Pressure Welding of Silver Nanowires Networks at Room Temperature as Transparent Electrodes for Efficient Organic Light‐Emitting Diodes

In this work, polymethylmethacrylate (PMMA) as a superior mediate for the pressure welding of silver nanowires (Ag NWs) networks as transparent electrodes without any thermal treatment is demonstrated. After a pressing of 200 kg cm^?2, not only the sheet resistance but also the surface roughness of the PMMA‐mediated Ag NWs networks decreases from 2.6 kΩ sq^?1 to 34.3 Ω sq^?1 and from 76.1 to 12.6 nm, respectively. On the other hand, high transparency of an average transmittance in the visible wavelengths of 93.5% together with a low haze value of 2.58% can be achieved. In terms of optoelectronic applications, the promising potential of the PMMA‐mediated pressure‐welded Ag NWs networks used as a transparent electrode in a green organic light‐emitting diode (OLED) device is also demonstrated. In comparison with the OLED based on commercial tin‐doped indium oxide electrode, the increments of power efficiency and external quantum efficiency (EQE) from 80.1 to 85.9 lm w^?1 and 19.2% to 19.9% are demonstrated. In addition, the PMMA‐mediated pressure welding succeeds in transferring Ag NWs networks to flexible polyethylene naphthalate and polyimide substrates with the sheet resistance of 42 and 91 Ω sq^?1 after 10 000 times of bending, respectively.     

Highly sensitive and selective trimethylamine sensor using one-dimensional ZnO-Cr2O3 hetero-nanostructures

Highly selective and sensitive detection of trimethylamine (TMA) was achieved by the decoration of discrete p-type Cr(2)O(3) nanoparticles on n-type ZnO nanowire (NW) networks. Semielliptical Cr(2)O(3) nanoparticles with lateral widths of 3-8 nm were deposited on ZnO NWs by the thermal evaporation of CrCl(2) at 630 °C, while a continuous Cr(2)O(3) shell layer with a thickness of 30-40 nm was uniformly coated on ZnO NWs at 670 °C. The response (R(a)/R(g): R(a), resistance in air; R(g), resistance in gas) to 5 ppm TMA of Cr(2)O(3)-decorated ZnO NWs was 17.8 at 400 °C, which was 2.4 times higher than that to 5 ppm C(2)H(5)OH and 4.3-8.4 times higher than those to 5 ppm p-xylene, NH(3), benzene, C(3)H(8), toluene, CO, and H(2). In contrast, both pristine ZnO and ZnO (core)-Cr(2)O(3) (shell) nanocables (NCs) showed comparable responses to the different gases. The highly selective and sensitive detection of TMA that was achieved by the deposition of semielliptical Cr(2)O(3) nanoparticles on ZnO NW networks was explained by the catalytic effect of Cr(2)O(3) and the extension of the electron depletion layer via the formation of p-n junctions.     

Fabrication and characterization of Ga-doped ZnO nanowire gas sensor for the detection of CO

We demonstrate an efficient CO sensor using Ga-doped ZnO (GZO) nanowires (NWs). Various GZO NWs are synthesized with Au catalysts on sapphire substrates by hot-walled pulse laser deposition. The deposition temperature of ZnO NWs was in the range of 800-900 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) characterizations indicate that the obtained NWs have the well-crystallized hexagonal structure with customized Ga-doping concentration of 0-5 wt.%. The NWs have the diameter of about 50 nm and the length of about 8 µm. After depositing the Ag electrodes on both sides of the NW cluster, the resistance change is checked with the exposure to CO gas in the self-designed gas chamber that can facilitate the detection of the resistance change and the control of gas flow as well as temperature. The detected resistance modulations are 1.0 kΩ and 83.2 kΩ in the cases of 3 wt.% GZO and pure ZnO NW clusters, respectively, indication that we successfully customize the sensitivity of the gas sensors by controlled doping.     

