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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Intrinsically stretchable electrode array enabled in vivo electrophysiological mapping of atrial fibrillation at cellular resolution

Electrophysiological mapping of chronic atrial fibrillation (AF) at high throughput and high resolution is critical for understanding its underlying mechanism and guiding definitive treatment such as cardiac ablation, but current electrophysiological tools are limited by either low spatial resolution or electromechanical uncoupling of the beating heart. To overcome this limitation, here we introduce a scalable method for fabricating a tissue-like, high-density, fully elastic electrode (elastrode) array capable of achieving real-time, stable, cellular level-resolution electrophysiological mapping in vivo. Testing with acute rabbit and porcine models, the device is proven to have robust and intimate tissue coupling while maintaining its chemical, mechanical, and electrical properties during the cardiac cycle. The elastrode array records epicardial atrial signals with comparable efficacy to currently available endocardial-mapping techniques but with 2 times higher atrial-to-ventricular signal ratio and >100 times higher spatial resolution and can reliably identify electrical local heterogeneity within an area of simultaneously identified rotor-like electrical patterns in a porcine model of chronic AF.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Precision Polishing of Ablator Capsules via in situ Process Monitoring and Machine Learning–Based Optimization

In inertial confinement fusion (ICF) experiments seeking output gains of unity and beyond, the quality of the ablator capsule is paramount for minimizing the hydrodynamic mix that quenches the central hot spot. Defects in the form of foreign particles or missing mass on the surface and within the wall of the capsule are primary offenders. High-density carbon capsules made for ICF experiments at the National Ignition Facility are precision polished to achieve surface smoothness on the order of a few nanometers as well as to minimize isolated defects in the form of pits. Given the critical role of this process, we are developing smart manufacturing techniques with the goal of elevating the efficiency of this process. Our approach is to use MEMS (micro-electromechanical systems)–based sensors to capture the fine vibration signals generated during the polishing process and combine them with synchronized visual feedback as needed. Beyond using these sensors for process monitoring, we use specific deep learning methods to analyze the data and extract correlations with both the process parameters and the final performance of the polishing run. Here, in this work, we describe the multiple fronts we have explored in this regard and the results we have gotten so far. This approach promises to have the potential to ultimately provide real-time feedback that can be used to ensure the progress of the run as well as a means for faster optimization.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Graphene engineering by neon ion beams

Achieving the ultimate limits of materials and device performance necessitates the engineering of matter with atomic, molecular, and mesoscale fidelity. While common for organic and macromolecular chemistry, these capabilities are virtually absent for 2D materials. In contrast to the undesired effect of ion implantation from focused ion beam (FIB) lithography with gallium ions, and proximity effects in standard e-beam lithography techniques, the shorter mean free path and interaction volumes of helium and neon ions offer a new route for clean, resist free nanofabrication. Furthermore, with the advent of scanning helium ion microscopy, maskless He + and Ne + beam lithography of graphene based nanoelectronics is coming to the forefront. Here, we will discuss the use of energetic Ne ions in engineering graphene devices and explore the mechanical, electromechanical and chemical properties of the ion-milled devices using scanning probe microscopy (SPM). By using SPM-based techniques such as band excitation (BE) force modulation microscopy, Kelvin probe force microscopy (KPFM) and Raman spectroscopy, we demonstrate that the mechanical, electrical and optical properties of the exact same devices can be quantitatively extracted. Additionally, the effect of defects inherent in ion beam direct-write lithography, on the overall performance of the fabricated devices is elucidated.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microfabrication of plastic-PDMS microfluidic devices using polyimide release layer and selective adhesive bonding

In this study, we present an improved method to bond poly(dimethylsiloxane) (PDMS) with polyimide (PI) to develop flexible substrate microfluidic devices. The PI film was separately fabricated on a silicon wafer by spin coating followed by thermal treatment to avoid surface unevenness of the flexible substrate. In this way, we could also integrate flexible substrate into standard micro-electromechanical systems (MEMS) fabrication. Meanwhile, the adhesive epoxy was selectively transferred to the PDMS microfluidic device by a stamp-and-stick method to avoid epoxy clogging the microfluidic channels. To spread out the epoxy evenly on the transferring substrate, we used superhydrophilic vanadium oxide film coated glass as the transferring substrate. After the bonding process, the flexible substrate could easily be peeled off from the rigid substrate. Contact angle measurement was used to characterize the hydrophicity of the vanadium oxide film. X-ray photoelectron spectroscopy analysis was conducted to study the surface of the epoxy. We further evaluated the bonding quality by peeling tests, which showed a maximum bonding strength of 100 kPa. By injecting with black ink, the plastic microfluidic device was confirmed to be well bonded with no leakage for a day under 1 atm. Finally, this proposed versatile method could bond the microfluidic device and plastic substrate together and be applied in the fabrication of some biosensors and lab-on-a-chip systems.

