AVS 63rd International Symposium & Exhibition
    2D Materials Focus Topic Thursday Sessions
       Session 2D-ThA

Paper 2D-ThA11
Driving Mechanochemical Wear on Graphene Using Local Stress and Heat

Thursday, November 10, 2016, 5:40 pm, Room 103B

Session: Surface Chemistry, Functionalization, Bio and Sensor Applications of 2D Materials
Presenter: Jonathan Felts, Texas A&M University
Authors: S. Raghuraman, Texas A&M University
J.R. Felts, Texas A&M University
Correspondent: Click to Email
Here we investigate the chemical dynamics of local graphene oxide reduction through the application of local temperature and stress using a heated atomic force microscope (AFM) tip. Specifically, a silicon AFM cantilever with an embedded Joule heater applies both local stress and heat to chemically functionalized graphene surfaces during tip sliding. The friction of the graphene sheet depends linearly on chemical group concentration, so monitoring friction force provides an in situ measure of chemical functionality on the surface over time. We demonstrate bond cleavage of oxygen via both local temperature and force during tip sliding on graphene oxide. Monitoring friction change over time for constant tip temperatures between 310 – 355 C and a load of 40 nN provides the kinetics of the reduction process, with an activation energy for bond scission of 0.7 ± 0.3 eV. Measurement noise contributed significantly to error and precluded determination of reaction order. In an effort to reduce measurement time and error, we introduce a new technique, called Scanning Thermal Desorption Microscopy (SThDM). The working principle of SThDM is similar to bulk thermal analysis techniques such as thermogravimetry or differential scanning calorimetry, where thermal kinetics are calculated from mass loss over time during a linear temperature ramp. We demonstrate the technique on graphene oxide during a linear temperature ramp between 50 - 450 C at low mechanical loads, providing an activation energy 0.62 ± 0.07 and a reaction order n ~ 1. Raising the applied load during the temperature ramp shifted the mass loss curve to lower temperatures, due to a lowering of the thermal energy barrier. The results show that the force lowers the energy barrier non-linearly--at odds with current models of mechanochemical atomic attrition found in the literature--where higher loads begin to impede the reaction rate. The results are compared to bulk measurements from the literature and current theoretical models of mechanochemical reactions. Based on the observed energy barriers and reaction order, a diffusion mechanism is proposed.