3D printed graphene-based self-powered strain sensors for smart tires in autonomous vehicles.

The transition of autonomous vehicles into fleets requires an advanced control system design that relies on continuous feedback from the tires. Smart tires enable continuous monitoring of dynamic parameters by combining strain sensing with traditional tire functions. Here, we provide breakthrough in this direction by demonstrating tire-integrated system that combines direct mask-less 3D printed strain gauges, flexible piezoelectric energy harvester for powering the sensors and secure wireless data transfer electronics, and machine learning for predictive data analysis. Ink of graphene based material was designed to directly print strain sensor for measuring tire-road interactions under varying driving speeds, normal load, and tire pressure. A secure wireless data transfer hardware powered by a piezoelectric patch is implemented to demonstrate self-powered sensing and wireless communication capability. Combined, this study significantly advances the design and fabrication of cost-effective smart tires by demonstrating practical self-powered wireless strain sensing capability.

Three-dimensional printing of piezoelectric materials with designed anisotropy and directional response.

Piezoelectric coefficients are constrained by the intrinsic crystal structure of the constituent material. Here we describe design and manufacturing routes to previously inaccessible classes of piezoelectric materials that have arbitrary piezoelectric coefficient tensors. Our scheme is based on the manipulation of electric displacement maps from families of structural cell patterns. We implement our designs by additively manufacturing free-form, perovskite-based piezoelectric nanocomposites with complex three-dimensional architectures. The resulting voltage response of the activated piezoelectric metamaterials at a given mode can be selectively suppressed, reversed or enhanced with applied stress. Additionally, these electromechanical metamaterials achieve high specific piezoelectric constants and tailorable flexibility using only a fraction of their parent materials. This strategy may be applied to create the next generation of intelligent infrastructure, able to perform a variety of structural and functional tasks, including simultaneous impact absorption and monitoring, three-dimensional pressure mapping and directionality detection.

Magnetic Field Sensing by Exploiting Giant Nonstrain-Mediated Magnetodielectric Response in Epitaxial Composites.

Heteroepitaxial magnetoelectric (ME) composites are promising for the development of a new generation of multifunctional devices, such as sensors, tunable electronics, and energy harvesters. However, challenge remains in realizing practical epitaxial composite materials, mainly due to the interfacial lattice misfit strain between magnetostrictive and piezoelectric phases and strong substrate clamping that reduces the strain-mediated ME coupling. Here, we demonstrate a nonstrain-mediated ME coupling in PbZr0.52Ti0.48O3 (PZT)/La0.67Sr0.33MnO3 (LSMO) heteroepitaxial composites that resolves these challenges, thereby, providing a giant magnetodielectric (MD) response of ∼27% at 310 K. The factors driving the magnitude of the MD response were found to be the magnetoresistance-coupled dielectric dispersion and piezoelectric strain-mediated modulation of magnetic moment. Building upon this giant MD response, we demonstrate a magnetic field sensor architecture exhibiting a high sensitivity of 54.7 pF/T and desirable linearity with respect to the applied external magnetic field. The demonstrated technique provides a new mechanism for detecting magnetic fields based upon the MD effect.

Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances.

Recent technological advances in developing a diverse range of lasers have opened new avenues in material processing. Laser processing of materials involves their exposure to rapid and localized energy, which creates conditions of electronic and thermodynamic nonequilibrium. The laser-induced heat can be localized in space and time, enabling excellent control over the manipulation of materials. Metal oxides are of significant interest for applications ranging from microelectronics to medicine. Numerous studies have investigated the synthesis, manipulation, and patterning of metal oxide films and nanostructures. Besides providing a brief overview on the principles governing the laser-material interactions, here, the ongoing efforts in laser irradiation of metal oxide films and nanostructures for a variety of applications are reviewed. Latest advances in laser-assisted processing of metal oxides are summarized.

Enhanced Self-Biased Magnetoelectric Coupling in Laser-Annealed Pb(Zr,Ti)O3 Thick Film Deposited on Ni Foil.

