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We investigate the effects of (N,N'-diphenyl)-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB) buffer layers on charge collection in inverted ZnO/MEH-PPV hybrid devices. The insertion of a 3-nm NPB thin layer enhances the efficiency of charge collection by improving charge transport and reducing the interface energy barrier, resulting in better device performances. S-shaped light J—V curve appears when the thickness of the NPB layer reaches 25 nm, which is induced by the inefficient charge extraction from MEH-PPV to Ag. Capacitance—voltage measurements are performed to further investigate the influence of the NPB layer on charge collection from both simulations and experiments. [ABSTRACT FROM AUTHOR]

Tb3+-doped Ca2BO3Cl compounds with different charge compensation approaches are synthesized by a high-temperature solid-state reaction method, and the luminescent properties and Commission Internationale de l'Eclairage (CIE) chromaticity coordinates are systematically characterized. Ca2BO3Cl:Tb3+ can produce green emission under 376 nm radiation excitation. With codoped A+ (A = Li, Na, K) as charge compensators, the relative emission intensities of Ca2BO3Cl:Tb3+ are enhanced by about 1.61, 1.97, and 1.81 times compared with those of the direct charge balance, which is considered to be due to the effect of the difference in ion radius on the crystal field. The CIE chromaticity coordinates of Ca2BO3Cl:Tb3+, A+ (A = Li, Na, K) are (0.335, 0.584), (0.335, 0.585), and (0.335, 0.585), corresponding to the hues of green. Therefore, A+ (A = Li, Na, K) may be the optimal charge compensator for Ca2BO3Cl:Tb3+. [ABSTRACT FROM AUTHOR]

A simple dielectric barrier discharge (DBD) jet array was designed with a liquid electrode and helium gas. The characteristics of the jet array discharge and the preliminary polymerization with acrylic acid (AA) monomer were presented. The plasma reactor can produce a cold jet array with a gas temperature lower than 315 K, using an applied discharge power between 6 W and 30 W (Vdis × Idis). A silk fibroin film (SFF) was modified using the jet array and AA monomer, and the treated SFF samples were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle (CA). The deposition rate of the poly acrylic acid (PAA) was able to reach 300 nm/min, and the surface roughness and energy increased with the AA flow rate. The FTIR results indicate that the modified SFF had more carboxyl groups (-COOH) than the original SFF. This latter characteristic allowed the modified SFF to immobilize more quantities of antimicrobial peptide (AP, LL-37) which inhibited the Escherichia coli (E. Coli) effectively. [ABSTRACT FROM AUTHOR]

With the aim of understanding the relationships between organic small molecule field-effect transistors (FETs) and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly (3-hexylthiophene) (RR-P3HT) field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is largely related to the morphology of the organic active layer. We observe that the change trends of the surface morphologies (average size and average roughness) of pentacene and RR-P3HT thin films are mutually opposite, as the thickness of the organic layer increases. Further, we demonstrate that the change trends of the field-effect mobilities of pentacene and RR-P3HT FETs are also opposite to each other, as the thickness of the organic layer increases within its limit. [ABSTRACT FROM AUTHOR]

This paper proposes a multi-channel magnetic induction tomography measurement system for biological conductivity imaging in a human brain model. A hemispherical glass bowl filled with a salt solution is used as the human brain model; meanwhile, agar blocks of different conductivity are placed in the solution to simulate the intracerebral hemorrhage. The excitation and detection coils are fixed co-axially, and the axial gradiometer is used as the detection coil in order to cancel the primary field. On the outer surface of the glass bowl, 15 sensor units are arrayed in two circles as measurement parts, and a single sensor unit for canceling the phase drift is placed beside the glass bowl. The phase sensitivity of our system is 0.204deg/S m[?]1 with the excitation frequency of 120 kHz and the phase noise is in the range of [?]0.03deg to +0.05deg. Only the coaxial detection coil is available for each excitation coil; therefore, 15 phase data are collected in each measurement turn. Finally, the two-dimensional images of conductivity distribution are obtained using an interpolation algorithm. The frequency-varying experiment indicates that the imaging quality becomes better as the excitation frequency is increased. [ABSTRACT FROM AUTHOR]

