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As the employment of halide perovskite films in single-junction and tandem solar cells continues to soar, there is a strong drive -from academia to industry- to produce these films using dry processes, avoiding the use of toxic solvents. Vapor deposition methods such as co-evaporation have shown advantages of solvent-free approaches to produce high-efficiency solar cells. However, co-evaporation requires the use of multiple sources that challenge the deposition rate control of complex halide perovskite compositions. Here, Pulsed Laser Deposition (PLD) is proposed as an alternative method to deposit hybrid halide perovskites films from a single-source and following a fully dry approach. We use the archetypical methylammonium lead iodide (MAPbI3) to demonstrate the formation of high-quality films with optimal optoelectronic properties by PLD on various substrates for single-junction and tandem devices. Furthermore, the important role of the PLD target composition and deposition parameters to achieve control over film microstructure and optoelectronic properties is discussed. The controlled conformal growth provided by PLD demonstrated in this work with MAPbI3 on device-relevant substrates will broaden opportunities to explore PLD of more complex hybrid halide perovskite compositions for efficient, stable, and scalable solar cell devices.

To benefit from the diverse functionalities of perovskite oxides in silicon-based complementary metal oxide semiconductor (CMOS) technology, integrating oxides into a silicon platform has become one of the major tasks for oxide research. Using the deposition of LaMnO3/SrTiO3 (STO) superlattices (SLs) as a case study, we demonstrate that (001) single oriented oxide SLs can be integrated on Si using various template techniques, including a single-layer buffer of STO prepared by molecular beam epitaxy (MBE) and pulsed laser deposition, a multilayer buffer of Y-stabilized zirconia/CeO2/LaNiO3/STO, and STO-coated two-dimensional nanosheets of Ca2Nb3O10 (CNO) and reduced graphene oxide. The textured SL grown on STO-coated CNO nanosheets shows the highest crystallinity, owing to the small lattice mismatch between CNO and STO as well as less clamping from a Si substrate. The epitaxial SL grown on STO buffer prepared by MBE suffers the largest thermal strain, giving rise to a strongly suppressed saturation magnetization but an enhanced coercive field, as compared to the reference SL grown on an STO single crystal. These optional template techniques used for integrating oxides on Si are of significance to fulfill practical applications of oxide films in different fields.

Excellent energy storage performance in combination with a low operating voltage is a very important factor for pulse-power dielectric capacitor devices to achieve miniaturization and integration. Here the heterostructure of the relaxor ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PL), with a slim hysteresis loop, on the normal ferroelectric Pb(Zr0.52Ti0.48)0.99Nb0.01O3 (PN), causing a large voltage imprint, is shown to improve the energy-storage performance. A large recoverable energy-storage density of 43.5 J/cm3 and a high energy-storage efficiency of 84.1%, under an electric field of 2450 kV/cm (i.e. a 49 V voltage bias), are obtained in the 180 nm PL/20 nm PN thin film heterostructure. Due to the small total film thickness the excellent energy-storage properties are obtained at a low operating voltage of 49 V. Moreover, the PL/PN heterostructure also exhibits an excellent charge-discharge endurance up to 1010 cycles and good thermal stability in a wide temperature range from room temperature to 200 °C. These performances show that these heterostructures form a promising design for high-temperature pulse-power capacitors, with superior energy-storage performance at low operating voltages.

The dielectric properties, tunability and figure-of-merit (FOM) of relaxor Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films have been investigated. Dielectric measurements indicated that the dielectric constant (at zero-bias field), tunability and FOM are enhanced as the film thickness increases, which are mainly attributed to the presence of an interfacial layer near the film-electrode interface. Experimental results illustrated that a slight reduction is observed in both dielectric constant and tunability (−2%) in a wide-frequency range (10 kHz–1 MHz), meanwhile, the FOM value decreases significantly (−17%) with increasing frequency, arising from the higher dielectric loss value. The 1000-nm PLZT film shows the largest tunability of 94.6% at a maximum electric-field of 1450 kV/cm, while the highest FOM factor is 37.6 at 1000 kV/cm, due to the combination of medium tunability (88.7%) and low dielectric loss (0.0236). All these excellent results indicated that the relaxor PLZT films are promising candidates for specific applications in microwave devices.

Functional oxides on silicon have been the subject of in-depth research for more than 20 years. Much of this research has been focused on the quality of the integration of materials due to their intrinsic thermodynamic incompatibility, which has hindered the flourishing of the field of research. Nevertheless, growth of epitaxial transition metal oxides on silicon with a sharp interface has been achieved by elaborated kinetically controlled sequential deposition while the crystalline quality of different functional oxides has been considerably improved. In this Research Update, we focus on three applications in which epitaxial ferroelectric oxides on silicon are at the forefront, and in each of these applications, other aspects of the integration of materials play an important role. These are the fields of piezoelectric microelectromechanical system devices, electro-optical components, and catalysis. The overview is supported by a brief analysis of the synthesis processes that enable epitaxial growth of oxides on silicon. This Research Update concludes with a theoretical description of the interfaces and the possibility of manipulating their electronic structure to achieve the desired coupling between (ferroelectric) oxides and semiconductors, which opens up a remarkable perspective for many advanced applications. © 2021 Author(s).

