Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding thermal transport nanoscale devices, individual nanostructures, nanostructured materials. This review emphasizes developments experiment, theory, computation that have occurred past ten years summarizes present status field. Interfaces between become increasingly important small scales. The conductance many solid–solid interfaces been...

We report experiments in which picosecond light pulses are used to generate and detect very short stress (coherent longitudinal phonons). present a theory of the generation process, describe how spatial shape pulse is related optical, electronic, acoustical properties material. The detected through measurement changes they induce optical reflectivity sample surface. this effect. experimental results we have obtained for a-${\mathrm{As}}_{2}$${\mathrm{Te}}_{3}$, a-Ge,...

A diverse spectrum of technology drivers such as improved thermal barriers, higher efficiency thermoelectric energy conversion, phase-change memory, heat-assisted magnetic recording, management nanoscale electronics, and nanoparticles for medical therapies are motivating studies the applied physics transport at nanoscale. This review emphasizes developments in experiment, theory, computation past ten years summarizes present status field. Interfaces become increasingly important on small...

Measurements of the Kapitza conductance ${\mathrm{\ensuremath{\sigma}}}_{\mathit{K}}$ made using a picosecond optical technique at temperatures between 50 and 300 K are presented for interfaces metals dielectrics. The Debye ${\mathit{FTHETA}}_{\mathit{D}}$ (Pb, Au, Al, Ti) were in range from 102 to 426 K, while those dielectrics (${\mathrm{BaF}}_{2}$, sapphire, diamond) varied 287 2200 K. Conductances measured materials with differing by less than about factor 5 found be reasonable agreement...

Using the picosecond pump and probe technique we have detected oscillations of photoinduced transmission reflection in thin films $a$-${\mathrm{As}}_{2}$${\mathrm{Te}}_{3}$ cis-polyacetylene. These are due to generation propagation coherent acoustic phonons film. We discuss detection mechanism, use this effect measure sound velocity a film $a$-Si${\mathrm{O}}_{2}$.

We present measurements of the lattice thermal conductivity ${\ensuremath{\kappa}}_{\ensuremath{\perp}}$ normal to interfaces $(\mathrm{GaAs}{)}_{n}/(\mathrm{AlAs}{)}_{n}$ superlattices with n between 1 and 40 monolayers. The was measured by an optical pump-and-probe technique in temperature range 100 375 K. In experiment, Al film is deposited onto a superlattice sample, rate at which this cools conduction into determined. find general decrease reduction period. At 300 K,...

In phonon-propagation studies using heat pulses it has been found that predominantly transverse phonons are observed for [100] propagation in LiF whereas mainly longitudinal this direction KCl. This result and similar effects previously reported on other crystals explained terms of a phonon-focusing effect arises from elastic anisotropy.

We have studied the ultrasonic pulses that are generated when a picosecond light pulse is absorbed in metallic film. The shape influenced by distance hot electrons diffuse before losing their energy to lattice. show this method can be used test theories of electron-phonon and electron-electron scattering rates. results excellent agreement with calculation which nonthermal character electron distribution taken into account.

We present a macroscopic, phenomenological theory for the heat flow between two material half-spaces of differing temperatures whose surfaces are separated by gap width l. Our calculation parallels Liftshitz's van der Waals force dielectric slabs. For l sufficiently small, is enhanced contribution from evanescent waves, and in limit very small varies as ${\mathit{l}}^{\mathrm{\ensuremath{-}}2}$.

With the use of a face-centered cubic model lattice dynamics we calculate group velocity acoustic phonons in growth direction periodic superlattices. Comparing with case bulk solids, this component phonon is reduced due to flattening dispersion curves associated Brillouin-zone folding. The results are used estimate semiquantitatively effects on thermal conductivity Si/Ge and GaAs/AlAs For superlattice an order magnitude reduction predicted ratio relaxation time [consistent P. Hyldgaard G. D....

The generation and detection of ultrasonic waves with picosecond time resolution are described. With ultrasonics, the frequency range acoustic is extended into 100-GHz range. It allows investigation thin-film materials, microstructures, materials large attenuation. Velocity attenuation measurements on a variety thin films reviewed. results complex including multilayers, presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The temperature dependence of the Kapitza resistance (thermal boundary resistance) at interface between two dissimilar solids is calculated for a model system consisting semi-infinite, harmonic fcc lattices in register. spectral density phonon flux transmitted across obtained from numerical calculation transmission coefficient and group velocity used to calculate resistance. Results flux, coefficient, thermal are presented. Calculation real systems using results this discussed.

