Phase-separated Layers Research Articles

A growth diagram for chemical beam epitaxy of GaP1−xNx alloys on nominally (001)-oriented GaP-on-Si substrates

The compound GaP1−xNx is highly attractive to pseudomorphically integrate red-light emitting devices and photovoltaic cells with the standard Si technology because it is lattice matched to Si with a direct bandgap energy of ≈1.96 eV for x = 0.021. Here, we report on the chemical beam epitaxy of GaP1−xNx alloys on nominally (001)-oriented GaP-on-Si substrates. The incorporation of N into GaP1−xNx was systematically investigated as a function of growth temperature and the fluxes of the N and P precursors, 1,1-dimethylhydrazine (DMHy) and tertiarybutylphosphine (TBP), respectively. We found that the N mole fraction exhibits an Arrhenius behavior characterized by an activation energy of (0.79 ± 0.05) eV. With respect to the fluxes, we determined that the N mole fraction is linearly proportional to the flux of DMHy and inversely proportional to the one of TBP. All results are summarized in a universal equation that describes the dependence of x on the growth temperature and the fluxes of the group-V precursors. The results are further illustrated in a growth diagram that visualizes the variation of x as the growth temperature and the flux of DMHy are varied. This diagram also shows how to obtain single-phase and flat GaP1−xNx layers, as certain growth conditions result in chemically phase-separated layers with rough surface morphologies. Finally, our results demonstrate the feasibility of chemical beam epitaxy to obtain single-phase and flat GaP1−xNx layers with x up to about 0.04, a value well above the one required for the lattice-matched integration of GaP1−xNx-based devices on Si.

Investigating the ranges of (meta)stable phase formation in (InxGa1−x)2O3 : Impact of the cation coordination

We investigate the phase diagram of the heterostructural solid solution (InxGa1-x)2O3 both computationally, by combining cluster expansion and density functional theory, and experimentally, by means of TEM measurements of pulsed laser deposited (PLD) heteroepitaxial thin films. The shapes of the Gibbs free energy curves for the monoclinic, hexagonal and cubic bixbyite alloy as a function of composition can be explained in terms of the preferred cation coordination environments of indium and gallium. We show by atomically resolved STEM that the strong preference of indium for six-fold coordination results in ordered monoclinic and hexagonal lattices. This ordering impacts the configurational entropy in the solid solution and thereby the (InxGa1-x)2O3 phase diagram. The resulting phase diagram is characterized by very limited solubilities of gallium and indium in the monoclinic, hexagonal and cubic ground state phases respectively but exhibits wide metastable ranges at realistic growth temperatures. On the indium rich side of the phase diagram a wide miscibility gap is found, which results in phase separated layers. The experimentally observed indium solubilities in the PLD samples are in the range of x=0.45 and x=0.55 for monoclinic and hexagonal single-phase films, while for phase separated films we find x=0.5 for the monoclinic phase, x=0.65-0.7 for the hexagonal phase and x>0.9 for the cubic phase. These values are consistent with the computed metastable ranges for each phase.

MRI Monitoring of the Mixed State of Admixtures Consisting of Moisturizing Cream and Steroid Ointment during the Mixing Process by a Revolution/Rotation-Type Hybrid Mixer.

The admixture of a steroid ointment and a moisturizing cream is frequently prescribed to patients suffering from atopic dermatitis. For the mixing operation, a revolution/rotation-type hybrid mixer is widely used in pharmacy. The purpose of this study was to monitor the mixed state of the admixtures during the mixing process of the hybrid mixer. The key technology used in this study was magnetic resonance imaging (MRI). Two different commercial mometasone furoate-containing ointments were used as a test steroid ointment. After layering the moisturizing cream and the steroid ointment in an ointment bottle, the sample was mixed for a predetermined period using the hybrid mixer. According to MRI transverse relaxation time (T2) mapping for nondestructive monitoring, it was confirmed that the Flumeta® ointment-containing admixture became homogeneous by mixing for 60 s or more. As for the mometasone furoate ointment 0.1%-containing admixture, the mixed state, after becoming homogeneous, was separated into two layers again by the prolonged mixing process. From the 1H-NMR spectra of the phase-separated layers, re-separation was caused by removing aqueous components from the bottom of the samples. MRI is a powerful tool for monitoring the mixed state of the admixture during the mixing process. We believe that our findings offer profound insights into the clinical practice of the mixing operation using a hybrid mixer.

