The present work is focused on the formulation of the relaxation time due to the hole surface-acoustic phonon and hole--remote-polar phonon scattering mechanisms in mesoscopic diamond-based devices. First of all, an introduction about the promising role of diamond in the realization of high-power and high-frequency devices is given, together with a focus on the current difficulties and attempts in the understanding and fabrication of devices based on this material. An extensive study on the existence of surface waves in such structures follows, in order to understand which surface-acoustic modes are possible; this is followed by the quantization of these waves in order to take into account the reduced number of phonons in a nanoscale structure, the formulation of the interaction Hamiltonian, and the final calculation of the relaxation time through Fermi Golden Rule.