Cyrus Zamani

Nanocasting Synthesis of Ultrafine WO3 Nanoparticles for Gas Sensing Applications

Ultrafine WO3 nanoparticles were synthesized by nanocasting route, using mesoporous SiO2 as a template. BET measurements showed a specific surface area of 700 m 2/gr for synthesized SiO2, while after impregnation and template removal, this area was reduced to 43 m 2/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated by deposition of WO3 nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this material has a high sensitivity to very low concentrations of NO2 at 250°C and 300°C.

Mesoporous Silica: A Suitable Adsorbent for Amines

Mesoporous silica with KIT-6 structure was investigated as a preconcentrating material in chromatographic systems for ammonia and trimethylamine. Its adsorption capacity was compared to that of existing commercial materials, showing its increased adsorption power. In addition, KIT-6 mesoporous silica efficiently adsorbs both gases, while none of the employed commercial adsorbents did. This means that KIT-6 Mesoporous silica may be a good choice for integrated chromatography/gas sensing micro-devices.

Nano- and microvoid formation in ultrafine-grained martensitic Fe-Ni-Mn steel after severe cold rolling

Severe cold-rolling was applied on solution annealed Fe-Ni-Mn steel with fully lath martensite structure to obtain ultrafine-grained structure. Field emission scanning electron microscopy and high resolution transmission electron microscopy (HRTEM) were employed to investigate the microstructural evolution after severe cold-rolling. HRTEM images showed the typical deformed structure consisting of lamellar dislocation cell blocks. HRTEM study also revealed strain-induced reverse martensitic transformation (activated during grain refinement). It was assumed that severe plastic deformation route and related deformation mode were responsible for microstructural evolutions. X-ray diffraction (XRD) diagram revealed 7% (volume fraction) reverted austenite after final deformation pass. Moreover, HRTEM images revealed nano-void nucleation at the interface of severely deformed martensite and reverted austenite presumably due to high strain energy of misfit and molar volume difference between the austenite and the martensite. It seems that the coalescence of nano-voids could lead to the formation of microvoids in the microstructure.

Nanocasting Synthesis of Ultrafine WO 3 Nanoparticles for Gas Sensing Applications

Ultrafine WO3 nanoparticles were synthesized by nanocasting route, using mesoporous SiO2 as a template. BET measurements showed a specific surface area of 700 m 2/gr for synthesized SiO2, while after impregnation and template removal, this area was reduced to 43 m 2/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated by deposition of WO3 nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this material has a high sensitivity to very low concentrations of NO2 at 250°C and 300°C.

Residual Stress Relaxation Induced by Mass Transport Through Interface of the Pd/SrTiO3

Metal interconnections having a small cross-section and short length can be subjected to very large mass transport due to the passing of high current densities. As a result, nonlinear diffusion and electromigration effects which may result in device failure and electrical instabilities may be manifested. Various thicknesses of Pd were deposited over SrTiO3 substrate. Residual stress of the deposited film was evaluated by measuring the variation of d-spacing versus sin2ψ through conventional X-ray diffraction method. It has been found that the lattice misfit within film and substrate might be relaxed because of mass transport. Besides, the relation between residual intrinsic stress and oxygen diffusion through deposited film has been expressed. Consequently, appearance of oxide intermediate layer may adjust interfacial characteristics and suppress electrical conductivity by increasing electron scattering through metallic films.

AC Electrophoresis, a New Technique for Deposition of Ceramic Nanoparticles; Introduction, Application and Mechanism

Deposition of ceramic nanoparticles (dispersed in non-aqueous suspension) on in-plane electrodes and under the influence of AC electric fields in the frequency range of 0.01 Hz - 10 kHz is investigated. Analysis of the particle response to the applied field is a difficult task due to the mutual effect of electric and hydrodynamic forces which are present in the system. In this work, however, we show the possibility of dividing the frequency range into four domains with four distinct governing mechanisms. Possible mechanisms are suggested and dominant forces are determined for each domain. In situ optical microscopy observations are used for visualization of nanoparticles´ movement dispersed in liquid medium. These observations show that applying AC electrophoresis at frequencies below 10 kHz is an effective way for manipulating ceramic nanoparticles and device fabrication.

Nano-Bio Structures Developed via Electrophoresis

In recent decades, application of electric fields for manipulation of biological particles has been witnessing a rapid growth. Electrophoresis, in particular, now is a phenomenon with widespread use in biological applications and processes for manipulation of biological species such as cells, enzymes and proteins. Electrophoretic deposition (EPD) is a cheap and versatile technique based on electrophoresis in which charged particles suspended in a liquid medium move toward a substrate and deposit there following the electric field lines. Historically, only DC fields have been tried for material deposition since it was theoretically accepted that AC electric fields cause particles oscillate at their position due to field reversal in each half cycle. Recently, however, researchers showed that alternating fields can also be employed for material deposition, a fact which attracted the attention of scientists to its potentiality in separation, trapping, assembling, transportation and characterization of nano/bio particles. Works on bio-particles are performed in a wide range of frequencies. However, low frequencies (below 10 kHz) are not preferred for manipulation of biosepecies. Thus, experimental and theoretical studies have been focused on application of high frequency AC electric fields so far. Ceramic particles, in contrast, are not sensitive to non-aqueous medium without the risk of electrolysis and working at low frequencies becomes possible. Therefore, low frequency AC electrophoretic deposition (LFACEPD) is considered as a promising process for manipulation and controlled deposition of bioactive ceramic oxide thin films. This chapter deals with electrophoretic manipulation of oxide nanoparticles—through experiments as well as theoretical computations—for being deposited as bioactive thin films on substrates of various conductivities introducing some phenomena arising in such systems.

Mesoporous ceria-zirconia solid solutions as oxygen gas sensing material using high temperature hot plates

Mesoporous ceria and ceria-zirconia solid solutions have been synthesized following a route based on the use of silica hard template. Two different structures have been selected, one based on a three dimensional gyroidal structure, named KIT6, and other based on a two dimensional layered structure named SBA15. The presence of zirconium in the ceria sub lattice enhances the capability to transform Ce+4 to Ce+3 such as it is proved from the thermogravimetry measurements that show a large increase of the oxygen storage capacity. Ce(1-x)ZrxO2 solid solutions prepared making replicas of previously synthesized mesoporous silica have been characterized and tested under different oxygen-containing atmospheres at sensing temperatures above 500oC with oxygen variation between 1% to 100% of oxygen. This binary compound oxide present a variation of its electrical conductivity with the oxygen partial pressure that follow a potential law R=Ro[O2]1/n with n = 4 corroborating that the sensing mechanism is dominated by electronic conductivity processes related to the contribution of the Ce+3. Therefore, these high stable mesoporous materials with high active surface become a promising candidate as oxygen sensing materials for gas sensing hotplate platforms.

Nanocasting Synthesis of Ultrafine WO3

Ultrafine WO3 nanoparticles were synthesized by nanocasting route, using mesoporous SiO2 as a template. BET measurements showed a specific surface area of 700 m 2/gr for synthesized SiO2, while after impregnation and template removal, this area was reduced to 43 m 2/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated by deposition of WO3 nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this material has a high sensitivity to very low concentrations of NO2 at 250°C and 300°C.