We are reporting on stress engineering utilizing AlN/GaN superlattices (SLs) for epitaxy of GaN layers on 200 mm silicon substrates carried out in Veeco's Propel™ rotating disk, single wafer metal organic chemical vapor deposition (MOCVD) reactor. The Turbodisc® reactor is designed to have homogeneous alkyl/hydride flow distribution and uniform temperature profile, which translate into excellent uniformity and concentric symmetry in epilayer thickness and alloy composition. This feature results in uniform and controllable stress in epilayers across large-size substrates. Crack-free 2 μm GaN layers were grown on 200 mm Si using uniformly strained AlN/GaN SLs with periods of 3–5 and 10–30 nm, respectively. Compressive and tensile stress can be precisely adjusted by changing the thickness of the AlN and GaN layers in the SLs, resulting in controllable wafer curvature/bow after cool down. For a fixed period thickness structure, the effects of growth conditions, such as growth rate of GaN, AlN V/III ratio, and growth temperature, on wafer stress were investigated.

We demonstrate in this paper the shape-controlled synthesis of α-Fe2O3 rhombohedra anchored graphene nanocomposites through a simple hydrothermal strategy by adopting inorganic species in the synthesis system. TEM investigations reveal that the rhombohedra with an average diameter of 80 nm is formed through oriented attachment of primary nanocrystals assisted by Ostwald ripening, and CH3COONa inorganic surfactant played an important role in control over the final morphology of the products. As high-performance anodes for lithium-ion batteries, the obtained Fe2O3 rhombohedra/graphene composite exhibits the first reversible capacity of 905.3 mAh g−1, and high capacity retention of 85.7% after 50 cycles. These values are much higher than those of bare Fe2O3 and Fe2O3 particle/graphene composites, indicating its excellent electrochemical stability. These results give us a guideline for the study of the morphology-dependent properties of functional oxide materials as well as further applications for magnetic materials, lithium-ion batteries, and gas sensors.

A model of reactive hot pressing of zirconium carbide (ZrCx, 0.5 < x < 1) has been constructed that incorporates four processes that occur in parallel: creep of zirconium (Zr), reaction of Zr and carbon (C), increase in volume fraction of hard phase with progressive reaction that reduces the creep of Zr and, finally, de-densification associated with volume reduction during reaction. The reasonable agreement of the model with experimental results verifies that plastic deformation of Zr is the main factor that is responsible for the low-temperature reactive densification of ZrC and that ZrC may be treated as a rigid inclusion that contributes little to densification. It predicts that densification is impaired by increasing carbon stoichiometry due to the increasing amount of starting hard phase and the greater contraction upon reaction. Additionally, the model predicts that mixtures of Zr and ZrC should show equal or better densification than Zr and C mixtures.

One of the defining properties of biological structural materials is self-healing, i.e., the ability to undergo long-term reparation after instantaneous damaging events, but also after microdamage due to repeated load cycling. To correctly model the fatigue life of such materials, self-healing must be included in fracture and fatigue laws, and related codes. Here, we adopt a numerical modelization of fatigue cycling of self-healing biological materials based on the hierarchical fiber bundle model and propose modifications in Griffith's and Paris' laws to account for the presence of self-healing. Simulations allow us to numerically verify these modified expressions and highlight the effect of the self-healing rate, in particular, for collagen-based materials such as human tendons and ligaments. The study highlights the effectiveness of the self healing process even for small healing rates and provides the possibility of improving the reliability of predictions of fatigue life in biomechanics, e.g., in sports medicine.

We introduce a novel approach to the synthesis of high-quality and highly uniform few-layer graphene on silicon wafers, based on solid source growth from epitaxial 3C-SiC films. Using a Ni/Cu catalytic alloy, we obtain a transfer-free bilayer graphene directly on Si(100) wafers, at temperatures potentially compatible with conventional semiconductor processing. The graphene covers uniformly a 2″ silicon wafer, with a Raman ID/IG band ratio as low as 0.5, indicative of a low defectivity material. The sheet resistance of the graphene is as low as 25 Ω/square, and its adhesion energy to the underlying substrate is substantially higher than transferred graphene. This work opens the avenue for the true wafer-level fabrication of microdevices comprising graphene functional layers. Specifically, we suggest that exceptional conduction qualifies this graphene as a metal replacement for MEMS and advanced on-chip interconnects with ultimate scalability.

