A reverse Monte Carlo modelling study of amorphous hydrogenated carbon

Abstract

The results of a Reverse Monte Carlo (RMC) modelling of amorphous hydrogenated carbon (a-C:H) are presented. The RMC method has been implemented with the introduction of maximum co-ordination number and "triplet" constraints, whilst fitting both neutron and x-ray diffraction data. The positions of 5000 "atoms" in a box, with full periodicity, are altered until the associated model structure factor, S(Q), and pair distribution function, G(r), agree with the analogous experimental data within the errors. Once the data has been fitted, it is possible to generate model partial pair distribution functions (i.e. those associated with C–C, C–H and H–H), bond angle distributions, co-ordination number distributions, etc. X-ray data is used to provide information on the carbon-carbon network, whilst neutrons are also sensitive to the cross-terms involving hydrogen. The fitting of both types of data simultaneously therefore provides sufficient information to generate a viable "physical" model for the structure of these materials. The effects of increasing the number density inside the box have also been investigated.