On the Boundary Scattering of Phonons

1973 ◽  
Vol 51 (2) ◽  
pp. 223-225 ◽  
Author(s):  
G. P. Srivastava ◽  
G. S. Verma
Keyword(s):  
Low Temperatures ◽  
Boundary Scattering ◽  
Variational Treatment

In this paper we have discussed the variational treatment of the boundary scattering of phonons. The procedure of Hamilton and Parrott for boundary scattering of phonons is modified; but still the method is shown to give Casimir's result at low temperatures.

Thermal conduction in artificial sapphire crystals at low temperatures I. Nearly perfect crystals

1955 ◽  
Vol 231 (1184) ◽  
pp. 130-144 ◽  
Keyword(s):  
Free Path ◽  
Low Temperatures ◽  
Thermal Conduction ◽  
Rough Surfaces ◽  
Mean Free Path ◽  
Boundary Scattering ◽  
Crystal Diameter ◽  
Different Sources

In order to obtain a detailed verification of the theory of thermal conduction in dielectric crystals, measurements have been made on a number of artificial sapphire crystals between 2° and 100° K. In the region of the maximum there are variations in conductivity between crystals from different sources. The highest conductivities measured are about 140 W/cm deg., which suggests that estimates of several hundred watts for the maxima of ideal sapphire crystals are not unreasonable. At sufficiently low temperatures the conductivity of a very perfect, long crystal with rough surfaces is observed, in agreement with Casimir’s theory of boundary scattering, to be proportional to T 3 and to the radius; the phonon mean free path is then nearly equal to the crystal diameter. Imperfect crystals show some anomalous effects. The extension of Casimir’s theory to apply to short specimens has been verified. Perfect crystals with smooth surfaces exhibit some specular reflexion of phonons; a statistical description of the surface is proposed which leads to the observed variation of this effect with temperature and is compatible with the results of interferometric examination of the surface.

Specular Scattering in Electrical Transport in the Thin Tilm System CoSi2/Si

1984 ◽  
Vol 37 ◽  
Author(s):  
J. C. Hensel ◽  
R. T. Tung ◽  
J. M. Poate ◽  
F. C. Unterwald
Keyword(s):  
Thin Films ◽  
Film Thickness ◽  
Size Effect ◽  
Electrical Transport ◽  
Low Temperatures ◽  
Boundary Scattering ◽  
Specular Scattering ◽  
Bulk Scattering ◽  
Scattering Lengths ◽  
High Degree

AbstractWe have investigated electrical transport in thin films of CoSi2 at low temperatures as a function of film thickness and observe in conductivity a size effect much smaller than seen heretofore indicative of a high degree of specularity in the boundary scattering. This in large part owes to the unique characteristics of these films, i.e., they are single crystal and continuous down to ∼60Å thickness with long bulk scattering lengths (≈1000Å) in transport at liquid He temperatures and have nearly atomically perfect interfaces.

The thermal conductivity of diamond at low temperatures

1953 ◽  
Vol 220 (1141) ◽  
pp. 171-183 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Temperature Variation ◽  
Finite Length ◽  
Low Temperatures ◽  
Room Temperature ◽  
Experimental Results ◽  
Theoretical Treatment ◽  
Type I ◽  
Boundary Scattering ◽  
Crystal Boundaries

The thermal conductivity of a type I diamond has been measured between 2° K and room temperature. Above 100° K the temperature variation of conductivity accords with Peierls’s theory of Umklapp processes. To account for the results at the lowest temperatures it is necessary to assume that some specular reflexion of phonons occurs at the crystal boundaries. Casimir’s theoretical treatment of boundary scattering has been extended to take into account the finite length of specimens and the smoothness of the crystal walls, and the experimental results show that at 3° K the proportion of specular reflexions is as great as 40%. Between 50 and 100° K the conductivity is considerably less than that calculated for an ideal diamond, and some conclusions are drawn as to the imperfections which cause this discrepancy.

scholarly journals Analysis of the Effect of Resonant Phonon Scattering on the Thermal Conductivity of CaF2

1976 ◽  
Vol 29 (2) ◽  
pp. 19 ◽  
Author(s):  
PRW Hudson ◽  
EE Gibbs
Keyword(s):  
Thermal Conductivity ◽  
Low Temperatures ◽  
Phonon Scattering ◽  
Low Frequency ◽  
Resonant Scattering ◽  
Boundary Scattering ◽  
Scattering Mechanism ◽  
Scattering Mechanisms ◽  
Phonon Conduction

An analysis is presented of the various phonon contributions to the thermal conductivity of CaF2 doped with 1�0% and 0�1 % of yttrium or thulium. The broad phonon resonant scattering term is found to reduce the low frequency phonon conduction significantly. This is responsible for the relatively stronger suppression of the conductivity at low temperatures in the phonon boundary scattering region. Thus broad quasilocalized phonon resonant scattering mechanisms have a similar effect to phonon precipitate scattering. It also follows that, in the case of a broad resonant scattering mechanism, a dip will not necessarily be seen in the conductivity.

Thermoelectric Power of Graphite Acceptor Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
Ko Sugihara
Keyword(s):  
Cross Section ◽  
Point Defects ◽  
Low Temperatures ◽  
Rayleigh Scattering ◽  
Boundary Scattering ◽  
Phonon Drag ◽  
Large Cross Section ◽  
Drag Effect ◽  
Temperature Variations ◽  
Graphite Intercalation

ABSTRACTTemperature variations of the thermopower (TEP) of acceptor graphite intercalation compounds (GIC) are very different from that of pristine graphite. At low temperatures the TEP increases monotonically with T, then levels off above 150 K. This behavior is ascribed to the phonon drag effect. In the region where the TEP is nearly constant, phonon relaxation is mainly controlled by the Rayleigh scattering due to point defects or impurities. This process leads to T-independent phonon drag TEP. The importance of Rayleigh scattering is due to the large cross section diameter of the Fermi surface in GIC. At low temperatures where the boundary scattering becomes important, the TEP is proportional to T3 . Detailed calculations are carried out by solving the phonon-carrier coupled Boltzmann equation.

Interpretation of irradiation-induced changes in electron diffractograms and images of extinction contours at low temperatures

1984 ◽  
Vol 42 ◽  
pp. 268-269
Author(s):  
E. Knapek ◽  
H. Formanek ◽  
G. Lefranc ◽  
I. Dietrich
Keyword(s):  
Low Temperatures ◽  
Carbon Films ◽  
Organic Crystals ◽  
Wide Spread ◽  
Lens System ◽  
Preparation Conditions ◽  
Thin Carbon ◽  
Electron Diffractograms ◽  
Diffraction Patterns ◽  
Induced Changes

A few years ago results on cryoprotection of L-valine were reported, where the values of the critical fluence De i.e, the electron exposure which decreases the intensity of the diffraction reflections by a factor e, amounted to the order of 2000 + 1000 e/nm2. In the meantime a discrepancy arose, since several groups published De values between 100 e/nm2 and 1200 e/nm2 /1 - 4/. This disagreement and particularly the wide spread of the results induced us to investigate more thoroughly the behaviour of organic crystals at very low temperatures during electron irradiation.For this purpose large L-valine crystals with homogenuous thickness were deposited on holey carbon films, thin carbon films or Au-coated holey carbon films. These specimens were cooled down to nearly liquid helium temperature in an electron microscope with a superconducting lens system and irradiated with 200 keU-electrons. The progress of radiation damage under different preparation conditions has been observed with series of electron diffraction patterns and direct images of extinction contours.

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