Elastic Resonance Research Articles

Absolute calibration of the 16O(α,α) 16O elastic scattering resonance at 7.30–7.65 MeV and applications to oxygen depth profiling

The differential cross-section of the 16O(α,α) 16O elastic scattering resonance at 7.30–7.65 MeV has been calibrated with an overall accuracy of 4% at 170° scattering angle (laboratory frame of reference) using anodized Ta 2O 5 films of pre-calibrated thickness as standards. This extremely strong (about 170 times the Rutherford cross-section) and broad (about 300 keV wide) resonance varies slowly with energy in the range 7.34–7.64 MeV, has a maximum value of 837 mb/sr at 7.61 MeV, and falls off abruptly above 7.64 MeV and below 7.34 MeV. The angular dependence of the resonance was measured in the range 140–172° at incident energy 7.62 MeV and was found to increase monotonically toward 180°. This strong resonance allowed us to measure the oxygen content in the very heavy element target ThO 2 pellets and in oxidized InP substrates with detection sensitivity in the atomic monolayer range. The large width of this resonance allowed oxygen depth profiling to several microns with depth resolution a few tens of nm. Measurements combined with RUMP computer simulations using TRIM stopping cross-sections and our measured values of the elastic resonance scattering cross-section have been used to depth profile SiO 2 surface and buried layers in SIMOX structures.

Plasma enhanced chemical vapor deposition silicon oxides as studied by x-ray photoelectron spectroscopy, Rutherford backscattering, electron recoil detection analysis, infrared spectroscopy, and electron spin resonance

SiO2 thin films were obtained by microwave plasma enhanced chemical vapor deposition. Plasma with two different gas mixtures were studied: Ar/O2/SiH4 and O2/SiH4, the gas ratio R=O2/SiH4 varying from 0.5 to 10 with two radio frequency bias powers (0 W and 100 W). Seventeen dielectric layers with a thickness of around 500 nm were studied to determine their chemical composition by x-ray photoelectron spectroscopy and valence band studies, Rutherford backscattering spectroscopy and elastic recoil detection analysis, infrared spectroscopy, and electronic spin resonance. These samples could then be classified into three groups corresponding to different SiOH and SiH or only SiOH concentrations. Their stoichiometries were also determined. An explanation of the valence band shift and its modifications is proposed.

Nuclear resonance effects in the analysis of proton backscattering from carbon and silicon films

The use of elastic resonance backscattering of protons in the analysis of thin films is sometimes an advantage. It allows precise and accurate thickness determination even when the energy calibration of the system is marginal. The availability of reliable values for the scattering cross section in the region of the resonance is essential. We have remeasured the elastic scattering cross section of protons on C and Si in the energy region between 450 and 2200 keV at a laboratory angle of 155°. Our data are compared with earlier measurements. The usefulness of the incorporation of resonance scattering in the spectrum analysis is demonstrated.

Quantification of oxygen and carbon in high Tc superconducting films by (α,α) elastic resonance technique

AbstractThe quantification of oxygen and carbon in high‐temperature (Tc) superconducting oxide thin films was made by employing elastic resonance in He backscattering analysis. A method combining the oxygen resonance technique and channeling was presented for measuring the nature of the oxygen disorder near the surface and the interface in a YBCO superconducting film grown on an MgO substrate. The oxygen resonance technique was used to quantify the oxygen profiling in the metal/YBCO contacts, showing that Zr and Nb act as sinks to oxygen from YBCO films and are oxidized in the forms Zr/ZrO2/YBCO/MgO and Nb0.2/YBCO/MgO after annealing in a vacuum at 350°C. We combined the carbon and oxygen resonances to determine the carbon contamination and oxygen concentration changes on the YBCO surface after coating and baking the photoresist. Residual carbon on the surface and a thin layer of oxygen depletion near the YBCO surface have been observed. The residual carbon in Bi2Sr2CaCu2O8 films made by the decomposition of metallo‐organic precursors was quantified using carbon resonance.

