Identification of a strong contamination source for graphene in vacuum systems

To minimize parasitic doping effects caused by uncontrolled material adsorption, graphene is often investigated under vacuum. Here we report an entirely unexpected phenomenon occurring in vacuum systems, namely strong n-doping of graphene due to chemical species generated by common ion high-vacuum gauges. The effect --reversible upon exposing graphene to air-- is significant, as doping rates can largely exceed 10^{12} cm^{-2}/hour, depending on pressure and the relative position of the gauge and the graphene device. It is important to be aware of the phenomenon, as its basic manifestation can be mistakenly interpreted as vacuum-induced desorption of p-dopants.Comment: 10 pages, 4 figure

Functionalization of carbon nanotube scanning probes for advanced studies of ferroic thin films

Ferroic materials at the nanoscale reveal new properties and functionalities as such they are recognized as extremely promising materials from both fundamental and application point of view. One of the major tool used to advance studies of ferroic thin films is the atomic force probe microscopy (AFM). In the present work, we study the synthesis, fabrication, processing, and characterization of carbon nanotube (CNT) scanning probes with a further application to ferroic thin film. Our main results include both experimental and theoretical studies of ultra-high resolution magnetic force microscopy imaging of spin nanostructures of soft magnetic materials with ferromagnetically-coated CNT probes, transport measurements of dielectric-coated-CNT AFM probes, and piezoresponse force microscopy studies of switching dynamics in ferroelectric thin films. Notably, we performed the non-perturbative imaging of spin nanostructures with a resolution higher than that of X-ray microscopy, and at ambient conditions

High-aspect ratio nanopatterning via combined thermal scanning probe lithography and dry etching

Thermal scanning probe lithography is an emerging nanofabrication technique for rapid prototyping of arbitrary topographies in thermally sensitive resist. This feature, paired to the recent advances in dry plasma etching techniques, allows the fabrication of high-resolution nanopatterns in hard substrates. Here, we investigate the key process parameters allowing the fabrication of high aspect ratio nanopatterns in silicon. By a combination of resist heat treatment, the use of a hard mask and optimized etch parameters during pattern transfer, we amplified the shallow resist patterns by a factor of 100 into the silicon substrate. Low surface roughness and vertical sidewalls are thereby maintained. We demonstrate the fabrication of 240 nm wide lines and 4 μm deep single crystal silicon patterns

Ultrahigh Currents in Dielectric-Coated Carbon Nanotube Probes

Carbon nanotubes used as conductive atomic force microscopy probes are expected to withstand extremely high currents. However, in existing prototypes, significant self-heating results in rapid degradation of the nanotube probe. Here, we investigate an alternative probe design, fabricated by dielectric encapsulation of multiwalled carbon nanotubes, which can support unexpectedly high currents with extreme stability. We show that the dielectric coating acts as a reservoir for Joule heat removal, and as a chemical barrier against thermal oxidation, greatly enhancing transport properties. In contact with Au surfaces, these probes can carry currents of 0.12 mA at a power of 1.5 mW and show no measurable change in resistance at current densities of 10¹² A/m² over a time scale of 10³ s. Our observations are in good agreement with theoretical modeling and exact numerical calculations, demonstrating that the enhanced transport characteristics of such probes are governed by their more effective heat removal mechanisms

Molecular phylogeny suggests transfer of Hemidiscus into Actinocyclus (Coscinodiscales, Coscinodiscophyceae)

Hemidiscus cuneiformis, type of the family Hemidiscaceae, is a diatom with a distinctive semi-circular shape in valve view. A strain of H. cuneiformis was established from the coastal region of the tropical southwestern Atlantic Ocean off Brazil. Cells of this strain showed semi-circular to asymmetrically elliptical valves, indicating morphological plasticity. In the small subunit (SSU) rDNA phylogeny, the type species of Hemidiscus branched between two clades of Actinocyclus, one of which was a sister group, the other in a basal position. Beyond cell shape, there are no significant morphological differences between Hemidiscus and Actinocyclus. We propose the transfer of H. cuneiformis and H. kanayanus into Actinocyclus. The family Hemidiscaceae remains for the genus Actinocyclus