Korrosionsuntersuchungen an mittels PVD mit Zn und Zn/Mn beschichteten Stählen

Corrosion Studies of Steels Coated by means of PVD with Zn and Zn/Mn Alternative methods for hot dip‐ or electrogalvanic deposition of zinc coatings on steel are gas phase depositions (PVD). They posess high flexibility with respect to alloy composition, and are environmentally harmless. However, a PVD‐coated steel must have at least the same corrosion resistance than steels with “classical” surface finishing. Therefore, the corrosion behaviour of Zn‐coatings and Zn/Mn/system‐coatings deposited by electron beam evaporation without and with ion beam assistance (IBAD) on low alloy steel, was determined by means of salt spray test and electrochemical potential/time measurements. At first the influence of chemical and irradiation pre‐treatment and ion bombardment during deposition on the corrosion resistance of the coatings was investigated. Than the effect of the Zn‐layer thickness was determined in comparison with an 8μm thick electrogalvanized reference coating. Finally Zn/Mn‐alloys, Zn/Mn‐multilayers and Zn‐coatings with Mn‐ or Zn/Mn‐surface layers (top layers) were investigated. By means of optimised pre‐treatment and ion bombardment conditions one obtains, considering the layer thickness, PVD‐Zn coatings with corrosion resistance comparable with the reference layer. The best Mn‐containing coatings are Zn‐coatings with Mn‐toplayer. They surpass the corrosion resistance of the reference layer considerably. Additionally it could be shown that in tendency the potential/time measurements agree very well with the results of the salt spray test.     

Controlled dielectrophoretic nanowire self-assembly using atomic layer deposition and suspended microfabricated electrodes

Effects of design and materials on the dielectrophoretic self-assembly of individual gallium nitride nanowires (GaN NWs) onto microfabricated electrodes have been experimentally investigated. The use of TiO(2) surface coating generated by atomic layer deposition (ALD) improves dielectrophoretic assembly yield of individual GaN nanowires on microfabricated structures by as much as 67%. With a titanium dioxide coating, individual nanowires were placed across suspended electrode pairs in 46% of tests (147 out of 320 total), versus 28% of tests (88 out of 320 total tests) that used uncoated GaN NWs. An additional result from these tests was that suspending the electrodes 2.75 μm above the substrate corresponded with up to 15.8% improvement in overall assembly yield over that of electrodes fabricated directly on the substrate.     

Ultra-high oxidation resistance of suspended single-wall carbon nanotube bundles grown by an "all-laser" process

Single-wall carbon nanotubes (SWCNTs) were laterally grown on SiO2/Si substrates by means of an "all-laser" growth process. Our "all-laser" process stands out by its exclusive use of the same pulsed UV laser, first, to deposit the CoNi nanocatalyst and, second, to grow SWCNTs through the laser ablation of a pure graphite target. The "all-laser" grown SWCNTs generally self-assemble into bundles (5-15 nm-diam.) sprouting from the CoNi nanocatalyst and laterally bridging the 2 microm gap separating adjacent catalysed electrodes (in either "suspended" or "on-substrate" geometries). A comparative study of the oxidation resistance of both suspended and on-substrate SWCNTs was achieved. The "all-laser" grown SWCNTs were subjected to annealing under flowing oxygen at temperatures ranging from 200 to 1100 degrees C. Systematic scanning electron microscopy observations combined with micro-Raman analyses revealed that more than 20% of suspended nanotubes were still stable at temperatures as high as 900 degrees C under flowing O2 while the on-substrate counterpart were completely burnt out at this temperature. Accordingly, the activation energy, as deduced from the Arrhenius plot, of the suspended SWCNTs is found to be as high as approximately 180 kJ mol(-1) (approximately 9 times higher than that of the on-substrate ones). The high quality (almost defect-free) of the nanotubes synthesized by the "all-laser" approach, their protected tips into the embedded CoNi catalyst nanolayer together with their suspended geometry are thought to be responsible for their unprecedented ultra-high oxidation resistance. This opens up new prospects for the use of these suspended nanotubes into nanodevices that have to operate under highly oxidizing environments.     

Photocurrent polarization anisotropy of randomly oriented nanowire networks

While the polarization sensitivity of single or aligned NW ensembles is well-known, this article reports on the existence of residual photocurrent polarization sensitivities in random NW networks. In these studies, CdSe and CdTe NWs were deposited onto glass substrates and contacted with Au electrodes separated by 30-110 microm gaps. SEM and AFM images of resulting devices show isotropically distributed NWs between the electrodes. Complementary high resolution TEM micrographs reveal component NWs to be highly crystalline with diameters between 10 and 20 nm and with lengths ranging from 1 to 10 microm. When illuminated with visible (linearly polarized) light, such random NW networks exhibit significant photocurrent anisotropies rho = 0.25 (sigma = 0.04) [rho = 0.22 (sigma = 0.04)] for CdSe (CdTe) NWs. Corresponding bandwidth measurements yield device polarization sensitivities up to 100 Hz. Additional studies have investigated the effects of varying the electrode potential, gap width, and spatial excitation profile. These experiments suggest electrode orientation as the determining factor behind the polarization sensitivity of NW devices. A simple geometric model has been developed to qualitatively explain the phenomenon. The main conclusion from these studies, however, is that polarization sensitive devices can be made from random NW networks without the need to align component wires.     

