National Institute Of Materials Physics - Romania

Publications

5714 articles found

1701. Orientation of the nanocrystallites in AlN thin film determined by FTIR spectroscopy

Authors: Antonova, K; Szekeres, A; Duta, L; Stan, GE; Mihailescu, N; Mihailescu, IN

Published: 2016, INERA CONFERENCE 2015: LIGHT IN NANOSCIENCE AND NANOTECHNOLOGY (LNN 2015), 682, DOI: 10.1088/1742-6596/682/1/012024

Aluminum Nitride (AlN) films were deposited at 450 degrees C in nitrogen ambient at a pressure of 0.1 Pa and at a laser incident fluence of similar to 3 J/cm(2) and pulse repetition rate of 40 Hz. Grazing Incidence X-ray Diffraction patterns evidenced the presence of nanocrystallites in the amorphous AlN matrix. In the FTIR spectra the characteristic Reststrahlen band of AlN crystal with a hexagonal lattice is observed but it is quite broadened (950-550 cm(-1)). The angular dependence of the reflectance spectra in p-polarised incidence radiation demonstrates the sensitivity of the A(1)LO phonon mode of the AlN nanocrystallites to their orientation toward the normal to the substrate surface. With decrease of the incidence beam angle the intensity of the A(1)LO phonon mode diminishes and softening of the resonance frequency occurs.

1702. Adhesion evaluation of different bioceramic coatings on Mg-Ca alloys for biomedical applications

Authors: Bita, AI; Stan, GE; Niculescu, M; Ciuca, I; Vasile, E; Antoniac, I

Published: 2016, JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY, 30, 1983, DOI: 10.1080/01694243.2016.1171569

The aim of this study was to evaluate the adhesion of different bioceramic coatings deposited by radio frequency magnetron sputtering on the biodegradable implant-type magnesium-calcium (MgCa) alloys. Hydroxyapatite (HA) and bioactive glass (BG) were chosen as coating materials, due to their remarkable biological potential. The morphology, composition, structure and adhesion of the deposited thin coatings was characterized by scanning electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy and pull-out adherence measurements. A variation of the coating-to-substrate adhesion has been recorded and correlated with the physico-chemical results. The bonding strength values of the coatings were promising (being superior to the ISO13779-2:2008 fabrication standard for load-bearing biomedical coatings), and thus, encourage us to further proceed with the biological evaluation of the HA or BG coatings-MgCa substrate couples.

1703. Magnetoelastic properties in polycrystalline ferromagnetic shape memory Heusler alloys

Authors: Sofronie, M; Tolea, F; Crisan, AD; Popescu, B; Valeanu, M

Published: 2016, 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21), 2, 1537, DOI: 10.1016/j.prostr.2016.06.194

The influence of the heat treatments on the martensitic transformation, magnetic properties and thermo- and magnetic induced strain on Ni50Fe20Ga27Cu3 ferromagnetic shape memory alloy prepared as ribbons by melt spinning technique are investigated. The degree of atomic order as effect of different thermal treatments produces important changes in the magneto-crystalline anisotropy of the martensite phase. The anomalies evidenced in the thermo-and magnetic-strain curves are discussed and correlated with the thermo-magnetic data. The transformation-induced strains with and without magnetic field have been measured, the results setting out the influence of the pre-martensitic transformation. Copyright (C) 2016 The Authors. Published by Elsevier B.V.

1704. Studies of Aperture-Coupled Rectangular Dielectric Resonator Antenna Arrays

Authors: Turcan, MG; Moni, MV; Banciu, G

Published: 2016, 2016 INTERNATIONAL CONFERENCE ON COMMUNICATIONS (COMM 2016), 120, DOI:

In this paper, the design of aperture-couplet rectangular dielectric resonator antennas arrays is illustrated. The effect of slot feed on the dielectric resonator antenna (DRA) and the effect of the spacing between array elements is observed. This paperwork can be useful for WLAN applications with the operating frequency 5.8 GHz.

