Optical properties of self-assembled TiO2-SiO2 double-layered photonic crystals.

The optical properties of self-assembled TiO2/SiO2 double-layered photonic crystals were examined using SiO2 and TiO2 nanopowders. The SiO2 and TiO2 nanopowders were fabricated using the well-known Stöber process, and the double-layered structure was self-assembled by an evaporation method. Self-assembled TiO2 thin film was coated at a 1.2 mm thickness by the evaporation process, and 3 atomic layers of the SiO2 layer was coated onto the TiO2 thin film. The relative reflectance peak intensity of the photonic bandgap in the specimen was 13% before thermal treatment. The peak value was increased by sequential heat-treatments and reached the highest value of 21% at 400 degrees C.

Thermal stability of atomic layer deposited Ru layer on Si and TaN/Si for barrier application of Cu interconnection.

The thermal stability of thin Ru single layer and Ru/TaN bilayers grown on bare Si by plasma enhanced atomic layer deposition (PEALD) have been studied with Cu/Ru, Cu/Ru/TaN structures as a function of annealing temperature. To investigate the characteristics as a copper diffusion barrier, a 50 nm thick Cu film was sputtered on Ru and Ru/TaN layers and each samples subjected to thermal annealing under N2 ambient with varied temperature 300, 400, and 500 degrees C, respectively. It was found that the single 5 nm thick ALD Ru layer acted as an effective Cu diffusion barrier up to 400 degrees C. On the other hand ALD Ru (5 nm)/TaN (3.2 nm) showed the improved diffusion barrier characteristics even though the annealing temperature increased up to 500 degrees C. Based on the experimental results, the failure mechanism of diffusion barrier would be related to the crystallization of amorphous Ru thin film as temperature raised which implies the crystallized Ru grain boundary served as the diffusion path of Cu atoms. The combination of ALD Ru incorporated with TaN layer would be a promising barrier structure in Cu metallization.

Optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres.

The optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres structures were studied. Colloidal crystal film of SiO2 microspheres were self-assembled by evaporation using SiO2 in solution at a constant 0.1 wt%. ZnO in thin films was then electrochemically deposited on to colloidal crystal film of SiO2 microspheres. During electrochemical deposition, the content of Zn(NO3)2 x 6H2O in solution was 5 wt%, and the process's conditions were varied between of 2-4 V and 30-120 s at room temperature, with subsequent heat-treatment between 200 and 400 degrees C. A smooth surface and uniform thickness of 1.8 microm were obtained at 3 V for 90 s. The highest PL peak intensity was obtained in the ZnO thin film heat-treated at 400 degrees C. The double layered ZnO/SiO2 colloidal crystals showed clearly better emission properties than the SiO2/ZnO and ZnO structures.

Out-coupling efficiency enhancement of organic light emitting diode device by SiO2-UV hardener composite layer.

The enhancement of out-coupling efficiency of organic light emitting diode (OLED) using SiO2-polymer composite layers was investigated. The SiO2-polymer composite was made from a SiO2 nanopowder and commercial UV-hardeners. The composite layer was coated on glass by dip-coating method in a SiO2 suspension, followed by spin-coating of 1 microm thick UV-hardener of was found that the optical properties were depend on the quantity of SiO2 nanopowder in the composite layer and dispersion of SiO2 suspension. 194/440 nm size of SiO2 nanopowders were added to the composite layer to enhance the light scattering effect. The OLED device which the SiO2-polymer composite layer was applied showed enhanced out-coupling efficiency around 30%.

Effect of content of Mg(NO3)2 x 6H2O on fabrication of alpha-alumina nanopowders by thermal decomposition of ammonium aluminum carbonate (AACH).

An alpha-Al2O3 and MgAl2O3 spinel phase doped alpha-Al2O3 nanopowders were fabricated by the thermal decomposition and synthetic of ammonium aluminum carbonate hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, 8 degrees C, and the highest [NH4+][AlO(OH)2-][HCO3] ionic concentration of pH 10 from the ammonium hydrogen carbonate (AHC) aqueous solution. The phase transformation of amorphous-s, theta-, alpha-Al2O3, MgAl2O3 spinel phases was examined at each temperature according to the amount of Mg(NO3)2 x 6H2O and AACH. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical alpha-Al2O3 nanopowders with a particle size of 60 nm were obtained by firing the crystallites, which had been synthesized from AACH at pH 10 and 8 degrees C, at 1050 degrees C for 6 h in air.

