A new well-aligned cone-shaped nanostructure of polypyrrole (WACNP) has been successfully grown on Au substrate by using a simple, one-step, reliable, and template-free anodic deposition method. The formation mechanism of WACNP is proposed, in which the hydrogen bonding introduced from phosphate buffer solution (PBS) promotes the formation of a well-aligned nanostructure of polypyrrole (PPy), while the steric hindrance effect arisen from high concentration of pyrrole (Py) boosts its vertical alignment and further forms a cone-shaped nanostructure. The 3D, arrayed, nanotubular architecture coated with an ultrathin layer of RuO2 by the magnetron sputtering deposition method was tailored to construct a supercapacitor. The unique structure and design not only reduces the diffusion resistance of electrolytes in the electrode material but also enhances its electrochemical performance. The modification of RuO2 on WACNP results in a capacitance higher than that of WACNP by three times. The specific capacitance of RuO2/WACNP is 15.1 mF cm−2 (∼302 F g−1) measured by the charge−discharge method with an applied current density of 0.5 mA cm−2 over a potential range of −0.2 to 0.7 V, and is greater than that of commercial carbon materials by 2−3 orders of magnitude. The high capacitance and good stability of the RuO2/WACNP electrode is very promising for applications in microsupercapacitor devices.
Nitrogen doped SrTiO 3 (STO) thin films have been fabricated on Si field emitter arrays (FEAs) using reactive RF magnetron sputtering in Ar-N 2 mixture ambient for electron emission applications. The nitrogen incorporation in STO films was revealed both in Fourier transform infrared (FTIR) spectroscopy and in Auger electron spectroscopy (AES). Low dose incorporation of nitrogen in STO films shows enhanced crystallinity, whereas the overdosed films show the degraded perovskite structure. The results demonstrate that the threshold emission field is lowered tremendously from 36.24 V/μm for uncoated FEAs to 17.37 V/μm for 30-nmthick STO coated FEAs deposited in 50% N 2 ambient. The enhanced electron emission characteristics are highly correlated with the nitrogen incorporation in STO and film thickness. The substitution of nitrogen for oxygen may result in the band-gap narrowing in STO with enhanced electron emission. The thickness dependence might be related to the formation of space-charge-induced band-bending interlayer at STO/Si interface.
The properties of superalloys are typically deteriorated by the coarsening of the nano-sized γ′ phase, which is the primary strengthening component at high temperatures. Stabilizing the γ′ phase represents one of the key challenges in developing next-generation superalloys. Herein, we fabricate a cobalt-nickel-based superalloy with a nanoscale coherent γ′ phase, (Ni,Co) 3 (Al,Ti,Nb), which is isolated by stacking-fault ribbons in the alloy matrix as a result of the Suzuki segregation of alloying atoms. Additionally, we demonstrate that this new nanostructure can slow down the coarsening of the γ′ phase at high temperatures. As a result, the cobalt-nickel-based superalloy displays considerably high tensile yield points, exceeding 1650 MPa at room temperature and 1250 MPa at 973 K, which are markedly higher than those of the commonly used nickel-and cobalt-based superalloys. This study thereby paves a new path for developing superalloys with exceptional mechanical performance and thermal stability. INTRODUCTIONGeometrically close-packed and coherent A 3 B-type (A = Ni, Co; B = Al, Ti, and so on) γ′ phases exist in various high-temperature superalloys, and this substantially affects their mechanical performance. 1,2 One of the most critical issues currently restraining the service life of these superalloys lies in the coarsening of the nanoscale γ′ phase upon exposure to high temperatures. To date, much effort has been devoted to probing the morphology of the γ′ phase and to clarifying its coarsening mechanism upon aging in cobalt-and nickel-based superalloys. 3-9 It has been predicted by the Lifshitz-Slyozov-Wagner model 10,11 that coarsening of the γ′ phase in superalloys follows the general relationship r 3 = kt, where r is γ′ phase particle radius, t is the aging time and k is the coarsening-related rate constant.In general, the coarsening of the γ′ phase in superalloys is a diffusion process where large particles grow at the expense of smaller ones in the alloy matrix; this is termed Ostwald ripening. [12][13][14] The factors that predominantly control the coarsening rate of the γ′ phase include the γ/γ′ phase interfacial energy, the solubility of the γ′ phase in the γ phase and the diffusion coefficient of the constituent elements of the γ′ phase through either the γ/γ′ phase interface or the γ phase matrix. 15 Typical values of the interfacial energy of the γ/γ′ phase have been clearly demonstrated to be~20 mJ m − 2 , 15 a value that is very low and essentially remains stable. In addition, for a given material system, the solubility of small γ′ phase particles and the diffusion coefficient of the constituent elements of the γ′ phase in the
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