Macroscopic Uniformity Research Articles

Improving the macroscopic uniformity of nanopaper by multi‐step coating of cellulose nanofibre dispersion

Promising versatile applications of cellulose nanofibres (CNFs) include film structures for device substrates and surface coatings. Although there are various factors that affect the textures of such ‘nanopapers’, the drying from aqueous dispersion of CNF is the typical process to fabricate them. The basic property on this drying process is focused on, paying attention to the influence of temperature on the macroscopic uniformity. On the one hand, higher drying temperature is advantageous for the fast fabrication. On the other hand, too high temperature leads to significant nonuniformity, are focused on of the film. They propose that this drawback is suppressed by the multi-step coating process. The multi-step coating technique is simple without extra introduction of apparatus or chemical species. Therefore, it is a good option, e.g. when trying to fabricate relatively thin film structures where coffee-ring-like phenomena tend to take place.

Effects of precursor concentration on the microstructure and properties of ZrC modified C/C composites prepared by precursor infiltration and pyrolysis

To improve the ablation resistance of C/C composites, ZrC modified composites were fabricated by precursor infiltration and pyrolysis combined with gradient chemical vapor infiltration process. The effects of ZrC precursor concentration on the microstructure, mechanical and ablation properties of the composites were studied. Results showed that with the increase of ZrC precursor concentration, the ZrC content and macroscopic uniformity of the composites increased but with obvious ZrC particle aggregation and the flexural strength decreased gradually. As the concentration of ZrC precursor improved to 60%, the fracture mode of the composites transformed from toughness to brittleness which was mainly attributed to the improved graphitization degree and reaction damage of carbon fiber in the precursor pyrolysis process. However, the ablation resistance was enhanced with the increasing precursor concentration which was resulted from the formation of ZrO2 in center ablation region and continuous ZrO2 coating in brim region serving as a barrier to heat and oxygen transfer.

Development of a continuous direct compression platform for low-dose drug products

In this work a continuous direct compression process was developed for a low-dosed drug product. Each unit operation of the GEA CDC-50 system was thoroughly investigated. This paper aimed to tackle the macroscopic and microscopic blend uniformity challenges inherently associated with continuous direct compression of cohesive and agglomerated APIs formulated at low dose. Density, compressibility and flow were identified as key material properties at the feeding stage. The screw speed coupled with powder flow regulated the gravimetric feeding performance. The impact of process and design variables was elucidated at the blending stage. The impeller configuration (number and pattern of radial mixing blades) and speed were key variables to steer the residence time distribution at the blending stage. An impeller configuration with distributed radial mixing blades could sufficiently filter the steady state feeding variability at low mixer speed, but exerted limited strain and shear on the blend. Hence micro-agglomerates persisted through the blending process and occasionally resulted in super potent tablets. Therefore, a new configuration was evaluated with more radial mixing blades centered on the impeller. This configuration resulted in a long mixing time at high tip speed which induced a maximized strain and shear. Consequently, excellent uniformity of the blend and tablets at macroscopic and microscopic level was achieved. Besides, this impeller improved robustness towards feeding disturbances, changes in process settings and variable blend properties. Next, it was demonstrated that the lubrication step requires critical attention during the design of the equipment, formulation and process. This study provided abundant evidence that an optimized continuous direct compression process allows direct compression of challenging low-dose drug products.

Fabrication of large area flexible nanoplasmonic templates with flow coating.

We describe the development of a custom-built two-axis flow coater for the deposition of polymeric nanosphere monolayers that could be used in the fabrication of large area nanoplasmonic films. The technique described here has the capability of depositing large areas (up to 7 in. × 10 in.) of self-assembled monolayers of polymeric nanospheres onto polyethylene terephthalate (PET) films. Here, three sets of films consisting of different diameters (ranging from 100 to 300 nm) of polymeric nanospheres were used to demonstrate the capabilities of this instrument. To improve the surface wettability of the PET substrates during wet-deposition, we enhanced the wettability by using a forced air blown-arc plasma treatment system. Both the local microstructure, as confirmed by scanning electron microscopy, describing monolayer and multilayer coverage, and the overall macroscopic uniformity of the resultant nanostructured film were optimized by controlling the relative stage to blade speed and nanosphere concentration. We also show using a smaller nanoparticle template that such monolayers can be used to form nanoplasmonic films. As this flow-coating approach is a scalable technique, large area films such as the ones described here have a variety of crucial emerging applications in areas such as energy, catalysis, and chemical sensing.

