Biomedical subjects

T Gemming

Publications and source records attributed to T Gemming.

7 recordsLinked to original sources

PubMed2006

Determination of manganese valency in La1-xSrxMnO3 using ELNES in the (S)TEM.

In this article several experimentally identified Mn valence-sensitive ELNES quantities for the La1-xSrxMnO3 compound class are presented, namely the energy separations between Mn-L3 and O-Ka, between O-Kb and O-Ka edges, the Mn-L2,3 white line intensity ratio, and the Mn-L3 line width. Valence sensitivities of these quantities are evaluated, and possible additional influences on them are considered. At high signal-to-noise ratio the two energy separations display most sensitively changes of the Mn valency. An experiment-based estimation of the total uncertainties of the quantities indicates that at low signal-to-noise ratio, which is the case when studying interface effects at high spatial resolution, again both energy separations allow to resolve the smallest valency changes.

Journal Article↗

PubMed2006

Structure and giant magnetoresistance behaviour of Co-Cu/Cu multilayers electrodeposited under various deposition conditions.

Electrodeposited Co-Cu/Cu multilayers were prepared under a variety of deposition conditions on either a polycrystalline Ti foil or on a silicon wafer covered by a Ta buffer and a Cu seed layer. X-ray diffraction (XRD) revealed a strong (111) texture for all multilayers with clear satellite peaks for the multilayers on Si/Ta/Cu substrates, in some cases for up to three reflections. Cross-sectional transmission electron microscopy investigations indicated a much more uniform multilayer structure on the Si/Ta/Cu substrates. The bilayer periods from XRD satellite reflections were in reasonable agreement with nominal values. An analysis of the overall chemical composition of the multilayers gave estimates of the sublayer thickness changes due to the Co-dissolution process during the Cu deposition pulse. The XRD lattice spacing data indicated a behaviour close to a simple "multilayer" Vegard's law which was, however, further refined by taking into account elastic strains as well. In agreement with the structural studies, magnetoresistance data also indicated the formation of more perfect multilayers on the smooth Si/Ta/Cu substrates. An analysis of the magnetoresistance behaviour revealed the presence of superparamagnetic (SPM) regions in the magnetic layers. The contribution of these SPM regions to the total observed giant magnetoresistance was found to be dominating under certain deposition conditions, e.g., for magnetic layer thicknesses less than 1 nm (about 5 monolayers).

Cobalt↗

PubMed2005

Extraction of EELS white-line intensities of manganese compounds: methods, accuracy, and valence sensitivity.

This article evaluates the valence sensitivity and accuracy of selected EELS white-line extraction methods based on the white-line intensity ratio in case of manganese oxides, predominantly in the valency range [Mn3+ ; Mn4+]. For this purpose Mn-L2,3 ionization edges of several Mn oxides were measured and four different methods were applied to extract the intensities. The obtained ratios have been analyzed in terms of their errors, their scatter, and their sensitivity on manganese valency. We found that the maximum-intensity as well as the Pearson and Walsh-Dray methods show larger relative changes of the ratio between Mn3+ and Mn4+ than curve-fitting. Taking the scatter into account, Walsh-Dray distinguishes more clearly between those two valencies than curve-fitting. Thus the Walsh-Dray method promises the most accurate determination of small valency shifts.

Journal Article↗

PubMed2004

Microstructure and composition of annealed Al/Ti-metallization layers.

Al/Ti multilayers with columnar grains were deposited by electron-beam evaporation on piezoelectric LiNbO(3) substrates. After annealing in air and under vacuum conditions dissolution of the Ti interlayer was observed for all samples. The original Ti interlayer dissolved completely and globular Al(3)Ti grains were formed within an Al matrix. All samples had an oxidized adhesive Ti bottom layer and a 10 nm thin Al layer below this adhesive Ti bottom layer, which remains intact after the applied heat treatment. This resistance against dissolution by interdiffusion could be caused by the oxidation. These changes in the microstructure and in the chemical composition were investigated by conventional and analytical TEM.

Alloys↗

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↗