Search

Three-dimensional (3D) configuration of in vitro cultivated cells has been recognised as a valuable tool in developing stem cell and cancer cell therapy. However, currently available imaging approaches for live cells have drawbacks, including unsatisfactory resolution, lack of cross-sectional and 3D images, and poor penetration of multi-layered cell products, especially when cells are cultivated on semitransparent carriers. Herein, we report a prototype of a full-field optical coherence tomography (FF-OCT) system with isotropic submicron spatial resolution in en face and cross-sectional views that provides a label-free, non-invasive platform with high-resolution 3D imaging. We validated the imaging power of this prototype by examining (1) cultivated neuron cells (N2A cell line); (2) multilayered, cultivated limbal epithelial sheets (mCLESs); (3) neuron cells (N2A cell line) and mCLESs cultivated on a semitransparent amniotic membrane (stAM); and (4) directly adherent colonies of neuron-like cells (DACNs) covered by limbal epithelial cell sheets. Our FF-OCT exhibited a penetrance of up to 150 μm in a multilayered cell sheet and displayed the morphological differences of neurons and epithelial cells in complex coculture systems. This FF-OCT is expected to facilitate the visualisation of cultivated cell products in vitro and has a high potential for cell therapy and translational medicine research.

In order to exploit future soft body armor to achieve a more comprehensive protection than just the torso part of the body, in this study, shear thickening fluids (STFs) with different rheological properties are fabricated by planetary mixer and three-roller mills to investigate the mixing process effect on the resultant rheological behavior. Rheological results indicate the critical shear rate and the maximum viscosity of STF are deeply influenced by the dispersion degree of nano-silica particles in PEG. These STFs are then filled into a paper honeycomb partition to prepare a STF-based protective structure. Different laminating sequences of the composite panels composed one STF structure layer and nineteen layers of Kevlar fabric are obtained by simply placing the STF structure at different positions in the composite panels. The ballistic tests are conducted according to the NIJ 0101.06—Type II standard using 9 mm Full Metal Jacketed Round Nose bullets. Our results show that the absorbed energy of the composite panel with STF that thickens at higher shear rate is higher compared to that using STF that thickens at a lower shear rate. It suggests the STF with higher critical shear rate would be optimally used in ballistic impacts. In addition, ballistic testing results confirm that the STF structure placed at the rear position can significantly contribute to the increase in impact resistance.

In this study, the ballistic performance of armors composed of a polyurea elastomer/Kevlar fabric composite and a shear thickening fluid (STF) structure was investigated. The polyurea used was a reaction product of aromatic diphenylmethane isocyanate (A agent) and amine-terminated polyether resin (B agent). The A and B agents were diluted, mixed and brushed onto Kevlar fabric. After the reaction of A and B agents was complete, the polyurea/Kevlar composite was formed. STF structure was prepared through pouring the STF into a honeycomb paper panel. The ballistic tests were conducted with reference to NIJ 0101.06 Ballistic Test Specification Class II and Class IIIA, using 9 mm FMJ and 44 magnum bullets. The ballistic test results reveal that polyurea/Kevlar fabric composites offer better impact resistance than conventional Kevlar fabrics and a 2 mm STF structure could replace approximately 10 layers of Kevlar in a ballistic resistant layer. Our results also showed that a high-strength composite laminate using the best polyurea/Kevlar plates combined with the STF structure was more than 17% lighter and thinner than the conventional Kevlar laminate, indicating that the high-strength protective material developed in this study is superior to the traditional protective materials.

The power and temperature dependent photoluminescence (PL) of epitaxially grown In-rich CuInSe2 (CIS) and Cu-rich CIS deposited on N-polar GaN and InN were investigated in this paper. The In-rich CIS/GaN has two PL emissions characterized by a donor-acceptor pair (DAP) peak at 0.92 eV and an excitonic peak at 1.08/1.1 eV. On the other hand, the Cu-rich CIS/GaN has four PL emissions characterized by two DAP peaks at 0.86 eV and 0.94 eV, free-to-bound recombination peak at 0.97 eV and an excitonic peak at 1.03 eV. Identification of these defects in the CIS absorber layer is crucial for the improvement of the device efficiency. The PL emission of the CIS/InN closely resembles that of the Cu-rich CIS/GaN. For all the samples, the PL intensity increased with excitation power while the PL intensity decreased with temperature. The obtained power coefficients and activation energies support the proposed mechanism causing the luminescence. The defects present in CIS/GaN and CIS/InN were also identified. The results from this study are consistent with those of CIS single crystals and show that the CIS absorber layer can be incorporated with III-nitride materials, and its absorption can be extended beyond the spectrum covered by plain CIS.

