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We demonstrate a magneto-optic technique to measure Brownian relaxation of magnetic nanoparticles suspended in liquids. We used AC susceptibility data as a function of frequency of the applied AC magnetic field to verify that the results agree with those obtained via a conventional inductive detection technique. However, compared with a commercial AC susceptometer using the conventional detection scheme, our magneto-optic setup is able to detect a density of nanoparticles at least three orders smaller. This technique has the potential of being used as a sensor for magnetic nanoparticles such as in local temperature, viscoelasticity, or molecular-binding measurements.

The recent development of bio-conjugated magnetic nanoparticles offers many opportunities for applications in the field of biomedicine. In particular, the use of magnetic nanoparticles for biosensing has generated widespread research efforts following the progress of various magnetic field sensors. Here we demonstrate substrate-free biosensing approaches based on the Brownian rotation of ferromagnetic nanoparticles suspended in liquids. The signal transduction is through the measurement of the magnetic ac susceptibility as a function of frequency, whose peak position changes due to the modification of the hydrodynamic radius of bio-conjugated magnetic nanoparticles upon binding to target bio-molecules. The advantage of this approach includes its relative simplicity and integrity compared to methods that use substrate-based stray-field detectors.

Aluminate glasses containing 45–71.5 mol% alumina, 10–40 mol% rare earth oxide, and 0–30 mol% silica were synthesized from precursor oxides. The glass transition and crystallization temperatures were determined by differential scanning calorimetry; the structural and mechanical properties were investigated by Raman and Brillouin spectroscopy. The range of the supercooled liquid region varies from ∼40 °C to 200 °C, providing a useful working range for compositions with 5–30 mol% silica. Raman scattering showed the presence of isolated SiO 4 species that strengthen the network-forming structure, enhance glass formation, and stabilize the glass even when they are present at fairly low concentrations. Sound velocities were measured by Brillouin scattering. From these and other values, various elastic moduli were calculated. The moduli increased with both aluminum and rare earth content, as did the hardness of the glasses. Young’s modulus was in the range 118–169 GPa, 60–130% larger than that for pure silica glass.

Inorganic glasses normally exhibit a network of interconnected, covalent-bonded, structural elements that has no long-range order. In silicate glasses, the network formers are based on SiO 4 tetrahedra interconnected through oxygen atoms at the corners. Conventional wisdom implies that alkaline and alkaline-earth orthosilicate materials cannot be vitrified, because they do not contain sufficient network-forming SiO 2 to establish the needed interconnectivity. We studied a bulk magnesium orthosilicate glass obtained by containerless melting and cooling. We found that the role of network former was largely taken on by corner and edge sharing of highly distorted, ionic Mg-O species that adopt 4-, 5-, and 6-coordination with oxygen. The results suggest that similar glassy phases may be found in the containerless environment of interstellar space.

The local structure of iron and uranium ions in a series of iron phosphate glasses with the general composition (40 – x)Fe2O3–xUO2–60P2O5 and (1–x–y)(40Fe2O3–60P2O5)– xUO2–y(Na2O or CaO) was investigated using Fe K-edge and U LIII-edge x-ray absorption fine structure spectroscopy. Replacing Fe2O3 by UO2 in the glass caused more distortion in the coordination environment of Fe(III) ions. Extended x-ray absorption fine structure fits revealed that the Fe–P bonds observed in the base glass also existed in all the waste-loaded glasses. X-ray absorption near-edge structure showed that the uranium ions were predominantly present as U(IV) in the glasses. Uranium ions were coordinated to approximately 8 ± 1 oxygen atoms and 2.5 ± 0.6 phosphorus atoms at an average distance of 2.47 ± 0.02 and 3.8 ± 0.02 Å, respectively. There were no Fe–U or U–Fe neighbors observed, indicating that uranium ions occupied voids in the glass away from the PO4 units. These conclusions were supported by Mössbauer, x-ray photoelectron, and Raman spectroscopic data.

