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Aliphatic hydroxamic acids (HA) with varying numbers of carbon atoms, C2, C6, C8, C10, C12 and C17, and corresponding Fe(II), Fe(III), Ni(II), Cu(II) and Zn(II) complexes have been synthesized and characterized by various methods, including structural determination by single crystal X-ray diffraction and theoretical calculations. The biological activities of HA and their complexes have been assessed on a panel of pathogens, including eight bacteria strains and one fungus. The C12 aliphatic HA displayed the lowest minimum inhibitory concentrations (MIC) towards several microbial strains and a selective antifungal activity. This antifungal selectivity was further improved considering the Ni(II), Cu(II) and Zn(II) complexes of C12 HA showed higher IC50 values, thus less impact on the SiHa human cell line viability. This work warrants further investigation to understand the underlying mechanism of action and potential biological applications of HA and the derived metal complexes.

With the development of alternative computing schemes working at cryogenic temperatures, superconducting memory elements have gained interest. In this context, superconducting quantum interference devices (SQUIDs) are promising candidates, as they may trap different discrete amounts of magnetic flux. We demonstrate that a field-assisted writing scheme allows such a device to operate as a multilevel memory by the readout of eight distinct vorticity states at zero magnetic field. We present an alternative mechanism based on single phase slips, which allows the vorticity state to be switched while preserving superconductivity. This mechanism provides a possibly deterministic channel for flux control in SQUID-based memories, under the condition that the field-dependent energy of different vorticity states are nearby. ispartof: Physical Review Applied vol:19 issue:3 status: published

The influence of a patterned substrate on obliquely deposited, exchange biased Co/CoO films was studied. It was found that substrates decorated with nanoparticle patterns provide the option to manipulate the orientation of the magnetic easy axis in obliquely deposited thin films. The complementary methods of SQUID magnetometry and polarized neutron reflectometry were used to disentangle the different contributions to the magnetic hysteresis of such complex magnetic systems.

We successfully identified native point defects that occur in Bi2Te3 crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown Bi2Te3 crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects. In particular, scanning tunneling spectroscopy reveals the dependence on not only the local atomic environment but also on the growth kinetics and the resulting sample doping from n-type toward intrinsic crystals with the Fermi level positioned inside the energy gap. Our results establish a bias-dependent STM signature of the Bi2Te3 native defects and shed light on the link between the native defects and the electronic properties of Bi2Te3, which is relevant for the synthesis of topological insulator materials and the related functional properties.

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 work, 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., Comment: 10 pages, 4 figures, 1 supplementary video

In this work, we study the current-phase relation ($\mathrm{C}\mathrm{\ensuremath{\Phi}}\mathrm{R}$) of lithographically fabricated molybdenum germanium (${\mathrm{Mo}}_{79}{\mathrm{Ge}}_{21}$) nanobridges that is intimately linked with the nanobridge's kinetic inductance. We do this by imbedding the nanobridges in a superconducting quantum interference device (SQUID). We observe that, for temperatures far below ${T}_{c}$, the $\mathrm{C}\mathrm{\ensuremath{\Phi}}\mathrm{R}$ is linear, as long as the condensate is not weakened by the presence of a supercurrent. We demonstrate lithographic control over the nanobridge kinetic inductance, which scales with the nanobridge aspect ratio. This allows the ${I}_{c}(B)$ characteristic of the SQUID to be tuned. The SQUID properties that can be controlled in this way include the SQUID's sensitivity and the positions of the critical-current maxima. These observations can be of use for the design and operation of future superconducting devices, such as magnetic memories or flux qubits.

Understanding the influence of the pH value towards microenvironments of bioanalytical systems, especially inside lab-on-a-chip or micro total analysis systems, is crucial for the success of experiments. Different approaches are known to control the pH value inside those microchannels and to tailor pH gradients. Nevertheless, the existing concepts often lack the possibility for a flexible adaption of these gradients. To overcome this limitation, the present work reports on light-addressable electrodes (LAEs) as a tool to create pH gradients at the micro scale. Light-addressable electrodes are based on semiconductor materials in which electron-hole pairs are generated by illumination. These free charge carriers can trigger chemical reactions at the semiconductor-electrolyte interface, including the change of the pH value. For this purpose, we have designed LAEs based on glass/fluorine-doped tin oxide/titanium dioxide heterostructures. This work studies the influence of the applied external potential, illumination brightness and illumination area on the maximum pH change and width of the pH gradient using a pH-sensitive fluorescent dye. Furthermore, we evaluate the correlation between the pH change and electrical charge transfer. Finally, we provide an outlook towards tailoring complex pH gradients inside microchannels.

