Search

Nano- and micro-electromechanical systems (N/MEMSs) are traditionally based on electrostatic or piezoelectric coupling, which couples electrical and mechanical energy through acoustic resonator structures. Most recently, N/MEMS devices based on magnetoelectrics are gaining much attention. Unlike electrostatic or piezoelectric N/MEMS that rely on an AC electric field or voltage excitation, magnetoelecric N/MEMS rely on the electromechanical resonance of a magnetostrictive/piezoelectric bilayer heterostructure exhibiting a strong strain-mediated magnetoelectric coupling under the excitation of a magnetic field and/or electric field. As a consequence, magnetoelectric N/MEMS enable unprecedented new applications, ranging from magnetoelectric sensors, ultra-compact magnetoelectric antennas, etc. This Tutorial will first outline the fundamental principles of piezoelectric materials, resonator design, specifically different acoustic modes, and piezoelectric-based N/MEMS applications, i.e., radio frequency front end filters and infrared radiation sensors. We will then provide an overview of magnetoelectric materials and N/MEMS focusing on the governing physics of the magnetoelectric effect, magnetic material properties for achieving high magnetoelectric coupling, state-of-the-art magnetoelectric N/MEMS devices, and their respective applications.

A detailed explanation of “azimuth dependent reflection anisotropy spectroscopy” (ADRAS) [B. F. Macdonald and R. J. Cole, Appl. Phys. Lett. 80, 3527 (2002)] is presented. Experimental data and simulations are used to illustrate the greater information content of ADRAS compared to the standard reflection anisotropy technique. The application of ADRAS to the study of chiral surface modifiers, relevant to biomolecular adsorption and enantioselective catalysis, is discussed.

The design and construction of a dielectric cell, used in time‐domain reflectance measurements at low temperature and high frequencies, are presented. Criteria are developed for cell construction, based on a transmission line model of bilinear form, and are applied to the physical construction of the cell. Bilinear parameters are derived for the cell model and compared with parameters calculated from short circuit measurements of two cells differing in design.

Minority carrier diffusion lengths (Ld) are measured for GaN, GaN/AlGaN, and GaN/InGaN core-shell nanowires using a technique based on imaging of recombination luminescence. The effect of shell material on transport properties is measured. An AlGaN shell produces Ld values in excess of 1 μm and a relative insensitivity to wire diameter. An InGaN shell reduces effective diffusion length, while a dependence of Ld on diameter is observed for uncoated nanowires.

We recently commissioned the SRC/Vanderbilt University 6‐m toroidal grating monochromator beamline. The problems with mirror heating, signal normalization, monochromator control, and scattered light reduction have led to several innovations on this line, making for a better user interface and adding to the stability and reliability of the final image. We discuss these innovations, and how they affect the user. They include a built‐in laser alignment system, a sapphire windowed gate valve, entrance mirror temperature stabilization, computer automation and control, a beam‐chopper, and the capability of real‐time monitoring of the photon flux during the experiment. We have used noble gas resonance lines to carefully characterize the wavelength resolution of the beamline as a function of energy over a range of beamline parameters. The results demonstrate that by limiting the horizontal width of the image at the slits, and by masking outer portions of the gratings, the flux/bandwidth ratio can be improved at t...

Mixed dielectric (Be12) and pressure (Bp12) second virial coefficients of CF3H–Ar and CFH3–Ar mixtures of 50 °C have been obtained by cyclic expansion and low pressure dielectric measurements. These give Be12=85 cm6/mole2 for CF3H–Ar and 2 cm6/mole2 for CFH3–Ar, the former being much larger and the latter much less than calculated for spherical polar molecule interactions and Lennard–Jones 12–6 central force parameters derived from Bp12 and interaction viscosity η12. The differences can be accounted for by values of the Buckingham and Pople shape factor of D=−0.18 for CF3H and +0.32 for CFH3; these values are in reasonable agreement with results of Copeland and Cole for the pure polar gases and with estimates from molecular models by Barnes and Sutton.

The stationary monoenergetic transport equation (the Lorentz model) is considered in a semiinfinite geometry with partially reflecting boundary conditions at x=0. The extrapolation length, the density, and the space‐dependent diffusion coefficient are studied as functions of the accommodation coefficient α, both for constant and renormalized current. The hydrodynamical description at the level of the evolution equation is practically unaffected by α and is still valid at distances of several mean free paths (mfp) from the boundary. Yet, when consistently applying the boundary condition, the boundary layer has to be considered in terms of the Milne extrapolation length, which varies like (1−α)−1. The case α=1 is a singular limit in the sense that the boundary layer solution disappears completely.

