Tyndall National Institute - Journal Articles

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1-to- N ring power combiners with common delta ports
(Institute of Electrical and Electronics Engineers (IEEE), 2019-01-04) Holzer, Kyle D.; Walling, Jeffrey S.; National Science Foundation
In this paper, we present a new 1-to-N way ring combiner that is an adaptation of the ring-hybrid (rat-race) structure. We present the general design guidelines for N-way planar ring combiners based on theoretical analysis of the structures. The proposed 1-to-N way ring structure offers a compact, planar layout that includes a single common delta port. This is beneficial to applications where power monitoring, calibration, or energy recycling can be leveraged. It offers similar loss to other N-way structures. To demonstrate the combiners operation, we present completely passive structures and structures with embedded power amplifiers for 4- and 6-way variants. The designs are optimized for operation in the 5-6 GHz unlicensed bands. The passive 4- and 6-way combiners achieve IL of 1.3 and 1 dB, respectively, with associated port isolations of <;-30 dB. The combiners with embedded amplifiers show similar performance and are validated using modulated signals and demonstrate good measured linearity when combining up to 6 amplifiers for output powers >1 W.
(2+1)-dimensional photonic crystals from Langmuir-Blodgett colloidal multilayers
(AIP Publishing, 2006) Romanov, Sergei G.; Bardosova, Maria; Pemble, Martyn E.; Torres, C. M. Sotomayor; Science Foundation Ireland; Sixth Framework Programme
Angle-resolved transmission spectra of multilayers of two-dimensional colloidal crystals prepared by the Langmuir-Blodgett technique have been studied. In contrast to the light diffraction in three-dimensional colloidal crystals, optical spectra revealed only very weak correlation between layers in the Langmuir-Blodgett multilayers. Two reasons for the observed transmission minima have been identified: the diffraction at a stack of layers and the scattering of the incident beam by guided modes of the two-dimensional colloidal crystals. (c) 2006 American Institute of Physics. (DOI:10.1063/1.2234568)
A 2-MS/s, 11.22 ENOB, extended input range SAR ADC with improved DNL and offset calculation
(Institute of Electrical and Electronics Engineers (IEEE), 2018-11) Asghar, Sohail; Afridi, Sohaib Saadat; Pillai, Anu; Schuler, Anita; de la Rosa José; O'Connell, Ivan; Enterprise Ireland; European Regional Development Fund; Junta de Andalucía
A 12-bit successive approximation register analog-to-digital converter (ADC) with extended input range is presented. Employing an input sampling scaling technique, the presented ADC can digitize the signals with an input range of 3.2 V pp-d (±1.33 V REF ). The circuit also includes a comparator offset compensation technique that results in a residual offset of less than 0.5 LSB. The chip has been designed and implemented in a 0.13-μm CMOS process and demonstrates the state-of-the-art performance, featuring an SNDR of 69.3 dB and the SFDR of 79 dB without requiring any calibration. Total power consumption of the ADC is 0.9 mW, with a measured differential non-linearity of 1.2/-1.0 LSB and INL of 2.3/-2.2 LSB.
2D and 3D photonic crystal materials for photocatalysis and electrochemical energy storage and conversion
(National Institute for Materials Science; Taylor & Francis, 2016-09) Collins, Gillian; Armstrong, Eileen; McNulty, David; O'Hanlon, Sally; Geaney, Hugh; O'Dwyer, Colm; National University of Ireland; Science Foundation Ireland
This perspective reviews recent advances in inverse opal structures, how they have been developed, studied and applied as catalysts, catalyst support materials, as electrode materials for batteries, water splitting applications, solar-to-fuel conversion and electrochromics, and finally as photonic photocatalysts and photoelectrocatalysts. Throughout, we detail some of the salient optical characteristics that underpin recent results and form the basis for light-matter interactions that span electrochemical energy conversion systems as well as photocatalytic systems. Strategies for using 2D as well as 3D structures, ordered macroporous materials such as inverse opals are summarized and recent work on plasmonic–photonic coupling in metal nanoparticle-infiltrated wide band gap inverse opals for enhanced photoelectrochemistry are provided.
