The nucleation and growth mechanism of aluminum oxide (Al2O3) in the early stages of atomic layer deposition (ALD) on monolayer epitaxial graphene (EG) on silicon carbide (4H–SiC) has been ...investigated by atomic force microscopy (AFM), conductive-atomic force microscopy (C-AFM) and Raman spectroscopy. Differently than for other types of graphene, a large and uniform density of nucleation sites was observed in the case of EG and ascribed to the presence of the buffer layer at EG/SiC interface. The deposition process was characterized by Al2O3 island growth in the very early stages, followed by the formation of a continuous Al2O3 film (∼2.4 nm thick) after only 40 ALD cycles due to the islands coalescence, and subsequent layer-by-layer growth. The electrical insulating properties of the deposited ultrathin Al2O3 films were demonstrated by nanoscale current mapping with C-AFM. Raman spectroscopy analyses showed low impact of the ALD process on the defect’s density of EG. The EG strain was also almost unaffected by the deposition in the regime of island growth and coalescence, whereas a significant increase was observed after the formation of a compact Al2O3 film. The obtained results can have important implications for device applications of epitaxial graphene requiring ultra-thin high-k insulators.
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Time dynamics of doping and strain induced in single layer graphene by thermal treatments up to 300°C in vacuum, nitrogen, carbon dioxide and oxygen controlled atmosphere are deeply studied by Raman ...spectroscopy and they are compared with its morphological evolution investigated by Atomic Force Microscopy. The reaction dynamics in oxygen treatments is determined down to a time scale of few minutes as well as that of dedoping process made by water vapor treatment. The interplay of strain modification and doping effects is separated. The strain is clarified to be strongly influenced by the cooling time. The doping removal is dominated by the water vapor, showing that the concentration of molecular water in gas phase governs the process rate. The opportune choice of heating/cooling and atmosphere enables to tune selectively the strain or doping.
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In the present investigation we report experimental data regarding the Raman and Infra-Red (IR) absorption activities of commercial silica nanoparticles. We compared the data of the nanoparticles ...with the ones acquired in the same experimental conditions for commercial bulk silica. By this comparison we highlighted that the variability of the spectral features of the matrix related Raman and IR bands in the nanoparticles is above the one observed for the bulk systems before any treatments. Furthermore, by studying nanoparticles with different sizes (diameters from 40 to 7nm) and applying the shell-model we can suggest that the core network of the nanoparticles is close to the one encountered in the bulk materials. By contrast for the surface shell, having a thickness of about 1nm, as suggested by previous investigations, the structure is strongly modified. In fact, from Raman and IR data it appears that the Si–O–Si angle has a lower main value than those encountered in bulk systems and that the ring statistic is shifted towards lower member rings.
► We studied the Raman and IR spectra of different commercial silica nanoparticles. ► The nanoparticles had different sizes (diameters from 40 to 7nm). ► Applying a shell-model we suggest that the core matrix is close some bulk materials. ► In the surface shell (thickness of about 1nm), the structure is strongly modified. ► The Si–O–Si angle has a lower main value and the lower member ring number is larger.
Fluorescent carbon nanodots are a novel family of carbon-based nanoscale materials endowed with an outstanding combination of properties that make them very appealing for applications in nanosensing, ...photonics, solar energy harvesting and photocatalysis. One of the remarkable properties of carbon dots is their strong sensitivity to the local environment, especially to metal ions in solution. These interactions provide a testing ground for their marked photochemical properties, highlighted by many studies, and frequently driven by charge transfer events. Here we combine several optical techniques, down to femtosecond time resolution, to understand the interplay between carbon nanodots and aqueous metal ions such as Cu
and Zn
. We find that copper inhibits the fluorescence of carbon dots through static and diffusional quenching mechanisms, and our measurements allow discriminating between the two. Ultrafast optical methods are then used to address the dynamics of copper-dot complexes, wherein static quenching takes place, and unveil the underlying complexity of their photocycle. We propose an initial increase of electronic charge on the surface of the dot, upon photo-excitation, followed by a partial electron transfer to the nearby ion, with 0.2 ps and 1.9 ps time constants, and finally a very fast (≪1 ps) non-radiative electron-hole recombination which brings the system back to the ground state. Notably, we find that the electron transfer stage is governed by an ultrafast water rearrangement around photo-excited dots, pointing out the key role of solvent interactions in the photo-physics of these systems.