Polarization fatigue, i.e., the loss of polarization of ferroelectric capacitors upon field cycling, has been widely discussed as an interface related effect. However, mechanism(s) behind the development of fatigue have not been fully identified. Here, we study the fatigue mechanisms in Pt/PbZr0.52Ti0.48O3/SrRuO3 (Pt/PZT/SRO) capacitors in which all layers are fabricated by pulsed laser deposition without breaking the vacuum. With scanning transmission electron microscopy, we observed that in the fatigued capacitor, the Pt/PZT interface becomes structurally degraded, forming a 5 nm–10 nm thick non-ferroelectric layer of crystalline ZrO2 and diffused Pt grains. We then found that the fatigued capacitors can regain the full initial polarization switching if the externally applied field is increased to at least 10 times the switching field of the pristine capacitor. These findings suggest that polarization fatigue is driven by a two-step mechanism. First, the transient depolarization field that repeatedly appears during the domain switching under field cycling causes decomposition of the metal/ferroelectric interface, resulting in a non-ferroelectric degraded layer. Second, this interfacial non-ferroelectric layer screens the external applied field causing an increase in the coercive field beyond the usually applied maximum field and consequently suppresses the polarization switching in the cycled capacitor. Our work clearly confirms the key role of the electrode/ferroelectric interface in the endurance of ferroelectric-based devices.

Integrating functional complex oxides with conventional (“non-oxide”) semiconductors emerges to be an important research field and has been attracting great interest. Because of their superior intrinsic material properties, such as a relatively high dielectric constant and polarization, the utilization of PbZr1- xTixO3 (PZT) materials as a dielectric layer is expected to greatly improve the performance of the GaN high electron mobility transistor. The functional PbZr1- xTixO3 exhibits quite different crystal structures and consequently physical properties depending on the composition. In this work we report the growth of full range of compositions of PZT films on MgO buffered GaN substrates. Besides revealing the temperature effect on phase formation and surface morphology, we demonstrated the strong effect of composition on the growth: pure (1 1 1) phase is formed in Ti-rich PZT (x > 0.48) while pyrochlore impurity phase is found in Zr-rich PZT (x < 0.48). By introducing an ultrathin Ti-rich PZT seed layer, we are able to achieve epitaxial growth of Zr-rich PZT. The epitaxial PZT films of different composition all exhibit good ferroelectric properties, showing great promise for future GaN device applications.

Controlling the crystalline structure of hafnium zirconate and its epitaxial relationship to a semiconducting electrode has high technological interest, as ferroelectric materials are key ingredients for emerging electronic devices. Using pulsed laser deposition, a phase-pure, ultrathin film of HfZrO4 is grown epitaxially on a GaN(0001)/Si(111) template. Since standard microscopy techniques do not allow us to determine with certitude the crystalline structure of the film due to the weak scattering of oxygen, differentiated differential phase contrast scanning transmission electron microscopy is used to allow the direct imaging of oxygen columns in the film. Combined with x-ray diffraction analysis, the polar nature and rhombohedral R3 symmetry of the film are demonstrated.

Despite its interest for CMOS applications, Atomic Layer Deposition (ALD) of GeO$_{2}$ thin films, by itself or in combination with SiO$_{2}$, has not been widely investigated yet. Here we report the ALD growth of SiO$_{2}$/GeO$_{2}$ multilayers on Silicon substrates using a so far unreported Ge precursor. The characterization of multilayers with various periodicities reveals successful layer-by-layer growth with electron density contrast and absence of chemical intermixing, down to a periodicity of 2 atomic layers., This manuscript has been submitted to Applied Physics Letters

Epitaxial growth of SrTiO3 (STO) on silicon greatly accelerates the monolithic integration of multifunctional oxides into the mainstream semiconductor electronics. However, oxide superlattices (SLs), the birthplace of many exciting discoveries, remain largely unexplored on silicon. In this work, LaNiO3/LaFeO3 SLs are synthesized on STO-buffered silicon (Si/STO) and STO single-crystal substrates, and their electronic properties are compared using dc transport and X-ray absorption spectroscopy. Both sets of SLs show a similar thickness-driven metal-to-insulator transition, albeit with resistivity and transition temperature modified by the different amounts of strain. In particular, the large tensile strain promotes a pronounced Ni (Formula presented.) orbital polarization for the SL grown on Si/STO, comparable to that reported for LaNiO3 SL epitaxially strained to DyScO3 substrate. Those results illustrate the ability to integrate oxide SLs on silicon with structure and property approaching their counterparts grown on STO single crystal, and also open up new prospects of strain engineering in functional oxides based on the Si platform. © 2020 The Authors. Advanced Materials published by Wiley-VCH GmbH

It is important to understand the effect of the interfaces between the oxide electrode layers and the ferroelectric layer on the polarization response for optimizing the device performance of all-oxide ferroelectric devices. Herein, the effects of the oxide La0.07Ba0.93SnO3 (LBSO) as an electrode material in an PbZr0.52Ti0.48O3 (PZT) ferroelectric capacitor are compared with those of the more commonly used SrRuO3 (SRO) electrode. SRO (top)/PZT/SRO (bottom), SRO/PZT/LBSO, and SRO/PZT/2 nm SRO/LBSO devices are fabricated. Only marginal differences in crystalline properties, determined by X-ray diffraction and scanning transmission electron microscopy, are found. High-quality polarization loops are obtained, but with a much larger coercive field for the SRO/PZT/LBSO device. In contrast to the SRO/PZT/SRO device, the polarization decreases strongly with increasing field cycling. This fatigue problem can be remedied by inserting a 2 nm SRO layer between PZT and LBSO. It is argued that strongly increased charge injection into the PZT occurs at the bottom interface, because of the low PZT/LBSO interfacial barrier and the much lower carrier density in LBSO, as compared with that in SRO, causing a low dielectric constant, depleted layer in LBSO. The charge injection creates a trapped space charge in the PZT, causing the difference in fatigue behavior.

