Elnaz Akbari

Analytical investigations of gas-sensor using methane decomposition system

AbstractThis paper reports on a set of experiments designed to develop a workable gas sensor prototype using an electronic system with methane. The current is found to be sensitive to the presence of methane gas, which is a conduit for a variety of gas sensors. The sensitivity is shown to depend on pointed or broad electrode configurations. Scanning electron microscopy images show the area of conductance that determines the quality of the electrodes in three configurations. Data processing is performed with a support vector regression algorithm in conjunction with statistical analysis for error and quality control. The reported results can be adapted to a broad range of industrial applications for enhanced productivity, safety, innovation, data processing, and overall total quality management.

Analytical calculation of sensing parameters on carbon nanotube based gas sensors

Carbon Nanotubes (CNTs) are generally nano-scale tubes comprising a network of carbon atoms in a cylindrical setting that compared with silicon counterparts present outstanding characteristics such as high mechanical strength, high sensing capability and large surface-to-volume ratio. These characteristics, in addition to the fact that CNTs experience changes in their electrical conductance when exposed to different gases, make them appropriate candidates for use in sensing/measuring applications such as gas detection devices. In this research, a model for a Field Effect Transistor (FET)-based structure has been developed as a platform for a gas detection sensor in which the CNT conductance change resulting from the chemical reaction between NH3 and CNT has been employed to model the sensing mechanism with proposed sensing parameters. The research implements the same FET-based structure as in the work of Peng et al. on nanotube-based NH3 gas detection. With respect to this conductance change, the I–V characteristic of the CNT is investigated. Finally, a comparative study shows satisfactory agreement between the proposed model and the experimental data from the mentioned research.

Gas Concentration Effects on the Sensing Properties of Bilayer Graphene

Graphene is a single-atom thin layer with sp2 hybridized and two-dimensional (2D) honeycomb structure of carbon. Because of its exclusive properties including high conductivity, high surface area and high mechanical strength, graphene has attracted a great deal of attention of many researchers in chemistry, physics, biology, nanoelectronics and nanotechnology in the recent years. Due to the fact that different kinds of nanoscale sensors including gas sensors and biosensors are playing important roles in human life, the idea of using promising materials such as graphene to achieve accuracy and higher speed in these devices is becoming a matter of attention. Although there are plenty of experimental studies in this field, the lack of analytical models is felt deeply. To start with modelling, the field effect transistor (FET)-based structure is employed as a platform and graphene conductivity has been studied under the impacts induces by the adsorption of different values of gas concentration on its surface. The reaction between graphene and gas makes new carriers in graphene which cause changes in the carrier concentration and consequently alters the conductance. In the presence of gas, electrons are donated to or withdrawn from the FET channel and this phenomenon is employed as a sensing mechanism. The I–V characteristic of bilayer graphene (BLG) has been incorporated as a measure to study the effects of gas adsorption. In order to assess the accuracy of the proposed models, the obtained results are compared with the existing experimental data and acceptable agreement is reported.

Graphene Nanoribbon Based Gas Sensor

Mono layer graphene (MLG) as a new kind of advanced material is in our focus. MLG indicates a twodimensional structure with quantum confinement effect in its thickness. The MLG based nanomaterial has remarkable potential on electrochemical catalysis and bio-sensing applications. Recently inter sheet sensing systems for graphene sensor have been reported which will be used in our model as well. We provide a new idea of electrochemical sensors based on the graphene application. In this paper carrier the concentration on the sensor as a function of gas concentration is reported. A field effect transistor (FET) base structure as a modeling platform is proposed. Gate voltage representing the gas concentration on the sensor, or in other words the gate voltage as a function of gas concentration can be employed. Finally the proposed model is used in simulation studies and evaluated by experimental result.

Analytical prediction of liquid-gated graphene nanoscroll biosensor performance

The latest discovery of the graphene nanoscroll has provided enormous new stimuli to carbon nanoresearch. Due to its one-dimensional structure and tunable core size, the graphene nanoscroll is suitable for nanoscale applications such as in nanotransistors, and biosensor devices. DNA sensing is critical in the identification of the genetic risk factors associated with complex human diseases, and continues to have an emerging role in therapeutics and personalized medicine. This paper presents the analytical model of liquid-gated field effect transistors (LGFETs) for zig-zag graphene nanoscrolls (ZGNSs) inspired by carbon nanotube behavior when exposed to DNA molecules. First of all, in order to gain physical insight into GNS-based devices, the conductance of GNSs is analytically modelled. Based on the sensing mechanism of the DNA sensor, GNS controlling elements (ηGNS and eGNS) are proposed and the behavior of LGFETs-based GNS nanomaterial in the presence of DNA molecules is predicted to get a greater insight into the rapid development of DNA sensors and their application. Because of the channel-doping effect due to the adsorption of the DNA molecules, the conductance of the channel is altered. On the other hand, the applied voltage effect in the form of tilted electron energy levels is utilized in the form of normalized Fermi energy variation which is used in the sensor modelling. This study emphasizes the promising nature of carbon nanoscrolls for a number of electronic device applications.

