Group III nitrides are promising materials for light emitting diodes (LEDs). The occurrence of structural defects strongly affects the efficiency of these LEDs. We investigate the optical properties of basal plane stacking faults (BFSs), and the assignment of specific spectral features to distinct defect types by direct correlation of localized emission bands measured by cathodoluminescence in a scanning electron microscope with defects found in high resolution (scanning) transmission electron microscopy and electron beam induced current at identical sample spots. Thus, we are able to model the electronic structure of BSFs addressing I1, I2, and E type BSFs in GaN and AlGaN with low Al content. We find hints that BSFs in semipolar AlGaN layers cause local changes of the Al content, which strongly affects the usability of AlGaN as an electron blocking layer in nitride based LEDs.

Nanocrystalline ceramics offer interesting and useful physical properties attributed to their inherent large volume fraction of grain boundaries. At the same time, these materials are highly unstable, being subjected to severe coarsening when exposed at moderate to high temperatures, limiting operating temperatures and disabling processing conditions. In this work, we designed highly stable nanocrystalline yttria stabilized zirconia (YSZ) by targeting a decrease of average grain boundary (GB) energy, affecting both driving force for growth and mobility of the boundaries. The design was based on fundamental equations governing thermodynamics of nanocrystals, and enabled the selection of lanthanum as an effective dopant which segregates to grain boundaries and lowers the average energy of YSZ boundaries to half. While this would be already responsible for significant coarsening reduction, we further experimentally demonstrate that the GB energy decreases continuously during grain growth caused by the enrichment of boundaries with dopant, enhancing further the stability of the boundaries. The designed composition showed impressive resistance to grain growth at 1100 °C as compared to the undoped YSZ and opens the perspective for similar design in other ceramics.

We investigate the structural evolution of Er/Si nanoclusters obtained in co-implanted fused silica upon annealing via Raman spectroscopy and transmission electron microscopy. The effect of annealing temperature (900–1200 °C) on the nature and the relative fraction of the formed amorphous-Si, Si nanocrystals (Si-nc), and amorphous Er nanoparticles (Er-np) was determined in this ternary Er–Si–O system, showing a change of growth regime above 1100 °C due to the formation of mixed Er/O/Si aggregates. We observe that the nucleation and growth of amorphous Er-np and Si-nc are mutually affected. The 2-fold increase in the size of Er-np when no excess Si+ is present in the matrix indicates that the formation of Si-nc in the proximity of Er clusters hinders Er diffusivity above 1100 °C. This finding shows the importance of nanoclustering for improving the thermal stability of Er-doped silica systems.

Nanoparticle-sized powders have seen more and more use in many of today's applications. As particle size decreases, many properties change including the ability to embed the small particles in liquids and other media. With decreasing size, however, surface energy becomes more important and can dictate the final shape of the particle. In applications based on polar molecules attaching to the nanoparticle surface, the surface morphology can become a key design parameter. A nucleation and growth model has been constructed for truncated body-centered cubic derivative materials, along with an update to previously published work on face-centered cubic materials. The model shows that for (110)- and (111)-truncations of a cube with a specified surface energy for each surface, the critical nuclei and equilibrium growth shapes are the same, supporting the theory of self-similar growth that had only been mentioned previously, but never proven. In this analysis, saddle points play an important role in determining the critical nuclei for comparison with the equilibrium growth shapes.

The electrophysical and structural properties of InAlAs/InGaAs/InAlAs quantum wells (QWs) with thin InAs inserts were investigated by means of Hall effect measurements and scanning transmission electron microscopy. The analyzed heterostructures are nearly the same ones using for high electron mobility transistors manufacturing except for heavily doped contact top layer. The increase of the electron mobility and concentration in the heterostructures with thin InAs layers in the center of the InGaAs QW as compared with the uniform QW was found and this effect strongly depended on the technological conditions during growth of the InAs inserts. The dependence of the InAs insert structural quality and heterointerface width on the As4 beam equivalent pressure PAs was revealed. The decreased PAs is required for obtaining uniform and smooth InAs inserts as opposed to higher PAs resulting in the interface spreading and lateral composition inhomogeneity of the InAs insert.

In the present article, the intermixing and clustering of U/Nd, O, and vacancies were studied by both laboratory and synchrotron-based x-ray diffraction in U1−yNdyO2−x alloys. It was found that an increased holding time at the high experimental temperature during initial alloy preparation results in a lower disorder of the Nd distribution in the alloys. Adjustment of the oxygen concentration in the U1−yNdyO2−x alloys with different Nd concentrations was accompanied by the formation of vacancies on the oxygen sublattice and a nanocrystalline component. The lattice parameters in the U1−yNdyO2−x alloys were also found to deviate significantly from Vegard's law when the Nd concentration was high (53%) and decreased with increasing oxygen concentration. Such changes indicate the formation of large vacancy concentrations during oxygen adjustment at these high temperatures. The change in the vacancy concentration after the oxygen adjustment was estimated relative to Nd concentration and oxygen stoichiometry.

