Asymmetric Crystal Structure Research Articles

Impact sensing, localization and damage assessment in Fiber-Reinforced composites with ZnO Nanowires-Based sensor array

The structural integrity and monitoring of load distributions in composites are critical for safety and economic efficiency but still challenging. Herein, zinc oxide nanowires (ZnO NWs) were embedded into a carbon fiber-reinforced composite serving as mechanical reinforcement and sensing components. The presence of ZnO NWs in the composite material increased the flexural strength, interlaminar, and interfacial shear strength by respectively 4.9 %, 8.8 %, and 19.9 % due to the strong bonding at the fiber/resin interface and the mechanical interlocking effect. Additionally, the piezoelectric nature of ZnO NWs with an asymmetric crystal structure generated piezoelectric charges under stress, thereby enhancing the sensitivity of capacitive monitoring. A self-developed algorithm was then designed to analyze the array capacitance changes collected from the prepared composite laminate to determine the impact load with high precision with an error margin of 3 mm and not exceeding 0.25 MPa. Furthermore, damage was also able to be detected by monitoring capacitance changes. Overall, the proposed high-precision and minimally aggressive approach for load localization and quantification provides a promising direction and strategic pathway for the development of smart self-monitoring composites.

High-Speed Self-Powered PdSe2/Si 2D-3D PIN-like Photodetector with Broadband Response Based on PdSe2 Quantum Island Structure.

As a two-dimensional (2D) material, palladium diselenide (PdSe2) has attracted extensive research attention due to its unique asymmetric crystal structure and extraordinary optoelectronic properties, showing great potential in electronic, optoelectronic, and other application fields. Thinner PdSe2 exhibits semiconductor properties, while the photoresponse of the photodetectors based on this film is weaker. Although increasing the thickness of the PdSe2 film can improve the photoresponse, thicker PdSe2 exhibits metallic-like properties, which is not conducive to the formation of the heterojunction. In this work, a PdSe2 2D material with a quantum island structure is prepared by a simple thermal-assisted conversion method. A new type of photodetector with a PdSe2/n--Si/n+-Si vertical PIN-like structure is innovatively proposed. Broad spectral absorption from 532 to 2200 nm and a high rectification ratio (106) of the device are achieved. The introduced n--Si layer concentrates the electric field in the depletion region, thereby shortening the transit time and accelerating the separation and collection of the carriers, resulting in the enhancement of the responsivity and 3 dB frequency compared to the traditional device with a PN structure. A recorded highest 3 dB frequency of ∼25 kHz is achieved for the PdSe2 2D-3D PIN-like device.

Environmental responsive peroxidase-like activity of MoS2@halloysite nanotubes mediated by piezoelectric effect

Nanozymes, as a class of synthetic enzymes, have the characteristics of abundant raw materials and powerful environmental adaptability, potentially serving as substitutes for natural enzymes. Herein, the MoS2 nanosheets were anchored on the surface of alkali activated halloysite nanotubes by utilizing a facile hydrothermal process, resulting in the formation of MoS2@halloysite (MoS2@HNTs) core-shell nanocomposites. The catalytic effect of material on peroxidase under the mechanical stress of applied ultrasonic vibration was systematically investigated with 3,3′,5,5′-tetramethylbenzidine (TMB) as the substrate for chromogenic reaction. The results demonstrated that the established piezoelectric polarization effect generated by MoS2 with asymmetric crystal structure under mechanical force can promote the in-situ coloration of TMB. Concretely, MoS2@HNTs possessing higher Michaels constant (3.42 mmol L-1) and reaction velocity (3.16 × 10–6 mol L-1 min-1) exhibited enhanced peroxidase-like activity compared to pristine MoS2 microspheres. This may be attributed to the fact that halloysite dispersed the MoS2 nanosheets, exposing more reactive sites, and the nanocomposites produced more pronounced structural deformation under mechanical stress. The detailed experiments and theoretical calculation have elucidated the structure-activity relationship and microscopic mechanism among the microstructures, piezoelectric polarization effects and peroxidase catalytic effects of materials. This work provides an advanced prototype for the research of environmental responsive enzyme-like catalytic effects of mineral-based nanozymes with the regulation of external environmental factors.