Relaxor ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films have been epitaxially grown via pulsed laser deposition on SrRuO3/SrTiO3 single crystal with different orientations. The high recoverable energy-storage density and energy-storage efficiency in the epitaxial PLZT thin films are mainly caused by the coexistence of relaxor and antiferroelectric-like behaviors. The recoverable energy-storage density of 12.03, 12.51 and 12.74 J/cm3 and energy-storage efficiency of 86.50, 88.14 and 88.44%, respectively, for the PLZT(001), PLZT(011) and PLZT(111) thin films measured at 1000 kV/cm. The high energy density and high efficiency indicate that the relaxor epitaxial PLZT(111) thin film is a promising candidate for high pulsed power capacitors.

Extreme ultraviolet and soft x-ray wavelengths have ever-increasing applications in photolithography, imaging, and spectroscopy. Adaptive schemes for wavefront correction at such a short wavelength range have recently gained much attention. In this Letter we report, to the best of our knowledge, the first demonstration of a functional actuator based on piezoelectric thin films. We introduce a new approach that allows producing a gradually varying surface deformation. White light interferometery is used to show the level of control in generating arbitrary surface profiles at the nanoscale.

The two-dimensional electron liquid which forms between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO3 substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of Ca2Nb3O10 which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface., 11 pages, 7 figures

Vanadium dioxide (VO2) is a much-discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of VO2 is realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X-ray transparent silicon nitride membranes. The out-of-plane orientation of the VO2 thin films is controlled at will between (011)M1/(110)R and (−402)M1/(002)R by coating the bulk substrates with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth. Temperature-dependent X-ray diffraction and automated crystal orientation mapping in microprobe transmission electron microscope mode (ACOM-TEM) characterize the high phase purity, the crystallographic and orientational properties of the VO2 films. Transport measurements and soft X-ray absorption in transmission are used to probe the VO2 metal–insulator transition, showing results of a quality equal to those from epitaxial films on bulk single-crystal substrates. Successful local manipulation of two different VO2 orientations on a single substrate is demonstrated using VO2 grown on lithographically patterned lines of Ti0.87O2 and NbWO6 nanosheets investigated by electron backscatter diffraction. Finally, the excellent suitability of these nanosheet-templated VO2 films for advanced lensless imaging of the metal–insulator transition using coherent soft X-rays is discussed.

Epitaxial (PbMg1/3Nb2/3O3)2/3-(PbTiO3)1/3 (PMN-PT) films with different out-of-plane orientations were prepared using a CeO2/yttria stabilized ZrO2 bilayer buffer and symmetric SrRuO3 electrodes on silicon substrates by pulsed laser deposition. The orientation of the SrRuO3 bottom electrode, either (110) or (001), was controlled by the deposition conditions and the subsequent PMN-PT layer followed the orientation of the bottom electrode. The ferroelectric, dielectric and piezoelectric properties of the (SrRuO3/PMN-PT/SrRuO3) ferroelectric capacitors exhibit orientation dependence. The properties of the films are explained in terms of a model based on polarization rotation. At low applied fields domain switching dominates the polarization change. The model indicates that polarization rotation is easier in the (110) film, which is ascribed to a smaller effect of the clamping on the shearing of the pseudo-cubic unit cell compared to the (001) case.

Thin film capacitors of the lead-free (K0.5Na0.5)NbO3 (KNN) with (100) orientation were grown on Pt/Ti/SiO2/SOI (silicon-on-insulator) substrates by pulsed laser deposition. The films are pure phases and do not show other crystal orientations. The remnant polarization Pr, saturation polarization Psat, longitudinal d33,f and transverse (d31,f and e31,f) piezoelectric coefficients of the KNN films were determined (Pr=12.6 µC/cm2, Psat=25.0 µC/cm2, d33,f=58 pm/V, d31,f=−42 pm/V and e31,f=−5.6 C/m2). These values are well comparable with the highest values reported for lead-free films of different compositions and therefore these KNN films form a potential alternative to PZT films in lead-free MEMS applications.

Near-infrared absorption in transparent conducting oxides (TCOs) is usually caused by electronic intraband transition at high doping levels. Improved infrared transparency is commonly explained by enhanced drift mobility in these TCOs. Here, an alternative cause behind the high infrared transparency of La-doped barium stannate (LBSO) transparent electrodes is presented. Following the Drude model formalism, we reconstructed spectrally resolved dielectric permittivity for a set of thin films with different free electron concentrations. A comparison of optical properties of LBSO with the tin-doped indium oxide thin films with identical carrier concentrations suggests that the redshift of the screened plasma wavelength for LBSO originates from its large high-frequency dielectric constant of 4.4, one of the highest reported for the s-orbital-based TCOs. Moreover, our measurements confirm an optical mobility significantly higher (>300 cm2/V s) than the drift mobility, effectively suppressing the free carrier absorption. These factors enable high infrared transparency of LBSO films and motivate further exploration of LBSO as broadband TCOs for solar cells and nanophotonics.

