(PMMA)3: The 2D flakes were exfoliated on a PMMA layer and thentransferred onto a target flake. This type of transfer technique, inwhich flake stacks are assembled from the bottom to the top, iscalled bottom-up transfer. Polymers can be used as a pickupmedium for 2D flakes on SiO2/Si substrates: 2D flakes are pickedup by a polymer stamp one by one, and this method is called top-down transfer4. Moreover, polymer sheets are also utilized assupporting layers to make larger flakes by mechanical exfoliation5.Various types of polymers have been reported to be applicable for2D material transfer, including polypropylene carbonate (PPC)4,6,7,polydimethylsiloxane (PDMS)8,9, PMMA3,10, polycarbonates (PC)11,Elvacite12, polyvinyl alcohol (PVA)13,14, nitrocellulose15, polycapro-lactone16, paraffin17, polyvinyl acetate18, and nail polish19. Eachpolymer has different characteristics, and an appropriate polymermust be selected depending on the specific requirements of thesituation. More recently, versatile manipulation—including sliding,folding, and peeling—of 2D flakes has been demonstrated usingpolyvinyl chloride (PVC)20. The key point of the manipulation wasthe strong adhesion of PVC, which enabled the control of theentire 2D flake only with a small part of the flake contactedby PVC.In this study, we evaluated the adhesion of PVC to 2D flakesusing a novel approach. In particular, we were able to distinguishthe effects of the surface and edge of the 2D flakes on the pickupforce. Although the anchoring effect is not significant for 2Dsurfaces, we show herein that PVC adheres to atomically flat 2Dsurfaces strong enough to pickup the flake via surface contactalone, without any contact between the edge of the flake andthe PVC.RESULTS AND DISCUSSIONPreparation of PVC/PDMS stampBefore proceeding to the main experiments, we present some keydetails of the PVC stamp preparation (full details are provided inthe Supplementary information). We prepared a PVC/PDMS stampon a glass slide for 2D flake pickup20. Here, we used a triple PDMSdome to specifically localize the area of contact between the PVCstamp and 2D flake. First, a PDMS dome was prepared on a glassslide as follows. A section of a PDMS sheet was attached to a glassslide, and liquid PDMS was dropped on the sheet to form a PDMSdome. The PDMS droplet was solidified by heating on a hotplate.To ensure that the tip of the PDMS dome possessed highcurvature (diameter, ~30 μm, Supplementary Fig. 1a, b), we addedfurther PDMS droplets to the PDMS dome, ultimately preparing atriple PDMS dome (Fig. 1a). Next, we covered the PDMS domewith PVC film (Supplementary Fig. 2). The PVC film used was acommercially available PVC food wrap (Riken Technos) whichincluded additives such as plasticizers. The degree of polymeriza-tion of the PVC was ~1000, and the thickness of the film was~7 μm. Before use, the surface of the PVC/PDMS stamp was gentlycleaned with isopropyl alcohol on a dustless wiper to removecontaminants. We confirmed that the transfer can be conductedusing PVC films fabricated from conventional PVC powder andplasticizer instead of commercially available PVC food wraps. (seeSupplementary Information).Systematical analysis on the adhesion of PVC to 2D crystalflakesPVC exhibits strong adhesion to 2D flakes as demonstrated byversatile 3D manipulation of 2D materials20. Notably, we observedthat PVC adheres to the atomically flat surfaces of 2D crystal flakes,as we will describe in detail below. Several mechanisms accountfor the adhesion force between polymers and 2D flakes. One ofthese mechanisms is the anchoring effect. The anchoring effect1Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan. 2Research Center for Functional Materials, National Institute for MaterialsScience, 1-1 Namiki, Tsukuba 305-0044, Japan. 