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To design fast memory devices, we need material combinations which can facilitate fast read and write operation. We present a heterostructure comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as a viable option for designing fast memory devices. We theoretically model spin-charge dynamics between the 2D magnets and 2D TIs. Using the adiabatic approximation, we combine the non-equilibrium Green's function method for spin-dependent electron transport, and time-quantified Monte-Carlo for simulating magnetization dynamics. We show that it is possible to switch the magnetic domain of a ferromagnet using spin-torque from spin-polarized edge states of 2D TI. We further show that the switching between TIs and 2D magnets is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an optimal interface exchange depending on the exchange interaction within the magnet is required for efficient switching. Finally, we compare the experimentally grown Cr-compounds and show that Cr-compounds with higher anisotropy (such as $\rm CrI_3$) results in lower switching speed but more stable magnetic order.

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.

The recent demonstration of ferroelectricity in ultrathin HfO2 has kickstarted a new wave of research into this material. HfO2 in the orthorhombic phase can be considered the first and only truly n...

To improve power efficiency and endurance of magnetic memory technologies, a voltage-controlled mechanism is desirable. The voltage control of magnetic anisotropy (VCMA) effect in MgO stacks is a promising option, however, its strength is too low for memory applications. Replacing the standard MgO layer by an oxide with a higher permittivity $\ensuremath{\kappa}$ may help improve the VCMA strength. We demonstrate a VCMA effect up to $\ensuremath{\xi}=75$ fJ/Vm at room temperature in a Co\ensuremath{\setminus}Pt bilayer grown on atomic layer deposited (ALD) high-$\ensuremath{\kappa}\phantom{\rule{4pt}{0ex}}{\mathrm{SrTiO}}_{3}$ (STO). After treating the STO surface with isopropanol, a thin ${\mathrm{CoO}}_{x}$ interfacial layer is observed, enabling VCMA. Upon cooling down from room temperature to 200 K, the VCMA effect strength increases by a factor of two. This increase is incompatible with the expected Arrhenius temperature dependence for an ionic effect and thus we argue that the observed VCMA effect is electronic. Electronic VCMA is desirable for adequate memory endurance, and hence the approach proposed here has great potential for applications.

Metal-organic frameworks (MOFs) are generally recognized as promising platforms for energy conversion and storage due to their structural diversity and ligands tunability features, yet there are still challenges before practical applications become possible. Herein, a two-dimensional metal-organic framework (MOF) with mono-coordinated ferrocenecarboxylic acid (Fc) is successfully prepared. Different from the pure MOF, the as-prepared Fc-MOF offers remarkable electrocatalytic activity, exhibiting a low overpotential of 273 mV (vs. reversible hydrogen electrode) at 200 mA cm−2 and a small driving potential of 1.49 V (10 mA cm−2) for the overall water splitting with Pt/C as a counterpart cathode. The advance nature of the as-prepared Fc-MOF could also be evidenced by its remarkable Urea oxidation reaction (UOR) activity as it drives a current density of 10 mA cm−2 with a potential of 1.35 V. Theoretical calculations and experimental results demonstrate that the introduction of highly electronegative Fc not only change the electronic structure of MOF but also expose more unsaturated active sites, which in turn varies the adsorption features of the intermediate species during the catalytic process. This work represents a new pathway for exploration of highly efficient MOF based electrocatalysts.

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.

The detailed understanding of magnetoelectric (ME) coupling in multiferroic oxide heterostructures is still a challenge. In particular, very little is known to date concerning the impact of the chemical interface structure and unwanted impurities that may be buried within short-period multiferroic BiFeO3–BaTiO3 superlattices during growth. Here, we demonstrate how trace impurities and elemental concentration gradients contribute to high ME voltage coefficients in thin-film superlattices, which are built from 15 double layers of BiFeO3–BaTiO3. Surprisingly, the highest ME voltage coefficient of 55 V cm–1 Oe–1 at 300 K was measured for a superlattice with a few atomic percent of Ba and Ti that diffused into the nominally 5 nm thin BiFeO3 layers, according to analytical transmission electron microscopy. In addition, highly sensitive enhancements of the cation signals were observed in depth profiles by secondary ion mass spectrometry at the interfaces of BaTiO3 and BiFeO3. As these interface features correlat...

