Optical alcohol sensor based on dye–Chitosan polyelectrolyte multilayers

The layer-by-layer deposition technique was used to prepare polyelectrolyte multilayer (PEM) thin films that are sensitive to ethanol content in water. Cationic Chitosan was assembled with anionic acid dye, (phenyl amino)-5-[[4-(3-sulphonatophenyl) azo]-(1-naphthalenyl) azo]-1-naphthalenesulfonic acid disodium salt (Nylosan) on glass slide and characterized using UV–vis spectroscopy. The layer-by-layer deposition of Chitosan–Nylosan into PEM was studied by monitoring the increase in absorbance in the visible region (500–600 nm). The typical linear relationship between increase in absorbance and number of layers was found. The PEM thin films responded to increasing concentrations of ethanol in water with a shift of maximum absorbance (λ_max) from 540 to 580 nm. This shift was also characterized by an increase in absorbance at 600 nm which was used to monitor the response of the thin film to ethanol content in water. The characteristic color shift of the Nylosan dye occurred at a higher ethanol concentration (from 10% to 45%) in the PEM compared to its usual shift in aqueous solution (from 0% to 30%). The Chitosan–Nylosan thin films response to ethanol content was found to be linear from 10% to 45% ethanol content, which renders them useful as ethanol sensing thin films.     

Phosphate functionalized (4,4)-armchair CNTs as novel drug delivery systems for alendronate and etidronate anti-osteoporosis drugs

The ability of (4,4)-armchair CNT and its three phosphate functionalized forms (CNT-nH₂PO₄, n = 1–3) were evaluated as novel drug delivery systems (DDSs) for the two commercially well-known anti-osteoporosis drugs namely alendronate (AL) and etidronate (ET). For this purpose, the DFT calculations were accomplished at both B3LYP and B3PW91 levels using 6–31g(d) basis set. The binding energy was increased by increasing number of H₂PO₄ moieties attached on the CNT with the most negative binding energy was measured for the carrier containing three phosphate groups. The dipole moments of all phosphate containing CNTs were much greater (∼2.2–4.4 D) than that of pristine CNT (∼0 D). The contour maps proved that when the CNT was functionalized by H₂PO₄ groups, the symmetric distribution of electric charge was vanished with the charge distribution was the highest asymmetric for the CNT-2H₂PO₄ while it was the lowest asymmetric for CNT-3H₂PO₄ leading to the greatest dipole moment for the CNT-2H₂PO₄ (4.177 D) while the smallest dipole moment for the CNT-3H₂PO₄ (1.614 D). Among all compounds, those containing the CNT-3H₂PO₄ exhibited the smallest band gap energy, chemical potential and hardness but the greatest electronegativity and electrophilicity index which were all suitable and effective for the attachment of drugs onto the bone surface (having partial positive charge due to the presence of Ca²⁺ as CaCO₃) and therefore inhibiting the osteoporosis. Consequently, it was established that the drug-CNT-3H₂PO₄ was the most appropriate drug-carrier compound for both of the AL and ET drugs and it could be used as the most effective drug vehicle. The attachment of AL, ET drugs as well as the AL-CNT-3H₂PO₄ and ET-CNT-3H₂PO₄ drug-carrier systems to the bone tissue was modelled by optimization of the structures of these compounds bonded to the hydroxyapatite (HA)-17water (w). It was found that among these four systems, the AL-CNT-3H₂PO₄ could be suggested as the most suitable DDS for application in the treatment of osteoporosis.     