This paper investigates the morphology and crystallization properties of the two crystalline phases of pentacene grown by thermal evaporation on p+-Si substrates at room temperature by the methods of atomic force microscopy and x-ray diffraction. This kind of substrate induces a thin film phase and a triclinic phase which are formed directly onto p+-Si substrates and constitute a layer consisting of faceted grains with a step height between terraces of 15.8 Å (1 Å=0.1 nm) and 14.9 Å, respectively. Above the critical thickness of the thin film phase, lamellar structures are found with an increasing fraction with the increase of the film thickness. When the film thickness is fixed, the fraction of lamellar structures increases with the increase of annealing temperature. These lamellar structures are identified as the second phase with a interplanar distance of 14.9 Å corresponding to the pentacene triclinic phase. Furthermore, the thin film phase consisting of several micrometre sized uniformly oriented grains at an annealing temperature of less than 80°C and a deposition rate of 0.6 Å/s is observed. [ABSTRACT FROM AUTHOR]

The influence of evaporation conditions of organic semiconductor material tris(8-hydroxyquinoline)aluminium (Alq3) on the performance of organic light emitting diodes (OLEDs) is reported. In the process of organic material thermal evaporation, the chamber was dark or had white light from a 100?W filament lamp. The devices prepared in the dark show higher emission intensity and efficiency compared with the ones prepared in white light under the same driving voltage. Atomic force microscopy measurements show that surface morphology and phase of Alq3thin films are quite different for the previous cases. The different evaporation conditions are found to have direct effects on the electrical and luminance performance. The Alq3thin films prepared in the dark as active emission layers of OLEDs show higher intensity and efficiency. [ABSTRACT FROM AUTHOR]

Metal copper films with thicknesses from several nanometres to several micrometres were deposited on the surface of cenosphere particles by the magnetron sputtering method under different working conditions. An ultrasonic vibrating generator equipped with a conventional magnetron sputtering apparatus was used to prevent the cenosphere substrates from accumulating during film growth. The surface morphology, the chemical composition, the average grain size and the crystallization of cenosphere particles were characterized by field emission scanning electron microscopy (FE-SEM), inductively coupled plasma-atom emission spectrometer, x-ray photoelectron spectroscopy and x-ray diffraction (XRD) analysis, respectively, before and after the plating process. The results indicate that the copper films were successfully deposited on cenosphere particles. It was found from the FE-SEM results that the films were well compacted and highly uniform in thickness. The XRD results show that the copper film coated on cenospheres has a face centred cubic structure and the crystallization of the film sample increases with increasing sputtering power. [ABSTRACT FROM AUTHOR]

We present a water-immersed ultrasound high-efficiency Fresnel lens based on the theory of extraordinary acoustic transmission of plate-wave resonance. We studied, experimentally and numerically, the acoustic pressure gain of the Fresnel lens with and without gratings on the back. We found that the transmission coefficient of the incident acoustic waves through the lens with gratings on the back was much higher than that of the lens without gratings, thus increasing the acoustic pressure gain at the focal point of an impedance-mismatched Fresnel lens by 14.1 dB. We then optimized the grating width in the structure, thereby increasing the acoustic pressure gain by 16.3 dB. This lens has potential applications in acoustic imaging and medical diagnosis. [ABSTRACT FROM AUTHOR]

The single crystals of Nd0.5Pr0.5FeO3 were successfully grown by optical floating zone method. Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal. The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure. At high temperatures (T > 66 K), it shows the typical characteristics of Γ4(Gx, Ay, Fz) state. With the decrease of the temperature, it undergoes a first-order spin reorientation transition from Γ4(Gx, Ay, Fz) to Γ2(Fx, Cy, Gz) state in the temperature window of 45–66 K under an applied magnetic field of 0.01 T. As the temperature drops to ∼ 17 K, a new magnetic interaction mechanism works, which results in a further enhancement of magnetization. The T–H phase diagram of Nd0.5Pr0.5FeO3 single crystal was finally constructed. [ABSTRACT FROM AUTHOR]

Low-field nuclear magnetic resonance magnet (2 MHz) is required for rock core analysis. However, due to its low field strength, it is hard to achieve a high uniform B0 field only by using the passive shimming. Therefore, active shimming is necessarily used to further improve uniformity for Halbach magnet. In this work, an equivalent magnetic dipole method is presented for designing shim coils. The minimization of the coil power dissipation is considered as an optimal object to minimize coil heating effect, and the deviation from the target field is selected as a penalty function term. The lsqnonlin optimization toolbox of MATLAB is used to solve the optimization problem. Eight shim coils are obtained in accordance with the contour of the stream function. We simulate each shim coil by ANSYS Maxwell software to verify the validity of the designed coils. Measurement results of the field distribution of these coils are consistent with those of the target fields. The uniformity of the B0 field is improved from 114.2 ppm to 26.9 ppm after using these shim coils. [ABSTRACT FROM AUTHOR]

