Narrow Results

A cylindrical graphene plasmon waveguide (CGPW) which consists of two rolled graphene ribbons, a dielectric core and a dielectric interlayer is proposed. An analytical model for the single-mode condition and cutoff frequency of high-order graphene surface plasmon (GSP) modes is presented and verified by finite element method (FEM) simulations. Single-mode operation region of CGPW is identified in the frequency–radius space. By varying the separation between two graphene sheets and the Fermi level of graphene, a large tunability of the mode behavior is also demonstrated. The proposed structure may provide a new freedom to manipulate GSPs, and would lead to novel applications in optics.

A single-mode buried heterostructure laser has been imaged using Cross-Sectional Scanning Tunneling Microscopy (X-STM). The problem of positioning the tip on the restricted active region on the (110) face has been overcome using combined Scanning Electron Microscopy (SEM).

In order to understand the change in the STM scans when biased, particularly the physical change in surface step defects caused by commercial sample preparation, the experimental setup has been modified to allow the sample to be biased. A simpler double quantum well test structure has been biased and it has been demonstrated that it is possible to continue performing STM whilst the device is powered. The change in the relative contrast across the image has been shown to be unaffected by this external bias for the range scanned, as predicted by a fully-coupled Poison drift–diffusion model calculated using Fermi–Dirac statistics.