In the search of lead-free piezoelectric materials,ceramic processing techniques offer potential tools to increase the piezoelectric and ferroelectric properties in addition to new chemical compositions.Powders of pur...In the search of lead-free piezoelectric materials,ceramic processing techniques offer potential tools to increase the piezoelectric and ferroelectric properties in addition to new chemical compositions.Powders of pure BNKT16(Bi0.5(Na0.84K0.16)0.5TiO3)phase were synthesized by sol–gel method with a low crystallization temperature(750℃).Ceramic samples were sintered by pressureless sintering(PLS),sinter-forging(SF),and spark plasma sintering(SPS)techniques.Structural,morphological,and chemical characterizations were performed by XRD,Raman,EDS,and SEM.Sintered samples by PLS and SF exhibit rod-like grains associated to bismuth volatility.The highest remanent polarization(11.05μC/cm2),coercive field(26.2 kV/mm),and piezoelectric coefficient(165 pC/N)were obtained for SF sample.The piezoresponse force microscopy(PFM)analysis shows that the crystallites at the nanoscale exhibit piezoelectric phenomenon and the highest piezoelectric response is reported for PLS sample.The presence of the rhombohedral phase,the increase in grain and crystallite size,and the oriented rod-like inclusions favoring the crystallographic texture are facts that enhance the piezoelectric coefficient for BNKT16 piezoceramics.展开更多
Multiferroic materials with two or more types of ferroic orders have attracted a great deal of atten- tion in the last decade for their magnetoelectric coupling, and new ideas and concepts have been ex- plored recentl...Multiferroic materials with two or more types of ferroic orders have attracted a great deal of atten- tion in the last decade for their magnetoelectric coupling, and new ideas and concepts have been ex- plored recently to develop multiferroic materials at nano-scale. Motivated by theoretical analysis, we synthesized single-phase BiFeO3 （BFO） nanofibers, Pb（Zr0.52Ti0.48）O3-CoFe2O4 （PZT-CFO） and Pb（Zro.52Tio.ns）Oa-NiFe204 （PZT-NFO） composite nanofibers, and CoFe2O4-Pb（Zr0.52Ti0.48）O3 （CFO-PZT） core-shell nanofibers using sol-gel based electrospinning. These nanofibers typically have diameters in the range of a few hundred nanometers and grain size in the range of 10s nanome- ters, and exhibits both ferroelectric and ferromagnetic properties. Piezoresponse force microscopy （PFM） based techniques have also been developed to examine the magnetoelectrie coupling of the nanofibers, which is estimated to be two orders of magnitude higher than that of thin films, con- sistent with our theoretical analysis. These nanofibers are promising for a variety of multiferroic applications.展开更多
Polarization switching in lead-free(K0.40Na0.60)NbO3(KNN)single crystals was studied by switching spectroscopy piezoresponse force microscopy(SS-PFM).Acquisition of multiple hysteresis loops on a closely spaced square...Polarization switching in lead-free(K0.40Na0.60)NbO3(KNN)single crystals was studied by switching spectroscopy piezoresponse force microscopy(SS-PFM).Acquisition of multiple hysteresis loops on a closely spaced square grid enables polarization switching parameters to be mapped in real space.Piezoresponse amplitude and phase hysteresis loops show collective symmetric/asymmetric characteristics,affording information regarding the switching behavior of different domains.As such,the out-of-plane polarization states of the domains,including amplitudes and phases can be determined.Our results could contribute to a further understanding of the relationships between polarization switching and polarization vectors at the nanoscale,and provide a feasible method to correlate the polarization hysteresis loops in a domain under an electric field with the polarization vector states.展开更多
In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage ...In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4 × 10^-6A/cm^2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3 film further.展开更多
Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett(LB)film results in severe space scatter in electrical,ferroelectric and piezoelectric characteristics,thus limiting the nanoscale res...Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett(LB)film results in severe space scatter in electrical,ferroelectric and piezoelectric characteristics,thus limiting the nanoscale research and reliability of nano-devices.However,no effective method aiming at large-area uniform organic ferroelectric LB film has ever been reported to date.Herein,we present a facile hot-pressing strategy to prepare relatively large-area poly(vinylidene fluoride)(PVDF)LB film with ultra-smooth surface root mean square(RMS)roughness is 0.3 nm in a 30μm×30μm area comparable to that of metal substrate,which maximized the potential of LB technique to control thickness distribution.More importantly,compared with traditionally annealed LB film,the hot-pressed LB film manifests significantly improved structure uniformity,less fluctuation in ferroelectric characteristics and higher dielectric and piezoelectric responses,owing to the uniform dipole orientation and higher crystalline quality.Besides,different surface charge relaxation behaviors are investigated and the underlying mechanisms