Stable, aqueous, red-to-near infrared emission is critical for the use of silicon nanoparticles (Si NPs) in biological fluorescence assays, but such Si NPs have been difficult to attain. We report a synthesis and surface modification strategy that protects Si NPs and preserves red photoluminescence (PL) in water for more than 6 mo. The Si NPs were synthesized via high temperature reaction, liberated from an oxide matrix, and functionalized via hydrosilylation to yield hydrophobic particles. The hydrophobic Si NPs were phase transferred to water using the surfactant cetyltrimethylammonium bromide (CTAB) with retention of red PL. CTAB apparently serves a double role in providing stable, aqueous, red-emitting Si NPs by (i) forming a hydrophobic barrier between the Si NPs and water and (ii) providing aqueous colloidal stability via the polar head group. We demonstrate preservation of the aqueous red emission of these Si NPs in biological media and examine the effects of pH on emission color.

Reusable thermal protection systems of reentry vehicles are adopted for temperatures ranging between 1000 and 2000 °C, when gas velocity and density are relatively low; they exploit the low thermal conductivity of their constituent materials. This paper presents a new class of light structural thermal protection systems comprised of a load bearing structure made of a macroporous reticulated SiSiC, filled with compacted short alumina/mullite fibers. Their manufacturing process is very simple and does not require special devices or ambient conditions. The produced hetoroporous heterogeneous ceramics showed high radiations shielding capabilities up to 2000 °C in vacuum. Even after repeated exposures at higher temperatures, a significant degradation of the SiSiC scaffold was not observed.

The linear elastic recovery measured from the nanoindentation unloading curve of a film/substrate system was used to determine the practical work for delamination using the proposed energy balance method and to estimate the delaminated area using the Hertz contact loaded model. The practical work for delamination was then calculated by dividing the external mechanical work required for generating interfacial crack by the delaminated area. The finite element model simulation demonstrated that the energy method was feasible and the estimation of delamination area using the Hertz model was accurate. The practical works for delamination in the plasma-enhanced chemical vapor deposition SiNx/GaAs film/substrate systems estimated using this method were in the range of 1–2.3 J/m2, which were in reasonably good agreement with those obtained from our another experimental approach.

Grain boundary segregation provides a method for stabilization of nanocrystalline metals—an alloying element that will segregate to the boundaries can lower the grain boundary energy, attenuating the driving force for grain growth. The segregation strength relative to the mixing enthalpy of a binary system determines the propensity for segregation stabilization. This relationship has been codified for the design space of positive enthalpy alloys; unfortunately, quantitative values for the grain boundary segregation enthalpy exist in only very few material systems, hampering the prospect of nanocrystalline alloy design. Here we present a Miedema-type model for estimation of grain boundary segregation enthalpy, with which potential nanocrystalline phase-forming alloys can be rapidly screened. Calculations of the necessary enthalpies are made for ∼2500 alloys and used to make predictions about nanocrystalline stability.

During peritectic solidification, besides the longitudinal remelting of the primary phase at the temperature of peritectic reaction $\left( {T_{\rm{p}}^K} \right)$, a lateral remelting phenomenon of the primary phase below $T_{\rm{p}}^K$ is observed under high velocity in directionally solidified Cu–Ge alloys. The lateral remelting occurs continuously along a liquid channel as temperature decreases, and the lateral remelting velocity is larger than that of peritectic transformation. The lateral remelting leads to the morphological change of the primary dendrites, even the fragmentation of dendrite arms. The phenomenon also means that the classical theory calculating the volume fraction of the primary phase during peritectic transformation can need to be modified under some conditions. However, under low velocity, the phenomenon is not so significant. The phenomenon is explained by means of solidification and remelting theory.

