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Temperature dependent switching of magnetoresistance in multiwall carbon nanotube-polypyrrole composite fibrils
No full textCarbon nanotubes (CNT) are considered one of the most significant materials in nanoelectronic device applications because they can be used in the fabrication of both CNT-inorganic hybrid structures and CNT-organic composite materials. Also, the study of the electrical properties of these materials has its own fundamental and technological significance. Here, we report on low temperature charge transport characteristics (down to 4.2 K in the magnetic fields up to 11 T) of multiwall carbon nanotube (MWCNT)-polypyrrole (PPy) coaxial composite fibrils synthesized by a facile electrochemical polymerization method. Two types of samples were synthesized by carrying out electrochemical polymerization at room temperature (RT) for different durations of 90 and 45 min, respectively. Scanning electron microscopy studies indicated that the diameters of as-prepared MWCNT-PPy fibril samples were similar to 1.5 mu m and 0.5 mu m, respectively. The dc electrical resistance of the two samples was similar to 10(3) and 10(2) Omega at RT and exhibited a pronounced temperature dependence, which is indicative of the hopping process being dominant. Furthermore, a large positive magnetoresistance (MR) of similar to 29% and similar to 18% is displayed at 4.2 K, which switched to negative MR with a maximum magnitude of similar to 11% and similar to 15% at 10 K for the two samples, respectively. The switching of MR as a function of temperature showed the dominance of two important competing phenomena, namely, wave function shrinkage and forward interference of electron waves. Published under license by AIP Publishing
Double-L Cantilever-Based Fiber Bragg Grating Accelerometer
No full textOptical accelerometers, especially the fiber Bragg grating accelerometers are the preferred sensors for vibration, and acceleration measurement in several fields of engineering. They are light, compact, immune to electromagnetic interference, and provide better noise immunity due to wavelength encoded nature of signal transduction. In the present work, analytical modeling, numerical simulation, fabrication, and characterization of a novel double-L cantilever based fiber Bragg grating accelerometer is presented. This design not only enhances the sensitivity in comparison to its single-L counterpart, but also provides self-temperature compensation. Modular design of the accelerometer provides flexibility in replacing specific components to achieve desired performance characteristics. Resonant frequency of 86 Hz, sensitivity of 406.7 pm/g with an excellent linearity of 99.86 %, and small temperature sensitivity of 0.016 pm/degrees C have been demonstrated for the fabricated model. The FBG accelerometer has a linear operating range of +/- 6 g
Highly Sensitive CO Sensor Based on Thickness-Selective ZnO Thin Film: Device Fabrication and Packaging
No full textIn this report, the thickness-dependent carbon monooxide (CO)-sensing characteristics of sputtered zinc oxide (ZnO) films are investigated, followed by their morphological and electrical characterizations. ZnO films, approximate to 21nm, show repeatable and high change in their resistances on exposure to CO and the observed maximum response is approximate to 52.2%, whereas approximate to 219nm films fail to show reproducibility in sensing performance. Response and recovery time of approximate to 21nm films are approximate to 28 and 250s, which are faster than the time observed in case of approximate to 219nm films. An approximate to 21nm film is able to resolve 100 parts-per-billions (ppb) CO concentration in air. Later, on-chip integration of approximate to 21nm film is successfully implemented on specifically designed Micro-Electro-Mechanical-System (MEMS) platform, inbuilt with microheater and utilizes power of approximate to 23.7Milliwatts (mW) (375 degrees C). The packaged sensor chip is further tested and qualified for indoor and outdoor detection of CO gas in the atmosphere
PECVD grown silicon nitride ultra-thin films for CNTFETs
No full textAs-fabricated carbon nanotube field effect transistors (CNTFLTs) exhibit p-type nature. In this work, silicon nitride (SiNx) films are deposited on CNTs to realize n-type CNTELTs. This method of fabricating n-type CNTELTs is advantageous as SiNx film serves both as a passivation layer and as a top-gate dielectric. There has been extensive work done on SiNx passivation phenomena previously, but very few have investigated the properties of ultra-thin SiNx films with thickness less than 20 nm. In this work, the ultra-thin SiNx films are deposited using plasma enhanced chemical vapor deposition (PECVD) method. This paper discusses the systematic investigation of the effect of PECVD process parameters such as flow rates of precursor gasses (NH3, SiH4), power of electrodes and deposition temperature on the properties of SiNx films such as refractive index, dielectric constant and stoichiometry. The quality of the SiNx thin films obtained is comparable with several reports that have investigated thicker films Using these ultra-thin SiNx films, we implement a CNTELT based logic inverter. The results indicate that ultra-thin films of SiNx have great potential in future transistor technology
On the Role of Interface States in AlGaN/GaN Schottky Recessed Diodes: Physical Insights, Performance Tradeoff, and Engineering Guidelines
No full textIn this paper, the impact of donor and acceptor states at the Schottky interface of fully recessed AlGaN/GaN Schottky diode is physically modeled using device TCAD and detailed experiments. This allowed us to develop physical insights into recessed AlGaN/GaN diode's reverse breakdown, reverse leakage, and ON-state performance as a function of interface states and provided design guidelines to engineer fully recessed AlGaN/GaN Schottky diode for the maximum reverse breakdown and least reverse leakage without compromising its ON-state performance. It has been observed that donor states are responsible for high reverse leakage and reduced breakdown performance in Schottky diodes. On the other hand, the presence of acceptor states at the interface improves the diode leakage and breakdown voltage. Experiments involve a number of dry and wet surface treatments to: 1) validate computational findings and 2) find ways to cure or passivate donor states affected Schottky interface/recessed region. The introduction of acceptor traps at the Schottky interface has been proposed and experimentally verified using the Fluorine implant to cure donor state-affected Schottky interface, which improves the breakdown and reverse leakage characteristics significantly
