Ge Epitaxy at Ultralow Growth Temperatures Enabled by a Pristine Growth Environment.

Germanium (Ge), the next-in-line group-IV material, bears great potential to add functionality and performance to next-generation nanoelectronics and solid-state quantum transport based on silicon (Si) technology. Here, we investigate the direct epitaxial growth of two-dimensional high-quality crystalline Ge layers on Si deposited at ultralow growth temperatures ( = 100-350 °C) and pristine growth pressures (≲10 mbar). First, we show that a decreasing does not degrade the crystal quality of homoepitaxial Ge/Ge(001) by comparing the point defect density using positron annihilation lifetime spectroscopy.

Enhancing anti-adhesion properties by designing microstructure - the microscopy and spectroscopy study of the intercellular bacterial response.

This study is the first one that investigates in detail the bacterial intercellular response to the high density of crystallographic defects including vacancies created in Cu by high pressure torsion. To this aim, samples were deformed by high pressure torsion and afterward, their antibacterial properties against Staphylococcus aureus were analyzed in adhesion tests. As a reference an annealed sample was applied.

Insights into the LiMnO Cathode Stability in Aqueous Electrolytes.

LiMnO (LMO) cathodes present large stability when cycled in aqueous electrolytes, contrasting with their behavior in conventional organic electrolytes in lithium-ion batteries (LIBs). To elucidate the mechanisms underlying this distinctive behavior, we employ unconventional characterization techniques, including variable energy positron annihilation lifetime spectroscopy (VEPALS), tip-enhanced Raman spectroscopy (TERS), and macro-Raman spectroscopy (with tens of μm-size laser spot). These still rather unexplored techniques in the battery field provide complementary information across different length scales, revealing previously hidden features.

Acute-to-chronic subdural hematoma: radiographic and clinical progression from acute subdural hematoma.

Introduction: The pathogenesis of chronic subdural hematoma (CSDH) has not been completely understood. However, different mechanisms can result in space-occupying subdural fluid collections, one pathway can be the transformation of an original trauma-induced acute subdural hematoma (ASDH) into a CSDH.

Materials And Methods: All patients with unilateral CSDH, requiring burr hole trephination between 2018 and 2023 were included.

Revisiting Metal-Organic Frameworks Porosimetry by Positron Annihilation: Metal Ion States and Positronium Parameters.

Metal-organic frameworks (MOFs) stand as pivotal porous materials with exceptional surface areas, adaptability, and versatility. Positron Annihilation Lifetime Spectroscopy (PALS) is an indispensable tool for characterizing MOF porosity, especially micro- and mesopores in both open and closed phases. Notably, PALS offers porosity insights independent of probe molecules, which is vital for detailed characterization without structural transformations.

Effect of annealing temperature on the structure and optical properties of ZnO thin films.

The effect of annealing temperature on the microstructure, defects and optical properties of ZnO thin films are investigated using sol-gel based spin coating method for a range of annealing temperatures from 200C to 500C. The correlation among the microstructure, defects, impurity content and the optical band gap of films of thickness about 10-12 nm is elucidated. The particle size increases and the optical band gap reduces with the annealing temperature.

Unravelling the Water Adsorption Mechanism in Hierarchical MOFs: Insights from In Situ Positron Annihilation Lifetime Studies.

Atmospheric water harvesting with metal-organic frameworks (MOFs) is a new technology providing a clean, long-term water supply in arid areas. In-situ positron annihilation lifetime spectroscopy (PALS) is proposed as a valid methodology for the mechanistic understanding of water sorption in MOFs and the selection of prospective candidates for desired applications. DUT-67-Zr and DUT-67-Hf frameworks are used as model systems for method validation because of their hierarchical pore structure, high adsorption capacity, and chemical stability.

Millisecond flash lamp curing for porosity generation in thin films.

Flash lamp annealing (FLA) with millisecond pulse durations is reported as a novel curing method for pore precursor's degradation in thin films. A case study on the curing of dielectric thin films is presented. FLA-cured films are being investigated by means of positron annihilation spectroscopy (PAS) and Fourier-transform infrared (FTIR) spectroscopy in order to quantify the nm-scale porosity and post-treatment chemistry, respectively.

Regulating Oxygen Ion Transport at the Nanoscale to Enable Highly Cyclable Magneto-Ionic Control of Magnetism.

Magneto-ionics refers to the control of magnetic properties of materials through voltage-driven ion motion. To generate effective electric fields, either solid or liquid electrolytes are utilized, which also serve as ion reservoirs. Thin solid electrolytes have difficulties in (i) withstanding high electric fields without electric pinholes and (ii) maintaining stable ion transport during long-term actuation.