In this study, the impact resistance of aramid fabric reinforced with shear thickening fluids (STFs), epoxy or polyurea elastomers is examined through ballistic tests. According to the ballistic test results, the aramid composite structure treated with polyurea elastomers absorbs the most impact energy per unit area density and has the best impact resistance. However, the occurrence of stress concentration during ballistic impact reduces the impact resistance of the aramid composite structure treated with epoxy. On the other hand, aramid fabric impregnated with STF improves structural protection, but it also increases the weight of the composite structure and reduces the specific energy absorption (SEA). The results of this study analyze the energy absorption properties, deformation characteristics, and damage modes of different aramid composites, which will be of interest to future researchers developing next-generation protective equipment.

The sintered aluminum nitride granules were prepared in a continuous process through a two-step heat treatment at 1600 °C for 5 h and 1850 °C for 5 h using the spherical γ-alumina/phenol-resin precursor obtained by spray granulation as the starting material. In the first step of heat treatment, the alumina powders were nitrided to form porous aluminum nitride granules via a carbothermal reduction reaction and then were continuously heated in the second step of heat treatment to produce dense spherical aluminum nitride granules without using sintering aids. The obtained porous and sintered aluminum nitride granules were characterized by XRD, SEM and BET measurements and exhibited an average grain size of about 1 and 3 µm, respectively. Furthermore, the specific surface area of the obtained porous and sintered aluminum nitride granules dramatically decreased from 2.49 to 0.16 m2/g showing that the low-porosity, dense, polycrystalline aluminum nitride granules were successfully prepared.

The paper proposes a method for measuring the refractive index of the plane-parallel samples of the material using laser profiler. The method is based on measurement of the displacement due to refraction of the laser beam passing through a sample of known geometry. The developed method was used to measure the refractive index of gallium nitride on the range of optical wavelengths (470, 561 and 632 nm). The measurement error of the refractive index was 10-3. The experimentally obtained values of the refractive index match with the reference data within measurement error. The relative simplicity of the measurement procedures distinguishes this method.

Near stoichiometric chalcopyrite Cu-rich and In-rich CuInSe 2 thin films have been simultaneously grown on GaN (0001) by molecular beam epitaxy. Microstructure analysis of the Cu-rich and In-rich CuInSe 2 showed that the rotation twin was formed at the interface of CuInSe 2 /GaN, and no interface reaction occurs between CuInSe 2 and GaN. Our experimental results show that GaN is stable for the epitaxial growth of CuInSe 2 thin film, which exhibits a promising potential for optoelectronic applications.

A high glass transition temperature (Tg = 220 °C), high triplet energy gap (ET = 2.76 eV) and high electron mobility material bis(m-terphenyl)oxadiazole was readily synthesized. It can serve as a universal electron transporter for blue, green and red phosphorescent OLEDs with excellent efficiencies. The material shows high current density compared to other electron transport materials and exhibits reduced driving voltage for all color PhOLEDs irrespective of the energy level of the host materials, due to efficient electron injection from 2,5-di([1,1′:3′,1″-terphenyl]-5′-yl)-1,3,4-oxadiazole (TPOTP) to the host material. For the green PhOLED, maximum external quantum efficiency (EQE) over 25%, current efficiency of 97.6 cd A−1 and power efficiency of 100.6 lm W−1 were achieved. The red and blue devices using TPOTP as the electron transporter also show EQE higher than 23% with very low roll-off in efficiencies in practical brightness level.

A new strategy for the synthesis of highly substituted benzofurans from meta-substituted hydroxybenzenes and alkynes via a rhodium(III)-catalyzed activation of a sterically hindered C-H bond is demonstrated. A possible mechanism involving dual directing group assisted ortho C-H bond activation is proposed.