In this paper, the effect of the addition of tungsten carbide on the behavior of Fe–WC system during the mechanical alloying (MA) process has been investigated. For this purpose, raw materials containing industrial ferrotungsten and carbon black with a bit of tungsten carbide powder were milled in a high energy ball mill, and sampling was done at different times. An XRD instrument was used for estimating the probable transformation of phases and properties in the milled sample. Microstructures of specimens were studied using electron microscopy. Results showed that MA even at high milling time could not transform raw materials to other materials in a system containing ferrotungsten and carbon black. In samples with primary tungsten carbide, this was synthesized gradually at a milling time of more than 75 h, and finally, the Fe–WC composite was produced as the final product. Crystalline sizes of the synthesized carbide were in nanometer order that was confirmed by transmission electron microscopy images.

Vanadium oxide nanorods (VONRs) and vanadium oxide nanotubes (VONTs) were fabricated by hydrothermal method with the induction of hydroxyl and carboxyl functionalized carbon nanotubes (CNTs). The functionalized CNTs not only facilitate the dispersion of CNTs but also serve as centers for polymerization in the hydrothermal reaction. The formation of (VONRs) and (VONTs) was observed by field emission scanning electron microscopy, transmission electron microscopy, x-ray powder diffraction and Fourier transform infrared spectroscopy tests. Self-assembling nanotubes and nanorods were formed together with the layered structures, but they followed different formation mechanisms. The “Rolling” and “Attaching-Oriented Attachment Growth” mechanisms are proposed to describe the formation of VONRs and VONTs, respectively.

Nanocrystalline anatase was synthesized, using both domestic and laboratory microwave ovens, from different precursors. Nanoparticulate anatase was obtained after microwave irradiation of tetra-butyl orthotitanate solution in benzyl alcohol. As-synthesized samples have orange color due to the presence of organics that were eliminated after annealing at 500 °C, whereas the size of small anatase nanocrystals (around 8 nm) was preserved. Other nanocrystalline anatase samples were obtained from hexafluorotitanate-organic salt ionic liquid-like precursors. In this case, use of a domestic microwave oven and very short processing times (1–3 min irradiation time) were involved. Good specific capacity values and capacity retention at high C rates for insertion/deinsertion of Li+were recorded when testing such nanoparticles as electrode material in lithium cells. The electrochemical performances were found be strongly dependent on the phase composition, which in turn could be tuned through the synthetic procedure.

Hyperbranched copper phthalocyanine (CuPc) with uniform spherical morphology has been firstly obtained by ethylene glycol solvothermal synthetic route. The highly dispersed spherical CuPc aggregates with a diameter of ∼500 nm. X-ray diffraction indicated that the molecules were stacked into one-dimensional b-axis aggregate. In addition, the split Soret band together with the broadened and blue-shifted Q-bands in the optical spectra suggested the H (face-to-face) type of interactions in the arrangement of macrocycles in a dense-packed structure. Due to its good symmetrical structure and unique morphology, the hyperbranched spherical CuPc showed excellent broadband microwave absorption behaviors in a frequency of 2–18 GHz. Over an absorber of 5 mm thickness, an absorption bandwidth of 12 GHz corresponding to reflection loss below −10 dB can be obtained. The high value of microwave reflection about −50 dB at the frequency of 16.5 GHz also suggested that the hyperbranched spherical CuPc can be used as promising microwave absorbing materials.

Nanoerythrocyte-shaped ytterbium orthovanadate (YbVO4) with substantially uniform size have been successfully synthesized by a simple and facile trisodium citrate-assisted hydrothermal method. The erythrocyte-shaped YbVO4 nanocrystals with self-assembled spherical and biconcave structure have a diameter of ∼500 nm, which were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The luminescent properties of erbium ion-doped ytterbium orthovanadate nanocrystals with different morphologies by different complexing agents were different in the relative intensity under identical measurement conditions, which exhibited the interesting morphology-dependent optical properties. The different energy transfer mechanisms and photoluminescence intensities might be the result of the greatly reduced defect centers.

