Non‐Invasive High‐Throughput Metrology of Functionalized Graphene Sheets

The utilization of fluorescence quenching microscopy (FQM) for quick visualization of chemical functionalization in relatively large regions of graphene, grown via chemical vapor deposition (CVD), is discussed. Through reactive ion plasma etching, patterns of p‐type CVD‐grown graphene functionalized with fluorine are generated. 4‐(dicyanomethylene)‐2‐methyl‐6‐(4‐dimethylaminostyryl)‐4H‐pyran (DCM) is used as the fluorescent agent. The emission of DCM is quenched to a different extent by fluorinated and pristine graphene, which provides the fluorescence‐imaging contrast essential for this metrology. To probe the functionalized surface patterns with DCM, the dye is dispersed in polymethylmethacrylate (PMMA) then the graphene surface is coated, forming a 30‐nm‐thick DCM‐PMMA layer. Fluorescence images of dye‐coated graphene distinctly reveal the difference between the chemically treated and as‐grown regions. The pristine graphene quenches the DCM emission more efficiently than the fluorinated graphene. Therefore, the regions with pristine graphene appear darker on the fluorescence images than the regions with fluorinated graphene, enabling large‐scale mapping of the functionalized regions in CVD grown graphene sheets Due to its simplicity and consistent results, FQM is now poised for widespread adoption by graphene manufacturers as a basis for facile and high throughput metrology of large‐scale graphene sheets.     

Models for electron and hole mobilities in MOS accumulation layers

We present new physically based effective mobility models for both electrons and holes in MOS accumulation layers. These models take into account carrier-carrier scattering, in addition to surface roughness scattering, phonon and fixed interface charge scattering, and screened Coulomb scattering. The newly developed effective mobility models show excellent agreement with experimental data over the range 1×10¹⁶-4×10¹⁷ cm^-3 for which experimental data are available. Local-field dependent mobility models have also been developed for both electrons and holes, and they have been implemented in the two-dimensional (2-D) device simulators, PISCES and MINIMOS, thus providing for more accurate prediction of the terminal characteristics in deep submicron CMOS devices. In addition, transition region mobility models have been developed to account for the transition in the mobility in going from the accumulation layer in the gate-to-source overlap region to the inversion layer region in the channel     

Influence of humidity on creep response of sandwich beam with a viscoelastic soft core

Polymer foam cored sandwich beams are widely used in load-bearing components due to their high strength to weight ratio. To improve the reliability in using sandwich beams, it is essential to understand their long-term creep response in terms of variation of stresses and deformations with time under external mechanical and environmental stimuli. This paper presents an analytical model for investigating the creep response of sandwich beams made with a viscoelastic soft core, including the effect of the variable ambient humidity under the sustained load and its influence on the creep behavior. The model is based on a high-order viscoelastic structural modeling. The soft core is modeled as a viscoelastic material using differential-type constitutive relations that are based on the linear Boltzman’s principle of superposition and accounting for the deformability of the core in shear and through its thickness. Several numerical examples are presented in order to show the capability of the model and to investigate the effect of moisture on the creep behavior of sandwich beams. Finite element simulations of the creep response of sandwich beams are also performed using ABAQUS software to validate the proposed theoretical model. The results show the concentrations of shear and transverse normal stresses near the edges and their variation in time and with the change of humidity.     

Effect of polyethylenimine on electrophoretic deposition of TiO2 nanoparticles in alternating current electric field

In this work, AC electric field was applied to deposit TiO₂ nanoparticles dispersed in Acetone on coplanar electrodes. The experiments were performed in presence and absence of an additive, polyethylenimine (PEI), at frequencies of 1 Hz and 10 kHz. It was revealed that deposition pattern changed dramatically by addition of PEI which makes particles to fill the inter electrode gap at both frequencies. When PEI is added, particles show different behavior. While they tend to fill the gap randomly at 1 Hz, they form chainlike pattern at 10 kHz. Chain formation of particles in the gap indicates presence of dielectrophoretic (DEP) forces. The ability of particles to polarize in both suspensions at 10 kHz are calculated by a multi-shell model in order to find DEP force. According to this model, the polarizability for particles in the suspension with PEI is more than the other, so DEP forces applied more strongly on them and promotes chain formation.     