The generation of thermal acoustic waves by a heated metallic film on the surface dielectric crystal at low temperatures is discussed. It shown that even if produced correspond to uniform distribution directions wave vector, there may be large enhancement energy flow in some crystallographic compared average. This effect arises because elastic anisotropy. Explicit expressions are given for expected principal cubic crystals.

A picosecond pump-probe technique is used to measure the room-temperature thermal conductivity κ and longitudinal sound velocity cl of amorphous diamond (a-D) diamondlike carbon (DLC) thin films. Both were found decrease with film hydrogen content. Depending on deposition technique, in range 5–10×10−2 W cm−1 K−1 for a-D, 3–10×10−3 DLC. Values be 14–18×105 cm s−1 6–9×105

A detailed analysis of the method picosecond acoustic interferometry to study attenuation and velocity longitudinal phonons in transparent materials Brillouin frequency range with laser pulses is presented. Experimental results for fused quartz from 90 300 K show good agreement previous scattering data. Measurements on a borosilicate glass (Corning 7059) sapphire have also been made. This makes these measurements possible under conditions where conventional approaches are not applicable.

The renormalization group theory of second-order phase transitions is described in a form suitable for presentation as part an undergraduate statistical physics course.

When two communicating vessels are filled to a different height with liquid, the levels equilibrate because liquid can flow. We have looked for such equilibration solid 4 He. For crystals no grain boundaries, we see flow of mass, whereas containing several detect mass Our results suggest that transport is due superfluidity boundaries.

The thermal conductivities of single crystals silicon and calcium fluoride have been measured in the temperature range 3-40 \ifmmode^\circ\else\textdegree\fi{}K 2.5-30 \ifmmode^\circ\else\textdegree\fi{}K, respectively. For samples form square cross-section rods, conductivity boundary scattering regime was found to depend on orientation rod axis, variation being as much 50% for silicon. This anisotropy is accounted terms phonon focusing due fact that elastically anisotropic phase group...

Large differences (up to a factor of 100) have been observed in the intensity phonons different polarizations propagating ballistically LiF, KCl, and ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$. These observations were made by means heat-pulse experiments carried out on single crystals, temperature range 1.5-3.5 \ifmmode^\circ\else\textdegree\fi{}K. The results are explained terms phonon focusing due fact that elastically anisotropic crystals phase group velocities are, general, not collinear....

This is a short review of recent experimental and theoretical studies phonon interactions in superfluid helium. Phonon-phonon scattering helium strongly influenced by the conservation laws peculiarities dispersion relation. Theory predicts that because these factors spontaneous decay rate varies dramatically with energy, experiments have confirmed this prediction. The can also be used to show phonon-phonon collisions are predominatly small-angle scattering. We discuss influence special...

Recent experiments on the attenuation and velocity of sound in liquid ${\mathrm{He}}^{4}$ at low temperatures are discussed terms excitation model ${\mathrm{He}}^{4}$. By assuming for long-wavelength excitations dispersion relation $\ensuremath{\epsilon}(p)=cp[1\ensuremath{-}\ensuremath{\gamma}{p}^{2}\ensuremath{-}\ensuremath{\delta}{p}^{4}\ensuremath{\cdots}]$ with $\ensuremath{\gamma}$ negative, we able to reconcile previous disagreements between theory experiment.

We have used the picosecond ultrasonic technique to study formation of acoustic solitons. In these experiments, a longitudinal pulse is generated at one surface sample. After has propagated across sample, its shape modified as result phonon dispersion and nonlinearity. found that change in can be described by Korteweg--de Vries equation. The experiments been performed on Si, MgO, \ensuremath{\alpha}-quartz, sapphire. For each we observed fully developed solitons, with shapes are reasonable...

We report measurements of the attenuation longitudinal-acoustic phonons in amorphous ${\mathrm{SiO}}_{2}$ for frequencies between 76 and 440 GHz, temperature range 80--300 K. The samples are chemical-vapor-deposited films grown on tungsten substrates, generated detected using picosecond optical techniques. phonon is found to depend only weakly temperature. In upper part frequency range, there some evidence that dependence faster than quadratic, thus indicating cannot be explained by...