title: Noble-transition metal nanoparticle breathing in a reactive gas atmosphere.
abstract: In situ high-energy X-ray diffraction coupled to atomic pair distribution function analysis is used to obtain fundamental insight into the effect of the reactive gas environment on the atomic-scale structure of metallic particles less than 10 nm in size. To substantiate our recent discovery we investigate a wide range of noble-transition metal nanoparticles and confirm that they expand and contract radially when treated in oxidizing (O2) and reducing (H2) atmospheres, respectively. The results are confirmed by supplementary XAFS experiments. Using computer simulations guided by the experimental diffraction data we quantify the effect in terms of both relative lattice strain and absolute atomic displacements. In particular, we show that the effect leads to a small percent of extra surface strain corresponding to several tenths of Ångström displacements of the atoms at the outmost layer of the particles. The effect then gradually decays to zero within 4 atomic layers inside the particles. We also show that, reminiscent of a breathing type structural transformation, the effect is reproducible and reversible. We argue that because of its significance and widespread occurrence the effect should be taken into account in nanoparticle research.
authors.affiliation: Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48859, USA. petko1vg@cmich.edu
authors.forename: Valeri
authors.initials: V
authors.lastname: Petkov
authors.forename: Shiyao
authors.initials: S
authors.lastname: Shan
authors.forename: Peter
authors.initials: P
authors.lastname: Chupas
authors.forename: Jun
authors.initials: J
authors.lastname: Yin
authors.forename: Lefu
authors.initials: L
authors.lastname: Yang
authors.forename: Jin
authors.initials: J
authors.lastname: Luo
authors.forename: Chuan-Jian
authors.initials: CJ
authors.lastname: Zhong
mesh_terms: D001272:Atmosphere; D005740:Gases / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010316:Particle Size; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D005740:Gases; D028561:Transition Elements; D006859:Hydrogen; D010100:Oxygen