The conventional magnetic resonance imaging (MRI) equipment cannot measure large volume samples nondestructively in the engineering site for its heavy weight and closed structure. In order to realize the mobile MRI, this study focuses on the design of gradient coil of unilateral magnet. The unilateral MRI system is used to image the local area above the magnet. The current density distribution of the gradient coil cannot be used as a series of superconducting nuclear magnetic resonance gradient coils, because the region of interest (ROI) and the wiring area of the unilateral magnet are both cylindrical side arc surfaces. Therefore, the equivalent magnetic dipole method is used to design the gradient coil, and the algorithm is improved for the special case of the wiring area and the ROI, so the X and Y gradient coils are designed. Finally, a flexible printed circuit board (PCB) is used to fabricate the gradient coil, and the magnetic field distribution of the ROI is measured by a Gauss meter, and the measured results match with the simulation results. The gradient linearities of x and y coils are 2.82% and 3.56%, respectively, less than 5% of the commercial gradient coil requirement. [ABSTRACT FROM AUTHOR]

Different concentrations of Mg2+-doped hexagonal phase NaGdF4:Yb3+, Er3+ nanocrystals (NCs) were synthesized by a modified solvothermal method. Successful codoping of Mg2+ ions in upconversion nanoparticles (UCNPs) was supported by XRD, SEM, EDS, and PL analyses. The effects of Mg2+ doping on the morphology and the intensity of the upconversion (UC) emission were discussed in detail. It turned out that with the concentration of Mg2+ increasing, the morphology of the nanoparticles turn to change gradually and the UC emission was increasing gradually as well. Notably the UC fluorescence intensities of Er3+ were gradually improved owing to the codoped Mg2+ and then achieved a maximum level as the concentration of Mg2+ ions was 60 mol% from the amendment of the crystal structure of β-NaGdF4:Yb3+, Er3+ nanoparticles. Moreover, the UC luminescence properties of the rare-earth (Yb3+, Er3+) ions codoped NaGdF4 nanocrystals were investigated in detail under 980-nm excitation. [ABSTRACT FROM AUTHOR]

In the backward propagation of acoustic waves, the direction of phase velocity is anti-parallel to that of group velocity. We propose a scheme to manipulate the backward propagation using a periodical structure. The dynamic backward propagation process is further experimentally observed. It is demonstrated that the oblique incident plane wave moves backward when it travels through the periodical structure and the backward shift can be controlled within a certain range. [ABSTRACT FROM AUTHOR]

We fabricate single electron transistors based on a single ZnO nanobelt using standard micro-fabrication techniques. The transport properties of the devices are characterized at room temperature and at low temperature (4.2 K). At room temperature, the source-drain current increases linearly as the bias voltage increases, indicating a good ohmic contact in the transistors. At 4.2 K, a Coulomb blockade regime is observed up to a bias voltage of a few millivolts. With scanning the back gate voltage, Coulomb oscillations can be clearly resolved with a period around 1 V. From the oscillations, the charging energy for the single electron transistor is calculated to be about 10 meV, which suggests that confined quantum dots exist with sizes around 35 nm in diameter. The irregular Coulomb diamonds are observed due to the multi-tunneling junctions between dots in the nanobelt. [ABSTRACT FROM AUTHOR]

The contact effect on the performances of organic thin film transistors is studied here. A C60 ultrathin layer is inserted between Al source--drain electrode and pentacene to reduce the contact resistance. By a 3 nm C60 modification, the injection barrier is lowered and the contact resistance is reduced. Thus, the field-effect mobility increases from 0.12 to 0.52 cm2/(V*s). It means that inserting a C60 ultra thin layer is a good method to improve the organic thin film transistor (OTFT) performance. The output curve is simulated by using a charge drift model. Considering the contact effect, the field effect mobility is improved to 1.15 cm2/(V*s). It indicates that further reducing the contact resistance of OTFTs should be carried out. [ABSTRACT FROM AUTHOR]

