Influence of driving electric field on electron-ripplon resonance in 2D electron crystal

No Heading Resonance features in the conductivity of a 2D electron crystal over liquid helium are studied experimentally depending on driving electric field. The experiment has been carried out at temperature T = 75 mK for the crystal with surface electron density n_s = 8 × 10⁸ cm^–2 in the frequency range 4–7 MHz where the resonance mode (0,1) of coupled electron-ripplon oscillations can be excited in the experimental cell. It is found that the resonance amplitude decreases as the exciting voltage increases. Additional features of the resonance curve are observed at frequencies lower than the (0,1) mode frequency. The results are analyzed within Monarkhas theory which takes into account an influence of non-linearity of interaction between electrons and liquid surface on the dynamics of 2D electron crystal moving along the surface of liquid helium.PACS numbers: 73.20.Dx; 73.90.+f     

Microwave dielectric properties of Ba5+nTinNb4O15+3n ceramics

New dielectric ceramics Ba_{5 + n}Ti_nNb₄O_{15 + 3n} (n = 1,2,3) with cation-deficient hexagonal perovskite-related structure were prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. These ceramics show dielectric constant (_r) of in the range of 45.1–48.6, _f in the range +59 to +175 ppm°C^{– 1}, and high quality factors with Q×f values up to 22882. The values of _r and _f of the ceramics gradually increase as the number of n increases.     

Quartz Oscillator Study of Monolayer 4He and 3He - 4He Mixture Films Adsorbed on Solid H2

The superfluid transition in submonolayer and monolayer ⁴ He films and ³ He - ⁴ He mixture films on solid H ₂ has been studied using a quartz crystal microbalance technique. Kosterlitz-Thouless (KT) transitions were observed in submonolayer ⁴ He films with density greater than 0.062 ± 0.002 Å ^–2 . We determine a binding energy of ⁴ He to 0.241 Å ^–2 H ₂ of –15.7 K in the. presence of 1 monolayer of ⁴ He. At several ⁴ He coverages, a range of submonolayer ³ He coverages was studied (n ₃ 0.0567 Å ^–2 ). With each increase in the ³ He coverage, the KT transition temperature decreased. For the higher coverage mixture films studied (n ₄ 0.0726 Å ^–2 ) we observed an apparent second decoupling of the film from the quartz oscillator frequency in addition to the KT transition. We have studied the. coverage dependence of this new feature.     

4He Fluid in Extremely Narrow 1D Channels 1.5?nm in?Diameter

To examine whether one-dimensional (1D) helium quantum fluid is realized in narrower channels than those studied previously, we have measured heat capacities of ⁴He adsorbed in nanoporous material FSM with straight 1D channels 1.5 nm in diameter. From the heat of desorption for adsorbed ⁴He, the coverage n _f, up to which ⁴He film grows in the channels, is determined to be 15.4 ??mol/m² using the Frenkel-Halsey-Hill model. At coverages sufficiently below n _f, the temperature dependence of the ⁴He heat capacity has a shoulder, above which adsorbed ⁴He is delocalized from the substrate. On the other hand, the depression of the heat capacity indicating quantum effects has not been observed up to n _f, which suggests that ⁴He film in the channels remains amorphous-like normal fluid. Just above n _f, the quantum effect is observed in ⁴He adatoms on the grain surface of FSM powder, which indicates that 1.5 nm channels are slightly below the limit required to realize quantum effect in the inside ⁴He fluid.     

