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Analogous to graphite, hexagonal boron nitride (h-BN) has a layered structure composed of boron and nitrogen atoms that are alternatively bond to each other in a honeycomb array. As the layers are held together by weak van der Waals forces, h-BN thin films can be grown on surfaces of various metal crystals in a layer-by-layer manner, which is again similar to graphene sheets and thus attracts a lot of research interests. In this work, scanning tunneling microscope and spectroscope (STM and STS) were applied to the study of an h-BN thin film with a thickness of about 10 nm grown on Cu foil by means of chemical vapor deposition. X-ray diffraction from the Cu foil shows only one strong peak of Cu(200) in the angle range of 40-60, indicating that the Cu foil is mainly Cu(100). After sufficient annealing in an UHV chamber, the h-BN film sample is transferred to a cooling stage (77 K) for STM/STS measurement. Its high quality is confirmed by a large-scale STM scan that shows an atomically flat topography. A series of dI/dV data taken within varied energy windows all exhibit similar U shapes but with different bottom widths that monotonously decrease with the sweeping energy window. The dI/dV curve taken in the energy window of [-1 V, +1 V] even shows no energy gap in spite that h-BN film is insulating with a quite large energy gap of around 6 eV, as observed in a large-energy-window dI/dV curve (from -5 V to +5 V). These results indicate that the STM images reflect the spatial distribution of tunneling barriers between Cu(100) substrate and STM tip, rather than the local density of states of the h-BN surface. At high sample biases (from 4 V to 1 V), STM images exhibit an electronic modulation pattern with short range order. The modulation pattern displays a substructure in low-bias STM images (less than 100 mV), which finally turns to the (11) lattice of h-BN surface when the sample bias is extremely lowered to 3 mV. It is found that the electronic modulation pattern cannot be fully reproduced by superimposing hexagonal BN lattice on tetragonal Cu(100) lattice, no matter what their relative in-plane crystal orientation is. This implies that the electronic modulation pattern in the STM images is not a Mori pattern due to lattice mismatch. We speculate that it may originate from spatial distribution of tunneling barrier induced by adsorption of H, B and/or N atoms on the Cu(100) surface in the CVD growth process.
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Keywords:
- boron nitride /
- tunneling barrier /
- scanning tunneling microscopy
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[36] Nagashima A, Tejima N, Gamou Y, Kawai T, Oshima C 1995 Phys. Rev. B 51 4606
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[40] Mller F, Stwe K, Sachdev H 2005 Chem. Mater. 17 3464
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[42] Corso M, Greber T, Osterwalder J 2005 Surf. Sci. 577 L78
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[44] Joshi S, Ecija D, Koitz R, Iannuzzi M, Seitsonen A P, Hutter J, Sachdev H, Vijayaraghavan S, Bischoff F, Seufert K, Barth J V, Auwrter W 2012 Nano Lett. 12 5821
[45] Tay R Y, Griep M H, Mallick G, Tsang S H, Singh R S, Tumlin T, Teo E H, Karna S P 2014 Nano Lett. 14 839
[46] Kim G, Jang A R, Jeong H Y, Lee Z, Kang D J, Shin H S 2013 Nano Lett. 13 1834
[47] Kidambi P R, Blume R, Kling J, Wagner J B, Baehtz C, Weatherup R S, Schloegl R, Bayer B C, Hofmann S 2014 Chem. Mater. 26 6380
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[1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Katsnelson M I, Grigorieva I V, Dubonos S V, Firsov A A 2005 Nature 438 197
[2] Zhang Y, Tan Y W, Stormer H L, Kim P 2005 Nature 438 201
[3] Geim A K, Novoselov K S 2007 Nature Mater. 6 183
[4] Lee C, Wei X, Kysar J W, Hone J 2008 Science 321 385
[5] Castro Neto A H, Guinea F, Peres N M R, Novoselov K S, Geim A K 2009 Rev. Mod. Phys. 81 109
[6] Gao Y, Zhang Y, Chen P, Li Y, Liu M, Gao T, Ma D, Chen Y, Cheng Z, Qiu X, Duan W, Liu Z 2013 Nano Lett. 13 3439
[7] Geim A K, Grigorieva I V 2013 Nature 499 419