Combining various (multi-)ferroic materials into heterostructures is a promising route to enhance their inherent properties, such as the magnetoelectric coupling in BiFeO3 thin films. We have previously reported on the up-to-tenfold increase of the magnetoelectric voltage coefficient &alpha, ME in BaTiO3-BiFeO3 multilayers relative to BiFeO3 single layers. Unraveling the origin and mechanism of this enhanced effect is a prerequisite to designing new materials for the application of magnetoelectric devices. By careful variations in the multilayer design we now present an evaluation of the influences of the BaTiO3-BiFeO3 thickness ratio, oxygen pressure during deposition, and double layer thickness. Our findings suggest an interface driven effect at the core of the magnetoelectric coupling effect in our multilayers superimposed on the inherent magnetoelectric coupling of BiFeO3 thin films, which leads to a giant &alpha, ME coefficient of 480 V c m -1 Oe-1 for a 16 &times, (BaTiO3-BiFeO3) superlattice with a 4 . 8 nm double layer periodicity.

In-plane compressively strained $\alpha$-Sn films have been theoretically predicted and experimentally proven to possess non-trivial electronic states of a 3D topological Dirac semimetal. The robustness of these states typically strongly depends on purity, homogeneity and stability of the grown material itself. By developing a reliable fabrication process, we were able to grow pure strained $\alpha$-Sn films on InSb(100), without heating of the substrate during growth, nor using any dopants. The $\alpha$-Sn films were grown by molecular beam epitaxy, followed by experimental verification of the achieved chemical purity and structural properties of the film's surface. Local insight into the surface morphology was provided by scanning tunneling microscopy. We detected the existence of compressive strain using M\"ossbauer spectroscopy and we observed a remarkable robustness of the grown samples against ambient conditions. The topological character of the samples was confirmed by angle-resolved photoemission spectroscopy, revealing the Dirac cone of the topological surface state. Scanning tunneling spectroscopy, moreover, allowed obtaining an improved insight into the electronic structure of the 3D topological Dirac semimetal $\alpha$-Sn above the Fermi level., Comment: APM19-AR-01221R

Understanding the mechanisms of magnetoelectric (ME) coupling within multiferroic structures is paramount from a fundamental as well as an applied point of view. We report here that the magnetoelectric properties, as well as the magnetization, of BaTiO$_3$-BiFeO$_3$ superlattices can be tuned by varying the BiFeO$_3$ layer thickness. The magnetoelectric voltage coefficient ($\alpha_{ME}$) reaches its maximum of 60.2 Vcm$^{-1}$Oe$^{-1}$ at 300 K, one of the highest values reported so far, for a sample with a BiFeO$_3$ thickness of 5 nm and a BaTiO$_3$ thickness of 10 nm. To gain deeper insight into the increased magnetoelectric coupling, and both the local and macroscopic magnetic properties, samples with varying BiFeO$_3$ thicknesses have been investigated. Correlations were established between the hyperfine field (HFF), the magnetoelectric voltage coefficient and the magnetization. The possible mechanisms responsible for the strong magnetoelectric coupling are discussed.

Combining various (multi-)ferroic materials into heterostructures is a promising route to enhance their inherent properties, such as the magnetoelectric coupling in BiFeO3 thin films. We have previously reported on the up-to-tenfold increase of the magnetoelectric voltage coefficient α ME in BaTiO3-BiFeO3 multilayers relative to BiFeO3 single layers. Unraveling the origin and mechanism of this enhanced effect is a prerequisite to designing new materials for the application of magnetoelectric devices. By careful variations in the multilayer design we now present an evaluation of the influences of the BaTiO3-BiFeO3 thickness ratio, oxygen pressure during deposition, and double layer thickness. Our findings suggest an interface driven effect at the core of the magnetoelectric coupling effect in our multilayers superimposed on the inherent magnetoelectric coupling of BiFeO3 thin films, which leads to a giant α ME coefficient of 480 V c m -1 Oe-1 for a 16 × (BaTiO3-BiFeO3) superlattice with a 4 . 8 nm double layer periodicity.