are explained in the light of the interplay of surface charge and polarization charge in the case of nanoscale non-uniform switching.We believe that our work not only presents a novel strategy to endow PVDF LB film with unprecedented reliability and improved performance as a competitive candidate for future ferroelectric tunnel junctions(FTJs)and nano electro mechanical systems(NEMS),but also reveals an attracting coupling effect between the surface potential distribution and nanoscale non-uniform switching behavior,which is crucial for the understanding of local transport characterization modulated by band structure,bit signal stability for data-storage application and the related surface charge research,such as charge gradient microscopy(CGM)based on the collection of surface charge on the biased ferroelectric domains.展开更多
BiFeO_(3),a room-temperature multiferroic material,has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping.In this work,12%Smdoped Bi...BiFeO_(3),a room-temperature multiferroic material,has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping.In this work,12%Smdoped BiFeO_(3)epitaxial thin films were fabricated on Nb-doped SrTiO_(3)(001)single crystal substrates via sol-gel method.The epitaxy was verified by reciprocal space mapping(RSM)and transmission electron microscope(TEM).The TEM results indicated the coexistence of R3c and Pbam phases in the film.The domains and piezoelectric properties from room temperature to 200℃were characterized by piezoresponse force microscopy(PFM).Domains became active from 110℃to 170℃,and domain configurations changed obviously.A partially fading piezoresponse indicated the emergence of antiferroelectric Pbam.The in-situ domain analysis suggested that the phase transition was accompanied by domain wall motion.Switching spectroscopy PFM(SS-PFM)was further conducted to investigate the piezoresponse during the phase transition.Anomalous responses were found in both ON and OFF states at 170℃,and the film exhibits typical antiferroelectric behavior at 200℃,implying that the completion of phase transition and structure turned to the Pbam phase.This work revealed the origin of the high piezoresponse of Sm-doped BiFeO_(3)thin films at the morphotropic phase boundary(MPB).展开更多
The switching process of ferroelectric thin films in electronic devices is one of the most important requirements for their application. Especially for the different external fields acting on the film surface, the mec...The switching process of ferroelectric thin films in electronic devices is one of the most important requirements for their application. Especially for the different external fields acting on the film surface, the mechanism of domain switching is more complicated. Here we observe the nanoscale domain switchings of Bi3.15Eu0.85Ti3O12 thin film under different mechanical forces at a fast scan rate. As the force increases from initial state to 247.5 n N, the original bright or grey contrasts within the selected grains are all changed into dark contrasts corresponding to the polarization vectors reversed from the up state to the down state, except for the clusters. As the mechanical force increases to 495 n N, the color contrasts in all of the selected grains further turn into grey contrasts and some are even changed into grey contrasts completely showing the typical 90° domain switching. When another stronger loading force 742.5 n N is applied, the phase image becomes unclear and it indicates that the piezoelectric signal can be suppressed under a sufficiently high force, which is coincident with previous experimental results. Furthermore, we adopt the domain switching criterion from the perspective of equilibrium state free energy of ferroelectric nanodomain to explain the mechanisms of force-generated domain switchings.展开更多
Alginate biopolymer from Tropicalgin C302245 was studied by means of piezoresponse force microscopy imaging, scanning electron microscopy, powder X-rays, infrared spectroscopy and computer simulations. Local piezoresp...Alginate biopolymer from Tropicalgin C302245 was studied by means of piezoresponse force microscopy imaging, scanning electron microscopy, powder X-rays, infrared spectroscopy and computer simulations. Local piezoresponse force microscopy images show possible ferroelectric domains detected in the out of plane mode and these results are confirmed by the second harmonic generation analysis. Alginate powder is composed by diatom frustules containing a cristobalite-like compound, amorphous silica and chitin. The experimental results are explained by MM+ and PM3 computer simulations that establish that the self-assembly of the alginate molecules enhance the polarization increasing the molecular collective dipole moment. Alginate molecular properties might open interesting possibilities for organic technological applications.展开更多
