National Institute Of Materials Physics - Romania

Publications

5781 articles found

4401. Characterization of the interstitial voids in the structural model of amorphous silicon derived from the diamond-like lattice

Authors: Sava, F

Published: 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 1080, DOI:

The simulation of interstitial void evolution in a model of crystalline silicon subjected to topological disordering revealed that the void size distribution broadens and shifts towards smaller mean diameter size, when the lattice disordering increases. The size distribution is not gaussian and the mean diameter of the voids is lower than the crystalline value. The calculation of the structure factor corresponding to void configuration evidences the absence of the short and long range order and point out to the presence of the medium range order.

4402. Microstrip patch antenna with dielectric substrate

Authors: Sandu, DD; Avadanei, O; Ioachim, A; Banciu, G; Gasner, P

Published: 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 1387, DOI:

The paper refers to the study of patch antennas with a high permittivity dielectric substrate ((Zr-0.8 Sn-0.2)TiO4) obtained at National Institute of Materials Physics Bucharest. Because of the high value of the permittivity of the substrate material it was necessary to perform a comparative investigation of different prototypes and arrays. It was considered two substrate thickness h(1)=1mm and h(2)=2mm and two frequencies f(1)=2.4 GHz and f(2)=1.8 GHz. For each case we presented the radiation pattern in the two principal planes (E and H) and input impedance. Also, some radiation pattern for rectangular array with n=4, 16, 36 patches are presented. In the Conclusion section a discussion on the suitability of patch antennas with high permittivity substrate is done.

4403. Structure and properties of high-temperature annealed CVD diamond

Authors: Ralchenko, V; Nistor, L; Pleuler, E; Khomich, AV; Vlasov, I; Khmelnitskii, R

Published: OCT-NOV 2003, DIAMOND AND RELATED MATERIALS, 12, 1970, DOI: 10.1016/S0925-9635(03)00214-0

Effects of high temperature, up to 1700 degreesC, annealing in vacuum of CVD diamond on its structure, optical and mechanical properties are investigated. Translucent polycrystalline diamond films of thickness 0.06-1.0 mm were grown by microwave plasma CVD method, and examined with transmission electron microscopy, optical absorption spectroscopy, and three-point bending technique to measure the fracture strength. A progressive darkening of the samples, with appearance of absorption features specific for graphite-like material, was observed upon annealing at temperatures above 1300 degreesC. The formation along grain boundaries of amorphous carbon and/or well crystallized graphite layers, 5-20 nm thick, as well as intra-granular graphite islands, was directly observed with TEM. This internal diamond-graphite transformation process can be described by two activation energies, both values being much less than those known for the surface graphitization of diamond. The fracture strength of the diamond films increases up to 50% with annealing temperature (1460-1640 degreesC), this being ascribed to a build up of compressive stress as a result of local diamond-graphite conversion. (C) 2003 Elsevier Science B.V. All rights reserved.

4404. BNT ceramics in paraelectric phase: Dielectric properties

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Plapcianu, C; Alexandru, H; Berbecaru, C; Stoica, G

Published: 2003, 2003 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 318, DOI: 10.1109/SMICND.2003.1252443

The paper describes the investigations of Nd doped Barium titanate (BNT) ferroelectric ceramic materials prepared by solid state reaction techniques. The decrease of the Curie temperature with the increase of the Nd2O3 concentration from 0 to 28 wt % was observed. High density values of BNT ceramics were obtained by adding 0.5 mol % PbO substitutional for BaO. The samples were sintered at temperatures T-s=1200divided by12600degreesC. At room temperature, the materials are in paraclectric phase, suitable for high frequency applications.

4405. Analysis of LGS resonators using the finite plate technique

Authors: Mateescu, I; Kosinski, J; Pastore, R; Johnson, G

Published: 2003, PROCEEDINGS OF THE 2003 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM & PDA EXHIBITION JOINTLY WITH 17TH EUROPEAN FREQUENCY AND TIME FORUM, 747, DOI:

This paper presents the results of an analysis using the finite plate technique of Y-cut langasite plan-parallel resonators with Al and Ag electrodes. We have extracted values for the piezoelectrically stiffened elastic stiffness c(66)(D), the elastic stiffness c(66)(E), the piezoelectric stress constant e(11), and the dielectric permittivity epsilon(11)(S). The measured material constants are in very good agreement with other reported values. This paper will present our new results on the langasite samples, and will include a comparison between an analysis of the data using the measurement method recommended by the current IEEE Standard on Piezoelectricity and the finite plate technique.

4406. Structural characterisation of advanced silicides

Authors: Bender, H; Richard, O; Nistor, L; Gutakovskii, A; Stuer, C; Detavernier, C

Published: 2003, MICROSCOPY OF SEMICONDUCTING MATERIALS 2003, 462, DOI:

The structural characterization by means of transmission electron microscopy (high resolution, electron diffraction, energy filtered, in-situ heating) is discussed for some advanced silicide processes. Both blanket layers and narrow line structures are investigated. Special attention is given to the influence of the initial layer stack on the epitaxial growth modes in the layer.

