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1. Exploring the Pb 1− x Sr x HfO 3 System and Potential for High Capacitive Energy Storage Density and Efficiency

   https://doi.org/10.1002/adma.202105967  

   Acharya, Megha ; Banyas, Ella ; Ramesh, Maya ; Jiang, Yizhe ; Fernandez, Abel ; Dasgupta, Arvind ; Ling, Handong ; Hanrahan, Brendan ; Persson, Kristin ; Neaton, Jeffrey B. ; et al ( October 2021 , Advanced Materials)

   The hafnate perovskites PbHfO₃(antiferroelectric) and SrHfO₃(“potential” ferroelectric) are studied as epitaxial thin films on SrTiO₃(001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb_1−xSr_xHfO₃system. The resulting (240)‐oriented PbHfO₃(Pba2) films exhibited antiferroelectric switching with a saturation polarization ≈53 µC cm⁻²at 1.6 MV cm⁻¹, weak‐field dielectric constant ≈186 at 298 K, and an antiferroelectric‐to‐paraelectric phase transition at ≈518 K. (002)‐oriented SrHfO₃films exhibited neither ferroelectric behavior nor evidence of a polarP4mmphase . Instead, the SrHfO₃films exhibited a weak‐field dielectric constant ≈25 at 298 K and no signs of a structural transition to a polar phase as a function of temperature (77–623 K) and electric field (–3 to 3 MV cm⁻¹). While the lack of ferroelectric order in SrHfO₃removes the potential for MPB, structural and property evolution of the Pb_1−xSr_xHfO₃(0 ≤x < 1) system is explored. Strontium alloying increased the electric‐breakdown strength (E_B) and decreased hysteresis loss, thus enhancing the capacitive energy storage density (U_r) and efficiency (η). The composition, Pb_0.5Sr_0.5HfO₃produced the best combination ofE_B = 5.12 ± 0.5 MV cm⁻¹,U_r = 77 ± 5 J cm⁻³, and η = 97 ± 2%, well out‐performing PbHfO₃and other antiferroelectric oxides.

    

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2. Electrochemical performance of ionic polymer metal composite under tensile loading

   https://doi.org/10.1088/1361-665X/acecca  

   Napollion, Liya ; Kim, Kwang J. ( August 2023 , Smart Materials and Structures)

   Cracks in polymer composites can lead to premature failure, which can be disastrous for polymer-based energy storage devices. Detecting these cracks is essential to guarantee the reliability and safety of such devices. However, detecting cracks in composite polymers such as ionic polymer metal composites (IPMCs) is a challenging task, which makes it difficult to ensure their performance and safety. The overall goal of this study is to investigate the effect of cracks or damage caused by tensile loading on the mechanical properties and electrochemical characteristics of IPMC based capacitors. During tensile testing, the deformation of the IPMC strips causes changes in the ion distribution and concentration in the polymer matrix, influencing the performance of the material. The measurements were conducted utilizing electrochemical impedance spectroscopy at a room temperature (${21}^{\circ }\text{C}$) and frequency range of 10 KHz to 1 Hz. The method utilized in this study proved to be easy and quick with consistent results. The IPMC capacitor was found to increase its capacitance after major cracking in the Pt electrodes from high tensile mechanical loads. Furthermore, at lower frequency range (<100 Hz), the real (${\epsilon }^{\mathrm{\prime }}$) and imaginary (${\epsilon }^{\mathrm{\prime }\mathrm{\prime }}$) part of permittivity increase with the addition of loads. This displays that the dielectric property of the material is affected due to the increasing of the loads. It is concluded that, at frequencies above 100 Hz, the permittivity is weakly load dependent.

    

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3. Reduced fatigue and leakage of ferroelectric TiN/Hf 0.5 Zr 0.5 O 2 /TiN capacitors by thin alumina interlayers at the top or bottom interface

   https://doi.org/10.1088/1361-6528/acad0a  

   Hsain, H Alex ; Lee, Younghwan ; Lancaster, Suzanne ; Lomenzo, Patrick D ; Xu, Bohan ; Mikolajick, Thomas ; Schroeder, Uwe ; Parsons, Gregory N ; Jones, Jacob L ( January 2023 , Nanotechnology)

   Abstract Hf 0.5 Zr 0.5 O 2 (HZO) thin films are promising candidates for non-volatile memory and other related applications due to their demonstrated ferroelectricity at the nanoscale and compatibility with Si processing. However, one reason that HZO has not been fully scaled into industrial applications is due to its deleterious wake-up and fatigue behavior which leads to an inconsistent remanent polarization during cycling. In this study, we explore an interfacial engineering strategy in which we insert 1 nm Al 2 O 3 interlayers at either the top or bottom HZO/TiN interface of sequentially deposited metal-ferroelectric-metal capacitors. By inserting an interfacial layer while limiting exposure to the ambient environment, we successfully introduce a protective passivating layer of Al 2 O 3 that provides excess oxygen to mitigate vacancy formation at the interface. We report that TiN/HZO/TiN capacitors with a 1 nm Al 2 O 3 at the top interface demonstrate a higher remanent polarization (2P r ∼ 42 μ C cm −2 ) and endurance limit beyond 10 8 cycles at a cycling field amplitude of 3.5 MV cm −1 . We use time-of-flight secondary ion mass spectrometry, energy dispersive spectroscopy, and grazing incidence x-ray diffraction to elucidate the origin of enhanced endurance and leakage properties in capacitors with an inserted 1 nm Al 2 O 3 layer. We demonstrate that the use of Al 2 O 3 as a passivating dielectric, coupled with sequential ALD fabrication, is an effective means of interfacial engineering and enhances the performance of ferroelectric HZO devices. 

