Cost-effective fabrication of memristive devices with ZnO thin film using printed electronics technologies

A prototype memristive device has been presented in this paper, for which the top and bottom electrodes have been fabricated through a simple and cost-effective technique, i.e. electrohydrodynamic printing. For deposition of the bottom electrode pattern, a silver ink containing 60 wt% silver by content was subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, thereby depositing uniform patterns of silver on glass substrate at a constant substrate speed. The top electrode has been deposited in a similar fashion. In between the top and bottom electrodes, a uniform layer of ZnO is fabricated using spin-coating technique. The nanoscale ZnO memristor stack has a channel length of 370 μm and channel width of 82 μm. A memristor thus fabricated was characterized and its current voltage curves were analyzed. The device showed a typical nonvolatile resistive switching behavior present in memristor devices thus highlighting the EHD printed patterning as a reliable method for the fabrication of memory devices.     

Controlled synthesis of colloidal silver nanoparticles in capillary micro-flow reactor

In this study, using a polytetrafluoroethylene (PTFE) capillary tube as a micro-flow reactor, well-dispersed colloidal silver nanoparticles were controllably synthesized with different flow rates of precursory solution. Scanning transmission electron microscopy images and UV–visible absorbance spectra showed that silver nanoparticles with large size can be prepared with slow flow rate in the PTFE capillary reactor. The effects of tube diameters on the growth of colloidal silver nanoparticles were investigated. Experiment results demonstrated that using tube with small diameter was more propitious for the controllable synthesis of silver nanoparticles with different sizes.

     

Extending plasma accelerators: guiding with capillary tubes

In order to extend plasma accelerators, the laser beam has to be guided inside gas or plasma over a distance of the order of the dephasing length, which is typically much larger than the diffraction length z_R of the laser. A capillary tube can be used as a waveguide for high-intensity laser pulses over distances well in excess of z_R. Experimental demonstration of monomode guiding over 100 z_R of 10¹⁶ W/cm² pulses has been obtained in evacuated capillary tubes (45-70-μm inner diameter). A drop of transmission has been observed when the intensity of the amplified spontaneous emission (ASE) is high enough to ionize the capillary tube entrance. Propagation in helium gas-filled (10-40 mbar) capillary tubes has been studied at intensities up to 10¹⁶ W/cm²; a plasma column with on-axis density of the order of 10¹⁷ cm^-3 has been created on a length of the order of 4 cm. The use of a capillary tube for an extended accelerator is discussed for the ease of linear, resonant excitation of plasma waves by laser wakefield     

用毛细管测量纯水表面张力系数的误差讨论

通过用毛细管测量纯水表面张力系数实验，得到管内径d与接触角θ的相对误差之间的关系曲线，由此说明实验测得的表面张力系数α和理论公式相比呈现一定的偏差，并简单地讨论了实验的理想状态与实际情况的差别．     

Mapping of local argon impingement on a virtual surface: an insight for gas injection during FEBID

During the last decades, focused electron beam induced deposition (FEBID) has become a successful approach for direct-write fabrication of nanodevices. Such a deposition technique relies on the precursor supply to the sample surface which is typically accomplished by a gas injection system using a tube-shaped injector nozzle. This precursor injection strategy implies a position-dependent concentration gradient on the surface, which affects the geometry and chemistry of the final nanodeposit. Although simulations already proposed the local distribution of nozzle-borne gas molecules impinging on the surface, this isolated step in the FEBID process has never been experimentally measured yet. This work experimentally investigates the local distribution of impinging gas molecules on the sample plane, isolating the direct impingement component from surface diffusion or precursor depletion by deposition. The experimental setup used in this work maps and quantifies the local impinging rate of argon gas over the sample plane. This setup simulates the identical conditions for a precursor molecule during FEBID. Argon gas was locally collected with a sniffer tube, which is directly connected to a residual gas analyzer for quantification. The measured distribution of impinging gas molecules showed a strong position dependence. Indeed, a 300-µm shift of the deposition area to a position further away from the impingement center spot resulted in a 50 % decrease in the precursor impinging rate on the surface area. With the same parameters, the precursor distribution was also simulated by a Monte Carlo software by Friedli and Utke and showed a good correlation between the empirical and the simulated precursor distribution. The results hereby presented underline the importance of controlling the local precursor flux conditions in order to obtain reproducible and comparable deposition results in FEBID.     

