Abstract
Quantum systems in confined geometries are host to novel physical phenomena. Examples include quantum Hall systems in semiconductors1 and Dirac electrons in graphene2. Interest in such systems has also been intensified by the recent discovery of a large enhancement in photoluminescence quantum efficiency3,4,5,6,7 and a potential route to valleytronics6,7,8 in atomically thin layers of transition metal dichalcogenides, MX2 (M = Mo, W; X = S, Se, Te), which are closely related to the indirect-to-direct bandgap transition in monolayers9,10,11,12. Here, we report the first direct observation of the transition from indirect to direct bandgap in monolayer samples by using angle-resolved photoemission spectroscopy on high-quality thin films of MoSe2 with variable thickness, grown by molecular beam epitaxy. The band structure measured experimentally indicates a stronger tendency of monolayer MoSe2 towards a direct bandgap, as well as a larger gap size, than theoretically predicted. Moreover, our finding of a significant spin-splitting of ∼180 meV at the valence band maximum of a monolayer MoSe2 film could expand its possible application to spintronic devices.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Klitzing, K. v., Dorda, G. & Pepper, M. New method for high-accuracy determination of the fine-structure constant based on quantized Hall resistance. Phys. Rev. Lett. 45, 494–497 (1980).
Geim, A. K. Graphene: status and prospects. Science 324, 1530–1534 (2009).
Mak, K. F. et al. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).
Tongay, S. et al. Thermally driven crossover from indirect toward direct bandgap in 2D semiconductors: MoSe2 versus Mos2 . Nano Lett. 12, 5576–5580 (2012).
Splendiani, A. et al. Emerging photoluminescence in monolayer MoS2 . Nano Lett. 10, 1271–1275 (2010).
Cao, T. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nature Commun. 3, 887 (2012).
Zeng, H. et al. Valley polarization in MoS2 monolayers by optical pumping. Nature Nanotech. 7, 490–493 (2012).
Xiao, D. et al. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).
Ellis, J. K., Lucero, M. J. & Scuseria, G. E. The indirect to direct band gap transition in multilayered MoS2 as predicted by screened hybrid density functional theory. Appl. Phys. Lett. 99, 261908 (2011).
Zhu, Z. Y., Cheng, Y. C. & Scwingenshlögl, U. Giant spin–orbit-induced spin splitting in two-dimensional transition-metal dichalcogenide semiconductors. Phys. Rev. B 84, 153402 (2011).
Cheiwchanchamnangij, T. & Lambrecht, W. R. L. Quasiparticle band structure calculation of monolayer, bilayer, and bulk MoS2 . Phys. Rev. B 85, 205302 (2012).
Kumar, A. & Ahluwalia, P. K. Electronic structure of transition metal dichalcogenides monolayers 1H-MX2 (M=Mo, W; X = S, Se, Te) from ab-initio theory: new direct band gap semiconductors. Eur. Phys. J. B 85, 186 (2012).
Balendhran, S. et al. Two-dimensional molybdenum trioxide and dichalcogenides. Adv. Funct. Mater. 23, 3952–3970 (2013).
Radisavljevic, B. et al. Single-layer MoS2 transistors. Nature Nanotech. 6, 147–150 (2011).
Larentis, S., Fallahazad, B. & Tutuc, E. Field-effect transistors and intrinsic mobility in ultra-thin MoSe2 layers. Appl. Phys. Lett. 101, 223104 (2012).
Lee, C. et al. Frictional characteristics of atomically thin sheets. Science 328, 76–80 (2010).
Laursen, A. B., Kegnæs, S., Dahl, S. & Chorkendorff, I. Molybdenum sulfides—efficient and viable materials for electro- and photoelectrocatalytic hydrogen evolution. Energy Environ. Sci. 5, 5577–5591 (2012).
Yoon, Y., Ganapathi, K. & Salahuddin, S. How good can monolayer MoS2 transistors be? Nano Lett. 11, 3768–3773 (2011).
Chang, K. & Chen, W. In situ synthesis of MoS2/graphene nanosheet composites with extraordinarily high electrochemical performance for lithium ion batteries. Chem. Commun. 47, 4252 (2011).
