Bulk Value Research Articles

Estimating the Density of Thin Polymeric Films Using Magnetic Levitation

While the density is a central property of a polymer film, it can be difficult to measure in films with a thickness of ∼100 nm or less, where the structure of the interfaces and the confinement of the polymer chains may perturb the packing and dynamics of the polymers relative to the bulk. This Article demonstrates the use of magneto-Archimedes levitation (MagLev) to estimate the density of thin films of hydrophobic polymers ranging from ∼10 to 1000 nm in thickness by employing a substrate with a water-soluble sacrificial release layer to delaminate the films. We validate the performance of MagLev for this application in the ∼1 μm thickness range by comparing measurements of the densities of several different films of amorphous hydrophobic polymers with their bulk values of density. We apply the technique to films < 100 nm and observe that, in several polymers, there are substantial changes in the levitation height, corresponding to both increases and decreases in the apparent density of the film. These apparent changes in density are verified with a buoyancy control experiment in the absence of paramagnetic ions and magnetic fields. We measure the dependence of density upon thickness for two model polymeric films: poly(styrene) (PS) and poly(methyl methacrylate) (PMMA). We observe that, as the films are made thinner, PS increases in density while PMMA decreases in density and that both exhibit a sigmoidal dependence of density with thickness. Such changes in density with thickness of PS have been previously observed with reflectometric measurements (e.g., ellipsometry, X-ray reflectivity). The interpretation of these measurements, however, has been the subject of an ongoing debate. MagLev is also compatible with nontransparent, rough, heterogeneous polymeric films, which are extremely difficult to measure by alternative means. This technique could be useful to investigate the properties of thin films for coatings, electronic devices, and membrane-based separations and other uses of polymer films.

Thermal Conductivity of β-Phase Ga2O3 and (AlxGa1-x)2O3 Heteroepitaxial Thin Films.

Heteroepitaxy of β-phase gallium oxide (β-Ga2O3) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of (2̅01)-oriented β-Ga2O3 heteroepitaxial thin films were investigated. Unintentionally doped β-Ga2O3 thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward ⟨112̅0⟩ via metal-organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the β-Ga2O3 thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the β-Ga2O3 films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick β-Ga2O3 thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye-Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of β-Ga2O3 films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the β-Ga2O3 films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the β-Ga2O3/sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown (2̅01)-oriented β-(AlxGa1-x)2O3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(AlxGa1-x)2O3 films exhibit lower thermal conductivities (2.8-4.7 W/m·K) than the β-Ga2O3 thin films. The dominance of the alloy disorder scattering in β-(AlxGa1-x)2O3 is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown β-phase Ga2O3 and (AlxGa1-x)2O3 thin films and lays the groundwork for the thermal modeling and design of β-Ga2O3 electronic and optoelectronic devices.

Engineering electronic structure of topological insulator Bi2Te3 thin films by highly uniform ripple arrays

‘Wrinkle engineering’, as an effective approach to modify the properties of materials without introducing additional chemical doping, has been widely used in a variety of two-dimensional materials, including graphene, phosphorene and transitional metal dichalcogenides, etc. One-dimensional wrinkle or ripple arrays, which breaks the crystalline symmetry of materials, may reformate the nontrivial band structure and greatly affect the electronic properties of topological materials. Until now, such method has been rarely applied experimentally in tuning topological materials. Here, we fabricate highly uniform ripple arrays directly in few-quintuple-layers (QL) Bi2Te3 thin films on SrTiO3 substrate realized by in-situ strained epitaxial growth, investigated by detailed low temperature scanning tunneling microscope/spectroscopy. Well-defined one-dimensional (1D) ripple structures induced by the interfacial strain from the lattice mismatch between the Bi2Te3 films and the substrate has been observed. As the thickness of Bi2Te3 thin films increases, the release of the strain leads to the reduction of the averaged corrugation height and the periodicity of ripple array. The dI/dV spectra and spatially resolved spectroscopic survey acquired on the epitaxial layers with different thicknesses, reveal that both the energy gap and the Fermi velocity of the Dirac surface states are greatly enhanced on thinner films. Dirac fermion velocity vF is estimated about 7.8 × 105 m s−1 for 3 QL, which is greatly enhanced by compared with the bulk values (4.8 × 105 m s−1). An asymmetric dispersion behavior along different − directions is observed, highly related with the modulation of 1D corrugated ripples on the electronic structure. Moreover, an unconventional Bi (S4) termination mainly observed on thinner films shows a stress-related behavior, agreed with previous theoretical calculations. Our work proposes a promising route to fabricate a highly uniform ripple structure on nontrivial topological materials, which can effectively tune the electronic structure. Specially, it may have an immediate application for realizing a high-performance topological-based device with higher operating temperature and speed.