Dünne PVD-Hartstoffschichten zur Online-Temperaturmessung

Thin PVD hard coatings for the online temperature measurement In the processing industry, process control and the improvement of manufacturing processes become increasingly important. Therefore the acquisition of important process data during production becomes the focus of attention. Physical Vapor Deposition (PVD) allows the deposition of only a few micrometers thin coatings, which follow the shape of the coated surface. They have functionalities and can also increase the wear and corrosion resistance of the coated production tool or components. The aim of this article was the development of thin PVD coatings which can measure temperatures ranging from room temperature up to several hundred centigrades. Therefore, two different coating systems are presented and analyzed with regard to their suitability for temperature measurement. The overall aim is intended to measure the temperature in the interface between the tool surface and the processed workpiece in cutting process or between the tool surface and the melt by primary forming. The sensor coating provides the possibility of an online temperature measurement and the forwarding of this process data. The operating principle is based on the thermoelectric effect, which is also known as the Seebeck effect.     

Higher Tool Productivity due to New Generation of PVD Coatings

PVD coating technology has seen many new developments in the past few years. HIPIMS⁺ is an example of these developments with excellent results on tool productivity and lifespan. The technology combines the advantages of arc evaporation with those of magnetron sputtering and results in a dense and defect‐free coating with tuneable residual stress. The coatings have been tested successfully by international tool manufacturers. Additional developments can be seen in DLC coatings and the hydrogen‐free variety ta‐C. These coatings are suitable for low temperature deposition and machining of special materials.     

Multifunctional FeCo/TiN Multilayer Thin Films with Combined Magnetic and Protective Properties

Coatings with thicknesses ranging from a few nanometer up to several micrometer produced by physical vapor deposition (PVD) processes have been established in engineering technologies since the early 1980s. In particular, magnetron sputtered wear resistance coatings are industrially established and capable to enhance tool lifetimes significantly. However, in cases where optical inspection of a coating in use is not possible, an intrinsic sensor function of the film would be beneficial. Therefore, the development of wear resistant coatings with an integrated sensor functionality based on the insertion of a magnetoelastic ferromagnetic phase is suggested. In combination with appropriate read‐out electronics such a film system would be ready for online monitoring of the coatings' actual state (e.g., strain, temperature, volume loss). This paper focuses on the development of wear resistance coatings which simultaneously supply beneficial mechanical properties as well as ferromagnetic properties optimized for online non‐contact read‐out applications. Multilayer coatings obtained through alternate stacking of magnetron sputtered TiN and FeCo layers with a nominal total thickness of 1000 nm were produced as a model system meeting the above conditions. The bilayer period was varied down to 2.6 nm while the individual layer thickness ratio t_TiN/t_FeCo was determined by the deposition rates and maintained constant at a value of about 3/1. The films were vacuum annealed ex situ in a static magnetic field subsequent to the deposition. The constitution of the as‐deposited and annealed coatings as well as their mechanical (nanohardness, Young's modulus) and magnetic properties (magnetization hysteresis, frequency‐dependent permeability) are described. Finally, the suitability of the coatings for the use in remote‐interrogable wear sensor applications is briefly discussed.     

Nanopatterning of ultrananocrystalline diamond nanowires

We report the fabrication of horizontally aligned ultrananocrystalline diamond (UNCD) nanowires (NWs) via two different approaches. First, with the top-down approach by using electron beam lithography (EBL) and reactive ion etching (RIE) with a photo resist layer as an etch mask. Using this approach, we demonstrate fabrication of 50?μm long UNCD NWs with widths as narrow as 40?nm. We further present an alternative approach to grow UNCD NWs at pre-defined positions through a selective seeding process. No RIE was needed either to etch the NWs or to remove the mask. In this case, we achieved UNCD NWs with lengths of 50?μm and smallest width of 90?nm respectively. Characterization of these nanowires by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that the UNCD NWs are well defined and fully released, with no indication of residual stress. Characterization using visible and ultraviolet (UV) Raman spectroscopy indicates that in both fabrication approaches, UNCD NWs maintain their intrinsic diamond structure.     

