JOURNAL OF SCIENCES (ISLAMIC AZAD UNIVERSITY)
Year:2005 | Volume:15 | Issue:55 (PHYSIC ISSUE)|Papers Count:13

Implantation of nitrogen in aluminum has been investigated by many authors and the results are partly different. In this study nitrogen ion implantation at doses from 4x1017 to 1X1019 ions/cm2 and energy of 80 keV in pure aluminum without any thermal annealing is investigated. By means of x-ray diffractometry the phase composition was characterized. Nitrogen and aliminium nitride distribution in samples at different doses was analyzed using SIMS. Hardness of samples before and after implantation was tested by Vickers instrument. The results show that the hardness of samples after ion implantation process and because of formation of aluminium nitride phase increases dramatically, but aho\e the dose of  5x1018 ions/cm2 it decreases.

Positronium Annihilation Lifetime Spectroscopy (PALS) is an extremely useful probe of the free volumes. There exist a linear relationship between free volumes size and the lifetime of ortho-positronium trapped in that volume and is usually described in the framework of simplified model, proposed by Tao-Eldrup et al. In the model the positronium trap has spherical shape and the potential is rectangular one (RTE model) with infinite depth. In spite of its simplicity in most cases the model gives proper value of o-Ps lifetime and its zero-point energy in the trap. It can be also easily extended toward nonspherical and large-size free volumes in this case. The location of Ps on higher excited levels of a particle in the potential well (population of particle states lying above the zero-point energy) has to taken into account.

A new kind of high power tunable radiation source, where the short electromagnetic pulse is generated by a perpendicularly magnetized plasma wake is studied. A gas jet flow is used to generate the sharp boundary plasma. Wakefield is excited by a mode locked Ti:sapphirc laser beam operating at 800 nm wavelength with the pulse width of 100 fs (FWHM) and maximum energy of 100 mJ per pulse with 10 Hz repetition rate. Different nozzles are used in order to generate different densities and gas profile. The neutral density of gas jet flow is measured with a Mach-Zehnder interferometer. Strength of the applied external dc magnetic field varies from 0 to 8 kG in the interaction region normal to the direction of laser pulse propagation. The frequency of the emitted radiation with the pulse width of 200 ps (detection limitation) is in the millimeter wave range. Radiation is polarized perpendicularly to the laser pulse propagation direction and dc magnetic field lines. Radiation propagates mainly in the forward direction. Intensity of the radiation in different plasma densities and different magnetic field strengths has been observed.

The high coercivity medium is necessary for magnetic information storage. The time variation of magnetization in a varying field is studied for fabricated Fe and FeCo high coercivity samples. The rate of magnetization reversal with different sweep-rates for magnetic field has been obtained by the hystersis loops. With the present method we can determine this quantity, just performing VSM measurements.

The aim of this work was to establish the basic characteristics of a relatively new type of two beam interferometer and to adapt this device to the measurement of Doppler temperature in the upper atmosphere. The emissions which would be obvious candidates for an investigation of these temperatures are the (OI)21 red line and the (OI)32 green line at l 6300 and 5577°A espectiveety Nightglow measurements from Mt.Sinhgah, pune (lat.18° N,long.73° E), with WAMI two-beam interferometer, the apparent intensity in the zenith was normally in the range of 900-300R and corresponding the Doppler temperature of 100-600K° K.

Recalling the construction of the two-point functions of free quantum scalar field in Hilbert space, we have calculated the two-point functions for free quantum scalar field in Krein space hown that of all singularities only the natural delta function singularity remains in the two-point functions for Krein space quantization. Proposed PA CS numbers: 04.62.+v, 98.80. Cq, 12.10.Dm.

Silver films of 80 to 230 nm thicknesses were deposited on glass substrates at 400 K substrate temperature. Their optical properties were measured by spectrophotometery in the spectral range of 185 - 3300 nm. Kramers Kronig method was used for the analysis of the reflectivity curves of silver films to obtain the optical constants of the films. The influence of substrate temperature on the microstructure of thin metallic films [Structure Zone Model (SZM)] is well established (Movchan and Demchishin (1969); Thornton (1975); Savaloni and coworkers (1992, 1995, 2002)), while there have been some works on the influence of film thickness and morphology (Messier (1986), Savaloni (1995), Grovenor (1984)), deposition rate (Savaloni (1992, 1995)) and deposition angle (Savaloni and Bagheri- Najmi (2002)). The Effective Medium Approximation (EMA) analysis was used to establish the relationship between the SZM and EMA predictions. Good agreements between SZM as a function of film thickness and the values of volume fraction of voids obtained from EMA analysis, is achieved. The unusual (anomalous) behavior of the void fraction as a function of wavelength for different deposition conditions, in certain wavelength region is explained, to be due to the roughness value of the film surface, which corresponds to this wavelength region scattering from the surface roughness, and suggestion is given 2 that, this phenomena may be used as a technique for the roughness estimation of surfaces.

In this paper we discuss the usual derivation of Hawking radiation for a spherical symmetric black hole and the problem connected with the appearance of high frequencies in the derivation of Hawking radiation. The important view of this paper is that problem may be overcomed if one takes the back reaction effect into account. We try to solve the problem by a heuristic method; this will confront us with the well known cosmological constant problem.

The diamond films were deposited on Si substrates by DCHFCVD technique at different nucleation time, substrate-filament distance and substrate temperature. Scanning electron microscopy and Raman spectroscopy reveal that the substrate temperature in the range of 600- soot has negligible effect on the diamond nucleation density and the film quality. On the contrary, the distance and the nucleation time effect were observed clearly on the deposited films. We could also modify the quality of the film by help of the hydrogen ions bombardment.

The q-deformation of d-boson limit of interacting d-boson model in vibrational region is analyzed. The angular momentum part deformation is preferred, rather than SU (1.1) quasi spin part of Hamiltonian. The energy levels of Cu and Pt are also studied.

In this report we represent results, which we achieved from the measurements of magnetic susceptibility changes and electrical resistivity changes versus temperature for inter-metallic compounds with Gd2AuxAl1-x formula. All of samples have same crystalline structure. For all samples, we witness increase in Curie temperature with increase of x parameter, but X(T) abates. In the measurement of the resistivity for compounds with x = 0.4 value, it was observed as Kondo behavior, we observed a 3% enhancement in T~ 80° K. We can consider this temperature, which illustrates to form a new phase, beginning of appearance of the ferromagnetic phase coexistence as second phase. Admittedly, a virtual band accumulates free electros around Gd ion by 4f layer and system forms a canted configuration. We can attribute this configuration as a competition between two different phenomenons, i.e. RKKY inter-ionic exchange interaction and Kondo cloud formation.