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RISS 인기검색어
- 검색키워드
- 저자 : Budhani, R C (검색결과 2 건)
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QUENCHING OF SURFACE PLASMON MODES IN COLLOIDAL SILVER NANOPARTICLES ON OZONIZATION
R. C. BUDHANI,R. K. RAKSHIT,SAYANTANI BHATTACHARYA 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.3
Oxidation characteristics of colloidal silver nanoparticles produced by pulsed laser ablation in pure and chemically treated water are studied as a function of the degree of ozonization. The bright yellow colloidal solution of silver characterized by a sharp surface plasmon mode at ~400 nm, becomes colorless in the initial stages of O3 flow, and then acquires a brown hue with a broad plasmon peak centered at ~440 to ~450 nm on further ozonization. The solution again becomes colorless in a few days once the O3 flow is stopped. We present a qualitative model for the reaction dynamics and analyze the optical absorption in the framework of an effective medium theory. The aqueous phase laser ablation chemistry described here provides a unique means to produce ionic silver for enhanced antimicrobial effects.
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Chaudhuri, S,Pandey, N K,Saini, Shrikant,Budhani, R C IOP Pub 2010 Journal of Physics, Condensed Matter Vol.22 No.27
<P>A dramatic drop of ≈5 orders of magnitude in the resistance (<I>R</I>) of La<SUB>0.175</SUB>Pr<SUB>0.45</SUB>Ca<SUB>0.375</SUB>MnO<SUB>3</SUB> epitaxial films upon exposure to optical photons derived from both continuous and pulsed lasers, as well as broad-band sources at temperatures (<I>T</I>) < 30 K is reported. The strength of change is a sensitive function of both the incident photon flux and temperature. Under isothermal conditions the photo-generated low resistance state persists eternally after removal of light. This non-equilibrium state is metallic, as revealed by the positive d<I>R</I>/d<I>T</I> for <I>T</I> ≤ <I>T</I><SUB><I>p</I></SUB> (≈120 K). This electrically conducting state is presumably ferromagnetic as <I>T</I><SUB><I>p</I></SUB> coincides with the temperature where a weak ferromagnetism sets in on cooling the insulating film from room temperature. To rule out the possibility of photon-induced local heating of the sample as a mechanism of the observed effects, photo-illumination experiments were performed under identical conditions on thin films of two non-charge-ordered manganites deposited on substrates of similar thermal conductivity. Our model for the observed transition encompasses a global charge-ordered state in which ferromagnetic metallic clusters of fraction <I>p</I> much less than the critical fraction <I>p</I><SUB>c</SUB> for percolation exists at low temperatures. Photo-induced melting of the charge-ordered state increases this fraction beyond <I>p</I><SUB>c</SUB> in a cumulative manner as successive pulses of light fall on the sample. </P>
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