References of "Nguyen, Ngoc Duy"
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See detailImprinting superconducting vortex footsteps in a magnetic layer
Brisbois, Jérémy ULg; Motta, Maycon; Avila Osses, Jonathan ULg et al

in Scientific Reports (2016), 6

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit ... [more ▼]

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories. [less ▲]

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See detailPolar interface phonons in ionic toroidal systems
Nguyen, Ngoc Duy ULg; Evrard, Roger ULg; Stroscio, Michael

in Journal of Physics : Condensed Matter (2016), 28(34), 345301

We use the dielectric continuum model to obtain the polar (Fuchs–Kliewer like) interface vibration modes of toroids made of ionic materials either embedded in a different material or in vacuum, with ... [more ▼]

We use the dielectric continuum model to obtain the polar (Fuchs–Kliewer like) interface vibration modes of toroids made of ionic materials either embedded in a different material or in vacuum, with applications to nanotoroids specially in mind. We report the frequencies of these modes and describe the electric potential they produce. We establish the quantum-mechanical Hamiltonian appropriate for their interaction with electric charges. This Hamiltonian can be used to describe the effect of this interaction on different types of charged particles either inside or outside the torus. [less ▲]

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See detailNote on the numerical solution of the scalar Helmholtz equation in a nanotorus with uniform Dirichlet boundary conditions
Nguyen, Ngoc Duy ULg; Evrard, Roger ULg; Stroscio, Michael

E-print/Working paper (2016)

This note describes the solution of the Helmholtz equation inside a nanotorus with uniform Dirichlet boundary conditions. The eigenfunction symmetry is discussed and the lower-order eigenvalues and ... [more ▼]

This note describes the solution of the Helmholtz equation inside a nanotorus with uniform Dirichlet boundary conditions. The eigenfunction symmetry is discussed and the lower-order eigenvalues and eigenfunctions are shown. The similarity with the case of a long cylinder and with that of the vibrations of a circular elastic membrane is discussed. This similarity is used to propose a classification scheme of the eigenfunctions based on three indices. [less ▲]

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See detailMagnetic flux penetration in Nb superconducting films with lithographically defined micro-indentations
Brisbois, Jérémy ULg; Adami, Obaïd-Allah ULg; Avila Osses, Jonathan ULg et al

in Physical Review B (2016), 93(5), 054521

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines ... [more ▼]

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d-lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n. In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities. [less ▲]

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See detailAnalysis of the time-dependent electrical current in reverse-biased p-GeSn/n-Ge mesa diodes
Baert, Bruno ULg; Gupta, Somya; Gencarelli, Federica et al

Poster (2015, September)

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See detailTransparent electrodes based on silver nanowire networks: physical properties and potential applications
Lagrange, Mélanie; Sannicolo, Thomas; Langley, Daniel et al

Conference (2015, September)

Transparent electrodes (TE) constitute a key component of optoelectronic devices such as solar cells, efficient organic light-emitting diodes (OLEDs), touch screens. Currently the most widely used TE is ... [more ▼]

Transparent electrodes (TE) constitute a key component of optoelectronic devices such as solar cells, efficient organic light-emitting diodes (OLEDs), touch screens. Currently the most widely used TE is indium tin oxide (ITO), which offers low resistivity and high transparency in the visible. However the scarcity of indium and the lack of flexibility of ITO has prompted the search for alternative materials. Among emerging TE, metallic nanowire (NW) networks appear to be a promising solution since these percolating networks exhibit excellent properties with sheet resistance of a few Ω/sq and optical transparency of 90%, fulfilling the requirements for many applications. In addition, the fabrication of these electrodes involves low-temperature process steps and upscaling methods, thus making them very appropriate for future use as TE for flexible devices. Our research is focused on both the fabrication of TE based on silver NW and the optimization of their physical properties, using experimental and modelling approaches. The influence of several key parameters such as network density, silver NW dimensions as well as thermal annealing, on the networks physical properties is thoroughly explored. A comprehensive understanding of the relationship between design and main physical properties of these promising nanostructured networks will be presented. Their stability will also be discussed. Finally, we will also show that such TE can be very well adapted as transparent heaters. [less ▲]

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See detailMagnesium-doped Cuprous Oxide (Mg:Cu2O) thin films as a transparent p-type semiconductor oxide
Avelas Resende, João ULg; Nguyen, Ngoc Duy ULg; Deschanvres, Jean-Luc et al

Poster (2015, September)

Oxide electronics is an important emerging area, notably for the development of transparent thin film transistors (TFTs) and other complex electronic circuits. The successful application of n-type oxides ... [more ▼]

