Multiple Operation Cycles Research Articles

Fabrication of stable low voltage organic bistable memory device

Organic bistable memory device was fabricated by spin coating of polymethyl methacrylate (PMMA):ZnO nanoparticles onto ITO coated glass. The thin films were characterized by Raman, SEM, AFM and FTIR spectroscopies. The electrical characterization showed that the two-terminal device exhibited excellent switching characteristics with ON/OFF ratio greater than 2 × 10 3 when the voltage was swept between −2 V and +2 V. The device maintained its state even after removal of the bias voltage. Device did not show degradation after 1-h retention test at 120 °C. The memory functionality was consistent even after multiple cycles of operation and the device is reproducible. The switching mechanism is discussed on the basis of carrier transport mechanism. This demonstration provides a class of memory devices with the potential for extremely low-cost, low-power consumption applications, such as digital memory cell.

All-inorganic spin-cast quantum dot based bipolar nonvolatile resistive memory

We introduce an all-inorganic solution processed bipolar nonvolatile resistive memory device with quantum dot/metal-metal oxide/quantum dot structure. The two terminal device exhibits excellent switching characteristics with ON/OFF ratio >103. The device maintained its state even after removal of the bias voltage. The switching time is faster than 50 ns. Device did not show degradation after 1-h retention test at 150 °C. The memory functionality was consistent even after multiple cycles of operation and the device is reproducible. The switching mechanism is discussed on the basis of charge trapping in quantum dots with metal oxide serving as the barrier.

Cutting Off Communication

Biotechnology![Figure][1] CREDIT: N. KEVITIYAGALA/ SCIENCE Many bacteria communicate with one another through the secretion and uptake of small signaling molecules. If this process, known as quorum sensing, is disrupted, bacterial communities can no longer collectively respond to environmental stresses or cooperatively build complex structures such as biofilms. Yeon et al. have leveraged such a disruption to prevent biofouling—the clogging of membrane pores by accumulated particulate matter and bacteria—in wastewater treatment apparatus. The addition of a deactivating enzyme (acylase) quenched the quorum-sensing signal required for bacteria to form biofilms and thus increased the long-term performance of the filtration membrane. Furthermore, the use of a cell-sized magnetic carrier stabilized the acylase and facilitated its recovery and reuse over multiple operation cycles. Fortunately, the quenching process did not interfere with other beneficial bacterially driven processes in the bioreactor, such as the degradation of solid-phase organic matter. Although acylase is only specific to one type of signaling molecule, this procedure could eventually incorporate additional enzymes to quench the few other known quorum-sensing signals, effectively blocking all bacterial communication channels. Environ. Sci. Technol. 43 , 10.1021/es901323k (2009). [1]: pending:yes

Ion source for ion beam deposition employing a novel electrode assembly

A rf inductively coupled ion source employing a novel electrode assembly for focusing a broad ion beam on a relatively small target area was developed. The primary application of this ion source is the deposition of thin films used in the fabrication of magnetic sensors and optical devices. The ion optics consists of a three-electrode set of multiaperture concave dished grids with a beam extraction diameter of 150 mm. Also described is a variation in the design providing a beam extraction diameter of 120 mm. Grid hole diameters and grid spacing were optimized for low beamlet divergence and low grid impingement currents. The radius of curvature of the grids was optimized to obtain an optimally focused ion beam at the target location. A novel grid fabrication and mounting design was employed which overcomes typical limitations of such grid assemblies, particularly in terms of maintaining optimum beam focusing conditions after multiple cycles of operation. Ion beam generation with argon and xenon gases in energy ranges from 0.3 to 2.0 keV was characterized. For operation with argon gas, beam currents greater than 0.5 A were obtained with a beam energy of 800 eV. At optimal beam formation conditions, beam profiles at distances about equal to the radius of curvature were found to be close to Gaussian, with 99.9% of the beam current located within a 150 mm target diameter. Repeatability of the beam profile over long periods of operation is also reported.