Two-dimensional energy-dependent models for the simulation ofsubstrate current in submicron MOSFET's

Two-dimensional energy-dependent substrate current models are described for NMOS and PMOS devices that have been developed using a multi-contour approach. The new models offer a significant improvement in the calculation of substrate current due to a more accurate calculation of the average energy as compared to the local-field model. The models are implemented in a post-processing manner by applying a one-dimensional energy conservation equation to each of many current contours in order to generate a two-dimensional representation of average energy and impact ionization rate, that is then integrated to calculate the substrate current. The new models have been compared to substrate current characteristics of a variety of NMOS and PMOS devices for a wide range of bias conditions and channel lengths, and very good agreement has been obtained with a single set of model parameters. An additional significance of this work is the enhancement of the standard multi-contour model by an energy-sink term that results in an improved prediction of the impact ionization process in PMOSFET's     

An energy-dependent two-dimensional substrate current model for thesimulation of submicrometer MOSFET's

A multicurrent contour, average-energy-based, substrate current model for silicon submicrometer NMOSFETs is presented as a significant improvement to the local-field model that is commonly used in modern drift-diffusion device simulators. The model is implemented as a post-processor by applying a one-dimensional energy conservation equation to many current contours in order to generate a two-dimensional representation of average energy and impact ionization rate which is integrated to calculate the substrate current. Comparisons of simulations and experimental I-V curves for both simple and LDD MOSFETs are presented. Outstanding agreement has been obtained over a wide range of bias conditions and channel lengths     

Thermionic emission model of electron gate current in submicronNMOSFETs

A thermionic emission model based on a non-Maxwellian electron energy distribution function for the electron gate current in NMOSFET's is described. The model uses hydrodynamic equations to describe more correctly the electron transport and gate injection phenomena in submicron devices. A generalized analytical function is used to describe the high-energy tail of the electron energy distribution function. Coefficients of this generalized function are determined by comparing simulated gate currents with the experimental data. This model also includes the self-consistent calculation of the tunneling component of the gate current by using the WKB approximation, and by using a more accurate representation of the oxide barrier by including the image potential. Good agreement with gate currents over a wide range of bias conditions for three different technological sets of devices are demonstrated by using a single set of coefficients     

Synthesis of CuInS2 nanoparticles via simple microwave approach and investigation of their behavior in solar cell

Copper indium sulfide, CuInS₂, nanocrystals were synthesized by a new precursor complex, [bis(2-hyroxyacetophenato)copper(ΙΙ)], [Cu(HAP)₂], via a microwave method. The effects of sulfur sources, solvents, heating time and microwave power on morphology of product were investigated. The as-synthesized CuInS₂ nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy, and room temperature photoluminescence (PL) spectroscopy. The nanoparticles of CuInS₂ were used to prepare CuInS₂ film by doctor's blade technique. The fill factor (FF), open circuit voltage (V_oc), and short circuit current (I_sc) were obtained by I–V characterization.     

Synthesis and characterization of CuInS2 microsphere under controlled reaction conditions and its application in low-cost solar cells

CuInS₂ microspheres were synthesized by Ultrasonic method in propylene glycol as solvent and copper oxalate, indium chloride and thioacetamde (TAA) as precursors. Optimum conditions such as reaction time, solvent type, sulfur source, and ultrasonic power were determined. Then, a thin film of CuInS₂ was prepared and its application in solar cells was investigated. Photovoltaic characteristics such as V_oc, J_sc and FF were measured. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy were performed to characterize the CuInS₂ microsphere. The optical band gap of the CuInS₂ microsphere was estimated to be 2.28 eV.     

Tribological Performance of Bamboo Fabric Reinforced Epoxy Composites

Bamboo fiber is one of the strongest natural fibers with high strength-to-weight and stiffness-to-weight ratios and can be used economically for manufacturing fiber-reinforced composites. In this paper, bamboo fabric-reinforced epoxy composite is manufactured and its tribological properties for load-bearing applications are investigated. Sliding wear tests are conducted using a linear reciprocating tribometer and the effect of dry and lubricated contact conditions, applied load, sliding speed, temperature, and woven fabric direction on the coefficient of friction and wear rate are investigated. A scanning electron microscope is used to define the wear mechanisms at room and elevated temperatures. It is observed that the fabric orientation influences the mechanical and tribological performances of the composite material. Wear rate increases at higher loads and working temperatures; however, the effect of sliding speed is not remarkable, especially under lubricated contact conditions. The results present in this paper can be used for designing bamboo-reinforced epoxy composites for load-bearing applications, under different working conditions.