Sr0.6 Ba0.4 Nb2 O6 micro-rods are prepared by the molten-salt method with K2 SO4,KCl-K2 SO4,and KCl as fluxes.It reveals that the Sr0.6 Ba0.4 Nb2 O6 synthesized with KCl as a flux exhibits a single phase with tetragon...Sr0.6 Ba0.4 Nb2 O6 micro-rods are prepared by the molten-salt method with K2 SO4,KCl-K2 SO4,and KCl as fluxes.It reveals that the Sr0.6 Ba0.4 Nb2 O6 synthesized with KCl as a flux exhibits a single phase with tetragonal tungsten bronze structure.The measurement of X-ray diffraction indicates that the Sr0.6 Ba0.4 Nb2 O6 micro-rods synthesized at 1 300℃are anisotropic.The morphology of the powers is examined by transmission electron microscope.It reveals that the length-diameter ratio of Sr0.6 Ba0.4 Nb2 O6 micro-rods increases with increasing annealing temperature from 900℃to 1 300℃.At 1 300℃,the rod possesses a large length-diameter ratio of 8∶1.Moreover,the analysis of the piezoelectric properties of single micro-rods using apiezo-response force microscope indicates that the domains of the material are arranged along its radial direction.展开更多
Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected...Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy(PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure,with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39 × 10^(-4) A·cm^(-2) at 2 V,with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.展开更多
Sol-gel based soft lithography technique has been developed to pattern a variety of ferroelectric Pb（Zr0.52Ti0.48）O3（PZT） microstructures,with feature size approaching 180 nm and good pattern transfer between the ...Sol-gel based soft lithography technique has been developed to pattern a variety of ferroelectric Pb（Zr0.52Ti0.48）O3（PZT） microstructures,with feature size approaching 180 nm and good pattern transfer between the master mold and patterned films.X-ray diffraction and high-resolution transmission electron microscopy confirm the perovskite structure of the patterned PZT.Piezoresponse force microscopy（PFM） and switching spectroscopy piezoresponse force microscopy（SSPFM） confirm their piezoelectricity and ferroelectricity.Piezoresponse as high as 2.75 nm has been observed,comparable to typical PZT films.The patterned PZT microstructures are promising for a wide range of device applications.展开更多
The controllable manipulation of polar topological structures(e.g.skyrmion bubble)in ferroelectric materials have been considered as a cornerstone for future programmable nano-electronics.Here,we present the effective...The controllable manipulation of polar topological structures(e.g.skyrmion bubble)in ferroelectric materials have been considered as a cornerstone for future programmable nano-electronics.Here,we present the effective creation and erasure of polar bubble states PbTiO_(3)(PTO)multilayers trigged by mechanical stress and light illumination,respectively.It was found that applying atomic force microscope(AFM)tip force can induced formation of nanoscale bubble domains from the initial monodomain state.Moreover,the created bubble domain can be eliminated by exposure to ultraviolet or infrared light illumination.The above results can be understood by modulation of depolarization screening charges and bias fields,as reflected by scanning Kelvin potential microscopic(SKPM)observations,whereby the flexoelectric effect from the tip force tends to remove the screening charges on top surface and modulate the bias field that favors the formation of bubble state while light illumination tends to recover the screen charges and favor the monodomain state.The results provide a good example for multi-field manipulation of polar topologies,which might create a new avenue towards the immerging new concept electronic devices.展开更多
在原子力显微镜(Atomic force microscope,AFM)基础上发展起来的扫描探针显微术(Scanning probe microscope,SPM)已成为推动当今纳米科学发展的最重要技术,综述了在商用AFM平台上所发展的超高分辨压电响应力显微术(PFM)、低频高分辨扫...在原子力显微镜(Atomic force microscope,AFM)基础上发展起来的扫描探针显微术(Scanning probe microscope,SPM)已成为推动当今纳米科学发展的最重要技术,综述了在商用AFM平台上所发展的超高分辨压电响应力显微术(PFM)、低频高分辨扫描探针声学显微术(SPAM)、三倍频双探针扫描热学显微术(3ω-STh M)等先进扫描探针显微术的工作原理及其应用研究,显示了该先进扫描探针显微术在纳米结构及其与外场互作用的机电、弹性、热学、热电等综合物理特性原位表征的重要潜力。展开更多
BiFeO_(3)-BaTiO_(3) based ceramics are considered to be the most promising lead-free piezoelectric ceramics due to their large piezoelectric response and high Curie temperature.Since the piezoelectric response of piez...BiFeO_(3)-BaTiO_(3) based ceramics are considered to be the most promising lead-free piezoelectric ceramics due to their large piezoelectric response and high Curie temperature.Since the piezoelectric response of piezoelectric ceramics just appears after poling engineering,in this work,the domain evolution and microscopic piezoresponse were observed in-situ using piezoresponse force microscopy(PFM)and switching spectroscopy piezoresponse force microscopy(SS-PFM),which can effectively study the local switching characteristics of ferroelectric materials especially at the nanoscale.The new domain nucleation preferentially forms at the boundary of the relative polarization region and expands laterally with the increase of bias voltage and temperature.The maximum piezoresponse(Rs),remnant piezoresponse(Rrem),maximum displacement(Dmax)and negative displacement(Dneg)at 45 V and 120C reach 122,69,127 pm and 75 pm,respectively.Due to the distinct effect of poling engineering in full domain switching,the corresponding d33 at 50 kV/cm and 120C reaches a maximum of 205 pC/N,which is nearly twice as high as that at room temperature.Studying the evolution of ferroelectric domains in the poling engineering of BiFeO_(3)-BaTiO_(3)ceramics provides an insight into the relationship between domain structure and piezoelectric response,which has implications for other piezoelectric ceramics as well.展开更多
