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Synthesis and characterization of strontium titanate powder via a simple polymer solution route
이상진,Pradheep Thiyagarajan,이만종 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.4
A simple chemical route has been used to synthesize highly sinterable strontium titanate (SrTiO3) powders using titanium isopropoxide, strontium nitrate and ethylene glycol. This method utilizes complexation-polymerization using ethylene glycol as an organic carrier, which leads to compositional homogeneity and fine particle sizes. The calcined SrTiO3 powder showing a porous nature was fully crystallized to a cubic phase at 1,300 oC for 1 hour. Through ball-milling the porous SrTiO3 powders with particle sizes of 200-300 nm were easily obtained, which was sintered to a bulk density of 4.8 g/cm3 at 1,400 oC for 1 h with a grain size of approximately 6.0 mm. The relative dielectric constant and loss tangent of SrTiO3 sintered at 1,400 oC for 1 hour were 2078 and 0.022, respectively.
Kim, Kwanghyun,Thiyagarajan, Pradheep,Ahn, Hyo-Jin,Kim, Sun-I,Jang, Ji-Hyun The Royal Society of Chemistry 2013 Nanoscale Vol.5 No.14
<P>A gold nanoparticle-coated and surface-textured TiO2 inverse opal (Au/st-TIO) structure that provides a dramatic improvement of photoelectrochemical hydrogen generation has been fabricated by nano-patterning of TiO2 precursors on TiO2 inverse opal (TIO) and subsequent deposition of gold NPs. The surface-textured TiO2 inverse opal (st-TIO) maximizes the photon trapping effects triggered by the large dimensions of the structure while maintaining the adequate surface area achieved by the small dimensions of the structure. Au NPs are incorporated to further improve photoconversion efficiency in the visible region via surface plasmon resonance. st-TIO and Au/st-TIO exhibit a maximum photocurrent density of 0.58 mA cm(-2) and 0.8 mA cm(-2), which is 2.07 and 2.86 times higher than that of bare TIO, respectively, at an applied bias of +0.5 V versus an Ag/AgCl electrode under AM 1.5 G simulated sunlight illumination via a photocatalytic hydrogen generation reaction. The excellent performance of the surface plasmon-enhanced mesoporous st-TIO structure suggests that tailoring the nanostructure to proper dimensions, and thereby obtaining excellent light absorption, can maximize the efficiency of a variety of photoconversion devices.</P>
Ahn, Hyo-Jin,Thiyagarajan, Pradheep,Jia, Lin,Kim, Sun-I,Yoon, Jong-Chul,Thomas, Edwin L.,Jang, Ji-Hyun The Royal Society of Chemistry 2013 Nanoscale Vol.5 No.5
<P>Dual-scale diamond-shaped gold nanostructures (d-DGNs) with larger scale diamond-shaped gold nanoposts (DGNs) coupled to smaller scale gold nanoparticles have been fabricated via interference lithography as a highly reliable and efficient substrate for surface enhanced Raman scattering (SERS). The inter- and intra-particle plasmonic fields of d-DGNs are varied by changing the periodicity of the DGNs and the density of gold nanoparticles. Because of the two different length scales in the nanostructures, d-DGNs show multipole plasmonic peaks as well as dipolar plasmonic peaks, leading to a SERS enhancement factor of greater than 10(9). Simulations are carried out by finite-difference time-domain (FDTD) methods to evaluate the dependence of the inter- and intra-particle plasmonic field and the results are in good agreement with the experimentally obtained data. Our studies reveal that the combination of two different length scales is a straightforward approach for achieving reproducible and great SERS enhancement by light trapping in the diamond-shaped larger scale structures as well as efficient collective plasmon oscillation in the small size particles.</P>
Graphene Oxide-terminated Partially Fluorinated Poly(arylene ether sulfone)
Lee, Jung-Soo,Yoon, Jong-Chul,Thiyagarajan, Pradheep,Jang, Ji-Hyun The Chemical Society of Japan 2012 Chemistry letters Vol.41 No.1
<P>Graphene oxide-terminated partially fluorinated poly(arylene ether sulfone) (GO-PAES) was synthesized via step growth polymerization with graphene oxide. A small amount of graphene oxide was incorporated into the polymer matrix to enhance the properties of the polymer/GO composites. The chemical structures of the synthesized copolymers containing graphene oxide were confirmed by <SUP>1</SUP>H NMR and FT-IR spectra. The thermal properties of GO-PAES analyzed by TGA and DSC were significantly improved due to the thermal stability of graphene oxide.</P>
Highly Enhanced Raman Scattering on Carbonized Polymer Films
Yoon, Jong-Chul,Hwang, Jongha,Thiyagarajan, Pradheep,Ruoff, Rodney S.,Jang, Ji-Hyun American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.25
<P>We have discovered a carbonized polymer film to be a reliable and durable carbon-based substrate for carbon enhanced Raman scattering (CERS). Commercially available SU8 was spin coated and carbonized (c-SU8) to yield a film optimized to have a favorable Fermi level position for efficient charge transfer, which results in a significant Raman scattering enhancement under mild measurement conditions. A highly sensitive CERS (detection limit of 10(-8) M) that was uniform over a large area was achieved on a patterned c-SU8 film and the Raman signal intensity has remained constant for 2 years. This approach works not only for the CMOS-compatible c-SU8 film but for any carbonized film with the correct composition and Fermi level, as demonstrated with carbonized-PVA (poly(vinyl alcohol)) and carbonized-PVP (polyvinylpyrollidone) films. Our study certainly expands the rather narrow range of Raman-active material platforms to include robust carbon-based films readily obtained from polymer precursors. As it uses broadly applicable and cheap polymers, it could offer great advantages in the development of practical devices for chemical/bio analysis and sensors.</P>