RESUMEN

In recent years unexpected magnetic field effects have been observed in dielectric measurements on insulating glasses at very low temperatures. Polarization echo experiments have indicated that atomic tunneling systems are responsible for these effects and that the nuclear properties of the tunneling particles are of importance. Subsequently, it was suggested that the magnetic field effects are caused by tunneling systems carrying a nuclear quadrupole moment. Now we have studied the isotope effect in echo experiments on fully deuterated and ordinary glycerol clearly showing the crucial role of the nuclear quadrupole moments for the magnetic field effects. In addition, we have observed a new effect in the decay of spontaneous echoes in zero magnetic field for the deuterated samples which can be explained in terms of a quantum beating involving the quadrupole levels.

RESUMEN

We have studied dielectric spectra of the glass-forming liquid metafluoroaniline under hydrostatic pressure up to 700 MPa. Its glass transition pressure p(g) increases approximately linearly with temperature. Above p(g)(T), a well pronounced secondary relaxation, the Johari beta peak, is observed showing activated behavior. The activation energy rises proportionally to pressure and, consequently, proportionally to the glass transition temperature T(g)(p). The activation volume is independent of temperature but exhibits different values for pressures higher and lower than the pressure where the liquid left the ergodic regime. The activation volumes are about 1/10 and 1/6 of the molecular volume of fluoroaniline, respectively, suggesting that there are two different species of clusters.

RESUMEN

We report on investigations of spontaneous polarization echoes in the nonmagnetic multicomponent glass BaO-Al2O3-SiO2 in static magnetic fields. While the echo decay is only marginally influenced, the echo amplitude depends strongly on magnetic fields. It seems that the intrinsic magnetic moment of tunneling systems causes dephasing effects which are detected in our echo experiments. In addition we find a strong increase of the echo amplitude with magnetic fields. This result shows that the coupling of the tunneling systems to magnetic fields is surprisingly strong and cannot be understood on the basis of current theories.

RESUMEN

The desorption behavior of quench-condensed rare gas films has been investigated using high frequency surface acoustic waves. Measurements of pure films of argon and neon and of the binary mixture Ar(1-c)/Ne(c) have been carried out. For small and very large neon concentration c(Ne) a behavior is found which indicates the existence of a substitutionally disordered solid. In contrast, in the wide range of concentration 0.25< c(Ne)< 0.92 two discrete temperatures for neon desorption exist. The data clearly indicate the occurrence of two separate phases, one of pure neon, the other of crystallites with either Ar(2)Ne or Ar(3)Ne structure.

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The internal friction Q-1 and the sound velocity deltav/v of vitreous silica were measured at very low temperatures using mechanical double paddle resonators operated at frequencies ranging from 0.33 to 14 kHz. Below approximately 40 mK the internal friction showed an unexpected temperature and frequency dependence, with absolute values of Q-1 clearly exceeding those predicted by the standard tunneling model. Even though the most plausible origin of the observed excess internal friction appears to be the mutual interaction between tunneling states, the results are difficult to reconcile quantitatively with present theories taking into account this interaction.

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We report on experiments giving evidence for quantum effects of electromagnetic flux in barium alumosilicate glass. In contrast to expectation, below 100 mK the dielectric response becomes sensitive to magnetic fields. The experimental findings include both lifting of the dielectric saturation by weak magnetic fields and oscillations of the dielectric response in the low temperature resonant regime. As the origin of these effects we suggest that the magnetic induction field violates the time reversal invariance leading to a flux periodicity in the energy levels of tunneling systems. At low temperatures, this effect is strongly enhanced by the interaction between tunneling systems and thus becomes measurable.

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Surface acoustic wave sensors operating in liquid generally cause problems resulting from wire bonding. The authors present an approach for a biosensor where the need for bonding wires is eliminated by utilizing inductive coupling of the sensor device to the RF circuitry. Protection of the electrodes from the liquid is achieved by coating the device surface with a SiO2 layer, resulting in a simplified handling of the devices. The first measurements with a sensor operating at 420 MHz are presented, demonstrating the potential of this operating principle for biosensing.

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RESUMEN

To study the viscoelastic behavior of antibody films on a surface acoustic wave device, we have measured the influence of multiple layers of antibodies onto the propagation of the wave. Attenuation and sound velocity variation caused by up to 20 layers have been measured. The results can be interpreted with the propagation of a viscously damped Love wave in a film with an extremely low velocity of sound. From our results, we conclude that, for the one- or two-layer films normally used in acoustic wave immunosensing, a pure mass effect is dominant. For thick films, a saturation of the sensor response is observed.

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RESUMEN

We present a new type of surface acoustic wave device for sensor applications where the need for bonding wires is eliminated. Instead the device is coupled inductively to the RF circuitry. The impedance of such devices and the necessary matching have been investigated both theoretically and experimentally. The devices have repeatedly been operated at temperatures up to 400 degrees C and have shown a good temperature resistance. In order to test the suitability of the new concept for sensor applications, several devices with an operating frequency of 363 MHz were coated with copper phthalocyanine for the detection of NO(2). From these measurements we derive a detection limit of these devices below 1 ppb for NO(2).

RESUMEN

In this paper the first application of horizontal polarized surface acoustic waves (HP-SAW) in LiTaO3 for an immunosensor is presented. A SAW device with two paths, a sensitive path and a reference path operating in liquid at 345 MHz, is used as the sensor. Antigens and antibodies were both immunoglobulins. The antibodies were immobilized via protein A on the sensitive path with a mass density of 0.4 ng/mm2, as shown by ELISA measurements. A theoretical detection limit of approximately 33 pg and a high sensitivity of 110 kHz/(ng/mm2) could be derived from the experiments. High signal enhancement factors of 4.5 and 12 are achievable by gold colloid labeled antigens with colloid diameters of 5 and 10 nm, respectively. Specificity of the antibody was demonstrated by a preabsorption experiment. As a further antibody/antigen system the binding of the anti-human serum albumin (HSA) to HSA was examined.

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RESUMEN

A laser scanner and a stepping xy stage have been developed for direct writing lithography in the micron and the submicron range. System design is described and examples of exposed photoresist with a structure size of 1 microm are presented.