2D and 3D vanadium oxide inverse opals and hollow sphere arrays
(Royal Society of Chemistry (RSC), 2014-10-24) Armstrong, Eileen; Osiak, Michal J.; Geany, Hugh; Glynn, Colm; O'Dwyer, Colm; Irish Research Council; Science Foundation Ireland; Seventh Framework Programme
High quality 2D and 3D inverse opals and hollow sphere arrays of vanadium oxide are grown on conductive substrates from colloidal polymer sphere templates formed by electrophoretic deposition or surfactant-assisted dip-coating. Inverse opals (IOs) are formed using variants of solution drop-casting, N2-gun assisted infiltration and high-rate (200 mm min−1) iterative dip-coating methods. Through Raman scattering, transmission electron microscopy and optical diffraction, we show how the oxide phase, crystallinity and structure are inter-related and controlled. Opal template removal steps are demonstrated to determine the morphology, crystallinity and phase of the resulting 2D and 3D IO structures. The ability to form high quality 2D IOs is also demonstrated using UV Ozone removal of PMMA spheres. Rapid hydrolysis of the alkoxide precursor allows the formation of 2D arrays of crystalline hollow spheres of V2O5 by utilizing over-filling during iterative dip-coating. The methods and crystallinity control allow 2D and 3D hierarchically structured templates and inverse opal vanadium oxides directly on conductive surfaces. This can be extended to a wide range of other functional porous materials for energy storage and batteries, electrocatalysis, sensing, solar cell materials and diffractive optical coatings.
2D nanosheet paint from solvent-exfoliated Bi2Te3 ink
(American Chemical Society, 2017-08-09) Carroll, Elaine; Buckley, Darragh; Mogili, N. V. V.; McNulty, David; Moreno, M. Sergio; Glynn, Colm; Collins, Gillian; Holmes, Justin D.; Razeeb, Kafil M.; O'Dwyer, Colm; Irish Research Council; Science Foundation Ireland; Consejo Nacional de Investigaciones Científicas y Técnicas; Agencia Nacional de Promoción Científica y Tecnológica; Horizon 2020; Analog Devices; Ministry of Science, Technology, Innovation and Communication, Brazil
Embedding 2D layered materials into polymers and other materials as composites has resulted in the development of ultrasensitive pressure sensors, tunable conductive stretchable polymers, and thermoelectric coatings. As a wettable paint or ink, many 2D materials may be penciled, printed, or coated onto a range of surfaces for a variety of applications. However, the intrinsic conductive properties of painted coatings using 2D and layered materials are not completely understood, and conductive polymer additives may mask underlying properties such as directional conductivity. We report a process for making a paint from solvent-exfoliated Bi2Te3 into solution-dispersible 2D and few-layer (multiple quintuple) nanosheet inks, that form smooth, uniform paint blends at several concentrations of Bi2Te3. The individual solvent-exfoliated nanosheets are edge-coated by (poly)ethylene glycol to produce a paint, stable over extended period in solution. Electrical transport is found to be sensitive to aspect ratio, and conduction along the painting direction is suppressed for longer strips so long as the aspect ratio is high (4–10× or more), but for short and wide paint strips (aspect ratio ≤1), conductance is improved by a factor of 3×. Square 2D paint regions show no clear directional preference for conductance at room temperature but are markedly affected by higher temperatures. Conductivity along a preferential conduction pathway through the nanosheet ensemble is modulated by 2D nanosheet stacking along the direction of paint application for a given aspect ratio. This paint and insights into geometrical 2D composite conduction may have implications for conductive composites, thermoelectrics, and writable circuits using 2D material paints or inks.
