National Institute Of Materials Physics - Romania

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847 articles found

421. MEMORY PROPERTIES OF GE NANOCRYSTALS-BASED CAPACITORS WITH DIFFERENT COMPOSITION OF INTERMEDIATE LAYER

Authors: Lepadatu, AM

Published: OCT-DEC 2016, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 17, 327, DOI:

In this work, the charge storage properties of trilayers with Ge nanocrystals (NCs) embedded in HfO2 matrix prepared by using two approaches for obtaining the intermediate layer with Ge NCs as nodes are investigated. Trilayer structures with tunnel and control oxides of HfO2, but with different intermediate layers of Ge and Ge-HfO2, respectively, were deposited by magnetron sputtering. Ge nanostructuring was achieved by subsequent rapid thermal annealing. Charge storage behaviour was studied by measurements of capacitance-voltage characteristics on MOS-like capacitors based on the annealed trilayers. The MOS samples with intermediate layer obtained by depositing a continuous Ge layer show hysteresis with memory windows up to similar to 1.3 V, while the ones with co-deposited Ge and HfO2 as intermediate layer present higher memory windows, similar to 1.8 V. In both cases, the memory windows are independent on the frequency demonstrating that the memory effect is due to storing the charge only inside Ge NCs. These show that the approach based on co-deposition of a Ge-HfO2 intermediate layer is more effective for charge storage with direct application in memory devices.

422. On the agent role of Mn2+ in redirecting the synthesis of Zn(OH)(2) towards nano-ZnO with variable morphology

Authors: Ghica, D; Vlaicu, ID; Stefan, M; Nistor, LC; Nistor, SV

Published: 2016, RSC ADVANCES, 6, 106741, DOI: 10.1039/c6ra23065b

One of the simplest routes to prepare polycrystalline Zn(OH)(2) is by coprecipitation, with zinc nitrate as a cation source. However, the addition of even minute amounts of manganese nitrate to the precursors used to prepare pure Zn(OH)(2) results in Mn2+ doped nanostructured ZnO. The comparison with other Mn2+ doped metal hydroxides prepared by the same coprecipitation method, involving metal nitrates precursors, shows that this behavior is unique, pertaining only to Zn(OH)(2). A systematic study of the samples prepared without and with variable amounts of Mn2+ ions, in the 1 to 5000 ppm nominal concentrations range showed that the re-routing of the reaction takes place even for the lowest nominal dopant concentration of 1 ppm. According to X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy investigations, both crystallite size and morphology of the resulting nanostructured ZnO samples varied with the Mn2+ nominal concentration. Moreover, quantitative electron paramagnetic resonance investigations showed that the incorporation rate of the Mn2+ ions at different sites in the nanostructured ZnO depended on the nominal Mn2+ concentration. The results are discussed in terms of the coordination properties of the Mn2+ and Zn2+ ions and the nature of the reaction precursors.

423. 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.

424. 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.

425. Fast atomic diffusion in amorphous films induced by laser pulse annealing

Authors: Teodorescu, VS; Ghica, C; Maraloiu, AV; Kuncser, A; Lepadatu, AM; Stavarache, I; Ciurea, ML; Scarisoreanu, ND; Andrei, A; Dinescu, M

Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 158, DOI:

Fast atomic diffusion was evidenced in the surface layer of amorphous thin films of oxides and semiconductors irradiated with low fluence UV pulse laser. This process takes place in a surface layer with a thickness related to the laser radiation absorption depth in the target material and was revealed by the cross section transmission electron microscopy studies. These high values of diffusivity can be explained by supposing the glass transition transformation in the amorphous structure, triggered by the action of the laser pulse field. This effect can have application for controlling structural modifications at nanoscale of the thin films surface and also for inducing structural modification of interfaces between the film and substrate.

426. Screen-printed Pb(Mg,Nb)O-3-PbTiO3 Thick Tilms on Ceramic Substrates for Sensor Applications

Authors: Ursic, H; Khomyakova, E; Drnovsek, S; Malic, B; Mercioniu, IF; Bencan, A; Makarovic, K; Schreiner, C; Ciobanu, R; Belavic, D; Bolado, P

Published: 2016, PROCEEDINGS OF THE 2016 INTERNATIONAL CONFERENCE AND EXPOSITION ON ELECTRICAL AND POWER ENGINEERING (EPE 2016), 58, DOI:

In this work the screen-printed piezoelectric 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) thick films were prepared on metalized low-temperature co-fired ceramic substrates. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators. The prepared thick films exhibit the piezoelectric coefficient d(33) equal to 120 pC/N.

