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This numerical research study focuses on impacts of using twisted rib geometry on the hydrothermal performance and entropy generation characteristics of biologically synthesized Ag/water nanofluid flowing in heat sink ‌minichannels. To this end, twelve different twisted rib geometries (Case 1 to 12) were designed where the double-row ribs were twisted at the bottom and top portions with twist angles between − 45° and + 45°. To elucidate the cooling performance comprehensively, four different Reynolds numbers (Re = 500, 1000, 1500, and 2000) and four different nanoparticle concentrations ( φ = 0%, 0.1%, 0.5%, and 1%) were included in the numerical computations. Results revealed that using twisted ribs significantly smoothen the fluid flow and reduces pressure drop remarkably depending on twist angles, nevertheless, it deteriorates the cooling performance. In Case 12, the convective heat transfer coefficient reduces by up to 15.8% at Re = 2000 and φ =1%, compared to the base case. However, pumping power requirement is decreased by 43.9% in this case. Nanoparticle incorporation contributes to enhancement of convective heat transfer coefficient by up to 13.5% at the lowest Re. Frictional entropy generation considerably decreases (up to 31%) when twisted ribs are utilized. However, thermal entropy generation can increase up to 36%, due to ineffective cooling with twisted ribs. This work can be regarded as a first study in the field concerning the effects of top and bottom twist angles on hydrothermal performance and entropy generation in nanofluid-cooled mini-channel heat sinks. [ABSTRACT FROM AUTHOR]

In this study, the electrical, optoelectronic, and thermoelectric properties of bilayer borophene moiré superlattices at different twist angles are investigated in detail. The results reveal that the transport properties of bilayer borophene are significantly impacted by different twist angles. Specifically, the device with 30° is of better transport properties compared to the two devices, due to the absence of interlayer covalent bond. The study reveals the essential influence of twist angle on the moiré superlattice of bilayer borophene and provides a theoretical basis for its potential applications in electronic, optoelectronic, and thermoelectric devices. [ABSTRACT FROM AUTHOR]

Abstract In this study, the electrical, optoelectronic, and thermoelectric properties of bilayer borophene moiré superlattices at different twist angles are investigated in detail. The results reveal that the transport properties of bilayer borophene are significantly impacted by different twist angles. Specifically, the device with 30° is of better transport properties compared to the two devices, due to the absence of interlayer covalent bond. The study reveals the essential influence of twist angle on the moiré superlattice of bilayer borophene and provides a theoretical basis for its potential applications in electronic, optoelectronic, and thermoelectric devices.

Few-layer black phosphorus (FLBP) exhibits valuable mechanical, optical, and electronic properties for potential applications in nanodevices, ranging from insulators to superconductors. In particular, their band structure and optical properties are closely related to layer numbers, stacking sequences, and twist angles. However, the mechanism behind these factors is not fully understood, as it is quite difficult to obtain stacking details using non-destructive probes. This article provides direct experimental evidence of the weak interlayer van der Waals (vdW) interaction of FLBP using a state-of-the-art, angular resolved, ultra-low frequency Raman spectroscopy system. A modified linear-chain model is presented to evaluate the layer number dependence on the extremely low-frequency breathing modes (Ag3 and Ag4). The polarization analysis illustrates that most bi-layer BP samples prefer the AB stacking sequence. Furthermore, the stacking angle of bi-layer BP was assigned based on its minimum intensity of Ag3 and Ag4 modes. This investigation on angular resolved extremely low-frequency Raman spectra sheds light on a new approach for analyzing the stacking details of FLBP, which is of great significance for developing novel FLBP-based nanodevices.

