Proceedings of the Technical Session of Institute of Physics, Sri Lanka 6 (1990) c1

National Telecommunication Network Configuration
G.J.N.L. Soysa
Planning & Information Systems, Telecommunication Department, Colombo

The paper gives an overview of the Telecommunication Network in Sri Lanka comprising of Switching. Transmission and Subscriber network. Signaling, Routing and Charging methods used will also be discussed. The discussion will also include a brief history, and the future of the national telecommunication network.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 6 (1990) c2

Electron vs Photon
I. Dayawansa
Department of Physics and Telecommunication Engineering, University of Moratuwa

The Electron and the Photon are two particles with several similarities. Electron was identified as a very versatile particle and the Technology is dominated by semiconductor Electronics particularly after the birth of Microelectronics, or the Integrated circuits. Electronic communication and Electronic Computers are common examples by which the Electron made its presence felt.

However the Electron cannot beat the photon in speed. The Photon can be obtained easily, though at the expense of higher cost, and of course using an electron. Thus electronic communication is now being taken over by Optical communication as the volume of traffic increases or the speed of data transfer increases. Optical switching, optical signal processing, Integrated Optics and Optoelectronic Integration, indicates that Optics will take over most of Telecommunications and Computers in the next decade with the electron and the Photon working of the two most versatile particles in nature.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 6 (1990) c3

Current-Voltage (IV) and Capacitance-Voltage (CV) Measurements on the GaAs/AlxGai-xAs Heterojunction
K. Premaratne
Department of Physics, University of Peradeniya, Peradeniya

In this Work the GaAs/AlxGai-xAs heteroJunction has been studies using both CV and IV techniques. The material was grown by Molecular Beam Epitaxy. Measurements were performed on GaAs/AI.3Ga.7As heterojunctions having carrier concentrations in the range of 10¹⁶ to 10¹⁷ cm^-3. The conduction band offset estimated from both methods was found to be about 65%. This is in good agreement with the values obtained from other electrical and optical methods.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 6 (1990) c4

Ionic Conductivity Enhancement in Li₂SO4 based Binary Systems by composite Effect
M.A.K.L. Dissanayake, M.A. Careem and P.W.S.K. Bandaranayake
Department of Physics, University of Peradeniya, Peradeniya

Ionic conductivity of the Li₂SO₄-Li₂CO₃, Li₂SO₄-CaSO₄, Li₂SO₄-MgSo₄ and Li₂SO₄-Li₂WO₄ binary salt systems has been measured below 500^oC using the complex impedance technique. Ionic conductivity in the two-phase regions of all four systems shows a significant enhancement evidently caused by the composite effect, arising from the grain boundary contribution to the conductivity. In each of the systems, the eutectic composition, having the smallest grain size and the maximum interfacial area between grains, exhibits the maximum conductivity enhancement observed in the two-phase region.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 6 (1990) c5

Effect of Addition of Different Elements on Superconducting Properties of the Bi-Sr-Ca-Cu-O System
S.H.S.P. Samarappuli¹ and M.A.K.L. Dissanayake^2
1 Institute of Fundamental Studies, Hantana Road, Kandy
² Department of Physics, University of Peradeniya, Peradeniya

Effect of Sn addition on superconducting properties of Bi4Sr3Cu4Oy and Ni, P, and Ag addition on superconducting properties of (Bio.7Pbo.3) Sr Ca Cu1.5Oy have been investigated using electrical resistivity, ac magnetic susceptibility and X-ray diffraction. Sn addition appears to favour the formation of the 85 K phase and reduce the (Bio.7Pbo.3) Sr Ca Cu1.5-xNixOy material, Ni appears to replace Cu up to about x=0.2 composition resulting a drop in Tc. Future addtion of Ni up to x=0.95 gives rise to a multiphase material but the superconductivity is retained with a lower Tc. For x>1, however, the material becomes semi-conducting.

Addtion of P a drop in (Bio.7Pbo.3) SrCaCu1.5Oy using Ca3(Po4)2 gives rise to a drop in Tc from 100 K to 70 K appears to favour the formation of the 85 k phase. Incorporation of a few atomic % of Ag in to this material appears to reduce the normal state resistivity significantly, without affecting the Tc.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 6 (1990) c6

Langmuir-Blodgett Films and their Applications
M.A. Careem
Department of Physics, University of Peradeniya, Peradeniya

Many organic substances such as fatty acids, alcohols, chlorophylls, proteins spread into insoluble monomoleculer layers on water surface. Irving Langmuir and Katherene Blodgett developed a fascinating technqiue of 'building up' multi-layer films on solid substrates by raising the latter repeatedly across the monolayer covered water surface. With this technique a new field in thin film investigation opened up. Unlike the films prepared by conventional methods, these films have attractive features of controllable thickness down to a monolayer~2 nm and the possibility of obtaining relatively ordered form without voids and inhomogeneities.

The procedure and apparatus used for the preparation of some of these films and their properties are described. Recent developments in the deposition technique and the possible uses of these films in electronic devices and in solar energy conversion are also discussed in this review.