3International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044,Japan. ✉email: monodera@iis.u-tokyo.ac.jp; tmachida@iis.u-tokyo.ac.jpwww.nature.com/npj2dmaterialsPublished in partnership with FCT NOVA with the support of E-MRS1234567890():,;http://crossmark.crossref.org/dialog/?doi=10.1038/s41699-022-00323-7&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41699-022-00323-7&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41699-022-00323-7&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41699-022-00323-7&domain=pdfhttp://orcid.org/0000-0001-7039-6694http://orcid.org/0000-0001-7039-6694http://orcid.org/0000-0001-7039-6694http://orcid.org/0000-0001-7039-6694http://orcid.org/0000-0001-7039-6694http://orcid.org/0000-0001-7471-7432http://orcid.org/0000-0001-7471-7432http://orcid.org/0000-0001-7471-7432http://orcid.org/0000-0001-7471-7432http://orcid.org/0000-0001-7471-7432http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1938-7415http://orcid.org/0000-0002-1938-7415http://orcid.org/0000-0002-1938-7415http://orcid.org/0000-0002-1938-7415http://orcid.org/0000-0002-1938-7415https://doi.org/10.1038/s41699-022-00323-7mailto:monodera@iis.u-tokyo.ac.jpmailto:tmachida@iis.u-tokyo.ac.jpwww.nature.com/npj2dmaterialsexplains the mechanical aspect of adhesion. The adhesive(polymer) fits into the surface structure of an adherend, andadhesion is reinforced. Thus, adhesion is strong when the surfaceof the adherend is rough (having pits or cracks). Considering theatomically flat nature of the surface of 2D flakes, the anchoringeffect is not involved in the adhesion process. However, flakeedges are not flat on the nanometer scale and are hence moresusceptible to adhesion to polymers via the anchoring effect (Fig.1c). However, as we will show later in this paper, PVC adheres toboth the edges and surfaces of flakes. To evaluate and understandthe excellent adhesion of PVC, we employed a novel experimentalapproach. Our experiment and analysis were systematicallydesigned to qualitatively characterize the adhesion force, whilealso enabling a semi-quantitative comparison between the surfaceand edge adhesions of 2D crystal flakes. The features of ourmethod are as follows: (1) a 2D crystal flake is shaped into acircular form to minimize the effects of shape variation on thepickup behavior, (2) the effects of the surface and edge aredistinguished by varying the contact position in a controlledmanner, and (3) a plot of the contact surface area vs. contact edgelength for each contact position reveals the surface and edgecontributions to the adhesion of the 2D crystal flake.The nature of the adhesion between the polymer and 2D flakesdepends on the shape and size of the 2D flakes. For quantitativeand systematic evaluation of the polymer adhesion force, the sizeand shape of the flakes should be normalized. Therefore, weexfoliated hexagonal boron nitride (h-BN) grown at high pressureand high temperature21 onto a SiO2/Si substrate and shaped theflakes (~30 nm thick) into circles (Fig. 1b, radius ~12 μm) via CF4plasma etching. The resultant circular shapes are highly symme-trical and minimize shape-related adhesion bias effects. Using thecircular h-BN flakes, we conducted pickup tests using PVC. Figure1a, b show schematics of the stamping apparatus and circular h-BN pickup procedure using the PVC/PDMS stamp, respectively. 2Dflakes on a SiO2/Si substrate were picked up using the stamp.Flakes of h-BN exfoliated onto a SiO2/Si substrate were placed on astage controlled by the actuator with stepper motors. The PVCstamp on a glass slide was fixed on the upper stage, and thecontact between the PVC stamp and the h-BN flakes was made bylifting the bottom stage. Then, the bottom SiO2/Si substrate wasFig. 1 Pickup of h-BN flakes using PVC/PDMS stamp. a Schematic of the stamping apparatus. The sample stage is controlled by an actuatorwith stepper motors, which enables precise control of the stage speed v. b Photographs and schematics of the pickup procedure. Scale bar:10 μm. c Schematic showing the area on a 2D flake over which adhesion to the PVC stamp occurs (highlighted in red).Fig. 2 Schematics of the pickup tests. a Pickup by surface contact alone using the PVC/triple PDMS dome. b Pickup by edge contact withminimal surface contact area using the PVC/semicylindrical PDMS, where the relationship between rS and rL is given by Eq. (1). c Pickup byedge and surface contact using the PVC/triple PDMS dome. The sky blue and red regions in (i–iv) indicate the areas of surface contact andedge contact between the PVC and h-BN, respectively.Y. Wakafuji et al.2npj 2D Materials and Applications (2022)    44 Published in partnership with FCT NOVA with the support of E-MRS1234567890():,;detached from the stamp by lowering the stage. The 2D flake waseither picked up by the PVC stamp or remained on the SiO2/Sisubstrate. Initial tests demonstrated that the stage speed v was animportant parameter for successful flake pickup, and v wasprecisely controlled by the stepper motors (Fig. 1a). In Fig. 1b, weshow photographs of the