Relation between surface helical waves and elastic cylinder resonances

In this paper, the authors deal with theoretical and experimental studies about the acoustic scattering by an elastic solid cylinder immersed in water, at oblique incidence. Comparisons are made between the calculated form function and measured scattered pressure for incidence angles varying from 0° to 30°, in the normalized frequency range 0–30. The behavior of the resonances when the incidence angle increases is shown and the connection between helical surface waves propagation and resonance is explained, using the contributions of the resonance scattering theory and the Sommerfeld–Watson transformation. More accurately, resonances are due to the phase matching of circumnavigating helical surface waves, and a refraction effect is found to take place between the incident and the helical surface wave direction of propagation, which clearly explains the resonance shift with respect to incidence angle variations. Guided waves appear at oblique incidence with a polarization primarily transverse at small incidence angles.

PECVD silicon oxides as studied by XPS, RBS, ERDA, IRS and ESR

SiO 2 thin films were obtained by microwave plasma-enhanced chemical vapour deposition. Plasmas with two different gas mixtures were studied: Ar/O 2/SiH 4 and O 2/SiH 4, the gas ratio R = O 2 SiH 4 varying from 0.5 to 10 with two radio frequency (RF) bias powers (0 and 100 W). Seventeen dielectric layers with a thickness around 500 nm were studied to determine their chemical composition by X-ray photoelectron spectroscopy (XPS) and valence-band studies, Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA), infrared spectroscopy (IRS) and electronic spin resonance (ESR). These samples could then be classified into three groups corresponding to different SiOH and SiH or only SiOH concentrations. Their stoichiometries were also determined. An explanation of the valence-band shift and its modifications is proposed.

Elastic Helmholtz resonators

The influence of wall elasticity on the response of a Helmholtz resonator is examined by analyzing the canonical case of a thin elastic spherical shell with a circular aperture subject to plane wave excitation. By neglecting the thickness of the wall and representing the elasticity via a ‘‘thin shell’’ theory the problem is reduced to one of solving an integral equation over the aperture for the polarization velocity, which is related to, but distinct from, the radial particle velocity of the fluid. The integral equation can be solved by asymptotic methods for small apertures, yielding closed-form expressions for the major resonator parameters. In general, wall compliance reduces the resonance frequency in comparison with an identically shaped rigid cavity. The Q value of the resonance is increased and the scattering strength of the cavity at resonance is enhanced by wall compliance. The asymptotic results are supported and supplemented by numerical calculations for thin steel shells in water.

Elastic Helmholtz resonators

The influence of wall elasticity on the response of a Helmholtz resonator is examined by analyzing the canonical case of a thin elastic spherical shell with a circular aperture subject to plane-wave excitation. By neglecting the thickness of the wall and representing the elasticity via a thin shell theory the problem is reduced to one of solving an integral equation over the aperture for the polarization velocity, which is related to, but distinct from, the radial particle velocity of the fluid. The integral equation can be solved by asymptotic methods for small apertures, yielding closed-form expressions for the major resonator parameters. In general, wall compliance reduces the resonance frequency in comparison with an identically shaped rigid cavity. The Q value of the resonance is increased and the scattering strength of the cavity at resonance is enhanced by wall compliance. The asymptotic results are supported and supplemented by numerical calculations for thin steel shells in water. [Work supported by ONR.]

Direct numerical solution of the Schrödinger equation for quantum scattering problems.

A direct numerical solution of the Schr\odinger equation for quantum scattering problems is presented. The wave function for each partial wave is expanded in coupled spherical harmonics and the corresponding radial functions are expanded in a local basis set using finite-element analysis, with the appropriate scattering boundary conditions. The method is shown to give very accurate results for elastic phase shifts (S,P,D, and F) and resonance positions for electron-hydrogen scattering.

Backscattering method possibilities for precise determination of the oxygen profile in oxide films by the use of the elastic resonance in reaction 16O(4He, 4He)16O at 3.045 MeV of 4He

AbstractElastic resonant backscattering can be used as a highly sensitive probe for the measurement of oxygen concentration for different oxides. This method of near‐surface analysis is absolute, non‐destructive and does not need calibration with the aid of standard samples. Our experimental results concern the investigation of the method possibilities for very precise determination of the concentration profile of oxygen for thin monocrystalline films of high‐temperature superconducting materials. An accuracy of better than 1.5 relative per cent (rel.%) for a 30 nm depth resolution and 0.6 rel.% for total oxygen content determination has been reached, which is an uncommon level of precision for the backscattering method. Our results are important for those application in which oxygen profiling is essential.

