Optimum Fabrication Conditions Research Articles

Femtosecond Laser Fabrication of Cavity Microball Lens (CMBL) inside a PMMA Substrate for Super-Wide Angle Imaging.

Since microlenses have to date been fabricated primarily by surface manufacturing, they are highly susceptible to surface damage, and their microscale size makes it cumbersome to handle. Thus, cavity lenses are preferred, as they alleviate these difficulties associated with the surface-manufactured microlenses. Here, it is shown that a high repetition femtosecond laser can effectively fabricate cavity microball lenses (CMBLs) inside a polymethyl methacrylate slice. Optimal CMBL fabrication conditions are determined by examining the pertinent parameters, including the laser processing time, the average irradiation power, and the pulse repetition rates. In addition, a heat diffusion modeling is developed to better understand the formation of the spherical cavity and the slightly compressed affected zone surrounding the cavity. A micro-telescope consisting of a microscope objective and a CMBL demonstrates a super-wide field-of-view imaging capability. Finally, detailed optical characterizations of CMBLs are elaborated to account for the refractive index variations of the affected zone. The results presented in the current study demonstrate that a femtosecond laser-fabricated CMBL can be used for robust and super-wide viewing micro imaging applications.

Effect of Substrate Temperature on Ti/TiO2 Layers Growth Using a Combined Sputtering/Sol-Gel Combustion Method.

A combined radio frequency sputtering/sol-gel combustion method was investigated in order to obtain optimum process condition for fabrication of a Titanium (Ti)/Titanium oxide (TiO2) films electrode of transparent conductive oxide-less dye-sensitized solar cells (TCO-less DSCs), Experimentally, the substrate temperature was changed from R.T. to 500 °C, and it was found that there existed an optimum value for efficient performance of the cell. The porous Ti layer with low sheet resistance (-2.5 Ω/sq.) can be prepared by substrate temperature 250 °C under RF power 300 W and Ar 8 mTorr. The efficiency (η) of the cell was 6.52% [FF: 0.76, VOC: 0.72 V, JSC: 11.91 mA/cm2].

Electrochromic properties of bipolar pulsed magnetron sputter deposited tungsten–molybdenum oxide films

There are great interests in electrochromic technology for smart windows and displays over past decades. In this study, the WMoOx thin films were deposited onto indium tin oxide glass and silicon substrates by pulsed magnetron sputter system with W and Mo targets. The films were deposited with fixed W target power while the variant parameter of Mo target power in the range 50, 100, 150 and 200W was investigated. The working pressure was fixed at 1.33Pa with a gas mixture of Ar (30sccm) and O2 (15sccm). The film thickness increased with the Mo target power. Higher plasma power resulted in a crystalline structure which would reduce the electrochromic property of the film. The influence of plasma powers applied to Mo target on the structural, optical and electrochromic properties of the WMoOx thin films has been investigated. WMoOx films grown at Mo target powers less than 100W were found to be amorphous. The films deposited at 150W, which is the optimal fabrication condition, exhibit better electrochromic properties with high optical modulation, high coloration efficiency and less color memory effect at wavelength 400, 550 and 800nm. The improvement resulted from the effect of doping Mo has been tested. The maximum ΔT (%) values are 36.6% at 400nm, 65.6% at 550nm, and 66.6% at 800nm for pure WO3 film. The addition of Mo content in the WMoOx films provides better resistance to the short wavelength light source and can be used in the concerned application.

Novel magnetic cross-linked lipase aggregates for improving the resolution of (R, S)-2-octanol.

Novel magnetic cross-linked lipase aggregates were fabricated by immobilizing the cross-linked lipase aggregates onto magnetic particles with a high number of -NH2 terminal groups using p-benzoquinone as the cross-linking agent. At the optimal fabrication conditions, 100% of immobilization efficiency and 139% of activity recovery of the magnetic cross-linked lipase aggregates were achieved. The magnetic cross-linked lipase aggregates were able to efficiently resolve (R, S)-2-octanol, and retained 100% activity and 100% enantioselectivity after 10 cycles of reuse, whereas the cross-linked lipase aggregates only retained about 50% activity and 70% enantioselectivity due to insufficient cross-linking. These results provide a great potential for industrial applications of the magnetic cross-linked lipase aggregates.