管状铝质材料的等离子体电解沉积行为研究

对管状铝质材料的等离子体电解沉积行为进行了研究.测试了不同工作电压和不同电极放置模式条件下铝管内部不同位置的电位分布，并通过显微分析观察，对比了不同电极放置模式对铝管内外壁陶瓷沉积层生长情况的影响.结果表明，不同的电极放置模式下，铝管内外壁陶瓷沉积层生长情况有很大差异.这是因为不同的电极放置模式对铝管内的电场分布具有很大影响，进而影响到铝管内外壁陶瓷层的沉积过程.只有外电极时，由于电场屏蔽作用，不能在铝管内壁形成均匀陶瓷层；在铝管内部加入辅助中心电极后，铝管内部产生均匀电场，这有利于在其内壁形成均匀的陶瓷层. 关键词： 等离子体电解沉积 铝管 表面改性 陶瓷层     

Fabrication and characterization of SERS‐active silver clusters on glassy carbon

In this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4‐aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS‐based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80–100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 × 10⁴ relative to silver colloid, which might have resulted from the presence of ‘hot‐spots’ at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 × 10⁷ by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface. SERS‐based Raman mapping technique in the form of line scanning further illustrates the good SERS activity and reproducibility on the silver clusters. Finally, 4‐mercaptopyridine (4‐Mpy) was chosen as an analyte and the lowest detected concentration was investigated by the SERS‐active silver clusters. A concentration of 1.6 × 10⁻¹⁰ M 4‐Mpy could be detected with the SERS‐active silver clusters, showing the great potential of the technique in practical applications of microanalysis with high sensitivity. Copyright © 2006 John Wiley & Sons, Ltd.     

Flexible small-bore hollow fibers with an inner polymer coating

Flexible hollow-glass fibers with small-bore diameters of 250 and 320 mum have been developed for Er:YAG laser delivery. The fibers consist of a glass capillary tube and an inner coating of silver and polymer thin films that are deposited by use of a simple liquid-phase technique. The 250-mum-bore fiber exhibits a straight loss of 0.8 dB/m and a bending loss of 1.2 dB when it is bent 180 degrees at the output end, with a bending radius of 2 cm. The maximum energy delivered by the fibers is ~100 mJ.     

银纳米颗粒/多孔硅复合材料的制备与气敏性能研究

采用双槽电化学腐蚀法以电阻率为10-15 Ω·cm的p型<100>晶向的单晶硅片制备了孔径约为1.5 μm, 孔深约为15-20 μm的p型多孔硅, 并以此多孔硅作为基底采用无电沉积法通过调控沉积时间在其表面沉积了不同厚度的银纳米颗粒薄膜. 采用扫描电子显微镜和X 射线衍射仪表征了银纳米颗粒/多孔硅复合材料的形貌和微观结构, 结果表明银纳米颗粒较均匀的分布于多孔硅的表面上且沉积时间对产物的形貌有重要影响. 采用静态配气法在室温下研究了银纳米颗粒/多孔硅复合材料对NH₃的气敏性能. 气敏测试结果表明沉积时间对产物的气敏性能影响较大. 当沉积时间较短时, 适量银纳米颗粒掺杂的多孔硅复合材料由于其较高的比表面积以及特殊的形貌和结构, 对NH₃气体表现出较高的灵敏度、优良的响应/恢复性能. 室温下, 其对50 ppm 的NH₃气体的气敏灵敏度可以达到5.8左右.     