The structure of vitreous iron phosphates containing up to 35 wt% of one or more common nuclear waste components such as Na2O, Cs2O, SrO, UO2 or Bi2O3 have been investigated using Fe-57 Mossbauer, X-ray absorption, X-ray photoelectron and Raman spectroscopies and high energy X-ray and neutron diffraction techniques. The glass samples investigated were prepared by melting appropriate chemicals in air at approximately 1200°C for 2 h in alumina crucibles. The chemical durability of the glasses was investigated by measuring their dissolution rates in distilled water at 90°C using the product consistency test (PCT) methodology. The chemical durability of these glasses is characterized by dissolution rates of 10−10–10−11 g/cm2/min. The Mossbauer spectra indicate the presence of both Fe(II) and Fe(III). However, the maximum Fe(II) fraction, Fe(II)/[Fe(II) + Fe(III)], was 0.34. X-ray absorption data show that, on average, both species of iron ions are coordinated with approximately 5 near neighbor oxygens and that the iron–oxygen coordination is only slightly (

The Brillouin spectroscopic measurements of elastic properties of polypropylene films fabricated by different processing techniques are described. We find that the elastic symmetry and the associated elastic constants are dependent on the molecular orientation brought about by the processing conditions used to produce the films. We have shown that Brillouin scattering techniques can successfully be used to track the molecular orientation induced by uniaxial stretching. We find a direct correspondence between the Brillouin measurements and optical birefringence measurements, illustrating that molecular orientation plays a dominant role in determining the mechanical anisotropy in these materials.

We report IR and Raman spectra obtained on a highly ion-conducting glass-forming system, x(AgI)2·(1 − x)Ag2SeO4 with x = 0.35, 0.40, 0.46, 0.48, 0.50, 0.54. For 0.48(AgI)2·0.52Ag2SeO4, spectra were...

Epitaxial Mo/NbN and W/NbN superlattices with modulation wavelengths Λ ranging from 1.3 to 120 nm were grown on MgO (001) substrates by dc reactive magnetron sputtering in Ar/N2 mixtures. The superlattices were shown to be epitaxial with nearly planar layers using high- and low-angle x-ray diffraction and transmission electron microscopy. Computer simulation fits of the x-ray data indicated that interface widths were ⩽0.3 nm. The epitaxial relationship between the layers was (001)metal∥(001)NbN and [110]metal∥[100]NbN. The nanoindenter microhardness values from W/NbN and Mo/NbN superlattices with 50 vol % metal were nearly identical. The largest hardnesses were 30 GPa, observed at superlattice periods Λ=2–3 nm, compared to rule-of-mixtures values of 10 GPa. The hardness decreased with increasing Λ above ≈3 nm, following the dependences H=10.3+26.70Λ−0.38 GPa for Mo/NbN and H=12.88+22.1Λ−0.3 GPa for W/NbN. Hardness versus metal volume fraction with Λ≈5 nm showed a flat-topped dependence. Brillouin scatteri...

Brillouin scattering results from the interaction of photons with thermal excitations in a medium. The energy and propagation direction of the photons are modified by the interaction giving rise to a measurable frequency shift. Because the excitations are not related to the order existing in the medium, they can be observed in gases, fluids, or solids, ordered (crystals) as well as disordered (amorphous or glasses). In crystals, the measured frequency shift depends on the propagation direction of the excitations (phonons). Hence, Brillouin scattering is well adapted to study phase transitions, driven either by pressure, temperature, or a combination of them. The use of the technique is illustrated by two examples: berlinites under pressure, and a high temperature study of silicate melts.

Nanoclusters of Se, Rb-Se, and Cs-Se were incorporated in the supercages of Y zeolite. Anomalous x-ray scattering established that the Se clusters take the form of weakly interacting chains with a disordered structure similar to that of amorphous Se, while the Rb-Se and Cs-Se clusters contain Se{sup 2{minus}}{sub 2} Zintl ions as in crystalline and liquid bulk phases. The Raman spectra of the nanoclusters exhibit features found in the bulk disordered phases. {copyright} {ital 1997} {ital The American Physical Society}

We report the first observation of the electronic Raman effect in semiconducting p-type, isotopically controlled diamonds. The Raman transition between the spin-orbit split 1s ground states of boron acceptors occurs at ${\ensuremath{\Delta}}^{\ensuremath{'}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.07\left(1\right)$ and 2.01(1) meV in natural and ${}^{13}\mathrm{C}$ diamonds, respectively. Polarization features show the transition to be predominantly ${\ensuremath{\gamma}}_{5}$ in character, placing an upper limit on the ratio of the nonspherical Luttinger parameters of the valence band. Host-isotope-related self-energy shifts are observed in both the electronic infrared and Raman spectra.