The energy-storage performance and piezoelectric properties were determined for epitaxial antiferroelectric (AFE) PbZrO3 (PZ), ferroelectric (FE) PbZr0.52Ti0.48O3 (PZT), and relaxor ferroelectric (RFE) Pb0.9La0.1Zr0.52Ti0.48O3 (PLZT) thin films that were deposited on to SrTiO3 buffered Si substrates. The films were investigated by directly measuring the polarization hysteresis loops and piezoelectric strain curves. The square polarization loop with a high remanent polarization and a large piezoelectric coefficient obtained in PZT thin films allow them to be useful for various applications in ferroelectric field effect transistors and/or in MEMS actuators. Meanwhile, there is a jump of about 0.9% in the strain curve of PZ thin films around the field-induced AFE-FE phase transition, which is useful in digital displacement transducers due to a good ON/OFF strain state. The large recoverable energy-storage density, excellent energy-storage efficiency, and low strain hysteresis due to a slim hysteresis loop combine to make PLZT thin films as a potential candidate for a broad range of applications from energy storage to nano-positioning precision systems.

Just Accepted Manuscript, In the present work, we study the hysteretic behavior in the electric-field-dependent capacitance and the current characteristics of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT)/ZnO bilayers deposited on 0.7 wt % Nb-doped (001)-SrTiO3 (Nb:STO) substrates in a metal-ferroelectric-semiconductor (MFS) configuration. The X-ray diffraction measurements show that the BCZT and ZnO layers are highly oriented along the c-axis and have a single perovskite and wurtzite phases, respectively, whereas high-resolution transmission electron microscopy revealed very sharp Nb:STO/BCZT/ZnO interfaces. The capacitance-electric field ( C- E) characteristics of the bilayers exhibit a memory window of 47 kV/cm and a capacitance decrease of 22%, at a negative bias. The later result is explained by the formation of a depletion region in the ZnO layer. Moreover, an unusual resistive switching (RS) behavior is observed in the BCZT films, where the RS ratio can be 500 times enhanced in the BCZT/ZnO bilayers. The RS enhancement can be understood by the barrier potential profile modulation at the depletion region, in the BCZT/ZnO junction, via ferroelectric polarization switching of the BCZT layer. This work builds a bridge between the hysteretic behavior observed either in the C- E and current-electric field characteristics on a MFS structure., Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013 and (ii) Project Norte-070124-FEDER-000070 Nanomateriais Multifuncionais. This research was partially supported by the COST Action MP1308 "Towards Oxide-Based Electronics (TO-BE)". The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal 20157018. The author J.P.B.S. is grateful for financial support through the FCT Grant SFRH/BPD/92896/2013. The author K.C.S. acknowledge UGC and DST-SERB, Govt. of India for the funds through the grant No.F.4-5(59-FRP/2014(BSR)) and ECR/2017/000068, respectively. The authors R.F.N. and C.G. acknowledge the financial support from Romanian Ministry of Research and Innovation in the frame of the Core Program PN18-11, info:eu-repo/semantics/publishedVersion

Due to its physical properties gallium-nitride (GaN) is gaining a lot of attention as an emerging semiconductor material in the field of high-power and high-frequency electronics applications. Therefore, the improvement in the performance and/or perhaps even extension in functionality of GaN based devices would be highly desirable. The integration of ferroelectric materials such as lead-zirconate-titanate (PbZrxTi1-xO3) with GaN has a strong potential to offer such an improvement. However, the large lattice mismatch between PZT and GaN makes the epitaxial growth of Pb(Zr1-xTix)O-3 on GaN a formidable challenge. This work discusses a novel strain relaxation mechanism observed when MgO is used as a buffer layer, with thicknesses down to a single unit cell, inducing epitaxial growth of high crystallinity Pb(Zr0.52Ti0.48)O-3 (PZT) thin films. The epitaxial PZT films exhibit good ferroelectric properties, showing great promise for future GaN device applications.

Piezoelectric lead-zirconate-Titanate (PZT) thin films were deposited on 4-inch (111)Pt/Ti/SiO2/Si(001) wafers using large-Area pulsed laser deposition (PLD). This study was focused on the homogeneity in film thickness, microstructure, ferroelectric and piezoelectric properties of PZT thin films. The results indicated that the highly textured (001)-oriented PZT thin films with wafer-scale thickness homogeneity (990 nm ± 0.8%) were obtained. The films were fabricated into piezoelectric cantilevers through a MEMS microfabrication process. The measured longitudinal piezoelectric coefficient (d 33f = 210 pm/V ± 1.6%) and piezoelectric transverse coefficient (e 31f = -18.8 C/m2 ± 2.8%) were high and homogeneity across wafers. The high piezoelectric properties on Si wafers will extend industrial application of PZT thin films and further development of piezoMEMS.

The integration of ferroelectric layers on gallium nitride (GaN) offers a great potential for various applications. Lead zirconate titanate (PZT), in particular Pb (Zr0.52Ti0.48)O3, is an interesting candidate. For that a suitable buffer layer should be grown on GaN in order to prevent the reaction between PZT and GaN, and to obtain PZT with a preferred orientation and phase. Here, we study pulsed laser deposited (100) rutile titanium oxide (R-TiO2) as a potential buffer layer candidate for ferroelectric PZT. For this purpose, the growth, morphology and the surface chemical composition of R-TiO2 films were analyzed by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. We find optimally (100) oriented R-TiO2 growth on GaN(0002) using a 675 °C growth temperature and 2 Pa O2 deposition pressure as process conditions. More importantly, the R-TiO2 buffer layer grown on GaN/Si substrates prevents the unwanted formation of the PZT pyrochlore phase. Finally, the remnant polarization and coercive voltage of the PZT film on TiO2/GaN/Si with an interdigitated-electrode structure were found to be 25.6 μC/cm2 and 8.1 V, respectively.