VUV spectroscopy of wide bandgap materials

In this paper we will present VUV spectroscopy experiments performed at the Superlumi station of Hasylab, DESY, Hamburg, on samples of BaF₂ crystals activated with Ce and BaF₂, (Ba,La)F₂ crystals activated with Er. The results of these experiments include time resolved luminescence and luminescence excitation spectra obtained under wavelength selective VUV and UV excitation by pulsed synchrotron radiation.We will reveal the information provided by the VUV/UV excitation spectra of the Ce³⁺ 5d → 4f as well as Er³⁺ 4fⁿ⁻¹5d → 4fⁿ and 4fⁿ → 4fⁿ emissions on energy transfer mechanisms from the fluoride host to the rare earth ion. We will demonstrate that the fast energy transfer channels involve bound excitons while the generation of free electrons and holes leads to slower processes dependant on hole and/or electron trapping.We will demonstrate that differences between the excitation spectra of the 5d → 4f emission in Ce and 4f¹⁰5d → 4f¹¹ emission in Er activated BaF₂ are generated by the coupling of the 4f → 5d transition to the 4f¹⁰ core of the Er³⁺ ion. We will also identify the additional band, absent for Ce, which is due to the exchange split high spin (HS) state of the 4f¹⁰5d configuration responsible for the slow decay of the excited Er³⁺ ions in BaF₂ and (Ba,La)F₂.Finally we will provide evidence and explain why the dominant VUV 4f¹⁰5d → 4f¹¹ Er³⁺ emission in BaF₂ is spin-forbidden and slow while in the mixed (Ba,La)F₂ crystals it is spin-allowed and fast.     

Sliding of the wigner solid from the coupled plasmon-ripplon surface deformation

The Wigner solid (WS) on a liquid⁴He surface is accompanied with the periodic surface deformation, i.e. the ripplons whose wavevectors equal the reciprocal WS lattice vectors. This unique situation plays a crucial role in the dynamics of the WS. We have performed an extensive measurement of the ac Corbino conductivity _xx. The WS conductivity shows extremely nonlinear behavior, and it jumps abruptly at a certain input voltage. The threshold input voltage V_th varies as V_thB^–0.8f^–1n_s ^1.5E, where B, f, n_s, and E are magnetic field, frequency, electron density and pressing electric field, respectively. We have interpreted the _xx jump as the collective sliding of the electrons out of the surface deformation.     

Anisotropic attenuation of zero sound in superfluid3He-A

The anisotropic attenuation of zero sound in superfluid³He-A at 29.3 bar pressure has been measured at 24.4, 34.2, 44.2, 54.0, 63.9, 73.7, 83.5, and 93.4 MHz. The clapping mode resonance has been observed at all frequencies, and the reentrant normal flapping resonance has been measured for the first time. Analysis of these results leads to anf-wave pairing parameter,x ₃ ^–1 –0.1±0.05, and a determination of strong coupling corrections to the energy gap far fromT _c. This is expressed by an enhancement of the zero-temperature energy gap by a factor 1.3±0.1 above that of weak coupling, 2.03k _B T _c . The clapping mode data is consistent with a nontrivial, strong coupling correction to the mode frequency, reducing it by 6%. The³He was confined to a slab 250 µm in thickness and the superfluid texture was oriented by a magnetic field. This allowed attenuations up to 100 cm^–1 to be resolved and the attenuation from pair-breaking processes alone to be determined for the first time. The sound attenuation was measured for angles between the sound propagation direction and the1vector of 0, /4, and /2. The sensitivity of the numerically evaluated attenuation to quasiparticle collision time,f-wave parameter, and uniformity of the orbital texture is explored.     

UV-cured hybrid inorganic-organic polymer electrolyte based on organically modified polysiloxane

Hybrid inorganic-organic polymer electrolyte based on the monomer of organically modified polysiloxane was prepared by UV radiation curing in the presence of liquid electrolyte. The organically modified polysiloxane monomer with acrylate groups at the terminal position was synthesized by hydrolytic condensation of tetramethoxysilane (TMOS) and followed by demethanolation reaction using 2-hydroxyethyl acrylate (2-HEA). The rational formula of the monomer was SiO_1.1436(OH)_0.01606(OCH₃)_1.3394(OCH₂CH₂OCOCH= CH₂)_0.3574 which was determined by proton nuclear magnetic resonance (¹H-NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and silica analysis. The monomer was polyfunctional with a number average molecular weight of 1185 and a weight average molecular weight of 2292 determined by GPC analysis. The electrochemical properties of the hybrid inorganic-organic polymer electrolyte were determined by ac impedance spectroscopy and cyclic voltammetry. Ionic conductivity was greatly enhanced with increasing amounts of liquid electrolyte. When the polymer electrolyte contained 80 wt% liquid electrolytes, the conductivities were around 3.3 × 10^–3 S cm^–1 at 21°C and 8.0 × 10^–4 S cm^–1 even at –23°C. Interface resistance increased initially and reached a steady value after 2 days. Oxidation stability was up to 5.0 V against the lithium reference electrode and electrochemical plating/stripping of lithium on the stainless steel electrode was reversible.     

