N. V. Belugina

Multimode Atomic Force Microscopy of Triglycine Sulfate Crystal Domain Structure

The same crystal surface regions in a triglycine sulfate (TGS) ferroelectric crystal were probed by varied SPM methods, namely contact and intermitted-contact AFM, piezoresponce force microscopy (PFM), scanning Kelvin microscopy (SKM) and electrostatic force microscopy (EFM). Criteria for identification of real (dynamic) domains and morphologically similar domain “memory” regions are proposed. Inaccuracy in identification may result in further errors in estimating the parameters of the domain structure. The images of ferroelectric domains in the spreading-resistance mode that directly indicate a contribution from an enhanced conductivity in the vicinity of the domain walls have been obtained for the first time.

About the nature of two-dimensional formations at the polar surface of cleaved triglycine sulfate crystals

Fine structure of the (010) polar surface of triglycine sulfate crystal has been investigated by atomic force microscopy in contact and resonant (tapping) modes at room temperature and after heating. It has been shown that the round islands and holes of nanometer lateral size and height (depth) of ½ b (0.63 nm) occur only at atomic-smooth regions of the surface of the crystal cleaved in ferroelectric phase; and they are characteristic steady details of its microrelief. They conserve their geometrical sizes at heating above the Curie temperature, existing irrespective of domain structure and direction of the polarization vector, but they can change under influence of mechanical stress. It has been revealed that repeated scanning of mono domain regions of the surface in contact mode and shock influence in resonant mode result in occurrence of characteristic round islands and holes of the nanometer lateral size and height (depth) about ½ b.

Features in atomic force microscopy studies of dielectric surfaces

To improve the accuracy of AFM measurements in air and the reproducibility of results, a clean room-based metrological facility has been designed and built. The main function of the facility is to control temperature and humidity in an operation zone in various combinations and to maintain them with high accuracy. Measurements under controlled conditions are particularly important for dielectric materials. It has been shown that special procedures allow one to avoid disturbances caused by static charges on the surface under study, i.e., to remove the already accumulated charge and prevent its appearance during experiments. The use of the proposed procedures makes it possible to adequately study the features of the dielectric surface relief at micro-and nanoscale levels.

AFM study of the microwave effect on hydrogen-containing ferroelectric triglycine sulfate

Nanoscale supramolecular structures and their transformations under exposure to microwaves in hydrogen-containing ferroelectric, i.e., triglycine sulfate (TGS), were studied by atomic-force microscopy. It was shown that prolonged (2–5 h) irradiation of TGS crystal at a frequency of 40 GHz results in changes in the cleavage surface, which can be interpreted as radiation-induced “annealing” of the crystal with simultaneous generation of new defects. An exposure mechanism based on the effects of commensurability of the time of flight of quasifree dipole particles (protons) with the high-frequency field’s period is proposed.

Application of the Fourier transforms for analysis of the domain structure images of uniaxial ferroelectric

The formation of ferroelectric domains in triglycine sulfate crystal in the para–ferroelectric phase transition has been investigated in situ by piezoresponse force microscopy. The domain structure has been analyzed using the images of Fourier transforms of the scanned (010) surface of natural cleavage. The formation of a quasi-periodic one-dimensional structure of 180° domains with dominant components of one sign below TC near the transition point is revealed and crystallographic reference to the laboratory coordinate system is performed.

Temperature dynamics of triglycine sulfate domain structure according to atomic force microscopy and dielectric spectroscopy data

A hydrogen-containing ferroelectric triglycine sulfate (TGS) was comprehensively studied with an atomic force microscopy (AFM) and dielectric spectroscopy. The domain structure dynamics was in situ investigated with piezoresponse force microscopy (PFM) during heating and cooling the TGS crystal near phase transition. Relaxation dependencies of domain boundaries general perimeter and domain dimensions were obtained. TGS dielectric spectra measured at the frequency range from 10 to 1011 Hz were analyzed on basis of significant contribution of conductivity into the dielectric response of ferroelectrics and a good agreement with the experimental data was received. It allows us to obtain more information about temperature dynamics of the domain structure.

Formation of a regular domain structure in TGS–TGS + Cr crystals with a profile impurity distribution

A complex investigation of TGS–TGS + Cr crystals with a profile impurity distribution of chromium ions Cr3+ has been carried out at the macrolevel (measurement of dielectric properties by the method of nematic liquid crystals) and microlevel (domain structure according to atomic force microscopy data). It is established that periodic doped layers are formed only in individual growth pyramids in the regions where the polarization vector has a nonzero component along the normal to the growth faces rather than throughout the entire crystal volume. The domain configuration at the boundary of growth layers with different impurity compositions has been studied by piezoelectric force microscopy. The static unipolarity of layers with and without chromium impurity is approximately identical, whereas the domain-wall density in doped regions is higher than that in undoped ones by a factor of about 7.

Domain structure of triglycine sulfate family crystals according to the data of piezoresponse force microscopy and their macroscopic dielectric properties

The domain structure of triglycine sulfate (TGS) crystals, specifically nominally pure crystals and those with impurities (LADTGS+ADP, DTSG, and TGS:Cr), is studied by piezoresponse force microscopy (PFM). The measured macroscopic dielectric characteristics are compared with microscopic data on the domain structure of these crystals. The values of the spontaneous polarization, bias voltage, and dielectric permeability as a function of temperature ɛ(T) are shown to be in agreement with the PFM data. The anomalous behavior of the dependence ɛ(T) was observed for LADTGS+ADP crystals.

Clean boxes with artificial climate for atomic force microscopy: New possibilities for diagnostics of nanodimensional objects

A clean box with an artificial climate is developed and designed to increase the accuracy of measurements by atomic force microscopy in the air and to improve the reproducibility of the results of diagnostics of the surface. The main functions of the box are the provision and maintenance of the temperature and humidity in the working zone with a high degree of accuracy and in various combinations. The main technical characteristics of the box are presented. The main advantages of operation under the conditions of an artificial climate are analyzed. It is shown that the special procedures give the possibility to eliminate the distorting effect of the static electricity on the surface under investigation and, specifically, to remove the already accumulated charge and prevent its appearance in the course of the experiment. The use of the suggested procedures allows one to correctly describe the specific features of the surface topography of dielectrics at the microscopic and nanoscopic levels.

Dielectric losses in the triglycine sulfate crystal under heating and cooling

Temperature dynamics of the dielectric spectra and domain structure in the triglycine sulfate (TGS) hydrogen-containing ferroelectric under heating and cooling has been studied using the dielectric spectroscopy and atomic-force microscopy methods. The dielectric spectra are analyzed by the temperature-frequency dependences of the losses ε″ and by the temperature behavior of the maximum losses ε″max in the dispersion region at frequencies ranging from 102 to 106 Hz. A dynamic conductivity model is proposed for calculating temperature dependences of losses ε″max. The domain structure dynamics during the heating and cooling of the TGS crystal near the phase transition is studied using the in situ piezoresponse force microscopy. It is experimentally and theoretically shown that the relaxation dispersion is governed by the binding of strongly correlated dipoles with the main lattice that serves as a thermostat.