I. Hevesi

Laser‐induced metal deposition on semiconductors from liquid electrolytes

Maskless deposition of gold and copper from electrolyte solutions onto n‐doped semiconductors (GaAs, Si) is investigated. The metal deposits are found to have lateral dimensions of about 1 μm and are in barrier contact with the semiconductor. The proposed deposition mechanism is governed by the electric fields resulting from the Dember effect, the p‐n junction, and the thermal emf.

Metal oxide layer growth under laser irradiation

Abstract A review of laser-assisted metal oxidation experiments is given. Results are obtained for V targets, and the manner in which temperature affects the Wagner oxidation constants is studied. The effect of an external electric field on the oxidation rate is considered. Morphological peculiarities of grown oxide layers are presented.

On the characteristics of the oxidation of vanadium effected by a continuous beam of laser light

The CW CO- laser induced oxidation of vanadium was investigated. On the surface of vanadium grew a V2O5 layer. During the oxidation of vanadium most of the V2O5 formed was in the liquid state. Times needed for melting of V2O5 were measured for various polarizations of CW CO2 laser light. Some interesting stochastic phenomena were observed during the oxidation of vanadium.

Kinetics of oxide crystal growth in the transition regime between Cabrera-Mott and Wagner thickness regions

Abstract We present a computational model for laser-induced Wagner oxidation in air of metals. We assume that oxidation is diffusion limited, but that the diffusion constant is a function of temperature. We suppose that there are not temperature gradients in the metal, and that the ambient temperature remains constant. Losses include convection and Stefan-Boltzmann terms; from the oxide-air surface at the focal spot these are modelled explicitly, and from the metal-oxide surfaces away from the focal spot they are approximated. We plot the rate of oxide layer growth as a function of laser power and time. The parabolic rate law in the case of a laser-induced oxidation process seems to be valid from the thickness of the oxide layer of about 0.5 μm at long times and high powers, but it is not true for the very beginning of the process for the metals without native oxide layers. At lower powers the validity of the Wagner parabolic law takes place at later times of irradiation and the mechanism of oxidation is governed by the temperature gradient in the oxide film arising during scale growth. Comparison with experiment is made for the case of vanadium/vanadium oxide systems.

Periodic nanostructures observed by STM on vanadium surface preilluminated with a cw Yag-laser

Abstract Metallic vanadium samples were oxidized in air by a cw Nd:YAG laser. The structure of developed V 2 O 5 crystals was investigated by optical and scanning tunneling microscopy (STM). Ripple morphologies with submicron spatial period have been observed. The grating-like structures have been attributed to the interference of surface scattered electromagnetic waves with incident laser light. The dispersion of the surface capillary waves has been taken into account since the oxide has developed partly in a liquid phase.

Laser light stimulated oxidation of vanadium at nonuniform illumination

Abstract An investigation was carried out of the nonuniform laser light (cw-CO2) stimulated oxidation of vanadium plates. It was found that conical crystals, with high developed surfaces grow in the direction of laser light from the metallic plates. The influence of the different diffusion processes was connected with the formation of these circulary-symmetrical crystalline cones.

Self-sustained oscillation processes observed on vanadium surfaces heated by laser light

Different laser-light induced dissipative structures arising under various irradiation conditions during oxidation of vanadium in air are discussed. The observed instabilities are explained in terms of hydrodynamics, since the oxidation process takes place in the liquid phase, taking into account the influence of surface tension forces and gravitational effects on liquids of different densities. The decisive role of positive feedback between thermal and hydrodynamic degrees of freedom in the process of instability development is emphasized.

Crystal formation under the influence of laser light

Abstract We study the dynamics of heating and crystal formation on the surface of metallic targets under continuous CO 2 laser light. Some examples of non-equilibrium Cu 2 O crystal formation at great speed, the appearance of V 2 O 5 dendrite crystals with highly developed surfaces and the reduction of Si from its oxide SiO 2 under the influence of laser light are discussed.

Time-resolved spectral investigations of laser light induced microplasma

Abstract The dynamical and spectral properties of an optical breakdown microplasma created by pulses of different lasers on surfaces of insulators (KCI), metals (Cu) and semiconductors (V 2 O 5 ), have been investigated. Experiments were carried out in air and vacuum using different wavelengths (λ = 0.694μm, type OGM-20,λ = 1.06μm with a home-made laser based on neodymium glass crystal, and λ = 10.6μm, similarly home-made) and pulse durations (Q-switched and free-running regimes). To follow the integral, dynamical and spectral characteristics of the luminous spot of microplasma we have used fast cameras (SFR-2M, IMACON-HADLAND), a high speed spectral camera (AGAT-2) and a spectrograph (STE-1). It has been shown that the microplasma consists of two parts: fast front (peak) with τ≈100 ns and slow front (tail) with τ≈1μs durations. The detonation front speed is of the order of ≈10 5 cm s −1 and follows the temporal dependence of to t 0.4 . It depends on the composition of the surrounding gas and its pressure and could be connected with quick evaporation of the material investigated (peak) and optical breakdown of the ambient gaseous atmosphere (tail). From the delay in appearance of different characteristic spectral lines of the target material and its gaseous surrounding we have shown that the evolution of the microplasma involves evaporation and ionization of the atoms of the parent material followed by optical breakdown due to the incident and absorbed laser light, together with microplasma expansion.

Mechanical properties of V2O5 polycrystals grown by laser light irradiation

Abstract Microhardness, stiffness and elasticity parameters of V2O5 polycrystals grown by irradiation with continuous wave IR laser light (IR ND:(Y-Al-garnet)) are discussed. Structural and metallographic analysis showed that the mechanical parameters strongly depend on the lateral and vertical directions with respect to the area irradiated. These dependences were attributed to the structural changes in polycrystals grow as a result of standing heat waves formed due to irradiation by laser light.