Mehdi Saeidmanesh

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.

The effect of concentration on gas sensor model based on graphene nanoribbon

Graphene nanoribbon (GNR), a superior material with two-dimensional structure and monolayer honeycomb of carbon, is noteworthy and important in all fields’ mainly electronic, chemistry, biology, physics and nanotechnology. Recently, observing about sensors demonstrates that for better accuracy, faster response time and enlarged sensitivity, it needs to be improved. Nowadays, carbon-based equipments as an exclusive substance are remarkable in the sensing technology. High conductivity as unique properties caused that graphene can be used in biological applications. Gas sensor based on graphene can be supposed to have great sensitivity for gas molecules detection. In this study, graphene-based carbon dioxide sensor analytically is modeled. In addition, new methods of gas sensor model based on the gradient of GNR conductance are provided. Also, a field effect transistor-based structure as a modeling platform is suggested. Ultimately, optimum model is evaluated by comparison study between analytical model and experimental performance.

Sensitivity Modelling of Graphene Nanoscroll-Based NO2 Gas Sensors

Graphene nanoscrolls (GNSs) as a new category of quasi one-dimensional (1D) belong to the carbon-based nanomaterials, which have recently captivated the attention of researchers. The latest discoveries of exceptional structural and electronic properties of GNSs like high mobility, controllable band gap, and tunable core size have become a great stimuli for graphene researchers. Due to the importance and critical role of nanoscale sensors and biosensors in medical facilities and human life, using a promising material like graphene has been widely studied to achieve better accuracy and sensitivity in these devices. Up until now, the majority of surveys conducted previously have focused on experimental studies for sensors family. Therefore, there is lake of analytical models in comparison to experimental surveys. In order to start and understand about the modelling of gas sensors structure, the field effect transistor(FET)-based structure is employed as a basic. In this study, graphene nanoscroll conductivity has been evaluated under the impacts which is induced by the adsorption of different values of NO2 gas concentration on GNS surface. So that, when GNS-gas sensor is exposed to NO2 gas molecules, the carrier concentration of GNS is changed which leads to the changes in the conductance, and consequently, in the current, this phenomenon is considered as sensing mechanism. The I–V characteristic of graphene nanoscroll-based gas sensor has been considered as a criterion to detect the effect of gas adsorption. In order to verify the accuracy of the proposed model, the results have been compared with the existing experimental works.

Carrier statistics and quantum capacitance models of graphene nanoscroll

As a new category of quasi-one-dimensional materials, graphene nanoscroll (GNS) has captivated the researchers recently because of its exceptional electronic properties like having large carrier mobility. In addition, it is admitted that the scrolled configurations for graphene indicate larger stability concerning the energy, as opposed to their counterpart planar configurations like nanoribbon, nanotube, and bilayer graphene. By utilizing a novel analytical approach, the current paper introduces modeling of the density of state (DOS), carrier concentration, and quantum capacitance for graphene nanoscroll (suggested schematic perfect scroll-like Archimedes spiral). The DOS model was derived at first, while it was later applied to compute the carrier concentration and quantum capacitance model. Furthermore, the carrier concentration and quantum capacitance were modeled for both degenerate and nondegenerate regimes, along with examining the effect of structural parameters and chirality number on the density of state and carrier concentration. Latterly, the temperature effect on the quantum capacitance was studied too.

Analytical modeling of the sensing parameters for graphene nanoscroll-based gas sensors

Graphene nanoscrolls (GNSs) as a new category of quasi one dimensional (1D) materials belong to the carbon-based nanomaterials, which have recently captivated the attention of researchers. The latest discoveries of the outstanding characteristics of GNSs in terms of their structural and electronic properties such as, high mobility, controllable band gap, tunable core size, high mechanical strength, high sensing capability and large surface-to-volume ratio make them a great candidate for nanoelectronic devices in future work. Due to the importance and critical role of nanoscale sensors and biosensors in medical facilities and human life, using promising materials like graphene and graphene nanoscrolls has widely attracted the interest and attention of researchers to achieve better accuracy and sensitivity in these devices. Up until now, the majority of surveys conducted previously have focused on experimental studies for sensors. Therefore, there is a lack of analytical models in comparison to experimental surveys. In order to start and understand the modeling of gas sensor structure, the field effect transistor (FET)-based structure has been employed as a basic model for a gas detection sensor. The graphene nanoscroll conductance has been affected under exposure to the NH3 gas molecules. The adsorption of NH3 gas concentration on the GNSs surface which is caused by a chemical reaction between NH3 and the GNSs. Therefore it makes the changes in the GNS conductance and current–voltage characteristics of the proposed GNS based gas sensor. This phenomenon is considered as the sensing mechanism with proposed sensing parameters. The I–V characteristics of a GNS-based sensor have been proposed as a criterion to detect the effect of gas adsorption. Finally, in order to verify the accuracy of the proposed model, the results are compared with the existing experimental works.

