Evgenii N. Lubnin

Dimensional effect of work function of electrons

For ultrathin carbon films with controllable graphite nanophase contents, direct experimental evidence is found that the work function of electrons decreases with reduction of characteristic dimensions (thickness). The observed effect is associated with the splitting of the electron states in ultrathin films, as in the 2D quantum well.

Thermal and optical properties of semitransparent ceramics : laser induced high temperature modifications

The laser combined express technique has been applied to high temperature measurements optical and thermal properties of different ceramics. It was found that the ambient atmosphere noticeably affects the physical properties of the heated ceramics that marks a noticeable structural and chemical modification of the material.

Laser processing of ceramics and metals by high-intensity picosecond and nanosecond laser pulses in UV, visible, and IR range of spectrum

Experimental investigations of ablation processes of AlN, Si3N4(MgO), Si3N4(YAI) ceramics, steels and aluminum have been conducted using first, second and fourth harmonics of picosecond and nanosecond Nd:YAP laser (1078 nm basic wavelength). The measurements have been carried out in a wide range of incident power density values: 1010 - 1014 W/cm2. The passive-active mode-locked/Q-switched laser with a high quality spatial and temporal distribution of output radiation operated at repetition rates of 1 - 10 Hz was used. The ablation rate dependencies obtained for multipulse irradiation regimes are presented and analyzed. The physical mechanisms responsible for ablation processes in pico- and nanosecond range of laser pulse duration are discussed. Special attention is paid to the role of plasma formation and modification of chemical composition of ceramic surface layers during the laser-matter interaction process. The scanning electron microscope pictures of ablated holes and cuts produced at different irradiation conditions are demonstrated. It is shown that at the relevant irradiation conditions the high quality regular microstructures consisted of holes, cuts, etc., with a typical size varied from tens to several microns could be produced using high peak power ultra short laser pulses.

Simultaneous measurements of optical and thermal properties of solids at laser heating up to 2500 degrees C

Detailed studies of optical and thermal properties of solids are necessary for fundamental science as well as for optimization of technologies of laser processing of materials. The essential temperature dependences of the physical parameters of solids strongly influence the laser-matter interaction processes. The advantage of our experimental technique is the possibility to perform simultaneous measurements of reflectivity, absorptivity, transmissivity, heat capacity, heat conductivity, temperature conductivity of solids in a broad range of investigated temperatures (up to 2500°C) with high temporal resolution (0.5 ms). Besides, the developed method allows to estimate values of heat of phase transitions and to reveal the influence of ambient atmosphere on the physical properties of samples undergoing noticeable structural and chemical modifications during laser heating. A possibility to record both the optical and thermal properties and temperature dependences of metals, ceramics, CVD (chemical vapor deposition) diamond films within a single experiment (for a few seconds) allows to apply this technique for studying and selecting novel materials with unknown properties.

Laser measurements of optical and thermal properties of CVD diamond at high temperatures

The laser express technique has been applied to high temperature measurements of CVD diamond reflectivity R and absorption coefficient (alpha) for radiation with 1.06 mm wavelength as well as heat capacity. It was found that at T > 1000 degrees C and heating cycles of a few seconds the sample surface layer with thickness of 100 nm becomes graphitized that leads to dramatic growth of (alpha) from initial value of about 10 cm-1. The obtained results on heat capacity at T >= 800 degrees C are well matched with the known data at lower temperatures.