Spontaneous Polarization Calculations in Wurtzite II-Oxides, III-Nitrides, and SiC Polytypes through Net Dipole Moments and the Effects of Nanoscale Layering.

Herein, the spontaneous polarization in crystals with hexagonal symmetry are calculated as a function of the number of monolayers composing a nanostructure by adding the dipole moments for consecutive units of the nanostructure. It is shown that in the limit of a large numbers of monolayers that the spontaneous polarization saturates to the expected bulk value of the spontaneous polarization. These results are relevant to understanding the role of the built-in spontaneous polarizations in a variety of nanostructures since these built-in polarizations are generally quite large, on the order of 1 × 108 to 1 × 1010 V/m. Using these formulations, we come to the prediction that small nanolayered structures are theoretically capable of having larger spontaneous polarizations than their bulk counterparts due to how the dipole moments of the anions and cations within a wurtzite lattice cancel out with one another more in larger structures.

Improved properties of atomic layer deposited ruthenium via postdeposition annealing

The resistivity, morphology, and effective work function of thin film ruthenium deposited by thermal atomic layer deposition (ALD) using η4-2,3-dimethylbutadiene ruthenium tricarbonyl [Ru(DMBD)(CO)3] and O2 are investigated before and after annealing at temperatures up to 500 °C. Annealing at 500 °C in either N2 or H2/N2 reduces the average resistivity of as-deposited 30 nm thick Ru films from 16.2 to as low as 13.7 or 9.1 μΩ cm, respectively, approaching the bulk value of Ru. X-ray diffraction shows that as-deposited films are polycrystalline hexagonal Ru. Annealing at 500 °C in either N2 or H2/N2 results in crystallite growth accompanied by a roughening of the surface from approximately 0.7 to 2.2 nm RMS, as shown by atomic force microscopy. Secondary ion mass spectroscopy shows low residual carbon and oxygen in as-deposited films. Annealing in N2 at 500 °C reduces only the carbon content, whereas annealing in H2/N2 at 500 °C results in a further reduction of carbon combined with reduction in oxygen as well. Using series of metal/oxide/silicon capacitors with varying oxide thickness, the effective work function of 500 °C H2/N2 annealed Ru films on ALD Al2O3 and HfO2 was determined to be approximately 4.9 and 5.3 eV, respectively. Using internal photoemission spectroscopy, the Ru/Al2O3 and Ru/HfO2 electron energy barrier heights were determined to be 3.4 ± 0.1 and 3.8 ± 0.1 eV, respectively.

Al-driven peculiarities of local coordination and magnetic properties in single-phase Alx-CrFeCoNi high-entropy alloys

Modern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties. Herein, peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic (fcc)- and body-centered cubic (bcc)-structured high-entropy Alx-CrFeCoNi alloys (x = 0.3 and 3, respectively) are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges. Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision. The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry. A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account. X-ray magnetic circular dichroism technique employed at L2.3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values. Extended to nanostructured versions of multicomponent alloys, such studies would bring new insights related to effects of high entropy mixing on low dimensions.

Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices

Nanoscale miniaturization of chalcogenide semiconductors such as lead sulfide (galena) can generate interesting quantum confinement effects in the field of optoelectronic applications. In this work, we developed a process in order to obtain SiO2 nanospheres coated with Galena, as the denominated core–shell system; this process is based on Stöber’s method, where the magnetic stirring was replaced by an ultrasonic bath to achieve well rounded and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. The nanostructures’ chemical composition, morphology, and optical properties were determined by transmission electron microscopy and UV–Vis spectroscopy. As a result, the nanoshells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nanoshell also shown an optical spectrum shift toward blue and a remarkable increase of 3.75 eV in its band gap, compared with the PbS bulk value. The chemical composition is studied by energy scattering spectroscopy and X-ray photoelectron spectroscopy analysis.

Evolution of Composting Process in Maize Biomass Revealed by Analytical Pyrolysis (Py-GC/MS) and Pyrolysis Compound Specific Isotope Analysis (Py-CSIA)

An innovative approach based on the combination of analytical pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) with compound-specific isotope analysis (Py-CSIA) is used to study the composting process of maize biomass. This multidisciplinary approach aims to elucidate the decomposition rate of the main biogenic materials (lignin, cellulose, proteins, lipids, and waxes) responses to the composting process. According to Py-GC/MS data/structural composition, a noticeable and significant decrease during the first stage of the composting process of carbohydrates and aromatic compounds is found, followed by a gradual increase of all compounds till the end of the experiment. This trend, along with an increase of fatty acids methyl-ester at the first composting stage, sustains the microbial activity and its stabilization over time. Py-CSIA data showed a significant enrichment in 13C in all identified compounds over time, supporting the semi-quantitative results and the decomposition of initial biomass throughout the composting process. This trend is also perceptible in lignin moieties, long-chain aliphatic structures, and isoprenoids, as highly recalcitrant compounds, presumably due to depolymerization and carbon translocation of side-chain molecules during the composting process. Compound-specific isotope values showed a good correlation with the bulk isotope data, and this served as validation of the technique. However, bulk values showed higher heterogeneity because those represent an average of all organic compounds in the sample. By combining isotopic and structural information using Py-GC/MS and Py-CSIA, we are able to provide further information and a more detailed approach to the study of the decomposition process of biomass by considering the diverse dynamics of the main biogenic compounds.

The effect of hydrogen bonding on the copolymerization kinetics of 2‐methoxyethyl acrylate with 2‐hydroxyethyl methacrylate in alcohol and aqueous solutions

AbstractThe influence of alcohol and alcohol/water solutions on the radical copolymerization kinetics of 2‐hydroxyethyl methacrylate (HEMA) with 2‐methoxyethyl acrylate (MEA) is studied using pulsed‐laser‐polymerization coupled with size exclusion chromatography. It is found that MEA incorporation into the copolymer is increased in butanol, methanol (MeOH), and MeOH/H2O solutions relative to the bulk system. Copolymer composition can be represented for solvent levels ≥50 vol.% by a single pair of reactivity ratios ( = 2.39 ± 0.16, = 0.28 ± 0.02) that differ from those in bulk ( = 3.14 ± 0.44, = 0.27 ± 0.04). MeOH as solvent slightly reduces the propagation rate coefficient of HEMA compared to the bulk system, in contrast to the increase in the MEA value. Thus, the value of is higher in MeOH for MEA‐rich systems compared to bulk, with the effect of the solvent reduced as the HEMA content in the comonomer mixture is increased. Adding water as cosolvent significantly increases values for both monomers, with in MeOH/H2O higher than bulk values over the complete composition range. Furthermore, for 50% monomer in the solvent systems studied can be represented by the implicit penultimate unit model using a single pair of radical reactivity ratios. It is concluded that the strongest influence of hydrogen‐bonding solvents compared to bulk is on the homopropagation values, rather than on copolymerization parameters, and that the difference in relative reactivity of non‐functional and functional monomers in bulk and aqueous solution should be accounted for when studying emulsion copolymerization.

