Search

BaTiO3 thin films emerge as a highly promising material platform for integrated photonics due to their outstanding electro‐optic properties and diverse functionalities. Despite extensive studies, there remains a notable gap in the understanding of the intricate relationship between the phase structure, domain switching kinetics and electro‐optic performance of these materials. By controlling the structural phase evolution, it is possible to gain deep insights into the physical mechanisms underlying the electro‐optic performance. Here, the phase constitution of BaTiO3 epitaxial thin films is successfully tuned by the insertion of a GdScO3 buffer layer. Continuous polarization rotation paths are observed from an out‐of‐plane tetragonal‐like phase, to an intermediate rhombohedral‐like phase, and finally an in‐plane tetragonal‐like phase, achieving an enhanced effective electro‐optic coefficient of 175 pm V−1 compared to unbuffered films. Furthermore, by in situ second harmonic generation microscopy and electro‐optic measurements, the domain switching behaviors in both statistical and spatially resolved manners are examined, resulting in a clear delineation of the key domain nucleation processes. The in‐depth explorations of these structural mechanisms and kinetics inform the rational design of strong electro‐optic thin films and help in the realization of high‐performance integrated photonic devices such as electro‐optic modulators and multilevel phase shifters. [ABSTRACT FROM AUTHOR]

Ferroelectric domain walls (DWs) are an important feature of ferroelectric materials and play a vital role in the ferroelectric materials, where charged DWs are a focus of extensive research due to their unique interfacial properties. Herein, epitaxial (K,Na)NbO3 (KNN)‐based thin films are prepared by a sol–gel method, and the monoclinic MC structure of the thin film is confirmed. Stripe‐shaped domain patterns with head‐to‐head and tail‐to‐tail charged DWs in the (110)pc and (1¯10)pc planes are observed in the KNN‐based epitaxial thin film. Although the screening of the bound charges in the charged DWs inevitably increases the energy of the system, the charged DWs in the KNN‐based epitaxial thin film are stabilized by the lattice mismatch strain between the thin film and the substrate. These interesting findings should shed light on the exploration of the functional charged DWs by strain engineering. [ABSTRACT FROM AUTHOR]

The orientation modulation of ferroelectric materials is a suitable method to optimize material performance. Textured Bi1‐xSmxFeO3 thin films (near the rhombohedral‐orthorhombic (R‐O) phase boundary, that is, x = 0, 0.1, 0.12, 0.14, and 0.16) were fabricated using the sol‐gel process by introducing a LaNiO3 (LNO) seed layer. Structural and ferroelectric characterizations were used to investigate the effect of texturing on the Sm doping‐induced R‐O phase transition of the BiFeO3 thin films. It was found that a phase transition occurred from the rhombohedral to the orthorhombic structure with increasing Sm content in the nontextured polycrystalline films, resulting in an R‐O phase boundary at x = 0.12. In contrast, the R‐O phase boundary in the textured films was more diffuse, indicating a two‐phase coexistence in a boarder range of Sm doping levels (x = 0.12‐0.16). This discrepancy was attributed to the complexity of the stress status in thin films. The dielectric and electrical properties of the nontextured and textured samples were investigated. The current study shows that the phase boundary in ferroelectric thin films can be altered by diverse means, thus providing insights into potential applications. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate [Pb(ZrxTi1-x)O3, PZT] thin films with various compositions, whose Zr/Ti ratio were varied as 40/60, 48/52, 47/53, and 60/40, were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel method. A seeding layer was introduced between the PZT layer and the bottom electrode to control the texture of overlaid PZT thin films. A single perovskite PZT thin film with absolute (100) texture was obtained, when lead oxide was used as the seeding crystal, whereas titanium dioxide resulted in highly [111]-oriented PZT films. The dielectric and ferroelectric properties of PZT films with different preferential orientations were evaluated systemically as a function of composition. The maximums of relative dielectric constant were obtained in the morphotropic phase boundary region for both (100)- and (111)-textured PZT films. The ferroelectric properties also greatly depend on films’ texture and composition. The intrinsic and extrinsic contributions to dielectric and ferroelectric properties were discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