Synthesis of bimetallic nanoparticles and their application to growth of multiwalled carbon nanotube forest.

We synthesized bimetallic nanoparticles and used them to grow CNTs with an atmospheric-pressure plasma-enhanced chemical vapor deposition system. FePt and FeCo bimetallic nanoparticles were synthesized by the bottom-up high-temperature polyol process using a simple centrifugal method. The diameter of synthesized nanoparticles ranged from 2 to 5 nm with high uniformity, as measured with a transmission electron microscope. The CNTs synthesis was carried out on bimetallic nanoparticles as a catalyst using acetylene as a carbon source gas. The CNT forests grown exhibited a maximum height of 96 microm, which is relatively high compared with other growth technologies. A forest of highly pure multiwalled CNTs with diameters of 10-20 nm was successfully synthesized on a bimetallic nanoparticle catalyzed substrate. As the growth temperature increased, the quality of CNTs improved remarkably, indicating that the graphitization could be controlled by varying the growth temperature. Furthermore, the oxygen plasma pre-treatment of dispersed bimetallic nanoparticles before CNTs growth could contribute to the production of highly pure CNTs. By TEM measurements, we observed that pure multiwall CNTs without defects or amorphous carbon could be synthesized.

Decrease in work function of transparent conducting ZnO tin films by phosphorus ion implantation.

To confirm the possibility of engineering the work function of ZnO thin films, we have implanted phosphorus ions into ZnO thin films deposited by radio-frequency magnetron sputtering. The fabricated films show n-type characteristics. It is shown that the electrical and optical properties of those thin films vary depending sensitively on the ion dose and rapid thermal annealing time. Compared to as-deposited ZnO films, the work-function of phosphorus ion-implanted ZnO thin films is observed to be lower and decreases with increasing ion doses. It is likely that the zinc or oxygen vacancies are firstly filled with the implanted phosphorus ions. With further increased ions, free electrons are generated as Zn2+ sites are replaced by those ions or interstitial phosphorus ions increase at the lattice sites, the fermi level by which approaches the conduction band and thus the work function decreases. Those films exhibit the optical transmittance higher than 85% within the visible wavelength range (up to 800 nm).

Investigation on growth behavior of CNTs synthesized by atmospheric pressure plasma enhanced chemical vapor deposition system on Fe catalyzed substrate.

We have studied growth behavior of carbon nanotubes (CNTs) on iron (Fe) catalyzed substrate using newly developed atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) system. To investigate the improved growth performance with simple equipment and process on large scale, a new AP-PECVD system containing different concept on downstream gas was designed and manufactured. As a catalyst, either sputtered or evaporated Fe thin film on SiO2/Si substrate was used and acetylene gas was used as a carbon source. We observed growth behavior of CNTs such as height, rate and density were strongly affected by plasma power. The maximum height of 427 microm and 267 microm was synthesized under RF plasma power of 30 W for 30 min and 40 W for 3 min, respectively. The growth rate dramatically increased to 6.27 times as plasma power increased from 30 to 40 W which opens the possibility the mass production of CNTs. By SEM and TEM observation, it was verified the grown CNTs was consists of mixture of single-wall and multi-wall CNTs. The graphitization ratio was measured to be 0.93, indicating that the graphitized CNTs forest was formed and relatively high purity of CNTs was synthesized, being useful for nano-composite materials to reinforce the strength. From our experiments, we can observe that the height and growth rate of CNTs is strong function of plasma power.

Optical properties of self-assembled ZnO/SiO2 photonic crystals.