Mg-doped AlxGa1-xN epilayers were grown on AlN/sapphire templates by metal organic chemical vapor deposition (MOCVD) using an indium-assisted growth method. At room temperature, the resistivity of Mg-doped Al0.43Ga0.57N epilayer grown under indium (In) ambient is of the order of 104 O-cm, while the resistivity of Mg-doped Al 0.43Ga0.57N grown without In assistance is of the order of 106 O-cm. The ultraviolet light-emitting diodes (UV-LEDs) using the In-assisted Mg-doped Al0.43Ga0.57N as the p-type layers were fabricated to verify the function of indium ambient. It is found that there are a lower turn-on voltage and a lower diode series resistance in the UV-LEDs fabricated with p-type Al0.43Ga0.57N layers grown under In-ambient. [ABSTRACT FROM AUTHOR]

A multilayer polydimethylsiloxane microdevice for cell-based high-throughput drug screening is described in this paper. This established microdevice was based on a modularization method and it integrated a drug/medium concentration gradient generator (CGG), pneumatic microvalves and a cell culture microchamber array. The CGG was able to generate five steps of linear concentrations with the same outlet flow rate. The medium/drug flowed through CGG and then into the pear-shaped cell culture microchambers vertically. This vertical perfusion mode was used to reduce the impact of the shear stress on the physiology of cells induced by the fluid flow in the microchambers. Pear-shaped microchambers with two arrays of miropillars at each outlet were adopted in this microdevice, which were beneficial to cell distribution. The chemotherapeutics Cisplatin (DDP)-induced Cisplatin-resistant cell line A549/DDP apoptotic experiments were performed well on this platform. The results showed that this novel microdevice could not only provide well-defined and stable conditions for cell culture, but was also useful for cell-based high-throughput drug screening with less reagents and time consumption. [ABSTRACT FROM AUTHOR]

Chaotic systems perform well as a new rich source of cryptography and pseudo-random coding. Unfortunately their digital dynamical properties would degrade due to the finite computing precision. Proposed in this paper is a modified digital chaotic sequence generator based on chaotic logistic systems with a coupling structure where one chaotic subsystem generates perturbation signals to disturb the control parameter of the other one. The numerical simulations show that the length of chaotic orbits, the output distribution of chaotic system, and the security of chaotic sequences have been greatly improved. Moreover the chaotic sequence period can be extended at least by one order of magnitude longer than that of the uncoupled logistic system and the difficulty in decrypting increases 2128*2128 times indicating that the dynamical degradation of digital chaos is effectively improved. A field programmable gate array (FPGA) implementation of an algorithm is given and the corresponding experiment shows that the output speed of the generated chaotic sequences can reach 571.4 Mbps indicating that the designed generator can be applied to the real-time video image encryption. [ABSTRACT FROM AUTHOR]

Methane clathrate hydrate (MCH) is a promising energy resource, but controllable extraction of CH4from MCH remains a challenge. Gradually replacing CH4in MCH with CO2is an attractive scheme, as it is cost efficient and mitigates the environmentally harmful effects of CO2by sequestration. However, the practicable implementation of this method has not yet been achieved. In this study, using in situ neutron diffraction, we confirm that CH4in the 51262cages of bulk structure-I (sI) MCH can be substituted by gaseous CO2under high pressure and low temperature with a high substitution ratio (∼44%) while conserving the structure of the hydrate framework. First-principles calculations indicate that CO2binds more strongly to the 51262cages than methane does, and that the diffusion barrier for CH4is significantly lowered by an intermediate state in which one hydrate cage is doubly occupied by CH4and CO2. Therefore, exchange of CO2for CH4in MCH is not only energetically favorable but also kinetically feasible. Experimental and theoretical studies of CH4/CO2substitution elucidate a method to harness energy from these combustible ice resources. [ABSTRACT FROM AUTHOR]

Acoustic trapping allows for the contactless manipulation of microparticles. It has led to many applications in chemistry, biology and engineering. In this paper, we report an acoustic cylindrical lens capable of modulating an ultrasound-dark field with minimal acoustic intensity in the center by interference. The ultrasound field, radiation force field and the flow field containing particles in the presence of the lens is simulated. Both simulation and experimental results confirmed that the ultrasound radiation field can be spatially modulated and trap small objects that are perpendicular to the direction of propagation of the ultrasonic waves, owing to the acoustic radiation forces in the system. This acoustic cylindrical lens has a simple structure and the potential to be used in vivo. [ABSTRACT FROM AUTHOR]

