Akhmad Herman Yuwono

Transparent nanohybrids of nanocrystalline TiO2 in PMMA with unique nonlinear optical behavior

PMMA is one of the most versatile polymeric materials for applications in various technological areas including optics and electro-optics. While the current applications of PMMA in optics and electro-optics are limited by their linear optical behavior, we report here in this paper the unique nonlinear optical behavior of nanohybrids consisting of nanocrystalline TiO2 in PMMA. Transparent thin films of TiO2–PMMA nanohybrid on substrates were synthesized by in-situ sol–gel and polymerisation, assisted by spin coating. Using titanium isoproproxide (Ti-iP) as the starting material for nanocrystalline titania, together with methyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate, nanohybrids containing up to 80% Ti-iP in PMMA were successfully realized. The resulting nanohybrid thin films coated on quartz substrates are optically transparent and demonstrate large nonlinear optical behavior, with an ultrafast response of <1.5 ps. The highest two-photon absorption coefficient (β) and nonlinear refractive index (n2) are observed with the nanohybrid thin film of 60 wt% Ti-iP in PMMA, as confirmed by the Z-scan technique.

Ultrafast optical nonlinearity in poly(methylmethacrylate)-TiO2 nanocomposites

With 780-nm, 250-fs laser pulses, ultrafast optical nonlinearity has been observed in a series of thin films containing poly(methyl methacrylate) (PMMA)-TiO2 nanocomposites, which are synthesized by a simple technique of in-situ sol-gel/polymerization. The best figures of merit are found in one of the films prepared with a 60 wt % of titanium isopropoxide. Transmission electron microscopy shows the presence of 5-nm-diameter particles in the film. The observed optical nonlinearity has a recovery time of ∼1.5 ps. These findings suggest the strong potential of PMMA-TiO2 nanocomposites for all-optical switching.

Controlling the crystallinity and nonlinear optical properties of transparent TiO2–PMMA nanohybrids

Titania–polymer nanohybrid thin films represent a new class of potential materials for optoelectronic applications. While most such nanohybrid thin films lack control in crystallinity, we report in this paper transparent nanohybrids of titania-polymethyl methacrylate (TiO2–PMMA) thin films having a remarkably enhanced nanocrystallinity. Post-treatments with water vapor at relatively low temperatures were applied on these thin films, following in situ sol–gel polymerization. They promoted rearrangement of flexible Ti–O–Ti bonds leading to enhanced crystallization of the TiO2 phase. The degree of TiO2 crystallinity in the resulting nanohybrid films was studied by using XRD, FTIR, UV–Vis spectroscopies and HRTEM. Both linear and nonlinear optical responses increase with the enhancement of TiO2 crystallinity in the nanohybrids. The highest two-photon absorption coefficient (β) and nonlinear refractive index (n2) were observed for the nanohybrid thin films with highest TiO2 crystallinity, as confirmed by open and closed aperture Z-scan techniques using 250 fs laser pulses at 800 nm, having a value of 2260 cm GW−1 and 6.2 × 10−2 cm2 GW−1, respectively.

TRANSPARENT TiO2-PMMA NANOHYBRIDS OF HIGH NANOCRYSTALLINITY AND ENHANCED NONLINEAR OPTICAL PROPERTIES

Nanohybrid thin films of titania-polymethyl methacrylate (TiO2-PMMA) with varying degrees of nanocrystallinity have been successfully synthesized via an in-situ sol gel-polymerization route, assisted by subsequent thermal and water vapor treatments. Post-hydrothermal treatment by water vapor at relatively low temperatures led to a higher degree of crystallinity for TiO2 nanoparticles than the conventional thermal annealing. The degree of TiO2 crystallinity in the resulting nanohybrid films was studied by using XRD, FTIR, UV-Vis spectroscopies and HRTEM. The resulting nanohybrid thin films are highly transparent in the visible region, with an estimated band gap energies, Eg, close to that of anatase TiO2 (~ 3.20 eV). The nanocrystallinity level of TiO2 phase strongly affects both linear and nonlinear optical properties of the nanohybrids. A significant enhancement in linear refractive index, no, up to 1.780 and a third-order nonlinear optical susceptibility, χ(3) as high as 5.27 × 10-9esu, were demonstrated with the nanohybrid exhibiting the enhanced TiO2 crystallinity and well-preserved PMMA matrix.

