Showing papers by "Anvar A. Zakhidov published in 2008"

Imprinted large-scale high density polymer nanopillars for organic solar cells

Abstract: Nanoimprint with a large-scale nanoporous Si mold is developed to fabricate high density periodic nanopillars (∼1010∕cm2) in various functional polymers. A anodic alumina membrane is first obtained using electrochemical anodization. The membrane is used as a mask for a two-step plasma etching process to obtain a Si mold of 50–80nm wide and 100–900nm deep pores. The mold is used in nanoimprint lithography to fabricate ordered and high density polymer nanopillars and nanopores in SU-8, hydrogen silsesquixane, polymethylmethacrylate, poly(3-hexylthiophane) (P3HT), and phenyl-C61-butyric acid methyl ester (PCBM). Then, the imprinted P3HT nanopillars were used to make bulk heterojunction solar cells by depositing PCBM on top of the pillars. Imprinting provides a way to precisely control the interdigitized heterojunction morphology, leading to improved solar cell performance.

Multiwalled carbon nanotube sheets as transparent electrodes in high brightness organic light-emitting diodes

Abstract: We have fabricated efficient organic light emitting diodes using strong, transparent carbon nanotube (CNT) sheets as the hole-injecting anode. These devices show a brightness of 4500 cd/m2 and current efficiency near 2.5 cd/A, which is close to the efficiency we achieve with a similar device, which uses indium tin oxide (ITO) as the anode. We demonstrate that proper planarization of the electrode using the water-soluble polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) is necessary for achieving high efficiency and can be accomplished by spin casting multiple layers. We believe that increased conductivity of the sheets could lead to CNT-based devices with efficiencies exceeding those on ITO.

ZnO lasing in complex systems with tetrapods

Abstract: A ZnO structure in the form of a core–shell wire was grown with a modified vapour transport and condensation method The wire consists of a dense core which may play the role of a waveguide and a shell formed mainly from tetrapod-type crystallites The high optical quality of the produced ZnO material is confirmed by continuous wave photoluminescence (PL) analysis demonstrating that low- temperature PL is related to the recombination of bound excitons, while room-temperature PL is due to free excitons Good quality of the crystal structure is demonstrated also by the Raman spectrum The shell of the wire exhibits room-temperature laser action due to lasing modes in tetrapods under the excitation by nanosecond laser pulses The nature of the lasing modes is discussed A simplified model for one of the possible modes is suggested

All-optical logical gates built on optically linear bandgap structures covered with nonlinear material

Abstract: In our work, we investigate photonic bandgap (PBG) structures coated by nonlinear covering as systems that are of interest for possible applications in the all-optical adders and logical gates. Two principal schemes of an all-optical adder based on the 1D PBG materials containing optically nonlinear layers are discussed. It is shown that the only nonlinear layer covering linear photonic crystal gives effective signal control and signal processing. Theoretical estimations of the adder cell parameters are made for Si/SiO2 photonic crystals covered with layers made from nonlinear doped glasses. The calculated angular-frequency diagrams exhibited extremely sensitive areas inside the total reflection range, where the weak nonlinearity leads to dramatic change in light reflection and transmission.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.