“Atomic scale dynamics of ultrasmall germanium clusters”. Bals S, Van Aert S, Romero CP, Lauwaet K, Van Bael MJ, Schoeters B, Partoens B, Yuecelen E, Lievens P, Van Tendeloo G, Nature communications 3, 897 (2012). http://doi.org/10.1038/ncomms1887
Abstract: Starting from the gas phase, small clusters can be produced and deposited with huge flexibility with regard to composition, materials choice and cluster size. Despite many advances in experimental characterization, a detailed morphology of such clusters is still lacking. Here we present an atomic scale observation as well as the dynamical behaviour of ultrasmall germanium clusters. Using quantitative scanning transmission electron microscopy in combination with ab initio calculations, we are able to characterize the transition between different equilibrium geometries of a germanium cluster consisting of less than 25 atoms. Seven-membered rings, trigonal prisms and some smaller subunits are identified as possible building blocks that stabilize the structure.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 12.124
Times cited: 90
DOI: 10.1038/ncomms1887
|
“A novel explanation for the increased conductivity in annealed Al-doped ZnO: an insight into migration of aluminum and displacement of zinc”. Momot A, Amini MN, Reekmans G, Lamoen D, Partoens B, Slocombe DR, Elen K, Adriaensens P, Hardy A, Van Bael MK, Physical chemistry, chemical physics 19, 27866 (2017). http://doi.org/10.1039/C7CP02936E
Abstract: A combined experimental and first-principles study is performed to study the origin of conductivity in
ZnO:Al nanoparticles synthesized under controlled conditions via a reflux route using benzylamine as a
solvent. The experimental characterization of the samples by Raman, nuclear magnetic resonance (NMR)
and conductivity measurements indicates that upon annealing in nitrogen, the Al atoms at interstitial
positions migrate to the substitutional positions, creating at the same time Zn interstitials. We provide
evidence for the fact that the formed complex of AlZn and Zni corresponds to the origin of the Knight
shifted peak (KS) we observe in 27Al NMR. As far as we know, the role of this complex has not been
discussed in the literature to date. However, our first-principles calculations show that such a complex is
indeed energetically favoured over the isolated Al interstitial positions. In our calculations we also
address the charge state of the Al interstitials. Further, Zn interstitials can migrate from Al_Zn and possibly
also form Zn clusters, leading to the observed increased conductivity.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.123
Times cited: 26
DOI: 10.1039/C7CP02936E
|
“Atomic-scale modification of hybrid FePt cluster-assembled films”. Dobrynin AN, Ievlev DN, Verschoren G, Swerts J, van Bael MJ, Temst K, Lievens P, Piscopiello E, Van Tendeloo G, Zhou SQ, Vantomme A, Physical review : B : condensed matter and materials physics 73, 104421 (2006). http://doi.org/10.1103/PhysRevB.73.104421
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 13
DOI: 10.1103/PhysRevB.73.104421
|
“Interplay between lattice dynamics and superconductivity in Nb3Sn thin films”. Couet S, Peelaers H, Trekels M, Houben K, Petermann C, Hu MY, Zhao JY, Bi W, Alp EE, Menéndez E, Partoens B, Peeters FM, Van Bael MJ, Vantomme A, Temst K;, Physical review : B : condensed matter and materials physics 88, 045437 (2013). http://doi.org/10.1103/PhysRevB.88.045437
Abstract: We investigate the link between superconductivity and atomic vibrations in Nb3Sn films with a thickness ranging from 10 to 50 nm. The challenge of measuring the phonon density of states (PDOS) of these films has been tackled by employing the technique of nuclear inelastic scattering by Sn-119 isotopes to reveal the Sn-partial phonon density of states. With the support of ab initio calculations, we evaluate the effect of reduced film thickness on the PDOS. This approach allows us to estimate the changes in superconducting critical temperature T-c induced by phonon confinement, which turned out to be limited to a few tenths of K. The presented method is successful for the Nb3Sn system and paves the way for more systematic studies of the role of phonon confinement in Sn-containing superconductors.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PhysRevB.88.045437