This study examined the optical properties and crystallinity of self-assembled ZnO/SiO2 photonic crystals using silica and ZnO nanopowders. The silica and ZnO nanopowders were fabricated using the well-known Stöber process. The photonic crystals were self-assembled using a evaporation method. The process temperature and heat-treatment temperature after evaporation were 80 degrees C and 250 approximately 450 degrees C, respectively. The highest reflectance peak intensity was obtained in the sample heat-treated at 350 degrees C with 0.3 wt% ZnO addition. The ZnO/SiO2 photonic crystals clearly showed better emission properties than the SiO2/ZnO and ZnO structures.

Decrease in work function of boron ion-implanted ZnO thin films.

We have fabricated boron ion-implanted ZnO thin films by ion implantation into sputtered ZnO thin films on a glass substrate. An investigation of the effects of ion doses and activation time on the electrical and optical properties of the films has been made. The electrical sheet resistance and resistivity of the implanted films are observed to increase with increasing rapid thermal annealing (RTA) time, while decreasing as the ion dose increases. Without any RTA process, the variation of the carrier density is insensitive to the ion dose. With the RTA process, however, the carrier density of the implanted films increases and approaches that of the un-implanted ZnO film as the ion dose increases. On the other hand, the carrier mobility is shown to decrease with increasing ion doses when no RTA process is applied. With the RTA process, however, there is almost no change in the mobility. We have achieved the optical transmittance as high as 87% within the visible wavelength range up to 800 nm. It is also demonstrated that the work function can be engineered by changing the ion dose during the ion implantation process. We have found that the work function decreases as the ion dose increases.

Multi-wavelength emitting InGan/GaN quantum well grown on V-shaped gan(1101) microfacet.

InGaN/GaN multiple quantum wells (MQWs) were successfully grown on the inclined GaN(1101) microfacets. Conventional photolithography and subsequent growth of GaN were employed to generate the V-shaped microfacets along (1120) direction. The well-developed microfacets observed by scanning electron microscopy and the clear transmission electron microscope interfacial images indicated that the MQW was successfully grown on the GaN microfacets. Interestingly, cathodoluminescence (CL) spectra measured on the microfacets showed a continuous change in the luminescence peak positions. The CL peaks were shifted to a longer wavelength from 420 nm to 440 nm as the probing points were changed along upward direction. This could be attributed to the nonuniform distribution of the In composition and/or the wavefunction overlapping between adjacent wells. Present works thus propose a novel route to fabricate a monolithic white light emitting diode without phosphors by growing the InGaN/GaN MQWs on (1101) facet.

Work function increase of Al-doped ZnO thin films by B+ ion implantation.

The work function of an Al-doped ZnO (AZO) thin film can be increased via B+ ion implantation from 3.92 eV up to 4.22 eV. The ion implantation has been carried out with the ion dose of 1 x 10(16) cm(-2) and ion energy of 5 keV. The resistance of the B+ implanted AZO films has been a bit raised, while their transmittance is slightly lowered, compared to those of un-implanted AZO films. These behaviors can be explained by the doping profile and the resultant band diagram. It is concluded that the coupling between the B+ ions and oxygen vacancies would be the main reason for an increase in the work function and a change in the other properties. We also address that the work function is more effectively alterable if the defect density of the top transparent conducting oxide layer can be controlled.

Defect healing of self-assembled SiO2 layer by heat-treatment and multi-coating.

This study examined the effect of heat-treatment and multi-coating on the microstructure and optical properties of photonic crystals (PCs) that had been self-assembled using mono-dispersed spherical SiO2 nanoparticles. When the heat-treatment temperature was increased, the reflectance peak due to the photonic bandgap moved to a shorter wavelength direction, and the peak intensity of the Fabry-Perot fringes increased. The highest reflectance peak intensity was obtained in the sample heat-treated at 250-300 degrees C. Heat-treatment reduced the average particle size and number of defects, and increased the packing density of the PC. When the heat-treatment temperatures were increased up to 900 degrees C, a large crack with an average size of approximately 1.3 microm was formed through the self-assembled layer. A multi-coating could effectively fill the open space of this crack and thereby reduce the total number of defects. The crystallinity and optical properties of the self-assembled PC were improved by the heat-treatment and multi-coating.