Ab initio predictions of magnetism and half-metallicity of (111)-surfaces of Co2CrSi full-Heusler alloy

The structural, electronic and magnetic properties of (111)-terminations of Co2CrSi full-Heusler alloy have been investigated using density functional theory (DFT) based on the generalized gradient approximation (GGA). For bulk alloy, the band gap is 0.57 eV, and magnetic moment is 4μB, which follows the Slater-Pauling rule. Half-metallic ferromagnetism is preserved in Si (111)-termination among all the terminations with 100% spin-polarization, which is a crucial property for spintronic devices. As for the termination, the band gap is 0.41 eV. In contrast, the spin-polarization clearly decreases for Co (111) and Cr (111)-terminations. Moreover, the atomic magnetic moments of (111)-terminations of Co2CrSi are close to the atomic bulk values. These results confirm the potential applications of surfaces of Co2CrSi full-Heusler alloy.

Influence of swift heavy ion irradiations on temperature dependent phononic behavior of epitaxial LaNiO3 thin film

The effects of Ag15+ (200 MeV) swift heavy ion irradiations on the structural and phononic properties of epitaxial LaNiO3 (LNO) thin film have been investigated using high resolution x-ray diffraction and Raman spectroscopy. After irradiation, the decrease in the out-of-plane lattice parameter of LNO toward its bulk value indicates the relaxation of epitaxial strain. The temperature dependency of phononic response for different ion irradiation doses was studied by performing the Raman measurements in a temperature range of 80−300 K. For pristine as well as irradiated samples of LNO, the observed phononic modes A1g and Eg shows softening with an increment in the temperature. The temperature coefficient of both modes varies with ion fluence. For the A1g mode, temperature coefficient increases from −0.087 cm−1 K−1 for pristine to −0.092 cm−1 K−1 for a maximum ion fluence of 1012 ions/cm2, while for the Eg mode, it decreases from −0.022 cm−1 K−1 for pristine to −0.015 cm−1 K−1 for 1012 ions/cm2. Raman frequency shift for both the modes shows non-linear behavior with temperature. This temperature dependent behavior was quantitatively analyzed by using a model which suggests that Raman shifts of the A1g mode emerged predominantly due to four phonon processes whereas, for the Eg mode, major contribution came from the thermal expansion effect. Ion irradiation did not change the dominating mechanism resulting in these temperature dependent Raman shifts, although the relative contribution of different processes was altered with ion fluence.

Effect of crystal structure on the Young’s modulus of GaP nanowires

Young’s modulus of tapered mixed composition (zinc-blende with a high density of twins and wurtzite with a high density of stacking faults) gallium phosphide (GaP) nanowires (NWs) was investigated by atomic force microscopy. Experimental measurements were performed by obtaining bending profiles of as-grown inclined GaP NWs deformed by applying a constant force to a series of NW surface locations at various distances from the NW/substrate interface. Numerical modeling of experimental data on bending profiles was done by applying Euler–Bernoulli beam theory. Measurements of the nano-local stiffness at different distances from the NW/substrate interface revealed NWs with a non-ideal mechanical fixation at the NW/substrate interface. Analysis of the NWs with ideally fixed base resulted in experimentally measured Young’s modulus of 155 ± 20 GPa for ZB NWs, and 157 ± 20 GPa for WZ NWs, respectively, which are in consistence with a theoretically predicted bulk value of 167 GPa. Thus, impacts of the crystal structure (WZ/ZB) and crystal defects on Young’s modulus of GaP NWs were found to be negligible.

Quantitative measurements of flow dynamics in 3D hoppers using MRI

This work uses a recently developed MRI method to measure the solid fraction and velocity in three-dimensional (3D) hoppers quantitatively. We demonstrate that the measurements are quantitative by calculating the mass flow rate within the hopper using MRI and show good agreement with the mass flow rate measured gravimetrically. We study the velocity and solid fraction in hoppers with various angles and outlet sizes. We show that the solid fraction decreases smoothly from the bulk value above the outlet, indicating that the assumption of a “free-fall arch” used in some mass flow correlations is invalid. Furthermore, we show that the solid fraction, velocity and vertical evolution of the acceleration are all self-similar when normalised by the value at the centre of the outlet in a 3D hopper, in agreement with recent studies of 2D hoppers. Thus, these quantitative measurements enable evaluation of phenomenological models describing the flow rate from hoppers.

