Pub Date : 2024-01-12DOI: 10.1038/s41427-023-00521-9
Chen-Yu Hu, Wei-De Chen, Yan-Ting Liu, Chao-Chung Huang, Chi-Feng Pai
The discovery of efficient magnetization switching upon device activation by spin Hall effect (SHE)-induced spin–orbit torque (SOT) changed the course of magnetic random-access memory (MRAM) research and development. However, for electronic systems with perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by the necessity of a longitudinal magnetic field to break magnetic symmetry and achieve deterministic switching. In this work, we demonstrate that robust and tunable field-free current-driven SOT switching of perpendicular magnetization can be controlled by the growth protocol in Pt-based magnetic heterostructures. We further elucidate that such growth-dependent symmetry breaking originates from the laterally tilted magnetic anisotropy of the ferromagnetic layer with PMA, a phenomenon that has been largely neglected in previous studies. We show experimentally and in simulation that in a PMA system with tilted anisotropy, the deterministic field-free switching exhibits a conventional SHE-induced damping-like torque feature, and the resulting current-induced effective field shows a nonlinear dependence on the applied current density. This relationship could be potentially misattributed to an unconventional SOT origin. This study explores a novel approach to achieve field-free current-driven spin–orbit torque switching of perpendicular magnetization for MRAM applications. By adjusting growth protocols in Pt-based magnetic heterostructures, a previously overlooked laterally tilted texture and magnetic anisotropy are harnessed. These findings allow deterministic switching of perpendicular magnetization without an external magnetic field. Contrary to conventional assumptions, the observed nonlinear dependence on current density resembles a damping-like torque, challenging previous notions about its origin.
自旋霍尔效应（SHE）诱导的自旋轨道力矩（SOT）可在器件激活时实现高效磁化切换，这一发现改变了磁性随机存取存储器（MRAM）的研究和开发进程。然而，对于具有垂直磁各向异性（PMA）的电子系统来说，由于需要纵向磁场来打破磁对称性并实现确定性开关，SOT 的使用仍然受到阻碍。在这项工作中，我们证明了在铂基磁异质结构中，垂直磁化的稳健、可调的无磁场电流驱动 SOT 开关可由生长协议控制。我们进一步阐明，这种依赖于生长的对称性破坏源于具有 PMA 的铁磁层的横向倾斜磁各向异性，而这一现象在以往的研究中基本上被忽视了。我们通过实验和仿真表明，在具有倾斜各向异性的 PMA 系统中，确定性无磁场切换表现出传统的 SHE 诱导阻尼转矩特征，由此产生的电流诱导有效磁场与外加电流密度呈非线性依赖关系。这种关系有可能被误认为是非常规 SOT 的起源。
{"title":"The central role of tilted anisotropy for field-free spin–orbit torque switching of perpendicular magnetization","authors":"Chen-Yu Hu, Wei-De Chen, Yan-Ting Liu, Chao-Chung Huang, Chi-Feng Pai","doi":"10.1038/s41427-023-00521-9","DOIUrl":"10.1038/s41427-023-00521-9","url":null,"abstract":"The discovery of efficient magnetization switching upon device activation by spin Hall effect (SHE)-induced spin–orbit torque (SOT) changed the course of magnetic random-access memory (MRAM) research and development. However, for electronic systems with perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by the necessity of a longitudinal magnetic field to break magnetic symmetry and achieve deterministic switching. In this work, we demonstrate that robust and tunable field-free current-driven SOT switching of perpendicular magnetization can be controlled by the growth protocol in Pt-based magnetic heterostructures. We further elucidate that such growth-dependent symmetry breaking originates from the laterally tilted magnetic anisotropy of the ferromagnetic layer with PMA, a phenomenon that has been largely neglected in previous studies. We show experimentally and in simulation that in a PMA system with tilted anisotropy, the deterministic field-free switching exhibits a conventional SHE-induced damping-like torque feature, and the resulting current-induced effective field shows a nonlinear dependence on the applied current density. This relationship could be potentially misattributed to an unconventional SOT origin. This study explores a novel approach to achieve field-free current-driven spin–orbit torque switching of perpendicular magnetization for MRAM applications. By adjusting growth protocols in Pt-based magnetic heterostructures, a previously overlooked laterally tilted texture and magnetic anisotropy are harnessed. These findings allow deterministic switching of perpendicular magnetization without an external magnetic field. Contrary to conventional assumptions, the observed nonlinear dependence on current density resembles a damping-like torque, challenging previous notions about its origin.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"16 1","pages":"1-10"},"PeriodicalIF":8.6,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00521-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139459829","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
For the development of spintronic devices, the control of magnetization by a low electric field is necessary. The microscopic origin of manipulating spins relies on the control of orbital magnetic moments (morb) by strain; this is essential for the high performance magnetoelectric (ME) effect. Herein, electric-field induced X-ray magnetic circular dichroism (XMCD) is used to determine the changes in morb by piezoelectric strain and clarify the relationship between the strain and morb in an interfacial multiferroics system with a significant ME effect; the system consists of the Heusler alloy Co2FeSi on a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Element-specific investigations of the orbital states by operando XMCD and the local environment via extended X-ray absorption fine structure (EXAFS) analysis show that the modulation of only the Fe sites in Co2FeSi primarily contributes to the giant ME effect. The density functional theory calculations corroborate this finding, and the growth of the high index (422) plane in Co2FeSi results in a giant ME effect. These findings elucidate the element-specific orbital control using reversible strain, called the ‘orbital elastic effect,’ and can provide guidelines for material designs with a giant ME effect. Schematic illustrations of the changes in the magnetic anisotropy by an applied electric field (E) in the strain directions are displayed. Under an applied E, the piezoelectric stress in the ferroelectric PMN-PT could be introduced in the tensile and compressive directions using positive and negative bias voltages, respectively, resulting in the changes in the magnetic anisotropy in the Co2FeSi layer. The XMCD spectra of Fe and Co L-edges in Co2FeSi under applying E showed the line shape changes only in the Fe site, which corresponds to the changes of orbital magnetic moment in Fe, while that in Co remains unchanged.
