Effect of gate barrier and channel buffer layer on electric properties and transparence of the a-IGZO thin film transistor

Different structures of a-IGZO (amorphous indium gallium zinc oxide) transparent thin film transistor (TTFT) were developed on glass substrate for study of gate barrier and channel buffer layer effects. The used gate barrier and the channel buffer layer are high energy band gap dielectric Al₂O₃ and the rapid thermally annealed ZnO film, respectively. With both gate barrier and channel buffer layers, the TTFT promoted ∼3 orders in on/off current ratio and reduced leakages current ∼800 times. Furthermore, the average transparence was also enhanced from 84% to 86.4% in the range of 500–800 nm wavelengths. The improvement mechanisms are interpreted with comprehensive models in details.     

Growth kinetics and surface properties of single-crystalline aluminum-doped zinc oxide nanowires on silicon substrates

We present here the results from a systematic investigation on the growth kinetics and surface properties of Al-doped ZnO (AZO) nanowires synthesized on (0 0 1)Si substrates under different hydrothermal conditions. The as-synthesized vertical AZO nanowires exhibited a hydrophilic characteristic and their crystal structures were determined to be perfectly single crystalline with the axis of the wire parallel to the [0 0 0 1] direction. TEM and EDS results revealed that the as-synthesized AZO nanowires have tapered tips, and the Al-doped concentration in the AZO nanowires was about 1.6 at%. After a series of SEM examinations, the average length of AZO nanowires synthesized at each temperature studied was found to follow a linear relationship with the reaction time, indicating that the hydrothermal growth of AZO nanowires was a reaction-controlled process. The activation energy for linear growth of AZO nanowires on Si substrate, as obtained from an Arrhenius plot, was found to be about 46 kJ/mol. From UV–vis spectroscopic measurements, it was found that the Si substrate coated with vertically-aligned AZO nanowire arrays exhibited remarkably reduced reflectance (10–12%) over a wide range of visible wavelengths (400–800 nm) and angles of light incidence (8–60°). The good broadband and omnidirectional antireflection characteristics can be attributed to the light trapping effect and the graded refractive index resulting from the tapered AZO nanowire structures.     

Modulation instability dynamics of coupling pulses with different powers in nonlinear fibers

In the paper, the modulation instability (MI) of the pulses with different powers is studied based on the modified coupled nonlinear Schrödinger equations in nonlinear fiber. By analyzing MI gain spectrum with different power ratios, it shows that the increase of power ratio leads to the diminution in the range of strongly unstable frequency and the decrease in the gain of MI spectra. With a fixed power ratio, the increased relaxation time is equally suppressing overall MI.     

A comprehensive theoretical study of halide perovskites ABX3

Solar cells based on halide perovskites have recently been attractive due to their excellent power conversion efficiency (PCE), lower cost and simple manufacture. Here, a series of halide perovskites (ABX₃: A = CH₃NH₃, CH(NH₂)₂, Cs, Rb; B = Pb, Sn, Ge; X = I, Br, Cl, F) were investigated by Density Functional Theory (DFT) calculations, together with Shockley-Queisser Maximum Solar Cell Efficiency (S-Q) and Spectroscopic Limited Maximum Efficiency (SLME) mathematical models. The results indicate that: the electronic structure of germanium perovskites bears a close similarity to that of lead perovskites with a small energy difference between the nonbonding orbital and antibonding orbitals, but with a large energy difference comparing with that of tin perovskites (0.6–1.7 eV for CsGeI₃ at Z point of the Brillouin zone, 0.7–1.4 eV for CH₃NH₃PbI₃ and 1.4–2.2 eV for CH₃NH₃SnI₃ at R point of the Brillouin zone), which is attributable to the atomic level, where the 4s orbital energy of Ge (−11.5 eV) is close to the 6s orbital energy of Pb (−11.6 eV), but the 5s orbital energy of Sn (−10.1 eV) is significantly high. Therefore, germanium perovskites possess as high absorption coefficient around solar spectrum as lead perovskites, while tin perovskites only have low absorption coefficient, which makes the short-circuit current of CsGeI₃ and CH₃NH₃PbI₃ (0.017 Acm⁻² and 0.016 Acm⁻², simulated by SLME with a 200 nm absorber under AM1.5G) are higher than that of CH₃NH₃SnI₃ (0.015 Acm⁻²) even if the bandgap of CsGeI₃ and CH₃NH₃PbI₃ (1.51 eV and 1.55 eV) are larger than that of CH₃NH₃SnI₃ (1.21 eV). Meanwhile, the effective mass of electrons and holes are approximate for germanium perovskites and lead perovskites (0.14:0.19 for CsGeI₃ and 0.12:0.12 for CH₃NH₃PbI₃), indicating a balanced electrons and holes transport, whereas the electrons transport is much slower than the holes transport for tin perovskites due to the effective mass of electron is much larger than that of hole (0.17:0.04 for CH₃NH₃SnI₃). As a result, the PCE of CsGeI₃ (27.9%) and CH₃NH₃PbI₃ (26.7%) is higher than that of CH₃NH₃SnI₃ (19.9%).     

Synthesis of graphene nanoribbons with various widths and its application to thin-film transistor

Novel precursor polymers containing phenylene, naphthalene and anthracene units were synthesized for fabrication of graphene nanoribbons (GNRs) by the Suzuki coupling reaction between dibrominated monomers and diboronic ester monomers. The precursor polymers were converted into GNRs by intramolecular cyclodehydrogenation using FeCl₃ as a catalyst. The degree of cyclodehydrogenation was determined by analysis of nuclear magnetic resonance spectra. All GNR films show ambipolar charge transport behavior in thin-film transistor (TFT). The GNR film prepared from anthracene-based polymer exhibits the highest TFT performance due to its longer conjugation length and larger width of nanoribbon than GNRs prepared from phenylene and naphthalene-based polymers.     

