In-plane Vibrational Modes Research Articles

In-plane vibration analysis of elastically restrained FGM skew plates using variational differential quadrature method

This work presents an accurate in-plane vibration analysis of functionally graded material (FGM) skew plates with elastically restrained boundaries using the variational differential quadrature method (VDQM). The weak form of the governing equations is derived by integrating two-dimensional elasticity theory with Hamilton's principle. The differential and integral operators are directly converted into matrix forms, thereby removing the necessity for higher-order derivative approximations in the displacement field. Transformation matrices are then developed for both interior and boundary nodes to link the governing equations with the boundary conditions, leading to the formulation of the vibration eigenvalue equations for FGM skew plates. Various factors, including aspect ratios, skew angles, boundary restraints, and gradient indices, are considered to investigate the in-plane vibration mode characteristics of FGM skew plates. Detailed solution procedures are provided, and numerical examples using the proposed solutions indicate that the VDQM exhibits superior numerical convergence and stability compared to other existing methods. The study also investigates the influence of highly skewed plates (75°), where stress singularities arise at the corners. This aspect is crucial for in-plane vibration analysis and has garnered limited attention in the existing literature. Furthermore, the dynamic analysis of FGM skew plates reveals a coupling between normal and tangential vibration modes.

Room temperature polarization-resolved Raman and photoluminescence in uniaxially strained layered MoS2

Transition metal dichalcogenides (TMDCs) are one of the material systems of choice toward achieving room temperature quantum coherence. Externally applied strain is used as a more common control mechanism to tune electro-optical properties in TMDCs like molybdenum disulfide (MoS2). However, room temperature electron–phonon interactions in the presence of strain in transition metal dichalcogenides are still not fully explored. In this work, we employ uniaxial strain dependent Raman and photoluminescence (PL) studies on monolayer and bilayer MoS2 to explore electron–phonon physics. Helicity-resolved Raman in MoS2 obeys robust selection rules. Our studies reveal clear modification in these helicity-based selection rules in the presence of moderate uniaxial strain (ϵ = 0.4%–1.2%). The selection rules are restored upon clear symmetry breaking of the in-plane vibrational mode (ϵ > 1.2%). We assign these changes to the onset of Fröhlich interaction in this moderate strain regime. The changes in Raman scattering are accompanied by changes in valley selective relaxation observed through non-resonant photoluminescence (PL). The moderate strain regime also exhibits the onset of PL polarization for indirect excitonic emission under non-resonant excitation. Our experimental observations point toward electron–phonon coupling mechanisms affecting both valley-selective electron relaxation during PL emission as well as polarization-selective Raman scattering of two-dimensional semiconductors at room temperature.

Disturbance-immune, fast response LITES gas sensor based on out-plane vibration mode employing micro Fabry-Perot cavity with heterodyne phase demodulation

The disturbance-immune, fast response light-induced thermoelastic spectroscopy (LITES) gas sensor based on out-plane vibration (OPV) mode employing micro Fabry-Perot cavity with heterodyne phase demodulation was firstly reported in this paper. Compared to the traditional in-plane vibration (IPV) mode, the OPV mode has a lower resonance frequency (f0) to enhance the energy accumulation time of the system. The OPV mode based H-LITES (OPV-H-LITES) sensor and the IPV mode based H-LITES (IPV-H-LITES) sensor were established using a standard quartz tuning fork (QTF) at the same conditions for performance comparison. Acetylene (C2H2) was selected as the target gas to verify the sensor performance. In comparison to the IPV-H-LITES sensor, there has been a 3.5-fold improvement in signal-to-noise ratio (SNR) of OPV-H-LITES sensor. In order to further improve the sensor performance, a novel self-designed low-frequency QTF was adopted to replace the standard QTF, leading to a 2.3-fold increase in the SNR of the OPV-H-LITES sensor. Finally, a minimum detection limit (MDL) of 7.22 ppm for C2H2 detection was obtained. The proposed technique holds the merits of high sensitivity, power disturbance resistance, wavelength independence, excellent linear concentration response and long-term stability.