Publisher’s Note: This conference presentation, originally published on 2 November 2016, was withdrawn per author request.

Renewed interest has been witnessed in utilizing the piezoelectric response of $PbZr_{0.52}Ti_{0.48}O_{3}$ (PZT) films on glass substrates for applications such as data storage and adaptive optics. Accordingly, new methodologies are being explored to grow well-oriented PZT thin films to harvest a large piezoelectric response. However, thin film piezoelectric response is significantly reduced compared to intrinsic response due to substrate induced clamping, even when films are well-oriented. Here, a novel method is presented to grow preferentially (100)-oriented PZT films on glass substrates by utilizing crystalline nanosheets as seed layers. Furthermore, increasing the repetition frequency up to 20 Hz during pulsed laser deposition helps to tune the film microstructure to hierarchically ordered columns that leads to reduced clamping and enhanced piezoelectric response evidenced by transmission electron microscopy and analytical calculations. A large piezoelectric response of 280 pm/V is observed in optimally tuned structure which almost triples the highest reported piezoelectric response on glass. To confirm that the clamping compromises the piezoelectric response, denser films are deposited using a lower repetition frequency and a $BiFeO_{3}$ buffer layer resulting in significantly reduced piezoelectric responses. This paper demonstrates a novel method for PZT integration on glass substrates without compromising the large piezoelectric response., Comment: 26 pages, 6 figures

Heterostructures formed by La0.7Sr0.3MnO3/ZnO (LSMO/ZnO) interfaces exhibit extremely interesting electronic properties making them promising candidates for novel oxide pn junctions, with multifunctional features. In this work, the structure of the interface is studied through a combined experimental/theoretical approach. Heterostructures were grown epitaxially and homogeneously on 4″ silicon wafers, characterized by advanced electron microscopy imaging and spectroscopy and simulated by ab initio density functional theory calculations. The simulation results suggest that the most stable interface configuration is composed of the (001) face of LSMO, with the LaO planes exposed, in contact with the (112̅0) face of ZnO. The ab initio predictions agree well with experimental high-angle annular dark field scanning transmission electron microscopy images and confirm the validity of the suggested structural model. Electron energy loss spectroscopy confirms the atomic sharpness of the interface. From statistical parameter estimation theory, it has been found that the distances between the interfacial planes are displaced from the respective ones of the bulk material. This can be ascribed to the strain induced by the mismatch between the lattices of the two materials employed.

The effect of two poling processes on the ferroelectric and piezoelectric properties of sol–gel and pulsedlaser-deposited Pb(Zr0.45Ti0.55)O3 (PZT) thin films has been investigated as a function of the poling field, poling temperature and poling time. In the case of dc-electric field poling at an elevated temperature (200 °C), the remnant polarization and effective piezoelectric coefficient are found to increase with and saturate at high dc-poling field (400 kV/cm) and long poling time (30 minutes). The room-temperature poling process using ac electric field poling, shows the same trend with poling field but much shorter poling times (100 seconds), with only a slightly lower saturation value of polarization. It is suggested that in room-temperature poling screening charges are merely rearranged, whereas in high temperature poling these charges are largely removed. A much larger improvement in the properties of sol–gel PZT thin films is found, as compared to those deposited using pulsed laser deposition (PLD), indicating that a poling process is required for sol–gel films.

The transverse piezoelectric coefficient e31,f and mass-sensitivity were measured on piezoelectric cantilevers based on epitaxial PZT thin-films with film-thicknesses ranging from 100 to 2000 nm. The highest values of e31,f and mass-sensitivity were observed at a film thickness of 500–750 nm, while the observed remnant polarization Pr and longitudinal piezoelectric coefficient d33,f values become saturated with a film thickness of 750–1000 nm. To obtain high performance by making use of its optimal film thickness, PZT thin films with various Zr/Ti ratios from 20/80 to 80/20 were studied. The experimental results indicated that the ferroelectric property reached a highest remnant polarization Pr at a Zr/Ti ratio of 20/80, while the longitudinal piezoelectric coefficient d33,f increased with increasing Zr content and reaches a maximum at a Zr/Ti ratio of 52/48. The findings suggest that the optimal composition for mass-sensitivity and transverse piezoelectric coefficient e31,f was shifted to the tetragonal part of the phase diagram with the Zr/Ti ratios of 45/55 and 40/60, respectively.

Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) metal oxide nanosheets (ns) are used as a buffer layer for epitaxial growth of piezoelectric capacitor stacks on Si and Pt/Ti/SiO2/Si (Pt/Si) substrates. Highly (001)- and (110)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) films are achieved by utilizing CNOns and TiOns, respectively. The piezoelectric capacitors are characterized by polarization and piezoelectric hysteresis loops and by fatigue measurements. The devices fabricated with SrRuO3 top and bottom electrodes directly on nanosheets/Si have ferroelectric and piezoelectric properties well comparable with devices that use more conventional oxide buffer layers (stacks) such as YSZ, CeO2/YSZ, or SrTiO3 on Si. The devices grown on nanosheets/Pt/Si with Pt top electrodes show significantly improved polarization fatigue properties over those of similar devices grown directly on Pt/Si. The differences in properties are ascribed to differences in the crystalline structures and the density of the films. These results show a route toward the fabrication of single crystal piezoelectric thin films and devices with high quality, long-lifetime piezoelectric capacitor structures on nonperovskite and even noncrystalline substrates such as glass or polished metal surfaces.