The Raman spectrum of icosahedral \ensuremath{\alpha}-boron presents a very sharp peak at $525{\mathrm{cm}}^{\ensuremath{-}1}$ that was consistently rejected from the lattice modes but is still unexplained. New Raman scattering experiments under pressure are compared with ab initio lattice dynamics calculations. The very good agreement of the mode frequencies and their pressure coefficients yields unambiguous assignment of all observed features, including the $525{\mathrm{cm}}^{\ensuremath{-}1}$ line which is a highly harmonic librational mode of the icosahedron and mainly involves bond bending. This mode is also identified in the Raman spectrum of other icosahedral boron-rich solids.

After excitation of selenium encapsulated in Y-zeolite with 476 nm radiation, decomposition of the initially present semiconductor chains is observed. The fragmentation is influenced by the nature ...

Equilibrium structures of Li 2 CO 3 and K 2 CO 3 were calculated using ab initio molecular orbital calculations carried out at the Hartree-Fock (HF) level. Of the four structures considered for Li 2 CO 3 and K 2 CO 3 , the most stable was a structure with all five atoms in a plane. The harmonic frequencies were also calculated and found to be in agreement with the present Raman measurements. Structure factors, calculated from the ab initio data for each of the four structures considered, are compared with existing X-ray results.

This Raman spectroscopic study on selenium incorporated in Nd−Y zeolite presents new aspects of the photochemistry of selenium. The formation of the Se2- radical anion has been established from its resonance Raman spectrum, consisting of ten almost equidistant bands between 328 and 3220 cm-1 on the low-energy side of the 476.24-nm laser excitation line. The derived spectroscopic constants of the electronic ground state are ω0 = 328 cm-1 and x0ω0 = 0.71 cm-1. Another broad band at 260 cm-1 resembles features in the Raman spectra of amorphous selenium and selenium chain structures encapsulated in zeolites. Continuous irradiation at sufficiently high laser power levels leads to depletion of the 260 cm-1 band and a simultaneous enhancement of the Se2- bands. These observations are discussed with respect to the defect states conventionally invoked for reversible photoinduced changes in amorphous selenium.

A Raman scattering study of the vibrational modes in K2Al2B2O7 crystals has been performed at room temperature. The vibrational modes are classified by the nuclear site group analysis method and the internal vibrational modes are assigned to vibrations of the BO3 triangle and AlO4 tetrahedron.

Changes in the elastic properties of Ge induced by room-temperature irradiation with 3.5-MeV Kr ions have been determined and correlated with changes in the microstructure determined by transmission electron microscopy. Elastic-shear-moduli changes were measured by Brillouin scattering, and changes in local atomic arrangement were determined by Raman scattering. Amorphization decreased the elastic shear modulus of Ge by 17%. The fractional decrease was correlated with the amorphous volume fraction with a cross section of 4.5\ifmmode\pm\else\textpm\fi{}0.5 ${\mathrm{nm}}^{2}$/ion. No change was observed in the shear modulus during void formation and growth. The elastic properties of the voided material are described by the Voigt averaging. However, as the voids evolved into a fibrous spongelike microstructure, a second dramatic elastic softening occurs which we attribute to the inability of the fibrous structure to support shear stresses. Raman scattering showed that, once formed, there was no change in the structure of the amorphous material at the atomic scale during void formation and subsequent void coalescence.