Dynamic analysis of cracked pipe elbows: Numerical and experimental studies

This study aims to investigate the dynamic behaviors of fluid-delivering cracked pipe elbows (FDCPEs), thereby providing theoretical and methodological guidance for vibration-based crack detection in pipe elbows. Specifically, an efficient spectral element-finite element (SE-FE) based modeling method for the FDCPEs is proposed firstly, which considers fluid-structure coupling and breathing effect. For the SE-FE method, the spectral element (SE) and finite element (FE) are constructed to simulate the healthy straight segments and cracked elbows of the pipe, respectively, and a penalty function method is adopted to simulate interface coupling and breathing effects. Furthermore, the computational accuracy and efficiency of the SE-FE method are verified through numerical and experimental studies. Finally, the effects of the elbow and crack parameters on the dynamic behaviors of FDCPE are analyzed. The results indicate that changes in the bending radius and angle may trigger frequency veering behaviors, leading to in-plane and out-plane vibration mode switching. Moreover, the even-mode harmonics of the stress responses can effectively detect cracks in the elbow. Most importantly, the strength of nonlinearity at different measuring locations can be used to predict the crack location and size.

Absorption and fluorescence spectroscopy of cold proflavine ions isolated in the gas phase.

Proflavine, a fluorescent cationic dye with strong absorption in the visible, has been proposed as a potential contributor to diffuse interstellar bands (DIBs). To investigate this hypothesis, it is essential to examine the spectra of cold and isolated ions for comparison. Here, we report absorption spectra of proflavine ions, trapped in a liquid-nitrogen-cooled ion trap filled with helium-buffer gas, as well as fluorescence spectra to provide further information on the intrinsic photophysics. We find absorption- and fluorescence-band maxima at 434.2 ± 0.1 and 434.7 ± 0.3nm, corresponding to a Stokes shift of maximum 48cm-1, which indicates minor differences between ground-state and excited-state geometries. Based on time-dependent density functional theory, we assign the emitting state to S2 as its geometry closely resembles that of S0, whereas the S1 geometry differs from that of S0. As a result, simulated spectra involving S1 exhibit long Franck-Condon progressions, absent in the experimental spectra. The latter displays well-resolved vibrational features, assigned to transitions involving in-plane vibrational modes where the vibrational quantum number changes by one. Dominant transitions are associated with vibrations localized on the NH2 moieties. Experiments repeated at room temperature yield broader spectra with maxima at 435.5 ± 1nm (absorption) and 438.0 ± 1nm (fluorescence). We again conclude that prevalent fluorescence arises from S2, i.e., anti-Kasha behavior, in agreement with previous work. Excited-state lifetimes are 5 ± 1ns, independent of temperature. Importantly, we exclude the possibility that a narrow DIB at 436.4nm originates from cold proflavine cations as the band is redshifted compared to our absorption spectra.

A Study of a Gain-Scheduled Individual Pitch Controller for an NREL 5 MW Wind Turbine

In order to reduce the asymmetric load acting on the blades of MW-class wind turbines, it is necessary to apply an individual pitch controller that independently adjusts the pitch angles of the three blades. This paper takes a new look at the relationship between the individual pitch controller applied to MW-class wind turbines and the vibration mode of the blades. The purpose of this study is to propose a method in which the individual pitch controller further reduces the 1P component of the bending moment in the out-of-plane direction acting on the blade, without exciting the in-plane vibration mode of the blade within the entire wind speed range, from the rated wind speed to the cut-out wind speed. To this end, a problem related to the excitation of the blade’s vibration mode that may occur when applying the individual pitch controller to an NREL 5 MW wind turbine is examined, and a method that uses gain scheduling to overcome this problem is presented. It is confirmed that it is possible to solve the problem of exciting the first-order vibration mode in the in-plane direction of the blade that can occur in the high wind speed range by applying the proposed gain scheduling method to the individual pitch controller aimed at reducing the 1P component of the out-of-plane bending moment of the blade.

Influence of pseudo-Jahn-Teller activity on the singlet-triplet gap of azaphenalenes.

