Tantalum Substrate Research Articles

Direct fabrication and nitridation of a high-quality NaTaO3 crystal layer onto a tantalum substrate

High-quality nano-/microtextured NaTaO3 crystal layers were successfully fabricated on Ta substrates at a relatively low temperature using molten NaNO3 as the starting material. Ta substrates coated with an aqueous NaNO3 solution were heated at 500 °C in an infrared heating furnace, whereupon Ta reacted with NaNO3 (which acted as both the Na source and the flux) to afford a layer of densely packed cubic NaTaO3 crystals that adhered readily onto the substrate. Nitridation of the NaTaO3 crystal layer by heating at 850 °C under an NH3 flow yielded a Ta3N5 crystal layer. The crystals retained their original size and shape but became highly porous after nitridation. TEM observations clearly indicated that the porous cubic crystals consisted of highly crystalline nanoparticles.

Preparation and Characteristic Measurement of Born Doped Diamond Film Electrode on Tantalum Substrate and its Properties for Degradation of High COD Wastewater

The boron-doped diamond film electrode grown on tantalum substrate (BDD/Ta) was prepared by hot filament chemical vapor deposition (HFCVD) technique. The morphology and quality of BDD/Ta film electrode were investigated by SEM and Raman spectroscopy respectively. The electrochemical behavior of the BDD/Ta film electrodes in Na2SO4 solution was also investigated by cyclic voltammetry and the window potential of BDD/Ta film electrode in Na2SO4 solution is of 4.1V, the hydrogen and oxygen evolution potentials are of-1.8V and +2.3V respectively. The characteristic measurements of BDD/Ta film electrode and its application to degradation of high concentration organic wastewater indicated that BDD/Ta film electrode have a series of advantages, including high overpotential for oxygen revolution, high current efficiency, good removal of chemical oxygen demand (COD).

Induction of strand breaks in DNA films by low energy electrons and soft X-ray under nitrous oxide atmosphere

Five-monolayer (5 ML) plasmid DNA films deposited on glass and tantalum substrates were exposed to Al K α X-rays of 1.5 keV under gaseous nitrous oxide (N 2O) at atmospheric pressure and temperature. Whereas the damage yields for DNA deposited on glass are due to soft X-rays, those arising from DNA on tantalum are due to both the interaction of low energy photoelectrons from the metal and X-rays. Then, the differences in the yields of damage on glass and tantalum substrates, essentially arises from interaction of essentially low-energy electrons (LEEs) with DNA molecules and the surrounding atmosphere. The G-values (i.e., the number of moles of product per Joule of energy absorbed) for DNA strand breaks induced by LEEs ( G LEE) and the lower limit of G-values for soft X-ray photons ( G XL) were calculated and the results compared to those from previous studies under atmospheric conditions and other ambient gases, such as N 2 and O 2. Under N 2O, the G-values for loss of supercoiled DNA are 103±15 nmol/J for X-rays, and 737±110 nmol/J for LEEs. Compared to corresponding values in an O 2 atmosphere, the effectiveness of X-rays to damage DNA in N 2O is less, but the G value for LEEs in N 2O is more than twice the corresponding value for an oxygenated environment. This result indicates a higher effectiveness for LEEs relative to N 2 and O 2 environments in causing SSB and DSB in an N 2O environment. Thus, the previously observed radiosensitization of cells by N 2O may not be only due to OH radicals but also to the reaction of LEE with N 2O molecules near DNA. The previous experiments with N 2 and O 2 and the present one demonstrate the possibility to investigate damage induced by LEEs to biomolecules under various types of surrounding atmospheres.

