Volume 98, Issue 11, 01 December 2005
Index of content:
98(2005); http://dx.doi.org/10.1063/1.2137878View Description Hide Description
We have performed a critical experimental evaluation of the dependence of both perpendicular magnetic anisotropy and exchange bias on the structure of the ferromagnet (FM)/nonferromagnet and FM/antiferromagnet interfaces of and multilayers. The growth of these heterostructures by ion-beam sputtering was optimized and the characteristics of their interfaces were systematically controlled by varying the ion-beam energy from 250 to 1500 eV. Calculated effective anisotropy constants and exchange bias fields from hysteresis loops were correlated with both structural roughness and the degree of interdiffusion measured by x-ray reflectivity. Whilst the physical roughness remained unchanged, the degree of interdiffusion was found to increase with higher ion-beam energy—concurrently the magnetic anisotropy changed from perpendicular to in plane—leading directly to a decrease in exchange bias and coercivity.
98(2005); http://dx.doi.org/10.1063/1.2137879View Description Hide Description
The presence of a threading edge dislocation terminated at the surface of GaN bulk substrates causes a dipole-like strain state ranging over a several micrometer square area. The local strain state is derived from microphotoluminescence mappings of the near-band-edge spectrum and is quantitatively reproduced by a three-dimensional elastic deformation model approach. These results are compared with the local electrical potential distortion due to the core charge and attracted defects as analyzed by scanning surface-potential microscopy. In contrast to the local strain, the potential profile does not show a dipole-like behavior and decreases laterally faster.
98(2005); http://dx.doi.org/10.1063/1.2126781View Description Hide Description
We study the doping of a free molecule by potassium atoms. Ab initio calculations based on density functional theory indicate that K atoms are fairly strongly bound to the carbon cage. The electrical conduction of the structure is also enhanced after each successive doping of K. We also observe a downward shift of energy levels toward the Fermi energy with the increase of doping. These properties are very consistent with experimental results. The K-doped structure is promising for applications in molecular electronics.
98(2005); http://dx.doi.org/10.1063/1.2140079View Description Hide Description
A nondestructive photoacoustic method for the evaluation of surface absorber distributions is presented. Ultrasound generated by absorption of a pulsed laser source is detected using optical beam deflection. Temporal encoding of the spatial absorber distribution is achieved using a nonparallel orientation of the probe beam relative to the sample surface. Sound waves launched from individual surface absorbers travel different distances before interacting with the probe beam, thus giving rise to acoustic signatures at different times. With this approach, we resolved eleven identical absorber features in a 3–cm-wide sample. Decreasing the probe beam diameter enhances the temporal and/or spatial resolution. A limiting spatial resolution of is predicted. The sound wave intensity decays in a roughly inverse square-root manner with increasing distance of travel.