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The lithographically tunable and small size features of Lamb wave resonators (LWRs) take a bright future for their use in high frequency narrow band filters. Resonant frequency drift due to temperature variation has a large impact on the narrower passband and a temperature coefficient of frequency (TCF) closer to 0 can broaden the stable temperature range of the resonator. This paper proposes a method of etching grooves in the area of the piezoelectric layer not covered by the Interdigital transducer (IDT) electrodes to improve the temperature stability of the Lamb resonator. Through the finite element method and theoretical analysis, the phase velocity, group velocity, and TCF dispersion curve of different modes of the resonator with groove structure were determined. The reason for the change of TCF under different normalized thicknesses of AlN was explained through the conversion of the LWR from a contour mode resonator (CMR) to a Cross-Sectional Lamé Mode Resonator. Simulation and test have shown that etching grooves have the effect of reducing TCF by adjusting the electromechanical coupling coefficient. The test shows that 205 nm-depth grooves can lower the TCF of the S0 mode IDT-Open LWR from −13.3 to −5.1 ppm/°C and S1 mode from −36.8 to −9.0 ppm/°C, respectively. The TCF of S0 and S1 mode LWRs decreased by 61.7% and 75.5%, respectively, after 205 nm groove etching. The groove etching method greatly raises the temperature stability of the LWR, enabling Lamb wave filters to operate stably over a wider temperature range. [ABSTRACT FROM AUTHOR]

To investigate the effects of confining pressure, strain rates, and temperatures on the mechanical properties of the Hydroxyl-terminated Polybutadiene (HTPB) propellant, uniaxial tensile tests were performed utilizing wide-temperature-confining pressure systems. The resulting damage was subsequently analyzed and characterized through scanning electron microscopy and mirco-ct. The results indicate that the stress–strain curves of HTPB at 20 and 70 °C are comparable, and the propellant damage is primarily attributed to de-wetting at 20 and 70 °C with respect to the mechanism. At −50 °C, the maximum tensile strength and ultimate tensile strain at 8 MPa surpass those at 0 and 2 MPa to a significant degree and the damage shifts from de-wetting and ductile fracture of particles to severe particle breakage with the elevated confining pressure. Ultimately, the primary curve of the HTPB propellant's maximum tensile strength was constructed by the curve fitting analysis based on the time–temperature equivalent superposition principle (TTSP) and time–pressure equivalent superposition principle (TPSP). Comparing to the properties of TPSP, TTSP exhibits a wider range of applicability and greater fitting precision in relation to the HTPB propellant. This study mainly serves to establish a fundamental theory and furnish data support for the enhancement of mechanical properties and structural integrity of solid rocket motors. [ABSTRACT FROM AUTHOR]

The Schwarzschild microscope is suitable for sample navigation in secondary ion mass spectrometry (SIMS) because of its advantages of a simple structure, large working distance, and good coordination with the ion extraction system. The high numerical aperture (NA) of the microscope significantly reduces diffraction effects, but the resulting high-order geometric aberrations seriously affect the imaging quality. In this paper, a novel design method of the Schwarzschild microscope with a high NA (0.47) was proposed. The aberration distributions and compensation methods were investigated through tolerance analysis. The results showed that the tilt and decenter tolerances become the dominant factors limiting the spatial resolution, which could only be improved by ensuring the alignment accuracy of mirrors. Finally, the spatial resolution of the microscope in the home-built SIMS reached 2.19 µm. [ABSTRACT FROM AUTHOR]

This paper proposes a method for investigating the Coulombic broadening, tcou, in an ambient pressure ion mobility spectrometer based on the analysis of peaks originating from O2−(H2O)n and electrons. It showed that the full width at half maximum (FWHM) of electrons was independent of electron density and remained at a constant contribution from the initial width of ion packets, tg, and amplifier broadening, tamp; in contrast, the FWHM of O2−(H2O)n increased with the rise of O2−(H2O)n density due to additional contributions from tcou and diffusion broadening tdiff. The tcou of O2−(H2O)n was extracted from the FWHM by subtracting tg, tamp, and tdiff. The tcou of O2−(H2O)n was found to increase from 0.14 ms to 0.24 ms as the O2−(H2O)n density increased from 7.35 × 105 to 1.22 × 107 cm−3. The percentage of tcou in the FWHM was in the range of 45%–80%, and the Coulomb-limited resolving power decreased from 70 to 40 as the ion density increased, which indicated that the Coulomb effect was dramatic. [ABSTRACT FROM AUTHOR]

