Electrode-induced lattice distortions in GaAs multi-quantum-dot arrays

Copyright © Materials Research Society 2019. Increasing the number of quantum bits while preserving precise control of their quantum electronic properties is a significant challenge in materials design for the development of semiconductor quantum computing devices. Semiconductor heterostructures can host multiple quantum dots that are electrostatically defined by voltages applied to an array of metallic nanoelectrodes. The structural distortion of multiple-quantum-dot devices due to elastic stress associated with the electrodes has been difficult to predict because of the large micrometer-scale overall sizes of the devices, the complex spatial arrangement of the electrodes, and the sensitive dependence of the magnitude and spatial variation of the stress on processing conditions. Synchrotron X-ray nanobeam Bragg diffraction studies of a GaAs/AlGaAs heterostructure reveal the magnitude and nanoscale variation of these distortions. Investigations of individual linear electrodes reveal lattice tilts consistent with a 28-MPa compressive residual stress in the electrodes. The angular magnitude of the tilts varies by up to 20% over distances of less than 200 nm along the length of the electrodes, consistent with heterogeneity in the metal residual stress. A similar variation of the crystal tilt is observed in multiple-quantum-dot devices, due to a combination of the variation of the stress and the complex electrode arrangement. The heterogeneity in particular can lead to significant challenges in the scaling of multiple-quantum-dot devices due to differences between the charging energies of dots and uncertainty in the potential energy landscape. Alternatively, if incorporated in design, stress presents a new degree of freedom in device fabrication

Interface Aspects in All‐Solid‐State Li‐Based Batteries Reviewed

Extensive efforts have been made to improve the Li-ionic conductivity of solid electrolytes (SE) for developing promising all-solid-state Li-based batteries (ASSB). Recent studies suggest that minimizing the existing interface problems is even more important than maximizing the conductivity of SE. Interfaces are essential in ASSB, and their properties significantly influence the battery performance. Interface problems, arising from both physical and (electro)chemical material properties, can significantly inhibit the transport of electrons and Li-ions in ASSB. Consequently, interface problems may result in interlayer formation, high impedances, immobilization of moveable Li-ions, loss of active host sites available to accommodate Li-ions, and Li-dendrite formation, all causing significant storage capacity losses and ultimately battery failures. The characteristic differences of interfaces between liquid- and solid-type Li-based batteries are presented here. Interface types, interlayer origin, physical and chemical structures, properties, time evolution, complex interrelations between various factors, and promising interfacial tailoring approaches are reviewed. Furthermore, recent advances in the interface-sensitive or depth-resolved analytical tools that can provide mechanistic insights into the interlayer formation and strategies to tailor the interlayer formation, composition, and properties are discussed

Size Evolution of Ordered SiGe Islands Grown by Surface Thermal Diffusion on Pit-Patterned Si(100) Surface

The ordered growth of self-assembled SiGe islands by surface thermal diffusion in ultra high vacuum from a lithographically etched Ge stripe on pit-patterned Si(100) surface has been experimentally investigated. The total surface coverage of Ge strongly depends on the distance from the source stripe, as quantitatively verified by Scanning Auger Microscopy. The size distribution of the islands as a function of the Ge coverage has been studied by coupling atomic force microscopy scans with Auger spectro-microscopy data. Our observations are consistent with a physical scenario where island positioning is essentially driven by energetic factors, which predominate with respect to the local kinetics of diffusion, and the growth evolution mainly depends on the local density of Ge atoms

Microstrain distributions in polycrystalline thin film measured by X-ray microdiffraction

Microstrain distributions were acquired in functional thin films by high resolution X-ray microdiffraction measurements, using a polycrystalline CuInSe2 thin film as model system. This technique not only provides spatial resolutions at the submicrometer scale but also allows for analysis of thin films buried within a complete solar-cell stack. The microstrain values within individual CuInSe2 grains were determined to be in the order of 10-4. These values confirmed corresponding microstrain distribution maps obtained on the same CuInSe2 layer by electron backscatter diffraction and Raman microspectroscopy

Strain distribution in single, suspended germanium nanowires studied using nanofocused x-rays

\u3cp\u3eWithin the quest for direct band-gap group IV materials, strain engineering in germanium is one promising route. We present a study of the strain distribution in single, suspended germanium nanowires using nanofocused synchrotron radiation. Evaluating the probed Bragg reflection for different illumination positions along the nanowire length results in corresponding strain components as well as the nanowire's tilting and bending. By using these findings we determined the complete strain state with the help of finite element modelling. The resulting information provides us with the possibility of evaluating the validity of the strain investigations following from Raman scattering experiments which are based on the assumption of purely uniaxial strain.\u3c/p\u3

Strain and Lattice Orientation Distribution in SiN/Ge CMOS Compatible Light Emitting Microstructures by Quick X-ray Nano-diffraction Microscopy

This paper presents a study of the spatial distribution of strain and lattice orientation in CMOS-fabricated strained Ge microstripes using high resolution x-ray micro-diffraction (µ-HRXRD). The recently developed model-free characterization tool, based on a quick scanning x-ray diffraction microscopy technique can image strain down to levels of 10-5 (Δa/a)with a spatial resolution of ~0.5 µm. Strain and lattice tilt are extracted using the strain and orientation calculation software package X-SOCS. The obtained results are compared with the biaxial strain distribution obtained by lattice parameter-sensitive µ-Raman and µ-photoluminescence measurements. The experimental data are interpreted with the help of finite element modeling (FEM) of the strain relaxation dynamics in the investigated structures

Fully coherent growth of Ge on free-standing Si(001)nano-mesas

Abstract We investigate the structural properties of Ge nanostructures selectively grown on Si. Defect-free nanostructures with lateral size of 100 nm and surrounded by a thick (~20 times larger than the coherent-film limit) Ge layer are achieved as demonstrated by Transmission Electron Microscopy. As demonstrated by modeling based on elasticity theory solved by Finite Element Methods, the peculiar combination of morphology and chemical composition of the nanostructures allows for a very efficient elastic relaxation of the heteroepitaxial strain. We demonstrate that, despite the relatively large size of the nanostructures, even a single dislocation would raise the energy of the system. A direct comparison between the strain field predicted by modeling and measured by energy-dispersive synchrotron-radiation grazing incidence x-ray diffraction shows substantial agreement

Reactor for nano-focused x-ray diffraction and imaging under catalytic in situ conditions

\u3cp\u3eA reactor cell for in situ studies of individual catalyst nanoparticles or surfaces by nano-focused (coherent) x-ray diffraction has been developed. Catalytic reactions can be studied in flow mode in a pressure range of 10\u3csup\u3e-2\u3c/sup\u3e-10\u3csup\u3e3\u3c/sup\u3e mbar and temperatures up to 900 °C. This instrument bridges the pressure and materials gap at the same time within one experimental setup. It allows us to probe in situ the structure (e.g., shape, size, strain, faceting, composition, and defects) of individual nanoparticles using a nano-focused x-ray beam. Here, the setup was used to observe strain and facet evolution of individual model Pt catalysts during in situ experiments. It can be used for heating other (non-catalytically active) nanoparticles (e.g., nanowires) in inert or reactive gas atmospheres or vacuum as well.\u3c/p\u3