The increase in superconducting transition temperature (TC) of Sn nanostructures in comparison to bulk, was studied. Changes in the phonon density of states (PDOS) of the weakly coupled superconductor Sn were analyzed and correlated with the increase in TC measured by magnetometry. The PDOS of all nanostructured samples shows a slightly increased number of low-energy phonon modes and a strong decrease in the number of high-energy phonon modes in comparison to the bulk Sn PDOS. The phonon densities of states, which were determined previously using nuclear resonant inelastic X-ray scattering, were used to calculate the superconducting transition temperature using the Allen-Dynes-McMillan (ADMM) formalism. Both the calculated as well as the experimentally determined values of TC show an increase compared to the bulk superconducting transition temperature. The good agreement between these values indicates that phonon softening has a major influence on the superconducting transition temperature of Sn nanostructures. The influence of electron confinement effects appears to be minor in these systems.

The densities of phonon states of thin Sn films on InSb substrates are determined during different stages of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ to $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ and $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ 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.

© 2019 Elsevier B.V. Magnetically removable plasmonic nanoparticles are of great interest for biomedical and catalytical applications. A novel and straightforward method to prepare a core-shell structure consisting of a superparamagnetic Fe 3 O 4 core coated with a plasmonic gold shell is described. The synthesis combines ease of functionalization, limited supervision and high reproducibility while being environmentally friendly. A gold shell with a tunable thickness of 30–70 nm was grown on a Fe 3 O 4 core 20 nm in diameter through reduction of gold salt in an ultrasonic bath. The thickness of the gold shell could be tuned by varying the amount of gold salt added. It was possible to prepare core-shell nanoparticles of sizes between 80 and 160 nm. The magnetic and plasmonic behavior of the core-shell nanoparticles is studied. To demonstrate potential use in biomedical applications, a functionalization with polyethylene glycol (PEG) is performed. ispartof: PHYSICA B-CONDENSED MATTER vol:560 pages:85-90 status: published

Bactericidal nanoparticle coatings are very promising for hindering the indirect transmission of pathogens through cross-contaminated surfaces. The challenge, limiting their employment in nosocomial environments, is the ability of tailoring the coating's physicochemical properties, namely, composition, cytotoxicity, bactericidal spectrum, adhesion to the substrate, and consequent nanoparticles release into the environment. We have engineered a new family of nanoparticle-based bactericidal coatings comprising Ag, Cu, and Mg and synthesized by a green gas-phase technique. These coatings present wide-spectrum bactericidal activity on both Gram-positive and Gram-negative reference strains and tunable physicochemical properties of relevance in view of their "on-field" deployment. The link between material and functional properties is rationalized based on a multidisciplinary and multitechnique approach. Our results pave the way for engineering biofunctional, fully tunable nanoparticle coatings, exploiting an arbitrarily wide number of elements in a straightforward, eco-friendly, high-throughput, one-step process.

We investigate percolating films of superconducting nanoparticles and observe an evolution from superconducting to metallic to insulating states as the surface coverage of the nanoparticles is decreased. We demonstrate that this evolution is correlated with a reduction in the effective/dominant dimensionality of the system, from 2D to 1D to 0D, and that the physics in each regime is dominated by vortices, phase slips and tunnelling respectively. Finally we construct phase diagrams that map the various observed states as a function of surface coverage (or, equivalently, normal state resistance), temperature and measurement current.

© 2017 American Physical Society. 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. ispartof: Physical Review B vol:95 issue:15 status: published

© 2017 American Chemical Society. Ultrathin metal nanoparticles coatings, synthesized by gas-phase deposition, are emerging as go-to materials in a variety of fields ranging from pathogens control and sensing to energy storage. Predicting their morphology and mechanical properties beyond a trial-and-error approach is a crucial issue limiting their exploitation in real-life applications. The morphology and mechanical properties of Ag nanoparticle ultrathin films, synthesized by supersonic cluster beam deposition, are here assessed adopting a bottom-up, multitechnique approach. A virtual film model is proposed merging high resolution scanning transmission electron microscopy, supersonic cluster beam dynamics, and molecular dynamics simulations. The model is validated against mechanical nanometrology measurements and is readily extendable to metals other than Ag. The virtual film is shown to be a flexible and reliable predictive tool to access morphology-dependent properties such as mesoscale gas-dynamics and elasticity of ultrathin films synthesized by gas-phase deposition. ispartof: Journal of Physical Chemistry C vol:121 issue:40 pages:22434-22441 status: published

