Fernando M.F. Rhen

Fernando M.F. Rhen
University of Limerick | UL · Department of Physics and Energy

PhD, Trinity College Dublin (TCD), Dublin, Ireland

About

69
Publications
11,805
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1,119
Citations
Citations since 2016
14 Research Items
497 Citations
2016201720182019202020212022020406080100
2016201720182019202020212022020406080100
2016201720182019202020212022020406080100
2016201720182019202020212022020406080100

Publications

Publications (69)
Article
The need to replace conventional sources of energy has driven the development of fuel cell technology. The polymer electrolyte membrane fuel cells (PEMFCs) show high performance and are important power sources for hydrogen fuel cell vehicles due to the fact that the cells can operate at relatively low temperatures (50 - 90 o C) , has high energy ef...
Article
The aim of this work is to determine the optimal platinum loading for the preparation of membrane-based electrochemical sensors for carbon monoxide detection. Platinum is a required constituent of the electrode. Its function is to catalyse CO as it enters the sensor. Initial results show that a Nafion based sensor hydrated with small amounts of sul...
Article
Single crystal L-amino acids can exhibit technologically useful piezoelectric and nonlinear optical properties. Here we predict, using density functional theory, the piezoelectric charge and strain and voltage tensors of the racemic amino acid DL alanine, and use the modeling data to guide the first macroscopic and nanoscopic piezoelectric measurem...
Article
Short-duration fluctuations of electricity supply and demand can cause instability in electricity grids and utility systems. These fluctuations are usually corrected using fast response time electrical energy storage devices that have high power and low storage capacity, hence they are never noticed by the end user. This chapter covers basic aspect...
Article
Full-text available
Thin films of Fex Pt100−x (0 < x < 80) alloy were prepared via magnetron sputtering deposition and investigated as electrocatalysts for the oxygen reduction reaction, a process that is central to hydrogen fuel cell technology. Room temperature sputtering produced smooth, uniform films of tightly packed nanocrystallites with a disordered face-centre...
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Piezoelectricity, the linear relationship between stress and induced electrical charge, has attracted recent interest due to its manifestation in biological molecules such as synthetic polypeptides or amino acid crystals, including gamma (γ) glycine. It has also been demonstrated in bone, collagen, elastin and the synthetic bone mineral hydroxyapat...
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Electrocatalysts with high performance, increased stability, and high surface area are essential for the widespread commercialization of fuel cells. Nanostructured materials emerge as potential candidates to meet these targets. We report on the synthesis and characterization of a nanostructured platinum electrocatalyst for methanol oxidation. Using...
Article
Here we report a systematic investigation into the effect of strain on the electrocatalytic activity of films of Pt. We use an electroless deposition process to deposit the Pt onto sputtered Au substrates and characterise their structural and electrochemical properties. We found a direct correlation between the rate of methanol oxidation and the fr...
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Full-text available
We have investigated the magnetic properties of Ni1-xBx nanotubes as a function of composition, temperature, and magnetic fields. The nanotubes were prepared by electroless deposition in polycarbonate membranes using dimethylamine borane as a reducing agent. The nanotube arrays are formed with a length of 20 μm, an outer diameter of 400 nm, and an...
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Co-B nanotubes were prepared via an electroless deposition method. The morphology, magnetic properties and the magnetization reversal mechanism of the nanotubes were investigated. Deposition was carried out in porous polycarbonate membranes leading to the formation of Co-B nanotubes with an average external diameter of 400 nm and lengths up to 6 μm...
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We investigated the structure and magnetic properties of SmxCo100-x (20 <x< 32) sputtered onto heated silicon substrates at 350°C (623K). We found that the (110) and (100) preferential orientations coexist in the films in different proportions depending on the Sm content. Coercivity and hysteresis loop shape are dependent on the Sm content and are...
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We prepared Co-Ni-Fe-B alloys by electroless plating into porous polycarbonate membranes and investigated the formation of the nanostructure using high-resolution scanning electron microscope images and magnetic measurements. The formation of the nanostructure occurs in five stages: nucleation, particle growth, percolation, film formation and films...
