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Review Paper
1.
Comparison of Photoinduced Atom Displacements in Glasses and Polymers
H.
Jain
When
exposed to visible-UV light, photoinduced atom displacement (PAD) may
occur in certain inorganic glasses as well as polymers, leading to similar
changes in their opto-electronic and structural properties. An
understanding of PAD is important for the use of these materials in
photonic applications such as optical storage, CD-RW, opto-mechanical
transducers, etc. In both classes of materials, PAD is caused by a
combination of electronic excitation and subsequent response of the
structure to the excited state configuration. There are indications of
photoinduced localized atomic restructuring as well as long-range
diffusion, which require bond-breaking. In spite of the initially
homogeneous, isotropic structure, the photoinduced effects can be
anisotropic, depending on the direction of polarization and/or the
direction of light propagation. In general, the PAD in polymers is much
larger but less stable than that in glasses, presumably due the greater
adaptability of polymer structure to the optically created polarization
and other stresses. A combination of these characteristics in a single
glass-polymer or organic-inorganic material is likely to yield superior
photoinduced properties. A comparative overview of PAD in inorganic
glasses and polymers is presented in this paper.
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Scientific and
Technological Researches
2.
Chalcogenide glasses – survey and progress
D.
Lezal
Chalcogenide
glasses are reviewed. The physical properties are discussed in relation to
the purity of the glass. The photo-luminescence properties and the
state-of-art of applications are presented.
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3.
Microhardness of Pb modified chalcogenide glasses
A.
K. Pattanaik, P. S. Robi, A. Srinivasan
Microhardness
of bulk PbxGe42-xSe58(3 ≤ x ≤
15), Pb20GexSe80-x(17 ≤ x ≤
24), PbxGe42-xSe48Te10(3 £
x £
15) and Pb20GexSe70-xTe10 (17 £
x £
24) glasses was measured at room temperature. In Pb20GexSe80-x
and Pb20GexSe70-xTe10 glasses,
microhardness attained a maximum value at the composition with 21 at. wt.
% Ge. In the case of PbxGe42-xSe58 and PbxGe42-xSe48Te10
glasses, the microhardness decreased with the addition of Pb. The
variation in microhardness with composition and the effect of Te
substitution on the microhardness of these glasses are discussed in the
light of the change in the average bond energy of the glasses.
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4.
On fabrication of large format optoelectronic elements
P. Sharlandjiev, B. Markova
We discuss different methods for synthesis and analysis
of large format optical elements with predetermined reflectance or/and
transmittance characteristics. Chemical vapor deposition, electron beam
evaporation and ion beam sputter deposition are well-established
techniques for production of optical coatings and multilayers. There are
some intrinsic limitations for the quality of such elements, i.e. position
of source, target and substrate. Holographic techniques are an alternative
to “classical” optical elements fabrication. We compare different
methods for analysis of the
optical response of large “classical” and holographic elements (Abélès
characteristic matrix and Lorenz – Mie theory) as well as some possible
applications, related to solar concentrators and holographic Fabry –
Perrot elements.
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5.
Optoelectronic properties of spray deposited SnO2:F thin films
for window materials in solar cells
E. Elangovan, K.
Ramamurthi
Spray pyrolysis
technique has been employed to prepare ~1.2 µm thick pure and fluorine
doped tin oxide films from SnCl2 precursor. The electrical and
optical studies on the as prepared films were carried out. The sheet
resistance was found to decrease with increasing doping concentration to a
minimum of 1.75 W/ÿ
for 15 wt. % of NH4F, but increased thereafter. The minimum
sheet resistance observed in the present study is the lowest among the
reported values for SnO2:F films prepared from SnCl2
precursor. The transmittance was found to increase with the increase in
fluorine concentration. The highest optical transmittance obtained is 85 %
(at 800 nm). The calculated reflectivity in the infrared region is in the
range of 94 - 98 % (for 5-30 wt% NH4F). On fluorine doping, the
figure of merit values of the tin oxide films were found to increase to a
maximum of 5.67 ´
10-2 (15 wt. % of NH4F) from 4.73´10-6
(at 800 nm) for undoped ones. The obtained values of figure of merit and
reflectivity are discussed in the context of the suitability of this
material for transparent and conducting window materials in heterojunction
thin film solar cells.
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6.
Effect of temperature annealing on periodically poled rare-earth
doped lithium niobate crystal
V.