(K,Na)NbO3 (KNN) is a promising lead‐free ferroelectric/piezoelectric system, to which incorporating BaZrO3 can greatly enhance its piezoelectricity, but the mechanism is not clear. This work was conducted to investigate the phase transition in the BaZrO3‐modifed KNN system and its contribution to piezoelectricity enhancement, using thin films with a fixed orientation and high compositional homogeneity fabricated by a sol‐gel method. Two ferroelectric‐to‐ferroelectric phase transitions are revealed, which correspond to monoclinic MC‐ MA phase transition at higher temperature and rhombohedral‐monoclinic MC phase transition at lower temperature. It is difficult to distinguish these phases in KNN‐based bulk materials, but their differences are clear when conducting high‐resolution X‐ray reciprocal space mapping (RSM) on the present thin films. Piezoresponse force microscopy experiments also revealed an interesting finding that local piezoelectricity of monoclinic phases was higher than that of rhombohedral ones in KNN‐based thin films. This work could shed insights on the fundamental understandings for the effect of the chemical doping, and offer guidance for property optimization in the KNN‐based lead‐free piezoelectrics. Phase transition and piezoelectricity were modified in (K,Na)NbO3 based lead‐free piezoelectric thin films, where the R to monoclinic MC phase transition temperature was elevated with increasing BaZrO3 doping levels and the local piezoelectricity reached the maximum value at the phase boundary. [ABSTRACT FROM AUTHOR]

Recently, lead‐free piezoelectric thin films have received increasing attention due to the growing demands for mircoelectromechanical systems and the significant progress in lead‐free piezoelectric research. Here, potassium sodium niobate [(K, Na)NbO3 (KNN)]‐based thin films were fabricated via a sol‐gel method. The effects of pyrolysis temperature on the resulting microstructure and electrical properties of KNN‐based films were investigated. The KNN‐based film pyrolyzed at 550°C and annealed at 700°C shows a dominant (100) orientation with a high texturing degree of 91.7%. The microstructures, morphologies, piezo‐ and ferroelectric properties of the KNN‐based films were discussed in association with different pyrolysis temperatures. The crystallization mechanism of the (100) textured KNN‐based thin films was elaborated in detail. [ABSTRACT FROM AUTHOR]

An enhanced efficiency organic light-emitting device (OLED) with corrugated nanostructures on a small-molecule organic film has been demonstrated. By patterning the hole transport layer via soft nano-imprinting lithography and coating with Ag, a nanostructured cathode is introduced to enhance the light extraction of the OLED without affecting the flatness and conductivity of the indium-tin-oxide film. Both luminance and current efficiency are improved compared with those of conventional planar devices. The observable improvement in luminance and current efficiency can be ascribed to the surface plasmonic and scattering effects caused by the Ag nanostructures. Moreover, theoretical simulations also demonstrate that the power loss to surface plasmon-polariton modes has been recovered. [ABSTRACT FROM AUTHOR]

We report a general approach to the control of grain shape and size in FePt–TiO2 nanocomposite thin films with high anisotropy energy and (001) orientation. By introducing an artificial nucleation layer of different materials (crystalline or amorphous) with different surface free energies (surface effect) and different thicknesses (ultrathin of 0–1 nm) and by separating the film growth process from the nucleation process, it is possible to have individual control over both the nucleation and growth processes. It is found that using crystalline materials of thickness 0–1 nm, such as FePt, having surface free energy of about 2000–3000 erg/cm \(^{2}\) , as the artificial nucleation layer, square-shape FePt grains were observed. The grain size decreases with the increase of sputter power for the artificial nucleation layer. Furthermore, the chemical ordering degree is improved using crystalline nucleation layer, through which more TiO2 can be doped into FePt layer, resulting in even smaller grain size without deteriorating the magnetic properties. While, with amorphous materials of thickness 0–1 nm, such as C, TiO2, and others, having a much smaller surface free energy of 50–100 erg/cm \(^{2}\) , as the artificial nucleation layer, smaller and circular-shape FePt grains were seen. When the thickness of artificial nucleation layer increases, a clear trend of grain size reduction and grain-shape evolution from square/rectangle shape to circular shape were observed. The mechanism for the grain-shape evolution and size control by using an artificial nucleation layer of different materials is discussed with regard to surface/interface effects. The findings offer a general way to the control of grain size and shape in nanostructured magnetic thin film for various applications. [ABSTRACT FROM AUTHOR]

