Modelling the response of polymeric thin-film devices subject to X-ray irradiation

The Monte Carlo technique has been used to model the response of polyphenylenevinylene-based (PPV) thin-film devices subject to X-ray irradiation. The energy deposition in the PPV film is predominantly due to secondary electrons generated in surrounding materials for the film thicknesses studied here (110nm). Similar calculations on silicon devices indicate that secondary radiation effects arc not as important in this respect. Hence PPV devices can be tailored to optimise the response to a degree not possible for Si devices. The calculations show that the energy deposited in a PPV film relative to that deposited in a Si film of equal thickness can be improved from 1% for a free standing film to 30% for a film surrounded by silica substrate and encapsulant layers when subject to 8keV X-rays.