Modeling of nanocrystals supported by advanced morphological and chemical characterization is a unique tool for the development of reliable nanostructured devices, which depends on the ability to synthesize and characterize materials on the atomic scale. Among the most significant challenges in nanostructural characterization is the evaluation of crystal growth mechanisms and their dependence on the shape of nanoparticles and the distribution of doping elements. This paper presents a new strategy to characterize nanocrystals, applied here to antimony-doped tin oxide (Sb-SnO(2)) (ATO) by the combined use of experimental and simulated high-resolution transmission electron microscopy (HRTEM) images and surface energy ab initio calculations. The results show that the Wulff construction can not only describe the shape of nanocrystals as a function of surface energy distribution but also retrieve quantitative information on dopant distribution by the dimensional analysis of nanoparticle shapes. In addition, a novel three-dimensional evaluation of an oriented attachment growth mechanism is provided in the proposed methodology. This procedure is a useful approach for faceted nanocrystal shape modeling and indirect quantitative evaluation of dopant spatial distribution, which are difficult to evaluate by other techniques.
The development of reliable nanostructured devices is intrinsically dependent on the description and manipulation of materials’ properties at the atomic scale. Consequently, several technological advances are dependent on improvements in the characterization techniques and in the models used to describe the properties of nanosized materials as a function of the synthesis parameters. The evaluation of doping element distributions in nanocrystals is directly linked to fundamental aspects that define the properties of the material, such as surface‐energy distribution, nanoparticle shape, and crystal growth mechanism. However, this is still one of the most challenging tasks in the characterization of materials because of the required spatial resolution and other various restrictions from quantitative characterization techniques, such as sample degradation and signal‐to‐noise ratio. This paper addresses the dopant segregation characterization for two antimony‐doped tin oxide (Sb:SnO2) systems, with different Sb doping levels, by the combined use of experimental and simulated high‐resolution transmission electron microscopy (HRTEM) images and surface‐energy ab initio calculations. The applied methodology provided three‐dimensional models with geometrical and compositional information that were demonstrated to be self‐consistent and correspond to the systems’ mean properties. The results evidence that the dopant distribution configuration is dependent on the system composition and that dopant atom redistribution may be an active mechanism for the overall surface‐energy minimization.
This work reports a detailed characterization of an anomalous oriented attachment behaviour for SnO 2 nanocrystals. Our results evidenced an anisotropic growth for two identical h110i directions, which are equivalent according to the SnO 2 crystallographic structure symmetry. A hypothesis is proposed to describe this behaviour.Semiconductor nanomaterials have been intensively studied over the last decade due to a number of novel applications in a variety of technological fields. Tin oxide (SnO 2 ) can be noticed among this group for its use in gas sensors, transparent conductive oxide and solar cell devices. Several works 1 report synthesis procedures for tailoring SnO 2 nanocrystals with controlled morphology and some studies 2 elucidated the crystal growth behavior for particular synthesis environments. Probing its low solubility in some typical solvents, some works 3 further evaluated SnO 2 and its doped forms growth behavior to enhance the oriented attachment (OA) growth mechanism theory. 4,5 The originally proposed OA mechanism concerns the adjacent nanocrystals self-organization and coalescence, which can occur after the effective collision between particles either with mutual orientation or followed by a particle rotation step. This communication concerns an anomalous oriented attachment growth behavior that has been repeatedly observed for SnO 2 nanoparticles obtained by a non-aqueous solution synthesis procedure. These results could not be explained using the crystal growth descriptions available in the literature.The SnO 2 nanocrystals were synthesized in a glovebox under a controlled atmosphere. A total of 5.47 mmol SnCl 4 (99.995%) was stirred in a vessel with 40 ml of benzyl alcohol, after which the reaction vessel was removed from the glovebox and heated at 150 1C for about 48 h in a silicone bath. SnO 2 nanoparticles were collected by centrifugation, washed twice with tetrahydrofuran, and stored in a concentrated THF dispersion. TEM samples were prepared right after the synthesis procedure by dripping a diluted SnO 2 solution onto copper grids covered with a thin amorphous carbon film. HRTEM characterization was performed using a JEM-3010 URP TEM at 300 kV with a LaB 6 electron gun and equipped with a 1024 Â 1024 thermoelectrically cooled CCD camera. HRTEM multislice simulation was performed using JEMS software. 6 XRD analysis of synthesized material indicated highly crystalline SnO 2 nanocrystals with cassiterite tetragonal P4 2 /mnm structure.7 Fig. 1a shows a representative TEM image depicting that the nonaqueous synthesis route produces dispersed and crystalline SnO 2 nanoparticles with elongated shape. The size distribution for 200 measurements shown in Fig. 1b reveals elongated particles with a mean length of 29.9 nm, mean width of 10.9 nm, and mean aspect ratio of 3.24. Fig. 2a and b depict SnO 2 nanocrystals HRTEM images which reveal some relevant features. It can be observed that the SnO 2 particles are single crystals elongated along the [110] direction, according with the aspect ratio...
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