The complete characterization of novel electropolymerizable organometallic complexes is presented. These are newly synthesized cyclometalated complexes of general formula (PPy)M(O ∧ N)(n) (H(PPy) = 2-phenylpyridine, M = Pd(II) or Pt(II), H(O ∧ N)(n) = Schiff base). Polymeric thin films have been obtained from these complexes by electropolymerization of the triphenylamino group grafted onto the H(O ∧ N)(n) ancillary ligand. The redox behavior and the photoconductivity of both of the monomers (PPy)M(O ∧ N)(n) and the electropolymerized species have been investigated. The polymeric films of (PPy)M(O ∧ N)(n) have shown a very significant enhancement of photoconductivity when compared to their monomeric amorphous counterparts. The high stability of the obtained films strongly suggests that electropolymerization of cyclometalated complexes represents a viable deposition technique of quality thin films with improved photoconduction properties, hence opening the door to a new class of materials with suitable properties for optoelectronic applications.
Plasmonic quasi-periodic structures are well-known to exhibit several surprising phenomena with respect to their periodic counterparts, due to their long-range order and higher rotational symmetry. Thanks to their specific geometrical arrangement, plasmonic quasi-crystals offer unique possibilities in tailoring the coupling and propagation of surface plasmons through their lattice, a scenario in which a plethora of fascinating phenomena can take place. In this paper we investigate the extraordinary transmission phenomenon occurring in specifically patterned Thue-Morse nanocavities, demonstrating noticeable enhanced transmission, directly revealed by near-field optical experiments, performed by means of a scanning near-field optical microscope (SNOM). SNOM further provides an intuitive picture of confined plasmon modes inside the nanocavities and confirms that localization of plasmon modes is based on size and depth of nanocavities, while cross talk between close cavities via propagating plasmons holds the polarization response of patterned quasi-crystals. Our performed numerical simulations are in good agreement with the experimental results. Thus, the control on cavity size and incident polarization can be used to alter the intensity and spatial properties of confined cavity modes in such structures, which can be exploited in order to design a plasmonic device with customized optical properties and desired functionalities, to be used for several applications in quantum plasmonics.
intriguing opportunity. HMMs are uniaxial structures manifesting a hyperbolic dispersion relation whose application range spans from hyperlensing to extreme biosensing. [13][14][15][16][17][18][19][20][21][22][23][24] In order to describe their optical constants, it is convenient to homogenize the dielectric permittivity of HMMs by using the effective medium theory (EMT). If the dimensions of the fundamental components of the HMM, that in our case consists of alternated metal/dielectric layer pairs, are chosen to be deeply subwavelength, a uniaxial anisotropy arises, due to the specific periodic arrangement, with the appearance of two distinct values of dielectric permittivity, one parallel (ε || ) and one perpendicular (ε ⊥ ) to the plane of the layersHere t D and t M are the dielectric and metal thickness, respectively, and ε D and ε M their relative dielectric permittivities. Equation (1) reveals that ε || can vanish at a specific wavelength where (ε D /ε M ) = -(t M /t D ). In the resulting regime, known as epsilon-near-zero (ε NZ ), many fascinating phenomena can occur. [25][26][27][28] Unfortunately, once the fundamental componentsThe quest for unconventional optical materials finds natural answers in the field of plasmonics. Here, special composites can manifest singularities in their dielectric permittivity. The so-called epsilon-near-zero (ε NZ ) condition is typically encountered in artificial materials called hyperbolic metamaterials (HMMs). Unfortunately, tuning the HMMs ε NZ is still challenging. Here it is demonstrated how the ε NZ frequency of an HMM can be reversibly tuned via thermally induced water absorption/desorption. The key element is a dielectric hygroscopic material, consisting of a blend of a polymer, a sol-gel unsintered TiO 2 , and an organic dye. Due to the hygroscopic nature of unsintered TiO 2 , an increase of temperature induces a reversible physical contraction of the thickness of the dielectric blend, as well as an increase of refractive index. This causes a remarkable 45 nm shift of the absorption peak of the embedded dye, acting as a chromatic label. When such a blend is embedded in an HMM, a reversible thermal tuning of the overall optical response, as well as an epsilon-near-zero wavelength shift by about 25 nm, is induced. The remarkable tuning range shown here, besides obvious HMM-based temperature sensing applications, paves the way toward a plethora of new functions in which tunable ε NZ materials are needed.
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