Phonon thermal

Molecules vibrate at fundamental frequencies that are usually in the mid-infrared. Some overtone and combination transitions occur at shorter wavelengths. Because infrared photons have enough energy to excite rotational motions also, the ir spectmm of a gas consists of rovibrational bands in which each vibrational transition is accompanied by numerous simultaneous rotational transitions. In condensed phases the rotational stmcture is suppressed, but the vibrational frequencies remain highly specific, and information on the molecular environment can often be deduced from hnewidths, frequency shifts, and additional spectral stmcture owing to phonon (thermal acoustic mode) and lattice effects. 

The result of the considerations made in (a) and (b) is that the phonon thermal conductivity goes through a maximum as illustrated in Figs 3.15 and 3.16. It is to be noted that,... 

Low-temperature thermometers are obtained by cutting a metallized wafer of NTD Ge into chips of small size (typically few mm3) and bonding the electrical contacts onto the metallized sides of the chip. These chips are seldom used as calibrated thermometers for temperatures below 30 mK, but find precious application as sensors for low-temperature bolometers [42,56], When the chips are used as thermometers, i.e. in quasi-steady applications, their heat capacity does not represent a problem. In dynamic applications and at very low temperatures T < 30 mK, the chip heat capacity, together with the carrier-to-phonon thermal conductance gc d, (Section 15.2.1.3), determines the rise time of the pulses of the bolometer. 

Non-radiative transitions invariably involve the conversion of excitation energy into phonons. Thermalization involves many inelastic transitions between states in the band or band tails. Three mechanisms of thermalization apply to a-Si H. Carriers in extended states lose energy by the emission of single phonons as they scatter from one state to another. Transitions between localized states occur either by direct tunneling or by the multiple trapping mechanism in which the carrier is excited to the mobility edge and recaptured by a different tail state. 

It is easily seen by inspection that the biorthogonal basis set definition (3.55) cmnddes with the definifion (3.18) ven in the discussion of the Lanczos method. We recall that the dynamics of operators (liouville equations) or probabilities (Fokker-Planck equations) have a mathematical structure similar to Eq. (3.29) and can thus be treated with the same techniques (see, e.g., Chapter 1) once an appropriate generalization of a scalar product is performed. For instance, this same formalism has been successfully adopted to model phonon thermal baths and to include, in principle, anharmonicity effects in the interesting aspects of lattice dynamics and atom-solid collisions. ... 

Ladd, A., B. Moran, and W.G. Hoover, Lattice Thermal Conductivity A Comparison of Molecular Dynamics andAnharmonic Lattice Dynamics. Physical Review B, 1986. 34 p. 5058-5064. McGaughey, A.J. and M. Kaviany, Quantitative Validation of the Boltzmann Transport Equation Phonon Thermal Conductivity Model Under the Single-Mode Relaxation Time Approximation. Physical Review B, 2004. 69(9) p. 094303(1)-094303(11). 

The c ontrol o f p honon t emperature i n e lectron-phonon c oupling measurements i s critical for a correct estimation of the electron-phonon coupling constant. In our experiment an additional electrically isolated S-Sm-S thermometer was placed near the Si film. Below IK the electron-phonon thermal resistance in silicon is considerably larger than the Kapitza resistance between Si film and the silicon oxide layer, and therefore the S-Sm-S thermometer next to the silicon film was assumed to be at approximately the same temperature as the phonon system in the silicon film. 

If there were no mechanism to scatter electrons from states corresponding to travel in one direction to states corresponding to travel in the other direction, the electrons would continue to pick up energy from the electric field and the current would increase continuously. Such scattering mechanisms are always present in the form of phonons (thermal vibrations of the atoms), impurities, dislocations, etc., so that the current settles to a finite value. These scattering mechanisms determine the mobility of the electrons. 

Localized electrons can also be considered as temporary negative ion states. The electron can leave its trap either by absorption of phonons (thermal activation) or by absorption of photons (photoassisted diffusion). The latter process requires an energy of the order of 1 eV, as can be deduced from the optical absorption spectrum of localized electrons in n-hexane. The process of photoassisted diffusion has been demonstrated experimentally by Balal et al. (Balakin et al., 1981 Balakin and Yakovlev, 1979). Electrons were produced by photoionization of anthracene in n-hexane or 2,2,4-trimethylpentane by a laser pulse of 347 nm. Subsequent illumination of the solution with a pulse of 694 nm led to a temporary increase in the photocurrent due to the liberation of trapped electrons. The process responsible for this increase can be envisaged as follows ... 

We have calculated the heat release taking one-phonon,thermally activated processes, and the experimental cooling process into account. We used the same parameters obtained from the fit to the acoustical data (Figs. 4.13 and 4.15). With only one free parameter, Wmin,... 

This chapter has given an introduction to vibrations at bare elemental surfaces, namely, surface phonons. Owing to the low energy of surface phonons, thermal excitations at surfaces nearly always include a significant thermal population of surface phonons. Consequently, the thermal properties are closely linked to phonon properties. 

Braginsky, L Lukzen, N. Shklover, V. Hofmann, H. (2002) High-temperature phonon thermal conductivity of nanostructures. Phys. Rev. B 66,13,134203,1-7, ISSN 1098-0121... 

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