Yimin Yang

Polarized Raman scattering of Ge nanocrystals embedded in a-SiO2

Ge nanocrystals randomly dispersed in amorphous silica films were prepared by magnetron cosputtering and postannealing to investigate the polarization characteristics of Raman scattering from the Ge nanocrystals. Two acoustic vibrational modes observed in the low-frequency Raman spectra were shown by theoretical calculation based on the isotropic continuum elasticity theory to be the torsional modes activated by elastic anisotropy and the nonspherical shape of the Ge nanocrystals. Enhanced depolarized scattering was also observed from the optical phonons of the Ge nanocrystals.

Modulation of surface-enhanced Raman spectra by depth selective excitation of embedded indium tin oxide nanoisland arrays

Embedded transparent conducting indium tin oxide (ITO) nanoisland arrays were prepared by pulsed laser deposition of ITO films on roughened Si templates and post-annealing to investigate the surface-enhanced Raman scattering activities. Considerable Raman enhancement of a rhodamine 6G probe during Ar+ laser excitation was observed and modulated by the thickness of the ITO film due to the exponentially decaying field of the localized surface plasmon polaritons at the interface. Because the Raman-enhancing functional layer is protected at the ITO/Si interface, this system is reusable and also believed to be immune to contamination and other surface activities.

Effect of absorption to nanopore on optical properties of conjugated polymers in porous anode alumina

The optical properties of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) in the nanopores of porous anodic alumina (PAA) are investigated using temperature-dependent photoluminescence (PL) spectra. The PL spectrum of MEH-PPV in PAA becomes wide because the polymer chains absorb to the nanopore walls to restrict excitation energy transfer. Unlike the MEH-PPV film, the PL peak wavelength of MEH-PPV in PAA is independent of temperature in the range of 80 to 290 K. The influence of temperature on the emission bandwidth of MEH-PPV in the nanopores is obviously less than that in the film because temperature-dependent inhomogeneous broadening is suppressed by the absorption effect.

Band-gap-dependent emissions from conjugated polymers coupled silver nanocap array

The optical properties of poly(2,5-dioctyloxy-p-phenylene) (PPP) and poly[3-(2,5,8-trioxanonyl) thiophene] (P3TT) coupled silver nanocap array have been investigated. The absorption spectrum of P3TT and the emission spectrum of PPP match the absorption of the silver nanocap array. Plasmon energy transfer occurs from the silver nanocap array to P3TT or from PPP to the silver nanocap array, resulting in the largely increased or decreased photoluminescence (PL), respectively. The PL enhancement of the P3TT coupled silver nanocap array is more than 9-fold; whereas the PL intensity of the PPP coupled silver nanocap array is less than one-tenth of the PPP film.

Interaction between indium tin oxide nanoparticles and cytochrome c: A surface-enhanced Raman scattering and absorption spectroscopic study

Indium-tin-oxide (ITO) nanoparticles were annealed in vacuum or reducing atmosphere to obtain different surface structures and investigate their influence on the adsorptive character and conformation of cytochrome c (Cyt c) molecule. Annealing-induced morphometric or structural changes of ITO nanoparticles were characterized by instruments of transmission electron microscopy, x-ray diffraction, and Raman scattering. Semiconductor ITO nanoparticle-enhanced Raman scattering of Cyt c was observed and the enhanced efficiency was found to closely depend on the surface structures which control the adsorbance of buffer anions needed for Cyt c loading. Direct electron transfer between Cyt c and ITO surface at the moment of molecular elastic collision was found and a reverse electron transfer process for O-terminated surface and metal-terminated surface was observed, according to absorption spectroscopic measurement on the residual solution.

Modulating emission from acceptor in donor-acceptor diblock copolymers by plasmon resonance energy transfer

We have investigated the optical properties of all-conjugated block copolymers, poly (2,5-dioctyloxy-p-phenylene)-b-poly[3-(2,5,8-trioxanonyl) thiophene] (PPP-b-P3TT), coupled silver nanocap array. The photoluminescence (PL) enhancement of the acceptor is increased with the mole fraction of the P3TT block in the coupled copolymer. The emission from the PPP blocks and the absorption of the P3TT blocks match the plasmon resonance frequency of the silver nanocap array. The emission from the PPP blocks is absorbed by the silver nanocap array to propagate surface plasmons or surface plasmon polaritons near the interfaces of the conjugated polymer/silver nanocap array, whose energies can be transferred to the P3TT blocks. As a result, more than 14-fold PL enhancement of the P3TT blocks has been observed in the coupled copolymer by photoexcitation at the absorption maximum of the PPP blocks.

Enhanced emission from the acceptor in all-conjugated diblock copolymers due to spatial effect of nanopores

We have investigated the emission properties of all-conjugated diblock copolymers, poly(2,5-dioctyloxy-p-phenylene)-b-poly[3-(2,5,8-trioxanonyl)thiophene] (PPP-b-P3TT), in the nanopores of porous anodic alumina membrane. In contrast with the copolymer solution and film, the relative intensity of the emission from the P3TT blocks in the copolymer in the nanopores is largely increased for excitation at the absorption maximum of the PPP blocks. Different from the copolymer film, the relative photoluminescence (PL) intensity of the P3TT blocks is obviously increased with the increase of the P3TT blocks in the copolymers in the nanopores. The separated copolymer chains and the efficient resonance energy transfer caused by spatial limit contribute to higher relative PL intensity of the P3TT blocks in the copolymers in the nanopores than those in the solutions and films.