Atomically thin two‐dimensional (2D) transition metal dichalcogenides (TMDs) are promising materials for photovoltaic (PV) applications. Their self‐terminated nature and strong absorption characteristics introduce an unprecedented possibility for high voltages to bandgap ratios, with secondary benefits including the potential for high internal quantum efficiencies/low recombination and strong absorption coefficients coupled with stability in a range of environments. However, despite the promise of such material systems, their PV performances still lag behind the conventional 3D materials. In principle, one possible way to manipulate the behavior of a 2D heterobilayer structure is to change its interlayer twist angle. In this study, the effects of twist angle between vertically stacked type‐II MoS2/WS2 heterobilayers on fundamental optical properties such as light absorbance, excess carrier lifetime, and diffusion are reported. These properties can have a direct effect on the final PV performance of these heterobilayers. It is found that the interlayer twist in MoS2/WS2 heterobilayers does not affect their absorbance. However, the carrier lifetime and photon emission across the heterobilayers are modulated with the interlayer twist. These findings could be useful to facilitate the optimization of monolayer TMD‐based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Graphene‐based moiré heterostructures are strongly correlated materials, and they are considered to be an effective platform to investigate the challenges of condensed matter physics. This is due to the distinct electronic properties that are unique to moiré superlattices and peculiar band structures. The increasing research on strongly correlated physics via graphene‐based moiré heterostructures, especially unconventional superconductors, greatly promotes the development of condensed matter physics. Herein, the preparation methods of graphene‐based moiré heterostructures on both in situ growth and assembling monolayer 2D materials are discussed. Methods to improve the quality of graphene and optimize the transfer process are presented to mitigate the limitations of low‐quality graphene and damage caused by the transfer process during the fabrication of graphene‐based moiré heterostructures. Then, the topological properties in various graphene‐based moiré heterostructures are reviewed. Furthermore, recent advances regarding the factors that influence physical performances via a changing twist angle, the exertion of strain, and regulation of the dielectric environment are presented. Moreover, various unique physical properties in graphene‐based moiré heterostructures are demonstrated. Finally, the challenges faced during the preparation and characterization of graphene‐based moiré heterostructures are discussed. An outlook for the further development of moiré heterostructures is also presented. [ABSTRACT FROM AUTHOR]

Abstract Graphene‐based moiré heterostructures are strongly correlated materials, and they are considered to be an effective platform to investigate the challenges of condensed matter physics. This is due to the distinct electronic properties that are unique to moiré superlattices and peculiar band structures. The increasing research on strongly correlated physics via graphene‐based moiré heterostructures, especially unconventional superconductors, greatly promotes the development of condensed matter physics. Herein, the preparation methods of graphene‐based moiré heterostructures on both in situ growth and assembling monolayer 2D materials are discussed. Methods to improve the quality of graphene and optimize the transfer process are presented to mitigate the limitations of low‐quality graphene and damage caused by the transfer process during the fabrication of graphene‐based moiré heterostructures. Then, the topological properties in various graphene‐based moiré heterostructures are reviewed. Furthermore, recent advances regarding the factors that influence physical performances via a changing twist angle, the exertion of strain, and regulation of the dielectric environment are presented. Moreover, various unique physical properties in graphene‐based moiré heterostructures are demonstrated. Finally, the challenges faced during the preparation and characterization of graphene‐based moiré heterostructures are discussed. An outlook for the further development of moiré heterostructures is also presented.

Based on first-principles density functional theory, we investigated the electronic structures of twisted bilayer nitrogene at various twist angles. This electron localization by the influence of the moiré superlattice with very small θ leads to flat bands, especially one of valence bands at the Fermi level on atoms in the AA zone whereas for a larger θ no strong localization occurs owning to a large proportion of the AB zone. Also, there is a linear relationship between the band gaps and the torsion angles of the twisted bilayer nitrogene. A smaller twist angle corresponds to a larger band gap, whereas a larger twist angle corresponds to a smaller band gap. This localization should also reduce considerably the mobility of the electrons and thus modify transport properties. • The relationship between band gap and twist angle of the twisted bilayer nitrogene is linear. • The twist angle of about 5.82° is sufficient to achieve the ultra-flat band for bilayer nitrogene. • The wave function distribution of the states at the top of the valence band is very localized. [ABSTRACT FROM AUTHOR]

Two-dimensional materials are expected to play an important role in next-generation electronics and optoelectronic devices. Recently, twisted bilayer graphene and transition metal dichalcogenides have attracted significant attention due to their unique physical properties and potential applications. In this study, we describe the use of optical microscopy to collect the color space of chemical vapor deposition (CVD) of molybdenum disulfide (MoS 2 ) and the application of a semantic segmentation convolutional neural network (CNN) to accurately and rapidly identify thicknesses of MoS 2 flakes. A second CNN model is trained to provide precise predictions on the twist angle of CVD-grown bilayer flakes. This model harnessed a data set comprising over 10,000 synthetic images, encompassing geometries spanning from hexagonal to triangular shapes. Subsequent validation of the deep learning predictions on twist angles was executed through the second harmonic generation and Raman spectroscopy. Our results introduce a scalable methodology for automated inspection of twisted atomically thin CVD-grown bilayers.

