Ahmad I. Ayesh

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 2u2009×u2009105 is achieved at low reading voltage of 1u2009V. 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 Characteristics of Hybrid-Organic Memory Devices Based on Au Nanoparticles

We report on the fabrication and characterization of hybrid-organic memory devices based on gold (Au) nanoparticles that utilize metal–insulator–semiconductor structure. Au nanoparticles were produced by sputtering and inert-gas condensation inside an ultrahigh-vacuum compatible system. The nanoparticles were self-assembled on a silicon dioxide (SiO2)/silicon (Si) substrate, then coated with a poly(methyl methacrylate) (PMMA) insulating layer. Aluminum (Al) electrodes were deposited by thermal evaporation on the Si substrate and the PMMA layer to create a capacitor. The nanoparticles worked as charge storage elements, while the PMMA is the capacitor insulator. The capacitance–voltage (C–V) characteristics of the fabricated devices showed a clockwise hysteresis with a memory window of 3.4xa0V, indicative of electron injection from the top Al electrode through the PMMA layer into Au nanoparticles. Charge retention was measured at the stress voltage, demonstrating that the devices retain 94% of the charge stored after 3xa0h of continuous testing.

Metal/Metal-Oxide Nanoclusters for Gas Sensor Applications

The development of gas sensors that are based on metal/metal-oxide nanoclusters has attracted intensive research interest in the last years. Nanoclusters are suitable candidates for gas sensor applications because of their large surface-to-volume ratio that can be utilized for selective and rapid detection of various gaseous species with low-power consuming electronics. Herein, nanoclusters are used as building blocks for the construction of gas sensor where the electrical conductivity of the nanoclusters changes dramatically upon exposure to the target gas. In this review, recent progress in the fabrication of size-selected metallic nanoclusters and their utilization for gas sensor applications is presented. Special focus will be given to the enhancement of the sensing performance through the rational functionalization and utilization of different nanocluster materials.

Single-Walled Carbon-Nanotubes-Based Organic Memory Structures

The electrical behaviour of organic memory structures, based on single-walled carbon-nanotubes (SWCNTs), metal–insulator–semiconductor (MIS) and thin film transistor (TFT) structures, using poly(methyl methacrylate) (PMMA) as the gate dielectric, are reported. The drain and source electrodes were fabricated by evaporating 50 nm gold, and the gate electrode was made from 50 nm-evaporated aluminium on a clean glass substrate. Thin films of SWCNTs, embedded within the insulating layer, were used as the floating gate. SWCNTs-based memory devices exhibited clear hysteresis in their electrical characteristics (capacitance–voltage (C–V) for MIS structures, as well as output and transfer characteristics for transistors). Both structures were shown to produce reliable and large memory windows by virtue of high capacity and reduced charge leakage. The hysteresis in the output and transfer characteristics, the shifts in the threshold voltage of the transfer characteristics, and the flat-band voltage shift in the MIS structures were attributed to the charging and discharging of the SWCNTs floating gate. Under an appropriate gate bias (1 s pulses), the floating gate is charged and discharged, resulting in significant threshold voltage shifts. Pulses as low as 1 V resulted in clear write and erase states.

PbS/CdS heterojunction quantum dot solar cells

The present work investigates the effects of combination of lead sulfide PbS quantum dots and cadmium sulfide CdS nanoparticles (NPs), with n-type and p-type semiconductors, on the photovoltaic performance of heterojunction solar cells. Namely, p-type semiconductors are: poly[3,4-ethylenedioxythiophene]–poly[styrenesulfonate] (PEDOT:PSS), copper oxide (CuO) NPs and graphene oxide (GO); while n-type semiconductors are: zinc oxide (ZnO) NPs and titanium dioxide (TiO2) NPs. The above were used to fabricate heterojunction solar cell structures via spin coating, chemical bath deposition and SILAR cycle methods. The morphology and energy band diagram for each solar cell were examined. The photovoltaic performance of the cells was measured under 1 sun illumination (irradiation of 100 mW/cm2). This efficiency ranged between 0.388 and 5.04xa0%. The solar cell with FTO/ZnO/TiO2/CdS/PbS/PEDOT:PSS/Au structure and optimum layers’ thickness exhibited a short-circuit current of 24.2xa0mA/cm2, open circuit voltage of 544xa0mV, a fill factor of 38.2xa0% and a power conversion efficiency of 5.04xa0% with reliably good stability. This is related to the uniform surface morphology throughout every cell layer without voids, pinholes or cracks. Furthermore, gradual band energy levels alignment of n-type and p-type NPs (CdS/PbS), as well as high hole mobility of PEDOT:PSS and the high electron affinity of ZnO and TiO2 are other major factors that controls quantum efficiency.

Synthesis and properties of phase-change Ge-Sb nanoparticles

We report on the synthesis and characterization of Ge15Sb85 phase-change nanoparticles by magnetron plasma sputtering and inert-gas condensation inside an ultra-high vacuum compatible system. Electrical and optical properties of Sb-rich nanoparticles for phase-change memory applications have been examined. The results show that phase-change properties of Ge15Sb85 material still exist for nanoparticles of 8.0 nm size. The amorphous to crystalline transformation proceeds at moderately elevated temperature (∼473 K) which shows that Ge15Sb85 nanoparticles are a good candidate for phase-change memory applications in terms of long data retention time. The observed phase transition in Ge15Sb85 nanoparticles is promising for down scaling the size of phase change solid-state memory devices.

Graphene-based nanopore approaches for DNA sequencing: A literature review

DNA (deoxyribonucleic acid) is the blueprint of life as it encodes all genetic information. In genetic disorder such as gene fusion, copy number variation (CNV) and single nucleotide polymorphism, DNA sequencing is used as the gold standard for successful diagnosis. Researchers have been conducting rigorous studies to achieve genome sequence at low cost while maintaining high accuracy and high throughput, as such sequencer devices have been developed which led to the evolvement of this technology. These devices are categorized into first, second, and third DNA sequencing generations. One successful endeavor for DNA sequencing is nanopore sequencing. This specific method is considered desirable due to its ability to achieve DNA sequencing while maintaining the required standards such as low cost, high accuracy, long read length, and high throughput. On the other hand, non-nanopore sequencing techniques require extensive preparation as well as complex algorithms, and are restricted by high cost, small throughput, and small read lengths. In this review, the concepts, history, advances, challenges, applications, and potentials of nanopore sequencing are discussed including techniques and materials used for nanopore production and DNA translocation speed control. Additionally, in light of the importance of the nanopore material configuration and fabrication, graphene which is a common and effective material will be discussed in the context of nanopore fabrication techniques. Finally, this review will shed light on some nanopore-related investigations in the area of molecular biology.

Organic Floating Gate Memory Structures

The evolution of information and communication technologies in the last few years resulted in more demands for new data storage systems benefit from higher storage capacities. The new applications and devices in the market such as high definition TVs, iPADs, iPODs, Kindles, MP3s and smart phones operate through the storage of large amounts of data. Most of these devices are portable for everyday use for communication or entertainment purposes.