Optical nanocircuit consisting of an Ag nanowire placed in feed-gaps of receiving and transmitting bowtie antennas pairs was investigated to realize an enhanced plasmon emission with a factor of 45 compared to the single Ag nanowire. The maximum emission was demonstrated sensitively depends on the length of nanowire, the arm-length of bowtie antennas and the incident angle of optical excitation. This enhanced plasmon emission was replicated by finite-difference time-domain simulations and explored with analytical calculations using the impedance matching theory at optical frequency.

We have probed single surface states and the involved interfacial charge transfer coupling on the TiO2 surface using a tip-enhanced near-field topographic-spectroscopic imaging analysis on a Niobium-doped rutile TiO2 (110) surface. The nanoscale optical images of single surface states are visualized by the strong exciton plasmon-polariton coupling localized at the sub-domain boundaries with a spatial resolution of ~ 15 nm (far beyond the optical diffraction limit). We suggest that the abundant surface states in the doped TiO2 generate excitons under laser excitation which are strongly coupled to the surface plasmon-polaritons of the Au tip. Moreover, the interfacial electronic molecule-substrate coupling has been characterized by probing the molecule-perturbed surface states distribution and the associated specific Raman vibrational modes. The imaging and characterization of the surface states and their distributions on TiO2 surfaces at nanoscale are critically relevant to a deep understanding of interfacial electron transfer dynamics and energetics involving in solar energy conversion, photocatalysis, and mechanistic understanding of surface enhanced Raman scattering spectroscopy.

We targeted at investigating the effect of the additive 1,8-octanedithiol (ODT) on the nanometer scale morphology and local photophysical properties of low band-gap polymer blends, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’] dithiophene) -alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Phase separations of the PCPDTBT:PCBM blend film induced by ODT were visualized by the morphologic changes from fibril-shaped features to spherical bumps, by the dramatically increased photoluminescence (PL) emission from PCPDTBT that was originally largely quenched, by the fluctuations of spectral features at different locations of the sample surface. The correlations between the morphology and the local photophysical properties of the blend film with/without ODT at both the micrometer and nanometer scales were revealed by the confocal and high-resolution near-field spectroscopic mapping technique.

Tip-enhanced near-field optical images and correlated topographic images of an organic semiconductor
film (diindenoperylene,DIP) on Si have been recorded with high optical contrast and high spatial
resolution (17nm) using a parabolic mirror with a high numerical aperture for tip illumination and signal
collection.The DIP molecular domain boundaries being one to four molecular layers (1.5–6nm) high are
resolved topographically by a shear-force scanning tip and optically by simultaneously recording the
6x1E5 times enhanced photoluminescence(PL).The excitation is 4x1E4 times enhanced and the
intrinsically weak PL-yield of the DIP-film is 15-fold enhanced by the tip.The Raman spectra indicate an
upright orientation of the DIP molecules.The enhanced PL contrast results from the local film
morphology via stronger coupling between the tip plasmon and the exciton-polariton in the DIP film.

Confocal and near-field spectroscopic mapping techniques are used to investigate the interplay between morphology, molecular distribution and photoluminescence (PL) quenching efficiencies in P3HT:PCBM blend films which have been annealed at 140 °C for different time. The relevant photophysical information from the blend solar cell films with 10 nm spatial resolution is achieved.

A versatile and efficient tip-enhanced spectroscopic imaging technique based on a parabolic mirror (PM) assisted near-field optical microscope is demonstrated. The replacement of the conventional objective lens with a parabolic mirror allows the non-restricted investigation of sample materials regarding their opacity. In addition, an improved signal collection efficiency and effective excitation of the longitudinal plasmonic oscillation in the tip apex are obtained. The capabilities of PM-assisted tip-enhanced Raman (TER) and photoluminescence (PL) imaging in distinguishing the individual domains made of different chemical components in poly (3-hexythiophene)/[6, 6]-penyl-C61 butyric acid methyl ester (P3HT/PCBM) solar cell blend film and in the investigation of the plasmonic properties of geometrically well-defined Au cones are demonstrated.

The poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) organic films are widely employed as electronic donor and acceptor in the field of organic film solar cell because of their high photovoltaic conversion efficiency. A home-built parabolic mirror assisted confocal and apertureless near-field optical microscope was used to investigate the degradation behavior of the film and to distinguish the donor and acceptor domains both topographically and optically. Under ambient condition, the degradation rates are decreased in the sequence of pristine P3HT, blend P3HT:PCBM film and pristine PCBM. N2 protection dramatically slows down the film degradation rate. Using confocal spectroscopic mapping, we are able to distinguish the local distributions of P3HT and PCBM. Micrometer PCBM aggregates were observed due to the thermal annealing process. Our experimental methods show the possibility to investigate morphology and the photochemistry properties of the organic solar cell films with high spatial resolution.