Graphene has sparked significant research interest in the past few years with the potential to replace many existing materials for various applications. For instance, graphene-ferric oxide composite has been used as anode material for Li-ion batteries and has indicated charge and discharge capacities of 1227 and 1693 mAh/g, respectively. Graphene oxide-ferric oxide nanotubes indicated a high specific capacitance of 133.2F/g while the cell electrode exhibited superior cycle stability.
In-plane thermal conductivity of graphene showed that thermal conductivity increases with length. Phonon defect as well as surface oxidation scattering at the surface oxidized groups suppress the density of state of the phonon mode reference to carbon-carbon bonds.
In addition to experimental studies aimed at exploring new applications of graphene as well as new attributes of derivatives, theoretical works have been conducted to simulate the structure as well as unique attributes of the carbon nanotubes and graphene. This simulation was conducted for the effect of optical and acoustic phonon scattering in the presence of line-edge-roughness on the electronic attributes of graphene nano-ribbons.
The substitution of atom in graphene is necessary for the production of soluble materials or perhaps adding the functional group onto the graphene wall to come up composite materials. Unfortunately, it is challenging for imaging methods to visualize the substitution on the wall of graphene or to reveal how substitutions affect the attributes of graphene. Therefore, Jifen Wang and Huaqing Xie at Shanghai Polytechnic University in collaboration with Zhixiong Guo at Rutgers, The State University of New Jersey implemented first-principles density functional theory to investigate the optical and thermal attributes of graphene. Their work also studied the sensitivity of infrared as well as Raman parameters and phonon attributes upon the absent carbon atom in graphene. The research work is published in Applied Thermal Engineering.
The authors calculated graphene phonon attributes using density-functional perturbation theory and then applied to acquire thermal attributes including specific heat, free and total energy, and entropy. The results indicated that peaks of phonon density of states at approximately 40-45.5 THz in the perfect graphene were shifted to 40.5 and 46 THz in the imperfect graphene. The authors observed peaks at 16.5, 19, 25, and 43.5 THz in the imperfect graphene curve and no peaks at the same frequencies in the perfect graphene curve. The entropy as well as specific heat were lower for the imperfect graphene than for the perfect graphene at temperatures above 280K. However, this tendency was reversed at temperatures below 200K.
Total energy, change in vibrational Helmholtz free energy and change in vibrational internal energy were all observed to be lower for imperfect graphene than for the perfect graphene. The Helmholtz free energy for the imperfect graphene was higher at temperature above 1300K but was lower at temperature below 1250K than for the perfect graphene. The research team observed no absorption peaks in the infrared spectrum for the perfect graphene. However, they observed strong absorption at approximately 233, 830, and 1392cm-1 for the imperfect graphene.
Jifen Wang, Huaqing Xie, Zhixiong Guo. First-principles investigation on thermal properties and infrared spectra of imperfect graphene. Applied Thermal Engineering, volume 116 (2017), pages 456–462.Go To Applied Thermal Engineering