Size dependence of core and valence binding energies in Pd nanoparticles: Interplay of quantum confinement and coordination reduction

Abstract

An analysis is given of the electronic structure of Pd nanoparticles synthesized by inert gas evaporation technique. A study of the effect of size on various core and valence electrons in Pd nanoparticles reveals a varied dependence of binding energy of electrons in different electronic levels. The shift in the Pd x-ray photoelectron spectroscopy 4d valence band centroid is more than the core level shift. The results of the present study provide a direct evidence of interplay of quantum confinement ͑a size effect͒ and coordination reduction ͑a surface effect͒.

Charge transfer, lattice distortion, and quantum confinement effects in Pd, Cu, and Pd–Cu nanoparticles; size and alloying induced modifications in binding energy

“…A similar LC has been reported in Pd metal nanoparticles with decrease in size. 4 This observed XRD shift has been attributed to surface bond contraction with coordination number reduction and enhanced surface area at lower particle size. 4 In case of Pd-Cu nanoparticles, ͑111͒ peak is observed to lie between the peaks of Pd and Cu nanoparticles ͑of same size͒, which confirms the Pd-Cu alloy formation.…”

“…4 This observed XRD shift has been attributed to surface bond contraction with coordination number reduction and enhanced surface area at lower particle size. 4 In case of Pd-Cu nanoparticles, ͑111͒ peak is observed to lie between the peaks of Pd and Cu nanoparticles ͑of same size͒, which confirms the Pd-Cu alloy formation. Energy dispersive x-ray analysis ͑EDX͒ studies carried out on Pd-Cu3.5 sample sintered at different temperatures ranging from 300 to 900°C has confirmed that the average atomic composition during compaction is 65:35 ͑Pd:Cu͒ and remains unchanged and thus the change in the XRD peak positions is not due to any composition change.…”

“…In general, the variation in BE of core levels and valence bands in Pd and Pd-thin film and bulk alloys has been explained in terms of initial state and final state effects. 4,5 In spite of its direct relevance in important technologies such as hydrogen sensing and storage, there are only limited reports on variation in core and valence levels in Pd and Pd-alloy nanoparticles. 4,6 The effect of size on valence and core levels in case of Pd, Pd-alloy islands and nanoparticulate thin films grown by vacuum evaporation technique was studied by controlling the thickness and coverage of the polycrystalline islands.…”

“…4,5 In spite of its direct relevance in important technologies such as hydrogen sensing and storage, there are only limited reports on variation in core and valence levels in Pd and Pd-alloy nanoparticles. 4,6 The effect of size on valence and core levels in case of Pd, Pd-alloy islands and nanoparticulate thin films grown by vacuum evaporation technique was studied by controlling the thickness and coverage of the polycrystalline islands. 4,6 In the present letter, metal and alloy nanoparticles have been prepared by gas phase synthesis followed by in-flight sintering to reduce the chemical ligand and polycrystallinity induced effects.…”

“…4,6 The effect of size on valence and core levels in case of Pd, Pd-alloy islands and nanoparticulate thin films grown by vacuum evaporation technique was studied by controlling the thickness and coverage of the polycrystalline islands. 4,6 In the present letter, metal and alloy nanoparticles have been prepared by gas phase synthesis followed by in-flight sintering to reduce the chemical ligand and polycrystallinity induced effects. Structural and electronic properties of Pd-Cu alloy nanoparticles of different sizes have been studied and compared with those of Pd and Cu nanoparticles of similar sizes prepared under identical conditions.…”