42 ENGINEERING↗
DOE OSTI2017

Quantification of in-contact probe-sample electrostatic forces with dynamic atomic force microscopy

Here, atomic force microscopy (AFM) methods utilizing resonant mechanical vibrations of cantilevers in contact with a sample surface have shown sensitivities as high as few picometers for detecting surface displacements. Such a high sensitivity is harnessed in several AFM imaging modes. Here, we demonstrate a cantilever-resonance-based method to quantify electrostatic forces on a probe in the probe-sample junction in the presence of a surface potential or when a bias voltage is applied to the AFM probe. We find that the electrostatic forces acting on the probe tip apex can produce signals equivalent to a few pm of surface displacement. In combination with modeling, the measurements of the force were used to access the strength of the electrical field at the probe tip apex in contact with a sample. We find an evidence that the electric field strength in the junction can reach ca. 1 V nm –1 at a bias voltage of a few volts and is limited by non-ideality of the tip-sample contact. This field is sufficiently strong to significantly influence material states and kinetic processes through charge injection, Maxwell stress, shifts of phase equilibria, and reduction of energy barriers for activated processes. Besides, the results provide a baseline for accounting for the effects of local electrostatic forces in electromechanical AFM measurements as well as offer additional means to probe ionic mobility and field-induced phenomena in solids.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Real-time studies of ferroelectric domain switching: a review

Ferroelectric materials have been utilized in a broad range of electronic, optical, and electromechanical applications and hold the promise for the design of future high-density nonvolatile memories and multifunctional nano-devices. The applications of ferroelectric materials stem from the ability to switch polarized domains by applying an electric field, and therefore a fundamental understanding of the switching dynamics is critical for design of practical devices. In this review, we summarize the progress in the study of the microscopic process of ferroelectric domain switching using recently developed in situ transmission electron microscopy (TEM). We first briefly introduce the instrumentation, experimental procedures, imaging mechanisms, and analytical methods of the state-of-the-art in situ TEM techniques. The application of these techniques to studying a wide range of complex switching phenomena, including domain nucleation, domain wall motion, domain relaxation, domain-defect interaction, and the interplay between different types of domains, is demonstrated. The underlying physics of these dynamic processes are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A compliant mechanism for inspecting extremely confined spaces

We present here a novel, compliant mechanism that provides the capability to navigate extremely confined spaces for the purpose of infrastructure inspection. Extremely confined spaces are commonly encountered during infrastructure inspection. Examples of such spaces can include pipes, conduits, and ventilation ducts. Often these infrastructure features go uninspected simply because there is no viable way to access their interior. In addition, it is not uncommon for extremely confined spaces to possess a maze-like architecture that must be selectively navigated in order to properly perform an inspection. Efforts by the imaging sensor community have resulted in the development of imaging sensors on the millimeter length scale. Due to their compact size, they are able to inspect many extremely confined spaces of interest, however, the means to deliver these sensors to the proper location to obtain the desired images are lacking. To address this problem, we draw inspiration from the field of endoscopic surgery. Specifically we consider the work that has already been done to create long flexible needles that are capable of being steered through the human body. These devices are typically referred to as 'steerable needles.' Steerable needle technology is not directly applicable to the problem of navigating maze-like arrangements of extremely confined spaces, but it does provide guidance on how this problem should be approached. Specifically, the super-elastic nitinol tubing material that allows steerable needles to operate is also appropriate for the problem of navigating maze-like arrangements of extremely confined spaces. Furthermore, the portion of the mechanism that enters the extremely confined space is completely mechanical in nature. The mechanical nature of the device is an advantage when the extremely confined space features environmental hazards such as radiation that could degrade an electromechanically operated mechanism. Here, we present a compliant mechanism developed to navigate maze-like arrangements of extremely confined spaces. The mechanism is shown to be able to selectively navigate past three 90° bends. The ability to selectively navigate extremely confined spaces opens up new possibilities to use emerging miniature imaging technology for infrastructure inspection.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Ultrasonic waves from radial mode excitation of a piezoelectric disc on the surface of an elastic solid