The dielectric and pressure second virial coefficients of CF3H and CFH3 as measured by Sutter and Cole are reproduced to 5% by a model of pair interactions taking account of central forces, electrostatic interactions, and shape effects. Lennard‐Jones 12–6 parameters from viscosity data of Casparian and Cole are used. To secure agreement, effects of molecular quadrupole moments of 4.5 and 2.3×10−26 esu and Buckingham and Pople shape factors −0.10 and +0.25 for CF3H and CFH3 are included. The latter are of proper sign and agree reasonably well with estimates from molecular models by Barnes and Sutton.

This report discusses the design and use of piezoelectric gauges for the measurement of rapidly varying hydrostatic pressures of large amplitude in gaseous and liquid media. Reasons are given for the selection of tourmaline in preference to other types of crystal. Fundamental principles of design are stated, and gauge construction is described in the light of these principles. A simplified theoretical analysis of transient response characteristics is presented.

Dielectric constants in the density range 0 to 4 moles/liter have been measured at temperatures between 25° and 75°C. Both gases show significant increases of the Clausius‐Mossotti function with density attributable to pair interactions. In CO2, these are consistent with the theory of quadrupole‐induced dipoles for a molecular quadrupole moment of about 5×10—26 esu cm2. In ethylene, the increased effect at higher temperatures is contrary to the theory, which is given in a more general form suitable at high temperatures for molecules such as ethylene, which lack axial symmetry. It is shown that for both gases the theory may be somewhat inaccurate at ordinary temperatures because effects of quadrupole coupling energies have not been adequately treated. Measurements of mixtures with a second gas of highly symmetrical molecules are proposed as a promising means of studying the questions raised by those results.

Dielectric constants for the polar gases CFH3, CF3H, CClF3, and CCl3H in the range 50–143°C, and for CCl3F at 96.3°C, have been measured as a function of pressure and density in the pair interaction range of densities. Accurate values of dipole moment and polarizability of the first four molecules have been derived from the limiting temperature dependence at zero density, and dielectric and pressure second virial coefficients from the variation with density. The pressure coefficients are in good agreement with other compressibility data. The dielectric coefficients are very large and positive for CF3H, very large and negative for CFH3 and CClH3, and positive with approximately the values predicted for spherical polarizable dipoles in the case of CClF3 and CCl3F. The deviations from simple theory indicate major effects of molecular shape, but they are not satisfactorily explained by Buckingham and Pople's anisotropic short‐range pair‐potential model.

The dielectric properties of ice have been measured from 0° to − 80°C using samples prepared from redistilled water which were further purified by zone refining. The resulting conductivities were low enough that dielectric and electrode space‐charge effects could be resolved in three terminal ac measurements to frequencies extended to 0.1 Hz. The relaxation times of the Debye behavior obey an Arrhenius rate equation only above − 50°C, smaller values being found at lower temperatures, the temperature dependence of static dielectric constant gives a Curie temperature of 38°K, and the dc conductance is 4 × 10−11 mho cm−1 at − 10°C for the best sample with an apparent activation energy which is much larger than for less pure ice but somewhat uncertain. The significance of these data for estimates of defect concentrations and other parameters is discussed.

Dielectric constants and loss have been measured to pressures of 1000 kg/cm2 at audio‐ and radio‐frequencies from 212 to 240°K for glycerol and 124 to 210°K for 1‐propanol. Compressions to 1000 kg/cm2 have been measured to room temperature.The increases in static dielectric constant are less than predicted from density increase alone, and the differences are discussed in terms of molecular compression and liquid structure effects. Larger increases of relaxation time with pressure are found at lower temperatures. Constant volume relaxation times do not conform to a simple rate law, and cannot be explained by activation energies depending only on volume. Glycerol shows small, temperature independent, percentage volume decrease with pressure over the whole range; 1‐propanol becomes much less compressible at low temperatures.

Results of measurements at 50°C for five mixtures and at 50, 100, and 150°C for pure ethylene are given. The pressure second virial coefficients of the mixtures are in reasonably good agreement with values predicted from combining rules and viscosity derived Lennard‐Jones parameters for the pure gases. The dielectric coefficients of pure ethylene vary approximately inversely as the absolute temperature, in contrast to earlier results which showed an anomalous increase with temperature. Attributing the major contribution to dipole moments induced by ethylene quadrupole fields gives an average quadrupole moment for ethylene of 3.9 × 10−26 esu·cm2 from the pure gas data and 4.2 × 10−26 esu·cm2 from the mixture data, but it is not possible to derive values of the two independent moments from the results.

Complex dielectric constants have been measured at frequencies from below 20 c/s to 5 mc/s over the temperature range −40° to −75°C in glycerol, −45° to −90° in propylene glycol, and −80° to −140° in n‐propanol. The results for n‐propanol are described by the Debye equation, but the values for the other two require a modified equation corresponding to a broader range of dispersion at higher frequencies. In all three liquids, evidence is found for a second dispersion region at still higher frequencies, which accounts for much of the difference between the radio frequency and optical dielectric constant. The relaxation times are quantitatively described over wide ranges by an empirical rate equation of a form which also fits viscosity data. The significance of the various results is discussed.