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We have prepared Ni-Fe-B nanotube arrays of length 20 μm and outer diameter of 400 nm in polycarbonate membranes via electroless deposition using dimethylamine borane (DMAB) as a reducing agent. The alloy composition was varied by controlling the FeSO4 concentration in the deposition solution and the effect of this variation on the nanostructures a...
Article
Full-text available
In this study we have deposited continuous and uniform Ni-B nanotubes with a length of 20 μm and outer diameter of 400 nm via an electroless deposition method and investigated their magnetic properties. We show that as the pH of the electroless deposition bath increases, the B content of the Ni-B deposit decreases. As the boron content decreases th...
Article
The mechanical, ferroelectric, and ferromagnetic properties of materials with dimensions in the nanometer range differ significantly from their bulk properties [1]. Unique magnetic properties can be tailored through compositional and morphological control of the deposited nanostructures [2]. These unique properties significantly increase the potent...
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Full-text available
We have investigated the magnetic properties of nanostructured Co-B alloys, that were prepared via electroless deposition. The deposition process results in the formation of a nanostructure consisting of nanotubes connected to thin films at both ends. Depending on the deposition time end-open or end-closed nanotubes can be formed. The overall nanos...
Conference Paper
Magnetic nanotubes have a wide variety of potential applications in modern technologies in areas such as energy conversion, electronic devices and high density memory storage [1]. Recently using electroless deposition, we have established a method to prepare continuous nanotubes 20 μm in length with external diameter of 400 nm and uniform wall thic...
Article
We have studied electroless deposition of Ni-B within a template structure as a model process to optimize the deposition of nanostructures. Our results show that depending on the deposition rate and deposition time employed end-opened or end-closed nanotubes connected at both ends by a thin film can be prepared. We have found that if the deposition...
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Full-text available
We have prepared Ni-Cu-B nanotube arrays with lengths of 20 μm and outer diameter of 400 nm via electroless deposition in a polycarbonate membrane and investigated their associated magnetic properties. The nanotube composition was varied by controlling the CuSO4 concentration in the deposition solution. The nanostructured deposit has a specific mag...
Conference Paper
Magnetic nanostructures can be formed via a variety of preparation methods. The most common of these is electrochemical deposition. However, recently there has been an increased interest in electroless deposition of magnetic nanostructures. Electroless deposition of nanotubes or nanowires requires a template, commonly a porous polycarbonate (PPC) o...
Conference Paper
We have prepared nanostructured Co-B catalysts via electroless deposition on a porous polycarbonate membrane for use as a hydrogen evolution catalyst from a sodium borohydride solution. Amorphous Co-B alloy is deposited to form nanotubes, connected together by a thin film at both ends. We have varied the deposition time to form a range of Co-B nano...
Conference Paper
Viable hydrogen fuel cells require a cheap, easily accessible source of pure hydrogen with a large storage capacity. Sodium borohydride is an ideal storage material with a storage capacity of 10.8 % wt. and the hydrogen can be controllably released with the use of a suitable catalyst. Nanostructured catalysts are of particular interest due to their...
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Here, we present an implementation of the moving Preisach model to describe the magnetic behaviour of Sm-Co films. We use two independent Preisach distributions to separate the magnetization into reversible and irreversible components. The numerical simulation works very well for a system where two magnetic phases are weakly or negligibility couple...
Conference Paper
The study of magnetic nanoparticles has attracted great attention of researchers in nanoscience and nanotechnology. It has been recognized that these systems can be applied in several fields, including catalysis, biomedicine, magnetic resonance imaging, data storage media, and drug delivery among others. We have produced Fe3O4 and CoFe2O4 magnetic...
Article
Micro-inductors, with an electrodeposited nickel–iron core have been fabricated on silicon substrates, and have been characterized in the frequency range up to 100 MHz. The core consists of a nickel iron, 45:55 alloy which is deposited using pulse-reverse electroplating in the presence of a magnetic field to control anisotropy. The operation of the...
