Fabrication and characterization of Au-nanoparticle/W-nanodendrite structures on Al2O3 substrate

An Au-nanoparticle/W-nanodendrite compound structure was fabricated on an insulator Al₂O₃ substrate using an electron-beam-induced deposition (EBID) process combined with an ion sputtering method. The as-fabricated compound structures were characterized and analyzed using conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) and X-ray energy dispersive spectroscopy (EDS). W-nanodendrite structures with the tips of 3 nm were grown self-standing at the edge of the Al₂O₃ substrate at positions separated from each other in distance of several nanometers. Au-nanoparticles with a grain size of 2.1 nm were uniformly distributed on the W-nanodendrites. The Au-nanoparticles were determined to be the equilibrium phase of Au with the face-centered cubic (fcc) structure.     

Deposition and characterization of a novel integrated ZnO nanorods/thin film structure

One-dimensional (1-D) ZnO (zinc oxide) nanostructures have received a lot of attention due to their superior properties. Various techniques have been developed to synthesize ZnO nanorods at high-temperature process using vapor–liquid–solid (VLS) mechanism. In this paper, we report a novel process to synthesize integrated ZnO nanorods/thin film structures using an RF magnetron sputter deposition under different deposition parameters and substrate conditions. The substrate used was glass plated with electroless Cu prepared using various conditions. The resulting specimens are analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The effect of the copper surface roughness was found to be significant. ZnO nanorods were found only when the copper layer is rough enough. The roughness of the copper in general increases with the plating time and/or the ratio of V_HCHO/V_Cu used in the plating bath. Post-plating annealing of the copper was also found to increase the surface roughness of the copper.     

One-pot morphology-controlled synthesis of various shaped mesoporous silica nanoparticles

A simple synthetic method has been developed for synthesis of mesoporous silica nanoparticles with versatile morphologies by adopting CTAB and C₁₂–OH as dual soft templates. In such a simple method, only by regulating the dose of C₁₂–OH and temperature, we can well-realize the silica nanoparticle morphological transformation from sphere to shell-like, rugby-like, peanut-like, hollow, and complex yolk–shell structures. These as-fabricated silica nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller (BET), and small-angle powder X-ray diffraction. The as-prepared mesoporous silica nanoparticles with versatile morphologies possessing varying BET surface areas, pore diameter, and pore distributions have some potential applications in separation, sensing, and heterogeneous catalysis.     

Diffraction contrast analysis of 90° and 180° ferroelectric domain structures of PbTiO3 thin films

Abstract

The ferroelectric domain structure of a PbTiO₃ thin film on (100) SrTiO₃ has been investigated by transmission electron microscopy (TEM). Two types of a-domain were found: one extended through the film to the surface and another comprised small a-domains confined within the film. Dark-field TEM (DFTEM) observation revealed that 180° domains formed near the substrate and stopped their growth 100 nm away from the substrate. The DFTEM observation also revealed that 90° domain boundaries had head-to-tail structures. To confirm the polarization direction obtained by experiments, diffracted intensities under a two-beam condition were simulated using the extended Darwin–Howie–Whelan equations. On the basis of the obtained results, a ferroelectric domain structure model of PbTiO₃ thin films on SrTiO₃ is proposed.     

Interfacial analysis and properties of regioregular poly(3-hexyl thiophene) spin-coated on an indium tin oxide-coated glass substrate

Interfacial analysis of the rrP3HT samples spin-coated on a glass substrate was studied in detail using transmission electron microscopy (TEM) and SEM measurements. Very homogeneous and smooth polymer (P3HT and PEDOT:PSS) layers are observed on the glass substrate. The ITO surface shows a surface roughness, with a layer of about 15 nm. Structural characteristics of the polymer blends were studied using Raman spectroscopy and photoluminescence (PL). The complete reduction of PL of P3HT after mixing with C₆₀ in a 1:1 wt.% indicates an effective charge transfer from P3HT to C₆₀. Thermo-gravimetric analysis showed that the commercially bought materials are of high purity.     

