bluuebunny/crossref_metadata_2025 huggingface dataset:
Space weather: science and effects
Authors: Crosby Norma B.
Published: March 2009

From the point-of-view of somebody standing outside on a cold winter night looking up at a clear cloudless sky, the space environment seems to be of a peaceful and stable nature. Instead, the opposite is found to be true. In fact the space environment is very dynamic on all spatial and temporal scales, and in some circumstances may have unexpected and hazardous effects on technology and humans both in space and on Earth. In fact the space environment seems to have a weather all of its own – its own “space weather”. Our Sun is definitely the driver of our local space weather. Space weather is an interdisciplinary subject covering a vast number of technological, scientific, economic and environmental issues. It is an application-oriented discipline which addresses the needs of “space weather product” users. It can be truly said that space weather affects everybody, either directly or indirectly. The aim of this paper is to give an overview of what space weather encompasses, emphasizing how solar-terrestrial physics is applied to space weather. Examples of “space weather product” users will be given highlighting those products that we as a civilization are most dependent on.
Evolution of several space weather events connected with Forbush decreases
Authors: Dorotovič I. , Kudela K. , Lorenc M. , Pintér T. , Rybanský M.
Published: March 2009

In our recent paper (Dorotovič et al. 2008a) we focused on a study of the Forbush decrease (FD) of January 17–18 and 21–22, 2005. It was shown that the corresponding recovery time can depend on the density of high-energy protons in the CME matter. In this paper we identified several additional events in the period between 1995 and 2007. We found that the majority of FDs studied is accompanied by an abrupt count increase in the proton channel P1 and by a simultaneous decrease in the channel P7 (GOES). However, the analysis of temporal evolution of all FDs did not confirm the hypothesis on different recovery time after FD as a function of the energy distribution of the particles penetrating into radiation belts of the Earth.
Solar and planetary dynamos: comparison and recent developments
Authors: Petrovay K.
Published: March 2009

While obviously having a common root, solar and planetary dynamo theory have taken increasingly divergent routes in the last two or three decades, and there are probably few experts now who can claim to be equally versed in both. Characteristically, even in the fine and comprehensive book “The magnetic Universe” (Rudiger & Hollerbach 2004), the chapters on planets and on the Sun were written by different authors. Separate reviews written on the two topics include Petrovay (2000), Charbonneau (2005), Choudhuri (2008) on the solar dynamo and Glatzmaier (2002), Stevenson (2003) on the planetary dynamo. In the following I will try to make a systematic comparison between solar and planetary dynamos, presenting analogies and differences, and highlighting some interesting recent results.
Processes in the magnetized chromosphere of the Sun
Authors: Hasan S. S.
Published: March 2009

We review physical processes in magnetized chromospheres on the Sun. In the quiet chromosphere, it is useful to distinguish between the magnetic network on the boundaries of supergranules, where strong magnetic fields are organized in mainly vertical flux tubes and internetwork regions in the cell interiors, which have traditionally been associated with weak magnetic fields. Recent observations from Hinode, however, suggest that there is a significant amount of horizontal magnetic flux in the cell interior with large field strength. Furthermore, processes that heat the magnetic network have not been fully identified. Is the network heated by wave dissipation and if so, what is the nature of these waves? These and other aspects related to the role of spicules will also be highlighted. A critical assessment will be made on the challenges facing theory and observations, particularly in light of the new space experiments and the planned ground facilities.
Long period oscillations of microwave emission of solar active regions: observations with NoRH and SSRT
Authors: Bakunina I. A. , Abramov-Maximov V. E. , Lesovoy S. V. , Shibasaki K. , Solov'ev A. A. , Tikhomirov Yu. V.
Published: March 2009

In this work we present the first results of study and comparison of the parameters of quasi-periodic long-term oscillations of microwave emission of large (>0.7 arcmin) sunspots as a result of simultaneous observations with two radioheliographs – NoRH (17 GHz) and Siberian Solar Radio Telescope (SSRT) (5.7 GHz) with 1 minute cadence. Radioheliographs have been working with quite large time overlap (about 5 hours) and have the high spatial resolution: 10 arcsec (NoRH) and 20 arcsec (SSRT). We have found that quasi-periodic long-term oscillations are surely observed at both frequencies with the periods in the range of 20–150 min. We detected common periods for common time of observations with two radioheliographs and interpret this as the consequence of the vertical-radial quasi-periodic displacements of sunspot as a whole structure.
Enhanced Rieger type periodicities' detection in X-ray solar flares and statistical validation of Rossby waves' existence
Authors: Dimitropoulou Michaila , Moussas Xenophon , Strintzi Dafni
Published: March 2009

The known Rieger Periodicity (ranging in literature from 150 up to 160 days) is obvious in numerous solar indices. Many sub-harmonic periodicities have also been observed (128–, 102–, 78–, and 51 – days) in flare, sunspot, radio bursts, neutrino flux and flow data, coined as Rieger Type Periodicities (RTPs). Several attempts are focused to the discovery of their source, as well as the explanation of some intrinsic attributes that they present, such as their connection to extremely active flares, their temporal intermittency as well as their tendency to occur near solar maxima. In this paper, we link the X-ray flare observations made on Geosynchronous Operational Environmental Satellites (GOES) to an existing theoretical model (Lou 2000), suggesting that the mechanism behind the Rieger Type Periodicities is the Rossby Type Waves. The enhanced data analysis methods used in this article (Scargle-Lomb periodogram and Weighted Wavelet Z-Transform) provide the proper resolution needed to argue that RTPs are present also in less energetic flares, contrary to what has been inferred from observations so far.
Coronal mass ejection: key issues
Authors: Harrison Richard
Published: March 2009