Large-Scale Uniform Two-Dimensional Hexagonal Arrays of Gold Nanoparticles Templated from Mesoporous Silica Film for Surface-Enhanced Raman Spectroscopy

A good surface-enhanced Raman spectroscopy (SERS) substrate requires precise control of the enhancement factor in large area which may be achieved with large-scale hot spot engineering. Here, we present a facile method for synthesizing 2-D hexagonally patterned gold nanoparticle arrays on centimeter-sized substrates of mesoporous silica thin films with vertical nanochannels by chemical reduction. Scanning electron microscopy images showed densely packed gold nanoparticles directly anchored on the openings of vertical mesopores (∼5 nm) leading to 2 nm nanogaps between the gold nanoparticles. The gold nanoparticle arrays showed red-shifted localized surface plasmon resonance spectra due to strong couplings between close-packed gold. The dense on-substrate 2 nm plasmonic nanogaps lead to highly enhanced local electric field and excellent macroscopic uniformity in SERS.

Fabrication and structural tuning of novel composite hollow fiber membranes for pervaporation

ABSTRACTA series of polysiloxaneimide (PSI)/polyetherimide (PEI) composite hollow fibers were fabricated by coextrusion and phase inversion. The hydrophobic PSI outer layer was set as the selective layer which was supported by the PEI inner layer. The PSI was synthesized by polycondensation of 3,3′,4,4′‐Biphenyltetracarboxylic Dianhydride (BPDA) with amino siloxane X‐22‐161A and a chain extender, 1,3‐Bis (3‐aminopropyl) −1,1,3,3‐tertramethyldisiloxane (BATS). It was found that the macroscopic uniformity of PSI layer was dependent on the dope formulation, coagulant composition and dope flow rate: (1) the higher similarity degree of the solvent(s) for different layers in terms of solubility parameters, (2) the utilization of surfactant as a component in the water coagulant, and (3) higher flow rates of the outer layer dopes, led to the formation of more uniform and smoother PSI outer layer. The maximum outer layer thickness was around 2 μm. The bulk of the PEI layers were porous with finger like macrovoids. The outer surface of the inner PEI layer for some batches of the hollow fibers was confirmed to be porous. The original dual‐layer hollow fibers showed poor pervaporation performance. Post treatment was applied to cure the hollow fiber, delivering composite membranes with performance dominated by the coating material of PDMS. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43324.

Designing Non‐uniform Wafer Micro‐topography for Macroscopic Uniformity in Multi‐scale CVD Processes

AbstractThe potential of an additional degree of freedom (DOF) in the effort to meet film or deposition rate uniformity along the wafer in CVD processes is investigated. The investigation applies to cases of deposition on a wafer with micro‐topography where the common practice is a uniform density of patterns or features (e.g., trenches or holes), with the additional DOF as the feature density along the wafer. A non‐uniform density is designed with the objective of improving the uniformity; as a consequence, the differences in the profiles of the deposited films in all the features on the wafer will be compensated. A multi‐scale modeling framework is utilized for the design. The case study is aluminum metal‐organic (MO)CVD from dimethylethylamine alane under conditions of low macroscopic uniformity. Compared to a uniform density of the same number of trenches, the multi‐scale computations predict that the designed density of features, namely trenches, induces a remarkable improvement of both the macroscopic uniformity and the number of trenches on the wafer where the uniformity exceeds 0.95. The methodology is applied to features, i.e., the simplest unit cell of topography on a wafer, even if practical implementation of the variation of feature density is difficult. The same methodology can be applied to design the density of a cluster of features comprising a single device, or a die on the wafer.

Crystallization of Amorphous Silicon Films Using Joule Heating

Joule heat is generated by applying an electric filed to a conductive layer located beneath or above the amorphous silicon film, and is used to raise the temperature of the silicon film to crystallization temperature. An electric field was applied to an indium tin oxide (ITO) conductive layer to induce Joule heating in order to carry out the crystallization of amorphous silicon. Polycrystalline silicon was produced within the range of a millisecond. To investigate the kinetics of Joule-heating induced crystallization (JIC) solid phase crystallization was conducted using amorphous silicon films deposited by plasma enhanced chemical vapor deposition and using tube furnace in nitrogen ambient. Microscopic and macroscopic uniformity of crystallinity of JIC poly-Si was measured to have better uniformity compared to that of poly-Si produced by other methods such as metal induced crystallization and Excimer laser crystallization.

