Co-patterning chitosan and bovine serum albumin on an aldehyde-enriched glass substrate by microcontact printing

Chitosan and bovine serum albumin were co-patterned onto a glass substrate by microcontact printing technique. The process uses a microfabricated polydimethylsiloxane stamp to transfer chitosan on an aldehyde functionalized glass substrate, followed by adding a drop of albumin solution to the patterned side and holding for 30 min. After being washed with phosphate-buffered saline and cleaned by ultrasonic, the co-patterns of chitosan and albumin, each with their own micropatterns, were formed on the same surface. In this procedure, ultrasonic cleaning takes an important role to obtain clear patterns, whereas the printing/adding sequence has less influence. Moreover, patterns printed could give higher contrast than those assembled from solution. These co-patterns could find applications in cell localization and cell growth guidance.     

Atomic-scale cellular model and profile simulation of Si etching: Formation of surface roughness and residue

Formation mechanisms for profile anomalies such as surface roughness and residue have been investigated numerically and experimentally for Si etching in Cl₂/O₂ plasmas. The numerical simulation employed an atomic-scale cellular model (ASCeM) based on the Monte Carlo algorithm, which reproduced the feature profile evolution experimentally observed during etching at increased O₂ concentrations. A comparison between simulation and experiment indicated that the local surface oxidation induces surface roughness at the bottom of the feature during etching; then, synergistic effects between surface oxidation and ion scattering in microstructural features on roughened surfaces increase the surface roughness, which in turn causes a number of significant residues or micropillars on bottom surfaces of the feature. In practice, in roughened microstructural features, geometrical shadowing effects for neutral oxygen suppress the surface oxidation at the local feature bottom, where the energetic ion incidence is increased owing to ion scattering on sidewalls of the local feature.     

Artifacts in SPM measurements of thin films and coatings

Ideally, scanning probe microscopy (SPM) should generate a three-dimensional map of a sample surface such that the result is an exact replication of the actual sample. Any measurement data that result in an image differing from the actual sample surface are artifacts. The chief sources of SPM artifacts are mechanical systems, piezoelectric crystals, electronic scanners, tip-sample interaction, and image processing. For example, choosing the proper SPM probe for a specific sample is only the first step in minimizing probe-related artifacts. In fact, geometrical effects cause the largest number of artifacts. Good quality atomic SPM images can be clearly seen in raw data and should respond appropriately when the scan range or rotation is changed. Because SPM images are often periodic, it is possible for heavily filtered “data” to sometimes be misinterpreted as “atomic resolution images”. This paper presents SPM image studies using a range of materials from hard rough diamond films to soft nanometer smooth polyimide films. The investigation brings out the hidden sources of SPM artifacts for samples with different geometries and physical properties. Ten suggestions are presented which, if implemented/followed, should minimize the number of SPM image artifacts thereby assuring high quality images.     

Ice nucleation in water droplets on glass surfaces: From micro- to macro-scale

Ice nucleation encountered in engineering systems is often induced by solid/water interfaces. When classical nucleation theory is used to analyze ice nucleation in such systems, the uniformity of interfaces that contribute to ice nucleation must be carefully considered, because classical nucleation theory cannot be directly applied to non-uniform interfaces. In this study, to discuss the uniformity of ice nucleating activity of solid/water interfaces, ice nucleation in water droplets prepared on glass surfaces was investigated for various droplet sizes from micrometer to sub-millimeter. When the interfacial area between water and the glass surface was smaller than 1 × 10⁻¹⁰ m², the ice nucleation temperature showed scatter of about 2 °C, suggesting uniformity of the interface. However, when the interfacial area was larger than 1 × 10⁻⁸ m², the ice nucleation temperature showed large scatter, suggesting the ice nucleating activity was no longer uniform.     