Article
We report the preparation, characterization of structure and magnetic properties of electrodeposited L10 FePt films with high coercivity. Equiatomic as-deposited films are nanocrystalline, soft and magnetically isotropic. The transition from the disordered to the ordered phase was studied by varying the annealing time and annealing temperature. The...
Article
Ni nanoparticles (~32 nm particle diameter) have been synthesized on the walls of microporous (~1 nm pore diameter) silica spheres (~2.6 μm sphere diameter) and characterised magnetically to potentially produce a new class of core (silica micro-spheres)-shell (nanometallic)-type nanocomposite material. These magnetic nanocomposite materials display...
Article
We have prepared thin Ni films by direct electrodeposition onto Si substrates and investigated the magnetization dynamics up to 9 GHz. Films with typical thickness of 200 nm show good adhesion to the substrate. Experimental absorption spectra were fitted using a model, which combines the magnetization dynamics according to Landau–Lifshitz–Gilbert a...
Conference Paper
The magnetic field effect in electrochemistry is associated with the coupling between magnetic forces and ionic transport. It has been observed that the corrosion rate can increase [1, 2, 3], decrease [4, 5] or remain the same with an applied magnetic field, depending on the system studied. We have recently found that the corrosion rate of Ag in co...
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We have investigated the magnetic properties of electroplated nickel nanowires with very distinct nanostructures, which are obtained by simply changing the plating temperature of the electrolyte. Low temperature (40 ° C ) resulted in larger average grain size comparable to the diameter of the wires, whereas higher temperature (60 ° C ) revealed sel...
Article
Electroless magnetic thin films have been deposited from borane-based baths suitable for use in integrated magnetics on Si applications. The baths were developed for compatibility with standard photoresist for microfabrication of integrated magnetics on Si. The specific formulations, which differ from those reported previously, yield uniform, high...
Article
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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...
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A method is described for the fabrication of magnetic force microscopy tips via localized electrodeposition and focused ion beam milling departing from commercial tapping mode tips. Very high aspect ratios and interacting magnetic moments are possible without altering significantly the tapping resonant frequency of the cantilever. These tips can ac...
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We have studied the influence of P and of plating current density on static/dynamic magnetic and electrical properties of CoNiFe high moment alloy. We found that morphology, electrical and magnetic properties of films with P content up to 10 at. % are quite different from those of pure CoNiFe. CoNiFeP morphology consists of a structure made of isol...
Article
We have investigated CoNiFe and CoNiFe–C electrodeposited by pulse reverse plating (PRP) and direct current (DC) techniques. CoNiFe(PRP) films with composition Co59.4Fe27.7Ni12.8 show coercivity of 95Am−1 (1.2Oe) and magnetization saturation flux (μ0Ms) of 1.8T. Resistivity of CoNiFe (PRP) is about 24μΩcm and permeability remains almost constant μr...
Article
We present a novel technique for the preparation of coaxial metal and magnetic alloy nanotubes, which is demonstrated for the coaxial nanotubes of Ni/Co and Ni/CoNiFe alloys deposited in activated polycarbonate templates using electroless plating. For each metal or alloy the tube wall thickness was controlled to be less than 100 nm. The process inv...
Conference Paper
Full-text available
High current inductor applications operating in the MHz range are generally limited to voltage regulator modules (VRMpsilas) and point of load (POL) power supplies, where the issue of fast transient response demands reduced inductance values. State-of-the-art controller ICpsilas enable switching frequencies up to 8 MHz for low current POL applicati...
Article
Full-text available
The magnetic properties of electrodeposited CoNiFe films with thicknesses varying from 0.20 to 10 μ m were studied. The films show a single face-centered-cubic CoNiFe phase with grain sizes ranging from 23 to 29 nm. The coercivity is controlled by a combination of the morphology and nanocrystalline structure of the deposits. The nanocrystalline gra...
Conference Paper
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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 sig...