In this paper, the cross-flow vortex-induced vibration (VIV) response of a top tension riser under different flow fields are comprehensively studied using a numerical simulation model based on time domain analysis. A semi-empirical time-domain analysis model that considers the fluid-structure interaction problem in the riser vibration process is proposed and verified by comparison with the previous experimental results. The influence of the flow velocity, the spanwise length of the flow field, and other factors on the VIV amplitude and frequency characteristics of the riser is analyzed in detail. The results show that the VIV response of the riser exhibits obvious multi-modal characteristics, which are accompanied by modal transition, lock-in vibration, synchronous vibration, etc., and the region where the lock-in or synchronous vibration occurs is exactly the region where the crest of the amplitude curve locates. Besides, the VIV intensity of the riser in the stepped flow and uniform flow fields show a tendency of fluctuating increase with the increase of the flow velocity and spanwise length of the flow field, while the VIV intensity of the riser in shear flow is positively correlated with the flow velocity and spanwise length of the flow field. The present study may provide a reference for the prediction of VIV of marine riser in the complex current environment. [ABSTRACT FROM AUTHOR]

An experimental demonstration of mu negative of the Bragg gap in a one-dimensional composite right/left-handed transmission line (CRLH-TL) is presented. In this structure, a band gap which is independent of the scale length and is insensitive to disorder may be mu negative (MNG) or epsilon negative, depending on the value of loading lumped-element components. Another band gap, which is induced by Bragg scattering, depends on the scale length and is sensitive to disorder of the structure of transmission line. As far as CRLH-TL is concerned, it is shown that the Bragg gap can be considered as a single negative gap, furthermore, it is always a MNG gap no matter what the gap between left-handed passband and right-handed passband is a mu-negative gap or an epsilon-negative gap. [ABSTRACT FROM AUTHOR]

Growth of ordered perylene thin films on the Ag(110) surface has been investigated with scanning tunneling microscope. By saturating the surface with a monolayer of perylene molecules, two kinds of ordered structures are simultaneously formed with flat-lying perylene molecules on the Ag(110) surface, in which one is commensurate relative to the Ag substrate with a periodicity of (Multiple line equation(s) cannot be represented in ASCII text) while the other is commensurate with a periodicity of (Multiple line equation(s) cannot be represented in ASCII text). There is one molecule within the former unit cell with a surface coverage of 0.1 molecule per Ag atom, while there are two molecules within the latter unit cell, which gives a slightly lower surface coverage of 0.091 molecule per Ag atom. Ab initio calculations have been carried out to identify the adsorption geometry and bonding sites. [ABSTRACT FROM AUTHOR]