This work studied the optical absorption properties and electronic properties of graphene nanosheets encapsulated in h-BN at different twisted angles based on first principles. UV–Vis spectrum shows that compared with the monolayer graphene nanosheets, the absorption’s peak of the encapsulated graphene nanosheets show a red shift and its molar absorption coefficient decreased significantly. The molar absorption coefficients of h-BN/graphene/h-BN heterostructures show an increasing trend when the graphene nanosheets are twisted relative to the packaging layer (twisted angles are 0°, 15°, 21.8°, 27.8° and 30°, respectively). More curiously, charge density difference (CDD) indicates that the region of electron aggregation in excited state mainly occurs at the centre of graphene nanosheets due to the introduction of h-BN packaging layer. The smoothed isosurface diagram of electron hole pairs shows that the distribution breadth of electron hole pair density decreases compared with that before encapsulation, and the distribution breadth of electron increase is larger than that of hole. With the increase of twisted angles, the distribution breadth of electron hole pair density increases gradually. Both CDD and smoothed isosurface diagram show that the system has strong boundary effect. This provides a method to adjust the photoelectric properties of graphene nanosheets by using different twisted angles, and provides a theoretical basis for its application in the field of micro-nano optoelectronics.

Apatite-type materials AI4AII6(BO4)6X2 have two unique cations sites AI and AII, which can host large mono-, di- tri- and tetra-valent cations. The average cation radii will affect the twist angle and lattice constants. However, there are few reports on the influence of B site substitutions on the twist angle and lattice parameters. It is believed that the lattice constant variation as a function of B site substitutions may not follow the same twist-angle model as proposed for A site. This work reports our results on the crystal chemistry of synthetic apatite Ca10(VxP1−xO4)6F2 obtained through the crystal structure characterization using Rietveld refinement and high-resolution transmission electron microscopy. The quantification of vanadium/phosphorus partitioning in BO4 tetrahedra showed that equilibrium with more than 70% substitution of phosphorous by vanadium was difficult to achieve unless longer annealing (about 1 week at 900 °C) was employed. In comparison with the apatites with different ionic radii at AI and AII sites, Ca10(VxP1−xO4)6F2 apatites with different ionic radii at B site show little twist angle variation for the whole series, which indicates that the dilation of unit cell constants is mainly because of the expansions of BO4 tetrahedra when A site cation is fixed. [ABSTRACT FROM AUTHOR]

Few-layer black phosphorus (FLBP) exhibits valuable mechanical, optical, and electronic properties for potential applications in nanodevices, ranging from insulators to superconductors. In particular, their band structure and optical properties are closely related to layer numbers, stacking sequences, and twist angles. However, the mechanism behind these factors is not fully understood, as it is quite difficult to obtain stacking details using non-destructive probes. This article provides direct experimental evidence of the weak interlayer van der Waals (vdW) interaction of FLBP using a state-of-the-art, angular resolved, ultra-low frequency Raman spectroscopy system. A modified linear-chain model is presented to evaluate the layer number dependence on the extremely low-frequency breathing modes (A g 3 and A g 4). The polarization analysis illustrates that most bi-layer BP samples prefer the AB stacking sequence. Furthermore, the stacking angle of bi-layer BP was assigned based on its minimum intensity of A g 3 and A g 4 modes. This investigation on angular resolved extremely low-frequency Raman spectra sheds light on a new approach for analyzing the stacking details of FLBP, which is of great significance for developing novel FLBP-based nanodevices. • Ultra-low frequency Raman spectroscopy of few-layer black phosphorous. • Thickness analysis of few-layer black phosphorous. • Stacking sequences analysis of bi-layer black phosphorous. • Twist angle analysis of bi-layer black phosphorous. [ABSTRACT FROM AUTHOR]

One important property of composite materials is the possibility to change their characteristics by changing the fiber orientation angle. By determining the optimal fiber orientation, the resistance to the torque effect, as well as the value of the critical rotational speed, can significantly be increased. In this paper, using the finite element method, we have examined the effects of fiber orientation angle on the basic static and dynamic characteristics of the shaft (twist angles, natural frequency). The shaft is composed of a combination of aluminum and composite layers of carbon and aramid fibers. In the conclusion section of the paper, optimal variants of the shaft have been identified. [ABSTRACT FROM AUTHOR]

The role of electronic substituent effects in determining the twist angle of 4-substituted biphenyls and the mechanism of their propagation through the biphenyl frame have been studied by quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory, carried out on 41 p-Ph-CH-X molecules in their equilibrium conformation. The twist angle φ about the C-C bond connecting the two benzene rings, ca 45° in unsubstituted biphenyl, almost invariably decreases when a para substituent is present. In the majority of cases the difference ∆ φ = φ(X) − φ(H) is small, less than a couple of degrees; the decrease of φ becomes substantial only when the substituent is a charged π-donor or π-acceptor. Multiple regression analysis using appropriate explanatory variables indicates a quadratic dependence of ∆ φ on the π-donor/acceptor ability of the substituent, and, to a lesser extent, on its field effect. The propagation of substituent effects through the biphenyl frame has been studied from the structural variation of the Ph group acting as a probe (ring B). This is best measured by a linear combination of the internal ring angles, termed S. Multiple regression analysis of S reveals a composite field effect, a substantial proportion of which is originated by resonance- and polarization-induced π-charges on the carbon atoms of the -CH- spacer (ring A). Extended conjugation between ring A and ring B, caused by resonance and polarization effects, gives rise to quadratic terms in the regression. The reliability of S as a measure of long-range polar effects is supported by correlations with various experimental parameters. [ABSTRACT FROM AUTHOR]