Metal-organic frameworks (MOFs) are an intriguing group of porous materials due to their potential influence on the development of indispensable technologies like luminescent sensors and solid-state ...light devices, luminescent multifunctional nanomaterials. In this research work we explored MIL-53(Al), an exceptional class of MOF that, along with guest adsorption, undergoes structural transitions exhibiting breathing behavior between narrow pore and large pore under temperature and mechanical stress. Therefore, we opted for the time resolved luminescence and FT-Raman spectroscopy to investigate the mechanochromic and thermochromic response of this material under external stimuli. Intriguingly, when subjected to temperature changes, MIL-53(Al) exhibited a ratiometric fluorescence behavior related to the reversible relationship of photoluminescence emission intensity with respect to temperature. Moreover, under higher mechanical stress MIL-53(Al) displayed turn-on behavior in emission intensity, hence offering a thrilling avenue for the application in mechanically deformed-based luminescent sensors and ratiometric fluorescence temperature sensors.
The photoluminescence behaviour of carbon-based nanodots is still debated. Both core and surface structures are involved in the emission mechanism, and the electronic transitions can be modified by ...external agents such as metal ions or pH, but the general relation between the structure and the optical function is poorly understood. Here, we report a comparative study on the effects of these variables, changing the core structure from crystalline to amorphous, and modifying the surface structure by different passivation procedures. Our results highlight that the emission mechanism of the tunable visible fluorescence is identical for crystalline and amorphous samples, indicating the independence of the emission from the core structure. Furthermore, surface functionalization weakly influences the emission peak position, but has large consequences on their interaction with different metal ions. This suggests the involvement of quasi-degenerate electronic states originating from the high density of different interacting groups on the surface. Finally, we report the presence of an unusual ultraviolet emission band for the amorphous sample, likely involving localized molecular-type chromophores with carboxyl ends. Our findings provide new information on the emission mechanisms of CDs and can be used to engineer sub-types of CDs displaying very similar emission features, but specifically tailored for different sensing applications.
Metal–organic frameworks (MOFs) are getting closer to finally being used in commercial applications. In order to maximize their packing density, mechanical strength, stability in reactive ...environments, and many other properties, the compaction of MOF powders is a fundamental step for the application field of research of these extraordinary materials. In particular, HKUST-1 is among the most promising and studied MOF. Contrary to what reported so far in the literature, here we prove that the tableting of HKUST-1 powders without any damage of the lattice is possible and easy to get. For the first time, this kind of investigation has been performed exploiting its peculiar magnetic properties with the aid of electron paramagnetic resonance spectroscopy. Indeed, they have allowed us to explore in detail all the smallest changes induced in the paramagnetic paddle-wheel units by the application of the mechanical pressure on the material. This original approach has permitted us to unveil the main source of structural instability of HKUST-1 during compaction, that is, the water molecules adsorbed by the powdered sample before tableting and finally to establish a proper compaction protocol. Our conclusions are also fully supported by the results obtained with powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, water sorption isotherms, and surface area estimation with the Brunauer–Emmett–Teller method, which prove that the tablet of HKUST-1 obtained by this new protocol actually preserves the crystal structure and porosity of the pristine powders. A morphological characterization has also been conducted with a combined use of optical and atomic force microscopies.
Background
Rhinitis is as an inflammation of the nasal mucosa, characterized by high prevalence, widespread morbidity, and a significant financial burden on health care systems. Nevertheless, it is ...often considered as no more than a mere annoyance. This point of view has progressively led to underestimate and trivialize the disease. Therefore, there are numerous, mostly overlapping classifications of rhinopaties, but clear and standardized guidelines for diagnosis and treatment are still lacking. In the context of Precision Medicine, the development of a classification system focused on the endotypes of rhinitis to be widely adopted appears of utmost importance, also by virtue of study of the nasal immunophlogosis that, thanks to nasal cytology (NC), has recently allowed to better define the different forms of rhinitis, giving a new nosological dignity to several rhinopaties.
Aim
We aimed to summarize the current knowledge regarding rhinitis and to propose a systematic classification of rhinitis, based on both etiology and cytological findings
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