KEYWORDS: Nanoparticles, Monte Carlo methods, Signal attenuation, X-rays, Modeling, Electrons, Photoemission spectroscopy, Chemical analysis, Particles, Oxidation
Shell-core nanofibres are structured nanoparticles that are increasingly of technological importance. Angle-resolved X-ray
photoelectron spectroscopy (ARXPS) is potentially an excellent technique to characterise surfaces formed by this
type of nanoparticles. We present both analytical and Monte Carlo models predicting the ARXPS intensity ratios of a
monolayer of shell-core nanofibres on a flat substrate as a function of the photoelectron emission angle, the core size and
the shell thickness. In the analytical model, the XPS intensities are calculated by integrating over one whole nanofibre
following the photoelectron trajectories towards the detector using a generalized XPS measurement expression. The
effects of nanoparticle structure, the influence from neighboring nanoparticles and the dependence of attenuation length
on material composition are all accounted for. The results are distributions of XPS intensity from shell and core at
various emission angles from which the ARXPS intensity ratios are obtained. In parallel we develop a Monte Carlo
simulation code to cross validate it in tractable special cases and to extend its potential application to a wider range of
geometry. A few artificial shell-core structured nanofibres of different geometrical and material parameters are used to
test the two models. Agreement between them is excellent. Their potential applications are illustrated and discussed
using scenarios corresponding to measuring oxidized, passivated, coated or contaminated nanoparticles and to
monitoring a process of oxidation or passivation.
Many of the schemes utilizing photon states under investigation for Quantum Information Processing (QIP) technology involve active and passive optical components. In order to be able to establish fidelity levels for these schemes, the performance of these optical components and their coupling efficiencies require careful and accurate characterization. Correlated photons, the basis of entangled photon states, offer a direct means of measuring detector quantum efficiency and source radiance in the photon counting regime. Detector and source calibration by correlated photon techniques therefore address some of the key factors critical to QIP technology and the developing techniques of correlated/entangled photon metrology. Work is being undertaken at NPL to establish the accuracy limitations of the correlated photon technique for detector and source calibration. This paper will report on investigations concerning the characterization of silicon avalanche photodiode detectors using the correlated photon technique.
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