Chemically sensitive structure-imaging with a scanning transmission electron microscope

Supported Pd–Cu Bimetallic Nanoparticles That Have High Activity for the Electrochemical Oxidation of Methanol

“…core-shell structures or phase-separation of Pd and Cu) because the intensity of the atomic columns in the HAADF image is approximately proportional to Z 1.7 . [44] However, as shown in Figure 4, except for some random intensity variation between adjacent atomic columns, no obvious regular or periodic intensity variation was observed within the bimetallic particles from these two samples, thereby indicating the absence of elemental-segregation/ phase-separation. Most of the bimetallic particles in the Pd 39 -Cu 61 /C sample ( Figure 4 D-F) were not well-crystalline, as revealed by their distorted lattice fringes and structurally disordered regions, whilst the crystal structure of the bimet- This chemically ordered structure has been proposed to exist in Pd-Cu systems within certain composition ranges (10-60 at % Pd) and at certain temperatures and pressures.…”

“…Moreover, the nominal particle-composition was also controlled by simply varying the ratio between the Pd and Cu precursors. The compositions of Pd-Cu bimetallic nanoparticles, as measured by ICP analysis, were Pd 85 -Cu 15 , Pd 56 -Cu 44 , and Pd 39 -Cu 61 (the numerical subscripts denote the atomic ratio of the alloying metal), which corresponded to the precursor Pd/Cu molar ratios of 5:1, 1:1, and 1:5, respectively. Representative TEM images and the corresponding particle sizedistributions of the as-prepared monometallic Pd and bimetallic Pd-Cu nanoparticles are shown in Figure 1 A-D (also see the Supporting Information, Figure S4), whilst the corresponding XRD patterns are shown in Figure 1 E. The diffraction patterns of the bimetallic nanoparticles displayed an FCC structure, similar to that of pure Pd nanoparticles www.chemeurj.org (centered at 2q values of about 39 and 448).…”

“…[35] All of the syntheses were carried out under an argon atmosphere. Taking the synthesis of Pd 56 -Cu 44 nanoparticles as an example, 1.5 mmol oleic acid (OA) and 1.5 mmol oleylamine (OAm) were mixed with ethylene glycol (EG, 50 mL). Next, two metal-precursor solutions, 0.5 mmol PdA C H T U N G T R E N N U N G (CH 3 COO) 2 in acetone and 0.5 mmol Cu-A C H T U N G T R E N N U N G (CH 3 COO) 2 ·H 2 O in water, were added.…”

“…[17] However, even with all of these research endeavors, the activities of Pd catalysts remain far Abstract: Monodisperse bimetallic PdCu nanoparticles with controllable size and composition were synthesized by a one-step multiphase ethylene glycol (EG) method. Adjusting the stoichiometric ratio of the Pd and Cu precursors afforded nanoparticles with different compositions, such as Pd 85 -Cu 15 , Pd 56 -Cu 44 , and Pd 39 -Cu 61 . The nanoparticles were separated from the solution mixture by extraction with non-polar solvents, such as n-hexane.…”

Atomic-Scale Nanostructures by Advanced Electron Microscopy and Informatics

“…ADF imaging uses a doughnut-shaped annular detector to selectively collect high-angle scattered electrons, building up images from the variation in this signal with probe position in a raster scan. Since the integrated intensity of high-angle scattered electrons strongly scales with the atomic number of the atoms under the probe, this imaging (so-called Z-contrast imaging) can sensitively visualize heavy element atoms [34]. However, ADF can seldom reliably visualize light elements due to their weak power to scatter electrons at higher angles.…”