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Poly(methyl methacrylate) (PMMA) terminated with elemental blocks containing polyhedral oligomeric silsesquioxane (POSS), hereafter referred to as PPMP, was synthesized by living anionic polymerization. Combining modern interfacial-sensitive spectroscopy with traditional contact angle measurements, static and dynamic structures at the surface of PPMP films in water were examined. The surface of the well-annealed PPMP films, where the POSS end groups were preferentially segregated, was flat at the sub-nanometer level. Once the PPMP film was immersed in water, the surface was reorganized, and the rate was much slower for PPMP than for the conventional PMMA. This implies that the POSS units hindered the interfacial dynamics of the polymer segments. Then, platelet-adhesion tests were performed on the PPMP films. The number of platelets adhered to the PPMP film was dependent on the pre-immersion time in phosphate-buffered saline before the platelet seeding, whereas that of the reference PMMA film was unaffected by the pre-immersion time. These results could be explained in terms of the aggregation states of water at the interface.

A dramatic rise in research interest in laser-induced graphene oxide (GO) reduction and modification requires an overview of the most recent works on this subject. Typical methods for the recognition and confirmation of modified graphene and its derivatives, such as Raman, Fourier-transform infra-red (FTIR), X-ray photoelectron (XP), and ultraviolet-visible (UV–vis) spectroscopies, are introduced briefly in this review. A major part of the survey is devoted to the main modification ways and the laser parameters used in the literature. A discussion of possible reduction and modification mechanisms is also presented. Recent applications, especially in the biomedical field such as cell therapy treatment, as well as significant results of GO modification, are discussed in detail. Finally, perspectives for the application of laser-induced GO modifications in passive THz photonics and biomedicine are briefly addressed.

Eumelanin photoprotects pigmented tissues from ultraviolet (UV) damage. However, UVA-induced tanning seems to result from the photooxidation of preexisting melanin and does not contribute to photoprotection. We investigated the mechanism of UVA-induced degradation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-melanin taking advantage of its solubility in a neutral buffer and using a differential spectrophotometric method to detect subtle changes in its structure. Our methodology is suitable for examining the effects of various agents that interact with reactive oxygen species (ROS) to determine how ROS is involved in the UVA-induced oxidative modifications. The results show that UVA radiation induces the oxidation of DHICA to indole-5,6-quinone-2-carboxylic acid in eumelanin, which is then cleaved to form a photodegraded, pyrrolic moiety and finally to form free pyrrole-2,3,5-tricarboxylic acid. The possible involvement of superoxide radical and singlet oxygen in the oxidation was suggested. The generation and quenching of singlet oxygen by DHICA-melanin was confirmed by direct measurements of singlet oxygen phosphorescence.

Lanthanide-doped upconversion nanoparticles have received growing attention in the development of low-background, highly sensitive and selective sensors. Here, we report a water probe based on ligand-free NaYF₄:Yb/Er nanoparticles, utilizing their intrinsically nonlinear upconversion process. The water molecule sensing was realized by monitoring the upconversion emission quenching, which is mainly attributed to efficient energy transfer between upconversion nanoparticles and water molecules as well as water-absorption-induced excitation energy attenuation. The nonlinear upconversion process, together with power function relationship between upconversion emission intensity and excitation power density, offers a sensitive detection of water content down to 0.008 vol % (80 ppm) in an organic solvent. As an added benefit, we show that noncontact detection of water can be achieved just by using water attenuation effect. Moreover, these upconversion nanoparticle based recyclable probes should be particularly suitable for real-time and long-term water monitoring, due to their superior chemical and physical stability. These results could provide insights into the design of upconversion nanoparticle based sensors.

This work highlights a strategy for the one-step synthesis of FeAu nanoparticles by the pulsed laser ablation of alloy targets in the presence of different solvents. This method allows particle generation without the use of additional chemicals; hence, solvent-metal interactions could be studied without cross effects from organic surface ligands. A detailed analysis of generated particles via transmission electron microscopy in combination with EDX elemental mapping could conclusively verify that the nature of the used solvent governs the internal phase structure of the formed nanoparticles. In the presence of acetone or methyl methacrylate, a gold shell covering a non-oxidized iron core was formed, whereas in aqueous media, an Au core with an Fe₃O₄ shell was generated. This core-shell morphology was the predominant species found in >90% of the examined nanoparticles. These findings indicate that fundamental chemical interactions between the nanoparticle surface and the solvent significantly contribute to phase segregation and elemental distribution in FeAu nanoparticles. A consecutive analysis of resulting Fe@Au core-shell nanoparticles revealed outstanding oxidation resistance and fair magnetic and optical properties. In particular, the combination of these features with high stability magnetism and plasmonics may create new opportunities for this hybrid material in imaging applications.

