ESCA applied to liquids. II. Valence and core electron spectra of formamide

Exploring surface science and restructuring in reactive atmospheres of colloidally prepared bimetallic CuNi and CuCo nanoparticles on SiO2in situ using ambient pressure X-ray photoelectron spectroscopy

“…The start-point of the XPS data is directly comparable to the TEM data above as they are both recorded on the as prepared sample, at room temperature and after evacuation in a vacuum 15 chamber. Spectra were acquired in vacuum and during the heating steps and introduction of 100 mtorr of H 2 .…”

“…This changes a number of important factors by essentially diminishing the importance of bulk energy terms relative to surface energy terms on the thermodynamic equilibrium structure of the particle. These are likely to include: 15  The greater importance of surface free energy (It is also noteworthy that the surface energy itself will be particle size dependant, 8 as has been shown experimentally for PtRh nanoparticles. 9 )  Surface-adsorbate interactions becoming a significant energetic term when balanced by very little 'bulk.'…”

“…29 The instrument also takes 10 advantage of the tunable incident photon energy of synchrotron-generated X-rays to enable acquisition of both very surface sensitive measurements as well as nearsurface depth profiles of both oxidation state and elemental composition of the samples. Owing to the range of accessible energies with this instrument, spectra were collected using electrons excited from the Cu 3p, Co 3p and Ni 3p levels 15 (rather than the 2p levels usually used in a conventional laboratory XPS when using an Al K source). The photoionisation cross section for these elements with a 380 eV source energy is comparable to that of the 2p levels when using an Al K source.…”

“…14 This technique, described elsewhere, 15 circumvents the usual limitation that emitted photoelectrons have too short a mean free path in ambient gas to be measured. This is achieved by 5 bringing a small, differentially pumped aperture cone very close to the sample surface.…”

“…These three all have similar metallic radii (128, 125 and 125 pm respectively) and much greater enthalpies of oxide formation per metal atom than the precious metals studied previously. 28 Here, CuCo and CuNi nanoparticles of 1:1 atomic composition of the two metals 15 and of similar sizes (~11 nm) were prepared using a new colloidal synthesis. These have then been supported on a planar SiO 2 surface and characterised in oxidising and reducing environments using ambient pressure XPS.…”