Condensate Fraction in Liquid 4He at Zero Temperature

We present results of the one-body density matrix ρ ₁(r) and the condensate fraction n ₀ of liquid ⁴He calculated at zero temperature by means of the Path Integral Ground State Monte Carlo method. This technique allows to generate a highly accurate approximation for the ground state wave function Ψ ₀ in a totally model-independent way, that depends only on the Hamiltonian of the system and on the symmetry properties of Ψ ₀. With this unbiased estimation of ρ ₁(r), we obtain precise results for the condensate fraction n ₀ and the kinetic energy K of the system. The dependence of n ₀ with the pressure shows an excellent agreement of our results with recent experimental measurements. Above the melting pressure, overpressurized liquid ⁴He shows a small condensate fraction that has dropped to 0.8% at the highest pressure of p=87?bar.     

Mobility of electrons in the surface state of liquid helium

The response of a sheet of electrons on the surface of liquid helium to an ac driving field parallel to the surface is investigated. A Corbino-type electrode arrangement is used to study the influence of a vertical magnetic field. The surface electron mobility is deduced from the observed temperature and magnetic field dependences of the ac response, by means of a simplified equivalent circuit analysis. The mobility data thus obtained show the ripplon-limited behavior at low temperature and are in reasonable agreement with the previous experimental result of Grimes and Adams and with the theoretical calculation of Saitoh. A similar measurement carried out on the surface of ³He has revealed that the mobility is determined by the gas atom scattering down to the lowest temperature (~ 0.5 K) of the present study.     

High-Resolution Measurements of the Coexistence Curve Very Near the 3He Liquid–Gas Critical Point

The shape of the liquid–gas coexistence curve of ³He very near the critical point temperature T _c was measured in the range –5× 10^–3c–1<–1.5 × 10^–6 using the quasistatic thermogram method. This study was performed in the Earth6s gravitational field using two cells of very different heights (0.5 and 48 mm). The measured coexistence curve near the critical point was strongly affected by the gravitational field. Away from the critical point, we compare the coexistence curve obtained using the thermogram method with earlier work by Pittman et al. The recently developed crossover parametric model of the equation-of-state is used to take gravity effects into account. The shape of the measured coexistence curve very near the critical point is remarkably symmetric about the critical density. Our results close to the critical point are consistent with the slope of the rectilinear diameter obtained by Pitman et al. from measurement farther away from T _c. The deviation from a law of rectilinear diameter predicted by revised scaling and the Yang–Yang anomaly were not observed in ³He within the 0.1% accuracy in our measurements.     

Investigation of Microinhomogeneities in a-SiC r :H Films Using the Chemical Induction Model

Amorphous hydrogenated silicon–carbon (a-SiC _r :H) films grown by decomposing silane–methane mixtures in a low-frequency (55 kHz) glow discharge at different methane concentrations are studied by IR spectroscopy. The absorption band in the range 1850–2300 cm^–1 is decomposed into four Gaussian components, and the results are compared with calculations in the chemical induction model. It is found that the carbon atoms are nonuniformly distributed in the nearest neighbor environment of the SiH groups in the form of HSi–Si_{3 – n} C _n (n= 0–3) structures. The random bonding model is used to evaluate the probability of formation of each HSi–Si_{3 – n} C _n structure as a function of the C/Si ratio. Comparison with experimental data points to an inhomogeneous microstructure of the films.     