Development of indium tin oxide thin film toluene sensor

Thin films of indium tin oxide (ITO) were deposited using thermal evaporation technique. Various sets of thin film sensors were prepared under the optimized fabrication conditions. The response of the sensors to the quantitative presence of toluene was studied. The sensing mechanism to explain the redox reactions on the surface of ITO film was developed. The films were coated with thin layers of metals and oxide to enhance the performance for the sensitive and selective detection of toluene. The response of toluene sensor in the detection range 10–1000ppm was examined.

The impact of solvent and modifier on ZnO thin-film transistors fabricated by sol-gel process

Techniques for fabricating solution-processed zinc oxide (ZnO)-based thin-film transistors (TFTs) are feasible with solution using various routes. Here, ZnO TFTs were fabricated via sol-gel method using zinc acetate as the starting reagent with different modifiers and solvents. The ZnO thin-film semiconductors with well-controlled, preferential crystal orientation and densely packed ZnO crystals can be prepared with the optimized fabrication conditions, exhibiting excellent field-effect far exceeding those of hydrogenated amorphous silicon (a-Si:H). However, the field-effect characteristics of ZnO TFTs were different for different precursor systems which were constituted by zinc acetate, modifiers and solvents. The co-modification of acetoin and monoethanolamine for the precursor system exhibited higher extent of crystal orientation and field-effect. The maximum mobility of 7.65 cm2V-1s-1 and current on-to-off ratio of ~105 - 106 have been obtained.

Production of mixed matrix hollow fiber membrane for CO2/CH4 separation

Studies on mixed matrix membrane (MMM) have been sprouting rapidly since the last few decades, but mostly fabricated in the form of dense, flat films. In this work, hollow fiber Polysulfone (PSF)-Cloisite®15A (C15A) MMM were produced using our in-house hollow fiber spinning machine. Various spinning parameters are at play in order to ensure the formation of defect-free high performance hollow fiber. Spinning process parameters such as dry gap height, force convection rate, dope extrusion rate, and take-up speed have been systematically studied in order to identify the optimum fabrication conditions. Extensive characterizations on the membrane morphology, membrane surface properties, polymer d-spacing and gas separation performance were conducted using SEM, AFM, XRD, and pure gas permeation experiment. The appropriate balance between dry-gap residence time and force convective rate is essential to yield membrane with good permeability–selectivity combinations. CO2 permeance was increased from 17.39 to 56.25×10−6cm3(STP)/cm2scmHg when the dope extrusion rate was increased from 1.5cm3/min to the optimum extrusion rate of 2.5cm3/min. Membranes spun at high collection speed (up to 35m/min) exhibited practically attractive fiber geometry comparable to commercial hollow fibers (∼300μm diameter) but the permeation properties were rather disappointing which might be caused by excessive deformation of polymer chain due to stretching. Hollow fiber MMM containing layered organoclay has exhibited excellent CO2/CH4 pure gas selectivity of 40.26%, 46% higher than that of pristine hollow fiber fabricated under the same optimized conditions without compromising the CO2 flux. The MMM was also found to be more thermally and mechanically robust in comparison to its neat counterpart.

Double-Deck Inverse Opal Photoanodes: Efficient Light Absorption and Charge Separation in Heterojunction

For the first time, double-deck WO3/BiVO4 inverse opal photoanodes (DDIO-WO3/BiVO4) were prepared by swelling–shrinking mediated polystyrene template synthetic routes, and the use of the photoanodes in photoelectrochemical cells under simulated solar light was investigated. The double-deck photoanodes represented the compact interface between WO3 and BiVO4, inheriting the periodically ordered macroporous nanostructure. More significantly, the DDIO-WO3/BiVO4 inverse opal photoanodes prepared from the optimized fabrication condition demonstrated a photocurrent that was ∼40 times higher than that of the pure inverse opal WO3 photoanodes at a bias of 1.23 V vs RHE. Even without an added catalyst, they produce an outstanding photocurrent density of ∼3.3 mA/cm2 at a bias of 1.23 V vs RHE, which profits from improving the poor charge carrier mobility of BiVO4 by combining it with a WO3 skeleton and a shrouded bilayer inverse opal structure with a large surface area and good contact with the electrolyte.

