High-reflectance GaInP/GaAs distributed Bragg reflector

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Quantitative measurements of electric fields at the mesoscale are essential for understanding and optimizing the performance of modern devices. However, achieving this using electron microscopy techniques is challenging due to the coexistence of electrostatic and diffraction-related contrast resulting from electron beam interactions with the material. This thesis investigates the capabilities and limitations of pixelated differential phase contrast (DPC) in scanning transmission electron microscopy for quan

Electron ptychography revolutionized materials science microscopy by achieving record-breaking resolutions through phase retrieval algorithms, but its application to radiation-sensitive biological specimens remains largely unexplored. This thesis pioneers the application of 4D-STEM ptychography to frozen hydrated biological specimens, where electron doses must remain substantially low to prevent radiation damage, orders of magnitude lower than materials science applications. We developed an automated 4D-STE

Jahn–Teller polarons are quasiparticles that stem from symmetry breaking and strong local electron–phonon coupling. They originate from an excess charge carrier being dressed by a local lattice distortion, caused by the Jahn–Teller effect, and they critically impact electrical, structural, and magnetic properties in transition metal oxides. The observation of the microscopic steps involved in their formation is essential for enabling control over material properties through the targeted activation of local,

This study explores the ferroelectric domain structure and mechanical properties of PbTiO3‐based membranes, which develop a well‐ordered and crystallographic‐oriented ripple pattern upon release from their growth substrate. The ferrolectric domain structure of the PbTiO3 layer is examined at various length scales using optical second harmonic generation, piezoresponse force microscopy, and scanning transmission electron microscopy. These methods reveal the presence of purely in‐plane domains organized into

This study investigates four Icelandic basalt types that vary in mineralogy, pore structure, and degree of geothermal alteration, with the aim of understanding how microstructural characteristics influence fluid flow and mineral precipitation in the context of CO₂ storage. Samples were imaged using X-ray micro computed tomography (µCT) and scanning electron microscopy (SEM), enabling multiscale characterisation of fracture networks, vesicularity, and microporosity. Particular attention is given to the effec

Coatings on SOFC interconnect steels are complex and challenging to investigate due to the high number of chemical elements which are present and interact with each other. In this work, advanced electron microscopy techniques are used to study the steel oxidation in its initial stage (first days), where scale is built up and first elemental diffusions and interactions may be clearly seen. First the surface of a coated steel piece is observed in an environmental scanning electron microscope (E-SEM) at high t

Linear crystal defects called dislocations are one of the most fascinating concepts in materials science that govern mechanical and optoelectronic properties of many materials across a broad range of application. Three-dimensional (3-D) study of dislocation network is in principle accessible by conventional tomographic and stereoscopic techniques in Transmission Electron Microscopy (TEM). In these techniques in general the need to tilt the specimen for acquiring image series over large tilt ranges remain ho

We report on the optimization of a multilayer platinum/aluminum nitride (AlN) stack with an AlN active layer thickness of 50 nm for piezoelectric actuation in nanoelectromechanical systems (NEMS). Experiments in reactive sputtering of AlN were used to find optimal parameters for good crystallinity and low residual stress of a four layer film stack, shown in Figure 1. A direct relationship was measured between the AlN seed layer thickness and the x-ray diffraction (XRD) rocking curve’s full width at half max

X-ray diffraction measurements show that the high-temperature superconductor YBa2Cu3O6.54, with ortho-II oxygen order, has charge-density-wave order in the absence of an applied magnetic field. The dominant wave vector of the charge density wave is q(CDW) = (0, 0.328(2), 0.5), with the in-plane component parallel to the b axis (chain direction). It has a similar incommensurability to that observed in ortho-VIII and ortho-III samples, which have different dopings and oxygen orderings. Our results for ortho-I

The activity and selectivity of structure-sensitive reactions are strongly correlated with the shape and size of the nanocrystals present in a catalyst. This correlation can be exploited for rational catalyst design, especially if each type of surface atom displays a different behavior, to attain the highest activity and selectivity. In this work, uniform Pd nanocrystals with cubic (in two different sizes), octahedral, and cuboctahedral shapes were synthesized through a solution-phase method with poly(vinyl

We grew epitaxial SrTiO3 (STO) thin films on (001) LaAlO3 substrates via a two-step procedure using pulsed laser deposition and studied them with transmission electron microscopy in plane-view and cross-sectional samples. We found that partial misfit dislocations are the main interfacial defects, whereas planar defects are the main defects in STO films. Our results suggest that a three-dimensional island mode dominates the growth of the STO film.