Yttrium-substituted bismuth titanate (Bi4−x Y x Ti3O12) thin film for use in non-volatile memories

Fatigue-free Bi_3.2Y_0.8Ti₃O₁₂ (BYT) thin films were grown on Pt/TiO₂/SiO₂/Si substrates using direct liquid injection–metal organic chemical vapor deposition. The BYT film capacitor with top Au electrode showed higher remanent polarization (2P _r) and lower leakage current density compared with Bi_3.2La_0.8Ti₃O₁₂ (BLT) film capacitors. BYT films showed strong (1 1 7) orientation with smaller grain size, while BLT films showed strong c-axis orientation. The 2P _r value of the BYT capacitor was 15 C cm^–2 and remained essentially constant up to 1×10¹⁰ read/write switching cycles at a frequency of 1 MHz. The leakage current of the BYT film was 3.5×10^–7 A cm^–2 at an applied voltage of 2 V, which is about three orders lower than that of the BLT film.     

4He in Liquid 3He below 0.1 K: Measurements of the Solubility and Prewetting Transition

We have measured the solubility of ⁴He in liquid ³He down to 0.04 K at various pressures. The solubility was obtained indirectly, from the thickness of the superfluid film in contact with unsaturated solutions. We determined the film thickness from the ratio of two parallel plate capacitors with different gaps, immersed in the unsaturated liquid. The technique is described in detail, with its advantages and drawbacks, including the effects of the edge capacitance and capillary condensation. For use in interpreting the data, the adsorption area and the van der Waals potential of the cell walls were found by measuring the thickness of ³He and ⁴He–³He films under their vapor pressure. By fitting the temperature dependence of the solubility to the predictions of Fermi liquid theory, we determined the ⁴He effective mass m*₄, the binding energy E ₄ and the partial volume v*₄, as a function of pressure. At 24 atm, a prewetting transition was observed in the ⁴He-rich film in contact with the liquid ³He. The transition, which is related to a similar phenomenon discovered by Tholen and Parpia at very low temperature, is explained by a simple model. An Appendix describes a new derivation of the thermodynamic functions of ³He-rich mixtures in Fermi liquid theory.     

Measurement of Superfluid 3He Film Flow by Inter-digitated Capacitors

We report the measurements of the critical current of superfluid ³He film for the thickness of 0.47 µm. By employing inter-digitated capacitors, 2.5×10^?2 mm^{3 3}He can be manipulated with 0.4% resolution. Critical current J ^f _c of superfluid ³He film were observed for the onset of dissipative flow. The magnitude of measured J ^f _c is considerably smaller than the theoretically predicted pair-breaking critical current. This resugt indicates that another mechanism must participate in the dissipation of superflow.     

Bounds for traces in complete intersections and degrees in the Nullstellensatz

In this paper we obtain an effective Nullstellensatz using quantitative considerations of the classical duality theory in complete intersections. Letk be an infinite perfect field and let f₁,...,f n–rk[X₁,...,X_n] be a regular sequence with d:=max_j deg f_j. Denote byA the polynomial ringk [X₁,..., X_r] and byB the factor ring k[X₁,...,X_n]/(f₁,...,f_n r); assume that the canonical morphism AB is injective and integral and that the Jacobian determinant with respect to the variables X_r+1,...,X_n is not a zero divisor inB. Let finally B^*:=Hom_A(B, A) be the generator of B^* associated to the regular sequence.We show that for each polynomialf the inequality deg (¯f) dⁿ r(+1) holds (¯fdenotes the class off inB and is an upper bound for (n–r)d and degf). For the usual trace associated to the (free) extensionA B we obtain a somewhat more precise bound: deg Tr(¯f) dⁿ r degf. From these bounds and Bertini's theorem we deduce an elementary proof of the following effective Nullstellensatz: let f₁,..., f_s be polynomials in k[X₁,...,X_n] with degrees bounded by a constant d2; then 1 (f₁,..., f_s) if and only if there exist polynomials p₁,..., p_sk[X₁,..., X_n] with degrees bounded by 4n(d+ 1)ⁿ such that 1=_ip_if_i. in the particular cases when the characteristic of the base fieldk is zero ord=2 the sharper bound 4ndⁿ is obtained.Partially supported by UBACYT and CONICET (Argentina)     

