3D Atomic Arrangement at Functional Interfaces Inside Nanoparticles by Resonant High-Energy X-ray Diffraction

Abstract

With current science and technology moving rapidly into smaller scales, nanometer-sized materials, often referred to as NPs, are produced in increasing numbers and explored for numerous useful applications. Evidence is mounting, however, that useful properties of NPs can be improved further and even new NP functionality achieved by not only controlling the NP size and shape but also interfacing chemically or structurally distinct entities into single, so-called "composite" NPs. A typical example is core-shell NPs wherein the synergy of distinct atoms at the core\shell interface endows the NPs with otherwise unachievable functionality. However, though advantageous, the concept of functional interfaces inside NPs is still pursued largely by trial-and-error. That is because it is difficut to assess the interfaces precisely at the atomic level using traditional experimental techniques and, hence, difficult to take control of. Using the core\shell interface in less than 10 nm in size Ru core-Pt shells NPs as an example, we demonstrate that precise knowledge of the 3D atomic arrangement at functional interfaces inside NPs can be obtained by resonant high-energy X-ray diffraction (XRD) coupled to element-specific atomic pair distribution function (PDF) analysis. On the basis of the unique structure knowledge obtained, we scrutinize the still-debatable influence of core\shell interface on the catalytic functionality of Ru core-Pt shell NPs, thus evidencing the usefulness of this nontraditional technique for practical applications.

Reverse Monte Carlo modeling for local structures of noble metal nanoparticles using high-energy XRD and EXAFS

“…Over the past few decades, synchrotron radiation based highenergy X-ray diffraction (HEXRD) coupled to atomic pair distribution function (PDF) analysis has emerged as an important tool to reveal the 3D atomic arrangement of unsupported or supported metal nanoparticles, [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] which have a pronounced effect on their structure and shape as well as on their functionality in applications such as catalysis. For example, Petkov and co-workers reported the 3D atomic structure of nanosized Ru [18][19][20] and Au [21][22][23] and binary alloy [24][25][26] particles, indicating that these nanoparticles less than 10 nm in diameter could be considered as nonperiodic, dense packing of metallic atoms that shows characteristic of the fcc lattice with some surface atomic disorder. Here it may be noted that atoms at the nanoparticle surfaces have incomplete coordination spheres, experience signicant surface relaxation and surface environment effects.…”

“…36,37 RMC simulations are an established and ideal technique for modeling structure functions of highly disordered materials that requires no crystallographic information. [18][19][20][21][22][23][24][25][26][38][39][40] Coordination number (CN) and bond angle distributions are calculated from the RMC-generated congurations as well, further showing a disordered crystalline structure in detail. Recently, we have reported the 3D atomic structures of Ru nanoparticles in several diameters by means of HEXRD techniques with the aid of RMC simulation.…”

Probing Dopant Locations in Silicon Nanocrystals via High Energy X-ray Diffraction and Reverse Monte Carlo Simulation

“…Both Bragg and diffuse features are collected in the Fourier transform, thus allowing for the structural analysis of materials with limited long-range order and intrinsic structural perturbation, such as those in doped nanocrystal systems . The atomic PDFs can further allow for noncrystallographic nanoparticle model construction to directly observe structural motifs of potential interest. − …”

Combinatorial appraisal of transition states for in situ pair distribution function analysis

“…At the same time, several studies have specifically indicated or addressed the presence of interphase correlations in PDF data [e.g. core-shell architectures (Petkov et al, 2015), nanoscale aggregates in bulk oxides (Proffen & Page, 2004) and surface interactions (Page et al, 2011;Chupas et al, 2011;Zhu et al, 2013)]. However, we are not aware of any systematic investigations that directly explore the utility of the PDF's sensitivity to interphase correlations, or exploit its use in tracking aggregation and growth processes.…”