Crystalline TiO2 film was formed on PET(polyethlene terephthalate) film by radio frequency sputter
deposition method using a sintered TiO2 target by adding H2O gas to Ar gas for sputtering. X-ray
diffraction analysis revealed that the crystal structure of the film of 100 nm thick was confirmed to be
anatase crystallites of TiO2. In order to elucidate the mechanism of low temperature crystallization thus
observed, direct measurement of surface temperature of growing films during sputter deposition was
carried out by two methods of an infrared thermometer from the outside of vacuum chamber and a
thermocouple attached to the growing film surface. Upon the beginning of sputter deposition in Ar gas,
film temperature increased rapidly and became constant at 120°C after 30 min. Addition of H2O gas to Ar
gas for sputtering resulted in further increase in film temperature and reached to 230 °C depending on the
deposition conditions. Furthermore, photocatalytic performance of decomposition of methylene blue was
examined to be enhanced remarkably as a result of crystallization of the film.
It was concluded that low temperature crystallization of TiO2 film by sputter deposition was explained in
terms of local heating of thin shallow surface region of growing film by kinetic energy deposition of
sputtered particles.
This review first describes the present status of research and development of visible light photocatalysts and then
application products on the market are introduced. Finally, future trends of technology and market of photocatalysts will
be discussed.
We report effective enhancement of external quantum efficiency of phosphorescent organic light-emitting devices (OLEDs) with facially encumbered and bulky meso-aryl substituted Pt(II) porphyrins, probably suppressing non-radiative deactivation. The peak external quantum efficiencies (QEs) of the phosphorescent OLEDs with facially non-encumbered Pt(II) porphyrin 1, facially encumbered Pt(II) porphyrin 2, Pt(II) porphyrin 3 that bears bulkier 3,5-di-tert-butylphenyl substituents, and "doubly-decamethylene-strapped" Pt(II) porphyrin 4 were 1, 4.2, 7.3, and 8.2 %, respectively. The trend increasing performance in the order of 1 < 2 < 3 < 4 is related to facial encumbrance and steric bulkiness of Pt(II) porphyrins. Furthermore, in the case of Pt(II) porphyrin 4, it is considered that the "double straps" severely restrict rotational freedom of the meso-aryl substituents. The lifetimes for Pt(II) porphyrins 1-4 at a current density of 0.55 mA/cm2 were 80, 103, 140, and 152 μs, respectively. The trend that the triplet lifetime becomes longer in the order of 1 < 2 < 3, 4 suggests that facial encumbrance and steric bulkiness suppress non-radiative deactivation. The triplet lifetimes of Pt(II) porphyrins 1-4 were all gradually shortened with increasing current densities, suggesting possible triplet-triplet annihilation and/or triplet-charge carrier recombination.
KEYWORDS: Thin films, Nanotechnology, Absorption, Photocatalysis, Ultraviolet radiation, Monte Carlo methods, Scanning electron microscopy, Thin film deposition, Magnetism, Diffusion
Photocatalytic properties of obliquely deposited TiO2 thin films with various shaped columns were investigated. The columnar films such as zigzag, cylinder and helix were prepared by dynamic oblique deposition (DOD) method. It was found that the optimum morphology for surface photocatalytic reaction has been obtained at the deposition angle (alpha) equals 70 degrees, where the photocatalytic activity is 2.5 times larger than that at (alpha) equals 0 degrees. In addition, effective surface area was estimated by Monte Carlo simulation and quantitative agreement was obtained between theoretical and experimental results. It was concluded that the enhanced surface photocatalytic properties of obliquely deposited TiO2 films can be explained in terms of effective changes in surface area originated from morphology modified by thin film nanotechnology.