Fine-grained Pb-free (Na0.535K0.485)0.95Li0.05(Nb0.8Ta0.2)O3 (NKLNT) piezoceramics prepared by spark plasma sintering (SPS) technique was used to fabricate NKLNT/epoxy 1-3 composites with a modified dice-fill method. Because of its good machinability, SPSed NKLNT ceramic rods could be miniaturized to a lateral width of 50 lm. After lapping down to 56 μm in thickness, the composite was used to fabricate an ultrasonic transducer as the active piezoelectric element. This composite transducer showed a bandwidth at - 6 dB nearly 90% at a center frequency of 29 MHz, demonstrating that this Pb-free composite thick film is very promising for the fabrication of high-frequency ultrasonic transducers in medical imaging applications. [ABSTRACT FROM AUTHOR]

Abstract: To develop high-performance piezoelectric films on conventional Pt(111)/Ti/SiO2/Si(100) substrates, sol–gel-derived highly [100]-textured Nb-doped Pb(ZrxTi1−x)O3 (PNZT) thin films with different Zr/Ti ratios ranging from 20/80 to 80/20 were prepared and characterized. The phase structure, ferroelectric and piezoelectric properties of the PZNT films were investigated as a function of Zr/Ti ratios, and it was confirmed that there was distinct phase transition of the PNZT system from tetragonal to rhombohedral when the Zr/Ti ratio varied across the morphotropic phase boundary (MPB). The Nb-doped PZT films showed enhanced remanent polarization but reduced coercive field, whose best values reached 75 μC/cm2 and 82 kV/cm, respectively at the composition close to MPB. In addition, the [100]-textured PNZT film at MPB also shows a high piezoelectric coefficient up to 161 pm/V. All these properties are superior to those for undoped PZT films. [Copyright &y& Elsevier]

Lead-free piezoelectric Na0.5K0.5NbO3 (NKN) thin films were prepared via sol-gel processing on both Pt (111)/Ti/SiO2/Si(100) and Si(100) substrates. XRD analysis showed that perovskite structure was achieved after annealing at 800∼900°C. The SEM morphology showed the NKN films with a total thickness of about 0.5 micron had relatively dense and uniform microstructure. Ferroelectric properties of NKN thin films are characterized at room temperature and the P-E hysteresis loop proved the ferroelectricity of the NKN films. The compensation of volatile components can help control the stoichiometry of the films and improve the film quality. [ABSTRACT FROM AUTHOR]