Evidence of disordered local structure of ZnO buffered MgB2 films via polarized extended X-ray absorption fine structure analysis

Herein, we investigated the mechanism by which the critical temperature (Tc) of a magnesium diboride (MgB2) superconductor is altered by the buffer layer. Zinc oxide (ZnO) layers with different thicknesses (28, 80, and 134 nm) were deposited epitaxially on a Hastelloy substrate beneath a ∼ 1 μm MgB2 film. To measure the local structural distortion of the boron plane, three different angle polarizations (0°, 45°, and 90° parallel to the ab-axis) on the Mg K-edge, extended X-ray absorption fine structure (EXAFS) measurements were performed. The EXAFS analyses revealed that the ZnO buffer layer caused the boron layer to disorient, leading to buckling between the Mg and B layers, which affected the charge transfer capability in the intra-layer structure. Furthermore, the uneven distribution of B atoms amid the surrounding Mg atoms resulted in an asymmetric crystal structure, which leads to Tc fluctuation. This study reveals the relationship between modifications made to the boron plane condition of MgB2 by the ZnO buffer layer and the superconducting Tc behavior of MgB2.

A new size-dependent nonlinear model for piezoelectric semiconductor nanofibers by considering the effects of strain gradient and flexoelectricity

Flexotronics induced by the strain gradient and flexoelectricity in a semiconductor with symmetric or asymmetric crystal structures have attracted considerable attention as a promising approach for tunable electronic processes. However, the electric nonlinear properties between the carriers and electric field are ignored in most of related studies. In this study, a new size-dependent nonlinear model is developed to investigate the interaction among the size effects (caused by strain gradient and flexoelectricity), piezo-effects and semiconducting properties in a piezoelectric semiconductor (PS) nanofiber with asymmetric crystal structures. In addition, the Von-Kármán's nonlinear strain is also considered to check the effect of geometric nonlinearity. It is found that the piezo-effect can be enhanced (reduced) by the effect of flexoelectricity (strain gradient) due to a new positive (negative) superimposed increment of electric field under a pair of tensile stress. Besides, the size effect will be weakened by the semiconducting property. The studies will provide guidance for theoretical analysis of size effect in nano PSs and design of flexotronic devices.

Optical anisotropy of crystallized vanillin thin film: the science behind the art

Vanillin, a common household flavoring agent, turns into mesmerizing artwork under a polarizing microscope. This artwork can be used to decipher crystal nucleation and growth mechanisms. The trick to create such artwork is to grow a crystalline vanillin thin film tens of micrometers thick to allow white light to be transmitted through a singular, instead of multiple overlapping, crystal grains. A series of experiments were carried out to determine the optimal conditions to grow such single crystal vanillin films. Vanillin crystal’s chemical structure is anisotropic, specifically monoclinic. When a light wave propagates through its anisotropic crystallographic planes, it splits into two orthogonal beams, which in turn generates optical interference patterns unique to its molecular packing structure. We hypothesized that the resulting spectacular color pattern of vanillin micrographs was driven by its asymmetric crystal structure when vanilla macromolecules grew with covalent and or hydrogen bonding force during solidification. We employed a long-range molecular bonding model to simulate chemical interaction of multiple vanillin molecules. We interpreted the vanillin film growth mechanism as the radial propagation of single crystal phases in combination of amorphous phases to fill spacing between crystalline phases. The relationship between the optical interference pattern of recrystallized vanillin thin film and its microstructure was established through this study. The outcome of this study may shed light into engineering anisotropic crystals into micro to nanoscale optical devices with preferred optical reflectance.

