Optoelectronic Performance Of Plasmonic And Organic Semiconductor Micro-Nanostructures

Surface plasmon is a resonance mode generated by the collective oscillation of the free electrons on the surface or inside micro-or nano-structured metals under excitation by electromagnetic fields.It has a series of novel photophysical properties,which may include enhancement of selective optical scattering/absorption and local electromagnetic fields.Therefore,plasmonic micro-and nano-structures can be widely used in surface-enhanced Raman scattering(SERS),chemical or biological sensors,and so on.In addition,metallic photonic structures can be incorporated into organic semiconductor light-emitting devices to improve performance and efficiency.This thesis focuses on the preparation of plasmonic and organic semiconductor micro-and nano-structures and the involved optoelectronic effects.The main contents include:(1)Preparation of randomly distributed dual-phase plasmonic micronanostructuresThe phase-separation pattern of the blend film of two polymeric semiconductors F8BT/PFB is utilized as a template for the preparation of a randomly distributed dual phase gold nanoisland structure.Laser irradiation induced crosslinking of F8 BT molecules selectively,thus,removal of the un-crosslinked PFB molecules leads to the liftoff and solidification of the phase-separation pattern.After metallization of this pattern,dual-phase gold nanoisland structures are achieved to distribute randomly.Strong localized surface plasmon resonance is observed in the spectral range from 400 nm to 1.7 ?m.Moreover,the dual-phase performance with plasmon resonance in the visible and near-infrared spectral regions can be used to improve the performance of random lasers and photovoltaic devices.(2)Direct writing of SERS substrates using femtosecond laser pulsesLarge-area randomly distributed gold nanoisland structures are produced by the strong interaction between femtosecond laser pulses and the thin film of colloidal gold nanoparticles.This structure consists of irregularly shaped and sharp-edged gold nanoparticle aggregates with specially extruding features,meanwhile,a large number of three-dimensional gold nanoparticle stacks are produced.Advantages of such configurations lie in the production of high density of hot spots,which can significantly improve the SERS performance.The enhancement factor of such SERS substrates prepared using femtosecond laser writing is increased by three orders of magnitude compared to ordinary heating treatment process.Furthermore,the relative standard deviation for the intensities of the SERS signals was measured to be 5.1% for a largearea distribution,indicating highly homogeneous SERS performance and excellent potentials for practical applications.(3)Periodical arrays of optically pumped organic semiconductor lasers and light emitting diodes(OLEDs)based on distributed Bragg reflector(DBR)microcavitiesA binary grating of distributed Bragg reflector(DBR)microcavity structures are produced by laser interference lithography and UV photolithography.Such structures are applied successfully in the construction of a periodical array of optically pumped organic semiconductor lasers,where low-threshold oscillation is achieved with multiple longitudinal modes,verifying effectiveness of the DBR microcavities.On the basis of these structures,the DBR microcavities are introduced further into light emitting diodes.The excellent photoelectric property and observation of narrowing electroluminescence spectrum with increasing the biased voltage on the OLEDs suggest that selective amplification of the electroluminescence by the DBR microcavities.This supplies a promising step toward electrically pumped polymer lasers.(4)Nano OLED arrays based on inclined metal nanoelectrodes with directional emissionNanoscale OLEDs are fabricated on the inclined surface of the side walls of the large-area nanograting lines.Different from the conventional device,where the light emitting is along the direction perpendicular to the plane of the active layer,these nano OLEDs enable light emitting along the active layer,so that it propagates over a distance shorter than 150 nm before it is output.This reduces largely the optical losses due to waveguide confinement and strong absorption by the metallic electrodes.Thus,the extraction efficiency of the device is large improved.Moreover,the output coupling direction of the nano OLEDs is along the side surface of the grating lines,thus,the directional emission can be adjusted by changing the morphology of the template grating.The realization of nanoscale OLEDs with directional emission performance has a great potential for the applications in the field of integrated optoelectronics.