Point defects on graphene on metals.

Understanding the coupling of graphene with its local environment is critical to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single carbon vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural, and magnetic properties of the graphene layer. Our low temperature scanning tunneling microscopy studies, complemented by density functional theory, show the existence of a broad electronic resonance above the Fermi energy associated with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment associated with carbon vacancies in freestanding graphene layers.

Theoretical calculations of refractive indices and optical effects in spectra of nitric acid and nitric acid monohydrate crystals.

The theoretical infrared refractive indices of two systems related to atmospheric research, nitric acid (NA) and nitric acid monohydrate (NAM) crystals, have been computed using a methodology based on first-principles. The effects of lack of coherence in the infrared beam in RAIR and transmission spectra have also been treated using a model based on classical optics. The optical constants of NA crystals are presented for the first time; the results on NAM are compared to empirical values previously published with good general agreement. With the optical constants of NA, polarized reflection-absorption infrared spectra are predicted and compared to experimental spectra recorded also for the first time, for a set of varying film thickness. The global agreement is satisfactory. The effects of a number of experimental factors in transmission spectra of NAM are assessed, in an attempt to explain observed differences among experimental spectra. It is concluded that the spectral disparities are probably due to differences in the nature of the samples.