Documents disponibles écrits par cet auteur

Anharmonic phonon interactions at interfaces and contributions to thermal boundary conductance / Patrick E. Hopkins in Journal of heat transfer, Vol. 133 N° 6 (Juin 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 6 (Juin 2011) . - pp. [062401/1-11] Titre : Anharmonic phonon interactions at interfaces and contributions to thermal boundary conductance Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur ; John C. Duda, Auteur ; Pamela M. Norris, Auteur Année de publication : 2011 Article en page(s) : pp. [062401/1-11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Thermal  boundary  conductance  Kopitza  resistance  Phonon  interfacial  scattering  Elastic  and  inelastic  scattering  Harmonic  and  anharmonic  processes Index. décimale : 536 Chaleur. Thermodynamique Résumé : Continued reduction in characteristic dimensions in nanosystems has given rise to increasing importance of material interfaces on the overall system performance. With regard to thermal transport, this increases the need for a better fundamental understanding of the processes affecting interfacial thermal transport, as characterized by the thermal boundary conductance. When thermal boundary conductance is driven by phononic scattering events, accurate predictions of interfacial transport must account for anharmonic phononic coupling as this affects the thermal transmission. In this paper, a new model for phononic thermal boundary conductance is developed that takes into account anharmonic coupling, or inelastic scattering events, at the interface between two materials. Previous models for thermal boundary conductance are first reviewed, including the diffuse mismatch model, which only considers elastic phonon scattering events, and earlier attempts to account for inelastic phonon scattering, namely, the maximum transmission model and the higher harmonic inelastic model. A new model is derived, the anharmonic inelastic model, which provides a more physical consideration of the effects of inelastic scattering on thermal boundary conductance. This is accomplished by considering specific ranges of phonon frequency interactions and phonon number density conservation. Thus, this model considers the contributions of anharmonic, inelastically scattered phonons to thermal boundary conductance. This new anharmonic inelastic model shows improved agreement between the thermal boundary conductance predictions and experimental data at the Pb/diamond and Au/diamond interfaces due to its ability to account for the temperature dependent changing phonon population in diamond, which can couple anharmonically with multiple phonons in Pb and Au. We conclude by discussing phonon scattering selection rules at interfaces and the probability of occurrence of these higher order anharmonic interfacial phonon processes quantified in this work. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Anharmonic phonon interactions at interfaces and contributions to thermal boundary conductance [texte imprimé] / Patrick E. Hopkins, Auteur ; John C. Duda, Auteur ; Pamela M. Norris, Auteur . - 2011 . - pp. [062401/1-11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 6 (Juin 2011) . - pp. [062401/1-11] Mots-clés : Thermal  boundary  conductance  Kopitza  resistance  Phonon  interfacial  scattering  Elastic  and  inelastic  scattering  Harmonic  and  anharmonic  processes Index. décimale : 536 Chaleur. Thermodynamique Résumé : Continued reduction in characteristic dimensions in nanosystems has given rise to increasing importance of material interfaces on the overall system performance. With regard to thermal transport, this increases the need for a better fundamental understanding of the processes affecting interfacial thermal transport, as characterized by the thermal boundary conductance. When thermal boundary conductance is driven by phononic scattering events, accurate predictions of interfacial transport must account for anharmonic phononic coupling as this affects the thermal transmission. In this paper, a new model for phononic thermal boundary conductance is developed that takes into account anharmonic coupling, or inelastic scattering events, at the interface between two materials. Previous models for thermal boundary conductance are first reviewed, including the diffuse mismatch model, which only considers elastic phonon scattering events, and earlier attempts to account for inelastic phonon scattering, namely, the maximum transmission model and the higher harmonic inelastic model. A new model is derived, the anharmonic inelastic model, which provides a more physical consideration of the effects of inelastic scattering on thermal boundary conductance. This is accomplished by considering specific ranges of phonon frequency interactions and phonon number density conservation. Thus, this model considers the contributions of anharmonic, inelastically scattered phonons to thermal boundary conductance. This new anharmonic inelastic model shows improved agreement between the thermal boundary conductance predictions and experimental data at the Pb/diamond and Au/diamond interfaces due to its ability to account for the temperature dependent changing phonon population in diamond, which can couple anharmonically with multiple phonons in Pb and Au. We conclude by discussing phonon scattering selection rules at interfaces and the probability of occurrence of these higher order anharmonic interfacial phonon processes quantified in this work. