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We report an in situ study of epitaxial island formation and alloying of FePd nanoparticles using reflection high-energy electron diffraction (RHEED) followed by ex situ atomic structure characterization. We used aberration corrected (AC) scanning transmission electron microscopy (STEM) with a high-angle annular dark field (HAADF) detector for the study of chemical ordering. The FePd nanoparticles were formed by sequential deposition of Pd and Fe onto NaCl substrates, which was then followed by heating to high temperatures to promote chemical ordering during a short period of annealing. We show that the epitaxial island growth and subsequent alloying of Fe into Pd can be clearly detected by RHEED. The high resolution and the atomic number (Z) contrast of AC HAADF-STEM allow a clear observation of nanometer-sized local chemical order in very small nanoparticles. The results revealed complex chemical structures at an intermediate stage of the ordering process with ordered regions of both L10 and L12 phases. [ABSTRACT FROM AUTHOR]

An excellent adhesion of hard coatings to steel substrates is paramount in practically all application areas. Conventional methods utilize Ar glow etching or cathodic arc discharge pretreatments that have the disadvantage of producing weak interfaces or adding droplets, respectively. One tool for interface engineering is high power impulse magnetron sputtering (HIPIMS). HIPIMS is based on conventional sputtering with extremely high peak power densities reaching 3 kW cm-2 at current densities of >2 A cm-2. HIPIMS of Cr and Nb was used to prepare interfaces on 304 stainless steel and M2 high speed steel (HSS). During the pretreatment, the substrates were biased to Ubias=-600 V and Ubias=-1000 V in the environment of a HIPIMS of Cr and Nb plasma. The bombarding flux density reached peak values of 300 mA cm-2 and consisted of highly ionized metal plasma containing a high proportion of Cr1+ and Nb1+. Pretreatments were also carried out with Ar glow discharge and filtered cathodic arc as comparison. The adhesion was evaluated for coatings consisting of a 0.3 μm thick CrN base layer and a 4 μm thick nanolayer stack of CrN/NbN with a period of 3.4 nm, hardness of HK0.025=3100, and residual stress of -1.8 GPa. For HIPIMS of Cr pretreatment, the adhesion values on M2 HSS reached scratch test critical load values of LC=70 N, thus comparing well to LC=51 N for interfaces pretreated by arc discharge plasmas and to LC=25 N for Ar etching. Cross sectional transmission electron microscopy studies revealed a clean interface and large areas of epitaxial growth in the case of HIPIMS pretreatment. The HIPIMS pretreatment promoted strong registry between the orientation of the coating and polycrystalline substrate grains due to the incorporation of metal ions and the preservation of crystallinity of the substrate. Evidence and conditions for the formation of cube-on-cube epitaxy and axiotaxy on steel and γ-TiAl substrates are presented. [ABSTRACT FROM AUTHOR]

Detailed crystallographic data on high-quality Li2MnO3 material has been obtained using a combination of X-ray diffraction (XRD), selected-area electron diffraction (SAED), high-resolution electron microscopy (HREM), and 0.1 nm probe high-angle annular dark-field imaging (HAADF) in a scanning transmission electron microscope. A high-purity Li2MnO3 powder was annealed at 950 °C for 3 days to obtain predominantly defect-free grains which average size was 3.0 ± 1.5 μm. Rietveld refinement indicated that the C2/m spacegroup provided the best fit for the XRD data. Electron diffraction patterns obtained along various zone axes, on defect-free oxide particles, could be uniquely indexed to the monoclinic structure. HREM and HAADF images of defect-free grains were consistent with a Li–Mn–Mn– arrangement, i.e., lithium ordering in the transition metal planes. Low-magnification TEM images occasionally revealed stacking defects within oxide particles. HREM images of sample areas containing defects revealed a low density of stacking faults within the monoclinic sequence, resulting in a trigonal P3 1 12 local arrangement. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure of the transfer layer, and the underlying severely plastically deformed layer (SPDL), formed during the dry sliding of a spinodally hardened Cu–15wt.% Ni–8wt.% Sn bronze against a stainless steel, is characterized at the nanoscale by conventional and analytical transmission electron microscopy, including energy-dispersive spectroscopy and electron energy loss spectroscopy. The SPDL consists of a Cu–Ni–Sn solid solution with elongated nanograins, due to extensive dislocation glide and twinning. In contrast, the transfer layer, 2–3μm thick, is an equiaxed nanocomposite comprised of a Cu-rich metallic phase with a (Fe,Cr)2O3-based oxide precipitates, and forms as a result of the mechanical mixing and compaction of wear debris. The bronze in this layer has undergone dealloying, indicative of the importance of thermal effects. The dispersion of oxide in the transfer layer suggests a different type of forced mixing, possibly turbulent mixing. The transfer layer is observed to improve significantly the wear resistance of the bronze. [Copyright &y& Elsevier]

