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Charge carrier trapping in thin films of lyotropic chromonic liquid crystals (LCLCs) based on ionic perylene diimide derivative and in chemically-similar neutral N,N′-dipentyl-3,4,9,10-perylene-dicarboximide (PTCDI-C5) films is investigated by thermally-stimulated luminescence (TSL) technique. The LCLC films comprise elongated molecular aggregates featuring a long-range orientational order. The obtained results provide direct evidence for the improved energetic ordering (smaller effective energetic disorder) in aggregated LCLC films as compared to conventional PTCDI-C5 films. The width of the density-of-state distribution of 0.09 eV and 0.13 eV was estimated for the LCLC and PTCDI-C5 films, respectively. Relatively small effective energetic disorder in LCLC films is ascribed to formation of macroscopically larger LCLC aggregates.
In this paper, the hole carrier mobility of organic semiconductor N,N′-diphenyl-N,N′bis(1,1′-biphenyl)-4,4′-diamine (NPD) was researched by negative differential susceptance spectra (−ΔB = −w(C − Cgeo) ~ f). Under the condition of space charge limited current (SCLC), through solving the drift current equation and Poisson equation and simulating the spectra −ΔB = −w(C − Cgeo) ~ f, the relationship between the peak of −ΔB = −w(C − Cgeo) ~ f spectra (1/ƒp = τp) and the transfer time of carrier (τdc) could be achieved to be τdc = k × τp. So the hole-only device of ITO/NPD/Ag was fabricated to determine the capacitance spectra, and through which its −ΔB = −w(C − Cgeo) ~ f could be plotted. According to the relationship of τdc = k × τp, where k was determined to be 0.56, the transfer time and further the carrier mobility could be obtained. The carrier mobility depended on the electric field according to Poole-Frenkel model was further investigated in this report.
In this work, we have investigated the structural, optical and electrical properties of rare earth co-doped zinc oxide thin films prepared by spray pyrolysis technique. X-ray diffraction has shown that the films are polycrystalline and textured with the c-axis of the wurtzite structure along the growth direction. Scanning electronic microscopy and transmission electronic microscopy were used to study the films composition and morphology. Photoluminescence measurements showed that all the films have a strong emission band at around 380 nm. Layers with electrical resistivity values as low as 5.7 × 10−2 Ω cm were obtained.
In this paper, we present the fabrication and characterization of sputter deposited thin-film Cr-CrOx-Cr MIM diodes for application in millimeter wave detectors. The oxide layers were grown by thermal oxidation of the first deposited Cr electrode at 300 °C and at atmospheric pressure. The appreciable nonlinearity shown by these diodes confirms their viability in millimeter wave and infrared applications. The fabricated MIM structures exhibited sensitivity as high as 2.58 V−1 at Vbias of 0.3 V. Additionally, numerical integration of Simmons tunneling equations were utilized to extract the MIM diodes parameters. The correlation between the extracted parameters, the diodes performance and the fabrication conditions would be very valuable to effectively design and fabricate structures with improved performance.
Plasma processing is an approach to modify the surface structure for improved performance of nitride semiconductor using in light emitting diodes. In this work, RF sputtered GaN thin films were synthesized on Si (1 0 0) substrates and processed at two different plasmas (N2 and O2) at various flow rates. The surface nature of plasma processed thin films was characterized using atomic force microscope (AFM) and scanning electron microscope (SEM). Energy dispersive spectrum (EDS) of all samples was recorded to do elemental analysis. Noticeable changes on surface morphology were recorded for the plasma processed GaN thin films at high flow rate (>20 sccm). The roughness and particle size of thin film got decreased as the flow rate of gases increased. Low value in surface roughness (0.26 nm) and particles size (14 nm) was observed at 30 sccm flow rate of O2. SEM images also revealed the surface modification at high gas flow rates during plasma process. Nitrogen deficient GaN thin film was confirmed by EDS spectra and improved N2 concentration was achieved for N2 and O2 plasma processing upto 20 sccm flow rates. I-V characteristics showed the Schottky-contact behavior for all thin films and revealed the improved surface quality to make good ohmic contact for the film processed at high gas flow rate (>30 sccm).
