Herstellung dünner metallischer Brücken durch Elektromigration und Charakterisierung mit Rastersondentechniken

In der vorliegenden Arbeit werden metallische Kontakte durch Elektronenstrahllithografie oder Bedampfen durch eine Maske sowie kontrollierte Elektromigration im Ultrahochvakuum hergestellt und mittels Rastersondentechniken charakterisiert. Aus den Rastersondenbildern lassen sich in Verbindung mit den Elektromigrationsdaten Rückschlüsse auf die Entstehung der Morphologie des erzeugten Kontakts ziehen

Herstellung dünner metallischer Brücken durch Elektromigration und Charakterisierung mit Rastersondentechniken

In der vorliegenden Arbeit werden metallische Kontakte durch Elektronenstrahllithografie oder Bedampfen durch eine Maske sowie kontrollierte Elektromigration im Ultrahochvakuum hergestellt und mittels Rastersondentechniken charakterisiert. Aus den Rastersondenbildern lassen sich in Verbindung mit den Elektromigrationsdaten Rückschlüsse auf die Entstehung der Morphologie des erzeugten Kontakts ziehen

STM-induced surface aggregates on metals and oxidized silicon

We have observed an aggregation of carbon or carbon derivatives on platinum and natively oxidized silicon surfaces during STM measurements in ultra-high vacuum on solvent-cleaned samples previously structured by e-beam lithography. We have imaged the aggregated layer with scanning tunneling microscopy (STM) as well as scanning electron microscopy (SEM). The amount of the aggregated material increases with the number of STM scans and with the tunneling voltage. Film thicknesses of up to 10 nm with five successive STM measurements have been obtained

Collisional processes and size distribution in spatially extended debris discs

We present a new multi-annulus code for the study of collisionally evolving extended debris discs. We first aim to confirm results obtained for a single-annulus system, namely that the size distribution in "real" debris discs always departs from the theoretical collisional equilibrium dN\proptoR^{-3.5}dR power law, especially in the crucial size range of observable particles (<1cm), where it displays a characteristic wavy pattern. We also aim at studying how debris discs density distributions, scattered light luminosity profiles, and SEDs are affected by the coupled effect of collisions and radial mixing due to radiation pressure affected small grains. The size distribution evolution is modeled from micron-sized grains to 50km-sized bodies. The model takes into account the crucial influence of radiation pressure-affected small grains. We consider the collisional evolution of a fiducial a=120AU radius disc with an initial surface density in $\Sigma(a)\propto a^{\alpha}$. We show that the system's radial extension plays a crucial role: in most regions the collisional and size evolution of the dust is imposed by small particles on eccentric or unbound orbits produced further inside the disc. The spatial distribution of small grains strongly departs from the initial profile, while the bigger objects, containing most of the system's mass, still follow the initial distribution. This has consequences on the scattered--light radial profiles which get significantly flatter, and we propose an empirical law to trace back the distribution of large unseen parent bodies from the observed profiles. We finally provide empirical formula for the collisional size distribution and collision timescale that can be used for future debris disc modeling.Comment: Accepted for publication in Astronomy and Astrophysics (with better figures) (note: full abstract in the *.pdf file

The early impact histories of meteorite parent bodies

We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces - compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 - 5% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.Comment: 30 pages, 11 figures, 3 tables. Accepted for publication in Meteoritics & Planetary Scienc

Herstellung dünner metallischer Brücken durch Elektromigration und Charakterisierung mit Rastersondentechniken

In der vorliegenden Arbeit werden metallische Kontakte durch Elektronenstrahllithografie oder Bedampfen durch eine Maske sowie kontrollierte Elektromigration im Ultrahochvakuum hergestellt und mittels Rastersondentechniken charakterisiert. Aus den Rastersondenbildern lassen sich in Verbindung mit den Elektromigrationsdaten Rückschlüsse auf die Entstehung der Morphologie des erzeugten Kontakts ziehen

Enhanced positioning precision and in situ macroscopic contacts for shadow-evaporated nanostructures

The authors present the design of a modular sample holder that offers the possibility of in situ fabrication of metallic nanostructures under ultrahigh vacuum. One of the crucial points is to bridge the gap between the macroscopic leads and the nanostructure itself. This problem is solved by using a set of two different masks. For a precise alignment of the two masks, a magnetic tripod connection system has been developed. With this new system, an alignment precision of 26 lm is obtained. As a result of the fabrication in ultrahigh vacuum, the nanostructures will be accessible to scanning probe techniques without surface contamination. First results show that electrical measurements are indeed possible.publishe

Magnetic characteristics of CV chondrules with paleointensity implications

We have conducted a detailed magnetic study on 45 chondrules from two carbonaceous chondrites of the CV type: (1) Mokoia and (2) Allende. Allende has been previously extensively studied and is thought to have a high potential of retaining an extra-terrestrial paleofield. Few paleomagnetic studies of Mokoia have previously been undertaken. We report a range of magnetic measurements including hysteresis, first-order reversal curve analysis (FORCs), demagnetization characteristics, and isothermal remanent (IRM) acquisition behavior on both Mokoia and Allende chondrules. The Mokoia chondrules displayed more single domain-like behavior than the Allende chondrules, suggesting smaller grain sizes and higher magnetic stability. The Mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the Allende chondrules. IRM acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral, likely to be a FeNi phase (taenite, kamacite, and/or awaruite) contributing to 48% of the Mokoia chondrules and 42% of the Allende chondrule characteristics. FORC analysis revealed that generally the Allende chondrules displayed low-field coercivity distributions with little interactions, and the Mokoia chondrules show clear single-domain like distributions. Paleointensity estimates for the two meteorites using the REMc and Preisach methods yielded estimates between 13 and 60 μT and 3–56 μT, respectively, for Allende and 3–140 μT and 1–110 μT, respectively, for Mokoia. From the data, we suggest that Mokoia chondrules carry a non-primary remagnetization, and while Allende is more likely than Mokoia to retain its primary magnetization, it also displays signs of post accretionary magnetization