We analyze the possibility of symmetry-lowering induced by pseudo-Jahn-Teller interactions in six previously studied azaphenalenes that are known to have their first excited singlet state (S1) lower in energy than the triplet state (T1). The primary aim of this study is to explore whether Hund's rule violation is observed in these molecules when their structures are distorted from C2v or D3h point group symmetries by vibronic coupling. Along two interatomic distances connecting these point groups to their subgroups Cs or C3h, we relaxed the other internal degrees of freedom and calculated two-dimensional potential energy subsurfaces. The many-body perturbation theory (MP2) suggests that the high-symmetry structures are the energy minima for all six systems. However, single-point energy calculations using the coupled-cluster method (CCSD(T)) indicate symmetry lowering in four cases. The singlet-triplet energy gap plotted on the potential energy surface also shows variations when deviating from high-symmetry structures. A full geometry optimization at the CCSD(T) level with the cc-pVTZ basis set reveals that the D3h structure of cyclazine (1AP) is a saddle point, connecting two equivalent minima of C3h symmetry undergoing rapid automerization. The combined effects of symmetry lowering and high-level corrections result in a nearly zero singlet-triplet gap for the C3h structure of cyclazine. Azaphenalenes containing nitrogen atoms at electron-deficient sites - 2AP, 3AP, and 4AP - exhibit more pronounced in-plane structural distortion; the effect is captured by the long-range exchange-interaction corrected DFT method, ωB97XD. Excited state calculations of these systems indicate that in their low-symmetry energy minima, T1 is indeed lower in energy than S1, upholding the validity of Hund's rule. Jahn-Teller analysis predicts the symmetries of the in-plane distortion vibrational modes as or B2: C2v → Cs agreeing with the vibrational frequencies of the saddle-points.

Research on interactions between different operating modes of piezoelectric motors

This paper explores interactions between multiple operating modes of piezoelectric motors. The developed motor can operate in the second-order in-plane bending modes (I), the third-order in-plane bending modes (II) and the first-order out-of-plane bending modes (III). These working modes excited separately and simultaneously, can be manipulated electronically. Each of the vibrational modes can both be driven by applying single-phase and two-phase voltages to piezoelectric ceramic plates. In order to produce all the vibration states, the structural parameters of stator were strictly designed to harmonize two eigenfrequencies of each type of vibrational modes by using finite element software ANSYS. Displacement characteristics of stator driving particles under all vibration states were calculated to evaluate mutual effects of different operating modes. Simulation results reveal that the superposition of I and II corresponds to a mode with lower resonance frequency and larger vibration amplitude in stator body. For the designed motor, the conjunction of modes I and II actually forms the first-order in-plane vibrational mode B01. Therefore, the response displacement of stator driving points reaches the maximum value when modes I and II are conjointly actuated by supplying single-phase excitation voltage under the premise of undistorted three-dimensional motion trajectory. The motor performances under that condition were also investigated experimentally. The dimension of the fabricated prototype motor is 10 mm × 10 mm × 20 mm. The stall torque is 0.2 N·m under 200 V single-phase excitation, when the motor operates in modes I and II simultaneously. The maximum no-load speed is 74 r min−1. Compared with separate actuation of vibrational modes I and II, mechanical properties of the prototype motor are significantly improved.

Modal analysis and vibration control of a vertical cable with dual tuned mass dampers

This paper proposes a vibration model for modal analysis and vibration control of a vertical cable-dual tuned mass damper (C-DTMD) coupled system. The proposed model introduces several non-dimensional parameters to describe the in-plane vibration of the coupled system. Moreover, the phenomenon of modal split is comprehensively studied to present the complex vibration modes. Parameter analysis is conducted to show the influence of length ratio, mass ratio, damping ratio, and frequency ratio on vibration reduction. In addition, the theoretical model is verified using finite element methods. A practical vertical cable in Jiangyin Bridge with designed wind loads is chosen as a numerical example. The results show that DTMD devices can effectively reduce the modal vibration and have great potential for multi-mode vibration control of vertical cables in suspension bridges. The proposed model can accurately describe the in-plane vibration modes of C-DTMD systems and provides a basis for the optimal design of damper parameters.

