D. K. Kuznetsov

Domain patterning by electron beam of MgO doped lithium niobate covered by resist

Periodical domain structuring by focused electron beam irradiation of MgO-doped lithium niobate (MgOCLN) single crystalline plate covered by resist layer was studied both experimentally and by computer simulation. The dependences of domain size on the charge dose and distance between isolated domains were measured. It has been shown that the quality of periodical domain pattern depends on the thickness of resist layer and electron energy. The experimentally obtained periodic domain structures have been divided into four types. The irradiation parameters for the most uniform patterning were obtained experimentally. It was shown by computer simulation that the space charge slightly touching the crystal surface produced the maximum value of electric field at the resist/LN interface thus resulting in the best pattern quality. The obtained knowledge allowed us to optimize the poling process and to make the periodical domain patterns in 1-mm-thick wafers with an area up to 1 × 5 mm2 and a period of 6.89 μm for ...

Polarization reversal induced by heating-cooling cycles in MgO doped lithium niobate crystals

Polarization reversal during heating-cooling cycles was investigated in MgO doped lithium niobate (MgO:LN) crystal using piezoresponse force microscopy. The essential dependence of the domain structure evolution scenario on the maximal temperature in the cycle has been revealed experimentally. It has been shown that the heating of the engineered domain matrix from room temperature to 85 °C leads to light size reduction of the isolated domains at the matrix edges, whereas the heating to 170 °C leads to essential reduction of the domain size. The opposite strong effect of the domain formation and growth during cooling after pulse heating have been revealed in single domain MgO:LN. The simulation of the time dependence of the pyroelectric field during heating-cooling cycle allowed to reveal the temperature hysteresis and to explain all observed effects taking into account the temperature dependence of the bulk conductivity.

Domain switching by electron beam irradiation of Z+-polar surface in Mg-doped lithium niobate

The appearance of the static domains with depth above 200 μm in the bulk of MgO-doped lithium niobate single crystals as a result of focused electron beam irradiation of Z+-polar surface was demonstrated. The created domain patterns were visualized by high-resolution methods including piezoresponse force microscopy, scanning electron microscopy, and confocal Raman microscopy. The main stages of the domain structure formation were revealed and explained in terms of the original model.

Electron Beam Domain Patterning of MgO-Doped Lithium Niobate Crystals Covered by Resist Layer

The electron beam domain patterning of MgO-doped congruent lithium niobate (LN) single crystals covered by electron beam resist layer were studied for various layer thicknesses and electron accelerating voltages. The obtained domain patterns were divided in four types. The increasing of the domain structure quality under presence of the resist layer on irradiated surface was confirmed. This effect was attributed to high concentration of the electron traps in resist, which localized incident electrons in limited volume over LN surface and formed effective electrode. The voltage dependence of space charge localization relative to the LN surface was studied by computer simulation.

Simulation of spatial distribution of electric field after electron beam irradiation of MgO-doped LiNbO3 covered by resist layer

ABSTRACT Spatial distribution of electric field after electron beam irradiation of MgO-doped LiNbO3 with resist layer on irradiated polar surface has been studied by computer simulation. The space distribution of electrons was simulated by Casino software and analyzed by original algorithm to construct analytical function. The distribution of electric field was evaluated by Comsol software. The correlation between the value of polar component of electric field on the resist – MgOLN interface and quality of the domain patterns has been demonstrated. The calculated optimal electron energy for given resist layer thickness allowed to create fine periodical domain structure for nonlinear optical application.

Micro- and Nanodomain Structures Produced by Pulse Laser Heating in Congruent Lithium Tantalate

Formation of the micro- and nanodomain structures under the action of pyroelectric field induced by pulse IR laser heating was studied in congruent lithium tantalate. Two types of the self-organized domain structures were found. The three-dimensional maze-type structure with average period about 100 nm appeared in the central part of the irradiated zone heated above Tc. The self-similar structure of oriented domain rays with nanoscale width formed at the edge of the irradiated zone. The obtained increase of the average distance between the nanodomain rays for irradiation at the elevated temperatures was attributed to the decrease of the pyroelectric field.

Formation of snowflake domains during fast cooling of lithium tantalate crystals

Formation of the original dendrite snowflake-shape domains during fast cooling after heating above phase transition temperature by pulse laser irradiation was revealed in congruent lithium tantalate crystals. The effect was attributed to polarization reversal under the action of spatially nonuniform pyroelectric field. Two stages of the domain shape evolution at the surface were separated: (1) growth of circular domains by sideways motion of the domain walls and (2) backswitching leading to formation of the snowflake domains. The simulated spatial distribution of the pyroelectric field in regular two-dimensional structure was used for an explanation of the obtained results. The backswitching process in the surface layer has been attributed to change of the sign of the pyroelectric field at the domain wall. The snowflake domain shape is caused by the formation of isolated nanodomain fingers and hampering of their merging.

Visualization of nanodomain structures in lithium niobate and lithium tantalate crystals by scanning electron microscopy

ABSTRACT Imaging of ferroelectric domains using scanning electron microscopy is challenging as ferroelectrics are usually highly insulating. However, micro and nanodomain patterns can be directly visualized in secondary electrons using proper parameters. Low accelerating voltage or local charge compensation allows visualizing isolated domains with sizes above 100 nm without any sample preparation. Nanodomain patterns can be visualized with resolution about 3 nm after proper preparation of the sample surface: controlled chemical etching to obtain nanoscale surface relief and subsequent covering of the crystal surface by conductive film. Features of visualization of various nanodomain structures by scanning electron microscopy are considered.

Self-Organized Nanodomain Structures Arising in Lithium Tantalate and Lithium Niobate after Pulse Heating by Infrared Laser

Formation of nanodomain structures during cooling after pulse heating by infrared laser has been studied in congruent lithium tantalate (CLT) and lithium niobate (CLN) single crystals. In situ study of the domain structure evolution allowed to reveal that in CLN the isolated domains appeared at the edges of the irradiated zone and grew to the center. In contrast, the quasi-regular stripe domain structure appeared in CLT near the edge of irradiated zone. The difference has been attributed to lower Curie temperature and larger pyroelectric coefficient of CLT. The self-organized domain structures can be used for periodical poling with submicron periods.

Synthesis of stable silver colloids by laser ablation in water

The stable colloid with silver nanoparticles has been produced by irradiation of metal target in deionized water by pulse 1064 nm laser. The dependences of the nanoparticle size and colloid stability on fluence, ablation time, surface conditions of the target, and thickness of the water layer have been studied. The sizes and shape of nanoparticles have been measured by dynamic light scattering and by scanning electron microscopy. It has been shown that decrease of the water layer thickness above the target surface leads to increase of the colloid stability. The proper number of treatment cycles allowed to prepare the target surface for production of the nanoparticles with average size about 34 nm obtained by statistical analysis of the scanning electron microscope images. Several methods have been used to increase the colloid stability: (1) increase of the laser fluence, (2) decrease of the water layer thickness above the target surface, (3) the treatment of the target surface by laser beam scanning. The subsequent increase of the colloid concentration by partial drying slightly enhanced the nanoparticle size. The optimized synthesis conditions and drying parameters allowed to produce the pure colloid with concentration about 0.5 g/l and stability over a month of almost spherical silver nanoparticles with typical size 45±5 nm.