Threshold voltage roll-off modelling of bilayer graphene field-effect transistors

An analytical model is presented for threshold voltage roll-off of double gate bilayer graphene field-effect transistors. To this end, threshold voltage models of short- and long-channel states have been developed. In the short-channel case, front and back gate potential distributions have been modelled and used. In addition, the tunnelling probability is modelled and its effect is taken into consideration in the potential distribution model. To evaluate the accuracy of the potential model, FlexPDE software is employed with proper boundary conditions and a good agreement is observed. Using the proposed models, the effect of several structural parameters on the threshold voltage and its roll-off are studied at room temperature.

Analytical model for threshold voltage of double gate bilayer graphene field effect transistors

A new model for threshold voltage of double-gate Bilayer Graphene Field Effect Transistors (BLG-FETs) is presented in this paper. The modeling starts with deriving surface potential and the threshold voltage was modeled by calculating the minimum surface potential along the channel. The effect of quantum capacitance was taken into account in the potential distribution model. For the purpose of verification, FlexPDE 3D Poisson solver was employed. Comparison of theoretical and simulation results shows a good agreement. Using the proposed model, the effect of several structural parameters i.e. oxide thickness, quantum capacitance, drain voltage, channel length and doping concentration on the threshold voltage and surface potential was comprehensively studied.

Analytical study of subthreshold behaviour of double gate bilayer graphene field effect transistors

In this paper, several analytical models have been developed for 2-D potential distribution, subthreshold current, drain induced barrier lowering (DIBL), and subthreshold-slope (SS) to study the subthreshold behaviour of bilayer graphene filed effect transistors (BLG-FETs). The models are grounded on the basis of the exact solution of the two-dimensional Poisson’s equation while the quantum capacitance effect has been considered throughout the models. The accuracy of the potential distribution model is verified by its analytical results that agree well with those of the FlexPDE Poissonʼs equation solver program. In addition, the effects of the channel length, the oxide thickness, quantum capacitance, and gate biases on subthreshold parameters of BLG-FETs have been explored and the results are compared with those of the silicon FETs.

Channel Length Modulation Effect on Monolayer Graphene Nanoribbon Field Effect Transistor