Coronal Mass Ejections (CMEs) have been addressed by a particularly active research community in recent years. With the advent of the International Heliophysical Year and the new STEREO and Hinode missions, in addition to the on-going SOHO mission, CME research has taken centre stage in a renewed international effort. This review aims to touch on some key observational areas, and their interpretation. First, we consider coronal dimming, which has become synonymous with CME onsets, and stress that recent advances have heralded a move from a perceived association between the two phenomena to a firm, well-defined physical link. What this means for our understanding of CME modeling is discussed. Second, with the new STEREO observations, and noting the on-going SMEI observations, it is important to review the opening field of CME studies in the heliosphere. Finally, we discuss some specific points with regard to EIT-waves and the flare-CME relationship. In the opinion of the author, these issues cover key hot topics which need consideration for significant progress in the field.
Solar prominences
Authors: Schmieder Brigitte , Aulanier Guillaume , Török Tibor
Published: March 2009

Solar filaments (or prominences) are magnetic structures in the corona. They can be represented by twisted flux ropes in a bipolar magnetic environment. In such models, the dipped field lines of the flux rope carry the filament material and parasitic polarities in the filament channel are responsible for the existence of the lateral feet of prominences.

Very simple laws do exist for the chirality of filaments, the so-called “filament chirality rules”: commonly dextral/sinistral filaments corresponding to left- (resp. right) hand magnetic twists are in the North/South hemisphere. Combining these rules with 3D weakly twisted flux tube models, the sign of the magnetic helicity in several filaments were identified. These rules were also applied to the 180° disambiguation of the direction of the photospheric transverse magnetic field around filaments using THEMIS vector magnetograph data (López Aristeet al. 2006). Consequently, an unprecedented evidence of horizontal magnetic support in filament feet has been observed, as predicted by former magnetostatic and recent MHD models.

The second part of this review concerns the role of emerging flux in the vicinity of filament channels. It has been suggested that magnetic reconnection between the emerging flux and the pre-existing coronal field can trigger filament eruptions and CMEs. For a particular event, observed with Hinode/XRT, we observe signatures of such a reconnection, but no eruption of the filament. We present a 3D numerical simulation of emerging flux in the vicinity of a flux rope which was performed to reproduce this event and we briefly discuss, based on the simulation results, why the filament did not erupt.
CMEs ‘en rafale’ observations and simulations
Authors: Dumitrache Cristiana
Published: March 2009

A CME is triggered by the disappearance of a stable equilibrium as a result of the slow evolution of the photospheric magnetic field. This disappearance may be due to a loss of ideal-MHD equilibrium or stability as in the kink mode, or to a loss of resistive-MHD equilibrium as a result of magnetic reconnection. We have obtained CMEs in sequence by a time dependent magnetohydrodynamic computation performed on three solar radii. These successive CMEs resulted from a prominence eruption. Velocities of these CMEs decrease in time, from a CME to another. We present observational evidences for large-scale magnetic reconnections that caused the destabilization of a sigmoid filament. These reconnections covered half of the solar disk and produced CMEs in squall (sequential CMEs).
The link between CME-associated dimmings and interplanetary magnetic clouds
Authors: Mandrini Cristina H. , Nakwacki María S. , Attrill Gemma , van Driel-Gesztelyi Lidia , Dasso Sergio , Démoulin Pascal
Published: March 2009

Coronal dimmings often develop in the vicinity of erupting magnetic configurations. It has been suggested that they mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the ejected flux. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud (MC) to find clues about the origin of the ejected flux rope. In the context of this interpretation, we present several events for which we have done a comparative solar-interplanetary analysis. We combine SOHO/Extreme Ultraviolet Imaging Telescope (EIT) data and Michelson Doppler Imager (MDI) magnetic maps to identify and measure the flux in the dimmed regions. We model the associated MCs and compute their magnetic flux using in situ observations. We find that the magnetic fluxes in the dimmings and MCs are compatible in some events; though this is not the case for large-scale and intense eruptions that occur in regions that are not isolated from others. We conclude that, in these particular cases, a fraction of the dimmed regions can be formed by reconnection between the erupting field and the surrounding magnetic structures, via a stepping process that can also explain other CME associated events.
Coherent emission
Authors: Melrose D. B.
Published: March 2009

The theory of plasma emission and of electron cyclotron maser emission, and their applications to solar radio bursts and to Jupiter's decametric radioation (DAM) and the Earth's auroral kilometric radiation (AKR) are reviewed, emphasizing the early literature and problems that remain unresolved. It is pointed out that there are quantitative measures of coherence in radio astronomy that have yet to be explored either observationally or theoretically.
On spatial variations of magnetic field and superthermal electron distribution in cm-radio burst source
Authors: Yasnov Leonid V. , Karlický Marian
Published: March 2009