Enhanced and self-biased magnetoelectric (ME) coupling is demonstrated in a laminate heterostructure comprising 4 µm-thick Pb(Zr,Ti)O3 (PZT) film deposited on 50 µm-thick flexible nickel (Ni) foil. A unique fabrication approach, combining room temperature deposition of PZT film by granule spray in vacuum (GSV) process and localized thermal treatment of the film by laser radiation, is utilized. This approach addresses the challenges in integrating ceramic films on metal substrates, which is often limited by the interfacial chemical reactions occurring at high processing temperatures. Laser-induced crystallinity improvement in the PZT thick film led to enhanced dielectric, ferroelectric, and magnetoelectric properties of the PZT/Ni composite. A high self-biased ME response on the order of 3.15 V/cm·Oe was obtained from the laser-annealed PZT/Ni film heterostructure. This value corresponds to a ∼2000% increment from the ME response (0.16 V/cm·Oe) measured from the as-deposited PZT/Ni sample. This result is also one of the highest reported values among similar ME composite systems. The tunability of self-biased ME coupling in PZT/Ni composite has been found to be related to the demagnetization field in Ni, strain mismatch between PZT and Ni, and flexural moment of the laminate structure. The phase-field model provides quantitative insight into these factors and illustrates their contributions toward the observed self-biased ME response. The results present a viable pathway toward designing and integrating ME components for a new generation of miniaturized tunable electronic devices.

Nanoscale Texturing and Interfaces in Compositionally Modified Ca3Co4O9 with Enhanced Thermoelectric Performance.

Oxide thermoelectric materials are nontoxic, chemically and thermally stable in oxidizing environments, cost-effective, and comparatively simpler to synthesize. However, thermoelectric oxides exhibit comparatively lower figure of merit (ZT) than that of metallic alloy counterparts. In this study, nanoscale texturing and interface engineering were utilized for enhancing the thermoelectric performance of oxide polycrystalline Ca3Co4O9 materials, which were synthesized using conventional sintering and spark plasma sintering (SPS) techniques. Results demonstrated that nanoscale platelets (having layered structure with nanoscale spacing) and metallic inclusions provide effective scattering of phonons, resulting in lower thermal conductivity and higher ZT. Thermoelectric measurement direction was found to have a significant effect on the magnitude of ZT because of the strong anisotropy in the transport properties induced by the layered nanostructure. The peak ZT value for the Ca2.85Lu0.15Co3.95Ga0.05O9 specimen measured along both perpendicular and parallel directions with respect to the SPS pressure axis is found be 0.16 at 630 °C and 0.04 at 580 °C, respectively. The peak ZT of 0.25 at 670 °C was observed for the spark plasma-sintered Ca2.95Ag0.05Co4O9 sample. The estimated output power of 2.15 W was obtained for the full size model, showing high-temperature thermoelectric applicability of this nanostructured material without significant oxidation.

Compositionally Graded Multilayer Ceramic Capacitors.

Multilayer ceramic capacitors (MLCC) are widely used in consumer electronics. Here, we provide a transformative method for achieving high dielectric response and tunability over a wide temperature range through design of compositionally graded multilayer (CGML) architecture. Compositionally graded MLCCs were found to exhibit enhanced dielectric tunability (70%) along with small dielectric losses (<2.5%) over the required temperature ranges specified in the standard industrial classifications. The compositional grading resulted in generation of internal bias field which enhanced the tunability due to increased nonlinearity. The electric field tunability of MLCCs provides an important avenue for design of miniature filters and power converters.

Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 lead-free piezoceramic system.

This paper is concerned with the development of a piezoelectric d15 shear-induced torsion actuator made of a lead-free piezoceramic material exhibiting giant piezoelectric shear stress coefficient (e15) and piezoelectric transverse shear actuation force comparable to that of lead-based shear-mode piezoceramics. The Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BT-Mn) composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C m-2. The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d15 mode piezoceramic shear patches, provided a rate of twist of 0.08 mm m-1 V-1 under quasi-static 150 V drive. The high value of piezoelectric shear d15 coefficient in NBT-BT-Mn sample further demonstrated its potential in practical applications. These results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts.