{"title":"Strain-induced specific orbital control in a Heusler alloy-based interfacial multiferroics","authors":"Jun Okabayashi, Takamasa Usami, Amran Mahfudh Yatmeidhy, Yuichi Murakami, Yu Shiratsuchi, Ryoichi Nakatani, Yoshihiro Gohda, Kohei Hamaya","doi":"10.1038/s41427-023-00524-6","DOIUrl":"10.1038/s41427-023-00524-6","url":null,"abstract":"For the development of spintronic devices, the control of magnetization by a low electric field is necessary. The microscopic origin of manipulating spins relies on the control of orbital magnetic moments (morb) by strain; this is essential for the high performance magnetoelectric (ME) effect. Herein, electric-field induced X-ray magnetic circular dichroism (XMCD) is used to determine the changes in morb by piezoelectric strain and clarify the relationship between the strain and morb in an interfacial multiferroics system with a significant ME effect; the system consists of the Heusler alloy Co2FeSi on a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Element-specific investigations of the orbital states by operando XMCD and the local environment via extended X-ray absorption fine structure (EXAFS) analysis show that the modulation of only the Fe sites in Co2FeSi primarily contributes to the giant ME effect. The density functional theory calculations corroborate this finding, and the growth of the high index (422) plane in Co2FeSi results in a giant ME effect. These findings elucidate the element-specific orbital control using reversible strain, called the ‘orbital elastic effect,’ and can provide guidelines for material designs with a giant ME effect. Schematic illustrations of the changes in the magnetic anisotropy by an applied electric field (E) in the strain directions are displayed. Under an applied E, the piezoelectric stress in the ferroelectric PMN-PT could be introduced in the tensile and compressive directions using positive and negative bias voltages, respectively, resulting in the changes in the magnetic anisotropy in the Co2FeSi layer. The XMCD spectra of Fe and Co L-edges in Co2FeSi under applying E showed the line shape changes only in the Fe site, which corresponds to the changes of orbital magnetic moment in Fe, while that in Co remains unchanged.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"16 1","pages":"1-10"},"PeriodicalIF":8.6,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00524-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139439847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The fabrication and development of high-entropy alloys (HEAs) with exceptional functionalities is a rapidly expanding field with numerous applications. When the role of entropy in HEAs is considered, the extrinsic factors, such as the existence of grains and different phases, need to be separated from the intrinsic configurations of the atomic lattice. Here, we fabricated the CoCrFeNi2Al0.5 HEA/muscovite heterostructures, and some were prepared as epitaxial bilayers and others were prepared as an amorphous system. These two systems are classified into atomic-site disordered (ASD) and structurally disordered (SD) states, respectively, without the extrinsic effects for the determination of the crystal lattice role in high-entropy states. In this study, we determined the role of the structure order in correlation with the structural, electronic, and magnetic properties of HEAs using a combination of energy-dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, magneto-transport, ac magnetometry, and X-ray absorption spectroscopy with magnetic circular dichroism. The ASD state showed fully metallic behavior. In contrast, the SD state showed a metallic behavior with intense magnetic saturation, which was called Kondo-like behavior, under 50 K with a low-temperature coefficient of resistivity of ~64 ppm/°C. The difference between the saturation magnetic moment and the electron relaxation behavior in the ASD and SD states resulted from the existence of the structural order affecting the atomic distance and periodicity to modify the exchange interaction and tune the electron-phonon interaction for scattering. The ferromagnetic behavior contributed by Co, Fe, and Ni atoms was probed by X-ray absorption and magnetic circular dichroism to understand the magnetic interactions in the ASD and SD states. The fabrication and development of high-entropy alloys (HEAs) with exceptional functionalities is a rapidly expanding field. The extrinsic factors, such as the existence of grains and different phases, would complicate understanding the physical phenomena. We classified the epitaxial system into atomic-site disordered (ASD) and amorphous system into structurally disordered (SD) states, respectively, to exclude the extrinsic effects of HEAs. With a comprehensive study of the magnetic and transport properties, we can further promote the research of high entropy systems.