We have fabricated highly efficient organic light-emitting diodes (OLEDs) using novel hole-transporting emissive materials with triphenylamine moiety. The novel emissive materials have a high glass transition temperature ranging from 141 - 152 degrees Celsius, which is attributed to nonplanar molecular structure. The OLEDs consist of an emitting layer of the novel emissive material and an electron-transport layer of tris(8-qunolinolato) aluminum (Alq3). Emission colors of the OLEDs were bluish-green and greenish-yellow. High external quantum efficiency of 1.2 - 2% was obtained at a luminance of 300 cd/m2, and good durability in a continuous operation at room temperature and high temperatures was achieved.
We have introduced acene such as anthracene, naphthacene and pentacene into the main chain of polyfluorene to improve stability and to realize color tuning to pure blue, green and red. High molecular weight acene-containing polyfluorenes are successfully synthesized by the Ni[0] mediated Yamamoto-coupling reaction. Average molecular weights of the copolymers are Mw equals 42000 - 96000 (determined by GPC). By the introduction of 10% of acene moiety, the device stability could be significantly improved, indicating the torsion between the acene and fluorene units suppresses interchain aggregation; the copolymers exhibits stable blue, green and red emission in the anthracene-, naphthacene- and pentacene-containing polyfluorenes, respectively. Onset voltage for light emission is 5 - 30 V and the maximum luminance is 240 - 5200 cd/m2. As a side effect an unique color change on UV irradiation could be observed as well as the reason for its appearance determined.
The electronic structures of 8-hydroxyquinoline aluminum (Alq3)/electron injection layer/Al interfaces, used in organic electroluminescent devices, were measured by ultraviolet photoelectron spectroscopy (UPS). LiF and alkaline earth fluorides (CaF2, SrF2 and BaF2) were used as an electron injection layer. Shifts of the highest occupied molecular orbital (HOMO) level and the vacuum level of Alq3 layer due to the insertion of the fluorides were observed. These shifts indicate that the alkaline earth fluoride layers as well as the LiF layer at the Alq3/Al interface reduce the barrier height for electron injection from the Al to Alq3. The reduction of the barrier height is consistent with the driving voltage in the organic EL device in which these fluorides are used as the electron injection layers. We believe that lowering in the driving voltage in organic EL devices with the thin insulator layers, such as LiF and alkaline earth fluorides, is attributable to the reduction of the barrier height.
More than 10 years ago, birefringent films of metal oxides were formed by oblique vapor deposition and investigated with a view of their application to optical retardation plates. The retardation function of the films was explained in terms of the birefringence caused by the characteristic anisotropic nanostructure inside the films. These films are now classified in the genre of the so-called sculptured thin films. However, the birefringent films thus prepared are not yet industrialized even now due to the crucial lack of the durability and the yield of products. In this review paper, we describe the present status of application process of the retardation films to the information systems such as compact disc and digital versatile disc devices with a special emphasis on the uniformity of retardation properties in a large area and the stability of the optical properties of the obliquely deposited thin films. Finally, further challenges for wide application of the obliquely deposited thin films are also discussed.
Both directionality and intensity of emitted light from the organic electroluminescent (EL) device were strongly modified using a Fabry-Perot microcavity. The microcavity EL device exhibited a single mode emission that was significantly enhanced and the emission was sharply directed along the direction normal to the device surface. The luminous efficiency in the normal direction was much higher than that of the noncavity EL device. The sharply directed pure green emission exceeded 40000 cd/m2 at a driving current of 800 mA/cm2.
There are increasing demands of surface modification of transpar-
ent substrates such as glass and plastics for windows in automobiles as
well as houses in view of adding them fascinating optical properties.
These properties include surface hardening of plastics, infrared re-
flection, ultraviolet absorption, optical switching and birefringence.
This paper reviews recent examples of applications of sophisticated
thin film processes of plasma treatment and Physical Vapour Deposition
(PVD). The novelty of functions by PVD method together with their
durability for practical usage are emphasized as areas where the thin
film process has a significant impact. Characterization of the
modified surface and interface is also included to demonstrate recent
advances in surface chemistry. Finally, future challenges for optical
modification of transparent substrates in the automobile industry are
also discussed.
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