Moiré patterns of two-dimensional (2D) van der Waals (vdW) heterostructures can induce novel electronic structures and physical properties. However, the effects of moiré pattern on magnetic properties of 2D materials are not clear yet. Herein, the electronic structures and magnetic properties of 2D graphene/Janus 2H–VSeTe (Gr/VSeTe) heterostructures with moiré patterns are investigated by density functional theory. It is found that twist angles (θ) can induce a band gap at Dirac cone of graphene. With further considering spin-orbit coupling and V magnetic moments of VSeTe monolayer along + z axis, valley polarization of graphene at K and K′ points appears and is found to be sensitive to the twist angle. Additionally, flat band occurs at θ = 5.2° and 10.9° due to the quasi-periodic potential induced by moiré patterns. A high spin polarization also appears in Gr/VSeTe heterostructures with certain twist angles of θ = 0°, 7.6°, 10.9° and 13.9°. Due to the changed occupation of interfacial Te- p orbitals, the magnetic anisotropy and Dzyaloshinskii-Moriya interaction of Gr/VSeTe heterostructures can be changed by twist angles. Therefore, twist angle provides a new degree of freedom for inducing the novel electronic structures and magnetic properties in the 2D magnetic vdW heterostructures. [Display omitted] • Moiré pattern has a significant impact on the physical properties of Gr/VSeTe heterostructures. • Valley splitting is found to be sensitive to the twist angles in Gr/VSeTe heterostructures. • Flat band can be induced by twist angles at θ = 5.2° and 10.9° in Gr/VSeTe heterostructures. • Magnetic anisotropy and Dzyaloshinskii-Moriya interaction can also be tuned by twist angles. [ABSTRACT FROM AUTHOR]

In this paper, two new parametric network models of robots are presented based on the systems' own functions. The complete dynamics of robots are given in a ready-to-used format which is constructed by finite dimensional static parametric networks for the inertia matrix and the potential energy (or the gravitational forces). As a result, dynamic models of robots can be automatically generated by software once given the number of degrees of freedom (DOF) and the sequence of the joint types, without knowing other parameters such as the lengths and the twist angles of the links. An existing adaptive controller is used as an example to show that some of the controllers can be easily modified such that adaptive controllers can be automatically generated. It is shown that all the closed-loop signals are bounded and tracking error goes to zero. [ABSTRACT FROM PUBLISHER]

Both the exact closed-form solution and a numerical solution by the differential quadrature method (D.Q.M.) are obtained to predict the out-of-plane static behavior of a curved beam subjected to torque, based on the curved-beam version of the classical (Bernoulli-Euler) and shear deformable (Bresse-Timoshenko) beam theories. Deflections, twist angles, angles of rotation, bending moments and twisting moments are calculated for the case of a circular are of circular cross section with clamped and simply supported boundary conditions, and the results obtained by both methods (exact and D.Q.M.) are compared. It is found that the D.Q.M. gives good accuracy for only a limited number of grid points. [ABSTRACT FROM AUTHOR]

Recently, twisted two-dimensional (2D) bilayers have attracted intense interest due to the emergence of exotic physics in moiré superlattices arising from strong interactions between electrons in the two misaligned lattices. Accurate determination and control of crystallographic orientation is vital to construct twisted 2D bilayers. Here, we demonstrate a very simple method to visualize crystallographic orientation in various 2D crystals by directly imaging n -tritriacontane crystallites epitaxially grown on 2D crystals using an ordinary optical microscope. The specific orientation of the molecular assembly allows the lattice orientation of the underlying 2D crystals to be determined with a high precision using an optical microscope. When tested on a 2D bilayer comprising staggered stacked MoS 2 crystals, the twist angle can also be determined accurately. Our findings offer a nondestructive method for determining the lattice structure of 2D crystals and their bilayers and can also be a metrology tool for establishing large-area surface crystalline order.

Twist-controlled bilayer graphene (tBLG) and double-twisted trilayer graphene (DTTG) with high precision are fabricated and their controllable optoelectronic properties are investigated for the first time. The successful fabrication of tBLG and DTTG with designated θ provides an attractive starting point for systematic studies of interlayer coupling in misoriented few-layer graphene systems with well-defined geometry., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)