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4. Bidirectional tuning of phase transition properties in Pt : VO 2 nanocomposite thin films

   https://doi.org/10.1039/D0NR04008H  

   He, Zihao ; Jian, Jie ; Misra, Shikhar ; Gao, Xingyao ; Wang, Xuejing ; Qi, Zhimin ; Yang, Bo ; Zhang, Di ; Zhang, Xinghang ; Wang, Haiyan ( September 2020 , Nanoscale)

   null (Ed.)

   A phase transition material, VO 2 , with a semiconductor-to-metal transition (SMT) near 341 K (68 °C) has attracted significant research interest because of drastic changes in its electrical resistivity and optical dielectric properties. To address its application needs at specific temperatures, tunable SMT temperatures are highly desired. In this work, effective transition temperature ( T c ) tuning of VO 2 has been demonstrated via a novel Pt : VO 2 nanocomposite design, i.e. , uniform Pt nanoparticles (NPs) embedded in the VO 2 matrix. Interestingly, a bidirectional tuning has been achieved, i.e. , the transition temperature can be systematically tuned to as low as 329.16 K or as high as 360.74 K, with the average diameter of Pt NPs increasing from 1.56 to 4.26 nm. Optical properties, including transmittance ( T %) and dielectric permittivity ( ε ′) were all effectively tuned accordingly. All Pt : VO 2 nanocomposite thin films maintain reasonable SMT properties, i.e. sharp phase transition and narrow width of thermal hysteresis. The bidirectional T c tuning is attributed to two factors: the reconstruction of the band structure at the Pt : VO 2 interface and the change of the Pt : VO 2 phase boundary density. This demonstration sheds light on phase transition tuning of VO 2 at both room temperature and high temperature, which provides a promising approach for VO 2 -based novel electronics and photonics operating under specific temperatures. 

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5. Structural Stability of Magnetic Tunnel Junction Based Molecular Spintronics Devices (MTJMSD)

   https://doi.org/10.1115/IMECE2020-24134  

   Dillard, Joshua ; Amir, Uzma ; Tyagi, Pawan ; Lamberti, Vincent ( November 2020 , roceedings of the ASME 2020 International Mechanical Engineering Congress and Exposition.)

   null (Ed.)

   Harnessing the exotic properties of molecular level nanostructures to produce novel sensors, metamaterials, and futuristic computer devices can be technologically transformative. In addition, connecting the molecular nanostructures to ferromagnetic electrodes bring the unprecedented opportunity of making spin property based molecular devices. We have demonstrated that magnetic tunnel junction based molecular spintronics device (MTJMSD) approach to address numerous technological hurdles that have been inhibiting this field for decades (P. Tyagi, J. Mater. Chem., Vol. 21, 4733). MTJMSD approach is based on producing a capacitor like a testbed where two metal electrodes are separated by an ultrathin insulator and subsequently bridging the molecule nanostructure across the insulator to transform a capacitor into a molecular device. Our prior work showed that MTJMSDs produced extremely intriguing phenomenon such as room temperature current suppression by six orders, spin photovoltaic effect, and evolution of new forms of magnetic metamaterials arising due to the interaction of the magnetic a molecule with two ferromagnetic thin films. However, making robust and reproducible electrical connections with exotic molecules with ferromagnetic electrodes is full of challenges and requires attention to MTJMSD structural stability. This paper focuses on MTJMSD stability by describing the overall fabrication protocol and the associated potential threat to reliability. MTJMSD is based on microfabrication methods such as (a) photolithography for patterning the ferromagnetic electrodes, (b) sputtering of metallic thin films and insulator, and (c) at the end electrochemical process for bridging the molecules between two ferromagnetic films separated by ∼ 2nm insulating gap. For the successful MTJMSD fabrication, the selection of ferromagnetic metal electrodes and thickness was found to be a deterministic factor in designing the photolithography, thin film deposition strategy, and molecular bridging process. We mainly used isotropic NiFe soft magnetic material and anisotropic Cobalt (Co) with significant magnetic hardness. We found Co was susceptible to chemical etching when directly exposed to photoresist developer and aged molecular solution. However, NiFe was very stable against the chemicals we used in the MTJMSD fabrication. As compared to NiFe, the Co films with > 10nm thickness were susceptible to mechanical stress-induced nanoscale deformities. However, cobalt was essential to produce (a) low leakage current before transforming the capacitor from the magnetic tunnel junction into molecular devices and (b) tailoring the magnetic properties of the ferromagnetic electrodes. This paper describes our overall MTJMSD fabrication scheme and process optimization to overcome various challenges to produce stable and reliable MTJMSDs. We also discuss the role of mechanical stresses arising during the sputtering of the ultrathin insulator and how to overcome that challenge by optimizing the insulator growth process. This paper will benefit researchers striving to make nanoscale spintronics devices for solving grand challenges in developing advanced sensors, magnetic metamaterials, and computer devices.

    

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