The paper presents a new method of an estimation of spatial variations of the magnetic field and superthermal electron distribution in solar cm-radio burst sources. The method is based on the analysis of several burst spectra recorded in the different moments of time and on the minimization of the difference between the theoretical and observed radio fluxes. It is found that the measure of the spatial variations of superthermal electron distribution in the radio source is always greater than that for the magnetic field. In most cases this measure has a minimum at the impulsive phase of cm-radio bursts.
A study on the relationship of type III radio bursts CME and solar flares during the active period October-November 2003
Authors: Thanassa Michaella , Mitsakou Eleftheria , Preka-Papadema Panagiota , Moussas Xenophon , Tsitsipis Panagiotis , Kontogeorgos Athanasios
Published: March 2009

Within a period of intense activity (20 October to 5 November 2003), the injection and propagation of near relativistic electrons, resulted in hundreds of type III bursts recorded by the ARTEMISIV radio spectrograph (20–650 MHz). For a number of these type III events association with GOES SXR/Hα flare and/or SOHO/LASCO CME was established. We study the variation of characteristic type III parameters and their relationship with features of the associated flares and/or CMEs.
History of research on solar energetic particle (SEP) events: the evolving paradigm
Authors: Cliver Edward W.
Published: March 2009

Forbush initiated research on solar energetic particle (SEP) events in 1946 when he reported ionization chamber observations of the first three ground level events (GLEs). The next key development was the neutron monitor observation of the GLE of 23 February 1956. Meyer, Parker and Simpson attributed this high-energy SEP event to a short time-scale process associated with a solar flare and ascribed the much longer duration of the particle event to scattering in the interplanetary medium. Thus “flare particle” acceleration became the initial paradigm for SEP acceleration at the Sun. A more fully-developed picture was presented by the Australian radio astronomers Wild, Smerd, and Weiss in 1963. They identified two distinct SEP acceleration processes in flares: (1) the first phase accelerated primarily ~100 keV electrons that gave rise to fast-drift type III emission as they streamed outward through the solar atmosphere; (2) the second phase was produced by an outward moving (~1000 km s−1) magnetohydrodynamic shock, occurring in certain (generally larger) flares. The second phase, manifested by slow-drift metric type II emission, appeared to be required for substantial acceleration of protons and higher-energy electrons. This two-stage (or two-class) picture gained acceptance during the 1980s as composition and charge state measurements strengthened the evidence for two distinct types of particle events which were termed impulsive (attributed to flare-resident acceleration process(es)) and gradual (shock-associated). Reames championed the two-class picture and it is the commonly accepted paradigm today. A key error made in the establishment of this paradigm was revealed in the late 1990s by observations of SEP composition and charge states at higher energies (>10 MeV) than previously available. Specifically, some large and therefore presumably “gradual” SEP events looked “impulsive” at these energies. One group of researchers attributes these unusual events to acceleration of high-energy SEPs by flares and another school favors acceleration of flare seed particles by quasi-perpendicular shocks. A revised SEP classification scheme is proposed to accommodate the new observations and to include ideas on geometry and seed particle composition recently incorporated into models of shock acceleration of SEPs.
Modeling and prediction of fast CME/shocks associated with type II bursts
Authors: Xie H. , Gopalswamy N. , Cyr O. C. St.
Published: March 2009

A numerical simulation with ENLIL+Cone model was carried out to study the propagation of the shock driven by the 2005 May 13 CME. We then conducted a statistical analysis on a subset of similar events, where a decameter-hectometric (DH) type II radio burst and a counterpart kilometric type II have been observed to be associated with each CME (DHkm CME). The simulation results show that fast CME-driven shocks experienced a rapid deceleration as they propagated through the corona and then kept a nearly constant speed traveling out into the heliosphere. Two improved methods are proposed to predict the fast CME-driven shock arrival time, which give the prediction errors of 3.43 and 6.83 hrs, respectively.
On the nature of the longitudinal anomaly of the southern hemisphere lower stratospheric temperature
Authors: Vieira Luis Eduardo Antunes , da Silva Ligia Alves
Published: March 2009

The effects of changes in the solar radiative emission on ozone levels in the stratosphere have been considered as a candidate to explain the link between solar activity and its effects on the climate. As ozone absorbs electromagnetic radiation, changes in ozone concentrations alter Earth's radiative balance by modifying both incoming solar radiation and outgoing radiation. In this way, ozone controls solar energy deposition in the stratosphere and its variations alter the thermal structure of the stratosphere. These changes are assumed to propagate downward through a chain of feedbacks involving thermal and dynamical processes. The effects of high energy particle precipitation on mesospheric and stratospheric ozone have also been investigated. However, while the effects of high energy particle precipitation on ozone distribution in the auroral region has been investigated during the last decades, little is known about the role of the high energy particle precipitation on the stratospheric composition and thermal structure in the tropical/subtropical region. Here we show that the spatial distribution of the lower stratosphere temperature is affected by the presence of the southern hemisphere magnetic anomaly. We found that during the austral winter and spring, in the subtropical region (below 30 deg S), the reduction of the lower stratosphere temperature occurs systematically in the magnetic anomaly area. This result is consistent with the observations that in the southern hemisphere subtropical region the energy of precipitating particles is deposited lower in altitude in regions with weaker magnetic field intensity.
Mesoscale and diel to monthly variability of CO2 and carbon fluxes at the ocean surface in the northeastern Atlantic
Authors: Merlivat Liliane , Gonzalez Davila Melchor , Caniaux Guy , Boutin Jacqueline , Reverdin Gilles
Published: March 2009