Conference Paper
Full-text available
The application of PCB integrated electroplated cores for VRM inductors is proposed, where the motivation is to increase frequencies beyond 1 MHz so that VRM transient response can be improved. It is shown that electroplated alloys have loss properties that are at least competitive with those of the highest frequency ferrite material available. Var...
Article
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There are suggestions in the electrochemical literature that a body force F ∇c acts when an electrolyte with a non-uniform concentration c of paramagnetic ions is subject to a uniform magnetic field. We demonstrate, experimentally and theoretically, that no such magnetic body force exists, to first order. A second-order correction associated with t...
Article
We have studied the effect of magnetic field (B) and rotation speed (ω) of a rotating disk electrode on the corrosion current and rest potential (open circuit potential) of Zn and Fe nitrate and dichromate solutions acidified with nitric acid and sulfuric acid, respectively. We show that the anodic area of Zn and Fe can be modulated by a magnetic f...
Article
A platinum coated electrode, which creates a magnetic field of 25mT and a field gradient of order 105Tm−1 within 100nm of the electrode surface is produced by embedding an array of CoPt nanowires in an alumina membrane. There is an enhancement by up to a factor of three for a model oxygen reduction reaction in an alkaline medium when the nanowires...
Article
Full-text available
peer-reviewed The application of PCB integrated electroplated cores for VRM inductors is proposed, where the motivation is to increase frequencies beyond 1 MHz so that VRM transient response can be improved. It is shown that electroplated alloys have loss properties that are at least competitive with those of the highest frequency ferrite material...
Article
We have investigated the field-induced rest potential shift of Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Bi, and stainless steel in nitric acid solution. Anodic rest potential shifts of up to 4 mV, 10 mV, 35 mV and 2.4 mV were observed for Mn, Zn, Fe and Ni, respectively, with an applied field of 1.5 T, whereas no shift was observed for Cr, Cu, Sn, Bi, or st...
Article
Full-text available
The magnetization of nickel foils electrodeposited under different conditions was not usually found to differ significantly from that of the bulk (55.4 A m2 kg−1). However, some galvanostatically deposited films from a citrate-based electrolyte showed a lower magnetization, which was rose to the bulk value after annealing at 575 K, with no change i...
Article
The partial suppression of corrosion of Ag and Cu in concentrated nitric acid solution by a magnetic field of up to 5 T was studied. The corrosion current density of these metals was found to diminish with magnetic field and rotation speed in a rotating disk electrode experiment. The suppression of corrosion is associated with removal of the cataly...
Article
Full-text available
The influence of an external magnetic field on the rest potential of ferromagnetic and nonferromagnetic electrodes is studied. The shift is measured as a function of magnetic field magnitude and direction, pH, electrolyte composition, solution agitation, and electrode roughness. Anodic shifts can be observed not only for ferromagnetic electrode...
Article
Thick films of nearly equiatomic Co–Pt produced by electrodeposition into nanoporous membranes exhibit an isotropic magnetic phase with square hysteresis loops (Mr/Ms = 0.95) and coercivity of up to 1.3 T. The initial magnetization curve is characteristic of pinning-type magnets. The coercivity can be controlled by the choice of annealing temperatu...
Article
Porous alumina membranes with a uniform pore size of 100 nm have been used to prepare arrays of oriented cobalt nanowires by electrodeposition in an applied magnetic field. The hexagonal c-axis lies in the plane of the membrane, perpendicular to the nanowire axis, for material deposited in 0 T or 1.5 T, but in 5 T the c-axis lies at about 70° to th...
Conference Paper
CoPt films are electrodeposited from a chlorite-based bath. Magnetically isotropic samples are then obtained after annealing under vacuum and H2 reducing atmosphere with coercivities as high as 1 T. It is found that annealing under H2 is likely to decompose hydroxides incorporated during the electrodeposition which leads to a smaller amount of impu...
Article
Nd–Fe–B films were prepared by DC magnetron sputtering and the effect of buffer layer and annealing conditions on the magnetic properties have been investigated. High degree of texture, highest coercivity and energy product are achieved in Ta-buffered films deposited on heated substrates. A linear increase of coercivity with film thickness up to 10...
