Effects of surface modification of the individual ZnO nanowire with oxygen plasma treatment

This study examined the effects of an oxygen plasma treatment on the properties of ZnO nanowires with diameters of 80 nm using a single nanowire field effect transistor. After the oxygen plasma treatment, the carrier concentration and mobility of individual ZnO nanowires decreased with a substantial positive shift in the threshold voltage. The shifting was accounted to the surface modification, resulted to the improved gas sensitivity under hydrogen gas exposure and an enhanced photocurrent response time in ultraviolet illumination. The plausible surface mechanisms responsible for these significant changes after the surface modification were suggested by considering the surface analysis and electrical transport mechanism.     

The surface scattering-based detection of hydrogen in air using a platinum nanowire

The performance of a single platinum (Pt) nanowire for detecting H(2) in air is reported. A Pt nanowire shows no resistance change upon exposure to H(2) in N(2), but H(2) exposure in air causes a reversible resistance decrease for H(2) concentrations above 10 ppm. The amplitude of the resistance change induced by H(2) exposure and the time rate of change of the nanowire resistance both increased with increasing temperature from 298 to 550 K. This resistance decrease of the Pt nanowire in the presence of H(2) results from reduced electron diffuse scattering at hydrogen-covered Pt surfaces as compared with oxygen-covered platinum surfaces, we hypothesize. The properties for the detection of H(2) in air of single Pt and Pd nanowires of similar size are compared in this study. Pt nanowires have a limit-of-detection for H(2) (LOD(H(2))) of 10 ppm; 3 orders of magnitude lower than for Pd nanowires of the same size, as well as a response time that is 1/100th of Pd for [H(2)] ≈ 1%.     

GH4169高温合金化学铣切表面粗糙度的影响因素

为了满足生产对GH4169高温合金化学铣切加工表面粗糙度的要求,通过单因素试验研究了化铣液的主要成分和化铣工艺参数对GH4169高温合金表面粗糙度的影响。结果表明:随着化铣液中FeCl3和HNO3浓度的升高,表面粗糙度呈下降趋势;当化铣液温度高于50℃时,表面粗糙度在1.4μm以下;HCl,HF浓度均为200 mL/L时,表面粗糙度最小;添加剂SA和SN能够降低表面粗糙度和消除凹槽;随着化铣液中Ni2+浓度的增加,表面粗糙度也随之变大,当Ni2+浓度大于26.95 g/L时,表面粗糙度达到1.6μm以上,不符合加工要求;最佳化铣工艺为200～250 g/L FeCl3,200 mL/L HF,150 mL/L HNO3,200 mL/L HCl,0.2 g/L添加剂SA,0.5 mL/L添加剂SN,温度53℃,该工艺下化铣的GH4169高温合金表面质量良好,无凹槽、沟蚀,表面光洁,粗糙度小于1.6μm,符合生产要求。     

Enhancement in the photodetection of ZnO nanowires by introducing surface-roughness-induced traps

We investigated the enhanced photoresponse of ZnO nanowire transistors that was introduced with surface-roughness-induced traps by a simple chemical treatment with isopropyl alcohol (IPA). The enhanced photoresponse of IPA-treated ZnO nanowire devices is attributed to an increase in adsorbed oxygen on IPA-induced surface traps. The results of this study revealed that IPA-treated ZnO nanowire devices displayed higher photocurrent gains and faster photoswitching speed than transistors containing unmodified ZnO nanowires. Thus, chemical treatment with IPA can be a useful method for improving the photoresponse of ZnO nanowire devices.     

SURFACE ROUGHNESS OF SPUTTERED SILICON. I. SURFACE MODELING

A mathematical model for the calculation of surface roughness was developed for focused ion beam (FIB) sputtering. The surface roughness function is a combination of the beam function and the material function. The beam function includes ion type, ion acceleration energy, and beam parameters. Furthermore, the beam parameter incorporates ion flux, the ion beam intensity distribution profile, tailing and neighboring of the successive beams, dwell time, etc. The intensity distribution inside the ion beam is considered to be Gaussian. The cumulative intensity over the total milling area is calculated by the algebraic summation of individual beam intensity delivered to every pixel successively. The material function includes the inherent material properties related to the ion beam micromachining. If one knows the beam function and material function, surface roughness at the bottom of the sputtered features can be calculated using this model.     

