Dielectrophoretic fabrication and characterization of a ZnO nanowire-based UV photosensor

Wide-gap semiconductors with nanostructures such as nanoparticles, nanorods, nanowires are promising as a new type of UV photosensor. Recently, ZnO (zinc oxide) nanowires have been extensively investigated for electronic and optoelectronic device applications. ZnO nanowires are expected to have good UV response due to their large surface area to volume ratio, and they might enhance the performance of UV photosensors. In this paper, a new fabrication method of a UV photosensor based on ZnO nanowires using dielectrophoresis is demonstrated. Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized materials in non-uniform electric fields. ZnO nanowires, which were synthesized by nanoparticle-assisted pulsed-laser deposition (NAPLD) and suspended in ethanol, were trapped in the microelectrode gap where the electric field became higher. The trapped ZnO nanowires were aligned along the electric field line and bridged the electrode gap. Under UV irradiation, the conductance of the DEP-trapped ZnO nanowires exponentially increased with a time constant of a few minutes. The slow UV response of ZnO nanowires was similar to that observed with ZnO thin films and might be attributed to adsorption and photodesorption of ambient gas molecules such as O(2) or H(2)O. At higher UV intensity, the conductance response became larger. The DEP-fabricated ZnO nanowire UV photosensor could detect UV light down to 10?nW?cm(-2) intensity, indicating a higher UV sensitivity than ZnO thin films or ZnO nanowires assembled by other methods.     

Synthesis and characterization of CaO-stabilized ZrO2 fine powders for oxygen ionic conductors

13 mol% calcia-stabilized zirconia (CSZ) powders were synthesized by the coprecipitation method. The characterization of powders has been investigated using thermogravimetry and differential thermal analysis for thermal analysis, X-ray diffraction and infrared spectroscopy for crystalline phases identification, Brunauer-Emmett Teller, X-ray diffraction-line broadening and transmission electron microscopy (TEM) for particle size and morphology determination. The characteristics of powders prepared by the coprecipitation method are discussed.     

Submicrometre resolved optical characterization of green nanowire-based light emitting diodes

The electroluminescent properties of InGaN/GaN nanowire-based light emitting diodes (LEDs) are studied at different resolution scales. Axial one-dimensional heterostructures were grown by plasma-assisted molecular beam epitaxy (PAMBE) directly on a silicon (111) substrate and consist of the following sequentially deposited layers: n-type GaN, three undoped InGaN/GaN quantum wells, p-type AlGaN electron blocking layer and p-type GaN. From the macroscopic point of view, the devices emit light in the green spectral range (around 550 nm) under electrical injection. At 100 mA DC current, a 1 mm2 chip that integrates around 10(7) nanowires emits an output power on the order of 10 μW. However, the emission of the nanowire-based LED shows a spotty and polychromatic emission. By using a confocal microscope, we have been able to improve the spatial resolution of the optical characterizations down to the submicrometre scale that can be assessed to a single nanowire. Detailed μ-electroluminescent characterization (emission wavelength and output power) over a representative number of single nanowires provides new insights into the vertically integrated nanowire-based LED operation. By combining both μ-electroluminescent and μ-photoluminescent excitation, we have experimentally shown that electrical injection failure is the major source of losses in these nanowire-based LEDs.     

Fabrication, characterization and simulation of high performance Si nanowire-based non-volatile memory cells

We report the fabrication, characterization and simulation of Si nanowire SONOS-like non-volatile memory with HfO(2) charge trapping layers of varying thicknesses. The memory cells, which are fabricated by self-aligning in situ grown Si nanowires, exhibit high performance, i.e. fast program/erase operations, long retention time and good endurance. The effect of the trapping layer thickness of the nanowire memory cells has been experimentally measured and studied by simulation. As the thickness of HfO(2) increases from 5 to 30 nm, the charge trap density increases as expected, while the program/erase speed and retention remain the same. These data indicate that the electric field across the tunneling oxide is not affected by HfO(2) thickness, which is in good agreement with simulation results. Our work also shows that the Omega gate structure improves the program speed and retention time for memory applications.     