The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4×4) structure is observed from a monolayer (about 4 Å thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 °C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 °C. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photofragment NO[sup +] excitation spectrum of N[sub 2]O[sup +] ions has been studied in the wavelength range of 278–328 nm, where the parent N[sub 2]O[sup +] ions were state-selectively prepared at the X [sup 2]Π[sub 1/2,3/2](000) levels by [3+1] multi-photon ionization of jet-cooled N[sub 2]O molecules at 360.55 nm. The spectrum was attributed completely to the A [sup 2]Σ[sup +]←X [sup 2]Π[sub 3/2,1/2](000) electronic transition of N[sub 2]O[sup +]. Totally 47 vibronic bands associated to 24 vibrational levels of the A [sup 2]Σ[sup +] state were identified in the present work, most of which were observed for the first time. The sufficient spectroscopic data made it possible to investigate the Fermi-resonance between the ν[sub 1] and ν[sub 2] vibrational modes at the A [sup 2]Σ[sup +] state. Based on the assignment, the spectral constants of the A [sup 2]Σ[sup +] state, such as vibrational frequencies, anharmonic constants, and Fermi interaction constant, were determined with relatively high reliability and precision. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The optical spectrum of jet-cooled Ge[sub 2] has been observed for the first time. Laser-induced fluorescence (LIF) and wavelength resolved emission spectra were recorded using the pulsed discharge technique with a tetramethylgermane precursor. Analysis of the spectra yielded the vibrational constants ω[sub e][sup ″]=287.9(47), ω[sub e]x[sub e][sup ″]=0.81(55), ω[sub e]y[sub e][sup ″]=0.0037(18), ω[sub e][sup ′]=189.0(15), ω[sub e]x[sub e][sup ′]=6.41(30), and T[sub e][sup ′]=20 610.8(16) cm-1. High-resolution rotationally resolved spectra of several bands of [sup 74]Ge[sub 2] show two strong P and R branches and two very weak Q branches. We have assigned the band system as a Hund’s case (c) Ω[sup ′]=1-Ω[sup ″]=1 transition from the ground [sup 3]Σ[sub g][sup -] state to a [sup 3]Σ[sub u][sup -] excited state. The bond lengths derived from the rotational constants are r[sub 0][sup ″]=2.3680(1) Å and r[sub e][sup ′]=2.5244(18) Å, an ∼0.16 Å increase on electronic excitation. Arguments are presented for assigning the transition to a σ[sub g][sup 2]π[sub u][sup 2]→σ[sub g][sup 2]π[sub u]π[sub g] electron promotion, although the observed increase in the bond length is much less than predicted by previous ab initio calculations. The absence of the 0[sub u][sup +]–0[sub g][sup +] component in the spectra has been attributed to an excited state predissociation. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Signal de-noising and feature extraction, whose performance directly affect the evaluation of non-destructive testing (NDT) results, is essential technology for ultrasonic NDT echo processing. Aiming to solve the problem of nonlinear distortion between measured ultrasonic echo and its mathematical model, which widely used are exponential model (EM) and Gauss model (GM), a dual Gaussian attenuation model (DGAM) of ultrasonic echo signal and its parameter estimation method are proposed in this paper. The proposed dual Gaussian attenuation model parameter estimation (DGAM-PE) method is introduced in three parts: calculating mean square error between measured signal and model, optimizing mean square error by particle swarm optimization, optimum parameters extraction based on optimization result. The simulation and experiment results show that compared with the exponential model and Gaussian model, the proposed dual gaussian attenuation mathematical model of ultrasonic signal in this paper can better simulate the measured ultrasonic echo signal, with a mean square error of 0.0073 and normalized correlation coefficient of 0.9816. Additionally, an improved adaptive particle swarm optimization is proposed in order to enhance the accuracy of parameter estimation results. [ABSTRACT FROM AUTHOR]

A dopant-enhanced atmospheric pressure direct current glow discharge ionization source for ion mobility spectrometry (APDCGD-IMS) has been described. It is shown that the ion intensity can be greatly increased by addition of species with ionization energy lower than that of buffer gas when the direction of the electric field between the target electrode and the extraction electrode was opposite to that of the drift field. With N2 as the buffer gas, adding O2 (or air), acetone, and CH2Cl2 with certain concentration can enhanced the ion intensity more than one order of magnitude, and for O2, it was found that the enhancement depending on both the concentration of O2 and the flow rate of the carrier gas, and the largest enhancements of the signal intensity for electron in negative mode and reaction ion in positive mode reached at O2 concentration about 1.5%–2%. The main physicochemical processes were summarized and discussed, and a zero-dimensional reaction rate model was set up to simulate the corresponding results. It was proposed that the enhancement of signal intensity was ascribed to the various ionization processes and reactions in APDCGD. [ABSTRACT FROM AUTHOR]

A less laborious, structure-simple, and performance-reliable printed circuit board (PCB) based Bradbury-Nielsen gate for high-resolution ion mobility spectrometry was introduced and investigated. The gate substrate was manufactured using a PCB etching process with small holes ([uppercase_phi_synonym] 0.1 mm) drilled along the gold-plated copper lines. Two interdigitated sets of rigid stainless steel spring wire ([uppercase_phi_synonym] 0.1 mm) that stands high temperature and guarantees performance stability were threaded through the holes. Our homebuilt ion mobility spectrometer mounted with the gate gave results of about 40 for resolution while keeping a signal intensity of over 0.5 nano-amperes. [ABSTRACT FROM AUTHOR]

Temperature-dependent electronic structures of RExC60 (where RE denotes Yb and Sm) films have been studied by high-resolution photoemission spectroscopy (PES). Our results indicate that Yb5C60 is the only metallic phase among all the phases in Yb doped C60 films. For the Sm fullerides, PES results show that there is no Sm valence transition during the negative thermal expansion in Sm2.75C60 below 32 K. The Sm valence state in Sm2.75C60 films is nearly +2 at room temperature and remains stable in the films down to 16 K. In addition, the negative thermal expansion effect does not result any distinct change in valence-band electronic structures of Sm2.75C60. [ABSTRACT FROM AUTHOR]

