Silicon nanocrystals (Si-nc) present several plus points as advanced fluorescent biomarkers but suffer from difficulties met in controlling their intrinsic photoluminescence (PL). Here, we first consider the reasons for this difficulty, showing results that support an interface defect-related origin of the PL. Attainment of a controlled PL emission would then require tuning of defects in the capping oxide, a hard and yet unaddressed task. Alternatively, we demonstrate the possible use of Si-nc as antennas, or sensitizers, of a luminescent rare-earth ion in an engineered fluorophore. In this approach the relatively high and broadband optical absorption of Si-nc was exploited, keeping the advantages of a near-infrared inorganic light emitter. Another fundamental part of the assessment of Si-nc for bioimaging is their biocompatibility. Here, we report toxicity tests based on the lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays on epithelial cells and fibroblasts, confirming that Si-nc in concentration suitable for luminescent labeling do not affect significantly the cells viability.

Novel europium- and gadolinium-doped bismuth phosphate (Eu/BiPO4 and Gd/BiPO4) microcrystals have been synthesized by a hydrothermal route. The morphologies and optical properties of the as-prepared samples were characterized carefully. Their photocatalytic activities were determined by oxidative decomposition of methylene blue (MB) in aqueous solution. The results revealed that europium and gadolinium doping greatly improves the photocatalytic efficiency of BiPO4 microcrystals. Among these as-prepared europium and gadolinium dopant samples, 1% Eu/BiPO4 and 5% Gd/BiPO4 displayed the highest photocatalytic activity, and the degradation rates are 2 and 2.7 times greater than pure BiPO4, respectively. The photodegradation reactions of MB by Eu- and Gd-BiPO4 followed first-order kinetics. The different photocatalytic mechanisms of Eu/BiPO4 and Gd/BiPO4 photocatalysts are discussed.

Red-emitting phosphor of Ca0.8Zn0.2TiO3:0.2 mol% Pr3+ was synthesized by the hydrothermal method with urea as a mineralizer. The crystalline structure, micromorphology, and luminescent properties of the resultant phosphor were investigated. Results show that elevated calcination temperature does not change the shape of particles that are hollow spheres with a shell thickness of 210–480 nm, and smaller particles are in the middle of the larger ones. The emission intensity at 612 nm originated from 1D2 → 3H4 transition of Pr3+ ions increases with the elevated calcination temperature due to a higher crystallinity. Excitation curves consist of two strong broad bands centered at about 330 and 380 nm and a weaker broad band range from 450 to 500 nm. The sample prepared by the hydrothermal method has better luminescent properties than that of its counterpart prepared by the solid-state method, especially the improvement of near-UV region (380 nm) excitation intensity.

We have investigated the formation of the rutile and the anatase polymorphs of TiO2, with emphasis on epitaxial growth characteristics, and defect content as a function of laser and substrate variables. X-ray diffraction (XRD) studies revealed that the rutile phase is more stable at higher substrate temperatures and lower oxygen pressures; in contrast, decreasing the temperature and increasing the oxygen pressure gave rise to formation of anatase. Epitaxial rutile films with a <100] orientation were obtained at 450 °C using the pressure of 5 × 10−4 Torr, and laser energy of 3.5–4.0 J/cm2. The epitaxial relationship, determined by 2θ−θ and φ scan of XRD and confirmed by transmission electron microscopy (TEM) diffraction patterns, was shown to be rutile(100)||sapphire(0001), rutile[001]||sapphire[10$\bar 1$0] and rutile[010]||sapphire[1$\bar 2$10]. An atomically sharp interface between the rutile epitaxial film and the sapphire substrate was observed in the scanning transmission electron microscopy (STEM) images. The films exhibited a transmittance of 75–90% over the visible region. The absorption edge was observed to shift toward longer wave lengths at higher deposition temperatures or lower pressures. X-ray photoelectron spectroscopy and photoluminescence results showed that concentration of lattice point defects, namely oxygen vacancies and titanium interstitials, increased at lower oxygen pressures. Formation of nanostructured films with a surface roughness of -1.5–13.1 nm was confirmed by atomic force microscopy investigations.