Low-temperature synthesis and characterization of ceria-based oxide ion conductors

Solid solutions of the general formula Ce_1–x Ln _x O_2–x/2x/2 (Ln = lanthanide (III) and = anion vacancy), were prepared by a novel sol-gel route. These materials were characterized by powder diffraction and scanning electron microscopy. The gels formed on sol evaporation were found to be solid solutions with the fluorite structure and a crystallite size of approximately 6 nm. This is the lowest temperature of formation to date. The gels densified readily at 700 °C and the lattice parameter of these materials was found to be directly proportional to the ionic radius of the dopant.     

Scattering of electromagnetic waves with a grating of microstrip conductors on an anisotropic substrate

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 45–46, February, 1992.     

On-line characterization of YBCO coated conductors using Raman spectroscopy methods

The use of Raman spectroscopy for on-line monitoring of the production of superconducting YBa2Cu3O6+X (YBCO) thin films on long-length metal tapes coated with textured buffer layers is reported for the first time. A methodology is described for obtaining Raman spectra of YBCO on moving tape exiting a metal-organic-chemical-vapor-deposition (MOCVD) enclosure. After baseline correction, the spectra recorded in this way show the expected phonons of the specific YBCO crystal orientation required for high supercurrent transport, as well as phonons of non-superconducting second-phase impurities when present. It is also possible to distinguish YBCO films that are properly textured from films having domains of misoriented YBCO grains. An investigation of the need for focus control on moving tape indicated that focusing of the laser on the surface of the highly reflective YBCO films exiting the MOCVD enclosure tends to produce aberrant photon bursts that swamp the Raman spectrum. These photon bursts are very likely a consequence of optical speckle effects induced by a combination of surface roughness, crystallographic texture, and/or local strain within the small grain microstructure of the YBCO film. Maintaining a slightly out-of-focus condition provides the best signal-to-noise ratio in terms of the obtained Raman spectra. In addition to examining moving tape at the post-MOCVD stage, Raman spectra of the film surface can also be recorded after the oxygen anneal performed to bring the YBCO to the optimum superconducting state. Consideration is given to data processing methods that could be adapted to the on-line Raman spectra to allow the tagging of out-of-specification tape segments and, at a more advanced level, feedback control to the MOCVD process.     

Polarimetric characterization of optically anisotropic flexible substrates

Phase Modulated Spectroscopic Ellipsometry as well as Liquid Crystal Mueller Matrix Polarimetry in reflection and in transmission configurations were used to systematically study five types of anisotropic polymer sheets: polyethylene-terephtalate (PET), polyethylene-naphtalate (PEN), polycarbonate (PC), polypropylene (PP) and triacetylcellulose (TAC). The measurements were performed at different sample azimuths in two ellipsometric configurations giving access to both standard ellipsometric data as well as to the entire Mueller matrix. Biaxial anisotropy, a common characteristic to all polymer types, as well as the in-depth optical properties, inhomogeneity present in the sheets were clearly evidenced. The data were interpreted in terms of a model consisting of a thick substrate (several microns) coated with a simple layer. Both, substrate and layer were anisotropic and characterized by a triplet of principal refractive indexes. The orientation of the principal indexes of the bulk and the layer were different revealing the in-depth inhomogeniety of the samples.     

Massive assembly of ZnO nanowire-based integrated devices

Although a directed assembly strategy has been utilized for the massive assembly of various nanowires and nanotubes (NWs/NTs), its application has usually been limited to rather small-diameter NWs/NTs prepared in solution. We report two complementary methods for the massive assembly of large-size ZnO nanowires (NWs). In the solution-phase method, ZnO NWs were assembled and aligned selectively onto negatively charged surface patterns in solution. In addition, the substrate bias voltage and capillary forces can be used to further enhance the adsorption rate and degree of alignment of ZnO NWs, respectively. In the direct-transfer method, a NW film grown on a solid substrate was placed in close proximity to?a?molecule-patterned substrate, and ultrasonic vibration was applied so that the NWs were directly transferred and aligned onto the patterned substrate. The solution-phase and direct-transfer methods are complementary to each other and suitable for the assembly of NWs?prepared in solution and on solid substrates, respectively.     