Oxide electronics is an important emerging area, notably for the development of transparent thin film transistors (TFTs) and other complex electronic circuits. The successful application of n-type oxides to TFTs has motivated the interest in p-type oxide based semiconductors, also to be applied to TFTs or to complementary metal-oxide semiconductor (CMOS) technology. However, until now there is a lack of p-type oxide semiconductors with performance similar to that of n-type oxide. Among the different metallic oxides, Cu (I)-based oxides exhibit one of the lowest ionic character. These compounds are therefore one of the most promising candidates as p-type transparent semiconductors.Nevertheless, the band gap of 2,17eV is modest for transparent electronics applications, since the transmittance of Cu2O films is low on the visible part of the light spectrum. The incorporation of cations with large radii than Cu has been proposed as a way to achieve a higher band gap, by diminishing of three-dimensional Cu-Cu interactions, only possible with larger cations than Cu+. Therefore, cation doped Cu2O thin films were grown by metal-organic chemical vapor deposition (MOCVD). The three doping elements studied (Sr2+, Sn2+ and La3+) were selected having in account theoretical predictions for the band structure and the deposition conditions of Cu2O. The study focus on thin films growth optimization combined with electronic transport analysis and optical transmittance measurements. [less ▲]

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See detailElectrical characterization of p-GeSn/n-Ge diodes with interface traps under dc and ac regimes
Baert, Bruno ULg; Gupta, Somya; Gencarelli, Federica et al

in Solid-State Electronics (2015), 110

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See detailHigh‐k Gate Stacks on Low Bandgap Tensile Strained Ge and GeSn Alloys for Field-Effect Transistors
Wirths, Stephan; Stange, Daniela; Pampillon, Maria-Angela et al

in ACS Applied Materials and Interfaces (2015), 7

We present the epitaxial growth of Ge and Ge0.94Sn0.06 layers with 1.4% and 0.4% tensile strain, respectively, by reduced pressure chemical vapor deposition on relaxed GeSn buffers and the formation of ... [more ▼]

We present the epitaxial growth of Ge and Ge0.94Sn0.06 layers with 1.4% and 0.4% tensile strain, respectively, by reduced pressure chemical vapor deposition on relaxed GeSn buffers and the formation of high-k/metal gate stacks thereon. Annealing experiments reveal that process temperatures are limited to 350 °C to avoid Sn diffusion. Particular emphasis is placed on the electrical characterization of various high-k dielectrics, as 5 nm Al2O3, 5 nm HfO2, or 1 nm Al2O3 / 4 nm HfO2, on strained Ge and strained Ge0.94Sn0.06. Experimental capacitance− voltage characteristics are presented and the effect of the small bandgap, like strong response of minority carriers at applied field, are discussed via simulations. [less ▲]

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See detailReverse current transient behavior of pGeSn/nGe diodes
Baert, Bruno ULg; Gupta, Somya; Gencarelli, Federica et al

Conference (2015)

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See detailCombining mesoporosity and Ti-doping in hematite films for water splitting
Toussaint, Caroline ULg; Tran, Hoang Son ULg; Colson, Pierre ULg et al

in Journal of Physical Chemistry C (2015), 119(4), 1642-1650

(Graph Presented). In this study, we report the synthesis of Ti-doped mesoporous hematite films by soft-templating for application as photoanodes in the photoelectrolysis of water (water splitting ... [more ▼]

(Graph Presented). In this study, we report the synthesis of Ti-doped mesoporous hematite films by soft-templating for application as photoanodes in the photoelectrolysis of water (water splitting). Because the activation of the dopant requires a heat treatment at high temperature (≥800°C), it usually results in the collapse of the mesostructure. We have overcome this obstacle by using a temporary SiO2 scaffold to hinder crystallite growth and thereby maintain the mesoporosity. The beneficial effect of the activated dopant has been confirmed by comparing the photocurrent of doped and undoped films treated at different temperatures. The role of the mesostructure was investigated by comparing dense, collapsed, and mesoporous films heated at different temperatures and characterized under front and back illumination. It turns out that the preservation of the mesotructure enables a better penetration of the electrolyte into the film and therefore reduces the distance that the photogenerated holes have to travel to reach the electrolyte. As a result, we found that mesoporous films with dopant activation at 850°C perform better than comparable dense and collapsed films. [less ▲]

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See detailElectrical modelling of interface traps in GeSn MOS structures
Baert, Bruno ULg; Cerica, Delphine ULg; Schmeits, Marcel ULg et al

Conference (2014, November 13)

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See detailClassical analogy for the deflection of flux avalanches by a metallic layer
Brisbois, Jérémy ULg; Vanderheyden, Benoît ULg; Colauto, Fabiano et al

in New Journal of Physics (2014), 16(10), 103003

Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably ... [more ▼]

Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably, in some cases the flux is totally excluded from the area covered by the conductive layer. We present a simple classical model that accounts for this behaviour and considers a magnetic monopole approaching a semi-infinite conductive plane. This model suggests that magnetic braking is an important mechanism responsible for avalanche deflection. [less ▲]

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See detailImpact of traps on the electrical characteristics of GeSn/Ge diodes
Baert, Bruno ULg; Gupta, Somya; Gencarelli, Federica et al

Poster (2014, September 15)

Germanium-tin alloys are currently receiving a lot of attention as materials for high performance MOSFET devices. Much interest is focused on the direct band gap for Sn concentrations above 8-10% and the ... [more ▼]

