Pulsed laser deposition of niobium thin films for in-situ device fabrication and their superconducting properties

Here, we studied the crystallographic and superconducting properties of niobium thin films grown by pulsed laser deposition. Depending on laser fluence our samples showed a critical temperature of up to 8.4 K and critical current densities of 3.0 · 10 6 A/cm 2 at 4.2 K. X-ray diffraction measurements and TEM images suggest a granular structure with a preferred orientation of the (110) lattice plane parallel to the substrate surface. The superconducting properties of our films are significantly influenced by this granularity and the oxygen content in the film. We discuss the temperature dependence of the critical current density in the framework of an crossover from Ginzburg-Landau to Ambegaokar-Baratoff type behaviour. According to this the current transport is mainly dominated by Josephson-tunnelling in a granular network

A classical description of subnanometer resolution by atomic features in metallic structures

Recent experiments have evidenced sub-nanometer resolution in plasmonic-enhanced probe spectroscopy. Such a high resolution cannot be simply explained using the commonly considered radii of metallic nanoparticles on plasmonic probes. In this contribution the effects of defects as small as a single atom found on spherical plasmonic particles acting as probing tips are investigated in connection with the spatial resolution provided. The presence of abundant edge and corner sites with atomic scale dimensions in crystalline metallic nanoparticles is evident from transmission electron microscopy (TEM) images. Electrodynamic calculations based on the Finite Element Method (FEM) are implemented to reveal the impact of the presence of such atomic features in probing tips on the lateral spatial resolution and field localization. Our analysis is developed for three different configurations, and under resonant and non-resonant illumination conditions, respectively. Based on this analysis, the limits of field enhancement, lateral resolution and field confinement in plasmon-enhanced spectroscopy and microscopy are inferred, reaching values below 1 nanometer for reasonable atomic sizes

Chemical effects during the formation of various types of femtosecond laser-generated surface structures on titanium alloy

Abstract In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil

Aqueous Black Colloids of Reticular Nanostructured Gold

Since ancient times, noble gold has continuously contributed to several aspects of life from medicine to electronics. It perpetually reveals its new features. We report the finding of a unique form of gold, reticular nanostructured gold (RNG), as an aqueous black colloid, for which we present a one-step synthesis. The reticules consist of gold crystals that interconnect to form compact strands. RNG exhibits high conductivity and low reflection and these features, coupled with the high specific surface area of the material, could prove valuable for applications in electronics and catalysis. Due to high absorption throughout the visible and infrared domain, RNG has the potential to be applied in the construction of sensitive solar cells or as a substrate for Raman spectroscopy

Tracing the Formation of Femtosecond Laser-Induced Periodic Surface Structures (LIPSS) by Implanted Markers

The generation of laser-induced periodic surface structures (LIPSS) using femtosecond lasers facilitates the engineering of material surfaces with tailored functional properties. Numerous aspects of their complex formation process are still under debate, despite intensive theoretical and experimental research in recent decades. This particularly concerns the challenge of verifying approaches based on electromagnetic effects or hydrodynamic processes by experiment. In the present study, a marker experiment is designed to conclude on the formation of LIPSS. Well-defined concentration depth profiles of 55 Mn + - and 14 N + -ions were generated below the polished surface of a cast Mn- and Si-free stainless steel AISI 316L using ion implantation. Before and after LIPSS generation, marker concentration depth profiles and the sample microstructure were evaluated by using transmission electron microscopy techniques. It is shown that LIPSS predominantly formed by material removal through locally varying ablation. Local melting and resolidification with the redistribution of the material occurred to a lesser extent. The experimental design gives quantitative access to the modulation depth with a nanometer resolution and is a promising approach for broader studies of the interactions of laser beams and material surfaces. Tracing LIPSS formation enables to unambiguously identify governing aspects, consequently guiding the path to improved processing regarding reproducibility, periodicity, and alignment

Rhodium-Complex-Functionalized and Polydopamine-Coated CdSe@CdS Nanorods for Photocatalytic NAD+ Reduction

[Image: see text] We report on a photocatalytic system consisting of CdSe@CdS nanorods coated with a polydopamine (PDA) shell functionalized with molecular rhodium catalysts. The PDA shell was implemented to enhance the photostability of the photosensitizer, to act as a charge-transfer mediator between the nanorods and the catalyst, and to offer multiple options for stable covalent functionalization. This allows for spatial proximity and efficient shuttling of charges between the sensitizer and the reaction center. The activity of the photocatalytic system was demonstrated by light-driven reduction of nicotinamide adenine dinucleotide (NAD(+)) to its reduced form NADH. This work shows that PDA-coated nanostructures present an attractive platform for covalent attachment of reduction and oxidation reaction centers for photocatalytic applications

Changes in the mechanical, structural and electrical properties of glassy carbon due to strontium and silver co-implantation and annealing

Please read abstract in the article.https://www.elsevier.com/locate/apsusc2022-09-22hj2022Physic

Characteristics of cracks formed at the surface of NiTi during a single cycle of pseudoelastic deformation

Abstract Pseudoelastic deformation of NiTi usually results in cracks at the surface. Cracking is promoted by surface oxide layers that form, e.g., during heat treatments required for shape-setting of minimally invasive implants. In connection with the advancing miniaturization of minimally invasive implants, the question arises whether their mechanical integrity may get impaired by such cracks. In the present work, the characteristics of the cracks was investigated in cross section with the help of targeted preparation using focused ion-beams. SEM and TEM on samples after a single cycle of pseudoelastic deformation revealed that cracks extend perpendicular to the loading direction in the surface oxide layer and change to angles between 90° and 45° in the Ni-rich layer below. Pores observed in the surface oxide close to the Ni-rich layer did not prevent the extension of cracks towards the NiTi bulk. When the cracks reach the NiTi, blunting of the crack tip was observed. The crack length essentially corresponds to the thickness of the surface oxide layer and the Ni-rich layer. The findings provide data for estimating crack propagation in according implants in the future.</jats:p