In this study, we report on the thermal oxidation of few-layer ZrS 3 flakes as a function of temperature and heating time. We characterize the changes to the material crystal structure caused by the thermal treatment using atomic force microscopy, transmission electron microscopy, Raman spectroscopy, and electrical transport measurements and link these results to the observed changes in optical contrast for on-substrate flakes. Importantly, we observe a very strong photoluminescence emission enhancement in the heated samples, with intensities comparable to those of direct-gap monolayer MoS 2 . We attribute this enhancement to mid-gap states in the thermally synthesized oxides of zirconium which form on the flake surface. We show that this emission is isotropic, unlike that of the untreated ZrS 3 , which unlocks an additional degree of freedom to the modulation of the optoelectronic properties of quasi-one-dimensional van der Waals materials.
Polydiacetylene (PDA) vesicles with various cross-linking degree were prepared by adding different quantity of ethylenediamine. Ag nanoparticles were added into above systems to form the cross-linked PDA/Ag composite vesicles. UV-vis spectra and transmission electron microscopy (TEM) were used to confirm the formation of the cross-linked PDA/Ag composite vesicles. Their thirdorder nonlinear optical (NLO) properties were investigated in detail. A pronounced enhancement of the third-order nonlinear optical susceptibility (3) was observed with increasing of the cross-linking degree, which should be ascribed to the coupling effect of strong local field near the adjacent PDA/Ag composite vesicles.
INTRODUCTIONAs the development of optical communication networks progresses, the demand for ultrafast optical switching with terahertz operation is rising. Nonlinear optical (NLO) materials with large third-order nonlinear susceptibility [1] are indispensable to these photonic devices. -Conjugated organic polymers, such as polyacetylene and polydiacetylene (PDA), are superior to inorganic systems in terms of chemical modification and high-speed responses for NLO materials. Among these organic NLO materials, PDA could be chemically tailored by means of polymerization reaction in a solid phase of a substituted mono diacetylene [2][3][4]. However, the magnitude of effective third-order NLO susceptibility Re (3) for PDA based materials is still not sufficient for device applications.It is worth noting that metallic nanostructures exhibited the enhancement of NLO properties induced by the quantum confinement effect and surface plasmons (SPs) effect [5][6][7]. Recently, various types of nonlinear nano-optical devices have been studied [8,9], especially the optical bistable devices, which have attracted much interest for their great applications in signal processing. According to the local field enhancement under the surface plasmon resonance condition, larger third-order nonlinearity of PDA composite films has been observed in the presence of metal or semiconductor nanoparticles [10][11][12][13]. Neeves and Birnboim theoretically predicted that the core-shell-type structure consisting of a PDA core and a metal nano-shell exhibited markedly large effective (3) ( ) values [14], which encouraged people to develop many novel types of core-shell-type nanoparticles [15][16][17][18][19]. The enhancement in
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