MoS2 is a material with great potentialities in electronic applications. Tuning its properties by halogenation is a possible route to expand its applicability.
Thermal stability of 2D materials under different conditions must be carefully examined since they can be submitted to heat during device fabrication and/or during application. In this work, the thermal stability of monolayer molybdenum disulfide (MoS2) under vacuum (∼10−7 mbar) annealing was investigated. While MoS2 bulk is stable up to 1050°C, monolayer MoS2 was only stable up to 700°C. At 800°C, significant degradation occurred, while at 900°C, all MoS2 was converted to MoO3 and MoO2. Results indicate that sulfur was lost during high temperature annealing, while no significant molybdenum loss was detected (no MoO3 evaporation occurred). Base pressure during annealing had a strong influence in the thermal degradation, since MoS2 was stable at 800°C when pressure was reduced to ∼10−9 mbar, while MoS2 was completely converted to MoO3 and MoO2 under 220 mbar of dry argon at 500°C, possibly due to the presence of oxidation agents. Results highlight the importance of the careful choice of conditions during growth and application of MoS2.
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.
In the present work, we investigated the thermally-driven H incorporation in HfO2 films deposited on Si and Ge substrates. Two regimes for deuterium (D) uptake were identified, attributed to D bonded near the HfO2/substrate interface region (at 300 °C) and through the whole HfO2 layer (400–600 °C). Films deposited on Si presented higher D amounts for all investigated temperatures, as well as, a higher resistance for D desorption. Moreover, HfO2 films underwent structural changes during annealings, influencing D incorporation. The semiconductor substrate plays a key role in this process.
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