Depositing nanoparticles inside millimeter-size hollow tubing

The inner and the outer walls of hollow tubing with an inner diameter of 0.4-0.9 cm and an outer diameter of 0.6-1.3 cm were coated with silver nanoparticles (NPs) by a one-step process using ultrasound irradiation. The structure and morphology of the nanoparticles (NPs) inside the hollow tubing and on the outer surface were characterized using methods such as XRD, TEM, HR-TEM, and HRSEM. The inner surface of the tubing was found to be coated with more silver than the outer surface. The coating was done on tubing made of rubber, PVC, Teflon and polyethylene. Sonochemistry is demonstrated as a method for depositing nanoparticles on the inner wall of a tube.     

Flow regulation in microchannels via electrical alteration of surface properties

The development of microfluidic (lab-on-a-chip) technology requires local control of fluid flow in the microchannels. Conventional microvalve approaches involve moving parts and/or complicated fabrication techniques, which makes them unreliable and prevents inexpensive integration in microanalytical systems. We have developed a simple low cost method for regulating fluid flow in microchannels that is compatible with existing microfabrication techniques and eliminates the need for moving parts. We use an electrical signal to stimulate silver deposition on a thin solid electrolyte layer in a small region of a microchannel. Since fluid flow is dominated by the nature of the channel surface, the electrodeposited silver changes the fluid–surface interaction and the effect can be used to control the movement of the fluid. Increases in the contact angles of both water and methanol, by 20 and 27 respectively, have been demonstrated. Such changes in hydrophobicity are sufficient to retard or stop capillary or external pressure-driven fluid flow in typical microchannels.     

纤维膜在膜蒸馏过程中的膜内毛细冷凝现象

膜蒸馏过程中的膜内冷凝现象是该技术在实际应用中不可忽视的一个重要问题。本文以疏水化改性处理的纤维膜作为研究对象,采用实验现象观察和理论分析并用的方法,研究了纤维膜在膜蒸馏过程发生膜内毛细管冷凝的影响因素包括膜蒸馏模块结构、蒸馏膜参数、热力学参数,探讨了毛细冷凝对膜蒸馏的影响。实验表明毛细冷凝可以在膜蒸馏过程中发生,但并不终止膜蒸馏过程,而是减小了传质系数。毛细冷凝容易发生在蒸馏膜厚度小、热料液温度高、冷却液温度低或气隙小的情况下。实验结果和理论分析表明,传质系数实验值的降低可作为膜孔内发生毛细冷凝的判定依据。通过简化蒸气在疏水多孔介质的传递过程,建立了膜蒸馏过程发生毛细冷凝时的传质平衡模型。     

Estimation of inner surface profile of a tube by two-wavelength phase-shifting digital holography

A novel phase-shifting digital holographic method for estimation of inner surface profiles of tubes is proposed. For surface contouring, a two-wavelength method using injection-current-induced wavelength changes of a laser diode is used. To obtain inner surface information on a tube, a cone-shaped mirror is set inside the tube. Speckle noise occurring in the reconstructed phase difference image is effectively suppressed by an adaptive filtering technique consisting of exponential averaging and masking filtering processes. Distribution of optical path length in the experimental alignment is calculated and well explains the experimental results. It is shown that the calculation of optical path length by a simple model can remove the distortion of profiles occurring in the experimental results and enable the estimation of the inner surface profile of an aluminum tube.     

Design parameters for measurements of local catalytic activity on surfaces

Computational fluid dynamics in combination with experiments is used to characterize a gas sampling device for measurements of the local catalytic activity on surfaces. The device basically consists of a quartz capillary mounted concentrically inside an aluminum tube. Reactant gas is blown toward the catalytic surface through the annulus between the tubes, and the gas is sampled close to the surface by the capillary. The influence of various design parameters on the lateral resolution and sensitivity of the measurements is investigated. It is found that the outer diameter of the annulus sets the upper limit for the lateral resolution of the measurement, and that a flow rate of the order of 240 (ml/min)_n is sufficient to achieve this resolution. The sensitivity is reasonable also with high flow rates, due to the presence of a pocket of stagnant gas under the tip of the capillary. Furthermore, the limits of the range in reaction rate, which can be studied are estimated.     