Localized growth of suspended SWCNTs by means of an "all-laser" process and their direct integration into nanoelectronic devices

We have successfully developed an "all-laser" processing for the localized growth of suspended single-wall carbon nanotubes (SWCNTs) on prepatterned SiO/sub 2//Si substrates. Our "all-laser" process stands out by its exclusive use of the same KrF excimer laser, first, to deposit the embedded-catalyst electrodes with a controllable architecture and, second, to grow SWCNTs through the pulsed laser ablation of a pure graphite target. Under the optimal growth conditions, the suspended SWCNTs are shown to bridge laterally adjacent electrodes separated by a gap of /spl sim/2 /spl mu/m. These SWCNTs (having diameters in the 1.25-1.64-nm range) generally tend to auto-assemble into bundles of /spl sim/5--15 nm in diameter. The "all-laser" process here developed offers the advantage of a direct integration of the SWCNTs into field-effect-transistor-like devices with no postprocessing, thereby permitting the investigation of their electrical transport properties. Thus, the suspended SWCNT bundles are shown to behave collectively as an ambipolar transistor with ON/OFF switching ratios as high as /spl sim/10/sup 4/.     

Rückseitenmetallisierung Wafer‐basierter Si‐Solarzellen mittels EB‐PVD

Back Side Metallization of Wafer Based Silicon Solar Cells by Means of Electron Beam Evaporation Electron beam evaporation is an innovative vacuum deposition technology regarding the wafer backside metallization of crystalline silicon solar cells. The motivation for the consideration of electron beam evaporation as cell finishing step is based on the one hand on the competition with thin film photovoltaic modules and on the other on the remarkable cost reduction potential by applying EB‐PVD (Electron Beam Physical Vapor Deposition). This article presents a highly productive coater concept and gives an explanation of important aspects for the adaption of the coater concept to typical solar cell features. Various PVD technologies are compared concerning their possible use as wafer backside metallization method. Challenges and chances of the introduction of EB‐PVD in the wafer based solar cell production are considered.     

Broadband photodetector of high quality Sb2S3 nanowire grown by chemical vapor deposition

Low dimensional semiconductors can be used for various electronic and optoelectronic devices because of their unique structure and property.In this work,one-dimensional Sb2S3 nanowires(NWs)with high crystallinity were grown via chemical vapor deposition(CVD)technique on SiO2/Si substrates.The Sb2S 3 NWs exhibited needle-like structures with inclined cross-sections.The lengths of Sb2S3 nanowires changed from 7 to 13 pm.The photodetection properties of Sb2S3 nanowires were comprehensively and systematically characterized.The Sb2S3 photodetectors show a broadband photoresponse ranging from ultraviolet(360 nm)to near-infrared(785 nm).An excellent specific detectivity of 2.1×1014 Jones,high external quantum efficiency of 1.5×104％,sensitivity of 2.2×104 cm2W-1 and short response time of less than 100 ms was achieved for the Sb2S3 NW photodetectors.Moreover,the Sb2S3 NWs showed out-standing switch cycling stability that was beneficial to the practical applications.The high-quality Sb2S3 nanowires fabricated by CVD have great application potential in semiconductor and optoelectronic fields.     

Junction‐Free Electrospun Ag Fiber Electrodes for Flexible Organic Light‐Emitting Diodes

Fabrication of junction‐free Ag fiber electrodes for flexible organic light‐emitting diodes (OLEDs) is demonstrated. The junction‐free Ag fiber electrodes are fabricated by electrospun polymer fibers used as an etch mask and wet etching of Ag thin film. This process facilitates surface roughness control, which is important in transparent electrodes based on metal wires to prevent electrical instability of the OLEDs. The transmittance and resistance of Ag fiber electrodes can be independently adjusted by controlling spinning time and Ag deposition thickness. The Ag fiber electrode shows a transmittance of 91.8% (at 550 nm) at a sheet resistance of 22.3 Ω □^?1, leading to the highest OLED efficiency. In addition, Ag fiber electrodes exhibit excellent mechanical durability, as shown by measuring the change in resistance under repeatable mechanical bending and various bending radii. The OLEDs with Ag fiber electrodes on a flexible substrate are successfully fabricated, and the OLEDs show an enhancement of EQE (≈19%) compared to commercial indium tin oxide electrodes.     

Phonon scattering enhancement in silicon nanolayers

Dimensional confinement in silicon nanowires (NWs) is well-known for enhancing phonon scattering, thus leading to a pronounced reduction of thermal conductivity κ with respect to bulk material. The effect of confinement on phonon scattering in nanolayers (NLs), however, has not been fully understood. In this work, thermal conductivity on polycrystalline silicon NLs with roughened surfaces and thicknesses ranging from 30 to 100 nm has been experimentally investigated. For measurement purposes, the nanostructures were fabricated with a dedicated surface nano-machining process, thus producing vertical silicon nanostructures suspended on Al/Si electrodes on a silicon substrate, using SiO₂ as a sacrificial layer. By designing such structures in a four-terminal configuration, their κ could be determined by the current-voltage method. Boron doped silicon NLs were examined, at resistivity ranging between 2 and 10 m $\Upomega$ cm. We found an increase of phonon scattering from the confinement, since κ decreased steadily with the thickness from values typical of thick films (around 30 W m^?1 K^?1) down to <15 W m^?1 K^?1. Compared to NWs, NLs had displayed figures of merit smaller by one order of magnitude. However, due to the larger filling factor, they were able of generating more than five times the electric power per area unit that could be obtained with high-density stacks of top-efficiency NWs.     