矿物锂快离子导体Li1+2xAlxSCyNbyTi2-x-2ySixP3-xO12系统的合成与表征

以LiTi2(PO4)3为母体,天然高岭石为起始原料,经高温固相反应制得了一系列新的锂快离子导体材料Li1+2xA1xScyNbyTi2-x-2ySixP3-xO12(以下简称Sc-Nb-Lisicon).X射线衍射分析表明x=0.1、x=0.2,y≤0.4;x=0.3,y≤0.25的组成范围内能得到类似于Nasicon的三方结构,即空间点群为R3C的合成物.应用交流阻抗技术测试其电导率,结果表明:x=0.1,y=0.3及x=0.2,y=0.15的合成物在室温下有较高的电导率,分别为1.05×10-4S/cm和2.78×10-4S/cm,二者在573K时的电导率可达8.00×10-3S/cm和7.82×10-3S/cm,同时在423～573K具有较低的活化能,分别为31.4kJ/mol和34.8kJ/mol.     

The fabrication and application of Ni-DNA nanowire-based nanoelectronic devices

DNA is a self-assembled, double stranded natural molecule that can chelate and align nickel ions between its base pairs. The fabrication of a DNA-guided nickel ion chain (Ni-DNA) device was successful, as indicated by the conducting currents exhibiting a Ni ion redox reaction-driven negative differential resistance effect, a property unique to mem-elements (1). The redox state of nickel ions in the Ni-DNA device is programmable by applying an external bias with different polarities and writing times (2). The multiple states of Ni-DNA-based memristive and memcapacitive systems were characterized (3). As such, the development of Ni-DNA nanowire device-based circuits in the near future is proposed.

     

Fabrication and characterization of anisotropic dielectrics for low-loss microwave applications

New magneto-photonic assembly designs for high-gain antennas require dielectrics with a significant anisotropy and low loss at GHz frequencies. This paper describes an approach to fabricate such dielectrics from ceramic laminates. These laminates consist of two ceramics with largely different permittivities and low dielectric losses. Alternating layers of commercially available α-Al₂O₃ and Nd-doped BaTiO₃ were laminated using organic adhesives. Equivalent permittivity tensors and loss tangents were characterized using a resonant cavity-based approach, which was coupled with a finite-element method full-wave solver. Measured permittivity values were in good agreement with mean field predictions; a minimum loss tangent 1.1 × 10^?3 was obtained when using one-component epoxy (Loctite^®-3982) adhesive. Application of two-component epoxy (M-bond 610) adhesive results in a slightly higher loss but better mechanical properties and machinability. These laminates were used to demonstrate high gain in a prototype antenna with 6 misaligned anisotropic dielectric layers.     

Electrical and mechanical characterization of stretchable multi-walled carbon nanotubes/polydimethylsiloxane elastomeric composite conductors

Stretchable, elastomeric composite conductor made of multi-walled carbon nanotubes (MWNTs) and polydimethylsiloxane (PDMS) has been fabricated by simple mixing. Electrical percolation threshold, amount of filler at which a sharp decrease of resistance occurs, has been determined to be ∼0.6 wt.% of MWNTs. The percolation threshold composition has also been confirmed from swelling experiments of the composite; the equilibrium swelling ratio slightly increases up to ∼0.6 wt.%, then decreases at higher amount of filler MWNTs. Upon cyclic stretching/release of the composite, a fully reversible electrical behavior has been observed for composites having filler content below the percolation threshold value. On the other hand, hysteretic behavior was observed for higher filler amount than the threshold value, due to rearrangement of percolative paths upon the first cycle of stretching/release. Finally, mechanical moduli of the composites have been measured and compared by buckling and microtensile test. The buckling-based measurement has led to systematically higher (∼20%) value of moduli than those from microtensile measurement, due to the internal microstructure of the composite. The elastic conductor may help the implementation of various stretchable electronic devices.     