The solid solubility of the isomorphous monosilicides during the silicide reaction of Ni-Pt, Ni-Pd and Pt-Pd alloys on Si(100) is comparatively studied in the full composition range. Our study reveals that PtSi and PdSi, exhibiting a minor lattice mismatch, directly form a solid solution. In contrast, for larger differences in lattice parameters such as is the case for NiSi-PtSi and NiSi-PdSi, the mutually soluble phases coexist, prior to the formation of a solid solution at increased temperatures. Hence, it appears that the direct formation of a ternary monosilicide solid solution is inherently related to the lattice mismatch of the binary monosilicides. This finding provides an explanation for important differences observed in the elemental redistribution between the three systems, considered to be very similar up to now. Moreover, the different formation of a solid solution results in a fundamentally different nucleation of PdSi: while Ni lowers the nucleation barrier by reducing the contribution of the interface energy, Pt strongly increases the entropy of mixing which triggers the formation of the Pd-monosilicide at surprisingly low temperatures. Our results show that the lattice mismatch is a crucial parameter and determines the phase formation sequence and elemental redistribution during the silicide reaction.

Herein, the magnetoelectric (ME) performance of epitaxial multilayer composite films built from nanometer‐thick layers of multiferroic BiFeO3 and ferroelectric BaTiO3 is reviewed. A successful implementation of shadow‐mask pulsed laser deposition considerably reduces the interface and surface roughness of the multilayers. In dependence of double‐layer thickness and the degree of structural perfection, the multilayers show high ME voltage coefficients up to 480 V cm−1 Oe−1 at 300 K and 0 T bias magnetic field. With decreasing double‐layer thickness, an interface‐driven effect critically enhances the ME coupling in this strain and charge-comediated system. Interestingly, the characteristics of temperature and DC magnetic field dependencies of magnetoelectric voltage coefficients change with the transition from the 2D to 3D character of the single layers, i.e., for BiFeO3 layers thicker than 5 nm within the multilayers. These changes are attributed to variations of the contributing ME coupling mechanisms. Furthermore, scanning transmission electron microscopy (STEM) with energy‐dispersive X‐ray (EDX) spectroscopy mapping‐based nanoanalysis indicates that chemical effects at the interfaces play an important role for the ME performance of the BiFeO3-BaTiO3 multilayer thin films.

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.

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 recent demonstration of ferroelectricity in ultrathin HfO

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 American Physical Society. Reducing the size of a superconductor below its characteristic length scales can either enhance or suppress its critical temperature (Tc). Depending on the bulk value of the electron-phonon coupling strength, electronic and phonon confinement effects will play different roles in the modification of Tc. Experimentally disentangling each contribution has remained a challenge. We have measured both the phonon density of states and Tc 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 Tc. ispartof: PHYSICAL REVIEW B vol:99 issue:6 status: published

We used lithographically fabricated nanoconstrictions made of Ag–Co granular thin films to achieve current densities above 10 A/cm during magnetotransport measurements. Systematically measured variations of the resistance with current under high applied magnetic fields did not reveal any dramatically large magnetoresistance effect, in contrast to the previous observations using mechanical point contact based techniques. Our experimental results on resistance switching by current injection in the Ag–Co nanoconstrictions reveal spin torque effects. The switching amplitudes are considerably smaller when compared to the results obtained for pillar shaped trilayers due to the large number of Co grains in the nanoconstrictions. We demonstrate that the use of point contact patterns with nanometer dimensions, where effects resulting from current induced mechanical distortions at high magnetic fields are negligible, has obvious advantages over the mechanical point contact technique for studying spin injection effects.

