Since their discovery, quasicrystals have attracted continuous research interest due to their unique structural and physical properties. Recently, it was demonstrated that dodecagonal quasicrystals ...could be used as bandgap materials in next-generation photonic devices. However, a full understanding of the formation mechanism of quasicrystals is necessary to control their physical properties. Here we report the formation of a two-dimensional dodecagonal fullerene quasicrystal on a Pt
Ti(111) surface, which can be described in terms of a square-triangle tiling. Employing density functional theory calculations, we identify the complex adsorption energy landscape of the Pt-terminated Pt
Ti surface that is responsible for the quasicrystal formation. We demonstrate the presence of quasicrystal-specific phason strain, which provides the degree of freedom required to accommodate the quasicrystalline structure on the periodic substrate. Our results reveal detailed insight into an interface-driven formation mechanism and open the way to the creation of tailored fullerene quasicrystals with specific physical properties.
The understanding of the resistive switching mechanisms in perovskites is of particular importance for the development of novel non-volatile memories. Nanoscale investigations recently revealed that ...in the model material SrTiO3 a filamentary type of switching is present. In this paper, we show that upon donor doping with Nb the switching type changes fundamentally. We report on the observation of conducting clusters that can be switched independently between a high resistance and a low resistance state when applying a voltage. Furthermore, we show that the resistive switching takes place in a semiconducting surface layer on top of the metallic bulk of SrTiO3:Nb single crystals, which can change its properties easily under external gradients. Based on various measurements, we postulate that ionic movements leading to the creation of secondary phases as nano-filaments between the clusters have to be taken into account in modelling the resistive switching.
Electroceramics research is driven by technology and device applications. This growing field includes a vast number of magnetic, dielectric, ionically conducting, semiconducting, and superconducting ...ceramics used in domains as diverse as transportation, industrial production, power engineering, medicine and health care, consumer electronics, and communication. At the turn of the decade, three major trends are gaining importance:•Materials integration issues play an increasingly important role driven by the interest in integrating electroceramic functions into conventional semiconductor chips as well as by the evolution of multifunctional components and systems.•The industrial production process currently is in a transition from empirical studies and physical demonstrators into virtual design and testing. To fit into this evolution, for integrated as well as for discrete electroceramic components, a rise in modeling and numerical simulation of material- and device-related properties presently occurs.•Electroceramic materials are following in the footsteps of conventional semiconductors with respect to further miniaturization, and are experiencing the same evolution from microtechnology towards nanotechnology. Nanosize effects and nanotechnology issues are therefore gaining importance.
In the context of these three issues, we discuss the research in electroceramics during the last decade and basic trends for the future.
Impurities and dopants in memristive devices determine their switching kinetics, performance, and neuromorphic functionalities.
Future development of the modern nanoelectronics and its flagships ...internet of things, artificial intelligence, and neuromorphic computing is largely associated with memristive elements, offering a spectrum of inevitable functionalities, atomic level scalability, and low-power operation. However, their development is limited by significant variability and still phenomenologically orientated materials’ design strategy. Here, we highlight the vital importance of materials’ purity, demonstrating that even parts-per-million foreign elements substantially change performance. Appropriate choice of chemistry and amount of doping element selectively enhances the desired functionality. Dopant/impurity-dependent structure and charge/potential distribution in the space-charge layers and cell capacitance determine the device kinetics and functions. The relation between chemical composition/purity and switching/neuromorphic performance is experimentally evidenced, providing directions for a rational design of future memristive devices.
Dynamic physics-based models of resistive switching devices are of great interest for the realization of complex circuits required for memory, logic and neuromorphic applications. Here, we apply such ...a model of an electrochemical metallization (ECM) cell to complementary resistive switches (CRSs), which are favorable devices to realize ultra-dense passive crossbar arrays. Since a CRS consists of two resistive switching devices, it is straightforward to apply the dynamic ECM model for CRS simulation with MATLAB and SPICE, enabling study of the device behavior in terms of sweep rate and series resistance variations. Furthermore, typical memory access operations as well as basic implication logic operations can be analyzed, revealing requirements for proper spike and level read operations. This basic understanding facilitates applications of massively parallel computing paradigms required for neuromorphic applications.
The homogeneity of Verneuil-grown SrTiO3:Nb crystals was investigated. Due to the fast crystal growth process, inhomogeneities in the donor dopant distribution and variation in the dislocation ...density are expected to occur. In fact, for some crystals optical studies show variations in the density of Ti(3+) states on the microscale and a cluster-like surface conductivity was reported in tip-induced resistive switching studies. However, our investigations by TEM, EDX mapping, and 3D atom probe reveal that the Nb donors are distributed in a statistically random manner, indicating that there is clearly no inhomogeneity on the macro-, micro-, and nanoscale in high quality Verneuil-grown crystals. In consequence, the electronic transport in the bulk of donor-doped crystals is homogeneous and it is not significantly channelled by extended defects such as dislocations which justifies using this material, for example, as electronically conducting substrate for epitaxial oxide film growth.
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