A simple stochastic model is developed to determine the pop-in load and maximum shear stress at pop-in in nanoindentation experiments conducted with spherical indenters that accounts for recent experimental observations of a dependence of these parameters on the indenter radius. The model incorporates two separate mechanisms: pop-in due to nucleation of dislocations in dislocation-free regions and pop-in by activation of preexisting dislocations. Two different types of randomness are used to model the stochastic behavior, which include randomness in the spatial location of the dislocations beneath the indenter and randomness in the orientation of the dislocations, i.e., randomness in the stress needed to activate them. In addition to correctly predicting the experimentally observed average maximum shear stress at pop-in, the model also correctly describes the scatter in pop-in loads and how it varies with indenter radius. Monte Carlo simulations are used to validate the model and visualize the scatter expected for a limited number of tests.

The S-doped BiOBr composite microspheres were successfully prepared through one-pot solvothermal method. The as-prepared samples exhibit higher photocatalytic activity for the degradation of Rhodamine B and phenol under visible light irradiation, attributed to the improvement of the photo-absorption property and the narrow band gap due to the dopants of S element. The higher efficiency for photodegradation of organic pollutant endows this material with a bright perspective in purification of waste water under visible-light irradiation.

Deformation mechanisms of a ZrTiAlV alloy with two ductile phases including a hexagonal close-packed (hcp) structure phase were investigated. A ZrTiAlV alloy was prepared via smelting, breakdown, forging, and suitable heat treatments. X-ray diffraction results show that the proposed ZrTiAlV alloy has two ductile phase structures, namely, hcp structure α-phase and bcc (body-centered cubic) structure β-phase. Scanning electron microscopy (SEM) results show that the plastic deformation of the examined ZrTiAlV alloy starts from the α-phase. Transmission electron microscopy (TEM) analysis shows that only dislocation slips can be found near fractured areas, and the main slip plane in the α-phase is the (0001) lattice plane. Both of the SEM and TEM results show the inexistence of deformation twin in the examined ZrTiAlV alloy including a hcp structure α-phase. Reasons for the abnormal deformation behavior of the hcp structure α-phase are also discussed.

The microstructures of the cast Mg–3Al–1Zn–xCe (x = 0, 0.2, 0.4, 0.8, and 1.2 wt%) alloys produced by twin-roll casting were observed to reveal the effect of cerium (Ce) on the Mg–3Al–1Zn (AZ31) alloy. Transmission electron microscopy (TEM) image of Al4Ce particles at the centers of grains was observed, and the crystallographic calculations between Al4Ce and α-Mg were examined on the basis of the edge-to-edge matching model. The results indicated that the addition of Ce effectively reduces the grain size of the cast AZ31 alloy produced by twin-roll casting. The finest grains with an average grain size of 55 μm are achieved at 0.4 wt% addition of Ce. TEM observation and good crystallographic matching between Al4Ce and α-Mg suggest that promotion of heterogeneous nucleation of α-Mg on Al4Ce particles formed in the melt is responsible for the grain refinement when adding Ce to the cast AZ31 alloy.

The structural properties, the formation enthalpies, and the mechanical properties of Co–Al compounds (CoAl, CoAl3, Co3Al, Co2Al5, Co2Al9, and Co4Al13) are studied by using Chen's lattice inversion embedded-atom method. The potential is transferable and therefore does well for studying different Co–Al compounds. The calculated lattice parameters and cohesive energies are consistent with the experimental and theoretical results. The formation enthalpies of all the Co–Al compounds are negative; therefore, the chemical bonding between Co and Al atoms increases the stability of compounds. According to elastic constant restrictions, all the six Co–Al compounds are mechanically stable. CoAl alloy with the larger moduli and lower Poisson's ratio is the hard or brittle phase. Moreover, CoAl3, Co3Al, Co2Al5, and Co2Al9 alloys are considered to be ductile materials, which have lower ratio of shear modulus to bulk modulus.

We present an experimental study on the epitaxy and orientational relationships of WO2 and NbO2 films on (0001) Al2O3, (111) MgAl2O4, and (111) MgO substrates, as well as WO2 on (111) SrTiO3. The higher symmetry of the substrate planes compared to the film planes leads to the formation of epitaxial structural variants, and they are related by the surface rotational symmetry elements of the substrates. WO2 and NbO2 crystallize in distorted versions of the rutile structure, and we discuss our findings in context of the rutile unit cell. Our results are applicable to other compounds that occur in (distorted) rutile structures. For the case of NbO2 thin films, we also demonstrate that they can be grown epitaxially on (10$\bar 1$2) and (10$\bar 1$0) Al2O3, lower symmetry surfaces; in these cases, surface symmetry does not induce the formation of epitaxial rotational variants, though domains related by glide symmetry are possible.