We investigated the residual stress and Young's modulus of Pb(ZrxTi1 - x)O3 (PZT) thin films with a (110) preferred orientation and a composition x ranging from 0.2 to 0.8. The films are grown by pulsed laser deposition on silicon cantilevers aligned along the and silicon crystal directions. Changes in resonance frequency and static bending of the cantilevers are used to determine the Young's modulus and residual stress respectively. The Young's modulus was found to be in the range of 100-200 GPa. The residual stress is tensile and shows a sharp increase from about 50 to 250 MPa at a composition of x = 0.2 to 0.4. These mechanical parameters clearly depend on the cantilever orientation with respect to the silicon crystal, which we suspect to be linked to the epitaxial growth of the films. The variation in stress with composition can be explained by the difference in thermal expansion between silicon and PZT, if we assume an intrinsic stress of 200-300 MPa to be already present immediately after deposition. Strain calculated from X-ray diffraction data leads to unreasonably high residual stress values, at least one order of magnitude higher than measured by cantilever bending. © 2016 Elsevier B.V. All rights reserved.

Letter.-- et al., Flexoelectricity allows a dielectric material to polarize in response to a mechanical bending moment and, conversely, to bend in response to an electric field. Compared with piezoelectricity, flexoelectricity is a weak effect of little practical significance in bulk materials. However, the roles can be reversed at the nanoscale. Here, we demonstrate that flexoelectricity is a viable route to lead-free microelectromechanical and nanoelectromechanical systems. Specifically, we have fabricated a silicon-compatible thin-film cantilever actuator with a single flexoelectrically active layer of strontium titanate with a figure of merit (curvature divided by electric field) of 3.33 MV−1, comparable to that of state-of-the-art piezoelectric bimorph cantilevers., The work at ICN2 was funded by an ERC Starting Grant from the EU (Project No. 308023), a National Plan grant from Spain (FIS2013-48668-C2-1-P) and the Severo Ochoa Excellence programme. The work at Cornell University was supported by the National Science Foundation (Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems) under grant number EEC-1160504.

Strain engineering enables modification of the properties of thin films using the stress from the substrates on which they are grown. Strain may be relaxed, however, and this can also modify the properties thanks to the coupling between strain gradient and polarization known as flexoelectricity. Here we have studied the strain distribution inside epitaxial films of the archetypal ferroelectric PbTiO3, where the mismatch with the substrate is relaxed through the formation of domains (twins). Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal an intricate strain distribution, with gradients in both the vertical and, unexpectedly, the horizontal direction. These gradients generate a horizontal flexoelectricity that forces the spontaneous polarization to rotate away from the normal. Polar rotations are a characteristic of compositionally engineered morphotropic phase boundary ferroelectrics with high piezoelectricity; flexoelectricity provides an alternative route for generating such rotations in standard ferroelectrics using purely physical means.

A method of fabricating oriented single-crystalline SrRuO3 nanowire arrays using a bottom-up approach relying on diffusion-controlled self-organization is demonstrated. DyScO3 substrates exhibiting an ordered striped phase of DyO and ScO2 chemical termination are used as a template for pulsed laser deposition growth of SrRuO3. Here SrRuO3 preferentially nucleates on one type of termination. The resulting nanowires are single crystalline, conducting and isolated from each other, typically 100 nm wide and 5-10 nm high. This preferential growth is studied using a kinetic Monte Carlo model, which provides a guide to optimize growth conditions and tune the dimensions of the nanowires.

The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. Herein we show that metallic interfaces can be realized in SrTiO3-based heterostructures with various insulating overlayers of amorphous LaAlO3, SrTiO3 and yttria-stabilized zirconia films. On the other hand, samples of amorphous La7/8Sr1/8MnO3 films on SrTiO3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of SrTiO3 substrates play an important role., 17 pages, 4 figures

This paper reports on the piezoelectric-microelectromechanical system micro-fabrication process and the behavior of piezoelectric stacks actuated silicon cantilevers. All oxide layers in the piezoelectric stacks, such as buffer-layer/bottom-electrode/film/top-electrode: YSZ/SrRuO3/Pb(Zr,Ti)3/SrRuO3, were grown epitaxially on the Si template of silicon-on-insulator substrates by pulsed laser deposition. By using an analytical model and finite element simulation, the initial bending of the cantilevers was calculated. These theoretical analyses are in good agreement with the experimental results which were determined using a white light interferometer. The dependences of the cantilever displacement, resonance frequency and quality factor on the cantilever geometry have been investigated using a laser-Doppler vibrometer. The tip displacement ranged from 0.03 to 0.42 µm V−1, whereas the resonance frequency and quality factor values changed from 1010 to 18.6 kHz and 614 to 174, respectively, for the cantilevers with lengths in the range of 100–800 µm. Furthermore, the effect of the conductive oxide electrodes on the stability of the piezoelectric displacement of the cantilevers has been studied.

PbZr0.53Ti0.47O3 (PZT) thin films containing nanoparticles of Pt (3–10 nm) were produced using pulsed laser deposition (PLD). The Pt content can be tuned by varying the energy density of the laser beam. Phase and microstructure analysis of the thin films was performed using XRD, SEM, TEM and AFM. The electrical properties were investigated by C–V and I–V measurements. The effective dielectric constant of the composite films increased substantially through the Pt dispersion. These films are promising candidates, for instance, for high-density dynamic random access memory (DRAM) devices.