Design,simulation and validation of a novel uncooled infrared focal plane array

This paper describes a novel single-layer bi-material cantilever microstructure without silicon (Si) substrate for focal plane array (FPA) application in uncooled optomechanical infrared imaging system (UOIIS). The UOIIS, responding to the radiate infrared (IR) source with spectral range from 8 to 14 μm, may receive an IR image through visible optical readout method. The temperature distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array, which is consisted of two materials with mismatching thermal expansion coefficients. In order to obtain a high detection to the IR object, gold (Au) film is coated alternately on silicon nitride (SiN_x) film in the flection beams of the cantilevers. And a thermal–mechanical model for such cantilever microstructure is proposed. The thermal and thermal–mechanical coupling field characteristics of the cantilever array structure are optimized through numerical analysis method and simulated by using the finite element simulation method. The thermal–mechanical rotation angle simulated and thermal–mechanical sensitivity tested in the experiment are 2.459 × 10⁻³ and 3.322 × 10⁻⁴ rad/K, respectively, generally in good agreement with what the thermal–mechanical model and numerical analysis forecast, which offers an effective reference for FPA structure parameters design in UOIIS.     

Ferroelectric properties of direct-patterned half-micron thick PZT film

Ferroelectric properties of direct-patterned PZT(PbZr_0.52Ti_0.48O₃) films with 460 μm × 460 μm size and 510 nm thick were analyzed for applying to micro-detecting devices. A photosensitive solution containing ortho-nitrobenzaldehyde was used for the preparation of direct-patterned PZT film. PZT solution was coated on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrate for three times to obtain half-micron thick film and three times of direct-patterning process were repeated to define a pattern on multi-layer PZT film. Through intermediate and final anneal procedure of direct-patterned PZT film, any shrinkage along horizontal direction was not observed within this experimental condition, i.e., the size of the pattern was preserved after annealing, only a thickness reduction was observed after each annealing treatment. Ferroelectric properties of direct-patterned PZT film with 460 μm × 460 μm size and 510 nm thick were compared with those of un-patterned conventional PZT film and shown to be almost the same. Through this work, the high potentiality of direct-patternable PZT film for applying to micro-devices without the introduction of physical damages from dry-etching could be confirmed.     

Ionic polymer–metal composite bending actuator loaded with multi-walled carbon nanotubes

Multi-walled carbon nanotube (M-CNT)/Nafion nanocomposites were prepared by the dispersion of treated M-CNTs in a Nafion solution; this procedure was done in order to evaluate the influence of M-CNT loading of up to 7 wt.% on the M-CNT distribution behavior, mechanical properties, and the related actuation performance of the composites. As the M-CNT loading rose above 1 wt.%, the uniformly distributed M-CNT bundles induced by the Nafion polymer were determined to be perturbed, resulting in an inhomogeneous distribution. The heterogeneously distributed M-CNT bundles may provide an undesired impact on the connectivity within the Nafion membrane, thus giving rise to the poor electrochemically-generated actuation properties. It is important to note that the nanocomposite having only a 1 wt.% of M-CNT loading exhibited the best actuation performance in terms of the blocking forces produced by the M-CNT nanocomposites in a cantilever form. It can be understood that the performance improvement is caused by the uniform distribution of the M-CNT bundles, which was confirmed by TEM, XRD and electromechanical actuation tests. It is concluded that the M-CNT distribution behavior, induced by interactions between the polymer matrix, Nafion and the M-CNTs and the related electromechanical performance of the composites, are mainly governed by the M-CNT content. Also, DMA testing was performed.     

Evaluation of response characteristics of resistive oxygen sensors based on porous cerium oxide thick film using pressure modulation method

In order to reduce the response time of resistive oxygen sensors using porous cerium oxide thick film, it is important to ascertain the factors controlling response. Pressure modulation method (PMM) was used to find the rate-limiting step of sensor response. This useful method measures the amplitude of sensor output (H(f)) for the sine wave modulation of oxygen partial pressure at constant frequency (f). In PMM, “break” response time, which is minimum period in which the sensor responds precisely, can be measured. Three points were examined: (1) simulated calculations of PMM were carried out using a model of porous thick film in which spherical particles are connected in a three-dimensional network; (2) sensor response speed was experimentally measured using PMM; and (3) the diffusion coefficient and surface reaction coefficient were estimated by comparison between experiment and calculation. The plot of log f versus log H(f) in the high f region was found to have a slope of approximately −0.5 for both porous thick film and non-porous thin film, when the rate-limiting step was diffusion. Calculations showed the response time of porous thick film was 1/20 that of non-porous thin film when the grain diameter of the porous thick film was the same as the thickness of non-porous thin film. At 973 K, “break” response time (t_b) of the resistive oxygen sensor was found by experiment to be 109 ms. It was concluded that the response of the resistive oxygen sensor prepared in this study was strongly controlled by diffusion at 923–1023 K, since the experiment revealed that the slope of plot of log f versus log H(f) in the high f region was approximately −0.5. At 923–1023 K, the diffusion coefficient of oxygen vacancy in porous ceria (D_V) was expressed as follows: D_V (m²s⁻¹) = 5.78 × 10⁻⁴ exp(−1.94 eV/kT). At 1023 K, the surface reaction coefficient (K) was found to exceed 10⁻⁴ m/s.     