Microporous carbon nanospheres were prepared from β-cyclodextrin (β-CD) by solvothermal carbonization in o-dichlorobenzene in the presence of various concentrations of p-toluene sulfonic acid (PTSA). The contribution of PTSA toward solvothermal char (STC) was established. The STC showed the highest surface area, porosity, and CO2 sorption capacity at a PTSA to β-CD weight ratio of 2.5. The surface area, pore volume, and CO2 sorption capacity were further increased by an in situ high-temperature activation due to the oxidation of carbon at high temperature by oxygen present in the STC. The high-temperature activation reduces the significance of PTSA concentration, as the activated STC showed surface area, micropore volume, and CO2 adsorption capacity in a close range at the PTSA to β-CD weight ratio in the range of 0.04–2.50. The highest CO2 adsorption capacity of the STC increased from 2.4 to 3.5 mmol/g upon the high-temperature activation. The activated STC adsorbs significant amount (0.35 mmol/g) of CO2 from dry air containing 400 ppm CO2. The activated STC showed excellent regeneration stability and selectivity over nitrogen.

Using galvanostatic pulse deposition, we studied the factors influencing the quality of electroformed Bi1–xSbx nanowires with respect to composition, crystallinity, and preferred orientation for high thermoelectric performance. Two nonaqueous baths with different Sb salts were investigated. The Sb salts used played a major role in both crystalline quality and preferred orientations. Nanowire arrays electroformed using an SbI3-based chemistry were polycrystalline with no preferred orientation, whereas arrays electroformed from an SbCl3-based chemistry were strongly crystallographically textured with the desired trigonal orientation for optimal thermoelectric performance. From the SbCl3 bath, the electroformed nanowire arrays were optimized to have nanocompositional uniformity, with a nearly constant composition along the nanowire length. Nanowires harvested from the center of the array had an average composition of Bi0.75Sb0.25. However, the nanowire compositions were slightly enriched in Sb in a small region near the edges of the array, with the composition approaching Bi0.70Sb0.30.

Atomic engineering of complex oxide thin films is now reaching a new paradigm: the possibility to control the cation coordination by oxygen anions. Here, we show two examples of stabilization of novel structural phases by manipulating the oxygen sublattices in complex Cu-based oxide thin films grown on SrTiO3: (i) epitaxial strain stabilization of a near cubic form of CuO and (ii) thickness-dependent structural transformation from bulk planar (polar) to chain-type (nonpolar) in SrCuO2 thin films that relieves the electrostatic instability. Experimental investigation on ultrathin CuO layer identifies the existence of an elongated (c/a ∼ 1.34) rocksalt-type CuO phase, pointing to metastable 6-fold coordinated Cu with the hole occupied in the 3dx2−y2 orbital. For ultrathin SrCuO2 layers, we demonstrate the possibility of moving oxygen ion from CuO2-plane to Sr-plane forming chain-type structure. X-ray absorption spectroscopy reveals preferential hole-occupation at the Cu-3d3z2−r2 orbital for chain-type structure unlike to the planar case. Our findings testify unique stabilization processes through atomic rearrangement and provide new insight into the experimental realization of novel cuprate-hybrids to look for exciting electronic properties.

This study investigated influences of vacancy defects on buckling behaviors of open-tip carbon nanocones (CNCs) by molecular dynamics simulations. Effects of vacancy location and temperature on the buckling behaviors were examined in the study. Some interesting findings were attained from the investigations. It was noticed that the CNC with an upper vacancy has comparable degradation in the critical strain and in the critical load with the CNC with a middle vacancy, whereas the CNC with a lower vacancy has lower degradation in the antibuckling ability than the above two CNCs. The antibuckling ability of the CNCs reduces with the growth of the temperature. This temperature effect is more apparent in the perfect CNC than in the vacancy-defect CNCs. It was also observed that the degradation in the antibuckling ability is obvious at a lower temperature, but it decreases as the temperature grows. Besides, all the CNCs (including the perfect and the vacancy-defect CNCs) exhibited a shrinking/swelling buckling mode shape at the studied temperatures. Existence of the vacancies did not alter the buckling mode shape of the CNCs.

