Showing papers by "Tyndall National Institute published in 2008"
TL;DR: In this article, an electromagnetic-based generator is presented for supplying generating power from human body motion and has application in providing energy for body worn sensors or electronics devices, and the experimental results show that the prototype could generate 300μW to 2.5mW power from Human Body Motion during walking and slow running.
Abstract: This paper presents an electromagnetic based generator which is suitable for supplying generating power from human body motion and has application in providing energy for body worn sensors or electronics devices. A prototype generator has been built and tested both by a shaker at resonance condition and also by human body motion during walking and slow running. The experimental results will show that the prototype could generate 300 μW to 2.5 mW power from human body motion. The measured results are analyzed and compared with the theoretical model.
547 citations
TL;DR: Colloidal semiconductor nanocrystals are promising luminophores for creating a new generation of electroluminescence devices, and potential advantages associated with nanocrystal-based devices, such as a spectrally pure emission color, which will certainly merit future research.
Abstract: Colloidal semiconductor nanocrystals are promising luminophores for creating a new generation of electroluminescence devices. Research on semiconductor nanocrystal based light-emitting diodes (LEDs) has made remarkable advances in just one decade: the external quantum efficiency has improved by over two orders of magnitude and highly saturated color emission is now the norm. Although the device efficiencies are still more than an order of magnitude lower than those of the purely organic LEDs there are potential advantages associated with nanocrystal-based devices, such as a spectrally pure emission color, which will certainly merit future research. Further developments of nanocrystal-based LEDs will be improving material stability, understanding and controlling chemical and physical phenomena at the interfaces, and optimizing charge injection and charge transport.
313 citations
TL;DR: Key research challenges to be addressed to deliver future, remote, wireless, chemo-biosensing systems include the development of low cost, low-power sensors, miniaturised fluidic transport systems, anti-bio-fouling sensor surfaces, sensor calibration, reliable and robust system packaging, as well as associated energy delivery systems and energy budget management.
263 citations
TL;DR: The development and implementation of an energy aware autonomous wireless condition monitoring sensor system (ACMS) powered by ambient vibrations that has been successfully demonstrated on an industrial air compressor and an office air conditioning unit, continuously monitoring vibration levels and thereby simulating a typical condition monitoring application.
Abstract: This paper reports the development and implementation of an energy aware autonomous wireless condition monitoring sensor system (ACMS) powered by ambient vibrations. An electromagnetic (EM) generator has been designed to harvest sufficient energy to power a radio-frequency (RF) linked accelerometer-based sensor system. The ACMS is energy aware and will adjust the measurement/transmit duty cycle according to the available energy; this is typically every 3 s at 0.6 m s?2 rms acceleration and can be as low as 0.2 m s?2 rms with a duty cycle around 12 min. The EM generator has a volume of only 150 mm3 producing an average power of 58 ?W at 0.6m s?2 rms acceleration at a frequency of 52 Hz. In addition, a voltage multiplier circuit is shown to increase the electrical damping compared to a purely resistive load; this allows for an average power of 120 ?W to be generated at 1.7 m s?2 rms acceleration. The ACMS has been successfully demonstrated on an industrial air compressor and an office air conditioning unit, continuously monitoring vibration levels and thereby simulating a typical condition monitoring application
262 citations
TL;DR: Density functional calculations reveal that penicillamine strongly distorts surface Cd, transmitting an enantiomeric structure to the surface layers and associated electronic states, and the quantum dot core is found to remain undistorted and achiral.
Abstract: We report and explain circular dichroism in semiconductor quantum dots. CdS nanocrystals capped with penicillamine enantiomers were prepared and found to be both highly luminescent and optically active. No new features in circular dichroism were observed as the nanocrystal grew larger. Density functional calculations reveal that penicillamine strongly distorts surface Cd, transmitting an enantiomeric structure to the surface layers and associated electronic states. The quantum dot core is found to remain undistorted and achiral.
177 citations
TL;DR: In this paper, the authors analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linwidth) in monolithic passively mode-locked semiconductor lasers.
