Fellowships

The loss of energy through friction at sliding interfaces is a significant issue. Graphene, a single-atom thick, two-dimensional lattice of honeycomb structured carbon, has been shown to be a potentially useful lubricant to decrease friction and mitigate wear at sliding interfaces. However, studies have shown that when conformed to nanoscopically rough surfaces, the graphene lattice is strained, leading to an increased risk of mechano-chemically accelerated oxidation and breakdown. My research is a fundamental examination of the reactivity of graphene under varying amounts of strain. Lattice strain can be tailored by transferring graphene to silica nanoparticle films of varying particle diameter, or by applying pressure to suspended graphene membranes. Raman spectroscopy and ambient pressure XPS can then be used to monitor the reactivity of these systems with O₂, or with a diazonium compound. Studying strained and suspended graphene helps build a stronger understanding of the role strain has on graphene reactivity, and ultimately the viability of graphene as a lubricant to cut down on energy losses from friction and wear. Furthermore, we plan to apply these concepts to other 2D lubricants, such as MoS₂.

Geophysics, especially seismic studies, can contribute to drilling and development of unconventional shale gas reservoirs by defining ‘fracability’ and ‘organic carbon content’ of shale. Un Young Lim’s doctoral research is mainly focused on the estimation of geomechanical properties (i.e., Young’s modulus and Poisson’s ratio) and total organic carbon (TOC) content in shales using a seismic inversion method, AVO inversion. He applied a new approach using an exact equation for seismic reflections, the Zoeppritz equation for PP reflection, instead of widely used approximations of the equation into the research problem. Consequently, noticeable improvements are achieved for the estimation. Specifically, anisotropy of acoustic parameters such as P– and S-wave velocities, and density are more accurately determined. This leads to more accurate estimations of Young’s modulus, Poisson’s ratio, and TOC of target shale. He also recently developed a new inversion method that jointly uses PP and PS seismic reflections together in order to improve inversion results.

Enhanced Geothermal Systems (EGS) produce energy from hot (i.e. >100°C) deep (i.e. >500m) reservoirs. Hot Dry Rocks (HDR) are generally deficient in permeability and water, so the injection of cold fluids (e.g. water) will generate thermal shock in the rock and trigger the formation of fractures that will enable geothermal-energy production from hot water. A 2006 MIT report estimated that EGS resources could reach 13,000 million exajoules in the USA, which would be able to meet worldwide energy demand for centuries. A good understating of fracture formation and the thermo-hydro-mechanical (THM) processes controlling water/vapor flow in fractured rocks is necessary for safe and economic energy production from EGS. Equally important is to develop numerical tools that allow a proper modeling of these phenomena and the engineering of EGS to optimize geothermal energy production. However, current computational tools are (typically) not able to deal with the presence of discontinuities as they are based on the theory of continuous media. In this research, we propose an advanced THM framework to model evolving cracks in rocks that combines the Finite Element (FE) method with the Mesh Fragmentation Technique (MFT). The MFT inserts solid FE with high aspect ratio in between the regular (standards) finite element of the original mesh. The technique has shown to be very promising for tackling this type of problem. For example, it has assisted to select the target temperature and flow rate of the injected fluid; as well as to design the number of wells required for a given reservoir, and to estimate the optimal distance between them to produce geothermal energy efficiently.

Sorghum has been one of the important energy crops in the world due to its high level of biomass production capacity, but the most challenging part that can significantly affect biomass production is sorghum damage caused by pests and there are no techniques to detect pest damage both quickly and accurately. Therefore, the overall objective for my dissertation research is to develop a new concept of infestation detection technique based on the determination of herbivore-induced plant volatile organic compounds (VOCs), which can prevent the infestation from spreading out throughout the field and keep the field healthy. Several specific research topics include: 1) Fundamental Sorghum VOCs analysis induced from sugarcane aphid damage by adsorbent-GC/MS technique; 2) Proof of concept that can determine many kinds of plant VOCs with adsorbent coupled Raman spectroscopy; 3) Fabrication of phase transferred Ag-nanosphere and its application of surface-enhanced Raman spectroscopy (SERS) for VOCs determination; and 4) Development of adsorbent coupled SERS technique for VOCs detection. I hope that these lab-scale VOCs sensor platforms will be employed in the field as a reliable health monitoring system in the near future.