Free-standing Tungsten Research Articles

Fully biodegradable electrochromic display for disposable patch

Flexible and biodegradable electronics have emerged as a promising solution for escalating electronic waste issue caused by the rapid development of skin patch electronics. Fully biodegradable displays are essential for visualizing biological/physical/chemical/electrochemical signals measured by a wide range of skin patch electronics. Here we propose fully biodegradable electrochromic display providing low operating voltage and low power consumption. The biodegradable transparent conductive electrode was fabricated by transferring free-standing tungsten nanomesh onto poly lactic-co-glycolic acid substrate using electrospinning templating, minimizing damage to the substrate. Electrochromic layer was tungsten oxide which is biodegradable, and a ferrocyanide/ferricyanide redox agent was utilized as a counter electrode reaction to enhance operational stability in an aqueous electrolyte by reducing operating voltage and side reactions. This display successfully visualized diverse signals from various biodegradable electronics such as UV sensors and electrochemical transistors, and finally underwent eco-friendly degradation in phosphate-buffered saline or soil under mild conditions.

Tungsten Nitride/Carbon Cloth as Bifunctional Electrode for Effective Polysulfide Recycling

The inevitable dissolution, diffusion, and migration of polysulfides cause an irreversible loss of active material, leading to poor cyclic performance in lithium sulfur batteries. Herein, a freestanding tungsten nitride nanorod/carbon cloth (WN/CC) interlayer is prepared by hydrothermal growth to function as both current collector and physicochemical barrier to soluble lithium polysulfides (Li2Sx). The cells containing a dual-functional interlayer deliver a significantly improved initial discharge capacity of 1337 mAh g–1 with a reversible capacity of 814.2 mAh g–1 after 500 cycles at 100 mA g–1. The enhanced electrochemical performance is attributed to the highly adsorptive WN nanorods grown on conductive CC to entrap polysulfides, leading to effective recycling of active materials. The density functional theory (DFT) calculations prove important roles of the WN (200) surface in entrapping polysulfides through their strong adsorption energies (3.21–4.67 eV) with Li2Sx and S8. The potential of the dual-fu...

Atomic resolution top-down nanofabrication with low-current focused-ion-beam thinning

► Developed a technique of size reduction to sub-ten nanometers by FIB milling. ► FIB milling is a top-down and site-specific approach with atomic resolution. ► No remarkable morphology and microstructure changes of W composite nanowires were observed after thinning. ► FIB thinning is an effective method towards size and quantum effects observation. Techniques for scalable fabrication of one-dimensional or quasi-one-dimensional nanowires are of great importance to observe quantum size effects and build quantum information devices. In this work, we developed a technique for size reduction of both lateral and freestanding tungsten composite nanostructures using focused-ion-beam (FIB) thinning. Different exposure times and ion-beam currents were used to control the final size and the thinning rate and accuracy of a group of nanowires, an individual nanowire and a portion of a nanowire by low-current site-specific milling. A transmission electron microscope image of a thinned superconducting tungsten composite nanowire with width reduced from 80 nm to 50 nm shows uniform shrinking along the length of the wire and high resolution image shows no obvious changes of the morphology after thinning. The variation of the superconducting critical current density upon thinning is insignificant; it is 1.7 × 10 5 and 1.4 × 10 5 A/cm 2 at 4.26 K for the as-deposited and wire with width reduced to 50 nm, respectively. These results suggest that FIB-milling is a potential approach for controllable size reduction enabling the observation of size- and quantum effects.

Superconductivity of Freestanding Tungsten Nanofeatures Grown by Focused-Ion-Beam

Freestanding tungsten composite nanofeatures were grown by focused-ion-beam-induced deposition with 1 pA ion beam current. The temperature dependent electrical measurements show that the flying nanoscale tungsten is conducting with a room temperature resistivity of 550 micro omega cm. It is also superconducting with a Tc, above 5.1 K and can be repeatedly thermally cycled. Our results suggest that FIB direct-writing of three-dimensional tungsten composites might be a potential approach to fabricate vertical nanodevices and mask-free superconducting devices.

Magnetism of a free-standing W monoatomic sheet

The magnetism of a free-standing tungsten monoatomic sheet under different magnetization states has been studied by using the first-principles method based on the density functional theory. The results show that W atomic sheet at the equilibrium state is not magnetized. However, ferromagnetic or antiferromagnetic state can appear in the sheet when the lattice is elongated, moreover, the magnetism appears earlier and increases more stably and smoothly in the antiferromagnetic states than the ferromagnetic one. The antiferromagnetic states are always more stable than the ferromagnetic ones under the same lattice parameter. The most stable W atomic sheet among all the structures studied is a near-hexagonal plane structure, due to the Jahn–Teller effect. All the magnetic states studied are shown to be metallic. The electronic structure properties of various magnetic plane structures are presented, with the effect of spin–orbit coupling included.