Abstract: We have analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linewidth) in monolithic passively mode-locked semiconductor lasers. Due to the absence of restoring force, the timing jitter is directly related to the RF linewidth, avoiding possible underestimations made with conventional methods of phase noise measurement. The RF linewidth is also analytically related to the pulse characteristics using Haus's model. The timing stability performance of a promising two-section quantum-dot laser is presented using RF linewidth measurements. Experimental evolution of the RF linewidth with power and pulsewidth is finally compared to the analytical expression.
158 citations
TL;DR: In this article, a single spin-coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C 2 H 3 O 2 ) 2 ], monoethanolamine [H 2 NC 2 H 4 OH ] and isopropanol was performed over the range 500 to 650°C.
136 citations
TL;DR: In this article, the authors applied DFT corrected for on-site Coulomb interaction (DFT+U) to describe reduced Ti ions and showed that the optimal value of U is 3 eV, determined from comparison of the computed Ti 3d electronic density of states with the UPS data.
Abstract: Point defects in metal oxides such as TiO2 are key to their applications in numerous technologies. The investigation of thermally induced nonstoichiometry in TiO2 is complicated by the difficulties in preparing and determining a desired degree of nonstoichiometry. We study controlled self-doping of TiO2 by adsorption of 1/8 and 1/16 monolayer Ti at the (110) surface using a combination of experimental and computational approaches to unravel the details of the adsorption process and the oxidation state of Ti. Upon adsorption of Ti, x-ray and ultraviolet photoemission spectroscopy (XPS and UPS) show formation of reduced Ti. Comparison of pure density functional theory (DFT) with experiment shows that pure DFT provides an inconsistent description of the electronic structure. To surmount this difficulty, we apply DFT corrected for on-site Coulomb interaction (DFT+U) to describe reduced Ti ions. The optimal value of U is 3 eV, determined from comparison of the computed Ti 3d electronic density of states with the UPS data. DFT+U and UPS show the appearance of a Ti 3d adsorbate-induced state at 1.3 eV above the valence band and 1.0 eV below the conduction band. The computations show that the adsorbed Ti atom is oxidized to Ti2+ and a fivefold coordinated surface Ti atom is reduced to Ti3+, while the remaining electron is distributed among other surface Ti atoms. The UPS data are best fitted with reduced Ti2+ and Ti3+ ions. These results demonstrate that the complexity of doped metal oxides is best understood with a combination of experiment and appropriate computations.
134 citations
TL;DR: In this paper, the effect of gold doping on oxygen vacancy formation and CO adsorption on the (1, 1, 0, 0) and (1, 0, 0) surfaces of ceria has been investigated.
126 citations
TL;DR: The results reveal that GNP may induce oxidative stress and is likely to cause unexpected biological responses.
116 citations
TL;DR: Comprehensive design considerations for an indoor light energy harvesting system for building management applications is provided and maximum power point tracking circuits are proposed which significantly increase the power obtained from the solar cells.
Abstract: For most wireless sensor networks, one common and major bottleneck is the limited battery lifetime. The frequent maintenance efforts associated with battery replacement significantly increase the system operational and logistics cost. Unnoticed power failures on nodes will degrade the system reliability and may lead to system failure. In building management applications, to solve this problem, small energy sources such as indoor light energy are promising to provide long-term power to these distributed wireless sensor nodes. This article provides comprehensive design considerations for an indoor light energy harvesting system for building management applications. Photovoltaic cells characteristics, energy storage units, power management circuit design, and power consumption pattern of the target mote are presented. Maximum power point tracking circuits are proposed which significantly increase the power obtained from the solar cells. The novel fast charge circuit reduces the charging time. A prototype was then successfully built and tested in various indoor light conditions to discover the practical issues of the design. The evaluation results show that the proposed prototype increases the power harvested from the PV cells by 30p and also accelerates the charging rate by 34p in a typical indoor lighting condition. By entirely eliminating the rechargeable battery as energy storage, the proposed system would expect an operational lifetime 10--20 years instead of the current less than 6 months battery lifetime.
TL;DR: pDNA hydrogels can be successfully targeted to the viable epidermis to potentially provide sustained gene expression therein and this study investigated the potential for improved delivery of plasmid DNA (pDNA) in skin by combining the microneedle delivery system with sustained release p DNA hydrogel formulations.
