Eisuke Yokoyama

Laser-induced forward transfer of TiO2–Au nanocomposite films for maskless patterning

Laser-induced forward transfer is investigated for maskless pattering of thin films. A 89TiO2–11Au (mol %) nanocomposite polycrystalline (100 nm thick) film fabricated by a sol-gel method shows a surface plasmon absorption produced by Au nanoclusters formed in the film. A second-harmonic generation sheet beam of a Q-switched Nd:YAG laser was irradiated on the film in air in contact with another glass substrate or with a 0.14 mm air gap. Regular stripe patterns of laser-induced transferred films were obtained. Transmittance spectra of laser-induced transferred films showed shifts of the surface plasmon absorption peak. Analysis of the spectra using the Mie scattering model revealed the porous character of transferred films.

Patterning of indium-tin-oxide (ITO) films using laser-induced forward transfer (LIFT) technique

The LIFT experiments were performed in air at room temperature for ITO films with the thickness of 180nm. A line pattern of the ITO film was obtained using a second harmonic generation SHG (532nm) beam of a Q-switched Nd:YAG laser (5.18W) with the repetition rate of 40kHz and the pulse width of 13ns. The beam was scanned using a galvano mirror optical setup system. Two kinds of sandwiched glass plate samples were used: (1) a glass plate deposited with ITO film (donor) is contact with another glass substrate (receiver) with no-gap, that is, the ITO film is in direct contact with a receiver glass, and (2) the donor is placed against the receiver glass with an 0.14mm air gap using a glass spacer. These samples were irradiated by the scanned beam with different scanning speeds. LIFT-transferred film pattern with the linear array of dot prints was obtained for the scanning speed of 200cm/s, but for the scanning speed of 10cm/s, the linear array of continuous printed tracks was produced. The edge of the printed track was clearer in (2) than (1) for the scanning speed of 10cm/s. As a result, the sample of type (2) with air-gap is preferable to obtain the line printed pattern with clear track edge, and the scanning speed should be smaller than 10 cm/s for this laser.

DIELECTRIC ANALYSIS ON OPTICAL PROPERTIES OF ZrO2 THIN FILMS DISPERSED WITH SILVER NANOPARTICLES

ZrO2 thin films containing silver nanoparticles were prepared using the sol-gel method with silver volume fractions from 5.3 to 53.9 %. An amorphous phase was observed for the ZrO2 matrix and a cubic crystalline phase was identified for the Ag nanoparticles by the XRD measurement. The diameter of silver nanoparticles distributed over 25 to 75 nm was analyzed by TEM measurement. The films showed an absorption band centered at 450 nm due to the surface plasmon resonance of silver nanoparticles. The absorption peak was analyzed using the effective dielectric function modeled with both Maxwell-Garnett and Bruggeman expressions. In the small Ag volume fractions, the calculated spectra using Maxwell-Garnett theory agreed well with the measured spectra. In the large Ag volume fraction, the calculated absorption spectra using the Bruggeman model gives a relatively good fitting to the experimental spectrum.

Optical properties of dielectric films dispersed with metal nanoparticles and applications to optically functional materials

Nanoparticles of noble metals exhibit variety of colors in the visible light region due to a surface plasmon resonance. The size-induced properties of nanoparticles enable addition of flexibility to existing systems in many areas. To design a material with desired electrical and optical properties is the aim in many composite materials. In this paper, we report the preparation and characterization of silver nanoparticles in SiO2, TiO2 and ZrO2 films and gold nanoparticles in TiO2 and ZrO2 films. To analyze the dielectric characteristic of the metal-dielectric nanocomposite film, three kinds of matrices with a different refractive index were compared. Titanium dioxide (TiO2) is one of the most promising photocatalysts and actively used in various practical applications. However, only a narrow band in the ultraviolet region of solar light, about 3-4%, is available for photocatalytic reaction. Therefore, the development of TiO2 photocatalysts with higher photoelectric conversion efficiency for visible light is required. Plasmon-induced photocatalytic activity in the ultraviolet and visible light region was studied for the TiO2 thin film dispersed with gold nanoparticles. Photocatalytic activity of Au/TiO2 film was analyzed by degradation of stearic acid, and compared with non-doped TiO2film.

