Biomedical subjects

S Nufer

Publications and source records attributed to S Nufer.

3 recordsLinked to original sources

PubMed2001

Quantitative atomic-scale analysis of interface structures: transmission electron microscopy and local density functional theory.

Transmission electron microscopy (TEM) and local density functional theory (LDFT) are combined to analyze the microscopic structure of the rhombohedral twin interface in alpha-Al2O3. LDFT provides interfacial energetics and atomic and electronic structures for three competing models. With high-resolution TEM the atomic structure at the interface is imaged quantitatively along two orthogonal zone axes. Electron energy loss spectroscopy in TEM with nanoscale spatial resolution yields the interfacial electronic structure. Both experiments confirm the theoretically preferred model quantitatively.

Journal Article↗

PubMed2001

Core-hole effect in the ELNES of alpha-Al2O3: experiment and theory.

The occurrence of the core-hole effect at the Al-K and Al-L1 edge in alpha-Al2O3 was studied by comparing experimental electron energy-loss near-edge structures (ELNES) and results of band-structure calculations with and without accounting for core-hole effects by the Z + 1 approximation. It was found that the theoretically calculated unoccupied p-like projected densities of states (PDOS) without Z + 1 approximation matches better to the experimental Al-L1 ELNES, whereas the PDOS with Z + 1 approximation matches better to the experimental Al-K ELNES. We conclude that the localisation of the initial state is an important prerequisite for the observability of the core-hole effect in the ELNES.

Journal Article↗

PubMed2001

Validity of the dipole-selection rule for the Al-L2,3 edge of alpha-Al2O3 under channeling conditions.

The validity of the dipole-selection rule for the Al-L2,3 electron energy-loss edge of alpha-Al2O3 is investigated. Dipole forbidden transitions can be observed in a transmission electron microscope operated with large collection apertures. In addition, it is shown that channeling along a highly symmetrical zone axis in alpha-Al2O3 can lead to the detection of dipole forbidden transitions even with small collection apertures. For an incident electron direction parallel to the <0001> orientation it is observed experimentally that the fine structure of the Al-L2,3 edge shows additional features compared to measurements with the electron beam parallel to <1100>. This effect is due to the occurrence of channeling conditions, indicated by the dependence of the additional dipole forbidden features on the sample thickness. These additional features disappear when tilting the crystal by 1.8 degrees (0.84 A(-1)) or even into the less-symmetrical <1100> zone axis. It is suggested that these observations are explained by differences in local symmetry at the excited center with respect to the incident beam directions.

Journal Article↗