Strain induced exchange-spring magnetic behavior in amorphous (TbDy)Fe2 thin films

In this paper, we report a strain induced exchange-spring magnetic behavior in sputter deposited (TbDy)Fe2 amorphous thin films with phase-separated layers of (TbDy)-rich and Fe-rich at room temperature. The magnetic hysteresis loops at different strain levels were obtained with a magneto-optic Kerr effect set-up incorporating a mechanical four-point bending fixture. The unstrained film exhibits a typical ferrimagnetic hysteresis loop while the strained structure exhibits step-like hysteresis loops representative of an exchange-spring magnetic system. The mechanically strained film changes the coercivity/remanence values from positive to negative. The observed magnetic changes under strain are attributed to magnetic anisotropy modifications in the highly magnetoelastic TbDy-rich layer.

Magnetic Resonance Imaging Study on the Physical Stability of Menthol and Diphenhydramine Cream for the Treatment of Chronic Kidney Disease-Associated Pruritus

A cream that contains menthol and diphenhydramine is widely prepared in hospital pharmacies and prescribed to patients for the treatment of pruritus associated with chronic kidney disease. However, there is a serious concern regarding its physical stability; therefore, we investigated this issue using magnetic resonance imaging (MRI). For a sample preparation, a menthol-containing ethanol solution was mixed with a commercial diphenhydramine cream. After storage for 7 d at 40°C, substantial phase separation into two distinct layers (upper and lower layers) was observed in the sample. This study further examined the components of the phase-separated layers using magnetic resonance (MR) spectroscopy and chemical shift selective images, and it was verified that the upper layer consisted of packed oil droplet layers, whereas the lower was an aqueous phase. Subsequently, the time-dependent phase separation of the sample at different temperatures was investigated. From the MR images, including a T2 relaxation time map and apparent diffusion coefficient maps, it was obvious that the phase separation developed further with increasing temperature; the most substantial phase separation was observed from the sample stored at 40°C, while no phase separation was detected at 25°C. In the final phase of this study, we conducted a formulation study and succeeded in improving the cream's physical stability by adding a hydrophilic surfactant to the preparation.

Facile formulation of alkaline-developable positive-type photosensitive polyimide based on fluorinated poly(amic acid), poly(amic acid), and fluorinated diazonaphthoquinone

An alkaline-developable, positive-type, and photosensitive polyimide (PSPI) based on fluorinated poly(amic acid) (FPAA), poly(amic acid) (PAA), and fluorinated diazonaphthoquinone (FDNQ-1) as a photoactive compound has been successfully developed. The solution of FPAA, PAA, and FDNQ-1 was spin-coated on a silicon wafer and prebaked. The two phase-separated layers, a thin top layer of FPAA containing FDNQ-1 and a thick bottom layer of PAA, were formed due to the high polarity difference between PAA and FPAA containing FDNQ-1. This phase separation was directly observed in an SEM image. The upper thin layer acted as a photosensitive layer, and a fine pattern was formed in the bottom layer. The PSPI containing PAA (85 wt%), FPAA (15 wt%), and FDNQ-1 (25 wt% to polymers) showed an excellent sensitivity of 60 mJ cm−2 and a high contrast of 3.3 when it was exposed to 365 nm wavelength light (i-line) and developed with a 0.238 wt% tetramethylammonium hydroxide aqueous solution (TMAHaq) at 25 °C. A fine positive pattern having a 6 μm resolution on the 1.0 μm film was obtained by exposure to 100 mJ cm−2i-line in the contact-printed mode. The resulting polymer film was converted to the corresponding PI cured at 300 °C. This novel positive patterning PI system can be one of the candidates for the next generation microchip fabrication process which provides a facile formulation of PSPI.

