The locally occurring mechanisms of hydrogen embrittlement significantly influence the fatigue behavior of a material, which was shown in previous research on two different AISI 300-series austenitic stainless steels with different austenite stabilities. In this preliminary work, an enhanced fatigue crack growth as well as changes in crack initiation sites and morphology caused by hydrogen were observed. To further analyze the results obtained in this previous research, in the present work the local cyclic deformation behavior of the material volume was analyzed by using cyclic indentation testing. Moreover, these results were correlated to the local dislocation structures obtained with transmission electron microscopy (TEM) in the vicinity of fatigue cracks. The cyclic indentation tests show a decreased cyclic hardening potential as well as an increased dislocation mobility for the conditions precharged with hydrogen, which correlates to the TEM analysis, revealing courser dislocation cells in the vicinity of the fatigue crack tip. Consequently, the presented results indicate that the hydrogen enhanced localized plasticity (HELP) mechanism leads to accelerated crack growth and change in crack morphology for the materials investigated. In summary, the cyclic indentation tests show a high potential for an analysis of the effects of hydrogen on the local cyclic deformation behavior.

The design of the coating architecture plays an important role in improving the mechanical performance of the hard coating. In present work, several novel multilayered diamond/beta-SiC composite architectures were deposited on cemented tungsten carbide substrates by hot filament chemical vapor deposition. Field emission scanning electron microscope (FE-SEM) observation reveals periodic multilayered configurations with diamond/beta-SiC composite layers and microcrystalline diamond (MCD) or nanocrystalline diamond (NCD) layers. Moreover, Rockwell indentation, scratch and nano-indentation tests indicate that multilayered diamond/beta-SiC composite and MCD coating possess not only good adhesion (52.9 +/- 0.5 N) and crack propagation resistance, but also high hardness (83.6 +/- 3.5 GPa) and modulus (856.1 +/- 87.5 GPa) among all as-deposited coatings. For this configuration, the hardness of the coating is inherited from the MCD layer, while the low residual stress, enhanced adhesion and crack propagation resistance are due to the composite coating and multilayer architecture. Thus, the mechanical properties of diamond coating are improved by the innovative diamond/beta-SiC composite multilayer, which provides a potential approach for high-performance diamond coated cutting tools. (c) 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The correlation between the choice of reference material and model utilized in determining fracture toughness from indentation-induced radial cracks was critically investigated with six commonly used reference materials. Initially, the empirical constants in Anstis's and Laugier's equations were calculated, compared and analyzed. According to the values of the constants, the reference materials were categorized into three groups. This classification was further verified by evaluating the corresponding constants of 13 additional equations. To account for the classification, FIB technique was employed to examine the crack morphology in the reference materials - Si (100) features an almost Half-penny-shaped crack while the cracks in SiC (0001) display nearly as a rectangle, both far from the assumptions employed by the models. Subsequently, an improved and more reliable procedure to determine fracture toughness is proposed. Finally, with this procedure, the fracture toughness of a diamond/SiC composite film is determined to be 11.1 +/- 1.1 MPa m(1/2).

Despite its relevance, fatigue is a phenomenon hardly investigated on the micro- and nano-scale. Recent developments in nanoindentation instrumentation have opened up new opportunities to study the behavior of materials dynamically probed on a small scale. Based on the experimental work on a single crystal copper sample as well as on polycrystalline copper, we show the possibility to sample fatigue information on the nanoscale, which corresponds well with existing literature. Consequently, the method introduced here provides a unique opportunity to explore the fatigue behavior and associated phenomena of surfaces or materials available only in small volumes.

A novel way was derived in this work to quantitatively determine the mechanical properties of thin films grown on silicon substrates from the initial-grown surface using nanoindentation. The as-deposited surface of the films was firstly glued to steel and subsequently, the silicon substrate was etched away in a hot potassium hydroxide (KOH) solution. Steel served as supporting material after the removal of the substrate. This procedure enables the exposure of the initial-grown surface of the film with a surface roughness close to the one of the silicon substrate (around 1 nm), which typically is significantly lower than the as-deposited surface (usually 20 to 30 nm). Carrying out indents on the initial-grown side allows us to acquire reliable results by avoiding any artifact due to surface roughness. Measurements were performed on nanocrystalline SiC and diamond films to confirm the validity of this method. Finally, a 13 mu m thick diamond/SiC composite film composed of nanocrystalline SiC and nanocrystalline diamond was prepared and characterized by applying this method. The composite film exhibits a hardness of 49.8 +/- 2.1 GPa, an elastic modulus of 598 +/- 25 GPa, which is directly comparable to the value gained by the surface acoustic wave (SAW) method. Moreover, the hardness and elastic modulus of the composite film both accord well with the values predicted from the mechanical properties of the individual phases. Therefore, mechanical property determination from initial-grown surface is a promising approach for a variety of hard brittle thin film systems with high surface roughness.