We report on the growth of thin NiSi films via the thermal reaction of Ni layers (13–35 nm) with Si(100) substrates modified by ion implantation. By introducing substrate damage or nitrogen impurities prior to the solid-phase reaction, several properties of the NiSi films can be modified: the formation temperature, texture, diffusion-limited growth rate and morphological stability. As some of the modifications to the NiSi films are rooted in the early silicide phases preceding the NiSi phase, particularly its formation temperature, special attention is devoted to the growth of the amorphous Ni-Si alloy and the crystalline δ-Ni2Si and θ-Ni2Si phases. We employed a number of experimental techniques, including in situ synchrotron x-ray diffraction (XRD), in situ Rutherford backscattering spectrometry (RBS), in situ sheet resistance measurements, ex situ ion beam channelling and ex situ pole figure measurements. We show that both the formation temperature of the NiSi films and the intensity of epitaxial and axiotaxial components of the NiSi texture can be either lowered or raised by selecting appropriate implantation conditions. Agglomeration of the NiSi films at high temperature (> 700 °C) can be slowed down, either by slowing down the mobility of the Ni and Si atoms, or by removing the morphologically destabilizing axiotaxial texture. Our results emphasize the strong interwoven nature of phase formation, texture and morphological degradation. We illustrate that the kinetics of the early stages of thin film reactions consist of more than just diffusion, i.e. nucleation can also play a crucial role.

© 2019 IOP Publishing Ltd. Solid-state amorphization, the growth of an amorphous phase during annealing, has been studied in a wide variety of thin film structures. Whereas research on the remarkable growth of such a metastable phase has mostly focused on strictly binary systems, far less is known about the influence of impurities on such reactions. In this paper, the influence of nitrogen, introduced via ion implantation, is studied on the solid-state amorphization reaction of thin (35 nm) Ni films with Si, using in situ x-ray diffraction (XRD), ex situ Rutherford backscattering spectrometry, XTEM, and synchrotron XRD. It is shown that due to small amounts of nitrogen (

In (Ga,Mn)As, a model dilute magnetic semiconductor, the electric and magnetic properties are strongly influenced by the lattice sites occupied by the Mn atoms. In particular, the highest Curie temperatures are achieved upon thermal annealing in a narrow temperature window around $200{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, by promoting the diffusion of interstitial Mn towards the surface. In this work, we determined the thermal stability of both interstitial and substitutional Mn in ferromagnetic (Ga,Mn)As thin films, using the emission channeling technique. At a higher Mn concentration, the temperatures at which substitutional and interstitial Mn become mobile not only decrease, but also become closer to each other. These findings advance our understanding of self-compensation in (Ga,Mn)As by showing that the strong dependence of the Curie temperature on annealing temperature around $200{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ is a consequence of balance between diffusion of interstitial Mn and segregation of substitutional Mn.

We report on the epitaxial growth and the characterization of thin FePt films and the subsequent patterning of magnetic lattice structures. These structures can be used to trap ultracold atoms for quantum simulation experiments. We use Molecular Beam Epitaxy (MBE) to deposit monocrystalline FePt films with a thickness of 50 nm. The films are characterized with X-ray scattering and Mossbauer spectroscopy to determine the long range order parameter and the hard magnetic axes. A high monocrystalline fraction was measured as well as a strong remanent magnetization of M = 900 kA/m and coercivity of 0.4 T. Using Electron Beam Lithography (EBL) and argon ion milling we create lattice patterns with a period down to 200 nm, and a resolution of 30 nm. The resulting lattices are imaged in a Scanning Electron Microscope in cross-section created by a Focused Ion Beam. A lattice with continuously varying lattice constant ranging from 5 micrometer down to 250nm has been created to show the wide range of length scales that can now be created with this technique., 8 pages, 10 figures

The structure, magnetic properties, and lattice dynamics of ordered Fe–Pt alloys with three stoichiometric compositions, Fe 3 Pt, FePt and FePt 3 , have been investigated using the density functional theory. Additionally, the existing experimental data have been complemented by new measurements of the Fe projected phonon density of states performed for the Fe 3 Pt and FePt 3 thin films using the nuclear inelastic scattering technique. The calculated phonon dispersion relations and phonon density of states have been compared with the experimental data. The dispersion curves are very well reproduced by the calculations, although, the softening of the transversal acoustic mode TA 1 leads to some discrepancy between the theory and experiment in Fe 3 Pt. A very good agreement between the measured spectra and calculations performed for the tetragonal structure derived from the soft mode may signal that the tetragonal phase with the space group P 4/ mbm plays an important role in the martensitic transformation observed in Fe 3 Pt. For FePt 3 , the antiferromagnetic order appearing with decreasing temperature has been also investigated. The studies showed that the phonon density of states of FePt 3 very weakly depends on the magnetic configuration.