All-oxide free-standing cantilevers were fabricated with epitaxial (001)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) and Pb(Zr0.52Ti0.48)0.99Nb0.01O3 (PNZT) as piezoelectric layers and SrRuO3 electrodes. The ferroelectric and piezoelectric hysteresis loops were measured. From the zero-bias values, the figure-of-merits (FOMs) for piezoelectric energy harvesting systems were calculated. For the PNZT cantilever, an extremely large value FOM = 55 GPa was obtained. This very high value is due to the large shifts of the hysteresis loops such that the zero-bias piezoelectric coefficient e31f is maximum and the zero-bias dielectric constant is strongly reduced compared to the value in the undoped PZT device. The results show that by engineering the self-bias field the energy-harvesting properties of piezoelectric systems can be increased significantly.

Atomic force microscopy is one of the most popular imaging tools with atomic resolution in different research fields. Here, a fast and gentle side approach for atomic force microscopy is proposed to image the same surface location and to reduce the time delay between modification and imaging without significant tip degradation. This reproducible approach to image the same surface location using atomic force microscopy shortly after, for example, any biological, chemical, or physical modification on a geometrically separated position has the potential to become widely used.

We report on the fabrication and mechanical properties of all-oxide, free-standing, heteroepitaxial, piezoelectric, microelectromechanical systems (MEMS) on silicon, using PbZr0.52Ti0.48O3 as the key functional material. The fabrication was enabled by the development of an epitaxial lift-off strategy for the patterning of multilayer oxide heterostructures grown on Si(001), employing a high temperature stable, sacrificial oxide template mask to obtain freestanding cantilever MEMS devices after substrate etching. All cantilevers, with lengths in the range 25–325 μm, width 50 μm, and total thickness of 300 nm, can be actuated by an external AC-bias. For lengths 50–125 μm, the second order bending mode formed the dominant resonance, whereas for the other lengths different or multiple modes were present.

In order to create crystal structures by depositing consecutive atomic or unit-cell layers of different materials, a layer-by-layer growth mode is a prerequisite: nucleation of each next layer may only occur after the previous layer is completed. We introduced a growth method based on a periodic sequence: very fast deposition of the amount of material needed to complete one monolayer followed by an interval in which no deposition takes place and the film can reorganize. This makes it possible to grow in a layer-by-layer fashion in a growth regime (temperature, pressure) where otherwise island formation would dominate the growth. Here, we present imposed layer-by-layer growth of homo-epitaxial SrTiO3 as monitored by high-pressure reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM).

Reflection high energy electron diffraction (RHEED) is, due to its surface sensitivity, often used for the analysis and monitoring of thin film growth in ultra-high vacuum deposition systems. RHEED is usually applied in combination with pulsed laser deposition (PLD) by adjusting the background pressure. However, the pressure during PLD is an important parameter because it influences the shape and size of the plasma. Low deposition pressures during PLD can lead to stress, usually compressive, in the film. Moreover, the oxidation power is much higher at higher pressures, which enables growth at higher temperatures, leading to better crystallinity of the as-deposited films. Therefore, relative high pressures are favourable in PLD. Unfortunately, these high pressures hamper the diagnostics of the growing film surfaces by in-situ RHEED. Here, a RHEED system designed for growth monitoring at high deposition pressures is presented. The main problem that has been solved is the increased scattering loss. The losses are minimised by keeping the travelling path of the electrons in the high-pressure region as short as possible. Using a two-stage differential pumping system, we are able to increase the deposition pressure up to 50 Pa. With this system, we have monitored the growth of SrTiO3, YBa2Cu3O7?? and SrCuOx, in a background pressure of 15 Pa of oxygen. The first two systems show clear oscillations of the diffracted intensity, indicating two-dimensional growth, with the possibility to control the thin film growth on an atomic level at standard PLD pressures. Furthermore, the mobility of material deposited with one single laser pulse is represented by an additional modulation of the intensity of the RHEED pattern. This gives excess information about the diffusion and nucleation of the deposited material.

We studied the morphology of ramps in REBa/sub 2/Cu/sub 3/O/sub 7/ (REBCO) epitaxial films on SrTiO/sub 3/ substrates, fabricated by RF magnetron sputter deposition and pulsed laser deposition (PLD), by Atomic Force Microscopy (AFM) and High Resolution Electron Microscopy (HREM). The ramps were fabricated by Ar ion beam etching using different masks of standard photoresist and TiN. AFM-studies on ramps in sputter deposited films show a strong dependence, i.e., formation of facets and ridges, on the angle of incidence of the ion beam with respect to the substrate surface as well as the rotation angle with respect to the crystal axes of the substrate. Ramps in pulsed laser deposited films did not show this dependence. Furthermore, we studied the effect of an anneal step prior to the deposition of barrier layers (i.e. PrBa/sub 2/Cu/sub 3-x/Ga/sub x/O/sub 7/) on the ramp. First results show a crystallization of the ramp surface, resulting in terraces and a non-homogeneous growth of the barrier material on top of it. The thickness variations, for thin layers of barrier material, can even become much larger than expected from the amount of deposited material and are dependent on the deposition and anneal conditions. HREM studies show a well-defined interface between barrier layer and electrodes. The angle of the ramp depends on the etch rate of the mask and REBCO and on the angle of incidence of the ion beam. Hard masks, like TIN, have a much lower etch rate compared to photoresist, resulting in an angle of the ramp comparable to the angle of incidence and, subsequently, in a low etching rate on the ramp.