Brillouin scattering from single crystals of NiO show that, apart from the expected phonon peaks, there is a broad central peak. The phonon peaks have Fano-like lineshapes, indicating a strong coupling between them and the broad feature, and lead to elastic constants that differ considerably from ultrasonic values. The broad feature is probably ‘magnetic’ in origin since it disappears at the Neel temperature. We speculate that it may be the lower of the two AFMR modes predicted for easy-plane antiferromagnets but which has previously been observed only in EuTe and MnO. The interaction between the phonons and the ‘magnetic’ excitation provides a phenomenological explanation for the differences in the elastic constants determined by different techniques.

The double-well potential model, well known to describe many low-temperature properties of amorphous materials, has been extended to incorporate effects of high pressures. The resulting model not only explains the temperature and time dependences of pressure-induced phenomena but also provides possible explanations for thermal annealing effects as well as irradiation compaction. The results of Brillouin-light-scattering experiments designed to test various predictions of the model are presented: good agreement is obtained.

Elastic moduli of $^{13}\mathrm{C}$ diamond, deduced from the Brillouin shifts experienced by inelastically scattered monochromatic radiation, are \ensuremath{\sim}0.5% higher than the corresponding values for natural diamond. This suggests $^{13}\mathrm{C}$ diamond is harder than natural diamond. A simple model incorporating the zero-point motion and the anharmonicity of the interatomic forces is proposed; it explains quantitatively the increase in the elastic moduli, the decrease in the lattice parameter, and a correction to the Raman frequency beyond its ${\mathit{M}}^{\mathrm{\ensuremath{-}}1/2}$ dependence (where M is the average atomic mass) observed for $^{13}\mathrm{C}$ diamond with respect to their values for natural diamond.

The individual lattice spacings in Nb/Cu superlattices are determined from a crystallographic study using transmission and reflection x-ray diffraction. The Cu layers show a small in-plane expansion which increases to 0.6\ifmmode\pm\else\textpm\fi{}0.1% as the modulation wavelength is reduced to 22 \AA{}. Arguments based solely on Poisson's effect predict that the strains perpendicular to the layers must be smaller and of opposite sign; contrary to this expectation a large perpendicular expansion (4.2\ifmmode\pm\else\textpm\fi{}0.7%) is measured. This finding brings into question the validity of models that rely only on interfacial forces to derive the perpendicular strains by using the bulk Poisson's ratio.

A complete description of the first-order Raman and Brillouin spectra of single-crystal aluminum nitride is provided. The frequency has been measured and the symmetry identified of each of the Raman-active zone-center optic modes, and the five independent elastic constants have been measured. The widths of the principal Raman modes increase with increasing oxygen content up to a critical value of approximately 1 at. %, after which they are constant. This behavior supports the hypothesis of a change in the nature of the oxygen defect at that concentration.

A complete description of the first-order Raman and Brillouin spectra of single-crystal aluminum nitride is provided. The frequency has been measured and the symmetry identified of each of the Raman-active zone-center optic modes, and the five independent elastic constants have been measured. The widths of the principal Raman modes increase with increasing oxygen content up to a critical value of approximately 1 at. %, after which they are constant. This behavior supports the hypothesis of a change in the nature of the oxygen defect at that concentration.

After excitation of selenium encapsulated in Y-zeolite with 476 nm radiation, decomposition of the initially present semiconductor chains is observed. The fragmentation is influenced by the nature ...

We report IR and Raman spectra obtained on a highly ion-conducting glass-forming system, x(AgI)2·(1 − x)Ag2SeO4 with x = 0.35, 0.40, 0.46, 0.48, 0.50, 0.54. For 0.48(AgI)2·0.52Ag2SeO4, spectra were...

A series of Cu/Pd superlattices with composition modulation wavelengths (Λ's) ranging from 1.6 to 3.5 nm and a strong [111] growth texture were prepared by electron beam evaporation. The elastic properties of the films were examined using the methods of uniaxial tension tests [a Young's modulus (1/s11), where sij is an elastic compliance] with the applied load parallel to the plane of the Cu/Pd interface and Brillouin scattering [a shear modulus (1/s44) with the shear waves parallel to the plane of the Cu/Pd interface]. Also, the films were characterized using both x-ray diffraction and high-resolution electron microscopy; this was done to assess the effect of the nanostructure on a possible “supermodulus effect.” The films are nanostructurally very similar to the superlattice films employed in previous studies at Northwestern in which a supermodulus effect was reported. But, contrary to previous studies, no anomalous behavior was observed for the measured elastic properties of the thin films. Therefore the present results negate the earlier results and cast a serious doubt on the existence of a supermodulus effect.