Four CARIOCA Lagrangian buoys were deployed in the northeast Atlantic Ocean as part of the Programme Océan Multidisciplinaire Méso Echelle (POMME) dedicated to the study of the role of mesoscale eddies in biological production, the carbon budget, and the subduction of mode waters. An extensive set of hourly surface measurements of temperature, salinity, and carbon dioxide fugacity (fCO2) was collected from February to August 2001. The high‐frequency spatial and temporal variability observed in surface fCO2 and in the derived dissolved inorganic carbon (DIC) concentrations suggests that abrupt changes of the carbon variables are being generated along frontal patterns and filaments by submesoscale and mesoscale eddy‐eddy interactions, especially in winter. On the basis of a 1‐D model of the diurnal mixed layer along the buoy trajectory, we show that under certain conditions the diel cycle of DIC is driven by the daily cycle of photosynthesis and metabolic CO2 release at the ocean surface. This information is quantitatively used to derive in‐situ primary production, carbon gross, and net community production. The analysis of 107 observed diel cycles of DIC shows that episodic biological production processes are triggered by the mesoscale activity of surface eddies. Over the sampled period, the POMME area is a sink for atmospheric CO2 with an estimated flux of −4 mmol m−2 day−1. The calculated amount of anthropogenic carbon transported into the ocean interior by subduction of subpolar mode water is equal to 2.8 1013 gC yr−1.
Mesoscale ocean dynamics observed by satellite altimeters in non‐repeat orbits
Authors: Smith Walter H. F. , Scharroo Remko
Published: March 2009

We compare sea surface height anomalies observed by satellite altimeters in exact repeat mission orbits to anomalies observed by altimeters in geodetic or drifting orbits. One experiment compares data from the drift of TOPEX between its Tandem and Interleaved missions to repeat‐orbit data from Jason‐1, ERS‐2 and GFO. A second experiment compares data from the ERS‐1 non‐repeating Geodetic Phases E and F to the repeating TOPEX data. Both studies cover the North Atlantic from 0° to 82°W and 15° to 55°N in order to sample both the Gulf Stream and quieter regions. Height anomalies are obtained along repeat and non‐repeat orbits alike by use of a mean sea surface model. Each experiment is performed twice, once with the EGM2008 and once with the DNSC08 models, showing that the results are model‐independent; DNSC08 yields an insignificant 2 mm lower RMS misfit. To compare anomalies between repeat and non‐repeat orbits with different spatio‐temporal sampling we grid the 1‐Hz along‐track point data and interpolate the grid to point values. RMS differences between grids and point values are around 4 cm in quiet areas and 6 cm over the entire region, with negligible difference between misfits to repeat and non‐repeat data. A mapped sea surface height anomaly grid built solely from ERS‐1 geodetic data captures at least 85% of the variance in repeat‐track TOPEX point data. From these results we can conclude that altimeters in suitable non‐repeating orbits are as useful for mesoscale oceanographic studies as are repeat orbit missions.
Energy taken up by co‐seismic chemical reactions during a large earthquake: An example from the 1999 Taiwan Chi‐Chi earthquake
Authors: Hamada Yohei , Hirono Tetsuro , Tanikawa Wataru , Soh Wonn , Song Sheng‐Rong
Published: March 2009

Frictional heat in a fault zone during earthquake slip transiently induces chemical reactions that may use energy released during the earthquake. We estimated the energy used by such reactions (EC) by a numerical analysis incorporating frictional heat, thermal diffusion, chemical kinetics, and energy conservation, and found that EC has an auto‐feedback effect that inhibits temperature rise in fault zone. During the 1999 Taiwan Chi‐Chi earthquake, estimated EC was 0.43 MJ/m2, corresponding to 0.79% of the frictional heat generated. This low percentage probably reflects the low initial concentrations of reactive materials. However, in the case of a fault with abundant reactive materials, EC could reach >50% of the frictional heat and the auto‐feedback effect could be large. At this case EC is a nonnegligible component on earthquake energy budget and can affect fault mechanics.
Influences of geomagnetic fields on longitudinal variations of vertical plasma drifts in the presunset equatorial topside ionosphere
Authors: Ren Zhipeng , Wan Weixing , Liu Libo , Heelis Roderick A. , Zhao Biqiang , Wei Yong , Yue Xinan
Published: March 2009

On the basis of the measurements from the ion drift meter on the Defense Meteorological Satellite Program F13 Satellite from 2000 to 2002, the relative longitudinal variations of E × B vertical plasma drifts in the presunset equatorial topside ionosphere at 1745 LT are examined. Obvious influences of geomagnetic fields on longitudinal variations of E × B vertical plasma drifts, which also show a seasonal dependence, have been found. During the June solstice, the relative vertical plasma drifts is most significantly influenced by the geomagnetic field declination. However, the relative vertical plasma drifts during the December solstice more strongly correlates with the geomagnetic field strength. Although the relative vertical plasma drifts during equinox are also influenced by the geomagnetic field declination, an underlying dependence on magnetic field magnitude, as seen in December, is also present.
A comparison of heterogeneous ice nucleation parameterizations using a parcel model framework
Authors: Eidhammer Trude , DeMott Paul J. , Kreidenweis Sonia M.
Published: March 2009