We present the first spatio-temporal mapping of two simultaneously present species in a plasma used for pulsed laser deposition. We apply laser induced fluorescence spectroscopy (LIF) to map ground state populations of Al and AlO in plasma plumes generated by ablation of LaAlO3 in an O2 or Ar atmosphere. Around a specific distance from the target, we observe Al vanish simultaneously with the turnup of AlO. This can be assigned to the oxidation of Al in the background atmosphere occurring after a sufficient slowing of the expanding Al front. This is consistent with the absence of such effects when argon is taken as background. A quantitative evaluation of data promises to reveal important dynamical reaction and deposition parameters for identification of the origin of specific properties of PLD grown films such as 2-dimensional conductive interfaces.

A set of LaAlO3/SrTiO3 (LAO-STO) interfaces has been probed by x-ray photoemission spectroscopy in order to contrast and compare the effects of LAO overlayer thickness and of the growth conditions on the electronic properties of these heterostructures. These effects are tracked by considering the band offset and the density of Ti+3 states, respectively. It is shown that the dominant effects on the local electronic properties are determined by the O2 partial pressure during the growth. In particular, a low PO2 yields Ti+3 states with higher density and lower binding energy compared to the sample grown at high PO2 or to the bare STO reference sample. Band-offset effects are all below about 0.7 eV, but a careful analysis of Ti 2p and Sr 3d peaks shows that valence-band offsets can be at the origin of the observed peak width. In particular, the largest offset is shown by the conducting sample, which displays the largest Ti 2p and Sr 3d peak widths

Piezoelectric thin films of PbZr0.45Ti0.55O3 were grown on Si substrates in four different ways, resulting in different crystalline structures, as determined by x-ray analysis. The crystalline structures were different in the spread in tilt angle and the in-plane alignment of the crystal planes between different grains. It is found that the deviations of the ferroelectric polarization loop from that of the ideal rectangular loop (reduction of the remanent polarization with respect to the saturation polarization, dielectric constant of the film, slanting of the loop, coercive field value) all scale with the average tilt angle. A model is derived based on the assumption that the tilted grain boundaries between grains affect the film properties locally. This model describes the observed trends. The effective piezoelectric coefficient d33,eff shows also a weak dependence on the average tilt angle for films grown in a single layer, whereas it is strongly reduced for the films deposited in multiple layers. The least affected properties are obtained for the most epitaxial films, i.e. grown on a SrTiO3 epitaxial seed layer, by pulsed laser deposition. These films are intrinsically stable and do not require poling to acquire these stable properties.

Functional perovskite oxides are recognized for their stunningly rich physics and for their potential as next-generation electronic materials. Their properties include high Tc superconductivity, colossal magnetoresistance, record-high dielectric/ferroelectric/piezoelectric performances, multiferroic behavior, resistive switching behavior, giant thermoelectric and magnetocaloric effects, giant ionic conduction, and catalytic behavior. Due to their intrinsic chemical and crystal similarities, functional oxides can be stacked in multilayer heterostructures exhibiting an astonishing degree of epitaxial perfection. Such artificial systems not only allow one to combine in a single device the functionalities of their individual layers, but often reveal an even wider range of emergent novel properties that can be surprisingly different from those of the single building blocks. The goal of this issue of MRS Bulletin is to present the state of the art of oxide interfaces in inscience and technology. Here we provide an introduction to their properties, serving as a base for the following topical articles.

During the initial growth of the ferromagnetic oxide SrRuO3 on TiO2-terminated SrTiO3, we observe a self-organized conversion of the terminating atomic layer from RuO2 to SrO. This conversion induces an abrupt change in growth mode from layer by layer to growth by step advancement, indicating a large enhancement of the surface diffusivity. This growth mode enables the growth of single-crystalline and single-domain thin films. Both conversion and the resulting growth mode enable the control of the interface properties in heteroepitaxial multilayer structures on an atomic level.

Pb 0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) relaxor-ferroelectric thin films were grown on SrRuO3/SrTiO3/Si substrates by pulsed laser deposition. A large recoverable storage density (U reco) of 13.7 J/cm3 together with a high energy efficiency (η) of 88.2% under an applied electric field of 1000 kV/cm and at 1 kHz frequency was obtained in 300-nm-thick epitaxial PLZT thin films. These high values are due to the slim and asymmetric hysteresis loop when compared to the values in the reference undoped epitaxial lead zirconate titanate Pb(Zr0.52Ti0.48)O3 ferroelectric thin films (U reco = 9.2 J/cm3 and η = 56.4%) which have a high remanent polarization and a small shift in the hysteresis loop, under the same electric field.

Here we demonstrate a method to tune a ferroelectric imprint, which is stable in time, based on the coupling between the non-switchable polarization of ZnO and switchable polarization of PbZrxTi(1−x)O3. SrRuO3/PbZrxTi(1−x)O3/ZnO/SrRuO3 heterostructures were grown with different ZnO thicknesses. It is shown that the coercive voltages and ferroelectric imprint vary linearly with the thickness of ZnO. It is also demonstrated that the ferroelectric imprint remains stable with electric field cycling and electric field stress assisted aging.

Films of piezoelectric and ferroelectric oxides have been widely investigated for various applications, including microelectromechanical systems (MEMS) for printing. Pb(Zr,Ti)O3 is of particular interest due to its excellent piezoelectric properties. Control of the density, crystalline orientation, and compositional uniformity is essential to obtain these properties. In this article, we review recent progress on the fabrication of epitaxial Pb(Zr,Ti)O3films, in which the aforementioned control can be achieved. We discuss the different approaches used for the deposition of the epitaxial piezoelectric layer as well as the achieved degrees of the epitaxy. Furthermore, the integration of these piezoelectric layers in MEMS and the corresponding performance are discussed.