High-performance ReSe2/PdSe2 polarized photodetectors with an ultrafast and broadband photoresponse

van der Waals heterostructures (vdWHs) fabricated by the stacking of transition-metal dichalcogenides (TMDCs) with different properties possess more significant properties beyond its individual materials, which allow them to provide excellent architectures for the optoelectronic devices. In this work, a novel polarized photodetector based on the ReSe2/PdSe2 heterostructure is constructed and explored thoroughly. The type-II band alignment is investigated by ultraviolet photoelectron spectroscopy (UPS), which facilitates the separation and transition of carriers. The device not only achieves a broadband response covering from near-ultraviolet to near-infrared, a high responsivity of 313 mA/W, but also a rapid photoswitching speed with rise/fall times about 70/82 μs owing to the built-in electric field at the heterointerface, which is further confirmed by the large 3 dB frequency over 66.4 kHz. The main advantage offered by highly asymmetric crystal structure of ReSe2 and PdSe2 is the polarization detection. Therefore, the photodetector exhibits remarkable polarization performance with a dichroism ratio as high as 1.42 by tuning the bias voltage, which is capable of extracting polarized information, and improves the ability to operate in complex situations. These results reveal the great potential of the ReSe2/PdSe2 heterostructure for ultrafast, broadband and high-performance polarized detection, promising for military and civil applications.

Tunable correlation in twisted monolayer–trilayer graphene

Flat-band physics of moiré superlattices, originally discovered in the celebrated twisted bilayer graphene, have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field. In this work, we experimentally find the evidence of correlated insulators at half filling of the electron moiré band of twisted monolayer–trilayer graphene with a twist angle around 1.2°. Van Hove singularity (VHS), manifested as enhanced resistance and zero Hall voltage, is observed to be distinct in conduction and valence flat bands. It also depends on the direction and magnitude of the displacement fields, consistent with the asymmetric crystal structure. While the resistance ridges at VHS can be enhanced by magnetic fields, when they cross commensurate fillings of the moiré superlattice in the conduction band, the enhancement is so strong that signatures of correlated insulator appear, which may further develop into an energy gap depending on the correlation strength. At last, Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields. It is found that electronic correlation has a negative dependence on the Fermi velocity, which in turn could be used to quantify the correlation strength.

Tuning the Electronic and Mechanical Properties of Kagome Graphene via Hydrogenation

Surface passivation is proved to be an effective way to adjust material properties or to explore new two-dimensional (2D) materials. Herein, we proposed three hydrocarbons with high stability for the first time via hydrogenation on the Kagome graphene, namely, C6H4, C6H6-I, and C6H6-II. Unlike the Kagome graphene, which is metallic, all these 2D monolayers are wide-bandgap semiconductors (4.06–4.81 eV). Among them, C6H4 is an indirect bandgap semiconductor, but both C6H6-I and C6H6-II possess the direct bandgap feature. Considerable carrier mobilities (102 to 103 cm2 V–1 s–1) have been further confirmed in the three hydrocarbons on the basis of modified deformation potential theory. Specifically, for C6H4, the hole mobilities are as high as 104 to 105 cm2 V–1 s–1, comparable to those of graphene and black phosphorus. The intrinsic vertical electric field induced by the asymmetric crystal structures in C6H4 and C6H6-I will be beneficial to the spatial separation of electrons and holes in semiconductors, promising in the field of optoelectronics. In addition, hydrogenation has a great influence on the mechanical properties of Kagome graphene, no matter whether it is Young’s modulus, Poisson’s ratio, or ideal tensile strength. Particularly, in-plane axial negative Poisson’s ratios (−0.011/–0.018 along the a-/b-direction) were found in C6H6-I, mainly originated from the interaction of carbon pentagons and octagons. These interesting findings in our work may pave the way for the application of hydrogenated Kagome graphene in the future.

Chiral Lead-Free Double Perovskite Single-Crystalline Microwire Arrays for Anisotropic Second-Harmonic Generation.

Halide double perovskites present a new branch for versatile optoelectronic devices because of their huge structural compatibility and environmental friendliness, whereas nonlinear optics (NLO) devices remain blank for this fascinating family. Simultaneously, the precise patterning of single-crystalline perovskite microwire arrays remains a challenge for the integration of NLO devices. Herein, we designed lead-free chiral 2D double perovskites with the nonsymmetrical structure presenting second-harmonic generation (SHG). Furthermore, perovskite single-crystalline arrays with regulated geometry, pure orientation, and high crystallinity are prepared using the capillary-bridge confined assembly technique. The efficient SHG originates from the asymmetric crystal structure and high crystallinity of the microwire arrays. Compared with their polycrystalline thin-film counterparts, linearly polarized SHG and a higher SHG conversion efficiency are demonstrated based on microwire arrays. The results not only expand the applications of lead-free double perovskites in the NLO-integrated fields but also provide a viable way for lead-free optoelectronic devices.

