Thin tetrahedrally coordinated amorphous carbon (ta-C) films have been grown using a filtered vacuum arc. ta-C is a new allotrope of carbon whose existence was previously thought to be unlikely. A model is proposed which accounts for the formation and structure of these films on the basis of the compressive stress generated by the shallow implantation of carbon ions. An optimal range of beam energies between 15 and 70 eV, a high film stress, and a graphitic surface are predicted and confirmed by experimental evidence. Computer simulation of the growth confirms that high compressive stress is generated by impact energies in this range.

Electron energy-loss spectroscopy measurements have been made on amorphous diamond-like carbon films produced by condensing the plasma stream from a filtered vacuum arc. The results are compared with spectra from diamond, graphitized carbon and amorphous carbon. Although the energy-loss spectra reveal the presence of a small quantity of sp²-bonded material in the diamond-like film, the high plasmon frequency and shape of the K-edge show that the material is essentially an amorphous form of diamond. The fraction of sp²- bonded carbon was quantified and found to be of the order of 15%. It was not possible to determine if the sp² carbon was on the surface or throughout the bulk.

Perovskite decomposition in detail: Solar cells are subject to heating when operating in sunlight, and the organic components of hybrid perovskite solar cells, especially the commonly used methylammonium cation, can undergo thermal decomposition. Encapsulation can limit decomposition by bringing such reactions to equilibrium and can prevent exposure to damaging ambient moisture. Shi et al. examined several encapsulation schemes for perovskite films and devices by probing volatile products with gas chromatography–mass spectrometry (see the Perspective by Juarez-Perez and Haro). Pressure-tight polymer/glass stack encapsulation was effective in suppressing gas transfer and allowed solar cells containing methylammonium to pass harsh moisture and thermal cycling tests. Science , this issue p. eaba2412 ; see also p. 1309