Unleashing the Full Potential of Magnetoelectric Coupling in Film Heterostructures.

A record-high, near-theoretical intrinsic magnetoelectric (ME) coupling of 7 V cm-1 Oe-1 is achieved in a heterostructure of piezoelectric Pb(Zr,Ti)O3 (PZT) film deposited on magnetostrictive Metglas (FeBSi). The anchor-like, nanostructured interface between PZT and Metglas, improved crystallinity of PZT by laser annealing, and optimum volume of crystalline PZT are found to be the key factors in realizing such a giant strain-mediated ME coupling.

Giant piezoelectric voltage coefficient in grain-oriented modified PbTiO3 material.

A rapid surge in the research on piezoelectric sensors is occurring with the arrival of the Internet of Things. Single-phase oxide piezoelectric materials with giant piezoelectric voltage coefficient (g, induced voltage under applied stress) and high Curie temperature (Tc) are crucial towards providing desired performance for sensing, especially under harsh environmental conditions. Here, we report a grain-oriented (with 95% <001> texture) modified PbTiO3 ceramic that has a high Tc (364 °C) and an extremely large g33 (115 × 10-3 Vm N-1) in comparison with other known single-phase oxide materials. Our results reveal that self-polarization due to grain orientation along the spontaneous polarization direction plays an important role in achieving large piezoelectric response in a domain motion-confined material. The phase field simulations confirm that the large piezoelectric voltage coefficient g33 originates from maximized piezoelectric strain coefficient d33 and minimized dielectric permittivity ɛ33 in [001]-textured PbTiO3 ceramics where domain wall motions are absent.

A new method for achieving enhanced dielectric response over a wide temperature range.

We report a novel approach for achieving high dielectric response over a wide temperature range. In this approach, multilayer ceramic heterostructures with constituent compositions having strategically tuned Curie points (T(C)) were designed and integrated with varying electrical connectivity. Interestingly, these multilayer structures exhibited different dielectric behavior in series and parallel configuration due to variations in electrical boundary conditions resulting in the differences in the strength of the electrostatic coupling. The results are explained using nonlinear thermodynamic model taking into account electrostatic interlayer interaction. We believe that present work will have huge significance in design of high performance ceramic capacitors.

Functionally Graded Interfaces: Role and Origin of Internal Electric Field and Modulated Electrical Response.

We report the tunable electrical response in functionally graded interfaces in lead-free ferroelectric thin films. Multilayer thin film graded heterostructures were synthesized on platinized silicon substrate with oxide layers of varying thickness. Interestingly, the graded heterostructure thin films exhibited shift of the hysteresis loops on electric field and polarization axes depending upon the direction of an applied bias. A diode-like characteristics was observed in current-voltage behavior under forward and reverse bias. This modulated electrical behavior was attributed to the perturbed dynamics of charge carriers under internal bias (self-bias) generated due to the increased skewness of the potential wells. The cyclic sweeping of voltage further demonstrated memristor-like current-voltage behavior in functionally graded heterostructure devices. The presence of an internal bias assisted the generation of photocurrent by facilitating the separation of photogenerated charges. These novel findings provide opportunity to design new circuit components for the next generation of microelectronic device architectures.

Integration of lead-free ferroelectric on HfO2/Si (100) for high performance non-volatile memory applications.

We introduce a novel lead-free ferroelectric thin film (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (x = 0.025) (BT-BCN) integrated on to HfO2 buffered Si for non-volatile memory (NVM) applications. Piezoelectric force microscopy (PFM), x-ray diffraction, and high resolution transmission electron microscopy were employed to establish the ferroelectricity in BT-BCN thin films. PFM study reveals that the domains reversal occurs with 180° phase change by applying external voltage, demonstrating its effectiveness for NVM device applications. X-ray photoelectron microscopy was used to investigate the band alignments between atomic layer deposited HfO2 and pulsed laser deposited BT-BCN films. Programming and erasing operations were explained on the basis of band-alignments. The structure offers large memory window, low leakage current, and high and low capacitance values that were easily distinguishable even after ~10(6) s, indicating strong charge storage potential. This study explains a new approach towards the realization of ferroelectric based memory devices integrated on Si platform and also opens up a new possibility to embed the system within current complementary metal-oxide-semiconductor processing technology.