Indium tin oxide (ITO) is broadly used as a transparent conducting material for electrodes in optoelectronic devices. Irradiation of ITO with low energy ions can result in the formation of periodic surface nanopatterns which can serve as an alternative for the polymer alignment layer in liquid crystal devices. We investigated the formation of the ion-induced surface nanopatterns on ITO with focus on the influence of the crystalline structure of the material. We find that the crystallinity plays a crucial role in the pattern formation, with no pattern developing on an amorphous ITO surface. We discuss these findings in the context of the state-of-the-art theory for ion-induced patterning. We show that the ion-induced pattern plays a critical role in the liquid crystal alignment on ITO surfaces.

The coexistence of superconductivity and ferromagnetism is investigated in granular Sn-Co nanocomposites. The nanocomposites have been prepared by co-deposition of Sn atoms and Co clusters, the morphology and composition of which can be tuned by varying the deposition rate of Co clusters relative to Sn atoms. Flat isolated Sn islands are obtained at zero or low Co cluster flux, while granular nanocomposites are formed with increasing Co cluster flux, reaching Co concentrations up to 44 vol.%. Interfaces with a low electronic transparency between superconductor and ferromagnet are obtained by a combination of the granular nature of the nanocomposites and the formation of Sn-Co alloys at the Sn/Co interfaces. The structure and composition of the nanocomposites have been thoroughly characterized by atomic force microscopy, x-ray diffraction and conversion electron Mössbauer spectroscopy. Over the entire Co concentration range, the hybrids show a ferromagnetic response. The superconducting phase boundary and the Meissner response depend on the morphology and composition of the nanocomposites. In particular, the superconducting critical temperature decreases with increasing Co concentration, while the Meissner response varies from a reversible to a strongly hysteretic behaviour depending on the morphology of the samples with different Co content. The persistence of superconductivity at high Co concentrations is attributed to a suppression of the superconducting proximity effect in these nanocomposites, which is ascribed to the low interface transparency between the Sn and Co components that make up these hybrid systems. publisher: Elsevier articletitle: Coexistence of superconductivity and ferromagnetism in cluster-assembled Sn–Co nanocomposites journaltitle: Journal of Alloys and Compounds articlelink: http://dx.doi.org/10.1016/j.jallcom.2015.03.007 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved. ispartof: Journal of Alloys and Compounds vol:637 pages:509-516 status: published

$\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ 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 $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ nanoparticles is associated with a tetragonal distortion of the fcc structure. Combining a wide range of complementary experimental techniques, including low-temperature M\"ossbauer spectroscopy, advanced transmission electron microscopy, and synchrotron radiation techniques, we unambiguously identify the tetragonally distorted ferromagnetic ground state, with lattice parameters $a=3.76(2)\phantom{\rule{4pt}{0ex}}\AA{}$ and $c=3.50(2)\phantom{\rule{4pt}{0ex}}\AA{}$, and a magnetic moment of 2.45(5) ${\ensuremath{\mu}}_{B}$ per Fe atom. Our findings indicate that the ferromagnetic order in nanostructured $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ is generally associated with a tetragonal distortion. This observation motivates a theoretical reassessment of the electronic structure of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ taking tetragonal distortion into account.

A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe

The detailed understanding of magnetoelectric (ME) coupling in multiferroic oxide heterostructures is still a challenge. In particular, very little is known to date concerning the impact of the chemical interface structure and unwanted impurities that may be buried within short-period multiferroic BiFeO