3D open-worked inverse opal TiO2 and GeO2 materials for long life, high capacity Li-ion battery anodes
(Elsevier, 2017-10-18) McNulty, David; Lonergan, Alex; O'Hanlon, Sally; O'Dwyer, Colm; Science Foundation Ireland; Irish Research Council
In this short review, we overview some advancements made in Li-ion battery anode development, where the structural arrangement of the material plays an important role. Specifically, we summarise the benefits of 3D macroporous structure imposed the anode material, in order to improve ionic and electronic conductivity in the absence of conductive additives and binders. Two anode materials are overviewed: TiO2 and GeO2. These are either high capacity anode materials or accessible, abundant materials that are capable of very stable and long-term cycling. We have focused this review on 3D inverse opal structures of these anodes and summarise their enhanced behaviour by comparing their performance metrics to a range of nanoscale and porous analogues of these materials.
A 3D printed electromagnetic nonlinear vibration energy harvester
(IOP Publishing Ltd, 2016-08-24) Constantinou, Peter; Roy, Saibal; Science Foundation Ireland
A 3D printed electromagnetic vibration energy harvester is presented. The motion of the device is in-plane with the excitation vibrations, and this is enabled through the exploitation of a leaf isosceles trapezoidal flexural pivot topology. This topology is ideally suited for systems requiring restricted out-of-plane motion and benefits from being fabricated monolithically. This is achieved by 3D printing the topology with materials having a low flexural modulus. The presented system has a nonlinear softening spring response, as a result of designed magnetic force interactions. A discussion of fatigue performance is presented and it is suggested that whilst fabricating, the raster of the suspension element is printed perpendicular to the flexural direction and that the experienced stress is as low as possible during operation, to ensure longevity. A demonstrated power of ~25 μW at 0.1 g is achieved and 2.9 mW is demonstrated at 1 g. The corresponding bandwidths reach up-to 4.5 Hz. The system's corresponding power density of ~0.48 mW cm−3 and normalised power integral density of 11.9 kg m−3 (at 1 g) are comparable to other in-plane systems found in the literature.
3D UAV trajectory and data collection optimisation via deep reinforcement learning
(IEEE, 2022-04) Nguyen, Khoi Khac; Duong, Trung Q.; Do-Duy, Tan; Claussen, Holger; Hanzo, Llajos; Royal Academy of Engineering; European Research Council; Engineering and Physical Sciences Research Council
Unmanned aerial vehicles (UAVs) are now beginning to be deployed for enhancing the network performance and coverage in wireless communication. However, due to the limitation of their on- board power and flight time, it is challenging to obtain an optimal resource allocation scheme for the UAV-assisted Internet of Things (IoT). In this paper, we design a new UAV-assisted IoT system relying on the shortest flight path of the UAVs while maximising the amount of data collected from IoT devices. Then, a deep reinforcement learning-based technique is conceived for finding the optimal trajectory and throughput in a specific coverage area. After training, the UAV has the ability to autonomously collect all the data from user nodes at a significant total sum-rate improvement while minimising the associated resources used. Numerical results are provided to highlight how our techniques strike a balance between the throughput attained, trajectory, and the time spent. More explicitly, we characterise the attainable performance in terms of the UAV trajectory, the expected reward and the total sum-rate.
3D vanadium oxide inverse opal growth by electrodeposition
(Electrochemical Society, 2015) Armstrong, Eileen; O'Sullivan, Maria; O'Connell, John; Holmes, Justin D.; O'Dwyer, Colm; Science Foundation Ireland
Three-dimensional vanadium pentoxide (V2O5) material architectures in the form of inverse opals (IOs) were fabricated using a simple electrodeposition process into artificial opal templates on stainless steel foil using an aqueous solution of VOSO4.χH2O with added ethanol. The direct deposition of V2O5 IOs was compared with V2O5 planar electrodeposition and confirms a similar progressive nucleation and growth mechanism. An in-depth examination of the chemical and morphological nature of the IO material was performed using X-ray crystallography, X-ray photoelectron spectroscopy, Raman scattering and scanning/transmission electron microscopy. Electrodeposition is demonstrated to be a function of the interstitial void fraction of the artificial opal and ionic diffusivity that leads to high quality, phase pure V2O5 inverse opals is not adversely affected by diffusion pathway tortuosity. Methods to alleviate electrodeposited overlayer formation on the artificial opal templates for the fabrication of the porous 3D structures are also demonstrated. Such a 3D material is ideally suited as a cathode for lithium ion batteries, electrochromic devices, sensors and for applications requiring high surface area electrochemically active metal oxides.