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Contributions of inter- and intraband excitations to electron heat capacity and electron-phonon coupling in noble metals / Patrick E. Hopkins in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014504-1/4] Titre : Contributions of inter- and intraband excitations to electron heat capacity and electron-phonon coupling in noble metals Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur Article en page(s) : pp. [014504-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Intraband  transition  Interband  transition  Electronphonon  coupling  factor  Short  pulsed  laser  heating  Electronic  band  structure Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on thermophysical properties in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor, which in turn impacts the evolution of the temperature after pulse absorption and electron thermalization. Expressions for heat capacity and electron-phonon coupling factor are derived for electrons undergoing both inter- and intraband transitions. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Contributions of inter- and intraband excitations to electron heat capacity and electron-phonon coupling in noble metals [texte imprimé] / Patrick E. Hopkins, Auteur . - pp. [014504-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014504-1/4] Mots-clés : Intraband  transition  Interband  transition  Electronphonon  coupling  factor  Short  pulsed  laser  heating  Electronic  band  structure Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on thermophysical properties in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor, which in turn impacts the evolution of the temperature after pulse absorption and electron thermalization. Expressions for heat capacity and electron-phonon coupling factor are derived for electrons undergoing both inter- and intraband transitions. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Criteria for cross-plane dominated thermal transport in multilayer thin film systems during modulated laser heating / Patrick E. Hopkins in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081302-1/10] Titre : Criteria for cross-plane dominated thermal transport in multilayer thin film systems during modulated laser heating Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur ; Justin R. Serrano, Auteur ; Leslie M. Phinney, Auteur Article en page(s) : pp. [081302-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pump-probe  thermoreflectance  Thin  film  thermal  conductivity  Thermal  boundary  conductance  Radial  heating  Cross-plane  transport Index. décimale : 536 Chaleur. Thermodynamique Résumé : Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring the thermophysical properties of thin films, such as thermal conductivity, Lambda, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on, Lambda and G, determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one-dimensional and axially symmetric cylindrical conduction models for thermal transport are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. The results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Criteria for cross-plane dominated thermal transport in multilayer thin film systems during modulated laser heating [texte imprimé] / Patrick E. Hopkins, Auteur ; Justin R. Serrano, Auteur ; Leslie M. Phinney, Auteur . - pp. [081302-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081302-1/10] Mots-clés : Pump-probe  thermoreflectance  Thin  film  thermal  conductivity  Thermal  boundary  conductance  Radial  heating  Cross-plane  transport Index. décimale : 536 Chaleur. Thermodynamique Résumé : Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring the thermophysical properties of thin films, such as thermal conductivity, Lambda, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on, Lambda and G, determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one-dimensional and axially symmetric cylindrical conduction models for thermal transport are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. The results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Influence of inter- and intraband transitions to electron temperature decay in noble metals after short-pulsed laser heating / Patrick E. Hopkins in Journal of heat transfer, Vol. 132 N° 12 (Décembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 12 (Décembre 2010) . - pp. [122402-1/6] Titre : Influence of inter- and intraband transitions to electron temperature decay in noble metals after short-pulsed laser heating Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur Année de publication : 2010 Article en page(s) : pp. [122402-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Intraband  transition  Electron-phonon  coupling  factor  Short-pulsed  laser  heating  Electronic  band  structure  Fermi  smearing  Two  temperature  model Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on the electron temperature decay in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. The two temperature model describing electron-phonon heat transfer after short-pulsed laser heating is solved using the expressions for heat capacity and electron-phonon coupling factor after intra- and interband excitations, and the predicted electron temperature change of the intra- and interband excited electrons are examined. A critical fluence value is defined that represents the absorbed fluence needed to fill all available states at a given photon energy above the Fermi level. