Articles in 2020

Combining Lorentz transmission electron microscopy and micromagnetic simulations, we discover a high-density homochiral Néel-type skyrmion phase in a Pt/Co/Ru/Pt/CoFeB/Ru magnetic multilayer structure that is stable at high temperatures up to 733 K. The domain phase in this system can be modulated between a high-density skyrmion phase, an isolated skyrmion phase, or a stripe domain phase by appropriate tuning of external and material parameters. This finding suggests that multilayer Néel-type skyrmions can be utilized in nonvolatile spin-based electronic devices that require operation at elevated temperatures.

Ultra-fast electrochromic supercapacitors (ECSs) are demonstrated based on mesoporous WO₃ prepared by evaporation-induced self-assembly (EISA). Mesoporous WO₃ based ECSs show excellent electrochromic and supercapacitor performances under fast operating condition. Furthermore, printing assisted EISA is introduced to produce patterned mesoporous WO₃ for ECS displays (ECSDs). The resulting ECSDs have great potential as next-generation smart electrochemical components.

There is a fundamental divide in symmetry between crystalline and glassy materials, where the structural disorder in glass leads to unique material properties and a myriad of applications. The provision of metrics for describing the order within disorder remains, however, an open challenge, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge by applying the method of persistent homology to characterize the structure of silica glass. The structural disorder is systematically engineered by preparing the glass under different high-pressure and temperature conditions, which impacts on the low-frequency vibrational and thermodynamic properties.

Zr₂SP₂O₁₂ has unique negative thermal expansion behavior involving both phase transition- and framework-type mechanisms. The volumetric CTE of α-Zr₂SP₂O₁₂ is approximately −70 ppm/K during the isosymmetric phase transition in the temperature range of 393–453 K. This value can be improved by decreasing the proportion of sulfur. The minimum volumetric CTE of α-Zr₂S_0.9P₂O_12-δ is approximately −108 ppm/K.

Flexible high-performance hybrid graphene photodetectors have been developed by introducing both perovskite materials and gold nanostars. The developed photodetectors exhibit significantly enhanced optoelectronic performances due to the synergistic effects of hybrid system including high light absorption of perovskites and strong plasmonic effects of gold nanostars with high mechanical stability, which extends the range of their practical applications.

We report on the formation and rupture of CFs through Ag ion migration inside a single-crystalline 2D van der Waals (vdW) solid electrolyte material within an ECM device structure. This study provides clear experimental evidence that CFs consisting of Ag can be formed inside single-crystalline 2D layered chromium thiophosphate (CrPS₄) and their configuration can be changed by an applied voltage. Density functional theory calculations confirm that the Ag ion migration is an energetically favorable process. The electrically induced changes in Ag CFs inside single-crystalline CrPS₄ raise the possibility of a reliable ECM device that exploits the properties of two-dimensionally confined materials.

The formation of the conductive region (n⁺ layer) in (Zn,Ba)SnO₃ (ZBTO) semiconductor is proposed to achieve high performance of thin-film transistors (TFTs). The aluminum metal capping layer is adopted to enhance the field-effect mobility of ZBTO TFTs. The capped Al layer takes out oxygen in the back-channel region, where the AlO_x interlayer is formed. As a result, the field-effect mobility of Al-capped ZBTO TFTs is remarkably increased from 20.8 to 153.4 cm²/Vs. Furthermore, the Al-capped ZBTO TFTs are stable even when exposed to air for 3 months.

The structural inhomogeneity is inherited by residual strain in perovskite crystals. The residual strain affects an electronic band structure of the perovskite film and thus determines its optoelectronic properties. Therefore, the strain engineering can be a powerful tool to not only govern structural defects but also derive demanding properties with an ensured phase stability. In this review, the effect of lattice strain is broadly explored, coupled with relevant affecting parameters.

We demonstrate an artificial tactile sensor system with a sensory neuron and a perceptual synaptic network that is composed of a single device type, i.e., a semivolatile carbon nanotube transistor. The system can differentiate the temporal features of tactile patterns, and its recognition accuracy can be improved by an iterative learning process.

We propose a novel approach to enhance the synaptic behavior of a SiN_x/a-Si bilayer memristor through Ge implantation. The SiN_x and a-Si layers serve as switching and internal current limiting layers, respectively. Ge implantation induces structural defects in the bulk and surface regions of the a-Si layer, enabling spatially uniform Ag migration and nanocluster formation in the upper SiN_x layer and increasing the conductance of the a-Si layer. As a result, the analog synaptic behavior of the SiN_x/a-Si bilayer memristor, such as the nonlinearity, on/off ratio, and retention time, is remarkably improved.

