Cation intercalated one-dimensional manganese hydroxide nanorods and hierarchical mesoporous activated carbon nanosheets with ultrahigh capacitance retention asymmetric supercapacitors.

We have reported the electrochemical performance of K+ ion doped Mn(OH)4 and MnO2 nanorods as a positive electrode and a highly porous activated carbon nanosheet (AC) made from Prosopis Juliflora as negative electrode asymmetric supercapacitor (ASC) with high rate capability and capacity retention. The cation K+ doped Mn(OH)4 and MnO2 nanorods with large tunnel sizes allow the electrolyte to penetrate through a well-defined pathway and hence benefits from the intercalation pseudocapacitance and surface redox reactions. As a result, they exhibit good electrochemical performance in neutral aqueous electrolytes. More specifically, the K+-Mn(OH)4 nanorods exhibit higher capacitance values than K+-MnO2 nanorods due to the homogenous distribution of 1D nanorods and optimum amount of OH bonds. The fabricated K+-Mn(OH)4 symmetric electrochemical Pseudocapacitor shows very high energy density of 10.11 Wh/kg and high-power density of 51.04 W/kg over the range of 1.0 V in aqueous electrolyte. The energy density of AC||K+-Mn(OH)4 ASC is improved significantly compared to those of symmetric supercapacitors. The fabricated ASC exhibits a wide working voltage window (1.6 V), high power (143.37 W/kg) and energy densities (41.38 Wh/kg) at 0.2 A g-1, and excellent cycling behavior with 107.3% capacitance retention after 6000 cycles at 2 A g-1 indicating the promising practical applications in electrochemical supercapacitors.

Revealing the Self-Degradation Mechanisms in Methylammonium Lead Iodide Perovskites in Dark and Vacuum.

Organic-inorganic lead halide perovskite phases segregate (and their structures degrade) under illumination, exhibiting a poor stability with hysteresis and producing halide accumulation at the surface.In this work, we observed structural and interfacial dissociation in methylammonium lead iodide (CH3 NH3 PbI3 ) perovskites even under dark and vacuum conditions. Here, we investigate the origin and consequences of self-degradation in CH3 NH3 PbI3 perovskites stored in the dark under vacuum. Diffraction and photoelectron spectroscopic studies reveal the structural dissociation of perovskites into PbI2 , which further dissociates into metallic lead (Pb0 ) and I2- ions, collectively degrading the perovskite stability. Using TOF-SIMS analysis, AuI2- formation was directly observed, and it was found that an interplay between CH3 NH3+ , I3- , and mobile I- ions continuously regenerates more I2- ions, which diffuse to the surface even in the absence of light. Besides, halide diffusion causes a concentration gradient between Pb0 and I2- and creates other ionic traps (PbI2- , PbI- ) that segregate as clusters at the perovskite/gold interface. A shift of the onset of the absorption band edge towards shorter wavelengths was also observed by absorption spectroscopy, indicating the formation of defect species upon aging in the dark under vacuum.

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors.

High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm(2)/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers.

Wettability control and water droplet dynamics on SiC-SiO2 core-shell nanowires.

We present a simple method for fabricating superhydrophobic SiC-SiO(2) core-shell nanowire surfaces via the facile dip-coating of alkyltrichlorosilanes. Water droplets displayed a variety of shapes with varying surface energies on the nanowire surfaces, which could be modified through chemisorption of alkyltrichlorosilanes with variable carbon chain length. The effects of UV irradiation on the superhydrophobic nanowire arrays were also investigated. UV light efficiently decomposed the chemisorbed molecules, and the superhydrophobic surface gradually converted into a hydrophilic surface with increasing UV exposure. The water droplet impact behavior on the modified surfaces was studied to test the stability of the superhydrophobicity under dynamic conditions.

Synthesis of Novel Double-Layer Nanostructures of SiC-WO(x) by a Two Step Thermal Evaporation Process.

A novel double-layer nanostructure of silicon carbide and tungsten oxide is synthesized by a two-step thermal evaporation process using NiO as the catalyst. First, SiC nanowires are grown on Si substrate and then high density W(18)O(49) nanorods are grown on these SiC nanowires to form a double-layer nanostructure. XRD and TEM analysis revealed that the synthesized nanostructures are well crystalline. The growth of W(18)O(49) nanorods on SiC nanowires is explained on the basis of vapor-solid (VS) mechanism. The reasonably better turn-on field (5.4 V/mum) measured from the field emission measurements suggest that the synthesized nanostructures could be used as potential field emitters.

Synthesis and Characterization of ZnO Nanowire-CdO Composite Nanostructures.

ZnO nanowire-CdO composite nanostructures were fabricated by a simple two-step process involving ammonia solution method and thermal evaporation. First, ZnO nanowires (NWs) were grown on Si substrate by aqueous ammonia solution method and then CdO was deposited on these ZnO NWs by thermal evaporation of cadmium chloride powder. The surface morphology and structure of the synthesized composite structures were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The optical absorbance spectrum showed that ZnO NW-CdO composites can absorb light up to 550 nm. The photoluminescence spectrum of the composite structure does not show any CdO-related emission peak and also there was no band gap modification of ZnO due to CdO. The photocurrent measurements showed that ZnO NW-CdO composite structures have better photocurrent when compared with the bare ZnO NWs.

Growth and characterization of stoichiometric tungsten oxide nanorods by thermal evaporation and subsequent annealing.

Stoichiometric tungsten oxide (WO(3)) nanorods are synthesized on tungsten (W) substrates by a high-temperature, catalyst-free, physical deposition process and by subsequent annealing in oxygen atmosphere. Tungsten oxide nanorods are grown by thermal evaporation of WO(3) powder at elevated temperature in a tube furnace. XRD, TEM and XPS analysis shows that the as-grown nanorods are single crystalline and non-stoichiometric (WO(x)). Annealing of WO(x) nanorods at 700 °C under oxygen atmosphere has led to the formation of stoichiometric WO(3) as evidenced by XRD, XPS and Raman analysis.