Gold nanoparticle-coated multiwall carbon nanotube-modified electrode for electrochemical determination of methyl parathion

We report on an electrochemical sensor for the determination of methyl parathion. It is based on an electrode modified with multi-walled carbon nanotubes that were covered with gold nanoparticles (Au-NPs). The vertically aligned array of MWCNTs on a tantalum substrate was coated with Au-NPs by overhead magnetron sputtering deposition. Scanning and transmission electron microscopy and XRD were used to characterize the Au-NP-MWCNTs composite. Cyclic voltammetry and differential pulse voltammetry were employed to evaluate the suitability of the new electrode for the determination of methyl parathion. Under the optimal conditions, the current response of the electrode to methyl parathion is linear in the range from 0.50 to 16.0 mg mL-1, with a detection limit of 50 μg mL-1 (signal/noise = 3), and the sensitivity is 4.5 times better than that of the plain MWCNTs electrode. We conclude that this method represents a simple, rapid, effective and sensitive approach for the detection of methyl parathion.

Soft X-ray and low energy electron-induced damage to DNA under N2 and O2 atmospheres.

DNA damage induced by low energy electrons (LEEs) and soft X-rays is measured under dry nitrogen and oxygen at atmospheric pressure and temperature. Five-monolayer plasmid DNA films deposited on tantalum and glass substrates are exposed to Al K(α) X-rays of 1.5 keV in the two different environments. From the damage yields for DNA, G values are extracted for X-rays and LEEs. The G values for LEEs are 3.5 and 3.4 higher than those for X-ray photons under N(2) and O(2) atmospheres, respectively. Because most of the measured damage is in the form of single strand breaks (SSB), this result indicates a much higher effectiveness for LEEs relative to X-rays in causing SSB in both environments. The results indicate that the oxygen fixation mechanism, which is highly effective in increasing radiobiological effectiveness, under aerobic conditions, is operative on the type of damage created at the early stage of DNA radiolysis by LEEs.

A low-potential, H 2O 2-assisted electrodeposition of cobalt oxide/hydroxide nanostructures onto vertically-aligned multi-walled carbon nanotube arrays for glucose sensing

A novel nanocomposite was synthesized using a cathodic, low-potential, electrochemical reduction of H 2O 2 to homogeneously deposit cobalt oxide/hydroxide (denoted as CoOx·nH 2O) nanostructures onto vertically well-aligned multi-walled carbon nanotube arrays (MWCNTs), while the MWCNTs were prepared by catalytic chemical vapor deposition (CVD) on a tantalum (Ta) substrate. The CoOx· nH 2O–MWCNTs nanocomposite exhibits much higher electrocatalytic activity towards glucose (Glc) after modification with CoOx· nH 2O than before. This non-enzymatic Glc sensor has a high sensitivity (162.8 μA mM −1 cm −2), fast response time (<4 s) and low detection limit (2.0 μM at signal/noise ratio = 3), and a linear dynamic range up to 4.5 mM. The sensor output is stable over 30 days and unaffected by common interferents that co-exist with Glc in analytical samples; it is also resistant to chloride poisoning. These features make the CoOx·nH 2O–MWCNTs nanocomposite a promising electrode material for non-enzymatic Glc sensing in routine analysis.

Studies on distribution of element contents in transient layer at interface between boron-doped diamond film electrode and tantalum substrate

The boron-doped diamond film (BDD) grown on tantalum (Ta) substrate as an electrode (BDD/Ta) was prepared by hot filament chemical vapor deposition method. The experimental results demonstrated that our BDD/Ta had high current efficiency, strong ability to degrade wastewater, good corrosion stability and long lifetime. These excellent characteristics of BDD/Ta have been explained in terms of Rutherford backscattering (RBS) experiments. RBS investigation revealed that the continuous transient layer at the interface between boron-doped diamond film and Ta-substrate was formed and the microstructure of the continuous transient layer given by the continuous distribution of all element contents at the interface was obtained. The thicknesses of boron-doped diamond film and the continuous transient layer were about equal to 8000 × 10 15 atoms/cm 2 and 5800 × 10 15 atoms/cm 2, respectively. The formation of the continuous transient layer at the interface can eliminate the mismatch of thermal expansion coefficients (TEC) at the interface and only lead to the slow change of TEC because of the continuous distribution of element contents of the film and substrate in the transient layer at the interface. Thus, there is no residual stress to concentrate on the interface and the stress-corrosion delamination of the film disappears. Therefore, the corrosion stability and lifetime of BDD/Ta increase and last well, that have been verified by X-ray diffraction (XRD) experiments.