制造和开发具有特殊功能的高熵合金（HEAs）是一个快速发展的领域，其应用领域众多。在考虑熵在高熵合金中的作用时，需要将晶粒和不同相的存在等外在因素与原子晶格的内在构型区分开来。在这里，我们制备了 CoCrFeNi2Al0.5 HEA/muscovite 异质结构，其中一些制备成了外延双层结构，另一些制备成了非晶态体系。这两种体系被分别划分为原子位点无序（ASD）态和结构无序（SD）态，在确定高熵态中晶格的作用时不需要考虑外在效应。在这项研究中，我们结合使用了能量色散 X 射线光谱法、X 射线衍射法、透射电子显微镜法、磁传输法、交流磁力测定法和带有磁圆二色性的 X 射线吸收光谱法，确定了结构顺序与 HEA 的结构、电子和磁特性之间的相关性。ASD 状态显示出完全的金属特性。与此相反，SD 状态在 50 K 下表现出具有强磁饱和度的金属行为，被称为近藤行为，其低温电阻系数约为 64 ppm/°C。在 ASD 和 SD 状态下，饱和磁矩和电子弛豫行为之间的差异是由于存在影响原子间距和周期性的结构顺序，从而改变了交换相互作用，并调整了电子-声子相互作用以实现散射。通过 X 射线吸收和磁圆二色性探测了 Co、Fe 和 Ni 原子的铁磁行为，以了解 ASD 和 SD 状态下的磁相互作用。
{"title":"Role of the structure order in the transport and magnetic properties of high-entropy alloy films","authors":"Jia-Wei Chen, Shih-Hsun Chen, Padraic Shafer, Wen-Yen Tzeng, Yi-Cheng Chen, Chih-Wei Luo, Wen-Wei Wu, Jien-Wei Yeh, Ying-Hao Chu","doi":"10.1038/s41427-023-00518-4","DOIUrl":"10.1038/s41427-023-00518-4","url":null,"abstract":"The fabrication and development of high-entropy alloys (HEAs) with exceptional functionalities is a rapidly expanding field with numerous applications. When the role of entropy in HEAs is considered, the extrinsic factors, such as the existence of grains and different phases, need to be separated from the intrinsic configurations of the atomic lattice. Here, we fabricated the CoCrFeNi2Al0.5 HEA/muscovite heterostructures, and some were prepared as epitaxial bilayers and others were prepared as an amorphous system. These two systems are classified into atomic-site disordered (ASD) and structurally disordered (SD) states, respectively, without the extrinsic effects for the determination of the crystal lattice role in high-entropy states. In this study, we determined the role of the structure order in correlation with the structural, electronic, and magnetic properties of HEAs using a combination of energy-dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, magneto-transport, ac magnetometry, and X-ray absorption spectroscopy with magnetic circular dichroism. The ASD state showed fully metallic behavior. In contrast, the SD state showed a metallic behavior with intense magnetic saturation, which was called Kondo-like behavior, under 50 K with a low-temperature coefficient of resistivity of ~64 ppm/°C. The difference between the saturation magnetic moment and the electron relaxation behavior in the ASD and SD states resulted from the existence of the structural order affecting the atomic distance and periodicity to modify the exchange interaction and tune the electron-phonon interaction for scattering. The ferromagnetic behavior contributed by Co, Fe, and Ni atoms was probed by X-ray absorption and magnetic circular dichroism to understand the magnetic interactions in the ASD and SD states. The fabrication and development of high-entropy alloys (HEAs) with exceptional functionalities is a rapidly expanding field. The extrinsic factors, such as the existence of grains and different phases, would complicate understanding the physical phenomena. We classified the epitaxial system into atomic-site disordered (ASD) and amorphous system into structurally disordered (SD) states, respectively, to exclude the extrinsic effects of HEAs. With a comprehensive study of the magnetic and transport properties, we can further promote the research of high entropy systems.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-8"},"PeriodicalIF":8.6,"publicationDate":"2024-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00518-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139093623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-29DOI: 10.1038/s41427-023-00519-3
Seungbae Jeon, Seungjae Lee, Junsu Kim, Sungoh Eim, Wooseop Lee, Woo Hyun Nam, Jeong Gon Son, Du Yeol Ryu
A block copolymer (BCP) with specific monomer structures of fluoroacrylate polymers was designed by exploiting the inorganic superhydrophobicity and low glass transition temperature of polydimethylsiloxane (PDMS). With the use of a fluorine-containing block providing a surface tension as low as that of PDMS (19.9 < $$gamma$$ < 21.5 mN/m), PDMS-b-poly(2,2,3,3,3-pentafluoropropyl acrylate) (PDMS-b-PPeFPA) copolymer was synthesized to create a volume-symmetric lamellar structure. The compositional randomness of the BCP chains adsorbed onto the substrates provided well-balanced interfacial interactions toward the overlaid PDMS-b-PPeFPA ( $$gamma$$ PDMS-ads ≈ $$gamma$$ PPeFPA-ads). Under this symmetric confinement with simultaneous dual neutral interfaces, lamellar microdomains with a sub-10 nm half-pitch feature size were successfully oriented perpendicular to the interfaces at room temperature. We showed the response of the BCP films to a lateral electric field, demonstrating that the perpendicular lamellae were adaptively aligned along the electric vector within a short treatment period. Furthermore, the PDMS-b-PPeFPA system exhibited a remarkable etch contrast for O2 reactive ion etching, yielding unidirectionally aligned air–inorganic nanoarrays emanating from the perpendicular lamellae between the electrodes. This study reports a system engineering approach for conceiving highly immiscible, silicon- and fluorine-containing BCP whose components exhibit identical surface tensions ( $$gamma$$ PDMS ≈ $$gamma$$ PPeFPA) and for generating perpendicularly oriented lamellar microdomains due to substrate neutrality. With the use of a fluorine-containing block providing a surface tension as low as that of PDMS (19.9 < $$gamma$$ < 21.5 mN/m), the PDMS-b-PPeFPA copolymer is synthesized to create a volume-symmetric lamellar structure. Under the symmetric confinement with simultaneous dual neutral interfaces, lamellar microdomains with a sub-10 nm half-pitch feature size are successfully oriented perpendicular to the interfaces at room temperature (RT). Together with unidirectionally aligned perpendicular lamellae along the electric vector in a short period (0.5 h) at RT, we demonstrate a unidirectional alignment of the perpendicular air–inorganic (oxidized PDMS) lamellae between the electrodes.
