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Molecular slip is expected to occur at the interface between the surface of a bulk-acoustic-wave quartz chemical sensor and a liquid with which it is in contact. A new property of the interface, called the interfacial slip parameter, accounts for molecular slip. It is introduced in the theory of the sensor-liquid system by generalizing the no-slip boundary condition. The interfacial slip parameter is a complex-valued quantity which is defined as the displacement of a particle of liquid in contact with the sensor surface divided by the displacement of a particle on the surface of the sensor. The theoretical expression for the impedance of the sensor is derived in terms of the interfacial slip parameter. The impedance of the sensor is measured by the network analysis method for hydrophilic and hydrophobic surfaces in contact with water-glycerol solutions. The experimental values of impedance are fitted to the theory by nonlinear regression analysis to find the interfacial slip parameter. A mechanical model of molecular slip is devised which explains the variation of the interfacial slip parameter with the viscosity of the liquid. The results indicate that there is some slip in low-viscosity liquids, near the viscosity of water, and very little slip in liquids of high viscosity, near that of glycerol.

The network analysls method was used to completely characterlre 5-and 9-MHz bulk acoustic wave quartz crystal sensors wtth alumhum and gold electrodes in the Uquld phase for ail conditions of the crystals. The behavlor of the sensors is evaluated In terms of the serles resonant frequency, frequency of maxhnum phase, minimum Impedance, motional reslstance, maxlmum phase, and slope of phase. The dlfference In resonant frequency In liquid relatlve to alr for crystals with gold and aiumlnum electrodes strongly lmplles that the electrode-llquld Interface plays a signlflcant role In acoustic wave propagatlon Into the liquld. Previous theories associated with liquid-phase sensor behavlor based on the Sauerbrey expression fail to explaln experlmental measurements of serles resonant frequency as a functlon of viscosity.

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Detailed measurements of electrical conductivity ( a ) , Hall coefficient ( R H ) , and Seebeck coefficient ( a ) were made on seven bismuth telluride samples of composition Bi?Tea+,, with x ranging from -0.06 to $0.48. Above room temperature the slope of R=T3I2 gave a n apparent energy gap about 50% higher than that from the a slope, and the Hall mobility decreased steeply with a T-4 dependence. These effects could be explained by a n electron-to-hole mobility ratio (b) near unity, but the magnitude of a a t higher temperatures appeared to require a b value of about 2. A t the highest temperature the Hall mobility was found to increase with increasing tellurium content. T h e electron effective mass (m,) was found to be less than that of the holes (nl,), a t least below room temperature. Both m, and m , increased with extrinsic carrier concentration, and to some extent with temperature. These facts may be due to a stronger warping of the valence band a t higher energies than the conduction band. The Hall mobility below room temperature could be explained by acoustic lattice scattering and degeneracy. At the Seebeck coefficient maxima, the value of a T was found to be roughly constant. T h e temperature slopes of a below the maxima were generally greater than expected classically. Anomalies were found in R H , R H U , and a above room temperature in a near intrinsic n-type sample.