Browsing by Author "Lefrant, Serge"

Now showing 1 - 5 of 5

Electrochemical Growth of Gold Nanostructures for Surface-Enhanced Raman Scattering
(2011-02-10)
Yang, Yu-Cheng
;
Huang, Ting-Kai
;
Chen, Yu-Liang
;
Mevellec, Jean-Yves
;
Lefrant, Serge
We demonstrate a facile fabrication of gold nanostructures including Au nanoplates (NPs), Au nanothorns (NTs), and Au nanowires (NWs) on indium tin oxide substrates via electrochemical growth. A simple two-electrode electrochemical deposition system was applied for the fabrication process. Dense Au nanostructures were grown directly on an Au seeding layer on the substrate. After 48 h, the Au NPs were 2-5 mu m in width and 150-200 nm in thickness. The Au NTs were 1-3 mu m in height, 300-500 nm in bottom side width, and 20 nm at the apex. The Au NWs were 30-80 nm in diameter and about 20 mu m in length. The entire process was template-free and economical. We investigated the correlation between surface plasmon resonance (SPR) and surface enhanced scattering (SERS) effects of the Au nanostructures with different excitation wavelengths. By using the SPR absorption maxima of the nanostructures as the excitation wavelengths for SERS, the highest SERS enhancements were achieved. SERS effects of the Au NWs were investigated further. We discovered that the length and the density of the Au NWs affected the SERS performance significantly. The result is rationalized by the amount of "hot spot" generated at the crossing of the Au NWs. With the Au NWs, Rhodamine 6G can be detected at a concentration as low as 10(-9) M.
Improved photoconductive properties of composite nanofibers based on aligned conjugated polymer and single-walled carbon nanotubes
(2013-02-01)
Massuyeau, Florian
;
Zhao, Yuanchun
;
El Mel, Abdel Aziz
;
Yaya, Abu
;
Geschier, Frederic
We successfully address the challenge of aligning single-walled carbon nanotubes (SWNTs) and conjugated polymer chains in composite nanofibers for enhancing their opto-electrical properties. A pore-filling template strategy has been developed to prepare such nanocomposites from SWNTs and poly(para-phenylene vinylene) (PPV) chains, with both species well-oriented aligned along the pore axis. Addition of the SWNTs leads to a remarkable increase in photocurrent of four orders of magnitude as compared to equivalent pristine PPV nanofibers. Further analysis indicates that the strong photocurrent enhancement is not simply an effect of alignment, but additionally benefits from alignment-enhanced interaction of polymer chains with SWNTs, as supported by density functional theory (DFT) calculations.
Induced Chain Alignment of Conjugated Polymers Within Nanoporous Template
(2011-07-22)
Lo, Kuan-Hsin
;
Ho, Rong-Ming
;
Liao, Yung-Ming
;
Hsu, Chain-Shu
;
Massuyeau, Florian
This work presents a simple method to generate ordered conjugated polymer nanoarrays through a pore-filling process for nanoporous polymer templates so as to enhance the efficiency of photoluminescence (PL). PL results combined with the morphological evolution examined by scanning probe microscopy revealed that the enhanced PL reaches maximum intensity as the template pores are completely filled by conjugated polymers. Polarized PL spectroscopy and grazing incidence Fourier transform infrared spectroscopy were used to determine the chain orientation of templated conjugated polymer; the spectroscopic results indicate a parallel chain orientation along the cylindrical direction of nanopores. The induced alignment of the polymer chains is attributed to a nanoscale spatial effect that increases the PL intensity and the lifetime of the conjugated polymer. The enhanced luminescence of nanostructured conjugated polymers is highly promising for use in designing luminescent nanodevices.
Interconversion of rutile TiO2 and layered ramsdellite-like titanates: New route to elongated mesoporous rutile nanoplates
(2008-10-01)
Peng, Chih-Wei
;
Richard-Plouet, Mireille
;
Tsai, Min-Chiao
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
We report the first soft chemistry synthesis of a new "layered ramsdellite-like" titanate structure, NaTi2O4(OH) (lattice parameters: primitive monoclinic system, a = 4.09 nm, b = 0.29 nm, c = 0.94 nm, and beta = 80 degrees), with high-aspect-ratio, platelike morphology (diameter. 20-200 nm; thickness. 10-40 nm; length. 0.05-5 mu m) from TiO2 rutile. The newly prepared titanate can be transformed back to TiO2 rutile with uniquely shaped mesoporous elongated nanoplate morphology. The reaction proceeds via the disintegration of rutile in NaOH(aq) into NaTi2O4(OH). Ion exchange of Na+ in NaTi2O4(OH) into H+ forms another new layered ramsdellite-like titanate, HTi2O4(OH). A final topotatic condensation of the titanate layers in HTi2O4(OH) by heat treatment at relatively low 673 K produces the mesoporous TiO2 rutile product with highly exposed (110) surfaces.
Luminescence Enhancement of Pyrene/Dispersant Nanoarrays Driven by the Nanoscale Spatial Effect on Mixing
(2013-02-05)
Lo, Kuan-Hsin
;
Li, Ming-Chia
;
Ho, Rong-Ming
;
Zhao, Yuan-Chun
;
Massuyeau, Florian
This work presents a simple method to generate ordered chromophore/dispersant nanoarrays through a pore-filling process for a nanoporous polymer template to enhance chromophore luminescence. Fluorescence results combining with the morphological evolution examined by scanning probe microscopy reveal that the enhanced luminescence intensity reaches the maximum intensity as the nanopores of the template are completely filled by the chromophore/dispersant mixture. The variation is attributed to nanoscale spatial effect on the enhanced mixing efficiency of chromophore and dispersant, that is, the alleviation of self-quenching problem, as evidenced by the results of attenuated total reflection Fourier transform IR spectroscopy combining with grazing incident wide-angle X-ray diffraction. The enhanced luminescence of the chromophore/dispersant nanoarrays driven by the nanoscale spatial effect is highly promising for use in designing luminescent nanodevices.