In this work, electrically and thermally conductive poly (butylene terephthalate) nanocomposites were prepared by in-situ ring-opening polymerization of cyclic butylene terephthalate (CBT) in ...presence of a tin-based catalyst. One type of graphite nanoplatelets (GNP) and two different grades of reduced graphene oxide (rGO) were used. Furthermore, high temperature annealing treatment under vacuum at 1700 °C was carried out on both RGO to reduce their defectiveness and study the correlation between the electrical/thermal properties of the nanocomposites and the nanoflakes structure/defectiveness. The morphology and quality of the nanomaterials were investigated by means of electron microscopy, x-ray photoelectron spectroscopy, thermogravimetry and Raman spectroscopy. Thermal, mechanical and electrical properties of the nanocomposites were investigated by means of rheology, dynamic mechanical thermal analysis, volumetric resistivity and thermal conductivity measurements. Physical properties of nanocomposites were correlated with the structure and defectiveness of nanoflakes, evidencing a strong dependence of properties on nanoflakes structure and defectiveness. In particular, a significant enhancement of both thermal and electrical conductivities was demonstrated upon the reduction of nanoflakes defectiveness.
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•Thermally conductive PBT nanocomposites prepared by ring-opening polymerization.•First-time evidences of rGO defectiveness vs. nanocomposite conductivity.•Low defectiveness of carbon nanoflakes: a must for highly conductive nanocomposites.•High temperature annealing suitable to reduce carbon nanoflakes defectiveness.
Silicene, the 2D silicon allotrope analogue of graphene, was theoretically predicted in 1994 as a metastable buckled honeycomb silicon monolayer. Similarly to its carbon counterpart it was predicted ...to present an electronic structure hosting Dirac cones. In the last decade a great deal of work has been done to synthesize silicene and exploit its properties. In this paper we will review our research group activity in the field, dealing in particular with silicon-substrate interaction upon silicon deposition, and discuss the still debated silicene formation starting from the chemistry of silicon unsaturated compounds.
In this study, the CO2 adsorption properties of different metal mixed oxides (MMO) obtained by calcination of different layered double hydroxides (LDH) are addressed. Four types of LDH, with ...composition M1-x2+Mx3+OH2x+·Ax/nn-·mH2Ox-, where M2+=Zn, Cu, Ni, M3+=Al, x = 0.33, n = 2 and A = CO32−, were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis coupled with mass spectrometry (TG-MS). Different thermal behaviors upon heating were observed depending on the LDH composition, resulting in the exploitation of different calcination temperatures to convert LDH into mixed metal oxides (MMO). MMO were exposed to ambient air or pure carbon dioxide atmosphere to evaluate CO2 adsorption properties. Aging in ambient condition leads to adsorption of both CO2 and water, from ambient moisture, with variable ratios depending on the MMO composition. Furthermore, all the MMO were demonstrated to be able to adsorb CO2 in pure gas stream, in the absence of moisture. In both ambient and pure CO2 conditions, the performance of MMO is strongly dependent on the metal composition of MMO. In particular, the presence of Cu in the structure turned out to be beneficial in terms of adsorption capacity, with a maximum mass gain for CuAl MMO of 4 and 15% in pure CO2 and in atmospheric conditions, respectively.
We report a study of the interface between antimony and the prototypical topological insulator Bi2Se3. Scanning tunnelling microscopy measurements show the presence of ordered domains displaying a ...perfect lattice match with bismuth selenide. Density functional theory calculations of the most stable atomic configurations demonstrate that the ordered domains can be attributed to stacks of β-antimonene.
Interest in the Si/Ag(110) system, which forms highly ordered linear nanostructures coined 'silicon nanoribbons', was recently boosted by the claim that such nanoribbons may be formed by silicon ...atoms arranged in a 2D honeycomb structure as in graphene, i.e. silicene. Despite such a revived interest, many discrepancies still exist in the recently reported results. This paper reports on a systematic investigation by scanning tunneling microscopy and low-energy electron diffraction of the Si/Ag(110) system as a function of the amount of deposited silicon and the deposition temperature. This reveals a complex interplay between these two factors, resulting in a rich array of possible self-assembled nanostructures and surface reconstructions. Several novel findings and clarification of the contradictory results reported in the literature are discussed in this work. In particular, the deposition temperature is demonstrated to be a key parameter to control the width of the Si nanoribbons produced. Recently, massive linear nanostructures were reported to be 'multilayer silicene', forming once the deposited silicon amount exceeds full coverage. However, we show that such nanostructures are also observed at low silicon coverage, demonstrating that their formation is exclusively determined by a deposition temperature higher than 460 K. On the other hand, for Si amounts higher than one monolayer the surface presents a novel c(8 × 4) reconstruction, which is responsible for the ×4 periodicity detected by LEED measurements, previously attributed to the 1.6 nm-wide nanoribbons overlayer or to 'multilayer silicene'. Finally, the large collection of acquired data also allowed us to single out image artifacts that may explain the contradictory results appearing in previous papers.