Liquid uranium corrosion studies of protective yttria coatings on tantalum substrate

Yttrium oxide has excellent thermodynamic and thermal stability, and also exhibits superior resistance to attack by various reactive metals, glass and slag at high temperature. Coupons with yttrium oxide coating on tantalum substrate with out bond coat were tested for compatibility against liquid uranium at 1573 K up to 80 h in vacuum. Optical microscopy and SEM/EDS investigations were done to evaluate the micro structural features of the coating and the liquid uranium attack. Experimental results show that yttrium oxide coating exhibits excellent corrosion resistance against liquid uranium at 1573 K.

Electrodeposition from a Liquid Cationic Cuprous Organic Complex for Seed Layer Deposition

Continuous layers of 20 nm of copper have been deposited on a tantalum substrate from the liquid cationic cuprous organic complex [Cu(MeCN)2][Tf2N]. This type of ionic liquid, with a high concentration of copper(I) ions permits to achieve high nucleation densities. Furthermore, extremely high overpotentials (up to 5.0 V) can be applied without decomposition of the ionic liquid. The deposition of copper has been investigated by cyclic voltammetry (CV), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The resulting copper deposits can be useful as seed layers for aqueous copper filling.

Electrochemical Capacitors Based on Aligned Carbon Nanotubes Directly Synthesized on Tantalum Substrates

We demonstrate that vertically aligned carbon nanotubes can be synthesized directly on tantalum substrate via water-assisted chemical vapor deposition and evaluate their properties as electrochemical capacitors. The mean diameter of the carbon nanotubes was <TEX>$7.1{\pm}1.5\;nm$</TEX>, and 70% of them had double walls. The intensity ratio of G-band to D-band in Raman spectra was as high as 5, indicating good quality of the carbon nanotubes. Owing to the alignment and low equivalent series resistance, the carbon nanotube based supercapacitors showed good rate performance. Rectangular shape of cyclic voltammogram was maintained even at the scan rate of > 1 V/s in 1 M sulfuric acid aqueous solution. Specific capacitance was well-retained (~94%) even when the discharging current density dramatically increased up to 145 A/g. Consequently, specific power as high as 60 kW/kg was obtained from as-grown carbon nanotubes in aqueous solution. Maximum specific energy of ~20 Wh/kg was obtained when carbon nanotubes were electrochemically oxidized and operated in organic solution. Demonstration of direct synthesis of carbon nanotubes on tantalum current collectors and their applications as supercapacitors could be an invaluable basis for fabrication of high performance carbon nanotube supercapacitors.

Growth of TiO&lt;SUB&gt;2&lt;/SUB&gt; Nanorods on a Ta Substrate by Metal-Organic Chemical Vapor Deposition

TiO2 nanorods were successfully grown on Tantalum (Ta) substrates using titanium tetra isopropoxide (TTIP) as a single precursor without any carriers or bubbling gases. For characterization of the TiO2 structures, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed. For substrate temperatures below 800 degrees C, a rough film structure without nanorods could be found. However, at a sample temperature of 800 degrees C, nanorod structures with a respective diameter and length of 0.1 approximately 0.2 microm and 0.7 approximately 1.5 microm, respectively, could be synthesized. The nanorods exhibited a rutile phase with a 2:1 stoichiometry of O:Ti, identified using XRD and XPS. When the growth temperature exceeded 800 degrees C, agglomeration of the nanorods was identified.