Electroless deposition of silver on synthesized calcite via surface modification

Metallic silver was deposited on the surface of synthesized calcite via a simple electroless deposition method. Calcite with cubic morphology was prepared first by homogeneous precipitation and it was subsequently surface modified using ammonium oxalate. The electroless deposition was carried out using formaldehyde as the reducing agent and silver nitrate as the silver source. Both calcite and the silver deposited calcite were characterized by different techniques. Surface modification of calcite with ammonium oxalate is necessary for the deposition of silver and the size of the deposited silver particles could be controlled by changing the deposition parameters such as concentration of the reagents and the deposition time. Lower concentration of silver ions (e.g. 0.01 M AgNO₃) and shorter deposition times (e.g. 30 min) lead to the formation of silver nanoparticles on calcite.     

A test of energy averaging in LEED: The coincidence lattice structure formed by Ag on Cu(111)

An analysis of LEED data from a structure believed to consist of a monolayer of silver on a clean copper (111) surface has been performed. Using a hard-sphere model as a guide for the surface structure, energy-averaged beam intensities from experiment have been compared with those from kinematical calculations as proposed by Tucker and Duke. Significant differences are found which are believed to be associated with multiple scattering. This casts doubt on the value of this technique for determining surface structures of strong-scattering adsorbates on metals.     

Lattice-Boltzmann Simulation of Capillary Rise Dynamics

We report results of extensive two-phase lattice-Boltzmann simulations of capillary rise dynamics. We demonstrate that the method can be used to model the hydrodynamic behaviour inside a capillary tube provided that the diameter of the tube is large enough, typically at least 30 lattice units. We also present results for the dependence of the cosine of the dynamic contact angle on the capillary number Ca. Its deviation from the static advancing contact angle has a power-law form, with the value of the exponent very close to 3/2 for capillary rise at zero gravity, while behaviour is more complex in the presence of gravity.     

Field emission studies of silver nanoparticles synthesized by electron cyclotron resonance plasma

Field emission has been studied for silver nanoparticles (25-200 nm), deposited within a cylindrical silver target in an electron cyclotron resonance (ECR) plasma. Particle size distribution was controlled by optimum biasing voltages between the chamber and the target. Presence of non-oxidized silver was confirmed from the X-Ray diffraction analysis; however, thin protective layer of oxide was identified from the selective area electron diffraction pattern obtained with transmission electron microscopy. The silver nanoparticles were seen to exhibit hilly pointed like structures when viewed under the atomic force microscopy (AFM). The emissive properties of these particles were investigated by field emission microscopy. It is found that this technique of deposition is ideal for formation of nanoparticles films on different substrate geometries with size controllability as well as its application to emission devices.     

Dynamics of Interface Displacement in Capillary Flow

The dynamics of capillary flow has several practical applications in the industry and has been extensively investigated. The main focuses in these studies are the motion of the interface, especially near the three-phase contact line, and the change of contact angle during the invasion process. In this work we present several simulations results of capillary invasion in two- and three-dimensions, using the Lattice–Boltzmann model based on field mediators. We investigate the velocity field near the solid surface, the changes in the contact angle as a consequence of the flow, and the boundary conditions that can be used in the inlet and outlet of the capillary tube. In all simulations the diameter of tube is made large enough to enable the evaluation of the contact angle directly from the density field and the results of capillary rise are compared with a theoretical model based on the Bosanquet equation, which includes capillary, viscous, inertial and gravitational effects.     

Silane decorated metallic nanorods for hydrophobic applications

A novel technique to modify a metallic surface for anti-icing applications is presented. An oblique angle deposition (OAD) technique has been used to fabricate metallic nanorods of Aluminum and Tungsten on a glass substrate. A conformal coating of a silane has been applied using a molecular vapor deposition technique. The resulting surface has shown a static contact angle of 134° with the water droplet. SEM, AFM and XPS have been used to study the surface modification. This is a highly promising approach for anti-icing applications due to its scalability at a very low cost.