Integration of SrTiO3 on crystallographically oriented epitaxial germanium for low-power device applications.

SrTiO3 integration on crystallographic oriented (100), (110), and (111) epitaxial germanium (Ge) exhibits a potential for a new class of nanoscale transistors. Germanium is attractive due to its superior transport properties while SrTiO3 (STO) is promising due to its high relative permittivity, both being critical parameters for next-generation low-voltage and low-leakage metal-oxide semiconductor field-effect transistors. The sharp heterointerface between STO and each crystallographically oriented Ge layer, studied by cross-sectional transmission electron microscopy, as well as band offset parameters at each heterojunction offers a significant advancement for designing a new generation of ferroelectric-germanium based multifunctional devices. Moreover, STO, when used as an interlayer between metal and n-type (4 × 10(18) cm(-3)) epitaxial Ge in metal-insulator-semiconductor (MIS) structures, showed a 1000 times increase in current density as well as a decrease in specific contact resistance. Furthermore, the inclusion of STO on n-Ge demonstrated the first experimental findings of the MIS behavior of STO on n-Ge.

Giant strain with ultra-low hysteresis and high temperature stability in grain oriented lead-free K0.5Bi0.5TiO3-BaTiO3-Na0.5Bi0.5TiO3 piezoelectric materials.

We synthesized grain-oriented lead-free piezoelectric materials in (K0.5Bi0.5TiO3-BaTiO3-xNa0.5Bi0.5TiO3 (KBT-BT-NBT) system with high degree of texturing along the [001]c (c-cubic) crystallographic orientation. We demonstrate giant field induced strain (~0.48%) with an ultra-low hysteresis along with enhanced piezoelectric response (d33 ~ 190pC/N) and high temperature stability (~160°C). Transmission electron microscopy (TEM) and piezoresponse force microscopy (PFM) results demonstrate smaller size highly ordered domain structure in grain-oriented specimen relative to the conventional polycrystalline ceramics. The grain oriented specimens exhibited a high degree of non-180° domain switching, in comparison to the randomly axed ones. These results indicate the effective solution to the lead-free piezoelectric materials.

Tensile-strained nanoscale Ge/In0.16Ga0.84As heterostructure for tunnel field-effect transistor.

Tensile strained Ge/In0.16Ga0.84As heterostructure was grown in situ by molecular beam epitaxy using two separated growth chambers for Ge and III-V materials. Controlled growth conditions led to the presence of 0.75% in-plane tensile strain within Ge layer. High-resolution transmission electron microscopy confirmed pseudomorphic Ge with high crystalline quality and a sharp Ge/In0.16Ga0.84As heterointerface. Atomic force microscopy revealed a uniform two-dimensional cross-hatch surface morphology with a root-mean-square roughness of 1.26 nm. X-ray photoelectron spectroscopy demonstrated reduced tunneling-barrier-height compared with Ge/GaAs heterostructure. The superior structural properties suggest tensile strained Ge/In0.16Ga0.84As heterostructure would be a promising candidate for high-performance and energy-efficient tunnel field-effect transistor applications.

BaTiO3 integration with nanostructured epitaxial (100), (110), and (111) germanium for multifunctional devices.