Measurements from 1 to 100 atm have been made at one or more temperatures between —30° and 70°C by a special transformer ratio arm bridge operating at 10 kc; derived values of the Clausius‐Mossotti function are of sufficient precision (0.1%) to justify comparison with theoretical pair fluctuation, polarizability and multipole moment interaction effects at higher densities. Helium shows a decrease of 0.3% and argon an increase of 0.1% in C‐M at 100 atm, while nitrogen and methane show somewhat larger positive effects, especially at lower temperatures. A decreased effective polarizability of atom pairs at small distances is discussed as a possible explanation of the data for helium and argon, while the effect in nitrogen is consistent with quadrupole‐induced dipole moments of pairs. A theory of octupole‐induced dipole interactions is shown to be capable of explaining the methane results with plausible estimated values of the octupole moment.

Ferroelectric properties of HBr in its low temperature solid phase have been studied by superposition of small signal ac and biasing dc fields in a special cell. The low frequency dispersion can be drastically changed by bias fields and thermal history and is attributed to dipole reorientations at domain boundaries, while the much smaller and faster (by a factor 104) high frequency dispersion is unchanged in amplitude and is attributed to dipole reorientations within domain regions. No evidence was found for low frequency dispersion or hysteresis in the low temperature phase of solid HI, and it is concluded that HI is not ferroelectric.

A modified cyclic‐expansion method has been used to determine dielectric constants as a function of relative density with a precision of less than 1 ppm for He, Ne, Ar, Kr, H2, and N2 at 49°C and pressures below 150 atm, which with data at measured pressures below 7 atm determine the first and second dielectric virial coefficients, and can also be used to determine pressure second virial coefficients.Dielectric second virial coefficients are for all six gases less than values predicted by present theories of fluctuations and pair polarizabilities, an effect believed to result from overlap interactions at short range. The low‐density values of the Clausius—Mossotti function are in good agreement with other recent determinations.

Dielectric second virial coefficients varying inversely with temperature have been determined by cyclic expansion measurements at 6.6, 49, and 100°C in the pressure range 1–100 atm. Attributing the temperature dependent contribution to dipole moments induced in one molecule by the octopole moment of a second gives 3.0× 10−34 and 4.4× 10−34 esu for the molecular octopole moments of CH4 and CF4.

Dielectric and pressure second virial coefficients of five mixtures and the pure gases have been determined at 49.7°C, the values for CO2 at 29.4°C. The pressure coefficients are in reasonably good agreement with values predicted from combining rule Lennard‐Jones parameters derived from viscosities of the pure gases. The large effect of quadrupole interaction energy on the dielectric coefficient of pure CO2 has been calculated numerically, and analytical treatments of the smaller effects of reaction fields of induced moments, quadrupole‐induced dipole energy, and anisotropy energy have also been made. These result in a calculated molecular quadrupole moment of CO2 of 4.3 × 10−26 esu cm2 from the data for pure CO2. For CO2–Ar pairs, the effects in addition to the direct quadrupole‐induced dipole contribution are much smaller, and the value 4.1 × 10−26 esu cm2 for the quadrupole moment of CO2 is derived from the dielectric coefficient. Both values are in good agreement with the Buckingham–Disch result and with other less direct estimates from infrared and microwave absorption and from pressure virial coefficients.

Dielectric constant and loss measurements have been made at frequencies from 5 to 225 MHz. These are in the range to characterize the relaxation in the intermediate solid phase of HBr from the 89°K λ transition to 98° K and, together with earlier data, the relaxation in HI from the 70°K transition to 92°K. The complex dielectric constant is described in both cases by a skewed arc function rather than the symmetric circular arc functions found for the low‐temperature phases. The corresponding loss of long‐time dipole correlations suggests a more liquidlike behavior. It is further suggested that deviations of the relaxation rates from temperature dependence of Arrhenius form may be explainable in terms of cooperative interaction effects in a disordered phase.

Dielectric constants and loss were measured from room temperature to —160°C for the pure liquids and mixtures with small amounts of water to facilitate supercooling. Two distinct dispersion regions were found below —100°C in the experimental frequency range from 1 cy/sec to 5 Mc/sec. The temperature dependences are similar and described by rate laws of the form found for similar measurements in 1‐propanol. An explanation of the multiple dispersions in terms of hydrogen bond breaking to permit reorientation of alkyl and hydroxyl groups is discussed.