Homopolymers as nanocarriers for the loading of block copolymer micelles with metal salts: a facile way to large-scale ordered arrays of transitionmetal nanoparticles Lianchen Shan,1 Sathya Punniyakoti,1 Margriet J. Van Bael,2 Kristiaan Temst,3 Marlies K. Van Bael,4 Xiaoxing Ke,5 Sara Bals,5 Gustaaf Van Tendeloo,5 Marc D'Olieslaeger,1,6 Patrick Wagner,1,6 Ken Haenenaf and Hans-Gerd Boyen*1,6 [ 1 ] Hasselt Univ, Inst Mat Res IMO, B-3590 Diepenbeek, Belgium [ 2 ] Katholieke Univ Leuven, Lab Solid State Phys & Magnetism, B-3001 Louvain, Belgium [ 3 ] Katholieke Univ Leuven, Inst Kern Stralingsfys, B-3001 Louvain, Belgium [ 4 ] Hasselt Univ, Inst Mat Res, B-3590 Diepenbeek, Belgium [ 5 ] Univ Antwerp, Electron Microscopy Mat Res EMAT, B-2020 Antwerp, Belgium [ 6 ] Imec Vzw Div IMOMEC, B-3590 Diepenbeek, Belgium A new and facile approach is presented for generating quasi-regular patterns of transition metal-based nanoparticles on flat substrates exploiting polystyrene-block-poly2vinyl pyridine (PS-b-P2VP) micelles as intermediate templates. Direct loading of such micellar nanoreactors by polar ransition metal salts in solution usually results in nanoparticle ensembles exhibiting only short range order accompanied by broad distributions of particle size and inter-particle distance. Here, we demonstrate that the use of P2VP homopolymers of appropriate length as molecular carriers to transport precursor salts into the micellar cores can significantly increase the degree of lateral order within the final nanoparticle arrays combined with a decrease in spreading in particle size. Thus, a significantly extended range of materials is now available which can be exploited to study fundamental properties at the transition from clusters to solids by means of well-organized, well-separated, size-selected metal and metal oxide nanostructures. ispartof: Journal of Materials Chemistry C vol:2 issue:4 pages:701-707 status: published

Magnetic nanoparticles embedded oxide semiconductors are interesting candidates for spintronics in view of combining ferromagnetic (FM) and semiconducting properties. In this work, Co-ZnO and Co-V2O3 nanocomposite thin films are synthesized by Co ion implantation in crystalline thin films. Magnetic orders vary with the implantation fluence in Co-ZnO, where superparamagnetic (SPM) order appears in the low-fluence films (2 × 1016 and 4 × 1016 ions cm-2) and FM order co-exists with the SPM phase in high-fluence films (1 × 1017 ions cm-2). Exchange bias (EB) appears in the high-fluence films, with an EB field of about 100 Oe at 2 K and a blocking temperature of around 100 K. On the other hand, Co-V2O3 thin films with an implantation fluence of 3.5 × 1016 ions cm-2 exhibit a clear antiferromagnetic (AFM) coupling at low temperatures without the EB effect. The different magnetic behavior of the Co-implanted films with different Co content leads us to conclude that the observed EB effect in the Co-ZnO films results from the FM/AFM coupling between sizable Co nanoparticles and their CoO/Co3O4 surroundings in the (Zn,Co)O matrix. On the other hand, the absence of EB effect in Co-V2O3 appears to be due to the small size of the FM Co nanoparticles in spite of an AFM magnetic order. Detailed studies of magnetic orders and EB effect in magnetic nanocomposite semiconductors can pave the way for their application in spintronics.

The immobilization of proteins on flat substrates plays an important role for a wide spectrum of applications in the fields of biology, medicine, and biochemistry, among others. An essential prerequisite for the use of proteins (e.g., in biosensors) is the conservation of their biological activity. Losses in activity upon protein immobilization can largely be attributed to a random attachment of the proteins to the surface. In this study, we present an approach for the immobilization of proteins onto a chemically heterogeneous surface, namely a surface consisting of protein-permissive and protein-repellent areas, which allows for significant reduction of random protein attachment. As protein-permissive, i.e., as protein-binding sites, ultra pure metallic nanoparticles are deposited under vacuum onto a protein-repellent PEG-silane polymer layer. Using complementary surface characterization techniques (atomic force microscopy, quartz crystal microbalance, and X-ray photoelectron spectroscopy) we demonstrate that the Au nanoparticles remain accessible for protein attachment without compromising the protein-repellency of the PEG-silane background. Moreover, we show that the amount of immobilized protein can be controlled by tuning the Au nanoparticle coverage. This method shows potential for applications requiring the control of protein immobilization down to the single molecule level.