In this work, we discuss the ultrasonic wave propagation characteristics in an isotropic elastic solid due to the radial mode excitation of a piezoelectric disc actuator bonded to its surface. Finite element simulations using coupled electromechanical modeling is employed to investigate the wave propagation behavior. We find that the radial mode vibrations on the surface of the elastic solid generates all the three types of ultrasonic waves: longitudinal, shear, and surface waves. The waves in the solid are comprised of a central lobe and multiple side lobes based on the frequency of the radial mode excitation. The central lobe is predominantly composed of longitudinal waves and the side lobes are composed of shear waves. While the longitudinal waves have a strong central lobe and weak side lobes that are not fully developed, shear waves consists of fully developed side lobes. In addition, we observe that the longitudinal waves have fewer side lobes inside the solid compared to the shear waves. A semi-analytical approach is presented to explain the above observations. The interface traction boundary condition between the piezoelectric disc and the elastic solid is approximated as a truncated 'Bessel' excitation over the area of the piezoelectric disc in contact with the solid. A Fourier–Bessel series expansion technique is used to investigate the wave propagation behavior from the above traction boundary condition. The results obtained explain the observations from the finite element simulations with regard to the number and distribution of side lobes pertaining to the longitudinal and shear waves generated from the radial modes of the piezoelectric disc. The proposed semi-analytical approach is general and can be applied to any arbitrary axisymmetric excitations on the surface of an elastic solid.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effects of stabilizer strength on the delamination strength of ReBCO coated conductors

Delamination strengths (DSs) of ReBCO tapes were evaluated using a transverse tensile anvil test. This study first demonstrated that the electromechanical DS is nearly equivalent to the purely mechanical DS for ReBCO tapes exhibiting abrupt delamination behavior. Mechanical DS was then examined for tapes with and without stabilizer edges to assess the influence of stabilizer strength. Scanning electron microscopy/energy-dispersive x-ray spectroscopy analysis revealed the delamination sites and crack propagation in ReBCO tapes. Further investigation revealed that the DS of ReBCO tapes is primarily determined by two factors: (1) interfacial bonding strength between the layers and (2) mechanical strength of the stabilizer edges. These findings point to a potential approach to enhancing DS by increasing the strength of the stabilizer (e.g. by optimizing the Cu electroplating process).

Cu stabilizer↗
DOE OSTI2020

Alignment of Polarization against an Electric Field in van der Waals Ferroelectrics

Polarization in ferroelectrics can be switched in the direction of an applied electric field by dipole reorientation, enabling numerous applications and fundamental phenomena. In this study, we demonstrate that, in the van der Waals (vdW) layered ferrielectric Cu In P 2 S 6 , a unique mechanism exists where polarization aligns against the direction of the applied electric field, seemingly in violation of the fundamental properties of a dipolar solid. The mechanism is the result of the electric field driving the Cu atoms unidirectionally across the vdW gaps, which is distinctively different from dipole reorientation. The crossing of Cu atoms is the fundamental process of ionic conductivity, yet it is compatible with the existence of polarization. These phenomena are confirmed by nanoscale imaging and spectroscopy of ferroelectric capacitors, coupled with dynamic density-functional-theory simulations. The symbiotic relationship of ferroelectric and ionic phenomena enables alternative approaches to control polarization and necessitates a change in perspective on nucleation, domain-wall dynamics, and other ferroelectric and electromechanical characteristics in material systems where ionic and ferroelectric phenomena manifest.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Continuous and Time-Domain Coherent Signal Conversion between Optical and Microwave Frequencies

A quantum network consisting of computational nodes connected by high-fidelity communication channels could expand information-processing capabilities significantly beyond those of classical networks. Superconducting qubits hold promise for scalable and high-fidelity quantum computation at microwave frequencies but must operate in an isolated cryogenic environment, obviating the potential for practical long-range communication. Quantum communication has, however, been demonstrated with optical photons. A fast efficient quantum-coherent interface between superconducting qubits and optical photons would provide a key resource for a large-scale quantum network or distributed quantum computer. Here, we describe the design and experimental operation of a device incorporating a silicon optomechanical nanobeam combined with an aluminum-nitride-based electromechanical transducer. We experimentally demonstrate classical continuous-wave operation of this device at room temperature with external conversion efficiencies of (2.5 +/- 0.4) x 10 -5 (microwave to optical) and (3.8 +/- 0.4) x 10 -5 (optical to microwave), corresponding to internal efficiencies of 2.4% and 3.7%, respectively. Finally, this device also has a larger bandwidth than previous efficient microwave-optical transducers, allowing us to operate in the time domain with 20-ns pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Temperature-Assisted Piezoresponse Force Microscopy: Probing Local Temperature-Induced Phase Transitions in Ferroics