Radioactive $^{27}\mathrm{M}\mathrm{g}$ (${t}_{1/2}=9.5\text{ }\text{ }\mathrm{min}$) was implanted into GaN of different doping types at CERN's ISOLDE facility and its lattice site determined via ${\ensuremath{\beta}}^{\ensuremath{-}}$ emission channeling. Following implantations between room temperature and $800\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, the majority of $^{27}\mathrm{M}\mathrm{g}$ occupies the substitutional Ga sites; however, below $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ significant fractions were also found on interstitial positions $\ensuremath{\sim}0.6\text{ }\text{ }\AA{}$ from ideal octahedral sites. The interstitial fraction of Mg was correlated with the GaN doping character, being highest (up to 31%) in samples doped $p$ type with $2\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ stable Mg during epilayer growth, and lowest in Si-doped $n$-GaN, thus giving direct evidence for the amphoteric character of Mg. Implanting above $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ converts interstitial $^{27}\mathrm{M}\mathrm{g}$ to substitutional Ga sites, which allows estimating the activation energy for migration of interstitial Mg as between 1.3 and 2.0 eV.

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.

Surface treatments using multiple Ar ion irradiation processes with a maximum energy and fluence of 200 keV and 1 × 10 16 ions/cm 2 , respectively, have been performed on two different metallic glasses: Zr 55 Cu 28 Al 10 Ni 7 and Ti 40 Zr 10 Cu 38 Pd 12 . Analogous irradiation procedures have been carried out at room temperature (RT) and at T = 620 K (≈0.9 T g , where T g denotes the glass transition). The structure, mechanical behavior, wettability and corrosion resistance of the irradiated alloys have been compared with the properties of the as-cast and annealed ( T = 620 K) non-irradiated specimens. While ion irradiation at RT does not significantly alter the amorphous structure of the alloys, ion irradiation close to T g promotes decomposition/nanocrystallization. Consequently, the hardness ( H ) and reduced Young’s modulus ( E r ) decrease after irradiation at RT but they both increase after irradiation at 620 K. While annealing close to T g increases the hydrophobicity of the samples, irradiation induces virtually no changes in the contact angle when comparing with the as-cast state. Concerning the corrosion resistance, although not much effect is found after irradiation at RT, an improvement is observed after irradiation at 620 K, particularly for the Ti-based alloy. These results are of practical interest in order to engineer appropriate surface treatments based on ion irradiation, aimed at specific functional applications of bulk metallic glasses.

The magnetic and electric properties of impurities in semiconductors are strongly dependent on the lattice sites which they occupy. While the majority site can often be predicted based on chemical similarities with the host elements and is usually simple to confirm experimentally, minority sites are far more complicated to predict, detect and identify. We have carried out extensive β − emission channeling studies on the lattice location of transition metal impurities in wide-gap dilute magnetic semiconductors, namely Co and Mn in GaN and ZnO, making use of radioactive 61 Co and 56 Mn implanted at the ISOLDE facility at CERN. In addition to the majority occupation of cation (Ga, Zn) sites, we located significant fractions (of the order of 20%) of the Co and Mn impurities in anion (N, O) sites, which are virtually unaffected by thermal annealing up to 900 °C. Here, we present the β − emission channeling experiments on 61 Co-implanted GaN. We discuss these results in the context of our recent reports of minority anion substitution in Mn-implanted GaN Pereira et al. (2012) [19] and Mn/Co-implanted ZnO Pereira et al. (2011) [20] , particularly in terms of the advantages of the emission channeling technique in such cases of multi-site occupancy.

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

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.

We present a fundamental study of the monolayer adsorption of sulfur on Ge(100) surfaces from aqueous (NH4)2S solution. This treatment shows promising perspectives for the passivation of high-mobility semiconductor surfaces and is therefore presently of great technological importance. The adsorption mechanisms as well as the adsorption geometry are thoroughly investigated at the atomic scale, by both experiment and theory, applying X-ray absorption spectroscopy and molecular dynamics simulations. Our findings indicate that sulfidation in solution results in the formation of Ge–S–Ge bridges along the [110] direction, with no indication for −SH surface groups. A S–Ge bond length of 2.25 ± 0.05 A was deduced, which is affected by the chemical environment of the sulfur atoms, i.e., by residual surface oxides. Our study provides novel insights into the surface termination and atomic structure of (NH4)2S-treated Ge(100) surfaces and discusses possible differences from in situ sulfur adsorption methods such as H...