Low-Temperature Processing of Printed Field-Effect Transistors from Sublimating-Stabilizer Derived Oxide Nanodispersions
No full textOxide semiconductors are becoming an increasingly attractive choice for solution processed/printed transistors and circuits, as they possess numerous critical advantages over the other printable semiconductor technologies, such as abundance, low-cost, environmental/thermal stability, nontoxicity, and most importantly, excellent electronic transport properties. However, on the downside, there are also major challenges, one of which is their high process temperatures, especially when they are processed from oxide precursors. In order to address this limitation, here, a general recipe for low temperature curable nanodispersions/nanoinks is proposed using aromatic surfactants that sublimates near room temperature. In this regard, stable nanoinks from In2O3 nanoparticles, with high particle loading, are developed using an inexpensive, nontoxic aromatic compound thymol as the stabilizer; while, thymol sublimates near room temperature (<40 degrees C), a quick heating at 100 degrees C is carried out to ensure its complete removal. The printed field-effect transistors from thymol-stabilized nanoinks show an on/off ratio >10(7), a maximum device mobility of 13.5 cm(2) V-1 s(-1), and transconductance values as high as 10 mu S mu m(-1). It is believed that this general route to obtain low temperature curable electronic grade nanodispersions may find applications beyond the printed logic electronics demonstrated in the present study
Non-equilibrium microstructure, crystallographic texture and morphological texture synergistically result in unusual mechanical properties of 3D printed 316L stainless steel
No full textMechanisms underlying the evolution of texture and microstructure during selective laser melting (SLM) and their combined effects on the mechanical response of 316L stainless steel are presented. Long columnar grains with a fiber texture < 110 > || build direction (BD) evolved in the SLM printed material. Fiber texture was stronger in the horizontal build compared to the vertical build. Use of bidirectional scanning strategy enforced epitaxial growth of grains across melt pools present within a single printed layer. < 110> || BD texture evolved as a consequence of maintaining the balance between epitaxy and growth of 100] along maximum thermal gradient. High dislocation density and not grain size effect of the ultra-fine cellular structure, imparted high strength to 316L. Lower average Schmid factor and smaller effective grain size in the horizontal build by virtues of crystallographic and morphological textures, respectively, imparted higher yield strength than the vertical build. The horizontal build demonstrated higher strain hardening rate in the early stages of deformation compared to the vertical build due to higher crystallographic texture dependent twinning. However, the higher rate of dislocation annihilation led to a continuous decline in the strain hardening rate of the horizontal build. In contrast, a stable strain hardening rate was maintained in the vertical build, which led to higher ductility than the horizontal build. In summary, the roles of non-equilibrium microstructure and texture (crystallographic and morphological) in regulating mechanical properties elucidated here, can be utilized in designing additively manufactured structural components of 316L stainless steel
Analysis for unloaded quality factor of a rectangular double-reentrant cavity with circular cylindrical ferrule for klystron using Wheeler's incremental inductance rule
No full textClosed-form formulation for the estimation of equivalent circuit capacitance and inductance of a rectangular double-reentrant klystron cavity with circular cylindrical ferrules was developed and used for arriving at the resonant frequency of the cavity. The closed-form expression for the cavity inductance and resonant frequency were subsequently used for estimating unloaded quality factor of the cavity using Wheeler's incremental inductance rule. The proposed analysis was validated against 3D electromagnetic analysis and measurements for a typical rectangular klystron cavity operating in C-X-bands
Effect of propeller-induced flow on the performance of biplane micro air vehicle dynamics
No full textThis paper presents the analysis of propeller-induced flow effects on the dynamics of a fixed wing biplane micro air vehicle. The analysis is based on wind tunnel tests and mathematical modeling. This analysis plays a pivotal role because the propeller-induced flow has significant effects on the dynamics of fixed wing micro air vehicle due to submergence of a large portion of the wing in propeller slipstream. Although the effect of the propeller-induced flow on the various aerodynamic parameter is reported in the literature; however, its effects on overall forces, moments and vehicle dynamics are not quantified so far. In this paper, propeller-induced flow effects are modeled as a function of motor rotation speed and mathematical analysis is performed to quantify their effects. The wind tunnel test is conducted at different propeller speeds on a biplane micro air vehicle ``Skylark'', having wingspan and chord length of 150 mm and 140 mm, respectively. Analysis of results shows that the propeller slipstream increases the overall lift, drag, side force, range, and endurance significantly. Propeller flow also contributes to the rolling moment and the pitching moment, while it has negligible effects on the yawing moment. It is shown that the trim angle of attack is lower when the propeller flow is considered in computing the trim conditions
High temperature creep-mediated functionality in polycrystalline barium titanate
No full textDislocations in oxides can be described as charged line defects and means for one-dimensional doping, which can tune electrical and thermal properties. Furthermore, theoretically it was shown that dislocations can pin ferroelectric domain walls. Broader application of this concept hinges on the development of a methodology to avail this approach to polycrystalline ceramics. To this end, we use different creep mechanisms as a method to introduce multidimensional defects and quantify structural changes. A deformation map for fine-grained barium titanate is provided and the influences of the defects and creep regimes are correlated in this first study to modifications of electrical conductivity, dielectric, ferroelectric, and piezoelectric properties. A plastic deformation of 1.29% resulted in an increase in the Curie temperature by 5 degrees C and a decrease in electromechanical strain by 30%, pointing toward electromechanical hardening by dislocations