GaN films were grown by plasma-assisted molecular beam epitaxy with a sputtered AlN buffer layer on Si (100) substrate. From the analyses of X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) measurements, we showed that the variant M -plane, A -plane and c -plane GaN wurtzite structures can be achieved by the selection of crystalline orientation of sputtered AlN buffer layer and the control of epitaxial growth temperature. We also found that the GaN layer grown on sputtered AlN buffer layer can be converted to GaN zinc-blende structure at the epitaxial growth temperature higher than 750 °C and under Ga-rich condition.

The effects of hydrazine on the synthesis of Cu 2 ZnSnSe 4 (CZTSe) and Cu 2 CdSnSe 4 (CCTSe) nanocrystals in an autoclave as a function of temperature and time were explored. On heating at 190 °C for 24-72 h, pure CZTSe and CCTSe nanocrystals could readily grow in the hydrazine-added solution, while in the hydrazine-free solution the intermediate phases such as ZnSe, Cu 2 Se, and Cu 2 SnSe 3 , and Cu 2 SnSe 3 and CdSe associated with the CZTSe and CCTSe nanocrystals grew, respectively. This result reveals that hydrazine can speed up the synthesis of pure CZTSe and CCTSe nanocrystals via a solvothermal process. The mechanisms for the hydrazine-enhanced growth of CZTSe and CCTSe nanocrystals were discussed. The pure CZTSe and CCTSe nanocrystals were subsequently fabricated to the smooth films by spin coating without further annealing in selenium atmosphere. This processing may be beneficial to the fabrication of the absorber layer for solar cells and thermoelectric devices.

Tactile sensor are widely used in different biomedical purposes. For more safe operation during cardiovascular surgery, the force signal feedback for doctor is very important. Therefore, the tactile sensor is one of potential technique to guiding the catheter when the contact part touch the blood vessel. In this study, we change the tactile sensor using pressure-based mechanism to force-based mechanism, which improving the signal resolution at higher contact angle between catheter and blood vessel. The prototype of assembled tactile sensor are designed and fabricated, and the mechanical and electrical performance of compressible diaphragm are evaluated.

The M -plane GaN thin films grown on pre-annealing LiGaO 2 (100) substrates by plasma-assisted molecular-beam epitaxy have been characterized. The LiGaO 2 (100) substrates were annealed in vacuum and in ambient air, respectively. The analyses of X-ray diffraction and Raman scattering measurements indicate that the crystal quality of M -plane GaN thin film grown on air-annealed LiGaO 2 (100) substrate is improved and the compressive stress between M -plane GaN and LiGaO 2 is reduced as well. The experimental results reveal that the thermal annealing LiGaO 2 substrate in air can effectively suppress the formation of lithium-rich surface to grow a high-quality M -plane GaN thin film on LiGaO 2 substrate.

In this paper, we report the growth of M-plane GaN thin films on LiGaO2 (100) substrates pre-annealed in vacuum and in air ambient. The surface of M-plane GaN film grown on the LiGaO2 (100) substrate pre-annealed in air ambient was significantly improved. X-ray diffraction data showed that the M-plane GaN thin film grown on the LiGaO2 (100) substrate pre-annealed in air ambient has better crystal quality than that grown on the LiGaO2 (100) substrate pre-annealed in vacuum. In addition, the strain generated between GaN thin film and LiGaO2 substrate was relaxed when the GaN thin film grew on the LiGaO2 substrate pre-annealed in air ambient. It revealed that the thermal annealing LiGaO2 substrate in air ambient can suppress the formation of lithium-rich surface effectively, and then one can grow a high quality M-plane GaN thin film on the LiGaO2 substrate.

M-plane GaN thin films have been grown on β-LiGaO2 (100) substrates by plasma-assisted molecular-beam epitaxy. Pure M-plane GaN crystal films have been verified by the measurements of X-ray diffraction, micro-Raman scattering, polarization-dependent photoluminescence and atomic force microscopy. The measurements of X-ray diffraction and micro-Raman scattering exhibited the evidences of large compressive stress on the M-plane GaN thin films. Based on experimental results, we showed that the large compressive stress is the major source leading to the peeling of M-plane GaN thin film off substrate after thermal recycles.

We have studied the microstructure property of InN epitaxial films grown on ZnO substrate by plasma-assisted molecular beam epitaxy. We found that the In2O3 compound was produced on ZnO substrate and many pits were formed on the InN films when InN was directly grown on ZnO substrate with the N/In flux ratio less than 40. We demonstrated that the quality of InN film was significantly improved when the In2O3 layer was used as a buffer to prevent the reaction between In and the ZnO substrate.