This study addresses the investigation of the nature of defects generated during the anodization of aluminum using oxalic acid electrolyte and their influence on the structure and properties of anodic aluminum oxide films (AAO). AAO films, which are obtained by anodization in oxalic acid, and their powdered samples are subjected to thermal annealing at temperatures up to 1050 °C and are subsequently investigated by 27Al solid-state nuclear magnetic resonance (NMR), electron spin resonance (ESR), powder X-ray diffraction, scanning electron microscopy (SEM), and nanoindentation. By NMR and continuous wave ESR, it is found that the anodization obtained in oxalic acid not only produces amorphous porous alumina, but also gives rise to bulk H defects and unpaired electrons originating from the decomposition of the oxalate ions. Paramagnetic defects are healed by annealing at temperatures of ∼800 °C in air, possibly by an oxidative conversion to CO2 with the oxygen in air, while the removal of the H defects requ...

As a potential material for biosensing applications, gallium nitride (GaN) films have attracted remarkable attention. In order to construct GaN biosensors, a corresponding immobilization of biolinkers is of great importance in order to render a surface bioactive. In this work, two kinds of n-alkenes with different carbon chain lengths, namely allylamine protected with trifluoroacetamide (TFAAA) and 10-aminodec-1-ene protected with trifluoroacetamide (TFAAD), were used to photochemically functionalize single crystalline GaN films. The successful linkage of both TFAAA and TFAAD to the GaN films is confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurement. With increased UV illumination time, the intensity of the secondary ions corresponding to the linker molecules initially increases and subsequently decreases in both cases. Based on the SIMS measurements, the maximum coverage of TFAAA is achieved after 14 h of UV illumination, while only 2 h is required in the case of TFAAD to reach the situation of a fully covered GaN surface. This finding leads to the conclusion that the reaction rate of TFAAD is significantly higher compared to TFAAA. Measurements by atomic force microscopy (AFM) indicate that the coverage of GaN films by a TFAAA layer leads to an increased surface roughness. The atomic terraces, which are clearly observable for the pristine GaN films, disappear once the surface is fully covered by a TFAAA layer. Such TFAAA layers will feature a homogeneous surface topography even for reaction times of 24 h. In contrast to this, TFAAD shows strong cross-polymerization on the surface, this is confirmed by optical microscopy. These results demonstrate that TFAAA is a more suitable candidate as biolinker in context of the GaN surfaces due to its improved controllability.

In this work, we demonstrate a new strategy to create WZ-GaN/3C-SiC heterostructure nanowires, which feature controllable morphologies. The latter is realized by exploiting the stacking faults in 3C-SiC as preferential nucleation sites for the growth of WZ-GaN. Initially, cubic SiC nanowires with an average diameter of ∼100 nm, which display periodic stacking fault sections, are synthesized in a chemical vapor deposition (CVD) process to serve as the core of the heterostructure. Subsequently, hexagonal wurtzite-type GaN shells with different shapes are grown on the surface of 3C-SiC wire core. In this context, it is possible to obtain two types of WZ-GaN/3C-SiC heterostructure nanowires by means of carefully controlling the corresponding CVD reactions. Here, the stacking faults, initially formed in 3C-SiC nanowires, play a key role in guiding the epitaxial growth of WZ-GaN as they represent surface areas of the 3C-SiC nanowires that feature a higher surface energy. A dedicated structural analysis of the interfacial region by means of high-resolution transmission electron microscopy (HRTEM) revealed that the disordering of the atom arrangements in the SiC defect area promotes a lattice-matching with respect to the WZ-GaN phase, which results in a preferential nucleation. All WZ-GaN crystal domains exhibit an epitaxial growth on 3C-SiC featuring a crystallographic relationship of [12̅10](WZ-GaN) //[011̅](3C-SiC), (0001)(WZ-GaN)//(111)(3C-SiC), and d(WZ-GaN(0001)) ≈ 2d(3C-SiC(111)). The approach to utilize structural defects of a nanowire core to induce a preferential nucleation of foreign shells generally opens up a number of opportunities for the epitaxial growth of a wide range of semiconductor nanostructures which are otherwise impossible to acquire. Consequently, this concept possesses tremendous potential for the applications of semiconductor heterostructures in various fields such as optics, electrics, electronics, and photocatalysis for energy harvesting and environment processing.

