Orders Of Magnitude Change Research Articles

Effect of TiO2 Nanofiller on Electrical Conductivity of ABS/TiO2 Polymer Nanocomposites: A Free Volume Study

Acrylonitrile Butadiene Styrene (ABS) / Titanium dioxide (TiO2) Polymer nanocomposites with different TiO2 wt % were prepared by solution casting method. Microstructural characterization of ABS/TiO2 polymer nanocomposites was performed by Positron Lifetime Spectroscopy. The increased positron lifetime parameters viz., o-Ps lifetime (τ3) and free volume size (Vf) from 0.2 to 1.0 wt% of TiO2 loading suggests the formation of interfaces due to the increased agglomeration of TiO2 nanoparticles. The increase of two orders of magnitude change in electrical conductivity (σ) of ABS/TiO2 polymer nanocomposites with the increasing free volume hole size (Vf) as a function of TiO2 nanoparticles loading . The increased electrical conductivity (σ) with the increased free volume hole sizes (Vf) indicates the increased interfacial space for the movements of charge carriers and TiO2 ions. Miyamoto and Shibayma model for ion conduction has been used to explore the effect of free volume hole size (Vf) on the electrical conductivity (σ) in ABS/TiO2 polymer nanocomposites. Fourier Transform Infrared Spectroscopy (FTIR) suggests the improved chemical and physical interaction between the functional groups of TiO2 and ABS polymer side chain

Electric field induced modulation of transport characteristics in multiferroic BZT–BCT/FeCo thin films

We report the fabrication of 60Ba(Zr0.2Ti0.8)O3–40(Ba0.7Ca0.3TiO3)/Fe65Co35 (60BZT–40BCT/Fe65Co35) films on Pt/Ti/SiO2/Si substrates. The 60BZT–40BCT films exhibit well defined piezoelectric properties and the magnetic properties of Fe65Co35 films were characterized, which suggests the multiferroic nature of the films. The transport characteristics of Fe65Co35 films could be modified when the samples are subjected to a bias voltage along the thickness direction for 60BZT–40BCT/Fe65Co35 films, which manifests itself in the variation of current–voltage (I–V) curves of Fe65Co35 films under the influence of applied bias voltage. This produces more than an order of magnitude change in resistance. The manipulation could be attributed to the strain-mediated coupling and the charge accumulation and depletion at the interface.

A facile hydrothermal approach for the density tunable growth of ZnO nanowires and their electrical characterizations

Controlling properties of one-dimensional (1D) semiconducting nanostructures is essential for the advancement of electronic devices. In this work, we present a low-temperature hydrothermal growth process enabling density control of aligned high aspect ratio ZnO nanowires (NWs) on seedless Au surface. A two order of magnitude change in ZnO NW density is demonstrated via careful control of the ammonium hydroxide concentration (NH4OH) in the solution. Based on the experimental observations, we further, hypothesized the growth mechanism leading to the density controlled growth of ZnO NWs. Moreover, the effect of NH4OH on the electrical properties of ZnO NWs, such as doping and field-effect mobility, is thoroughly investigated by fabricating single nanowire field-effect transistors. The electrical study shows the increase of free charge density while decrease of mobility in ZnO NWs with the increase of NH4OH concentration in the growth solution. These findings show that NH4OH can be used for simultaneous tuning of the NW density and electrical properties of the ZnO NWs grown by hydrothermal approach. The present work will guide the engineers and researchers to produce low-temperature density controlled aligned 1D ZnO NWs over wide range of substrates, including plastics, with tunable electrical properties.