Three m-terphenyl oxadiazole derivatives, 3,3″-bis(5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl)-1,1':3',1″-terphenyl (4PyOXD), 3,3″-bis(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-yl)-1,1':3',1″-terphenyl (3PyOXD), and 3,3″-bis(5-phenyl-1,3,4-oxadiazol-2-yl)-1,1':3',1″-terphenyl (PhOXD), were synthesized. They exhibit relatively high electron mobilities compared with those of known electron-transport materials such as TAZ, BAlq, and BCP+Alq3. These materials were then utilized as electron transporters and hole/exciton blockers for blue, green, and red phosphorescent organic light-emitting diodes. The devices exhibited reduced driving voltages, very high efficiency, and negligible roll-off. More importantly, among these three oxadiazole derivatives, PhOXD performed as an ideal electron-transporting material for the blue, green, and red devices with excellent external quantum efficiencies (EQEs,26%) as well as current and power efficiencies. Using these materials as an electron-transporting/exciton-blocking layer, low roll-off was achieved for the devices, indicative of excellent confinement of the triplet excitons in the emitting layer even at high current densities. At the normal operation brightness of 1000 cd m(-2), the EQEs remained21.3% for these basic color devices. In addition, the relationships between physical properties and structures of the molecules such as the electron mobility, triplet energy gap, and efficiency can be clearly rationalized.

This efficient reaction which proceeds regioselectively at the sterically more congested C—H bond can be scaled up.

Applying an oscillating magnetic field perpendicularly on the high-quality magnetic fluid thin film, the phase separation of particles in the liquid matrix will occur. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. The ordered structure of magnetic fluid thin films is the basis for the potential optical application. We explore the dynamical ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields in this study.

We have studied the growth of high-indium-content In x Ga1− x N/GaN double quantum wells (QWs) for yellow and green light emitters by plasma-assisted molecular beam epitaxy at a low substrate temperature (570 °C). By introducing a graded In y Ga1− y N buffer layer, the PL intensity of QWs can be increased sixfold compared with that of the original structure. In addition, the indium content in InGaN QWs was increased owing the prolonged growth time of the graded In y Ga1− y N buffer layer. After adjusting to optimal growth conditions, we achieved In x Ga1− x N/GaN QWs with x = 0.32. Photoluminescence measurements showed that the emission wavelength from In x Ga1− x N/GaN QWs was 560 nm (2.20 eV). The optimal condition for the gradient In y Ga1− y N buffer layer was obtained for light emission from green to yellow.

In this paper, we reviewed the current development and patents for the application of high-brightness and high-efficiency white light-emitting diode (LED). The high-efficiency GaN nanostructures, such as disk, pyramid, and rod were grown on LiAlO(2) substrate by plasma-assisted molecular-beam epitaxy, and a model was developed to demonstrate the growth of the GaN nanostructures. Based on the results, the GaN disk p-n junction was designed for the application of high brightness and high efficiency white LED.

A power/ground planes design for efficiently eliminating the ground bounce noise (GBN) in high-speed digital circuits is proposed by using low-period coplanar electromagnetic band-gap (LPC-EBG) structure. However, it is unavoidable the signals will cross the LPC-EBG power plane. In this paper, the effects of signal integrity (SI) and electromagnetic interference (EMI) for differential coupled microstrip lines over the LPC-EBG power/ground planes will be investigated. The resonant frequency of LPC-EBG power plane will be picked up and appear in the radiation. The bandgap frequencies of LPC-EBG power plane will loss in weakly coupling case of differential lines at the received end. Further, the more coupling factor of differential lines is the less noise of SI and EMI is. The simulated results based on full-wave simulator will provide a good reference for the design of differential coupled microstrip lines over LPC-EBG power/ground planes.

We have studied the GaN grown on ZnO micro-rods by plasma-assisted molecular beam epitaxy. From the analyses of GaN microstructure grown on non-polar M-plane ZnO surface ( 10 1 ̄ 0 ) by scanning transmission electron microscope, we found that the ZnGa2O4 compound was formed at the M-plane hetero-interface, which was confirmed by polarization-dependent photoluminescence. We demonstrated that the M-plane ZnO micro-rod surface can be used as an alternative substrate to grow high quality M-plane GaN epi-layers.