Ferroelectric-germanium heterostructures have a strong potential for multifunctional devices. Germanium (Ge) is attractive due to its higher electron and hole mobilities while ferroelectric BaTiO3 is promising due to its high relative permittivity, which can make next-generation low-voltage and low-leakage metal-oxide semiconductor field-effect transistors. Here, we investigate the growth, structural, chemical, and band alignment properties of pulsed laser deposited BaTiO3 on epitaxial (100)Ge, (110)Ge, and (111)Ge layers. Cross-sectional transmission electron microscopy micrographs show the amorphous nature of the BaTiO3 layer and also show a sharp heterointerface between BaTiO3 and Ge. The appearance of strong Pendellösung oscillation fringes from high-resolution X-ray diffraction implies the presence of parallel and sharp heterointerfaces. The valence band offset relation of ΔEV(100) ≥ ΔEV(111) > ΔEV(110) and the conduction band offset relation of ΔE(C)(110) > ΔE(C)(111) ≥ ΔE(C)(100) on crystallographically oriented Ge offer significant advancement for designing new-generation ferroelectric-germanium-based multifunctional devices.

Nanostructured lead-free ferroelectric Na0.5Bi0.5TiO3-BaTiO3 whiskers: synthesis mechanism and structure.

Nanostructured lead-free ferroelectric Na(0.5)Bi(0.5)TiO(3)-BaTiO(3) (NBTBT) whiskers with a high aspect ratio were synthesized topochemically using Na(2)Ti(6)O(13) (NTO) as a host structure for the first time. High energy X-ray diffraction coupled with an atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of the lead-free NBTBT whiskers, which was found to be rhombohedral, i.e. a ferroelectric enabling type. High resolution transmission electron microscopic (HRTEM) analysis revealed local monoclinic-type structural distortions, indicating a modulated structure at the nanoscale in the morphotropic phase boundary (MPB) composition of the lead-free NBTBT whiskers. The structural rearrangement during the synthesis of the lead-free NBTBT whiskers was found to occur via translation of the edge shared octahedra of NTO into a corner sharing coordination. High temperature morphological changes that depict the disintegration of the isolated whiskers into their individual grains due to the higher grain boundary energy have been found to occur in close analogy with Rayleigh-type instability.

Magnetoelectric Interactions in Lead-Based and Lead-Free Composites.

Magnetoelectric (ME) composites that simultaneously exhibit ferroelectricity and ferromagnetism have recently gained significant attention as evident by the increasing number of publications. These research activities are direct results of the fact that multiferroic magnetoelectrics offer significant technological promise for multiple devices. Appropriate choice of phases with co-firing capability, magnetostriction and piezoelectric coefficient, such as Ni-PZT and NZFO-PZT, has resulted in fabrication of prototype components that promise transition. In this manuscript, we report the properties of Ni-PZT and NZFO-PZT composites in terms of ME voltage coefficients as a function of frequency and magnetic DC bias. In order to overcome the problem of toxicity of lead, we have conducted experiments with Pb-free piezoelectric compositions. Results are presented on the magnetoelectric performance of Ni-NKN, Ni-NBTBT and NZFO-NKN, NZFO-NBTBT systems illustrating their importance as an environmentally friendly alternative.

Magnetic studies of multiferroic Bi(1-x)Sm(x)FeO(3) ceramics synthesized by mechanical activation assisted processes.

Bi(1-x)Sm(x)FeO(3) (x = 0.0-0.2) ceramic samples were prepared by mechanical activation assisted solid-state-reaction synthesis. A stoichiometric mixture of Bi(2)O(3), Sm(2)O(3), and Fe(2)O(3) powders was mechanically milled and this was followed by heat treatment at 700 °C for 1 h. Room temperature x-ray diffraction patterns confirmed the formation of perovskite structured Bi(1-x)Sm(x)FeO(3) phase. Vibrating sample magnetometry measurements showed that to a certain extent, Sm doping of BiFeO(3) leads to increased magnetization and a sharp magnetic transition at ∼380 °C. Mössbauer spectroscopy confirmed the presence of single-phase material for the doped compositions whereas electron paramagnetic resonance analysis showed the effect of doping on the variation in the degree of canting in the samples. At doping levels of 10 at.% Sm, the improvement in the magnetic behaviour appears to arise from a combination of the propensity of the samples to form pure phase material, partial destruction of spin cycloids, increased canting of spins and interaction between magnetic ions.