Fatigue crack growth tests of NiAl bronze (NAB) alloy heat treated at different temper temperature after quenching at 920 °C are performed using direct current potential drop method. The influences of heat treatment on the fatigue crack growth behavior of NAB alloy are investigated. The results show that the fatigue crack growth rate (FCGR) of NAB alloy decreases with the increase of temper temperature. A few large secondary cracks are obtained as the sample is tempered at 350 °C and the secondary cracks diminish with the increase of temper temperature. With further increasing temper temperature to 550 °C, a large number of small secondary cracks are obtained, which is responsible for its lower FCGR. The as-cast NAB alloy has a lower FCGR than that tempered at 550 °C at low stress intensity factor range (ΔK) region, and the lower FCGR is attributed to the crack deflection effect of the as-cast microstructure. At high ΔK region, the crack deflection effect diminishes, which leads to the higher FCGR of as-cast sample.

Niobium is an important alloying element in steels. In the present work an effort has been made to investigate the effect of electropulsing on the niobium carbide (NbC) at an elevated temperature (800 °C). The results show that the electropulsing treatment can generate an evenly distributed NbC by decreasing the kinetics barriers for precipitation. It has been also found that a semitransformed pearlite structure forms in such a way that the grains are oriented toward a direction parallel to that of the electric current flow. Furthermore, the electropulsed sample benefits from refined grain size. This is thought to be due to the electropulse-enhanced nucleation rate. Tensile testing has been carried out to compare the properties of electropulsed sample with that of without electropulsing. The results show that the sample with treatment has greater yield strength and ultimate tensile stress while its elongation is only 1% less that of the unelectropulsed samples. The improved mechanical properties of the sample with pulsing are attributed to its finer grain sizes as well as the elimination of precipitation free zones caused by the electropulsing treatment.

The aim of the present investigation is to identify the wear mechanisms of multilayer coated carbide tool under different machining conditions during turning of hardened AISI 4340 steel. The chemical vapor deposited multilayer coated (TiN/MT TiC,N/Al2O3) carbide tool was used. The worn surfaces of the cutting tools were examined under digital optical microscope, scanning electron microscope, and elemental analysis. The investigation results showed a strong correlation between the cutting conditions and tool wear. The cutting speed and feed rate ensure the dominant effects on the tool wear followed by the depth of cut and also the progress of tool wear were verified under different intervals of time. The flank and rake faces of the cutting tool were severely gouged by the hard particles of workpiece material exhibited abrasive wear phenomenon. Intermittently, chipping at cutting edge, notching and catastrophic failure modes were observed in continuous machining.

Quantitative characterization of interface adhesion and fracture properties of thin film materials is of fundamental and technological interests in modern technologies. Sandwich beam specimens used in fracture mechanics techniques, such as four-point bending and double-cantilever beam have been widely adopted, including the semiconductor industry. In this work, we highlight some of the challenges that these techniques are facing in characterizing ever thinner films and tough interfaces, and propose a simple strategy to address these challenges by engineering the stack structure of the specimen. We show that crack propagation in a multilayer stack can be controlled using a super-layer (SL) structure, and the dependence of the cracking behavior on the thickness and mechanical properties of the SL is studied. The effectiveness of the SL strategy is demonstrated for a range of technologically important material systems used in the on-chip interconnects of modern microprocessors, which represents one promising path to extend the industry-standard techniques to meet future characterization needs.

A micro-indentation system integrated with an acoustic emission (AE) sensor is used as a damage test method for crack detection of the specimen during the indentation loading–unloading cycle. The specimens investigated are the Si die, and various stacked structures of metallization (Al or Cu) deposited over the dielectric layers (SiO2 or Si3N4) on the Si substrate. The 1st AE event detected during the loading stage corresponded to the ‘pop-in’ observation in the force–displacement curve, which was related to the brittle cracking in the dielectric or Si substrate. However, during unloading, a 2nd AE event was detected, but no “pop-out” was observed, which was mainly due to the delamination between the dielectric and Si substrate. It was also found that for Si die, “pop-out” was observed without any AE event during the unloading stage, which was related to the Si phase transformation. This observation is unique to sharp indenter tip but not for a blunt indenter tip.

The effect of surface preparation—grinding, polishing, and electrochemical etching—on the duplex stainless steel passive film conductivity was investigated by in situ current sensing atomic force microscopy. The current maps show that the current in the passive film on three prepared surfaces is different, especially for the ferrite and austenite phase surface. The current on the austenite and ferrite is similar on either mechanical ground or polished surfaces, but the current on the austenite surface is much higher than current on the ferrite surface after electrochemical etching. The difference in the passive film conductivity originates from the changes in the chemical composition and thickness of the passive film and the change in topographical properties induced by the preparation procedures. This is confirmed by AFM, x-ray photoelectron spectroscopy, and auger electron spectroscopy measurements.