An analytical approach to evaluate the performance of graphene and carbon nanotubes for NH3 gas sensor applications

Summary Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds great potential for applications in variety of sensors because of dangling π-bonds that can react with chemical elements. In spite of their excellent features, carbon nanotubes (CNTs) and graphene have not been fully exploited in the development of the nanoelectronic industry mainly because of poor understanding of the band structure of these allotropes. A mathematical model is proposed with a clear purpose to acquire an analytical understanding of the field-effect-transistor (FET) based gas detection mechanism. The conductance change in the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules is emphasized. NH3 has been used as the prototype gas to be detected by the nanosensor and the corresponding current–voltage (I–V) characteristics of the FET-based sensor are studied. A graphene-based gas sensor model is also developed. The results from graphene and CNT models are compared with the experimental data. A satisfactory agreement, within the uncertainties of the experiments, is obtained. Graphene-based gas sensor exhibits higher conductivity compared to that of CNT-based counterpart for similar ambient conditions.

Analytical modeling of trilayer graphene nanoribbon Schottky-barrier FET for high-speed switching applications

Recent development of trilayer graphene nanoribbon Schottky-barrier field-effect transistors (FETs) will be governed by transistor electrostatics and quantum effects that impose scaling limits like those of Si metal-oxide-semiconductor field-effect transistor s. The current–voltage characteristic of a Schottky-barrier FET has been studied as a function of physical parameters such as effective mass, graphene nanoribbon length, gate insulator thickness, and electrical parameters such as Schottky barrier height and applied bias voltage. In this paper, the scaling behaviors of a Schottky-barrier FET using trilayer graphene nanoribbon are studied and analytically modeled. A novel analytical method is also presented for describing a switch in a Schottky-contact double-gate trilayer graphene nanoribbon FET. In the proposed model, different stacking arrangements of trilayer graphene nanoribbon are assumed as metal and semiconductor contacts to form a Schottky transistor. Based on this assumption, an analytical model and numerical solution of the junction current–voltage are presented in which the applied bias voltage and channel length dependence characteristics are highlighted. The model is then compared with other types of transistors. The developed model can assist in comprehending experiments involving graphene nanoribbon Schottky-barrier FETs. It is demonstrated that the proposed structure exhibits negligible short-channel effects, an improved on-current, realistic threshold voltage, and opposite subthreshold slope and meets the International Technology Roadmap for Semiconductors near-term guidelines. Finally, the results showed that there is a fast transient between on-off states. In other words, the suggested model can be used as a high-speed switch where the value of subthreshold slope is small and thus leads to less power consumption.

Current–voltage modeling of graphene-based DNA sensor

Graphene is considered as an excellent biosensing material due to its outstanding and unique electronic properties such as providing large area detection, ultra-high mobility and ambipolar field-effect characteristic. In this paper, general conductance model of DNA sensor-based graphene is obtained, and the electrical performance of nanostructured graphene-based DNA sensor is evaluated by the current–voltage characteristic. As a result, by increasing the complementary DNA concentration, the drain current is going toward higher amounts.

Bilayer graphene application on NO 2 sensor modelling

Graphene is one of the carbon allotropes which is a single atom thin layer with sp2 hybridized and two-dimensional (2D) honeycomb structure of carbon. As an outstanding material exhibiting unique mechanical, electrical, and chemical characteristics including high strength, high conductivity, and high surface area, graphene has earned a remarkable position in todays experimental and theoretical studies as well as industrial applications. One such application incorporates the idea of using graphene to achieve accuracy and higher speed in detection devices utilized in cases where gas sensing is required. Although there are plenty of experimental studies in this field, the lack of analytical models is felt deeply. To start with modelling, the field effect transistor- (FET-) based structure has been chosen to serve as the platform and bilayer graphene density of state variation effect by NO2 injection has been discussed. The chemical reaction between graphene and gas creates new carriers in graphene which cause density changes and eventually cause changes in the carrier velocity. In the presence of NO2 gas, electrons are donated to the FET channel which is employed as a sensing mechanism. In order to evaluate the accuracy of the proposed models, the results obtained are compared with the existing experimental data and acceptable agreement is reported.

Silicene and graphene nano materials in gas sensing mechanism

Silicene, the Si analogue of graphene, has recently extended the short list of existing two-dimensional (2D) atomic crystals. There are many remarkable electrical properties as well as unique thermal conductivities associated with graphene and silicene making them perfect materials that possess great potential to replace and provide an even better performance than silicon in future generation semiconductor devices. It is expected that novel devices developed with these will be much faster and smaller in size than their contemporary counterparts. Although graphene and silicene display different electrical conductivity behavior, their carrier concentration has similar behavior. The current–voltage characteristics of silicene/graphene field effect transistors (FETs) have been demonstrated at different operating temperatures under the flow of different NH3 gas concentrations. It was found that in similar conditions, the suggested model for a gas sensor based on graphene shows higher electrical conductivity compared to silicene.