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Crystalline Au nanoparticles embedded in epitaxially grown SrTiO3 layers were prepared by an annealing and coating procedure of Au seed layers on SrTiO3 (STO) substrates. X-ray diffraction and transmission electron microscopy measurements were performed to investigate the size, shape, and deformation of the particles and their crystal orientation. The shape and size of the crystalline Au nanoparticles can be tuned by controlling the Au seed layer thickness and single crystalline elliptically shaped Au nanoparticles have been generated. Furthermore, the orientation of the surrounding SrTiO3 matrix changes significantly from homoepitaxially grown (001) to secondary (111) and (011) orientations for Au seed layers that are thicker than 4 nm. This is of great interest for modifying the electrical properties of SrTiO3 layers, whereas the anisotropically shaped crystalline particles are relevant for optical applications, due to localized surface plasmon resonances. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: We fabricate multi-cellular aggregates of human gingival fibroblasts (hGFs) using a novel in vivo method that omits supportive flexible substrates. On the basis of the multi-cellular aggregates, constructive and destructive effects of mechanical stimulation are investigated. Methods: hGFs were seeded onto aligned glass slides (one fixed, one mobile) with an initial gap <30μm between their connecting edges. After the cells adhere, one of the glass slides is displaced using high precision threads and a piezoelectric element, widening the gap gradually. Results: After several days of gradually widening the gap, multiple multi-cellular hGF aggregates formed, bridging the gap between the glass slides. The effects of discrete displacement events on previously established multi-cellular aggregates ranged from considerable growth and consolidation to collapse and disintegration. A quantitative criterion for assessing the probability for collapse/disintegration of hGF multi-cellular aggregates based on evaluating the meniscus curvature at the free edges before and after displacement is presented and discussed. The curvature is suggested as a representative parameter to characterize the mechanical condition of multi-cellular aggregates, as it is affected by adhesion of cells to the glass slides, cohesion inside the multi-cellular aggregate and the external mechanical load generated by the displacement of the glass slides. Significance: The presented results clarify the potential and limitations of using mechanical stimulation for initiating and controlling regeneration of (gingival) tissue. Further potential applications include usage as biological substrate for co-culturing hierarchical tissue with multiple cell types (e.g. for vessels) and bio-membranes for filters (e.g. in microfluidics). [Copyright &y& Elsevier]

Abstract: Acicular structures on NiTi are often interpreted as martensite or martensitic surface relief. These structures are identified as artifacts and form during etching using hydrofluoric acid based etching solutions. Their origin is clarified in the present work. After standard metallographic preparation, the acicular structures cannot be distinguished from bulk material by standard analysis, e.g. energy dispersive X-ray analysis and Auger electron spectroscopy. By investigating samples after etching, but previous to cleaning with water, rod-like crystals on the NiTi surface were detected. The crystals are identified as NiTiF6⋅6H2O by X-ray diffraction. During etching, the crystals develop on the surface and locally prevent contact of etching solution and NiTi base material. Further etching solely removes NiTi at adjacent uncovered areas. During the final cleaning with water the crystals completely dissolve and the surface relief with a shape according to that of the dissolved crystals remains. The surface relief does not represent the bulk microstructure. [ABSTRACT FROM AUTHOR]

Thin medical grade Ni-Ti wires, pseudo-elastic at ambient temperature, were annealed to set the final shape and the properties of the material. In order to investigate the influence of the annealing, high-resolution bend and free recovery tests were carried out. With the newly constructed device, the reverse deformation (free recovery) of the bent wires was recorded in detail. Wire segments with a weight of <1 mg are sufficient to attain reliable results. The high resolution of the testing device is based on a precise temperature control and a video monitoring system equipped with a microscope lens. In addition to the determination of the transformation temperatures, which is possible with common bend and free recovery tests, the high resolution allows for the identification and quantification of the reverse deformation stages attributed to the martensite-to-austenite transformation and the occurrence of the R-phase. The variations of the transformation properties attained by evaluating the different types of reverse-deformation curves are presented and discussed. [ABSTRACT FROM AUTHOR]

Short-time annealing is commonly applied as shape setting or passivation treatment on Ni–Ti wire. Its influence on the austenite finish (A f) temperature and the martensite–austenite transformation characteristics has been investigated in detail using a newly constructed device implementing a bend and free recovery test with high resolution. Short-time annealing at 450–600°C can shift the A f temperature from ΔA f =+25 to −15K and can render the phase transformation either one-stage or two-stage. [Copyright &y& Elsevier]

