"A Raman scattering and photoluminescence in single

"A Raman scattering and photoluminescence in singleand few-layered WS2 films "
Impartido por:
Humberto Rodríguez Gutiérrez
Department of Physics & Astronomy
University of Louisville, KY
Día:
Martes, 11 de Marzo de 2014
Hora:
12:00 horas
Lugar:
Sala Polivalente del Departamento de Física Aplicada
Facultad de Ciencias, Fase II (2ª Pta.)
ABSTRACT
Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals
with attractive physical properties different from their bulk layered counterpart. The spotlight of
this presentation will be the optical behavior of WS2 monolayers with triangular morphologies.
The Raman response as well as the photoluminescence (PL) as a function of the number of SW-S layers will be discussed. The PL of layered WS2 becomes weaker with the increase of SW-S layers number due to a transition from direct (in a monolayer) to indirect band gap (in
multilayers). The edges of WS2 monolayers exhibit PL signals with extraordinary intensity,
around 25 times stronger than the platelets center. The structure and composition of the platelet
edges appear to be critical for the PL enhancement effect. Raman scattering from single- and
few-layered WS2 was also studied as a function of the number of S-W-S layers and the
excitation laser wavelength in the visible range (488, 514 and 647 nm). For the three excitation
wavelengths used in this study, the frequency of the A1g(Γ) phonon mode monotonically
decreases with the number of layers, while the E12g(Γ) frequency increases. For single-layer
WS2, 514.5 nm excitation induces a second-order Raman resonance for the longitudinal
acoustic mode at the M point. This resonance, arises do to a coupling between the electronic
band structure and lattice vibrations, an effect not previously seen in any single-layered metal
dichalcogenide. Tuning the excitation wavelength this mechanism may be applicable in
characterizing the structural, electronic and vibrational properties of other layered systems.
ORGANIZA:
Departamento de Física Aplicada
Vicerrectorado de Extensión Universitaria