Magnetic properties of permanent magnet for cryogenic undulator of permanent Shanghai synchrotron radiation facility

M-H and M-T curve at cryogenic (10-300 K) of domestic Nd2Fe14B (N50M) permanent magnet are tested by physical property measurement system (PPMS). Br-T and Hci-T figure under the cryogenic condition for N50M are obtained. The orientation degree and three-dimensional magnetization are also analyzed and researched under the cryogenic conditon. The results show that N50M has a strong spin reorientation effect(SRT) between 80 and 150 K, Br shows a peak between 120 and 130 K and Hci increases linearly with temperature decresing. At 130 K, Br increases 15.6% and Hci increases 220% compared with at room temperature (300 K), reaching 1.65 T and 3638 kA/m respectively. Between 150 and 300 K, with temperature declining, the macroscopic orientation degree uniformity and the external magnetic field uniformity of N50M are improved gradually. Between 80 and 235 K, the micro-external magnetic field uniformity shows a deterioration phenomenon. The experimental research also indicates that near 235 K the N50M perpendicular to orientation direction presents a “remanent magnetization jump” phenomenon. The experimental results provide a reference for the physical design of cryogenic undulator for Shanghai Synchrotron Radiation Facility II and other high-precision cryogenic permanent magnet instruments and equipment.

Aligned carbon cones in free‐standing UV‐Curable polymer composite

AbstractA concept where an alternating electric field (dielectrophoresis) is used to assemble and align carbon nanocone particles (CNCs) into microscopic wires in self‐supporting polymer films is demonstrated. The particle fraction is kept low (one‐tenth of the percolation threshold of isotropic mixture), which allows uniform dispersion and efficient UV curing. The alignment leads to the conductivity enhancement of three to four orders of magnitude (from ∼10−7 to ∼10−3 S/m) in the alignment direction. It does not require passing current so the material can be isolated from the alignment electrodes. This prevents electrodes attaching to the film, if the film is adhesive in nature. The alignment can be done using either in‐plane or out‐of‐plane geometries. It is proposed that this concept could be applied in areas such as electrostatic discharge applications where inexpensive conductive or dissipative materials and macroscopic uniformity are prerequisites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

A morphological study of porous polylactide scaffolds prepared by thermally induced phase separation

Polylactide (PLA) has been widely used as a three-dimensional scaffold for cell transplantation and as a drug carrier for controlled release due to its superior biocompatibility and biodegradability. The technique of thermally induced phase separation (TIPS) is favorable for the fabrication of a porous scaffold due to its various advantages. A diverse range of porous structures can be obtained by TIPS through adjustment of process parameters. In this study, PLA scaffolds were prepared from a ternary PLA–dioxane–water system by the TIPS method. The effects of fabrication parameters, such as quenching route and the composition of the ternary system, on the macroscopic and microscopic morphologies of the scaffolds were studied. The phase diagram of this system showed that the presence of water non-solvent is essential for a liquid–liquid phase separation to occur. Accordingly, a binary PLA–dioxane system (100/0) exhibited only a solid–liquid phase separation. For a ternary PLA–dioxane–water system, the cloud-point temperature corresponding to a liquid–liquid phase separation was highly dependent on its water content and polymer concentration, while the freezing point corresponding to a solid–liquid phase separation was nearly independent of the polymer concentration and water content. Given a slight increase in the water content of the solvent mixture of 5%, i.e. a change in dioxane/water ratio from 90/10 to 85/15, or an increase in the polymer concentration of 2–30%, there was a substantial 40–50 °C increase in cloud-point temperature, in contrast with a nearly constant freezing point of between −10 and −20 °C. Morphology of the scaffold prepared via solid–liquid phase separation of a binary dioxane–PLA system gave a highly anisotropic tubular morphology with an internal ladder-like structure, while scaffolds prepared via liquid–liquid phase separation of a ternary PLA–dioxane–water system exhibited isotropic morphology. The ultimate pore structure of a scaffold was controlled by various processing parameters such as polymer concentration, water content, quench route and molecular weight of the polymer. Liquid–liquid de-mixing is a highly dynamic process that is subject to the effects of coarsening at the intermediate or later stage of the de-mixing process. For scaffolds prepared from solutions with polymer concentration of less than 7.5 wt%, the pore size decreases with the increase of polymer concentration. The coarsening effect was minimal and the final pore structure was found to be mainly determined by the liquid–liquid de-mixing mechanism, attributable to the smaller liquid–liquid de-mixing gap. For polymer concentrations higher than 7.5 wt%, the coarsening effect was more important, and a bimodal pore-size distribution was observed; in addition to the uniform small pores caused by instantaneous spinodal decomposition, large pores formed during the subsequent coarsening process. SEM micrographs showing that sedimentation occurred by aging time of about 5 and 60 min for scaffolds prepared from a 7.5 wt% PDLLA solution with dioxane/water ratio of 90/10 at −5 and −12 °C, respectively. Although this result suggests that such scaffolds rapidly lost macroscopic uniformity, porosity data indicates that the specimens did not lose integrity by aging for up to 120 min.