A liquid‐phase Lagrangian parcel model was expanded to include nucleation and growth of ice crystals. Intercomparisons between three heterogeneous ice nucleation parameterizations that link aerosol type and number to ice crystal concentration were conducted. Results indicate large differences in the prediction of ice formation in modestly supercooled clouds and in the susceptibility of cirrus to heterogeneous ice nucleation for the same assumed aerosol distribution. Only one parameterization has an observational constraint that limits the maximum ice crystal number concentrations to be a fraction of the total number concentrations of potential ice‐nucleating particles (typically, all insoluble particles larger than about 0.1μm). The constrained parameterization compares well with most ice nucleation measurements. The nonconstrained parameterizations are capable of predicting several orders of magnitude higher ice crystal concentrations than the constrained parameterization for the same parcel‐forcing conditions. Ice crystal concentrations in the unconstrained parameterizations are controlled by the total number concentration of potential ice‐nucleating particles and, importantly, negative feedback on ice supersaturation. This feedback control often masks the large discrepancy that exists between predicted ice crystal number concentrations and the maximum number concentrations that can be attributed to atmospheric ice nuclei based on our current understanding of the latter. It also permits unrealistic conclusions regarding the role of certain aerosols as ice nuclei. It is recommended that a constraint on ice crystal number concentrations, related to number concentrations of relevant aerosol particles, should be included in ice nucleation parameterizations used in cloud to global‐scale models.
Metal-ferroelectric-metal capacitor based persistent memory for electronic product code class-1 generation-2 uhf passive radio-frequency identification tag
Authors: Yoon Bongno , Sung Man Young , Yeon Sujin , Oh Hyun S. , Kwon Yoonjoo , Kim Chuljin , Kim Kyung-Ho
Published: March 2009

With the circuits using metal-ferroelectric-metal (MFM) capacitor, rf operational signal properties are almost the same or superior to those of polysilicon-insulator-polysilicon, metal-insulator-metal, and metal-oxide-semiconductor (MOS) capacitors. In electronic product code global class-1 generation-2 uhf radio-frequency identification (RFID) protocols, the MFM can play a crucial role in satisfying the specifications of the inventoried flag’s persistence times (Tpt) for each session (S0–S3, SL). In this paper, we propose and design a new MFM capacitor based memory scheme of which persistence time for S1 flag is measured at 2.2 s as well as indefinite for S2, S3, and SL flags during the period of power-on. A ferroelectric random access memory embedded RFID tag chip is fabricated with an industry-standard complementary MOS process. The chip size is around 500×500 μm2 and the measured power consumption is about 10 μW.
Physical concepts of memory device operation based on piezoacousto and pyroelectric properties of ferroelectric films
Authors: Krieger Ju. H.
Published: March 2009

The paper presents physical concepts of universal memory device operation based on piezoacousto and pyroelectric properties of ferroelectric materials. It is suggested to extract information about ferroelectric memory cell polarization by heating (pyroelectric approach) or mechanical deformation (piezoacousto approach) of the memory cell. The physical concepts of universal memory device operation and alternative memory array architectures are presented here, which satisfies the requirements of both a faster operation and a small effective memory cell size. For high density memory application the lowest cost can be achieved by the piezoacoustic approach, exploiting array architectures, such as cross point passive arrays and multilayer stacks. A new ferroelectric random access memory (RAM) structure, which is called acoustoferroelectric RAM, makes use of acoustic method of detecting polarization of the ferroelectric memory cells.
Dielectric and piezoelectric properties of Bi2O3 added (Pb,Ca,Sr)(Ti,Mn,Sb)O3 ceramics sintered at low temperature
Authors: Kim Dohyung , Yoo Juhyun , Kim Insung , Song Jaesung
Published: March 2009

In this study, in order to develop low temperature sintering ceramics for a thickness mode multilayer piezoelectric transformer, (Pb,Ca,Sr)(Ti,Mn,Sb)O3 ceramics were fabricated using Na2CO3, Li2CO3, MnO2, and Bi2O3 as sintering aids at 870, 900, and 930 °C. Their respective dielectric and piezoelectric properties were investigated according to the amount of Bi2O3 addition. At the sintering temperature of 900 °C, the optimum value was shown for the density of 6.94 g/cm3, thickness vibration mode electromechanical coupling factor (henceforth, kt) of 0.497, thickness vibration mode mechanical quality factor (henceforth, Qmt) of 3162, and dielectric constant (henceforth, εr) of 209 for thickness mode multilayer piezoelectric transformer application.
Effect of Bi2O3 seed layer on crystalline orientation and ferroelectric properties of Bi3.25La0.75Ti3O12 thin films prepared by rf-magnetron sputtering method
Authors: Yunyi Wu , Duanming Zhang , Jun Yu , Yunbo Wang
Published: March 2009