Computational design of multiaxial tests for anisotropic material characterization

Although anisotropic materials provide more capabilities for mission‐ and application‐tailored design and functional flexibility to final structures than regular isotropic materials, the directional behavior of the anisotropic materials further complicates their inelastic and damage behavior. Such a non‐linear behavior can be effectively observed and characterized by multiaxial testing, but how to design a multiaxial test for material characterization given a specimen remains an untouched issue. This paper presents a methodology that numerically designs the loading path of a multiaxial testing machine to characterize anisotropic materials. The multiaxial test must be able to exhibit quantities used to characterize materials as distinctly as possible. The proposed methodology formulates distinguishability and uniqueness as such quantities by first analyzing the specimen on a continuum basis with finite element method and then applying singular value decomposition. Associating the distinguishability and uniqueness with the informativeness of the loading path, the design problem is formulated such that an effective loading path can be found efficiently by a standard optimization method. Numerical examples first investigate the validity of the distinguishability and the uniqueness as performance measures to evaluate loading paths. The efficacy of the proposed methodology has been then confirmed by analyzing it with and applying it to design problems. Copyright © 2007 John Wiley & Sons, Ltd.     

四甲基氢环四硅氧烷(D_4~H)的合成与表征

研究了以一甲基氢二氯硅烷为原料通过水解缩合的方式合成四甲基氢环四硅氧烷(D4H)的方法。在一甲基氢二氯硅烷∶介质(乙醚∶蒸馏水)反应的体积比为1∶2(1∶1),反应温度为30℃以内,反应时间3~4h的工艺条件下首先制备得到一甲基氢硅二醇,进一步以20%氢氧化钾为催化剂,在130~140℃下减压回流4h,得到最终产物。利用FT-IR1、H-NMR对产物结构进行了表征,结果表明,该物质即为目标产物—四甲基氢环四硅氧烷(D4H)。     

聚醚醚酮的合成与表征

以二苯砜为溶剂,在无水碳酸钾/碳酸钠的催化下,通过对苯二酚与4,4-二氟二苯甲酮进行亲核取代反应,合成了特性黏度为0.89的聚醚醚酮(PEEK);探讨了溶剂与反应温度对分子量的影响.通过IR、DSC、TG和XRD对其结构与性能进行了表征,确定其结构为PEEK;TG测试表明,在N2气氛下开始分解温度为541℃,且到1200℃时也没分解完全;DSC和XRD衍射图表明其为半晶态聚合物,且由DSC曲线可知其熔点(Tm)为347℃.     

Observation of diameter dependent carrier distribution in nanowire-based transistors

The successful implementation of nanowire (NW) based field-effect transistors (FET) critically depends on quantitative information about the carrier distribution inside such devices. Therefore, we have developed a method based on high-vacuum scanning spreading resistance microscopy (HV-SSRM) which allows two-dimensional (2D) quantitative carrier profiling of fully integrated silicon NW-based tunnel-FETs (TFETs) with 2 nm spatial resolution. The key elements of our characterization procedure are optimized NW cleaving and polishing steps, the use of in-house fabricated ultra-sharp diamond tips, measurements in high vacuum and a dedicated quantification procedure accounting for the Schottky-like tip-sample contact affected by surface states. In the case of the implanted TFET source regions we find a strong NW diameter dependence of conformality, junction abruptness and gate overlap, quantitatively in agreement with process simulations. In contrast, the arsenic doped drain regions reveal an unexpected NW diameter dependent dopant deactivation. The observed lower drain doping for smaller diameters is reflected in the device characteristics by lower TFET off-currents, as measured experimentally and confirmed by device simulations.     

新型聚噁唑烷酮的合成与表征

采用甲苯二异氰酸酯与自制的对苯二甲酸二缩水甘油酯生成聚噁唑烷酮.并用红外光谱、DSC、热重分析仪对其进行表征.检测出其玻璃化温度为110℃,其失重5%时需要的温度为257℃,并研究了其绝缘性能.     

矿物钠快离子导体Na1+3x+yAlxNdyTi2-x-ySi2xP3-2xO12合成与表征

Na1 3x yAlxNdyTi2-x-ySi2xP3-2xO12钠快离子导体(以下简称Al-Nd-Nasicon)可以用精选的天然叶腊石A12[Si4O10](OH)2为起始原料与其它化合物,经过高温(900～1100℃)固相反应约15h制得.在y=0.3,x≤0.3和y=0.5,x≤0.2的组成范围内可得到具有Nasicon的三方结构空间群属于R3C的固溶体.该相具有较高的电导率,其中起始组成y=0.3,x=0.1的合成物在350℃时电导率为1.80×10-2S/cm.