|
“Lattice dynamics in Sn nanoislands and cluster-assembled films”. Houben K, Couet S, Trekels M, Menendez E, Peissker T, Seo JW, Hu MY, Zhao JY, Alp EE, Roelants S, Partoens B, Milošević, MV, Peeters FM, Bessas D, Brown SA, Vantomme A, Temst K, Van Bael MJ, Physical review B 95, 155413 (2017). http://doi.org/10.1103/PHYSREVB.95.155413
Abstract: To unravel the effects of phonon confinement, the influence of size and morphology on the atomic vibrations is investigated in Sn nanoislands and cluster-assembled films. Nuclear resonant inelastic x-ray scattering is used to probe the phonon densities of states of the Sn nanostructures which show significant broadening of the features compared to bulk phonon behavior. Supported by ab initio calculations, the broadening is attributed to phonon scattering and can be described within the damped harmonic oscillator model. Contrary to the expectations based on previous research, the appearance of high-energy modes above the cutoff energy is not observed. From the thermodynamic properties extracted from the phonon densities of states, it was found that grain boundary Sn atoms are bound by weaker forces than bulk Sn atoms.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PHYSREVB.95.155413
|
“Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in gamma-Fe nanoparticles”. Augustyns V, van Stiphout K, Joly V, Lima TAL, Lippertz G, Trekels M, Menendez E, Kremer F, Wahl U, Costa ARG, Correia JG, Banerjee D, Gunnlaugsson HP, von Bardeleben J, Vickridge I, Van Bael MJ, Hadermann J, Araujo JP, Temst K, Vantomme A, Pereira LMC, Physical review B 96, 174410 (2017). http://doi.org/10.1103/PHYSREVB.96.174410
Abstract: <script type='text/javascript'>document.write(unpmarked('gamma-Fe and related alloys are model systems of the coupling between structure and magnetism in solids. Since different electronic states (with different volumes and magnetic ordering states) are closely spaced in energy, small perturbations can alter which one is the actual ground state. Here, we demonstrate that the ferromagnetic state of gamma-Fe nanoparticles is associated with a tetragonal distortion of the fcc structure. Combining a wide range of complementary experimental techniques, including low-temperature Mossbauer spectroscopy, advanced transmission electron microscopy, and synchrotron radiation techniques, we unambiguously identify the tetragonally distorted ferromagnetic ground state, with lattice parameters a = 3.76(2) angstrom and c = 3.50(2) angstrom, and a magnetic moment of 2.45(5) mu(B) per Fe atom. Our findings indicate that the ferromagnetic order in nanostructured gamma-Fe is generally associated with a tetragonal distortion. This observation motivates a theoretical reassessment of the electronic structure of gamma-Fe taking tetragonal distortion into account.'));
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 1
DOI: 10.1103/PHYSREVB.96.174410
|
“Experimental observation of electron-phonon coupling enhancement in Sn nanowires caused by phonon confinement effects”. Lozano DP, Couet S, Petermann C, Hamoir G, Jochum JK, Picot T, Menendez E, Houben K, Joly V, Antohe VA, Hu MY, Leu BM, Alatas A, Said AH, Roelants S, Partoens B, Milošević, MV, Peeters FM, Piraux L, Van de Vondel J, Vantomme A, Temst K, Van Bael MJ, Physical review B 99, 064512 (2019). http://doi.org/10.1103/PHYSREVB.99.064512
Abstract: Reducing the size of a superconductor below its characteristic length scales can either enhance or suppress its critical temperature (T-c). Depending on the bulk value of the electron-phonon coupling strength, electronic and phonon confinement effects will play different roles in the modification of T-c. Experimentally disentangling each contribution has remained a challenge. We have measured both the phonon density of states and T-c of Sn nanowires with diameters of 18, 35, and 100 nm in order to quantify the effects of phonon confinement on superconductivity. We observe a shift of the phonon frequency towards the low-energy region and an increase in the electron-phonon coupling constant that can account for the measured increase in T-c.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 11