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ and are shown to affect temporal electron temperature profiles. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Influence of inter- and intraband transitions to electron temperature decay in noble metals after short-pulsed laser heating [texte imprimé] / Patrick E. Hopkins, Auteur . - 2010 . - pp. [122402-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 12 (Décembre 2010) . - pp. [122402-1/6] Mots-clés : Intraband  transition  Electron-phonon  coupling  factor  Short-pulsed  laser  heating  Electronic  band  structure  Fermi  smearing  Two  temperature  model Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on the electron temperature decay in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. The two temperature model describing electron-phonon heat transfer after short-pulsed laser heating is solved using the expressions for heat capacity and electron-phonon coupling factor after intra- and interband excitations, and the predicted electron temperature change of the intra- and interband excited electrons are examined. A critical fluence value is defined that represents the absorbed fluence needed to fill all available states at a given photon energy above the Fermi level. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ and are shown to affect temporal electron temperature profiles. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Measuring the thermal conductivity of porous, transparent SiO2 films with time domain thermoreflectance / Patrick E. Hopkins in Journal of heat transfer, Vol. 133 N° 6 (Juin 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 6 (Juin 2011) . - pp. [061601/1-8] Titre : Measuring the thermal conductivity of porous, transparent SiO2 films with time domain thermoreflectance Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur ; Bryan Kaehr, Auteur ; Leslie M. Phinney, Auteur Année de publication : 2011 Article en page(s) : pp. [061601/1-8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Time  domain  thermoreflectance  Thermal  conductivity  Differentail-effective  medium  theory  Porous  SiO2 Index. décimale : 536 Chaleur. Thermodynamique Résumé : Nanocomposites offer unique capabilities of controlling thermal transport through the manipulation of various structural aspects of the material. However, measurements of the thermal properties of these composites are often difficult, especially porous nanomaterials. Optical measurements of these properties, although ideal due to the noncontact nature, are challenging due to the large surface variability of nanoporous structures. In this work, we use a vector-based thermal algorithm to solve for the temperature change and heat transfer in which a thin film subjected to a modulated heat source is sandwiched between two thermally conductive pathways. We validate our solution with time domain thermoreflectance measurements on glass slides and extend the thermal conductivity measurements to SiO2-based nanostructured films. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Measuring the thermal conductivity of porous, transparent SiO2 films with time domain thermoreflectance [texte imprimé] / Patrick E. Hopkins, Auteur ; Bryan Kaehr, Auteur ; Leslie M. Phinney, Auteur . - 2011 . - pp. [061601/1-8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 6 (Juin 2011) . - pp. [061601/1-8] Mots-clés : Time  domain  thermoreflectance  Thermal  conductivity  Differentail-effective  medium  theory  Porous  SiO2 Index. décimale : 536 Chaleur. Thermodynamique Résumé : Nanocomposites offer unique capabilities of controlling thermal transport through the manipulation of various structural aspects of the material. However, measurements of the thermal properties of these composites are often difficult, especially porous nanomaterials. Optical measurements of these properties, although ideal due to the noncontact nature, are challenging due to the large surface variability of nanoporous structures. In this work, we use a vector-based thermal algorithm to solve for the temperature change and heat transfer in which a thin film subjected to a modulated heat source is sandwiched between two thermally conductive pathways. We validate our solution with time domain thermoreflectance measurements on glass slides and extend the thermal conductivity measurements to SiO2-based nanostructured films. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

On the linear temperature dependence of phonon thermal boundary conductance in the classical limit / John C. Duda in Journal of heat transfer, Vol. 133 N° 7 (Juillet 2011) 

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Re-examining electron-fermi relaxation in gold films with a nonlinear thermoreflectance model / Patrick E. Hopkins in Journal of heat transfer, Vol. 133 N° 4 (Avril 2011) 

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