A highly sensitive non-enzymatic glucose sensor based on a simple two-step electrodeposition of cupric oxide (CuO) nanoparticles onto multi-walled carbon nanotube arrays

A novel, stable and highly sensitive non-enzymatic glucose (Glc) sensor was developed using vertically well-aligned multi-walled carbon nanotubes array (MWCNTs) incorporated with cupric oxide (CuO) nanoparticles. The MWCNTs array was prepared by catalytic chemical vapor deposition on a tantalum (Ta) substrate, while a simple and rapid two-step electrodeposition technique was used to prepare the CuO–MWCNTs nanocomposite. First, Cu nanoparticles were deposited onto MWCNTs at constant potential and then they were oxidized into CuO by potential cycling. The electrocatalytic activity of CuO–MWCNTs array was investigated for Glc under alkaline conditions using cyclic voltammetry and chronoamperometry. The sensor exhibited a linear response up to 3 mM of Glc and sensitivity of 2190 μA mM −1 cm −2, which is two to three orders of magnitude higher than that of most non-enzymatic Glc sensors reported in the literature. The sensor response time is less than 2 s and detection limit is 800 nM (at signal/noise = 3). When tested with human blood serum samples, the sensor exhibited high electrocatalytic activity, stability, fast response and good selectivity against common interfering species, suggesting its potential to be developed as a non-enzymatic Glc sensor.

Production and investigation of thin films of metal actinides (Pu, Am, Cm, Bk, Cf)

Under limited availability of transplutonium metals some special techniques and methods of their production have been developed that combine the process of metal reduction from a chemical compound and preparation of a sample for examination. In this situation the evaporation and condensation of metal onto a substrate becomes the only possible technology. Thin film samples of metallic 244Cm, 248Cm and 249Bk were produced by thermal reduction of oxides with thorium followed by deposition of the metals in the form of thin layers on tantalum substrates. For the production of 249Cf metal in the form of a thin layer the method of thermal reduction of oxide with lanthanum was used.238Pu and 239Pu samples in the form of films were prepared by direct high temperature evaporation and condensation of the metal onto a substrate. For the production of 241Am films a gram sample of plutonium-241 metal was used containing about 18 % of americium at the time of production. Thermal decomposition of Pt5Am intermetallics in vacuum was used to produce americium metal with about 80% yield. Resistivity of the metallic 249Cf film samples was found to decrease exponentially with increasing temperature. The 249Cf metal demonstrated a tendency to form preferably a DHCP structure with the sample mass increasing. An effect of high specific activity on the crystal structure of 238Pu nuclide thin layers was studied either.

Direct Cu-on-Ta Electroplating from Ionic Liquids in High Vacuum

Smooth layers of 20 nm of copper have been deposited on a tantalum substrate from ionic liquids under high vacuum conditions. By electrochemical vacuum deposition (EVD) it is possible to achieve extremely low concentrations of oxygen and water, so that the tantalum electrode does not oxidize. Due to the low vapor pressure of ionic liquids, no evaporation of the electrolyte was observed in vacuum. The wide electrochemical windows of the ionic liquids are advantageous to obtain nucleation densities up to 8 1014 m-2 of copper on the tantalum electrode by applying a very large overpotential. Copper was deposited at potentials as negative as -3 V versus a Cu pseudo-reference electrode.

Copper Plating on Resistive Substrates, Diffusion Barrier and Alternative Seed Layers

We have studied electrochemical deposition of copper on ruthenium-tantalum (Ru-Ta) alloy, tantalum (Ta), and cobalt (Co) substrates using cyclic voltammetry and galvanostatic methods. We show that a single-step direct-plating from acidic Cu bath approach is favorable on thin Ru-Ta films, while it presents a significant challenge for plating on resistive Ta and Co substrates.

Thermal stability studies of plasma sprayed yttrium oxide coatings deposited on pure tantalum substrate

Plasma sprayed Yttrium oxide is used for coating of crucibles and moulds that are used at high temperature to handle highly reactive molten metals like uranium, titanium, chromium, and beryllium. The alloy bond layer is severely attacked by the molten metal. This commonly used layer contributes to the impurity addition to the pure liquid metal. Yttrium oxide was deposited on tantalum substrates (25 mm × 10mm × 1mm thk and 40 mm × 8mm × 1mm thk) by atmospheric plasma spray technique with out any bond coat using optimized coating parameters. Resistance to thermal shock was evaluated by subjecting the coated specimens, to controlled heating and cooling cycles between 300K to 1600K in an induction furnace in argon atmosphere having ≤ 0.1ppm of oxygen. The experiments were designed to examine the sample tokens by both destructive and non-destructive techniques, after a predetermined number of thermal cycles. The results upto 24 thermal cycles of 25 mm × 10mm × 1mm thk coupons and upto 6 cycles of 40 mm × 8mm × 1mm thk coupons are discussed. The coatings produced with the optimized parameters were found to exhibit excellent thermal shock resistance.