Brillouin scattering measurements have been carried out on single‐crystal lattice‐matched TiN/(V0.6Nb0.4)N and mismatched TiN/NbN superlattices. Measured surface wave velocities were found to be independent of superlattice wavelength over the entire range investigated, 1.5–30 nm, and were averages of the measured velocities of pure homogeneous TiN, NbN, and (V0.6Nb0.4)N. These results indicate that there is no anomaly in the C44 elastic constant. X‐ray diffraction results from the superlattices indicated that the average lattice spacing did not vary with wavelength. This is consistent with previous observations where elastic anomalies were related to changes in lattice spacing. The absence of a correlation between the C44 elastic constant and previously reported hardness enhancements indicates that the latter are not caused by anomalies in C44; they could, however, be correlated with other elastic moduli.

The structure of pressure-densified vitreous ${\mathrm{SiO}}_{2}$ has been investigated using neutron-diffraction and molecular-dynamics techniques. After compression to 16 GPa at room temperature, recovered samples have densities 20% higher than normal vitreous ${\mathrm{SiO}}_{2}$ and show substantial changes in the first sharp diffraction peak (FSDP): an indication of modification in the intermediate-range order. The changes in the FSDP are due to increased frustration caused by the decrease in the Si-O-Si bond angle and a shift in the Si-Si and O-O correlations in the range of 4--8 \AA{} toward lower distances.

The pressure dependence of the elastic constants C{sub ij} of GaP have been measured up to 15 GPa in a diamond anvil cell. Brillouin backscattering experiments along the principal crystallographic directions yielded four combinations of elastic constants from which the three independent C{sub ij} were extracted. Above 15 GPa the closure of the energy band gap prevents the detection of the signal. {copyright} {ital 1999} {ital The American Physical Society}

The shear elastic modulus and structural properties of a series of Ag Co superlattice films have been characterized using Brillouin scattering and X-ray diffraction. A softening of the shear modulus of the unirradiated Ag Co superlattices with decreasing modulation wavelength is observed and is correlated with an expansion in the average lattice spacing. With increasing irradiation fluence, a reduction in the anomalous shear modulus softening and lattice expansion are observed. These reductions imply that the anomalous elastic properties are related to lattice strains present, which are relieved by the irradiation.

The modulation wavelength dependence of the surface‐wave velocity in Cu/Ni superlattices has been investigated using Brillouin scattering. It is the first compositionally modulated system to be studied by this technique and the first for which elastic properties have been determined by both ‘‘macroscopic’’ methods and Brillouin scattering. Contrary to the enhancements previously reported in the biaxial modulus and in the Young’s modulus, the modulus associated with the surface‐wave velocity shows no evidence of anomalous behavior.

Etude des surfaces ondulees d'Ag. L'ondulation joue un role important dans les lois de selections du vecteur d'onde gouvernant le couplage aux phonons de surface. Cet effet est substantiellement different quand le vecteur d'onde effectif est colineaire ou perpendiculaire au plan de diffusion. Le mecanisme de couplage est gouverne par les plasmons de surface qui introduisent une nouvelle interaction de diffusion avec une polarisation inhabituelle

Confinement alters the energy landscape of nanoscale magnets, leading to the appearance of unusual magnetic states, such as vortices, for example. Many basic questions concerning dynamical and interaction effects remain unanswered, and nanomagnets are convenient model systems for studying these fundamental physical phenomena. A single vortex in restricted geometry, also known as a non-localized soliton, possesses a characteristic translational excitation mode that corresponds to spiral-like motion of the vortex core around its equilibrium position. Here, we investigate, by a microwave reflection technique, the dynamics of magnetic soliton pairs confined in lithographically defined, ferromagnetic Permalloy ellipses. Through a comparison with micromagnetic simulations, the observed strong resonances in the subgigahertz frequency range can be assigned to the translational modes of vortex pairs with parallel or antiparallel core polarizations. Vortex polarizations play a negligible role in the static interaction between two vortices, but their effect dominates the dynamics., supplemental movies on http://www.nature.com/nphys/journal/v1/n3/suppinfo/nphys173_S1.html