1705. Theoretical investigation of a Ge 2D photonic crystal by optical reflectivity correlated with band distributions

Authors: Popescu, DG

Published: SEP-OCT 2016, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 18, 774, DOI:

A two dimensional photonic crystal with hexagonal symmetry is investigated by finite-difference time-domain and finite difference frequency-domain theoretical calculations. The system consist in a germanium substrate patterned with holes of different radii, varying from 0.1 alpha to 0.45 alpha, The photonic band gaps (PBGs) and the reflectance spectra allow a complete characterization of the structure. It was shown the presence of PBGs at telecommunication wavelengths which makes the present systems suitable for optoelectronic applications, representing a potential alternative to Si-based technology

1706. MODEL OF ENERGY EXCHANGE THROUGH ELECTRON-PHONON COUPLING DURING TRANSIENT PHENOMENA IN MATERIALS FOR DETECTORS

Authors: Lazanu, S; Lazanu, I

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 1023, DOI:

The direct detection of dark matter candidates, for which semiconductor materials are used, is based on the detection of low energy selfrecoils. We show that the corrections to the energy partition curves due to the energy exchange during the transient processes modify the predictions of the standard Lindhard theory. These effects, calculated in the frame of a new model developed by the authors, depend on the initial temperature at which the detector operates, and on the energy of the recoil. Most of the available experimental data accumulated during more than fifty years. support these results.

1707. Direct bandgap GeSn light emitting diodes for short-wave infrared applications grown on Si

Authors: von den Driesch, N; Stange, D; Wirths, S; Rainko, D; Mussler, G; Stoica, T; Ikonic, Z; Hartmann, JM; Grutzmacher, D; Mantl, S; Buca, D

Published: 2016, SILICON PHOTONICS XI, 9752, DOI: 10.1117/12.2211641

The experimental demonstration of fundamental direct bandgap, group IV GeSn alloys has constituted an important step towards realization of the last missing ingredient for electronic-photonic integrated circuits, i.e. the efficient group IV laser source. In this contribution, we present electroluminescence studies of reduced-pressure CVD grown, direct bandgap GeSn light emitting diodes (LEDs) with Sn contents up to 11 at.%. Besides homojunction GeSn LEDs, complex heterojunction structures, such as GeSn/Ge multi quantum wells (MQWs) have been studied. Structural and compositional investigations confirm high crystalline quality, abrupt interfaces and tailored strain of the grown structures. While also being suitable for light absorption applications, all devices show light emission in a narrow short-wave infrared (SWIR) range. Temperature dependent electroluminescence (EL) clearly indicates a fundamentally direct bandgap in the 11 at.% Sn sample, with room temperature emission at around 0.55 eV (2.25 mu m). We have, however, identified some limitations of the GeSn/Ge MQW approach regarding emission efficiency, which can be overcome by introducing SiGeSn ternary alloys as quantum confinement barriers.

1708. The combined action of methanolysis and heterogeneous photocatalysis in the decomposition of chemical warfare agents

Authors: Petrea, N; Petre, R; Epure, G; Somoghi, V; Tanase, LC; Teodorescu, CM; Neatu, S

Published: 2016, CHEMICAL COMMUNICATIONS, 52, 12959, DOI: 10.1039/c6cc07551g

We report the applicability of a hybrid system comprising a La3+-based catalyst and an Au/TiO2 photocatalyst in the decomposition of chemical weapons. This system is able to perform complete degradation of soman, sarin and VX in less than 1 minute under low basic conditions and visible light irradiation.

1709. Non-volatile memory structures with Ge NCs-HfO2 intermediate layer

Authors: Palade, C; Slav, A; Lepadatu, AM; Maraloiu, AV; Lazanu, S; Logofatu, C; Teodorescu, VS; Ciurea, ML

Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 166, DOI:

The structure and charge storage properties of a trilayer structure with Ge nanocrystals embedded in HfO2 oxide were studied. The trilayer structure HfO2/Ge-HfO2/HfO2/p-Si was prepared by magnetron sputtering and subsequent rapid thermal annealing at 600 degrees C. The TEM investigations reveal the formation of Ge NCs embedded in crystalline HfO2 at the position of the Ge-HfO2 layer. The capacitors were made by Al evaporation on both front and backside of the trilayer structure. The C-V characteristics show a counterclockwise hysteresis with large memory window of 0.85 V which is given only by the contribution of the Ge NCs embedded in HfO2. The I-V characteristics show an asymmetric behavior, the currents are three times higher for the negative voltage than the positive one.

1710. MODIFICATION OF LINDHARD ENERGY PARTITION FOR LOW ENERGY RECOILS IN GERMANIUM AND SILICON FOR DETECTORS DUE TO ELECTRON PHONON COUPLING

Authors: Lazanu, S; Lazanu, I

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 603, DOI:

One of the methods of direct detection of the massive component of dark matter is the registration of self-recoils in semiconductor detectors at cryogeniC temperatures after the WIMPS scattering. In this contribution, after a short presentation of Lindhard curves, derived from the integro-differential equations of the general theory, we discuss the discrepancies between experimental data and theoretical predictions, as well as the corrections suggested in the literature. A new correction is proposed, which is due to the energy transfer between the electronic and atomic subsystems in the solid during the transient phenomena following the primary interaction, and some numerical results are presented.