A technique for the manufacture of long hollow diamond fibres by chemical vapour deposition

Diamond possesses a unique combination of physical, mechanical and chemical properties, and many of these properties can now be obtained in diamond produced by chemical vapour deposition (CVD) [13]. Hitherto, CVD diamond has only been available as thin (micrometre) films on suitable substrates, which has limited CVD diamond applications to optical or wear resistant coatings and cutting tools [4]. Recently, continuous CVD diamond fibres have been produced by coating CVD diamond onto wires or ceramic fibre cores [5-7]. The diameter of the fibre cores can vary from < 50 gm, typical of the commercial fibres present in flexible multifilament tows such as HI-nicalon, Altex and Nextel 480, t o about 100-150gm, typical of commercial fibre monofilaments such as SiC and A1203 (Saphikon) [5, 8]. CVD diamond fibres can have tensile modulus values of 1 0 0 0 GPa [8,9], over twice that of monofilament SiC fibres [5], and are suitable for reinforcing polymer, metal [6, 10] or ceramic matrices. Thus, diamond fibres offer the engineer, for the first time, the possibility of exploiting the properties of diamond on a large scale in conventional engineering components and structures [5, 10]. In order to increase the compressive stiffness and decrease the density of glass fibre reinforced composites, hollow glass fibres, made by extruding and drawing, have been developed with the same mass per unit length as solid glass fibres [11]. Hollow diamond fibres have also been produced by etching out the diamond fibre core [6]. The possibility of obtaining the properties of diamond in hollow fibres is particularly attractive, but the etching method is unsuitable for very long, small diameter fibres. This letter describes a method for manufacturing long hollow fibres that does not rely on etching. The manufacturing technique involves CVD of diamond onto a helical tungsten wire coil. The diameter of the tungsten wire was in the range d l = 10-20 gm. The coil was made by winding annealed tungsten wire around a stiff wire or ceramic fibre core, as shown schematically in Fig. 1. After winding and relaxing the wire coil, the core was removed to leave a free-standing tungsten coil (Fig. 2a). Diamond deposition was carried out in a specially designed hot filament reactor (designed and built by Thomas Swan, Cambridge, UK) using a 1% CH4/H2 gas mixture and a flow rate of 200 standard

Measurement of thermal diffusivity and anisotropy of plasma-sprayed coatings

The thermal diffusivity of free-standing tungsten and zirconia plasma-sprayed coatings was measured in the directions parallel and perpendicular to their surface. The parallel thermal diffusivity was evaluated by a double-sensing Laplace-transform technique and compared to the perpendicular values obtained by the (lash technique. Ratios between the parallel and the perpendicular thermal diffusivity values were in the range of 1.1 to 1.5 for zirconia and 4 to 6 for tungsten. The results are discussed in terms of the coating thickness and microstructure.

Fabrication of thin‐wall, freestanding inertial confinement fusion targets by chemical vapor deposition

To meet the requirements for plasma physics experiments in the inertial confinement fusion (ICF) program, chemical vapor deposition (CVD) in fluid beds was used to fabricate freestanding tungsten spheres and cylinders with wall thicknesses less than 5.0 μm. Molybdenum and molybdenum alloy (TZM) mandrels of the desired geometry were suspended in a carrier bed of dense microspheres contained in an induction‐heated fluid‐bed reactor. The mandrels were free to float randomly through the bed, and using the reaction WF6+3H2→723 KW +6HF, very fine‐grained tungsten was deposited onto the surface at a rate and in a grain size determined by temperature, gas flow rate, system pressure, and duration of the reaction. After coating, a portion of each mandrel was exposed by hole drilling or grinding. The mandrel was then removed by acid leaching, leaving a freestanding tungsten shape. Experimental procedures, mandrel preparation, and results obtained are discussed.

Interrelationships between process parameters, structure, and properties of CVD tungsten and tungsten–rhenium alloys

The development of CVD techniques for fabricating free-standing tungsten and tungsten–rhenium alloy structures is reviewed. Relationships between plating parameters, kinetics, morphology, microstructure, and properties of thick polycrystalline deposits are discussed. It is emphasized that porosity may be grown into the grain boundaries when the depostition rate is controlled by gas phase diffusion, and that fully dense deposits are generally obtained when the rate is limited by a surface process. The origin and control of many of the microstructural features peculiar to CVD are also discussed.

Tungsten Fabrication by Arc Spraying

This paper is concerned with the development of the plasma-arc spray process for the fabrication of free-standing tungsten bodies and its projection from the laboratory into the production of full-scale hardware.