ARTICLE | doi:10.20944/preprints201610.0099.v1
Subject: Materials Science, General Materials Science Keywords: Moiré patterns; MoS2; Graphene; WS2; WSe2; HRTEM
Online: 24 October 2016 (05:03:50 CEST)
We present a series of computer-assisted high resolution transmission electron (HRTEM) simulations to determine Moiré patters by induced twisting effects between slabs at rotational angles of 3°, 5°, 8°, and 16°, for molybdenum disulfide, graphene, tungsten disulfide, and tungsten selenide layered materials. In order to investigate the electronic structure, a series of numerical simulations using DFT methods was completed using CASTEP with a generalized gradient approximation to determine both band structure and density of states on honeycomb like new superlattices. Our results indicate metallic transitions when rotation approaches 8° with respect to each other for most of the two-dimensional systems that were analyzed.
ARTICLE | doi:10.20944/preprints202107.0298.v1
Subject: Engineering, Automotive Engineering Keywords: Soot; TEM; HRTEM; EELS; soot nanostructure; premixed flames
Online: 13 July 2021 (11:20:59 CEST)
Soot is characterized by a multiscale structural organization and Transmission Electron Microscope (TEM) is the only diagnostic tool giving access to it. However, being a diffraction-based technique, TEM images only aromatic systems and thus, it is particularly useful to combine it with electron energy-loss spectroscopy (EELS), able to provide quantitative information about the relative abundance of sp3 and sp2 hybridized carbon. In this paper a method for the EELS spectrum analysis of carbonaceous materials recently developed for electron-irradiated graphite and glassy carbon composition analysis has been applied for the first time on soot samples, in order to test its performance in soot nanostructure study in combination with TEM and High Resolution TEM (HRTEM). Soot samples here analysed were collected in the soot inception region of premixed flames of different hydrocarbon fuels. EELS, in agreement with TEM and HRTEM, showed a quite disordered and heterogeneous structure for young soot, without any significant distinction between soot formed from methane and ethylene fuels.
ARTICLE | doi:10.20944/preprints201704.0014.v1
Subject: Materials Science, Nanotechnology Keywords: tin oxide pellets; doping; HRTEM analysis; CO; sensitivity
Online: 4 April 2017 (08:16:13 CEST)
In this work, we report synthesis of Cu, Pt and Pd doped SnO2 powders and their comparative CO gas sensing studies. Dopants were incorporated into SnO2 nanostructures using chemical and impregnation methods by using urea and ammonia as precipitation agents. The synthesized samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and High resolution transmission electron microscopy (HR-TEM). The presence of dopants within the SnO2 nanostructures was evidenced from HR-TEM. Doped powders utilizing chemical methods with urea as precipitation agent presented higher sensitivities compared to the remaining, which is due to the formation of uniform and homogeneous particles resulted from the temperature assisted synthesis. The particle sizes of doped SnO2 nanostructures were in the range of 40-100 nm. An enhanced sensitivity around 1783 was achieved with Cu doped SnO2 when compared with two other dopants i.e., Pt (1200) and Pd: SnO2(502). The high sensitivity of Cu: SnO2 is due to formation of CuO and its excellent association and dissociation in the presence of CO with adsorbed atmospheric oxygen at sensor operation temperatures resulted in high conductance. Cu: SnO2 may be an alternative and cost effective sensor for industrial applications.
ARTICLE | doi:10.20944/preprints202011.0579.v1
Subject: Chemistry, Analytical Chemistry Keywords: heterostructures; TiO2 nanosheets; few layers MoS2/TiO2; ex-situ and in-situ approaches; FTIR; Raman; UV-Vis; XRD; HRTEM
Online: 23 November 2020 (10:17:48 CET)
MoS2/TiO2 nanostructures made of MoS2 nanoparticles covering TiO2 nanosheets have been synthesized, either via ex-situ or in-situ approaches. Morphology and structure of MoS2/TiO2 hybrid nanostructures have been investigated and imaged by means of X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM), while the vibrational and the optical properties have been investigated by Raman, Fourier-transform infrared spectroscopy (FTIR) and UV−visible (UV-Vis) techniques. The different stacking degrees together with the size distribution of the MoS2 nanosheets, decorating the TiO2 nanosheets, have been carefully obtained from HRTEM images. The nature of the surface sites on the main exposed faces of both materials has been detected by means of in-situ FTIR spectra of adsorbed CO probe molecule. The results coming from the ex-situ and in-situ approaches will be compared, by highlighting the role of the synthesis processes in affecting morphology and structure of MoS2 nanosheets, including their curvature, surface defects, and stacking order. Some more, it will be shown that the in-situ approach is affecting the reactivity of the TiO2 nanosheets too, hence in turn affects the MoS2/TiO2 nanosheets interaction.