The combination of local heating and biasing at the tip-surface junction in temperature-assisted piezoresponse force microscopy (TPFM) opens a pathway for probing local temperature-induced phase transitions in ferroics, exploring the temperature dependence of polarization dynamics in ferroelectrics and potentially discovering coupled phenomena driven by strong temperature and electric field gradients. In this study we analyze the signal-formation mechanism in TPFM and explore the interplay between thermal- and bias-induced switching in model ferroelectric materials. Furthermore, we explore the contributions of the flexoelectric and thermopolarization effects to the local electromechanical response and demonstrate that the latter can be significant for “soft” ferroelectrics. These results establish a framework for the quantitative interpretation of TPFM observations, predict the emergence of nontrivial switching and relaxation phenomena driven by nonlocal thermal-gradient-induced polarization switching, and open a pathway for exploring the physics of thermopolarization effects in various noncentrosymmetric and centrosymmetric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Finite-size effects in lead scandium tantalate relaxor thin films

Large electromechanical effects in relaxor ferroelectrics are generally attributed to the collective response of an ensemble of correlated, nanometer-sized polar structures induced by chemical and charge disorder. Here, we study finite-size effects on such polar order (i.e., how it evolves when sample dimensions approach the polarization correlation length) in 7–70-nm-thick films of the relaxor ferroelectric PbSc 0.5 Ta 0.5 O 3 . Temperature-dependent polarization studies reveal a linear suppression of the polarization and nonlinearity associated with relaxor order as the film thickness decreases to ≈ 30 nm. Below this thickness, however, the suppression rapidly accelerates, and polarization is completely absent by film thicknesses of ≈ 7 nm, despite the continued observation of a broad peak in dielectric permittivity and frequency dispersion. Diffuse-scattering measurements reveal the diffuse-scattering symmetry, and analysis suggests the films have a polarization correlation length of ≈ 23 nm. Finally, taken together, it is apparent that reduction of sample size and the resulting distribution of polar structures drive suppression and eventual quenching of the electrical response of relaxors, which may be attributed to increasing dipole-dipole and dipole-interface interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Dynamical origins of weakly coupled relaxor behavior in Sn-doped (Ba,Ca)TiO 3 -BiScO 3

The peculiar characteristics of relaxors, viz., a frequency-dependent dielectric permittivity peak and good functional properties (dielectric, electromechanical, electrocaloric, etc.), are attributed to nanoscale regions with correlated dipoles, or polar nanoregions (PNRs). However, the exact nature of PNRs and their contribution to relaxor behavior remains debatable. In recent years, solid solutions of BaTiO3-BiMeO3 (where Me is a metal), have emerged as an interesting system with characteristics in between that of relaxors and dipole glasses. Here, we have examined the atomistic origins of weakly coupled relaxor behavior, specifically with regard to formation of PNRs, in Sn-doped (1-x)(Ba,Ca)TiO 3-x BiScO 3 using macroscopic polarization and neutron dynamic pair distribution function measurements. We show that the short-range atomic correlations observed within the PNRs dynamically fluctuate with frequencies of the order of THz. Furthermore the composition-dependent dielectric and polarization behaviors are critically influenced by the relative stability of the atomic correlations near ~1 THz, while the instantaneous atomic correlations are largely independent of x. The current results are discussed based on a model of intrinsic local modes distributed in a dielectrically soft matrix.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Probing phonon softening in ferroelectrics by scanning probe microwave spectroscopy