Microcrystalline silicon deposition: Process stability and process control

Applying in situ process diagnostics, we identified several process drifts occurring in the parallel plate plasma deposition of microcrystalline silicon (μc-Si:H). These process drifts are powder formation (visible from diminishing dc-bias and changing spatial emission profile on a time scale of 10⁰ s), transient SiH₄ depletion (visible from a decreasing SiH emission intensity on a time scale of 10² s), plasma heating (visible from an increasing substrate temperature on a time scale of 10³ s) and a still puzzling long-term drift (visible from a decreasing SiH emission intensity on a time scale of 10⁴ s). The effect of these drifts on the crystalline volume fraction in the deposited films is investigated by selected area electron diffraction and depth-profiled Raman spectroscopy. An example shows how the transient depletion and long-term drift can be prevented by suitable process control. Solar cells deposited using this process control show enhanced performance. Options for process control of plasma heating and powder formation are discussed.     

Etching process optimization using NH4Cl aqueous solution to texture ZnO:Al films for efficient light trapping in flexible thin film solar cells

0.5 μm-thick aluminum-doped zinc oxide (ZnO:Al) films were deposited at 100 °C on polyethylene terephthalate substrates by Radio Frequency magnetron sputtering. The as-deposited films were compact and dense, showing grain sizes of 32.0 ± 6.4 nm and resistivities of (8.5 ± 0.7) × 10^− 4 Ω cm. The average transmittance in the visible wavelength range of the structure ZnO:Al/PET was around 77%. The capability of a novel two-step chemical etching using diluted NH₄Cl aqueous solution to achieve efficient textured surfaces for light trapping was analyzed. The results indicated that both the aqueous solution and the etching method resulted appropriated to obtain etched surfaces with a surface roughness of 32 ± 5 nm, haze factors at 500 nm of 9% and light scattering at angles up to 50°. To validate all these results, a commercially ITO coated PET substrate was used for comparison.     

Round pinholes in indium-tin-oxide thin films on the glass substrates: a Taguchi method analysis and theoretical approach to their origins

The origin of the round pinholes, ranging 30-70 μm in diameter, in indium-tin-oxide (ITO) thin films on the glass substrates were investigated. It has been found that the round pinholes in ITO thin films might arise from the tiny particles and organics, adsorbed onto the residual water of imperfectly pre-dried glass substrates at the pre-drying bath. The tiny particles and organics on the glass substrates might cause to weaken the adhesive powers between the ITO thin films and the glass substrates, finally resulting in the round pinholes at the photopatterning process.By Taguchi methods, it was revealed that the generation of the round pinholes in ITO thin films was directly related to the temperature and the amount of heat supply at the pre-drying bath. A simplified mechanism on the formation of the round pinholes in ITO thin films is proposed and verified.     

Structural and optical properties of electrospun ZnO nanofibres applied to P3HT:PCBM organic photovoltaic devices

Electrospun ZnO nanofibres with a diameter in the range of 74–125 nm were synthesised by optimising various parameters. Zinc acetate was used as a precursor and optimised to obtain a homogeneous and interconnected porous ZnO nanofibres network. The ZnO/poly(vinylpyrrolidone) composite nanofibres were calcined at 450 °C for 2.5 h to obtain continuous nanofibres network. The morphology of the nanofibres was studied by scanning electron microscopy and imageJ software. The structural and optical properties of the synthesised nanofibres were studied by surface profiler, X-ray diffraction and ultraviolet–visible spectroscopy. The grain size increased while the bandgap was observed to decrease with increased precursor concentration. The effect of precursor concentration was also studied to improve the power conversion efficiency of ZnO nanofibres/poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) photovoltaic device. The efficiency was improved from 0.896 ± 0.007% to 2.29 ± 0.03% by introducing the electrospun ZnO nanofibres.     

Electron spectroscopy (UPS(HeI and II) and metastable impact electron spectroscopy (MIES)) applied to molecular surfaces: the interaction of atoms and molecules with solid water

