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Both57Fe and151Eu Mossbauer resonances were used to study polycrystallineRBa2Cu3O7-δ samples. The dependence of hyperfine interaction parameters on the oxygen deficiency δ is studied in detail with151Eu. For57Fe spectra, a site assignment is proposed.

The influence of high-frequency magnetic modulation on Mossbauer resonance is investigated using the67Zn resonance. A phase-modulation theory theory explaining the experimental results is presented. Implications to magnetic modulation experiments with the57Fe resonance are also discussed.

Optically readable silicon cantilevers have been designed, fabricated and applied to photoacoustic spectroscopy. The working principle is based on detecting the acoustic wave induced displacement of the cantilever with laser interferometry. The rectangular, 9.5 mum thick components were fabricated using two-sided anisotropic etching of silicon-on insulator (SOI) wafers. The flexible cantilever is surrounded by narrow gaps from three sides and it moves very sensitively relative to the thick frame. The cantilever sensor has been applied to detect weak pressure variations in trace gas analysis and it has been shown to improve the sensitivity of photoacoustic measurements by many orders of magnitude.

A method to measure built-in voltages on the material interfaces in capacitive MEMS-devices inside closed cavities is presented. The method is based on a vibrating capacitor (Kelvin-probe) principle and it can even be used to measure closed cavity samples. The suggested set-up is tested by measuring various capacitive accelerometers and the results are compared with those obtained from capacitance–voltage (C–V) measurements. The potential of the method for high-speed measurements is explored by demonstrating an accurate determination of built-in voltages by measuring only a few data points for a device due to a very highly linear response of the method.

We describe experiments on trapping of atoms in microscopic magneto-optical traps on an optically transparent permanent-magnet atom chip. The chip is made of magnetically hard ferrite-garnet material deposited on a dielectric substrate. The confining magnetic fields are produced by miniature magnetized patterns recorded in the film by magneto-optical techniques. We trap Rb atoms on these structures by applying three crossed pairs of counter-propagating laser beams in the conventional magneto-optical trapping (MOT) geometry. We demonstrate the flexibility of the concept in creation and in-situ modification of the trapping geometries through several experiments., Comment: Modifications: A) Reference I. Barb et al., Eur. Phys. JD, 35, 75 (2005) added. B)Sentence rewritten: We routinely capture more than 10^6 atoms in a micro-MOT on a magnetized pattern. C) The magnetic field strengths are now given in Teslas. D) The second sentence in the fourth paragraph has been rewritten in order to more clearly describe the geometry and purpose of the compensation coils.E) In the seventh paragraph we have rewritten the sentence about the creation of the external magnetic field for the magnetic-domain patterning. F) In the ninth paragraph, we clarify the way to shift the trap center. G) Caption of Fig. 4 changed. H) We have modified paragraph 12 to improve the description on the guiding of the trap center along a toroidal pattern. I) The last two sentences of the manuscript have been rewritten

A 180-nm gap micromechanical resonator biased at 20 V and full custom integrated electronics are used to implement a 13-MHz oscillator that has noise floor of -147 dBc/Hz and power consumption of 240 µW including both the loop amplifier and the buffer to a 10-pF load. The design of Pierce type MEMS oscillator is discussed in terms of noise, power, and oscillator stability. Mixing of 1/f-noise is simulated and nonlinear electrostatic coupling is identified as a significant noise aliasing mechanism.

A 180-nm gap micromechanical resonator biased at 20 V and full custom integrated electronics are used to implement a 13-MHz oscillator that has noise floor of -147 dBc/Hz and power consumption of 240 /spl mu/W including both the loop amplifier and the buffer to a 10-pF load. The design of Pierce type MEMS oscillator is discussed in terms of noise, power, and oscillator stability.

We put forward the idea of a surface-mounted microscopic electro-optical atom trap. The trap is formed on an evanescent-wave atom mirror by the strongly localized static electric field of two oppositely charged transparent electrodes placed close to each other. The electrodes are embedded in a refractive-index-matched thin dielectric layer on the surface of a glass prism. In our example, the phase-space density in the trap center reaches 0.1, when the trap is loaded with atoms from a gravito-optical surface trap.

