Volume 95, Issue 6, 15 March 2004
Index of content:
Comment on “The effects of electric field on the electronic structure of a semiconductor quantum dot” [J. Appl. Phys. 84, 1454 (1998)]95(2004); http://dx.doi.org/10.1063/1.1647265View Description Hide Description
In a recent article Chang and Xia [J. Appl. Phys. 84, 1454 (1998)] studied theoretically the effects of the electric field on the electronic structure of a spherical semiconductornanocrystal. The computed hole energies versus electric field intensity show a pattern of avoided crossings and nonzero slopes at zero field. It is argued here that these results are physically incorrect and are possibly due to the use of an incomplete basis set.
95(2004); http://dx.doi.org/10.1063/1.1643197View Description Hide Description
We have imaged the micromagnetic structure of 50 nm films after different low-temperature anneals. Samples annealed in vacuum for 10 min display a very random domain structure with small (∼3–5 μm) domains. In contrast a sample which was further annealed in air for 50 h exhibited the highest Curie temperature and very large (∼100 μm) domains. Even within large domains we resolve magnetic disorder which has not been removed by the annealing procedure. Micron-sized regions near domain walls remain ferromagnetic well above in all the films, possibly indicating the presence of regions with above average Mn density or very small MnAs precipitates, which act as pinning centers and strongly influence the coercive fields of the films.
95(2004); http://dx.doi.org/10.1063/1.1646450View Description Hide Description
The handling and manipulation of carbon nanotubes continues to be a challenge to those interested in the application potential of these promising materials. To this end, we have developed a method to deposit pure nonoriented nanotubefilms over large flat areas on substrates of arbitrary composition. The method bears some resemblance to the Langmuir–Blodgett deposition method used to lay down thin organic layers. We show that this redeposition technique causes no major changes in the films’ microstructure and that they retain the electronic properties of as-deposited films laid down on an alumina membrane.
95(2004); http://dx.doi.org/10.1063/1.1647266View Description Hide Description
We report the effect of finer structures, or more levels, in a particular type of planar metallic fractal pattern on the stop bands or band gaps in the transmission spectrum of electromagnetic wave. It is found that the band gaps shift to low frequencies with the increase of levels, showing tunable band gapproperties. In addition, we find from both experiments and theoretical calculations that the bands appearing in long wavelength range are determined by individual patterns which compose a fractal array, while those bands located in the range of short wavelength are strongly influenced by their neighboring residents. Our experimental observations are in good agreement with those of finite difference time domain simulations.