Contains reports on summary of research and two research projects.Joint Services Electronics Program (Contract DAAB07-71-C-0300

Chin, Brymer Han-Yu

Free, John U., Jr.

Strandberg, Malcom W. P.

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X. TRANSPORT PHENOMENA IN SOLIDSAcademic and Research StaffProf. Malcolm W. P. Strandberg Dr. Corrado LeonardiProf. Robert L. Kyhl John D. KiersteadGraduate StudentsJohn U. Free, Jr.A. SUMMARY OF RESEARCH JSJoint Services Electronics Program (Contract DAAB07-71-C-0300)Malcolm W. P. StrandbergDuring the past half year one phase of a study of bulk and surface thermal energytransport has been finished and described in a Ph. D. thesis by John U. Free, Jr., sub-mitted to the Department of Physics. In this work experiments were made with coherentX-band phonons. This work carefully reviews the theory and a model of the reflectionof an acoustical wave from a dielectric-metal boundary. It has been found that for anydegree of realism the degree of bonding of the metal and substrate must be parametrized.The surface roughness must be considered. Acoustic attenuation in the metal is alsofound to be an important parameter when boundary mismatch is calculated.In other work, using heat pulses, we studied bulk and surface heat transport in sap-phire and tin, and in germanium and tin. The aim of this research was to replace thevirtuoso thermometric techniques that are usually applied in this work with the study ofthe thermal impulse response of the system, and the effect of the thermal properties ofthe substrate on the effective frequency-dependent impedance of a tiny thin-film resistorevaporated on the substrate. Since borrowed vector impedance meters proved to beerratic in performance and were not always available, we made and tested our ownimpedance-measuring equipment. Initial measurements are being analyzed to evaluatethe sapphire-helium Kapitza resistance, and the tin-sapphire boundary-layer thermalconductance.An initial series of experiments on bulk and surface heat transport in germanium hasbeen completed. It appears that germanium enables the study of a heat pulse reflectedfrom one surface. This is useful in studying the effect of surface polish on surface heattransport. This work is described in an S. B. thesis by Brymer Han-Yu Chin, submittedto the Department of Physics. JSQPR No. 114(X. TRANSPORT PHENOMENA IN SOLIDS)JS B. ATTENUATION OF COHERENT MICROWAVE PHONONSIN THIN METAL FILMSJohn U. Free, Jr.This report summarizes a thesis submitted to the Department of Physics, M. I. T.,on February 28, 1974, in partial fulfillment of the requirements for the degree of Doctorof Philosophy.A new technique for the measurement of ultrasonic attenuation in metals in the giga-hertz range is described. The method used in this research is to evaporate a thin metal-lic film onto the end of a quartz rod transducer and measure the ultrasonic wave reflectedfrom the thin film. This method obviates the normal difficulties encountered in producinga thin flat metal sample and in bonding the sample to the ultrasonic transducer. Theadvantages of this technique over the conventional reflection or transmission methods aretwofold. First, ultrasonic attenuation measurements can be made at higher frequenciesthan before. Second, this method enables measurement of ultrasonic reflection coef-ficients and residual attenuation coefficients, as well as of the electronic attenuationcoefficient. The ultrasonic reflection-coefficient measurements make a valuable con-tribution to experimental work in thermal boundary resistance.The theory for the reflection of an acoustical wave from a plane boundary is reviewedand extended to include such nonideal features as a rough interface, bubbles on the inter-face, and one medium having a large acoustical attenuation. The theory of an acousticalwave reflected from two interfaces or a thin film is then developed. The effects of a non-ideal thin film are discussed.Results are reported for evaporated tin samples. Measurements were made on 12samples. The experiments were carried out over an 8. 9-9. 4 GHz frequency range atliquid-helium temperatures. The nature of the experiment and the relationship betweenphysical parameters such as the reflection coefficient and the residual attenuation coef-ficient made the absolute determination of the parameters impossible. Hence the phys-ical parameters were determined within some range of values. Analysis of the dataindicated close agreement with the theory of Pippard for the electronic attenuation coef-ficient. The electronic attenuation coefficient is consistent in both magnitude and fre-quency dependence. The residual attenuation was found to be due mainly to grainboundary scattering and is in agreement with the results of Splitt. The ultrasoniclongitudinal reflection coefficient between quartz and tin was found to be 0. 35 ± 0. 15.This value is in agreement with the value calculated by using the mismatch theory andwith measurements made at lower frequencies. Finally, the ultrasonic longitudinalvelocity in this tin was measured and found to be approximately 10% less than in bulk tinat lower frequencies. This is consistent with the fact that the density of evaporated tinJS is less than that of bulk tin.QPR No. 114(X. TRANSPORT PHENOMENA IN SOLIDS)C. ON THE PROPAGATION OF HEAT PULSES IN GERMANIUM JSBrymer Han-Yu ChinThis report summarizes a thesis submitted to the Department of Physics, M. I. T.,on May 16, 1974, in partial fulfillment of the requirements for the degree of Bachelorof Science.The high sensitivity and fast response of thin-film, superconducting bolometers havemade heat-pulse studies in solids at liquid-helium temperatures an important area ofsolid-state research. We present the basic theory and experimental techniques for suchstudies. We discuss in detail data for heat-pulse propagation along the [ 111] directionof germanium. In our work, 3 pulses were observed. Two pulses correspond to the purelongitudinal and quasi-transverse modes predicted from elastic wave theory. The anom-alous third pulse is interpreted as a reflection from the sample boundaries. JSQPR No. 114

Transport Phenomena in Solids

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Transport Phenomena in Solids

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