New investigation on critical running speeds of a high-speed elastic space mechanism

An analytic and experimental investigation on critical running speeds of high-speed spatial linkages with elastic members is presented. First, the elastic resonance caused by the change of operating speeds of a completely elastic RSS'R spatial mechanism has been studied theoretically. Some important factors that greatly affect the dynamic properties of the elastic mechanism in the state of resonance have been found. Three key characteristic indices for evaluation and determination of the critical running speeds of an elastic mechanism are also given. Second, an experimental study is presented to verify the theory developed in the paper. The strain gauge technique is applied to obtain dynamic responses in the links of an RSS'R mechanism. The experimental results show fairly good agreement with the analytical theory.

Phaseshifts, total elastic cross sections and resonances in Ar-Ar scattering

The authors have performed systematic quantal calculations of Ar-Ar elastic scattering events using accurate pair potentials. Specifically, they have calculated a large number of partial wave phaseshifts, total cross sections and resonance energies over a range covering most of the glory region. The cross sections from two accurate potentials are compared over one glory oscillation and over a region including several shape resonances. The resonance energies obtained from these two potentials also are compared. The authors discuss the inappropriateness of using Levinson's theorem to define the absolute scale of the phaseshifts for realistic atomic potentials. As an alternative, the authors define an 'absolute phaseshift' that explicitly accounts for the difference in phase between the true wavefunction and its free particle counterpart.

The electromagnetic wave resonant reemission by a conductive magnetostrictive plate

The problem of normal electromagnetic wave transmission by a magnetostrictive metallic plate is solved. Two cases of the plate magnetic polarization are considered: perpendicular and parallel to its surface. Expressions for the transmission and reflection coefficients are obtained in analytic form. The analysis has revealed anomalous electromagnetic wave penetration behind the reflecting sheet in the plate elastic resonance range. The resonant amplitude of the plate transmission coefficient does not depend either on magnetoelastic coupling intensity, the growth of which leads to increase of the resonant frequency only, or the magnetic permeability of the sample.

Depth profiling of light-Z elements with elastic resonances: Oxygen profiling with the 3.045 MeV 16O( α, α) 16O resonance

Depth profiling of light elements in high-Z substrates can be done with RBS using elastic resonances. With the resonant signal in the backscattered spectrum several parameters can be associated as such as height, position, yield and FWHM. The dependence of the parameters on incident beam energy will be described. The influence of the energy spread and of the detector resolution, which limits the use and accuracy, is discussed. Computer calculations are given to establish the validity of the model and to illutrate the restrictions. A methodology which uses the different parameters is proposed. Experimental results are shown for the depth profiling of oxygen in 20 nm, 89 nm and 500 nm thick oxides with the elastic 3.045 MeV 16 O( α, α) 16 O resonance.

Measurement of Elastic Moduli by Rectangular Parallelepiped Resonance Method

The elastic resonance spectra of rectangular parallelepiped specimens of a polycrystalline sample and a pseudo-single crystal YBaCuO sample grown by the quench-melt-growth method have been measured. A new procedure which is based on the genetic algorithm has been applied for the determination of elastic moduli starting from the random sets of elastic moduli. The elastic moduli of polycrystalline YBaCuO specimen have been determined as follows: λ=0.46×1011 N/m2 and µ=0.46×1011 N/m2. They are much larger than the previously published data by Ledbetter, Austin, Kim and Lei. The determination of the elastic moduli of the pseudo-single crystal has not yet been completed.