We present a simple and quick procedure for the one-pot synthesis of manganese oxides under a basic solvothermal condition in the presence of cationic surfactants acting as the template in a 2-butanol/water solution. Three-dimensional spinel-type MnO2 microspheres composed of small nanoparticles have been fabricated for the first time using our method. Their corresponding electrochemical performances in the applications of supercapacitor electrodes exhibit a good specific capacitance (SC) value of ∼190 F/g at 0.5 A/g and excellent SC retention and Coulombic efficiency of ∼100% and ∼95% after 1000 charge/discharge cycles at 1 A/g, respectively. This suggests its potential applications in energy storage devices. Further, we demonstrate that this solvothermal technique enables the morphological tuning of manganese oxides in various forms such as schists, rods, fibers, and nanoparticles. This work describes a rapid and low-cost technique to fabricate novel architectures of manganese oxides having the desired crystal phase, which will highly benefit various supercapacitor applications.

Multilayer thin films have been widely used for their enhanced mechanical and tribological properties relative to the monolayers of equivalent thickness. However, the mechanical properties of the each constituent layer are rarely investigated due to the difficulty in separating the effects of the constituent layers. An inverse analysis method to identify the elastic moduli of the constituent layers of multilayer films is developed by fitting the finite element calculations with indentation measurements within the framework of numerical optimization. The method is verified against typical monolayer, bilayer, and trilayer film structures both numerically and experimentally. Uniqueness and substrate-independence of the extracted moduli are ensured by the multiple loading–unloading cycles of the indentation tests. The method provides a feasible way to characterize the intrinsic mechanical properties of the constituent layers of multilayered thin films and further to explore the dominant mechanism for the enhancement of their mechanical properties.

Graphene, a single atomic sheet of sp2-bonded carbon atoms arranged in a honeycomb lattice, exhibits extraordinary electrical and mechanical properties, attracting much attention in both academia and industry. The preparation of high quality large-area graphene and the tuning of graphene electronic properties are important topics in this field. In this feature paper, we review our recent work on epitaxial graphene (EG) on SiC(0001). First, we introduce the bottom-up growth mechanism of the first few EG layers on SiC(0001), and the modification of graphene electronic properties by means of surface transfer doping with electron withdrawing materials (F4-TCNQ and MoO3). Next, we summarize the adsorption behaviors of organic (PTCDA, ClAlPc, and C60F48) and inorganic (bismuth) materials on EG/SiC(0001). Finally, as an example of tuning the electronic properties of graphene by reducing its dimensionality, we demonstrate the molecular self-assembly of atomically precise armchair graphene nanoribbons with varying widths and electronic structures.

A straightforward approach allowing three-dimensional (3D) visualization of subsurface deformation beneath nanoindents using reconstructed cross-sectional transmission electron microscopy (TEM) data is demonstrated. This approach relies on generating an array of nanoindents, extracting a thin (<200 nm) cross section using a focused ion beam (FIB) and imaging with a transmission electron microscope. By rotating the orientation of the FIB cross section with respect to the array of nanoindents at the optimal angle, it is guaranteed that a different section of each nanoindent's subsurface plastic zone is contained within the final cross section. Subsequently, TEM images corresponding to different sections are reconstructed into a 3D image of a representative nanoindentation plastic zone. This approach can be extended to any array of nominally identical features that can be patterned with regular spacing and included in a single FIB cross section. It was also found to significantly enhance the throughput of preparing routine site-specific TEM samples, even when 3D visualization is not necessary. In this article, the approach is applied to visualize the plastic zones beneath nanoindents in GaAs (001), for loads of 50–1000 µN.

Rubberlike insect cuticle is a light fibrous composite, which exhibits great deformability and long-range elasticity due to the presence of a large amount of the elastomeric protein resilin. The presence of resilin in specific locations in the insect body leads to the assumption that its main function is loss-free storage of energy. Rubberlike cuticle was identified, for the first time, in the femur base of the sand field cricket, Gryllus firmus, using fluorescence microscopy and various staining methods. Dynamic nanoindentation testing was then used to investigate the differences in the mechanical properties of rubberlike cuticle between males and females and wing morphs of this species. Significant changes in storage, loss moduli, and resilience were captured between female wing morphs. The results provide insight into the structure–function relations associated with the properties of insect joints from different morphs and genders.

Fe3O4@TiO2 magnetic photocatalysts containing sub-10-nm TiO2 nanocrystals with two different morphologies (nanoparticles and nanorods) were prepared via a facile straight dipping process. A series of comparative experiments on organic pollutant degradation demonstrated that Fe3O4@TiO2 nanorods show superior activity and faster degradation rates than Fe3O4@TiO2 nanoparticles. Combined with the study of high resolution transmission electron microscopy, crystal models are given to analyze the morphology effect of TiO2 nanocrystals on their photocatalytic activities for organic degradation. TiO2 nanorods with more (100) crystal planes, which have relatively higher surface energy and relative higher density of Ti atoms, showed a higher activity than that of TiO2 nanoparticles. Furthermore, both Fe3O4@TiO2 nanorods and Fe3O4@TiO2 nanoparticles show better photocatalytic activities than several comparison Fe3O4@TiO2 samples due to the strong size effect arising from the tiny size of TiO2 nanorods and nanoparticles. These magnetic photocatalysts also show advantages in separation and recycling utilization.