No abstract

Oxygen transport during thermal oxidation of Ge and desorption of the formed Ge oxide are investigated. Higher oxidation temperatures and lower oxygen pressures promote GeO desorption. An appreciable fraction of oxidized Ge desorbs during the growth of a GeO2 layer. The interplay between oxygen desorption and incorporation results in the exchange of O originally present in GeO2 by O from the gas phase throughout the oxide layer. This process is mediated by O vacancies generated at the GeO2/Ge interface. The formation of a substoichiometric oxide is shown to have direct relation with the GeO desorption.

The reversibility of graphene photochemical chlorination was investigated. A high content of Cl is obtained through photochlorination, without changing C hybridization. To accommodate the incorporated Cl, graphene corrugation takes place. However, due to weak bonding, Cl atoms desorb during air exposure and long periods of storage. Chlorination also leads to graphene doping. When Cl is removed, doping decreases and graphene returns to its original morphology. Only a small amount of Cl (Cl/C ∼ 0.1) remains strongly bonded to graphene, most likely at grain edges and defects. Therefore, to maintain a precise doping level, Cl trapping methods are essential. Moreover, Cl removal using laser irradiation can be used to tune doping in micrometric areas, making it a promising technique to be used in applications where different doping levels are needed.

Removal of residues from CVD-grown graphene and its doping are key issues to fully explore its properties. In the present work, we propose a two-step process to remove PMMA residuals from graphene's surface and to incorporate dopants in its lattice by NO annealing. Nevertheless, NO thermal treatments also promoted etching of the graphene layer. This effect was shown to be induced by the decomposition products of NO, which are strong oxidizing agents like NO 2 . However, this undesirable side effect of NO annealing can be strongly suppressed by carefully choosing the annealing conditions, constituting a promising approach to dope graphene.

In the present work, we investigated the interaction of hydrogen with single-layer graphene. Fully hydrogenated monolayer graphene was predicted to be a semiconductor with a bandgap of 3.5 eV in contrast to the metallic behavior of its pristine counterpart. Integration of these materials is a promising approach to develop new electronic devices. Amidst numerous theoretical works evidencing the efficient formation of fully hydrogenated graphene, few experimental studies have tackled this issue. A possible explanation for that is the difficulty to directly quantify hydrogen by usual characterization techniques. Using an isotopically enriched gas in deuterium in conjunction with nuclear reaction analysis, we were able to quantify deuterium deliberately incorporated in graphene as a result of thermal annealing. The highest D areal density obtained following annealing at 800 °C was 3.5 × 10 14 D/cm 2 . This amount corresponds to ∼10% of the carbon atoms in graphene. Spectroscopic results evidence that deuterium is predominantly incorporated in grain boundaries accompanied by rippling and etching of graphene, the latter effect being more pronounced at higher temperatures. Desorption experiments show that hydrogen (deuterium) incorporation is not completely reversible due to the damage induced in the graphene layer through the hydrogen adsorption/desorption cycle.