Study of deposition parameters for the fabrication of ZnO thin films using femtosecond laser

Femtosecond (fs) pulsed laser deposition (fs-PLD) of ZnO thin film on borosilicate glass substrates is reported in this work. The effect of important fs-PLD parameters such as target–substrate distance, laser pulse energy and substrate temperature on structure, morphology, optical transparency and luminescence of as-deposited films is discussed. XRD analysis reveals that all the films grown using the laser energy range 120–230 μJ are polycrystalline when they are deposited at room temperature in a ~10−5 Torr vacuum. Introducing 0.7 mTorr oxygen pressure, the films show preferred c-axis growth and transform into a single-crystal-like film when the substrate temperature is increased to 100 °C. The scanning electron micrographs show the presence of small nano-size grains at 25 °C, which grow in size to the regular hexagonal shape particles at 100 °C. Optical transmission of the ZnO film is found to increase with an increase in crystal quality. Maximum transmittance of 95 % in the wavelength range 400–1400 nm is achieved for films deposited at 100 °C employing a laser pulse energy of 180 μJ. The luminescence spectra show a strong UV emission band peaked at 377 nm close to the ZnO band gap. The shallow donor defects increase at higher pulse energies and higher substrate temperatures, which give rise to violet-blue luminescence. The results indicate that nano-crystalline ZnO thin films with high crystalline quality and optical transparency can be fabricated by using pulses from fs lasers

Zeolite microtunnels and microchunnels

Using a new fabrication strategy, novel, self-enclosed microporous silicalite-1 zeolite microtunnel and microchunnel architectures were successfully prepared

Zeolite micromembranes

Free-standing silicalite-1 (Sil-1) zeolite micromembranes have been successfully fabricated onto silicon substrate. Gas permeation test using permanent gases (i.e., helium, hydrogen, argon and nitrogen) and hydrocarbons (i.e., methane and n-butane) indicates that the micromembranes have excellent permeance flux and high permselectivity

Incorporating zeolites in microchemical systems

Using a new fabrication method based on microelectronic fabrication and zeolite thin film technologies, MFI-type zeolites with engineered structures were incorporated as catalyst, membrane and structural material within the design architecture of a microreactor, membrane microseparator and microeletrochemical cell. Complex microchannel geometry and network (<5 mum), as well as zeolite arrays (<10 mum) were successfully fabricated onto highly orientated supported zeolite films. The zeolite micropatterns were stable even after repeated thermal cycling between 303 and 873 K for prolonged period of time. Blueprints for zeolite-based microchemical systems were presented, and test units were fabricated and the structural details of the microdevices' architecture were analysed. (C) 2002 Elsevier Science B.V. All rights reserved

TS-1 zeolite microengineered reactors for 1-pentene epoxidation

A zeolite-based microengineered reactor was fabricated and tested for 1-pentene epoxidation over titanium silicalite-1 (TS-1) catalyst, which has been selectively incorporated within the microreactor channel using a new synthesis procedure

1-pentene epoxidation in catalytic microfabricated reactors

Silicon-glass microreactors with TS-1 catalyst wall coatings were fabricated and used for 1-pentene epoxidation with hydrogen peroxide in continuous flow. Seeding of the microchannels before zeolite growth was necessary to obtain a small crystal size and a sufficient zeolite film thickness. Crystal size was further reduced by adjusting synthesis conditions and utilizing triethoxymethylsilane (TEMS) as a crystal growth inhibitor. Zeolite film morphology and crystal orientation did not show any significant effect on reactor performance. However, reaction rate was found to increase with decreasing TS-1 crystal size in the zeolite films and with increasing amount of tetrahedrally coordinated Ti(IV). Catalyst deactivation was observed, caused by the presence of organic compounds and Ti leaching from the microporous framework. (C) 2003 Elsevier Inc. All rights reserved

Preparation of supported Sil-1, TS-1 and VS-1 membranes - Effects of Ti and V metal ions on the membrane synthesis and permeation properties

The incorporation of titanium and vanadium metal ions into the structural framework of MFI zeolite imparts the material with catalytic properties. These zeolites are good candidates for catalytic membranes. The Sil-1, TS-1 and VS-1 membranes were grown on pre-seeded porous stainless steel support using hydrothermal synthesis method. The effects of silica and metal (i.e. Ti and V) contents, template concentration and temperature on the zeolite membrane growth and morphology were investigated. The addition of Ti and V metal ions inhibits the zeolite growth and, thus, restricting the amount of metals (i.e. Ti and V) that can be effectively incorporated into the membrane without compromising its separation performance. Optimum Si and TPAOH concentrations were identified for the synthesis of well-intergrown zeolite membranes. An increase in the synthesis temperature can result in a change in film crystallographic orientation and the appearance of imperfections in the form of imbedded zeolite crystals. Single gas permeation experiments were conducted for noble gases (He and Ar), inorganic gases (H-2, N-2, SF6) and hydrocarbons (methane, n-C-4, i-C-4) to determine the separation performance of these membranes. The results indicate that the gas transport through Sil-1 and VS-1 membranes is predominantly through the zeolite pores and that the presence of vanadium in VS-1 has significant influence on the permeance of adsorbed gases (e.g. hydrocarbons). Laminar flow is important for the TS-1 membrane that exhibited microscopic cracks. (C) 2001 Elsevier Science B.V. All rights reserved

Hydrogen and proton transport properties of nanoporous zeolite micromembranes

This work reports the fabrication of HZSM-5 zeolite micromembrane and its performance for hydrogen permeation and proton transport. Although there are numerous works that discuss the fabrication of zeolite micromembranes, to our knowledge this is the first successful demonstration of gas permeation and proton transport in the zeolite micromembrane