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Controlled Growth of Highly Aligned Cu Nanowires by Pulse Electrodeposition in Nanoporous Alumina
No full textMetallic nanowire networks are emerging as potential replacements for transparent conducting oxide coatings because of their high conductivity, flexibility and relative transparency. However, a cheap, reliable and controlled manufacturing process is required to exploit this and the surface of the copper nanowire needs to be protected if high conductivity is to be retained. In this study a fabrication method for highly aligned and densely packed copper nanowires with controlled length using pulse-electrodeposition and a nanoporous alumina template has been developed. Nanoporous alumina was obtained by anodisation of pure aluminum in oxalic acid using a two-step anodisation process. In order to provide the conductivity at the bottom of the pores, a dendritic structure at the interface was created through the stepwise voltage reduction method with a voltage reduction rate of 15 V/s followed by mild chemical etching. Highly repeatable near 100% filling of copper is achieved. Copper nanowire length was highly controllable from 100 nm to 2 mu m with a fixed diameter of 60 +/- 5 nm by monitoring current density during the deposition. Such controlled growth of Cu nanowires could lead towards transparent conducting layer applications but the protection of the material against oxidation remains an issue
Dielectric based charge carrier tuning for CNT CMOS inverters
No full textThe realization of Carbon nanotube (CNT) based CMOS compatible complementary logic circuits is one of the bottlenecks that needs to be overcome in order to consider CNTs as an alternative to silicon in future CMOS technology. In this work, we demonstrate complementary logic inverters using solution-processed CNTs. The type of charge carriers in the CNT field effect transistors (FET) have been tuned by changing the dielectric environment to realize both p-type and n-type CNTFETs. We have fabricated p-type CNTFETs using electron beam evaporated HfO2 as the top-gate dielectric and n-type CNTFETs using plasma enhanced chemical vapor deposition grown Silicon nitride as the top-gate dielectric. Using this fabrication approach, we realize high performance p- and n-CNTFETs employing regular metals such as Palladium for the source/drain contacts instead of rare earth metal contacts such as scandium. We demonstrate complementary logic inverters with a DC gain as high as 6.7 and operating voltages within 1 V
A new DNA sensor system for specific and quantitative detection of mycobacteria
No full textIn the current study, we describe a novel DNA sensor system for specific and quantitative detection of mycobacteria, which is the causative agent of tuberculosis. Detection is achieved by using the enzymatic activity of the mycobacterial encoded enzyme topoisomerase IA (TOP1A) as a biomarker. The presented work is the first to describe how the catalytic activities of a member of the type IA family of topoisomerases can be exploited for specific detection of bacteria. The principle for detection relies on a solid support anchored DNA substrate with dual functions namely: (1) the ability to isolate mycobacterial TOP1A from crude samples and (2) the ability to be converted into a closed DNA circle upon reaction with the isolated enzyme. The DNA circle can act as a template for rolling circle amplification generating a tandem repeat product that can be visualized at the single molecule level by fluorescent labelling. This reaction scheme ensures specific, sensitive, and quantitative detection of the mycobacteria TOP1A biomarker as demonstrated by the use of purified mycobacterial TOP1A and extracts from an array of non-mycobacteria and mycobacteria species. When combined with mycobacteriophage induced lysis as a novel way of effective yet gentle extraction of the cellular content from the model Mycobacterium smegmatis, the DNA sensor system allowed detection of mycobacteria in small volumes of cell suspensions. Moreover, it was possible to detect M. smegmatis added to human saliva. Depending on the composition of the sample, we were able to detect 0.6 or 0.9 million colony forming units (CFU) per mL of mycobacteria, which is within the range of clinically relevant infection numbers. We, therefore, believe that the presented assay, which relies on techniques that can be adapted to limited resource settings, may be the first step towards the development of a new point-of-care diagnostic test for tuberculosis
Quadratic to linear magnetoresistance tuning in TmB4