Using a combination of high-resolution dilatometric measurements and microstructural analysis, this study investigated the bainitic transformation behavior in ultra-high strength 30CrNi3MoV steel after experiencing small deformation at 850 °C (in the nonrecrystallization austenite region). Under the influence of the small deformation in the nonrecrystallization austenite region, the bainite starting temperature (Bs) raised, the bainite finishing temperature (Bf) decreased, granular bainite was promoted to form, and intersections of differently oriented bainite laths became more common in the microstructure. The increase of Bs is owing to the stored energy in distorted austenite grain boundaries, which can serve as an extra mechanical driving force for bainitic transformation during continual cooling. The decrease of Bf can attributed to the more universal intersections of bainite laths with different orientations, which can decelerate the overall growth rate of bainite. The promoted formation of granular bainite is closely related to the increase of Bs because granular bainite usually forms at relatively high temperatures in the bainite range, above upper bainite and lower bainite.

The hardness changes caused by formation of the metastable and stable phases were examined and correlated with the microstructural changes in grain interior and grain boundary during aging at 350 °C to clarify the age-hardening and softening mechanism of a low-gold Au-Cu-Ag-Pd dental alloy. Aging in this context refers to the time-delay that occurs wherein such alloys are kept at elevated temperatures for periods upto many hours to allow precipitation or ordering to take place. During the period of increasing hardness, the matrix was separated into the Ag-rich α1 and AuCu I phases through the metastable phases, forming block-like structure. The apparent hardening was attributed primarily to lattice strain due to the tetragonality of AuCu I′ [the primer (′) here indicates a metastable phase; likewise (I) and (I′) indicate stable AuCu I and metastable AuCu I′ phases, respectively] and AuCu I phases along the c-axis, secondarily to the coherency or semicoherency strain between the metastable α1′ and AuCu I′ phases and between the α0 and AuCu I phases along the a-axis. The apparent softening was caused primarily by growth and coarsening of the lamellar structure in the grain boundaries, secondarily by coarsening of the block-like structure in the grain interior.

In this work, we succeeded in synthesis of spinel LiMn2O4 via a facile self-template method. The product displays a micro-/nanohybrid structure. Nanoparticles/plates act as the primary nanoblocks to build the secondary microarchitecture. There is the open space between the nanoblocks and the void space between the secondary structures. Electrochemical tests demonstrate that the as-synthesized sample exhibits superior rate capability and high-rate cycleability when contrasted with its solid counterpart. The initial discharge capacity is 126 mAh/g at 0.1 C, 110 mAh/g at 10 C, and 84 mAh/g at 20 C. The discharge capacity retention of about 80% is obtained after 800 cycles at 10 C. The high capacity and excellent cycling life of the material shows its potential for application as high-power batteries. The improved rate capability and cycleability can be attributed to its secondary structure that can facilitate fast Li-insertion/extraction and buffer the volume expansion/contraction upon cycling.

Fabrication of nanosized silicon carbide (SiC) crystals is a crucial step in many biomedical applications. Here we report an effective fabrication method of SiC nanocrystals based on simple electroless wet chemical etching of crystalline cubic SiC. Comparing an open reaction system with a closed reaction chamber, we found that the latter produces smaller nanoparticles (less than 8 nm diameter) with higher yield. Our samples show strong violet-blue emission in the 410–450 nm region depending on the solvents used and the size. Infrared measurements unraveled that the surface of the fabricated nanoparticles is rich in oxidized carbon. This may open an opportunity to use standard chemistry methods for further biological functionalization of such nanoparticles.