Sum-frequency generation vibrational spectroscopy (SFG-VS) was first developed in the 1980s and it has been proven a uniquely sensitive and surface/interface selective spectroscopic probe for characterization of the structure, conformation and dynamics of molecular surfaces and interfaces. In recent years, there have been many progresses in the development of methodology and instrumentation in the SFG-VS toolbox that have significantly broadened the application to complex molecular surfaces and interfaces. In this review, after presenting a unified view on the theory and methodology focusing on the SFG-VS spectral lineshape, as well as the new opportunities in SFG-VS applications with such developments, some of the controversial issues that have been puzzling the community are discussed. The aim of this review is to present to the researchers and students interested in molecular surfaces and interfacial sciences up-to-date perspectives complementary to the existing textbooks and reviews on SFG-VS.

Understanding interactions of calcium with lipid membranes at the molecular level is of great importance in light of their involvement in calcium signaling, association of proteins with cellular membranes, and membrane fusion. We quantify these interactions in detail by employing a combination of spectroscopic methods with atomistic molecular dynamics simulations. Namely, time-resolved fluorescent spectroscopy of lipid vesicles and vibrational sum frequency spectroscopy of lipid monolayers are used to characterize local binding sites of calcium in zwitterionic and anionic model lipid assemblies, while dynamic light scattering and zeta potential measurements are employed for macroscopic characterization of lipid vesicles in calcium-containing environments. To gain additional atomic-level information, the experiments are complemented by molecular simulations that utilize an accurate force field for calcium ions with scaled charges effectively accounting for electronic polarization effects. We demonstrate that lipid membranes have substantial calcium-binding capacity, with several types of binding sites present. Significantly, the binding mode depends on calcium concentration with important implications for calcium buffering, synaptic plasticity, and protein-membrane association.

Cu-chalcopyrite based solar cells, such as Cu(In,Ga)Se₂ (generally called CIGS) have been established as the most efficient thin-film technology in converting sunlight into electricity. High efficiency, flexibility and small weight make this technology attractive for future developments. Large scale production of these devices requires innovative technological solutions including the laser scribed monolithic interconnects. Laser scribing is needed to maintain module efficiency by dividing large scale device to smaller cells interconnected in series. Serious challenges in laser scribing technology have to be solved, including the laser induced thermal modification of the CIGS absorber layer. CIGS layer is thermally sensitive material, and laser modification can induce local structural changes and phase transitions to the metallic state. That is undesirable for the P3 scribing since superior isolating properties are needed. However, this effect can be used for the P2 process – interconnection of the adjacent cells. In this study, we investigated the picosecond laser modification of the CIGS active layer to form the series interconnect. The P2 laser process was optimized relying on the scribe electrical resistivity measurements with the best value of 3.5 Ω·cm. The EDS analysis revealed the increase of Cu/(Ga + In) ratio in laser treated areas while Raman measurements indicated changes in main CIGS peak and the formation of the Cu-rich CuGaSe₂ phase. Therefore, this resulted in a significant electrical conductivity increase in laser-treated areas which is acceptable for the cell serial interconnection.

Among the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter θ, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor:acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over wide ranges to reproduce typical experimental conditions. The results unify the fill factors of several very different donor:acceptor combinations and give insight into why fill factors change so much with thickness, light intensity and materials properties. To achieve fill factors larger than 0.8 requires further improvements in charge transport while reducing recombination.

New results on development of the Direct Laser Interference Patterning (DLIP) technique using the interference of several beams to directly ablate the material are presented. The method is capable of producing sub-wavelength features not limited by a beam spot size and is an effective method of forming two-dimensional periodic structures on relatively large area with just a single laser shot. Surface texturing speed of DLIP method and the direct laser writing was compared. Fabrication time reduction up to a few orders of magnitude using DLIP was evaluated. The sub-period scanning technique was applied for formation of the complex periodic structures. A new method of laser scanning for fabrication of periodic structures on large areas without any visible stitching signs between laser irradiation spots was tested.