Orientation and thickness dependence of electrical and gas sensing properties in heteroepitaxial indium tin oxide films

Heteroepitaxial indium tin oxide (ITO) films were grown on three differently oriented yttria-stabilized zirconia (YSZ) substrates ((1 0 0), (1 1 0), (1 1 1)) by rf magnetron sputtering, and their structural characteristics and electrical and gas sensing properties were investigated. The initially formed ITO exhibited an island structure on the very thin layer and became a continuous film after the prolonged deposition. The heteroepitaxial relationships between ITO films and YSZ substrates were confirmed by X-ray diffraction, pole figure, and high resolution transmission electron microscopy (HRTEM). The chemical composition, determined by X-ray photoelectron spectroscopy (XPS), was slightly different at early stage depending on the substrate orientation, but it became similar after the longer deposition. Hall measurements indicated that the electrical resistivity of ITO films decreased with increasing the deposition time (or film thickness) irrespective of the film orientation. The ITO film deposited on (1 1 0) YSZ for 10 s showed the highest electrical resistivity. The gas sensor fabricated from the ITO film on (1 1 0) YSZ deposited for 10 s showed the highest NO₂ gas response at relatively low temperature (100 °C), which was attributed to the higher Sn concentration and higher surface roughness of that film.     

Fabrication and characterization of polyaniline-based gas sensor by ultra-thin film technology

Pure polyaniline (PAN) film, polyaniline and acetic acid (AA) mixed film, as well as PAN and polystyrenesulfonic acid (PSSA) composite film with various number of layers were prepared by Langmuir–Blodgett (LB) and self-assembly (SA) techniques. These ultra-thin films were characterized by ultraviolet–visible (UV–VIS) spectroscopy and ellipsometry. It is found that the thickness of PAN-based ultra-thin films increases linearly with the increase of the number of film layers. The gas-sensitivity of these ultra-thin films with various layers to NO₂ was studied. It is found that pure polyaniline films prepared by LB technique had good sensitivity to NO₂, while SA films exhibited faster recovery property. The response time to NO₂ and the relative change of resistance of ultra-thin films increased with the increase of the number of film layers. The response time of three-layer PAN film prepared by LB technique to 20 ppm NO₂ was about 10 s, two-layer SA film was about 8 s. The mechanism of sensitivity to NO₂ of PAN-based ultra-thin films was also discussed.     

The effect of protonation of cytosine and adenine on their interactions with carbon nanotubes

Placing electrical charges on nanomaterials is a means to extend their functional capabilities in nanoelectronics and sensoring applications. This paper explores the effect of charging nitrogen bases cytosine (Cyt) and adenine (Ade) via protonation on their noncovalent interaction with carbon nanotubes (CNT) using quantum chemical calculations performed at the M05-2X/6-31++G** level of theory alongside with a molecular graphics method. It is shown that the protonation of the bases causes threefold increase of the interaction energy in the CNT·Cyt·H⁺ and СNT·Ade·H⁺ complexes as compared to the CNT complexes formed with neutral bases. There is also some shortening of the base-CNT distance by ca 0.13 Ǻ. The visualization of the electrostatic potential distribution with the molecular graphics reveals that the positive potential due to the protonated bases extends to a cylindrical domain of the nanotube segment adjacent to the base binding site. Furthermore, subtraction of the electrostatic potential maps of the protonated bases from the maps of their complexes with CNTs reveals an area of negative potential on the CNT surface, which reflects the location of the adsorbed base. The positive charge transfer of ca 0.3 e from the protonated bases to the CNT strengthens the interaction in the CNT·Cyt·H⁺ and СNT·Ade·H⁺ complexes. The analysis of the frontier orbitals shows that the LUMOs of the complexes mainly reside on the CNT, while the HOMOs spread over both components of each complex. The observed effects may facilitate the design of nanomaterials involving nitrogen bases and CNTs.     