Piezoelectricity is the electric charge which accumulates in certain materials in response to mechanical stimuli,while piezoelectric nanogenerators(PENGs)converting mechanical energy into electricity can be widely use...Piezoelectricity is the electric charge which accumulates in certain materials in response to mechanical stimuli,while piezoelectric nanogenerators(PENGs)converting mechanical energy into electricity can be widely used for energy harvesting and self-powered systems.The group IV-VI monochalcogenides may exhibit strong piezoelectricity because of their puckered C_(2v)symmetry and electronic structure,making them promising for flexible PENG.Herein,we investigated the synthesis and piezoelectric properties of multilayer SnSe nanosheets grown by chemical vapor deposition(CVD).The SnSe nanosheets exhibited high single-crystallinity,large area,and good stability.The strong layer-dependent in-plane piezoelectric coefficient of SnSe nanosheets showed a saturated trend to be~110 pm/V,which overcomes the weak piezoelectric response or odd-even effects in other layered nanosheets.A high energy conversion efficiency of 9.3%and a maximum power density of 538 mW/cm^(2)at 1.03%strain have been demonstrated in a SnSe-based PENG.Based on the enhanced piezoelectricity of SnSe and attractive output performance of the nanogenerator,a self-powered sensor for human motion monitoring is further developed.These results demonstrate the strong piezoelectricity in high quality CVD-grown SnSe nanosheets,allowing for application in flexible smart piezoelectric sensors and advanced microelectromechanical devices.展开更多
Piezoresponse force microscopy(PFM)has emerged as one of the most powerful techniques to probe ferroelectric materials at the nanoscale,yet it has been increasingly recognized that piezoresponse measured by PFM is oft...Piezoresponse force microscopy(PFM)has emerged as one of the most powerful techniques to probe ferroelectric materials at the nanoscale,yet it has been increasingly recognized that piezoresponse measured by PFM is often influenced by electrostatic interactions.In this letter,we report a capacitive excitation PFM(ce-PFM)to minimize the electrostatic interactions.The effectiveness of ce-PFM in minimizing electrostatic interactions is demonstrated by comparing the piezoresponse and the effective piezoelectric coefficient measured by ce-PFM and conventional PFM.The effectiveness is further confirmed through the ferroelectric domain pattern imaged via ce-PFM and conventional PFM in vertical modes,with the corresponding domain contrast obtained by ce-PFM is sharper than conventional PFM.These results demonstrate ce-PFM as an effective tool to minimize the interference from electrostatic interactions and to image ferroelectric domain pattern,and it can be easily implemented in conventional atomic force microscope(AFM)setup to probe true piezoelectricity at the nanoscale.展开更多
Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric ...Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric materials can also generate the“hysteresis-loop-like”responses from the PFS measurements due to many other factors such as electrostatic effects.This work therefore studies the signal of the contact resonance frequency during the PFS measurements.By comparing the results from ferroelectric and non-ferroelectric materials,it is found there are distinct differences between these two types of materials in the variation of the contact resonance frequency during the PFS measurements.A momentary and sharp increase of the contact resonance frequency occurs when the domain is switched by applying the DC bias,which can be regarded as a unique characteristic for the ferroelectric materials.After analyzing the reliability and mechanism of this method,it is proposed that the contact resonance frequency variation at the coercive bias is capable to differentiate the electromechanical responses of the ferroelectric and non-ferroelectric materials during the PFS measurements.展开更多
基金CONACYT grant A1-S-9232CONACYT for the Ph.D. scholarship
文摘In the search of lead-free piezoelectric materials,ceramic processing techniques offer potential tools to increase the piezoelectric and ferroelectric properties in addition to new chemical compositions.Powders of pure BNKT16(Bi0.5(Na0.84K0.16)0.5TiO3)phase were synthesized by sol–gel method with a low crystallization temperature(750℃).Ceramic samples were sintered by pressureless sintering(PLS),sinter-forging(SF),and spark plasma sintering(SPS)techniques.Structural,morphological,and chemical characterizations were performed by XRD,Raman,EDS,and SEM.Sintered samples by PLS and SF exhibit rod-like grains associated to bismuth volatility.The highest remanent polarization(11.05μC/cm2),coercive field(26.2 kV/mm),and piezoelectric coefficient(165 pC/N)were obtained for SF sample.The piezoresponse force microscopy(PFM)analysis shows that the crystallites at the nanoscale exhibit piezoelectric phenomenon and the highest piezoelectric response is reported for PLS sample.The presence of the rhombohedral phase,the increase in grain and crystallite size,and the oriented rod-like inclusions favoring the crystallographic texture are facts that enhance the piezoelectric coefficient for BNKT16 piezoceramics.