A series of poly(3-alkylthiophene)s (P3ATs) (P1–P5) has been synthesized via a Ni(dppp)-mediated polymerization, varying the bulkiness of the alkyl side chains in order to investigate the influence of the bulkiness of the alkyl substituent on the aggregation and magnetic properties of P3ATs. UV–Vis spectroscopy, performed in solution as well as in film, shows that the stacking of the polymers becomes more complicated as the bulkiness of the side chains increases. Both the π-interactions and the planarization of the polymer chains are diminished. While aggregation is absent in poor solvent for the polymer with the most bulky side chains, aggregation was present in film, albeit slowed down. This behavior was also confirmed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) experiments. Electron spin resonance (ESR) measurements, performed at 300 K on powders, confirmed the trend of decreasing supramolecular order with increasing bulkiness of the side-chain. Magnetization measurements, performed at 5 and 300 K, are in line with our hypothesis on the influence of π-interactions and the fraction of planar polymer chains on the coercivity and saturation magnetization, respectively. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 76–86

Composite multiferroics are a new class of material where magneto-electric coupling is achieved by creating an interface between a ferromagnetic and a ferroelectric compound. The challenge of understanding the chemical and magnetic properties of such interface is a key to achieve good magneto-electric coupling. The unique possibilities offered by isotope sensitive techniques are used to selectively investigate the interface's chemistry and magnetism in Fe/BaTiO3 and Fe/LiNbO3 systems during the application of an electric field. With a large enough electric field, a strong oxidation of Fe is triggered, which creates a magnetically dead interface. This leads to an irreversible decrease of the magneto-electric coupling properties. Material parameters are identified that determine under which electric field the interface may be modified. The results are confirmed on the two systems and are expected to be widespread in this new class of hybrid material.

Epitaxial multiferroic BaTiO₃-BiFeO₃ composite thin films exhibit a correlation between the magnetoelectric (ME) voltage coefficient αME and the oxygen partial pressure during growth. The ME coefficient αME reaches high values up to 43 V/(cm·Oe) at 300 K and at 0.25 mbar oxygen growth pressure. The temperature dependence of αME of the composite films is opposite that of recently-reported BaTiO₃-BiFeO₃ superlattices, indicating that strain-mediated ME coupling alone cannot explain its origin. Probably, charge-mediated ME coupling may play a role in the composite films. Furthermore, the chemically-homogeneous composite films show an oxygen vacancy superstructure, which arises from vacancy ordering on the {111} planes of the pseudocubic BaTiO₃-type structure. This work contributes to the understanding of magnetoelectric coupling as a complex and sensitive interplay of chemical, structural and geometrical issues of the BaTiO₃-BiFeO₃ composite system and, thus, paves the way to practical exploitation of magnetoelectric composites. ispartof: Materials vol:9 issue:1 pages:1-13 ispartof: location:Switzerland status: published

© 2017 Author(s). Nanostructured and disordered superconductors exhibit many exotic fundamental phenomena, and also have many possible applications. We show here that films of superconducting lead nanoparticles with a wide range of particle coverages, exhibit non-linear V(I) characteristics that are consistent with percolation theory. Specifically, it is found that V (I-Ic)a, where a = 2.1 ± 0.2, independent of both temperature and particle coverage, and that the measured critical currents (I c ) are also consistent with percolation models. For samples with low normal state resistances, this behaviour is observable only in pulsed current measurements, which suppress heating effects. We show that the present results are not explained by vortex unbinding [Berezinskii-Kosterlitz-Thouless] physics, which is expected in such samples, but which gives rise to a different power law behaviour. Finally, we compare our results to previous calculations and simulations, and conclude that further theoretical developments are required to explain the high level of consistency in the measured exponents a. ispartof: Journal of Applied Physics vol:122 issue:22 status: published

Co-rich ZnCoO nanoparticles embedded in wurtzite Zn0.7Co0.3O thin films are grown by pulsed laser deposition on a Si substrate. Local superconductivity with an onset Tc at 5.9 K is demonstrated in the hybrid system. The unexpected superconductivity probably results from Co3+ in the Co-rich ZnCoO nanoparticles or from the interface between the Co-rich nanoparticles and the Zn0.7Co0.3O matrix.