Lattice expansion boosting photocatalytic degradation performance of CuCo2S4 with an inherent dipole moment

Realizing efficient charge separation and directional transfer is a challenge for single-component semiconductors. The spatial electric field generated by dipole moment could promote charge separation. Here, three-dimensional hierarchical CuCo2S4 microspheres with lattice distortion were prepared, and lattice distortion was modulated by changing feed Co/Cu molar ratios in synthesis. CuCo2S4 showed asymmetric crystal structure, leading to generation of dipole moment. The charge separation efficiency of CuCo2S4 was related to lattice distortion, and lattice expansion was in favor for charge separation. The CuCo2S4 with feed Cu/Co molar ratio of 1:4 (CCS-4) showed the maximum lattice expansion and exhibited the highest photocatalytic activity, which was attributable to the highest charge separation efficiency and the largest specific surface area. CCS-4 can remove 95.4% of tetracycline hydrochloride within 40 min photocatalysis, and effectively improve the biodegradability of pharmaceutical wastewater. Importantly, this study provides a new vision for constructing single-component photocatalysts with high photocatalytic performance.

Induced Chirality in Halide Perovskite Clusters through Surface Chemistry.

Chiroptical properties are of interest for various applications, including structure determination, polarized photodetectors, and spintronics. Inducing chiroptical activity into semiconductors is challenging because of difficulties in creating asymmetric crystal structures. One promising method is to use chirality transfer by deploying chiral organic molecules as capping ligands for nanocrystals. Experimentally, chiral-capped nanocrystals show emergent chiroptical signatures, but the mechanisms for chirality transfer remain unclear. Here we utilize atomistic modeling using time-dependent density functional theory calculations to explore chirality transfer in CsPbX3 (X = Cl, I) clusters capped with chiral diaminocyclohexane (DACH) enantiomers. When DACH enantiomers are bound to the cluster surface, the perovskite optical transitions gain chiral signatures. This observed chirality transfer is best rationalized by chiral molecular dipole-cluster transition dipole coupling. With multiple DACH molecules bound to the cluster surface, anisotropy factors are found to increase proportionally to the surface ligand density, providing mechanistic insight toward improving chiroptical functionality in semiconductor nanomaterials.

Function-related asymmetry of the specific cardiolipin binding sites on the mitochondrial ADP/ATP carrier

The ADP/ATP carrier (AAC) transports matrix ATP and cytosolic ADP across the inner mitochondrial membrane (IMM). It is well known that cardiolipin (CL) plays an important role in regulating the function of AAC, yet the underlying mechanism still remains elusive. AAC is composed of three homologous domains, and three specific CL binding sites are located at the domain-domain interfaces near the matrix side. Here we report an in-depth investigation on the dynamic properties of the bound CL within the three specific sites through all-atom molecular dynamics simulations of up to 13 μs in total. Our results highlight the importance of the basic and polar residues in CL binding. The basic residues from the linker helix and/or the [Y/W/F][K/R]G motif enable the bound CL to form an intra-domain binding mode, and the canonical inter-domain binding mode only forms when these basic residues are occupied by an additional phospholipid. Of special significance, differences in the basic and polar residues lead to remarkable asymmetry among the three specific CL binding sites. We found that the bound CL at the interface of domains 2 and 3 predominantly adopts inter-domain binding mode, while CLs at the other two sites have much more intra-domain populations. This is consistent with the asymmetric crystal structure of the matrix state (m-state) AAC which implies an asymmetric transport mechanism. The dynamic equilibrium between the inter-domain and intra-domain binding modes observed in our simulations could be highly important for the bound CLs to adapt to the movements during state transitions.

High-Pressure Synthesis and Ferrimagnetism of Ni3TeO6-Type Mn2ScMO6 (M = Nb, Ta).