Abstract: Purpose
Microneedles disrupt the stratum corneum barrier layer of skin creating transient pathways for the enhanced permeation of therapeutics into viable skin regions without stimulating pain receptors or causing vascular damage. The cutaneous delivery of nucleic acids has a number of therapeutic applications; most notably genetic vaccination. Unfortunately non-viral gene expression in skin is generally inefficient and transient. This study investigated the potential for improved delivery of plasmid DNA (pDNA) in skin by combining the microneedle delivery system with sustained release pDNA hydrogel formulations.
TL;DR: In this article, the fabrication and electrical properties of a variety of nanowire-based field effect transistors (FETs) are discussed, including Si, Ge, and Ge/Si core/shell nanowires.
Abstract: The development of semiconductor nanowires has recently been the focus of extensive research as these structures may play an important role in the next generation of nanoscale devices. Using semiconductor nanowires as building blocks, a number of high performance electronic devices have been fabricated. In this review, we discuss synthetic methodologies and electrical characteristics of Si, Ge, and Ge/Si core/shell nanowires. In particular the fabrication and electrical properties of a variety of nanowire-based field effect transistors (FETs) are discussed. Although the bottom-up approach has the potential to go far beyond the limits of top-down technology, new techniques need to be developed to realize precise control of structural parameters, such as size uniformity, growth direction, and dopant distribution within nanowires to produce nanowire-based electronics on a large scale.
TL;DR: The feasibility of miniaturized chemiluminescent ELISA is demonstrated by presenting rapid, reproducible and sensitive detection of protein antibodies using microfluidics, compared with the classical Pharmacia CAP system.
16 May 2008
TL;DR: In this article, the design and measured results for micro-fabricated inductors suitable for use in high frequency (> 10 MHz), low power (1 -2 W) dc-dc converters were presented.
Abstract: This paper presents the design and measured results for micro-fabricated inductors suitable for use in high frequency (> 10 MHz), low power (1 -2 W) dc-dc converters. The design has focused on maximizing inductor efficiency for a given converter specification. Inductors in the range of 100 nH to 300 nH have been fabricated and tested. The small signal measurements show a relatively flat inductance profile, with a 10% drop in inductance at 30 MHz. Inductance vs. dc bias current measurements show less than 15% decrease in inductance at 500 mA current. The performance of the micro-inductors have also been compared to a conventional wire-wound inductor in a 20 MHz dc-dc converter. The converter efficiency is shown to be approximately 4% lower when the micro-inductor is used compared to the when the wire- wound inductor is used. The peak efficiency of the micro-inductor in the converter is estimated to be approximately 93%.
TL;DR: In this article, density functional theory and low-temperature scanning tunneling microscopy (STM) have been combined to examine the bonding of individual molecules on Cu(111), and the binding conformation of the molecules and their orientation with regard to the copper surface can be deduced by this joint experimental-theoretical approach.
Abstract: Density functional theory (DFT) and low-temperature scanning tunneling microscopy (STM) have been combined to examine the bonding of individual ${\mathrm{C}}_{60}$ molecules on Cu(111). Energy-resolved differential-conductance maps have been measured for individual ${\mathrm{C}}_{60}$ molecules adsorbed on a Cu(111) surface by means of low-temperature STM, which are compared to and complemented by theoretically computed spectral images. It has been found that ${\mathrm{C}}_{60}$ chemisorbs with a six-membered ring parallel to the surface at two different Cu(111) binding sites that constitute two exclusive hexagonal sublattices. On each sublattice, ${\mathrm{C}}_{60}$ is bonded in one particular rotational conformer, i.e., ${\mathrm{C}}_{60}$ molecules bind to the Cu(111) surface in two different azimuthal orientations differing by 60\ifmmode^\circ\else\textdegree\fi{} depending on which sublattice the binding site belongs to. The binding conformation of ${\mathrm{C}}_{60}$ and its orientation with regard to the copper surface can be deduced by this joint experimental-theoretical approach. Six possible pairs of ${\mathrm{C}}_{60}$ configurations on three different Cu surface binding sites have been identified that fulfil the requirements of the two sublattices and are consistent with all experimental and theoretical data. Theory proposes that two of these configuration pairs are most likely. We have found that DFT does not get the binding energy between rotational conformers in the correct order. We also report two different ${\mathrm{C}}_{60}$ monolayers on Cu(111): one with alternating orientations of neighboring molecules at low temperature and the other with $(4\ifmmode\times\else\texttimes\fi{}4)$ structure after annealing above room temperature.
