National Institute Of Materials Physics - Romania

Publications

860 articles found

431. Nano and Microtechnology for Monitoring Stem Cell Differentiation

Authors: Cheran, LE; Cheran, A; Lupu, AR; Popescu, T

Published: 2016, STEM CELLS BETWEEN REGENERATION AND TUMORIGENESIS, 320, DOI:

This chapter gives an overview of the new micro- and nano-technologies designed to monitor SC differentiation in the context of their potential applications in disease modeling, tissue engineering, regenerative medicine, as well as drug screening and toxicology. Representative examples of such applications are presented and the crucial importance of the differentiation processes for the safety of SC therapies is discussed. The roles of the main factors that influence SC differentiation are briefly summarized and the vital need to control and monitor the differentiation process using non-invasive methods is emphasized. The basic principles of new micro- and nano-technologies for monitoring SC differentiation are presented, with special focus on the use of acoustic vibrational fields to characterize SC. Literature studies on SC differentiation, involving methods based on Impedance Sensing (IS), Surface Enhanced Raman Spectroscopy ( SERS), Fourier Transformed Infrared (FTIR) spectroscopy, Microelectrode Array (MEA) sensors, Light-addressable Potentiometric Sensors (LAPS), Field-effect Transistors ( FET), Surface Plasmon Resonance (SPR) and Quartz Crystal Microbalance (QCM), are briefly described.

432. FTDT investigations for fabrication of sub-wavelength metal wire-grid polarizes and quarter waveplate

Authors: Cotirlan-Simiontuc, C; Logofatu, C; Iordache, G; Rizea, A; Ursu, DV

Published: NOV-DEC 2016, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 18, 927, DOI:

Ultracompact polarization components modeled and analyzed with Finite Difference Time Domain Photonics Simulation Software (FTDT) are: a wire-grid linear polarizer and a quarter waveplate for infrared (IR) domain. They will be integrated into a polarization state analyzer (PSA). The components will be manufactured with metamaterials (MTMs). These are composite materials consisting of artificial meta-atoms, i.e. conductive nano- or micro-structures regularly arranged in a dielectric or semiconductor matrix. These conductive structures are made-up smaller than the wavelength of the radiation work. MTMs show extraordinary electromagnetic properties, typically not found in nature, such as negative refractive index. They increase the interaction between radiation and matter. The use of optical polarization components in IR imaging systems dedicated to difficult conditions of visibility is a must, as it allows improving performance and reducing the dimension of optoelectronic devices used in air, car and naval navigation. We will focus on developing the components for applications of imaging polarimetry in long-wave infrared (LWIR) range.

433. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

Authors: Oumezzine, M; Galca, AC; Pasuk, I; Chirila, CF; Leca, A; Kuncser, V; Tanase, LC; Kuncser, A; Ghica, C; Oumezzine, M

Published: 2016, DALTON TRANSACTIONS, 45, 15040, DOI: 10.1039/c6dt01914e

Epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO3 (STO) (001) substrates. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) investigations revealed that the films are epilayers with a four-fold symmetry around the [001] direction. Cross-sectional TEM and the presence of Pendellosung fringes in the XRD profiles demonstrate smooth interfaces. The STO substrate induces an in-plane compressive strain, which leads to a slight tetragonality of the film structure. The epilayers exhibit paramagnetic-to-ferromagnetic phase transitions at the Curie temperature T-C (286 K), close to room temperature. The magnetization easy axis lies in the film plane along the [100] direction of the (001) substrate. The magnetic entropy change (Delta S-M) associated with the second-order magnetic phase transition was determined via magnetization measurements in the temperature range between 210 and 350 K under different magnetic fields. The relative cooling power (RCP) of this film is about 220 J kg(-1), somewhat lower than that of bulk Gd (410 J kg(-1)) for a 50 kOe field change, making the LBTMO ferromagnetic thin films a promising candidate for micro/nanomagnetic refrigeration around room temperature. The proposed universal curve provides a simple method for extrapolating Delta S-M in a wide range of fields and temperatures, thus confirming the order of the magnetic transition in this system. The magnetic entropy (Delta S-M)(max) around T-C is proportional to (mu H-0/T-C)(2/3) in agreement with the mean-field theory, indicating the existence of long-range ferromagnetic interactions in epitaxial LBTMO thin films.

434. 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.

435. 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.

436. 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.

437. 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.

438. 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.

439. 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.

440. 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.