Li and Ti co-doped NiO thin films of 250 nm in thickness were deposited onto Pt/Ti/SiO2/Si(100) substrates using a sol-gel spin-coating method. The effect of Li doping content on microstructure and dielectric properties of the LixTyNi1-x-yO thin films in which the Ti content was fixed at 2 and 20 at% was investigated. All the thin films consisted of a mixture of NiO, NiTiO3, Li2NiO2 and/or LiNiO2 phases and show the high dielectric constant ranged from 235-370 in 100 Hz depending on the proportion of various phases. Excess Li content which results in increasing Li2NiO2 and the formation of LiNiO2 led to decrease the dielectric constant especially for the 2% Ti containing thin films in 100 Hz. The increased NiTiO3 and Li-dissolved Ni(Li)O phases by increasing Ti content from 2 to 20 at% is more beneficial for the formation of the core-shell like microstructure and hence enhancing the dielectric constant. However, the frequency stability of the dielectric constants was lowered by the formation of the excess NiTiO3 phase as Ti content was increased from 2 to 20 at%. The doping content of Li and Ti is necessary to control in an appropriate range in order to obtain the high dielectric property. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) films with composition near the morphotropic phase boundary were fabricated on Pt(111)/Ti/SiO2/Si(100) using sol-gel method, and the pyrolysis temperature effects on the preferential orientation and ferroelectric properties of PZT films were investigated. It has been found that the PZT films pyrolyzed at 450 °C and then annealed at 650 °C shown a dominated (100) orientation, whereas the pyrolysis treatment at lower or higher temperatures favored the (111) orientation. Different pyrolysis temperatures also lead to differences in electrical properties, including dielectric constant, polarization values, leakage current and fatigue behavior. [Copyright &y& Elsevier]

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary region were deposited onto Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates using a sol–gel method. A seeding layer was introduced between the most underlying surface of the PZT film and the platinum electrode surface to control the texture of the PZT thin film. The lead oxide seeding layer resulted in the formation of a single-phase perovskite and absolutely (1 0 0)-textured PZT film. SEM, XRD, XPS, and AES were used to characterize the evolution of the lead oxide layer and the PZT thin films. The growth kinetic mechanism of the (1 0 0)-textured PZT thin films was proposed phenomenologically. The ferroelectric and piezoelectric properties of the PZT films were also evaluated and discussed in association with different preferential orientations. [Copyright &y& Elsevier]

The temperature dependence of the Raman spectra of Bi2Te3 and Bi0.5Sb1.5Te3 thermoelectric films was investigated. The temperature coefficients of the Eg(2) peak positions were determined as -0.0137 cm-1/°C and -0.0156 cm-1/°C, respectively. The thermal expansion of the crystal caused a linear shift of the Raman peak induced by the temperature change. Based on the linear relation, a reliable and noninvasive micro-Raman scattering method was shown to measure the thermal conductivity of the thermoelectric films. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine thin film doped with Fe3O4 has been demonstrated an efficient p-type hole-injection layer (HIL) in organic light-emitting devices (OLEDs). The tris-(8-hydroxyquinoline) aluminum-based OLEDs with the p-type HIL exhibit a very low turn-on voltage of 2.4 V and a high luminance of 29 360 cd/m2 at 8 V, while it is 3 V and 6005 cd/m2, respectively, for the nondoped devices. The improvement in the device performance is clarified as arising from the improved hole injection and transport by the results of ultraviolet/visible/near-infrared absorption, x-ray photoelectron spectra and current density-voltage characteristics of hole-only devices. [ABSTRACT FROM AUTHOR]

Epitaxial Pb(Zr,Ti)O3 (PZT) films were deposited on Nb-doped SrTiO3 (Nb:STO) monocrystalline wafers by a sol-gel method. It was observed that phase structure of prepared films depends on the orientation of Nb:STO substrates. Interestingly, tetragonal structure was only found for [001]-oriented PZT film on Nb:STO(100) substrate, whereas Nb:STO(111) substrate resulted in a [111]-oriented rhombohedral PZT film, regardless of Zr/Ti ratios ranging from 40/60 to 60/40. The influence of substrate orientation on phase structure of epitaxial PZT films was discussed on basis of the lattice matching. Ferroelectric and piezoelectric properties of PZT films on different Nb:STO substrates were also studied. [ABSTRACT FROM AUTHOR]

Single-crystal Nb-doped Pb(Zr,Ti)O3 (PNZT) films were grown on electric conducting single-crystal Nb-doped SrTiO3 (Nb:STO) wafers by a sol-gel method. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PNZT film was formed on the {100} surface of the Nb:STO substrate, whereas [111]-oriented rhombohedral PNZT film on the {111} surface. The PNZT films on SrTiO3 substrates showed considerably high remnant polarization and low coercive field, as compared with conventional PZT films on Si wafers. In particular, high d33 value was obtained in the [001]-oriented PNZT films. [ABSTRACT FROM AUTHOR]

