AVS 63rd International Symposium & Exhibition
    Spectroscopic Ellipsometry Focus Topic Friday Sessions
       Session EL+AS+EM+MI+TF-FrM

Paper EL+AS+EM+MI+TF-FrM8
Conducting, Semi-Conducting and Insulating 2D-Materials Characterized by Spectroscopic Imaging Ellipsometry

Friday, November 11, 2016, 10:40 am, Room 104C

Session: Spectroscopic Ellipsometry: Novel Applications and Theoretical Approaches
Presenter: Matthias Duwe, Accurion GmbH, Germany
Authors: M.D. Duwe, Accurion GmbH, Germany
S. Funke, Accurion GmbH, Germany
U. Wurstbauer, Technical University of Munich, Germany
A. Matkovic, University of Belgrade, Serbia
A. Green, SUNY College of Nanoscale Science and Engineering
A. Molina-Mendoza, Universidad Autonoma de Madrid, Spain
A. Castellanos-Gomez, IMDEA Nanoscience, Spain
P.H. Thiesen, Accurion GmbH, Germany
Correspondent: Click to Email
Finding thin-film flakes of 2D-materials after the fabrication and identifying their layer thicknesses often is a challenging and time-consuming task. Here, we present various applications of spectroscopic imaging ellipsometry (SIE) to a variety of conducting, semi-conducting, and insulating 2D-Materials such as graphene, molybdenum disulfide (MoS2), hexagonal boron nitride, and black phosphorus. As a combination of polarization-contrast microscopy and spectroscopic ellipsometry, SIE measurements localize microscopic flakes of the 2D-materials, yield the samples’ optical dispersion functions, and determine the layer thicknesses.

Matkovic et al. [1] characterized monolayers of graphene by SIE, and they obtained the optical dispersion by Fano-resonance modelling. Using this dispersion, SIE offers a straightforward search for and identification of few-layer graphene flakes on various opaque or transparent substrates. As this flake search uses ellipsometric measurements, it depends far less on the used substrate compared to e.g. conventional light-microscopy. In a similar procedure, SIE identified monolayers of insulating hexagonal boron nitride, and it yielded the material‘s optical properties.

SIE measurements on MoS2 revealed the repercussion of the used substrate [2]. Ellipsometric contrast micrographs showed the lateral variation of the optical parameters for a structured flake. Spectroscopic measurements of the ellipsometric values (Ψ & Δ) obtained from selected regions of interest on the flake yielded the optical dispersion for the in-plane and out-of-plane components of the dielectric function in the visible spectral range.

Finally, we will present imaging Mueller-matrix ellipsometry (IMME) for the characterization of thin-film flakes of the semi-conducting 2D-material black phosphorus. In contrast to MoS2, black phosphorus also features an optical in-plane anisotropy. IMME-micrographs easily reveal this anisotropy as the Mueller matrix's off-diagonal blocks deviate from zero. By performing spectroscopic Mueller-Matrix mapping and rotational Mueller-matrix measurements combined with atomic force microscopy, we obtained the flake’s layer thickness, the orientations of the optical axes, and the material's optical properties in the visible spectral range.

[1] A. Matković, A. Beltaos, M. Milićević, U. Ralević, B. Vasić, D. Jovanović, and R. Gajić, Spectroscopic imaging ellipsometry and Fano resonance modeling of graphene, J. Appl. Phys., 112 123523, (2012)

[2] S.Funke, E. Parzinger, B. Miller, P. H. Thiesen, A.W. Holleitner, U. Wurstbauer, Imaging Ellipsometry of Mono- to Multilayer ofMoS2 on Tranparent Sapphire Substrate, Manuscript in preperation