[8] Gilje S, Han S, Wang M, Wang K L, Kaner R B 2007 Nano Lett. 7 3394
[9] Oostinga J B, Heersche H B, Liu X, Morpurgo A F, Vandersypen L M K 2007 Nature Mater. 7 151
[10] Blake P, Brimicombe P D, Nair R R, Booth T J, Jiang D, Schedin F, Ponomarenko L A, Morozov S V, Gleeson H F, Hill E W, Geim A K, Novoselov K S 2008 Nano Lett. 8 1704
[11] Xia F, Mueller T, Lin Y M, Valdes-Garcia A, Avouris P 2009 Nature Nanotech. 4 839
[12] Dean C R, Young A F, Meric I, Lee C, Wang L, Sorgenfrei S, Watanabe K, Taniguchi T, Kim P, Shepard K L, Hone J 2010 Nature Nanotech. 5 722
[13] Lu X B, Zhang G Y 2015 Acta Phys. Sin. 64 077305 (in Chinese) [卢晓波, 张广宇 2015 物理学报 64 077305]
[14] Liu M X, Zhang Y F, Liu Z F 2015 Acta Phys. Sin. 64 078101 (in Chinese) [刘梦溪, 张艳锋, 刘忠范 2015 物理学报 64 078101]
[15] Zhang K, Zhang H, Cheng X 2016 Chin. Phys. B 25 037104
[16] Li G F, Hu J, Lv H, Cui Z, Hou X, Liu S, Du Y 2016 Chin. Phys. B 25 027304
[17] Jin C, Lin F, Suenaga K, Iijima S 2009 Phys. Rev. Lett. 102 195505
[18] Alem N, Erni R, Kisielowski C, Rossell M D, Gannett W, Zettl A 2009 Phys. Rev. B 80 155425
[19] Shi Y, Hamsen C, Jia X, Kim K K, Reina A, Hofmann M, Hsu A L, Zhang K, Li H, Juang Z Y, Dresselhaus M S, Li L J, Kong J 2010 Nano Lett. 10 4134
[20] Song L, Ci L, Lu H, Sorokin P B, Jin C, Ni J, Kvashnin A G, Kvashnin D G, Lou J, Yakobson B I, Ajayan P M 2010 Nano Lett. 10 3209
[21] Kim K K, Hsu A, Jia X, Kim S M, Shi Y, Hofmann M, Nezich D, Rodriguez-Nieva J F, Dresselhaus M, Palacios T, Kong J 2012 Nano Lett. 12 161
[22] Yin J, Yu J, Li X, Li J, Zhou J, Zhang Z, Guo W 2015 Small 11 4497
[23] Li X, Yin J, Zhou J, Guo W 2014 Nanotechnology 25 105701
[24] Radisavljevic B, Radenovic A, Brivio J, Giacometti V, Kis A 2011 Nature Nanotech. 6 147
[25] Ross J S, Wu S, Yu H, Ghimire N J, Jones A M, Aivazian G, Yan J Q, Mandrus D G, Xiao D, Yao W, Xu X D 2013 Nat. Commun. 4 1474
[26] Ma Y D, Dai Y, Guo M, Niu C W, Lu J B, Huang B B 2011 Phys. Chem. Chem. Phys. 13 15546
[27] Georgiou T, Jalil R, Belle B D, Britnell L, Gorbachev R V, Morozov S V, Kim Y J, Gholinia A, Haigh S J, Makarovsky O, Eaves L, Ponomarenko L A, Geim A K, Novoselov K S, Mishchenko A 2013 Nature Nanotech. 8 100
[28] Chiritescu C, Cahill D G, Nguyen N, Johnson D, Bodapati A, Keblinski P, Zschack P 2007 Science 135 351
[29] Fang H, Chuang S, Chang T C, Takei K, Takahashi T, Javey A 2012 Nano Lett. 12 3788
[30] Watanabe K, Taniguchi T, Kanda H 2004 Nature Mater. 3 404
[31] Kim K K, Hsu A, Jia X, Kim S M, Shi Y, Dresselhaus M, Palacios T, Kong J 2012 ACS Nano 6 8583
[32] Kubota Y, Watanabe K, Tsuda O, Taniguchi T 2007 Science 317 932
[33] Laskowski R, Blaha P, Gallauner T, Schwarz K 2007 Phys. Rev. Lett. 98 106802
[34] Brugger T, Gnther S, Wang B, Hugo Dil J, Bocquet M L, Osterwalder J, Wintterlin J, Greber T 2009 Phys. Rev. B 79 045407
[35] Sutter P, Lahiri J, Albrecht P, Sutter E 2011 ACS Nano 5 7303
[36] Nagashima A, Tejima N, Gamou Y, Kawai T, Oshima C 1995 Phys. Rev. B 51 4606
[37] Rokuta E, Hasegawa Y, Suzuki K, Gamou Y, Oshima C, Nagashima A 1997 Phys. Rev. Lett. 79 4609
[38] Auwrter W, Suter H U, Sachdev H, Greber T 2004 Chem. Mater. 16 343
[39] Schulz F, Drost R, Hmlinen S K, Demonchaux T, Seitsonen A P, Liljeroth P 2014 Phys. Rev. B 89 235429
[40] Mller F, Stwe K, Sachdev H 2005 Chem. Mater. 17 3464
[41] Morscher M, Corso M, Greber T, Osterwalder J 2006 Surf. Sci. 600 3280
[42] Corso M, Greber T, Osterwalder J 2005 Surf. Sci. 577 L78
[43] Preobrajenski A B, Vinogradov A S, Ng M L, Ćavar E, Westerstrm R, Mikkelsen A, Lundgren E, Mrtensson N 2007 Phys. Rev. B 75 245412
[44] Joshi S, Ecija D, Koitz R, Iannuzzi M, Seitsonen A P, Hutter J, Sachdev H, Vijayaraghavan S, Bischoff F, Seufert K, Barth J V, Auwrter W 2012 Nano Lett. 12 5821
[45] Tay R Y, Griep M H, Mallick G, Tsang S H, Singh R S, Tumlin T, Teo E H, Karna S P 2014 Nano Lett. 14 839
[46] Kim G, Jang A R, Jeong H Y, Lee Z, Kang D J, Shin H S 2013 Nano Lett. 13 1834
[47] Kidambi P R, Blume R, Kling J, Wagner J B, Baehtz C, Weatherup R S, Schloegl R, Bayer B C, Hofmann S 2014 Chem. Mater. 26 6380
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