Low friction C/Cr coatings have been successfully deposited by the combined steered cathodic arc/unbalanced magnetron sputtering technique. The present paper focuses on the properties, tribological performance and microstructure evolution of C/Cr coatings as a function of the bias voltage Ub ranging from -65 to -350 V. As the bias voltage increases from -65 to -95 V, the structure changes from columnar to dense structure which comprises of randomly distributed onionlike carbon clusters. Further increase in the bias voltage to -350 V led to segregation and self-organisation of the carbon atoms induced by the high energy ion bombardment and finally to the formation of a new type self-organised multilayer structure. On the other hand, the phase composition transforms from graphitic (sp2 C–C bonded) to Me carbon (Cr–C bonded), where the content of the carbide phase increases with increasing the bias voltage. The C/Cr coatings showed an excellent adhesion (Lc>70 N), with hardness ranging from 8·23 to 25 GPa depending on the bias voltage. Pin on disc tests showed that the friction coefficient was reduced from 0·22 to 0·16 when the Ub was increased from -65 to -95 V. A strong correlation was found between the microstructure, the residual stress, the sp2/sp3 content and the coating friction behaviour. Dry high speed milling trials on automotive aluminium alloy (Al–Si8Cu3Fe) showed that C/Cr coated cemented carbide end mills enhance the tool performance and the tool life compared with the uncoated tools by a factor of 2, suggesting the potential for dry high speed machining of 'sticky' alloys. [ABSTRACT FROM AUTHOR]

Various amorphous SiO[sub x] nanotube structures nucleated by GeO[sub x] nanoparticles were synthesized by thermal evaporation method. The presence of Ge does not only nucleate the growth of the SiO[sub x] nanomaterials, but also dopes them. The nanostructure morphology is affected by the substrate temperature, source temperature and GeO[sub x] vapor density through their effect on the size and lifetime of the nucleation center. In general, low substrate temperature promotes the formation of the nanotube bundle structure with 2-3% atomic ratio of Ge doping, and high temperature produces Ge-free much less bundled nanotubes. [ABSTRACT FROM AUTHOR]

A quad-phase surface acoustic wave filter is designed as a power divider/combiner for RF power amplifiers. Due to its function it is equivalent to a quadrature hybrid with embedded balun and filter, and when applied to a balanced dual-fed push-pull PA configuration the effectiveness is demonstrated. [ABSTRACT FROM AUTHOR]

We have investigated the stability and solidification of nanometer size Au-Si droplets using an ultrafast heating/cooling nanocalorimetry and in situ growth techniques. The liquid can be supercooled to very low temperatures for both Au-rich (ΔT ∼ 95 K) and Si-rich (ΔT ∼ 220 K) samples. Solidification of a unique metastable phase δ1 is observed with a composition of 74 ± 4 at. % Au and a b-centered orthorhombic structure (a = 0.92, b = 0.72, and c = 1.35 nm; body-center in the a-c plane), which grows heteroepitaxially to Aus. Its melting temperature Tm is 305 ± 5 °C. There is competition during formation between the eutectic and δ1 phases but δ1 is the only metastable alloy observed. For small size droplets, both the δ1 and eutectic phases show considerable depression of the melting point (size-dependent melting). [ABSTRACT FROM AUTHOR]