{"title":"Two-dimensional directed lamellar assembly in silicon- and fluorine-containing block copolymer with identical surface energies","authors":"Seungbae Jeon, Seungjae Lee, Junsu Kim, Sungoh Eim, Wooseop Lee, Woo Hyun Nam, Jeong Gon Son, Du Yeol Ryu","doi":"10.1038/s41427-023-00519-3","DOIUrl":"10.1038/s41427-023-00519-3","url":null,"abstract":"A block copolymer (BCP) with specific monomer structures of fluoroacrylate polymers was designed by exploiting the inorganic superhydrophobicity and low glass transition temperature of polydimethylsiloxane (PDMS). With the use of a fluorine-containing block providing a surface tension as low as that of PDMS (19.9 < $$gamma$$ < 21.5 mN/m), PDMS-b-poly(2,2,3,3,3-pentafluoropropyl acrylate) (PDMS-b-PPeFPA) copolymer was synthesized to create a volume-symmetric lamellar structure. The compositional randomness of the BCP chains adsorbed onto the substrates provided well-balanced interfacial interactions toward the overlaid PDMS-b-PPeFPA ( $$gamma$$ PDMS-ads ≈ $$gamma$$ PPeFPA-ads). Under this symmetric confinement with simultaneous dual neutral interfaces, lamellar microdomains with a sub-10 nm half-pitch feature size were successfully oriented perpendicular to the interfaces at room temperature. We showed the response of the BCP films to a lateral electric field, demonstrating that the perpendicular lamellae were adaptively aligned along the electric vector within a short treatment period. Furthermore, the PDMS-b-PPeFPA system exhibited a remarkable etch contrast for O2 reactive ion etching, yielding unidirectionally aligned air–inorganic nanoarrays emanating from the perpendicular lamellae between the electrodes. This study reports a system engineering approach for conceiving highly immiscible, silicon- and fluorine-containing BCP whose components exhibit identical surface tensions ( $$gamma$$ PDMS ≈ $$gamma$$ PPeFPA) and for generating perpendicularly oriented lamellar microdomains due to substrate neutrality. With the use of a fluorine-containing block providing a surface tension as low as that of PDMS (19.9 < $$gamma$$ < 21.5 mN/m), the PDMS-b-PPeFPA copolymer is synthesized to create a volume-symmetric lamellar structure. Under the symmetric confinement with simultaneous dual neutral interfaces, lamellar microdomains with a sub-10 nm half-pitch feature size are successfully oriented perpendicular to the interfaces at room temperature (RT). Together with unidirectionally aligned perpendicular lamellae along the electric vector in a short period (0.5 h) at RT, we demonstrate a unidirectional alignment of the perpendicular air–inorganic (oxidized PDMS) lamellae between the electrodes.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-10"},"PeriodicalIF":8.6,"publicationDate":"2023-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00519-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139066880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-29DOI: 10.1038/s41427-023-00520-w
Yuqiao Zhang, Hiromichi Ohta
Oxide-based thermoelectric materials that show a high figure of merit are promising because of their good chemical and thermal stabilities and their relative harmlessness compared with chalcogenide-based state-of-the-art thermoelectric materials. Although several high-ZT thermoelectric oxides (ZT > 1) have been reported thus far, their reliability levels are low due to the lack of careful observations of their stabilities at elevated temperatures. Herein, we review the epitaxial film growth and thermoelectric properties of representative p-type layered cobalt oxides: Na3/4CoO2, Ca1/3CoO2, Sr1/3CoO2, Ba1/3CoO2, and Ca3Co4O9. Among these specimens, Ba1/3CoO2 and Ca3Co4O9 are stable in air at elevated temperatures (~600 °C). The ZT of Ba1/3CoO2 reaches ~ 0.55 at 600 °C in air, which is reliable and the highest among thermoelectric oxides. Moreover, this value is comparable to those of p-type PbTe and p-type SiGe. Oxide-based thermoelectric materials that exhibit a high figure of merit are promising because of their good chemical and thermal stabilities and their relative harmlessness compared with chalcogenide-based state-of-the-art thermoelectric materials. The layered barium-cobalt oxide (Ba1/3CoO2) exhibits a record-high ZT of 0.55 at 600 °C in air. The increase in ZT is directly originated by the decreased thermal conductivity of Ba1/3CoO2. As we hypothesized, the greater the atomic mass, the lower the thermal conductivity, resulting in higher ZT. The ZT is reliable and the highest among thermoelectric oxides. Moreover, this value is comparable to those of p-type PbTe and p-type SiGe.