We report an effective method to selectively produce highly charged ions by photoionization of cluster beams using commercial nanosecond Nd:yttrium–aluminum–garnet lasers at different wavelengths. He-like ions of C4+, N5+, O6+, S6+ and highly charged Xeq+ (q∼19) ions are produced when cluster beams of benzene, ammonia, acetone, hydrogen sulfide, and xenon are irradiated, respectively, by 1064 nm laser with intensity of ∼1011 W/cm2. While the cluster beams are irradiated by 532 nm laser of similar intensity, the ions of the highest charge state switch to C3+, N3+, O3+, S4+ and Xe11+, respectively. [ABSTRACT FROM AUTHOR]

The ground state vibrational energy levels of jet-cooled H[sub 2]CSi and D[sub 2]CSi have been studied by a combination of wavelength-resolved fluorescence and stimulated emission pumping (SEP) techniques. By taking advantage of the vibrational selection rules and Franck-Condon factors and selectively pumping upper state single vibronic levels, readily assignable low-resolution emission spectra were obtained. Higher resolution SEP spectra were recorded to give precise measurements of the vibrational band origins of many of the lower-lying vibrational levels. All of the vibrational frequencies, except for the Franck-Condon inactive CH asymmetric stretching mode, ν[sub 5], have been determined for both isotopomers. The CH[sub 2] rocking mode (ν[sub 6]) is found to have a very low 263 cm-1 frequency in the ground state. The spectra are complicated by unexpected activity in the out-of-plane bending vibration. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ground state vibrational energy levels of jet-cooled SiCH and SiCD have been studied by a combination of laser-induced fluorescence and wavelength-resolved fluorescence techniques. The radicals were produced by a pulsed electric discharge at the exit of a supersonic expansion using tetramethylsilane or methyltrichlorosilane as the precursor. Emission spectra have been obtained by pumping both perpendicular and parallel (vibronically induced) bands, providing complementary information on the Si-C stretching and Si-C-H bending modes. Ground state energy levels up to 4000 cm-1 have been assigned and fitted using a vibrational Hamiltonian that incorporates Renner-Teller, spin-orbit, vibrational anharmonicity, and Fermi resonance interactions. The validity of the derived parameters has been tested using the isotope relations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The A˜ [sup 2]Σ[sup +]-X˜ [sup 2]Π[sub i] electronic transition of jet-cooled germanium methylidyne has been recorded in the 730-555 nm region by laser-induced fluorescence techniques. The radical was produced in a pulsed electric discharge using tetramethylgermane as the precursor. The band system consists of perpendicular and vibronically induced parallel bands with upper state frequencies of ν[sub 2][sup ′]=638/497 cm[sup -1] and ν[sub 3][sup ′]=990/952 cm[sup -1] for GeCH/GeCD. The [sup 2]Σ[sup +]-[sup 2]Π[sub 3/2] components of the 0[sub 0][sup 0] bands of GeCH and GeCD and the 2[sub 0][sup 1] band of GeCH have been recorded with sufficient resolution to assign the transitions of the [sup 70]Ge, [sup 72]Ge, [sup 74]Ge, and [sup 76]Ge isotopomers. The rotational constants of the various hydrogen and germanium isotopomers were used to derive the following molecular structures: r[sub 0][sup ″](Ge-C)=1.775 79(21) Å, r[sub 0][sup ″](C-H)=1.0673(12) Å, r[sub 0][sup ′](Ge-C)=1.673 66(8) Å, and r[sub 0][sup ′](C-H)=1.0589(5) Å. The ground state germanium-carbon bond length is typical for a Ge=C double bond, but in the excited state it corresponds to a triple bond. This is a consequence of promotion of an electron from a nonbonding σ orbital to a π bonding orbital to form the ...σ[sup 1]π[sup 4]([sup 2]Σ[sup +]) excited state. In this study we provide the first experimental value for the length of the germanium-carbon triple bond. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The A˜ [sup 2]Σ[sup +]-X˜ [sup 2]Π[sub i] transition of jet-cooled silicon methylidyne, SiCH, has been recorded by laser-induced fluorescence in the 850-600 nm region. The radical was produced in an electric discharge using tetramethylsilane as the precursor. Fifteen cold bands of SiCH and 16 bands of SiCD have been assigned vibrationally, giving the upper state frequencies as v[sub 2][sup ′]=715/558 cm[sup -1] and v[sub 3][sup ′]=1168/1127 cm[sup -1] for SiCH/SiCD. Rotational analysis of the 0[sub 0][sup 0] and 3[sub 0][sup 3] bands for each isotopomer has given the following molecular structures: r[sub 0][sup ″](Si-C)=1.692 52(8), r[sub 0][sup ″](C-H)=1.0677(4), r[sub 0][sup ′](Si-C)=1.6118(1), and r[sub 0][sup ′](C-H)=1.0625(5) Å. The silicon-carbon bond length in the X˜ [sup 2]Π ground state of SiCH (electron configuration ...σ[sup 2]π[sup 3]) is typical for a Si=C double bond; in the A˜ [sup 2]Σ[sup +] excited state (...σ[sup 1]π[sup 4]) it corresponds to a triple bond. This work provides the first experimental measurement of the length of the carbon-silicon triple bond. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The adsorption of tetracene on Si(100)-2x1 substrate has been studied by ultraviolet photoemission spectroscopy (UPS). Six features deriving from the organic material are located at 1.22, 2.41, 3.63, 4.67, 7.11, and 8.77 eV below the Fermi level. These features shift in binding energy with increasing the thickness of the organic film. In the case of a monolayer, angle-resolved UPS measurements suggest that the molecular plane is parallel to the substrate. Further theoretical density functional theory calculation reveals the most stable structure of tetracene molecule on Si substrate in which six covalent Si-C chemical bonds are formed between carbon atoms of the tetracene molecule and the Si atoms on the substrate.

