Heat%20Transfer%20in%20Thin%20Films

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Heat Transferin Thin Films

• Thomas Prevenslik
• Berlin, Germany
• Hong Kong, China

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Background

• Over the past 30 years, heat transfer in thin
  films has been based on classical methods.
• However, for films less than about 100 nm,
  classical heat transfer cannot explain the
  reduced thermal conductivity found in
  experiments.

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Experiment
Pulse Method (Thin Solid Films, Kelemen, 36
(1976) 199-203)
W
dS
dF
Substrate
Film
T2
X2
T1
Problem Diffusivity ?
diverges as c ? 0 Can conductivity K
be measured by Pulse Method?
X1
Wire
Data Shows K ? 0 as ? ? 0
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Current Approach

• To explain reduced conductivity data, Fourier
  heat conduction theory is thought not applicable
  to thin films having thickness smaller than the
  mean free paths of phonons.
• Heat Transfer in thin films is modified to treat
  phonons as particles in the Boltzmann Transport
  Equation (BTE).

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Experiment and BTE Theory
Bulk Copper
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Purpose

• To provide a QM explanation
• for thin film heat transfer based on
• QED induced EM radiation using
  Standard Mixing Rules.

QM Quantum Mechanics QED
Quantum Electro Dynamics EM
Electromagnetic
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QED induced EM radiation

• Classically, heat is conserved by
  an increase in temperature.
• But at the nanoscale, QM forbids heat to be
  conserved by an increase in temperature because
  specific heat vanishes.
• QED allows heat to be conserved at the nanoscale
  by the emission of nonthermal EM
  radiation

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Nanoparticle or Quantum Dot
NP, QD
Laser Radiation

No Temperature change
Molecular Collisions
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Thin Film
QCond
Current Approach QCond QJoule
Kelemen KF KS
(?FS/?S)-1(dS /dF) KF ltlt KBulk
QQED
QED Heat Transfer
QCond QJoule -QQED
Standard Mixing Rules
?eff Keff /?effceff

ceff cS and cF 0
?eff (?FKF?SKS)(?F/?S)1/cS(?F?F?S?S
KF ?eff
cS ?F ?S(?S/?F) - (?S/?F)KS

KF KBulk
T2
x2-x1
T1
QJoule
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EM Confinement
Photons in Rectangular cavity resonator, nr gt 1
For ? ltlt W and L, ? ? 2?nr
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Specific Heat

• Thin films cannot conserve the Joule heat
  by an increase in temperature because specific
  heat vanishes
• Specific heat by Debye/Einstein Model for
  atomic vibration gives slow phonon (ps) response.
  
• Excitons in QDs produced promptly (fs).
• Modify Einstein Model for atom vibration to
  photon vibration inside the thin film.

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QM Restrictions
Free Molecule
Film
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Thin Film as an Einstein Solid
NA Number of Atoms in Film 3 NA Degrees of
Freedom
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Einstein Specific Heat
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Thin Film Specific Heat
3 microns
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QED Induced Heat Transfer
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Conductivity Response Kelemen - 1976
Experiment
Copper Film Glass Substrate
Mixing Rule
Substrate
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QED induced Heat Transfer
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QED induced Heat Transfer
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UV Laser Emission
Mat. Sci. Eng. B56 (1998) 239-245
(QED cavity by Refractive
Indices-Not Film Conductivity )
QED radiation 388 nm d 388/2(2.03 ) 95
nm
He-Cd Laser 325 nm
QLaser QQED
QCond 0
Zinc Oxide
d lt 100 nm
Sapphire
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Conclusions

• Thin film specific heat vanishes. Transient
  film temperatures follow the substrate allowed
  by QM to have specific heat.
• Bulk conductivity is maintained in the film, but
  there is no conductive heat loss parallel to the
  surface. The film loses heat normal to the
  surface by EM emission.
• Pulse Method requires modification using Standard
  Mixing Rules to measure thin film thermal
  conductivity
• QED induced EM emission can and should be
  measured with standard photomultipliers for 100
  nm films.

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Extensions

• Nanocatalysts
• Surface Chemical Reactions

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Nanocatalysts
Unsupported
Supported
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Surface Chemical Reactions
God made solids, but surfaces are the work of
the Devil. W. Pauli
(1900-1958)
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Questions Papers

• Email thomas_at_nanoqed.net
• http//www.nanoqed.net

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