578 research outputs found
Anti‐Stokes Photoluminescence of Monolayer WS2
Anti‐Stokes photoluminescence excitation of a WS2 monolayer flake between 10 and 300 K is reported herein. Even with continuous‐wave lasers at low power, the emission of the exciton at excitation 100 meV below its emission energy at room temperature is observed. A mechanism which involves the trions as the intermediate state is proposed, leading to an efficient up‐conversion process. In addition, it is demonstrated that phonons are the source of the additional energy needed by the system. Overall, the results provide evidence that anti‐Stokes luminescence in transition metal dichalcogenides is very efficient.EC/FP7/259286/EU/Characterizing and Controlling Carbon Nanomaterials/CCCANDFG, 53244630, EXC 315: Neue Materialien und Prozesse - Hierarchische Strukturbildung für funktionale BauteileDFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeTU Berlin, Open-Access-Mittel - 201
In-situ Raman study of laser-induced graphene oxidation
We present in-situ Raman measurements of laser-induced oxidation in
exfoliated single-layer graphene. By using high-power laser irradiation, we can
selectively and in a controlled way initiate the oxidation process and
investigate its evolution over time. Our results show that the laser-induced
oxidation process is divided into two separate stages, namely tensile strain
due to heating and subsequent -type doping due to oxygen binding. We discuss
the temporal evolution of the -mode ratio during oxidation and explain the
unexpected steady decrease of the defect-induced mode at long irradiation
times. Our results provide a deeper understanding of the oxidation process in
single-layer graphene and demonstrate the possibility of sub-m patterning
of graphene by an optical method.Comment: 5 pages, 4 figures [submitted as IWEPNM 2015 conference publication
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