48 research outputs found
Interplay between Nitrogen Dopants and Native Point Defects in Graphene
To understand the interaction between nitrogen dopants and native point
defects in graphene, we have studied the energetic stability of N-doped
graphene with vacancies and Stone-Wales (SW) defect by performing the density
functional theory calculations. Our results show that N substitution
energetically prefers to occur at the carbon atoms near the defects, especially
for those sites with larger bond shortening, indicating that the defect-induced
strain plays an important role in the stability of N dopants in defective
graphene. In the presence of monovacancy, the most stable position for N dopant
is the pyridinelike configuration, while for other point defects studied (SW
defect and divacancies) N prefers a site in the pentagonal ring. The effect of
native point defects on N dopants is quite strong: While the N doping is
endothermic in defect-free graphene, it becomes exothermic for defective
graphene. Our results imply that the native point defect and N dopant attract
each other, i.e., cooperative effect, which means that substitutional N dopants
would increase the probability of point defect generation and vice versa. Our
findings are supported by recent experimental studies on the N doping of
graphene. Furthermore we point out possibilities of aggregation of multiple N
dopants near native point defects. Finally we make brief comments on the effect
of Fe adsorption on the stability of N dopant aggregation.Comment: 10 pages, 5 figures. Figure 4(g) and Figure 5 are corrected. One
additional table is added. This is the final version for publicatio
Preparation and morphology of electrically conductive and transparent poly(vinylchloride)-polypyrrole composite films
The chemical process of preparing poly(vinylchloride)-polypyrrole composite films with high electrical conductivity and transparency has been studied. Pyrrole has been diffused into the poly(vinylchloride) matrix in the swelling medium of n-hexane and acetone mixture. The oxidative polymerization of the diffused pyrrole in the binary solvent system of acetonitrile and methanol gives high conductivity of the polypyrrole as well as the good penetration of the oxidant into the PVC polymer matrix. The analytical testing of the composite film shows the formation of homogeneous mixture of polypyrrole and poly(vinylchloride) conductive layer within the 1.0μm of thickness on the film surface. The transparency of the composite film showed about 50-60% at 500 nm. The electrical conductivity of the composite was about 20 s/cm. © 1993 Springer-Verlag