It is common and fundamental technique for developments of hydrogen storage materials to investigate atomic arrangements of hydrogen during the absorption and desorption process. Since neutron is sensitive probe against hydrogen, the structural environment of hydrogen in atomic scale is clarified by neutron scattering method. High intensity total diffractometer, NOVA, was constructed in the pulsed neutron facility of Japan Proton Accelerator Research Complex (J開PARC).The most characteristic feature of NOVA is that it covers a wide scale of atomic distance from nearest neighbor to several ten nano meters by wide-Q (momentum transfer) measurement in short-time. By Fourie,r transformation of the obtained wide-Q diffraction data, Pair Distribution Function (PDF) useful for the analysis of disordered structures can be derived with high real-space resolution. On NOVA, both the wide-d space crystal structure analysis (Rietveld analysis) and the high -resolution PDF analysis can be performed. This means that various structures of crystals, amorphous and liquids for hydrogen storage materials are elucidated with NOVA. Aluminum hydride, Lanthanum hydride under GPa pressure and so on have been analyzed. Furthermore, time-transient measurement during hydrogen absorption and desorption process under hydrogen gas atmosphere (max 10 MPa) have been equipped on NOVA. It is expecting that structural analysis with NOVA will accelerate developments of hydrogen storage materials by industries.T is currently an unmet need for an optimal biomaterial that can substitute for autograft bone or serve as a temporary matrix that can induce regeneration of native bone at implant sites. Developing scaffolds that mimic the architecture of bone tissue at the nanoscale level and that parallel the physical properties of bone tissue in the categories of mechanical strength, pore size, porosity, hardness, and overall three-dimensional (3D) architecture is one of the major focuses in the field of tissue engineering. Our specific objective is to design 3D synthetic biodegradable scaffolds comprising electrospun nanofibers that will not only be osteoconductive but also contain porosity for bone cell ingrowth enhanced with Mesenchymal Stem Cells (MSCs) and a sufficient amount of bioactive ingredients such as Demineralized Bone Matrix (DBM) that would serve as a more conducive framework for cell adhesion, proliferation, and differentiation. Our central hypothesis is that the MSCs can migrate inside the functionalized 3D nanoscaffold to produce abundant extracellular matrix and differentiate into bone cell lineages, and that incorporation of DBM into the network of nanofibers will enhance osteogenesis and bone formation. The rationale for the proposed research is that if such complex constructs can mimic the native in vivo microenvironment, they could provide a promising nanotechnology based surgical tool for bone tissue engineering directed at orthopedic and bone tissue clinical applications.N the scientists are faced with the challenging development of highly sensitive multiple protein detection methods. The outstanding physicochemical properties of noble metal nanoparticles enable to envisage them as robust and versatile support to developing nanotags encapsulated in an antibody-functionalized nanostructure that is active in surface enhanced Raman scattering (SERS). This optical sensing technology allows single molecule detection with high potential to simultaneous recognition of closely related targets based on the narrow bandwidths of the vibrational Raman spectra of the reporter molecules. In this presentation, we will demonstrate how one-spot detection of multiple proteins in parallel can be efficiently achieved by using SERS encoded probes consisting of noble metal NPs each reporting unique Raman code and antibody-tagging entities. Further, this study may contribute to the development of targeting, tracking, and imaging systems for labelling cells..Purpose: The available implantable dosimeters in radiotherapy,i.e. semiconductor, MOSFET, radio luminescence of gallium nitride, etc, are imperfect and need a correction factors. In this study,we probos by simulation the size limit for a new generation of dosimeters at micro/nano scale for real time measurements in routine radiotherapy. Materials & Methods: Monte-Carlo simulations were carried out to study the influence of nanodosimeter size on the accuracy in dose measurements using a water volume irradiated with 60Co photons. The mean specific energy ( ), characterizing the actual deposited dose, was calculated for variousdose values and various radii of cylindrical targets placed within the irradiated volume. Then, the probability that a measurement yields a value outside the intervals [ -γ ; +γ ] with γ equal to 3%, 5% and 10% was calculated. Results & Discussion: The distributions for the smallest target show a very high dispersion of specific energy values, while those for the largest target tend to become gaussian and narrower, with increasing dose. An excessively small radius renders the measurements chaotic and not statistically-reproducible, even for a dose as high as 10 Gy. On the other hand, a target radius of 10 μm may allow for a better reproducibility of the measurements in a wider range of doses. Conclusion: The ability of the nano dosimeter to yield measurements dependent on its size and on the deposited dose.Nano dosimeter should be large enough to produce a statistically-reproducible measurement in the intended range around the irradiation dose value. Biography Abdulhamid Chaikh, has completed his PhD at Grenoble-Alpes University, France. He was qualified for Assistant Professor position in French University. He is working as scientist for Medical Physics & Radiation Oncology and teaching in master degree at the medical school of Grenoble-Alpes University. He has published more than 15 papers in international journals and participated to over 15 national and international conferences. He is carrying out peer reviewed articles and serving as an Editorial Board Member of the Journal of Case Reports in Oncology and Therapy. He is a member of American Association of Physicists in Medicine.T importance of nanostructures made by plasmonic metals, e.g., silver or gold, has been recognized by many researchers because plasmon resonance of such nanostructures, which is a resonant oscillation of conduction electrons stimulated by incident light, causes unique plasmonic properties including surface enhanced spectroscopy, acceleration of photo-catalysis and photo-thermotherapy. Controlling the synthesis and assembly of those metallic nanostructures has been of particular interest and several methods, e.g., random/self-assembly, bond formation and nanolithography, are well established. However, these methods have limitations for fabrication cost and time, thus, more efficient techniques are required to satisfy the basic industrial needs. In recent years, Galvanic Displacement Reaction (GDR) is rediscovered as a rapid and cost-effective technique for preparing various plasmonic nanostructures. Various kinds of nanostructures have been synthesized by GDR. However, most previous works have some limitations in creating efficient plasmonic nanostructures because during GDR processes, nanostructures tend to elongate and overlap with each other, preventing efficient production of plasmonic hot spots. To solve this problem, we introduced a novel GDR for the synthesis of silver Nano-Hexagonal Thin Columns (NHCs). NHCs synthesized generate strong surface-enhanced Raman scattering signals of adsorbates. Thus, they have a potential to be used widely across industry. Multi-elements depth profile analysis of NHCs by X-ray photoelectron spectroscopy shows that NHCs have a less conductive layer on their outermost surface, resulting that NHCs are kept from fusion and high-density plasmonic hot spots remain.