氧化物热电材料具有良好的化学稳定性和热稳定性，而且与最先进的钙基热电材料相比相对无害，因此具有很高的性能指标。虽然迄今为止已经报道了几种高 ZT 热电氧化物（ZT >1），但由于缺乏对其高温稳定性的仔细观察，其可靠性水平较低。在此，我们回顾了具有代表性的 p 型层状钴氧化物的外延薄膜生长和热电特性：Na3/4CoO2、Ca1/3CoO2、Sr1/3CoO2、Ba1/3CoO2 和 Ca3Co4O9。在这些试样中，Ba1/3CoO2 和 Ca3Co4O9 在高温（约 600 ℃）空气中是稳定的。Ba1/3CoO2 在 600 ℃ 空气中的 ZT 值达到约 0.55，在热电氧化物中是可靠和最高的。此外，该值与 p 型 PbTe 和 p 型 SiGe 的 ZT 值相当。
{"title":"Recent progress in thermoelectric layered cobalt oxide thin films","authors":"Yuqiao Zhang, Hiromichi Ohta","doi":"10.1038/s41427-023-00520-w","DOIUrl":"10.1038/s41427-023-00520-w","url":null,"abstract":"Oxide-based thermoelectric materials that show a high figure of merit are promising because of their good chemical and thermal stabilities and their relative harmlessness compared with chalcogenide-based state-of-the-art thermoelectric materials. Although several high-ZT thermoelectric oxides (ZT > 1) have been reported thus far, their reliability levels are low due to the lack of careful observations of their stabilities at elevated temperatures. Herein, we review the epitaxial film growth and thermoelectric properties of representative p-type layered cobalt oxides: Na3/4CoO2, Ca1/3CoO2, Sr1/3CoO2, Ba1/3CoO2, and Ca3Co4O9. Among these specimens, Ba1/3CoO2 and Ca3Co4O9 are stable in air at elevated temperatures (~600 °C). The ZT of Ba1/3CoO2 reaches ~ 0.55 at 600 °C in air, which is reliable and the highest among thermoelectric oxides. Moreover, this value is comparable to those of p-type PbTe and p-type SiGe. Oxide-based thermoelectric materials that exhibit a high figure of merit are promising because of their good chemical and thermal stabilities and their relative harmlessness compared with chalcogenide-based state-of-the-art thermoelectric materials. The layered barium-cobalt oxide (Ba1/3CoO2) exhibits a record-high ZT of 0.55 at 600 °C in air. The increase in ZT is directly originated by the decreased thermal conductivity of Ba1/3CoO2. As we hypothesized, the greater the atomic mass, the lower the thermal conductivity, resulting in higher ZT. The ZT is reliable and the highest among thermoelectric oxides. Moreover, this value is comparable to those of p-type PbTe and p-type SiGe.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-9"},"PeriodicalIF":8.6,"publicationDate":"2023-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00520-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139066883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-22DOI: 10.1038/s41427-023-00515-7
Yoshitake Masuda, Ayako Uozumi
A diabetes sensor was developed to detect low concentrations of acetone gas, which is a diabetes biomarker. A WO3 nanoneedle film was synthesized via an aqueous process for use as a sensitive sensing membrane. Acetone was adsorbed and oxidized on the WO3 nanoneedle film, which changed the sensor resistance. The sensor exhibited a high response of Ra/Rg = 19.72, where Ra is the sensor resistance in air, and Rg is the sensor resistance in air containing 10 ppmv acetone gas. The sensor also exhibited a high response (25.36) to 1 ppmv NO2, which is related to asthma. Furthermore, the sensor responded to various biogases associated with diseases. The sensor responses to 10 ppmv of the lung cancer marker gases acetaldehyde and toluene were 13.54 and 9.49, respectively. The sensor responses to 10 ppmv isoprene, ethanol, para-xylene, hydrogen, and NH3 were 7.93, 6.33, 4.51, 2.08, and 0.90, respectively. Trace amounts of acetone and NO2 gases (25 and 250 ppbv, respectively) were detected. The limits of detection for acetone and NO2 gases were estimated to be 2.4 and 1.5 ppbv, respectively. The sensor exhibited superior ability to detect low concentrations of biomarker gases. The unique characteristics of the WO3 nanoneedle film contributed to its high response rates. A WO3 nanoneedle film was developed for a gas sensor to detect low concentrations of acetone gas, which is a diabetes biomarker. The sensor exhibited a high response (19.72) to 10 ppmv acetone gas. The sensor also exhibited a high response (25.36) to 1 ppmv NO2, which is related to asthma. The limits of detection for acetone and NO2 gases were estimated to be 2.4 and 1.5 ppbv, respectively. The sensor exhibited superior ability to detect low concentrations of biomarker gases. The unique characteristics of the WO3 nanoneedle film contributed to its high response rates.