© 2015, Springer Science+Business Media New York. This paper reports a thorough microstructural investigation of bismuth ferrite (BFO) thin films subjected to various processing conditions and discusses their influence on the stability of the BiFeO3 perovskite phase. The formation of secondary phases in BFO thin films is studied as a function of annealing temperature and time, film thickness, Bi excess, and Ti substitution. While films annealed at 600 °C consist of the desired BiFeO3 phase, higher temperatures induce the decomposition leading to a significant amount of secondary phases, particularly the iron-rich Bi2Fe4O9 phase. A longer annealing time at 700 °C further enhances the decomposition of BiFeO3. Qualitative microstructural analysis of the films is performed by electron backscattered diffraction which provides phase analysis of individual grains. The morphology of the single-crystalline Bi2Fe4O9 grains that are embedded in the BiFeO3 matrix drastically changes as a function of the film thickness. Nucleation of these Bi2Fe4O9 grains probably occurs at the film/substrate interface, after which grain growth continues toward the surface of the film through the depletion of the BFO phase. Addition of Bi excess or the substitution of Fe with Ti in the precursor solutions significantly reduces the formation of an iron-rich secondary phase. Influence of the secondary phases as well as Ti substitution on magnetic properties of BFO films was investigated. ispartof: Journal of Materials Science vol:50 issue:13 pages:4463-4476 status: published

© 2015 AIP Publishing LLC. Magnetic spin structures in epitaxial BiFeO3 single layer and an epitaxial BaTiO3/BiFeO3 multilayer thin film have been studied by means of nuclear resonant scattering of synchrotron radiation. We demonstrate a spin reorientation in the 15 × [BaTiO3/BiFeO3] multilayer compared to the single BiFeO3 thin film. Whereas in the BiFeO3 film, the net magnetic moment m → lies in the (1-10) plane, identical to the bulk, m → in the multilayer points to different polar and azimuthal directions. This spin reorientation indicates that strain and interfaces play a significant role in tuning the magnetic spin order. Furthermore, large difference in the magnetic field dependence of the magnetoelectric coefficient observed between the BiFeO3 single layer and multilayer can be associated with this magnetic spin reorientation. ispartof: Applied Physics Letters vol:106 issue:8 pages:1-4 status: published

We studied the off-specular intensity in polarized neutron reflectivity from regular arrays of circular and rectangular Co dots with sizes in the micrometer range. The dots were lithographically prepared and placed on a square lattice with a period of 10 μm, the rectangular dots having an aspect ratio of 4:1. In both cases, we observed enhanced intensity at particular angles off the specular condition. The positions of these satellites are correlated to the lateral periodicity of the ferromagnetic dots. The magnetic information could be revealed by measuring the off-specular intensity as a function of the magnetic field applied in-plane parallel to the rows of the dots. The magnetization reversal process could be analyzed by separating the spin-flip and non-spin-flip contributions to the off-specular signal. The measured spin-flip intensities clearly prove that for both samples the magnetization reversal is dominated by domain wall movement and not by a uniform rotation of single-domain particles.

We have studied the magnetic and superconducting properties of a nanostructured magnetic/superconducting hybrid system, consisting of a Co layer with a square array of rectangular antidots, covered with a thin 500 A superconducting Pb layer. The magnetic force microscopy data have revealed that the domain walls are located between neighbouring antidots and are pinned at the antidot corners. The superconducting pinning properties of the hybrid system are studied by means of SQUID magnetisation measurements for different magnetic states of the Co antidot lattice. The results show that the stray field, coming from the domain walls in the antidot array, contributes more to the pinning potential than the periodic modulation of the underlying Co layer. The flux lines seem to be pinned at the domain walls between the antidots. In this way, possible matching effects are lost. The network of domain walls thus creates a new type of an artificial pinning array.

© 2017 Author(s). Perpendicular magnetic anisotropy (PMA) is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\CoFe(B) interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\Ta bilayer deposited on amorphous high-κ dielectric (relative permittivity κ=20) HfO2, grown by atomic layer deposition (ALD). PMA with interfacial anisotropy energy Ki up to 0.49 mJ/m2 appears after annealing the stacks between 200°C and 350°C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350°C coincides with the onset of interdiffusion in the materials. High-κ dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA). The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-κ dielectrics. ispartof: AIP Advances vol:7 issue:5 ispartof: location:New Orleans: LA status: published

Ultrathin coatings based on bi-elemental nanoparticles (NPs) are very promising to limit the surface-related spread of bacterial pathogens, particularly in nosocomial environments. However, tailoring the synthesis, composition, adhesion to substrate, and antimicrobial spectrum of the coating is an open challenge. Herein, we report on a radically new nanostructured coating, obtained by a one-step gas-phase deposition technique, and composed of bi-elemental Janus type Ag/Ti NPs. The NPs are characterized by a cluster-in-cluster mixing phase with metallic Ag nano-crystals embedded in amorphous TiO2 and present a promising antimicrobial activity including also multidrug resistant strains. We demonstrate the flexibility of the method to tune the embedded Ag nano-crystals dimension, the total relative composition of the coating, and the substrate type, opening the possibility of tailoring the dimension, composition, antimicrobial spectrum, and other physical/chemical properties of such multi-elemental systems. This work is expected to significantly spread the range of applications of NPs coatings, not only as an effective tool in the prevention of healthcare-associated infections but also in other technologically relevant fields like sensors or nano-/micro joining.