文摘Multiferroic materials with two or more types of ferroic orders have attracted a great deal of atten- tion in the last decade for their magnetoelectric coupling, and new ideas and concepts have been ex- plored recently to develop multiferroic materials at nano-scale. Motivated by theoretical analysis, we synthesized single-phase BiFeO3 （BFO） nanofibers, Pb（Zr0.52Ti0.48）O3-CoFe2O4 （PZT-CFO） and Pb（Zro.52Tio.ns）Oa-NiFe204 （PZT-NFO） composite nanofibers, and CoFe2O4-Pb（Zr0.52Ti0.48）O3 （CFO-PZT） core-shell nanofibers using sol-gel based electrospinning. These nanofibers typically have diameters in the range of a few hundred nanometers and grain size in the range of 10s nanome- ters, and exhibits both ferroelectric and ferromagnetic properties. Piezoresponse force microscopy （PFM） based techniques have also been developed to examine the magnetoelectrie coupling of the nanofibers, which is estimated to be two orders of magnitude higher than that of thin films, con- sistent with our theoretical analysis. These nanofibers are promising for a variety of multiferroic applications.
基金This work was supported by Science Challenge Project(No.TZ2018003)National Natural Science Foundation of China(Grant Nos.51822206 and 5171101344).
文摘Polarization switching in lead-free(K0.40Na0.60)NbO3(KNN)single crystals was studied by switching spectroscopy piezoresponse force microscopy(SS-PFM).Acquisition of multiple hysteresis loops on a closely spaced square grid enables polarization switching parameters to be mapped in real space.Piezoresponse amplitude and phase hysteresis loops show collective symmetric/asymmetric characteristics,affording information regarding the switching behavior of different domains.As such,the out-of-plane polarization states of the domains,including amplitudes and phases can be determined.Our results could contribute to a further understanding of the relationships between polarization switching and polarization vectors at the nanoscale,and provide a feasible method to correlate the polarization hysteresis loops in a domain under an electric field with the polarization vector states.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61471301,61078057,51202195,and 511172183)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20126102110045)the NPU Foundation for Fundamental Research(Grant Nos.JC201155,JC201271,and JC20120246)
文摘In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4 × 10^-6A/cm^2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3 film further.
基金supported by the National Natural Science Foundation of China(51625202)the National Key Research&Development Program of China(2017YFB0701603)。
文摘Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett(LB)film results in severe space scatter in electrical,ferroelectric and piezoelectric characteristics,thus limiting the nanoscale research and reliability of nano-devices.However,no effective method aiming at large-area uniform organic ferroelectric LB film has ever been reported to date.Herein,we present a facile hot-pressing strategy to prepare relatively large-area poly(vinylidene fluoride)(PVDF)LB film with ultra-smooth surface root mean square(RMS)roughness is 0.3 nm in a 30μm×30μm area comparable to that of metal substrate,which maximized the potential of LB technique to control thickness distribution.More importantly,compared with traditionally annealed LB film,the hot-pressed LB film manifests significantly improved structure uniformity,less fluctuation in ferroelectric characteristics and higher dielectric and piezoelectric responses,owing to the uniform dipole orientation and higher crystalline quality.Besides,different surface charge relaxation behaviors are investigated and the underlying mechanisms are explained in the light of the interplay of surface charge and polarization charge in the case of nanoscale non-uniform switching.We believe that our work not only presents a novel strategy to endow PVDF LB film with unprecedented reliability and improved performance as a competitive candidate for future ferroelectric tunnel junctions(FTJs)and nano electro mechanical systems(NEMS),but also reveals an attracting coupling effect between the surface potential distribution and nanoscale non-uniform switching behavior,which is crucial for the understanding of local transport characterization modulated by band structure,bit signal stability for data-storage application and the related surface charge research,such as charge gradient microscopy(CGM)based on the collection of surface charge on the biased ferroelectric domains.