The long-term stability of single-crystal silicon microresonators is evaluated. The vacuum-encapsulated length-extensional mode resonators (fr ∼ 13 MHz) are demonstrated to be capable of a ppm-level aging rate for a follow-up period of 42 days. Comparison with unsealed devices reveals that the silicon microresonators are sensitive to water contamination from the ambient humidity. © 2004 Elsevier B.V. All rights reserved.

The small size and integrability make the silicon micromechanical rf-resonators attractive components for future wireless communication devices. In particular, we show that using the microresonators one can construct oscillators exhibiting low phase noise and good long-term stability. Such compact solutions challenge conventional quartz crystals in frequency reference applications.

An all-optical microwave frequency standard based on coherent population trapping (CPT) in 85Rb is developed. The CPT resonances are detected by an ordinary edge-emitting diode laser in a simple optical setup. A buffer-gas mixture is carefully optimized to yield a narrow linewidth and a reduced temperature dependence of the resonance frequency. With the developed system we are able to measure ultranarrow optically induced hyperfine CPT resonances at −11 τ−1/2(1 s−13 is reached at an integration time of τ=2000 s. This stability is sufficient for many high-precision applications. Frequency-shift measurements were made to evaluate the frequency dependencies on the operation parameters.

A micromechanical 13.1 MHz bulk acoustic mode (BAW) silicon resonator is demonstrated. The vibration mode can be characterized as a 2-D plate expansion that preserves the original square shape. The prototype resonator is fabricated of single-crystal silicon by reactive ion etching a silicon-on-insulator (SOI) wafer. The measured high quality factor (Q=130000) and current output (i/sub MAX/ /spl ap/ 160 /spl mu/A) make the resonator suitable for reference oscillator applications. An electrical equivalent circuit based on physical device parameters is derived and experimentally verified.

An alternative technique is proposed to create microscopic atom traps loaded with atoms from a gravito-optical surface trap (GOT), which is composed of an evanescent-wave mirror and a vertically aligned hollow laser beam. Our trap design is based on the use of current-carrying transparent conductors and transparent permanent magnets fabricated on the surface of a glass prism in the form of an internal structure of a refractive-index-matched thin dielectric film. The conductors can be fabricated of indium tin oxide (ITO) and the magnets of yttrium iron garnet (YIG). Different kinds of traps may be envisaged: i) spin-independent electro-optical ii) magneto-optical for either high- or low-field seeking atoms, and iii) purely magnetic for atoms in the low-field seeking states. In case iii), the magnetic-field minimum is located far enough from the film surface to make the contribution of the optical field negligible.

An all-optical RF standard based on dark states of 85Rb atoms has been developed. With this system we were able to measure ultra-narrow optically induced hyperfine dark resonances below 20Hz (Q-value > 1.5 × 108). The frequency of a signal generator was stabilized to the dark resonance giving a relative frequency stability (square root of Allan variance) of 3.5 × 10−11τ−1/2 (1 s < t < 2000 s). The best stability reached at an integration time of t = 2000 s was 6.4 × 10−13, which is sufficient for many high-precision applications. The frequency shifts caused by various experimental parameters were also studied.

Mechanical oscillators that have a stable resonance with high quality factor have applications as reference oscillators, sensors and in even very sophisticated high- precision experiments for observing quantum effects. In order to obtain a high quality factor the mechanical energy dissipation has to be minimised. At atmospheric pressure the most significant loss mechanism is gas damping, but for an oscillator working in vacuum the major part of the mechanical energy losses is caused by the coupling to the support structure and by internal friction which in turn is a result of a variety of physical mechanisms like thermoelastic effects and phonon scattering. Thus a great attention should to be paid to the material choice and the oscillator design.

We describe the use of bulk acoustic mode in micromechanical silicon resonators operating at radio frequencies. Based on measured data from the fabricated resonator (f/sub r//spl sim/14 MHz, Q>100 000) we analyze the characteristic impedance and signal levels in such microdevices and compare the values with conventional quartz crystals. We find that the high impedance level of microresonators can be met with integration of the readout electronics and that silicon can accommodate significantly larger vibration energy densities than quartz. Based on the results, we anticipate a wide application range for the micromechanical bulk acoustic wave structures in future wireless communication devices and microsensors.