The effective passivation of germanium surfaces and interfaces has been claimed to be the key to a substantial progress in developing Ge-based microelectronic devices. This paper compares the currently most promising passivation routes, i.e. oxidation and sulfidation, focusing on the underlying atomic scale processes and highlighting similarities and discrepancies between both approaches. The effect of oxidation and sulfidation on electrically active defects is addressed, and the chemical and structural properties of the passivated surfaces are described in detail.

International audience; A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe2 nanopillars using a room temperature pulsed electrodeposition process. Ba0.70Sr0.30TiO3–CoFe2O4 multiferroic nanocomposites were grown through direct deposition of Ba0.7Sr0.3TiO3 films by radio-frequency sputtering on the top surface of the pillar structure, with in situ simultaneous oxidation of CoFe2 nanopillars. The vertically aligned multiferroic nanocomposites were characterized using various techniques for their structural and physical properties. The large interfacial area between the ferrimagnetic and ferroelectric phases leads to a magnetoelectric voltage coefficient as large as ~320 mV cm−1 Oe−1 at room temperature, reaching the highest values reported so far for vertically architectured nanocomposite systems. This simple method has great potential for large-scale synthesis of many other hybrid vertically aligned multiferroic heterostructures.

© 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

et al., The combination of lithography and ion implantation is demonstrated to be a suitable method to prepare lateral multilayers. A laterally, compositionally, and magnetically modulated microscale pattern consisting of alternating Co (1.6 µm wide) and Co-CoO (2.4 µm wide) lines has been obtained by oxygen ion implantation into a lithographically masked Au-sandwiched Co thin film. Magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an effective positive giant magnetoresistance (GMR) behavior at room temperature. Conversely, anisotropic magnetoresistance and GMR contributions are distinguished at low temperature (i.e., 10 K) since the O-implanted areas become exchange coupled. This planar GMR is principally ascribed to the spatial modulation of coercivity in a spring-magnet-type configuration, which results in 180° Néel extrinsic domain walls at the Co/Co-CoO interfaces. The versatility, in terms of pattern size, morphology, and composition adjustment, of this method offers a unique route to fabricate planar systems for, among others, spintronic research and applications., This work was financed by the Research Foundation-Flanders (FWO), the Concerted Research ActionGOA/14/007, the 2014-SGR-1015 project of the Generalitat de Catalunya, and the European Commission under the 7th Framework Programme through the “Research Infrastructure” action of the “Capacities” Programme, NMI3-II Grant No. 283883. This work is based upon experiments (Proposal Nos. 5928 and 9384) performed at the MARIA instrument operated by JCNS at Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany. The authors would like to thank IMEC for access to its lithography facilities as well as J. Moonens and J. Loo for technical support. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

In this contribution, we discuss the crystalline properties of strained and strain-relaxed CVD-grown GeSn layers with Sn content in the range 6.4-12.6 at.%. A positive deviation from Vegard's law was observed and a new experimental bowing parameter was extracted for GeSn: bGeSn = 0.041 Å (in excellent agreement with recent theoretical predictions). The GeSn critical thickness for strain relaxation as a function of Sn concentration was determined, resulting in significantly higher values than those predicted by equilibrium models. A composition-dependent strain relaxation mechanism was also found, with the formation of an increasing density of GeSn pyramidal islands in addition to misfit dislocations at lower Sn concentration. © 2013 The Electrochemical Society. ispartof: ECS Journal of Solid State Science and Technology vol:2 issue:4 pages:P134-P137 status: published

© 2016 Author(s). Strained Ge1-xSnx thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge0.94Sn0.06 films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge0.94Sn0.06 films grown by molecular beam epitaxy. ispartof: Journal of Applied Physics vol:120 issue:8 pages:1-11 status: published