4407. Chemical interaction of chalcogenide vitreous semiconductors with absorbed impurities induced by gamma-irradiation

Authors: Shpotyuk, O; Kovalskiy, A; Kavetskyy, T; Golovchak, R; Popescu, M

Published: 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 1185, DOI:

The chemical interaction of chalcogenide vitreous semiconductors (ChVS) with absorbed impurities induced by high-energetic (E>1 MeV) gamma-irradiation has been investigated at the example of vitreous v-As2S3. Radiation-induced processes of oxidation, hydrogenization, hydratation, carbonization and hydrocarbonization have been observed in this material after prolonged gamma-irradiation and studied using IR spectroscopy (4000-400 cm(-1)), laser mass-spectroscopy methods and electron microprobe analysis.

4408. ZST type material for dielectric resonators and substrates for hybrid integrated circuits

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Stoica, G; Annino, G; Cassettari, M; Martinelli, M; Ramer, R

Published: 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 1398, DOI:

(Zr0.8Sn0.2)TiO4 ceramic (ZST) has been prepared and characterized. The effects of sintering parameters such as sintering temperature, sintering time and NiO addition on structural and dielectric properties were investigated. The material has a dielectric constant epsilon(r) similar to 36.0 and high values of the Q . f product from 32,170 to 50,000 at microwave frequencies. The tan delta values are decreased by low level doping, of NiO, while the temperature coefficient of the resonance frequency tau(f) takes values in the range (-2divided by+4) ppm/degreesC. Investigations on whispering gallery modes revealed low dielectric losses in millimeter wave domain. An intrinsic quality factor of 480 was measured at 136.3 GHz. Dielectric resonators and substrates of ZST material were manufactured. The dielectric properties make the ZST material very attractive to microwave and millimeter wave applications such as filters, hybrid microwave integrated circuits, etc.

4409. Investigations on the langasite resonators by X-ray topography

Authors: Mateescu, I; Capelle, B; Detaint, J; Johnson, G; Dumitrache, L; Bran, C

Published: 2003, PROCEEDINGS OF THE 2003 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM & PDA EXHIBITION JOINTLY WITH 17TH EUROPEAN FREQUENCY AND TIME FORUM, 641, DOI:

In this paper the results of electrical measurements of the mass-loading influence on Y-cut langasite resonator parameters are compared with those obtained by X-ray topography analysis of the same resonators. Based on the Ballato's transmission-line analogs of the trapped-energy ;resonators vibrating in thickness-shear mode [1], the mass-loading effect on resonator characteristics was studied. The effective mass-loading, motional inductance and quality factor of langasite resonators were computed. Sawyer plan-parallel polished Y-cut langasite resonators with 14mm diameter, 5 MHz resonant frequency, Au electrodes of 7 mm diameters and various thickness were used in experiments. X-ray topography measurements were performed by conventional transmission Laue setting using the white beam synchrotron radiation on fundamental, third and fifth overtones. The results are in agreement with those obtained by electrical measurements. The comparison of X-ray diffraction topography images previously performed on AT-cut quartz resonators with X-ray topographs on langasite resonators pointed out that the Y-cut langasite resonators are less influenced by the mass-loading than the AT-cut quartz resonators.

4410. Raman spectroscopy of amorphous carbon modified with iron

Authors: Yastrebov, SG; Ivanov-Omskii, VI; Dumitrache, F; Morosanu, C

Published: 2003, SEMICONDUCTORS, 37, 476, DOI: 10.1134/1.1568471

Raman spectroscopy has been employed to study spectra of the vibrational frequencies of carbon in the range 1000-1800 cm(-1) in amorphous carbon films modified with iron. The content of iron in a film has been set technologically by varying between the samples the area ratio of the graphite and iron parts of the target and monitored by Rutherford backscattering. Amorphous carbon layers containing 3, 26, 38, and 54 at. % iron have been obtained. The Raman spectra have the form of a broad band with features that are characteristic of amorphous carbon and lie at 1332 cm(-1) (D-band) and 1552 cm(-1) (G-band). At iron content of 38 and 54 at. %, the spectrum breaks up into a number of bands, which points to fragmentation of the matrix of amorphous carbon with increasing iron content. It is shown that the integral amplitude of scattering decreases nonlinearly with increasing iron content in a sample. The effect is analyzed in terms of a model that accounts for the linear dependence of the rate at which the number of atoms contributing to the scattering changes with the atomic fraction of carbon relative to the total number of carbon atoms in the film. (C) 2003 MAIK "Nauka/Interperiodica".