The role of substrate purity and its crystallographic orientation in the defect density of chemical vapor deposition grown monolayer graphene

Defect free mono-layer graphene sheet growth has remained a challenge towards its huge potential applications in electronic and photonic devices. Here, we are reporting about the role of the copper substrate purity and its crystallographic orientation in the quality of the graphene grown using a low pressure chemical vapor deposition technique. Graphene is grown on three different (Cu-I, Cu-II and Cu-III) substrates of different purity under analogous conditions of optimized pre-growth annealing and cleaning processes. Irrespective of the purity level of all the substrates, it is demonstrated that monolayer graphene (I-G'/I-G similar to 4) with different defect density is observed. The amount of defects and the defect density in the three samples is correlated with the different lattice planes of Cu, which are participating during the growth process. The size of the lattice grain advance upon annealing is observed and it is substrate purity dependent. This reveals that graphene growth is favored by either the (111) or the (100) plane or both. It is demonstrated that the substrate purity is extremely accountable for the growth of defect free monolayer graphene for device applications which require ballistic transport properties

Effect of filler content on the properties of expanded-graphitebased composite bipolar plates for application in polymer electrolyte membrane fuel cells

Minimization of the weight and volume of a hydrogen-based PEM fuel cell stack is an essential area of research for the development and commercialization of PEMFCs for various applications. Graphite-based composite bipolar plates have significant advantages over conventional metallic bipolar plates due to their corrosion resistivity and low cost. On the other hand, expanded graphite is seen to be a potential candidate for facilitating the required electrical, thermal and mechanical properties of bipolar plates with a low density. Therefore, in the present study, the focus is on minimization of the high loading of graphite and optimizes its composition to meet the target properties of bipolar plates as per the USDOE target. Three types of expanded graphite (EG)phenolic-resin-based composite bipolar plates were developed by partially replacing the expanded graphite content with natural graphite (NG) and carbon black as an additional filler. The three types of composite plate with the reinforcing constituent ratio EG: NG: R (25: 25: 50) give a bending strength of 49 MPa, a modulus of similar to 6 GPa, electrical conductivity > 100 S cm(-1), a shore hardness of 55 and a bulk density of 1.55 g/cc. The 50 wt% loading of resin is sufficient to wet the 50 wt% filler content in the composite plate. This study gives an insight into using hybrid reinforcements in order to achieve the desired properties of bipolar plates

Role of limited hydrogen and flow interval on the growth of single crystal to continuous graphene by low-pressure chemical vapor deposition

A method for defect-free large crystallite graphene growth. remains unknown despite much. research effort. In this work, we. discuss the role of flow duration of H-2 gas for the production of graphene as per requirement and production. at a minimum flow rate considering the safety issue of hydrogen utilization. The copper substrate used for growth was treated for different time intervals (0 to 35 min) in H-2 flow prior to growth. Structural and chemical changes occurring. in the copper substrate surface were. probed by grazing incidence. x-ray diffraction and x-ray photoelectron spectroscopy. The results were correlated with the Raman spectroscopy data, which can quantify the quality of graphene. With increasing. H-2 flow interval, secondary nucleation sites were observed and growth favored. few-layer graphene structures. The surface-adsorbed oxygen molecules and its conversion to an. OH terminated surface. with increasing hydrogen flow interval was found to be a key factor in. enhancing nucleation density. The Stranski-Krastanov type of nucleation was observed for samples grown with different time intervals of H-2 treatment, except 5 min of H-2 flow prior to growth for which the Volmer-Weber type of growth favored. monolayer graphene crystallite growth