微细立铣削硬铝2A12表面粗糙度分析与预测

利用自行研制的精密三轴联动立式铣床（300mm×300mm×290mm）,微径硬质合金两刃平头立铣刀（直径0．1～0．5mm）微立铣硬铝2A12,观察微铣刀悬伸量、直径、轴向切深和每齿进给量对加工表面粗糙度的影响．表面粗糙度由激光扫描共聚焦显微镜（奥林巴斯OLS3000）测量．结果发现微径立铣刀的直径和悬伸量对表面粗糙度的影响大于轴向切深和每齿进给量．另外,在刃口半径尺寸效应的作用下,表面粗糙度并不一直随每齿进给量的减小而减小．基于响应曲面法建立了表面粗糙度的二阶预测模型,方差分析表明该模型回归显著,拟合度为97．5％,可以用于预测表面粗糙度和优化工艺参数．     

Enhanced gas sensing by individual SnO2 nanowires and nanobelts functionalized with Pd catalyst particles

The sensing ability of individual SnO(2) nanowires and nanobelts configured as gas sensors was measured before and after functionalization with Pd catalyst particles. In situ deposition of Pd in the same reaction chamber in which the sensing measurements were carried out ensured that the observed modification in behavior was due to the Pd functionalization rather than the variation in properties from one nanowire to another. Changes in the conductance in the early stages of metal deposition (i.e., before metal percolation) indicated that the Pd nanoparticles on the nanowire surface created Schottky barrier-type junctions resulting in the formation of electron depletion regions within the nanowire, constricting the effective conduction channel and reducing the conductance. Pd-functionalized nanostructures exhibited a dramatic improvement in sensitivity toward oxygen and hydrogen due to the enhanced catalytic dissociation of the molecular adsorbate on the Pd nanoparticle surfaces and the subsequent diffusion of the resultant atomic species to the oxide surface.     

Effects of surface treatment of field emitter arrays on electrical characteristics of active matrix cathode

The effects of a wet chemical surface treatment of molybdenum-tip (Mo-tip) emitters on the electrical characteristics of an active matrix cathode composed of hydrogenated amorphous silicon thin film transistors and Mo-tip emitters are described. X-Ray photoelectron spectroscopy measurements showed that the surface treatment removed MoO₃ from the surface of the e-beam evaporated Mo film. In addition, the surface roughness of the Mo film was increased as the result of the surface treatment. The surface-treated active matrix cathode showed stable emission characteristics and immunity from emitter failures during its operation. The response time of the active matrix cathode was decreased by the surface treatment of the Mo-tip emitters. A change in surface composition and surface roughness appear to be responsible for the enhancement of the active matrix cathode.     

Effect of surface mechanical attrition treatment (SMAT) on microhardness,surface roughness and wettability of AISI 316L

Surface roughness and wettability are among the surface properties which determine the service lifetime of materials. Mechanical treatments subjected to the surface layer of materials are often performed to obtain the desired surface properties and to enhance the mechanical strength of materials. In this paper, the surface microhardness, roughness and wettability of AISI 316L stainless steel resulting from surface mechanical attrition treatment (SMAT) are discussed. The SMAT was conducted with various processing parameters, including the duration of treatment, the number and diameter of milling ball, and the motor speed of the SMAT machine. The result indicates an increasing surface microhardness due to the SMAT. A harder surface is yielded by the SMAT with a longer duration, a bigger and a larger number of milling balls, and a higher vibration frequency. The SMAT also creates craters on the steel surfaces which correspond to the increasing roughness from 0.046 μm to the values in ranging from 0.681 to 0.909 μm. The change on the surface roughness by the SMAT does not only depend on the duration of treatment, but also the other processing parameters. In addition, the wettability of AISI 316L surface slightly increases by the SMAT as seen on the decreasing droplet contact angle from 88.6° to the values ranging from 74.4° to 87.0°. Such a droplet contact angle reduction is related to the increasing surface roughness after the SMAT. In conclusion, this study reveals the possibility of the SMAT to be used for surface properties optimization in addition to the strength enhancement of stainless steel.     

Microstructural enhancement of high coercivity L1(0)-FePt films for next-generation magnetic recording media

The effects of substrate Ar-ion milling and Ta adhesion layer on the microstructural and magnetic properties of L1(0)-FePt films prepared on Si, SiO2, and glass substrates were investigated. It was discovered that the relatively large in-plane surface roughness of CrRu/MgO/FePt films deposited on Si substrates was due to the deformation of the CrRu layer when the composition was heated to 550 degrees C. More than an order of magnitude improvement for the in-plane surface roughness was achieved when substrate Ar-ion milling or Ta adhesion layer was incorporated into the process. While the Ta adhesion layer proved to be detrimental to the (200) growth of the CrRu layer, optimal FePt film properties with coercivity values larger than 2 Tesla and out-of-plane roughness less than 1 nm were achieved when only substrate Ar-ion milling was implemented.     

