Environmental Engineering Reference
In-Depth Information
properties are revealed, such as the universal quantum thermal
conductance, periodic transmission behaviors, stop-frequency gap,
and so on. These results will be helpful to understand the behaviors
of ballistic phonon thermal transport in quantum structures with
inhomogeneities,and to thedesign of thermal quantumdevices.
4.1 Introduction
In the past two decades, the electronic transport properties in
nanoscale structures have attracted considerable attention [1-3],
since they possess novel physical properties in comparison with
bulkmaterials,aswellaspotentialapplicationsinnewdevices.Now
it has become well known that the electronic properties can be
engineered to a high degree of precision in quantum structures by
usingquantumsizeeffectsonelectrons.Ontheotherhand,currently
there is an increasing interest in the thermal properties due to
practicalneedsandfundamentalscience.Asknown,heatneedstobe
removed as much as possible, and the search for specific materials
or structures that conduct heat well has become essential for the
design of new integrated circuits and 3D electronics [4], due to the
fact that a continuous scaling down of the sizes of these devices
leads to an increase in power dissipation per unit area. However,
for the thermoelectric energy conversion, it needs materials or
structures of a strongly suppressed thermal conductance in order
to improve their thermoelectric e
ciency [5-7]. Especially, for the
functional thermal devices, such as thermal rectifier [8-9], thermal
transistor [10], thermal diode [11], thermal memory [12], and
so on, the heat fluxes must be reasonably tunable to implement
special given thermal functions. Therefore, scientifically exploring
the thermal-transport mechanisms in quantum systems becomes
critically important from a physics perspective and for practical
applications of variousnanodevices.
Inrecentyears,thethermaltransportassociatedwithphononsin
low-dimensional nanostructures has attracted increasing attention
both experimentally [13-19] and theoretically [20-27]. It has
been demonstrated that the thermal conductivity of nanostructures
is much smaller than their bulk values due to the boundary