Completely hard amorphous Si–C–N films were prepared by electron cyclotron resonance microwave plasma assisted chemical vapor deposition and characterized by atomic force microscopy and nanoindentation. In contrast to common findings of sink-in effects for hard films on soft substrates, anomalous pile-up effects were observed in such kinds of hard films. Inherently different from the traditional measurements of hardness, which are taken from the residual impression after unloading, load–displacement curves from nanoindentation measurements reveal the feature of a large elastic deformation based on the evaluation of the total work and the elastic work. The reduced modulus shows an approximately linear relationship with the measured hardness, while no linear relation can be extracted for the energy dissipation and the ratio of hardness and Young modulus, H/E. Mechanical behaviors of Si–C–N films measured by the Oliver and Pharr method match well with the fitted data from the modified King's model within the investigated range of the indentation depth.

Bandgap engineering of semiconductor nanostructures is of significant importance either for the optical property tailoring or for the integration of functional optoelectronic devices. Here, an efficient way to control the bandgap and emission wavelength is reported for a binary compound semiconductor through alloying with another binary compound. Taking GaP‐ZnSe system as an example, the bandgap of quaternary GaP‐ZnSe solid‐solution nano­wires can be selectively tailored in the range of 1.95–2.2 eV by controlling the solubility of ZnSe dopants in GaP host. High‐resolution transmission electron microscopy measurement and chemical analyses using an X‐ray energy dispersive spectrometer (EDS) demonstrate the solid‐solution feature of GaP‐ZnSe semiconductor alloy, while X‐ray photoelectron spectroscopy (XPS) characterization verifies the formation of some new chemical bonds corresponding to Zn‐P and Ga‐S bonds in GaP‐ZnSe nanowires. The strategy to tailor the optoelectronic property of semiconductor nanostructures through the solid‐solution of two different binary compounds represents a general routine to the property modification of all pseudobinary systems and will open more opportunity for their applications in electronics, optics and optoelectronics.

GaN nanowires with homoepitaxial decorated GaN nanoparticles on their surface along the radial direction have been synthesized by means of a chemical vapor deposition method. The growth of GaN nanowires is catalyzed by Au particles via the vaporliquidsolid (VLS) mechanism. Screw dislocations are generated along the radial direction of the nanowires under slight Zn doping. In contrast to the metal-catalyst-assisted VLS growth, GaN nanoparticles are found to prefer to nucleate and grow at these dislocation sites. High-resolution transmission electron microscopy (HRTEM) analysis demonstrates that the GaN nanoparticles possess two types of epitaxial orientation with respect to the corresponding GaN nanowire: (I) [(1) over bar2 (1) over bar0](np)//[(1) over bar2 (1) over bar0](nw), (0001)(np)//(0001)(nw); (II) [(1) over bar2 (1) over bar3](np)//[1 (2) over bar 10](nw), (10 (1) over bar0)(np)//(10 (1) over bar0)(nw). An increased Ga signal in the energy-dispersive spectroscopy (EDS) profile lines of the nanowires suggests GaN nanoparticle growth at the edge surface of the wires. All the crystallographic results confirm the importance of the dislocations with respect to the homoepitaxial growth of the GaN nanoparticles. Here, screw dislocations situated on the (0001) plane provide the self-step source to enable nucleation of the GaN nanoparticles.

A plethora of applications in pharmacy, cosmetics, food industry and other areas are directly linked to the research fields of particle technology and contact mechanics. Here, a typical particle ensemble features particle sizes ranging from the nanometer up to the micrometer regime. In this context we introduce a nanoindentation based approach capable of probing mechanical interaction of micron-sized particles. Basically, the concept of the colloid probe technique, which is well established in the AFM community, is transferred to a nanoindenter. In particular, this setup allows addressing limitations, which are typically associated with AFM based techniques, such as particle weight and accessible load regime. Additionally, we will show the versatility of this approach by presenting simple experimental paths capable of probing sliding, rolling and torsional friction. The potential of such setting is shown by studying rolling friction of silica microspheres featuring radii of about 2.5µm, 10µm, 25 and 50µm in contact with various substrates, respectively. Substrates utilized within the framework of this study are Si surfaces featuring various roughness as well as flat gold films (300nm film thickness). Key aspects of this work include the influence of surface roughness, adhesion force, humidity and the elastic/plastic transition on the rolling contact of the corresponding particles.