Hierarchical Zn0.5Cd0.5S nanohexagon dendrites were synthesized by a one-step hydrothermal method. The Zn0.5Cd0.5S nanohexagon dendrites were made up of nanohexagons with a side length of about 90 nm. The nanohexagons were regularly arranged forming as embranchments which were parallel to each other along certain hexagonal directions. Furthermore, these embranchments made up primary trunks shaping as dendrites. The growth mechanism of Zn0.5Cd0.5S nanohexagon dendrites was proposed in which molecular soft template and lowest energy principle played key roles. By adjusting the composition of the reactants, a series of ZnxCd1–xS solid solutions could be obtained. The morphology of the synthesized ZnxCd1–xS depended much on the x value. The UV-vis spectra absorb edges of the ZnxCd1–xS samples continuously shifted indicating the changes of the band gap.
In this article, the vibrational behavior of a microcantilever (MC) with an extended piezoelectric layer in the air ambient undergoes examination. To model the vibrational motion of this type of cantilever, the Hamilton’s principle has been used. For this purpose, the MC vibrational equation has been derived by the assumption of the continuous beam based on the Euler-Bernoulli beam theory. By adopting the finite element method (FEM), the MC differential equation has been solved. In the present simulation not only van der Waals and contact forces but also the capillary forces resulting from the condensation of the water vapors in air on MC tip have been considered. The results illustrate that the force between the sample surface and the probe affects the MC amplitude; furthermore, it causes the reduction in the resonance frequency. In addition, to reduce the time delay during topography from the surface roughness, it is better to select MCs with larger width and length and smaller thickness. Furthermore, the results indicate that the best imaging takes place when the vibration is in its second vibrational mode. Finally, the effects of MC geometric parameters on the time delay between the starting moment of surface roughness and the moment of variation in the MC amplitude (surface roughness topography) have been analyzed.
The flip-flop, which has been widely used in digital circuits, has two stable states and can be used to store state information. Because traditional flip-flops based on digital circuits suffer from a barrier to higher performance, it is necessary to explore some new alternative devices. For this purpose, we utilize molecular dynamics simulations to design a molecular flip-flop, which contains one water molecule confined within a single-walled carbon nanotube. Its two states can be switched within 0.5 ps (2000 GHz), and its state information can be exported by the charged atomic-force microscope force probes. The mechanism of the flip-flop depends on the behavior of a water molecule in a nonuniform electric field. In particular, a water molecule always moves toward the location of lowest electric energy in a nonuniform electric field generated by point charges. The resulting flip-flop could be utilized for designing nanoscale devices.
The EPR parameters (zero-field splitting D and g-factors g//, g⊥) of Mn5+-doped solid state laser materials Ca2(MO4)Cl (M = P, As, V) are calculated from the complete high-order perturbation formulas of EPR parameters based on the two-mechanism model for 3d2 ions in a approximately tetragonal tetrahedron. The model includes the contributions from both the crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (the latter is neglected in crystal field theory). The calculated results suggest that the contribution to EPR parameters due to CT mechanism is important. So, in the cases of high valence state 3dn ions in crystals, the reasonable explanation of EPR parameters should take both CF and CT mechanisms into account.
Energy shifts in K X-ray peaks of potassium and calcium in different chemical compounds have been determined from their X-ray spectra recorded in an energy dispersive X-ray fluorescence (EDXRF) set-up. The set-up comprises low-power X-ray tube photon source and Si(PIN) detector (AMPTEK model XR-100 CR). A statistical procedure has been followed to determine the shifts and t-test was applied to find the statistical significance of the results. The shifts were determined in potassium compounds; KCl, KBr, KI, K2CO3, K2Cr2O7, K2CrO4, K2SO4, K3Fe(CN)6, K4Fe(CN)6, KHSO4, KMnO4 and KSCN with KNO3 as reference and in calcium compounds; Ca(NO3)2 · 4H2O, Ca(OH)2, CaCl2, CaCO3, CaSO3 and CaSO4 · 2H2O with CaO as reference and correlated with differences in electro-negativity, number of ligands, structural changes, type of bonding, axial distances, etc. in the compounds. The shifts in potassium compounds have been evaluated for the first time while the same for calcium compounds almost agree well with the earlier reported measurements in literature.