Tellurium nanosheets with structural anisotropy formed from defective MoTe2 multilayers

We report on the formation of a tellurium nanosheet with a MoOx cap by thermal annealing of ion-implanted 2H–MoTe2 multilayers. The presence of crystal defects generated by ion implantation at an energy of 90 keV accelerates the incorporation of O atoms and the surface desorption of Te atoms in the defective MoTe2 during thermal annealing, and subsequently, a tellurium nanosheet is formed around the bottom regions in the defective MoTe2 due to tellurium segregation. For the angle-resolved Raman spectroscopy, polar plots exhibit two-fold and four-fold symmetries for peak intensities of 121 and 143 cm−1, respectively, signifying the structural anisotropy of the tellurium nanosheet. On reducing the ion energy, the two Raman peak intensities collected from the tellurium nanosheet remarkably decrease, and they disappear for the sample at 30 keV. On the other hand, the decrease of the implantation energy increases the E2g peak intensity at 235 cm−1, which corresponds to the in-plane vibration mode of 2H–MoTe2. The distribution of crystal defects along the depth direction tuned by ion implantation energy is very critical for the formation of a tellurium nanosheet with structural anisotropy from the 2H–MoTe2 multilayers.

Realizing high-temperature superconductivity in borophene with Dirac states assembled by kagome and honeycomb boron layers

Boron's unique electron deficiency allows for the formation of various borophene polymorphs that have the potential for superconductivity. Herein, we have introduced a new route to realize high superconductivity in borophene through kagome and honeycomb boron layers assembly. We have designed a tri-layer borophene, named hP8-B, consisting of two AA-stacked kagome layers with a honeycomb layer serving as the interlayer. hP8-B possesses high superconductivity with an estimated Tc of 35.6 K, holding the highest value in any elemental 2D materials. The high Tc is mainly contributed by the strong coupling of σ-bonding electrons of the kagome layers and in-plane vibrational modes, which differs from that in other superconductive borophene polymorphs. Electronic band structure calculations showcase the existence of a Dirac cone near the Fermi level, indicating that hP8-B may be a potential topological superconductor. The superconductivity of hP8-B can be enhanced to 46.4 K under a biaxial tensile strain of 3% and doping density of 0.0375 holes per atom, due to the softening of the in-plane vibrational modes.

Growth of nanostructured molybdenum disulfide (MoS2) thin films on a nanohole-patterned substrate using plasma-enhanced atomic layer deposition (ALD)

Nanostructured molybdenum disulfide (MoS2) thin films were grown on a nanohole-patterned silicon substrate using plasma-enhanced atomic layer deposition. A nanoscale hole-patterned silicon substrate was fabricated for the growth of MoS2 film using the self-assembly-based nanofabrication method. The nanoscale holes can significantly increase the surface area of the substrate while the formation and growth of nanostructures normally start at the surface of the substrate. Hydrogen sulfide (H2S) gas was used as the S source in the growth of molybdenum disulfide (MoS2) while molybdenum (V) chloride (MoCl5) powder was used as the Mo source. The MoS2 film had a stoichiometric ratio of 1 (Mo) to 2 (S), and had peaks of E12g and A1g, which represent the in-plane and out-plane vibration modes of the Mo–S bond, respectively. It was found that the MoS2 film grown in the nanoscale hole, especially at the wall of the hole, has more hexagonal-like structures due to the effects of nanoscale space confinement and the nanoscale interface although the film shows an amorphous structure. Post-growth high-temperature annealing ranging from 800 to 900 °C produced local crystalline structures in the film, which are compatible with those reported by other researchers.

Jet-Cooled Phosphorescence Excitation Spectrum of the T1(n,π*)←S0 Transition of 4H-Pyran-4-one.