successful pickup of an h-BN flake usingthe stamp at T= 70 °C. Whether a flake is picked up depends onthe stage speed and temperature, as well as the area on the flakethat comes into contact with the PVC stamp. In the subsequentPVC pickup tests, we fixed the stage speed v at 500 μm s−1 andthe stage temperature T at 80 °C.First, we focus on the adhesion between PVC and the surface ofthe h-BN flake. Figure 2a shows a schematic of the surface pickuptest. To exclude edge effects, we ensured that contact betweenthe PVC stamp and the h-BN surface occurred only at the center ofthe flake (sky blue region in Fig. 2a). Then, the PVC stamp wasdetached from the substrate by reversing the direction of motionof the stage, i.e., by lowering the sample stage. At this point, theflake had been either picked up by the PVC stamp or hadremained on the SiO2/Si substrate, depending on the forcebetween the PVC and flake surfaces (Fig. 3). Pickup occurred whenthe adhesion force between the PVC and the flake was larger thanthat between the flake and the SiO2/Si substrate. We repeated thisprocess, varying the contact area ratio rS≡ Scontact/Stotal, whereScontact is the surface area of the flake in contact with the stampand Stotal is the total surface area of the flake and recordedwhether the flake was picked up (Supplementary Table 1). Pickupwas successful when rS was greater than 0.30. Because theadhesion force is assumed to be proportional to the contact area,this value can be regarded as the critical contact area ratio.We next focus on the effect of the flake edge. To systematicallydiscuss the edge effects and surface effects during pickup, wecreated a PVC/PDMS stamp based on a semicylindrical PDMSstructure (Fig. 2b). This was prepared by placing PDMS liquid on aFig. 3 Schematics and images of the pickup tests. Cases where h-BN is a picked up and b not picked up. The microscope was focused on theposition indicated by the dashed line. Scale bar: 10 μm.Fig. 4 Evaluation of surface and edge adhesion. a Plot of pickup test results versus relative contact surface area and relative contact edgelength. Closed circles indicate successful pickups and open circles indicate unsuccessful pickups. The blue, green, and red colors correspondto the pickup by (i) surface contact alone, (ii) mainly-edge contact, and (iii) edge and surface contact, respectively (see discussion in the maintext). The green line was calculated using Eq. (1). The yellow-shaded region is the region in which pickup occurs (the pickup region), and thewhite region is the region in which pickup is impossible. The gray-shaded region (iv) is the experimentally unfeasible region. b–e Schematicsof the pickup regions: b surface-dominant adhesion, c edge-dominant adhesion, d, e both surface and edge adhesion. d is the case where 2Dflakes can be picked up by surface contact alone, and e is the case where 2D flakes cannot be picked up by surface contact alone.Y. Wakafuji et al.3Published in partnership with FCT NOVA with the support of E-MRS npj 2D Materials and Applications (2022)    44 PDMS sheet cut into a long rectangle (Supplementary Fig. 1c).Although some of the surfaces were also in contact with thestamp, the semicylindrical PDMS shape ensured that the contactsurface area ratio rS was minimized for the same contact edgelength ratio rL≡ Lcontact/Ltotal, where Lcontact is the length of theedge of the flake in contact with the stamp and Ltotal is the totaledge length for the flake (mainly-edge pickup condition). Theborder of the contact region was initially set to the tangent of thecircular h-BN flake and was moved such that it remained parallelto its original position (Fig. 2b). In this case, the relationshipbetween rS and rL is given by an analytical formula:rS ¼ rL � sin 2πrLð Þ2π: (1)(see Supplementary Fig. 3 and preceding discussion for thederivation of Eq. (1)). We repeated this procedure whilst varying rLwith rS given by Eq. (1) (Supplementary Table 1). The pickup wasobserved to be successful when rL was greater than 0.29.Further, we conducted pickup tests under the intermediateconditions between the surface-only and mainly-edge pickupconditions discussed above. This part of the study uses the triplePDMS dome previously used for the surface-only pickup, and thecontact region extends beyond the chord joining the pointsdefining the extent of the edge contact (Fig. 2c). We repeated thepickup test whilst varying rS and rL, and