Nanolithography: Painting with block copolymers.

news & views can be resolved with a spatial resolution of ~20 nm. Furthermore, the potential for high-resolution magnetic imaging is demonstrated by resolving Abrikosov vortices with 120 nm minimum lateral distance in a Nb thin film at B ~0.2 T (Fig. 1b). The combination of high spatial sensitivity with high bandwidth suggests the approach could have a range of exciting applications including the nanoscale investigation of dissipation and noise due to vortex dynamics in superconductors. Despite their impressive performance, SQUID-on-tips still have room for further improvement. Vasyukov and colleagues have shrunk the SQUIDs to unprecedented values, but at this scale it becomes increasingly difficult to use conventional flux bias and feedback routines for maintaining optimum device performance while an external field is swept. This causes an oscillation of the sensitivity with magnetic field for the devices and loss of sensitivity on approaching zero field. The latter might be avoided by implementing asymmetries in the SQUID-on-tips. Moreover, the comparison between lead-based devices and (less sensitive) niobium-based devices indicates that a careful choice of material with proper characteristic parameters, such as the superconducting coherence length, may further improve device performance. In this context, a better understanding of the properties of the constriction junctions should allow for further systematic optimization. And in this regard, it still remains to be seen whether other types of nano-SQUID, such as those based on the cuprate superconductors that can operate in huge magnetic fields, may be able to compete. Another open issue is the experimental determination of the coupling strength of a tiny magnetic dipole to a nano-SQUID; so far, the spin sensitivity is usually derived by measurements of the flux noise and estimates of the coupling strength, which together yields S n 1/2 as an important figure of merit for these devices. The work of Vasyukov and co-workers is an important step towards quantitative nanoscale magnetic imaging. Furthermore, the ability to easily control the nanoscale position (and orientation) of the SQUID-on-tip relative to a magnetic nanoparticle (fixed on a surface), will most likely boost future investigations on individual magnetic nanoparticles and improve the understanding of their properties, which are very hard to access at present. B lock copolymer nanolithography — a process in which self-assembled polymeric nanodomain patterns are transferred into a substrate or replicated in an inorganic material — can be used to create precise nanoscale structures, and can potentially augment or replace traditional …