A fundamental knowledge of quantum mechanics is a prerequisite to understand the wave effects at the nano level, since wave effects are dominant in nanoscale energy transport. This fact can be elucidated with a simple example where quantum effects are predominant in the nanoscale regime. Consider a thin film of semiconductor material made of germanium or silicon. The thickness (L) of the thin film could be of the order of 1–100 nm. One end of the thin film is maintained at a higher temperature ( \(T_1\) ) and the other end at a lower temperature ( \(T_2\) ). Heat transfer takes place from the hot side to the cold side by conduction. The thermal conductivity of the thin film can be calculated by using Fourier’s law of heat conduction.