Interface-related Effects Research Articles

Thermal Annealing Driven Enhancement of Perpendicular Magnetic Anisotropy and the Interfacial Dzyaloshinskii–Moriya Interaction in Ultrathin Ru/Co/W/Ru Films

Spin-related effects discovered in ultrathin magnetic films generally have an interfacial nature. The quality of interfaces between a heavy metal and a ferromagnet is the main driver of surface anisotropy, antisymmetric exchange, chiral damping, spin Hall effect, and spin–orbit torques. To understand the physics and usage of these phenomena for future atomic-scale devices, one has to study systems with disordered interfaces and search there for novel practically desirable effects, which lie beyond the atomic order and surface flatness. Here, we report the interface-related effects in Ru/Co/W/Ru ultrathin films treated by thermal annealing in vacuum. The surface roughness and degree of atomic intermixing at Ru/Co and Co/W interfaces change with increasing annealing temperature up to 240 °C, promoting an enhancement of perpendicular magnetic anisotropy and the interfacial Dzyaloshinskii–Moriya interaction (i-DMI). Further annealing at higher temperatures brings the interface deterioration and, consequently, a drastic degradation of the magnetic properties. Our first-principles calculations qualitatively support the experimental findings, providing an understanding of the i-DMI enhancement nature.

Exchange bias and interface-related effects in two-dimensional van der Waals magnetic heterostructures: Open questions and perspectives

The exchange bias (EB) effect is known as a fundamentally and technologically important magnetic property of a magnetic bilayer film. It is manifested as a horizontal shift in a magnetic hysteresis loop of a film subject to cooling in the presence of a magnetic field. The EB effect in van der Waals (vdW) heterostructures offers a novel approach for tuning the magnetic properties of the newly discovered single-layer magnets, as well as adds a new impetus to magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been reported in a variety of low-dimensional vdW magnetic systems ranging from a weakly interlayer-coupled vdW magnet (e.g., Fe3GeTe2) to a bilayer composed of two different magnetic vdW materials (e.g., Fe3GeTe2/CrCl3, Fe3GeTe2/FePS3, Fe3GeTe2/MnPS3, Fe3GeTe2/CrSe, Fe3GeTe2/CrOCl, Fe3GeTe2/CoPc, Fe5GeTe2/FePS3), to bilayers of two different vdW defective magnets (e.g., VSe2/MoS2), or to metallic ferromagnet/vdW defective magnet interfaces (e.g., Fe/MoS2). Despite their huge potential in spintronic device applications, the physical origins of the observed EB effects have remained elusive to researchers. We present here a critical review of the EB effect and associated phenomena such as magnetic proximity (MP) in various vdW heterostructure systems and propose approaches to addressing some of the emerging fundamental questions.

Fiber- and Particle-Reinforced Composite Materials With the Gurtin–Murdoch and Steigmann–Ogden Surface Energy Endowed Interfaces

Abstract Modern advances in material science and surface chemistry lead to creation of composite materials with enhanced mechanical, thermal, and other properties. It is now widely accepted that the enhancements are achieved due to drastic reduction in sizes of some phases of composite structures. This leads to increase in surface to volume ratios, which makes surface- or interface-related effects to be more significant. For better understanding of these phenomena, the investigators turned their attention to various theories of material surfaces. This paper is a review of two most prominent theories of that kind, the Gurtin–Murdoch and Steigmann–Ogden theories. Here, we provide comprehensive review of relevant literature, summarize the current state of knowledge, and present several new results.

Amyloid aggregation at solid-liquid interfaces: Perspectives of studies using model surfaces

The aggregation of proteins and peptides into cytotoxic oligomeric and fibrillar amyloid aggregates represents an important mechanism in the development of numerous degenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and type 2 diabetes mellitus. Amyloid aggregation is notoriously hard to control both in vivo and in vitro, because aggregation kinetics, aggregate morphology, and molecular aggregate structure are influenced by a multitude of environmental parameters, including monomer concentration, ionic strength, temperature, pH, and the presence of interfaces. While for a long time, amyloid aggregation has been studied mostly in bulk solution, surface and interface-related effects have recently become the focus of intense research efforts. Understanding the complex influences that solid-liquid interfaces exert on the aggregation of amyloidogenic proteins and peptides not only promises deeper insights into the molecular mechanisms of in-vivo membrane toxicity, but may also result in novel therapeutic approaches utilizing for instance amyloid-inhibiting nanoparticles. A particularly important route toward this goal is represented by studies using model surfaces with well-defined physicochemical properties in order to elucidate the involved physical and chemical mechanisms and interactions on a molecular level. This perspective article will provide an overview over the experimental techniques and model surfaces that so far have been utilized in such studies, summarize the obtained findings and insights, and address future challenges.