the results are listed inSupplementary Table 1.The results of the three types of pickup tests discussed so far(surface-only, mainly-edge, and combined edge and surfacecontacts) are plotted in Fig. 4a. On the vertical axis, r= Scontact/Stotal is plotted, and on the horizontal axis, rL= Lcontact/Ltotal. Theclosed circles indicate successful pickup, and the open circlesindicate unsuccessful pickup. This graph is divided into fourregions. Region (i) is in fact a line (blue) corresponding to thevertical axis rL= 0, i.e., surface contact without edge contact (Fig.2a). Pickup was successful when rS≳ 0.30 (rL= 0), as discussed inthe previous paragraph (Supplementary Table 1). PVC adheres tothe flake surface even without any anchoring effect, which is instark contrast to our observations when PC was used as the pickupmaterial, as discussed later. Region (ii), which is a line given by Eq.(1) (green), corresponds to mainly-edge pickup with minimalsurface contact, achieved using the semicylindrical PDMS struc-ture (Fig. 2b). Along this line, pickup was successful when rL≳ 0.29(rS given by Eq. (1)). Region (iii) (red) corresponds to pickupattempts via contact with both the surface and edge using thetriple PDMS dome (Fig. 2c). The data point at (rL, rS)= (1, 1) on theplot corresponds to the case in which the entire flake is coveredby the stamp. Region (iv) (gray) corresponds to the experimentallyunfeasible region.The yellow-shaded region corresponds to the region in whichpickup is likely to occur (the pickup region). The boundarybetween successful and unsuccessful pickup is highlighted by thedashed line in Fig. 4a. The boundary line defines the criticalcondition for pickup, and this can be expressed asrSr�Sþ rLr�L¼ 1; (2)where r�S and r�L are the critical contact surface ratio and criticalcontact edge length ratio, respectively. In our experiment, r�S =0.30 and r�L = 0.50. When surface adhesion is dominant, theboundary does not depend on rL, and r�S « r�L (Fig. 4b). In contrast,when edge adhesion is dominant, the boundary is independent ofrS, and r�S » r�L (Fig. 4c). The intermediate of these extreme cases (r�S~ r�L ) is shown in Fig. 4d, e. Surface-only pickup is possible in Fig.4d and impossible in Fig. 4e. Our experimental results resemblethe plot in Fig. 4d.In the preceding pickup tests, the speed of the stage v and itstemperature T were fixed at v= 500 μm s−1 and T= 80 °C. Thesevalues were selected based on another series of pickup tests usingPVC/PDMS in which v and T were varied. In general, flakes aremore likely to be picked up when the stage speed is higher, as hasbeen reported for other polymers such as PDMS8,22. Similarly, thestage speed seems to enhance the adhesion force between thePVC surface and the flake. We conducted pickup tests with precisecontrol of v using our motor-driven stage. Contact between the h-BN and PVC stamp was made at a stage speed of 10 μm s−1 (fixed),and then the stage and the flake were detached at the speed of v.Starting from a small v, we repeated the contact–detach move-ments using the same flake and increasing v, recording whetherthe flake was picked up. Figure 5 lists the test results, with yellowcells indicating successful pickups and light blue cells indicatingunsuccessful pickups. It should be noted that although the resultis indicated as either yellow or light blue, the pickup probabilitygradually changed in the vicinity of the boundary of yellow andlight blue. From this figure, we defined threshold stage speed v*corresponding to the limiting value for flake pickup. v* wasminimized at T ~ 70 °C. Considering that the stage speedcompensates for the pickup force, the adhesion between thePVC and the flake is greatest at T ~ 70 °C, which approximatelycorresponds to the glass transition temperature Tg of PVC.We also conducted pickup tests using PC, which is a commonlyused pickup polymer11. A thin PC film was placed on the triplePDMS dome on a glass slide, and we conducted pickup tests as inthe case of PVC. The stage speed and temperature were fixed atv= 500 μm s−1 and T= 110 °C. Supplementary Fig. 4 shows theresults of the pickup test using PC, which resembles the schematicof Fig. 4e rather than Fig. 4d. In contrast to PVC, PC cannot pickupthe flake via surface adhesion alone as far as we have optimized.This result suggests that the PC film cannot pickup the flakewithout the occurrence of an anchoring effect at the edge.So far, we have shown that PVC is adhesive to both the surfaceand the edge of 2D flakes. This strong adhesion is highly useful forthe fabrication of vdW heterostructures (Supplementary Fig. 5).Besides thick h-BN, monolayer graphene and monolayer MoS2 canbe picked up by PVC. Thus, this method is applicable to various 2Dmaterials. Moreover, the flake can be released on a SiO2/Sisubstrate at T= 130 °C without melting the PVC (SupplementaryFig. 