We present the experimental details of observing the influence of NMR transitions between sublevels of Zeeman split nuclear states on Mossbauer spectra of FeNi alloys. Magnetically soft FeNi foils were subjected to radio-frequency (rf) magnetic fields and 57 Fe Mossbauer spectra were recorded. Splitting of Mossbauer resonance lines was observed when the frequency of the external transverse rf magnetic field was close to the resonance frequency of either the ground or the excited state. We discuss the possible reasons why a well-resolved line splitting has not been previously observed in earlier works.

Operation of a 14 MHz micromechanical oscillator is demonstrated and analyzed. Single-crystal silicon microbridge with submicron electrode gaps is utilized as the resonator element. The oscillator shows a noise floor of −112 dBc/Hz and a near-carrier noise of −90 dBc/Hz at 1 kHz offset. The oscillator noise is dominated by amplifier noise. By comparing the oscillator performance with conventional quartz oscillators, advantages and limitations of the micromechanical components in RF-technology are discussed.

The use of micromechanical resonant structures in RF electronics possesses often a problem caused by a very low signal amplitude. In order to alleviate the influence of parasitic capacitance we propose here the use of the differential amplifier and demonstrate its use here on the processed electrostatically driven resonators. The component used in verifying the use of differential amplifier is a clamped-clamped beam resonator with Q = 8000 and resonant frequency of f 0 = 12.3 MHz. A low-noise high input-impedance amplifier was used as a reference.

Nonlinearities in electrostatically driven micromechanical resonators are studied with circuit simulations. Models for the resonators are built of elementary electrical equivalent-circuit blocks constructed of nonlinear voltage-controlled current and charge sources. They are simulated with the harmonic balance method in the RF-simulation program APLAC. Spring softening effects due to the capacitive transducer and spring hardening effects due to the resonator's third order spring coefficient are demonstrated by simulations. For verification, a model for a micromachined high-Q beam resonator structure has been constructed, and its measured large-displacement frequency-domain transfer characteristics are successfully reproduced by model simulations.

We perform a quantum theoretical calculation of the noise power spectrum for a phase measurement of the light output from a coherently driven optical cavity with a freely moving rear mirror. We examine how the noise resulting from the quantum back action appears among the various contributions from other noise sources. We do not assume an ideal (homodyne) phase measurement, but rather consider phase modulation detection, which we show has a different shot noise level. We also take into account the effects of thermal damping of the mirror, losses within the cavity, and classical laser noise. We relate our theoretical results to experimental parameters, so as to make direct comparisons with current experiments simple. We also show that in this situation, the standard Brownian motion master equation is inadequate for describing the thermal damping of the mirror, as it produces a spurious term in the steady-state phase fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi, Europhys. Lett. {\bf 22}, 1 (1993)] rectifies this inadequacy., Comment: 12 pages revtex, 2 figures

Diode lasers are widely used in experiments in optical and atomic physics and increasingly in spectroscopy and frequency stabilization.

Bogolyubov-De Gennes equations for the excitations of a Bose condensate in the Thomas-Fermi regime in harmonic traps of any asymmetry and introduce a classification of eigenstates. In the case of cylindrical symmetry we emphasize the presence of an accidental degeneracy in the excitation spectrum at certain values of the projection of orbital angular momentum on the symmetry axis and discuss possible consequences of the degeneracy in the context of new signatures of Bose-Einstein condensation., 4 pages, LaTeX, other comments are at http://WWW.amolf.nl/departments/quantumgassen/TITLE.HTML

An economical method of fabricating large-area (up to a 100-mm wafer) silver (Ag)-coated black silicon (BS) substrates is demonstrated by cryogenic deep reactive ion etching with inductively coupled plasma. This method enables a simple adjustment of the spike structure (e.g., height, width, sidewall slope and density of the spikes) on the silicon substrate, which thus offers the advantages of accurate tuning the density and amplitude of the localized surface plasmons after Ag coating. Using this method, an enhancement factor of 109 is achieved for the probe molecule of rhodamine 6G (around two orders of magnitude higher than previous results based on Ag-coated BS) in surface-enhanced Raman scattering (SERS) measurement. The presented results pave the way to make Ag-coated BS substrates as economic and large-area platforms for diverse surface plasmon related applications (such as SERS and surface plasmon based biosensors).