Silicone Rubber (SR) filled with graphene nanoplatelets (GNPs) and carbon black (CB) is prepared for high performance flexible pressure sensor. Due to the synergetic effect of mixed GNPs and CB, the percolation threshold of GNPs/CB/SR is lower than that of CB/SR, which indicates the addition of GNPs is contributed to enhance the electrical conductivity of GNPs/CB/SR. Moreover, the GNPs/CB/SR has a higher electrical stability and weaker resistance creep than that of GNPs/SR. That is to say, the addition of CB can promote the electrical and mechanical performance of GNPs/CB/SR, simultaneously. The pressure sensor array based on GNPs/CB/SR with weight on different sensing element is tested, and the results show that the size of applied loading on the pressure-sensitivity array can be recognized accurately.

Indentation deformation of glass under a sharp diamond indenter causes cracking during and after a loading–unloading cycle. To get a deeper insight into the indentation cracking in glass, it is critical to understand the elastic and inelastic deformation behavior of glass under the indenter. In this study, in situ observations during Vickers indentations are carried out for silica, soda-lime, and lead–silicate glasses. It is found that the true contact area during indentation is different from the area estimated from the contact depth and the indenter geometry, and that the ridges of a Vickers indenter affect the contact shape during indentation. The contact region of silicate glasses under a Vickers indenter is not a regular square but a concave square. This results in edge cracking during indentation. It is concluded that the contact shape and the deformation mechanism of glass under the indenter are closely related to its cracking behaviors.

Polymer precursors for Si(N)OC ceramics have been synthesized by hydrosilylation reaction of polyhydridomethylsiloxane (PHMS) with three different nitrogen containing compounds. The results obtained by combining characterization techniques such as FTIR, 13C- and 29Si-NMR confirm the occurrence of the cross-linking reaction between Si–H and vinyl groups. The structural characterization of the corresponding ceramic phase shows that the type of N-containing compounds strongly influences the pyrolytic transformation as well as the crystallization behavior of the final ceramics. Elemental analysis clearly indicates that N is present in the Si(N)OC matrix and the degree of N retention after pyrolysis is related to the type of N-containing starting compound. XPS data show that N–C bonds are present in the Si(N)OC ceramic samples even if only N–Si bonds are present in the starting N-containing precursors. However, if nitrogen atoms form bonds with sp2 carbon atoms in the preceramic polymer then a larger fraction of C–N bonds is retained in the final Si(N)OC ceramic.

Fabrication of nanoperforated TiO2 thin films (NP-TiO2) on various substrates utilizing evaporation-induced self-assembly has been widely reported during recent years. For many applications, such as solar cells and gas sensors, it would be beneficial if the active material could be deposited onto a desired area or in the form of a pattern or array. In this study, inkjet printing was successfully used to produce NP-TiO2 at both ambient temperature and 60 °C. Especially for intermediate drop spacings (40 and 50 µm), millimeter-sized homogeneous NP-TiO2 patches were obtained with similar NP structure as those being processed by dip coating and drop casting. Compared to ambient temperature, inkjet printing at 60 °C provides a narrower height distribution of the NP structures of about 5 nm. Compared to dip coating and drop casting, inkjet printing enables the deposition of the ink onto target areas, thus enabling the fabrication of microscale arrays and other patterned structures.

A catalytic depolymerization (a reversible polymerization) of 3D-polymerized C60 phases (including an ultrahard fullerite phase) takes place in the presence of sulfur under the conditions of a large plastic deformation at room temperature. The sulfur atoms remain in the samples of 3D C60 polymers after catalytic synthesis using carbon disulfide (CS2) as a catalyst (the presence of sulfur has a considerable impact on the 3D C60 polymerization by decreasing the polymerization pressure). Raman, infrared, and transmission electron microscope studies show that the depolymerized fullerite samples have a structure typical for dimers, 1D and 2D C60 polymers. The 3D C60 samples with some remaining sulfur can be quenched under ambient conditions if the samples have not undergone a large plastic deformation. There is no depolymerization for pure C60 3D-polymerized phases synthesized without a sulfur-based catalyst.

While planar graphene has revolutionized science and engineering in many different areas, one of its close relatives, vertical graphene (VG), also known as carbon nanowalls, has not been investigated as extensively. Compared to planar graphene that is grown parallel to the substrate, VG can grow almost vertically on a wide variety of substrates. In this study, we report the fabrication and characterization of VG-based nanocomposite thin films, where the graphene sheets are uniformly distributed in the host polymer. A novel fabrication method was developed and the properties of the fabricated nanocomposites were characterized. The results showed that in our method graphene sheets are much more uniformly dispersed and common issues in graphene nanocomposites, such as agglomeration and breaking of the sheets during dispersion, are avoided. The increase in the Young's modulus and tensile strength of the fabricated nanocomposites is much higher than that of the samples fabricated using the traditional methods of randomly dispersing graphene using a sonicator or high-speed stirrer.