Carbon nanotube junctions are of great interest in the fundamental research and nanoelectronic applications. Identical carbon nanotube Y junctions have been successfully synthesized by pyrolysis of methane over cobalt supported on magnesium oxide. The Y junctions have very straight arms with uniform diameters, and the angles between the three arms are close to 120°. Based on the analysis on the structure of the Y junctions the growth mechanism has been discussed. The fact that all the Y junctions grow in a similar way may be very important in the development of nanoelectronic devices. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Bi-based superconducting phases have been studied by transmission electron microscopy. The strong one-dimensional modulations in undoped and Ce-doped monoclinic Bi2 Sr2 CuO6 (2201) samples are different from one another. We have found a new 2201 phase containing Pb and Ca with orthorhombic symmetry in nominal (Bi0.90 Pb0.10 )2 Sr2 CaCu2 O8 crystals. Its structure with space group Bbmb and two-dimensional modulation are analogous to those of the Pb-doped higher members of the structural series Bi2 Sr2 Can-1 Cun O2n+4 . Hence, this new orthorhombic rather than the monoclinic 2201 phase should be the first member of the structural series. [ABSTRACT FROM AUTHOR]

Nanocrystalline films with high hardness have attracted increasing interest for wear resistant applications. Specifically, nanocrystalline Ti–B–N layers have been demonstrated to exhibit enhanced hardness and thermal stability. Here, we show that Ti–B–N films grown at 300 °C and consisting of a high volume fraction, ∼50%, of a fully percolated disordered phase encapsulating 2–3 nm wide TiN and TiB2 grains, have a hardness of 37 GPa and an elastic modulus of 332 GPa which increase with annealing to 43 and 362 GPa, respectively, at Ta=800 °C. The structural rearrangement which occurs during annealing results in the formation of compact interface boundaries which lead, in turn, to the observed hardness increase. Annealing at Ta>900 °C decreases the hardness, although the elastic modulus continues to increase, due to the combination of grain growth and B loss via the formation of volatile boron oxides and hydroxides. These conclusions, obtained based upon a combination of x-ray diffraction, nanoindentation, electron probe microanalysis, and transmission electron microscopy, are corroborated by calorimetric investigations. The overall results provide insight toward developing “design rules” for high-temperature superhard nanoscale based coatings. [ABSTRACT FROM AUTHOR]

Here, we present the observation of a bias-induced, degradation-enhancing defect process in plasma-assisted molecular beam epitaxy grown reverse gate-biased AlGaN/GaN high electron mobility transistors (HEMTs), which is compatible with the current theoretical framework of HEMT degradation. Specifically, we utilize both conventional transmission electron microscopy and aberration-corrected transmission electron microscopy to analyze microstructural changes in not only high strained regions in degraded AlGaN/GaN HEMTs but also the extended gate-drain access region. We find a complex defect structure containing an I2 basal stacking fault and offer a potential mechanism for device degradation based on this defect structure. This work supports the reality of multiple failure mechanisms during device operation and identifies a defect potentially involved with device degradation. [ABSTRACT FROM AUTHOR]

We developed a simple approach to carry out in situ electron microscopy of single Li-ion battery cathode particles during electrochemical cycling. We focused on Li(Ni0.8Co0.15Al0.05)O2-based cathode materials because life-cycle tests suggest a strong contribution of the cathode material to changes in cell impedance. In situ scanning electron microscopy was carried out operando during cycling and at various stages by interrupted cycling. Our work revealed several important aspects of cathode oxide particle dynamics: significant separations develop between grains even during the very first charge (oxide delithiation) and electrolyte penetration through that crack network all the way into the particle interior. Comparing these results to post-test microstructural characterization of oxide particles subjected to extensive cycling confirms the occurrence of these processes in practical cells and suggests that the physical separation and isolation of grains may contribute to performance degradation of lithium-ion cells. [ABSTRACT FROM AUTHOR]