Bi 3.25 La 0.75 Ti 3 O 12 (BLT) thin films with Bi2O3 seed layers were prepared on Pt(111)/Ti/SiO2/Si substrate by rf-magnetron sputtering method. The effect of annealing procedure, thickness, and position of Bi2O3 seed layer on the structural and electrical properties of BLT thin film was investigated. When using a two-step annealing procedure, the x-ray diffraction pattern indicated that BLT thin film with a Bi2O3 seed layer showed c-axis preference orientation. Compared with Pt/BLT/Bi2O3/Pt structure film, the Pt/Bi2O3/BLT/Bi2O3/Pt structure film showed higher oriented to c direction. The ferroelectric property of BLT thin film improved remarkably with the incorporation of Bi2O3 seed layer. Under the applied voltage of 14 V, the remnant polarization and coercive voltage of the Bi2O3/BLT/Bi2O3 capacitor with 18-nm-thick Bi2O3 seed layer were 45.2 μC/cm2 and 9.2 V, respectively. Moreover, the Pt/Bi2O3/BLT/Bi2O3/Pt film with 18-nm-thick Bi2O3 seed layers exhibited good fatigue endurance even after 6×109 switching cycles, which was attributed to the double-sided Bi2O3 layer. They decreased the grain boundary density by enhancing the grain size of BLT film and enhanced the c-axis preferential orientation. Compared with BLT film deposited directly on Pt, double-sided Bi2O3 layer would greatly enhance the leakage current resistance of the BLT film.
Congruent charge-injection spectrum from independent measurements of fatigue and imprint in ferroelectric thin films
Authors: Jiang A. Q. , Tang T. A.
Published: March 2009

The fundamental physics of fatigue and imprint in ferroelectric thin films is pertinent to the by-electrode charge injection. The detectable charge injection depends on the applied voltage and time. However, a broad-time description of the charge injection is still lacking. It is not clear if the charge-injection spectra are derivable and comparable from two independent measurements. In our works, we obtained two charge-injection spectra from discrete fatigue and imprint measurements with a time span of more than eight orders of magnitude. The charge-injection spectra are in agreement with the direct measurements of charge-injection current transients under/after different biasing voltages. All results are congruently described by a series of analytical equations derived from the assumption of interfacial Schottky emission for the films with the presence of interfacial passive layers. The initial time below which the charge injection is minor is found to be of the order of 2.5 μs under −6.0 V on the top electrode but ten times slower under 6.0 V for Pt/IrO2/Pb(Zr,Ti)O3/IrO2/Pt thin-film capacitors.
Nanoscale piezoresponse studies of ferroelectric domains in epitaxial BiFeO3 nanostructures
Authors: Hong Seungbum , Klug Jeffrey A. , Park Moonkyu , Imre Alexandra , Bedzyk Michael J. , No Kwangsoo , Petford-Long Amanda , Auciello Orlando
Published: March 2009

We report the dependence of the ferroelectric domain configuration and switching behavior on the shape (square versus round) of epitaxial BiFeO3 (BFO) nanostructures. We fabricated (001) oriented BFO(120 nm)/SrRuO3(SRO,125 nm) film layers on (001) SrTiO3 single crystals by rf magnetron sputter deposition, and patterned them to square (500×500 nm2) and round (502 nm in diameter) shaped nanostructures by focused ion-beam lithography. The surface morphology and the crystalline structure of the nanostructures were characterized by scanning electron microscopy and x-ray diffraction, respectively, while the domain configuration was investigated using piezoelectric force microscopy. We found that the square-shaped nanostructures exhibit a single variant domain configuration aligned along the [1¯11¯] direction, whereas the round-shaped nanostructures exhibit seven variants of domain configuration along the [1¯11¯], [11¯1¯], [111¯], [111], [1¯11], [11¯1], and [1¯1¯1] directions. Moreover, local d33 piezoelectric coefficient measurements showed hysteresis loops with a strong displacement in the voltage axis (strong imprint) for the square-shaped nanostructures, while the round-shaped ones exhibited more symmetric loops. These findings have critical implications for the development of nanocapacitors for gigabyte to terabyte nonvolatile ferroelectric memories.
Effect of bottom electrode on dielectric property of sputtered-(Ba,Sr)TiO3 films
Authors: Ito Shinichi , Yamada Tomoaki , Takahashi Kenji , Okamoto Shoji , Kamo Takafumi , Funakubo Hiroshi , Koutsaroff Ivoyl , Zelner Marina , Cervin-Lawry Andrew
Published: March 2009

( Ba 0.5 Sr 0.5 ) TiO 3 (BST) films were deposited on (111)Pt/TiO2/SiO2/Al2O3 substrates by rf sputtering. By inserting a thin layer of SrRuO3 in between BST film and (111)Pt electrode, the BST films grew fully (111)-oriented without any other orientations. In addition, it enables us to reduce the growth temperature of BST films while keeping the dielectric constant and tunability as high as those of BST films directly deposited on Pt at higher temperatures. The dielectric loss of the films on SrRuO3-top substrates was comparable to that on Pt-top substrates for the same level of dielectric constant. The results suggest that the SrRuO3 thin layer on (111)Pt electrode is an effective approach to growing highly crystalline BST films with (111) orientation at lower deposition temperatures.
Piezoelectric thin films and their applications for electronics
Authors: Yoshino Yukio
Published: March 2009