TL;DR: In this paper, the authors apply first-principles density functional theory to investigate how dopants with a range of ionic radii, oxidation states, and electronic structure can be used to tune the band gap.
Abstract: Materials derived from copper oxide, Cu2O, are potential p-type transparent conducting oxides. Cu2O displays some unusual features, including p-type semiconductivity and the importance of cation−cation interactions in determining the band gap and transparency. We apply first-principles density functional theory to investigate how dopants with a range of ionic radii, oxidation states, and electronic structure can be used to tune the band gap. Unlike many oxides, in which the band gap is reduced by the appearance of dopant induced states in the host band gap, the band gap of Cu2O can be both increased or decreased by a suitable choice of dopant. Two effects dominate: (i) dopant-induced changes to the Cu−Cu interactions through structural distortions around the dopant site and (ii) the alignment of the dopant electronic states with the valence band or conduction band of Cu2O. Dopants with ionic radii larger than Cu+ (Ba2+, Sn2+, Cd2+, In3+, La3+, and Ce4+) produce strong structural distortions around the dop...
16 May 2008
TL;DR: In this article, the authors examined the impact of packaging parasitics on the efficiency of a synchronous DC-DC buck converter and developed an analytical model of the losses in the converter and compared to practical results at switching frequencies in the range of 1-2 MHz.
Abstract: This work examines the impact of packaging parasitics on the efficiency of a synchronous DC-DC buck converter. An analytical model of the losses in the converter is developed and this is compared to practical results at switching frequencies in the range of 1-2 MHz. The effect that the packaging parasitic inductance has on efficiency is highlighted by predicting the expected losses from a converter with optimised packaging parasitics.
TL;DR: In this article, first-principles electronic structure methods are used to find the rates of inelastic intravalley and intervalley $n$-type carrier scattering in alloys.
Abstract: First-principles electronic structure methods are used to find the rates of inelastic intravalley and intervalley $n$-type carrier scattering in ${\text{Si}}_{1\ensuremath{-}x}{\text{Ge}}_{x}$ alloys. Scattering parameters for all relevant $\ensuremath{\Delta}$ and $L$ intra- and intervalley scattering are calculated. The short-wavelength acoustic and the optical phonon modes in the alloy are computed using the random mass approximation, with interatomic forces calculated in the virtual crystal approximation using density functional perturbation theory. Optical phonon and intervalley scattering matrix elements are calculated from these modes of the disordered alloy. It is found that alloy disorder has only a small effect on the overall inelastic intervalley scattering rate at room temperature. Intravalley acoustic scattering rates are calculated within the deformation potential approximation. The acoustic deformation potentials are found directly and the range of validity of the deformation potential approximation verified in long-wavelength frozen phonon calculations. Details of the calculation of elastic alloy scattering rates presented in an earlier paper are also given. Elastic alloy disorder scattering is found to dominate over inelastic scattering, except for almost pure silicon $(x\ensuremath{\approx}0)$ or almost pure germanium $(x\ensuremath{\approx}1)$, where acoustic phonon scattering is predominant. The $n$-type carrier mobility, calculated from the total (elastic plus inelastic) scattering rate, using the Boltzmann transport equation in the relaxation time approximation, is in excellent agreement with experiments on bulk, unstrained alloys.
TL;DR: The nitrogen-vacancy (NV) center is a paramagnetic defect in diamond with applications as a qubit as mentioned in this paper, and its electronic structure is investigated by using ab initio density functional theory for five different NV center models of two different cluster sizes.
Abstract: The nitrogen-vacancy (NV) center is a paramagnetic defect in diamond with applications as a qubit Here, we investigate its electronic structure by using ab initio density functional theory for five different NV center models of two different cluster sizes We describe the symmetry and energetics of the low-lying states and compare the optical frequencies obtained to experimental results We compute the major transition of the negatively charged NV centers to within 25--100 meV accuracy and find that it is energetically favorable for substitutional nitrogens to donate an electron to ${\text{NV}}^{0}$ The excited state of the major transition and the ${\text{NV}}^{0}$ state with a neutral donor nitrogen are found to be close in energy
TL;DR: In this paper, a microinductor fabricated on silicon using electrochemical techniques has been used in a low power dc-dc converter with a self resonant frequency of 130 MHz.