Self-assembly of conductive Cu nanowires on Si(111)'5 × 5 '-Cu surface

Upon room-temperature deposition onto a Cu/Si(111)'5 × 5' surface in ultra-high vacuum, Cu?atoms migrate over extended distances to become trapped at the step edges, where they form Cu?nanowires (NWs). The formed NWs are 20-80?nm wide, 1-3?nm high and characterized by a resistivity of ～8?μΩ?cm. The surface conductance of the NW array is anisotropic, with the conductivity along the NWs being about three times greater than that in the perpendicular direction. Using a similar growth technique, not only the straight NWs but also other types of NW-based structures (e.g. nanorings) can be fabricated.     

The effect of PVD coatings on the tensile strength and low‐cycle fatigue resistance of stainless steel and titanium alloys

PVD coatings applied to components form hard, stronger layers and generate high residual compressive stresses that limit the plastic deformation in surface layers of the base metal thus increasing its tensile strength and resistance to fatigue loading. The purpose of this paper is to experimentally determine the influence of the deposition of 2 to 16.5‐μm‐thick PVD coatings of TiN, Cr, (Cr+TiN), (TiC)N, (TiAl)N onto specimens of stainless steel 321 and titanium alloys of types MILT‐81556A and (10‐2‐3; 4966) on their tensile strength and low‐cycle fatigue resistance when the development of large elastic–plastic strains takes place. The tensile and low‐cycle fatigue tests were conducted under conditions of axial zero‐to‐tension cycle of the stress‐controlled loading on flat 1‐ to 1.5‐mm‐thick specimens in the initial state (uncoated specimens) and after application of a PVD coating, including those after pretensioning or after cyclic prestraining in the low‐cycle fatigue range. The deposition of PVD coatings is found to enhance the characteristics of tensile strength and low‐cycle fatigue resistance in the quasi‐static fracture range. The deposition of PVD coatings on specimens cyclically prestrained to the values of 53–86% of the number of cycles to fracture, changes the cyclic properties of the material and predetermines the fatigue fracture mode only.     

A Facile One‐Step Approach for Constructing Multidimensional Ordered Nanowire Micropatterns via Fibrous Elastocapillary Coalescence

Nanowire (NW) based micropatterns have attracted research interests for their applications in electric microdevices. Particularly, aligning NWs represents an important process due to the as‐generated integrated physicochemical advantages. Here, a facile and general strategy is developed to align NWs using fibrous elastocapillary coalescence of carbon nanotube arrays (ACNTs), which enables constructing multidimensional ordered NW micropatterns in one step without any external energy input. It is proposed that the liquid film of NW solution is capable of shrinking unidirectionally on the top of ACNTs, driven by the dewetting‐induced elastocapillary coalescence of the ACNTs. Consequently, the randomly distributed NWs individually rotate and move into dense alignment. Meanwhile, the aggregating and bundling of ACNTs is helpful to produce carbon nanotube (CNT) yarns connecting neighboring bundles. Thus, a micropatterned NW network composed of a top‐layer of horizontally aligned NWs and an under‐layer of vertical ACNT bundles connected by CNT yarns is prepared, showing excellent performance in sensing external pressure with a sensitivity of 0.32 kPa^?1. Moreover, the aligned NWs can be transferred onto various substrates for constructing electronic circuits. The strategy is applicable for aligning various NWs of Ag, ZnO, Al₂O₃, and even living microbes. The result may offer new inspiration for fabricating NW‐based functional micropatterns.     

Structural and optical properties of glancing angle deposited TiO2 nanowires array

TiO2 nanowires (NWs) have been synthesized by glancing angle deposition technique using e-beam evaporator. The average length 490 nm and diameter 80 nm of NWs were examined by field emission-scanning electron microscopy. Transmission electron microscopy emphasized that the NWs were widely dispersed at the top. X-ray diffraction has been carried out on the TiO2 thin film (TF) and NW array. A small blue shift of 0.03 eV was observed in Photoluminescence (PL) main band emission for TiO2 NW as compared to TiO2 TF. The high temperature annealing at 980 degrees C partially removed the oxygen vacancy from the sample, which was investigated by PL and optical absorption measurements.