DOI: 10.1103/PHYSREVB.99.064512
|
“In situ study of the \alpha-Sn to \beta-Sn phase transition in low-dimensional systems : phonon behavior and thermodynamic properties”. Houben K, Jochum JK, Lozano DP, Bisht M, Menendez E, Merkel DG, Ruffer R, Chumakov A I, Roelants S, Partoens B, Milošević, MV, Peeters FM, Couet S, Vantomme A, Temst K, Van Bael MJ, Physical review B 100, 075408 (2019). http://doi.org/10.1103/PHYSREVB.100.075408
Abstract: The densities of phonon states of thin Sn films on InSb substrates are determined during different stages of the alpha-Sn to beta-Sn phase transition using nuclear inelastic x-ray scattering. The vibrational entropy and internal energy per atom as a function of temperature are obtained by numerical integration of the phonon density of states. The free energy as a function of temperature for the nanoscale samples is compared to the free energy obtained from ab initio calculations of bulk tin in the alpha-Sn and beta-Sn phase. In thin films this phase transition is governed by the interplay between the vibrational behavior of the film (the phase transition is driven by the vibrational entropy) and the stabilizing influence of the substrate (which depends on the film thickness). This brings a deeper understanding of the role of lattice vibrations in the phase transition of nanoscale Sn.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 9
DOI: 10.1103/PHYSREVB.100.075408
|
“Metastable states and hidden phase slips in nanobridge SQUIDs”. Nulens L, Dausy H, Wyszynski MJ, Raes B, Van Bael MJ, Milošević, MV, Van de Vondel J, Physical review B 106, 134518 (2022). http://doi.org/10.1103/PHYSREVB.106.134518
Abstract: We fabricated an asymmetric nanoscale SQUID consisting of one nanobridge weak link and one Dayem bridge weak link. The current phase relation of these particular weak links is characterized by multivaluedness and linearity. While the latter is responsible for a particular magnetic field dependence of the critical current (so-called vorticity diamonds), the former enables the possibility of different vorticity states (phase winding numbers) existing at one magnetic field value. In experiments the observed critical current value is stochastic in nature, does not necessarily coincide with the current associated with the lowest energy state and critically depends on the measurement conditions. In this paper, we unravel the origin of the observed metastability as a result of the phase dynamics happening during the freezing process and while sweeping the current. Moreover, we employ special measurement protocols to prepare the desired vorticity state and identify the (hidden) phase slip dynamics ruling the detected state of these nanodevices. In order to gain insights into the dynamics of the condensate and, more specifically the hidden phase slips, we performed time-dependent Ginzburg-Landau simulations.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
Times cited: 1
DOI: 10.1103/PHYSREVB.106.134518
|
“Morphological TEM studies and magnetoresistance analysis of sputtered Al-substituted ZnO films : the role of oxygen”. Van Gompel M, Atalay AY, Gaulke A, Van Bael MK, D'Haen J, Turner S, Van Tendeloo G, Vanacken J, Moshchalkov VV, Wagner P, Physica status solidi : A : applications and materials science 212, 1191 (2015). http://doi.org/10.1002/pssa.201431888
Abstract: In this article, we report on the synthesis of thin, epitaxial films of the transparent conductive oxide Al:ZnO on (0001)-oriented synthetic sapphire substrates by DC sputtering from targets with a nominal 1 at.% Al substitution. The deposition was carried out at an unusually low substrate temperature of only 250 °C in argonoxygen mixtures as well as in pure argon. The impact of the processgas composition on the morphology was analysed by transmission electron microscopy, revealing epitaxial growth in all the cases with a minor impact of the process parameters on the resulting grain sizes. The transport properties resistivity, Hall effect and magnetoresistance were studied in the range from 10 to 300 K in DC and pulsed magnetic fields up to 45 T. While the carrier density and mobility are widely temperature independent, we identified a low fieldlow temperature regime in which the magnetoresistance shows an anomalous, negative behaviour. At higher fields and temperatures, the magnetoresistance exhibits a more conventional, positive curvature with increasing field strength. As a possible explanation, we propose carrier scattering at localised magnetic trace impurities and magnetic correlations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.775