基金This work was supported by the National Nature Science Foundation of China(Grants no.51332002,11374174,51390471,51527803 and 51221291)the Ministry of Science and Technology of China under Grant 2015CB654605,National 973 Project of China(2015CB654902)+1 种基金National key research and development program(2016YFB0700402)This work made use of the resources of the National Center for Electron Microscopy in Beijing and the BL14B1 beamline of the Shanghai Synchrotron Radiation Facility under project no.14SRBL14B10499.
文摘BiFeO_(3),a room-temperature multiferroic material,has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping.In this work,12%Smdoped BiFeO_(3)epitaxial thin films were fabricated on Nb-doped SrTiO_(3)(001)single crystal substrates via sol-gel method.The epitaxy was verified by reciprocal space mapping(RSM)and transmission electron microscope(TEM).The TEM results indicated the coexistence of R3c and Pbam phases in the film.The domains and piezoelectric properties from room temperature to 200℃were characterized by piezoresponse force microscopy(PFM).Domains became active from 110℃to 170℃,and domain configurations changed obviously.A partially fading piezoresponse indicated the emergence of antiferroelectric Pbam.The in-situ domain analysis suggested that the phase transition was accompanied by domain wall motion.Switching spectroscopy PFM(SS-PFM)was further conducted to investigate the piezoresponse during the phase transition.Anomalous responses were found in both ON and OFF states at 170℃,and the film exhibits typical antiferroelectric behavior at 200℃,implying that the completion of phase transition and structure turned to the Pbam phase.This work revealed the origin of the high piezoresponse of Sm-doped BiFeO_(3)thin films at the morphotropic phase boundary(MPB).
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51272158 and 11302185)the Scientific Research Fund of Hunan Provincial Education Department,China(Grant No.13C901)the Hunan Provincial Natural Science Foundation,China(Grant Nos.14JJ3081 and 13JJ1019)
文摘The switching process of ferroelectric thin films in electronic devices is one of the most important requirements for their application. Especially for the different external fields acting on the film surface, the mechanism of domain switching is more complicated. Here we observe the nanoscale domain switchings of Bi3.15Eu0.85Ti3O12 thin film under different mechanical forces at a fast scan rate. As the force increases from initial state to 247.5 n N, the original bright or grey contrasts within the selected grains are all changed into dark contrasts corresponding to the polarization vectors reversed from the up state to the down state, except for the clusters. As the mechanical force increases to 495 n N, the color contrasts in all of the selected grains further turn into grey contrasts and some are even changed into grey contrasts completely showing the typical 90° domain switching. When another stronger loading force 742.5 n N is applied, the phase image becomes unclear and it indicates that the piezoelectric signal can be suppressed under a sufficiently high force, which is coincident with previous experimental results. Furthermore, we adopt the domain switching criterion from the perspective of equilibrium state free energy of ferroelectric nanodomain to explain the mechanisms of force-generated domain switchings.
文摘Alginate biopolymer from Tropicalgin C302245 was studied by means of piezoresponse force microscopy imaging, scanning electron microscopy, powder X-rays, infrared spectroscopy and computer simulations. Local piezoresponse force microscopy images show possible ferroelectric domains detected in the out of plane mode and these results are confirmed by the second harmonic generation analysis. Alginate powder is composed by diatom frustules containing a cristobalite-like compound, amorphous silica and chitin. The experimental results are explained by MM+ and PM3 computer simulations that establish that the self-assembly of the alginate molecules enhance the polarization increasing the molecular collective dipole moment. Alginate molecular properties might open interesting possibilities for organic technological applications.