Improving Radiochromic Film’s Sensitivity Limit with an Optical Common-mode Rejection and a Flatbed Color Scanner

A novel method, an optical common-mode rejection (CMR), which can greatly improve the dosimetric sensitivity limit of a radiochromic film (RCF) through use of a set of color outputs from an RGB color scanner has been developed. RCFs are known to have microscopic and macroscopic uniformity, which comes from the intrinsic thickness variations in the film’s active radiochromic layer and coating. These variations in the response make the optical S/N (signal-to-noise ratio) lower, resulting in lower film sensitivity. The basic principle of the optical CMR is the compensation of RCF film nonuniform response by creating a ratio of the two signals where the factors common to both numerator and denominator cancel out. The scheme was applied to create two types of ratios using two combinations, red/green and red/blue. MD-55-2 type dosimetry films, which were exposed to100 kV X-ray beams in the range from 5 mGy to 8.1 Gy, were scanned with a flatbed color image scanner and the digital data was analyzed. The results obtained with the optical CMR and the conventional analysis method using the only red pixel values were compared. The detection limit can be greatly improved with the optical CMR scheme using the combination of red and green.

Ag nanorod arrays tailored for surface-enhanced Raman imaging in the near-infraredregion

Using a dynamic oblique angle deposition technique, we demonstrate the direct formationof Ag nanorods with quasi-parallel major axes on a template layer of oxide having astrongly anisotropic surface morphology. The optical properties of the nanorods are tunedby varying the deposition conditions without any pre- or post-treatment, and the resultingAg nanorod arrays exhibit high surface-enhanced Raman scattering (SERS) activity. Inaddition to high macroscopic uniformity over a large area, our nanorod arrays contain ahigh density of isolated nanorods. Using the optimum Ag nanorod arrays, theSERS imaging of the microdroplets of a rhodamine 6G solution is successfullydemonstrated. The space resolution of the imaging is of the order of at least a fewµm. These features are suitable for the SERS imaging of biomaterials.

Generations and applications of atmospheric pressure glow discharge by integration of microplasmas

Integration of microplasmas enables us to obtain atmospheric pressure discharges with good macroscopic uniformity and various functions. We demonstrate two specific electrodes of microplasmas for generations of dielectric barrier discharges at atmospheric pressure, and integrated microplasmas on large two-dimensional area are sustained with electron density more than 1012cm-3. Especially "fabric" type electrode has a promising structure to provide various flexible discharge space and plasma processing on winding surface. Integrated microplasmas in array structure will serve as electromagnetic-wave control devices as well as processing tools, and two aspects are discussed in terms of equivalent dielectrics and metals.

Enhanced critical current density of YBa2Cu3Ox films grown on Nd1/3Eu1/3Gd1/3Ba2Cu3Ox with nano-undulated surface morphology

We report a simple and easily controllable method where a nano-undulated surface morphology of superconducting Nd1/3Eu1/3Gd1/3Ba2Cu3Ox (NEG) films leads to a substantial increase in the critical current density in superconducting YBa2Cu3Ox (YBCO) films deposited by pulsed laser deposition on such NEG layers. The enhancement is observed over a wide range of fields and temperatures. Transmission electron microscopy shows that such YBCO films possess a high density of localized areas, typically 20×20nm2 in size, where distortion of atomic planes give rotational (2–5°) moiré patterns. Their distribution is random and uniform, and expected to be the origin of the enhanced flux pinning. Magneto-optical imaging shows that these films have excellent macroscopic magnetic uniformity.