Role of AAO template filling process parameters in controlling the structure ofone-dimensional polymer nanoparticles

Solution template wetting is a common technique used to fabricate elongated polymernanostructures; however, the parameters controlling the resulting morphology remainunclear. The purpose of this investigation was to elucidate the effects of process variableson the types of nanostructures obtained and to understand the physical mechanismsassociated with structure development. 1 wt% polystyrene–THF solutions were infiltratedinto commercial and homemade anodized aluminum oxide (AAO) templates. The wettinginteraction between the AAO template and the polymer solution was examinedthrough contact angle measurements. In general, for moderate dipping times (<18 h), the morphology of the nanopolymer was rod-like at low molecular weights, while tubeswere observed at high molecular weight, even at this low concentration. Nanorods wereobtained for all molecular weights for extended dipping times. The data suggest that phaseseparated layers may grow sequentially from the pore walls and yield nanotubes if thegrowth is interrupted or produce nanorods for unhindered deposition over longperiods.

Highly Ordered Hierarchical Poly(ethylene oxide)-b-polystyrene/Organoclay Nanocomposites

A lamellar forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS)/organoclay nanocomposite with a unique hierarchical structure has been fabricated, by casting solution blends of the block copolymer and organoclay, with subsequent annealing at 180 °C for 8 h under uniaxial constraint. PEO-b-PS provided the nanocomposite lamellar structure with a slightly increased long period. Lamellar layers of the nanocomposite block copolymer were oriented parallel to the film plane. Fully exfoliated clay platelets were localized mostly in the aligned PEO layers, and all platelets were found to be parallel to the interface between PEO and PS layers. PEO crystals in the nanocomposite were oriented with the c-axis perpendicular to the phase-separated layers. The orientation function degree of the PEO crystals within the nanocomposite was lower than that of the crystals within the neat block copolymer.

Determination of Inter-Phase Line Tension in DMPC/D-Cholesterol mixed Langmuir Films

The hydrodynamic response of a thin fluid film, whether a Langmuir monolayer at the air/water interface or a cell membrane, is difficult to model, since it involves the coupling of both bulk and surfaces phases. However, such hydrodynamic response is not only intrinsically critical for transport within the layer, it also provides a major available means to evaluate an important parameter for phase-separated layers such as rafts, the line tension. We have developed a line-integral formulation of the hydrodynamic response of phase-separated layers with short-ranged forces, and tested it by comparisons between numerical simulations based on this model and experiment. These experiments both validate the model and demonstrate that the line tension can be determined with unprecedented accuracy and precision. Long-range dipole-dipole interactions are introduced into the model. The method is applied to coexistence between phases in binary phospholipid/cholesterol mixed layers. Data is evaluated for both Brewster and microscopy and fluorescence microscopy and implications of the use of fluorescent probes are discussed.

Temperature Dependence of the Miscibility Gap on the GaN-Rich Side of the Ga-N-As System

We have investigated the temperature dependence of the transition from single phase films of GaN1—xAsx to phase separated layers, which show regions of hexagonal [0001] oriented GaN, cubic [111] oriented GaAs and hexagonal [0001] oriented GaN1—xAsx. We see a strong temperature dependence of the arsenic flux at which GaAs inclusions are first observed. Finally the intensity of blue emission observed in As-doped GaN samples decreases strongly with decreasing growth temperature.

Temperature Dependence of the Miscibility Gap on the GaN-Rich Side of the Ga–N–As System

We have investigated the temperature dependence of the transition from single phase films of GaN1—xAsx to phase separated layers, which show regions of hexagonal [0001] oriented GaN, cubic [111] oriented GaAs and hexagonal [0001] oriented GaN1—xAsx. We see a strong temperature dependence of the arsenic flux at which GaAs inclusions are first observed. Finally the intensity of blue emission observed in As-doped GaN samples decreases strongly with decreasing growth temperature.

Influence of ion exchange on liquid–liquid phase separation in alkali borosilicate glasses: effect of ion-exchange-induced metastable glass homogenization

Experimental results of studying the metastable liquid–liquid phase separation and homogenization induced by ion exchange in (15- x)Li 2O · xNa 2O · 35B 2O 3 · 50SiO 2 glass-forming system are presented. Both a homogeneous under-surface layer in a phase-separated glass and a phase-separated under-surface layer in a homogeneous glass have been formed by an ion exchange technique. The Li-for-Na ion exchange in the glass with x=15 led to phase-separated layers while the Na-for-Li ion exchange in the phase-separated glass with x=5 led to the homogeneous vitreous layers. These effects and the conditions that produce them are discussed from the viewpoint of phase equilibria in the system involved.