In the present study, the thermal cycling stability of mirrors made of silicon particle reinforced aluminum compounds, containing an amount of 42 ± 2 wt.% silicon particles, is investigated with respect to thermal loading. The compound is processed by single-point diamond turning to optical mirrors that were subsequently thermally cycled in a temperature range between 40 °C to −60 °C and between 20 °C and −196 °C, respectively. The residual shape change of the optical surface was analyzed using Fizeau interferometry at room temperature. The change of shape deviation of the mirrors is compared with dilatometric studies of cylinders using the same temperature regime. Due to different coefficients of thermal expansion of the two constituents of the compound, thermal mismatch stresses in the ductile aluminum matrix and the brittle silicon particles are induced by the investigated thermal loads. The plasticity that occurs causes the formation of dislocations and stacking faults as substantiated by Transmission Electron Microscopy. It could be shown that the silicon particles lead to the cold working process of the reinforced aluminum matrix upon thermal cycling. By using interferometry, a higher dimensional stability of mirrors made of silicon particle reinforced aluminum due to thermal loads is demonstrated. [ABSTRACT FROM AUTHOR]

Embedding quantum dots into porous matrices is a very beneficial approach for generating hybrid nanostructures with unique properties. In this contribution we explore strategies to dope nanoporous SiO2 thin films made by atomic layer deposition and selective wet chemical etching with precise control over pore size with CdSe quantum dots. Two distinct strategies were employed for quantum dot deposition: in situ growth of CdSe nanocrystals within the porous matrix via successive ionic layer adsorption reaction, and infiltration of pre-synthesized quantum dots. To address the impact of pore size, layers with 10 nm and 30 nm maximum pore diameter were used as the matrix. Our results show that though small pores are potentially accessible for the in situ approach, this strategy lacks controllability over the nanocrystal quality and size distribution. To dope layers with high-quality quantum dots with well-defined size distribution and optical properties, infiltration of preformed quantum dots is much more promising. It was observed that due to higher pore volume, 30 nm porous silica shows higher loading after treatment than the 10 nm porous silica matrix. This can be related to a better accessibility of the pores with higher pore size. The amount of infiltrated quantum dots can be influenced via drop-casting of additional solvents on a pre-drop-casted porous matrix as well as via varying the soaking time of a porous matrix in a quantum dot solution. Luminescent quantum dots deposited via this strategy keep their luminescent properties, and the resulting thin films with immobilized quantum dots are suited for integration into optoelectronic devices. [ABSTRACT FROM AUTHOR]

The first oxide crystals formed during the early oxidation stages are considered to be the critical stage for the corrosion resistance of metallic materials against oxidants. The corrosion resistance of Cr-containing alloys is generally linked to Cr-rich oxide layers; however, their applicative performance varies remarkably. Classical models addressing the formation of these layers fail to account for the associated dynamics. We present evidence that Cr-containing Fe-, Co-, Ni-base and high-entropy alloys exhibit a parallel phenomenon during the initial transient stage: two-layered, multicompositional oxide grains with Cr always occupying the inner layer adjacent to the bulk. We propose that oxide growth occurs at a single location which allows to consistently incorporate all presented results. Oxide layer growth occurs inside the oxide grains at the transition to the Cr enrichment, independent of the initial oxide crystal structure. A potential multi-scale model for oxidation requires implementing the presented results which emphasizes the dominance of kinetic contributions during the early stages of oxidation.

In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract A new concept of mechano-responsive colour-change is introduced in the present work that allows for turning flexible materials into an optical mechano-sensitive sensor. For this purpose diffraction gratings based on laser-induced periodic surface structures (LIPSS) are produced on ductile stainless steel surfaces (X2CrNiMo17–12–2) using a femtosecond laser (fs-laser). When the material is deformed, the increase of the lattice spacing in the diffraction grating leads to a mechano-responsive change of the initial structural colour in the direction of longer wavelengths. With increasing plastic deformation of the metal, the formation of tilted and twisted slip bands leads to a disappearance of the structural colours before the material fails. Using metal masters, the LIPSS can be transferred to elastomers by replica casting. For elastomers produced by replica casting, the mechano-responsive colour change is reversible. The mechanically induced colour change of LIPSS is of particular interest for the development of novel switches, safety devices, strain gauges, sensors, hazard classification and early detection of material failure. [ABSTRACT FROM AUTHOR]

Abstract Ion irradiation can cause burrowing of nanoparticles in substrates, strongly depending on the material properties and irradiation parameters. In this study, it is demonstrated that the sinking process can be accomplished with ion irradiation of cube‐shaped Ag nanoparticles on top of silicon; how ion channeling affects the sinking rate; and underline the importance of the amorphous state of the substrate upon ion irradiation. Based on these experimental findings, the sinking process is described as being driven by capillary forces enabled by ion‐induced plastic flow of the substrate.