This paper describes a technique to compute magnetic normal modes of nanosized particles. The technique is based on the Landau-Lifshitz formalism of micromagnetics and accounts fully for both the exchange and the dipolar field. It requires no more than the specification of the material parameters and the geometry of the sample; in particular, it does not require the specification of boundary conditions. It also allows the large-amplitude nonlinear regime to be probed. The technique is applied to a model of a polycrystalline iron particle, which is shown to possess a rich variety of normal modes. Some of these modes are reminiscent of standing waves, while others are more or less localized in parts of the sample. The variation of the mode frequencies with the applied field is analyzed and compared with existing approximations.

We have used Brillouin scattering to measure the temperature dependence of the sound velocities of the longitudinal and transverse vibrational modes in various directions in small single crystals of monoclinic ZrO2. Using these velocities and the Christoffel equation, we have calculated the 13 elastic stiffness moduli between room temperature and the monoclinic—tetragonal transformation temperature.

The Raman spectrum of icosahedral α-boron presents a very sharp peak at 525cm−1 that was consistently rejected from the lattice modes but is still unexplained. New Raman scattering experiments under pressure are compared with ab-initio lattice dynamics calculations. The very good agreement of the mode frequencies and their pressure coefficients yields unambiguous assignment of all observed features, including the 525 cm−1 line which is a highly harmonic librational mode of the icosahedron. This mode is also identified in the Raman spectrum of other icosahedral boron-rich solids.

We present detailed structural characterization and shear elastic constant measurements of sputtered W/Ni multilayers. Structural refinement of the reflection x-ray-diffraction spectra was used to determine the out-of-phase lattice spacings of the constituent layers. The Ni(111) lattice spacing expands \ensuremath{\approxeq}3% and the W(110) lattice spacing is constant with decreasing modulation wavelength \ensuremath{\Lambda} down to \ensuremath{\Lambda}\ensuremath{\approxeq}30 \AA{}. Transmission x-ray diffraction was used to determine the in-plane structure. The W layers undergo an anisotropic contraction in plane with the [002] directions contracting \ensuremath{\approxeq}2% and the [11\ifmmode\bar\else\textasciimacron\fi{}0] remaining constant with decreasing \ensuremath{\Lambda}. The Ni [22\ifmmode\bar\else\textasciimacron\fi{}0] expands \ensuremath{\approxeq}1.5% with decreasing \ensuremath{\Lambda}. The Ni layer expands both in plane and out of plane, contradicting Poisson ratio arguments relating in-plane and out-of-plane strains. Below \ensuremath{\Lambda}=35 \AA{} the multilayers undergo a structural transition in which both layers transform into a random close-packed structure. The shear velocity decreases \ensuremath{\approxeq}22% with decreasing \ensuremath{\Lambda} down to the disorder transition and then is \ensuremath{\Lambda} independent. The results imply that there is a correlation between the origin of the elastic anomalies and amorphization.

We report photoinduced antiferromagnetic (AF) interlayer coupling in sputtered Fe/(Fe-Si) superlattices. The superlattices are intrinsically AF coupled at room temperature and become increasingly ferromagnetically coupled when cooled below 100 K, but the AF coupling is restored at low temperature by exposure to visible light of sufficient intensity ([gt]10 mW/mm[sup 2]). These effects are due to charge carriers in the Fe-Si spacer layer which, when thermally or optically generated, are capable of communicating spin information between the Fe layers.

We discuss here the complete determination of the elastic properties of a polyimide film using two experimental techniques. One technique employs the polymer film as a vibrating membrane and allows a direct determination of the ’macroscopic’ biaxial modulus. Brillouin scattering, which measures the elastic properties on a ∼ 100 μ scale, allows for a complete characterization of the elastic behavior. The results obtained by the two techniques are in agreement within the reported error bars.