In this paper, we report on the well-aligned zinc oxide (ZnO) nanorods synthesized on Ag buffer layer/glass substrate using a modified hydrothermal method, which adopts the strategy of Ag layer facing down. The effects of position, thickness, and annealing temperature of Ag layer on the shape of ZnO nanocrystals were systematically investigated. It was found that the diameter and length of ZnO nanorods decrease with the Ag layer height up to 12 mm, above which no obvious decrease was observed. Oppositely, the density, diameter, and length of ZnO rods all increase with an increase in the Ag layer thickness, except that the length becomes constant above a critical thickness of 60 nm. In addition, when the Ag layer annealing temperature increases from 300 to 400 °C, the nanorod density decreases, the diameter increases, and the length remains nearly invariable, respectively. Surprisingly, randomly inclined nanorods with two different diameters dispersedly coexist on the Ag layer that was annealed at 500 °C. This work may provide an effective approach for the shape control in ZnO-based applications.

Properties of entangled materials, made of fibers, depend on the number and the nature of contacts between fibers and fibers orientation. Nonsintered and sintered steel wools have been characterized by x-ray tomography to extract structural information such as fibers orientation and number of contacts before and during compression. Image analysis techniques were developed on tomography images and validated on virtual materials, generated and deformed by numerical simulation based on molecular dynamic equations. The structural parameters measured during the structural characterization were finally used to link the structure of the studied material with the measured mechanical properties. To do this link, an analytical model usually used for this kind of material was modified to describe the evolution of mechanical properties in compression.

Er3+-doped oxyfluoride transparent glass and glass-ceramics (GCs) containing SrF2 nanocrystals were prepared and their spectroscopic properties were investigated. The formation of SrF2 nanocrystals in GCs has been confirmed by x-ray diffraction (XRD) and transmission electron microscopy. The Judd-Ofelt (JO) parameters have been evaluated from absorption spectra of the Er3+-doped glass and GCs, which are used to predict radiative properties for some important luminescence levels of Er3+ ions in glass and GCs. The XRD and JO parameters suggest that the Er3+ ions are progressively incorporated into the SrF2 nanocrystals in the GCs compared with glass. The up-conversion luminescence intensity increases significantly in GCs with increase in time of thermal treatment. The lifetime of the 4S3/2 level of the Er3+ ions in GCs is found to be slightly higher than that in the glass due to the incorporation of Er3+ ions into the lower phonon energy of SrF2 nanocrystals in the GCs.

A method of growing SiC nanowires (NWs) on 4H–SiC surfaces by in situ vapor-phase catalyst delivery was developed as an alternative to the ex situ deposition of the metal catalyst on the targeted surfaces before the NW chemical vapor deposition (CVD) growth. In the proposed method, sublimation of the catalyst from a metal source placed in the hot zone of the CVD reactor, followed by condensation of the catalyst-rich vapor on bare substrate surface was used to form the catalyst nanoparticles required for the vapor–liquid–solid (VLS) growth of SiC NWs. The NW density was found to gradually decrease downstream from the catalyst source and was influenced by both the gas flow rate and by the catalyst diffusion through the boundary layer above the catalyst source. Formation of poly-Si islands at too low value of the C/Si ratio created preferential nucleation centers for misaligned SiC NWs and NW bushes. The flexibility of controlling the nanoparticle density made this technique suitable for NW growth on horizontal surfaces as well as on patterned SiC substrates, including the vertical sidewalls of SiC mesas.

Four-layer multiwalled carbon nanotube (MWNT) thin films were deposited via dropcasting (1 mg/mL MWNTs and 10 mg/mL SDBS) onto filter papers that vary in pore size (1, 5, 25, and 40 µm) to determine the effect of the underlying substrate structure on the in-plane properties of the films. The films (<100 nm thick) were dried using vacuum filtration, and drying in a 65 °C heater with and without a ceramic heating board. DC resistance of the films ranged from 6 × 103 to 9.3 × 109 Ω. Impedance spectroscopy analysis revealed a low and a high frequency inductive response and two parallel R–C circuits for the more conducting thin films. High resistance films were fit by a single RC circuit with a constant-phase element. The differences in the in-plane electrical responses of the different MWNT films can be explained by the degree of carbon nanotube surface coverage, obtained as a result of using different pore size filter papers. The drying method utilized also affected the CNT network formation and its resultant electrical properties.