Type 304L stainless steel (SS) samples were used to investigate the correlation between carbide precipitation and triple junction structure derived from crystallographic data obtained by the orientation imaging microscopy associated with electron backscattered diffraction. The samples were solution treated and annealed at different sensitization temperatures/time to introduce various degrees of carbide precipitation at the interface region, thus different degrees of selectivity toward triple junctions. Four models were used to characterize triple junction microstructures: (i) the I-line and U-line model, (ii) the coincident axial direction (CAD) model, (iii) the coincident site lattice (CSL)/grain boundary (GB) model and (iv) the plane matching (PM)/GB model. Among them, the I-line and U-line model is the most effective in identifying special triple junctions, i.e., those exhibiting the beneficial property of high resistance to carbide precipitation. The results showed that the percentage of special triple junctions (I-lines) immune to carbide precipitation, increased from 35 to 80%, as the precipitation became more selective toward triple junction structures due to the corresponding sensitization heat treatment conditions, whereas more than 80% of random triple junctions (U-lines) exhibited susceptibility to carbide precipitation regardless of the sensitization conditions.

Luminescent nanocrystals or quantum dots (QDs) have great potential for bioanalysis as well as optoelectronics. Here we report an effective and inexpensive fabrication method of silicon carbide quantum dots (SiC QDs), with diameter below 8 nm, based on electroless wet chemical etching. Our samples show strong violet-blue emission in the 410–450 nm region depending on the solvents used and particle size. The cytotoxic properties of the SiC QDs based on alamarBlueTM assay cells were studied. The presence of the QDs dots does not affect cell growth in a wide concentration range. Two-photon excitation showed significant response from SiC nanocrystals that were injected into hippocampal CA1 pyramidal cells.

Large surface area, homogenous, and adhesive TiO2 coatings on stainless steel substrates were prepared by electrophoretic deposition (EPD) of colloidal dispersions of TiO2 nanoparticles in water and ethanol. Several chemical additives were used to optimize the deposition process. The best results were obtained for dispersions in water containing a mixture of Tiron and Pluronic® F127, which gave homogeneous layers, showing excellent adhesion and a large BET surface area, close to 200 m2/g. Ethanol dispersions also gave much adhesive coatings when poly(acrylic acid) was used as an additive. Nevertheless, their thickness was lower, and their surface area was less than 100 m2/g. We have shown that water splitting, occurring in the aqueous sol during the EPD, led to deposited masses lower than those expected from the Hamaker law. However, the electrolysis of water and also the small cracks in the coatings had no detrimental effects on adhesion.

Titanium dioxide (TiO2) nanomaterials, as important photocatalysis materials, have been synthesized with many approaches. In this study, we reported the synthesis of TiO2 nanomaterials by reacting titanium isopropoxide with ethylene glycol under basic condition followed by calcination at high temperatures. The structural, optical, and photocatalytic properties of the TiO2 nanomaterials were studied with x-ray diffraction, Raman spectroscopy, transmission electron microscopy, differential scanning calorimetry, Fourier-transformed infrared spectroscopy, x-ray and ultraviolet (UV) photoemission spectroscopy, UV–vis diffusive reflectance, and photocatalytic decomposition of methylene blue. We found that the titanium ethylene glycolide decomposes at 330 °C and transforms into pure anatase TiO2 around 400 °C. The anatase phase further transforms into core/shell rutile/anatase TiO2 composite at 550 °C and displays the highest photocatalytic activity among the samples prepared. The high photocatalytic activity can be attributed to the improved charge separation at the rutile/anatase n/n junction interface and the high crystallinity of the sample after calcination.

The organic light-emitting (OLE) materials have attracted great interest due to their potential applications in sensors, biodetectors and OLE devices. However, highly efficient emission from organic solids is still a great challenge because of the aggregation-caused quenching effect. In this article, a three-dimensional (3D) organic-inorganic hybrid nanoparticle, based on polyhedral oligomeric silsesquioxane (POSS), was precisely fabricated via click chemistry with high yield, and its structure was characterized by Fourier transform infrared spectroscopy, 1H, and 29Si nuclear magnetic resonance spectroscopies, and Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry, respectively. The resultant 3D organic-inorganic nanohybrid showed significantly enhanced emission in solid film (Φfilm 80%) with a slight red-shift as compared with its organic counterpart, (Φfilm 14%), which exhibits a large red-shift in solid film, due to the deaggregation effect of POSS. Simultaneously, the resultant nanohybrid also exhibited good film formability, excellent spectrum and thermal stability (>250 °C) due to the introduction of POSS.

Due to its excellent physical properties, graphene acting as reinforcing fillers has attracted intense interests. To achieve a controlled distribution, the formation of a conductive network composed of graphene sheets within polymer matrix is of critical importance. In this work, polystyrene (PS) microspheres wrapped by graphene oxide (GO) sheets were prepared via layer-by-layer (LBL) assembly of oppositely charged GO sheets onto PS microspheres. The deposited GO was then reduced, and the composite films with a graphene conductive network were prepared by hot pressing. The morphology of graphene conductive network was studied, and the thermal and electrical properties of the composite films were measured. The as-prepared composites showed an improved thermal stability as well as electrical conductivity with a percolation threshold as low as 0.2 vol%. The combination of latex technology and LBL self-assembly method thus demonstrated an efficient and facile approach to fabricate electrically conductive graphene/polymer composites.