We report studies of the interaction of atoms and molecules with solid molecular surfaces, water in particular, by combining photoelectron spectroscopy, UPS with HeI and II, and metastable impact electron spectroscopy (MIES). In MIES charge exchange processes of the Auger-type taking place between metastable He atoms and the surface under study are utilized to gain information on their electronic structure. The MIES spectra give a rather direct image of the surface DOS. We concentrate on the following processes taking place on water films produced at 80 K:(1) Interaction of Na Atoms with Amorphous Solid H₂O Films: emphasis was on the role of the 3sNa electrons in the water dissociation process. In order to make a detailed comparison with density functional theory (DFT), DOS (density of states) information is compared with the MIES spectra. Our results are consistent with the theoretical prediction that the 3s-electron is delocalized from the Na-core and trapped (solvated) between the Na-core and water molecules of the surrounding water shell.(2) Ionization and Solvation of NaCl Interacting with Amorphous Solid Water: at 90 K there is no interpenetration of H₂O and NaCl. However, ionic dissociation of NaCl takes place when H₂O and NaCl are in direct contact. At 105 K the solvation of the ionic species Cl⁻ and Na⁺ becomes significant. The desorption of H₂O from the mixed film takes place between 145 and 170 K; those species bound ionically to Na⁺ and Cl⁻ are removed last.(3) The Interaction of PBTs (persistent, bio-accumulative, and toxic substances), chlorobenzene and chlorophenyl, with amorphous solid water: the organic layers produced at 80 K were annealed up to 200 K under in situ control of MIES and UPS. The different behaviour of the interfaces for the three studied cases is traced back to the different mobilities of the molecules with respect to that of water. The interaction between H₂O and the benzene derivatives is discussed on the basis of qualitative free energy profiles.     

A quality-by-design study to develop Nifedipine nanosuspension: examining the relative impact of formulation variables,wet media milling process parameters and excipient variability on drug product quality attributes

Abstract

Wet milling is a multifunctional and the most common method to prepare a drug nanosuspension for improving the bioavailability of poorly water soluble drugs. A suitable way of preparing a high drug-loaded nifedipine nanosuspension using wet stirred media milling was investigated in the present study. Nifedipine, a poorly water soluble drug, was selected as a model drug to enhance its dissolution rate and oral bioavailability by preparing an appropriate crystalline nanosuspension. Process parameters, such as milling media volume, milling speed and milling time, were optimized using the one variable at a time (OVAT) approach. A similar method was used to select an appropriate polymeric stabilizer and a surfactant from different categories of polymeric stabilizers (HPC SL, HPC SSL Soluplus®, Kollidon^® VA 64 and HPMC E 15) and surfactants (Poloxamer 407, Kolliphor TPGS and Docusate sodium). A systematic optimization of critical formulation parameters (such as drug concentration, polymer concentration and surfactant concentration) was performed with the aid of the Box-Behnken design. Mean particle size, polydispersity index and zeta potential as critical quality attributes (CQAs) were selected in the design for the evaluation and optimization of the formulation and validation of the improved product. The nifedipine nanosuspension that was prepared using HPC and poloxamer 407 was found to be most stable with the lowest mean particle size as compared with the formulations prepared using other polymeric stabilizers and surfactants. The optimized formulation was further spray-dried and characterized using the Fourier Transform Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), polarized light microscopy (PLM) and in-vitro dissolution study. Results have shown no interaction between the drug particles and stabilizers, nor a reduction in the crystallinity of drug, nor an increase in the saturation solubility and rapid in vitro dissolution as compared with pure nifedipine crystals. Thus, the current study supports the suitability of the wet stirred media milling method and a combination of HPC SSL and poloxamer 407 as stabilizers for the preparation of nifedipine nanosuspension.     

The particle finite element method: a powerful tool to solve incompressible flows with free‐surfaces and breaking waves

Particle Methods are those in which the problem is represented by a discrete number of particles. Each particle moves accordingly with its own mass and the external/internal forces applied to it. Particle Methods may be used for both, discrete and continuous problems. In this paper, a Particle Method is used to solve the continuous fluid mechanics equations. To evaluate the external applied forces on each particle, the incompressible Navier–Stokes equations using a Lagrangian formulation are solved at each time step. The interpolation functions are those used in the Meshless Finite Element Method and the time integration is introduced by an implicit fractional‐step method. In this manner classical stabilization terms used in the momentum equations are unnecessary due to lack of convective terms in the Lagrangian formulation. Once the forces are evaluated, the particles move independently of the mesh. All the information is transmitted by the particles. Fluid–structure interaction problems including free‐fluid‐surfaces, breaking waves and fluid particle separation may be easily solved with this methodology. Copyright © 2004 John Wiley & Sons, Ltd.