This review focuses on in situ functionalization of gallium nitride (GaN) with different adsorbates in the presence of an etchant. The low-temperature aqueous nature of this process provides a safe, environmentally friendly technique for tailoring the semiconductor's properties for various applications. Surface binding to GaN relies on a native oxide layer or direct attachment to the metal center present on the etched surface. The specifics of the binding mechanism are based on the functional groups present on the adsorbate. The effects of the GaN surface polarity and quality on the modification approach are analyzed. The review summarizes the alteration of GaN properties after the in situ treatment. Quantitative data until now have shown changes in morphological, surface chemical, optical, electronic, and aqueous stability properties. The review concludes with a short outlook on future studies associated with this surface modification approach.

A ternary Nickel foam (NF)–graphene/MnO2/polyaniline (PANI) nanocomposite has been synthesized using green chemistry approach (in situ polymerization). All reactants were dispersed homogeneously in precursor solution in the form of ions and molecules. PANI and MnO2 molecules on the NF–graphene contact each other and are arranged alternately in the composite. Alternative arrangement of PANI and MnO2 nanoparticles separates them and prevents the aggregation of PANI and MnO2 to decrease the particle size of the composite on the surface of NF–graphene. The intermolecule contact improves the conductivity of the composite. The composite showed excellent specific capacitance of 1081 F/g at a scan rate of 1 mV/s and specific capacitance of 815 F/g at a current density of 3 A/g, having excellent cycling stability. Current study provides an alternative pathway to improve the rate capability and cycling stability of nanostructured electrodes, by offering a great promise for their applications in supercapacitors.

Sn–Ag–Cu solder interconnects were made by solidifying the solder balls in a magnetic field and subsequently tested for their electromigration behavior. The orientation of the tin grains was analyzed by electron backscattered diffraction. It was found that the c-axis of Sn grain tended to rotate away from the direction of the magnetic field during solidification, resulting in an enhanced electromigration resistance for the solder joint when the current was applied along the direction of the magnetic field, as evidenced by a smaller electromigration-induced polarity effect in the growth of the interfacial intermetallic compound. Such a reduced polarity-effect of electromigration is shown to agree well with the anisotropy in the diffusivity of the active diffusion species, Cu, in the tetragonal Sn. The difference of free energy change caused by the anisotropy in the magnetic susceptibility of the tetragonal Sn during solidification is suggested to be the main factor for this phenomenon.

Adhesion between soft matter is a universal mechanical problem in bio-engineering and bio-integration. The Johnson–Kendall–Roberts (JKR) method is widely used to measure the work of adhesion and work of separation between soft materials. In this study, the JKR theory is recaptured and three complementary dimensionless parameters are summarized to help design adhesion measurement experiments compatible with the JKR theory. The work of adhesion/separation between two commonly used soft elastomers, polydimethylsiloxane (PDMS, Sylgard® 184) and Ecoflex® 0300, is measured by the JKR method using a dynamical mechanical analyzer. Effects of base polymer to curing agent mixing ratio and solvent extraction are examined. A unified adhesion mechanism is proposed to explain the different adhesion behaviors. It is concluded that chain–matrix interaction is the most effective adhesion mechanism compared with chain–chain or matrix–matrix interactions. Chain–chain interaction obstructs chain–matrix interaction as it either blocks or entangles with surface chains which could have interacted with the matrix.

JANNUS (Joint Accelerators for Nanosciences and Nuclear Simulation), the unique triple beam facility in Europe, offers the possibility to produce three ion beams simultaneously for nuclear recoil damage and implantation of a large array of ions for well-controlled modeling-oriented experiments. The first triple beam irradiation was performed in March 2010. Along with irradiation developments, continuous efforts have been made to implement ex situ and in situ characterization tools. In this study, we set out the present status of the JANNUS facility of the Saclay site. We focus on the instrumentation used for conducting multi-ion beam irradiations and implantations as well as for characterizing bombarded samples. On-line control of irradiation parameters, in situ modification monitoring using Raman spectroscopy or ion beam induced luminescence, and ex situ characterization by ion beam surface analysis [Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), and elastic recoil detection analysis (ERDA)] of implanted samples are detailed. Some examples of single, dual, and triple beam irradiation configurations are presented. Access to the facility is provided by the French network EMIR for national and international users (http://emir.in2p3.fr/).