The acoustical background for a submerged elastic shell

The resonance process can be viewed as a superposition of an acoustical background (a rigid scatterer for elastic solids) and the resonance response. [H. Überall, ‘‘Modal and surface-wave resonances in acoustic-wave scattering from elastic objects and in elastic-wave scattering from cavities’’ in Proceedings of the IUTAM Symposium: Modern Problems in Elastic Wave Propagation, Northwestern Univ., Evanston, IL, 12–15 Sept. 1977, edited by J. Miklowitz and J. D. Achenbach (Wiley, New York, 1978), pp. 239–263; L. Flax, L. R. Dragonette, and H. Überall, ‘‘Theory of elastic resonance excitation by sound scattering,’’ J. Acoust. Soc. Am. 63, 723–731 (1978)]. The subtraction of an appropriate acoustical background proved valuable for isolating the lower-frequency resonances as well as understanding the nature of resonances excited by acoustical signals impinging on elastic solids. In particular, the rigid background could be subtracted mode by mode in partial wave space to isolate the resonances. An analogous background for elastic shells has been elusive to find over the years, although for very thin shells a soft background has proven adequate for the lower-frequency region; for thicker shells and at appropriately higher frequencies, a rigid background has in some cases proven useful. In this work a new model is proposed that describes the background of an elastic shell for a suitable thickness region over the entire frequency range. Further, in the limit of thin shells at the lower frequency end, it is shown to equal a soft background, while for thicker shells and at higher frequencies it goes into a rigid background. The appropriate mass dependence for the new background is also observed. The usefulness of the new background is demonstrated for several examples, where it is shown that by subtracting the new background, resonances can be better isolated than for the elastic soft/rigid analogs.

Prompt observation of elastic resonance spectra via the use of short ultrasonic pulses : IEEE 1985 Ultrasonics Symposium, San Francisco, California (United States), 16–18 Oct. 1985, pp. 1056–1059. Edited by B.R. McAvoy. IEEE, Piscataway, New Jersey (1985)

Prompt observation of elastic resonance spectra via the use of short ultrasonic pulses : IEEE 1985 Ultrasonics Symposium, San Francisco, California (United States), 16–18 Oct. 1985, pp. 1056–1059. Edited by B.R. McAvoy. IEEE, Piscataway, New Jersey (1985)

Magnetoelastic instabilities in the ferrimagnetic resonance of magnetic garnet films.

The nonlinear magnetoelastic interaction in [111]-oriented films of yttrium iron garnet is investigated theoretically and experimentally. A system of nonlinear equations of motion, including boundary conditions, is introduced. An appropriate numerical method to solve such a boundary-value problem is developed. It is shown that the ferrimagnetic resonance (FMR) couples to elastic resonances. This nonlinear coupling leads to instability oscillations of the FMR or even to chaos, if the excitation level exceeds a critical threshold. The numerical calculations agree very well with experimental results. The influences of the material parameters on the nonlinear dynamics of the FMR have been investigated.

Epitaxy of barium titanate thin films grown on MgO by pulsed-laser ablation

Thin films of barium titanate (BaTiO3) have been deposited by pulsed-laser ablation onto (001)-oriented MgO substrates. The films were epitactic with the c-axis perpendicular to the film-substrate interface, as evidenced by both transmission electron microscopy (TEM) and ion-channeling techniques. The elastic resonance of 3.045 MeV α-particles, generating the 16O(α, α)16O reaction was used to determine the oxygen stoichiometry of the film and the minimum yield based on the oxygen peaks, thereby enabling conclusions to be drawn about the crystalline perfection of the oxygen sublattice.

Force constant and effective mass of 90° domain walls in ferroelectric ceramics

Domain wall contributions to the dielectric, piezoelectric, and elastic properties of tetragonal ferroelectric ceramics, as discussed extensively in the past, are calculated. A simple model shows that the motion of 90° domain walls causes a shear deformation and an approximately homogeneous electric field in the grain. The elastic and electric field energies involved allow the calculation of the force constant for the domain wall displacement by external fields. The displacements agree with experimental results. In a moderate electric field the displacement is a small fraction of the lattice cell only. By averaging over the orientational distributions of all grains the contributions of the 90° domain walls to the material properties are calculated for unpolarized and for polarized ceramics and agree with experimental results. The effective mass, which has to be attributed to the domain walls is the mass of the whole grain reduced by the factor S0 (spontaneous deformation), is independent of the domain width. The resonance frequency of the domain walls therefore is lower than the elastic resonance frequency of the grain.