In-Depth Investigation of Copper Surface Chemistry Modification by Ultrashort Pulsed Direct Laser Interference Patterning.

Surface patterning in the micro- and nanometer-range by means of pulsed laser interference has repeatedly proven to be a versatile tool for surface functionalization. With these techniques, however, the surface is often changed not only in terms of morphology but also in terms of surface chemistry. In this study, we present an in-depth investigation of the chemical surface modification occurring during surface patterning of copper by ultrashort pulsed direct laser interference patterning (USP-DLIP). A multimethod approach of parallel analysis using visualizing, topography-sensitive, and spectroscopic techniques allowed a detailed quantification of surface morphology as well as composition and distribution of surface chemistry related to both processing and atmospheric aging. The investigations revealed a heterogeneous surface composition separated in peak and valley regions predominantly consisting of Cu2O, as well as superficial agglomerations of CuO and carbon species. The evaluation was supported by a modeling approach for the quantification of XPS results in relation to heterogeneous surface composition, which was observed by means of a combination of different spectroscopic techniques. The overall results provide a detailed understanding of the chemical and topographical surface modification during USP-DLIP, which allows a more targeted use of this technology for surface functionalization.

Surface Modification of Brass via Ultrashort Pulsed Direct Laser Interference Patterning and Its Effect on Bacteria-Substrate Interaction.

In recent decades, antibiotic resistance has become a crucial challenge for human health. One potential solution to this problem is the use of antibacterial surfaces, i.e., copper and copper alloys. This study investigates the antibacterial properties of brass that underwent topographic surface functionalization via ultrashort pulsed direct laser interference patterning. Periodic line-like patterns in the scale range of single bacterial cells were created on brass with a 37% zinc content to enhance the contact area for rod-shaped Escherichia coli (E. coli). Although the topography facilitates attachment of bacteria to the surface, reduced killing rates for E. coli are observed. In parallel, a high-resolution methodical approach was employed to explore the impact of laser-induced topographical and chemical modifications on the antibacterial properties. The findings reveal the underlying role of the chemical modification concerning the antimicrobial efficiency of the Cu-based alloy within the superficial layers of a few hundred nanometers. Overall, this study provides valuable insight into the effect of alloy composition on targeted laser processing for antimicrobial Cu-surfaces, which facilitates the thorough development and optimization of the process concerning antimicrobial applications.

Hydroxyapatite Pellets as Versatile Model Surfaces for Systematic Adhesion Studies on Enamel: A Force Spectroscopy Case Study.

Research into materials for medical application draws inspiration from naturally occurring or synthesized surfaces, just like many other research directions. For medical application of materials, particular attention has to be paid to biocompatibility, osseointegration, and bacterial adhesion behavior. To understand their properties and behavior, experimental studies with natural materials such as teeth are strongly required. The results, however, may be highly case-dependent because natural surfaces have the disadvantage of being subject to wide variations, for instance in their chemical composition, structure, morphology, roughness, and porosity. A synthetic surface which mimics enamel in its performance with respect to bacterial adhesion and biocompatibility would, therefore, facilitate systematic studies much better. In this study, we discuss the possibility of using hydroxyapatite (HAp) pellets to simulate the surfaces of teeth and show the possibility and limitations of using a model surface. We performed single-cell force spectroscopy with single Staphylococcus aureus cells to measure adhesion-related parameters such as adhesion force and rupture length of cell wall proteins binding to HAp and enamel. We also examine the influence of blood plasma and saliva on the adhesion properties of S. aureus. The results of these measurements are matched to water wettability, elemental composition of the samples, and the change in the macromolecules adsorbed over time on the surface. We found that the adhesion properties of S. aureus were similar on HAp and enamel samples under all conditions: Significant decreases in adhesion strength were found equally in the presence of saliva or blood plasma on both surfaces. We therefore conclude that HAp pellets are a good alternative for natural dental material. This is especially true when slight variations in the physicochemical properties of the natural materials may affect the experimental series.

Molecular Origin of Electrical Conductivity in Gold-Polythiophene Hybrid Particle Films.

Hybrid electronic materials combine inorganic metals and semiconductors with π-conjugated polymers. The orientation of the polymer molecules in relation to the inorganic components is crucial for electrical material properties and device performance, but little is known of the configuration of π-conjugated polymers that bind to inorganic surfaces. Highly curved surfaces are common when using nanoscale components, for example, metal nanocrystal cores covered with conductive polymers. It is important to understand their effect on molecular arrangement. Here, we compare the molecular structures and electrical conductivities of well-defined nanoscale gold spheres and rods with shells of the covalently bound polythiophene PTEBS (poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate]). We prepared aqueous sinter-free inks from the particles and printed them. The particles formed highly conductive films immediately after drying. Films with spherical metal cores consistently had 40% lower conductivities than films based on nanorods. Raman and X-ray photoelectron spectroscopy revealed differences in the gold-sulfur bonds of PTEBS on rods and spheres. The fractions of bond sulfur groups implied differences in the alignment of PTEBS with the surface. More polymer molecules were bound in an edge-on configuration on spheres than on rods, where almost all polymers aligned "face-on" with the metal surface. This leads to different interface resistances: gold-polythiophene-gold interfaces between rods with π-π-tacked face-on PTEBS apparently foster electron transport along the surface-normal direction, while edge-on PTEBS does not. Molecular confinement thus increases the conductivity of hybrid inks based on highly curved nanostructures.