When determining exact quantitative elemental composition of thin films, the ultimate solution is often an application of ion beam analytical techniques, mostly Rutherford Backscattering Spectrometry (RBS). This technique is usually treated to be insensitive for the density of the layers, however, in some cases it became obvious that surface roughness, voids and precipitates may affect the shape of the spectral signature of a particular chemical element. In order to use RBS efficiently for nanostructured thin films, it is essential to know how the given surface topography (or above parameters) influences the relevance of the measurements. In this paper we present our contributions to the topic: the outline of a new simulation of RBS spectra of rough and nanostructured thin layers; and a brief discussion how the character and parameters of the geometrical structure (shapes, filling factors, etc.) can affect the interpretation of the measured data.
An inherent problem of Pulsed Laser Deposition (PLD) is the undesired particulate formation which is assigned to the deterioration of the solid target surface upon repetitive ablation and instabilities due to fast phase transitions. It could be expected (and has also been claimed by several authors) that ablating liquid targets, i.e. self-reproducing smooth surfaces allows for particulate-free film deposition. In spite of a couple of impressive experiments, it was not yet clarified whether particulate formation was avoided by the use of the liquid target, or only particulate deposition was avoided by choosing appropriate experimental circumstances. In this paper we aimed at answering this question. For this purpose we deposited indium films by ablating solid and liquid indium targets in vacuum (i.e. we deposited the same metal as we ablated). The substrates were held at roomtemperature in order to collect and preserve the droplets formed. Using molten targets, the particulate number density decreased by orders of magnitude as compared to the solid-target case. However, particulate formation could not be totally eliminated, which led us to the conclusion that this technique does not offer an ultimate solution, either. Keywords: thin films, pulsed laser deposition, PLD, particulates
Combined thermally induced etching and deposition of W in a mixture of WF6 and H2 is investigated by local laser-induced patterning of thin tungsten layers on quartz. The process divides into areas of pure etching and deposition, depending on the partial pressures of the gases.
The time evolution of ablation and material transport during ArF excimer laser induced blow off of tungsten films from glass substrates is studied by fast photography using delayed dye laser pulses. The analysis of experimental results combined with heat flow calculations provides evidence that tungsten removal in the solid phase is the dominant mechanism in the 40 - 200 mJ/cm2 fluence domain, while partially inhomogeneous melting is observed between 200 and 800 mJ/cm2. In this fluence range, solid fragments and a halo consisting of molten droplets are observed indicating spatial separation of the two phases. The molten phase advances faster, forming a protective mist in front of the solid piece(s). At yet higher fluences (800 - 1000 mJ/cm2), a well separated solid phase could be recorded under the halo although model calculations suggest full vaporization of the layer. This unexpected phenomenon is explained by the optical shielding effect of the halo.
Laser ablation of layer structures made of optically and thermally dissimilar materials is markedly different from ablation of homogeneous bulk materials. In the case of supported thin films the ablation characteristics are influenced by the variation of the material properties at the interface. This concept is highlighted by comparing experimental and thermal calculation data on pulsed laser ablation of metal, tin oxide and indium-tin oxide films from glass support to those of characterizing bulk ablation.
A simple and inexpensive single-step technique for surface patterning in the micrometers regime is presented. As a result of a systematic study on laser-induced ablation and transfer of tungsten thin films it is shown that deposition of well adhering micrometer sized patterns of 100% coverage preserving the shape and dimensions of the laser processed area can be attained by single pulses of peak power up to 100 mW and 100 microsecond(s) - 1 ms duration from a diode laser pumped YAG laser.