Preparation of Pyrochlore Potassium Tantalate Thin Films on Ta/ITO Glass via Mild Hydrothermal Growth

Potassium tantalate with perovskite structure (KTaO 3 ) is an incipient ferroelectric material that has promising functions in electromechanical and sensing sectors. Potassium tantalate with pyrochlore structure (K 2 Ta 2 O 6 ) appears promising in a photocatalystic field. Potassium tantalate powders and bulks were fabricated at high temperature such as over 400°C from Ta 2 O 5 and KOH. A sheet of tantalum was hard to react with potassium hydroxide in the mild hydrothermal condition at 100-150°C and low alkaline concentrations (0-2M). Pyrochlore potassium tantalate film was synthesized with a mild hydrothermal method (100-150°C) at short reaction time by using a sputtered tantalum substrate on ITO glass. Synthesis of this film employed significantly low concentrations of KOH solution (0.1-1M). The potassium tantalate film fabricated by the hydrothermal condition of 0.5 M-KOH solution, 100°C and 3h reaction time was a smooth surface and became transparent. The particle size of this film was 150 nm.

Deposition and characterisation of MoSi 2 films

Deposition of MoSi 2 films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi 2 films were prepared directly from stoichiometric MoSi 2 tetragonal target on room temperature and heated substrates (500 °C). Textured MoSi 2 films having privileged (110) and (115) orientations and average crystallite size of about 105 nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi 2 films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100 nm and 50 nm on substrates kept at room temperature and at 500 °C, respectively. Vickers hardness for 1.2 μm thick MoSi 2 films on Si(111) substrates resulted to be 15 GPa both at room temperature and 500 °C, while for 0.4 μm thick MoSi 2 films on Ta(211) substrates — 26 GPa at room temperature and 30 GPa at 500 °C.

Electrochemical formation of uranium–zirconium alloy in LiCl–KCl melts

Since zirconium is considered an electrochemically active species under practical conditions of the electrorefining process, it is crucial to understand the electrochemical behavior of zirconium in LiCl–KCl melts containing actinide ions. In this study, the electrochemical codeposition of uranium and zirconium on a solid cathode was performed. It was found that the δ-(U, Zr) phase, which is the only intermediate phase of the uranium–zirconium binary alloy system, was deposited on a tantalum substrate by potentiostatic electrolysis at −1.60 V (vs. Ag +/Ag) in LiCl–KCl melts containing 0.13 in mol% UCl 3 and 0.23 in mol% ZrCl 4 at 773 K. To our knowledge, this is the first report on the electrochemical formation of the δ-(U, Zr) phase. The relative partial molar properties of uranium in the δ-(U, Zr) phase were evaluated by measuring the open-circuit-potentials of the electrochemically prepared δ-phase electrode.

From shelled Ge nanowires to SiC nanotubes

Shelled germanium nanowires up to 100 nm in diameter and several micrometers in length wereprepared by low pressure chemical vapor deposition (LPCVD) of tris(trimethylsilyl)germane(SiMe3)3GeH. Vapors of the precursor were deposited on tantalum substrates in an oven at365 °C. Subsequently, the products were annealed at700 °C in vacuum. The wires consist of a crystalline Ge core surrounded by a two-layer jacket. Thepresence of hexagonal Ge in the core was documented in some of the nanowires. The inner jacketis formed by amorphous germanium, the outer part by an Si/C material. By annealing at900 °C, germanium in the core is expelled and nanotubes formed by the Si/C material remain.The samples were studied by SEM, HRTEM, EDX, FTIR and Raman spectroscopy, andthe XRD technique.