High-performance epitaxial niobium-doped lead zirconate titanate thin films [Pb(ZrxTi1-x)0.98Nb0.02O3] with a fixed thickness were deposited on [111]-cut single-crystalline SrTiO3 substrates by a sol-gel process as a function of Zr/Ti ratio ranging from 20/80 to 80/20. An obvious shift of morphotropic phase boundary (MPB) was observed in the [111]-oriented epitaxial films. Deviating from the Zr/Ti ratio of 52/48 in bulk materials, the MPB composition in the as-deposited films was found to move to a lower Zr/Ti ratio between 30/70 and 40/60, which agrees with the theoretical analysis on the basis of lattice mismatch between films and substrates and is further confirmed by the XRD patterns and Raman spectrum as well as ferroelectric test. Furthermore, a superior remnant polarization (Pr) value among all the compositions was obtained at a Zr/Ti ratio of 30/70, indicating that the extrinsic ferroelectric polarization near the new morphotropic phase boundary will lead to outstanding dielectric and piezoelectric performance in the epitaxial PZT thin film system. [ABSTRACT FROM AUTHOR]

Extensive research and great progress of (K,Na)NbO3 (KNN)‐based lead‐free piezoelectric films have been driven by the current legislation and the requirement for sustainable development of society and environment in the applications of microelectromechanical systems. A comprehensive discussion of the recent achievement in KNN‐based films is presented herein. First, the available synthetic techniques, chemical modification, the ferroelectric and piezoelectric properties of KNN‐based films are reviewed, followed by an introduction of the crystal structures and electrical properties of KNN‐based epitaxial films in comparison with the bulk ceramics. Finally, the applications of KNN‐based films for the sensors, the energy harvesters, and energy storage devices are addressed, and current challenges and prospects for future work are discussed. [ABSTRACT FROM AUTHOR]

Future microelectromechanical systems will need environmentally friendly lead‐free piezoelectrics in the form of thin films, like Bi1/2Na1/2TiO3 (BNT); however, its application is limited due to the relatively low depolarization temperature (Td). In this work, not only enhanced piezoelectric properties, but also higher Td, are achieved in (001)‐textured 0.94Bi1/2Na1/2TiO3‐0.06BaTiO3 (BNT‐BT6) thin films on widely used platinized Si wafers with a LaNiO3 buffer layer. The piezoelectric coefficient a33,eff is increased by 65% to 43 pm V−1 in the textured films from 26 pm V−1 in the nontextured counterparts. The texturing also raises the Td to ≈140 °C, about 40 °C higher than that in nontextured films. The increase of Td is attributed to the in‐plane tensile thermal stress and the (001)‐textured structure. The present work provides a guideline to improve piezoelectric properties and the thermal stability of BNT‐based lead‐free piezoelectric thin films. Through (001)‐texturing, both depolarization temperature Td and piezoelectric property d33,eff of BNT‐BT6 thin films are efficiently enhanced. Such a (001)‐textured structure is realized on commonly used platinized Si wafers by introducing a LaNiO3 buffer layer. [ABSTRACT FROM AUTHOR]

0.8(Bi 0.5 ,Na 0.5)TiO 3 -0.2SrTiO 3 (BNT-0.2ST) thin films, with thicknesses ranging from 90 to 364 nm, were fabricated on platinized silicon substrates by sol-gel method. These films were investigated by switching spectroscopy piezoresponse force microscope (SS-PFM) as a function of frequency at room temperature, revealing the enhanced ferroelectric response in ∼ 210 nm film at all frequencies (0.1 Hz - 1.5 Hz). This enhancement was ascribed to the largest thermally-activated stress at such thicknesses generated during film fabrications. As the temperature of the investigated films increases from room temperature to 200 oC, the piezoelectric parameters were obtained from SS-PFM, such as switching polarization (R s), coercive bias (V 0), work of switching (A s), maximum strain (S max), and negative strain (S neg), indicating an occurrence of phase transition from ferroelectrics to relaxors. This work revealed that thickness plays a crucial role for ferroelectric response and temperature-dependent phase transition in BNT-0.2ST films, since it affects the stress state and switching behavior. [ABSTRACT FROM AUTHOR]