The interfacial electronic states of tetracene on Si(111) 7x7 substrate were studied by using ultraviolet photoelectron spectroscopy (UPS). After deposition of tetracene on the Si(111) 7x7 surface, the features originating from the tetracene molecule appear at 1.55, 3.36, 6.78, 9.24, and 10.76 eV below the Fermi level; they shift in binding energy with increasing organic film coverage. From the UPS measurements, the work function of the sample surface was found to decrease with increasing molecular coverage in the submonolayer range suggesting that an interfacial dipole is formed. A density functional theory calculation had also been carried out to determine the favorable adsorption structure. The molecule near the top of a center adatom with the longer molecular axis along the [110] azimuth is the most favorable.

The valence electronic states of three kinds of fluorinated derivatives of perylene diimides, D2MFPP, D3MFPP, and D4MFPP, on Cu(110) and SiO(2)Si surface were studied by photoemission and density functional calculations. When these organic molecules were deposited on the Cu(110) and thermally oxidized SiO(2) surfaces, five well-resolved photoemission features originating from the molecules were observed. On Cu(110) surface, two emission features with pi-like character increased their binding energy with increasing the coverage of organic molecule, indicating a strong interaction between the organic molecules and Cu substrate. The density functional calculations suggest flat-lying adsorption geometry for D3MFPP and D4MFPP on Cu(110) surface.

The electronic structure of tetracene on Cu (110) surface has been studied by using ultraviolet photoemission spectroscopy (UPS). The emission features from the organic molecule are located from 1 to 10 eV below the Fermi level, and they shift in binding energy with increasing the coverage of the organic material. For the surface with multilayer of tetracene, six well-resolved features were found at 1.90, 3.40, 4.70, 5.95, 6.95, and 9.15 eV below the Fermi level, respectively. On the surface with a lower coverage of tetracene, angle-resolved UPS measurements suggest that the molecular plane is parallel to the substrate. Density functional theory calculation confirms the flat-lying adsorption mode and shows that the tetracene molecule prefers to be adsorbed on the long bridge site with its long axis in the [110] azimuth.

The Coulomb explosion of ammonia clusters induced by nanosecond laser field with intensity in the range of 10(10)-10(12) W cm(-2) and wavelength of 532 and 1064 nm has been studied. N2+ and N3+ ions are the main multicharged ions at 532 nm, while He-like N5+ ion is the domain multicharged ion at 1064 nm.

The direct hydrogen abstraction reactions of Cl atom with SiH(n)Cl(4-n) (n=1,2,3,4) have been studied systematically using ab initio molecular orbital theory. Geometries have been optimized at the MP2 level with 6-311+G(d) basis set, QCISD(T)/6-311+G(d,p) has been used in the final single point energy calculation. The kinetic calculations of these reactions have been explored using the canonical variational transition (CVT) state theory method with small-curvature tunneling (SCT) effect correction over the temperature range of 200-2000 K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior and three-parameter rate-temperature formulas have been fitted for the reactions of Cl with SiH4, SiH3Cl, SiH2Cl2, and SiHCl3, respectively (in unit of cm(3) molecule(-1) s(-1)). The calculated CVT/SCT rate constants are in agreement with the available experimental values.