Cladocera assemblages from reservoirs in Sri Lanka and their relationship to measured limnological variables

AbstractThe potential of using surface‐sediment assemblages of Cladocera as bioindicators for reservoirs in Sri Lanka was assessed for their subfossil remains, along with contemporary physical and chemical measurements from each reservoir. The reservoirs span five climatic regions, from extremely arid environments to tropical montane forests, as well as three orders of magnitude changes in many physical and chemical variables. In total, although the remains of 39 Cladocera taxa from 21 genera were identified, only 31 taxa from 37 sites were present at sufficiently high abundances to assess their relation to measured environmental variables. Canonical correspondence analysis (CCA) identified surface area, maximum depth and chloride as the three most important measured environmental variables that could account for the variation in the cladoceran assemblages. Taxa such as Chydorus sphaericus, Alona aff. verrucosa and Leydigia acanthocercoides were more abundant in generally deeper, larger reservoirs, whereas Alonella excisa, Euryalona orientalis, Notoalona globulosa and Chydorus eurynotus were more abundant in shallow smaller reservoirs. Although there was a strong separation between climatic zones in terms of factors related to specific conductance, this factor only appears marginally important in separating cladoceran assemblages. Quantitative inference models developed to assess the strength of inferring environmental variables using partial least squares regression and calibration were all relatively weak, with jackknifed coefficient of determination values of 0.40, 0.28 and 0.27 for surface area, maximum depth and chloride, respectively. These results, in conjunction with large differences in eigenvalues between constrained and unconstrained ordinations, suggest that unmeasured environmental variables are also important in structuring cladoceran assemblages.

Geochemical modelling of livestock mortality leachate transport through the subsurface

Leachate chemistry arising from carcass disposal burial pits may pose a significant threat to the environment. Based on the results of previous studies, models were created to assess these impacts. Simple 2D models using CTRAN were created to evaluate the impacts of three orders of magnitude changes in hydraulic conductivity representative of glacial tills common to Western Canada, as well as impacts of burial trench/pit spacing on the subsurface for a conservative ion. Sorption properties were included in one scenario to provide insight on transport and sorption for ammonium ions based on published distribution coefficients. The conservative and sorption models for the mid-range hydraulic conductivity indicated transport up to 10 m after 100 years with concentrations at 40% and 1% of initial values respectively for the conservative and sorption model. The CTRAN sorption model estimates ion sorption, but does not account for ion exchange effects with soil properties, therefore, PHREEQC was used to also provide a geochemical contaminant transport model including ion exchange reactions occurring along the flow path. The PHREEQC model demonstrated elevated concentrations of a calcium and magnesium plume forming in front of an ammonium plume due to ion exchange occurring on the soil particles. After 50 years of transport, ammonium concentrations were approximately 4% of initial values in a soil with a cation exchange capacity (CEC) of 10 meq [100 g] −1 . Modelling demonstrated high concentrations of ammonium, orthophosphate, sulphate and other ions in mortality leachate where transport and precipitation of these ions could occur beyond 100 years.

Two-dimensional hybrid layered materials: strain engineering on the band structure of MoS2/WSe2 hetero-multilayers

In this paper, we report a comprehensive modeling and simulation study of constructing hybrid layered materials by alternately stacking MoS2 and WSe2 monolayers. Such hybrid MoS2/WSe2 hetero-multilayers exhibited direct bandgap semiconductor characteristics with bandgap energy (Eg) in a range of 0.45–0.55 eV at room temperature, very attractive for optoelectronics (wavelength range 2.5–2.75 μm) based on thicker two-dimensional (2D) materials. It was also found that the interlayer distance has a significant impact on the electronic properties of the hetero-multilayers, for example a five orders of magnitude change in the conductance was observed. Three material phases, direct bandgap semiconductor, indirect bandgap semiconductor, and metal were observed in MoS2/WSe2 hetero-multilayers, as the interlayer distance decreased from its relaxed (i.e., equilibrium) value of about 6.73 Å down to 5.50 Å, representing a vertical pressure of about 0.8 GPa for the bilayer and 1.5 GPa for the trilayer. Such new hybrid layered materials are very interesting for future nanoelectronic pressure sensor and nanophotonic applications. This study describes a new approach to explore and engineer the construction and application of tunable 2D semiconductors.