Germanium-tin alloys are currently receiving a lot of attention as materials for high performance MOSFET devices. Much interest is focused on the direct band gap for Sn concentrations above 8-10% and the achievement of high mobility values, which can be further increased by the strain due to the lattice mismatch with Ge or Si. GeSn is therefore expected to play a key role in the development of either source and drain stressors for Ge p-MOSFETs or for GeSn channel MOSFETs. However, despite recent tremendous progress in the growth of such materials, the impact of defects at the interface between Ge and GeSn has not been completely characterized. As the processing of diodes contains many of the steps necessary to the fabrication of MOSFET devices, we have investigated the effect of traps on the electrical characteristics of p-GeSn/n-Ge diodes, made from GeSn layers grown by CVD on Ge and in-situ doped with Boron. Using temperature-dependent current-voltage (I-V) and capacitance- voltage (C-V) measurements, we have calculated the ideality factor of the diodes, the activation energy of the reverse saturation current and the carrier concentration of the Ge substrate. In this work, based on the comparison with results obtained from numerical simulations, we discuss these characteristics in view of assessing the extent to which electronic trap states in these heterostructures affect their electrical properties. [less ▲]

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See detailElectrical characterization of pGeSn/nGe diodes
Baert, Bruno ULg; Gupta, Somya; Gencarelli, Federica et al

Conference (2014, June 03)

I-V characteristics of pGeSn/nGe diodes have been measured and show very good properties. Simulations of the same structure are able to reproduce most of the observed behavior and point to the ... [more ▼]

I-V characteristics of pGeSn/nGe diodes have been measured and show very good properties. Simulations of the same structure are able to reproduce most of the observed behavior and point to the predominating influence of parameters such as the band gap energy of the GeSn layer. C-V characteristics showing little frequency dependence have also been measured, and their analysis for the determination of the carrier concentration is confirmed by simulations. More investigations, including the effect of temperature and other defects at the interface or in the bulk of either layers are still required in order to explain some of the observed behaviors, notably the reverse saturation current. [less ▲]

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See detailMetallic nanowire networks: effects of thermal annealing on electrical resistance
Langley, Daniel ULg; Lagrange, Mélanie; Giusti, Gael et al

in Nanoscale (2014), 6

Metallic nanowire networks have huge potential in devices requiring transparent electrodes. This article describes how the electrical resistance of metal nanowire networks evolve under thermal annealing ... [more ▼]

Metallic nanowire networks have huge potential in devices requiring transparent electrodes. This article describes how the electrical resistance of metal nanowire networks evolve under thermal annealing. Understanding the behavior of such films is crucial for the optimization of transparent electrodes which find many applications. An in-depth investigation of silver nanowire networks under different annealing conditions provides a case study demonstrating that several mechanisms, namely local sintering and desorption of organic residues, are responsible for the reduction of the systems electrical resistance. Optimization of the annealing led to specimens with transmittance of 90% (at 550 nm) and sheet resistance of 9.5 Ω sq−1. Quantized steps in resistance were observed and a model is proposed which provides good agreement with the experimental results. In terms of thermal behavior, we demonstrate that there is a maximum thermal budget that these electrodes can tolerate due to spheroidization of the nanowires. This budget is determined by two main factors: the thermal loading and the wire diameter. This result enables the fabrication and optimization of transparent metal nanowire electrodes for solar cells, organic electronics and flexible displays. [less ▲]

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See detailTransparent electrodes composed of silver nanowire networks: physical properties and potential applications
Langley, Daniel ULg; Lagrange, Mélanie; Munoz-Rojas, David et al

Conference (2014)

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See detailTransparent electrodes composed of silver nanowire networks for photovoltaic applications
Langley, Daniel ULg; Lagrange, Mélanie; Munoz-Rojas, David et al

Conference (2014)

Research is increasingly being dedicated towards replacing rare earth elements in Transparent Conductive Materials (TCMs). In this work we present the investigation of silver nanowire (AgNW) networks as ... [more ▼]

Research is increasingly being dedicated towards replacing rare earth elements in Transparent Conductive Materials (TCMs). In this work we present the investigation of silver nanowire (AgNW) networks as transparent electrodes for solar cell applications. Metallic nanowire networks can be deposited via low cost deposition techniques and exhibit very interesting electrical, optical and mechanical properties. Experimental and simulation approaches aim at improving their physical properties. Indeed, we show that a thermal annealing can drastically improve transport properties of the nearly transparent networks. We also explore the optimization of the network density. These percolating networks exhibit excellent properties (i.e. sheet resistances (Rs) of about 10 Ω/sq and optical transparency of approximately 90%) compatible with solar applications requirements. This makes them very appropriate for future uses in low cost, large area and flexible solar and display technologies. A comprehensive understanding of the main physical properties of this promising nanostructured network and its integration with solar cells will then be presented [less ▲]

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See detailInnovative Electrodes for Dye Sensitized Solar Cells
Langley, Daniel ULg; Giusti, Gael; Zhang, Shanting et al

Conference (2014)

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