Development of ITO thin film sensor for detection of benzene

Benzene being a major pollutant and a potential human carcinogen, development of a sensitive and selective sensor for its detection is the need of the hour. In the present work, the studies on the development of indium tin oxide thin film sensor for detection of benzene are presented. Thin films of indium tin oxide (ITO) were deposited using thermal evaporation technique, and, under the optimized fabrication conditions, sets of sensors were fabricated. Their response to benzene vapours was studied. The sensing mechanism explaining the redox reactions on the surface of ITO has been proposed. The films were coated with thin layers of metals and oxides to enhance the performance for the sensitive and selective detection of benzene. Cross sensitivity of benzene with respect to toluene was studied and selectivity was obtained with a two layered structure of Cr/ITO.

Influence of nano-sized LSCF cathode and its firing temperature on electrochemical performance in oxygen-excess-type solid electrolyte (OESE)-based fuel cells

Dense films of an oxygen-excess-type solid electrolyte (OESE) based on Mg-doped lanthanum silicate (MDLS) were fabricated and applied to electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). To obtain dense MDLS films on NiO-MDLS porous substrates, a conventional spin-coating technique using the MDLS printable paste, obtained by mixing nano-sized MDLS particles and a dispersant, was employed. The Ni-MDLS anode supported single cells were then fabricated by printing porous cathode layer onto the electrolyte film surface. By optimizing fabrication conditions of an MDLS film and cathode, the highly active cathode/OESE interface (ASR = 0.23 Ω cm2 at 873 K) were successfully obtained, which resulted in high power density of 0.166 W cm−2 at 873 K in the fuel cell test when operated with argon-diluted hydrogen and pure oxygen as the fuel and the cathode gas, respectively.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows.

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Efficient in vitro gene delivery by hybrid biopolymer/virus nanobiovectors.

Recombinant retroviruses provide highly efficient gene delivery and the potential for sustained gene expression, but suffer from significant disadvantages including low titer, expensive production, poor stability and limited flexibility for modification of tropism. In contrast, polymer-based vectors are more robust and allow cell- and tissue-specific deliveries via conjugation of ligands, but are comparatively inefficient. The design of hybrid gene delivery agents comprising both virally derived and synthetic materials (nanobiovectors) represents a promising approach to development of safe and efficient gene therapy vectors. Non-infectious murine leukemia virus-like particles (M-VLPs) were electrostatically complexed with chitosan (χ) to replace the function of the viral envelope protein. At optimal fabrication conditions and compositions, ranging from 6 to 9μg chitosan/10(9) M-VLPs at 10×10(9)M-VLPs/ml to 40μg chitosan/10(9) M-VLPs at 2.5×10(9)M-VLPs/ml, χ/M-VLPs were ~300-350nm in diameter and exhibited efficient transfection similar to amphotropic MLV vectors. In addition, these nanobiovectors were non-cytotoxic and provided sustained transgene expression for at least three weeks in vitro. This combination of biocompatible synthetic agents with inactive viral particles to form a highly efficient hybrid vector is a significant extension in the development of novel gene delivery platforms.

Fabrication of Sr silicate buffer layer on Si(100) substrate by pulsed laser deposition using a SrO target

The authors fabricated 2 × 1 Sr-reconstructed Si(100) substrates using thin SrO layers, and used them to direct growth of crystalline perovskite oxide on Si. The SrO layers used to reconstruct the Si(100) substrates were grown by pulsed laser deposition from a SrO single crystal target, followed by postdeposition-annealing (PDA) of the SrO/Si(100) structure. In situ observations of reflective high-energy electron diffraction during PDA confirmed a 2 × 1 reconstruction of the Si surface and x-ray photoemission spectroscopy of the annealed samples confirmed the existence of Sr atoms in a silicate phase, which indicated that a 2 × 1 Sr-reconstructed Si surface was achieved. The optimal fabrication conditions were annealing at 720 °C for 1 min and an equivalent SrO layer thickness (MLeq) of 2.5 MLeq. The temperature condition was very narrow, at 720 ± 20 °C, for an acceptable product. Subsequently, the authors demonstrated the growth of crystalline SrTiO3 films on the 2 × 1 Sr-reconstructed Si(100) surfaces.