Spatial length scales of large-scale structures in atmospheric surface layers

Synchronous multipoint measurements were performed in the atmospheric surface layer at theQingtu LakeObservationArray site to obtain high-Reynolds-number [Re-tau similar to O(10(6))] data. Based on the selected high-quality data in the near-neutral surface layer, the spatial length scales of the large-scale dominant structures in the outer region of the turbulent boundary layer are investigated. The characteristic length scales are extracted from the two-point streamwise velocity correlations. Results show that the spatial length scales are invariant over a three order of magnitude change in Reynolds number [Re-tau similar to O(103) - O(10(6))]. However, they increase significantly with the wall-normal distance, showing reasonable collapses on outer-scaled axes. The variation of the spanwise width scale in the logarithmic region follows a linear increase, with the rate of increase much larger than that in the wake region. Moreover, the variation of the wall-normal length scale is also revealed, which displays a qualitative behavior similar to that of the spanwise width scale. The universal laws revealed in the present work contribute to a better understanding of the dominant structures in the outer region of the turbulent boundary layer at high Reynolds numbers.

Comparative study of TiN and TiN/Ti as bottom electrodes for layered type devices with phase transition VO2 films

DC-sputtered TiN and TiN/Ti conductive layers grown on Si substrates were investigated as bottom electrodes with the aim of realizing phase transition VO2-based layered type devices. The VO2 films prepared at a substrate temperature of 250°C on both layers were revealed to show more than two orders of magnitude change in resistance in out-of-plane direction. However, the oxidation of TiN layer was found to degrade the out-of-plane semiconductor-metal transition (SMT) of VO2 film in the case of VO2/TiN/Si structure at 400°C. On the other hand, VO2 film deposited on TiN/Ti/Si substrate at same temperature exhibits an abrupt out-of-plane SMT, in which oxidation of TiN layer was not observed. It was found through the X-ray photoelectron spectroscopy (XPS) depth profiles that the Ti layer played an indispensable role for avoiding oxidation of TiN, due to its high gettering effect for oxygen. Present results show advantage for introducing TiN/Ti layer as bottom electrode with high anti-oxidation ability.

Spray deposition of V4O9 and V2O5 thin films and post-annealing formation of thermochromic VO2

Abstract Vanadium oxide (VO x ) thin films were deposited at various substrate temperatures ( T s ) by spray pyrolysis technique using 0.05 M vanadyl acetylacetonate precursor. V 4 O 9 films are formed at T s = 300 °C, while mixed V 2 O 5 phases are formed at higher T s (400 and 500 °C). Annealing in forming gas of V 4 O 9 films shows the formation of higher content of thermochromic VO 2 phase than V 2 O 5 films. V 4 O 9 films show little higher electric resistivity ( ρ ), higher temperature coefficient of resistance ( TCR ), and higher thermal carrier activation energy ( E a ) than V 2 O 5 films. Annealed VO x films show a 2–3 order of magnitude change in ρ , optical transmission switch of 19–39%, and higher E a than the as deposited films. Annealed films deposited at T s = 500 °C presents a high TCR of −4.6%K −1 . Optical absorption, electronic transitions, and energy gaps of the formed VO x phases have been discussed in relation to its electronic band structure.

Invariant Fast Diffusion on the Surfaces of Ultrastable and Aged Molecular Glasses.

Surface diffusion of molecular glasses is found to be orders of magnitude faster than bulk diffusion, with a stronger dependence on the molecular size and intermolecular interactions. In this study, we investigate the effect of variations in bulk dynamics on the surface diffusion of molecular glasses. Using the tobacco mosaic virus as a probe particle, we measure the surface diffusion on glasses of the same composition but with orders of magnitude of variations in bulk relaxation dynamics, produced by physical vapor deposition, physical aging, and liquid quenching. The bulk fictive temperatures of these glasses span over 35K, indicating 13 to 20 orders of magnitude changes in bulk relaxation times. However, the surface diffusion coefficients on these glasses are measured to be identical at two temperatures below the bulk glass transition temperature T_{g}. These results suggest that surface diffusion has no dependence on the bulk relaxation dynamics when measured below T_{g}.

Time-resolved light-induced insulator-metal transition in niobium dioxide and vanadium dioxide thin films

While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.

