Development of a Scanning Probe Microscope and Studies of Graphene Grown on Copper
A description of the construction of a low noise fiber interferometer deflection sensor is presented in order to illustrate the capabilities of the developed home built scanning probe microscope (SPM). A description of the critical components and a rationale behind their implementation in the design of the sensor is provided. An analysis of an ideal interference cavity is used to understand the optimization of the deflection sensor towards achieving the highest possible sensitivity and lowest deflection noise density. The low noise interferometer can be used to detect the motion of micron sized resonators without the need for external lenses or polarization sensitive optical components, allowing for simplified implementation in a variety of circumstances. True atomic resolution imaging of muscovite mica in water by atomic force microscopy (AFM) is demonstrated using the developed sensor in the home built SPM.
Results on graphene grown on copper substrates by chemical vapor deposition (CVD) is provided. Graphene appears to grow over grains of different identities and across grain boundaries of the copper. Graphene island growth on the surface appears to depend on the underlying substrate. Temperature dependent growth studies show a significant decrease in growth rate with decreasing temperature. The graphene grown on copper is shown to be transferable to arbitrary substrates and can be suspended across perforations in a receiving substrate. The knowledge gained from the growths on copper allowed for the successful fabrication of a new type of hybrid polymeric - conductive AFM probe using patterned silicon substrates and thin copper films.
Scanning tunneling microscopy (STM) was performed on graphene grown on copper substrates using the home built instrument. First, atomic scale STM imaging of graphene on polycrystalline copper substrates was accomplished. Graphene is shown to grow continuously over atomic steps, edges, and vertices of these corrugated copper surfaces. Continuous graphene growth is observed to exist over facets of different identities. The results on polycrystalline copper strongly suggests that the copper atoms are mobile during growth and that the underlying substrate does not limit graphene growth. In addition, STM was performed on graphene grown on copper (100) single crystals. The growth is again shown to be continuous over a wide range of surface features. The grown graphene exists in a variety of orientations with respect to the underlying copper crystal lattice. This leads to graphene overlayers which are polycrystalline in nature. Transmission electron microscopy (TEM) is used to reveal the crystallinity of graphene grown on single crystals and the real space distribution of the crystal domains in grown graphene. The compiled results of graphene growth on copper suggest that understanding and controlling the nucleation at the surface will ultimately be required for wafer scale growth of monolayer single crystal graphene on copper.