The martensitic microstructure decides on the functional properties of shape memory alloys. However, for the most commonly used alloy, NiTi, it is still unclear how its microstructure is built up because the analysis is hampered by grain boundaries of polycrystalline samples. Here, we eliminate grain boundaries by using epitaxially grown films in (111)B2 orientation. By combining scale-bridging microscopy with integral inverse pole figures, we solve the puzzle of the hierarchical martensitic microstructure. We identify two martensite clusters as building blocks and three kinds of twin boundaries. Nesting them at different length scales explains why habit plane variants with ⟨011⟩B19' twin boundaries and {942} habit planes are dominant; but also some incompatible interfaces occur. Though the observed hierarchical microstructure agrees with the phenomenological theory of martensite, the transformation path decides which microstructure forms. The combination of local and global measurements with theory allows solving the scale bridging 3D puzzle of the martensitic microstructure in NiTi exemplarily for epitaxial films.

[Display omitted] • LIPSS were fabricated on different stainless steels using fs-lasers. • All stainless steels exhibit regular LIPSS with similar geometrical properties. • A laser-induced oxide is formed with a two-layered structure. • Ageing depends on extent and chemical composition of superimposed nanoparticles. • Repeated water contact leads to less pronounced ageing. The time-dependent wetting behavior was investigated for commercially available austenitic, martensitic and duplex stainless steel surfaces after femtosecond (fs) laser irradiation. For this purpose, highly regular LIPSS with almost identical geometric properties were generated on the stainless steels in an air environment by near-infrared fs-laser processing (λ = 1025 nm, τ = 300 fs, f rep = 100 kHz, v = 0.67 m/s, Δx = 6 μm, F = 1.1 J/cm2) and compared to the polished initial surfaces as reference. The wetting with distilled water was evaluated as a function of aging time by contact angle measurements using the sessile drop method. The laser-induced morphological, topographical and chemical alteration of the surface was characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, glow-discharge optical emission spectroscopy as well as high-resolution imaging and scanning transmission electron microscopy. Despite an almost identical LIPSS-based topography alteration, the stainless steels revealed very different ageing behavior. For permanently used samples, it was shown that the ageing effect is less pronounced than for samples that were stored in ambient air following fs-laser irradiation until the wetting measurement. The results obtained make an important contribution to understanding and controlling the ageing effect of metal surfaces and thus facilitate the transfer of LIPSS-based functional surface engineering and design to industrial processes. [ABSTRACT FROM AUTHOR]

In this study, the Ti-6Al-4V powder material for additive manufacturing was mixed with amorphous carbon and processed by powder bed fusion using a laser beam. The specimens were subjected to mechanical and microstructural analyses to investigate the impact of the organic constituent that may become introduced unintentionally as an impurity along the powder handling chain. It is documented that hardness and tensile strength increase with increasing carbon content up to 0.2 wt.%. Above this carbon concentration, extensive crack formation in the samples prevents successful procession.

Abstract: The present study explored the avenues for the improvement of native Nitinol surfaces for implantation obtained using traditional procedures such as mechanical polishing, chemical etching, electropolishing and heat treatments for a better understanding of their electrochemical behavior and associated surface stability, conductivity, reactivity and biological responses. The corrosion resistance (cyclic potential polarization, open circuit potential and polarization resistance) of Nitinol disc and wire samples were evaluated for various surface states in strain-free and strained wire conditions. The surface response to tension strain was studied in situ. Surface chemistry and structure were explored using XPS and Auger spectroscopy and photoelectrochemical methods, respectively. It was found that the polarization resistance of the Nitinol surfaces varied in a range from 100kΩ to 10MΩcm2 and the open circuit potentials from −440mV to −55mV. The surfaces prepared in chemical solutions showed consistent corrosion resistance in strain-free and strained states, but mechanically polished and heat treated samples were prone to pitting. Nitinol surface oxides are semiconductors with the band gaps of either 3.0eV (rutile) or 3.4eV (amorphous). The conductivity of semiconducting Nitinol surfaces relevant to their biological performances is discussed in terms of oxide stoichiometry and variable Ni content. Such biological characteristics of Nitinol surfaces as Ni release, fibrinogen adsorption and platelets behavior are re-examined based on the analysis of the results of the present study. [Copyright &y& Elsevier]