High-temperature structural change of CrOx-LaOx-Al2O3 catalyst for lean-burn exhaust treatment

Solid-state reaction in the system of CrOx-Al₂O₃ and CrOx-LaOx-Al₂O₃ and their sintering at 500–1100°C were examined by X-ray diffraction, electron spin resonance (ESR) and surface area measurement for the development of heat-stable catalytic ceramic in lean-burn exhaust treatment. CrOx-LaOx-Al₂O₃ catalyst, even heated at 1000°C in air, showed the removal conversion of 100% for C₃H₆, 95% for CO and 7% for NO at 500°C for high velocity automotive lean-burn exhaust with A/F = 18 and S.V. = 10⁵h^–1. La-modification of catalyst was effective to high surface area stabilization and the improvement of complete oxidation activity of CO and hydrocarbons.     

A New Method to Measure the Oxide Layer Thickness on Steels Using Electromagnetic Acoustic Resonance

Electromagnetic acoustic resonance of 2.25 Cr–1Mo steel plates with (Fe, Cr)₃O₄ oxide layers of thickness from 0.03 mm to 0.18 mm were investigated. Due to the phase shift at the interface between the metal and the oxide layer, the resonance frequency, f _n, was not proportional to resonance order, n, but n/f _n varied depending both on the frequency and the oxide layer thickness. A model to derive the amount of the phase shift at the interface was developed, and a good agreement with experiments was found. It was shown that the oxide layer thickness, h, could be obtained as h = 0.33 × c _oxide/f _max, where c _oxide is the shear wave velocity in the oxide layer and f _max is the frequency at which n/f _n had a maximum. The shear wave velocity in the oxide layer was determined as 3400 m/sec and the reflection coefficient at the interface as 0.09.     

Observation of tunneling and magneto-tunneling out of a 2D Wigner crystal

We measured the escape rates of surface state electrons from an electron layer confined at the liquid helium-vacuum interface in the temperature range of 30–450mK, and for densities 0.02–2.2×10⁸ cm ^–2. Below 200mK the escape rates were temperature independent and converged to the expected single particle tunneling rates in the zero density limit, where correlations are negligible. The single particle rates were enhanced exponentially as the density was increased up to a critical densityn _c. Atn _c the escape process becomes extremely nonlinear. As the barrier is raised so that the escape rates decrease below 5.0×10^–4sec^–1, a new very weakly density and external field dependent mechanism seems to dominate the escape. Thermally activated escape was observed above 250mK and the activation energies were in good agreement with the expected values. Upon application of a magnetic field in the plane of the electron layer, the rates become strongly temperature and field dependent even at the lowest temperaturesT40mK. At these temperatures and low densities rates are suppressed four orders of magnitude in a few kGauss magnetic fields.     

3He-CMN boundary resistance

The boundary resistance between liquid and solid³He and CMN is calculated taking the coupling to be due to the nuclear spin-electron spin dipolar interaction. The boundary resistance is calculated using a relationship betweenR _K ^–1 and the longitudinal relaxation timeT ₁. We find qualitative agreement with the results of Leggett and Vuorio for the temperature dependence and impurity dependence ofR _K ^–1 . Quantitative agreement with experiment is possible using a number of plausible assumptions. An important insight emerges: the relative rates of motion of the spins in³He and CMN are crucial to their coupling. Solid³He at low pressure is in near synchronism with CNM. As a consequence its boundary resistance should be very low.Supported in part by the National Science Foundation and the A. P. Sloan Foundation.