Piezoelectric Characteristics of LiNbO3 Thin-film Heterostructures via Piezoresponse Force Microscopy

Electro-optic LiNbO3 thin films were deposited on Si(100) and Si(111) substrates using a radio-frequency magnetron sputtering process. The piezoelectric properties of the LiNbO3 films were investigated using the scanning probe microscopy in the piezoresponse mode. The obtained results show the high degree of grains orientation in polycrystalline structure. The piezoelectric modulus (dzz) was estimated to be 16 pm/V (for LiNbO3 / Si(100)) and 22 pm/V (for LiNbO3 / Si(111)) and the polarization about of 0.37 C·m – 2. These values are larger than those reported previously for LiNbO3 films. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3366

Formation of the Electric Field Distribution in Thin Electro-Optic Layers for Precision Correction their Optical Characteristics

A method of making given field distribution within thin electro-optical layers by using narrow band electrodes placed at the same electric potential. A formula for electric field intensity produced by a single band electrode is obtained. Electric field modeling for different band electrode configurations is undertaken. It was shown, by applying piezoresponse force microscopy, that in case of highly inhomogeneous field the polarization of lithium niobate electro-optical film persisted only in the area above the band electrode. Lithium niobate, electro-optical structures, piezoresponse force microscopy, Computer simulation

Recent Developments of NEMO: Detection of Solar Eruptions Characteristics

The recent developments in space instrumentation for solar observations and telemetry have caused the necessity of advanced pattern recognition tools for the different classes of solar events. The Extreme ultraviolet Imaging Telescope (EIT) of solar corona on-board SOHO spacecraft has uncovered a new class of eruptive events which are often identified as signatures of Coronal Mass Ejection (CME) initiations on solar disk. It is evident that a crucial task is the development of an automatic detection tool of CMEs precursors. The Novel EIT wave Machine Observing (NEMO) (http://sidc.be/nemo) code is an operational tool that detects automatically solar eruptions using EIT image sequences. NEMO applies techniques based on the general statistical properties of the underlying physical mechanisms of eruptive events on the solar disc. In this work, the most recent updates of NEMO code - that have resulted to the increase of the recognition efficiency of solar eruptions linked to CMEs - are presented. These updates provide calculations of the surface of the dimming region, implement novel clustering technique for the dimmings and set new criteria to flag the eruptive dimmings based on their complex characteristics. The efficiency of NEMO has been increased significantly resulting to the extraction of dimmings observed near the solar limb and to the detection of small-scale events as well. As a consequence, the detection efficiency of CMEs precursors and the forecasts of CMEs have been drastically improved. Furthermore, the catalogues of solar eruptive events that can be constructed by NEMO may include larger number of physical parameters associated to the dimming regions.Comment: 12 Pages, 5 figures, submitted to Solar Physic

Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 Substrate by RF Magnetron Sputtering under Electric Field

LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric field to study the self-polarization effect. The films have been characterized crystallographically by x-ray diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization for LiNbO3 thin film

The dependence of the EIT wave velocity on the magnetic field strength

"EIT waves" are a wavelike phenomenon propagating in the corona, which were initially observed in the extreme ultraviolet (EUV) wavelength by the EUV Imaging Telescope (EIT). Their nature is still elusive, with the debate between fast-mode wave model and non-wave model. In order to distinguish between these models, we investigate the relation between the EIT wave velocity and the local magnetic field in the corona. It is found that the two parameters show significant negative correlation in most of the EIT wave fronts, {\it i.e.}, EIT wave propagates more slowly in the regions of stronger magnetic field. Such a result poses a big challenge to the fast-mode wave model, which would predict a strong positive correlation between the two parameters. However, it is demonstrated that such a result can be explained by the fieldline stretching model, \emph{i.e.,} that "EIT waves" are apparently-propagating brightenings, which are generated by successive stretching of closed magnetic field lines pushed by the erupting flux rope during coronal mass ejections (CMEs).Comment: 11 pages, 8 figures, accepted for publication in Solar Phy

Coronal Shock Waves, EUV Waves, and Their Relation to CMEs. III. Shock-Associated CME/EUV Wave in an Event with a Two-Component EUV Transient

On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a freely expanding coronal shock wave including correspondence to the fast-mode speed distribution, while the transient sweeping over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption. Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law fit matches expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected far from the eruption region.Comment: 18 pages, 10 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.co

Formation of the Electric Field Distribution in Thin Electro-Optic Layers for Precision Correction their Optical Characteristics

A method of making given field distribution within thin electro-optical layers by using narrow band electrodes placed at the same electric potential. A formula for electric field intensity produced by a single band electrode is obtained. Electric field modeling for different band electrode configurations is undertaken. It was shown, by applying piezoresponse force microscopy, that in case of highly inhomogeneous field the polarization of lithium niobate electro-optical film persisted only in the area above the band electrode. Lithium niobate, electro-optical structures, piezoresponse force microscopy, Computer simulation

Formation of the Microcrystalline Structure in LiNbO3 Thin Films by Pulsed Light Annealing

LiNbO3 thin films with a thickness of 200 nm were deposited onto Al2O3 substrate by RF-magnetron sputtering technique without intentional substrate heating. The results demonstrate that post-growth infrared pulsed light annealing of the amorphous LiNbO3 films leads to the formation of two phases, LiNbO3 and LiNb3O8. After annealing at temperatures of 700 to 800 °C, the percentage of the nonferroelectric phase LiNb3O8 was minimal. The surface composition of the films annealed at different temperatures was examined by X-ray photoelectron spectroscopy. Piezoresponse force microscopy was used to study both the vertical and the lateral polarization and to visualize the piezoelectric inactivity of LiNb3O8 grains. A comparison of the results of PFM and XPS measurements revealed that there is a correlation between the fraction of the piezoelectric phase and the film composition: At an annealing temperature higher than 850 °C, the atomic ratio of lithium to niobium decreases compared to the initial value along with a decrease of the fraction of the piezoelectric phase

Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"

``EIT waves" are large-scale coronal bright fronts (CBFs) that were first observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}. Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100--700 km s$^{-1}$ with front widths of 50-100 Mm. As their speed is greater than the quiet coronal sound speed ($c_s\leq$200 km s$^{-1}$) and comparable to the local Alfv\'{e}n speed ($v_A\leq$1000 km s$^{-1}$), they were initially interpreted as fast-mode magnetoacoustic waves ($v_{f}=(c_s^2 + v_A^2)^{1/2}$). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure

Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of "EIT waves", Type II Radio Bursts, and Leading Edges of CMEs

We show examples of excitation of coronal waves by flare-related abrupt eruptions of magnetic rope structures. The waves presumably rapidly steepened into shocks and freely propagated afterwards like decelerating blast waves that showed up as Moreton waves and EUV waves. We propose a simple quantitative description for such shock waves to reconcile their observed propagation with drift rates of metric type II bursts and kinematics of leading edges of coronal mass ejections (CMEs). Taking account of different plasma density falloffs for propagation of a wave up and along the solar surface, we demonstrate a close correspondence between drift rates of type II bursts and speeds of EUV waves, Moreton waves, and CMEs observed in a few known events.Comment: 30 pages, 15 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.co