The contact mechanics of individual, very small particles with other particles and walls is studied using a nanoindenter setup that allows normal and lateral displacement control and measurement of the respective forces. The sliding, rolling and torsional forces and torques are tested with borosilicate microspheres, featuring radii of about 10$μ$m. The contacts are with flat silicon substrates of different roughness for pure sliding and rolling and with silicon based, ion-beam crafted rail systems for combined rolling and torsion. The experimental results are discussed and compared to various analytical predictions and contact models, allowing for two concurrent interpretations of the effects of surface roughness, plasticity and adhesion. This enables us to determine both rolling and torsion friction coefficients together with their associated length scales. Interestingly, even though normal contacts behave elastically (Hertzian), all other modes of motion display effects due to surface roughness and consequent plastic deformation. The influence of adhesion is interpreted in the framework of different models and is very different for different degrees of freedom, being largest for rolling.

Most carbon nanofibers (CNFs) are grown at temperatures higher than 700°C with a chemical vapor deposition (CVD) process and their growths are explained using the vapor–liquid–solid (VLS) mechanism. Herein we report the realization of low temperature growth of CNFs and the interpretation of their growth with a vapor–facet–solid (VFS) mechanism. CNFs were synthesized via a thermal CVD process at the temperature as low as 350°C and characterized using elemental analysis, gas chromatography–mass spectrometry, X-ray photoelectron spectroscopy, and Raman spectroscopy. They feature unique structures of partly ordered discontinuous and hydrogen rich polymer sheets with a diameters of 0.5–1.5nm. Based on a trimerization reaction occurring on the Fe catalyst surface, their initial growth step is the formation of six-membered rings from the source gas (i.e. C2H2). Subsequently, these rings act as structural unit and construct various larger planar molecules. Due to catalytic difference of the crystalline faces for a given Fe catalyst particle, a concentration gradient of hydrocarbon molecule introduces simultaneously. This gradient drives the diffusion of hydrocarbon molecule from the Fe(110) to the Fe(100) face, leading to the formation of disordered hydrogen-rich polymer structures. Highly graphitic CNFs can be obtained simply by annealing those polymer structures at higher temperatures. This growth mode proposed is workable whenever transition metal catalyzed nanostructures are synthesized by a thermal CVD process at low temperatures.

Smooth spherical micro glass particles are the reference particle system to demonstrate the correlation between single contacts and the particle packing properties. To investigate the influence of the van der Waals attraction force, the particles will be functionalized to obtain hydrophilic and hydrophobic surfaces. To remove the impurities and hydrophilize the particle surfaces a very strong oxidizing agent is used—the peroxymonosulfuric acid. In order to generate a hydrophobic glass surface, the process of silanization is applied. The comprehensive force displacement model of elastic-plastic and adhesive contacts are discussed. Therefore the model ‘stiff particles with soft contacts’ is used to quantify and compare the elastic-plastic contact properties. In this work, the particle contacts are experimentally investigated by means of atomic force microscopy (AFM), nanoindentation and shear tests. While the AFM and nanoindenter measurements are aimed to analyse single particle contacts, shear tests are used for particle packing studies. The fundamental challenge and question is addressed and answered: How do the micro mechanical material properties change when the glass surfaces are functionalized? Do we obtain the same behavior for the used micro glass particles when we compare the different methods?

An approximately linear relation between reduced modulus (Er) and stiffness (S) was observed based on the characterization of completely amorphous Si–C–N hard films by means of nanoindentation. This linear relation was verified by a series of amorphous Si–C–N films prepared under different experimental conditions. Furthermore the linear relation can be extended to amorphous Si–B–C–N film systems. This finding provides one possible way to evaluate the hardness and reduced modulus of a material without involving the contact area.

In order to understand the contact phenomena of micron-sized particles, which have a tremendous impact on a variety of applications in industry and technology, direct access to the loads as well as the displacements accompanying such contacts are mandatory. Typical particle ensembles show a size variation ranging from the nanometer to the tenths of micron scale. Especially the contact behavior of particles featuring radii of several up to several tenths of microns is scarcely studied as these particles are typically too large for atomic force microscopy (AFM) based approaches and too small for conventional macroscopic testing setups. In this work a nanoindenter based approach is introduced to gain insight into the contact mechanics of micron-sized glass beads sliding on rough silicon surfaces at various constant low normal loads. The results are analyzed by a simple modified Coulomb friction law, as well as Hertz, JKR, and DMT contact theory.