42.6 Gbit/s fully integrated all-optical XOR gate
(Institution of Engineering and Technology, 2009-09) Dailey, James M.; Ibrahim, Selwan K.; Manning, Robert J.; Webb, Rod P.; Lardenois, Sébastien; Maxwell, Graeme D.; Poustie, Alistair J.; Science Foundation Ireland
We demonstrate an SOA-based all-optical high-speed Mach-Zehnder interferometer exclusive- OR (XOR) gate fabricated in a silica III-V hybrid-integration technology platform. The device includes integrated time delays for rapid differential operation as well as integrated phase shifters for fine tuning of power splitters and interferometer bias enabling highly optimized XOR gate operation. XOR functionality is verified through inspection of the output pulse sequence and the carrier-suppressed output spectrum. A 2.3 dB penalty for a 42.6 Gb/s RZ-OOK signal at a 10-9 bit error rate is observed.
4x25 Gbps polarization diversity silicon photonics receiver with transfer printed III-V photodiodes
(Institute of Electrical and Electronics Engineers (IEEE), 2018-12-27) Muliuk, Grigorij; Van Gasse, Kasper; Van Kerrebrouck, Joris; Trindade, Antonio José; Corbett, Brian M.; Van Thourhout, Dries; Roelkens, Günther; Horizon 2020
We demonstrate the transfer-printing-based integration of III-V substrate-illuminated p-i-n photodetectors onto a 4-wavelength-channel silicon photonics polarization diversity receiver circuit. 4x25 Gbps operation is demonstrated for 2.5 nm wavelength channel spacing in the C-band. Transfer printing is an enabling technology for massively parallel heterogeneous III-V-on-Si integration.
50 years of CMD
(EDP Sciences, 2018-11-30) Devreese, Jozef T.; O'Reilly, Eoin P.; van der Beek, Kees
A 7-bit 7-GHz multiphase interpolator-based DPC for CDR applications
(Institute of Electrical and Electronics Engineers (IEEE), 2022-07-21) Khanghah, Meysam M.; Sadeghipour, Khosrov D.; Kelly, Denis; Antony, Cleitus; Ossieur, Peter; Townsend, Paul D.; Science Foundation Ireland; Enterprise Ireland; IDA Ireland
This paper presents a 7-bit digital to phase converter (DPC) for high speed clock and data recovery (CDR) applications which is capable of generating multi-phase clocks at 7-GHz frequency. Fabricated in a standard 65-nm CMOS technology, the design introduces a modified phase interpolator (PI) and a quadrature phase corrector (QPC) to reduce the effect of the circuit imperfections on the DPC's resolution and linearity. Employing a 14-GHz quadrature reference clock, the DPC achieves DNL/INL of 0.7/6 LSB respectively while consuming 40.5 mW power from 1.05 V supply.