基金supported by the National Natural Science Foundation of China(No.11475086)
文摘Sr0.6 Ba0.4 Nb2 O6 micro-rods are prepared by the molten-salt method with K2 SO4,KCl-K2 SO4,and KCl as fluxes.It reveals that the Sr0.6 Ba0.4 Nb2 O6 synthesized with KCl as a flux exhibits a single phase with tetragonal tungsten bronze structure.The measurement of X-ray diffraction indicates that the Sr0.6 Ba0.4 Nb2 O6 micro-rods synthesized at 1 300℃are anisotropic.The morphology of the powers is examined by transmission electron microscope.It reveals that the length-diameter ratio of Sr0.6 Ba0.4 Nb2 O6 micro-rods increases with increasing annealing temperature from 900℃to 1 300℃.At 1 300℃,the rod possesses a large length-diameter ratio of 8∶1.Moreover,the analysis of the piezoelectric properties of single micro-rods using apiezo-response force microscope indicates that the domains of the material are arranged along its radial direction.
基金supported by the National Natural Science Foundation of China(Grant No.61471301)Natural Science Basic Research Program of Shaanxi,China(Grant No.2017JQ5083)PhD Research Startup Foundation of Xi’an University of Science and Technology,China(Grant No.2017QDJ044)
文摘Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy(PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure,with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39 × 10^(-4) A·cm^(-2) at 2 V,with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.
基金support from National Natural Science Foundation of China (Grant Nos. 10772155,10732100 and 10902095)the Provincial Natural Science Foundation of Hunan Province, China (Grant Nos.07JJ1008 and 09JJ7004)+2 种基金the Scientific Research Fund of Hunan Provincial Education Department (Grant No.08C864)The Asylum Research MFP-3D Atomic Force Microscope was acquired through an ARO DURIP grant(W911NF-08-01-0262)support from US National Science Foundation (DMR 0706100 and OS)
文摘Sol-gel based soft lithography technique has been developed to pattern a variety of ferroelectric Pb（Zr0.52Ti0.48）O3（PZT） microstructures,with feature size approaching 180 nm and good pattern transfer between the master mold and patterned films.X-ray diffraction and high-resolution transmission electron microscopy confirm the perovskite structure of the patterned PZT.Piezoresponse force microscopy（PFM） and switching spectroscopy piezoresponse force microscopy（SSPFM） confirm their piezoelectricity and ferroelectricity.Piezoresponse as high as 2.75 nm has been observed,comparable to typical PZT films.The patterned PZT microstructures are promising for a wide range of device applications.
基金the financial support from the National Key Research and Development Programs of China(Grant Nos.2022YFB3807603)National Natural Science Foundation of China(Grant Nos.92163210,11674108,52002134,U22A20117)+2 种基金Funding by Science and Technology Projects in Guangzhou(202201000008)the Science and Technology Planning Project of Guangdong Province(No.2019KQNCX028)the Natural Science Foundation of South China Normal University(No.19KJ01).
文摘The controllable manipulation of polar topological structures(e.g.skyrmion bubble)in ferroelectric materials have been considered as a cornerstone for future programmable nano-electronics.Here,we present the effective creation and erasure of polar bubble states PbTiO_(3)(PTO)multilayers trigged by mechanical stress and light illumination,respectively.It was found that applying atomic force microscope(AFM)tip force can induced formation of nanoscale bubble domains from the initial monodomain state.Moreover,the created bubble domain can be eliminated by exposure to ultraviolet or infrared light illumination.The above results can be understood by modulation of depolarization screening charges and bias fields,as reflected by scanning Kelvin potential microscopic(SKPM)observations,whereby the flexoelectric effect from the tip force tends to remove the screening charges on top surface and modulate the bias field that favors the formation of bubble state while light illumination tends to recover the screen charges and favor the monodomain state.The results provide a good example for multi-field manipulation of polar topologies,which might create a new avenue towards the immerging new concept electronic devices.
基金supported by the National Natural Science Foundation of China(52072028 and 52032007)the National Key Research and Development Program(2022YFB3807400).
文摘BiFeO_(3)-BaTiO_(3) based ceramics are considered to be the most promising lead-free piezoelectric ceramics due to their large piezoelectric response and high Curie temperature.Since the piezoelectric response of piezoelectric ceramics just appears after poling engineering,in this work,the domain evolution and microscopic piezoresponse were observed in-situ using piezoresponse force microscopy(PFM)and switching spectroscopy piezoresponse force microscopy(SS-PFM),which can effectively study the local switching characteristics of ferroelectric materials especially at the nanoscale.The new domain nucleation preferentially forms at the boundary of the relative polarization region and expands laterally with the increase of bias voltage and temperature.The maximum piezoresponse(Rs),remnant piezoresponse(Rrem),maximum displacement(Dmax)and negative displacement(Dneg)at 45 V and 120C reach 122,69,127 pm and 75 pm,respectively.Due to the distinct effect of poling engineering in full domain switching,the corresponding d33 at 50 kV/cm and 120C reaches a maximum of 205 pC/N,which is nearly twice as high as that at room temperature.Studying the evolution of ferroelectric domains in the poling engineering of BiFeO_(3)-BaTiO_(3)ceramics provides an insight into the relationship between domain structure and piezoelectric response,which has implications for other piezoelectric ceramics as well.
