Open Access

Laser materials processing is an important tool for creating and shaping new materials. Laser machining, especially with ultrashort pulses offers the modification of surfaces, thin coatings, and bulk materials with an unprecedented precision and control. The most desired feature of pulsed laser processing in the femtosecond range is that the heat-affected zone in the irradiated material will be extremely small. To better understand the mechanisms involved during laser irradiation, it is important to analyse the outcome of light-matter interaction with spectroscopic methods. Ellipsometry, especially spectroscopic imaging ellipsometry (SIE), has become an important tool for this in recent times, as it gives access to local layer thicknesses, materials dielectric functions, and features like changes in surface roughness. This work includes an overview over our recent studies examining near-infrared fs-laser surface processing of different group IV materials. The superficial phase change of silicon from crystalline to amorphous has been investigated in the past as the result of laser processing strongly depends on the crystal orientation. Moreover, SIE is capable of determining the properties of buried a-Si interfaces with micrometer lateral and sub-nanoneter vertical precision. Additionally, the growth of native and laser-induced oxides can be revealed.

Synthetic polymer hydrogels are valuable matrices for biotransformations, drug delivery, and soft implants. While the bulk properties of hydrogels depend on chemical composition and network structure, the critical role of interfacial features is often underestimated. This work presents a nanoscale modification of the gel−water interface using polymer brushes via a straightforward “grafting-to” strategy, offering an alternative to more cumbersome “grafting-from” approaches. Functional block copolymers with photoreactive anchor blocks are successfully self-assembled and UV-immobilized on hydrogel substrates despite their low solid content (<30 wt %). This versatile technique works on both bulk- and surface-immobilized hydrogels, demonstrated on poly(hydroxypropyl acrylate), poly(N-isopropylacrylamide), and alginate gels, allowing precise control over grafting density. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry revealed a homogeneous bilayered architecture. By “brushing-up”, the hydrogels’ interface can be tailored to enhance protein adsorption, improve cell adhesion, or impair the diffusive uptake of small molecules into the bulk gels. This effective interfacial nanoengineering method is broadly applicable for enhancing hydrogel performance across a wide range of applications.

Graphene oxide (GO) has emerged as a promising biomaterial as it is easily and cheaply synthesized, strong, cytocompatible, osteoinductive, and has a well-characterized aqueous degradation pathway. It is also a great substrate for functionalization with biomolecules such as proteins, peptides, and small molecules that can enhance or add bioactivity. Covalent chemical linkages as opposed to typical noncovalent association methods are preferable so that the biomolecules do not quickly diffuse away or face replacement by other proteins, which is critical in long time scale applications like bone regeneration. However, covalent chemistry tends to carry a drawback of harsh reaction conditions that can damage the structure, conformation, and therefore function of a delicate biomolecule like a protein. Here, the Mitsunobu reaction is introduced as a novel method of covalently attaching proteins to graphene oxide. It features gentle reaction conditions and has the added benefit of utilizing the plentiful basal plane alcohol functionalities on graphene oxide, allowing for high yield protein functionalization. The amino acid Glycine (G), the protein bovine serum albumin (BSA), and the small molecule SVAK-12 are utilized to create the three Mitsunobu Graphene (MG) materials G-MG, BSA-MG, and SVAK-MG that demonstrate the wide applicability of this functionalization method.

Proper physicochemical characterization of advanced materials and complex industrial composites remains a significant challenge, particularly for nanomaterials, whose nanoscale dimensions and mostly complex chemistry challenge the analysis. In this work, we employed a correlative analytical approach that integrates atomic force microscopy (AFM), scanning electron microscopy (SEM) coupled with energy‐dispersive X‐ray spectroscopy (EDS), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), Auger electron spectroscopy (AES), and Raman spectroscopy. This combination enables detailed chemical and structural characterization with sub‐micrometer spatial resolution. Three commercial graphene‐based materials of varying complexity were selected and investigated to test the analytical performance of this approach. Furthermore, one of the commercial graphene oxide samples was chemically functionalized via amination and fluorination. This allowed us to assess how surface modifications influence both the material properties and the limits of the applied analytical techniques.

Since the original report in 2004 by Novoselov and Geim, Graphene gained incredible attention due to its fascinating properties. In the past 20 years, the synthesis and functionalization of graphene has evolved significantly[3]. Different synthesis techniques were developed which led to other graphenerelated materials such as graphene oxide (GO) or elemental-doped graphene. Further chemical functionalization can enhance but also alter or reduce specific properties of the graphene. To reveal the nature of these materials a proper physico‑chemical characterization with different analytical techniques is crucial. Single-layer GO flakes kindly provided by Graphenea (Spain) were prepared for systematic image analysis. These flakes were disposed on an alignment-marked SiO2 substrate and correlatively imaged by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Raman spectroscopy. The high lateral resolution and/ or extreme surface sensitivity of the mentioned techniques is necessary to explore monolayers. The ToF-SIMS images match well with the SEM and AFM images and provide information about the chemistry. With 2D Raman spectroscopy it is possible to differentiate between the number of stacked single-layer flakes. This is visualized in a 3D image (Figure b). Well-defined GO flakes could be used as a reference material for imaging of graphene-like structures but also of other types of 2D materials. In addition to these monolayer GO flakes, commercial graphene-containing inks (Haydale) with a more complex morphology were also correlatively imaged. ToF-SIMS and SEM images were merged to identify the origin of different chemical fragments. The findings correlate closely with the expectation that the specific functionalizations (with fluorine and nitrogen as marker elements) are present only on the graphene flakes as presumed from the SEM images. Energy-dispersive X-ray spectroscopy (EDX) supports these results, yet with a much lower sensitivity compared to ToF-SIMS.