Search

BiFeO3 thin films are deposited on FTO coated glass substrates using a simple sol-gel deposition technique, limiting thickness about 70 nm and Ag/BiFeO3/FTO RRAM devices are prepared. The devices showed low-voltage bipolar switching with the maximum Ion/Ioff ~ 450, and low set and reset voltages ~ 1.1 V and -1.5 V, respectively. The devices are stable against on-off cycles with ~ 104 s retention time without any significant degradation. The variations in the set and reset voltages are 0.4 V and 0.6 V, respectively. We found that ohmic and trap-controlled space charge limited conductions are responsible for low and high resistance states, respectively. The resistive switching mechanism is attributed to the formation and rupturing of the metal filament during the oxidation and reduction of Ag ions for the set and reset states., 15 Pages, 4 Figures, Submitted for publication in Journal of American Ceramic Society

Zinc oxide (ZnO) and zinc rich zinc oxide (Zn:ZnO) thin films are synthesized using vapor phase trapping assisted thermal chemical vapor deposition (CVD) process. X-ray diffraction measurements indicate the highly textured c-axis growth for Zn:ZnO thin films as compared to ZnO thin film structures. The observed insignificant change in lattice parameters suggests that excess Zn is in interstitial sites. The optical studies substantiate that the excess Zn in ZnO matrix is contributing to the point defects, with integrated luminescence towards the light blue color with respect to that for the pristine ZnO thin film. The electronic carrier concentration is about four orders of magnitude higher for Zn:ZnO thin films, causing Burstein-Moss shift of ∼0.13 eV in Zn:ZnO thin films.

BiFe 0.99 Cr 0.01 O 3 thin film is deposited on FTO glass using sol-gel technique. The deposited film is used in Ag/ BiFe 0.99 Cr 0.01 O 3 /FTO configuration to understand its potential as RRAM device. The device showed forming free bipolar RRAM characteristics with Ion/Ioff~80. The device showed non-volatile behaviour by maintaining its LRS and HRS states for 104 s. The device exhibits excellent reproducibility up to 100 cycles and reliability of V set and V reset voltage is observed. The endurance characteristics for 200 cycles ensures the stability of the device, further, conduction mechanism is attributed to filament formation and switching mechanism is assigned to migration of silver ion inside the film.

Ureolytic-type bacteria has been used to improve the strength of cement mortar by the precipitation of calcium carbonate. In the present study Bacillus sphaericus has been used to improve the properties of cement mortar such as setting time, compressive strength and sorptivity. The setting time is found to be unaffected by the presence of bacteria. It is found that compressive strength at both 7-days and 28-days of mortar cube increases with the increase of bacteria concentration. At the optimum bacteria dosage of 107 cells/ml, the average compressive strength increases by 58% (at 7 day) and 23% (at 28 day) over the control specimen. The sorpitivity coefficient decreases as the concentration of bacterial cells increases. The mineralogy and morphology of the calcium carbonate precipitation have been tested by XRD and FESEM.

n-ZnO nanorod/p-si hetrojunction diode is synthesized using a simple chemical solution method on p-type silicon substrates for light emitting diode applications. The grown ZnO nanorods showed highly textured hexagonal crystallographic phase along c-axis. An intense band to band photoluminescence peak is observed at 377 nm in conjunction with the weak deep-level emissions in visible region centred at 500 nm. The current–voltage measurements show diode-like characteristics. The work will also discuss the emission response with bias field for these solution processed n-ZnO/p-Si heterostructures under dark and UV conditions in the context of possible UV photo-response and light emitting diode applications.

BiFeO3 based resistive random access memory (RRAM) devices are fabricated using a low-cost solution process to study the effect of an Al top electrode on switching behavior and reliability. Fabricated devices demonstrated bipolar switching characteristics with a moderate Ion/Ioff ratio, set and reset voltages of ∼−1.3 V and ∼0.8 V, DC and AC endurance of more than 250 cycles and 7100 cycles, respectively, and a retention time of over 104 s, confirming the non-volatile resistive switching behavior. The ohmic and trap filled space charge limited conduction dominates the conduction mechanism in the devices at lower and higher voltages, respectively. Moreover, impedance spectroscopy measurements substantiate the presence of an AlOx layer at the Al/BiFeO3 interface resulting from the Al–O interaction at the junction, which is the possible rationale of reliable complementary switching in these RRAM devices. The switching mechanism is elucidated using the formation and rupture of the oxygen vacancy mediated filament, assisted by the participation of a thin AlOx layer at the Al/BFO interface. The role of the thin AlOx layer is explained by modeling of impedances.