The interplay between magnetocrystalline anisotropy and exchange bias is investigated in CoO/Co bilayer films, which are grown epitaxially on MgO (0 0 1), by magnetization reversal measurements based on the anisotropic magnetoresistance (AMR) effect. While an asymmetric magnetization reversal survives after training for cooling field (CF) along the hard axis, the magnetization reversal becomes symmetric and is dominated in both branches of the hysteresis loop by domain wall motion before and after training for CF along the easy axis. When performing an in-plane hysteresis loop perpendicular to the CF, the hysteresis loop along the easy axis becomes asymmetric: magnetization rotation dominates in the ascending branch, while there is a larger contribution of domain wall motion in the descending branch. Furthermore, the azimuthal angular dependence of the AMR shows two minima after performing a perpendicular hysteresis loop, instead of only one minimum after training. Relying on the extended Fulcomer and Charap model, these effects can be related to an increased deviation of the average uncompensated antiferromagnetic magnetization from the CF direction. This model provides a consistent interpretation of training and asymmetry of the magnetization reversal for epitaxial films with pronounced magnetocrystalline anisotropy as well as for the previously investigated polycrystalline films.

In this article we present a detailed investigation of the structural and magnetic properties of exchange biased NiFe (ferromagnet)/FeMn (antiferromagnet) thin films. The influence of the shape anisotropy on exchange bias and the magnetization reversal mechanism in a sample with patterned lines is compared with a continuous two-dimensional reference sample. Polarized neutron reflectivity (PNR) is employed to study the magnetization reversal by analyzing the spin-flip and non-spin-flip reflectivities. PNR measurements show that the magnetization reversal in the reference two-dimensional film and patterned lines is by domain wall motion rather than coherent rotation of magnetization.

Germanium is considered to be a potential semiconductor to replace silicon in future high-performance microelectronic devices. Yet, when compared to Si, very little is known about the surface chemistry of Ge surfaces. In this article, we report on the oxygen adsorption on Ge(100)-(2 × 1) surfaces and the related changes in the density of surface states. In particular, the adsorption geometry is examined both in reciprocal- and real-space using reflection high-energy electron diffraction and scanning tunneling microscopy, respectively. Our findings reveal that the insertion of oxygen atoms into the Ge backbonds is not favored under the investigated reaction conditions, i.e., at a moderate O2 exposure. The O2-exposed surface exhibits a local (1 × 1) surface reconstruction, which implies that dimer bonds are destroyed upon oxygen adsorption. Surface states related to Ge dangling surface bonds present on the clean Ge(100) surface are found to be passivated. In addition, a high density of expelled substrate at...

The last decennia, a lot of effort has been made to introduce new channel materials in a Si process flow. High mobility materials such as Ge need a good gate stack passivation in order to ensure optimal MOSFET operation. Several routes for passivating the Ge gate stack have been explored in the last years. We present here the S-passivation of the Ge gate stack: (NH4)2S is used to create a S-terminated Ge surface. In this paper the S-treatment is discussed. The S-terminated Ge surface is not chemically passive but can still react with air. After gate oxide deposition, the Ge-S bonds are preserved and an adequate passivation is found for pMOS operation.

We investigated the reversal mechanism in a Co/CoO exchange bias bilayer with a pronounced magnetocrystalline anisotropy in the ferromagnet. The anisotropy, which is induced by the growth of a highly textured Co layer, imposes a distinct reversal mechanism along the magnetically easy and hard direction. It is shown that exchange bias can be induced along both directions, despite the magnetocrystalline anisotropy. The interplay between the magnetocrystalline anisotropy and exchange bias induces a different reversal mechanism for the subsequent reversals in the two crystallographic directions. Along the hard axis, the magnetization reverses according to the reversal mechanism observed before in polycrystalline exchange bias bilayers, i.e. domain wall nucleation and motion for the first reversal and coherent rotation for the subsequent ones. Along the easy axis, domain wall motion remains the dominant reversal mechanism and magnetization rotation has only a minor contribution.

In this paper, we reports our recent studies of the electrical and crystalline properties of heteroepitaxial Ge1-xSnx layers with various Sn content of 0~25%. We examined Ga-doping in strained Ge1-xSnx layers for developing source/drain stressor in CMOS applications and investigated the effect of Sn on the doping profile. The impact of Sn on carrier properties has been also studied with the Hall measurement of Ge1-xSnx/SOI structures. Also, we achieved the epitaxial growth of Ge1-xSnx layers with a Sn content as high as 25% on InP considering misfit between the epitaxial layer and substrate.