National Institute Of Materials Physics - Romania

Publications

5975 articles found

5261. Determination of valence band offsets from Si/Si1-xGex/Si using temperature-dependent current-voltage characteristics

Authors: Chretien, O; Souifi, A; Apetz, R; Vescan, L; Luth, H; Popescu, C

Published: MAR 1 1996, JOURNAL OF APPLIED PHYSICS, 79, 2466, DOI: 10.1063/1.361174

We have determined the valence band discontinuity Delta E(upsilon) of strained Si1-xGex on unstrained (100) Si using temperature-dependent current-voltage characteristics (I-V-T) of Si/Si0.83Ge0.17/Si heterostructures. In a first step, the measurements were performed on a Schottky diode, and in a second step, on a sample with ohmic contacts. The values of Delta E(upsilon) obtained by these two different procedures are comparable. Moreover, they are in good agreement with the theoretical value of Delta E(upsilon)=0.84x=143 meV predicted by Van de Walle measurements. (C) 1996 American Institute of Physics.

5262. Preparation and structure of ordered films of iron carboxylate complexes

Authors: Popescu, M; Turta, C; Meriacre, V; Zubareva, V; Gutberlet, T; Bradaczek, H

Published: MAR 1996, THIN SOLID FILMS, 274, 146, DOI: 10.1016/0040-6090(95)07080-X

Several iron complexes containing a tri-iron-oxo-cation linked to short chain fatty acids have been used in the preparation of films by self-assembling from solution on glass slides via two procedures: direct evaporation and dragging out. The ordered lamellar structure thus obtained has been investigated by X-ray diffraction. A relation between the lamellar spacing and the disorder in the film has been obtained from the X-ray diffraction data.

5263. Electronic structure and spectral characteristics of trinuclear iron(III) carboxylates

Authors: Spatar, FA; Meriakre, VM; Zubareva, VE; Ogurtsov, IY; Filoti, G; Turte, KI

Published: MAR 1996, KOORDINATSIONNAYA KHIMIYA, 22, 193, DOI:

5264. Hall effect and magnetoresistance in four-probe tight-binding mesoscopic rings

Authors: Gartner, P; Aldea, A

Published: MAR 1996, ZEITSCHRIFT FUR PHYSIK B-CONDENSED MATTER, 99, 373, DOI: 10.1007/s002570050050

The Hall effect and magnetoresistance of a mesoscopic system having a four-probe ring geometry are calculated in a tight-binding model, either ordered or disordered, as function of magnetic flux and Fermi energy. The changes induced in the spectrum by the magnetic field affect differently the Aharonov-Bohm (AB) oscillating pattern of the two resistances: after the gap reaches the Fermi energy, the Hall effect remains bounded while the magnetoresistance increases exponentially with the sample size. The results are shown to depend significantly on the number and geometry of the probes.

5265. Temperature induced surface transitions in liquid crystal tilted homogeneous cells

Authors: Moldovan, R; Frunza, S; Beica, T; Tintaru, M

Published: MAR 1996, LIQUID CRYSTALS, 20, 335, DOI: 10.1080/02678299608032042

Temperature induced surface transitions in liquid crystal tilted homogeneous cells are experimentally studied. The results are theoretically explained by an elastic theory of surface transitions and the resulting values for the effective splay-bend elastic constant (k) over bar(13) for each liquid crystal material are compared with the results from experience with other types of surface anchoring.

5266. Influence of pyrolization temperature on final characteristics of BSCCO ceramic produced by spray-frozen, freeze drying method

Authors: Badica, P; Aldica, G; Alexeev, AF; Gridasova, TY; Morozov, VV

Published: FEB 1 1996, JOURNAL OF MATERIALS SCIENCE LETTERS, 15, 188, DOI: 10.1007/BF00274446

5267. Spin probe investigation of molecular motions in polyepichlorohydrin .1.

Authors: Chipara, MI; Barb, D; Notingher, PV; Georgescu, L; Sarbu, T

Published: FEB 1996, POLYMER, 37, 712, DOI: 10.1016/0032-3861(96)83160-0

Spin probe investigations on the molecular motions in the glass transition range are reported. Within the free volume approximation, a Fox-Flory dependence of the narrowing temperature on the molecular masses is derived. The experimental results support this theoretical prediction. The glass transition temperature is estimated from the spin probe data, within various approaches, and compared to the results obtained by differential scanning calorimetry.

5268. Ag-substituted Al-Cu-Fe icosahedral phases

Authors: Manaila, R; Macovei, D; Jianu, A; Popescu, R; Nicula, R; Zavaliche, F; Devenyi, A; Xie, Y; Hu, T

Published: FEB 1996, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 193, 294, DOI: 10.1002/pssb.2221930202

The gradual substitution of Cu by Ag in the Al62Cu25.5-xAgxFe12.5 icosahedral phase (x less than or equal to 10) is investigated by X-ray diffraction from the viewpoint of the induced structural changes. The phonon and random phason disorders, estimated from diffraction linewidths, increase with x, the latter showing, however, an induction range of Ag concentrations. EXAFS results at the CuK and FeK edges show. for low Ag contents, and enhanced disorder in the first coordination sphere, partly relaxed for higher x values. The 6D hypercubic lattice parameter is found to be independent of the Ag content, despite the large diameter of monovalent Ag. The latter facts suggest a d-sp hybridization of the Ag bonds to the surrounding Al, taking place above a certain x value.

5269. The effect of Pt and Pd surface doping on the response of nanocrystalline tin dioxide gas sensors to CO

Authors: SchweizerBerberich, M; Zheng, JG; Weimar, U; Gopel, W; Barsan, N; Pentia, E; Tomescu, A

Published: FEB 1996, SENSORS AND ACTUATORS B-CHEMICAL, 31, 75, DOI: 10.1016/0925-4005(96)80018-9

SnO2 sensors were prepared by precipitating Sn(OH)(4) from an aqueous solution of SnCl4 or by evaporating SnO2 in the UHV. Subsequent X-ray and TEM measurements show grain sizes in the nanometer range after annealing at different temperatures or annealing times. The effect of Pt and Pd doping upon the response to CO is studied. Parameters, which we focused on, are sensor signal dependent on the operating temperature and dependent on the gas concentration. The results for ceramic sensors are compared with those for thin film sensors.

5270. The one-dimensional model of the off-centre potential of the fluorine ion in the NaBr lattice

Authors: Despa, F

Published: JAN 15 1996, JOURNAL OF MATERIALS SCIENCE LETTERS, 15, 173, DOI: 10.1007/BF00291458