Booth, Tim

Bøggild, Peter

Thomsen, Joachim Dahl

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 18, 2017Intrinsic roughness in suspended van der Waals heterostructuresThomsen, Joachim Dahl; Bøggild, Peter; Booth, TimPublication date:2016Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Thomsen, J. D., Bøggild, P., & Booth, T. (2016). Intrinsic roughness in suspended van der Waalsheterostructures. Poster session presented at Carbonhagen 2016, Copenhagen, Denmark.Intrinsic roughness in suspended van der Waals heterostructures Joachim Dahl Thomsen, Peter Bøggild, Timothy J. Booth DTU Nanotech, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark Introduction Methods – In-situ TEM and Fabrication Roughness and normal angle spread                                                The work leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° FP7-604000 Conclusion    Graphene 0o tilt Graphene 18o tilt Graphene/hBN 0o tilt Graphene/hBN 18o tilt Reciprocal space of rough graphene The full 3D Fourier transform of rough graphene in reciprocal space (u,v,w) consists of a set of cones (Fig. 1)  If the graphene is rough the diffraction spots become diffuse when tilting the sample   For G/hBN samples the spots remain the same   Roughness of heterostructures [1] – M. Yamamoto et.al, ACS Nano 6, no. 9 (2012) ,p. 8335-8341 [2] – J.C. Meyer et. Al, Nature 446, p. 60-63 (2007) [3] – M.I. Katsnelson and A.K. Geim, Phil. Trans R. Soc. 336, p. 195-204 (2008)  [4] – E.V. Castro et. al, Phys. Rev. Lett. 105, p. 266601 (2010) [2] - N. D. Mermin, Phys. Rev. 176, p.  250 (1968) [5] – D.A. Kirilenko et. al, Phys. Rev. B 84, 235417 (2011) [6] – F. Pizzocchero et. al, Nat. Comm. 7, 11894 (2016) Fig. 2 – diffration patterns of graphene and graphene/hBN at 0o, 18o and 36o tilt.  Fig. 1 – the 3D Fourier transform of rippled graphene consists of cones. The green plane represents the Ewald sphere intersecting the density distribution to form diffraction patterns. Figure taken from Ref. [5] Fig. 4 –  Optical image (a) and optical dark field image (b) showing a G/BN heterostructure (sample 2) on silicon dioxide, (c) TEM image of the same sample. Graphene Graphene /hBN Plots of ln(A) vs. G2 for the samples are shown in Fig. 5 and the corresponding measured roughnesses are listed in the legend.                Encapsulated graphene • Making hBN-G-hBN heterostructures is a well known strategy for obtaining high mobility grapene samples   • Measurements of supported graphene on hBN have shown root mean square (RMS) roughnesses around 1.4 Å similar to the roughness of suspended graphene [1] • Here we show that the roughness can  be reduced further by suspending the  heterostructure.  Fig. by Jannick C. Meyer Intrinsic roughness/ripples • Ripples in graphene are ubiquitous – seen for both for graphene on hBN, SiO2 [1] and suspended graphene [2] • Ripples may be a large factor limiting electron mobility [3] [4] Roughness The spot intensity of rough graphene varies as 𝐴𝐴 ∝ exp − 2𝜋𝜋𝐺𝐺 2 ℎ2 , where ℎ2  is the RMS roughness [5]. Hence   ℎ2 = 12𝜋𝜋𝑑𝑑ln A𝑑𝑑𝐺𝐺2  Sample fabrication The samples were made using the hot pick-up method (Fig. 3) [6]   Fig. 3 – Hot pick-up procedure, (i) pick-up of hBN, (ii)  drop down on graphene, (iii) release of polymer stack. Fig. taken from ref. [6] The roughness of two BN/G heterostructures and three suspended graphene samples were measured in a TEM. Fig. 5 – plots of the logarithm of the diffraction spot amplitude as a function of the square of the distance from the zero order diffraction spot to the spot center. The slope of the linear fits is proportional to the RMS roughness of the graphene. On one heterostructure sample the roughnes of the suspended graphene part was also measured  (Fig. 4) hBN Graphene Figure taken from ref. [6] 20 22 24 26 28 30 32-4-3-2-10ln(A) (arb. u)G2 (nm-2)                            Sample RMS roughness (Å)      1 - G/BN 0.23 ± 0.01      2 – G/BN 0.19 ± 0.04      2 – G only 1.22 ± 0.03      3 – G only 1.14 ± 0.02      4 – G only 1.19 ± 0.02      5 – CVD G 1.56 ± 0.05                                                                          hBN/G Suspended  graphene • Roughness is possibly the main factor limiting mobility in suspended samples • Even graphene encapsulated in hBN shows a RMS roughness around 1.4 Å • By suspending the heterostructures we have measured a significant decrease in RMS roughness – around 0.2 Å.  2G (20o) 2G (0o) Graphene/hBN 36o tilt Graphene 36o tilt  (18o) 2G (36o) a b c hBN-G-hBN heterostructure 

Intrinsic roughness in suspended van der Waals heterostructures

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Intrinsic roughness in suspended van der Waals heterostructures

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