Hoffrogge et al. recently posted a pre-print to the arXiv describing a laser-heated field emission source demonstrating sub-100 femtosecond pulsed electron emission. There have been previous disclosures of laser-heated field emission cathodes (see, for example US 6,828,996 and references therein), but none have been designed for pulsed emission.

The new source should find application in time-resolved electron diffraction. The coherence of the source has apparently not yet been established. The implementation shown operates at 30 keV.

Another application comes to mind – pump-probe spectroscopy. In the usual scheme, a femto-second laser pulse is used to excite a target molecule, while a second, time-delayed pulse measures the decay product. One can envision replacing the pump laser pulse with a pump electron beam pulse. Since the selection rules for energy absorption are entirely different for photons and electrons, the excited states and resultant decay channels will also differ. Comparing photo-pumped and electron-pumped systems could, for example, clarify why EUV resists are generally not particularly good electron-beam resists and vice versa.

A recent advance in laser pump-probe spectroscopy, involving a third photon pulse, would be very useful here as well, since we know that electron impact with resist yields a vast number of excited states.

Apart from the buzz generated by IBM’s paper in Science , graphene research continues apace. Here I will bring your attention to two sub-topics: graphene on boron nitride, and patterning of graphene.

Experimental research led by the LeRoy group at the University of Arizona has shown that graphene lays down nearly flat on boron nitride substrate. This is in contrast to the wrinkling that occurs when graphene is placed onto silicon dioxide. Consequently the electronic properties of graphene on BN are much closer to those properties for free-standing graphene, but the material is much more robust and therefore more accessible to experiment. [Nature Materials, also found at arXiv:1102.2642]

From the Kavli Institute of Nanoscience in Delft comes a report that multi-layer graphene can be sculpted by high-energy e-beam without defects. If one irradiates graphene at room temperature, one finds that the graphene rapidly converts to amorphous carbon. The Kavli Institute has discovered that raising the temperature to 600C allows the graphene to heal while being irradiated, so that patterning is possible. [arXiv:1102.0971]

Finally, work at the Cavendish Laboratory, Cambridge, shows that apparent scanning probe nanolithography on graphene may be deceptive. A voltage is applied between tip and substrate during contact mode scanning. One then inspects the sample in tapping mode, and finds indentations wherever the tip was dragged. However, it seems that current flow through the probe tip causes oxidation of the graphene substrate only if the current flowing through the tip drops to (near) zero. This current drop depends on setting the tip voltage high enough to drive the oxidation to completion. The authors do not report what atomic state the “pseudo-cut” (that is, indented) graphene remains in. [arXiv: 1102.2781]