We study the effect of Al doping on thermoelectric power factor of ZnO films grown using atomic layer deposition method. The overall doping level is tuned by either varying the precursor pulsing sequence or by varying the number of precursor pulses while keeping the sequence unchanged. We observe that commonly utilized doping approach when periodic dopant layers are densely packed results in reduced power factor. At the same time, we find that thermoelectric performance can be improved by clustering the dopants. In addition, the clustering was found to tune the preferred crystal orientation of the polycrystalline film.

In this work a silicon voltage controlled microelectromechanical tuning fork resonator with electrostatic actuation and separate frequency tuning electrodes is presented. The released device is fab ...

The modification of material characteristics by introducing dopant atoms into a crystal lattice is a fundamental basis for modern micro- and nanosystems technology. In this work, the uneven distribution of dopants is shown to have a remarkable effect on the residual stress and the consequent deformation of released, mechanical silicon structures. In particular, the focus is on segregation of initial dopants inside the bulk silicon which takes place in such fabrication processes as thermal oxidation. A theoretical model based on perceiving the dopant-induced change in Si crystal lattice parameter is developed. We experimentally investigate a series of silicon-on-insulator wafers, including samples with dopant types B, P, and Sb, and concentrations in the range from 1015 to 5 × 1019 atoms cm−3. Released cantilevers are fabricated as test structures and the residual stress is determined by measuring their final curvature. Experimental results are compared with the modelled values obtained utilizing the dopant profiles determined by secondary ion mass spectrometry and concentration distribution simulations. The use of lightly doped substrates or the selection of processes not modifying the underlying Si surface (e.g., plasma enhanced chemical vapour deposition PECVD or metal deposition) is shown to be an effective solution for minimizing the dopant redistribution-induced stress. Besides the scientific impact, knowledge of the stress generated by dopants is of great significance for industrial manufacturing of a wide range of micro- and nanomechanical systems.

We demonstrate a new method for accessing the broad-bandwidth polarization-independent operation of a microring resonator based on the standard photonic nanostrip waveguides. The method employs the selective application of atomic layer deposition to form highly uniform TiO(2) overlayers with the specific dispersion properties. The wide operation window is achieved by matching the wavelength dependencies of the free spectral ranges of the two orthogonal polarizations.

In this paper, we demonstrate silicon microdevice fabrication by a combination of focused ion beam (FIB) and cryogenic deep reactive ion etching (DRIE). Applying FIB treatment only to a thin surface layer enables very high writing speed compared with FIB milling. The use of DRIE then defines the micro- and nanodevices utilizing the FIB-modified silicon as a mask. We demonstrate the ability to create patterns on highly 3D structures, which is extremely challenging by other nanofabrication methods. The alignment of optically made and FIB-defined patterns is also demonstrated. We also show that complete microelectromechanical systems (MEMS) can be fabricated by this method by presenting a double-ended tuning fork resonator as an example. Extremely short process time is achieved as the full fabrication cycle from mask design to electrical measurements can be completed during one working day.

We present the first experimental observation of the Rabi splitting of M\"ossbauer resonance lines. A radio-frequency magnetic field is tuned to induce transitions between hyperfine sublevels of the Zeeman-split excited or ground state of $^{57}\mathrm{Fe}$ nuclei. The line splitting corresponding to the Rabi flopping frequency is observed using a magnetically soft $^{57}\mathrm{FeNi}$ absorber foil of composition with almost zero magnetostriction.

This item is a correction to the paper entitled "Towards micromechanical radio: overtone excitations of a microresonator through the nonlinearities of the second and third orderrdquo.

The down-conversion performance of a multimodal microelectromechanical mixer-filter is improved over 30 dB by parametric amplification. The input signal is an amplitude-modulated signal with a carrier frequency of 0.5 GHz. The obtained amplification is shown to depend on the particular eigenmode in a predetermined way. Finally, a qualitative explanation for the behavior is given.

Temporal aspects related to the Mossbauer resonance are reviewed, in particular time-dependent transient effects produced by high-frequency modulation of the recoilless gamma radiation. These phenomena are in many respects similar to those observed in NMR and laser spectroscopy. Transient effects can be described within a classical field model in terms of phase modulation of recoilless gamma radiation. Experimentally, use of the very narrow Mossbauer resonance of67Zn gives access to undisturbed transient phenomena without excessive difficulties due to nonideal modulation. Application of transient experiments facilitates determination of several physical parameters, of which some arc tedious to evaluate by other methods.

