National Institute Of Materials Physics - Romania

Publications

5781 articles found

3251. Microwave Investigations on Some Microstrip Left-Handed Structures

Authors: Banciu, MG; Mihai, IA; Militaru, N; Lojewski, G; Petrescu, T

Published: 2009, TELSIKS 2009, VOLS 1 AND 2, +, DOI:

Microstrip structures with left-handed properties are investigated in frequency domain. A method of extracting material effective parameters from the two-port scattering parameters is developed and applied to the proposed left-handed structures.

3252. The Influence of Growth Conditions on the Annealing of Irradiation Induced EH6,7 Defects in 4H-SiC

Authors: Pintilie, I; Lovlie, LS; Irmscher, K; Wagner, G; Svensson, BG; Thomas, B

Published: 2009, SILICON CARBIDE AND RELATED MATERIALS 2008, 615-617, 372, DOI: 10.4028/www.scientific.net/MSF.615-617.369

Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by deep level transient spectroscopy after irradiation with 6 MeV electrons or 1.6 MeV protons. The influence of silane and propane flows used during the epilayers growth on the behaviour of radiation induced EH6,7 levels is studied. Samples grown under different conditions were investigated: 1 sample grown in steps of different C/Si ratio obtained by changing the propane flow only; 1 sample grown in steps of different C/Si ratio obtained by changing the silane flow only; 2 samples grown with a C/Si ratio of 1.5 but with different flows of propane and silane. These investigations revealed that the low thermal stability of EH6,7 (the defects anneal out at temperatures as low as 750K) is due to the magnitude of silane now used during the growth irrespective of the C/Si ratio. A possible structure of the EH6,7 defect is discussed.

3253. Phase diagram of a lattice of pancake vortex molecules

Authors: Tanaka, Y; Crisan, A; Shivagan, DD; Iyo, A; Shirage, PM; Tokiwa, K; Watanabe, T; Terada, N

Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1131, DOI: 10.1016/j.physc.2009.05.202

On a superconducting bi-layer with thickness much smaller than the penetration depth, lambda, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

3254. Influence of Ionizing Radiations (Electrons and Gamma) on the Electrical Characteristics of LGS Resonators

Authors: Mateescu, I; Georgescu, S; Iliescu, B; Enculescu, I; Georgescu, R; Oproiu, C; Ghita, G

Published: 2009, FERROELECTRICS, 389, 31, DOI: 10.1080/00150190902987517

In this paper results concerning the changes of the electric characteristics of langasite resonators irradiated with electron and gamma rays are reported. For both electron and gamma irradiations the quality factor increases significantly, presumably due to the re-distribution of the point defects. Preliminary optical investigations in UV-VIS domain confirm the modification of defect structure.

3255. VIBRATIONAL PROPERTIES OF POLYANILINE FUNCTIONALIZED PbI2

Authors: Baltog, I; Baibarac, M; Mihut, L; Preda, N; Velula, T; Bucur, C; Husanu, M

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 688, DOI:

Functionalization of PbI2 with polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES) is demonstrated by Raman spectroscopy. Two functionalization methods were used: electrochemical polymerization of aniline onto the PbI2 modified Pt electrode and the mechanico-chemical reaction between PANI and PbI2. The functionalization induces changes in the Raman spectrum of PbI2 that consist in the appearance of new Raman lines with the peaks at 80, 144 and 170 cm(-1) The first line is the signature of the "stacking faults" that disrupt the stacking sequence of layers I-Pb-I atomic layers along the c crystalline axis by the intercalation of polymer molecules The bands at 144 and 170 cm(-1) are attributed to a vibrational mode associated to the Pb-NHR"(2) (R" = C6H4) bond.

3256. Radio proximity Doppler sensor with high K dielectric materials

Authors: Nicolaescu, I; Radu, A; Ioachim, A; Vizitiu, C

Published: 2009, 2009 EUROPEAN RADAR CONFERENCE (EURAD 2009), +, DOI:

One of the most important trend in electronic devices manufacturing is miniaturisation. Among other techniques used to decrease the physical dimensions of microwave devices one is to employ materials with high permitivity [1], providing that the dimension of the device is proportional to the wavelength in the material, which is square effective permittivity times less than the wavelengths in free space. The paper shortly presents the manufacturing process to obtain a high permittivity ZST ((Zr-0.8, Sn-0.2)TiO4) material used to build a dielectric resonator oscillator, which is used as a proximity Doppler sensor. Computed and experimental results as well as the procedure to measure the parameters of the Doppler sensor are presented. The sensor described in the paper may be considered as a short range radar device.