Elasticity is of profound significance to evaluating the function of a biological soft tissue. When the elasticity of a tissue is macroscopically changed, it means that the biological function of the tissue is abnormal and some disease or injury may occur. In the present work, an elastometer is developed to measure the elasticity of biological soft tissues. The measurement is based on the indentation method and the force is measured by the bending of the cantilever. The force-indentation data of the soft tissue is experimentally measured by this elastometer and Young's modulus of the tissue is calculated using the Hertz—Sneddon model. For comparison, a numerical model for the indentation method is established using the finite element method. The difference between the actual modulus and the measured modulus is discussed. The effect of the thickness of the specimen on the measurement is investigated. Young's moduli of beef, porcine liver and porcine kidney are experimentally measured. The results indicate that our elastometer is effective in measuring Young's modulus of a soft tissue quantitatively. [ABSTRACT FROM AUTHOR]

The ZnO quantum dots (QDs) were synthesized with improved chemical solution method. The size of the ZnO QDs is exceedingly uniform with a diameter of approximately 4.8 nm, which are homogeneously dispersed in ethanol. The optical absorption edge shifts from 370 nm of bulk material to 359 nm of QD materials due to the quantum size effect, while the photoluminescence peak shifts from 375 nm to 387 nm with the increase of the density of ZnO QDs. The stability of ZnO QDs was studied with different dispersion degrees at 0 °C and at room temperature of 25 °C. The agglomeration mechanisms and their relationship with the emission spectra were uncovered for the first time. With the ageing of ZnO QDs, the agglomeration is aggravated and the surface defects increase, which leads to the defect emission. [ABSTRACT FROM AUTHOR]

We present a systematic analysis of the exciton-recombination zone within all-quantum-dot (QD) multilayer films using sensing QD layers in QD-based light-emitting diodes (QLEDs), and demonstrate the all-QD multilayer films with different sequences of layers prepared by inserting a sensing blue QD layer denoted as B at various positions within four red QD multilayers denoted as R. We also use different hole transporting layers (PVK, CBP as well as poly-TPD) to prevent the formation of leakage current and to improve the luminance. The results show that the total EL emission is mostly at the fourth (60%) and fifth (40%) QD monolayers, adjacent to ITO. This presents both decreasing current density and increasing brightness with different hole transporting layers, thus resulting in more efficient performance. [ABSTRACT FROM AUTHOR]

The enhanced performance of a squaraine compound, with 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine as the donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor, in solution-processed organic photovoltaic devices is obtained by using UV-ozone-treated MoO3 as the hole-collecting buffer layer. The optimized thickness of the MoO3 layer is 8 nm, at which the device shows the best power conversion efficiency (PCE) among all devices, resulting from a balance of optical absorption and charge transport. After being treated by UV-ozone for 10 min, the transmittance of the MoO3 film is almost unchanged. Atomic force microscopy results show that the treated surface morphology is improved. A high PCE of 3.99% under AM 1.5 G illumination (100 mW/cm2) is obtained. [ABSTRACT FROM AUTHOR]

The principle of maximum conformality (PMC) provides a convenient way for setting the optimal renormalization scales for high-energy processes, which can eliminate the conventional renormalization scale error via an order-by-order manner. At present, we make a detailed PMC analysis on the Higgs decay H → γγ up to three-loop QCD corrections. As an important point of deriving reliable PMC estimation, it is noted that only those {βi}-terms that rightly determine the running behavior of coupling constant via the renormalization group equation should be absorbed into the coupling constant, and those {βi}-terms that pertain to the quark mass renormalization and etc should be kept as a separate. To avoid confusion of separating and absorbing different types of {βi}-terms into the coupling constant, we first transform the decay width in terms of top-quark mass into that of on-shell mass and then apply the PMC scale setting. After applying PMC scale setting, the final estimation is conformal and is scheme-independent and scale-independent. Up to three-loop QCD corrections, we obtain a PMC scale GeV ∼2MH, which is optimal and highly independent of any choice of initial scale. Thus, we obtain a more accurate scale-independent prediction by taking the Higgs mass as the same as that of ATLAS and CMS measurements, i.e., and keV, where the error is caused by the measured Higgs mass, i.e. the Higgs mass MH is taken as GeV for ATLAS and 125.7 ± 0.3 ± 0.3 GeV for CMS, respectively. [ABSTRACT FROM AUTHOR]

