Role Of Interfacial Structure Research Articles

Irradiation tolerance enhanced by coherent interfaces of FCC/BCC HEA multilayers

Eutectic high entropy alloys (EHEAs) with excellent mechanical properties are considered as potential nuclear structural materials due to their unique atomic-level microstructure and abundant heterogeneous interfaces. However, an understanding of EHEAs irradiation tolerance from the perspective of heterogeneous interface structure is still lacking. In this work, to explore the intrinsic mechanism of interface structure-irradiation tolerance in EHEAs, we constructed FCC/BCC high-entropy alloys (HEAs) multilayers with different interfacial structures by a radiofrequency (RF) magnetron sputtering. The prepared multilayers were irradiated at room temperature using 50 keV He+ in an ion irradiation and implantation facility. The irradiation-induced structural damage and irradiation-hardening behavior of the multilayers were systematically analyzed using X-ray diffractometer (XRD), transmission electron microscopy (TEM) and nanoindentation instrument, respectively. It is found that the coherent and semicoherent interfaces mainly affect helium (He) behavior in the multilayers. We demonstrate that the coherent interfaces enable HEAs to have lower bubble swelling and irradiation hardening capability by promoting the migration ability of He bubbles. These results provide insight into the role of interfacial structures in the irradiation tolerance of nanostructured EHEAs, which should lead us to reconsider some design rules for advanced radiation-tolerant materials.

The Influence of Order on the Nucleation Barrier

AbstractWhile it is conventionally thought that liquids turn to solids at their “freezing” point, it is often the case that materials must be supercooled (cooled below the freezing temperature) before nucleation actually happens. There is growing evidence that coupled processes, including chemical–structural ordering and orientational–translational ordering, are among the factors that affect exactly when and how nucleation occurs in liquids and crystals. Recent density functional calculations have demonstrated that such coupled routes, which are not incorporated within the one-dimensional framework of the classical theory, can dramatically influence the overall nucleation process. Here, some recently observed cases in metal alloys are discussed, establishing a relationship between developing order in undercooled liquids and the nucleation barrier, the influence of magnetic ordering on nucleation in Co-based melts, and the role of interfacial structure and chemistry on the catalytic efficiency of inoculants for heterogeneous nucleation.

Microemulsification of Triglyceride Sebum and the Role of Interfacial Structure on Bicontinuous Phase Behavior

A unique triblock surfactant is reported that allows for the efficient microemulsification of triglycerides. Unlike the results of all previous efforts, these triglyceride microemulsions can be formed without the use of cosurfactants or dilution with co-oils and follow the classical patterns of surfactant phase behavior exhibited by mixtures of water, alkane oils, and nonionic oligoethylene glycol surfactants, i.e., progression from oil/water emulsions to one-phase microemulsions to water/oil emulsions with increasing temperature. Lamellar phases that usually dominate the aqueous phase behavior of surfactant/triglyceride mixtures are suppressed, allowing for the formation of single-phase microemulsions containing equal amounts of triglyceride and water. These isotropic and low-viscous fluids are particularly useful for cleansing and delivery of functional ingredients in skin care products. The effects of mixing a variety of typical skin care ingredients and components of sebum (skin oil) were also explored. Fatty acids significantly reduce the average microemulsion temperature, while other ingredients and oils, which do not partition at the oil/water interface, have less impact on the phase behavior. In all cases, one-phase microemulsions containing equal amounts of oil and water can be formed even at high additive concentrations. Indeed, partial replacement oftriglyceride with any of the additives examined consistently reduced the amount of surfactant necessary to form single-phase microemulsions. However, the greatest boost in surfactant efficiency was found with the addition of medium molecular weight amphiphilic block copolymers.

Scanning Tunneling Microscopy Studies of Glucose Oxidase on Gold Surfaces

Three immobilization methods have been used for scanning tunneling microscopy (STM) studies of glucose oxidase (GOD) on gold. They are based on (a) physical adsorption from solution, (b) microcontact printing, and (c) covalent bonding onto self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA). The STM images are used to provide information about the organization of individual GOD molecules and more densely packed monolayers of GOD on electrode surfaces, thus providing information on the role of interfacial structure on biosensor performance. The use of atomically flat gold substrates enables easy distinction of deposited enzyme features from the flat gold substrate. Microcontact printing is found to be a more reliable method than adsorption from solution for preparing individual GOD molecules on the gold surface. STM images of printed samples reveal two different shapes of native GOD molecules. One is a butterfly shape with dimensions of 10 ± 1 nm × 6 ± 1 nm, assigned to the lying position of...

Role of interfacial structure in nanostructured elemental metals: a new thermo-mechanical process for the preparation of nanostructured binary alloys

In this article we present the first results obtained for nanostructured γ-Ni 20Zn 80 alloy prepared by a thermo-mechanical (TM) process developed in our laboratory. The process uses the energy stored in the defect structure, generated via mechanical milling of the nickel, to accelerate the reaction in the solid state, allowing a more rapid alloy formation. The process presents several advantages, when compared with techniques currently used for the production of this class of materials. The X-ray diffraction pattern for the alloy produced by the TM process is compared with that measured for the same alloy, produced by the mechanical alloying technique. The results show that the TM process holds the potential to become a valuable alternative method for the production of nanostructured materials.

The role of interfacial structure in determining magnetic behaviour in MBE-grown Fe 3O 4–MgO multilayers on MgO(001)

The atomic structure at the Fe 3O 4–MgO interface and its role in defining magnetic behaviour in Fe 3O 4–MgO multilayers, grown by MBE on MgO(001), has recently been a subject of much interest and controversy: the existence of a “dead” magnetic layer at the interface has been proposed to explain why ultra-thin magnetite layers become nonmagnetic. By using Mössbauer probe layers it was shown that this model is incorrect. In this paper we present additional structural evidence, from X-ray reflectivity and RHEED measurements, showing that the magnetite layers have the same structure and composition at the interface and in the bulk in agreement with a uniform magnetic structure throughout the entire layer.

Schottky barrier formation for Fe on GaAs(001) and the role of interfacial structure (abstract)

Spin injection into a semiconductor is expected to utilize a ferromagnetic material as the electrical contact. One system of potential interest consists of Fe contacts to a GaAs-based device structure. We have used photoreflectance spectroscopy to measure the Schottky barrier height formed for Fe films on GaAs(001) as a function of the GaAs surface reconstruction. The samples were grown by molecular-beam epitaxy in a multichamber UHV facility which includes chambers for photoelectron diffraction and scanning tunneling microscopy. These techniques were used to obtain a detailed atomic model of the Fe/GaAs interface, enabling us to correlate the measured barrier heights with the interfacial structure, and further discuss the results in the framework of several models for Schottky barrier formation. For the As-rich 2×4 and c(4×4) surfaces, we conclude that the interface is formed by Fe bonding with an As monolayer after dissolution of the surface As dimers and some Ga into the Fe film. The samples were removed from the UHV system after coating with 50 Å of Au for the photoreflectance measurements. While the pure Schottky model predicts a value of 0.43 eV, we find nearly identical barrier heights of 0.8 eV for both the 2×4 and c(4×4) surfaces. This is consistent with the similar interfacial structure resulting from Fe growth on each surface, and the value of 0.8 eV is in agreement with that predicted by the effective work function model assuming predominantly Fe–As bonding. We compare these results with similar data for growth on the Ga-rich 4×6 reconstruction and on ZnSe(001) surfaces.