The density of states is dependent upon the dimensional limits of the object itself. In a system described by three orthogonal parameters (3 Dimension), the units of DOS is [Energy] [Volume], in a two dimensional system, the units of DOS is [Energy] [Area], in a one dimensional system, the units of DOS is [Energy] [Length]. The referenced volume is the volume of k -space; the space enclosed by the constant energy surface of the system derived through a dispersion relation that relates E to k. An example of a 3-dimensional k -space is given in Fig. 1. It can be seen that the dimensionality of the system confines the momentum of particles inside the system.