We report that chalcopyrite CuInSe2 thin films were grown on free-standing N-polar GaN (000 1 ̄ ) by molecular beam epitaxy. X-ray diffraction showed that the CuInSe2 thin film was grown in (112) orientation, and its peak of rocking curve with full width at half maximum of about 897.8 arc-sec indicated the epitaxial growth of CuInSe2 (112) film on N-polar GaN. Microstructure analysis of the CuInSe2 showed that the large lattice mismatch (28.5%) between CuInSe2 and GaN is accommodated by domain matching, and no interface reaction occurs between CuInSe2 and GaN. Our experimental results show that GaN is stable for the epitaxial growth of CuInSe2 thin film, which exhibits a promising potential for optoelectronic applications.

The characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy on LiAlO2 substrate was studied by cathodoluminescence and photoluminescence measurements. We demonstrated that the cathodoluminescence from oblique semi-polar surfaces of mushroom-shaped GaN was much brighter than that from top polar surface due to the reduction of polarization field on the oblique semi-polar surfaces. It implies that the oblique semi-polar surface is superior for the light-emitting surface of wurtzite nano-devices.

We have grown In{sub x}Ga{sub 1-x}N/GaN quantum wells atop GaN microdisk with {gamma}-LiAlO{sub 2} substrate by using plasma-assisted molecular beam epitaxy. The structural and optical properties of the samples were analyzed by transmission electron microscopy, x-ray diffraction, cathodoluminescence, and photoluminescence measurements. Based on the measured results, we obtained the indium concentration of the In{sub x}Ga{sub 1-x}N/GaN single quantum well to be x = 0.25 with a band-gap energy of 2.31 eV, which is consistent with the bowing effect of bulk In{sub x}Ga{sub 1-x}N: E{sub g}(x) = [3.42 - x * 2.65 - x * (1 - x) * 2.4] eV.

Two m-terphenyloxadiazole-based electron transporting materials, bis(2-tert-butyl-1,3,4-oxadiazole-5-diyl)-3,3′-m-terphenyl (tOXD-mTP) and bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazole-5-diyl)-3,3′-m-terphenyl (tpOXD-mTP) were synthesized and characterized. These two molecules contained two oxadiazolyl groups and a m-terphenyl linkage as the core structure achieving high triplet energy gaps (ET) of 2.83 and 2.90 eV, respectively. The application of tOXD-mTP and tpOXD-mTP as the electron transporting materials (ETM) in bis(4′,6′-difluorophenylpyridinato)-iridium(III) picolinate (FIrpic)-based blue phosphorescent light-emitting devices effectively confines the triplet exciton in the emitting layers. One of the electroluminescent (EL) devices using FIrpic as the dopant showed an excellent current efficiency of 43.3 cd A−1 and an external quantum efficiency (EQE) of 23.0% with CIE (Commission International de l'Eclairage) coordinates of (0.13, 0.29). The bis(4′,6′-difluorophenylpyridinato)-iridium(III) tetra(1-pyrazolyl)borate (FIr6)-based deeper blue EL device exhibited a high current efficiency of 42.5 cd A−1 and external quantum efficiency of 25.0% with CIE coordinates of (0.14, 0.23). These two tOXD-mTP and tpOXD-mTP based devices show device efficiencies two to three times higher than that based on the well-known electron transporting material 1,3-bis[(4-tertbutylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7).

Wurtzite/zinc-blende/wurtzite GaN heterophased quantum wells (QWs) were grown by plasma-assisted molecular beam epitaxy. A self-assembling mechanism was used to simulate the heterophased QW, in which a wurtzite/zinc-blende phase transition was created by rotating the threefold symmetric N-Ga vertical bond 60°. The GaN heterophased QW was attested by transmission electron microscopy, selective area electron diffraction and cathodoluminescence measurements.

We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasma-assisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated by transmission electron microscopy (TEM). The already reported epi-taxial relationship "Equation missing" and "Equation missing" for M -plane GaN is confirmed. The main defects are threading dislocations and stacking faults in both samples. For the M -plane sample, the density of threading dislocations is around 1 × 1011 cm-2 and the stacking fault density amounts to approximately 2 × 105 cm-1. In the A-plane sample, a threading dislocation density in the same order was found, while the stacking fault density is much lower than in the M -plane sample.