Microwave measurements have recently been successfully applied to measure ferroelectric materials on the nanoscale, including detection of polarization switching and ferroelectric domain walls. In this study we discuss the question of whether scanning probe microscopy operating at microwave frequency can identify the changes associated with the soft phonon dynamics in a ferroic. The analytical expressions for the electric potential, complex impedance, and dielectric losses are derived and analyzed, since these physical quantities are linked to experimentally measurable properties of the ferroic. As a ferroic we consider virtual or proper ferroelectric with an optic phonon mode that softens at a Curie point. We also consider a decay mechanism linked to the conductance of the ferroic, thus manifesting itself as the dielectric loss in the material. Our key finding is that the influence of the soft phonon dispersion on the surface potential distribution, complex impedance, and dielectric losses are evidently strong in the vicinity (~10–30 K) of the Curie temperature. Additionally, we quantified how the spatial distribution and frequency spectra of the complex impedance and the dielectric losses react on the dynamics of the soft phonons near the Curie point. These results set the stage for characterization of polar phase transitions with nanoscale microwave measurements, providing a complementary approach to well established electromechanical measurements for fundamental understanding of ferroelectric properties as well as their applications in telecommunication and computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Enhanced ferroelectric and piezoelectric properties of BCT-BZT at the morphotropic phase boundary driven by the coexistence of phases with different symmetries

The discovery of lead-free piezoelectric materials is crucial for future information and energy storage applications. Enhanced piezoelectric and other physical properties are commonly observed near the morphotropic phase boundary (MPB) composition of ferroelectric solid solutions. The (1 – x)Ba(Zr 0.2 Ti 0.8 )O 3 -x(Ba0.7Ca0.3)TiO 3 (BZT-xBCT) system exhibits a large electromechanical response around its MPB region at x = 0.5. Here, we report experimental and theoretical results of BZT-xBCT over a wide composition range (0.3 ≤ x ≤ 1.0). X-ray diffraction and Raman spectroscopy studies indicate a composition-induced structural phase transition from a rhombohedral (R3m) phase at x ≤ 0.4 to a tetragonal (P4mm) phase at x ≥ 0.6 through a multiphase coexistence region at 0.45 ≤ x ≤ 0.55 involving orthorhombic + tetragonal (Amm2 + P4mm) phases. First-principles calculations elucidate the phase competition in the coexistence region. The critical composition (x = 0.5) displays enhanced dielectric, ferroelectric, and piezoelectric properties, where notably d 33 ~ 320 pC/N. This paper provides clear evidence of Amm2+P4mm crystallographic phases in the MPB region, which is responsible for the improved functional properties.

MPB↗
DOE OSTI2022

Colossal piezoresistance in narrow-gap Eu 5 In 2 Sb 6

Piezoresistance, the change of the electrical resistance (R) of a material in response to an applied mechanical stress (σ), is the driving principle of electromechanical devices such as strain gauges, accelerometers, and cantilever force sensors. Enhanced piezoresistance has been traditionally observed in two classes of uncorrelated materials: nonmagnetic semiconductors and composite structures. In this study, we report the discovery of a remarkably large piezoresistance in Eu 5 In 2 Sb 6 single crystals, wherein anisotropic metallic clusters naturally form within a semiconducting matrix due to electronic interactions. Eu 5 In 2 Sb 6 shows a highly anisotropic piezoresistance, and uniaxial pressure along [001] of only 0.4 GPa leads to a resistivity drop of >99.95%, which results in a colossal piezoresistance factor of 5000×10 –11 Pa –1 . Our result not only reveals the role of interactions and phase separation in the realization of colossal piezoresistance, but it also highlights a route to multifunctional devices with large responses to both pressure and magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Surface acoustic wave generation and detection in the quantum paraelectric regime of SrTiO 3 -based heterostructures

Strontium titanate (STO), apart from being a ubiquitous substrate for complex-oxide heterostructures, possesses a multitude of strongly coupled electronic and mechanical properties. Surface acoustic wave (SAW) generation and detection offers insight into electromechanical couplings that are sensitive to quantum paraelectricity and other structural phase transitions. Propagating SAWs can interact with STO-based electronic nanostructures, in particular LaAlO 3 /SrTiO 3 (LAO/STO). Here, we report the generation and detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures ( T ≥ 2 K) using superconducting interdigitated transducers. Further, the temperature dependence shows an increase in the SAW quality factor that saturates at T ≈ 8 K. The effect of backgate tuning on the SAW resonance frequency shows the possible acoustic coupling with the ferroelastic domain wall evolution. This method of generating SAWs provides a pathway towards the dynamic tuning of ferroelastic domain structures, which are expected to influence the electronic properties of complex-oxide nanostructures. Devices that incorporate SAWs may in turn help to elucidate the role of ferroelastic domain structures in mediating electronic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