基金supported by the grants from Research Grants Council of Hong Kong(Nos.GRF PolyU 153025/19P,SRFS2122-5S02,and AoE/P-701/20)PolyU Otto Poon Charitable Foundation Research Institute for Smart Energy(No.Q-CDBD).
文摘Piezoelectricity is the electric charge which accumulates in certain materials in response to mechanical stimuli,while piezoelectric nanogenerators(PENGs)converting mechanical energy into electricity can be widely used for energy harvesting and self-powered systems.The group IV-VI monochalcogenides may exhibit strong piezoelectricity because of their puckered C_(2v)symmetry and electronic structure,making them promising for flexible PENG.Herein,we investigated the synthesis and piezoelectric properties of multilayer SnSe nanosheets grown by chemical vapor deposition(CVD).The SnSe nanosheets exhibited high single-crystallinity,large area,and good stability.The strong layer-dependent in-plane piezoelectric coefficient of SnSe nanosheets showed a saturated trend to be~110 pm/V,which overcomes the weak piezoelectric response or odd-even effects in other layered nanosheets.A high energy conversion efficiency of 9.3%and a maximum power density of 538 mW/cm^(2)at 1.03%strain have been demonstrated in a SnSe-based PENG.Based on the enhanced piezoelectricity of SnSe and attractive output performance of the nanogenerator,a self-powered sensor for human motion monitoring is further developed.These results demonstrate the strong piezoelectricity in high quality CVD-grown SnSe nanosheets,allowing for application in flexible smart piezoelectric sensors and advanced microelectromechanical devices.
基金We acknowledge the National Key Research and Development Program of China(Grant 2016YFA0201001)the National Natural Science Foundation of China(Grants 11372268,11627801,and 1472236)+2 种基金Unite State National Science Foundation(Grant CBET-1435968)the Leading Talents Program of Guangdong Province(Grant 2016LJ06C372)Shenzhen Science and Technology Innovation Committee(Grant KQJSCX20170331162214306).
文摘Piezoresponse force microscopy(PFM)has emerged as one of the most powerful techniques to probe ferroelectric materials at the nanoscale,yet it has been increasingly recognized that piezoresponse measured by PFM is often influenced by electrostatic interactions.In this letter,we report a capacitive excitation PFM(ce-PFM)to minimize the electrostatic interactions.The effectiveness of ce-PFM in minimizing electrostatic interactions is demonstrated by comparing the piezoresponse and the effective piezoelectric coefficient measured by ce-PFM and conventional PFM.The effectiveness is further confirmed through the ferroelectric domain pattern imaged via ce-PFM and conventional PFM in vertical modes,with the corresponding domain contrast obtained by ce-PFM is sharper than conventional PFM.These results demonstrate ce-PFM as an effective tool to minimize the interference from electrostatic interactions and to image ferroelectric domain pattern,and it can be easily implemented in conventional atomic force microscope(AFM)setup to probe true piezoelectricity at the nanoscale.
基金the financial support by Ministry of Education,Singapore,through National University of Singapore(NUS)under the Academic Research Fund(ARF)of grant number R-265-000-596-112the post-graduate scholarship provide by NUSthe support for post-doctoral research fellow from ARF of R-265-000-596-112 by Ministry of Education,Singapore.
文摘Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric materials can also generate the“hysteresis-loop-like”responses from the PFS measurements due to many other factors such as electrostatic effects.This work therefore studies the signal of the contact resonance frequency during the PFS measurements.By comparing the results from ferroelectric and non-ferroelectric materials,it is found there are distinct differences between these two types of materials in the variation of the contact resonance frequency during the PFS measurements.A momentary and sharp increase of the contact resonance frequency occurs when the domain is switched by applying the DC bias,which can be regarded as a unique characteristic for the ferroelectric materials.After analyzing the reliability and mechanism of this method,it is proposed that the contact resonance frequency variation at the coercive bias is capable to differentiate the electromechanical responses of the ferroelectric and non-ferroelectric materials during the PFS measurements.
