National Institute Of Materials Physics - Romania

Publications

830 articles found

601. COMMUTON - A NEW CONCEPT IN SWITCHING MATERIALS

Authors: Popescu, M; Velea, A; Lorinczi, A; Sava, F

Published: MAR-APR 2009, JOURNAL OF OVONIC RESEARCH, 5, 34, DOI:

A switching unit can be defined as the smallest unit that preserves the property of switching in memory materials. Atomic switching unit is discussed, molecular switching units are described and supramolecular units in phase change materials are evidenced and discussed. The "commuton", as basic switching unit, could give more insight into the particular properties of the switching phenomena in various solid materials.

602. PHASE CHANGE MATERIALS: CHEMICAL BONDING AND STRUCTURAL PROPERTIES

Authors: Velea, A; Popescu, M

Published: SEP-DEC 2009, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 10, 236, DOI:

The phase change materials are the most important materials in the class of chalcogenides (combination of chalcogens (S, Se and Te) with metalloids or metals). The outstanding property of these materials is the switching from a high electrical resistivity state to low electrical resistivity state and back under a moderate voltage. The thin film materials are used in computer memories, CD and DVD devices with performing speed and storage capacity. We have studied several thin solid films made of Ge-Sb-Te in order to assess the switching quality of different compositions. In order to systemize the whole class of chalcogenide phase change materials we have investigated the correlation between different crystallo-chemical parameters and the ionicity of the elements. Binary and ternary compounds are distributed into several distinct groups. The most favorable phase change materials are situated in a specific range of mean ionicity and mean glass formation ability. The results give the possibility to design new compositions with better switching properties.

603. Radiation induced defects in Pb2+-doped LiF crystals

Authors: Somma, F; Montereali, RM; Vincenti, MA; Polosan, S; Secu, M

Published: 2009, 2008 INTERNATIONAL CONFERENCE ON LUMINESCENCE AND OPTICAL SPECTROSCOPY OF CONDENSED MATTER, 2, 221, DOI: 10.1016/j.phpro.2009.07.013

The influence of Pb2+ doping on the optical properties of LiF crystals before and after irradiation with X-ray was studied by using optical absorption and photoluminescence measurements. After irradiation it was observed an increase of the absorption due to primary and aggregate electronic defects together with a higher photoluminescence signals associated with the F-2 and F-3(+) colour centres in doped samples compared with the undoped ones.

604. Study of Ester-Type Liquid Crystals by TSDC and Optical Investigations

Authors: Manaila-Maximean, D; Rosu, C; Zgura, I; Frunza, L; Stoenescu, D

Published: 2009, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 512, 2012, DOI: 10.1080/15421400903050830

We study ester-type liquid crystal, 4'-cyanophenyl 4-n-hexyl benzoate and its homologue 4'-cyanophenyl 4-n-pentyl benzoate. We used the Thermally Stimulated Depolarization Currents method and found information about phase transition temperature, and activation energies. The temperatures of phase transitions were compared to those obtained by classical DSC/DTA measurements. Simultaneously with the TSDC, we measured the optical transmission; we found a decrease of the optical transmission when it was measured after a greater pre-applied polarizing electric field.

605. Interference lithography using chalcogenide inorganic photoresist

Authors: Indutnyy, IZ; Popescu, M; Lorinczi, A; Sava, F; Min'ko, VI; Shepeliavyi, PE

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3192, DOI:

There was investigated the application of inorganic photo-resist based on three-component chalcogenide films for fabrication of submicrometer periodic relief on silicon wafers using interference lithography. For this purpose. technological process of resistive two-layer chalcogenide-Cr mask formation on a silicon surface was developed, and silicon anisotropic etching was optimized, too. This technology has been used for the fabrication of diffraction gratings and two-dimensional periodic structures on Si (100) surface. The obtained relief patterns were used to form photonic structures by oblique deposition of silicon monoxide in vacuum.