We report the synthesis of L,L-diphenylalanine conjugated BF₂-oxasmaragdyrin (FF-BSC), and fabrication of monodispersed spherical self-assemblies (FF-BSC NP), using USP class 3 solvent-water mixture. FF-BSC NPs exhibited excellent photo-stability (NIR exposure), photothermal efficacy and NIR fluorescence. Further, the formulation was lyophilized to enhance the storage. In vivo studies of these nanoparticles, demonstrated nontoxicity, efficient whole-body NIRF imaging, fractional passive tumour homing, and excellent photothermal tumor ablation efficacy.

Mechanistic insights into the LSPR-mediated yet semiconductor-free photoelectrochemistry of H₂O₂ over Ag NWs under sunlight illumination.

Cobaltosic oxide hollow dodecahedra with abundant oxygen vacancy defects was synthesized and manifested extraordinary catalytic performance toward the oxygen evolution reaction.

Nonuniform principal curvatures of air-water interfaces confer superdiffusive motion to single charge microgels attached onto the interface, and are responsible to bring microgel particles to common sites for cluster formation. The balance between various forces prior to cluster formation gives rise to a pseudoequilibrium state.

Soft, transient silicon-based gas sensing system capable of detecting nitrogen oxides with remarkable sensitivity and selectivity is presented in this report. The results provide materials, device layouts, manufacturing process, and theorectical modeling illlustrating the capabilities and operational aspects. In vitro experiments demonstrate the possibilities for disposable environmental monitors and temporary biomedical implants.

We present a promising technique for transparent flexible conducting oxide heteroepitaxial films: the direct fabrication of epitaxial molybdenum-doped indium oxide (IMO) thin films on a transparent flexible muscovite substrate. An n-type epitaxial IMO film is demonstrated with a mobility of 109 cm² V⁻¹ s⁻¹, a figure of merit of 0.0976 Ω⁻¹, a resistivity of 4.5 × 10⁻⁵ Ω cm and an average optical transmittance of 81.8% in the visible regime. IMO heterostructure not only exhibits excellent performance but also shows excellent mechanical durability. This study demonstrated an extraordinary achievement for the evolution and expansion of next-generation smart devices.

Ferromagnetic semiconductors are promising candidates for high-performance multifunctional spintronic devices due to the peculiar magneto-electric and magneto-optical properties. However, the low spin ordering temperature limits their applications. By using high pressure to stabilize the crystal structure and oxygen content, an oxygen-deficient perovskite SrCr_0.5Fe_0.5O_2.875 was synthesized. This compound displays ferromagnetic behavior with a spin ordering temperature as high as 600 K. Benefiting from the semiconducting direct bandgap (~2.28 eV), a field-tunable green fluorescent effect is observed. This work opens up a new avenue for research on room-temperature multifunctional materials with coupled magnetic, electrical, and optical performance.

The characteristics of I/Cl alloying structures in MAPbI_3-xCl_x mixed-halide perovskites and their influences on the optoelectronic properties have been issues of long-standing controversy. In this work, by using on the time-dependent X-ray diffraction, ²⁰⁷Pb and ²H NMR, the authors investigated the I/Cl alloying structures and its long term stability in MAPbI_3-xCl_x (x = 0.0 to 0.3) single crystals. It was found that Cl can substitute for I of the PbI₃ inorganic lattice, leading to the tetragonal to cubic phase transition. Moreover, it revealed that the alloying structures of the MAPbI_3-xCl_x crystals are metastable and may decompose over time.

An imprinted four-fold magnetic anisotropy was observed in the amorphous ferromagnetic layer of FeRh/CoFeB heterostructures. The easy magnetization axes of the CoFeB layer are along the FeRh〈110〉 and FeRh〈100〉 directions for the epitaxially grown FeRh layer in the antiferromagnetic and ferromagnetic states, respectively. The fourfold magnetic anisotropy of the amorphous CoFeB layer is imprinted due to the interfacial exchange coupling between the CoFeB and FeRh moments from the magnetocrystalline anisotropy of the epitaxial FeRh layer, which may be applied to probe the magnetic structures of antiferromagnetic materials without using synchrotron methods.