Hydrogen gas sensor using Pd nanowires electro-deposited into anodized alumina template

This paper demonstrates a new kind of hydrogen sensor using palladium (Pd) nanowires. Hydrogen sensors using Pd metal have usually been utilizing the incremental change in electrical resistance of Pd upon hydrogen incorporation. Unlike the conventional Pd hydrogen sensors, however, the electrical resistance of the present Pd nanowire sensor decreases when hydrogen is incorporated into Pd nanowires. It is considered to be due to swelling of the nanowires as the result of hydrogen incorporation and subsequent narrowing of gaps between the nanowires, even though each nanowire should have had the higher resistance inherently. Because of extraordinarily high surface area of nanowires, the performance of sensing the hydrogen concentration was found to superior by far to the conventional Pd sensors. The response and recovery times are quite fast to be about 0.7 and 20 s, respectively and the sensing range of 0.2 /spl sim/ 1% 1% hydrogen concentration is suitable for the hydrogen safety sensors. The sensor introduced in this paper is unique with regard to both the sensing mechanism and performance.     

Reduction of Pd catalytic particle size by a double activation process

We have used a double activation method to reduce the size of Pd catalytic particles commonly used as an activation layer for electroless Cu deposition. The method produces Pd particles with sizes reduced by a factor of 4 and density increased by a factor of 10 compared to the single activation method. The first activation and the Pd etching process in the double activation removes the native Ti oxide on TiN surface and largely increase the nucleation sites for Pd. With more nucleation sites, nucleation events outrun ripening events throughout the deposition time range. However, excessive etching of Pd and the underlying TiN layer could lead to rougher electroless Cu films. Secondary ion mass spectrometry data show that the double activation step does not increase the net amount of Pd deposited on TiN surface; it only changes its particle size and density. Electroless Cu deposited on a doubly Pd activated surface has a larger grain size and appears to have a lower resistivity.     

Joule Heating a Palladium Nanowire Sensor for Accelerated Response and Recovery to Hydrogen Gas

The properties of a single heated palladium (Pd) nanowire for the detection of hydrogen gas (H₂) are explored. In these experiments, a Pd nanowire, 48–98 µm in length, performs three functions in parallel: 1) Joule self‐heating is used to elevate the nanowire temperature by up to 128 K, 2) the 4‐contact wire resistance in the absence of H₂ is used to measure its temperature, and 3) the nanowire resistance in the presence of H₂ is correlated with its concentration, allowing it to function as a H₂ sensor. Compared with the room‐temperature response of a Pd nanowire, the response of the heated nanowire to hydrogen is altered in two ways: First, the resistance change (ΔR/R₀) induced by H₂ exposure at any concentration is reduced by a factor of up to 30 and second, the rate of the resistance change – observed at the beginning (“response”) and at the end (“recovery”) of a pulse of H₂ – is increased by more than a factor of 50 at some H₂ concentrations. Heating nearly eliminates the retardation of response and recovery seen from 1–2% H₂, caused by the α → β phase transition of PdH_x, a pronounced effect for nanowires at room temperature. The activation energies associated with sensor response and recovery are measured and interpreted.     

Direct synthesis of ZnO nanowire arrays on Zn foil by a simple thermal evaporation process

ZnO nanowire arrays were synthesized on zinc foil by a simple thermal evaporation process at relatively low temperature. Morphology and size controlled synthesis of the ZnO nanostructures was achieved by variation of the synthesis temperature, reaction time and the surface roughness of the substrate. A gas-solid and self-catalytic liquid-solid mechanism is proposed for the growth of nanowires at different temperatures. High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction. Photoluminescence exhibited strong UV emission at ～382?nm and a broad green emission at ～513?nm with 325?nm excitation. Raman spectroscopy revealed a phonon confinement effect when compared with results from bulk ZnO. The nanowire arrays also exhibited a field emission property.     

不同振动方式下的钛合金超声振动铣削表面完整性研究

钛合金在机械工程领域应用广泛,其加工表面完整性对钛合金工件的耐磨性、疲劳强度、使用寿命有着非常重要的影响.通过对工件施加不同振动方向的超声振动,开展了不同振动方向下的TC4钛合金超声振动侧铣平面试验,分析了不同振动方式的运动学轨迹特征,研究了振动方式、切削参数对钛合金加工表面完整性的影响规律.结果表明:法向振动铣削后的...     

