This work reports facile and well-controlled synthesis of a number of binary, ternary, and quaternary nanocomposites using combinations of metal oxides (CuO, NiO), multiwalled carbon nanotubes (MWCNTs), and conducting polymer polyaniline (PANI) for application as electrode in supercapacitor. X-ray diffraction and electron microscopic analyses confirmed the formation of different composites made of binary CuO@NiO, ternary CuO@PANI/ MWCNT, NiO@PANI/MWCNT, and quaternary CuO@ NiO/PANI/MWCNT nanocomposites. Such combination of materials has not been reported previously, and with specific capacitance of 1372 F g −1 and good cyclic stability (83% capacity retention after 1500 cycles), the quaternary nanohybrid electrode shows the best performance compared to all other binary and ternary electrodes tested and promises to be a very good electrode material for supercapacitor application. The improved performance of the quaternary nanocomposite is attributed to the well-designed structural advantages and the synergistic effects of the components that lead to significant reduction in the charge transfer resistance as revealed by electrochemical impedance spectroscopy. Thus, we show a simple method to control the charge storage capacity of CuO-and/ or NiO-based electrodes by suitable selection of their surface morphology and combining with MWCNT and PANI. The results may have large potential in the development of novel electrode materials for a supercapacitor using CuO and/or NiO and may be further extended to other transition-metal-oxide-based electrodes.

No abstract

No abstract

Diode-like threshold switching and high on/off ratio characteristics by using an Al/Ag/Al2O3/TiN conductive bridge resistive random access memories (CBRAM) have been obtained. The 5 nm-thick Al2O3 device shows superior memory parameters such as low forming voltage and higher switching uniformity as compared to the 20 nm-thick switching layer, owing to higher electric field across the material. Capacitance-voltage (CV) characteristics are observed for the Ag/Al2O3/TiN devices, suggesting the unipolar/bipolar resistive switching phenomena. Negative capacitance (NC) at low frequency proves inductive behavior of the CBRAM devices due to Ag ion migration into the Al2O3 oxide-electrolyte. Thicker Al2O3 film shows diode-like threshold switching behavior with long consecutive 10,000 cycles. It has been found that a thinner Al2O3 device has a larger on/off ratio of >108 as compared to a thicker one. Program/erase (P/E) cycles, read endurance, and data retention of the thinner Al2O3 oxide-electrolyte shows superior phenomena than the thicker electrolyte. The switching mechanism is also explored.

Resistive switching characteristics by using the Al2O3 interfacial layer in an Al/Cu/GdOx/Al2O3/TiN memristor have been enhanced as compared to the Al/Cu/GdOx/TiN structure owing to the insertion of Al2O3 layer for the first time. Polycrystalline grain, chemical composition, and surface roughness of defective GdOx film have been investigated by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). For bipolar resistive switching (BRS) characteristics, the conduction mechanism of high resistance state (HRS) is a space-charge limited current for the Al/Cu/GdOx/TiN device while the Al/Cu/GdOx/Al2O3/TiN device shows Schottky emission. However, both devices show Ohmic at a low resistance state (LRS). After the device has been SET, the Cu filament evidences by both TEM and elemental mapping. Oxygen-rich at the Cu/GdOx interface and Al2O3 layer are confirmed by energy dispersive X-ray spectroscopy (EDS) line profile. The Al/Cu/GdOx/Al2O3/TiN memristor has lower RESET current, higher speed operation of 100 ns, long read pulse endurance of > 109 cycles, good data retention, and the memristor with a large resistance ratio of > 105 is operated at a low current of 1.5 µA. The complementary resistive switching (CRS) characteristics of the Al/Cu/GdOx/Al2O3/TiN memristor show also a low current operation as compared to the Al/Cu/GdOx/TiN device (300 µA vs. 3.1 mA). The transport mechanism is the Cu ion migration and it shows Ohmic at low field and hopping at high field regions. A larger hopping distance of 1.82 nm at the Cu/GdOx interface is obtained as compared to a hopping distance of 1.14 nm in the Al2O3 layer owing to a larger Cu filament length at the Cu/GdOx interface than the Al2O3 layer. Similarly, the CRS mechanism is explained by using the schematic model. The CRS characteristics show a stable state with long endurance of > 1000 cycles at a pulse width of 1 µs owing to the insertion of Al2O3 interfacial layer in the Al/Cu/GdOx/Al2O3/TiN structure.