In this study, nanocrystalline ZrN films were successfully deposited onto AZ91 alloy using an ion beam sputtering method at substrate temperatures of 373–673 K. Strain and adhesion were calculated using the classic Williamson–Hall and indentation cracking methods, respectively. Microstructure and crystalline properties were evaluated using scanning electron microscopy and x-ray diffraction. XRD results showed that the crystallographic properties of the films were strongly dependent upon substrate temperature. An increase in temperature increased adhesion of the film to the AZ91 alloy and decreased film microstrain. The corrosion behavior of ZrN/AZ91 samples in Ringer's solution was studied to evaluate corrosion potential and corrosion current density. Potentiodynamic corrosion tests showed that all ZrN-coated samples had a corrosion resistance superior to the blank substrate, mainly at 400 °C. A correlation was also established between vacancy defects in the film and corrosion behavior.

Carbon nanotubes (CNTs) supported Pd nanoparticle (NP) catalysts (Pd/CNTs) were prepared by a green and facile synthesis method based on hydrogen-bonding self-assembly. The size and loading of Pd NPs on catalysts were easily controlled by tuning both the relative amount of citrate to Pd salt in the solution and the relative amount of Pd NPs to CNTs. The size of Pd NPs on as-prepared catalysts can be tuned in the range of 3–6 nm, and Pd loading can be controlled in the range of 0–19 wt%. The catalysts were characterized by Brunauer–Emmett–Teller measurement, x-ray diffraction spectroscopy, and x-ray photoelectron spectroscopy. The performance of Pd/CNTs catalysts was evaluated in the hydrogenation of nitrobenzene. Compared with the catalysts prepared by the impregnation method or supported on conventional supports, Pd/CNTs catalysts show relatively higher activity and selectivity. The recyclability tests indicate that the Pd/CNTs catalysts can be used at least five times without significant loss in activity and selectivity.

Epitaxial graphene and carbon nanotubes (CNTs) grown on SiC have shown big potential in electronics. The motivation to produce faster and smaller electronic devices using less power opened the way to a study of how to produce controlled epitaxial graphene and CNTs on SiC. Since defects are among the important tools to control the properties of materials, the effects of defects on the carbon formation on SiC have been analyzed. In this study, the effects of defects on the carbon formation on SiC have been analyzed. We produced carbon films on the surface of four different SiC materials (polycrystalline sintered SiC disks, single crystalline SiC wafers, SiC whiskers, and nanowhiskers) by chlorination and vacuum annealing with the goal to understand the effects of surface defects on the carbon structure and the SiC decomposition rate. We have shown that grain boundaries, dislocations, scratches, surface steps, and external surfaces may greatly enhance the reaction rate and affect the final structure of carbon derived from SiC.

Polyaniline (PANI)–PbTiO3 composites were prepared by using different inorganic and organic acids by in situ polymerization technique using sodium dodecyl benzene sulfonic acid as a surfactant. The structural analysis was studied by using x-ray diffraction, and it was found that PANI is amorphous in nature. The scanning electron microscopy studies reveal that they are agglomerated and irregular, and size of these grains increase by increasing the amount of PANI with different organic and inorganic acids. The real part of complex permittivity (εʹ) and imaginary part of complex permittivity (εʹʹ) and the real part of the permeability (μ′) are studied at X-band frequency where (εʹ) and (εʹʹ) decreas with increase in frequencies, whereas μ′ increases with increase in X-band frequency and exhibits a maximum value of 0.87 at the resonance frequency of 9–11 GHz of 30 wt% PbTiO3 in PANI matrix. Reflection loss peak of 30 wt% of PANI–PbTiO3 composites is 28.6 dB at 10.8 GHz, which may be attributed to the maximum reflection of the microwave power for the particular doping concentration.

Calcium phosphates (CaPs) are major chemical constituents of mammalian bone. Their osteoconductivity in vitro and in vivo has encouraged their use in biomaterial applications such as implant materials and drug delivery. High aspect ratio nanoparticles are attractive for many biomedical applications; however, precise control of the phase and morphology is challenging. The impact of fuel-to-oxidant ratio, pH, and cation chemistry on morphology and phase was studied for CaP-based compositions by microwave-assisted solution combustion synthesis (MASCS) in a urea–nitrate (fuel–oxidant) system. An initial calcium to phosphate ratio of 1.5 was used. Highly crystalline hydroxyapatite (HA) and biphasic CaP nanoparticle compositions were produced as confirmed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. MASCS was capable of synthesizing high aspect ratio (∼5 to 20) single and biphasic CaP nanoparticles with diameters ranging from 250 to 500 nm and lengths between 2 and 10 μm.

