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<div class="moz-text-html" lang="x-western"> <tt>Dear all,
</tt><br>
<br>
<tt> welcome to today's physics colloquium, </tt> <br>
<br>
<tt> Friday 18 March, at 10:15 in FYS1 Speaker:**Mika
Prunnila, VTT*** </tt> <br>
<tt> Title: **</tt><strong></strong><tt>*</tt><strong>Phonon
tunneling and related near-field heat transfer effects</strong><tt>
****</tt> <small><small><small><small><tt><span
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Abstract:</tt> <br>
<br>
Non-contact heat transfer between distant objects is
described by the well known black body radiation law. When
the inter-body distance d is smaller than the
characteristic wave length of Planck’s spectrum near-field
effects start to play crucial role in the inter-body heat
transport and new physics emerges (see Refs. [1,2] for a
review). Due to advances in experimental techniques
various near-field heat transfer effects from micron down
to nm body distances have been also verified
experimentally.[3–5] A recent paper [6] proposes that at
such distances a new type of near-field heat transfer
mechanism due to acoustic phonons can exist. It should be
noted that even though acoustic phonons are the major<br>
heat carriers in dielectrics and semiconductors, their
effect on non-contact heat transfer (through a vacuum gap)
has been previously considered to be negligible, because
they couple weakly to photons. However, significant energy
transmission and heat flux is possible if the acoustic
phonons can induce a time-dependent electric field, which
then can leak into the vacuum.[6] Suitable
field-to-displacement coupling mechanism is provided, for
example, by the piezoelectric effect. Solid-vacuum-solid
acoustic phonon transmission can be thought of as an
acoustic phonon tunneling through vacuum. In this
presentation, we will discuss near-field heat<br>
transfer effects and, especially, focus on the heat
transfer due to phonon tunneling.<br>
[1] K. Joulain et al., Surface Science Reports 57, 59
(2005).<br>
[2] A. I. Volokitin and B. N. J. Persson, Rev. Mod. Phys.
79, 1291 (2007).<br>
[3] A. Kittel et al., Phys. Rev. Lett. 95, 224301 (2005).<br>
[4] A. Narayanaswamy, S. Shen, and G. Chen, Phys. Rev. B
78, 115303 (2008).<br>
[5] E. Rousseau et al., Nature Photonics 3, 514 (2009).<br>
[6] M. Prunnila and J. Meltaus, Phys. Rev. Lett. 105,
125501 (2010).<br>
<br>
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Best regards,<br>
</p>
<p class="MsoNormal" style="text-align: justify;">Kari
Eskola and Ilari Maasilta </p>
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