Correlative atomic force microscopy and scanning electron microscopy of bacteria-diamond-metal nanocomposites.

Research investigating the interface between biological organisms and nanomaterials nowadays requires multi-faceted microscopic methods to elucidate the interaction mechanisms and effects. Here we describe a novel approach and methodology correlating data from an atomic force microscope inside a scanning electron microscope (AFM-in-SEM). This approach is demonstrated on bacteria-diamond-metal nanocomposite samples relevant in current life science research. We describe a procedure for preparing such multi-component test samples containing E. coli bacteria and chitosan-coated hydrogenated nanodiamonds decorated with silver nanoparticles on a carbon-coated gold grid. Microscopic topography information (AFM) is combined with chemical, material, and morphological information (SEM using SE and BSE at varied acceleration voltages) from the same region of interest and processed to create 3D correlative probe-electron microscopy (CPEM) images. We also establish a novel 3D RGB color image algorithm for merging multiple SE/BSE data from SEM with the AFM surface topography data which provides additional information about microscopic interaction of the diamond-metal nanocomposite with bacteria, not achievable by individual analyses. The methodology of CPEM data interpretation is independently corroborated by further in-situ (EDS) and ex-situ (micro-Raman) chemical characterization as well as by force volume AFM analysis. We also discuss the broader applicability and benefits of the methodology for life science research.

Indentation Size Effect in CoCrFeMnNi HEA Prepared by Various Techniques.

High entropy alloys (HEAs) are materials of great application potential and which have been extensively studied during the last two decades. As the number of possible element combinations is enormous, model materials representing certain groups of HEAs are used for the description of microstructure, properties, and deformation mechanisms. In this study, the microstructure and mechanical properties of the so-called Cantor alloy composed of Co, Cr, Fe, Mn, and Ni in equiatomic ratios prepared by various techniques (casting, melt-spinning, spark plasma sintering) were examined. The research focused on the indentation measurements, namely, the indentation size effect describing the evolution of the hardness with penetration depth. It was found that the standard Nix-Gao model can be used for this type of alloy at higher penetration depths and its parameters correlate well with microstructural observations. The Nix-Gao model deviates from the measured data at the submicrometer range and the applied modification affords additional information on the deformation mechanism.

Printable Resin Modified by Grafted Silver Nanoparticles for Preparation of Antifouling Microstructures with Antibacterial Effect.

The usage of three-dimensional (3D) printed materials in many bioapplications has been one of the fastest-growing sectors in the nanobiomaterial industry in the last couple of years. In this work, we present a chemical approach for grafting silver nanoparticles (AgNPs) into a resin matrix, which is convenient for 3D printing. In this way, the samples can be prepared and are able to release silver ions (Ag+) with excellent antibacterial effect against bacterial strains of E. coli and S. epidermidis. By the proposed process, the AgNPs are perfectly mixed and involved in the polymerization process and their distribution in the matrix is homogenous. It was also demonstrated that this approach does not affect the printing resolution and the resin is therefore suitable for the construction of microstructures enabling controlled silver ion release and antifouling properties. At the same time the physical properties of the material, such as viscosity and elasticity modulus are preserved. The described approach can be used for the fabrication of facile, low-cost 3D printed resin with antifouling-antibacterial properties with the possibility to control the release of Ag+ through microstructuring.

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. We studied the evolution of vacancies in bulk samples and in the sub-surface region and their interaction with hydrogen at different temperature levels during in-situ and ex-situ annealing.

Influence of Heat Treatment on Microstructure and Properties of NiTi46 Alloy Consolidated by Spark Plasma Sintering.

Ni-Ti alloys are considered to be very important shape memory alloys with a wide application area including, e.g., biomaterials, actuators, couplings, and components in automotive, aerospace, and robotics industries. In this study, the NiTi46 (wt.%) alloy was prepared by a combination of self-propagating high-temperature synthesis, milling, and spark plasma sintering consolidation at three various temperatures. The compacted samples were subsequently heat-treated at temperatures between 400 °C and 900 °C with the following quenching in water or slow cooling in a closed furnace. The influence of the consolidation temperature and regime of heat treatment on the microstructure, mechanical properties, and temperatures of phase transformation was evaluated. The results demonstrate the brittle behaviour of the samples directly after spark plasma sintering at all temperatures by the compressive test and no transformation temperatures at differential scanning calorimetry curves. The biggest improvement of mechanical properties, which was mainly a ductility enhancement, was achieved by heat treatment at 700 °C. Slow cooling has to be recommended in order to obtain the shape memory properties.

Effect of Initial Powders on Properties of FeAlSi Intermetallics.

FeAlSi intermetallics are materials with promising high-temperature mechanical properties and oxidation resistance. Nevertheless, their production by standard metallurgical processes is complicated. In this study, preparation of powders by mechanical alloying and properties of the samples compacted by spark plasma sintering was studied. Various initial feedstock materials were mixed to prepare the material with the same chemical composition. Time of mechanical alloying leading to complete homogenization of powders was estimated based on the microstructure observations, results of XRD and indentation tests. Microstructure, phase composition, hardness and fracture toughness of sintered samples was studied and compared with the properties of powders before the sintering process. It was found that independently of initial feedstock powder, the resulting phase composition was the same (Fe3Si + FeSi). The combination of hard initial powders required the longest milling time, but it led to the highest values of fracture toughness.

Structure and Properties of Fe-Al-Si Alloy Prepared by Mechanical Alloying.

Fe-Al-Si alloys have been previously reported as an interesting alternative to common high-temperature materials. This work aimed to improve the properties of FeAl20Si20 alloy (in wt.%) by the application of powder metallurgy process consisting of ultrahigh-energy mechanical alloying and spark plasma sintering. The material consisted of Fe3Si, FeSi, and Fe3Al2Si3 phases. It was found that the alloy exhibits an anomalous behaviour of yield strength and ultimate compressive strength around 500 °C, reaching approximately 1100 and 1500 MPa, respectively. The results also demonstrated exceptional wear resistance, oxidation resistance, and corrosion resistance in water-based electrolytes. The tested manufacturing process enabled the fracture toughness to be increased ca. 10 times compared to the cast alloy of the same composition. Due to its unique properties, the material could be applicable in the automotive industry for the manufacture of exhaust valves, for wear parts, and probably as a material for selected aggressive chemical environments.