Large-Area, Near-Infrared (IR) Photonic Crystals with Colloidal Gold Nanoparticles Embedding
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A polymeric composite material composed of colloidal gold nanoparticles (<10 nm) and SU8 has been utilized for the fabrication of large-area, high-definition photonic crystal. We have successfully fabricated near-infrared photonic crystal slabs from composite materials using a combination of multiple beam interference lithography and reactive ion etching processes. Doping of colloidal gold nanoparticles into the SU8 photopolymer results in a better definition of structural features and hence in the enhancement of the optical properties of the fabricated photonic crystals. A 2D air hole array of triangular symmetry with a hole-to-hole pitch of ∼500 nm has been successfully fabricated in a large circular area of 1 cm diameter. Resonant features observed in reflectance spectra of our slabs are found to depend on the exposure time, and can be tuned over a range of near-infrared frequencies.Keywords:
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Gold Colloid
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In this paper,the SERS enhancement of gold colloid film and gold colloid solution under the condition of p H= 6 and p H = 13 was studied by using crystal violet( CV) as the probe molecule. Gold colloid solution was prepared using chemical reduction method and its p H value was changed by adding Na OH solution. Gold colloid films were prepared by the self-assembly method. The enhancements of gold colloid film and gold colloid solution with p H = 6 and p H= 13 were evaluated by comparing their enhancement factors( EFs) and the limits of detection( LODs). The EFs of these three substrates were 5. 9 × 103,1. 5 × 105 and 2. 3 × 107 respectively and their LODs of CV were 70. 7 nmol / L,9. 6 nmol / L and 1. 8 nmol / L respectively. The results show that the enhancement of gold colloid solution is better than the gold colloid film. By changing the p H value of gold colloid solution,the aggregation degree and the adsorption properties for adsorbate of gold nanoparticles have been changed as well so that the enhancement of gold colloid solution can be significantly improved.
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A novel photonic crystal in which the refractive index of the interstitial void region in a colloidal crystal is gradually changed with respect to the specific direction of the crystal was proposed. This was achieved by infiltrating polymers using the interfacial-gel polymerization with high refractive index dopants. Therefore, the resulting colloidal photonic crystal has a gradually varying stop-band at different positions of the crystal when the incident light was normal to the [111] crystallographic axis. This structure could be a kind of tunable photonic crystals based on the positional variations. The optical properties and potentials for other photonic applications will be investigated.
Colloidal crystal
Yablonovite
Photonic metamaterial
Void (composites)
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A (001) oriented three-dimensionally periodic photonic crystal, free of cracks, has been fabricated via a modified template-assisted colloidal self-assembly method with polystyrene spheres. Analysis of the opal-type crystals has revealed the structure to be noncubic. This is a face-centered tetragonal (fct), (001) oriented photonic crystal. The optical properties of the crystals have been characterized at near-normal incidence by reflectance spectroscopy. It is found that the photonic stop band shifts to shorter wavelengths compared with an identical cubic structure oriented along the (001) direction. We have also simulated the stop band behavior of such fct crystals and their inverse silicon analogs, revealing that the polymer opal could provide an inverse template for the formation of photonic crystals with a complete band gap.
Tetragonal crystal system
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Yablonovite
Polystyrene
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An electrostatic interaction is responsible for the attachment of gold seeds of 1-3 nm onto APTMS (3-aminopropyl trimethoxysilane)-coated silica cores in the formation of gold clusters. A surface plasmon resonance and morphology of gold clusters were significantly affected by the pH of gold colloids prepared by THPC reducing agent. Gold colloids of alkaline pH induced the heterogeneous deposition of gold seeds onto the silica nanoparticles, probably due to the continuous reduction of residual gold ions during the attachment process. Gold colloids of acidic pH induced the monodisperse deposition of gold seeds, consequently leading to the formation of smooth gold layer on the silica nanoparticles surface. The gold nanoshells (core radius = 80 nm) prepared by gold colloids of pH 3.1 exhibited the more red-shift and relatively stronger intensity of plasmon absorption bands, compared with gold nanoshells prepared by alkaline gold colloids of pH 9.7.
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The orientation of adsorbates on metal colloids was studied by Surface enhanced Raman spectroscopy. We studied the orientation of cyanopyridines, aminomethylpyridines and 4-biphenylcarbonitrile on gold and copper colloids as a function of concentration of the adsorbates. It was found that the orientation of the adsorbate did not change as a function of concentration when adsorbed on gold colloids and was end-on for all concentrations. The orientation of 4-biphenylcarbonitrile was flat-on on gold colloid. The orientation of the adsorbate changed with change in concentration when adsorbed on copper colloids. The orientation was flat-on for higher concentrations and end-on for lower concentrations of 4- and 3-aminomethylpyridines. The orientation was end-on for higher concentrations and flat-on for lower concentrations for 2-aminomethylpyridines when adsorbed on copper colloid. We modeled the surface-adsorbate system using SpartanPro software and calculated the frequencies. The frequencies obtained for these systems were in close agreement with the experimental results.
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As the second paper of a series of our studies on surface-enhanced Raman scattering (SERS) of biological molecules on metal colloid, this paper reports effects of aggregation of gold colloid on the SERS intensity of glycine (Gly) in aqueous solutions and comparison of effects of pH of the Gly solutions between gold and silver colloids. In order to investigate the relation between the SERS effect and colloidal aggregation, we have developed a spectroscopic system by which we can measure simultaneously time-resolved SERS spectra and a time-dependent intensity change in a surface plasmon absorption of a metal colloid system. By use of this instrument we monitored time-dependent intensity changes in the SERS signals and in an absorption band at 802 nm of Gly on gold colloid at pH 3.9 and 6.0. For both pH values, the intensities of the SERS and the absorption band change in concert with each other at the emergence of the SERS effect. The intensity changes in the SERS signals are rather slow for the solution of pH 6.0 while rapid for that of pH 3.9. The coagulation proceeds slowly near the isoelectric point of Gly, whereas the rapid coagulation happens in the acidic region. SERS spectra of Gly adsorbed on silver colloid were measured at various pH values, and it was found that, in sharp contrast to the gold colloid system, which we reported in our previous paper, the SERS intensity of Gly on the silver colloid decreases markedly at pH 2.0 where most of Gly in the solution has a COOH group instead of a COO − group. It seems that the coagulation of the silver colloid particles does not occur very much below p K 1 (2.35) because the COOH groups do not interact strongly with the positively charged silver particles.
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Surface-Enhanced Raman Spectroscopy
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