Zs. Geretovszky

Excimer laser processing of indium‐tin‐oxide films: An optical investigation

dc sputtered indium‐tin‐oxide films have been excimer laser irradiated at subablation threshold fluences (<510 mJ/cm2). Optical characterization of irradiated products has been performed aiming at resolving the finer structure appearing in the IR–visible absorption spectra, as a function of laser fluence, and assigning such features to specific electronic defects which are produced upon irradiation. Four individual Gaussian‐like contributions to absorption spectra are identified at 0.7, 1.0, 1.6, and 2.6 eV, the intensity of which is observed to vary with fluence. Being absent in the original films and emerging in optical spectra at fluences exceeding 300 mJ/cm2, the 2.6 eV contribution is most characteristic to excimer laser processing and is responsible for the darkening of the film. Thermal model calculations reveal that such defects are produced only upon melting and fast resolidification of the film. The evolution of the chemistry actually taking place in the film upon irradiation is followed by x‐ra...

Can laser deposition from the liquid phase be made competitive

Conclusions from a critical analysis of the existing literature data on laser induced liquid phase processes are compared with experimental results on the effect of scanning speed and precursor concentration on the deposition rate and pattern morphology in laser direct writing of MoO3 stripes from their aqueous solutions. The peculiarities and general trends of laser deposition from solutions are presented in terms of material transport processes. The competitiveness of this technique in specific applications is judged in comparison with LCVD and deposition from surface layers.

Structure and composition of carbon-nitride films grown by sub-ps PLD

CNx (0.01<x<0.20) films have been deposited by ablating a graphite target in N2 atmosphere with a hybrid dye/excimer laser system delivering pulses of 500 fs duration at 248 nm. Changes in surface composition and morphology of the as grown films, as a function of N2 pressure (between 0.3 and 60 Pa), laser pulse energy (maximum 10 mJ), and spot area are reported, by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. In the pressure domain investigated, the nitrogen content increases as a power function. While both pulse energy and spot area influence the chemical composition of the films, the same fluence achieved by using different spot sizes results in films of different N content. Deposition of micrometer sized particulates is apparently suppressed, while sub-micron features of typically circular shape are present over the smooth film surface.

A time-resolved imaging and electrical study on a high current atmospheric pressure spark discharge

We present a time-resolved imaging and electrical study of an atmospheric pressure spark discharge. The conditions of the present study are those used for nanoparticle generation in spark discharge generator setups. The oscillatory bipolar spark discharge was generated between two identical Cu electrodes in different configurations (cylindrical flat-end or tipped-end geometries, electrode gap from 0.5 to 4 mm), in a controlled co-axial N2 flow, and was supplied by a high voltage capacitor. Imaging data with nanosecond time resolution were collected using an intensified CCD camera. This data were used to study the time evolution of plasma morphology, total light emission intensity, and the rate of plasma expansion. High voltage and high current probes were employed to collect electrical data about the discharge. The electrical data recorded allowed, among others, the calculation of the equivalent resistance and inductance of the circuit, estimations for the energy dissipated in the spark gap. By combining imaging and electrical data, observations could be made about the correlation of the evolution of total emitted light and the dissipated power. It was also observed that the distribution of light emission of the plasma in the spark gap is uneven, as it exhibits a “hot spot” with an oscillating position in the axial direction, in correlation with the high voltage waveform. The initial expansion rate of the cylindrical plasma front was found to be supersonic; thus, the discharge releases a strong shockwave. Finally, the results on equivalent resistance and channel expansion are comparable to those of unipolar arcs. This shows the spark discharge has a similar behavior to the arc regime during the conductive phase and until the current oscillations stop.

Morphological study of PLD grown carbon films

Carbon films have been deposited by ArF excimer laser ablation of a graphite target in argon ambient of pressures between 10 � 4 and 200 Pa. Besides carbon, ex situ RBS and ERDA measurements reveal the presence of argon, hydrogen and oxygen in the films. Below 0.5 Pa the apparent growth rate, defined as the measured thickness per number of pulses, is almost constant at

Low-fluence excimer laser irradiation-induced defect formation in indium–tin oxide films

Abstract DC sputtered indium-tin oxide (ITO) films of 500 nm thickness are irradiated with single pulses of fluences between 190 and 510 mJ/cm 2 from a KrF excimer laser. The irradiation induced changes in optical spectra are consistently described through the behaviour of four (Gaussian-like) absorption bands at 0.7, 1.0, 1.6 and 2.6 eV. Being absent in the original films and emerging at fluences exceeding 300 mJ/cm 2 , the 2.6 eV contribution is most characteristic to excimer laser processing. X-ray photoelectron spectroscopic analysis suggests that the irradiation-induced changes should be associated with oxygen displacement within the atomic network rather than surface reduction via oxygen removal. Thermal model calculations reveal that the principal effect of single pulse processing in this fluence domain is deep melting of the films. Defects created during molten phase resolidification are assumed to be responsible for the irradiation-induced changes in the short range chemical structure of the films.

Quest for high quality local electroless laser deposition from the liquid phase: decomposition of ammonium molybdate

Abstract A systematic study on concentration (0.001–0.1M), laser power (up to 200 mW) and scanning speed (from 10 to 200 μm/s) dependence of pyrolytic laser decomposition of ammonium molybdate is reported. It is shown that there exists an optimal concentration range in which best quality deposition is observed and all the disadvantageous features typical for slow writing can significantly be improved by the increase of scanning speed. At speeds exceeding 0.1 mm/s well defined lines without macrostructure and of excellent morphology can be written and all the important characteristics of the lines remain virtually unchanged in a wide range of processing parameters.

Laser direct writing of tin oxide patterns

Abstract Tin oxide pattern generation by laser deposition from SnCl 4 · 5H 2 O in isopropanol is reported. Smooth, even stripes of thicknesses ranging from 20 to 120 nm with sharp, well defined edges and cross-section are deposited by scanning Ar + laser beam (λ = 514.5 nm) focused onto the substrate—solution interface with a constant speed of 1 mm s −1 . The linewidth linearly increases from 26 to 42 μm with increasing the power from 40 to 120 mW. The reproducibility of pattern generation is extremely good as revealed by SEM-EDXI and μRBS. The minimum DC resistivity of 1.7×10 −2 Ωcm, measured without any process optimization, favourably compares with those reported for films prepared by other techniques. The chemical composition of the film material is SnO x with 1.1 x

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.

Test particle Monte Carlo study of backward deposition during evaporation into a background gas

A study on backward flow of laser ablated material during low-intensity evaporation into a background gas using the test particle Monte Carlo method is reported. Thickness profiles of the material deposited in the target plane are obtained for different evaporated particle masses and background gas pressures. The crossing of thickness profiles experimentally observed for different pressures is confirmed. Optimum background gas pressures, which yield the largest backward deposition rate, are determined for different mass ratios of the evaporated and background gas species.