ZnO and AlN piezoelectric thin films have been studied for applications in bulk acoustic wave (BAW) resonator. This article introduces methods of forming ZnO and AlN piezoelectric thin films by radio frequency sputtering and applications of BAW resonators considering the relationship between the crystallinity of piezoelectric thin films and the characteristics of the BAW resonators. Using ZnO thin films, BAW resonators were fabricated for a contour mode at 3.58 MHz and thickness modes from 200 MHz to 5 GHz. The ZnO thin films were combined with various materials, substrates, and thin films to minimize the temperature coefficient of frequency (TCF). The minimum TCF of BAW resonators was approximately 2 ppm/°C in the range −20 to 80 °C. The electromechanical coupling coefficient (k2) in a 1.9 GHz BAW resonator was 6.9%. Using AlN thin films, 5–20 GHz BAW resonators with an ultrathin membrane were realized. The membrane thickness of a 20 GHz BAW resonator was about 200 nm, k2 was 6.1%, and the quality factor (Q) was about 280. Q decreased with increasing resonant frequency. The value of k2 is almost the same for 5–20 GHz resonators. This result could be obtained by improving the thickness uniformity, by controlling internal stress of thin films, and by controlling the crystallinity of AlN piezoelectric thin film.
Photovoltaic characteristics in polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films sandwiched between different top and bottom electrodes
Authors: Qin Meng , Yao Kui , Liang Yung C.
Published: March 2009

Photovoltaic responses, including photovoltage, photocurrent, illuminated J-V curve, and light-to-electricity power conversion efficiency, were investigated in chemical-solution-derived polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLZT) thin films sandwiched between different metal and oxide electrodes. The epitaxial PLZT films with Au/PLZT/Nb-doped SrTiO3 structure exhibited about one order of magnitude larger photocurrent and efficiency over the randomly oriented polycrystalline PLZT films with Au/PLZT/Pt structure due to the high crystalline quality with the reduced defects and enhanced depolarization field. The illuminated J-V curve was approximately linear for both polycrystalline and epitaxial PLZT thin films. The nonzero photovoltaic outputs in the unpoled films were induced by asymmetric interfacial Schottky barriers. The illuminated J-V curve shifted toward the positive voltage direction after positive poling and toward the negative voltage direction after negative poling, and the enhancement of efficiency only occurred when the polarization direction accorded with the direction of Schottky barrier difference at the two electrode interfaces. Thickness dependences of photovoltage, photocurrent, and light-to-electricity conversion efficiency were also examined. It was observed that photovoltage linearly increased with film thickness while both photocurrent and efficiency exponentially increased with the decrease in thickness. Furthermore, at a fixed small film thickness, efficiency was also found to increase reciprocally with the decrease of incident UV intensity.
Crystal structure and electrical property comparisons of epitaxial Pb(Zr,Ti)O3 thick films grown on (100)CaF2 and (100)SrTiO3 substrates
Authors: Fujisawa Takashi , Nakaki Hiroshi , Ikariyama Rikyu , Yamada Tomoaki , Ishikawa Mutsuo , Morioka Hitoshi , Funakubo Hiroshi
Published: March 2009

Epitaxial Pb(Zr,Ti)O3 (PZT) thick films of 2.0–3.0 μm thickness were grown at 600 °C on (100)cSrRuO3∥(100)SrTiO3 and (100)cSrRuO3∥(100)LaNiO3∥(100)CaF2 substrates by pulsed-metal organic chemical vapor deposition. All films showed (100) and/or (001) orientations with tetragonal symmetry. It was found that there is an almost linear relationship between the estimated thermal strain from the deposition temperature to the Curie temperature and the volume fraction of (001) orientation in the mixture of (100) and (001) orientations for the films on both substrates. Consequently, the perfectly (001)-oriented, i.e., polar-axis-oriented, PZT thick films were obtained on CaF2 with the Zr/(Zr+Ti) ratio from 0.20 to 0.40. Moreover, the lattice parameter of a- and c-axes and their ratio (c/a) of those polar-axis-oriented films were almost the same as the reported data for the powder, suggesting that the large strain is not remaining in those films. The relative dielectric constant (εr) of the polar-axis-oriented Pb(Zr0.35Ti0.65)O3 thick film on CaF2 was 180 at 1 kHz, which is lower than that of (100)/(001)-oriented thick films on SrTiO3 but almost agrees with the theoretically calculated value for the c-axis of PZT single crystals. Well saturated polarization-electric-field hysteresis loops with a good square shape were observed for the polar-axis-oriented thick films, and the saturation polarization and the coercive field values were 74 μC/cm2 and 64 kV/cm, respectively. These data clearly show that the electrical properties of the polar-axis-oriented epitaxial thick films are similar to the theoretical predictions for PZT single crystals.
Epitaxial thin films of the multiferroic double perovskite Bi2FeCrO6 grown on (100)-oriented SrTiO3 substrates: Growth, characterization, and optimization
Authors: Nechache Riad , Harnagea Catalin , Carignan Louis-Philippe , Gautreau Olivier , Pintilie Lucian , Singh Mangala P. , Ménard David , Fournier Patrick , Alexe Marin , Pignolet Alain
Published: March 2009

The influence of the deposition pressure (PO2) and substrate temperature (TS) during the growth of Bi2FeCrO6 thin films grown by pulsed laser deposition has been investigated. It is found that the high volatility of Bi makes the deposition very difficult and that the growth of pure Bi2FeCrO6 thin films on SrTiO3 substrates is possible only in a narrow deposition parameter window. We find that the pure Bi2FeCrO6 phase is formed within a narrow window around an oxygen pressure PO2=1.2×10−2 mbar and around a substrate temperature TS=680 °C. At lower temperature or higher pressure, Bi7.38Cr0.62O12+x (also called b∗Bi2O3) and Bi2Fe4O9/Bi2(Fe,Cr)4O9+x phases are detected, while at lower pressure or higher temperature a (Fe,Cr)3O4 phase forms. Some of these secondary phases are not well known and have not been previously studied. We previously reported Fe/Cr cation ordering as the probable origin of the tenfold improvement in magnetization at saturation of our Bi2FeCrO6 film, compared to BiFeO3. Here, we address the effect of the degree of cationic ordering on the magnetic properties of the Bi2FeCrO6 single phase. Polarization measurements at room temperature reveal that our Bi2FeCrO6 films have excellent ferroelectric properties with ferroelectric hysteresis loops exhibiting a remanent polarization as high as 55–60 μC/cm2 along the pseudocubic [001] direction.
Intrinsic asymmetry and angular dependence of the junction resistance for high TMR read sensors
Authors: Sapozhnikov Victor , Gao Kai-Zhong , Chen Yonghua
Published: March 2009

