The effect of sputtering current that flow in a carbon rod on the structural and transport properties of Si-C junction is studied. Si-C junction is fabricated by plasma sputtering in Argon gas atmosphere without catalysts with thickness of 20, 40 and 60 nm. Images of the specimen by scanning electron microscope (SEM) and atomic force microscope (AFM) show that the carbon layer is as carbon nanotubes with diameters about 20-30 nm. X-ray and Raman spectrums show peak characteristics of the carbon nanotubes, the G and D bands appear for all thicknesses indicating free of defect carbon nanotubes. Two parameters about the thickness of the carbon layer and the sputtering current for different thicknesses and currents were studied. Nanotubes evidence was clear. We noticed that the sputtering current and thickness of layers affect the structure of CNT layer leading to the formation of grains. Increasing plasma current led to decrease grain formation however increasing thickness ends to increase grain size; moreover it led to amorphous structure formation and this was proved through X-ray, Raman spectra and AFM images.

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The research studies the effect of the distance between the sample and the plasma sputtering source on the properties of the junction (silicon wafer-carbon nanotubes). The silicon wafer is fixed at (near, medium and far distances from the plasma source which is in the form of high purity graphite rod heated electrically). For the three cases, thickness of the sample is constant (20 nm). The samples were studied by scanning electron (SEM) and atomic force microscopes (AFM), X-ray and Raman spectra. For optimum distances the carbon layer is in the form of multi wall carbon nanotube (MWCNT). SEM images shows no formation of CNT on the Si wafer for near distance, which is consistent with the AFM images, X-ray and Raman spectrograms and no existence of characteristics (002) peaks whereas it appears for medium and longer distances, and by experience the optimum distance was found. This means that at closer distance high energy and high intensity plasma particles prevent the formation of CNT. This effect decreases with increasing distance of substrate from the graphite rod.

The aim of the research is to understand the mechanism of process of substitution of the ion 2 + Sr instead of La +3 in the superconductor 4 2 CuO La. Calculations of electrostatic potential(E. P.) for two probable positions is done to determine the site of minimum energy, the site of La around Cu ion is the minimum in energy on all the range of concentrations of the Sr ion. The changes in E. P. by substitution helps in understanding some aspects of the complex synthesis procedure of 4 2 CuO La compound and especially the high and the long period preparation temperature which gives full action of electrostatic forces.

In this research, the influence of calcium content on the binding energy and Cooper pairing is investigated for the high temperature superconducting () 1 2 3 7 Y Ca Ba Cu O x x − − δ compound where x = 0-0.2). This is done by using model considering that the formation of Cooper pairs happens during tunneling mechanism of holes between the two CuO 2 layers in the YCBCO crystal which are considered as forming adjacent potential wells. In this work, we make some modifications on the mentioned model and a modified equation for the binding energy as a function of Ca concentration is formulated to study the effect of Ca content by considering the change in the distance between the CuO 2 layer as a function of Ca. The calculated results agree very well with experimental results. This happens because the Ca 2+ substitution for Y 3+ leads to decreasing the distance between the two CuO 2 layers and hence potential energy of the system will be decreased. This leads to decreasing the binding energy between the Cooper pairs, and decreasing the distance between the two CuO 2 layers increasing the tunneling probability of holes between the two CuO 2 layers and thus increasing conduction mechanism and thus increasing current density, but this will decrease the energy gap and as a result decrease the critical temperature. The calculated results agree very well with experimental results.