The corundum-related oxides Mn2ScNbO6 and Mn2ScTaO6 were synthesized at high pressure and high temperature (6 GPa and 1475 K). Analysis of the synchrotron powder X-ray diffraction shows that Mn2ScNbO6 and Mn2ScTaO6 crystallize in Ni3TeO6-type noncentrosymmetric crystal structures with space group R3. The asymmetric crystal structure was confirmed by second harmonic generation measurement. X-ray absorption near-edge spectroscopies indicate formal valence states of Mn2+2Sc3+Nb5+O6 and Mn2+2Sc3+Ta5+O6, also supported by the calculated bond valence sums. Both samples are electrically insulating. Magnetic measurements indicate that Mn2ScNbO6 and Mn2ScTaO6 order ferrimagnetically at 53 and 50 K, respectively, and Mn2ScTaO6 is found to have a field-induced magnetic transition.

Energetics and conformational pathways of functional rotation in the multidrug transporter AcrB.

The multidrug transporter AcrB transports a broad range of drugs out of the cell by means of the proton-motive force. The asymmetric crystal structure of trimeric AcrB suggests a functionally rotating mechanism for drug transport. Despite various supportive forms of evidence from biochemical and simulation studies for this mechanism, the link between the functional rotation and proton translocation across the membrane remains elusive. Here, calculating the minimum free energy pathway of the functional rotation for the complete AcrB trimer, we describe the structural and energetic basis behind the coupling between the functional rotation and the proton translocation at atomic resolution. Free energy calculations show that protonation of Asp408 in the transmembrane portion of the drug-bound protomer drives the functional rotation. The conformational pathway identifies vertical shear motions among several transmembrane helices, which regulate alternate access of water in the transmembrane as well as peristaltic motions that pump drugs in the periplasm.

Characterizations of the nonlinear optical properties for (010) and (2¯01) beta-phase gallium oxide.

We report, for the first time, the characterizations on optical nonlinearities of beta-phase gallium oxide (β-Ga2O3), where both (010) β-Ga2O3 and (2¯01) β-Ga2O3 were examined for two-photon absorption coefficient, Kerr nonlinear refractive index, and their polarization dependence. The wavelength dependence of two-photo absorption coefficient and Kerr nonlinear refractive index were also estimated by a widely used analytical model. β-Ga2O3 exhibits a two photon absorption (TPA) coefficient of 1.2 cm/GW for (010) β-Ga2O3 and 0.6 cm/GW for (2¯01) β-Ga2O3. The Kerr nonlinear refractive index is -2.1 × 10-15 cm2/W for (010) β-Ga2O3 and -2.9 × 10-15 cm2/W for (2¯01) β-Ga2O3. In addition, β-Ga2O3 shows stronger in-plane nonlinear optical anisotropy on (2¯01) plane than on (010) plane. Compared with GaN, TPA coefficient of β-Ga2O3 is 20 times smaller, and the Kerr nonlinear refractive index of β-Ga2O3 is also found to be 4-5 times smaller. These results indicate that β-Ga2O3 have the potential for ultra-low loss waveguides and ultra-stable resonators and integrated photonics, especially in UV and visible wavelength spectral range.

Selective detection of Cu2 + and Co2 + in aqueous media: Asymmetric chemosensors, crystal structure and spectroscopic studies

Two new azo-azomethine receptors, H2L1 and H2L2, containing hydrazine, naphthalene and different electron withdrawing groups, Cl and NO2, have been designed and synthesized for qualitative and quantitative detection of Cu2+ and Co2+ in aqueous media. The crystal structure of H2L1is reported. The H2L1was used as a chemosensor for selective detection of trace amount of Cu2+ in aqueous media. H2L2 was also applied to naked-eye distinction of Cu2+ and Co2+ from other transition metal ions in aqueous media. Detection limit of Cu2+ is 1.13μM and 1.26μM, in water, for H2L1 and H2L2, respectively, which are lower than the World Health Organization (WHO) recommended level. The binuclear Cu2+ and Co2+ complexes of the receptors have been also prepared and characterized using spectroscopic methods and MALDI-TOF mass analysis. Furthermore, the binding stoichiometry between the receptors upon the addition Cu2+ and Co2+ has been investigated using Job's plot. Moreover, the fluorescence emission spectra of the receptors and their metal complexes are also reported.

