Angle Resolved TEM Imaging of Pt Nanoparticles

Abstract

Particle shape and size are two of the most important characteristics of nanoparticulate catalysts that determined their activity and selectivity. In many studies, the shapes of nanoparticles are characterized using transmission electron micrographs obtained at a single nanoparticle orientation and thus, the shape determination is based on viewing a single cross-sectional profile of the nanoparticle. A full determination of particle shape should require viewing over a range of angles. In this work Pt nanoparticles with controlled shapes and sizes have been synthesized using a high pressure technique. Angle resolved transmission electron microscopy techniques (electron tomography) are necessary to view the crystals over a range of orientations and determine their three dimensional shapes. In this work, angle resolved TEM imaging of nanoparticles reveals information about the nanoparticle shape and orientation on substrates that cannot be determined from single cross-sectional TEM images. Angle resolved TEM imaging of nanoparticles will be very valuable in catalysis and in the fields where the shapes of nanoparticles play an important role.

HAADF‐STEM characterization and simulation of nanoparticle distributions in an inhomogeneous matrix

“…In several studies, TEM is compared with other techniques frequently employed to measure NPs, such as atomic force microscopy (Boyd & Cuenat 2011), dynamic light scattering (Hagendorfer et al 2012), EXAFS (Agostini et al 2014) or small angle X-ray scattering (Cervera Gontard et al 2006;Vippola et al 2016). A large number of studies are also performed in scanning TEM (STEM); STEM imaging provides the means to suppress diffraction contrast from images, which may help to study more quantitatively individual particles (Treacy & Rice 1989;Carlsson et al 2006;Young et al 2008) even in 3D (Cervera Gontard et al 2006;Benlekbir et al 2009, Shukla et al 2010Thiedmann et al 2012). In the high-angle annular dark field (HAADF) mode, the intensity collected from a single atom depends mainly on the electron Rutherford scattering, and has been proven to be proportional to the square of the atomic number, Z².…”

Synthesis of shaped Pt nanoparticles using common anions or small molecules as shape-directing agents: observation of a strong halide or pseudo-halide effect

“…A vast literature is available on the synthesis and catalytic reactivity of Pt metal catalysts, and synthesis strategies for preparing shape-and size-controlled Pt metal colloids have been reviewed. 3 More recent methods of preparing shaped Pt metal nanoparticles include: Pt-ion reduction by H 2 in the presence of carboxylic acid [4][5][6] or amine 7 capping agents; Pt-ion reduction by citrate ion 4 or formic acid; 8 polyol reduction of Ption in the presence of polyvinylpyrrolidone (PVP), 9 PVP/ AgNO 3 , 10 PVP/NaNO 3 , 11 or oleylamine; 12 thermal decomposition of organometallic Pt precursors; [13][14][15] Pt(acetylacetonate) 2 reduction by oleylamine, 16 alkenes, 17 or metal carbonyls in the presence of oleylamine/oleic acid; 18 photo-induced reduction of Pt(IV) ion within micelles; 19 reduction of Pt-ion with wood nanobers; 20 and supported Pt nanoparticles formed by borohydride reduction, 21 electrochemical reduction, 8 or electron-beam deposition. 22 Control of Pt nanoparticle shape is usually achieved by the choice of surfactant or shape-directing agent used and by careful regulation of experimental conditions, such as surfactant or shape-directing agent concentration, pH, temperature, ambient light intensity, and reaction time.…”