Equilibrium States and Their Macroscopic Uniformity in Fermion Lattice Systems

We study equilibrium states and their macroscopic uniformity in the fermion lattice system satisfying the assumptions presented by Araki and Moriya [5]. We show that every translation-invariant KMS state of the even part of the fermion algebra extends uniquely to a translation-invariant KMS state of the whole fermion algebra. The macroscopic uniformity is established for an extremal translation-invariant equilibrium state of the fermion algebra.

Wet-etching characteristics of Ge/sub 2/Sb/sub 2/Te/sub 5/ thin films for phase-change memory

Etching of phase-change memory thin films is essential in the processing for the manufacture of devices. The Ge/sub 2/Sb/sub 2/Te/sub 5/ thin film as a typical material for such purposes can be control-etched by an aqueous solution of 20% nitric acids (HNO/sub 3/). It was found that the Ge/sub 2/Sb/sub 2/Te/sub 5/ films in amorphous state could be etched more uniformly than that in crystalline state. The etch rate can be well controlled to be 4.6 nm/s using such a solution, resulting in macroscopic and microscopic uniformity on amorphous films. It is therefore suggested that the crystallization annealing of Ge/sub 2/Sb/sub 2/Te/sub 5/ thin films should be done after a wet etching process in the manufacture of phase-change random access memories.

Continuous liquid crystal pretilt control through textured substrates

Reliable control on the pretilt alignment of nematic liquid crystal (LC) in the 30°–50° range is a well-known challenge. An unconventional approach, involving microtextured surfaces with domains favoring dissimilar LC alignments, has recently demonstrated applicability in bi- and tristable displays. These textured domains realize the so-called frustrated boundary condition in which the LC elastic energy built-up (frustration) can drive the LC alignment into macroscopic uniformity. Here we show that one can harness the frustrated boundary to achieve variable LC pretilt control up to 40°.

Macroscopic Uniformity of Oxygen Concentration in Czochralski Silicon Crystals Closely Related to Evaporation of SiO from the Free Surface of Melts

To propose a new concept of macroscopic uniformity of oxygen concentration for large diameter Czochralski silicon single crystal, two kinds of experiments from the viewpoint of SiO evaporating from free surface of melts were explored. First, evaporation rate of SiO were measured by using a thermogravimetric method. Subsequently, several CZ crystals with various increasing diameters were grown by the two characteristic growth conditions, the speed control and the temperature control, respectively. It was revealed, from comparison of diverse analysis of the oxygen concentration in these silicon crystals with the evaporation rate of SiO, that the oxygen heterogeneity induced by the speed control was closely related to the enhanced variation of evaporation rate of SiO. We have newly developed the evaporation rate mapping as a function of ration (Ac, contact area between melt and silica crucible; area of free melt surface) by using the melt temperature as a parameter. It was concluded that introducing a new parameter which denotes the variation of the evaporation rate and to suppress would achieve the macroscopic oxygen uniformity in the silicon crystal. © 2003 The Electrochemical Society. All rights reserved.

Surface Pressure−Area Isotherms and Fluorescent Behavior of a ω-6-(N-Methyl-N-alkylamine) Naphthoylalkanoic Acid (MANA)

This paper reports the surface pressure−area isotherms for the new fluorescent probe ω-[6-(N-methyl-N-ethylamino)naphthoyl]undecanoic acid (MANA10-2) obtained by changing experimental variables such as the subphase conditions, pH, temperature, and the compression rate. The surface monolayer technique was used in combination with surface fluorescence measurements. Changes in pH and temperature of the aqueous subphase were found to significantly influence isotherm shape. The fluorescent properties of the molecule were studied both in the monolayer and in the subphase. This allowed us to determine the orientation of MANA10-2 on the surface and revealed that the monolayer is dissolved at both low and high pH values and high temperatures. Monolayers were also examined by Brewster angle microscopy. The morphology and size of the domains formed are clearly governed by temperature and the pH of the aqueous subphases. Only with monolayers spread on pure water at 20 °C was the transition from the liquid phase to the condensed phase observed. This was also the only occasion when the monolayers exhibited high macroscopic uniformity. A large number of small bright nuclei (typical of a densely packed two-dimensional phase or a three-dimensional phase) are formed at low surface pressure in the presence of HCl and NaOH subphases (pH 1 and 9, respectively).