Liu, K-K. et al. Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates. Nano Lett. 12, 1538–1544 (2012).
Shi, Y. et al. Van der Waals epitaxy of MoS2 layers using graphene as growth templates. Nano Lett. 12, 2784–2791 (2012).
Wang, Q. et al. Large-scale uniform bilayer graphene prepared by vacuum graphitization of 6H-SiC(0001) substrates. J. Phys. 25, 095002 (2013).
Zhang, Y. et al. Crossover of the three-dimensional topological insulator Bi2Se3 to the two-dimensional limit. Nature Phys. 6, 584–588 (2010).
Koma, A. Van der Waals epitaxy—a new epitaxial growth method for a highly lattice-mismatched system. Thin Solid Films 216, 72–76 (1992).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Tsai, W-F. et al. Gated silicene as a tunable source of nearly 100% spin-polarized electrons. Nature Commun. 4, 1500 (2013).
Sun, L. et al. Spin–orbit splitting in single-layer MoS2 revealed by triply resonant Raman scattering. Phys. Rev. Lett. 111, 126801 (2013).
Hasan, M. Z. & Kane, C. L. Colloquium: topological insulators. Rev. Mod. Phys. 82, 3045–3067 (2010).
Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).
Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).
Acknowledgements
The work at the ALS is supported by the US Department of Energy (DoE) Office of Basic Energy Science contract no. DE-AC02-05CH11231. The work at the Stanford Institute for Materials and Energy Sciences and Stanford University is supported by the US DoE Office of Basic Energy Science under contract no. DE-AC02-76SF00515. The work at Oxford University is supported from a Defense Advanced Research Projects Agency MesoDynamic Architectures (DARPA MESO) project (no. 187 N66001-11-1-4105). The work at Northeastern University is supported by the US DoE Office of Basic Energy Sciences under contract no. DE-FG02-07ER46352 and benefited from Northeastern University's Advanced Scientific Computation Center (ASCC), theory support at the Advanced Light Source, Berkeley, and the allocation of time at the National Energy Research Scientific Computing Center (NERSC) supercomputing centre through DoE grant no. DE-AC02-05CH11231. T.R.C. and H.T.J. are supported by the National Science Council, Taiwan. H.T.J. also thanks National Center for High-Performance Computing (NCHC), Computer and Information Network Center (CINC) – National Taiwan University (NTU) and National Center for Theoretical Sciences (NCTS), Taiwan, for technical support.
Author information
Authors and Affiliations
Contributions
Y.Z. led the thin-film growth effort with F.S., J.L., R.M. and S.K.M., performed ARPES measurements with B.Z., Z.L. and S.K.M., and analysed the data. Y.Z., H.L. and S.K.M. wrote the paper with suggestions and comments by A.B. and Z.X.S. Y.T.C. and Y.H. characterized samples with Raman spectroscopy and AFM. T.R.C., H.L., H.T.J. and A.B. provided theoretical support. S.K.M., Y.L.C., Z.H., A.B. and Z.X.S. were responsible for project direction, planning and infrastructure.
Corresponding authors
Ethics declarations
Competing interests
The authors declare no competing financial interests.
Supplementary information
Supplementary information
Supplementary Information (PDF 1554 kb)
Rights and permissions
About this article
Cite this article
Zhang, Y., Chang, TR., Zhou, B. et al. Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2. Nature Nanotech 9, 111–115 (2014). https://doi.org/10.1038/nnano.2013.277
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/nnano.2013.277
This article is cited by
-
Excitonic devices based on two-dimensional transition metal dichalcogenides van der Waals heterostructures
Frontiers of Chemical Science and Engineering (2024)
-
Exploring modern developments in diverse 2D photocatalysts for water oxidation
Journal of Porous Materials (2024)
-
From Stoner to local moment magnetism in atomically thin Cr2Te3
Nature Communications (2023)
-
Valley-optical absorption in planar transition metal dichalcogenide superlattices
Scientific Reports (2023)
-
Curvature-controlled band alignment transition in 1D van der Waals heterostructures
npj Computational Materials (2023)