{"title":"Highly responsive diabetes and asthma sensors with WO3 nanoneedle films for the detection of biogases with low concentrations","authors":"Yoshitake Masuda, Ayako Uozumi","doi":"10.1038/s41427-023-00515-7","DOIUrl":"10.1038/s41427-023-00515-7","url":null,"abstract":"A diabetes sensor was developed to detect low concentrations of acetone gas, which is a diabetes biomarker. A WO3 nanoneedle film was synthesized via an aqueous process for use as a sensitive sensing membrane. Acetone was adsorbed and oxidized on the WO3 nanoneedle film, which changed the sensor resistance. The sensor exhibited a high response of Ra/Rg = 19.72, where Ra is the sensor resistance in air, and Rg is the sensor resistance in air containing 10 ppmv acetone gas. The sensor also exhibited a high response (25.36) to 1 ppmv NO2, which is related to asthma. Furthermore, the sensor responded to various biogases associated with diseases. The sensor responses to 10 ppmv of the lung cancer marker gases acetaldehyde and toluene were 13.54 and 9.49, respectively. The sensor responses to 10 ppmv isoprene, ethanol, para-xylene, hydrogen, and NH3 were 7.93, 6.33, 4.51, 2.08, and 0.90, respectively. Trace amounts of acetone and NO2 gases (25 and 250 ppbv, respectively) were detected. The limits of detection for acetone and NO2 gases were estimated to be 2.4 and 1.5 ppbv, respectively. The sensor exhibited superior ability to detect low concentrations of biomarker gases. The unique characteristics of the WO3 nanoneedle film contributed to its high response rates. A WO3 nanoneedle film was developed for a gas sensor to detect low concentrations of acetone gas, which is a diabetes biomarker. The sensor exhibited a high response (19.72) to 10 ppmv acetone gas. The sensor also exhibited a high response (25.36) to 1 ppmv NO2, which is related to asthma. The limits of detection for acetone and NO2 gases were estimated to be 2.4 and 1.5 ppbv, respectively. The sensor exhibited superior ability to detect low concentrations of biomarker gases. The unique characteristics of the WO3 nanoneedle film contributed to its high response rates.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-18"},"PeriodicalIF":8.6,"publicationDate":"2023-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00515-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138946309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-22DOI: 10.1038/s41427-023-00517-5
Ning Zhao, Shubham Tyagi, Udo Schwingenschlögl
Two-dimensional semiconductors are considered as channel materials for field-effect transistors to overcome short-channel effects and reduce the device size. As the contacts to the metallic electrodes are decisive for the device performance, we study the electronic properties of contacts between Janus MoSSe and various two-dimensional metals. We demonstrate that weak interactions at these van der Waals contacts suppress Fermi level pinning and show that ohmic contacts can be formed for both terminations of Janus MoSSe, generating favorable transport characteristics. Two-dimensional semiconductors are considered as field-effect transistors to overcome short channel effects and reduce the device size. As contacts to the metallic electrodes are decisive for the device performance, we study the electronic properties of contacts between Janus MoSSe and various two-dimensional metals. We demonstrate that weak interactions at these van der Waals contacts suppress Fermi level pinning and show that ohmic contacts can be formed for both terminations of Janus MoSSe, generating favorable transport characteristics.
{"title":"Design of ohmic contacts between Janus MoSSe and two-dimensional metals","authors":"Ning Zhao, Shubham Tyagi, Udo Schwingenschlögl","doi":"10.1038/s41427-023-00517-5","DOIUrl":"10.1038/s41427-023-00517-5","url":null,"abstract":"Two-dimensional semiconductors are considered as channel materials for field-effect transistors to overcome short-channel effects and reduce the device size. As the contacts to the metallic electrodes are decisive for the device performance, we study the electronic properties of contacts between Janus MoSSe and various two-dimensional metals. We demonstrate that weak interactions at these van der Waals contacts suppress Fermi level pinning and show that ohmic contacts can be formed for both terminations of Janus MoSSe, generating favorable transport characteristics. Two-dimensional semiconductors are considered as field-effect transistors to overcome short channel effects and reduce the device size. As contacts to the metallic electrodes are decisive for the device performance, we study the electronic properties of contacts between Janus MoSSe and various two-dimensional metals. We demonstrate that weak interactions at these van der Waals contacts suppress Fermi level pinning and show that ohmic contacts can be formed for both terminations of Janus MoSSe, generating favorable transport characteristics.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-7"},"PeriodicalIF":8.6,"publicationDate":"2023-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00517-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138947688","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-22DOI: 10.1038/s41427-023-00516-6
Ashutosh Rathi, Z. Chowdhry, Anand Patel, Siming Zuo, Thulya Chakkumpulakkal Puthan Veettil, John A. Adegoke, Hadi Heidari, Bayden R. Wood, Vidya Praveen Bhallamudi, Weng Kung Peng
Malaria continues to be among the most lethal infectious diseases. Immediate barriers include the detection of low-parasitemia levels in asymptomatic individuals, which act as a reservoir for future infections, and the emergence of multidrug-resistant strains in malaria-endemic, under-resourced regions. The development of technologies for field-deployable devices for early detection and targeted drugs/vaccines is an ongoing challenge. In this respect, the identification of hemozoin during the Plasmodium growth cycle presents a unique opportunity as a biomarker for malaria infection. The last decade has witnessed the development of numerous opto-/magnetic- based ultrasensitive hemozoin sensing technologies with tremendous potential of rapid and accurate malaria diagnosis and drug testing. The unique information in hemozoin formation can also shed light on the development of targeted drugs. Here, we present a comprehensive perspective on state-of-the-art hemozoin-based methodologies for detecting and studying malaria. We discuss the challenges (and opportunities) to expedite the translation of the technology as a point-of-site tool to assist in the global eradication of malaria infection. Malaria continues to be among the most lethal infectious diseases. In the last two decades, we have witnessed unprecedented success in reducing the mortality rate. With the UN resolution of eradicating malaria by 2030 approaching fast, the scientific community has devoted substantial attention to interdisciplinary research using the latest opto-/magnetic-based technologies to detect a novel biomarker coming from the malarial pigment (hemozoin), which also carries vital information for discovering targeted drugs. This perspective article looks into the growing interest in this field and discusses the practical applicability of these sensing technologies.