Two kinds of emission colour-tunable phosphorescent organic light-emitting diodes (PhOLEDs) were realized by changing the Ir(III) bis [2-(4,6-difluorophenyl)-pyridinato-N,C²'] (picolinate) (FIrpic) doping levels in the host polymer poly(9-vinylcarbazole) (PVK) or by adjusting the driving voltage on the devices with neat FIrpic film as the emission layer. The Commission Internationale del'Eclairage (CIE) coordinates of PhOLEDs could be changed from (0.14, 0.37) to (0.29, 0.55) by adjusting the FIrpic doping levels from 0.08 : 1 to 2 : 1 in the host polymer PVK. It is worthwhile to mention that all PhOLEDs with a FIrpic : PVK film as the emission layer show high emission colour stability dependence on the driving voltage. The photoluminescence emission colour tunability of the FIrpic : PVK films was also observed under the same excitation conditions when the FIrpic : PVK doping level was changed, which is very similar to that observed from electroluminescence (EL) emission of PhOLEDs. For devices with a neat FIrpic film as the emission layer, the EL emission colour of the PhOLEDs could be adjusted by the driving voltage. The CIE coordinates of the PhOLEDs could be tuned from (0.31, 0.50) to (0.44, 0.50) along with an increase in driving voltage from 8 to 20V. The emission colour tunability of the neat FIrpic or FIrpic : PVK films should be attributed to the FIrpic self-absorption effect and the occurrence of a new emission peak at about 530 nm. The emission peak at about 530 nm was proved to be FIrpic excimer emission by investigating this emission intensity dependence on FIrpic doping levels in PVK or photo/electric-excitation density on FIrpic : PVK and neat FIrpic films. [ABSTRACT FROM AUTHOR]

Vibrational spectra (Raman 4000-95 cm[?]1 and mid-IR 4000-400 cm[?]1) of the atacamite-structure Ni2(OH)3Cl, including a rarely reported kind of asymmetric trimetric hydrogen bond, as a member of the geometrically frustrated material series and its deuteride Ni2(OD)3Cl are, to the best of our knowledge, reported for the first time and analyzed at room temperature. Through a comparative study of four spectra according to their crystal structural parameters, we assign OH stretching modes v(OH) in a functional group region (3700-3400 cm[?]1) and their deformation modes d(NiOH/D) in the correlation peak region (900-600 cm[?]1) with the corresponding mode frequency ratios ov(OD)/ov(OH)[?]73% and od(NiOD)/od(NiOH)[?]75%, and further self-consistently suggest NiO and Ni-Cl related modes in the fingerprint region (500-200 cm[?]1 and 200-0 cm[?]1, respectively) by use of the unified six-ligand NiO5Cl and NiO4Cl2 frames. This report may contribute to the spectral analysis of other hydroxyl transition-metal halides and to the understanding of the fundamental physics of their exotic magnetic geometrical frustration property from the spectral changes around the corresponding low transition temperatures. [ABSTRACT FROM AUTHOR]

This paper investigates the temperature dependence of the specific resistance in annealed V/Al/V/Au (15 nm/85 nm/20 nm/95 nm) contacts on n-Al0.4Ga0.6N. Contacts annealed at 700 degC and higher temperatures show Ohmic behaviour. Annealing at 800 degC produces the lowest contact resistance. Samples annealed at 800 degC have been analysed by using cross-sectional transmission electron microscopy and an energy dispersive x-ray spectrum. Limited reaction depths are observed between V-based contacts and n-AlGaN. The VN grains are found to form in the contact layer of the annealed samples, which can be considered as the key to the successful formation of Ohmic contact. The contact layer adjacent to AlGaN material consists of V-Al-Au-N, AlN and AlAu alloys. [ABSTRACT FROM AUTHOR]

The mid-infrared absorption spectra of geometrically frustrated hydroxyl cobalt halogenides Co2(OH)3Cl and Co2(OH)3Br are measured by FTIR spectrometers, and the stretching vibrational modes of hydroxyl groups are found to be 3549cm[?]1 and 3524cm[?]1 respectively. Through finding their true terminal O-H group stretching vibration frequencies, we obtain 107cm[?]1 and 99cm[?]1 red shift caused by the corresponding O-H***Cl and O-H***Br hydrogen bonds. Rarely reported trimeric hydrogen bonds (Co3[?]O-H)3***Cl/Br are pointed out to demonstrate the relative weakness of this kind of hydrogen bond which may have a critical effect on the lattice symmetry and magnetic structures. [ABSTRACT FROM AUTHOR]

