Preparation Of Plasmonic Materials Via The Photoinduced Growth Process And Their Spectroscopic Studies

Metal particles on the nanoscale are of great interest due to their distinct properties in the field of optics, electronics, magnetic, and catalysis, as compared to their bulk materials. Noble metal nanoparticles, especially silver and gold nanoparticles, have attracted even more attentions for their unique spectral response in the visible and infrared waveband. The spectral response of the metal nanoparticles, known as the surface plasmon resonance (SPR), is localized on the surface of the nanostructure. These resonances stem from the collective oscillation of surface conduction electrons driven by the incident electromagnetic field. Studies on the SPR properties have improved the development of nanoscience, and gave birth to several novel applications, such as surface plasmon spectroscopy (SPS), chemical and biological sensing, and photothermal therapy of cancers. The SPR properties of metal nanoparticles are strongly dimension and morphology dependent. Thus, control over the size and shape of metal nanoparticles is of considerable importance.1. Laser-Induced Growth of Monodisperse Silver Nanoparticles with Tunable SPR Properties and Wavelength Self-Limiting EffectWe present a method for the tunable production of monodisperse silver nanoparticles. Using monochromatic light of different laser wavelengths to irradiate an initial solution of seed crystals, the size and shape of the products can be controlled. By monitoring the absorption spectrum during growth, it is found that initially the absorption maximum shifts to longer wavelengths and broadens, indicating increase in particle size and size dispersion. Remarkably, this effect comes to a halt and reverses, displaying a shift to shorter wavelengths and simultaneously narrower bandwidths, until on completion, a final size and relatively narrow distribution is reached. The final size and shape is found to depend on laser wavelength and power. Both discs and triangular prisms as well as pyramidal and pentagonal prisms may be produced. A mechanism based on a wavelength dependent self-limiting process governed by the surface plasmon resonance controlling the photochemical reduction of particles is suggested.2. Photochemical Formation of Silver Nanodecahedra: Structural Selection by the Excitation WavelengthSilver decahedra have been successfully synthesized with high yield via a photochemical reaction using blue light-emitting diodes (LED) as the exciting light source. The decahedra display distinct properties with respect to the ability of light scattering. The photochemical growth process of silver decahedra was monitored by both extinction and scattering spectral evolution. A suggested formation mechanism of silver decahedron is discussed.3. Adjustment of LSPR Properties of Silver Nanoparticles via Wavelength Self-Limiting Effect(1) The Case of Dual-Light ExcitationPreparation of silver nanoparticles with the excitation of dual light system is present. Both argon ion laser lines and LEDs are employed as the exciting light. By adjusting the relative light intensity in the dual-light system, silver colloid with tunable LSPR properties can be prepared. The self-limiting effect during the growth of silver nanoparticles is discussed.(2) The Case of Etching SystemWe present a new route to adjust the SPR properties of silver nanoparticles via the etching effect of KCl and the wavelength self-limiting effect. The photochemically prepared silver nanotriangles were etched at the corners in the present of Cl-, and the obtained nanostructures were disk-like in shape. The silver clusters remained the colloidal system triggered the regrowth of silver nanodisks under the irradiation of visible light. The SPR properties of the products were finely adjusted when using different excitation wavelengths. The SPR properties were tuned in the range between 450 nm and 800 nm, and were linear with the excitation wavelengths.4. Photochemical Modification of an Optical Fiber Tip with Silver Nanoparticle Film: A SERS Chemical SensorWe provide a method of photochemical modification of an optical fiber tip with a silver nanoparticle film. The deposited silver nanoparticle film displays alternating―light‖and―dark‖cycles, which are similar to a radial diffraction pattern. The modified optical fiber is examined as a chemical sensor for in situ detection. The modified fibers show excellent SERS activity, low limit of detection (LOD), and good reproducibility. The maximum SERS activity of the sensor was achieved within 5 minutes of deposition. Thus the method is also quite rapid.