A single nanotrench in a palladium microwire for hydrogen detection

The hydrogen sensing characteristics of a single nanotrench fabricated by focused ion beam milling (FIB) in an evaporated palladium microwire are presented. In situ atomic force microscopy (AFM) measurements proved that, in the presence of H(2), the trench closes and electrically connects the initially separated parts of the wire due to the increase in volume of the material. Therewith, an electrical current can be switched through the wire. With experiments under various H(2) concentrations and a mathematical model, we describe the closing mechanism of the trench with respect to various parameters, including the substrate material, film thickness, trench size and wire dimensions. Results have been compared with those from equivalent continuous wires. Thin SiO(2) and polyimide (PI) layers on silicon were used to study the effect of substrate elasticity. Sufficient lateral expansion of Pd to close trenches of up to 70?nm in width has only been observed on PI, which we attribute to its advantageous elastic properties. The scale of the response times allowed the observation of two superposing effects: the chemical conversion of Pd to PdH(x) and the mechanical closing of the trench.     

Fabrication of superhydrophobic surfaces by a Pt nanowire array on Ti/Si substrates

Superhydrophobic surfaces were prepared on Ti/Si substrates via the fabrication of a platinum (Pt) nanowire array. The Pt nanowire array was obtained by dc electrodeposition of Pt into the pores of an anodic aluminium oxide (AAO) template on the substrate followed by the removal of the template. Transmission electron microscopy (TEM) examination demonstrated that all the nanowires have uniform diameter of about 30?nm. Field emission scanning electron microscopy (FE-SEM) showed that the structures at both the micrometre scale and nanometre scale bestowed the prerequisite roughness on the surfaces. The chemical surface modification made the Pt nanowire array superhydrophobic. The surface modified Pt nanowire array exhibited superhydrophobicity even in corrosive solutions over a wide pH range, such as acidic or basic solutions. The results demonstrated that the Pt nanowire array will have good potential applications in the preparation of superhydrophobic surfaces.     

The electrical characterization of a multi-electrode odor detection sensor array based on the single SnO2 nanowire

The variation of electrical properties of individual SnO₂ wedge-like nanowire along its length was characterized comparatively in a vacuum, low-pressure oxygen environment and in synthetic air mixed with various analytes. For characterization, a vapor-solid grown nanowire was indexed with multiple Pt mesoscopic contacts fabricated by e-beam induced deposition from Pt containing metalorganic precursor. The surface of the selected nanowire segments was functionalized with a catalyst via deposition of Pd nanoparticles. Detailed analysis of the electrical properties of the nanowire shows that the effective diameter of the conducting channel of the nanowire can be substantially modified along its length by the surface functionalization and nanowire width change. These variations of the electrical properties of nanowire segments are sufficient for reliable discrimination of acetone, 2-propanol, CO and hydrogen by this elemental multisensor array.     

Hydrogen gas sensing with networks of ultrasmall palladium nanowires formed on filtration membranes

Hydrogen sensors based on single Pd nanowires show promising results in speed, sensitivity, and ultralow power consumption. The utilization of single Pd nanowires, however, face challenges in nanofabrication, manipulation, and achieving ultrasmall transverse dimensions. We report on hydrogen sensors that take advantage of single palladium nanowires in high speed and sensitivity and that can be fabricated conveniently. The sensors are based on networks of ultrasmall (<10 nm) palladium nanowires deposited onto commercially available filtration membranes. We investigated the sensitivities and response times of these sensors as a function of the thickness of the nanowires and also compared them with a continuous reference film. The superior performance of the ultrasmall Pd nanowire network based sensors demonstrates the novelty of our fabrication approach, which can be directly applied to palladium alloy and other hydrogen sensing materials.     

Effects of nanoscale size dependent parameters on lattice thermal conductivity in Si nanowire

The effects of nanoscale size dependent parameters on lattice thermal conductivity are calculated using the Debye-Callaway model including transverse and longitudinal modes explicitly for Si nanowire with diameters of 115, 56, 37 and 22 nm. A direct method is used to calculate the group velocity for different size nanowire from their related calculated melting point. For all diameters considered, the effects of surface roughness, defects and transverse and longitudinal Gruneisen parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the reported experimental curve. The obtained fitting value for mean Gruneisen parameter has a systematic dependence on all Si nanowire diameters changing from 0·791 for 115 nm diameter to 1·515 for the 22 nm nanowire diameter. The dependence also gave a suggested surface thickness of about 5–6 nm. The other two parameters were found to have partially systematic dependence for diameters 115, 56, and 37 nm for defects and 56, 37 and 22 nm for the roughness. When the diameters go down from 115 to 22 nm, the concentration of dislocation increased from 1·16 × 10¹⁹cm⁻³ to 5·20 × 10¹⁹cm⁻³ while the surface roughness P found to increase from 0·475 to 0·130 and the rms height deviation from the surface changes by about 1·66 in this range of diameter. The diameter dependence also indicates a strong control of surface effect in surface to bulk ratio for the 22 nm wire diameter.