(1- x )(Bi 0.5 Na 0.5 )TiO 3 - x SrTiO 3 (BNT- x ST) (0 ≤ x ≤ 0.4) thin films were fabricated using a sol-gel technique on Pt(111)/Ti/SiO 2 /Si(100) substrates, which were investigated by piezoresponse force microscopy (PFM) and Raman spectroscopy. The composition-induced phase transition was analyzed by acquiring structural variations and the domain distribution on a local scale. Raman spectra showed phonon anomalies with peak broadening and shifting when increasing SrTiO 3 (ST) concentrations were used. Changes in the domain morphology with changes in the composition were observed, and grains smaller than 0.5 µm were observed at lower concentrations of x = 0–0.25, while larger grains appeared with increasing ST contents. The switching spectroscopy PFM (SS-PFM) results supported a ferroelectric (FE) to relaxor ferroelectric (RFE) phase transition at approximately x ≈ 0.3 by means of analyzing the parameters as a function of the composition including the piezoresponse parameters of hysteresis loops ( D max , D rem ) and amplitude butterfly loops ( S total , S neg ). Hence, these results demonstrated that the composition-driven FE to RFE phase transition behavior, which is consistent with the localized response behavior, is dependent on the ST content in bulk BNT- x ST ceramics. [ABSTRACT FROM AUTHOR]

(K,Na)NbO 3 (KNN) based lead-free materials have gained great progress and drawn much attention recently, due to their attractive piezoelectric performance and the demand for environmental protection. As is known, domain motion is essential for piezoelectric output; however, there is limited understanding on this topic for KNN. In the present study, the domain growth process of the KNN thin film is studied by piezoresponse force microscopy (PFM). The domain size shows a linear dependence on the pulse voltage and a complex dependence, unlike the commonly accepted logarithmic relationship, on the pulse duration. Meanwhile, a power decay relationship between the domain wall velocity and the domain size is observed. The extremely low dynamical exponent proves that our sample is influenced by extremely strong pinning effects caused by defects, resulting in the uncommon pulse duration dependence of domain size. [ABSTRACT FROM AUTHOR]

Ternary copper tin sulfide (Cu–Sn–S) compounds have been investigated for decades as promising candidates of earth-abundant thin film solar cell absorbers. Cu 2 SnS 3 is a representative member of this material system, and is highly expected to be a potential thermoelectric material by the first-principles calculations. In this work, Cu 2 SnS 3 bulk materials were synthesized by the mechanical alloying (MA) combined with spark plasma sintering (SPS), and their crystal structures, electronic transport properties and enhanced thermoelectric performance were systematically investigated. We found that pristine Cu 2 SnS 3 is a p-type thermoelectric material with a relatively high thermopower up to 300 μV/K and low thermal conductivity below 1.0 W/m K above 700 K. It revealed that In doping is an effective means to improve the electrical transport properties, which leads to a figure of merit ( ZT ) of Cu 2 Sn 0.9 In 0.1 S 3 close to 0.6 at the relatively low temperature (773 K). [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanocrystalline n-type Bi2Te3 films are deposited by magnetron sputtering. [•] Pb doping increases the Seebeck coefficient of Bi2Te3 thin films. [•] Pb doping reduces the carrier thermal conductivity of Bi2Te3 thin films. [•] Optimal Pb doping enhances the power factor of Bi2Te3 thin films. [ABSTRACT FROM AUTHOR]