Abstract: This paper presents a microinductor fabricated on silicon using electrochemical techniques that has high efficiency in a low power dc-dc converter. Small signal measurements show a flat frequency response up to 20 MHz with a self resonant frequency of 130 MHz. The inductance at low frequency is approximately 440 nH with a dc resistance of 0.5 Omega , and a high quality factor of 11.7 at 5.5 MHz. The current handling capability test shows less than 10% decrease in inductance at 500-mA current. The performance of the microinductor has been compared to a conventional chip inductor in a commercially available 8-MHz buck converter. The converter maximum efficiency when using the microinductor is shown to be approximately 3% lower than the one using the conventional discrete chip inductor. However, the profile of the microinductor is much lower than that of the discrete chip inductor. The maximum efficiency of the microinductor in the converter is estimated to be approximately 92%.
TL;DR: Chlorine doped ZnO thin films were grown by metal-organic chemical vapour deposition (MOCVD) on sapphire and fused silica substrates as discussed by the authors.
TL;DR: In this article, a two-section diode with different slot patterns in each section allowing Vernier tuning was proposed and demonstrated, achieving a discontinuous tuning range of 30 nm with a side mode suppression greater than 30 dB.
Abstract: A novel widely tunable laser diode is proposed and demonstrated. Mode selection occurs by etching perturbing slots into the laser ridge. A two-section device is realized with different slot patterns in each section allowing Vernier tuning. The laser operates at 1.3 mum and achieves a maximum output power of 10 mW. A discontinuous tuning range of 30 nm was achieved with a side mode suppression greater than 30 dB. Wavelength switching times of approximately 1.5 ns between a number of wavelength channels separated by 7 nm have been demonstrated.
TL;DR: This paper presents an approach of how wireless sensors can be seamlessly integrated into existing and future intelligent building management systems supporting improved building performance and diagnostics with an emphasis on energy management.
TL;DR: In this paper, the authors used first principles density functional theory (DFT) to investigate the defect chemistry of Cu 2 O, CuAlO 2 and SrCu 2 O 2.
TL;DR: A hysteresis loop of the output power in the uninjected mode as a function of the power injected in the long-wavelength primary mode is shown, which shows the co-existing steady states associated with the bistability.
Abstract: We study the injection locking bistability of a specially engineered two-color semiconductor Fabry-Perot laser. Oscillation in the uninjected primary mode leads to a bistability of single mode and two-color equilibria. With pulsed modulation of the injected power we demonstrate an all-optical memory element based on this bistability, where the uninjected primary mode is switched with 35 dB intensity contrast. Using experimental and theoretical analysis, we describe the associated bifurcation structure, which is not found in single mode systems with optical injection.
TL;DR: In this paper, X-ray diffraction measurements carried out on nanotube arrays embedded in host templates indicate a polymer chain alignment along the long axes of the template pores and, as a result, along the length of the nanotubes themselves.
Abstract: Polyfluorene nanotubes are synthesized by solution assisted wetting of porous anodic alumina membranes. Well aligned arrays of close packed (∼109 tubes/cm−2) discrete nanotubes are obtained. Individual tubes have diameters of ∼260 nm and wall thicknesses of ∼50 nm. X-ray diffraction measurements carried out on nanotube arrays embedded in host templates indicate a polymer chain alignment along the long axes of the template pores and, as a result, along the long axes of the nanotubes themselves. Optical spectroscopic studies of mats of nanotubes on glass substrates yield well resolved emission spectra reflecting a narrowed distribution of emitting chain segments with increased effective conjugation lengths. The data indicate intrachain reorientation of the amorphous random poly(9,9-dioctylfluorene-2,7-diyl) molecular conformation to the more planar (low energy) extended 21 helical β-phase conformation within the tubes. Raman spectra acquired for template embedded tubes are also consistent with β-phase forma...
TL;DR: In this paper, a novel technique for the preparation of coaxial metal and magnetic alloy nanotubes was presented, which is demonstrated for the coaxial nano-structures of Ni/Co and Ni/coNiFe alloys deposited in activated polycarbonate templates using electroless plating.