Ab initio study of the atomic level structure of the rutile TiO2 (110) – titanium nitride (TiN) interface
(American Chemical Society, 2017-09-22) Gutiérrez Moreno, José Julio; Nolan, Michael; Environmental Protection Agency; Partnership for Advanced Computing in Europe AISBL; Science Foundation Ireland; Higher Education Authority; Department of Jobs, Enterprise and Innovation; Department of Education and Skills
Titanium nitride (TiN) is widely used in industry as a protective coating due to its hardness and resistance to corrosion and can spontaneously form a thin oxide layer when it is exposed to air, which could modify the properties of the coating. With limited understanding of the TiO2 – TiN interfacial system at present, this work aims to describe the structural and electronic properties of oxidized TiN based on a density functional theory (DFT) study of the rutile TiO2 (110) – TiN (100) interface model system, also including Hubbard +U correction on Ti 3d states. The small lattice mismatch gives a good stability to the TiO2 – TiN interface after depositing the oxide onto TiN through the formation of interfacial Ti – O bonds. Our DFT+U study shows the presence of Ti3+ cations in the TiO2 region, which are preferentially located next to the interface region as well as the rotation of the rutile TiO2 octahedra in the interface structure. Although the vacancy formation energies for Ti in TiN (Evac (Ti) ≥ 4.03 eV) or O in the oxide (Evac (O) ≥ 3.40 eV) are quite high relative to perfect TiO2 – TiN, defects are known to form during the oxide growth and can therefore be present after TiO2 formation. Our results show that a structure with exchanged O and N can lie 0.82 eV higher in energy than the perfect system, suggesting the stability of structures with interdiffused O and N anions at ambient conditions. The presence of N in TiO2 introduces N 2p states localized between the top edge of the O 2p valence states and the mid-gap Ti3+ 3d states, thus reducing the bandgap in the TiO2 region for the exchanged O/N interface EDOS. The outcomes of these simulations give us a most comprehensive insight on the atomic level structure and the electronic properties of oxidised TiN surfaces.
An ab initio study of the structural and mechanical alterations of Ti-Nb alloys
(AIP Publishing, 2018-12-27) Gutiérrez Moreno, José Julio; Papageorgiou, D. G.; Evangelakis, G. A.; Lekka, Ch. E.; FP7 People: Marie-Curie Actions; Shenzhen University
This article describes a systematic theoretical investigation of the role of Nb substitution on the structural and mechanical properties of Ti-Nb alloys. The aim is to understand the origin of the low-rigidity of some of these materials. This quality makes these materials suitable for metallic implants. The mechanical stability conditions in conjunction with the calculated elastic constants of Ti-Nb predict the destabilization of α′ and ω structures, while the β-phase can be stabilized for Nb content above 10 at. %. The evaluated Young's moduli (E) follow the sequence of Eω > Eα′ > Εα″ > Εβ, revealing high Eω and Eα′ values (greater than 120 GPa), while the Eβ value converges to approximately 87 GPa. The averaged E, estimated from a weighted average of Eω, Eα′, Εα″, and Εβ ab initio values, reproduces the experimental Ti-Nb Young's modulus w-shaped curve. Young's modulus surface reveals highly anisotropic E values for all Ti-Nb phases. Eβ exhibits values under 30 GPa along the [100] direction for Nb compositions larger than 12 at. %, suggesting that the orientational growth of a Ti-Nb alloy is important for the design of low-rigidity alloys, especially at small Nb concentrations. These results can be used as a guide for the design of novel low-rigidity alloys for biomedical applications.
Ab-initio and experimental study of phase stability of Ti-Nb alloys
(Elsevier, 2016-11-18) Gutiérrez Moreno, José Julio; Bönisch, M.; Panagiotopoulos, N. T.; Calin, M.; Papageorgiou, D. G.; Gebert, A.; Eckert, J.; Evangelakis, G. A.; Lekka, Ch. E.; European Commission; Seventh Framework Programme; Deutsche Forschungsgemeinschaft
A systematic theoretical and experimental study concerning the crystallographic structure and electronic properties of Ti-xNb (x < 50 at%) alloys is presented, aiming to enlighten the electronic origins of the β-phase stability which is of high interest for the development of novel β stabilized Ti-based alloys for biomedical applications. Both quantum-mechanical calculations and X-ray diffraction found several structural phases depending on Nb concentration. The ab-initio total energy results reveal that at low Nb contents the α′ and ω phases are favoured while at Nb content >18.75 at% the β-phase is favoured against all other crystallographic structures in line with the experimental results. Interestingly, at high Nb content the α′ and ω hexagonal phases become unstable due to the electronic band filling close to the Fermi level EF, which is mainly due to Nb-p and Ti-d antibonding hybridizations. On the contrary, in the cubic β-Ti-25Nb (at%) the depletion of the occupied electronic states at the EF occurs mainly due to Nb-d and Ti-d bonding interactions, resulting in a stable β-TiNb structure. These data could enlighten the electronic origin of the Ti-Nb phase stability, thus, may contribute to the design of β stabilized low moduli Ti-based alloys suitable for load-bearing biomedical applications.