Terbium (Tb3+) doped yttrium aluminium borate phosphors (YAl3(BO3)4) with different compositions such as YAl3(BO3)4:Tb3+, Y1−xAl3(BO3)4:Tbx3+ and YAl(3−x)(BO3)4:Tbx3+ (x = 1−8 mol.%) were synthesized using modified solid state reaction technique. The synthesized phosphor was studied using powder X-ray diffraction analysis (XRD), photoluminescence spectroscopy (PL), high resolution-scanning electron microscope (HR-SEM). Lattice parameters are calculated for the Tb3+ doped and substituted YAB phosphors using XRD analysis. The phosphor exhibits green emission at 572 nm with 375 nm of excitation. It is found that the Tb3+ ions substitution in the sites Y3+ and Al3+ ions in Y1–xAl3(BO3)4:Tbx3+ and YAl(3–x)(BO3)4:Tbx3+ leads to overlapping of energy levels which affects the PL intensity of the phosphor significantly. Thus, phosphor synthesized with the composition YAl3(BO3)4:Tb3+, acquires higher photoluminescence (PL) intensity when compared to Y1–xAl3(BO3)4:Tbx3+ and YAl(3–x)(BO3)4:Tbx3+ phosphors. Temperature dependent PL property (thermal quenching studies) of YAl3(BO3)4:Tb3+ was also performed up to 250 °C. Further, it is found that the PL intensity of the studied phosphor is comparable with commercial green phosphor. HR-SEM analysis demonstrates that the phosphors are grown as nanorods with an average diameter of 50–80 nm and length 250–500 nm.
The electrical explosion characteristics of Schottky diode for one-shot switch applications were acquired by analysis of photographs of high speed camera and current-voltage histories. Four types of connections among Schottky diode, top electrode and discharge capacitor were studied. Results show that type B has the longest time (1.4 ms) of optical radiation and highest energy consumption, which makes it easier to turn on the switch. The charge flux of plasma was determined to be 24.5 Q/(s m2) by parallel electrode plates method. Atomic emission spectroscopic measurements were devoted to determine plasma temperature and density during electrical explosion. Results show that temperature is between 4000 K and 5000 K, and density is about 1024 m−3. The one-shot switch based on ceramics has been fabricated and characterized and the results show that the peak current and the rise time are about 963.77 A and 381.6 ns, respectively.
Physics of Energy Transfer, Conversion and Storage
First-principles calculations based on density functional theory (DFT) have been carried out to investigate the effects of crystal defects (intrinsic vacancy defects and ion doping) on the microwave dielectric response and the correlative electromagnetic properties of α-MnO2 systematically. The possible role of crystal defects in electromagnetic performance is studied utilizing density of states (DOS) and the bond length between the manganese and oxygen. Lattice distortion is induced by the introduction of crystal defects. The spin-electronic DOS demonstrates that Ni doping enhances the spin-polarization of MnO2, which indicates that the Ni-doped MnO2 possesses certain magnetic characteristic, which is helpful for magnetic loss. The emergence of a new defect mode, contributes to the relaxation polarization phenomenon, so as to enhance the dielectric loss ability. In addition, through the change of the bond length and pseudo gap width, it can be learned that the bond strength and covalency of Mn-O bonds are weakened, which increases the dielectric loss of MnO2. The results throw light on the exploration of theoretical research on the microwave absorbing properties of MnO2 with crystal defects.
BaTiO3 crystals, grown by Remeika method, were studied by means of acoustic emission and dielectric response. It is established, that the phase transition in the surface layer occurs on 13 °C below in comparing with the crystals bulk. It is observed, that the imaginary dielectric response of a crystal surface layer exhibits an essential smearing and slight frequency shift to higher temperatures. Reasons of such properties are discussed from a viewpoint of diffusive phase transition, taking place in the surface layer, enriched by K+ ions from KF flux.