L. Égerházi

High repetition rate PLD grown titanium oxide thin films

In this paper, we present a comprehensive study on the potentials and limitations of high repetition rate pulsed laser deposition (PLD), using a diode-pumped solid state (DPSS) Nd : YAG laser, operated at 532 nm. Titanium oxide thin films were deposited at 5 Pa of oxygen on silicon substrates with a different number of pulses, typically several tens of millions, and at pulse repetition rates (PRR) between 10 and 30 kHz, while keeping the pulse energy at a constant value. The lateral variation of thickness, void content and optical parameters along the radii of the circularly symmetric films were measured by spectroscopic ellipsometry and atomic force microscopy images were taken to reveal the surface topography of the films. In contrast to the conventional, i.e. low repetition rate PLD, the optical and topographical properties of the films were found to be uniform within an area of approximately 50 mm in diameter, while a decrease in the roughness of the films was evidenced towards the edges. The effects of an inherent property of DPSS lasers, namely the interrelated nature of PRR and pulse duration, were investigated. By means of a simple thermal model, it was shown that careful consideration of the characteristics of the laser is required to explain the experimentally revealed trends in the PRR dependence of the film growth rate.

Thin film homogenization by inverse pulsed laser deposition

Recently we proposed a novel PLD arrangement, termed inverse pulsed laser deposition (IPLD). Being able to produce thin films of better surface morphology without any complex instrumentation, this method can represent an alternative to the traditional PLD technique while preserving versatility. Two configurations of this new target-substrate arrangement, namely static and co-rotating IPLD were developed. In the static IPLD configuration, the substrate is stationary with respect to the ablated spot; while in the co-rotating IPLD configuration the substrate is fixed to the target surface and rotates simultaneously with the target. Co-rotating IPLD proved to be capable of homogenizing the film thickness. Here we report a model calculation supported by experimental results to describe the radial growth rate variation of corotating IPLD films. To characterize the homogeneity of CNx, TiOx, and Ti co-rotating IPLD films, a thickness inhomogeneity index (TII) was introduced, which allows the comparison of thickness homogeneity between films of different lateral dimensions. The presented semi-analytical, semi-numerical model derives the radial variation of the growth rate of co-rotating IPLD films from the lateral growth rate distributions measured along the symmetry axes of the static IPLD films. The laterally averaged growth rate (LAGR) was used to describe how the ambient pressure affects thin film growth in the 0.5-50 Pa domain. As an example, the absolute error between the measured and calculated radial growth rate variation of CNx layers grown by co-rotating IPLD at 5 Pa, was less than 3%, while the LAGR was predicted with 20% accuracy.

Thermal diffusion control of femtosecond laser generated modifications of nanoscale pulsed-laser deposited diamond-like carbon films

Single 60-femtosecond laser pulse modification threshold fluences (φth) of nanometer-thin diamond-like carbon (DLC) films generated by Inverse Pulse Laser Deposition (IPLD) [1] show strong dependencies on the film thickness l (Fig. 1, left). Experiments were performed in an ultrahigh precision microscope setup with a high numerical aperture objective (NA = 0.7).