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Pulsed laser deposition was used to grow DLC and molybdenum-doped DLC (DLC:Mo) films, with metal contents up to 3.2 at.%, on silicon substrates. The microstructural details of the films were investigated using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scan electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Residual stresses were quantified through curvature measurements while the nanoscale mechanical properties of the films were probed using an instrumented indentation platform in the nanoindentation and nanoscratch mode, respectively. The deposition conditions used in this study resulted in an amorphous carbon matrix with sp3 content of 77 at.% and density of 2.9 g/cm3. Molybdenum-doping reduced the percentage of sp3 hybridization within the amorphous carbon matrix and generated Mo-C bonds as detected through XPS. The increase in the molybdenum content reduced the residual stresses which can be related to the percentage reduction of the highly directional four-fold coordinated carbon atoms and the subsequent release of the strain energy in the system. Furthermore, the resistance to penetration of the DLC:Mo films was also reduced which again could be attributed to the severe graphitization of the amorphous carbon matrix. The effect of molybdenum on the coefficient of friction (COF) was of secondary importance with deviations from the COF of pure DLC on the order of ± 12%. In contrast, all DLC:Mo films deposited herein exhibited higher critical loads to failure/delamination with DLC:Mo3.2 at.% showing the highest enhancement (+ 87% compared to pure DLC). This improvement on the critical load to failure can be traced back to (a) the graphitization and softening of the amorphous carbon matrix that increased the ductility of the matrix, (b) the formation of the Mo-C bonds that can operate as obstacles to the micro-fracture processes and (c) the reduction of the residual stresses that increased the mechanical capacity of the film/substrate material system. © 2017 Elsevier B.V. 330 185 195 185-195

Segmented polyurethane elastomers for biomedical applications were synthesized and studied at macroscopic (by mechanical testing) and meso/nanoscopic length scales (by atomic force microscopy, AFM). The polyurethanes are composed of 4,4'-methylenebis(phenyl isocyanate), 1,4-butanediol and an ε-polycaprolactone diol. The stoichiometric ratio of the isocyanate and hydroxyl groups is constant, but the polymer diol to total diol—varies from 0 to 100 %. We show the representative features of the morphology from phase separation to mixed phases, how this is related to the mechanical properties in the bulk and locally, at exposed free surfaces and at the nanoscale. We propose a morphological model considering the molecular structure, the length of hard segments, and the dimensions of both the soft and the hard phases, respectively. Understanding such structure–property relations is pivotal to establishing designer materials and controlling the performance of the final product to achieve optimal properties in polyurethane based medical devices.

Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS) that possesses a potential for minimizing the ratio C/S from above 3 in OPC down to 1, which significantly reduces the amount of CO$_2$ released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca concentration. Without the buffering role of Ca(OH)$_2$ the concentration of the dissolved species c(Ca$^{2+}$) and c(SiO$_4^{4-}$) and the corresponding pH must be controlled to ensure a reproducible reaction. Pure hCHS reacts isochemically with water, resulting in a C-S-H phase with the same chemical composition as a single hydration product, with a homogeneous distribution of the main elements Ca and Si throughout the sample. Here we study via nanoindentation the mechanical properties of two different types of hardened pastes made out of Celitement (C/S=1.28), with varying amounts of hCHS and variable water to cement ratio. We couple nanoindentation grids with Raman mappings to link the nanoscale mechanical properties to individual microstructural components, yielding in-depth insight into the mechanics of the mineralogical phases constituting the hardened cement paste. We show that we can identify in hardened Celitement paste both fresh C-S-H with varying density, and C-S-H from the raw material using their specific Raman spectra, while simultaneously measuring their mechanical properties. Albeit not suitable for phase identification, EDX measurements provide valuable information about the distribution of alkalis, thus further helping to understand the reaction pattern of hCHS., Comment: 32 pages, 8 figures

In the past 25 years the atomic force microscope (AFM) has become a true enabling platform in the life sciences opening entire novel avenues for structural and dynamic studies of biological systems. It enables visualization, probing and manipulation across the length scales, from single molecules to living cells in buffer solution under physiological conditions without the need for labeling or staining of the pecimen. Currently there is a great interest in AFM based high resolution echanical mapping techniques providing single molecule resolution of mechanical properties to derive molecular structure-function relationships. In this article selected examples of the recent literature are highlighted including own results obtained by peak force tapping AFM to elaborate the mechanical properties of lysozyme molecules adsorbed to mica substrates.

In the past 25 years the atomic force microscope (AFM) has become a true enabling platform in the life sciences opening entire novel avenues for structural and dynamic studies of biological systems. It enables visualization, probing and manipulation across the length scales, from single molecules to living cells in buffer solution under physiological conditions without the need for labeling or staining of the pecimen. Currently there is a great interest in AFM based high resolution echanical mapping techniques providing single molecule resolution of mechanical properties to derive molecular structure-function relationships. In this article selected examples of the recent literature are highlighted including own results obtained by peak force tapping AFM to elaborate the mechanical properties of lysozyme molecules adsorbed to mica substrates.

The micro phase separated nanoscale morphology of phase separated polyurethanes (PUs) was visualized by atomic force microscopy (AFM) height and phase imaging of smooth surfaces obtained by ultramicrotonomy. PUs were obtained from 4,4′-methylenbis (phenyl isocyanate) (MDI), 1,4-butanediol (BD) and poly(tetrahydrofurane) polyether polyol (PTHF). The segmented polyether PUs with varying stoichiometric ratio of the isocyanate and hydroxyl groups were prepared to investigate the effect of molar mass, as well as the type and number of end-groups on their morphology and mechanical performance. The PU samples studied show characteristic “fingerprint” AFM phase images. Novel dynamic imaging modes of AFM, including HarmoniX material mapping and Peak Force Tapping were used to assess the mechanical performance of phase separated polyurethanes quantitatively as a function of their molecular structure. The values of surface elastic moduli were determined with nanoscale resolution and were in excellent agreement for both AFM modes. While tensile testing provides a bulk average value for the elastic modulus of the elastomers, the novel AFM based elastic moduli mappings introduced enable the study of surface stiffness with nanoscale resolution in a quantitative way.