Following the current interest in transition metal doped dielectrics for spintronic applications, Mn-doped ZnO is being made by thermal decomposition of Mn-doped hydrozincite,  (MnxZn1–x)5(OH)6–2n (CO3)1+n, precursors that have been prepared by a novel synthesis method. While the aim is to make solely (MnxZn1–x)O phase, experiments show that the Mn-Zn-O system is very susceptible to the formation of “contaminant” Mn-rich phases such as zinc manganate. For instance, TEM analysis shows that thermal decomposit

Focused electron beam induced depositions of nickel-containing materials obtained by using bis(methylcyclopentadienyl)nickel(II) Ni(C5H4CH3)(2) and tetrakis(trifluorophosphine)nickel(0) Ni(PF3)(4) as precursors, were compared in terms of chemical composition and electrical resistivity. Ni(PF3)(4) decomposed into higher Ni content materials than that obtained with Ni(C5H4CH3)(2) (typically 40 and 10 at. %, respectively). Attempts of increasing the Ni content by injecting controlled flows of molecular oxygen

In this thesis we address the subject of strong electron-phonon coupling in pyramidal quantum dots and pursue detailed physical, analytical and numerical investigations. The strong coupling polaron states in a pyramidal GaAs/AlGaAs quantum dot are computed numerically with an enhanced matrix diagonalization method that accounts for the particular structure of the Hamiltonian and uses an irregular reciprocal space discretization. Electron-electron interactions and multiple phonon interactions are neglected.

We report on the growth by metalorganic vapor phase epitaxy of a InGaN/GaN resonant-cavity light emitting diode (RCLED) emitting at 454 nm and incorporating a 12-pair Al0.82In0.18N/GaN distributed Bragg reflector as bottom mirror. A(1-x)In(x)N layers with an Al content around x similar to 0.17 are lattice matched to GaN, thus avoiding strain-related issues in the subsequent active layers while keeping a high refractive index contrast of 7%, comparable to that achievable in the Al0.5Ga0.5N/GaN system. Device

High-resolution transmission electron microscopy (HRTEM) and HRTEM simulation by the Bloch wave method (JEMS) are used to determine the structure and thickness of micro- and nanocrystals of biominerals and hydroxyapatite grown from aqueous solutions. It is established that thin (from one to several lattice parameters) crystals, including hydroxyapatite in mineralized biological tissues, are usually formed in low-temperature (up to 40degreesC) solutions. Relatively thick (up to several tens of lattice parame

In the following, we report investigations of the dependencies of the structural, optical and electrical characteristics of InN thin films grown by MOCVD on the growth temperature. The layer thicknesses range from 70 to 400 nm. Their carrier concentrations range from 7 x 10 18 to 4 x 10(19) cm(-3). Hall mobility values from 150 to 1300 cm(2)/V/s were determined in these films. The variation of the growth temperature and V/III ratio brought about different growth modes and rates. Using TEM, in addition to me

Wetting and sticking of soda-lime glass on two types of stainless steel as well as on platinum and vitreous carbon substrates are studied in a neutral gas atmosphere between 860 and 1200degreesC. Wetting is measured by the "transferred drop" version of the sessile drop technique, enabling fully isothermal spreading kinetics to be monitored. Sticking is investigated by measuring the temperature of glass drop detachment from the substrate during cooling below the vitreous transition temperature. Characterizat

During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation ins

High-reflectance GaInP/GaAs distributed Bragg reflector

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Probing (ferro)electric fields using pixelated differential phase contrast imaging aided by precession

Coherent Diffractive Imaging in Biological Transmission Electron Microscopy

Ultrafast Formation of Jahn–Teller Polarons Revealed by State-Selective Excitation in Correlated Spinel Co 3 O 4

Curvature‐Controlled Polarization in Adaptive Ferroelectric Membranes

Microstructural Controls on Reactive Flow and CO2 Mineralisation in Basalts: A µCT, SEM, and Modelling Approach

Live observation of the oxidation of coated interconnects with environmental electron microscopy

Three-dimensional electron imaging of dislocations from a single sample tilt

50 nm thick AlN Films for Actuation and Detection of Nanoscale Resonators

NanoSIMS and Electron Microscopy: A powerful combination in Life Science Research.

X-Ray Diffraction Observations of a Charge-Density-Wave Order in Superconducting Ortho-II YBa_{2}Cu_{3}O_{6.54} Single Crystals in Zero Magnetic Field

Structure Sensitivity of Alkynol Hydrogenation on Shape- and Size-Controlled Palladium Nanocrystals: Which Sites Are Most Active and Selective?

Growth-mode induced defects in epitaxial SrTiO3 thin films grown on single crystal LaAlO3 by a two-step PLD process

In-Situ vs. Ex-Situ Nanocrystallization of Mn-Doped ZnO

Focused electron beam induced deposition of nickel

Theory of Polaron States in Pyramidal GaAs/AlGaAs Quantum Dots

InGaN/GaN resonant-cavity LED including an AlInN/GaN bragg mirror

HRTEM simulation in determination of thickness and grain misorientation for hydroxyapatite crystals

Structural and optical characterization of InN layers grown by MOCVD

Wetting, interfacial interactions and sticking in glass/steel systems

Reinforcement of single-walled carbon nanotube bundles by intertube bridging