A tubular array of TiO2-nanotubes on a Ti substrate was used as a support for an Ag sputter-deposited layer intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples of Ag/TiO2-nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the TiO2-nanotube/Ti substrates covered with the Ag deposit. In addition, SERS spectra on a bulk electrochemically-roughened Ag reference substrate, were also measured.The SERS activity of the composite samples was strongly dependent on the amount of Ag deposit and, in some cases, was even higher than that for the Ag reference substrate. The SERS intensity vs. electrode potential dependences measured were interpreted in terms of the modified electronic structure of the Ag deposits due to the interaction of the Ag clusters with the TiO2-nanotube/Ti substrate. 相似文献
Tubular arrays of TiO2 nanotubes (ranging in diameter from 40 to 110 nm) on a Ti substrate were used as a support for Ag, Au or Cu deposits obtained by the sputter deposition technique, where the amount of metal varied from 0.01 to 0.2 mg/cm2. Those composite supports were intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the metal-covered TiO2 nanotube/Ti substrates. In addition, SERS spectra on a bulk standard activated Ag, Au and Cu substrates were also measured. The SERS activity of the composite samples was strongly dependent on the amount of metal deposit, e.g. at and above 0.06 mg Ag/cm2, the intensity of SERS signal was even higher than that for the Ag reference substrate. The high activity of these composites is mainly a result of their specific morphology. The high SERS sensitivity on the surface morphology of the substrate made it possible to monitor very small temporal changes in the Ag metal clusters. This rearrangement was not detectable with microscopic (SEM) or microanalytical (AES) methods. The SERS activity of Au or Cu clusters was distinctly lower than those of Ag. The spectral differences exhibited by the three kinds of composites as compared to the reference metal samples are discussed. 相似文献
SERS spectra of pyridine adsorbed on various kinds of vacuum evaporated (10?5 Torr) metals (Ag, Au, Ni, Pd, Pt, Ti and Co) and on single crystals of semiconductors (NiO and TiO2) were obtained at room temperature. The peak frequencies as shifted from those of free pyridine are assigned to the bands of N-bonded pyridine (chemisorbed pyridine). The λ0 dependence varied remarkably from metal to metal. The peak frequency and the λ0 dependence for the pyridine adsorbed on NiO or TiO2 are in good agreement with those on Ni or Ti, respectively, showing the chemical bonding between the N atom and the Ni or Ti atom. The effects of background and of polarization on the SERS spectra were examined in detail, thus revealing the orientation of the adsorbed molecules. Carbon monoxide chemisorbed on Ag was measured by infrared specular reflection as well as by SERS. The results indicate that chemisorbed species on the same substrate do not always give SERS. The SERS spectra obtained are well interpreted as being due to the mechanism of resonance Raman scattering via charge transfer excitation of the adsorbent-adsorbate interaction. 相似文献
We have proposed dye-sensitized solar cells (DSSCs) with trench-type TiO2 nanotube structure to improve the low device efficiency of conventional TiO2 nanotube DSSCs using Ti substrate. Compared to the conventional standing-type TiO2 nanotube structure based DSSCs, the trench-type TiO2 nanotube structure based DSSCs have shown an improvement of device efficiency of approximately 40% due to the large increase of Jsc. In the trench-type TiO2 nanotube structure, the contact area between the TiO2 nanotube sidewall and the Ti substrate is significantly increased. This increase of contact area provides more charge transport paths than exist in the conventional standing-type TiO2 nanotube structure and reduces the electrical resistance between the Ti substrate and the TiO2 nanotubes. Therefore, the remarkable increase of Jsc is the result of the charge collection efficiency, which is improved due to the increase of contact area between the TiO2 nanotube sidewall and the Ti substrate in the trench-type TiO2 nanotube structure. The fabrication of the trench-type TiO2 nanotube structure is an effective manufacturing process for improving the device efficiency of TiO2 nanotube based DSSCs using Ti substrate. DSSCs having an 11.9 μm thick trench-type TiO2 nanotube structure have shown an efficiency of 5.74%. 相似文献
Very thin films of TiO2 and Ti2O3 were deposited by evaporation on Ag, on silver oxidized by an oxygen plasma and on Pt. Depending on the coverage, there were changes in the values of the binding energy (BE) and the Auger parameter (α′) of O and Ti. These shifts occur in the opposite direction with respect to that previously found for TiO2 supported on insulators. Among others, reasons for these shifts are the different relaxation energy of photoholes and the occurrence of charge transfer processes at the metal oxide/metal interface. UV-visible absorption spectra of thin films of TiO2Ag composites have shown a narrowing in the gap energy (Eg) of the oxide in respect to bulk titania. This observation shows the existence of a correlation between Eg and α′ when TiO2 is supported on a metal surface. The Auger parameter of O and Ti is also sensitive to the intercalation of TiO2 within a “sandwich” structure of SiO2 and Ag, and the values found for the spectroscopic parameters are intermediate between those of TiO2 supported on Ag and SiO2. This result opens up the possibility of modulating the electronic properties of thin layers of TiO2 by interaction with other materials. 相似文献
We synthesized titanium dioxide (TiO2) and nitrogen-doped TiO2 nanoparticles (N-TiO2 NPs) via a sol-hydrothermal method using ammonium chloride (NH4Cl) as the nitrogen (N) source. Furthermore, an N-TiO2/4-mercaptobenzoic acid (4-MBA)/silver (Ag) nanocomplex served as an active substrate for surface-enhanced Raman scattering (SERS) and was prepared by self-assembly. During SERS, the Raman signals of 4-MBA of the N-TiO2/MBA/Ag nanocomplexes exhibited higher intensity and sensitivity than pure TiO2/MBA/Ag, with 1% N doping in N-TiO2, producing the strongest Raman signals. We characterized the N-TiO2 hybrid materials by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectra. N doping did not influence the phase of the TiO2 crystal. The doped N entered into the crystal lattice of the TiO2, replacing some oxygen (O) to form Ti-O-N or Ti-N-O linkage. The results indicated that an appropriate amount of N doping could enhance the SERS performance of the TiO2 SERS substrate via N substitution doping. These doping forms were beneficial to the molecular charge transfer (CT), and this resulted in improved SERS performance for N-doped TiO2 NPs. We attributed this improvement to the formation of N-doping energy levels that were beneficial to the process of TiO2 to MBA molecule CT. This work not only enriched the nonmetal-doped CT mechanism in SERS but also provided several reference values for practical applications.
Graphical abstract N-doped TiO2 nanoparticles were synthesized. Whereafter, N-TiO2/MBA/Ag nanocomplexes were prepared and served as a SERS-active substrate. An appropriate amount of N doping can enhance the SERS properties of TiO2 SERS-active substrate by nitrogen substitution doping. The nonmetal doping TiO2-to-molecule CT mechanism and the synergistic effect in N-TiO2/MBA/Ag charge transfer systems have been studied.