{"title":"Hemozoin in malaria eradication—from material science, technology to field test","authors":"Ashutosh Rathi, Z. Chowdhry, Anand Patel, Siming Zuo, Thulya Chakkumpulakkal Puthan Veettil, John A. Adegoke, Hadi Heidari, Bayden R. Wood, Vidya Praveen Bhallamudi, Weng Kung Peng","doi":"10.1038/s41427-023-00516-6","DOIUrl":"10.1038/s41427-023-00516-6","url":null,"abstract":"Malaria continues to be among the most lethal infectious diseases. Immediate barriers include the detection of low-parasitemia levels in asymptomatic individuals, which act as a reservoir for future infections, and the emergence of multidrug-resistant strains in malaria-endemic, under-resourced regions. The development of technologies for field-deployable devices for early detection and targeted drugs/vaccines is an ongoing challenge. In this respect, the identification of hemozoin during the Plasmodium growth cycle presents a unique opportunity as a biomarker for malaria infection. The last decade has witnessed the development of numerous opto-/magnetic- based ultrasensitive hemozoin sensing technologies with tremendous potential of rapid and accurate malaria diagnosis and drug testing. The unique information in hemozoin formation can also shed light on the development of targeted drugs. Here, we present a comprehensive perspective on state-of-the-art hemozoin-based methodologies for detecting and studying malaria. We discuss the challenges (and opportunities) to expedite the translation of the technology as a point-of-site tool to assist in the global eradication of malaria infection. Malaria continues to be among the most lethal infectious diseases. In the last two decades, we have witnessed unprecedented success in reducing the mortality rate. With the UN resolution of eradicating malaria by 2030 approaching fast, the scientific community has devoted substantial attention to interdisciplinary research using the latest opto-/magnetic-based technologies to detect a novel biomarker coming from the malarial pigment (hemozoin), which also carries vital information for discovering targeted drugs. This perspective article looks into the growing interest in this field and discusses the practical applicability of these sensing technologies.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-27"},"PeriodicalIF":8.6,"publicationDate":"2023-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00516-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138944753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shape-memory polymers (SMPs) are smart materials that have gained significant attention in recent years owing to their widespread application in smart structures and devices. Digital light processing (DLP), a vat-photopolymerization-based technique, is a significantly faster technology for printing a complete layer in a single step. The current study reports a facile and fast method for the 3D printing of SMP-based smart structures using a DLP 3D printer and a customized resin. A liquid crystal (LC, RM257) was combined with the resin to introduce shape-memory properties. The combination of LCs in photocurable resin provides the opportunity to directly 3D-print thermoresponsive structures, avoiding the complexity of SMP resin preparation. The structures were printed with different geometries, and the shape-memory response was measured. Lattice structures were fabricated and programmed to obtain tunable mechanical properties. Furthermore, the strain-sensing response was measured to demonstrate the utility of these lattice structures as smart patches for joint-movement sensing. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors. Shape-memory polymers, also known as shape-shifting materials, can morph due to changes in their environment. However, the optimal use of these materials for complex 3D designs is still uncertain. Scientists from King Abdullah University of Science and Technology utilized a commercially available 3D printer to investigate this issue. They merged a shape-memory polymer with a liquid crystal (a substance that can modify its characteristics with temperature), to produce a resin for use in the 3D printer. They showed the possibility of printing diverse complex objects, from lattice structures to toys, which could transform their shape when heated and regain their original shape upon reheating. This study underscores the potential of 3D printing for developing smart materials with shape-memory features. This technology could be advantageous in various domains, including medicine and robotics. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author. In this work, 3D printing shape of memory polymer (SMP) based smart structures is conducted using a Digital light processing 3D printer and a customized resin in combination with liquid crystals. Lattice structures are fabricated and programmed to achieve tunable mechanical properties. The strain-sensing response is measured to demonstrate the utility of these lattice structures as smart patches for joint movement sensing. Changes in the electrical resistance are measured during the stretching and compression of the structure. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors.