Fabrication of dye-sensitized solar cells from thin films of zinc oxide nanocrystalline particles and organic dye

Photovoltaic solar modules, which are mostly made of silicon based solar cells, are still expensive to the common people of Nepal. The high cost is, mainly, due to the processing difficulties to get pure crystalline silicon. Here, we present results on devising efficient and low-cost dye sensitized solar cells (DSSCs). The solar cells were fabricated from transparent thin film of zinc oxide (ZnO), as a semiconductor, on top of which a thin layer of synthetic organic dye was deposited for efficient light harvesting. In order to achieve the films with optimum conditions for solar cell fabrication, we prepared transparent thin films of ZnO of various thicknesses and characterized by measuring their light transmittance by UV-Visible spectrophotometry. The results clearly show variation in transmittance curves with variation in film’s thickness. Also for finding appropriate sensitizer for ZnO nanoparticles, we extensively investigated the light absorbance of synthetic organic dyes. Among the dye species investigated, Green-VS, Patent-Blue, and Black-ADLI show strong absorbance over the wide range in the visible spectrum, demonstrating prospect of utilizing for DSSCs. Then prototype solar cells from ZnO film with various thicknesses were constructed and were sensitized with the mixture of Green-VS and Black-ADLI dyes (with 1:1 ratio). The measured photo-voltage and photo-current from solar cell, from our modest ZnO film, after irradiation with 200 W commercial bulb (calibrated with Pyranometer) as a light source, were about 20 mV and 1 μA, respectively. Also, with increment of the power of radiation both the measured photo-current and photo-voltage increase. Performance of the cell in real sun condition has also been made. With the solar radiation power of 930 W, the observed photo-voltage and photo-current were ca. 230 mV and 50 μA, respectively. DOI: http://dx.doi.org/10.3126/bibechana.v11i0.10380 BIBECHANA 11(1) (2014) 53-59

Investigation of Process Parameters and Characterization of Nanowire Anisotropic Conductive Film for Interconnection Applications

In this paper, the assessment of the electrical and mechanical performance of the Cu nanowire anisotropic conductive film (NW-ACF) flip-chip interconnects has been performed. The influence of bonding conditions (bonding temperature and bonding force) has been studied in order to understand their impact on bonding resistance and shear strength for two types of NW-ACF based on different templates with varying porosity and thickness. An overgrowth-stripping method has been employed to obtain uniform NW (200 and 220 nm) arrays in the track-etch polymer membranes. The bonding substrate was coated with indium so that a diffusion soldering between Cu NWs and bulk In film can occur at a relatively low eutectic point (156.6 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> ). The bonding interface and the fractural surface of NW-ACFs have been characterized by scanning electron microscope and energy dispersive X-ray analysis. Under optimized fabrication conditions, process at the bonding profile of 200 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> , 20 N shows that the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$z$</tex></formula> -axis resistance can be below 1 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm m}\Omega$</tex></formula> and the shear strength can be above 10 MPa, which is very promising for the fine pitch, 3-D interconnection applications in the future.

Metallization‒induced recombination losses of bifacial silicon solar cells

AbstractIn this study, we investigate the metallization‒induced recombination losses of high efficiency bifacial n‒type and p‒type crystalline Si solar cells. From the experimental data, we found that the most efficiency limiting parameter by the screen‒printed metallization is the open‒circuit voltage (VOC) of the cells. We investigated the mechanism responsible for this loss by varying the metallization fraction on either side of the cell and determined the local enhancement in the dark saturation current density beneath the metal contacts (J0(met)). Under optimum fabrication conditions, the J0(met) at metal‒p+ (boron) emitter interfaces was found to be significantly higher compared with the values obtained for metal‒n+ emitters. A two‒dimensional simulation model was used to get further insight into the recombination mechanism leading to these VOC losses. The model assumes that metal contacts penetrate (or etch) into the diffused region following the firing process and depassivate the interface. Applying this model to our n‒type solar cells with a boron p+ emitter, we demonstrated that the simple loss of passivated area beneath the metal contact cannot explain the degradation observed in the VOC of the cell without considering a significant etching or metal penetration into the emitter region. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Vortex pinning and magnetic peak effect in Eu(Eu,Ba)2.125Cu3Ox

Eu–Ba–Cu–O composition was synthesized by solid state reaction technique. To determine optimum growth temperature, heat treatment was examined on the material at 880–1,100 °C. Microstructural evolution, phase formation and elemental distribution depending on heat treatments were examined by using X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope analysis. Optimum fabrication conditions were determined as 1,020 °C for 24 h under oxygen atmosphere and detailed characterization of corresponding compound was performed. The magnetization hysteresis loops are expounded to be the product of superconducting Eu-123 grains and magnetic Eu2+ ions. The peak effect on the magnetization curves was described by the extended critical state model. Scaling of the pinning force was found such that the peak position is proportional to the irreversibility field H irr and the maximum pinning force is proportional to H irr 2 .