Novel 2D self-assembled arrays of SiOx nanowire bundles

Novel 2D ordered arrays formed by self-assembly of SiO_x nanowire bundles have been prepared on a silicon wafer via a facile metal-mediated gas-phase reaction. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Two types of arrays were grown on a substrate surface by adjusting the preparation parameters. The findings suggest that the growth atmosphere, the flow rate of carrier gas and the relative placement of source and substrate are all responsible for the formation of these unique self-assembled structures. The intermolecular action is the internal driving force for the self-assembly. The formation mechanism of the arrays was proposed on the basis of the growing process.     

Intergranular films at Au-sapphire interfaces

The existence of nanometer-thick amorphous equilibrium films at metal-ceramic interfaces has been experimentally verified for the Au–Al₂O₃ system. The films were formed using a novel experimental approach, in which thin sputtered films of Au were dewetted on a sapphire substrate which was previously partially wetted with drops of anorthite glass (CaO–2SiO₂–Al₂O₃). High-resolution transmission electron microscopy and qualitative analytical transmission electron microscopy were used to confirm the existence of the amorphous films. In addition, positive and relatively large Hamaker constants were calculated for the Au-film-Al₂O₃ interface, which indicates the existence of an attractive van der Waals force which stabilizes the film, similar to equilibrium films at grain boundaries in ceramics. A ∼ 1 nm thick surface film was also detected on the (0001) surface of sapphire substrates partially wetted by anorthite glass. The refractive index required to stabilize the surface films, via a positive Hamaker constant, is explored.     

A study of the physical,chemical and biological properties of TiO2 coatings produced by micro-arc oxidation in a Ca–P-based electrolyte

In this work, a porous and homogeneous titanium dioxide layer was grown on commercially pure titanium substrate using a micro-arc oxidation (MAO) process and Ca–P-based electrolyte. The structure and morphology of the TiO₂ coatings were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and profilometry. The chemical properties were studied using electron dispersive X-ray spectroscopy (SEM–EDS) and X-ray photoelectron spectroscopy. The wettability of the coating was evaluated using contact angle measurements. During the MAO process, Ca and P ions were incorporated into the oxide layer. The TiO₂ coating was composed of a mixture of crystalline and amorphous structures. The crystalline part of the sample consisted of a major anatase phase and a minor rutile phase. A cross-sectional image of the coating–substrate interface reveals the presence of voids elongated along the interface. An osteoblast culture was performed to verify the cytocompatibility of the anodized surface. The results of the cytotoxicity tests show satisfactory cell viability of the titanium dioxide films produced in this study.     

Synthesis,characterization and growth mechanism of ZnO nanowires on NiCl<Subscript>2</Subscript>-coated Si substrates

Well-crystallized ZnO nanowires have been successfully synthesized on NiCl₂-coated Si substrates via a carbon thermal reduction deposition process. The pre-deposited Ni nanoparticles by dipping the substrates into NiCl₂ solution can promote the formation of ZnO nuclei. The as-synthesized nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The results demonstrate that the as-fabricated nanowires with about 60 nm in diameter and several tens of micrometers in length are preferentially arranged along [0001] direction with (0002) as the dominate surface. Room temperature PL spectrum illustrates that the ZnO nanowires exist a UV emission peak and a green emission peak, and the peak centers locate at 387 and 510 nm. Finally, the growth mechanism of the nanowires is briefly discussed.     

High temperature oxidation of Ti-48Al-8Cr-2Ag alloy with sputtered coating at 1000°C in air

Magnetron-sputter deposition was used to produce a Ti-48Al-8Cr-2Ag (at.%) coating on a cast alloy substrate with the same composition. The oxidation behaviour of the cast Ti-48Al-8Cr-2Ag alloy and its sputtered coating was investigated in air at 1000°C. The resulting scale structures were analyzed in great detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanocrystalline coating showed higher oxidation rate than the cast alloy, because an outer TiO₂ layer formed over a finegrain Al₂O₃ scale on the coating. The oxidation mechanism was discussed.     