Titanium (Ti) thin films were deposited by DC magnetron sputtering at conventional conditions with different substrate temperature, deposition rate, and inert gas pressure. The compositional, structural, morphological, and optical properties of the Ti films were investigated. It is shown that the films were crystalline with α-Ti phase and hcp structure only. The crystallinity increased with increase in substrate and deposition rate. Analysis of the atomic force microscopy images shows that the films were uniform, crack free, and adhered well to the substrate. It is found that, a strong relation existed between the structural and optical properties of the films. The optical properties of the Ti films were most influenced under the deposition conditions. From this dependence, the optimum deposition conditions are obtained to prepare metallic, crystalline, and dense Ti films with smooth surface under conventional conditions.

This work presented a study on the improvement of laser surface treatment on rolling contact fatigue resistance of gray cast iron. Sample surface covered with carbon powder was coupled with localized treatment by high-energy laser beam—a process defined as “laser cladding (LC).” With this method, the optimum precoating thickness was experimentally studied. Compared to the region treated by laser remelting, the crystal in LC region was finer, more compact, and uniform. Mechanical property testing showed not only high micro-hardness of LC region, but also improved tensile and compressive resistance of treated material. Fatigue wear tests and thorough analysis of fatigue detects suggested that LC treatment significantly improved fatigue wear resistance (FWR). Improved FWR was likely facilitated by delayed initiation and propagation of cracks, as well as the reduction of contact stress on substrate. Additionally, formations of fatigue defects on sample surface were thoroughly discussed.

Experimental evidences for a recently proposed mechanism of tin-induced crystallization of amorphous silicon are presented. The mechanism discusses a crystalline phase growth through cyclic processes of formation and decay of a super-saturated solution of silicon in molten tin at the interface with the amorphous silicon. The suggested mechanism is validated using a nonlinear dynamical model that takes into account the mass diffusion of the components of the system, heat transfer caused by latent (crystallization) heat release and amorphous silicon dissolution events, and concentration nonuniformities created by silicon crystallization. The analysis of a stationary-state solution of the model confirms the existence of periodic solutions for the partial volume of the crystalline phase and other system's variables. Possible applications of the proposed mechanism in manufacturing of cost-effective nanocrystalline silicon films for the third-generation solar cell technology are discussed.

Novel 1–1.5 μm BiOCl0.5Br0.5 composite microspheres were prepared by coprecipitation method, then calcined at different temperatures. The BiOCl0.5Br0.5 samples before and after calcination were characterized by powder x-ray diffraction, thermogravimetric analysis, N2-physical adsorption, scanning electron microscopy, Fourier transformed infrared spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of Rhodamine B under visible light irradiation. The results showed that the thermostability of BiOCl0.5Br0.5 composite microspheres is lower than BiOCl and higher than BiOBr. Heat treatment at low 500 °C could obviously improve the crystallinity of BiOCl0.5Br0.5 microspheres, resulting in a significant increase in activity. BiOCl0.5Br0.5 microspheres calcined at 450 °C displayed the highest activity and stability. At elevated temperature calcination (600–800 °C), phase transition occurred over BiOCl0.5Br0.5. Br element was gradually lost and new phase of Bi24O31Br10 appeared. High temperature calcination did not change the morphology of BiOCl0.5Br0.5, but the surface area and surface OH groups decreased, which resulted in a large decrease in activity.

The structural color films with enough brilliant color have attracted a special attention because of the great advantages in some practical application, which has currently become a research hot-spot. But their simple fabrication is still a great challenge. This study presents brilliant polymer opal structural color films (PSCFs) from polystyrene spheres under natural light by using a simple preparation and assembly strategy. In this strategy, the black organic dye water solution was used as the dispersion medium for polystyrene spheres, and then polystyrene spheres were rapidly fabricated to one ordered structures by the thermal assistance self-assembly method, which is cheap and commonly available. Contrast to other many structural color films irradiated by external light source under black background, the PSCFs exhibit brilliant and tunable structural colors under natural light even in a white environment, which is significant for the potential application of PSCFs in paint, photonic paper, external decoration of architectures, display, and bioassay.

Nanometer-sized fibers are recently getting increased attention in heterogeneous catalysis due to the superior transport properties and effective dispersion they offer. A key challenge in this application is creation of nanofibers with internal open porosity that can provide larger accessible catalytic surface and easier mass transport into the fibers. The synthesis of potassium doped iron/aluminum oxides ceramic nanofibers with mesoporous structure is presented herein. Uniform fiber mats were prepared by electrospinning (ES) using two different precursors: an aqueous solution of metal nitrates and an organic solution of metal acetylacetonates. The organic precursors gave rise to a promising mesoporous structure with fibers diameter mainly in the 300–400 nm range. Precursor viscosity was used as a stability indicator and its influence on the ES process was studied. Collection efficiency of as high as 90% was achieved. The increased understanding in fiber morphological evolution can open new possibilities in heterogeneous catalysis.