The growth of thin films is an important field of fundamental and applied research and has many industrial applications. Pulsed laser deposition is on the verge to become an industrial technique for the thin film growth, mainly due to its ability to grow films of complex materials types. A fundamental understanding of the film growth and, in the case of metal oxide films, a control over the oxygen content by tuning the deposition conditions could advance the whole field. Fundamentally, it is important to understand the film growth during pulsed laser deposition (PLD) in greater detail, and the role of different species in the plasma for the growth of thin films. Previous studies have shown that the plume consists of neutral and ionic species (positive and negative) in atomic form but also of molecules, mainly as diatomic species. Our preliminary data show, however, that negative ions may account for up to ~ 40% of the total ion yield. The open question is therefore to study the role of negative ions for film growth, if we consider that positive ions are suggested to be the most important species for PLD? Negative ions have been detected in sputter deposition and the film growth benefits from an increased adatom mobility or larger “oxide formation capability”, whereas resputtering is noted as negative side effect. It is therefore important to investigate whether similar trends should be considered for PLD.
The main goal is to study the role of diatomic species, mainly metal-oxygen species, on the oxygen content of the films and the general role of negative ions for film growth. In a second step we will investigate under which conditions the “best” films in terms of quality are obtained and whether this can be related to specific plume properties. The final step will be an analysis which conditions must be chosen to obtain these specific plume properties. This will allow us to optimize thin film growth by PLD and therefore to obtain possibly better films which can be utilized in applications.
The combination of mass spectrometry/emission spectroscopy will be used to obtain complementary information about the plume composition. Plasma mass spectrometry will be used to detect and quantify the positive/negative ions as well as diatomic species and relate their appearance/amount and kinetic energies to the properties of films deposited for selected conditions. Emission imaging will be used additionally to analyze the distribution of species in the plasma plume and to detect conditions or materials where the distribution is non-homogenous. Plume imaging will be used to probe whether excited state species are beneficial for films growth if they reach the growing film.
For conditions where pronounced differences in the plume are detected thin films will be grown and characterized to evaluate the influence of the plume properties on the film quality, i.e. oxygen content, crystallinity, morphology, and properties.