Stability of LSCF electrode with GDC interlayer in YSZ-based solid oxide electrolysis cell

Abstract The performance and stability of La0.6Sr0.4Co0.2Fe0.8O3 − δ (LSCF) air electrode with Gd0.2Ce0.8O2 − δ (GDC) as an interlayer were tested in the Solid Oxide Electrolysis Cell (SOEC) mode. In order to study the stability and performance of the LSCF air electrode, an 8 mol% Y2O3-stabilized zirconia (YSZ) electrolyte supported on a Ni–YSZ fuel electrode was fabricated with and without a GDC interlayer, which was inserted between YSZ and LSCF. To determine the stability of the interlayer and find the optimum fabrication conditions, cells with the GDC interlayer were also co-fired at temperatures in the range of 1300–1500 °C and their performance was compared. Single cells were tested with an anodic polarization of 800 mA/cm2 in 80% H2O + 20% H2 at 800 °C. The cell without an interlayer showed a large increase in Ohmic Area Specific Resistance (ASR) from 0.09 Ωcm2 to 0.16 Ωcm2 during 50 h of operation due possibly to the observed delamination between the LSCF and YSZ. On the other hand, the cell with the interlayer showed a slower increase in Ohmic ASR from 0.14 Ωcm2 to 0.153 Ωcm2 with little delamination. The electrode polarization ASR of the cell with the interlayer also had a similar slower change, from 0.16 to 0.185 Ωcm2, compared to that of the cell without an interlayer, from 0.143 to 0.35 Ωcm2, after 50 h. The cell co-fired at 1400 °C had the smallest and most stable value of the total ASR for 100 h.

Controlled release of glial cell line-derived neurotrophic factor from poly(ε-caprolactone) microspheres.

Glial cell line-derived neurotrophic factor (GDNF), a growth factor expressed in the central nervous system, promotes the survival of both dopaminergic and motor neurons, making it a promising candidate for neurodegenerative disease therapy. Although GDNF is currently being evaluated in clinical trials for the treatment of Parkinson's disease (PD), the current delivery method using catheter implantation has certain limitations in terms of delivering GDNF safely and effectively. As a proof of concept, we encapsulated GDNF into poly(ε-caprolactone) (PCL) microspheres to enable controlled drug release for 25days. First, microspheres were loaded with bovine serum albumin (BSA) to determine the optimal fabrication conditions necessary to achieve the desired release rates of protein. BSA was then used as a carrier protein to preserve GDNF activity during the fabrication process in the presence of organic solvents. GDNF-encapsulated microspheres were created and characterized using scanning electron microscopy. Next, the in vitro release of GDNF along with microsphere morphology was tracked over 25days. Finally, the bioactivity of the released GDNF was confirmed using PC12 cells. This work demonstrates the potential of such microspheres for the delivery of bioactive GDNF with the end goal of developing a suitable, clinically relevant formulation for injection to appropriate regions of the brain in PD patients.

Post-Electrophoretic Deposition Electrochemical Separation (PEPDECS): Optimization of the Fabrication of Freestanding Carbon Nanotube Films

Scalable fabrication of freestanding carbon nanotube films (buckypapers) is of notable interest in nanotechnology due to emerging, real world applications for these lightweight and flexible materials. Post-electrophoretic deposition electrochemical separation (PEPDECS), a recently developed method for the scalable production of buckypapers, involves the electrophoretic deposition (EPD) of charged carbon nanotubes onto a flat substrate in a parallel-plate capacitor configuration, followed by a reversal of the direction of the electric field to detach the film. This study explored the characteristics of the deposition and liberation of the delaminated film, such as the applied voltage and the electrode size, in search of the optimum conditions for high quality buckypaper fabrication. Bubble formation on the film, due to the electrolysis of the suspension, increased as a function of the current density. The time required to delaminate a film completely from its underlying substrate was higher at higher initial current densities. Additionally, only when the applied EPD voltage was ≥2.8 V was the integrity of the buckypaper sufficient for them to be handled. The mechanical properties of the resulting films were examined to quantify their integrity. These experiments demonstrate the dependency of successful film fabrication on variable conditions during the initial EPD and provide a means to control the properties of the final films.