Relation between Ga Vacancies, Photoluminescence, and Growth Conditions of MOVPE-Prepared GaN Layers.

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and the concentration of gallium vacancies (V). Different correlations between technological parameters and V concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa, the formation of V was significantly influenced by the type of reactor atmosphere (N or H), while no similar behaviour was observed for growth from TMGa.

Chemical deposition of CuO films with ultra-low resistivity: correlation with the defect landscape.

Cuprous oxide (CuO) is a promising p-type semiconductor material for many applications. So far, the lowest resistivity values are obtained for films deposited by physical methods and/or at high temperatures (~1000 °C), limiting their mass integration. Here, CuO thin films with ultra-low resistivity values of 0.

Nanoscaled LiMnO for Extended Cycling Stability in the 3 V Plateau.

Extending the potential window toward the 3 V plateau below the typically used range could boost the effective capacity of LiMnO spinel cathodes. This usually leads to an "overdischarge" of the cathode, which can cause severe material damage due to manganese dissolution into the electrolyte and a critical volume expansion (induced by Jahn-Teller distortions). As those factors determine the stability and cycling lifetime for all-solid-state batteries, the operational window of LiMnO is usually limited to 3.

Defect Nanostructure and its Impact on Magnetism of α-Cr O Thin Films.

Thin films of the magnetoelectric insulator α-Cr O are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. In contrast to single crystals, the quality of thin Cr O films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, the impact of the defect nanostructure, including sparse small-volume defects and their complexes is studied on the magnetic properties of Cr O thin films.

Magneto-Ionics in Single-Layer Transition Metal Nitrides.

Magneto-ionics allows for tunable control of magnetism by voltage-driven transport of ions, traditionally oxygen or lithium and, more recently, hydrogen, fluorine, or nitrogen. Here, magneto-ionic effects in single-layer iron nitride films are demonstrated, and their performance is evaluated at room temperature and compared with previously studied cobalt nitrides. Iron nitrides require increased activation energy and, under high bias, exhibit more modest rates of magneto-ionic motion than cobalt nitrides.

An experimental investigation of light emission produced in the process of positronium formation in matter.

The excess energy emitted during the positronium (Ps) formation in condensed matter may be released as light. Spectroscopic analysis of this light can be a new method of studying the electronic properties of materials. We report the first experimental attempt, according to our knowledge, to verify the existence of this emission process.

A new mechanism for void-cascade interaction from nondestructive depth-resolved atomic-scale measurements of ion irradiation-induced defects in Fe.

The nondestructive investigation of single vacancies and vacancy clusters in ion-irradiated samples requires a depth-resolved probe with atomic sensitivity to defects. The recent development of short-pulsed positron beams provides such a probe. Here, we combine depth-resolved Doppler broadening and positron annihilation lifetime spectroscopies to identify vacancy clusters in ion-irradiated Fe and measure their density as a function of depth.

Vacancy-Hydrogen Interaction in Niobium during Low-Temperature Baking.

A recently discovered modified low-temperature baking leads to reduced surface losses and an increase of the accelerating gradient of superconducting TESLA shape cavities. We will show that the dynamics of vacancy-hydrogen complexes at low-temperature baking lead to a suppression of lossy nanohydrides at 2 K and thus a significant enhancement of accelerator performance. Utilizing Doppler broadening Positron Annihilation Spectroscopy, Positron Annihilation Lifetime Spectroscopy and instrumented nanoindentation, samples made from European XFEL niobium sheets were investigated.

Boosting jet power in black hole spacetimes.

The extraction of rotational energy from a spinning black hole via the Blandford-Znajek mechanism has long been understood as an important component in models to explain energetic jets from compact astrophysical sources. Here we show more generally that the kinetic energy of the black hole, both rotational and translational, can be tapped, thereby producing even more luminous jets powered by the interaction of the black hole with its surrounding plasma. We study the resulting Poynting jet that arises from single boosted black holes and binary black hole systems.

Magnetized neutron-star mergers and gravitational-wave signals.

We investigate the influence of magnetic fields upon the dynamics of, and resulting gravitational waves from, a binary neutron-star merger in full general relativity coupled to ideal magnetohydrodynamics. We consider two merger scenarios: one where the stars have aligned poloidal magnetic fields and one without. Both mergers result in a strongly differentially rotating object.

Critical collapse of a complex scalar field with angular momentum.

We report a new critical solution found at the threshold of axisymmetric gravitational collapse of a complex scalar field with angular momentum. To carry angular momentum the scalar field cannot be axisymmetric; however, its azimuthal dependence is defined so that the resulting stress-energy tensor and spacetime metric are axisymmetric. The critical solution found is nonspherical, discretely self-similar with an echoing exponent Delta=0.