Fabrication of surface-treated BN/ETDS composites for enhanced thermal and mechanical properties

The ceramic/polymer composites based on epoxy-terminated dimethylsiloxane (ETDS) and boron nitride (BN) were prepared for use as thermal interface materials (TIMs). 250 µm-sized BN was used as a filler to achieve high-thermal-conductivity composites. To improve the interfacial adhesion between the BN particles and the ETDS matrix, the surface of BN particles were modified with silica via the sol–gel method with tetraethyl orthosilicate (TEOS). The interfacial adhesion properties of the composites were determined by the surface free energy of the particles using a contact angle test. The surface-modified BN/ETDS composites exhibited thermal conductivities ranging from 0.2 W/m K to 3.1 W/m K, exceeding those of raw BN/ETDS composites at the same weight fractions. Agari׳s model was used to analyze the measured thermal conductivity as a function of the SiO₂-BN concentration. Moreover, the storage modulus of the BN/ETDS composites was found to increase with surface modification of the BN particles.     

General features of spatiotemporal instability induced by arbitrary high-order nonlinear dispersions in metamaterials

Spatiotemporal instability (STI) in metamaterials (MMs) with a Kerr-type nonlinear polarization is investigated. A general expression for instability gain, taking account of the effects of arbitrary high-order linear and nonlinear dispersions, is derived. Special attention is paid to the general features of instability induced by nonlinear dispersion effects originating from the combination of dispersive magnetic permeability and nonlinear polarization. It is shown that, just like their linear counterparts, all even-order nonlinear dispersions not only deform the original instability regions, but also may lead to the appearance of new instability regions. However, all odd-order nonlinear dispersions always suppress STI irrespective of their signs, quite different from their linear counterparts which exert no influence on instability. Moreover, we find that, unlike the linear dispersions, the nonlinear dispersions lead to the dependence of gain peak on the spatial modulation frequency. The role of the first-order nonlinear dispersion, namely self-steepening (SS), and second-order nonlinear dispersion (SND) in STI is particularly analyzed to illustratively demonstrate the general results.     

Bioinspired interactive neuromorphic devices

The performance of conventional computer based on von Neumann architecture is limited due to the physical separation of memory and processor. By synergistically integrating various sensors with synaptic devices, recently emerging interactive neuromorphic devices can directly sense/store/process various stimuli information from external environments and implement functions of perception, learning, memory, and computation. In this review, we present the basic model of bioinspired interactive neuromorphic devices and discuss the performance metrics. Next, we summarize the recent progress and development of bioinspired interactive neuromorphic devices, which are classified into neuromorphic tactile systems, visual systems, auditory systems, and multisensory system. They are discussed in detail from the aspects of materials, device architectures, operating mechanisms, synaptic plasticity, and potential applications. Additionally, the bioinspired interactive neuromorphic devices that can fuse multiple/mixed sensing signals are proposed to address more realistic and sophisticated problems. Finally, we discuss the pros and cons regarding to the computing neurons and integrating sensory neurons and deliver the perspectives on interactive neuromorphic devices at the material, device, network, and system levels. It is believed the neuromorphic devices can provide promising solutions to next generation of interactive sensation/memory/computation toward the development of multimodal, low-power, and large-scale intelligent systems endowed with neuromorphic features.     

Synthesis and characterization of Ni-Mo2C particles supported over hydroxyapatite for potential application as a catalyst for hydrogen production

Ni-Mo₂C particles supported over hydroxyapatite were synthesized as potential catalysts to hydrogen production applications due their physiochemical properties observed in characterization results, this favorable for biomass gasification. Mo₂C particles doped with Ni were synthesized by temperature programmed reaction method at 900 °C under hydrogen reducing atmosphere. Hydroxyapatite support was obtained from thermal extraction of bovine bones, in a temperature range from 700 to 900 °C. Ni-Mo₂C impregnation over hydroxyapatite support was made by incipient humidity method. X-ray diffraction analysis determined crystallographic phases of β-Mo₂C, NiC and hydroxyapatite. Though, bone organic matter degradation was observed by X-ray diffraction and confirmed by Infrared Spectroscopy with Fourier Transform (FTIR) the final structure of hydroxyapatite was maintained. Finally, textural properties analysis of support showed an increase in porosity structure with the increment of temperature. β-Mo₂C and NiC were obtained with similar catalytic activity than noble metals, also nickel improves hydrocarbons bonds rupture. Hydroxyapatite showed high stability and porosity at elevated temperatures attributable to synthesis conditions.     

Rubrene-based interfacial engineering toward enhanced performance in inverted polymer solar cells

Rubrene, an organic semiconductor having stable fused-ring molecular structure was used as a double interfacial layer in inverted organic solar cells. When a thin, 3 nm-thick layer of rubrene was introduced between a MoO₃-based hole-collecting layer and a bulk-heterojunction (BHJ) photo-active layer consisting of poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl} (PTB7) and [6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM), the power conversion efficiency was improved over 12% (from 7.2% to 8.1%). It was demonstrated that the insertion of thin rubrene layer showed suppressed exciton quenching and improved exciton dissociation, resulting in more efficient charge carrier collection and weaker charge recombination, thus improving the device performance.