X-ray Photoelectron Spectroscopy of Isolated Nanoparticles

Abstract

X-ray photoelectron spectroscopy (XPS) is a very efficient and still progressing surface analysis technique. However, when applied to nano-objects, this technique faces drawbacks due to interactions with the substrate and sample charging effects. We present a new experimental approach to XPS based on coupling soft X-ray synchrotron radiation with an in-vacuum beam of free nanoparticles, focused by an aerodynamic lens system. The structure of the Si/SiO2 interface was probed without any substrate interaction or charging effects for silicon nanocrystals previously oxidized in ambient air. Complete characterization of the surface was obtained. The Si 2p core level spectrum reveals a nonabrupt interface.

One-step femtosecond laser ablation synthesis of sub-3 nm gold nanoparticles stabilized by silica

“…The control silica NPs synthesized in water contain the same peaks in the Si2p spectrum, confirming that these species are formed from laser ablation of the silicon wafer in liquid, regardless of the presence of metal salt. A small peak (2%) corresponding to Si 1+ [69][70][71] was also present in the control silica NPs; the other peaks are shifted to slightly higher binding energies compared to the silica-Au NPs. This could also be due to the general oxide layers being thicker [69,74], or due to the absence of Au NPs [68].…”

“…The Si2p spectrum for the silica-Au NPs in Figure 5b peak at 98.0 eV, which has not been previously reported. Due to its proximity to the neutral Si 0 species, the peak at 98.0 eV is most likely in the form of Si 1− , since the Si 1+ is shifted up by ∼1 eV from the Si 0 peak [69][70][71]. The presence of this putative Si 1− species is surprising due to the electropositive nature of Si, but the accessibility of metastable phases in the nonequilibrium environment formed at the plasma-water interface [3,14,47,72] could enable the formation of such exotic species.…”

Complete Bromide Surface Segregation in MixedNaCl/NaBrAerosols Grown from Droplets

“…The experiments were performed at the SOLEIL synchrotron radiation facility (Saint-Aubin, France) at the PLEIADES beam line [31], which is dedicated to soft x-ray spectroscopy studies of dilute samples ranging in size from atoms [32] and molecules [33][34][35][36] to clusters [37] and nanoparticles [24,38,39]. The polarization vector of the radiation was chosen to be parallel to the spectrometer axis.…”

Soft X-ray spectroscopy of nanoparticles by velocity map imaging

“…For example, an aerodynamic lens coupled to a hemispherical analyzer was used to perform valence band photoelectron spectroscopy of aqueous aerosols of biomolecules, which observed changes in the charge-transfer mechanism at different pH conditions of a solvent. 18,19 A similar setup has been used at synchrotron SOLEIL to investigate solid silicon 20 and flame generated nanoparticles (soot) 21 by means of XPS and NEXAFS. The spectroscopies performed at the carbon 1s edge compared the oxidation states of the surface (detected by XPS) and bulk (shown by NEXAFS) of soot nanoparticles.…”