Modeling Atom Probe Tomography: A review.

Improving both the precision and the accuracy of Atom Probe Tomography reconstruction requires a correct understanding of the imaging process. In this aim, numerical modeling approaches have been developed for 15 years. The injected ingredients of these modeling tools are related to the basic physic of the field evaporation mechanism. The interplay between the sample nature and structure of the analyzed sample and the reconstructed image artefacts have pushed to gradually improve and make the model more and more sophisticated. This paper reviews the evolution of the modeling approach in Atom Probe Tomography and presents some future potential directions in order to improve the method.

Reactive diffusion under Laplace tension.

Nanostructures such as nanospheres or nanowires may contain surfaces and interfaces of pronounced curvature. To investigate the impact of severe curvature on the kinetic of reactions, thin-film Al/Cu/Al and Cu/Al/Cu triple layers are deposited on tungsten tips of 25nm curvature radius. The thermal reaction of the layer structure is studied by atom probe tomography. Experiments demonstrate that the reaction rate depends significantly on the deposition sequence of metals. Interpretation of the observed reaction kinetics leads to the conclusion that under the influence of interfacial tension probably the two limiting cases of atomic transport, Darken and Nernst-Planck kinetics, are realized in dependence on the stacking sequence.

Laser-assisted atom probe analysis of sol-gel silica layers.

Semi-conducting nanocrystals embedded in a non-conducting matrix of silicate glass may be used as non-volatile data storage device. Structures of silicate glasses are conveniently produced by a sol-gel process, which offers the possibility to coat tip-shaped substrates with a silica layer. The study presents first results of their local chemical analysis by laser-assisted atom probe. Till date the exact mechanisms of laser pulsing are still controversial. But it is common sense that there is an at least considerable heating effect on the tip, which leads to a short temperature rise and a prolonged cooling period in materials of low heat conductivity. This effect alters the shape of mass peaks and is examined here using a one-dimensional model of heat transport.

New tomographic atom probe at University of Muenster, Germany.

Currently atom probe tomography provides the highest spatial resolution compared to all other volume analysis techniques. Owing to its single atom sensitivity, it is specially suited to study nano-structured materials. Therefore, a new atom probe was installed at the Institute for Material Physics at University of Muenster, Germany, to study thin film reactions. Since the available budget was rather limited, a cost-effective non-commercial atom probe was constructed. The instrument is based on a 2D delay line detector system of 120 mm diameter. To achieve a large collecting angle and thus large volumes of analysis, a straight flight tube without a reflectron is used. This way, the flight distance may be reduced down to 160 mm. However, the variable chamber layout allows using a reflectron as an alternative. Furthermore, a laser system is implemented that delivers pulses in the 500 ps range to make possible laser-assisted evaporation of atoms. The article describes instrumental details and presents first characteristic data.

Inhibition of human herpes simplex virus type 2 by interferon gamma and tumor necrosis factor alpha is mediated by indoleamine 2,3-dioxygenase.

Genital herpes simplex virus type 2 (HSV-2) is a significant clinical problem. Infection in pregnancy may result in disseminated infection of the newborn with encephalitis. We analyzed the antiviral effects induced by interferon-gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) in cervix carcinoma cells (HeLa) and astrocytoma cells (86HG39). We found that replication of HSV-2 in HeLa cells and in 86HG39 cells is inhibited after stimulation of the cells by IFN-gamma and TNF-alpha. The antiviral effect of IFN-gamma is enhanced in the presence of TNF-alpha, while stimulation by TNF-alpha alone did not induce antiviral activity. We found that IFN-gamma induces a strong activation of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) and in addition, that the IFN-gamma-induced IDO activity was enhanced in the presence of TNF-alpha. Furthermore, we found that the induction of IDO activity is responsible for the inhibition of herpes simplex virus replication, since the presence of excess amounts of l-tryptophan abrogates the antiviral effect induced by IFN-gamma and the combination of IFN-gamma and TNF-alpha. We therefore conclude that the antiviral effect against HSV-2 mediated by type II interferon and TNF-alpha are dependent on IDO activation.

Role of indoleamine-2,3-dioxygenase in alpha/beta and gamma interferon-mediated antiviral effects against herpes simplex virus infections.

Gamma interferon (IFN-gamma)-mediated indoleamine-2,3-dioxygenase (IDO) activity in human astrocytoma cells and in native astrocytes was found to be responsible for the inhibition of herpes simplex virus replication. The effect is abolished in the presence of excess amounts of L-tryptophan. Both IFN-alpha and IFN-beta restricted herpes simplex virus replication in both cell types, but (in contrast to the results seen with IFN-gamma) the addition of an excess amount of L-tryptophan did not inhibit the induced antiviral effect.

Infection of man by Dirofilaria repens.

Dirofilaria repens, a natural parasite of dogs and cats in Europe, Asia, and Africa, sometimes infects man. In man the worms are usually in subcutaneous tissues or in the orbit. A case is herein reported in which a non-gravid, adult Dirofilaria, probably D. repens, was in the subcutaneous tissue of a resident of Wisconsin. The patient, however, acquired the infection 8 years previously in Greece.