Inherent Size Effects on XANES of Nanometer Metal Clusters: Size-Selected Platinum Clusters on Silica

Dai, Yang; Gorey, Timothy J.; Anderson, Scott L.; Lee, Sungwon; Seifert, Söenke; Winans, Randall E.

doi:10.1021/acs.jpcc.6b10167

Cited by 60 publications

(77 citation statements)

References 90 publications

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“…Attenuation at this level could result from Pt24 sintering into larger, more multilayer clusters, or simply restructuring of initially flattened clusters into more three-dimensional structures. Previous GISAXS results for Pt24/SiO2 heated to 423 K are consistent with a modest degree of cluster sintering, as discussed above [17]. For the heated sample, the Pt signal also decreases monotonically with He + exposure, but more slowly than for the unheated sample.…”

supporting

confidence: 81%

“…For temperatures of 423 K or higher, sintering was evident in GISAXS, but for 423 K (the temperature used in many of the ALD experiments), the scatterer size distribution remained peaked near 10 Å, with a tail extending to larger sizes. [17,40] The extent of broadening was smaller than that observed after a single cycle of room temperature ALD.…”

Section: Shown Inmentioning

confidence: 77%

“…After subtracting the scattering signal from the SiO2/Si support, the GISAXS data can be fit to estimate the scatterer size distributions, which are shown in Fig. 3b For comparison, in a previous study, [17] we studied the effects of annealing Pt24/SiO2/Si to various temperatures. Temperatures up to 372 K resulted in no significant change in the GISAXS of as-deposited Pt24/SiO2/Si, i.e., no significant sintering occurred.…”

Section: Shown Inmentioning

confidence: 99%

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Selective Growth of Al2O3 on Size-Selected Platinum Clusters by Atomic Layer Deposition

Gorey¹,

Dai²,

Anderson

et al. 2019

Preprint

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In heterogeneous catalysis, atomic layer deposition (ALD) has been developed as a tool to stabilize and reduce carbon deposition on supported nanoparticles. Here, we discuss use of high vacuum ALD to deposit alumina films on size-selected, sub-nanometer Pt/SiO2 model catalysts. Mass-selected Pt24 clusters were deposited on oxidized Si(100), to form model Pt24/SiO2 catalysts with particles shown to be just under 1 nm, with multilayer three dimensional structure. Alternating exposures to trimethylaluminum and water vapor in an ultra-high vacuum chamber were used to grow alumina on the samples without exposing them to air. The samples were probed in situ using X-ray photoelectron spectroscopy (XPS), low-energy ion scattering spectroscopy (ISS), and CO temperature-programmed desorption (TPD). Additional samples were prepared for ex situ experiments using grazing incidence small angle x-ray scattering spectroscopy (GISAXS). Alumina growth is found to initiate at least 60 times more efficiently at the Pt24 cluster sites, compared to bare SiO2/Si, with a single ALD cycle depositing a full alumina layer on top of the clusters, with substantial additional alumina growth initiating on SiO2 sites surrounding the clusters. As a result, the clusters were completely passivated, with no exposed Pt binding sites.

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supporting

confidence: 81%

Section: Shown Inmentioning

confidence: 77%

Section: Shown Inmentioning

confidence: 99%

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Selective Growth of Al2O3 on Size-Selected Platinum Clusters by Atomic Layer Deposition

Gorey¹,

Dai²,

Anderson

et al. 2019

Preprint

Self Cite

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“…It must be noted that the intensity of pre-edge features in the experimental spectrum is lower compared to the theoretically calculated spectra. The smearing of pre-edge features is the cumulative effect of broadening due to instrumental resolution, and nanocrystalline structure of the sample, as also observed in other metallic nanoparticles [68][69][70].…”

Section: Resultsmentioning

confidence: 63%

X-ray absorption spectroscopy study of cobalt mononitride thin films

et al. 2019

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We present a comprehensive study to resolve the debate about the structure of cobalt mononitride (CoN). In contradiction with theoretical predictions, experimentally CoN has been claimed to synthesize in a rock-salt (RS) and in a zincblende (ZB)-type structure under ambient pressure and temperature. Utilizing X-ray absorption near-edge spectroscopy (XANES) at Co and N K-edges and extended X-ray absorption fine structure (EXAFS) at Co K-edge, we investigated the structure of CoN in detail. The presence of a strong pre-edge feature at the Co K-edge and the absence of t 2 feature at the N K-edge indicate towards the tetrahedral coordination that is expected in the ZB-type structure of CoN. Theoretical simulations of XANES spectra unambiguously confirm the ZB-type structure in CoN. Also from EXAFS data, we found that CoN and Co-Co bond distances match well with ZB-CoN. Magnetic properties of CoN were examined using polarized neutron reflectivity and bulk magnetization measurements. It was found that CoN sample exhibits a paramagnetic behaviour as expected in ZB-CoN. Obtained results clearly demonstrate that CoN indeed crystalizes in the ZB-type structure, and the possibility of the RS-type CoN can be ruled out under ambient pressure and temperature. It is anticipated that the information about the structure of CoN can be utilized for its usage in emerging areas such as low-cost catalyst in oxygen and hydrogen evaluation reactions, high capacity anode in ion batteries and in photovoltaic applications.

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“…4,5 The binding energies of atomic core orbitals can be very sensitive to the size of the nanoparticles and can be probed by X-ray absorption near-edge structure (XANES) spectroscopy. 6 Mercury clusters reveal a band gap closure with increasing cluster size, which corresponds to an insulator-metal transition. 7 Optical properties represent another interesting case.…”

Section: Introductionmentioning

confidence: 97%