Room temperature magnetoelectric BiFeO3-BaTiO3 superlattices with strong out-of-plane magnetic anisotropy have been prepared by pulsed laser deposition. We show that the out-of-plane magnetization component increases with the increasing number of double layers. Moreover, the magnetoelectric voltage coefficient can be tuned by varying the number of interfaces, reaching a maximum value of 29 V/cm Oe for the 20×BiFeO3-BaTiO3 superlattice. This enhancement is accompanied by a high degree of perpendicular magnetic anisotropy, making the latter an ideal candidate for the next generation of data storage devices.

© 2014 American Physical Society. We investigated the surface morphology and magnetic properties of Co films grown on MgO (100) substrates before and after treatment with a NaOH solution. The surface morphology evolves from a continuous film into isolated hexagonal nanodisks resulting from the formation of cobalt hydroxide. In the as-grown Co films the magnetic anisotropy behaves as a superposition of fourfold magnetocrystalline anisotropy and uniaxial magnetic anisotropy (UMA), and the magnetization reversal proceeds by two-step domain-wall motion. After the NaOH treatment the UMA is reduced and the magnetization reversal appears to be dominated by magnetization rotation. In addition, the exchange bias effect, which in the as-deposited films results from the presence of a cobalt oxide layer, disappears after the NaOH treatment, and can be reinduced by annealing the sample. The observed significant changes in the magnetic properties can be related to the disappearance and reappearance of a cobalt oxide top layer. ispartof: Physical Review B, Condensed Matter and Materials Physics vol:90 issue:13 pages:1-5 status: published

To utilize iron oxide nanoparticles in biomedical applications, a sufficient magnetic moment is crucial. Since this magnetic moment is directly proportional to the size of the superparamagnetic nanoparticles, synthesis methods of superparamagnetic iron oxide nanoparticles with tunable size are desirable. However, most existing protocols are plagued by several drawbacks. Presented here is a one-pot synthesis method resulting in monodisperse superparamagnetic iron oxide nanoparticles with a controllable size and magnetic moment using cost-effective reagents. The obtained nanoparticles were thoroughly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) measurements. Furthermore, the influence of the size on the magnetic moment of the nanoparticles is analyzed by superconducting quantum interference device (SQUID) magnetometry. To emphasize the potential use in biomedical applications, magnetic heating experiments were performed. ispartof: Materials vol:9 issue:7 pages:554-564 ispartof: location:Switzerland status: published

Multiferroic superlattices consisting of 15 double layers BaTiO3–BiFeO3 show a very high magnetoelectric voltage coefficient αME of up to 49 V cm−1 Oe−1 at 300 K, measured at 1 kHz with zero direct current (DC) bias magnetic field. However, the microscopic origins of such high αME values, and the temperature and DC magnetic field dependencies of αME are not understood up to now. Therefore, in this study two superlattices grown at high/low oxygen partial pressures having high/low αME values, respectively, are compared. While at high growth pressure the strain contrast in high-resolution transmission electron microscopy images is limited to few layers at the substrate interface, the low-pressure sample shows much more pronounced microstrain. This is additionally visualized in Fourier transformed images, and the out-of-plane lattice parameter of the single BaTiO3 layer is increased near the interface. In addition to a low density of oxygen vacancies, it seems to be important to avoid micromechanical clamping of the 2D single-phase nanolayers of the multiferroic BaTiO3–BiFeO3 superlattices to achieve high magnetoelectric coupling.