427. Room temperature ammonia sensing with barium strontium titanate under humid air background

Authors: Simion, CE; Sackmann, A; Teodorescu, VS; Rusti, CF; Stanoiu, A

Published: DEC 1 2015, SENSORS AND ACTUATORS B-CHEMICAL, 220, 1246, DOI: 10.1016/j.snb.2015.07.045

Within the field of chemical gas sensing, ammonia detection represents one of the nowadays challenges, due to its adverse effects for human health. Real operating investigations are imposed by the high solubility potential of NH3 at room temperature. Thick films of Ba0.75Sr0.25TiO3 material have been investigated by means of electrical resistance and capacitance changes and correlated with the photoacoustic outputs. The experimental findings have been discussed in terms of Grotthuss mechanism, with respect to the ionic/electronic conduction within BST, toward ammonia detection enhanced by the presence of water vapors when operated at room temperature. So an appropriate NH3 sensing mechanism was proposed. (C) 2015 Elsevier B.V. All rights reserved.

428. Magnetization reversal via a Stoner-Wohlfarth model with bi-dimensional angular distribution of easy axis

Authors: Kuncser, A; Kuncser, V

Published: DEC 1 2015, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 395, 40, DOI: 10.1016/j.jmmm.2015.07.035

A numerical extension of the simple Stoner-Wohlfarth model to the case of bi-dimensional angular distributions of easy axis is provided. The results are particularized in case of step-like, Gaussian-like and user defined distributions. In spite of its simplicity, the model can be applied to magnetically textured thin films and multilayers with in-plane magnetic anisotropy, independently on the texture source. Exemplifications are provided for a simple ferromagnetic textured FeCo film as well as for a FeMn/FeCoi CufFeCo spin valve structure. (C) 2015 Elsevier B.V. All rights reserved.

429. Atomic scale elemental mapping of light elements in multilayered perovskite coatings

Authors: Negrea, RF; Teodorescu, VS; Ghica, C

Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 255, DOI: 10.1016/j.apsusc.2015.07.106

Spherical aberration corrected transmission electron microscopes offer unprecedented capabilities in materials structural characterization down to atomic resolution. Electron energy loss spectroscopy (EELS) - spectrum imaging (SI) and annular bright field (ABF) imaging allow to simultaneously identify both the position and nature of the atomic species in a crystalline material. These techniques, along with conventional high-resolution transmission electron microscopy are particularly useful in heterostructures interfaces like epitaxial multilayers characterization, for identifying possible atomic interdiffusion at sub-nanometric scale. This paper presents the structural and compositional microanalysis down to atomic resolution of an epitaxial BaTiO3/SrRuO3/SrTiO3 ferroelectric heterostructure using complex complementary analytical electron microscopy techniques. The atomic arrangement of both heavy and light atomic species across the interfaces in the BaTiO3/SrRuO3/SrTiO3 heterostructures is revealed. (C) 2015 Elsevier B.V. All rights reserved.

430. Pattern formation on silicon by laser-initiated liquid-assisted colloidal lithography

Authors: Ulmeanu, M; Petkov, P; Ursescu, D; Maraloiu, VA; Jipa, F; Brousseau, E; Ashfold, MNR

Published: NOV 13 2015, NANOTECHNOLOGY, 26, DOI: 10.1088/0957-4484/26/45/455303

We report sub-diffraction limited patterning of Si substrate surfaces by laser-initiated liquid-assisted colloidal lithography. The technique involves exposing a two-dimensional lattice of transparent colloidal particles spin coated on the substrate of interest (here Si) immersed in a liquid (e.g. methanol, acetone, carbon tetrachloride, toluene) to a single picosecond pulse of ultraviolet laser radiation. Surface patterns formed using colloidal particles with different radii in the range 195 nm <= R <= 1.5 mu m and liquids with differing indices of refraction (n(liquid)) are demonstrated, the detailed topographies of which are sensitively dependent upon whether the index of refraction of the colloidal particle (n(colloid)) is greater or smaller than n(liquid) (i.e. upon whether the incident light converges or diverges upon interaction with the particle). The spatial intensity modulation formed by diffraction of the single laser pulse by the colloidal particles is imprinted into the Si substrate.