In the solid state cathodoluminescence (SSCL), organic materials were excited by hot electrons accelerated in silicon oxide (SiO2) layer under alternating current (AC). In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence (exciton emission and recombination radiation), it was demonstrated that recombination radiation should benefit from the exciton ionization. [ABSTRACT FROM AUTHOR]

Presented is a simple method combining a pre-stretching process with stencil lithography for high-resolution patterning of liquid metal wires on polydimethylsiloxane (PDMS) substrates. The PDMS substrate is pre-stretched to several times its original length before casting liquid metals, it is released and restores back to its original length after casting liquid metals through a stencil mask; hence, the width and spacing of the patterned liquid metal wires decrease simultaneously with the PDMS substrate. The degree to which the width and spacing of liquid metal wires decrease is approximately equal to the times that the PDMS substrate is pre-stretched. An ultraviolet-ozone surface modification method was used to enhance the adhesion between liquid metals and PDMS substrates, and an alternative method based on applying an external electric field was proposed to remove excess liquid metals over the stencil mask. Sub-30 µm liquid metal wires were successfully patterned. As a demonstration, a liquid metal based flexible strain sensor was fabricated, the sensor exhibited excellent stretchability, stability, sensitivity and durability. [ABSTRACT FROM AUTHOR]

Inorganic lead halide perovskite nanocrystals (NCs) with superior photoelectric properties are expected to have excellent performance in many fields. However, the anion exchange changes their features and is unfavorable for their applications in many fields. Hence, impeding anion exchange is important for improving the composition stability of inorganic lead halide perovskite NCs. Herein, CsPbX3 (X = Cl, Br) NCs are coated with Cs4PbX6 shell to impede anion exchange and reduce anion mobility. The Cs4PbX6 shell is facily fabricated on CsPbX3 NCs through high temperature injection method. Anion exchange experiments demonstrate that the Cs4PbX6 shell completely encapsulates CsPbX3 NCs and greatly improves the composition stability of CsPbX3 NCs. Moreover, our work also sheds light on the potential design approaches of various heterostructures to expand the application of CsPbM3 (M = Cl, Br, I) NCs. [ABSTRACT FROM AUTHOR]

A four-photomask method for fabricating a polyimide (PI)-based electrostatically actuated MEMS relay is presented. The processes for patterning the SiO2 sacrificial layer and curing the PI layer for making the movable structure were optimized. The substrate and the movable structure of the relay were all made of PI, and thus the relay exhibited excellent flexibility and could be used for flexible electronics. Moreover, using PI as the substrate of the drain electrode significantly reduced the effective hardness of the contact material. The hardness of a Au film on a PI substrate was only 42% of that of the Au film on a silicon substrate. In turn, the decrease of the hardness of the contact material contributed to obtaining a lower contact resistance. The contact resistance of the MEMS relay with a PI substrate was less than half of that of the MEMS relay with a silicon substrate. [ABSTRACT FROM AUTHOR]

In this study, an InGaN lighting-emitting diode (LED) containing GaN/AlGaN/GaN triangular barriers is proposed and investigated numerically. The simulation results of output performance, carrier concentration, and radiative recombination rate indicate that the proposed LED has a higher output power and an internal quantum efficiency, and a lower efficiency droop than the LED containing conventional GaN or AlGaN barriers. These improvements mainly arise from the modified energy bands, which is evidenced by analyzing the LED energy band diagram and electrostatic field near the active region. The modified energy bands effectively improve carrier injection and confinement, which significantly reduces electron leakage and increases the rate of radiative recombination in the quantum wells. [ABSTRACT FROM AUTHOR]

Lead halide perovskite materials are thriving in optoelectronic applications due to their excellent properties, while their instability due to the fact that they are easily hydrolyzed is still a bottleneck for their potential application. In this work, water-resistant, monodispersed and stably luminescent cesium lead bromine perovskite nanocrystals coated with CsPb2Br5 were obtained using a modified non-stoichiometric solution-phase method. CsPb2Br5 2D layers were coated on the surface of CsPbBr3 nanocrystals and formed a core–shell-like structure in the synthetic processes. The stability of the luminescence of the CsPbBr3 nanocrystals in water and ethanol atmosphere was greatly enhanced by the photoluminescence-inactive CsPb2Br5 coating with a wide bandgap. The water-stable enhanced nanocrystals are suitable for long-term stable optoelectronic applications in the atmosphere. [ABSTRACT FROM AUTHOR]