In this paper we investigate the enzyme conjugation of CdSe/ZnS core/shell quantum dots (QDs) by means of their photoluminescent properties, as well as the influence of the enzymatic reaction on these properties. The QDs were first transferred from toluene to water by encapsulation in poly(ethylene glycol)-phospholipid micelles. The water solubilized QDs were bioconjugated with the enzymes glucose oxidase (GOX) and horseradish peroxidase (HRP). For covalent coupling the crosslinkers 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and hydroxysulfosuccinimide (sulfo-NHS) were used. Photoluminescence (PL) measurements showed that EDC had a large effect on the PL intensity. Also, the PL intensity increased in PBS buffer as compared to water. The enzyme conjugation caused a noticeable shift in the PL peak wavelength, but had a minor effect on the PL intensity. Sensing experiments confirmed the well-known quenching of PL by H 2 O 2 . Similarly, the PL intensity was sensitive to glucose in the mM range in the presence of GOX. This can be understood since the conversion of glucose by GOX yields H 2 O 2 as a by-product. Measurements of the quantum yield (QY) showed increased values for QD solutions treated with EDC. The QY decreased with increasing glucose concentration in the presence of GOX. The change in QY was accompanied by a change in pH, suggesting a correlation between pH and QY.

We present an approach to control the immobilization process of biomolecules by functionalization of SiO2substrates decorated with nanostructures. The creation of specific protein permissive and protein resistant areas leads to a directed and site-specific immobilization of proteins. We make use of molecular beam epitaxy and laser assisted cluster deposition to create Au nanostructures on PEG-silanized SiO2substrates. The chemical contrast provided by the two materials, namely Au and PEG on the substrate surface supports the specificity of thiol-based Au functionalization for biomolecule attachment. © 2012 IEEE. ispartof: pages:1-4 ispartof: 2012 12TH IEEE CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO) pages:1-4 ispartof: IEEE International Conference on Nanotechnology (IEEE-NANO) location:Birmingham, UK date:20 Aug - 23 Aug 2012 status: published

Amyoid peptides Aβ40 and Aβ42 are directly related to the Alzheimer's disease (AD) pathology. More specifically small alterations in the ratio Aβ42:Aβ40 have been shown to influence dramatically the synaptic function in vitro and in vivo. In this study we use Atomic Force Microscopy to investigate the morphology of the species formed during aggregation at different moments in time. In agreement with literature data, we found that a small increase of this ratio appears to delay the fibrilization process. Moreover, in the case of the Aβ42, known to be more pathogenic than Aβ40, small oligomers seem to coexist with higher molecular weight species from very early to very late moments in time. This suggests the continuous presence of intermediates that might have a synapto-toxic effect.

The functionality and electronic properties of metal/ferroelectric systems rely heavily on the chemical and structural properties of the interface. The isotope sensitive technique of nuclear resonant scattering is used to selectively study the chemistry and magnetic state of the Fe/BaTiO3 interface. An electric polarity-dependent modification of the metal/ferroelectric oxide interface has been systematically observed. The results show that the interface can be oxidized or reduced by inverting the polarity of the electric field applied across the interface above a threshold field value of ±400 kV m−1. Remarkably, the final interface state depends on the polarization history of the system. Based on these results, a model for the electric field induced ion transport at the Fe/BaTiO3 interface has been suggested. Such subtle structural changes at the interface deteriorate the magnetoelectric coupling. However, for certain applications where an oxide layer is required at metal/ferroelectric oxide interfaces, the electric fields can be used to control interdiffusion processes.

The fields of bioscience and nanomedicine demand precise thermometry for nanoparticle heat characterization down to the nanoscale regime. Since current methods often use indirect and less accurate techniques to determine the nanoparticle temperature, there is a pressing need for a direct and reliable element-specific method. In-situ extended X-ray absorption fine structure (EXAFS) spectroscopy is used to determine the thermo-optical properties of plasmonic branched gold nanoparticles upon resonant laser illumination. With EXAFS, the direct determination of the nanoparticle temperature increase upon laser illumination is possible via the thermal influence on the gold lattice parameters. More specifically, using the change of the Debye-Waller term representing the lattice disorder, the temperature increase is selectively measured within the plasmonic branched nanoparticles upon resonant laser illumination. In addition, the signal intensity shows that the nanoparticle concentration in the beam more than doubles during laser illumination, thereby demonstrating that photothermal heating is a dynamic process. A comparable temperature increase is measured in the nanoparticle suspension using a thermocouple. This good correspondence between the temperature at the level of the nanoparticle and at the level of the suspension points to an efficient heat transfer between the nanoparticle and the surrounding medium, thus confirming the potential of branched gold nanoparticles for hyperthermia applications. This work demonstrates that X-ray absorption spectroscopy-based nanothermometry could be a valuable tool in the fast-growing number of applications of plasmonic nanoparticles, particularly in life sciences and medicine.