DOI: 10.1002/pssa.201431888
|
“Thermal decomposition synthesis of Al-doped ZnO nanoparticles : an in-depth study”. Damm H, Kelchtermans A, Bertha A, Van den Broeck F, Elen K, Martins JC, Carleer R, D'Haen J, De Dobbelaere C, Hadermann J, Hardy A, Van Bael MK;, RSC advances 3, 23745 (2013). http://doi.org/10.1039/c3ra43328e
Abstract: Al-doped ZnO nanoparticles are synthesized by means of a heating up solution based thermal decomposition method. The synthesis involves a reaction of zinc acetylacetonate hydrate, aluminium acetylacetonate and 1,2-hexadecanediol in the presence of oleic acid and oleyl amine. A proposed reaction mechanism from reagents to monomers is corroborated by analysis of the evolving gases using headspace GC-MS analysis. The Al-doped ZnO nanoparticles synthesized are dynamically stabilized by adsorbed oleate ions, after deprotonation of oleic acid by oleyl amine, as was found by NOESY proton NMR and complementary FTIR spectroscopy. Precession electron diffraction shows a simultaneous increase in lattice parameters with Al concentration. This, together with HAADF-STEM and EDX maps, indicates the incorporation of Al into the ZnO nanoparticles. By the combination of complementary characterization methods during all stages of the synthesis, it is concluded that Al is incorporated into the ZnO wurtzite lattice as a dopant.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 10
DOI: 10.1039/c3ra43328e
|
“Hierarchical hexagonal boron nitride nanowall-diamond nanorod heterostructures with enhanced optoelectronic performance”. Sankaran KJ, Duc Quang Hoang, Korneychuk S, Kunuku S, Thomas JP, Pobedinskas P, Drijkoningen S, Van Bael MK, D'Haen J, Verbeeck J, Leou K-C, Leung KT, Lin I-N, Haenen K, RSC advances 6, 90338 (2016). http://doi.org/10.1039/C6RA19596B
Abstract: A superior field electron emission (FEE) source made from a hierarchical heterostructure, where two-dimensional hexagonal boron nitride (hBN) nanowalls were coated on one-dimensional diamond nanorods (DNRs), is fabricated using a simple and scalable method. FEE characteristics of hBN-DNR display a low turn-on field of 6.0 V mu m(-1), a high field enhancement factor of 5870 and a high life-time stability of 435 min. Such an enhancement in the FEE properties of hBN-DNR derives from the distinctive material combination, i.e., high aspect ratio of the heterostructure, good electron transport from the DNR to the hBN nanowalls and efficient field emission of electrons from the hBN nanowalls. The prospective application of these heterostructures is further evidenced by enhanced microplasma devices using hBN-DNR as a cathode, in which the threshold voltage was lowered to 350 V, affirming the role of hBN-DNR in the improvement of electron emission.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 8
DOI: 10.1039/C6RA19596B
|
“Ti surface doping of LiNi0.5Mn1.5O4−δpositive electrodes for lithium ion batteries”. Ulu Okudur F, D'Haen J, Vranken T, De Sloovere D, Verheijen M, Karakulina OM, Abakumov AM, Hadermann J, Van Bael MK, Hardy A, RSC advances 8, 7287 (2018). http://doi.org/10.1039/C7RA12932G