6), that is, PVC can transfer 2D flakes without the need forimmersion in a solvent. The surface of the transferred flakes canbe easily cleaned by high-temperature annealing (SupplementaryFig. 5 Results of pickup tests conducted using various values of vand T. Yellow cells indicate successful pickups and light blue cellsindicate unsuccessful pickups.Y. Wakafuji et al.4npj 2D Materials and Applications (2022)    44 Published in partnership with FCT NOVA with the support of E-MRSFig. 7). Additionally, once a structure has been fabricated, the PVCstamp can be reused until it is severely damaged. This reusabilityincreases the pickup reproducibility because the polymer stampconditions are preserved.Finally, we discuss the possible mechanisms of adhesion.Although the anchoring effect is responsible for mechanicaladhesion, many more existing adhesion mechanisms should beconsidered23 (Supplementary Fig. 8). Considering the h-BN flakesurface is atomically flat and inert, static electricity is the mostprobable mechanism accounting for the observed strong adhe-sion between the PVC stamp and the 2D crystal surface. BecausePVC includes negatively polarized chloride atoms, an electrostaticpotential will be generated at the PVC surface. The electrostaticforce between atomically flat surfaces is significant when thedistance between the two interfaces is small at the atomic level24.Close to the pickup temperature, PVC is sufficiently soft to bemolded to fit the surface of the flake, and the distance betweenthe two interfaces is minimized to maximize the electrostaticforce. It would be highly interesting to investigate the correlationbetween the chloride atom content of PVC and its pickupbehavior in a future experiment.In conclusion, we demonstrated that PVC adheres strongly to2D flakes. The adhesion was first examined by repeatedly makingcontact between PVC and a 2D flake and then detaching them,changing the detachment speed and stage temperature. We theninvestigated the ratios of the surface and edge adhesioncontributions by localizing the PVC contact area within specificregions of the flake. Although the anchoring effect does not occurfor an atomically flat surface, the adhesion of PVC to the 2D flakesurface was sufficiently strong to allow the pickup of flakes whenonly surface contact, with no edge contact, occurred. In additionto the specific results on the effectiveness of PVC as a pickupmaterial, our findings demonstrate a practical evaluation techni-que that can be applied to other polymers.METHODSFabrication of PVC/PDMS stampTo make PDMS domes, a PDMS elastomer kit (SYLGARD®184, Dow Corning)was used. A polymeric base and curing agent were mixed at a 10:1 (w/w)ratio. To eliminate air bubbles, the liquid mixture was placed under avacuum in a desiccator for ~10min. Next, a small piece (4 mm2 × 4mm2)was cut from a PDMS sheet (PF-X4- 17mil., Gel-Pak) and placed on a glassslide. A droplet of the PDMS liquid mixture was placed on the piece ofPDMS sheet using a toothpick and then cured at 130 °C for 5 min on ahotplate. The diameter of the dome was ~2mm. Next, another PDMSdroplet was placed on the first dome to make the second dome, which hada diameter of ~0.4mm, and this was then cured at 130 °C for 5 min. Finally,a third droplet was placed on the second dome to form a third dome of~30 μm in diameter using a gold wire designed for wire bonding(diameter, 25 µm), and this was cured at 130 °C for 5 min. (SupplementaryFig. S1a, b).To create the semicylindrical PDMS structure, an elongated rectangle(4 mm× 10mm) was cut from a PDMS sheet and placed on a glass slide.The PDMS mixture was placed on the PDMS rectangle and then cured at130 °C for 5 min on a hotplate. Finally, the PDMS structure was cut intosemicylindrical sections (4 mm2 × 4mm2) (Supplementary Fig. 1c).We used a PVC-based food wrap (Riken Technos) for the PVC stamp.First, the PVC wrap was placed on a glass slide. Double-sided tape wasattached to form a square frame surrounding a ~5mm2 × 5mm2 area