Objective: The epidermal growth factor (EGF) system is expressed in the rat prostate, and growth factors from this system induce proliferation in prostate epithelial and stromal cell cultures. The aim of the study was to investigate the possible growth-promoting effects of the system during the hyperplastic growth phase of the prostate in newborn rats. Material and Methods: Newborn rats were treated for 8 weeks with EGF (150 µg/kg body weight per day), administered as daily subcutaneous injections. Sections of the prostate tissue were examined by a stereological technique to determine tissue composition. Results: Treatment with EGF increased the weight of the ventral prostate, relative to body weight, by 50% compared with placebo (p < 0.005). Neither the dorsolateral prostate, seminal vesicles nor coagulating glands were affected by EGF. Prostate tissue showed a significant increase in the volume of the prostate epithelium, the stroma and the lumen following EGF treatment, in a pattern resembling physiological growth of the ventral prostate. A significant correlation (r = 0.78, p < 0.0001) of the volume fraction of the lumen with the glandular weight of the ventral prostate was seen. Serum testosterone was not affected by chronic EGF administration. Conclusions: EGF selectively induces growth of the ventral lobe of the prostate in newborn rats, in a pattern comparable to normal physiological growth. It may be hypothesized that the physiological growth of the prostate is directly correlated to endogenous activity of the EGF system in the rat prostate gland. [ABSTRACT FROM AUTHOR]

High quality In2O3 films are grown by chemical vapor transport and condensation using high purity commercial In2O3 and ZnO powders as starting materials, under an Ar/O2 gas mixture. The cubic structure of the In2O3 films is determined by x-ray diffraction and Raman spectroscopy. At 300 K, the photoluminescence (PL) results from In2O3 films display only an intense deep level emission line centered at 1.968 eV, similar to that obtained from the commercial In2O3 powder. In the UV range, 5 K PL measurements of the films reveal sharp lines which are not observed on the 5 K PL spectrum from commercial In2O3 powder. The dominating peak at 3.3672 eV, as well as energy differences of 72 meV between lines are characteristic of ZnO and correspond to a neutral donor bound exciton (D0X) emission and the energy of the LO phonon in ZnO, respectively. In comparison to the D0X line position from ZnO nanostructures, this D0X line displays a blueshift of 8 meV which is well explained by a quantum confinement of ZnO nanocrystallites in In2O3. Low temperature PL measurements reveal ZnO nanocrystallites embedded in In2O3 film, which are not observed by either x-ray diffraction and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

TiB2 thin films are well known for their high hardness which makes them useful for wear-resistant applications. Overstoichiometric TiB2 deposited at 300 °C by nonreactive sputtering has been shown to exhibit superhardness (H>=40 GPa), while the hardness of their bulk stoichiometric counterparts is ∼25 GPa. We show, using high-resolution transmission electron microscopy, that overstoichiometric TiB2.4 layers have a complex self-organized columnar nanostructure. The ∼20 nm wide columns, encapsulated in excess B and oriented along 0001, consist of a bundle of ∼5 nm diameter TiB2 subcolumns separated by an ultrathin B-rich tissue phase. The nanocolumnar structure, which is thermally stable to postannealing temperatures up to 700 °C, inhibits nucleation and glide of dislocations during hardness indentation measurements, while the high cohesive strength of the B-rich tissue phase prevents grain-boundary sliding. The combination of these effects results in the observed superhardness of ∼60 GPa. [ABSTRACT FROM AUTHOR]

We use a combination of alloying and low-energy ion irradiation during film growth to controllably manipulate the nanostructure of TiN-based layers. Ti0.8Ce0.2N films are grown on SiO2 at 350 °C using UHV reactive magnetron sputtering in N2. The N2+-to-metal ratio incident at the growing film is maintained constant at 15, while the ion energy EN2+ is varied from 14 to 45 eV. Films grown with EN2+=14 eV consist of equiaxed nanograins with an average size of 2.0 nm, while layers deposited with EN2+=45 eV exhibit a 2-nm-wide nanocolumnar structure. In both cases, the films are dense, atomically smooth, and have strong 002 texture with low stress. This is in dramatic contrast to TiN films deposited under the same conditions, which are underdense with extremely rough surfaces and consist of broad (≃ 30 nm) columns. We attribute the formation of controlled nanostructures to the interplay between ion-irradiation-induced effects and thermally driven Ce surface segregation, leading to continuous renucleation during film growth. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Boron carbide nanolumps are formed on the surface of multiwall carbon nanotubes by a solid-state reaction between boron and carbon nanotubes. The reaction is localized so that the integrity of the structure of carbon nanotubes is maintained. Inner layers of multiwall carbon nanotubes are also bonded to boron carbide nanolumps. These multiwall carbon nanotubes with boron carbide nanolumps are expected to be the ideal reinforcing fillers for high-performance composites because of the favorable morphology. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We show that electroplated Re films in multilayers with noble metals such as Cu, Au, and Pd have an enhanced superconducting critical temperature relative to previous methods of preparing Re. The dc resistance and magnetic susceptibility indicate a critical temperature of approximately 6 K. The magnetic response as a function of field at 1.8 K demonstrates type-II superconductivity, with an upper critical field on the order of 2.5 T. Critical current densities greater than 107 A/m2 were measured above liquid-helium temperature. Low-loss at radio frequency was obtained below the critical temperature for multilayers deposited onto resonators made with Cu traces on commercial circuit boards. These electroplated superconducting films can be integrated into a wide range of standard components for low-temperature electronics. [ABSTRACT FROM AUTHOR]