Abstract: The particle surface of LiNi0.5Mn1.5O4−δ (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis–condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500–850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous ‘TiOx’ layer into the LNMO surface during annealing at 500 °C. This results in a 2–4 nm thick Ti-rich spinel surface having lower Mn and Ni content compared to the core of the LNMO particles, which was observed with scanning transmission electron microscopy coupled with compositional EDX mapping. An increase in the annealing temperature promotes the formation of a Ti bulk doped LiNi(0.5−w)Mn(1.5+w)−tTitO4 phase and Ti-rich LiNi0.5Mn1.5−yTiyO4 segregates above 750 °C. Fourier-transform infrared spectrometry indicates increasing Ni–Mn ordering with annealing temperature, for both bare and surface modified LNMO. Ti surface modified LNMO annealed at 500 °C shows a superior cyclic stability, coulombic efficiency and rate performance compared to bare LNMO annealed at 500 °C when cycled at 3.4–4.9 V vs. Li/Li+. The improvements are probably due to suppressed Ni and Mn dissolution with Ti surface doping.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 9
DOI: 10.1039/C7RA12932G
|
“Enhanced optoelectronic performances of vertically aligned hexagonal boron nitride nanowalls-nanocrystalline diamond heterostructures”. Sankaran KJ, Hoang DQ, Kunuku S, Korneychuk S, Turner S, Pobedinskas P, Drijkoningen S, Van Bael MK, D' Haen J, Verbeeck J, Leou K-C, Lin I-N, Haenen K, Scientific reports 6, 29444 (2016). http://doi.org/10.1038/srep29444
Abstract: Field electron emission (FEE) properties of vertically aligned hexagonal boron nitride nanowalls (hBNNWs) grown on Si have been markedly enhanced through the use of nitrogen doped nanocrystalline diamond (nNCD) films as an interlayer. The FEE properties of hBNNWs-nNCD heterostructures show a low turn-on field of 15.2 V/mum, a high FEE current density of 1.48 mA/cm(2) and life-time up to a period of 248 min. These values are far superior to those for hBNNWs grown on Si substrates without the nNCD interlayer, which have a turn-on field of 46.6 V/mum with 0.21 mA/cm(2) FEE current density and life-time of 27 min. Cross-sectional TEM investigation reveals that the utilization of the diamond interlayer circumvented the formation of amorphous boron nitride prior to the growth of hexagonal boron nitride. Moreover, incorporation of carbon in hBNNWs improves the conductivity of hBNNWs. Such a unique combination of materials results in efficient electron transport crossing nNCD-to-hBNNWs interface and inside the hBNNWs that results in enhanced field emission of electrons. The prospective application of these materials is manifested by plasma illumination measurements with lower threshold voltage (370 V) and longer life-time, authorizing the role of hBNNWs-nNCD heterostructures in the enhancement of electron emission.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.259
Times cited: 15
DOI: 10.1038/srep29444
|
“The superconducting proximity effect in epitaxial Al/Pb nanocomposites”. Wang H, Picot T, Houben K, Moorkens T, Grigg J, Van Haesendonck C, Biermans E, Bals S, Brown SA, Vantomme A, Temst K, Van Bael MJ;, Superconductor science and technology 27, 015008 (2014). http://doi.org/10.1088/0953-2048/27/1/015008
Abstract: We have investigated the superconducting properties of Pb nanoparticles with a diameter ranging from 8 to 20 nm, synthesized by Pb+ ion implantation in a crystalline Al matrix. A detailed structural characterization of the nanocomposites reveals the highly epitaxial relation between the Al crystalline matrix and the Pb nanoparticles. The Al/Pb nanocomposites display a single superconducting transition, with the critical temperature T-c increasing with the Pb content. The dependence of T-c on the Pb/Al volume ratio was compared with theoretical models of the superconducting proximity effect based on the bulk properties of Al and Pb. A very good correspondence with the strong-coupling proximity effect model was found, with an electron-phonon coupling constant in the Pb nanoparticles slightly reduced compared to bulk Pb. Our result differs from other studies on Pb nanoparticle based proximity systems where weak-coupling models were found to better describe the T-c dependence. We infer that the high interface quality resulting from the ion implantation synthesis method is a determining factor for the superconducting properties. Critical field and critical current measurements support the high quality of the nanocomposite superconducting films.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.878
Times cited: 2
DOI: 10.1088/0953-2048/27/1/015008
|