Halogen vacancy migration at surfaces of CsPbBr3 perovskites: insights from density functional theory

Migration of halogen vacancies is one of the primary sources of phase segregation and material degradation in lead-halide perovskites. Here we use first principles density functional theory to compare migration energy barriers and paths of bromine vacancies in the bulk and at a (001) surface of cubic CsPbBr3. Our calculations indicate that surfaces might facilitate bromine vacancy migration in these perovskites, due to their soft structure that allows for bond lengths variations larger than in the bulk. We calculate the migration energy for axial-to-axial bromine vacancy migration at the surface to be only half of the value in the bulk. Furthermore, we study the effect of modifying the surface with four different alkali halide monolayers, finding an increase of the migration barrier to almost the bulk value for the NaCl-passivated system. Migration energies are found to be correlated to the lattice mismatch between the CsPbBr3 surface and the alkali halide monolayer. Our calculations suggest that surfaces might play a significant role in mediating vacancy migration in halide perovskites, a result with relevance for perovskite nanocrystals with large surface-to-volume ratios. Moreover, we propose viable ways for suppressing this undesirable process through passivation with alkali halide salts.

Abnormal Enhanced Free Ions of Ionic Liquids Confined in Carbon Nanochannels.

Revealing the structure and behavior of confined ionic liquids (ILs) is essential for their applications in green chemical processes. Here, we explore the electroconductivity (σ) and ionic correlation of imidazole ILs confined in graphene nanochannels via joint molecular dynamics simulation and theoretical analysis. The ideal and actual σ of ILs are first calculated, showing a growing tendency and up to the bulk value as the nanochannel size ranges from 1 to 10 nm. To account for the ionic correlation, the ionicity was determined by the ratio of the actual to ideal σ, reflecting the average fraction of free ions in the confined ILs. Amazingly, the ionicity of all three ILs shows an abnormal changing tendency, which first increases and reaches the maximum at 2 nm and then decreases to the bulk value. The conformational analysis, pair dissociating energy, and residence time are further obtained, proving that the abnormal enhanced ionicity should be attributed to the structure reconstruction of ILs near the graphene wall. The analytical model of ionicity herein can guide the rational design of efficient IL-based nanoporous electrodes and solid catalysts.

Evolution of Superconducting Properties of Coexistent Bi-2212 and Bi-2223 phases in BSCCO

The evolution of superconducting properties of BSCCO superconductors, inadvertently hosting the two superconducting phases Bi-2212 and Bi-2223 have been investigated in pristine and Pb doped BSCCO. The superconducting transition temperature TC of Bi-2212 phase monotonically increases with increasing Bi-2223 phase fraction. On the other hand Bi-2223 phase exhibits depression in TC for its lower phase fractions (<24%) but attains its bulk value as Bi-2223 phase fraction is increased to 30%. This behavior has been rationalized by invoking the interplay of proximity effects between the two coexisting phases and establishment of Bi-2223 superconducting percolation path. In addition to aiding the formation of BSCCO with higher Bi-2223 phase fraction, the Pb substitution also leads to an enhancement of critical current density by the creation of pinning centres.

A coupled MD-FE methodology to characterize mechanical interphases in polymeric nanocomposites

This contribution introduces an unconventional procedure to characterize spatial profiles of elastic and inelastic properties inside polymer interphases around nanoparticles. Interphases denote those regions in the polymer matrix whose mechanical properties are influenced by the filler surfaces and thus deviate from the bulk properties. They are of particular relevance in case of nano-sized filler particles with a comparatively large surface-to-volume ratio and hence can explain the frequent observation that the overall properties of polymer nanocomposites cannot be determined by classical mixing rules, which only consider the behavior of the individual constituents.Interphase characterization for nanocomposites poses hardly solvable challenges to the experimenter and is still an unsolved problem in many cases. Instead of real experiments, we perform pseudo experiments using our recently developed Capriccio method, which is an MD-FE domain-decomposition tool specifically designed for amorphous polymers. These pseudo-experimental data then serve as input for a typical inverse parameter identification. With this procedure, spatially varying mechanical properties inside the polymer are, for the first time, translated into intuitively understandable profiles of continuum mechanical parameters.As a model material, we employ silica-enforced polystyrene, for which our procedure reveals exponential saturation profiles for Young’s modulus and the yield stress inside the interphase, where the former takes about seven times the bulk value at the particle surface and the latter roughly triples. Interestingly, hardening coefficient and Poisson’s ratio of the polymer remain nearly constant inside the interphase. Besides gaining insight into the constitutive influence of filler particles, these unexpected and intriguing results also offer interesting explanatory options for the failure behavior of polymer nanocomposites.