Abstract: The paper discusses the effect of ion irradiation on a new type of nanoscale multilayer structure in C/Cr PVD coatings formed by a self-organisation mechanism. C/Cr coatings were deposited by the combined steered cathodic arc/unbalanced magnetron sputtering technique, at wide range of bias voltages, U b from −65 to −550 V. Plasma diagnostics carried out by electrostatic probe measurements revealed that C/Cr films grow under conditions of intensive ion bombardment with ion-to-neutral ratio exceeding J i/J n =6. Under these conditions the high diffusion mobility and the reactivity of the C leads to distinct changes in the coatings microstructure and phase composition. Raman spectroscopy and XPS (X-ray photoelectron spectrometer) analysis of the chemical bonding in the films showed that the phase composition of the films gradually transforms from more graphite like (sp2 C–C bonded) to more Me-carbon (Cr–C bonded), where the content of the carbide phase increases with increase of the bias voltage to U b =−350 V and higher. In parallel HRTEM (high-resolution transmission electron microscopy) employing HAADF (high-angle annular dark field) imaging revealed that the microstructure evolved from columnar with carbon accumulated at the column boundaries (U b =−65 V, −95 V) to a structure dominated by onion like C–Cr clusters (U b =−120 V), which than converts to a distinct nanoscale layered structure (U b =−350 V, −450 V), finally transforming to a uniform fine grain structure at U b =−550 V. The new nanoscale layered structure forms via ion irradiation induced self-organisation mechanism. It is characterized by an abnormally large values for the bi-layer thickness of 20 nm and 25 nm, which are not related to substrate rotation, for films grown at U b =−350 V and U b =−450 V, respectively. ADF (annular dark field) STEM (scanning TEM) imaging and quantitative EELS (electron-energy loss spectroscopy) analysis showed that the nanoscale multilayer structure comprises of alternating layers of Me-carbide phase (48%C, 52%Cr) and almost pure C (91.34%C), where the bias voltage defines the bi-layer thickness. A coating growth model is proposed accounting for the irradiation-induced ion mixing, re-sputtering, condensation surface temperature effects, nucleation and kinetic segregation process, as well as the diffusivity of the coating elements to explain the phase separation and formation of the self-organised layered nanostructure observed in C/Cr coatings. [Copyright &y& Elsevier]