Ca3Co4O9 and Ca2.8Bi0.2Co4O9 thin films were fabricated on LaAlO3 (LAO) substrate using pulsed laser deposition technique and were studied for their thermoelectric (TE) properties in Stranski–Krastanov mode for the first time. The thin films consisted of 3D clusters/islands on a ∼14-nm thick 2D layer with cluster density being higher for Ca2.8Bi0.2Co4O9 thin films. The clusters also represent areas of dislocation and therefore act as carrier scattering centers, which leads to a temperature-activated type conductivity. Seebeck coefficient as high as 136 and 163 μ V/K was measured for the Ca3Co4O9 and Ca2.8Bi0.2Co4O9 thin films, respectively, which is among the highest reported values for this system. The 3D island formation was also found to be useful in reducing the thermal conductivity of the thin film/substrate system by increased phonon scattering. This work shows that the island formation in thin films can be utilized as a means of enhancing TE properties of a thin film system, however, a detailed work including optimization of the film thickness and cluster/inland density is required.

Dielectric aging of Dy and Mn-codoped BaTiO3 multilayer ceramic capacitors was investigated. The increase of Dy concentration significantly decreased the aging rate and caused a disappearance of the thermally stimulated depolarization current peak associated with the defect dipole of Mn such as ${\rm{Mn}}_{{\rm{Ti}}}^{\prime \prime } {\rm{ - V}}_{\rm{O}}^{\cdot\cdot}$ or ${\rm{Mn}}_{{\rm{Ti}}}^\prime {\rm{ - V}}_{\rm{O}}^{\cdot\cdot}$, which was observed in low Dy-concentration specimens. These results experimentally demonstrate that the rare earth element, Dy, decreases the concentration of the defect dipoles and thereby controls dielectric aging.

Dynamic recrystallization (DRX) of 99.9999% aluminum single crystal at room temperature was examined under frictionless deformation mode. To exclude the self-heating of the specimen due to applied high strain, a microcrack that localizes the stress at a very small region was intentionally introduced by controlled local necking. For the in situ observation of DRX, a specially designed in situ microdeformation device was positioned inside an electron backscattered diffraction system chamber. Recrystallized grains showed relatively random texture and preferred growth direction. The subgrains with low-angle grain boundaries formed by dynamic recovery transformed into small grains with high-angle grain boundaries, acting as nuclei for discontinuous dynamic recrystallization and growing by further deformation. The DRX in pure aluminum can take place under frictionless tensile deformation conditions at room temperature, and the stress localization and high purity are key issues for the DRX of aluminum at room temperature.

Sn–40 at.% Mn peritectic alloys were directionally solidified at different growth rates (1–100 μm/s) under a steep temperature gradient (40 K/mm). The migration of secondary dendrite arm was observed in this peritectic alloy in which both the primary phase and the peritectic phase are intermetallic compounds with nil solubility. This migration is caused by coupling remelting/solidification at the hot/cold sides of the liquid pool between two adjacent secondary dendrite arms by temperature gradient zone melting. Its novel feature is that the remelting temperature of primary phase is a little higher than the solidification temperature of peritectic phase. Analytical solutions based on the assumption that the solubility of both primary and peritectic phases are nil have been proposed to describe this migration. It has also been found that the migration of secondary dendrite arm is most obvious at intermediate growth rates under steep temperature gradient in the directionally solidified Sn–40 at.% Mn peritectic alloy.

Textured epitaxial HfO2 thin films of monoclinic structure were grown on r-cut Al2O3 by atomic layer deposition from HfCl4 and H2O at temperatures 450–750 °C. The film-to-substrate out-of-plane orientation was determined to have a single (001)HfO2//(1$\bar 1$02)α-Al2O3 relationship. The in-plane orientation showed the existence of two possible relationships: [100]HfO2//[110]α-Al2O3 and [$\bar 1$00]HfO2//[110]α-Al2O3. In films deposited at 400 °C traces of (010) growth plane were observed in addition to the preferential (001) growth. The lattice of HfO2 was compressed in the surface plane and expanded in the surface normal direction. The strain was highest in the films grown at 450–550 °C. With the increase of deposition temperature to 750 °C, the strain decreased. The strain relaxation in films deposited at 750 °C was in correlation with marked surface roughening in the initial stage of deposition at this temperature. The roughness of the epitaxial films was lower than that of polycrystalline films with comparable thickness deposited on Si(100) and SiO2 substrates.