Some novel results of a combined sequential study of growth spirals on the basal surface of the richly polytypic CdI₂ crystals by optical microscopy, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) are presented and discussed. In confirmation of the known structural data, the STM pictures clearly reveal the value of unit cella(= b) dimension to be equal to 0.428 nm a and the value of the interaxial angle γ to be equal to 120°. Under the high resolution and magnification achieved in the scanning electron microscope, the growth steps of large heights seen in the optical micrographs are found to have a large number of additional steps of smaller heights existing between any two adjacent large height growth steps. When further seen by a scanning tunneling microscope, which provides still higher resolution, several unit substeps are seen to exist between two consecutive additional steps. The height of each substep is found to be equal to the unit cell height of the underlying polytype. The height of the larger additional steps are found to be integral multiple of the unit cell height. The horizontal distance between two consecutive growth steps is found to be an integral multiple of the lattice parametera. The interspacing of the growth steps of same step height is found to vary at different positions on the same crystal face.

The research in the field of layered materials, especially in monolayer and few layer forms, have surged in the past decade owing to their unique properties enabling a new kind of nano-dimensional device architecture. Electrical contacts connecting these materials to the outside circuit play very important role in deciding the device performance. In layered materials, particularly when considering the 2D regime, metal–semiconductor contacts become even more crucial. In this review, we present a comprehensive overview of the importance of metal contacts to 2D materials and discuss about the challenges faced which hinder the ultimate device performance. In particular, we discuss about the recent investigations towards improvement in electronic device performance by engineering the metal–semiconductor interfaces based on 2D semiconductors.