Nanoscale multilayer C/Cr coatings (bilayer thickness ∼2 nm) were produced by the combined steered cathodic arc/unbalanced magnetron deposition technique. The mirror-polished M2 substrates were treated by Cr+ ion etching/implantation followed by the deposition of a 0.25 μm thick CrN base layer. A 1.6 μm thick C/Cr multilayer coating was then deposited by non-reactive unbalanced magnetron sputtering while rotating the substrates in front of three graphite and one Cr targets. During the multilayer deposition, a bias potential between −65 and −95 V was applied to the substrates. The ion flux measured by a flat electrostatic probe was 1.2 mA cm−2 and the deposition rate was 0.4 μm h−1, which resulted in ion-to-neutral ratio of Ji/Jn=5.2. Cross-sectional transmission electron microscopy diffraction and Z-contrast imaging investigations revealed a novel nanostructure in which the basic nano-lamellae obtained as a result of substrate rotation in front of the C and Cr targets were modified by ion-irradiation-induced nanocolumnar structure. The intense ion-irradiation of the immiscible film components caused local enrichment of Cr and C that propagated in the growth direction resulting in Cr-rich nanocolumns separated by C-rich boundaries in an overall amorphous structure. Tribological studies of the composite C/Cr coatings were conducted using a pin-on-disk apparatus under a load of 5 N, at velocities of 0.13–0.15 m s−1 and for distances of ∼500 m in dry nitrogen (∼0% humidity) and open air (30% relative humidity). Results indicated that the C/Cr composite coatings provided friction coefficients of 0.7–0.8 in dry nitrogen, while the values were significantly lower in open air, 0.21–0.24, during sliding against both the coated and uncoated balls for coatings deposited at bias voltage of −75 V. The friction coefficient decreases to 0.16 when the bias voltage of −95 V was used. [Copyright &y& Elsevier]

Large periodic arrays of carbon nanotubes have been grown by plasma-enhanced hot filament chemical vapor deposition on periodic arrays of nickel dots that were prepared by polystyrene nanosphere lithography. A single layer of self-assembled polystyrene spheres was first uniformly deposited on a silicon wafer as a mask, and then electron beam vaporization was used to deposit a nickel layer through the mask. The size of and spacing between the nickel dots are tunable by varying the diameter of the polystyrene spheres, which consequently determines the diameter and site density of carbon nanotubes. The technique can be scaled up at much lower cost than electron beam lithography. [ABSTRACT FROM AUTHOR]

Pulse-current electrochemical deposition has been used to prepare Ni nanoparticles that are used as the catalysts for the growth of aligned carbon nanotubes. The nucleation site density of the Ni nanoparticles was controlled by changing the magnitude and duration of the pulse current. The aligned carbon nanotubes from the nickel nanoparticles were grown by plasma enhanced hot filament chemical vapor deposition. The site density of the aligned carbon nanotubes varied from 10[sub 5] to 10[sup 8] cm[sup -2]. The achievement of controlling the site density is significant for applications of carbon nanotubes as field emitters, nanoelectrodes array, etc. [ABSTRACT FROM AUTHOR]

The ground-state electronic order in doped manganites is frequently associated with a lattice modulation, contributing to their many interesting properties. However, measuring the thermal evolution of the lattice superstructure with reciprocal-space probes alone can lead to ambiguous results with competing interpretations. Here we provide direct observations of the evolution of the superstructure in La1/3Ca2/3MnO3 in real space, as well as reciprocal space, using transmission electron microscopic (TEM) techniques. We show that the transitions are the consequence of a proliferation of dislocations plus electronic phase separation. The resulting states are well described by the symmetries associated with electronic-liquid-crystal (ELC) phases. Moreover, our results resolve the long-standing controversy over the origin of the incommensurate superstructure and suggest a new structural model that is consistent with recent theoretical calculations. [ABSTRACT FROM AUTHOR]

The in-field critical current of commercial YBa2Cu3O7 coated conductors can be substantially enhanced by post-fabrication irradiation with 4 MeV protons. Irradiation to a fluence of 8 × 1016 p/cm2 induces a near doubling of the critical current in fields of 6 T || c at a temperature of 27 K, a field and temperature range of interest for applications, such as rotating machinery. A mixed pinning landscape of preexisting precipitates and twin boundaries and small, finely dispersed irradiation induced defects may account for the improved vortex pinning in high magnetic fields. Our data indicate that there is significant head-room for further enhancements. [ABSTRACT FROM AUTHOR]

We have performed magnetic and transport measurements on La[sub 0.67]Ca[sub 0.33]MnO[sub 3] polycrystalline and partially melted samples. The magnetization and resistance decrease as sintering temperature is increased. The insulator-to-metal transition temperature is remarkably enhanced in the partially melted sample, enabling its possible applications at room temperature. The microscopic studies in melt samples show an excellent connectivity between grains, suggesting the enhancement of percolative transport by opening new conduction channels and the disappearance of magnetic phase boundary at elevated temperature by the ordering of Mn spins blocked at the grain boundary of sintered samples. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]