Enhancement of Electrochromic Polymer Switching in Plasmonic Nanostructured Environment

We explore color switching properties of thin polyaniline (PANI) films deposited on plasmonic nanomesh structures in comparison with the films deposited on flat gold. The nanostructured systems show a much steeper color switching with increasing voltage than the films prepared on flat substrates. A strong difference between nanostructured and flat systems is also observed at small voltages, where nanostructured samples often demonstrate an additional feature in cyclic voltammetry curves and nonmonotonous changes in optical properties. Possible origins of the observed effects are discussed in terms of acceleration of charge transport in nanostructured plasmonic environment and interface-related effects. The results can provide opportunities for enhancing and controlling the electrochromic polymer performance in smart windows or display applications.

Exploring the Flatlands: Synthesis, Characterization and Engineering of Two-Dimensional Materials

In this talk, we report the controlled vapor phase synthesis of MoS2 atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. The atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulfide atomic layers are examined and first-principles calculations are applied to investigate their energy landscape. The electrical properties of the atomic layers are examined and the role of grain boundaries is evaluated. More importantly, if precise two-dimensional domains of graphene, h-BN and MoS2 atomic layers can be seamlessly stitched together, in-plane heterostructures with interesting electronic applications could potentially be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically-patterned h-BN atomic layers. Our approach can create periodic arrangements of domains with size that ranging from tens of nanometers to millimeters. The resulting graphene/h-BN atomic layers can be peeled off from their growth substrate and transferred to various platforms including flexible substrate. Finally, we demonstrate how self-assembled monolayers with a variety of end termination chemistries can be utilized to tailor the physical properties of single-crystalline MoS2 atomic-layers. Our data suggests that combined interface-related effects of charge transfer, built-in molecular polarities, varied densities of defects, and remote interfacial phonons strongly modify the electrical and optical properties of MoS2, illustrating an engineering approach for local and universal property modulations in two-dimensional atomic-layers.

Tailoring the Physical Properties of Molybdenum Disulfide Monolayers by Control of Interfacial Chemistry

We demonstrate how substrate interfacial chemistry can be utilized to tailor the physical properties of single-crystalline molybdenum disulfide (MoS2) atomic-layers. Semiconducting, two-dimensional MoS2 possesses unique properties that are promising for future optical and electrical applications for which the ability to tune its physical properties is essential. We use self-assembled monolayers with a variety of end termination chemistries to functionalize substrates and systematically study their influence on the physical properties of MoS2. Using electrical transport measurements, temperature-dependent photoluminescence spectroscopy, and empirical and first-principles calculations, we explore the possible mechanisms involved. Our data shows that combined interface-related effects of charge transfer, built-in molecular polarities, varied densities of defects, and remote interfacial phonons strongly modify the electrical and optical properties of MoS2. These findings can be used to effectively enhance or modulate the conductivity, field-effect mobility, and photoluminescence in MoS2 monolayers, illustrating an approach for local and universal property modulations in two-dimensional atomic-layers.

Interface-related effects on confined excitons in GaAs/Al xGa 1− xAs single quantum wells

Confined excitons in non-abrupt GaAs/Al x Ga 1− x As single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning α with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al 0.3Ga 0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces.

Novel microscopic properties and the electronic structure of SiGe heterostructures and related systems

We report local-density ab-initio pseudopotential calculations designed to link structural properties of real interfaces to carrier dynamics and recombination observed in spectroscopic studies of Si–Ge and similar heterostructures. We find novel interface-related effects of deep localisation which may provide a fresh basis for explaining the optical and scattering phenomena reported in these systems. In particular, the electronic structure of Si–Ge interfaces is significantly modified by the presence of new well-localised levels due to dopants such as Sb which are commonly used to improve molecular beam epitaxy growth.

The effect of transients on hot carriers

The influence of time-dependent voltages on hot-carrier generation in MOSFETS is studied by transient device simulation. For transient times down to the nanosecond range, no transient effects on hot-carrier formation and injection are found. This result is confirmed experimentally by substrate current measurements under various dynamic voltage conditions down to rise/fall times of 3 ns. This result has important consequences for the interpretation of dynamic stress data, since it means that device-related dynamic effects can be neglected in comparison with interface-related effects in transient ranges relevant to practical applications. >