Nanocrystallinity Enhancement of TiO2 Nanotubes by Post-Hydrothermal Treatment

In the present research, a modified post-hydrothermal treatment with different temperature of 80-150°C has been applied on as-annealed TiO2 nanotubes derived from conventional hydrothermal process. The treatment has two-fold objectives, i.e. enhancing the nanocrystallinity of anatase TiO2, and at the same time maintaining the integrity of nanotube structures. The resulting TiO2 nanotubes were characterized by using XRD and UV-Vis spectroscopy. The XRD analysis revealed that the as dried TiO2 nanotubes contain combined crystalline structures of sodium-titanate and anatase. It was also found that by increasing the post-hydrothermal temperature from 80 to 150°C, the nanocrystallinity of nanotubes enhances as indicated by increasing the crystallite size of anatase TiO2 from 6.93 to 7.81 nm. The anatase crystallite growth affected the optical characteristic of nanotubes, as represented with the reduction of the band gap energy, Eg from 3.75 to 3.67 eV by using Kubelka-Munk analysis for the obtained UV-Vis reflectance spectra. TEM observation confirms that the integrity of nanotubes structure can be well-maintained upon post-hydrothermal treatment.

Influence of Mass Ratio of Aquadest and TTIP on the Synthesis of TiO2 Nanoparticles to Improve the Performance of DSSC with Beta-Carotene as Sensitizer

TiO2 nanoparticles have been successfully synthesized using the sol-gel method with main materials of titanium tetraisopropoxide (TTIP) and HClO4 solutions. Mass ratios (Rw) of aquadest and TTIP were 0.85, 2.00, and 3.50 which were going to be investigated in crystallization of TiO2 phases. Pre-heating was performed on TiO2 at 60°C for one day then it was annealed at 150°C for 3 hours. The DSSC structure was formed by using the synthesized-TiO2 as semiconductor material and beta-carotene as dye sensitizer. The x-ray diffraction (XRD) spectrum indicated that TiO2 peaks had anatase phases on crystal orientation of (101), (004), and (200) while TiO2 of rutile phase only appeared on orientation of (211). The highest intensity for all Rw was dominated by (101) anatase phase. From XRD spectrum data of (101) peak, the Scherrer’s method predicted that crystal size of TiO2 was 3.48 nm, 4.36 nm, and 4.47 nm for Rw of 0.85, 2.00, and 3.50, respectively. The Tauc’s method was applied on the UV-Vis data that predicted the bandgap energy (Eg) of TiO2 for Rw of 2.00 (Eg=3.14 eV) was higher than Rw of 0.85 (Eg=3.02 eV) and 3.50 (Eg=3.04 eV). The I-V characteristic calculation of DSSC structures were obtained that the efficiency optimum is 0.01% for Rw of 2.00. It is considered that bandgap energy value correlated to stability of Ti-OH bonds that caused the exited-electrons are easily injected to conduction band of TiO2. The performance of DSSC using the synthesized-TiO2 which consists of anatase and rutile can be improved about ten times compared to that using the pure-TiO2 rutile.