The use of an alternating magnetic field for phase modulation of recoilless gamma radiation is studied. The measurements were performed with the Mossbauer resonances of Fe-57 and Zn-67. Novel time-domain data are presented from experiments on the nuclear Zeeman effect at high modulation frequencies.

We report on detailed simultaneous measurements of electrical resistivity and ac magnetic susceptibility of a carefully prepared granular ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{5}$${\mathrm{O}}_{6.92}$ sample in the superconducting transition region. The observed features are explained in terms of a two-stage model. The first stage is attributed to the growing of superconducting inclusions. In the second stage of the transition we simulate both isotropic and anisotropic superconductivities by bond percolation models, where the conduction between nearest-neighbor grains is assumed to be correlated one or two dimensional or noncorrelated three dimensional. We observe no qualitative differences in the bulk matter between the superconductivities of different dimensionalities. Thus the general behavior of the bulk matter can be attributed to general properties of random media. The percolation models can be applied to all observed polycrystalline superconductors.

Oxygen stoichiometry plays an important role in the new high-temperature superconductors of the type YBa2Cu3O7-δ. Variation of the parameter S from 0 to 1 changes the crystal structure from orthorhombic to tetragonal. Superconductivity has been reported only for values δ ≤ 0.5. With these 1-2-3 compounds, substitution of copper atoms by transition metal elements has been studied extensively. Doping with iron atoms allows to probe the oxygen symmetry around the lattice sites of copper by 57Fe Mossbauer spectroscopy. Several research groups have reported Mossbauer studies of iron-doped 1-2-3 compounds.l–6 The rare-earth site has been investigated for example by the 151Eu Mossbauer resonance.1,7

57 Fe-doped and undoped single crystals were grown for Mossbauer and magnetic AC susceptibility measurements. The effects of cooling rate and the concentration of the YBa 2 (Cu 1− x 57 Fe x ) 3 O 7−δ -powder in the melt were examined. The lattice parameters of the single crystals were determined by x-ray diffraction. Growth in air yielded orthorhombic crystals with a - and b -axes differing only slightly and having T c =77K for undoped and 57 K for 57 Fe-doped crystals. Mossbauer spectra indicated the presence of regions with different oxygen contents.

Organic light-emitting transistors are photonic devices combining the function of an electrical switch with the capability of generating light under appropriate bias conditions. Achieving high-performance light-emitting transistors requires high-mobility organic semiconductors, optimized device structures, and highly efficient emissive layers. In this work, we studied the optoelectronic response of green blends (TCTA:Ir(ppy)3) with varying doping concentrations in the limit of field-effect within a transistor device configuration. Increasing the dye concentration within the blend leads to a quenching of the photoluminescence signal; however, when implemented in a multilayer stack in a transistor, we observed an approximately 5-fold improvement in the light output for a 10% Ir(ppy)3 doping blend. We analyzed our results in terms of balanced charge transport in the emissive layer, which, in the limit of field-effect (horizontal component), leads to an improved exciton formation and decay process. While the performances of our devices are yet to achieve the state-of-the-art diode counterpart, this work demonstrates that engineering the emissive layer is a promising approach to enhance the light emission in field-effect devices. This opens the way for a broader exploitation of organic light-emitting transistors as alternative photonic devices in several fields, ranging from display technology to flexible and wearable electronics.

Well-defined Dahlia type gallium nitride flowers (GaNFs) have been synthesized on c-plane sapphire substrates at different growth conditions using chemical vapour deposition system. The growth was carried out without any catalyst medium for favouring the nucleation process. Crystal structure of the GaNFs was obtained using x-ray diffractometer (XRD). Scanning electron microscopy (SEM) revealed the morphology of GaNFs. The elemental traces and compositions of the samples were obtained using energy dispersive x-ray (EDX) spectroscopy and x-ray photoelectron spectroscopy (XPS). The optical properties of the samples were analysed using cathodoluminescence (CL) spectroscopy and Raman spectroscopy. From the current-voltage (I-V) response, it was observed that there are no interface and surface related inhomogeneities in the samples. The fabricated photodetector showcased good device performance due to high carrier density in the sample.