No full textThe change of a material's electrical resistance (R) in response to an external magnetic field (B) provides subtle information for the characterization of its electronic properties and has found applications in sensor and storage related technologies. In good metals, Boltzmann's theory predicts a quadratic growth in magnetoresistance (MR) at low B and saturation at high fields. On the other hand, a number of nonmagnetic materials with weak electronic correlation and low carrier concentration for metallicity, such as inhomogeneous conductors, semimetals, narrow gap semiconductors and topological insulators, and two dimensional electron gas, show positive, nonsaturating linear magnetoresistance (LMR). However, observation of LMR in single crystals of a good metal is rare. Here we present low-temperature, angle-dependent magnetotransport in single crystals of the antiferromagnetic metal, TmB4. We observe large, positive, and anisotropic MR(B), which can be tuned from quadratic to linear by changing the direction of the applied field. In view of the fact that isotropic, single crystalline metals with large Fermi surface (FS) are not expected to exhibit LMR, we attribute our observations to the anisotropic FS topology of TmB4. Furthermore, the linear MR is found to be temperature independent, suggestive of quantum mechanical origin
Design and Experimental Validation of a Robust Output Feedback Control for the Coupled Dynamics of a Micro Air Vehicle
No full textThis paper addresses the design and experimental validation of a linear robust static output feedback controller for a 150 mm span fixed wing micro air vehicle (MAV). Severe coupling between longitudinal and lateral dynamics of the MAV lead to the design of a multivariable controller for the combined dynamics. The control design problem is posed in the framework of static output feedback (SOF) due to the inexpensive computational requirements for implementation. The multiobjective control design problem including stability requirements, closed loop damping ratio requirements and H norm minimization is solved using the hybrid technique of linear matrix inequalities (LMI) and genetic algorithm (GA). The design is carried out in the discrete time domain, facilitating in direct implementation of the multivariable controller in the onboard autopilot hardware. The robustness of the resulting closed loop system under parametric uncertainties is evaluated using structured singular value analysis. The effectiveness of the proposed controller is demonstrated through outdoor flight trial of the micro air vehicle with a customized lightweight autopilot hardware
The spatio-temporal variability of groundwater storage in the Amazon River Basin
No full textIn large Tropical River basins such as the Amazon, groundwater plays a major role in the water and ecological cycles with large influences on the rainforest ecosystems and climate variability. However, due to the lack of monitoring networks, Amazon groundwater storage and its variability remain poorly known. Here, we provide an unprecedented direct estimate of the spatio-temporal variations of the anomaly of groundwater storage over the period January 2003 -September 2010 in the Amazon Basin by decomposing the total terrestrial water storage measured by the Gravity Recovery and Climate Experiment (GRACE) mission into the individual contributions of other hydrological reservoirs, using multi-satellite data for the surface waters and floodplains and models outputs for the soil moisture. We show that the seasonal variations of groundwater storage represent between 20 and 35% of the terrestrial water storage seasonal volume variations of the Amazon. Larger seasonal amplitudes of groundwater storage (>450 mm) are found in the Alter do Chao and Ica aquifers in the central part of the Amazon Basin. Anomalies of groundwater storage exhibit a strong interannual variability (STD reaching 120 mm along the central corridor) during the study period in response to hydrologic variability and climatic events such as the extreme drought that occurred in 2005
Time-Temperature Scaling and Dielectric Modeling of Conductivity Spectra of Single-Ion Conducting Liquid Dendrimer Electrolytes
No full textWe discuss here the time temperature scaling and dielectric modeling of the variation of single-ion conductivity with frequency of first generation (G(1)) liquid dendrimer electrolyte, viz., Poly(propyl ether imine) (PETIM):Li-salt. The PETIM:Li-salt electrolyte exhibits a cation/anion transference number close to unity in the liquid state. On switching from an ester (G(1)-COOR) to cyano (G(1),-CN)peripheral group, keeping constant the linker (ether) and branching groups (amine), an interesting transformation from cationic (t(+) similar to 1) to anionic conductor(t(-) similar to 1) takes place. The switch in the nature of the predominant charge carrier is directly related to the change in the magnitude of anion diffusion (D-), which increases by 1 order of magnitude from D- = 1.1 x 10(-12) m(2) s(-1) (at 30 degrees C) in G(1)-COOR to D- = 1.3 x 10(-11) m(2) s(-1) (at 30 degrees C) in G(1)-CN. This intriguing ion transport mechanism is probed comprehensively using ac-impedance spectroscopy. The frequency dependent ionic conductivity of G(1)-CN/G(1)-COOR, comprised of distinct frequency regimes, is analyzed using the time temperature superposition scaling principle (TTSP) based on Summerfield and Baranovski scaling methods. To gain insight into the electrical polarization (EP) phenomenon, the relevant frequency regime is converted from conductivity to dielectric versus frequency. The dielectric versus frequency data is modeled using Macdonald and Coelho. The combined approach of TTSP and dielectric modeling provide explicitly the extent of the influence of ion dendrimer, ion ion interactions, and also the mobile charge carrier density on the effective ion transport in the homogeneous single-ion conducting dendrimer electrolytes. The combined analysis suggests that ion transport in PETIM-COOR is only due to enhanced ion mobility, whereas in PETIM-CN it is due to both mobile charge carrier concentration and ion mobility. To the best of our knowledge, the scaling and modeling approaches employed here constitute a rare example for validation of such concepts in the context of dendrimer electrolytes