In this study, the CO
2
adsorption properties of different metal mixed oxides (MMO) obtained by calcination of different layered double hydroxides (LDH) are addressed. Four types of LDH, with ...composition
M
1
-
x
2
+
M
x
3
+
OH
2
x
+
·
A
x/n
n
-
·
m
H
2
O
x
-
,
where M
2+
=Zn, Cu, Ni, M
3+
=Al,
x
= 0.33,
n
= 2 and A = CO
3
2−
, were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis coupled with mass spectrometry (TG-MS). Different thermal behaviors upon heating were observed depending on the LDH composition, resulting in the exploitation of different calcination temperatures to convert LDH into mixed metal oxides (MMO). MMO were exposed to ambient air or pure carbon dioxide atmosphere to evaluate CO
2
adsorption properties. Aging in ambient condition leads to adsorption of both CO
2
and water, from ambient moisture, with variable ratios depending on the MMO composition. Furthermore, all the MMO were demonstrated to be able to adsorb CO
2
in pure gas stream, in the absence of moisture. In both ambient and pure CO
2
conditions, the performance of MMO is strongly dependent on the metal composition of MMO. In particular, the presence of Cu in the structure turned out to be beneficial in terms of adsorption capacity, with a maximum mass gain for CuAl MMO of 4 and 15% in pure CO
2
and in atmospheric conditions, respectively.
Abstract
Topological surface states usually emerge at the boundary between a topological and a conventional insulator. Their precise physical character and spatial localization depend on the complex ...interplay between the chemical, structural and electronic properties of the two insulators in contact. Using a lattice-matched heterointerface of single and double bilayers of β-antimonene and bismuth selenide, we perform a comprehensive experimental and theoretical study of the chiral surface states by means of microscopy and spectroscopic measurements complemented by first-principles calculations. We demonstrate that, although β-antimonene is a trivial insulator in its free-standing form, it inherits the unique symmetry-protected spin texture from the substrate via a proximity effect that induces outward migration of the topological state. This “topologization” of β-antimonene is found to be driven by the hybridization of the bands from either side of the interface.
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•Ring-opening polymerization successfully used to produce thermally conductive nanocomposites.•Infiltration of oligomers between nanoflakes is the key for their dispersion.•Nanoflakes ...aspect ratio reduction demonstrated during polymerization in extruder.•Thermal conductivity of nanocomposites decreases upon nanoflakes fragmentation.•Large nanoflakes with low defectiveness are mandatory for high thermal conductivity.
In this work, the study of thermal conductivity before and after in-situ ring-opening polymerization of cyclic butylene terephthalate into poly (butylene terephthalate) in presence of graphene-related materials (GRM) is addressed, to gain insight in the modification of nanocomposites morphology upon polymerization. Five types of GRM were used: one type of graphite nanoplatelets, two different grades of reduced graphene oxide (rGO) and the same rGO grades after thermal annealing for 1h at 1700°C under vacuum to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and nanoparticle organization were investigated by means of differential scanning calorimetry, electron microscopy and rheology. Electrical and thermal properties were investigated by means of volumetric resistivity and bulk thermal conductivity measurement. In particular, the reduction of nanoflake aspect ratio during ring-opening polymerization was found to have a detrimental effect on both electrical and thermal conductivities in nanocomposites.
Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a ...very small lattice parameter forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high annealing temperatures, intercalation of atoms through graphene occurs, opening the path for formation of vertical heterojunctions constituted of two-dimensional layers. In this paper, we report on the ability of silicon atoms to penetrate the graphene network, fully epitaxially grown on a Ni(111) surface, even at room temperature. Our scanning tunneling microscopy (STM) experiments show that the presence of defects like vacancies and dislocations in the graphene lattice favor the Si atoms intercalation, forming two-dimensional, flat and disordered islands below the Gr layer. Ab-initio molecular dynamics calculations confirm that Gr defects are necessary for Si intercalation at room temperature and show that: i) a hypothetical intercalated silicene layer cannot be stable for more than 8 ps and ii) the corresponding Si atoms completely lose their in-plane order, resulting in a random planar distribution, and form strong covalent bonds with Ni atoms.
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The surface electronic structure of Si(1 1 1)-7×7 has been studied by angle-resolved photo electron spectroscopy. Replicas of the S1 surface state are found in correspondence with several 7×7 unit ...cells in the reciprocal space. This observation resolves in a direct way the long-standing dichotomy between the structural and electronic properties of the system previously discussed on the basis of the 2×2 or 3×3 R30° surface models.
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