ofthe PVC sheet (Supplementary Fig. 2). Then, the frame was cut out using arotary cutter and transferred onto the triple PDMS dome on the glass slidewith the adhesive tape facing the glass slide. The PVC sheet was attachedto a glass slide to obtain the PVC/PDMS stamp in its final usable format.The surface of the PVC/PDMS dome was wiped with isopropyl alcohol toeliminate contaminants and then blown with N2 gas. This wiping processwas necessary because it was observed that oily substances, probably theplasticizer contained in the PVC wrap, covered the surface of the PVC wrap.DATA AVAILABILITYThe data generated during this study are available from the corresponding author onreasonable request.Received: 25 January 2022; Accepted: 10 June 2022;REFERENCES1. Geim, A. K. & Grigorieva, I. V. Van der Waals heterostructures. Nature 499,419–425 (2013).2. Onodera, M., Masubuchi, S., Moriya, R. & Machida, T. Assembly of van der Waalsheterostructures: exfoliation, searching, and stacking of 2D materials. Jpn. J. Appl.Phys. 59, 010101 (2020).3. Dean, C. R. et al. Boron nitride substrates for high-quality graphene electronics.Nat. Nanotechnol. 5, 722–726 (2010).4. Wang, L. et al. 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B 15, 1 (1998).ACKNOWLEDGEMENTSThis work was supported by the JST-CREST, JST-Mirai, and JST-PRESTO Programs(grant numbers JPMJCR15F3, JPMJCR20B4, JPMJMI21G9, and JPMJPR20L5), JSPSKAKENHI (grant numbers JP19H02542, JP19H01820, JP20H00127, JP20H00354,JP21H05232, JP21H05233, JP21H05234, JP21K20345 JP22H01898, and JP22K14559),the Murata Science Foundation, the Advanced Technology Institute Research Grants,the Mazda Foundation, the Izumi Science and Technology Foundation, the KenjiroTakayanagi Foundation, and the Inoue Foundation for Science, and Iketani ScienceY. Wakafuji et al.5Published in partnership with FCT NOVA with the support of E-MRS npj 2D Materials and Applications (2022)    44 and Technology Foundation. We are also grateful to Taketo Hashimoto, KiyotakaSuzuki, Hegun Now, and Yasushi Seta in Riken Technos for discussions, technicalinformation, and for providing a PVC film sample. Y.W. acknowledges the JSPSResearch Fellowship for Young Scientists.AUTHOR CONTRIBUTIONSY.W. and T.M. conceived and designed the experiments; Y.W. performed theexperiments with the help of M.O., S.M., R.M., and Y.Z., K.W. and T.T. grew the h-BNcrystals; M.O., Y.W., and T.M. wrote the manuscript using contributions from allauthors.COMPETING INTERESTSThe authors declare no competing interests.ADDITIONAL INFORMATIONSupplementary information The online version contains supplementary materialavailable at https://doi.org/10.1038/s41699-022-00323-7.Correspondence and requests for materials should be addressed to MomokoOnodera or Tomoki Machida.Reprints and permission information is available at http://www.nature.com/reprintsPublisher’s note Springer Nature remains neutral with regard to jurisdictional claimsin published maps and institutional affiliations.Open Access This article is licensed under a Creative CommonsAttribution 4.0 International License, which permits use, sharing,adaptation, distribution and reproduction in anymedium or format, as long as you giveappropriate credit to the original author(s) and the source, provide a link to the CreativeCommons license, and indicate if changes were made. The images or other third partymaterial in this article are included in the article’s Creative Commons license, unlessindicated otherwise in a credit line to the material. If material is not included in thearticle’s Creative Commons license and your intended use is not permitted by statutoryregulation or exceeds the permitted use, you will need to obtain permission directlyfrom the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.© The Author(s) 2022Y. Wakafuji et al.6npj 2D Materials and Applications (2022)    44 Published in partnership with FCT NOVA with the support of E-MRShttps://doi.org/10.1038/s41699-022-00323-7http://www.nature.com/reprintshttp://www.nature.com/reprintshttp://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/ Evaluation of polyvinyl chloride adhesion to 2D crystal flakes Introduction Results and discussion Preparation of PVC/PDMS stamp Systematical analysis on the adhesion of PVC to 2D crystal flakes Methods Fabrication of PVC/PDMS stamp DATA AVAILABILITY References Acknowledgements Author contributions Competing interests ADDITIONAL INFORMATION