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This article belongs to the Special Issue Luminescence Properties of Nanomaterials and Nanocomposites. ; Band gap engineering of atomically thin two-dimensional (2D) materials has attracted a huge amount of interest as a key aspect to the application of these materials in nanooptoelectronics and nanophotonics. Low-loss electron energy loss spectroscopy has been employed to perform a direct measurement of the band gap in atomically thin MoxW(1−x)S2 nanoflakes. The results show a bowing effect with the alloying degree, which fits previous studies focused on excitonic transitions. Additional properties regarding the Van Hove singularities in the density of states of these materials, as well as high energy excitonic transition, have been analysed as well. ; Research supported by the Spanish MICINN (PID2019-104739GB-100/AEI/10.13039/ 501100011033), Government of Aragon (project DGA E13-20R) and European Union H2020 programs "ESTEEM3" (823717), Graphene Flagship (881603), JST-CREST (JPMJCR20B1, JPMJCR20B5, JPMJCR1993) and JSPS A3 Foresight Program. ; Peer reviewed

1 figure.-- Talk delivered at the HeteroNanoCarb-2019 Conference, Advances and applications in carbon related nanomaterials: From pure to doped structures including heteroatom layers, 2019, December 09th -- 13th, Centro de Ciencias de Benasque Pedro Pascual in Benasque (Aragon, Spain). ; For the last fifteen years, graphene oxide (GO) has become a material of great importance within the subject of chemically modified graphene (CDG) for its vast potential applications. However, both the chemical structure of Graphene oxide and the diverse processes taking place in thermal reduction of GO into reduced graphene oxide (RGO) are still not completely clear despite the sizable amount of studies concerning this issue. TEM and EELS, using a sample holder capable of heating samples up to 1200ºC within the TEM, is a unique and extensive technique for the analysis of the reduction of GO. Using this technique, we can measure, simultaneously and in situ, four main properties essential to this analysis at several intermediate temperatures and under high vacuum: the oxidation rate, its thickness, its mass density and its sp2-sp3 bond ratio. This study presents an analysis of GO by studying all of the aforementioned properties in two different studies: a first one heating up to 300ºC to better understand the physisorbed and chemisorbed water desorption, and a second one up to 1200ºC focused on the desorption of various oxygen functional groups; as well as the graphitisation of GO. Our results will be compared with previous studies on the matter. ; This work was supported by the Spanish MINECO (MAT2016-79776-P, AEI/FEDER, EU), and European Union H2020 programs Marie Sklodowska-Curie Enabling Excellence (642742), ESTEEM3 (823717), Flag-ERA GATES (JTC - PCI2018-093137) and Graphene Flagship (785219).