A biomimetic approach to the deposition of ZrO2 films on self-assembled nanoscale templates

Zirconium oxide thin films were deposited on a phosphonate-terminated self-assembled monolayer (SAM) on a single crystal silicon substrate by a hydrolysis of zirconium sulfate solution in acid environment at 80 °C. The ZrO₂ films consist of tetragonal ZrO₂ crystallites with a size of 5–10 nm. Surface nucleation and attraction between the SAM surface and bulk precipitates in solution can explain the film formation. In both mechanisms, the surface functionality of the SAM plays a crucial role. This deposition approach was inspired by biomineralization through controlled deposition of inorganic solids on an ordered organic matrix. Microstructures and mechanical properties of the ZrO₂ thin films were studied using scanning electron microscope (SEM), cross-sectional transmission electron microscope (TEM) and nanoindentation. Microstructures were tailored at different stages of the film growth, as well as with processing parameters and substrate surface conditions. The nanoindentation modulus and hardness of the as-deposited ZrO₂ films were much lower than those of the bulk ZrO₂. The addition of extra pressure during this process, however, restores mechanical properties of ZrO₂ films.     

Electron field emitters based on multi-walled carbon nanotubes coated with conducting polymer/metal/metal-oxide composites

The present work describes the field emission properties of multi-walled nanotubes (MWNTs)-based conducting polymer/metal-oxide/metal/MWNTs composites (polyaniline (PANI)/SnO₂/Sn/MWNTs). MWNTs were synthesised by chemical vapour deposition technique. SnO₂/Sn/MWNTs were prepared by using chemical reduction followed by calcination. By in situ polymerisation method, surface of SnO₂/Sn/MWNTs were coated with PANI. PANI/SnO₂/Sn/MWNTs field emitters were fabricated over flexible graphitised carbon fabric substrate by spin coating technique. High-resolution transmission electron microscopy and scanning electron microscopy were used to characterise the field emitters. Field emission properties have been studied using an indigenously made facility. The fabricated PANI/SnO₂/Sn/MWNTs field emitters exhibited excellent field emission properties with a turn on field of 1.83 V µm^?1 and a field enhancement factor of 4800.     

Laser and electron-beam melted amorphous layers

Metallic-glass layers were produced on metallic bulk material using laser or electron beam melting. The requisite composition (FeCr₁₂)₈₀(C,B)₂₀ for steel and Ni _x Nb(_100–x ), (x = 30 to 60) for niobium was obtained by coating the substrate prior to melting. X-ray, scanning electron microscopy, transmission electron microscopy and calorimetric methods were used to demonstrate and investigate the amorphous nature of the surface layer.     

Suppressing Twin Formation in Bi2Se3 Thin Films

The microstructure of Bi₂Se₃ topological‐insulator thin films grown by molecular beam epitaxy on InP(111)A and InP(111)B substrates that have different surface roughnesses has been studied in detail using X‐ray diffraction, X‐ray reflectivity, atomic force microscopy and probe‐corrected scanning transmission electron microscopy. The use of a rough Fe‐doped InP(111)B substrate results in complete suppression of twin formation in the Bi₂Se₃ thin films and a perfect interface between the films and their substrates. The only type of structural defect that persists in the twin‐free films is an antiphase domain boundary, which is associated with variations in substrate height. We also show that the substrate surface termination influences which family of twin domains dominates.     

Biaxial CdTe/CaF2 films growth on amorphous surface

A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF₂ nanorods as a buffer layer. The interface between the CdTe film and CaF₂ nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {111}<121> biaxial texture of the CaF₂ nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.     