Layered SnSe nano-plates with excellent in-plane anisotropic properties of Raman spectrum and photo-response.

In-plane anisotropy in optical, electronic and thermal properties of two-dimensional (2D) materials has attracted significant interest because of the huge potential applications for developing novel devices. In this work, outstanding angle-dependent Raman property of layered SnSe nano-plates is obtained via polarized Raman system and it is confirmed that the Raman polarization directions of two Ag modes (130 cm-1 and 150 cm-1) are consistent with specific crystalline directions (zigzag direction or armchair direction) of SnSe flakes under parallel polarization configuration at home temperature and low temperature. Furthermore, the SnSe nano-plate devices show excellent angle-resolved photo-response at home temperature and low temperature (150 K) with a 90° cycle period and the polarized directions are also along zigzag direction and armchair direction, which is ascribed to the unique in-plane asymmetric crystal structure. These prominent in-plane anisotropic properties provide a precise and rapid method to determine the crystal orientation of SnSe nano-flakes and open up the new applications of 2D asymmetric structure materials.

Reflection phase characteristics and their applications based on one-dimensional coupled-cavity photonic crystals with gradually changed thickness ofsurface layer

In this paper, we first improve the traditional transfer matrix method to adapt to one-dimensional photonic crystal consisting of arbitrary materials, and then use it to study the reflection phase characteristics of two kinds of photonic crystals, i.e., a simple periodic photonic crystal structure and a coupled-cavity asymmetric photonic crystal with gradually changed thickness of surface layer. For both of the structures, the reflectivity within photonic band gap is above 98% and hardly affected by the thickness of the surface layer. However, their reflection phases exhibit distinctly different properties. For the simple photonic crystal structure, the reflection phases of both TE and TM polarizations are sensitively dependent on the thickness of surface layer, but their phase difference is almost the same as the thickness of surface layer varies, which cannot change the polarization of reflected light. While for the coupled-cavity asymmetric photonic crystal structure, studies show that the degenerate defect modes within photonic band gap will split as the thickness of the surface layer varies. Moreover, around the splitting defect modes the reflection phases of both TE and TM polarizations, as well as their phase difference, are sensitively dependent on the thickness of surface layer, resulting in sensitive polarization change of reflected light. The physical reason is attributed to the dramatic phase change caused by the splitting of degenerate defect modes. The above reflection phase characteristics of coupled-cavity asymmetric photonic crystals have potential in lowering or even eliminating the coherence of lasers in some special application cases. As an example, we design a one-dimensional photonic crystal structure with two-dimensional periodic varying thickness of surface layer. After an oblique incident narrowband laser beam is reflected from this structure and then focused by a lens, various polarized light beams (including linear polarized light beams along different directions, left-hand (or right-hand) circular (or elliptical) polarized light beams) will exist simultaneously, whose superposition will produce optical field with random phase and polarizations in the focal region. These results can effectively reduce the coherence of lasers, which holds promise in many fields such as laser nuclear fusion.

新規無鉛圧電材料の状態図に関する第一原理計算

Ferroelectric thin films are using the actuators and sensors in medical devices. Therefore, developments of biocompatible novel lead-free piezoelectric materials are required. In previous study, novel lead-free piezoelectric materials, which were solitary crystals ABO3 and complex crystals (A,A’)BO3 and A(B,B’)O3 of perovskite-type oxide, were discovered by employing first principle calculation based on density functional theory (DFT). In this paper, to support the fabrication of novel lead-free piezoelectric thin films, the phase diagram was predicted through first principle calculation. Firstly, stable crystal structure of perovskite oxides was evaluated. Secondly, total energy, spontaneous polarization, elastic compliance and electrostrictive coefficient were calculated from crystal structures. Thirdly, the free energy function with consideration of misfit strain was approximated from total energy and spontaneous polarization of asymmetric crystal structures. Finally, the stable thin film phase with minimum energy was investigated by employing the approximated free energy function. The developed prediction procedure was applied to existing materials PZT and novel lead-free piezoelectric materials. Especially, the effect of material composition on phase diagram was discussed.