Graphene continues to tantalize and frustrate experimentalists. A year ago, we saw that graphene was susceptible to contamination by exposure to a cold-cathode vacuum gauge. This week, a group led by IHP in Germany reports that graphene grown on copper is irreversibly contaminated by copper and iron. The contaminant concentration is high enough to adversely affect not only the electronic properties of the graphene, but also those of the silicon to which the graphene is transferred.

Ref: Lupina, et al., “Residual metallic contamination of transferred chemical vapor deposited graphene”, arXiv:1505.0889.

What could we do with a 22 eV photon source? The Materials Science Division at LBL has demonstrated a high efficiency, table-top source of femtosecond pulse, high repetition rate EUV photons with 22.3 eV energy. The power output (117 µW) is more than enough to selectively explore chemical reaction pathways of EUV resists, without all the messiness that comes from using the 13.5 nm (91.8 eV), actinic photons contemplated for EUV lithography. Actinic photons have such high energy that they open many reaction channels simultaneously. Lower energy photons confine the excitations to the valence shell alone.

At some loss of efficiency, the source can be tuned to give 15.9 eV or 28.7 eV pulses instead. Tantalizingly, the 15.9 eV peak happens to be the first ionization potential of CF4, and so could be useful in exciting the valence bonds of flourine-rich materials.

Reference: Wang et al., “Bright high-repetition-rate source of narrowband extreme-ultraviolet harmonics beyond 22 eV”, arXiv:1408.6827