Ahmed Sayeed

Some unusual features in the Raman spectrum of amorphous carbon films obtained by pyrolysis of maleic anhydride

Laser micro-Raman spectroscopic measurements were done on the amorphous conducting carbon films obtained from maleic anhydride by pyrolysis process. We have found a predominant broad peak around 1140 cm−1, in addition to the normally observed peaks in amorphous carbons around 1350 and 1600 cm−1, and peak of medium intensity around 800 cm−1. Here we discuss the possibility of conjugated polymer like bond alternating structure which can give rise to these unusual Raman features.

D.C. conductivity measurements on amorphous conducting carbon

Amorphous conducting carbon films are obtained by pyrolysis of PTCDA (perylene tetracarboxylic dianhydride) at different temperatures (in the range 700-1000°C) and their DC conductivity is studied as a function of temperature in the range 4.2-300 K. It is observed that the conductivity has an activated temperature dependence with small activation energies (0.02-0.004 eV). The effects of pyrolysis temperature and also of heat treatment after preparation are studied. It is observed that the conductivity increases and the activation energy decreases with the increasing pyrolysis temperature. Heat treatment of samples at temperatures higher than that of pyrolysis has a similar effect on properties, even though the structure does not appear to depend appreciably on the pyrolysis temperature.

Electronic properties of ion irradiated amorphous carbon films prepared by plasma assisted CVD method

Abstract Amorphous hydrogenated carbon films were prepared by plasma assisted CVD method. Their dc conductivity was studied as a function of temperature in the range of 300 K to 10 K. Films were then subjected to high energy (170 MeV) ion irradiation. After irradiation a marked change was observed in the conductivity and its temperature dependence. The conductivity decreased by 2–3 orders of magnitude and a gap appeared in the electronic structure. UPS studies of the material show a decrease in the π states of the electronic density of states spectrum. A change in the C1s peak shape was observed in XPS study of the irradiated carbon film.

Rotation of propane molecules in supercages of Na-Y zeolite

Rotational dynamics of propane in Na-Y zeolite at room temperature is studied by molecular dynamics (MD) simulations and quasi-elastic neutron scattering (QENS) measurements. It is found that propane undergoes very fast rotational motion in the cages of Na-Y zeolite as first observed in the MD study and later confirmed by the QENS measurements. The dynamics of propane is described by isotropic rotational diffusion on a sphere of radius 1.88 ( +/-0.05) Angstrom, which is also the average distance of the hydrogen atoms from the center of mass of the propane molecule. The rotational diffusion constant as obtained from the QENS and MD simulation is in close agreement. This is the first ever study of the rotational dynamics of propane in a zeolite.

Low temperature conductivity of irradiated amorphous conducting carbon

Abstract Conducting carbon films prepared by pyrolysis of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) were subjected to high energy ion irradiation with I 13+ ions (170 MeV). Different doses in the range 10 11 –10 13 were used. XRD observation (at room temperature) and electrical conductivity measurements down to 6.3 K were carried out on these films before and after irradiation. XRD shows that the structure remained amorphous as before. The temperature dependence of conductivity showed an interesting change below about 20 K, suggesting an emergence of a mobility gap in the electronic structure.

Structure of highly conducting amorphous carbon

We report on neutron diffraction study of a new form of conducting amorphous carbon up to Q similar to 14.5 Angstrom(-1). The bond distances from first two peaks in g(r) are 1.45 and 2.49 Angstrom, very similar to those in sputtered truly amorphous carbon films (Li and Lannin, Phys. Rev. Lett. 65 (1990) 1905). The first coordination number is 3.1 (+/- 0.1) indicating predominantly sp(2) hybridisation (ideal no. = 3). However, S(Q) itself shows vestiges of (0 0 2), (1 0) and (1 1) peaks, typical of glassy carbon (Mildner, J. Non-Cryst. Solids 47 (1982) 391)