3257. Raman and FTIR spectroscopy as valuable tools for the characterization of polymer and carbon nanotube based composites

Authors: Lefrant, S; Baibarac, M; Baltog, I

Published: 2009, JOURNAL OF MATERIALS CHEMISTRY, 19, 5704, DOI: 10.1039/b821136a

The combination of the unique properties of carbon nanotubes (CNTs) with conjugated polymers makes their combined composite materials interesting as multifunctional systems with great potential. Supercapacitors, lithium rechargeable batteries, sensors, photovoltaic cells and photodiodes, optical limiting devices, solar cells, high-resolution printable conductors, electromagnetic absorbers and advanced transistors are among the most promising applications. Knowledge of the molecular structure of such compounds is essential for a better use, and for that reason vibrational spectroscopies are fruitful techniques. Therefore, this feature article presents recent progress in the characterization of composites based on conjugated polymers and carbon nanotubes. The contribution of Raman scattering and FTIR spectroscopy to establish the type of interaction between the two constituents will be discussed for different cases, i.e. bi-layers of polymers and carbon nanotubes, doped conjugated polymers with carbon nanotubes and covalently functionalized carbon nanotubes with conjugated polymers. In addition, surface enhanced Raman scattering (SERS) has also proven to be a suitable technique for characterization by providing signal enhancements, allowing for instance the detection of reactions at interfaces or the exploitation of properties associated with nanostructures. As an example, an extra increase of the Raman signal of a polymer deposited on a carbon nanotube thin film demonstrates the generation of surface plasmons in metallic tubes.

3258. DEFECT PRODUCTION IN SILICON AND GERMANIUM BY LOW TEMPERATURE IRRADIATION

Authors: Lazanu, S; Lazanu, I; Lepadatu, A; Stavarache, I

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

In this communication, we study the production of defects by energetic ions in silicon and germanium, at very low temperatures, as dependencies of non-ionizing energy loss and number of displacements on the ion kinetic energy, and also the partition of the energy deposited between ionization, creation of defects and phonons, short time after the interaction.

3259. Analysis of the Electron Traps at the 4H-SiC/SiO2 Interface of a Gate Oxide Obtained by Wet Oxidation of a Nitrogen pre-Implanted Layer

Authors: Pintilie, I; Moscatelli, F; Nipoti, R; Poggi, A; Solmi, S; Svensson, BG

Published: 2009, SILICON CARBIDE AND RELATED MATERIALS 2008, 615-617, 536, DOI: 10.4028/www.scientific.net/MSF.615-617.533

This work is focusing oil the effect of a high concentration of nitrogen (N) introduced by ion implantation at the SiO2/4H-SiC interface in MOS capacitors. The N implanted sample (N-interface similar to 1 x 10(19) cm(-3)) is compared with a non-implanted one (N-interface similar to 1 x 10(16) cm(-3)) by means of the electron interface trap density (D-it). The Dit is determined via High-Low frequency C-V method and Thermal Dielectric Relaxation Current (TDRC) technique. It is shown that the TDRC method, mainly used so far for determination of near interface oxide charges, call be exploited to gain information about the D-it too. The determined value of D-it in the N-implanted sample is nearly one order of magnitude lower than that in the sample without N implantation. Good agreement between the TDRC results and those obtained from High-Low frequency C-V measurements is obtained. Furthermore, the TDRC method shows a high accuracy and resolution of D-it,evaluation in the region close to the majority carrier band edge and gives information about the traps located into the oxide.

3260. Surface states- and field-effects at p- and n-doped GaAs(111)A/solution interface

Authors: Scurtu, R; Ionescu, NI; Lazarescu, M; Lazarescu, V

Published: 2009, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 11, 1770, DOI: 10.1039/b817045b

We have investigated the behaviour of n- and p-doped GaAs(111) A electrodes in sulfuric acid solution by electrochemical impedance spectroscopy (EIS) and second harmonic generation (SHG) measurements. The potential dependence of the SHG response was found to be closely related to the changes in the surface state population, as revealed by analysis of the impedance data. The nature of the majority of carriers turned out to be a key factor in shaping the surface state- and field-effect on the second harmonic generation process.