Analysis of high-Q,gallium nitride nanowire resonators in response to deposited thin films

Gallium nitride nanowires (GaN-NWs) are systems of interest for mechanical resonance-based sensors due to their small mass and, in the case of c-axis NWs, high mechanical quality (Q) factors of 10,000–100,000. We report on singly-clamped NW mechanical cantilevers of roughly 100 nm diameter and 15 μm length that resonate near 1 MHz and describe the behavior of GaN-NW resonant frequencies and Q factors following coating with various materials deposited by atomic layer deposition (ALD), including alumina (Al₂O₃), ruthenium (Ru), and platinum (Pt). Changes in the GaN-NW resonant frequencies with ALD deposition clearly distinguish conformal film growth versus island film growth. Conformal films lead to a stiffening of the NW and typically increase resonant frequency, whereas island films simply increase the NW mass and cause decreased resonant frequencies. We find that conformal growth of ALD alumina leads to stiffening of ～4 kHz per nm of alumina, in agreement with previously measured material properties. Conformal growth of Ru and Pt, respectively, qualitatively confirm our analytical predictions of positive and negative resonant frequency shifts. Island growth of ALD Ru has demonstrated a decrease in resonant frequency consistent with mass loading of ～0.2 fg for a 150 ALD-cycle film, also consistent with analytical predictions. Resonant Q factors are found to decrease with ALD film growth, offering the additional possibility of studying mechanical dissipation processes associated with the ALD-NW composite structures.     

Fabrication and characterization of Pb-free transparent dielectric layer for plasma display panel

Glasses within the Bi₂O₃–B₂O₃–BaO–ZnO system were examined as potential replacements for PbO-based glass frits with low firing temperatures. These frits are used in the transparent dielectric layer of plasma display panels (PDP). The glass transition temperature (T_g) of the prepared glasses varied between 450 and 460 °C. These glasses display dynamic dielectric properties, high transparency and thermal expansion as well as matching well with substrate glass. The thermal coefficient of expansion (TCE) was with the desired range of 81–86×10⁻⁷/K. Moreover, when the screen printed film was heat-treated at 570 °C for 30 min, optical transmittance (83%), root-mean square (rms) roughness (177.6 Å), dielectric constant (10.25) and withstand voltage (4.15 kV) satisfied the requirements necessary for transparent dielectric layers to be used in PDP applications.     

Electrical stimuli-induced deformation and material properties of electro-active polymer Nafion117

The material properties of Nafion117 in water are investigated through experiments and finite-element analysis (FEA) to derive parameters for use in future FEA studies of the coupling diffusion of water and structural mechanics of EAPs in aqueous solution. The deformation behavior of Nafion117 in distilled water under the application of an electric potential is examined experimentally to clarify the relationships between applied voltage, current and deformation. The water content in wet Nafion117 and the coefficient of linear expansion due to water absorption are found experimentally to be 0.434 [(mm³)_aq/(mm³)_dp] and 0.243 [(mm³)_dp/(mm³)_aq]. Through experiments and corresponding FEA simulations on the free vibration of a Nafion117 cantilever in distilled water and a gold-plated cantilever, the Young's modulus and β coefficient of Rayleigh damping are found to be 7.0 MPa and 0.02 s, respectively.     