606. Electrical transport in crystalline perylene derivatives films for electronic devices

Authors: Stanculescu, A; Stanculescu, F; Socol, M; Grigorescu, O

Published: DEC 2008, SOLID STATE SCIENCES, 10, 1767, DOI: 10.1016/j.solidstatesciences.2008.03.023

This paper presents investigations on the electrical transport phenomena in perylene and PTCDA emphasising the particularities of the charge carrier injection at the contacts with inorganic semiconductors (Si) and metals (Cu, Al) and the effect of the supplementary organic layer (ZnPc, alpha-NPD) on the electrical conduction. The I-V characteristics for different delay and integration times, at forward and reverse bias, have evidenced a dominant ohmic behaviour of these SIS and MIS structures at low voltage (<0.1 V) and limitations of the current induced by the space charge and trap charge at voltages >1 V. An intermediate organic layer (ZnPc) with higher ionisation potential than PTCDA and lower electron affinity than perylene improves the charge carrier injection and the conduction properties of the Si/PTCDA/Si and forward biased Cu/perylene/Si heterostructures. No increase in the hole injection was obtained in Si(p)/perylene/Si(p) heterostructure introducing an a-NPD layer. (C) 2008 Elsevier Masson SAS. All rights reserved.

607. The modification induced by UV radiation in spherical microlenses made of glassy arsenic sulphide

Authors: Rusu, M; Velea, A; Popescu, M

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3171, DOI:

Spherical arsenic chalcogenide glass microlenses have been attached to optical fibers. The assembly was subjected to UV-radiation for different time intervals in different conditions of temperature. As a consequence, the focusing of the beam changes due to the modification of the refractive index, and of the structure, induced by photo-melting followed by crystallization. In the same time for high irradiation times the habitus of the lens changes into a prismatic one due probably to photomelting of the glass accompanied by a crystallization process.

608. Alternating barium stearate and copper stearate LB thin films

Authors: Popescu, M; Lorinczi, A; Velea, A; Sava, F

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3415, DOI:

Alternating layers based on copper and barium stearate have been prepared. The interlayer distance for both type of stearates have been determined by X-ray diffraction. It was found that the interlayer distance for an alternating assembly depends on the actual type of the stearate layer. Thus we demonstrated the possibility to control the inter-layer distance by choosing an appropriate sequency of layers. It is suggested that such layers may serve as high precision thickness standard at the angstrom level.

609. SBN thin films growth by RF plasma beam assisted pulsed laser deposition

Authors: Scarisoreanu, ND; Dinescu, G; Birjega, R; Dinescu, M; Pantelica, D; Velisa, G; Scintee, N; Galca, AC

Published: NOV 2008, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 93, 800, DOI: 10.1007/s00339-008-4753-2

SBN thin films were grown on MgO and Silicon substrates by PLD and RF-PLD (radiofrequency assisted PLD) starting from single crystal Sr0.6Ba0.4Nb2O6 and ceramic Sr0.5Ba0.5Nb2O6 stoichiometric targets. Morphological and structural analyses were performed on the SBN layers by AFM and XRD and optical properties were measured by spectroellipsometry. The films composition was determined by Rutherford Backscattering Spectrometry. The best set of experimental conditions for obtaining crystalline, c-axis preferential texture and with dominant 31 degrees in-plane orientation relative to the MgO (100) axis is identified.

610. Optical spectroscopy and thermoluminescence of electrolytically colored KCl:Tl+ crystals

Authors: Polosan, S; Enculescu, M; Secu, M; Apostol, E

Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3011, DOI:

The paper presents the spectroscopic properties of electrolytic colored KCl:Tl and KCI:Tl+Ca crystals and the assignments of the new defects which are formed during electron injection process. The new formed defects Tl-0 and Tl-0+Ca2+ with the metal in the anionic sites, presents very high photoluminescence properties in the near infrared region. Together with those centers, the F-centers, their aggregates and the holes centers are formed during electrolytic coloring process. Their properties were studied by optical absorption (OA), photoluminescence (PL) and thermoluminescence (TL) measurements and compared with those obtained by ionizing irradiation in uncolored KCl:Tl crystals. The results suggest a more efficient Tl+-> Tl-0 process in the case of Ca2+ codoped samples due to the prolonged time of electrons injection, low temperature and high electric field.