A simple dip coat patterning of aluminum oxide to constitute a bistable memristor

Charge transport studies on a bipolar resistive random access memory device based on aluminum oxide were successfully undertaken. The device was designed in a simple metal–insulator–metal format, which was characterized in detail for structural, morphological and electrical measurements. A low cost technique has been adopted for the formation of the memristive element, exhibiting three orders of magnitude change between its two states of conductivity. The obtained memristive behavior is explained based on evidence obtained from charge transport characteristics. Formation/rupture of the conducting filament by external electric field is found to be the main mechanism behind resistive switching.

Charge transport, doping and luminescence in solution-processed, phosphorescent, air-stable tellurophene thin films

Recently synthesized small molecule tellurophenes containing ring-appended pinacolboronate (BPin) side groups possess remarkable guest-free air-stable solid-state phosphorescence, structure-based color-tunability and aggregation induced enhanced emission. The charge transport, doping and luminescence behavior of thin transparent films of a tellurophene with BPin groups positioned at the 2,5-positions (B-Te-6-B) was investigated. Film formation played a critical role in determining the hole mobility and the photoluminescence (PL) lifetime. Drop-coated films showed the strongest crystallinity, the highest PL quantum yields and a hole mobility (μp) of 1.1 × 10−4 cm2 V−1 s−1, which places tellurophenes in a select group of high mobility phosphorescent emitters. B-Te-6-B was also found to spontaneously form high aspect-ratio microwires upon drop-casting from supersaturated solutions. Oxidative doping in solution by a N(C6H4Br)3[SbCl6]/LiNTf2 reagent combination (Tf = SO2CF3) increased conductivity by 2-4 orders of magnitude without inducing a color change in the films, while exposure to iodine vapor induced a dramatic change in color together with a 4-6 order of magnitude change in the conductivity. The optical transparency, facile electrical doping and relatively high hole mobilities of B-Te-6-B in solution processed thin films offer promise for the use of tellurophenes as host-free emissive layers and hole transport layers in organic optoelectronic devices.

A hybrid tunable THz metadevice using a high birefringence liquid crystal.

We investigate a hybrid re-configurable three dimensional metamaterial based on liquid crystal as tuning element in order to build novel devices operating in the terahertz range. The proposed metadevice is an array of meta-atoms consisting of split ring resonators having suspended conducting cantilevers in the gap region. Adding a “third dimension” to a standard planar device plays a dual role: (i) enhance the tunability of the overall structure, exploiting the birefringence of the liquid crystal at its best, and (ii) improve the field confinement and therefore the ability of the metadevice to efficiently steer the THz signal. We describe the design, electromagnetic simulation, fabrication and experimental characterization of this new class of tunable metamaterials under an externally applied small voltage. By infiltrating tiny quantities of a nematic liquid crystal in the structure, we induce a frequency shift in the resonant response of the order of 7–8% in terms of bandwidth and about two orders of magnitude change in the signal absorption. We discuss how such a hybrid structure can be exploited for the development of a THz spatial light modulator.

Antimony selenide core fibers

A new type of thermally sensitive fibers with an antimony selenide (Sb2Se3) core and phosphate glass cladding is demonstrated. The fibers were fabricated by a molten core method and maintained overall diameters ranging from 250 to 800 μm and core diameters of 35–200 μm. A 2.8 cm long Sb2Se3 core fiber, electrically contacted to external circuitry through fiber end facets, exhibited a four orders of magnitude change in conductivity after the whole fiber was heated from 25 to 195 °C. In addition, the fiber exhibited enhanced photoconductivity under illumination. These results indicate that Sb2Se3 core multimaterial fibers have promising applications in temperature sensing, optical switches and photodetectors.

Quantifying redox-induced Schottky barrier variations in memristive devices via in operando spectromicroscopy with graphene electrodes.

The continuing revolutionary success of mobile computing and smart devices calls for the development of novel, cost- and energy-efficient memories. Resistive switching is attractive because of, inter alia, increased switching speed and device density. On electrical stimulus, complex nanoscale redox processes are suspected to induce a resistance change in memristive devices. Quantitative information about these processes, which has been experimentally inaccessible so far, is essential for further advances. Here we use in operando spectromicroscopy to verify that redox reactions drive the resistance change. A remarkable agreement between experimental quantification of the redox state and device simulation reveals that changes in donor concentration by a factor of 2–3 at electrode-oxide interfaces cause a modulation of the effective Schottky barrier and lead to >2 orders of magnitude change in device resistance. These findings allow realistic device simulations, opening a route to less empirical and more predictive design of future memory cells.

Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions

Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.

Organ-specific SPECT activity calibration using 3D printed phantoms for molecular radiotherapy dosimetry.

BackgroundPatient-specific absorbed dose calculations for molecular radiotherapy require accurate activity quantification. This is commonly derived from Single-Photon Emission Computed Tomography (SPECT) imaging using a calibration factor relating detected counts to known activity in a phantom insert.MethodsA series of phantom inserts, based on the mathematical models underlying many clinical dosimetry calculations, have been produced using 3D printing techniques. SPECT/CT data for the phantom inserts has been used to calculate new organ-specific calibration factors for 99mTc and 177Lu. The measured calibration factors are compared to predicted values from calculations using a Gaussian kernel.ResultsMeasured SPECT calibration factors for 3D printed organs display a clear dependence on organ shape for 99mTc and 177Lu. The observed variation in calibration factor is reproduced using Gaussian kernel-based calculation over two orders of magnitude change in insert volume for 99mTc and 177Lu. These new organ-specific calibration factors show a 24, 11 and 8 % reduction in absorbed dose for the liver, spleen and kidneys, respectively.ConclusionsNon-spherical calibration factors from 3D printed phantom inserts can significantly improve the accuracy of whole organ activity quantification for molecular radiotherapy, providing a crucial step towards individualised activity quantification and patient-specific dosimetry. 3D printed inserts are found to provide a cost effective and efficient way for clinical centres to access more realistic phantom data.

Temporal Modulation of Stem Cell Activity Using Magnetoactive Hydrogels.

Cell activity is coordinated by dynamic interactions with the extracellular matrix, often through stimuli-mediated spatiotemporal stiffening and softening. Dynamic changes in mechanics occur in vivo through enzymatic or chemical means, processes which are challenging to reconstruct in cell culture materials. Here a magnetoactive hydrogel material formed by embedding magnetic particles in a hydrogel matrix is presented whereby elasticity can be modulated reversibly by attenuation of a magnetic field. Orders of magnitude change in elasticity using low magnetic fields are shown and reversibility of stiffening with simple permanent magnets is demonstrated. The broad applicability of this technique is demonstrated with two therapeutically relevant bioactivities in mesenchymal stem cells: secretion of proangiogenic molecules, and dynamic control of osteogenesis. The ability to reversibly stiffen cell culture materials across the full spectrum of soft tissue mechanics, using simple materials and commercially available permanent magnets, makes this approach viable for a broad range of laboratory environments.

High-strength semi-crystalline hydrogels with self-healing and shape memory functions

We present a non-covalent approach and bulk photopolymerization method of hydrophilic and hydrophobic monomers to generate high-strength self-healing hydrogels with shape-memory effect. The hydrogels consist of linear poly(N,N-dimethylacrylamide) (PDMA) or polyacrylic acid (PAAc) chains containing (meth)acrylate units with long alkyl side chains. The existence of crystalline domains and hydrophobic associations formed by side alkyl chains produces hybrid-crosslinked PDMA and PAAc hydrogels with particularly high fracture energy of 20±1kJm−2 and Young’s modulus up to 308±16MPa. The mechanical properties of the hydrogels could be tailored by varying the degree of crystallinity. By choosing suitable comonomer pairs and compositions, one may vary the degree of crystallinity between 3 and 33%, which leads to two orders of magnitude change in the modulus, elongation at break, and toughness. The hydrogels undergo up to 1000 fold change in their elastic moduli by changing the temperature between below and above the melting temperature of the crystalline regions. They also exhibit self-healing and shape memory functions triggered by heating above the melting temperature. Healed hydrogels sustain up to 138±10MPa compressive stresses, which are around 87% of the compressive stress of the virgin gel samples.