Fabrication and frequency response of dual-element ultrasonic transducer using PZT-5A thick film

Ultrasonic transducers based on PZT-5A thick films deposited onto polycrystalline Al₂O₃ substrates using screen-printing were successfully fabricated. Considering the relatively high sintering temperature of PZT-5A thick films and better impedance matching characteristics with PZT-5A, polished polycrystalline Al₂O₃ were used as substrates. For electrodes, high quality platinum (Pt) was deposited by a thin film process, because the surface state of electrodes greatly affects the quality of piezoelectric films. Applying Pt/PZT-5A/Pt/Al₂O₃ structures, dual-element ultrasonic transducers were assembled. The assembled transducers included a wear plate (normally alumina with 40.21 × 10⁶ kg/m² s of impedance), backing (tungsten carbide-epoxy), electrical matching, an epoxy glue layer, and a housing. The optimum measurement ranges of 5 and 10 MHz ultrasonic transducers were 2.51–300.2 and 2.50–250.1 mm, respectively. From the time and frequency response measurements of the assembled 10 MHz DEUTs, the value of −20 dB level waveform duration and the −6 dB bandwidth was 481.8 ns and 34.4%, respectively. Also, the measurement accuracies of both 5 and 10 MHz DEUTs assembled in this study were below 0.1 and 0.4%, respectively.     

Reliability and usability of an internet-based computerized cognitive testing battery in community-dwelling older people

Cognitive decline is an early feature of neurodegenerative conditions. CogState has developed a game-like computerized test battery with demonstrated acceptability, validity, reliability, stability, efficiency and sensitivity to detecting cognitive decline in older people under supervised conditions. This study aimed to evaluate an internet-based version of this test when used remotely and self-administered in a cohort of healthy, community-dwelling older adults aged 55 and above over a 12 month period at 1–3 monthly intervals. Test usability and reliability was examined in terms of acceptability, stability and reliability. Of 150 participants (age: 63.6 ± 5.6, range 55–83 years), 143 (95%) successfully completed a valid baseline test. Of these, 67% completed 3 month and 43% 12 months of testing. Technical difficulties were reported by 9% of participants. For those participants who completed 12 months tests, all tasks showed moderate to high stability and test–retest reliability.This brief computerized test battery was shown to have high acceptability for baseline self-administered testing and moderate to high stability for repeated assessments over 12 months. Attrition was high between baseline and 3 months. These data suggest that this tool may be useful for high frequency monitoring of cognitive function over 6–12 months, and deserves further evaluation.     

Vibrational analysis of graphene based nanostructures

This paper deals with the molecular mechanics simulations of graphene nanostructures and their vibration behavior for potential applications on nano-electronics and nanocomposites. The fundamental frequencies for CNTs range from 10 to 250 GHz and 100 to 1000 GHz for the cantilevered and bridged conditions, respectively. As the ratio L/d increases the fundamental frequency decreases, as expected. A decrease on fundamental frequencies with the bending waviness was noticed for all conditions. The mode shape for bent carbon nanotubes seems to be a superposition of the vibration mode and the bending mode for the zigzag configuration. Multi-layered graphene nanosheets were also investigated. The fundamental frequencies ranged from 50 to 150 GHz, with an odd/even shape mode switch.     

Thin film temperature sensor for real-time measurement of electrolyte temperature in a polymer electrolyte fuel cell

This paper describes a technique for the measurement of the electrolyte temperature in an operating polymer electrolyte fuel cell (PEFC). A patterned thin film gold thermistor embedded in a 16 μm thick parylene film was laminated in the Nafion^® electrolyte layer for in situ temperature measurements. Experimental results show that the sensor has a linear response of (3.03 ± 0.09) × 10⁻³ °C⁻¹ in the 20–100 °C temperature range and is robust enough to withstand the electrolyte expansion forces that occur during water uptake. An electrolyte temperature increase of 1.5 °C was observed in real-time when operating the fuel cell at 0.2 V and a current density of 0.19 A/cm². The temperature sensitivity of the present sensor is in an order of magnitude better than the conventional micro-thermocouples that have been reported. Additionally, use of micro-fabrication techniques allows for an accurate placement of the temperature sensor within the fuel cell. Simulation results show that the sensor has no significant effect on the local temperature distribution.     

