Mechanochemical Fabrication and Characterization of Novel Low-dimensional Materials

In this research, for the first time, a novel nanofabrication process is developed to produce graphene-based nanoparticles using mechanochemical principles. Utilizing strain energy at the interface of Si and graphite via the use of a tribometer, a reaction between nanometer sized graphite particles with a reducing agent (hydrazine) was initiated. This simple method demonstrated the synthesis of lamellar platelets (lamellae of ~2nm) with diameters greater than 100 micrometers and thicknesses less than 30 nm directly on the surface of a substrate under rubbing conditions. Spectroscopic evaluation of the particles verified them to be graphene-based platelets, with functionalized molecules including C-N and C-Si bonding. Furthermore, the size of the particles was shown to be highly correlated to the applied pressure at the point of contact, such that three-body friction (with intermediate particles) was shown to enhance the size effect, though with greater variation in size among a single test sample. A chemical rate equation model was developed to help explain the formation of the chemically modified graphene platelets, wherein the pressure applied at the surface can be used to explain the net energy supplied in terms of local flash temperature and strain energy. The activation energy calculated as a result of this method (~42kJ/mol) was found to be extraordinarily close to the difference in bond enthalpies for C-O and the C-N, and C-Si bonds, indicating the input energy required to form the platelets is equivalent to the energy required to replace one chemical bond with another, which follows nicely with the laws of thermodynamics.

The ability to produce graphene-based materials using a tribochemical approach is a simple, one-step process that does not necessarily require specialized equipment. This development could potentially be translated into a direct-write nanopatterning procedure for graphene-based technologies, which promise to make electronics faster, cheaper and more reliable. The tribochemical model proposed provides insight into nanomanufacturing using a tribochemical approach, and suggests that further progress can be accomplished through the reduction of the activation energy required for graphene formation.