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We report a rest potential shift for a nonmagnetic electrode in a magnetic field. When a 1.5 T magnetic field is applied to zinc electrode, anodic shifts of 42 mV in paramagnetic solution (16 mM CuSO4) and 5 mV in diamagnetic solution (1 M KNO3 at pH 1) are observed. This shows that neither a ferromagnetic electrode nor a paramagnetic electrolyte i...
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A novel bath for electrodepositing FePt films was developed and films were electrodeposited on copper substrates with thickness up to 0.45 μm. The magnetic and structural properties of the films were measured. The films developed 0.3-T coercivity after annealing at 400°C and formed the L1<sub>0</sub> FePt phase. Films are shiny and smooth. Morpholo...
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This work focuses on a search for magnets that can be used at elevated temperature. We have studied the effect of ZrB2 addition on the magnetic properties and stability of nanocrystalline 1:7 type Sm(Co,Ti,Zr) magnets up to 500 degreesC. Amorphous ball milled powder was annealed to develop the TbCu7 type structure. The room temperature coercivity o...
Article
Full-text available
The application of a magnetic field unexpectedly alters the rest potential of ferromagnetic electrodes in paramagnetic solutions of their salts. Anodic shifts of up to 60 mV in a field of 1 tesla were observed for 1 M iron electrodes in iron nitrate solution. The magnitude of the shift depends on magnetic field strength and orientation and it varie...
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peer-reviewed A novel method of producing magnetoresistive oxides is described, which involves low temperature combustion synthesis from a mixture of nitrates and fuel, as applied to Sr2FeMoO6. The method yields ceramics with a fine crystallite size of 100–200 nm and a room temperature resistivity of 200 mV m. Low field magnetoresistance (6.5% in 0...
Conference Paper
Full-text available
Summary form only given. Nanocrystalline Sm-Co-Cu-Ti magnets prepared by mechanical milling and subsequent annealing were reported to exhibit excellent room temperature coercivity. In this study, investigations of the effects of Fe, Cu, Zr and Ti substitution on magnetic properties of 1:7 magnets at temperatures up to 450°C were investigated. The a...
Article
Full-text available
We used the moving Preisach model to study the magnetization-reversal process in epitaxial SmCo (11¯00)/Fe bilayers prepared by magnetron sputtering. The SmCo(20nm)/Fe(/tnm) (/t=0,5,10,20) bilayers were grown onto single-crystal (110)MgO substrates with an epitaxial 20nm Cr(211) buffer layer. The second-quadrant magnetization curves were strictly r...
Article
Full-text available
SmCo films with a Cr underlayer have been investigated as potentially attractive candidates for high density recording media. Magnetron sputtering was used here to produce Cr/SmCox/Cr films on Si (100) substrates. The magnetic films were deposited at a substrate temperature of 350 °C and an Ar pressure of 5 mTorr. Cr underlayers were deposited both...
Article
O sucesso obtido, recentemente, na aplicação do modelo móvel de Preisach (MMP) em materiais nanocristalinos motivou-nos a aplicar o modelo em outros sistemas. Preparamos filmes finos de SmCo pelo processo de sputtering. As caracterizações da composição e da espessura do filme foram feitas por medidas de retroespalhamento Rutherford (RBS) e/ou por m...
Article
Full-text available
peer-reviewed The effect of Fe, Cu, Zr, and Ti substitution on magnetic properties of SmCo 1:7 magnets at temperatures up to 500°C were studied. As-milled amorphous Sm(Co,Fe,Cu,Ti-Zr)7 magnets crystallized in the TbCu7-type structure after annealing at 750°C for 2 h. A room-temperature intrinsic coercivity of around 2.5 T is obtained for compositio...
Article
Full-text available
peer-reviewed High current inductor applications operating in the MHz range are generally limited to Voltage Regulator Modules (VRM’s) and Point of Load (POL) power supplies, where the issue of fast transient response demands reduced inductance values. State-of-the-art controller IC’s enable switching frequencies up to 8 MHz for low current POL app...

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