形状记忆聚合物（SMPs）是一种智能材料，近年来因其在智能结构和设备中的广泛应用而备受关注。数字光处理（DLP）是一种基于大桶光聚合的技术，是一种可在一个步骤中打印完整层的快速技术。本研究报告了一种使用 DLP 3D 打印机和定制树脂轻松快速地 3D 打印基于 SMP 的智能结构的方法。液晶（LC，RM257）与树脂的结合引入了形状记忆特性。液晶与光固化树脂的结合为直接三维打印热致伸缩结构提供了机会，避免了 SMP 树脂制备的复杂性。打印出的结构具有不同的几何形状，并对形状记忆响应进行了测量。通过制造和编程晶格结构，获得了可调的机械性能。此外，还测量了应变传感响应，以证明这些晶格结构可用作关节运动传感的智能贴片。智能贴片的制备非常方便，可用于智能工具、玩具和超材料传感器等多种应用。
{"title":"Swift 4D printing of thermoresponsive shape-memory polymers using vat photopolymerization","authors":"Fahad Alam, Jabir Ubaid, Haider Butt, Nazek El-Atab","doi":"10.1038/s41427-023-00511-x","DOIUrl":"10.1038/s41427-023-00511-x","url":null,"abstract":"Shape-memory polymers (SMPs) are smart materials that have gained significant attention in recent years owing to their widespread application in smart structures and devices. Digital light processing (DLP), a vat-photopolymerization-based technique, is a significantly faster technology for printing a complete layer in a single step. The current study reports a facile and fast method for the 3D printing of SMP-based smart structures using a DLP 3D printer and a customized resin. A liquid crystal (LC, RM257) was combined with the resin to introduce shape-memory properties. The combination of LCs in photocurable resin provides the opportunity to directly 3D-print thermoresponsive structures, avoiding the complexity of SMP resin preparation. The structures were printed with different geometries, and the shape-memory response was measured. Lattice structures were fabricated and programmed to obtain tunable mechanical properties. Furthermore, the strain-sensing response was measured to demonstrate the utility of these lattice structures as smart patches for joint-movement sensing. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors. Shape-memory polymers, also known as shape-shifting materials, can morph due to changes in their environment. However, the optimal use of these materials for complex 3D designs is still uncertain. Scientists from King Abdullah University of Science and Technology utilized a commercially available 3D printer to investigate this issue. They merged a shape-memory polymer with a liquid crystal (a substance that can modify its characteristics with temperature), to produce a resin for use in the 3D printer. They showed the possibility of printing diverse complex objects, from lattice structures to toys, which could transform their shape when heated and regain their original shape upon reheating. This study underscores the potential of 3D printing for developing smart materials with shape-memory features. This technology could be advantageous in various domains, including medicine and robotics. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author. In this work, 3D printing shape of memory polymer (SMP) based smart structures is conducted using a Digital light processing 3D printer and a customized resin in combination with liquid crystals. Lattice structures are fabricated and programmed to achieve tunable mechanical properties. The strain-sensing response is measured to demonstrate the utility of these lattice structures as smart patches for joint movement sensing. Changes in the electrical resistance are measured during the stretching and compression of the structure. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-12"},"PeriodicalIF":8.6,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00511-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138683505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-15DOI: 10.1038/s41427-023-00514-8
Meixiang Wang, Jian Hu, Michael D. Dickey
Ionogels are crosslinked networks—typically polymeric networks—swollen with ionic liquids. The unique properties of ionogels, such as nonvolatility, ionic conductivity, nonflammability, and high thermal and electrochemical stability, make them promising for a variety of applications. Examples include sensors, adhesives, energy storage devices, and ionotronics. While many ionogels require complex syntheses and suffer from poor mechanical properties, simpler strategies are emerging to produce tough ionogels, thereby improving the durability, enabling 3D printing, and broadening the application space of ionogels. This perspective highlights promising applications and future opportunities of ionogels. This perspective highlights recent applications of ionogels that take advantage of their ionic conductivity, nonvolatility, and high thermal and electrochemical stability. Examples include sensors, batteries, electronics, 3D printing, and adhesives. Improving the mechanical properties of ionogels broadens the application space; thus, simple strategies to achieve tough ionogels are introduced. Finally, the potential applications and future opportunities of ionogels are discussed.
{"title":"Emerging applications of tough ionogels","authors":"Meixiang Wang, Jian Hu, Michael D. Dickey","doi":"10.1038/s41427-023-00514-8","DOIUrl":"10.1038/s41427-023-00514-8","url":null,"abstract":"Ionogels are crosslinked networks—typically polymeric networks—swollen with ionic liquids. The unique properties of ionogels, such as nonvolatility, ionic conductivity, nonflammability, and high thermal and electrochemical stability, make them promising for a variety of applications. Examples include sensors, adhesives, energy storage devices, and ionotronics. While many ionogels require complex syntheses and suffer from poor mechanical properties, simpler strategies are emerging to produce tough ionogels, thereby improving the durability, enabling 3D printing, and broadening the application space of ionogels. This perspective highlights promising applications and future opportunities of ionogels. This perspective highlights recent applications of ionogels that take advantage of their ionic conductivity, nonvolatility, and high thermal and electrochemical stability. Examples include sensors, batteries, electronics, 3D printing, and adhesives. Improving the mechanical properties of ionogels broadens the application space; thus, simple strategies to achieve tough ionogels are introduced. Finally, the potential applications and future opportunities of ionogels are discussed.","PeriodicalId":19382,"journal":{"name":"Npg Asia Materials","volume":"15 1","pages":"1-9"},"PeriodicalIF":8.6,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41427-023-00514-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138683510","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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