Enhanced sodium-ion storage capability of P2/O3 biphase by Li-ion substitution into P2-type Na0.5Fe0.5Mn0.5O2 layered cathode
No full textIntegration of P2 and O3 phases in Na0.5Fe0.5Mn0.5O2 cathode via Li-ion substitution is proposed to enhance its electrochemical performance for sodium-ion battery applications. The formation of P2 and the combination of P2/O3 intergrowth were confirmed by X-ray diffraction refinement, high resolution transmission electron microscopy and X-ray photoelectron microscopy analyses. Various content of lithium was used to find optimum P2+O3 combinations. The optimized Li-ion substituted Na-0.5(Li0.10-Fe0.45Mn0.45)O-2 showed a high initial discharge capacity of 146.2 mAh g(-1) with improved cycling stability, whereas the pristine Na0.5Fe0.5 Mn0.5O2 initially delivered a discharge capacity of 127.0 mAh g(-1). In addition, the combination of P2+O3 increased its average voltage, which is important for achieving high energy density sodium-ion batteries. Overall, the prepared Na-0.5 (Li0.10Fe0.45Mn0.45)O(2)electrode exhibited the improved cycling performance in terms of reversible capacity and rate capability compared to pristine Na0.5Fe0.5Mn0.5O2 electrode material. (C) 2018 Elsevier Ltd. All rights reserved
The dual role of ozone-treated aluminum doped zinc oxide for CH3NH3PbI3 solar cells
No full textWe present perovskite solar cells using ozone-treated aluminum doped zinc oxide (AZO:O-3) in the dual role: as a transparent electrode and as an electron transport layer (ETL). Aluminum doped zinc oxide (AZO) replaces the conventional FTO/TiO2(c)/TiO2(m) stack, considerably simplifying the fabrication process and reducing thermal budget. Photoelectron spectroscopy suggests that AZO is an effective ETL for perovskite (CH3NH3PbI3) thin films, with a large valence band offset and a small conduction band offset, but with a possible path for carrier recombination at the interface. We show that treating the surface of AZO with ozone gas (AZO:O-3) improves the charge carrier extraction at the interface. Detailed characterization of the AZO:O-3/CH3NH3PbI3 interface shows that ozone reduces the oxygen vacancies and de-dopes top 6-9 nm of the AZO surface. The gradient in doping induces an electric-field at the AZO surface which enhances the carrier extraction. AZO:O-3/CH3NH3PbI3/spiro-OMeTAD/Au devices show champion J(SC), V-OC and eta of 20.92 mA/cm(2), 1.03 V and 10.5% respectively. Meanwhile, average short-circuit current density (J(SC)) has improved from 16.32 mA/cm(2) (AZO) to 19.74 mA/cm(2) (AZO:O-3). This is attributed to the induced electric-field at AZO:O-3 surface leading to an enhanced extraction of photo-generated charge carriers. Devices hysteresis is also much lower than previously reported results
Experimental investigation of heat transfer over double disk spike-blunt body at Mach 5.7
No full textThe forefront research in the territory to the regime of hypersonic flow is intended to focus on improving the overall performance of the existing aerospace vehicle. Two major hindrances for the development of an effective high speed vehicle are aerodynamic drag acts against the vehicle and heat transfer rate on the body. In this study, we explore the possibility of addressing this issue by placing an aerospike at the nose portion (Le., stagnation region) of the high speed vehicle and as a result, wave drag of vehicle is considerably reduced. However, this will lead to the increase in heat transfer at the localized spot of the main body. In an attempt to reduce this localized high heat transfer, the current study evaluates the variation in the heat transfer on the body, by modifying the spike through the addition of a smaller hemisphere on the mid-section of the aerodisk spike. In this regard, shock tunnel experiments and computational studies were carried out on this modified spike configuration, termed as ``double-disk spike'' or ``double spike''. The experimental results indicate that heat transfer near the localized spot of the blunt body with spike decreases for a double spike case in comparison to single disk spike. The decrease in heat transfer varies from 5% to 30% depending on the double spike configuration (i.e. varying cap radius and length of the spike). To supplement these results, 3D Finite Volume simulation, ``HiFUN'' (High Resolution Flow Solver on Unstructured), showed a good trend in heat transfer compared to that obtained from the experiment; it was found that simulated drag from the double spike is less than single spike case