We suggest using a different expression for the angular dependence of the junction resistance to match the convenient definition of tunneling magnetoresistive ratio (TMR). In addition, we demonstrate that readers with high TMR have a significant intrinsic asymmetry and we suggest methods of solving the problem.
A theory for viral capsid assembly around electrostatic cores
Authors: Hagan Michael F.
Published: March 2009

We develop equilibrium and kinetic theories that describe the assembly of viral capsid proteins on a charged central core, as seen in recent experiments in which brome mosaic virus capsids assemble around nanoparticles functionalized with polyelectrolyte. We model interactions between capsid proteins and nanoparticle surfaces as the interaction of polyelectrolyte brushes with opposite charge using the nonlinear Poisson Boltzmann equation. The models predict that there is a threshold density of functionalized charge, above which capsids efficiently assemble around nanoparticles, and that light scatter intensity increases rapidly at early times without the lag phase characteristic of empty capsid assembly. These predictions are consistent with and enable interpretation of preliminary experimental data. However, the models predict a stronger dependence of nanoparticle incorporation efficiency on functionalized charge density than measured in experiments and do not completely capture a logarithmic growth phase seen in experimental light scatter. These discrepancies may suggest the presence of metastable disordered states in the experimental system. In addition to discussing future experiments for nanoparticle-capsid systems, we discuss broader implications for understanding assembly around charged cores such as nucleic acids.
Premicellar aggregation of amphiphilic molecules: Aggregate lifetime and polydispersity
Authors: Hadgiivanova Radina , Diamant Haim
Published: March 2009

A recently introduced thermodynamic model of amphiphilic molecules in solution has yielded under certain realistic conditions a significant presence of metastable aggregates well below the critical micelle concentration—a phenomenon that has been reported also experimentally. The theory is extended in two directions pertaining to the experimental and technological relevance of such premicellar aggregates. (a) Combining the thermodynamic model with reaction rate theory, we calculate the lifetime of the metastable aggregates. (b) Aggregation number fluctuations are examined. We demonstrate that over most of the metastable concentration range, the premicellar aggregates should have macroscopic lifetimes and small polydispersity.
Structure and motion at the liquid-vapor interface of some interalkali binary alloys: An orbital-free ab initio study
Authors: González David J. , González Luis E.
Published: March 2009

We report the results of orbital-free ab initio molecular dynamics simulations of the liquid-vapor interfaces of three liquid binary alloys, Na1−xKx, Na1−xCsx, and Li1−xNax, whose bulk behaviors exhibit rather differing ordering tendencies. The study has been performed using samples of 2000 and 3000 particles in a slab geometry with periodic boundary conditions. In these alloys the total ionic density distributions along the normal to the interface display some layering with a virtually pure monolayer of the lower surface tension component located outermost at the interface. However, these systems have very different behaviors below the interface, which can be explained by their ordering tendencies in the bulk. The variations in diffusivity across the interface are, on the other hand, rather insensitive to the ordering properties, being dictated by the reduced atomic coordination at the surface.
Resonant microwave cavity for 8.5–12 GHz optically detected electron spin resonance with simultaneous nuclear magnetic resonance
Authors: Colton J. S. , Wienkes L. R.
Published: March 2009

We present a newly developed microwave resonant cavity for use in optically detected magnetic resonance (ODMR) experiments. The cylindrical quasi-TE011 mode cavity is designed to fit in a 1 in. magnet bore to allow the sample to be optically accessed and to have an adjustable resonant frequency between 8.5 and 12 GHz. The cavity uses cylinders of high dielectric material, so-called “dielectric resonators,” in a double-stacked configuration to determine the resonant frequency. Wires in a pseudo-Helmholtz configuration are incorporated into the cavity to provide frequencies for simultaneous nuclear magnetic resonance (NMR). The system was tested by measuring cavity absorption as microwave frequencies were swept, by performing ODMR on a zinc-doped InP sample, and by performing optically detected NMR on a GaAs sample. The results confirm the suitability of the cavity for ODMR with simultaneous NMR.
A wireless-compatible optics-free fluorescent array reader
Authors: Anwar M. , Aytur T. , Matsudaira P.
Published: March 2009

Optical-based bioassays, particularly fluorescent-based arrays, form the basis for biological detection in both biological and clinical assays, yet their use is restricted by the need for sensitive optical detectors and optics. To address this, we developed an integrated circuit-based fluorescent imaging platform that functions without the use of optics while directly integrating electronics, enabling a low-cost integrated solution. Additionally, we incorporate a wireless interface, enabling optical detection within any biological environment. As a proof of concept, we demonstrate the detection of 20 nM of Streptavidin on an array without the use of optical filters and lenses.