Optical properties of ZnO thin films dispersed with noble metal nanoparticles synthesized by sol-gel method

Zinc Oxide (ZnO) is an inexpensive n-type semiconductor having a direct band gap of 3.3eV with a large exciton binding energy of 60meV. Noble metal nanoparticles show a surface plasmon resonance in the visible region due to collective oscillations of electrons at the surface of metal nanoparticles. The unique features in the composite system of dielectrics-metal nanoparticles have potential applications in optoelectronic devices such as transparent conductive films, solar cells, photocatalysts and so on. In this study, ZnO thin films dispersed with Ag or Au nanoparticles were synthesized using a sol-gel technique. X-ray diffraction peaks of ZnO films exhibited a pattern corresponding to the hexagonal wultzite structure. In the TEM analysis of ZnO-Au composite films, spherical Au nanoparticles were observed within the ZnO crystalline matrix. The distribution of the diameter of Au nanoparticles was centered at around 20nm and broadened with the half width of about 20nm. In the ZnO-Ag composite films, Ag nanoparticles grow larger as the annealing temperature becomes higher and various shape of Ag precipitations like triangular and square plates were observed in ZnO-Ag (50:50) composite films. The optical absorption peaks were observed at 580nm and 410nm due to the surface plasmon resonance of gold and silver nanoparticles, respectively. The absorption spectra were analyzed using a typical effective medium approximation of Maxwell-Garnett model and good fitting was obtained for a ZnO-Au composite film assuming spherical Au nanoparticle. The spectra were discussed relating with the size and shape of the nanoparticles, and the refractive index of the matrix.

Optical Properties of Oxide Films Dispersed with Nanometal Particles

Solid materials reveal some special behaviors like quantum effects in semiconductors and surface-enhanced effects in metals by decreasing their diameters. In this review, the enhancement of the optical response due to the electric field of the light is reviewed as the recent active field of plasmonics. The production methods of various metal nanoparticles are summarized for the bared state and for the embedded state within the dielectric medium. The features of the optical properties of these nanoparticles are reviewed, and typical formula to reproduce the absorption spectra due to the surface plasmon resonance is summarized. Several applications of these systems are shortly introduced.

Optical properties of MgF2 composite films dispersed with Au or Ag nanoparticles synthesized by sol-gel method

Absorption spectra due to the surface plasmon resonance (SPR) in porous MgF2 films embedded with Au or Ag nanoparticles were analyzed considering the effective medium approximation relating with the particle size distributions obtained by TEM.

Dielectric analysis on optical properties of ZrO2 thin films dispersed with silver nanoparticles prepared by sol-gel method

Nanoparticles of noble metals exhibit variety of colors in the visible wavelength region due to the surface plasmon resonance. The size-induced properties of nanoparticles offer the flexibility in material design to conventional material systems for a variety of fields. In many composite materials, the aim is to design a material with desired electrical and optical properties. The dielectric properties of nanocomposites can be calculated by an effective medium approximation (EMA). Maxwell-Garnett (M-G) and Bruggeman models are well known mixing rules in EMA. In the M-G model, the available region is restricted to relatively small volume fraction of the inclusions because of the assumptions imposed on the model. For large volume fraction of the inclusions and for randomly intermixed constituents, Bruggeman derived EMA by considering the host material as an effective medium. The aim of this study is to examine the applicability of the effective medium theory to the synthesized ZrO2-Ag compsite materials. The silver nanoparticle/ZrO2 thin film composites were prepared by the sol-gel method with various silver fill fractions. The films were analyzed by a UV-Vis- NIR spectrophotometer, a transmission electron microscope and an X-ray diffractometer. The absorption due to the silver surface plasmon resonance was simulated using the dielectric function reflecting the M-G and the Bruggeman mixture rules. It was found the applicability of M-G model is limited to smaller densities than 50 mol% and that of the Bruggeman model is over 70 mol% of silver density in this composite system.

Photocatalytic Activities of TiO 2 Thin Films with Au Nanoparticles under Ultraviolet and Visible Light Irradiation

TiO2thin films containing Au nanoparticles were prepared using the sol-gel method. Photocatalytic activities were analyzed for degradation of stearic acid. The results of the experiment showed the Au nanoparticles increase photocatalytic activity of TiO2.

Sol-Gel Synthesis and Characterization of Ag, Au Nanoparticles in ZrO 2 Thin Films

ZrO2thin films containing silver and gold nanoparticles were prepared using the sol-gel and dip coating methods. The physical properties of the films were studied as the basic materials for the plasmonic devices.