Mohammed F. Mabrook

Effect of composition on the electrical conductance of milk

Abstract The contribution of the various components in cow’s milk to its electrical conductivity has been studied using the technique of admittance spectroscopy. Measurements at 100 kHz and 8 °C confirm previous observations that the milk conductance is predominantly determined by the salt fraction. Lactose showed very little effect on the conductivity, while the presence of fat resulted in a decrease in the milk conductance with increasing fat content. Sodium caseinate possessed a very low conductance; nevertheless, we suggest that the physical and chemical nature of the casein micelles can influence the overall milk conductivity.

A pentacene-based organic thin film memory transistor

An organic memory device based on a pentacene thin film transistor is demonstrated. Gold nanoparticles have been used as the charge storage elements while a thin film of polymethylmethacrylate formed the gate insulator. The electrical characteristics and the memory behavior of the organic thin film memory transistor (OTFMT) are reported. Under an appropriate gate bias (1 s pulses), the gold nanoparticles are charged and discharged, resulting in significant threshold voltage shifts of the OTFMT. The detailed programing and erasing procedures are reported.

An inkjet-printed chemical fuse

Inkjet printing of the conductive polymer poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid has been used as the basis for a sensor for organic vapors. The electrical resistance of the film was monitored as it was exposed to atmospheres containing alcohol. Ultrathin films exhibited a sharp and nonreversible increase in their resistance. This resulted from a change in the morphology of the organic layer, thereby disrupting the current flow through the polymer. An intended application for these inkjet-printed devices is in disposable handheld instruments to monitor the presence of organic vapors above a threshold level.

Electronic memory device based on a single-layer fluorene-containing organic thin film

The authors report on a simple bistable switching device based on a thin film of an electroactive polymer containing a fluorene group sandwiched between aluminum electrodes. No additional materials (e.g., metallic or semiconductive nanoparticles) are required for the devices to operate. This improves considerably the scalability of the memory elements at nanometer dimensions. The device operation is thought to depend on charge trapping at fluorenone defects within the organic film.

Organic bistable devices utilizing carbon nanotubes embedded in poly(methyl methacrylate)

The electrical and memory behavior of organic bistable memory devices in the form of metal-embedded insulator-metal (MIM) structure are described. The devices utilize layer-by-layer (LbL) deposited single walled carbon nanotubes (SWCNTs) as charge traps embedded between two polymethylmethacrylate (PMMA) insulating layers. The stack was sandwiched between two aluminium electrodes to form an Al/PMMA/SWCNTs/PMMA/Al structure. The current-voltage (I-V) characteristics of the devices exhibit electrical bistability and non-volatile memory characteristics in terms of switching between high conductive (ON) and low conductive (OFF) states. The different conductive states were programmed by application of a positive and negative voltage pulse for the ON and OFF states, respectively. A maximum ON/OFF ratio of 2 × 105 is achieved at low reading voltage of 1 V. Space-charge-limited-current (SCLC) conduction model was used to describe the carriers transport and the electrical bistability in the devices, which was attri...

Electrical behavior of memory devices based on fluorene-containing organic thin films

We report on switching and negative differential resistance (NDR) behaviors of crossed bar electrode structures based on Al/organic layer/Al devices in which the organic layer was a spin-coated layer of 7-{4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-9,9-dihexyl-N,N-diphenyl-fluoren-2-amine. The addition of gold nanoparticles (0.5wt%) did not change the switching behavior of thicker film structures; however, devices incorporating the nanoparticles showed more reproducible characteristics. In most cases, a “forming” process, in which a large positive voltage was applied to the top Al electrode, was required before the NDR and conductivity switching were observed. Three different electrical conductivity mechanisms have been identified: Poole–Frenkel conductivity in unformed structures, linear current versus voltage characteristics for the ON state in formed devices, and superlinear current versus voltage behavior for the OFF state in formed devices. Models based on metallic filaments or on the inj...

Mechanism of resistive switching in Cu/AlOx/W nonvolatile memory structures

The mechanism for resistive switching in aluminum oxide (AlOx) based electrochemical metallization memory cells is presented. Copper/AlOx/tungsten (Cu/AlOx/W) cells show reproducible resistive switching with an ON/OFF ratio of about 5 × 102 at a reading voltage of 0.1 V and reliable retention characteristics. Resistive switching occurs due to the formation and rupture of a Cu filament between the active electrode (Cu) and the counter electrode (W). The conduction of the devices was explained through back-to-back Schottky contacts in the OFF state, while it exhibits ohmic behavior in the ON state. Thermionic emission model was used to calculate the barrier heights of the Schottky contacts. The rupture of the Cu filament proved to occur at the weakest point of the filament inside the AlOx. Using Ohms Law, the slope of the linear I-V characteristics in the ON state was used to extract the Cu filament resistance and its diameter was estimated to be between 6 and 23 nm.

Charge Storage in Pentacene/Polymethylmethacrylate Memory Devices

The electrical behavior of organic metal-insulator-semiconductor (MIS) structures incorporating a layer of self-assembled metallic nanoparticles is described. These have been based on thermally evaporated pentacene (semiconductor) and spin-coated polymethylmethacrylate (insulator). The MIS devices containing the nanoparticles exhibited significant hysteresis in their capacitance-versus-voltage and conductance-versus-voltage characteristics, which was attributed to the charging and discharging of the nanoparticles. The memory structure reported here offers a useful advance in the development of flexible organic memory structures.

Floating-gate memory based on an organic metal-insulator-semiconductor capacitor

A floating gate memory element is described which incorporates an evaporated gold film embedded in the gate dielectric of a metal-insulator-semiconductor capacitor based on poly(3-hexylthiophene). On exceeding a critical amplitude in the voltage sweep, hysteresis is observed in the capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the device. The anticlockwise hysteresis in C-V is consistent with strong electron trapping during the positive cycle but little hole trapping during the negative cycle. We argue that the clockwise hysteresis observed in the negative cycle of the I-V plot, arises from leakage of trapped holes through the underlying insulator to the control gate.

Quality control of dairy products using single frequency admittance measurements

A reusable device for the detection of adulteration in dairy products such as milk and cream has been developed. The ac electrical admittance spectra of different samples have been studied using both uncoated and alkyl mercaptan-coated gold electrodes. Uncoated gold electrodes exhibited a polarization at around 250 Hz for full fat milk, while mercaptan-coated gold electrodes showed a similar effect at around 2 kHz. The characteristics at 100 kHz and 8 °C for all skimmed milk samples revealed a linear decrease in conductance with increasing water content over the entire range of water concentration. In contrast, the conductance of full fat milk, single and double cream, showed a linear decrease only at added water concentration higher than 6%. At lower concentrations, these dairy products exhibited anomalous conductivity maxima.