Absence of evidence ≠ evidence of absence: statistical analysis of inclusions in multiferroic thin films
(Nature Publishing Group, Macmillan Publishers Limited, 2014-07-16) Schmidt, Michael; Amann, Andreas; Keeney, Lynette; Pemble, Martyn E.; Holmes, Justin D.; Petkov, Nikolay; Whatmore, Roger W.; Science Foundation Ireland
Assertions that a new material may offer particularly advantageous properties should always be subjected to careful critical evaluation, especially when those properties can be affected by the presence of inclusions at trace level. This is particularly important for claims relating to new multiferroic compounds, which can easily be confounded by unobserved second phase magnetic inclusions. We demonstrate an original methodology for the detection, localization and quantification of second phase inclusions in thin Aurivillius type films. Additionally, we develop a dedicated statistical model and demonstrate its application to the analysis of Bi6Ti2.8Fe1.52Mn0.68O18 (B6TFMO) thin films, that makes it possible to put a high, defined confidence level (e.g. 99.5%) to the statement of ‘new single phase multiferroic materials’. While our methodology has been specifically developed for magnetic inclusions, it can easily be adapted to any other material system that can be affected by low level inclusions.
AC-assisted single-nanowire electromechanical switch
(Royal Society of Chemistry (RSC), 2013-09-10) Andzane, Jana; Meija, Raimonds; Livshits, Alexander I.; Prikulis, Juris; Biswas, Subhajit; Holmes, Justin D.; Erts, Donats; Latvijas Zinātnes Padome; Science Foundation Ireland
A unique two-source controlled nanoelectromechanical switch has been assembled from individual, single-clamped Ge nanowires. The switching behaviour was achieved by superimposing the control signals of specific frequencies to the electrostatic potential of the output terminals, eliminating the need for an additional gate electrode. Using an in situ manipulation technique inside a scanning electron microscope, we demonstrate that the pull-out force required to overcome adhesion at the contact can be significantly reduced by exciting mechanical resonant modes within the nanowire.
Access resistance reduction in Ge nanowires and substrates based on non-destructive gas-source dopant in-diffusion
(The Royal Society of Chemistry, 2014-10-03) Duffy, Ray; Shayesteh, Maryam; Thomas, Kevin K.; Pelucchi, Emanuele; Yu, Ran; Gangnaik, Anushka S.; Georgiev, Yordan M.; Carolan, Patrick B.; Petkov, Nikolay; Long, Brenda; Holmes, Justin D.; Higher Education Authority; Science Foundation Ireland
To maintain semiconductor device scaling, in recent years industry has been forced to move from planar to non-planar device architectures. This alone has created the need to develop a radically new, non-destructive method for doping. Doping alters the electrical properties of a semiconductor, related to the access resistance. Low access resistance is necessary for high performance technology and reduced power consumption. In this work the authors reduced access resistance in top–down patterned Ge nanowires and Ge substrates by a non-destructive dopant in-diffusion process. Furthermore, an innovative electrical characterisation methodology is developed for nanowire and fin-based test structures to extract important parameters that are related to access resistance such as nanowire resistivity, sheet resistance, and active doping levels. Phosphine or arsine was flowed in a Metalorganic Vapour Phase Epitaxy reactor over heated Ge samples in the range of 650–700 °C. Dopants were incorporated and activated in this single step. No Ge growth accompanied this process. Active doping levels were determined by electrochemical capacitance–voltage free carrier profiling to be in the range of 1019 cm−3. The nanowires were patterned in an array of widths from 20–1000 nm. Cross-sectional Transmission Electron Microscopy of the doped nanowires showed minimal crystal damage. Electrical characterisation of the Ge nanowires was performed to contrast doping activation in thin-body structures with that in bulk substrates. Despite the high As dose incorporation on unpatterned samples, the nanowire analysis determined that the P-based process was the better choice for scaled features.

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