Pavel Zelenovskiy

Strong piezoelectricity in single-layer graphene deposited on SiO2 grating substrates

Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V−1, that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphenes carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

Micro- and nanodomain imaging in uniaxial ferroelectrics: Joint application of optical, confocal Raman, and piezoelectric force microscopy

The application of the most effective methods of the domain visualization in model uniaxial ferroelectrics of lithium niobate (LN) and lithium tantalate (LT) family, and relaxor strontium-barium niobate (SBN) have been reviewed in this paper. We have demonstrated the synergetic effect of joint usage of optical, confocal Raman, and piezoelectric force microscopies which provide extracting of the unique information about formation of the micro- and nanodomain structures. The methods have been applied for investigation of various types of domain structures with increasing complexity: (1) periodical domain structure in LN and LT, (2) nanodomain structures in LN, LT, and SBN, (3) nanodomain structures in LN with modified surface layer, (4) dendrite domain structure in LN. The self-assembled appearance of quasi-regular nanodomain structures in highly non-equilibrium switching conditions has been considered.

Nanodomain structures formation during polarization reversal in uniform electric field in strontium barium niobate single crystals

We have studied the ferroelectric nanodomain formation in single crystals of strontium barium niobate Sr0.61Ba0.39Nb2O6 using piezoelectric force microscopy and Raman confocal microscopy. The nanodomain structures have been created by application of the uniform electric field at room temperature. Four variants of nanodomain structure formation have been revealed: (1) discrete switching, (2) incomplete domain merging, (3) spontaneous backswitching, and (4) enlarging of nanodomain ensembles. Kinetics of the observed micro- and nanodomain structures has been explained on the basis of approach developed for lithium niobate and lithium tantalate crystals.

Domain Kinetics in Lithium Niobate Single Crystals with Photoresist Dielectric Layer

The influence of the artificial surface layer (photoresist film) on the domain kinetics was studied in congruent lithium niobate single crystals. The switching current data was fitted by modified Kolmogorov-Avrami formula. The qualitative change of the domain structure evolution for photoresist film thickness above 2 μm was revealed by in situ optical visualization and analysis of the switching current data. The linear dependence of the threshold field increase on the film thickness was found. The quasi-regular nanodomain structures on Z+ polar surface were studied by scanning probe and Raman confocal microscopy and the domain evolution scenario was revealed.

Morphology and Piezoelectric Properties of Diphenylalanine Microcrystals Grown from Methanol-Water Solution

Morphology and piezoelectric properties of diphenylalanine microcrystals grown by drying the droplet of methanol and water mixture in various proportions have been studied. We have found that the increase of water concentration leads to the significant change of the microcrystal morphology from flat dendrite structures to elongated microcrystals: microtubes and microrods. The effect was attributed to increasing of the drying time. The morphology of the dendrite structures was revealed and empirical dependence of the dendrite thickness on diameter was found. Finally, the piezoelectric activity of the microtubes was demonstrated using the piezoresponse force microscopy.

Micro-Raman Visualization of Domain Structure in Strontium Barium Niobate Single Crystals

Raman confocal microscopy was applied for visualization of the ferroelectric domain structure in strontium barium niobate single crystals. The studied domain structure was produced by electric field poling of the single domain state at room temperature. Essential frequency shift of the certain Raman band in the vicinity of domain walls was revealed. Recording of this parameter during two-dimensional scanning was used for reconstruction of the domain images both at the surface and in the bulk.

Formation of self-organized domain structures with charged domain walls in lithium niobate with surface layer modified by proton exchange

We have studied the self-organized dendrite domain structures appeared as a result of polarization reversal in the uniform field in lithium niobate single crystals with the artificial surface layer created by proton exchange. We have revealed the self-organized sub-micron scale dendrite domain patterns consisting of domain stripes oriented along the X crystallographic directions separated by arrays of dashed residual domains at the surface by scanning probe microscopy. Raman confocal microscopy allowed visualizing the quasi-regular dendrite domain structures with similar geometry in the vicinity of both polar surfaces. The depth of the structure was about 20 μm for Z+ polar surface and 70 μm for Z− one. According to the proposed mechanism, the dendrite structure formation at the surface was related to the ineffective screening of the residual depolarization field. The computer simulation of the structure formation based on the cellular automata model with probabilistic switching rule proved the eligibilit...

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.

Piezoelectric and ferroelectric properties of organic single crystals and films derived from chiral 2-methoxy and 2-amino acids

ABSTRACT Local piezoelectric and ferroelectric properties as well as morphology of single crystals and films of two novel chiral organic compounds derived from chiral 2-methoxy and 2-amino acids have been investigated. The crystals demonstrated piezoelectric response exceeding that of lithium niobate. The piezoelectric response was registered also in compound films. Piezoelectric properties and domain structure of single crystals and films have been studied by piezoresponse force microscopy.

Graphite-diamond relations in mantle rocks: Evidence from an eclogitic xenolith from the Udachnaya kimberlite (Siberian Craton)

Abstract Relations of graphite and diamond have been studied in a garnet-kyanite-clinopyroxene+sulfide+coesite/quartz+diamond+graphite eclogite xenolith from the Udachnaya-East kimberlite pipe in the Yakutian diamond province. Euhedral crystals of diamond and graphite occur in the intra- and intergranular space. The equilibrium conditions of diamond formation reconstructed by geothermobarometry for the Grt-Cpx-Ky-Coe mineral assemblage are 1020 ± 40 °C and 4.7 GPa. Raman imaging of graphite enclosed in diamond shows high ordering and a 9 cm–1 shift of the ~1580 cm–1 band. This Raman shift of graphite, as well as a 5 cm–1 shift of the 1332 cm–1 band of diamond, indicate large residual stress in graphite and in diamond around the inclusion, respectively. According to FTIR spectroscopy, nitrogen in diamond is highly aggregated and exists mainly as the A centers, while no other phases occur near graphite inclusions. Therefore, diamond in the analyzed eclogite sample must be quite old: it likely had crystallized long (~1 Byr) before it became entrained with kimberlite melt. New data show that graphite can stay in the upper mantle for billions of years without converting to diamond. Crystallization of various carbon polymorphs, both in laboratory and natural systems, remains poorly constrained. Graphite present in mantle and UHP rocks may be a metastable phase crystallized in the diamond stability field. This fact should be taken into consideration when deducing petrological constrains and distinguishing diamond and graphite subfacies in upper mantle.