Search

The polymer spin coating is critical in flexible electronic manufaction and micro-electro-mechanical system (MEMS) devices due to its simple operation, and uniformly coated layers. Some researchers focus on the effects of spin coating parameters such as wafer rotating speed, the viscosity of the coating liquid and solvent evaporation on final film thickness. In this work, the influence of substrate curvature on film thickness distribution is considered. A new parameter which represents the edge bead effect ratio (re) is proposed to investigate the influence factor of edge bead effect. Several operation parameters including the curvature of the substrate and the wafer-spin speed are taken into account to study the effects on the film thickness uniformity and edge-bead ratio. The morphologies and film thickness values of the spin-coated PDMS films under various substrate curvatures and coating speeds are measured with laser confocal microscopy. According to the results, both the convex and concave substrate will help to reduce the edge-bead effect significantly and thin film with better surface morphology can be obtained at high spin speed. Additionally, the relationship between the edge-bead ratio and the thin film thickness is like parabolic curve instead of linear dependence. This work may contribute to the mass production of flexible electronic devices. [ABSTRACT FROM AUTHOR]

Multiferroic properties in a polycrystalline terbium orthoferrite are investigated. Different thermomagnetic behaviors are observed in different magnetic fields, which is attributed to the suppression of the low temperature magnetic phase by an external magnetic field. Further studies reveal that the ferroelectricity originates from the spin configuration below 3.5 K. In addition, the magnetic field control of electric polarization and dielectric constant is observed, which suggests a magnetoelectric effect in TbFeO3. The origin of ferroelectricity in this rare-earth orthoferrite is discussed. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the magnetic and ferroelectric properties of polycrystalline MnW1–xMoxO4 (x = 0, 0.05, 0.10, 0.20) compounds. The substitution of nonmagnetic Mo6+ ions for W6+ ions modifies the magnetic transition temperatures of MnW1–xMoxO4 by changing the Mn—O—Mn bond. As a result, distinct ferroelectric properties and enhanced magnetoelectric effects are observed in Mo6+ -doped MnWO4 compounds. The effects of substitution of Mo6+ ions on magnetic properties and magnetoelectric coupling are discussed. [ABSTRACT FROM AUTHOR]

Based on the idea of tracking control and stability theory of fractional-order systems, a controller is designed to synchronize the fractional-order chaotic system with chaotic systems of integer orders, and synchronize the different fractional-order chaotic systems. The proposed synchronization approach in this paper shows that the synchronization between fractional-order chaotic systems and chaotic systems of integer orders can be achieved, and the synchronization between different fractional-order chaotic systems can also be realized. Numerical experiments show that the present method works very well. [ABSTRACT FROM AUTHOR]

A specific state variable in a class of 3D continuous fractional-order chaotic systems is presented. All state variables of fractional-order chaotic systems of this class can be obtained via a specific state variable and its (q-order and 2q-order) time derivatives. This idea is demonstrated by using several well-known fractional-order chaotic systems. Finally, a synchronization scheme is investigated for this fractional-order chaotic system via a specific state variable and its (q-order and 2q-order) time derivatives. Some examples are used to illustrate the effectiveness of the proposed synchronization method. [ABSTRACT FROM AUTHOR]

This paper studies chaotic dynamics in a fractional-order unified system by means of topological horseshoe theory and numerical computation. First it finds four quadrilaterals in a carefully-chosen Poincare section, then shows that the corresponding map is semiconjugate to a shift map with four symbols. By estimating the topological entropy of the map and the original time-continuous system, it provides a computer assisted verification on existence of chaos in this system, which is much more convincible than the common method of Lyapunov exponents. This new method can potentially be used in rigorous studies of chaos in such a kind of system. This paper may be a start for proving a given fractional-order differential equation to be chaotic. [ABSTRACT FROM AUTHOR]

An iterative method in the Kirchhoff approximation is proposed for high frequency multiple electromagnetic scattering from two-dimensional dielectric sea surface. The multiple interaction of the scattering field is characterized with the corrected electromagnetic currents of the wind-driven sea surface. The actual surface currents are approximated with the iterative solution of the corrected currents. A newly developed sea spectrum, Elfouhaily spectrum, is utilized to build the sea surface model. The shadowing correction is improved by the Depth-Buffer algorithm. The validity of the iterative Kirchhoff approximation is verified by the agreement of backscattering coefficients with the measured data. [ABSTRACT FROM AUTHOR]

Based on the Ising spin, the phase transition on fractal scale-free networks with tree-like skeletons is studied, where the loops are generated by local links. The degree distribution of the tree-like skeleton satisfies the power-law form . It is found that when , the renormalized scale-free network will have the same degree distribution as the original network. For a special case of δ = 4.5, a ferromagnetic to paramagnetic transition is found and the critical temperature is determined by the box-covering renormalization method. By keeping the structure of the fractal scale-free network constant, the numerical relationship between the critical temperature and the network size is found, which is the form of power law. [ABSTRACT FROM AUTHOR]

Based on crystallographic theory, there are 63 kinds of polytypes of 13H long-period stacking order (LPSO) structure, 126 kinds of polytypes of 14H LPSO structure, 120 kinds of polytypes of 39R LPSO structure, and 223 kinds of polytypes of 42R LPSO structure in a hexagonal close-packed (HCP) system, and their stacking sequences and space groups have been derived in detail. The result provides a theoretical explanation for the various polytypes of the LPSO structure. [ABSTRACT FROM AUTHOR]

We demonstrate that the GaAs/AlGaAs nanowires (NWs) ensemble is fabricated into photo-detectors. Current–voltage (I–V) characteristics are measured on GaAs/AlGaAs core–shell ensemble NW photo-detectors at room-temperature before and after 1-MeV proton irradiation with fluences from cm to cm. The degradation of photocurrent suggests that the point defects induced by proton radiation could cause both carrier lifetime and carrier mobility to decrease synchronously. Comparing with a GaAs quantum well, the degradations of light and dark current for the irradiated NWs photo-detector indicate that NWs material is a preferable potential candidate for space applications. [ABSTRACT FROM AUTHOR]

To gain a physical insight into the radiation effect on nanowires (NWs), the time resolved photoluminescence (TRPL) technique is used to investigate the carrier dynamic behaviors in GaAs/AlGaAs core–shell NWs before and after 1-MeV proton irradiation with fluences ranging from cm to cm. It is found that the degradations of spectral peak intensity and minority carrier lifetime show similar trends against irradiation fluence, which is closely related to the displacement defects induced by irradiation. We also find that the proton irradiation-induced defects behave as Shockley–Read–Hall (SRH) recombination center trapping free carriers. Finally, the defect concentration could be estimated through measuring the minority carrier lifetime. [ABSTRACT FROM AUTHOR]

Colloidal ZnAgInSe (ZAISe) quantum dots (QDs) with different particle sizes were obtained by accommodating the reaction time. In the previous research, photoluminescence (PL) of ZAISe QDs only could be tuned by changing the composition. In this work the size-tunable photoluminescence was observed successfully. The red shift in the photoluminescence spectra was caused by the quantum confinement effect. The time-resolved photoluminescence indicated that the luminescence mechanisms of the ZAISe QDs were contributed by three recombination processes. Furthermore, the temperature-dependent PL spectra were investigated. We verified the regular change of temperature-dependent PL intensity, peak energy, and the emission linewidth of broadening for ZAISe QDs. According to these fitting data, the activation energy () of ZAISe QDs with different nanocrystal sizes was obtained and the stability of luminescence was discussed. [ABSTRACT FROM AUTHOR]