ABSTRACT
Imaging strain fields at the nanoscale is crucial for understanding the physical properties as well as the performance of oxide heterostructures and electronic devices. Based on scanning transmission electron microscopy (STEM) techniques, we successfully imaged the random strain field at the interface of core-shell ZnO nanowires. Combining experimental observations and image simulations, we find that the strain contrast originates from dechanneling of electrons and increased diffuse scattering induced by static atomic displacements. For a thin sample with a random strain field, a positive strain contrast appears in the low-angle annular dark-field (LAADF) image and a negative contrast in the high-angle annular dark-field (HAADF) image, but for a thick sample (> 120 nm), the positive contrast always occurs in both the LAADF and HAADF images. Through the analysis of the relationship between strain contrast and various parameters, we also discuss the optimum experimental condition for imaging random strain fields.
ABSTRACT
The synthesis of TiO(2) nanostructures including nanowires and nanobelts has been demonstrated experimentally by anodization of Ti foil in an electrolyte, and by treatment in a PdCl(2) ethanol solution together with UV light irradiation and annealing at a temperature below 800 degrees C. The TiO(2) nanotube arrays resulting from the anodization were used as source precursor and transformed into nanowires and nanobelts respectively with high efficiency during the subsequent processes. The resulting TiO(2) nanowires and nanobelts, characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman and surface photovoltage (SPV) spectroscopy, are single rutile crystals of high quality. In addition to the synthesis of the nanostructure at low temperature, this method also shows great advantages for the selectable morphology of the final TiO(2) nanostructures via adjustment of the UV light irradiation time and annealing temperature.
Subject(s)
Crystallization/methods , Electrochemistry/methods , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/methods , Palladium/chemistry , Titanium/chemistry , Catalysis , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface Properties , TemperatureABSTRACT
Rapid and ultrahigh sensing is realized from Au-coated ZnO rods with diameters down to 15 nm. Both the small diameters and the Au coating make the surface-depletion effect more pronounced for gas sensing. Such enhanced surface depletion increases the sensitivity, lowers the operation temperature and decreases the response time. A sensitivity of 89.5-100 ppm ethanol is obtained with response time shorter than 2 s at 300 °C, and the operation temperature can be as low as 150 °C. It is found that the Au coating improves the sensitivity by three times; this is much higher than that of noble metal-doped metal oxide sensors controlled by a grain-boundary barrier. Our results imply that the surface-depletion model is very helpful in fabricating high performance gas sensors.
ABSTRACT
ZnO nanorod close-packed arrays are successfully fabricated in a substrate-free manner by a citric acid assisted annealing process at a low growth temperature of 400 °C. Each nanorod of ZnO nanorod close-packed arrays grows along the [0001] direction and is single crystalline with an average diameter of 50 nm, and an average length of 0.5 µm. The aspect ratio is 10. The ZnO nanorod close-packed arrays show a strong exciton absorption peak at 372 nm in UV-visible absorption spectra, exhibiting a blue-shift relative to the bulk exciton absorption (387 nm). Finally, a new growth mechanism is proposed for the substrate-free preparation of ZnO nanorod close-packed arrays by a citric acid assisted annealing process.
ABSTRACT
The ternary oxide functional nanomaterial Zn2SnO4 has been synthesized by the thermal evaporation method. The products in general contain numerous kinds of nanowires. In the present work, a remarkable type of Zn2SnO4 nanowires with a pseudoperiodical twinning structure has been investigated by transmission electron microscopy (TEM). These nanowires with a diameter of about 100 nm grow along the 111 direction. High-resolution TEM examinations suggest that a large fraction of the (111) twin boundaries are extended to a thickness of a few nanometers. The twining plane for the perfect case is localized on the Zn atom layer.
ABSTRACT
The microstructural features of silver nanorods with the average length of 50 microm and diameters of around 100 nm have been investigated by means of SEM, X-ray diffraction, and transmission-electron microscopy (TEM). Silver nanorods in general have a pentagonal shape with a remarkable fivefold symmetry as revealed in cross-section observations. The fivefold axis, i.e. the growth direction, normally goes along the [110]-zone axis direction of the basic fcc Ag-structure. The twinning relationships and relevant twin boundaries among the five subunits in the pentagonal nanorod have been examined by high-resolution TEM and selected-area electron diffraction. Defects and stacking faults in this kind of nanorods have been briefly analyzed.
ABSTRACT
We have performed a systematic investigation on the microstructural features of SmCo(7-x)Cu(x) (x = 0, 3.5) alloys. Transmission electron microscopy observations suggest that the SmCo7 is essentially a superstructure phase with a modulation wave vector q = (a* + b*)/3 + c*/2. The superstructure can be well interpreted by the partial ordered substitution of Co-pairs for Sm atoms within the basic structure of SmCo5. In situ cooling and heating observations indicated that the superstructure phase is stable below 670 K. Additional substitution of Cu for Co in SmCo3.5Cu3.5 does not result in evident changes of crystal structure, but makes the superstructure phase unstable at temperatures >480 K.