The 4H-pyran-4-one (4PN) molecule is a cyclic conjugated enone with spectroscopically accessible singlet and triplet (n,π*)excited states. Vibronic spectra of 4PN provide a stringent test of electronic-structure calculations, through comparison of predicted vs measured vibrational frequencies in the excited state. We report here the T1(n,π*) ← S0 phosphorescence excitation spectrum of 4PN, recorded under the cooling conditions of a supersonic free-jet expansion. The jet cooling has eliminated congestion appearing in previous room-temperature measurements of the T1 ← S0 band system and has enabled us to determine precise fundamental frequencies for seven vibrational modes of the molecule in its T1(n,π*) state. We have also analyzed the rotational contour of the 000 band, obtaining experimental values for spin-spin and spin-rotation constants of the T1(n,π*) state. We used the experimental results to test predictions from two commonly used computational methods, equation-of-motion excitation energies with dynamical correlation incorporated at the level of coupled cluster singles doubles (EOM-EE-CCSD) and time-dependent density functional theory (TDDFT). We find that each method predicts harmonic frequencies within a few percent of observed fundamentals, for in-plane vibrational modes. However, for out-of-plane modes, each method has specific liabilities that result in frequency errors on the order of 20-30%. The calculations have helped to identify a perturbation from the T2(π,π*) state that leads to unexpected features observed in the T1(n,π*) ← S0 origin band rotational contour.

Development of a novel radial-torsional hollow ultrasonic motor and contact interface coating test

A novel miniature radial-torsional hollow ultrasonic motor is proposed in this work, which is mainly composed of a base, a hollow rotor, a stator. One piece of piezoelectric wafer bonded on the bottom face of the stator is used to excite the radial in-plane vibration mode of the outer ring, which is converted into the revolved motion of the inner ring through the connection beams. The revolved motion of the inner ring can drive the rotor pressed on the inner ring to rotate through friction. The finite-element method was performed to verify the working principle of the motor and optimize the key dimensions of the motor. One prototype motor with the appearance size of Φ35 mm × 12 mm and weight of 20.1 g is fabricated and characterized. In addition, Si3N4 thin film is coated on the contact interface of the stator by the magnetron sputtering coating machine to improve the output performance of the ultrasonic motor. The experiment results show that the locked-rotor torque of the motor with coated stator can reach 0.42 mN m, which is 55.56 % higher than that of the uncoated motor.

Optical and Optoelectronic Properties of Bi2Te3, Sb2Te3, and Bi0.5Sb1.5Te3 Flakes

In this study, a mechanical exfoliation method was developed for the synthesis of high purity Bi2Te3, Sb2Te3, and Bi0.5Sb1.5Te3 flakes. The synthesized Bi2Te3, Sb2Te3, and Bi0.5Sb1.5Te3 flakes were characterized by atomic force microscope, Raman spectroscopy, and photoluminescence (PL). The effect of the thickness of the Bi2Te3, Sb2Te3, and Bi0.5Sb1.5Te3 flakes on PL and Raman spectra was investigated. As the thickness increased in the Bi2Te3 flakes, the out of plane vibration mode (A21g) shows a blue shift. For the thicker Sb2Te3 flakes, the A11g and E2g modes indicated a blue shift and a red shift, respectively. When the thickness of Bi0.5Sb1.5Te3 flakes decreased, the in-plane vibration mode (E2g) shifted to lower frequencies. A new Raman peak has been observed in Bi0.5Sb1.5Te3 flakes, which is not active in the thin films. PL measurements of Bi0.5Sb1.5Te3 flakes with various thickness revealed PL peaks in the range of 2.15 - 2.54 eV at room temperature (300 K). A Bi0.5Sb1.5Te3 flakes-based photodetector exhibited photoresponsivity as high as 661.5 A/W at a 0.02 mW power density with an 1800 nm laser at room temperature (300 K). Compared to the optoelectronic properties of Bi2Te3 flake, a twice higher responsivity at a wavelength of 1800 nm was observed with the Bi0.5Sb1.5Te3 flake-based photodetector.

Strong phonon mode induced by carbon vacancy accelerating hole transfer in SiC/MoS2 heterostructure

The van der Waals SiC/MoS2 heterostructure with a type-II band alignment is promising for potential applications in photocatalytic and optoelectronic devices. By performing time-dependent nonadiabatic molecular dynamics simulations, we study the dynamics of single sulfur and carbon vacancy-mediated of photoexcited hole transfer at the interface of SiC/MoS2. The results indicate that single C-vacancy in SiC atomic layer promotes interlayer hole transfer more sufficiently in a shorter timescale of 68 fs than those of S-vacancy and pristine heterostructures. This promotion is attributed to the decreased energy gap related to intralayer hole transfer in SiC layer, resulting from the split of acceptor state, the excitation of a stronger in-plane carbon atom vibration mode at 600 cm−1, and the enhancement of electron–phonon coupling. Meanwhile, electron-hole recombination is three orders of magnitude slower than hole transfer, ensuring an effective charge separation in SiC/MoS2 with C-vacancy. This work provides theoretical insights into the dynamics of photoexcitation hole transfer in MoS2/SiC heterostructure.