On the Importance of Joint Mitigation Strategies for Front, Bulk, and Rear Recombination in Ultrathin Cu(In,Ga)Se2 Solar Cells.

Several optoelectronic issues, such as poor optical absorption and recombination, limit the power conversion efficiency of ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. To mitigate recombination losses, two combined strategies were implemented: a potassium fluoride (KF) post-deposition treatment (PDT) and a rear interface passivation strategy based on an aluminum oxide (Al2O3) point contact structure. The simultaneous implementation of both strategies is reported for the first time on ultrathin CIGS devices. Electrical measurements and 1D simulations demonstrate that in specific conditions, devices with only KF-PDT may outperform rear interface passivation based devices. By combining KF-PDT and rear interface passivation, an enhancement in an open-circuit voltage of 178 mV is reached over devices that have a rear passivation only, and of 85 mV over devices with only a KF-PDT process. Time-Resolved Photoluminescence measurements showed the beneficial effects of combining KF-PDT and the rear interface passivation at decreasing recombination losses in the studied devices, enhancing charge carrier lifetime. X-ray photoelectron spectroscopy measurements indicate the presence of an In and Se-rich layer that we linked to be a KInSe2 layer. Our results suggest that when bulk and front interface recombination values are very high, they dominate, and individual passivation strategies work poorly. Hence, this work shows that for ultrathin devices, passivation mitigation strategies need to be implemented in tandem.

The Role of Grain Boundary Precipitates during Intergranular Fracture in 6xxx Series Aluminium Alloys

During ageing, 6xxx aluminium alloys will develop a microstructure characterised by needle-shaped Mg/Si-rich precipitates in the bulk, precipitate-free zones along the grain boundaries and larger Mg/Si-rich precipitates on the grain boundary. Depending on, among other things, the size of the precipitate-free zone, these alloys are prone to intergranular fracture. The role of the grain boundary precipitates during the initiation and propagation of the intergranular fracture is still not fully understood. Transmission Electron Microscopy has been used to characterise the grain boundaries and grain boundary precipitates. The precipitates were found to be of the β′ type surrounded by a layer of U2 structure. The atomic details of relevant interfaces of Al-β′ were characterised for further investigation. Density Functional Theory simulations were performed on the bulk precipitate structures and on the interfaces obtained experimentally. The decohesion energy of these interfaces was calculated and compared to bulk values. In addition, simulated tensile tests were performed in order to find values for the tensile strength σt. The dependence of the interfacial energy and tensile strength of β′ grain boundary precipitates were found to depend on the orientation and type of interface in addition to the amount of defects on the interface.

Interfacial properties of [Pt/Co/Pt] trilayers probed through magnetometry

The magnetic and interface properties of [Pt/Co/Pt] were investigated. First, the magnetic properties were determined from the magnetic dead layer plots, in which the Co layer was considered as two distinct parts representing different magnetic properties. The two parts with low and high tCo ranges are close to and away from the top interface (Co/Pt), respectively. The part close to the top interface shows a smaller magnetization (M) value and nonlinear behavior. However, the other part shows a higher M value closer to the bulk value and a linear behavior. The nonlinear behavior of the M values of the low tCo range was converted to an impurity level using simple assumptions. The results showed the effect of the top Pt layer on the magnetic properties of the Co layer. The results clearly demonstrate that magnetometry could be utilized as a means to understand the interface quality of magnetic multilayer systems.