The experimental fact that measured elastic and structural properties of superlattices are strongly correlated can be understood on the basis of a simple model based on the packing of hard spheres. The model is consistent with features of many models that have been proposed to explain the supermodulus effect, but contrary to previous explanations, it allows predictions for a given pair of constituents to be made. For an arbitrary pair of elements, it predicts the existence or non-existence of an elastic anomaly, and a rough estimate of its magnitude.

A study of the mechanical properties of Cu/Nb superlattices shows that for modulation wavelengths below \ensuremath{\sim}50 \AA{} the biaxial modulus increases by \ensuremath{\sim}15%, the shear modulus decreases by \ensuremath{\sim}30%, and the flexural modulus does not change. These observations show that anomalies with different signs for elastic moduli can coexist in the same material. Measurements performed on both supported and unsupported films show that the anomalous effects are not induced by the presence of a substrate. The superlattices are also found to have a hardness larger than either Cu or Nb.

The elastic and structural properties of Cu/Pd and Cu/Ni superlattices have been determined. Microstructurally the films have the same growth mechanisms, growth textures, and composition modulation amplitudes, as in past studies where the ``supermodulus effect'' was reported. Advanced techniques have been used to measure the flexural, shear, and Young's moduli of the thin films, and no significant anomalous elastic behavior has been observed.

The presence of a {ital nonrandom} fractional number of atomic planes in each layer of a superlattice produces unusual diffraction patterns in which the peaks cannot be indexed in the usual fashion as due to a single series. The x-ray line broadenings are distinctly different from earlier measurements and calculations in which the interfacial roughness is due to random variations of the scattering function. Therefore, interfacial roughness encountered at a single interface may just be a consequence of controlled, but not random, roughness and that under proper growth conditions superlattices with atomically sharp interfaces may be produced. These results are in good agreement with experimental measurements.

The dynamics of individual magnetic vortices and vortex pairs confined in lithographically defined ferromagnetic ellipses were measured using a microwave reflection technique. Resonance frequencies were detected in the subgigahertz range for Ni80Fe20 (Permalloy) ellipses ranging in size from 3 by 1.5μm to 1 by 0.5μm, 40nm in thickness. Micromagnetic simulations indicate that the single mode observed for one vortex is a translational mode and that the two eigenmodes associated with a vortex pair correspond to coupled translational modes of vortices with parallel or antiparallel core polarizations. The single-vortex resonance scales inversely with the ellipse size, in agreement with the simulations and analytical theory.

A Raman-scattering study of the vibrational modes in a BiB3O6 crystal was conducted at room temperature. The numbers of external and internal modes obtained in experiment are consistent with the results of a group theoretical analysis. The Raman lines below ∼300cm−1 and from ∼300to1600cm−1 are assigned to the external modes of the lattice and internal vibrations of the BO3 and BO4 subunits of the BiB3O6 structure, respectively.

Using Brillouin scattering we have succeeded in observing the normal modes of vibration of unsupported films in a region where the dispersion relationship is quadratic. Extremely low-lying excitations were observed in thin films with thicknesses as small as 200 A\r{}. Contrary to what has been found in work on supported films, we are able to extract information on a number of the elastic moduli because the measured velocities in very thin films do not depend on the properties of the substrate. This technique should be a valuable addition to the tools which can be used in the study of materials in thin-film form.

Using Brillouin scattering, we have measured the sound velocity in fluid and solid helium 4 at room temperature up to 20 GPa. Our results show that the pair potentials currently used to describe helium are inadequate. The density of the fluid is determined as a function of pressure up to the fusion point. In the solid, the sound velocity and the elastic anisotropy are compared with lattice dynamics calculations.

Brillouin-scattering measurements show an anomalous dip in the elastic constants of Nb/Cu superlattices for superlattice wavelengths of \ensuremath{\lesssim} 100 \AA{}. This dip is correlated with changes in the electrical resistivity of the samples giving the first evidence that electronic effects are responsible for phonon softening in these materials.