Dielectric and piezoelectric properties of [0 0 1] and [0 1 1]-poled relaxor ferroelectric PZN–PT and PMN–PT single crystals

The properties of PZN–PT and PMN–PT single crystals of varying compositions and orientations have been investigated. Among the various compositions studied, [0 0 1]-optimally poled PZN-(6–7)%PT and PMN-30%PT exhibit superior dielectric and piezoelectric properties, with K^T ≈ 6800–8000, d₃₃ ≈ 2800 pC/N, d₃₁ ≈ −(1200–1800) pC/N for PZN-(6–7)%PT; and K^T = 7500–9000, d₃₃ = 2200–2500 pC/N and d₃₁ = −(1100–1400) pC/N for PMN-30%PT. These two compositions are also fairly resistant to over-poling. The [0 0 1]-poled electromechanical coupling factors (k₃₃, k₃₁ and k_t) are relatively insensitive to crystal composition. [0 1 1]-optimally poled PZN-7%PT single crystal also exhibits extremely high d₃₁ values of up to −4000 pC/N with k₃₁ ≈ 0.90–0.96. While [0 1 1]-poled PZN-7%PT single crystal becomes over-poled with much degraded properties when poled at and above 0.6 kV/mm, PZN-6%PT crystal shows no signs of over-poling even when poled to 2.0 kV/mm. The presence of a certain amount (i.e., 10–15%) of orthorhombic phase in a rhombohedral matrix has been found to be responsible for the superior transverse piezoelectric properties of [0 1 1]-optimally poled PZN-(6–7)%PT. The present work shows that flux-grown PZN–PT crystals exhibit superior and consistent properties and improved over-poling resistance to flux-grown PMN–PT crystals and that, for or a given crystal composition, flux-grown PMN–PT crystals exhibit superior over-poling resistance to their melt-grown counterparts.     

Design of embedded TCAM based longest prefix match search engine

The content addressable memory (CAM) based solutions are very useful in network applications due to its high speed parallel search mechanism. This paper presents a novel Ternary CAM (TCAM) based NAND Pseudo CMOS–Longest Prefix Match (NPC–LPM) search engine. The proposed system provides a simple hardware based solution using novel 11T TCAM cell structures and NPC word line technique, for network routers. The experiments were performed on 256 × 128 NPC–LPM system under 0.13 μm technology. The simulation result shows that the proposed design provides low power dissipation of 5.78 mW and high search speed of 315 MSearches/s under 1.3 V supply voltage. The presented NPC–LPM system meets the speed requirement of Optical Carrier (OC) 3072 with line-rate of 160 Gb/s in Ethernet networking and IPv6 protocol. The experimental results also show that the proposed system improves power-performance by 65%.     

Charge-tunable insertion process of carbon nanotubes into DNA nanotubes

Control over interactions with biomolecules holds the key of the applications of carbon nanotubes (CNTs) in biotechnology. Here we report a molecule dynamics study on the encapsulation process of different charged CNTs into DNA nanotubes. Our results demonstrated that insertion process of CNTs into DNA nanotubes are charge-tunable. The positive charged CNTs could spontaneously encapsulate and confined in the hollow of DNA nanotubes under the combination of electrostatic and vdW interaction in our ns scale simulation. The conformation of DNA nanotubes is very stable even after the insertion of CNTs. For pristine CNTs, it could not entirely encapsulated by DNA nanotubes in simulation scale in this study. The encapsulation time of pristine CNTs into DNA nanotubes was estimated about 21.9 s based on the potential of mean force along the reaction coordination of encapsulation process of CNTs into DNA nanotubes. In addition, the encapsulation process was also affected by the diameter of CNTs. These findings highlight the charge-tunable self-assembly process of nanomaterials and biomolecules. Our study suggests that the encapsulated CNTs-DNA nanotubes could be used as building blocks for constructing organic–inorganic hybrid materials and has the potential applications in the field of biosensor, drug delivery system and biomaterials etc.