This paper reports the use of electrohydrodynamic jet (E-jet) printing technique for producing a wide range of graphene micro-scale structures. Ethyl cellulose-dispersed graphene ink and Nafion-dispersed graphene ink were prepared and used for E-Jet printing. A glass slide and PDMS substrate were used for E-Jet printing of graphene ink. The E-jet printed graphene micro-scale structures using ethyl cellulose-dispersed graphene ink presented a feature of center arrayed graphene surrounded by the track of evaporated solution. However, the E-Jet printed graphene structures using Nafion-dispersed graphene ink exhibited uniform arranged features. It was observed that the resistivity of the graphene structures printed from the ethyl cellulose-dispersed graphene ink was much lower than that from the Nafion-dispersed graphene ink. In addition, the graphene micro-scale electrodes were E-Jet printed for preliminary electrochemical applications. The results showed that the graphene micro-scale electrodes had a distinct response for the lead ion. Furthermore, a Pt/graphene composite electrode was formed and an electrochemistry test was conducted. It was found that the Pt /graphene composite electrode had a more sensitive response compared with the pure Pt electrode for electrochemical sensing. [ABSTRACT FROM AUTHOR]

Raman vibrational spectra of the selected basic (hydroxyl OH and deuteroxyl OD) transition-metal halides, geometrically frustrated material series a-, b-, g-Cu2(OH)3Cl, a-Cu2(OH)3Br, b-Ni2(OH)3Cl, b-Co2(OH)3Cl, b-Co2(OH)3Br, g-Cu2(OD)3Cl, and b-Co2(OD)3Cl are measured at room temperature and analysed to investigate the relationship between the microstructured OH environments and their respective Raman spectra. Among these selected samples, the last two are used to determine the OH stretching vibration region (3600 cm[?]1[?]3300 cm[?]1) and OH bending vibration region (1000 cm[?]1[?]600 cm[?]1) of OH systems in the spectra. Through the comparative analysis of the distances d(metal--O), d(O--halogen), and d(OH), the strong metal--O interaction and trimeric hydrogen bond (C3v, Cs or C1 symmetry) are found in every material, but both determine simultaneously an ultimate d(OH), and therefore an OH stretching vibration frequency. According to the approximately linear relationship between the OH stretching vibration frequency and d(OH), some unavailable d(OH) are guessed and some doubtful d(OH) are suggested to be corrected. In addition, it is demonstrated in brief that the OH bending vibration frequency is also of importance to check the more detailed crystal microstructure relating to the OH group. [ABSTRACT FROM AUTHOR]

Mid-infrared absorption and Raman spectra of the geometrically frustrated material series, hydroxyl cobalt halides ss-Co2(OH)3Cl and ss-Co2(OH)3Br, are first, to the best of our knowledge, measured at room temperature, to study the corresponding relationship between their vibrational spectral properties and crystal microstructures. Through the comparative analysis of the four spectra we have categorically assigned the OH-related vibration modes of hydroxyl groups in the trimeric hydrogen bond environment (Co3 [?]OH)3 ... Cl/Br, and tentatively suggested vibration modes of O-Co-O, Co-O and Cl/Br-Co-Cl/Br units. These results can also become the basis for analysing their low-temperature spectral properties, which can help to understand the underlying physics of their exotic geometric frustration phenomena around phase transition temperatures. [ABSTRACT FROM AUTHOR]

We report on the growth and fabrication of deep ultraviolet (DUV) light emitting diodes (LEDs) on an AlN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317 nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved. [ABSTRACT FROM AUTHOR]

Lanthanide phosphate microspheres composed of single-crystal CePO4 and CePO4:Tb nanorods were successfully synthesized, respectively, using the functionalized composite aggregate as a template, which is composed of P123, H6P4O13 and Ce3+, and also as a resource of reaction species with high chemical potential. The shape and the phase structure of the CePO4 nanocrystal can be easily controlled via adjusting reaction temperature, monomer concentration and annealing temperature. SEM images show the spherical superstructure composed of nanorods. HRTEM and SAED images reveal the single-crystalline nature of nanorod and TEM images show the hollow interiors of the superstructure. XRD patterns indicate that the crystal structure of the nanorods is hexagonal before and monoclinic after annealing. The formation mechanism was proposed. Strong UV and green luminescence were observed for the CePO4 and CePO4:Tb microspheres, respectively. The synthesis method can be extended to the fabrication of NRHS and core-shell microspheres of other rare-earth or doped LnPO4 materials for wide applications. [ABSTRACT FROM AUTHOR]