Dielectric constant and loss were measured between −40° and +40°C at audio frequencies and at twelve frequencies from 10 Mc/sec to 9 Gc/sec. The frequency dependences deviate slightly from a Davidson—Cole skewed‐arc function with β=0.67 by having slightly lower loss near the center of the dispersion. The dependence of relaxation frequency on temperature gives an average value 4.3 kcal/mole for the heat of activation, but the rate plot shows curvature. Previous measurements on alkyl halides believed to show symmetrical or ``left‐skew'' complex dielectric constant loci are shown to be consistent with the present skewed arc dependence if certain data are systematically in error.

Dielectric loss and conductance data for octadecyltributylammonium thiocyanate in benzene show large changes in the significant frequency region of absorption and in the magnitude of conductance when the temperature is lowered from 25° to 6°C, but their variation with concentration is very similar at the two temperatures. The broad frequency range of absorption observed at concentrations in the range 0.008–0.02 molal and the failure of the change in macroscopic viscosity to account for the temperature effect suggest that a better understanding of similar systems requires more detailed examination of the interaction of the ionic and dipolar aggregates with the solvent.

A transient method is described which measures the equivalent of the polarization following application of a step voltage by recording the changing current resulting from a linearly rising potential across a dielectric cell. The circuits described permit recording over intervals from 10−3 sec to several seconds and are intended for use with cells employing guard electrodes. Examples of results on dielectric relaxation in solids are given and limitations of the method discussed.

Two dispersion regions in the liquid in addition to the primary dispersion have been measured at audio‐and radiofrequencies below −120°C, which make small but significant contributions to the dielectric constant. Both move rapidly to lower frequencies with decreasing temperature and the relaxation times of the intermediate dispersion are 200 times smaller than for the primary one. The temperature and frequency dependences are those to be expected for orientation rather than induced polarization.

The design procedure and the experimental details are given for the construction of a magnetic deflection system which has been used in an electron beam spectrometer to measure the angular distribution of the energy loss spectra of thin solid films. A collimated electron beam is deflected in such a way that it is incident on the specimen at the angle of scatter at which measurements are required. Electrons which emerge normally from the far side of the specimen are then momentum analyzed. The deflection was found to be proportional to current up to an angle of at least 0.04 rad.

To determine how the ac and dc magnetic properties are affected by elastic strain, the magnetic properties in the rolling direction of Epstein strips of elastically bent grain‐oriented 3% silicon iron were measured in an Epstein frame and in a Carr single‐strip permeameter. As the degree of bending becomes more pronounced, the coercive force and the ac core loss increase and the permeability decreases. The domain theory gives a rather simple approximate interpretation of the permeability data for magnetic intensities between one and ten oersteds.

A rotating disk instrument for rapid comparison of crystal anisotropies is described. In it a circular disk rotates in a magnetic field parallel to the place of the disk. Because of crystal anisotropy the magnetization I makes an angle θ with the magnetic intensity H. Some instruments, called torque magnetometers or magnetic torquemeters, measure the torque per unit volume, HI sinθ. In this instrument the disk rotates at 1800 rpm with its axis perpendicular to H.The changes in I sinθ, the component of the magnetization perpendicular to H, induce an emf in pickup coils, which are placed with their common axis perpendicular to the axis of the rotating disk and perpendicular to H. If the pickup coils are spherical, as in the similar instrument built by Siegel, the ratio of the flux through the coil to the magnetic moment of the specimen can be accurately calculated. Without such an absolute calibration the flux instrument is nevertheless convenient for rapidly comparing the disks of oriented polycrystalline ...

Second dielectric and pressure virial coefficients at 50°, 100°, and 150° are reported, together with low‐density dielectric results which give a dipole moment μ = 1.48 D and polarizability 5.3 × 10−24 cm3. The second virial data can be reasonably well fitted by a pair potential including a Lennard‐Jones radial function, polarizable dipole interactions, and an anisotropic shape factor proposed by Buckingham and Pople, but difficulties in consistently accounting for these and other results for polar molecules are pointed out.

Note: Synchrotron radiat ctr,stoughton,wi 53589. univ calif berkeley,lawrence berkeley lab,ctr xray opt,berkeley,ca 94707. xerox corp,webster res ctr,webster,ny 14580. univ minnesota,dept chem engn & mat sci,minneapolis,mn 55455. univ wisconsin,dept med phys,madison,wi 53706. Cerrina, f, univ wisconsin,dept elect & comp engn,madison,wi 53706.ISI Document Delivery No.: AG222Part 2B Reference LSE-ARTICLE-1989-001doi:10.1063/1.1140782 Record created on 2006-10-03, modified on 2017-05-12

An experimental study was made of the instability of an accelerated water‐air interface. The measured growth rate agreed with theory. The method of analysis of the data reduced scatter in the results and allowed the growth rate of second order waves to be determined. The growth rate of second‐order waves agreed reasonably well with theory of Emmons, Chang, and Watson.