Properties of carbon nanotubes-doped Fe-sheath MgB2 for superconducting wires

Magnesium diboride (MgB2) is a potential superconductor materials that could be applied as superconducting wires due to its relatively high critical temperature. To study the influence of carbon nanotubes (CNT) on MgB2 wire manufacture, CNT-doped MgB2 superconducting wires have been fabricated from MgB2 and CNT powders sheathed in a SS304 stainless steel tube. In the process, the mixtures of MgB2 and CNT powders were inserted into the SS304 tubes and then were rolled and drawn. The properties of the fabricated superconducting wires were then analyzed through the crystal structure, surface morphology and temperature dependence of resistivity. The addition of CNT did not seem to have a significant influence on the crystal structure of Magnesium diboride. However, the addition of CNT caused the particle size of MgB2 became smaller. The temperature dependence of resistivity results showed that the critical temperatures were shifting linearly toward low temperatures due to the addition of CNT.

Ex-situ manufacturing of SiC-doped MgB2 used for superconducting wire in medical device applications

Magnesium diboride (MgB2) is a superconductor material with a relatively high critical temperature. Due to its relatively high critical temperature, this material is promising and has the potential to replace Nb3Sn for wire superconducting used in many medical devices. In this work, nanoparticle SiC-doped MgB2 superconducting material has been fabricated through an ex-situ method. The doping of nanoparticle SiC by 10 and 15 wt% was conducted to analyze its effect on specific resistivity of MgB2. The experiment was started by weighing a stoichiometric amount of MgB2 and nanoparticles SiC. Both materials were mixed and grounded for 30 minutes by using an agate mortar. The specimens were then pressed into a 6 mm diameter stainless steel tube, which was then reduced until 3 mm through a wire drawing method. X-ray diffraction analysis was conducted to confirm the phase, whereas the superconductivity of the specimens was analyzed by using resistivity measurement under cryogenic magnetic system. The results indi...

Optimizing the Nanostructural Characteristics of Chemical Bath Deposition Derived ZnO Nanorods by Post-Hydrothermal Treatments

Zinc oxide (ZnO) is an inorganic semiconductor material which has been widely studied due to its various potential applications. Over the past decades, one-dimensional (1-D) nanostructures such as nanowires and nanorods have stimulated significant scientific interests because of their unique properties in comparison to bulk materials. For the application of dye sensitized solar cell (DSSC), 1-D ZnO nanostructures are more desired than the spherical nanoparticles since the former provides ballistic effect leading to faster electron transfer which in turn can increase the device performance. Motivated by this consideration, in the current study ZnO nanorods were deposited on ITO glass substrate via chemical bath deposition (CBD) process where the seeding solution was prepared at 0°C. In order to increase their crystallinity and optical properties, the as-deposited ZnO nanorods were subjected to post-hydrothermal treatment at 150°C for 3, 6 and 9 hours. The scanning electron microscope (SEM) analysis revealed that the ZnO nanorods were successfully grown as vertically-aligned hexagonal structure, while the X-ray diffraction (XRD) study showed that the intensity of (002) crystal plane is the highest peak for all nanorod samples. The optical study by UV-Vis spectroscopy showed that the absorption edge of the as-deposited sample was slightly red-shifted to visible region after post-hydrothermal treatment. The ZnO nanorods sample derived from post-hydrothermal treatment for 6 hours provided the optimum nanostructural characteristics with an average diameter of 228 nm, crystallite size of 27.97 nm and the band gap energy, Eg, of 3.12 eV.

High Coverage ZnO Nanorods on ITO Substrates via Modified Chemical Bath Deposition (CBD) Method at Low Temperature

In the present work, ZnO nanorods array were successfully grown on ITO substrate via chemical bath deposition method (CBD). The seeding solution was prepared at low temperature (0°C) using zinc nitrate tetrahydrate and hexamethylenetetramine. The as-deposited ZnO nanorods were hexagonal wurtzite structure growing vertically on the substrate. Various reaction times from 3 to 5 hours were applied upon the CBD process at 90°C. The results showed that the duration of reaction time has affected the nanorods array properties. With the increase of reaction time from 3 to 5 hours has increased the diameter and crystallite size of nanorods from 325 to 583 nm, and from 22.68 to 34.28 nm. As a result, the band gap energy, Eg of ZnO nanorods decreased from 3.63 to 3.13 eV.