X. F. Duan

Microstructure and formation mechanism of titanium dioxide nanotubes

Titanium dioxide nanotubes are synthesized using sol-gel method. Electron energy-loss spectroscopy has been used to investigate the chemical composition of the nanotubes. The results show that the atomic ratio of O/Ti is very close to two. Electron diffraction studies indicate that the nanotubes have the anatase structure. High-resolution transmission electron microscopy studies show that the nanotubes possess a layered structure with layer spacing of about 7.1 Angstrom. The tube axis is determined to be along [010] direction of the anatase phase. The formation mechanism of the nanotubes can be explained as 3D --> 2D --> 1D. The two-dimensional lamellar TiO2 is essential for the formation of the nanotubes

Thickness and dielectric constant of dead layer in Pt/(Ba0.7Sr0.3)TiO3/YBa2Cu3O7−x capacitor

Pt/(Ba0.7Sr0.3)TiO3 (BST)/YBa2Cu3O7−x capacitors were prepared and investigated for the dead-layer (DL) thickness (td) and the DL dielectric constant (ed). Based on the series capacitor model, the td/ed ratio of 0.066 nm and the bulk BST ferroelectric-layer dielectric constant of 1370 were obtained through the measurements of the capacitance–voltage characteristics. The td×ed value of 120 nm was obtained through the measurements of the current–voltage characteristics. Combining these data, the DL thickness and the DL dielectric constant are respectively estimated to be 2.8 nm and 42.6.

Straight β-SiC nanorods synthesized by using C–Si–SiO2

Straight beta-silicon carbide nanorods have been grown on silicon wafers using hot filament chemical vapor deposition with iron particles as catalyst. A plate made of a C–Si–SiO2 powder mixture was used as carbon and silicon sources. Hydrogen, which was the only gas fed into the deposition system, acts both as a reactant and as a mass transporting medium. The diameter of the β-SiC nanorod ranged from 20 to 70 nm, while its length was approximately 1 μm. A growth mechanism of beta-silicon carbide nanorods was proposed. The field emission properties of the beta-silicon carbide nanorods grown on the silicon substrate are also reported.

Crystalline boron nanowires

Crystalline boron nanowires were produced through post-annealing amorphous boron nanowires synthesized by rf magnetron sputtering. High-resolution transmission electron microscopy was used to characterize the microstructure of the crystalline boron nanowires. Selected-area electron diffraction studies showed that the crystalline boron nanowires belong to a rhombohedral structure (β-boron), with lattice parameters of a=10.95 A and c=23.82 A. Electron energy-loss spectroscopy was used to characterize the chemical composition of the boron nanowires.

Link‐up of 90° domain boundaries with interface dislocations in BaTiO3/LaAlO3

Interface microstructures of BaTiO3/LaAlO3 grown by metalorganic chemical vapor deposition (MOCVD) are studied using high‐resolution transmission electron microscopy (HRTEM). Interface dislocations in BaTiO3/LaAlO3 have been shown to be directly linked up with the 90° domain boundaries in BaTiO3. This association is a result of strain relief due to a phase transformation when cooled down from the growth temperature. The Burgers vector of the interface dislocations is 〈010〉.

Amorphous feather-like boron nanowires

Abstract Large-scale arrays of feather-like boron nanowires have been successfully prepared using magnetron sputtering with a target of highly pure boron and boron oxide mixture. The morphology, microstructure and composition of the feather-like boron nanowires are characterized in detail using scanning electron microscopy, transmission electron microscopy, and electron energy-loss spectroscopy. Elemental mapping has been used to investigate the distribution of boron and oxygen in the boron nanowires. It is revealed that the feather-like boron nanowires possess the microstructure of outer oxidized coating layer and inner pure boron. The thickness of the outer oxidized layer is about 1–2 nm. Our results may provide opportunities to understand the fundamentals of boron chemistry and to fabricate new nanodevices.

Cobalt valence in epitaxial Ti0.93Co0.07O2 anatase

Anatase Ti0.93Co0.07O2 films, synthesized by pulsed-laser deposition, have been investigated in the transmission electron microscope using selected area electron diffraction, energy dispersive x-ray analysis, and electron-energy-loss spectroscopy (EELS), and by x-ray diffraction measurements. It is found that Co ions are soluble in anatase, and that the unit-cell c-axis parameter is shortened, in some areas to even less than that in pure TiO2 anatase films. This observation was ascribed to substitution of the smaller Co3+ ions into the TiO2 anatase lattice. The EELS data confirm that Co is in either a +2 or +3 formal oxidation state in ferromagnetic Ti0.93Co0.07O2 films.

Microstructure of GaN films grown on Si(111) substrates by metalorganic chemical vapor deposition

We report the transmission electron microscopy (TEM) study of the microstructure of wurtzitic GaN films grown on Si(I I I) substrates with AlN buffer layers by metalorganic chemical vapor deposition (MOCVD) method. An amorphous layer was formed at the interface between Si and AlN when thick GaN film was grown. We propose the amorphous layer was induced by the large stress at the interface when thick GaN was grown. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations from passing through the MQW. But no evident reduction of the edge dislocations by the MQW was observed. It was found that dislocations located at the boundaries of grains slightly in-plane misoriented have screw component. Inversion domain is also observed

Structure and magnetic properties of nanostructured PrCo7−xTix(x=0–0.4) prepared by mechanical milling and subsequent annealing

The Pr(Co,Ti)7 phase alloy, which can not be prepared directly by arc melting, has been synthesized by mechanical milling and subsequent annealing. A coercivity of 7.3 kOe, remanence ratio of 0.69 and maximum energy product of 10.6 MGOe have been achieved for the PrCo6.7Ti0.3 powder milled for 3 h and annealed at 800 °C for 3 min. The high coercivity obtained indicates that the addition of Ti causes the anisotropy of PrCo7 phase to change from planar to uniaxial. Transmission electron microscopy reveals that a uniform Pr(Co,Ti)7 microstructure with an average grain size of about 20 nm is developed in the powders. The electron energy-loss spectrum acquired from one grain proves that the Ti enters the Pr(Co,Ti)7 grain. The high coercivity obtained apparently arises from the high uniaxial anisotropy of Pr(Co,Ti)7 phase and the uniform nanoscale microstructure developed by mechanical milling and subsequent annealing.

Thin film relaxation in cross‐sectional transmission electron microscopy specimens of GexSi1−x/Si strained‐layer superlattices

A large‐angle convergent‐beam electron diffraction (LACBED) pattern with fine diffraction lines from a cross‐sectional specimen of GexSi1−x/Si strained‐layer superlattices (SLS) can give much information on local strain and misfit stress relaxation. The shift of the diffraction lines in the GeSi layers from those in the Si layers can be used to determine the strain relaxation. A profile of the thin film relaxation versus the specimen thickness is presented.