Synthesis and characterization of large area well-aligned carbon nanotubes by ECR-CVD without substrate bias

Large area, well-aligned carbon nanotubes (CNTs) were synthesized on porous silicon by electron cyclotron resonance chemical vapor deposition (ECR-CVD). No bias was applied on the substrate in this experiment. CH₄ and H₂ were used as source gases and Fe₃O₄ nanoparticles as the catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and Raman spectrum were used to evaluate the structure and composition. The results show that these CNTs have varying outer diameters from 10 to 90 nm and uniform length over 10 μm. They display hollow tubular and chain structures. The possible formation mechanism of aligned CNTs is discussed.     

The effect of sulphur-terminated GaAs substrates on the MOVPE growth of CuGaS2 thin films

In this study, various CuGaS₂ layers were grown on GaAs (001) substrates using metalorganic vapour phase epitaxy, for the purpose of studying the effect of sulphur-termination of the substrate on layer quality. The resultant films were investigated using X-ray diffractometry, and transmission electron microscopy, with high-resolution transmission electron microscopy providing additional insights into crystallite growth on the control substrates. This paper will demonstrate that sulphur-termination limits substrate degradation. In the absence of sulphur-termination, atypical three-dimensional MOVPE growth is observed, with epitaxial crystallites varying in size from 10 nm to 200 nm. Substrate degradation inhibits lateral growth at the interface resulting in amorphous regions, cavities, and epitaxial crystallites demonstrating overgrowth into mushroom-like structures.     

Microstructure and mechanical properties of silicon carbide fibre-reinforced aluminium nitride composite

SiC continuous fibre (15 vol%)/AlN composite was fabricated using a sintering additive of 4Ca(OH)₂ · Al₂O₃ by hot-pressing at 1650 °C and 17.6 MPa in vacuum. Analytical transmission electron microscopy and scanning electron microscopy were used to investigate the microstructure of as-fabricated and crept SiC fibre/AlN composites. The room-temperature mechanical and high-temperature creep properties of the composite were investigated by four-point bending. The incorporation of SiC fibre into AlN matrix improved significantly the room-temperature mechanical properties. This improvement could result from the crack deflections around the SiC fibres. However, the incorporation degraded severely the high-temperature creep properties under oxidizing atmosphere. This could be attributed to the development of the pores and various oxides at the matrix grain boundary and matrix/fibre interface during creep test.     

Fabrication of bulk Al2O3 dispersed ultrafine-grained Cu matrix composite by self-propagating high-temperature synthesis casting route

Bulk Al₂O₃ dispersed ultrafine-grained (UFG) Cu matrix composite has been fabricated by self-propagating high-temperature synthesis (SHS) casting route. The microstructures and mechanical properties of the as-fabricated materials have been investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, and microhardness measurements and compression tests, respectively. The results show that the as-fabricated material has small amount of entrapped Al₂O₃ particles in uniform microstructure Cu having a grain size ranging from 200-500 nm with an elevated compressive yield stress (298 MPa) and an improved microhardness value (1.06 GPa). The possible strengthening mechanism of the product has been discussed.     

Sintering of silver and copper nanoparticles on (001) copper observed by in-situ ultrahigh vacuum transmission electron microscopy

The sintering of copper and silver nanoparticles with single crystal copper substrates has been studied using a novel in-situ ultrahigh vacuum transmission electron microscope (UHV TEM). The system is equipped with a UHV DC sputtering attachment enabling metal nanoparticles to be generated in-situ and transferred directly into the microscope in the gas phase. In both cases, we find the particles to be of initially random orientation on the substrate. Upon annealing, however, the particles reorient and assume the same orientation as the substrate. The process apparently occurs by a mechanism involving sintering and grain growth. In the case of silver on copper, grain growth cannot occur since the metals are immiscible. Our observations show that, upon annealing, the particles wet the substrate surface and form epitaxially oriented islands by surface diffusion and grain boundary migration. The post-anneal islands exhibit the orientation relationship (111)_Ag∥001)_Cu, [110]_Ag∥[110]_Cu.