2H-MoS 2 Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

2H-MoS ₂ Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

Superconductivity and topological properties in the kagome metals CsM3Te5 ( M =Ti, Zr, Hf): A first-principles investigation

Inspired by the discovery and fascinating properties of kagome metals $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A$= K, Rb, Cs), we investigate the superconductivity and topological properties of the $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$-prototype kagome materials $\mathrm{Cs}{M}_{3}{\mathrm{Te}}_{5}$ ($M$=Ti, Zr, Hf) using first-principles calculations. The calculated results of formation energy and phonon dispersion indicate that this family of kagome materials are stable and may be synthesized in experiments. By analytically solving the Allen-Dynes-modified McMillan formula, the superconducting critical temperatures for ${\mathrm{CsTi}}_{3}{\mathrm{Te}}_{5}, {\mathrm{CsZr}}_{3}{\mathrm{Te}}_{5}$, and ${\mathrm{CsHf}}_{3}{\mathrm{Te}}_{5}$ are predicted as 8.02, 5.47, and 3.51 K, respectively. The electron-phonon couplings are dominated by the coupling between the in-plane atomic vibrational modes and the in-plane electronic orbitals. In addition, the ${\mathrm{CsZr}}_{3}{\mathrm{Te}}_{5}$ and ${\mathrm{CsHf}}_{3}{\mathrm{Te}}_{5}$ can be categorized as ${\mathbb{Z}}_{2}$ topological metals according to the calculations of topological invariant and surface states. Such coexistence of superconductivity and nontrivial topological properties in ${\mathrm{CsZr}}_{3}{\mathrm{Te}}_{5}$ and ${\mathrm{CsHf}}_{3}{\mathrm{Te}}_{5}$ are beneficial to study the interaction between superconductivity and nontrivial band character.

Defect-Induced Ultrafast Nonadiabatic Electron-Hole Recombination Process in PtSe2 Monolayer.

Defects are inevitable in two-dimensional materials due to the growth condition, which results in many unexpected changes in materials' properties. Here, we have mainly discussed the nonradiative recombination dynamics of PtSe2 monolayer without/with native point defects. Based on first-principles calculations, a shallow p-type defect state is introduced by a Se antisite, and three n-type defect states with a double-degenerate shallow defect state and a deep defect state are introduced by a Se vacancy. Significantly, these defect states couple strongly to the pristine valence band maximum and lead to the enhancement of the in-plane vibrational Eg mode. Both factors appreciably increase the nonadiabatic coupling, accelerating the electron-hole recombination process. An explanation of PtSe2-based photodetectors with the slow response, compared to conventional devices, is provided by studying this nonradiative transitions process.

Temperature-dependent Raman spectroscopy and thermal conductivity of TiS2 hexagonal nanodiscs

Transition metal dichalcogenides (TMDC) possess a unique combination of properties well-suited for the creation of novel optoelectronic and photonic devices. The titanium disulphide (TiS2) outstands among those as the lightest of TMDCs besides allowing low production cost and high stability. In this work, we present a comprehensive study of electron-phonon interaction induced vibrational properties of suspended TiS2 hexagonal nanodisks for an extended and elevated temperature range from 88 K to 538 K and a variety of laser powers. Our study reveals a stronger temperature dependence for out-of-plane vibrational mode (A1g) in comparison to that of in-plane vibration mode (Eg) which is attributed to a significant difference between strong intralayer covalent bonds and weak interlayer van der Waals bonds within the material. Furthermore, we observed that both Eg and A1g modes linearly undergo a red shift at higher temperatures, and in addition, a broadening at higher in-laser powers. On the basis of the present study, we propose that the thermal conductivity of the material is 5.049 W/mK.