arXiv subjects

Debabrata Pramanik

Publications and source records attributed to Debabrata Pramanik.

21 records · Page 2Linked to original sources

arXiv2018

Opening of large band gap in metallic carbon nanotubes by mannose functionalized dendrimers: Experiments and theory

Despite many theoretical schemes, the direct experimental observation of supramolecular control on band gap opening in single-walled carbon nanotubes (SWNT) is still lacking. We report experimental and theoretical demonstration of metal to semiconductor transition with precisely measured large band gap in SWNTs due to the wrapping of mannose functionalized poly (propyl ether imine) dendrimer (DM) molecules. Semiconductor behaviour of SWNT-DM complex is comprehensively established with a band gap value of ~ 0.45 eV measured using scanning tunnelling spectroscopy (STS), ionic liquid top gated field effct transistor (FET) characteristics and Raman spectroscopy. Further, a validated molecular picture of SWNT-DM complex obtained from fully atomistic molecular dynamic (MD) simulations was used to carry out ab-initio density functional theory (DFT) and GW calculations of the electronic structure, evaluating experimentally estimated band gap value. We attribute this large band gap opening in SWNTs to the complexation induced asymmetric strain developed in the carbon-carbon bond length.

cond-mat.mtrl-sci↗

arXiv2016

Dendrimer Assisted Dispersion of Carbon Nanotubes: A Molecular Dynamics Study

Various unique physical, chemical, mechanical and electronic properties of carbon nanotube (CNT) make it very useful materials for diverse potential application in many fields. Experimentally synthesized CNTs are generally found in bundle geometry with a mixture of different chirality and present a unique challenge to separate them. In this paper we have proposed the PAMAM dendrimer to be an ideal candidate for this separation. To estimate efficiency of the dendrimer in dispersion of CNTs from the bundle geometry, we have calculated potential of mean forces (PMF). Our PMF study of two dendrimer wrapped CNTs shows lesser binding affinity compared to the two bare CNTs. PMF study shows that the binding affinity decreases for non-protonated dendrimer and for the protonated case, the interaction is fully repulsive in nature. For both the non-protonated as well as protonated cases, the PMF increases with increasing dendrimer generations from 2 to 4 gradually compare to the bare PMF. We have performed PMF calculations with (6,5) and (6,6) chirality to study the chirality dependence of PMF. Calculated PMF for protonated dendrimer wrapped chiral CNTs is more compared to the protonated dendrimer wrapped armchair CNTs for all the generations studied. However, for non-protonated dendrimer wrapped CNTs such chirality dependence is not very prominent. Our study suggests that the dispersion efficiency of protonated dendrimer is more compared to the non-protonated dendrimer and can be used as an effective dispersing agent in dispersion of CNT from the bundle geometry.

cond-mat.soft↗

arXiv2012

Structure of Carbon Nanotube-dendrimer composite

Using all atomistic molecular dynamics (MD) simulations we report the microscopic picture of the nanotube-dendrimer complex for PAMAM dendrimer of generation 2 to 4 and carbon nanotube of chirality (6,5). We find compact wrapping conformations of dendrimer onto the nanotube surface for all the three generations of PAMAM dendrimer. The degree of wrapping is more for non-protonated dendrimer compared to the protonated dendrimer. For comparison we also study the interaction of another dendrimer, poly(propyl ether imine) (PETIM), with nanotube and show that PAMAM dendrimer interacts strongly as compared to PETIM dendrimer as is evident from the distance of closest approach as well as the number of close contacts between the nanotube and dendrimer. We also calculate the binding energy between the nanotube and the dendrimer using MM/PBSA methods and attribute the strong binding to the charge transfer between them. Dendrimer wrapping on CNT will make it soluble and can act as an efficient dispersing agent for nanotube.

cond-mat.soft↗