Bermúdez, D. Callejo, E. Diéguez
Rare
earth doped Periodic Poled Lithium Niobate crystals prepared by the
off-centered Czochralski growth technique have been submitted to several
annealing proceses either at T>Tc as T<Tc. It
is shown that an annealing process at T>Tc eliminates the
periodic domain structure in the surface but not in the bulk crystal,
where the periodic structure is not damaged for a low cooling rate, while
it is strongly damaged for a quenching process. When the annealing process
is performed at temperatures very close to the Curie temperature but
below, the periodic domain structures do not disappear even from the
surface, but they are strongly damaged when temperature is cooled down
following a quenching procedure. When temperature is reduced following a
low cooling rate process the surface domain structure is not affected.
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7.
Periodically poled structures in lithium niobate crystals: growth and
photoelectric properties
I.
A. Ghambaryan, R. Guo, R. K. Hovsepyan, A. R. Poghosyan, E. S. Vardanyan,
V. G. Lazaryan
The
advantages of producing a periodically poled lithium niobate (PPLN)
structure during crystal growth process are the possibility to get thicker
and wider structures that leads to greater useful surfaces in addition to
the elimination of the subsequent poling process.
We report in
this paper a new technology of creating bulk periodically poled
LiNbO3 single crystals with antiparallel ferroelectric domains,
by direct electric field poling during growth processes. Growth system
configuration, crystal composition and geometry selection are explored to
allow successful control of the direction of spontaneous polarisation
using external electric field. PPLN crystal samples with
periodicity 10 - 200 mm
were grown using this electric field modulated growth technique. The
photoelectric and photorefractive properties of PPLN crystals were
investigated.
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8. Some optical
properties of BaO - PbO - B2O3 glasses
J.
Schwarz, H. Tichá
Glasses from the system
PbO-BaO-B2O3 with the value of the molar ratio R (=
PbO/B2O3) in the interval 0.125 £
R £
2.0, were prepared. The hydrostatic density, the softening temperature,
Raman and infrared reflectivity spectra and transmittivity in the UV-VIS
region of prepared glasses have been measured. The compositional
dependence of experimental values of optical gap and refractive index were
compared with the values calculated using the assumption of the additivity
of the “local gaps” and Maxwell-Garnet theory, resp. The agreement is
satisfactory. It is suggested
also that in the region where 0.125 £
R £
~ 0.6 the lead atoms behave rather as a network modifier, while at higher
values of R the lead atoms behave as network formers.
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9.
Growth and characterisation of InGaAs(P) by CBE technique
M. Udhayasankar, J. Kumar, P. Ramasamy
Growth
and evaluation of InGaAs(P) epilayers grown on InP by CBE technique for
optical telecommunication applications is discussed.
The grown InP epilayers have HALL mobility values of 70.000 and
2800 cm2/V.s with background impurities as low as 1 ´
1014 cm-3
and 2
´
1015 cm-3 at 77 K and 300 K respectively. FWHM of
the (004) Bragg reflection peak as narrow as 17 arcsec was obtained for
these samples by HRXRD measurements. RT PL measurements also show typical
spectra with a peak FWHM of about 19 nm. Lattice matched In0.53Ga0.47As
was grown on InP and the strain value of 0.34 µm thick layers was about
6.7 ´
10-4. The mobilities of the thick undoped ternary layer were
5970 (300 K) and 37,550 cm2/V.s (77 K) with carrier
concentration in the range of 1.2 ´
1015 – 4.2 ´
1014 cm-3. Be-doped In0.53Ga0.47As
layers with p300K = 9 ´
1018 cm-3 and µ300K
= 58 cm2/V.s were also grown on InP which exhibits a line
width (HRXRD) of nearly 25-30 arcsec. In1-xGaxAsyP1-y
quaternary epilayers (x = 0.24, y = 0.52) closely lattice matched to
InP have also been grown. The HRXRD pattern of the quaternary layers shows
a lattice mismatch of 2.4 ´
10-3 and a luminescence peak FWHM of 8 meV. Further, the
homogeneity of these layers was checked using FTPL study at different
positions of the full wafer and it was extremely good.
MQWs structures were also grown for the fabrication of SOA devices
and are characterised by PL, absorption, ECV measurements.
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10. Application
of microtechnology in biotechnology. Microarray analytical systems – an
overview
G. De Bellis , G. Caramenti, M.
Ilie, E. Cianci, V. Foglietti
The evolution of
modern biology, that recently entered the genome era, requires faster and
cheaper analytical systems. Techniques as microlithography, micromachining,
laser induced fluorescence detection, microfluidics contributed to the
development of the DNA microarray technology, having as result complex
analytical systems able to perform hybridization of nucleic acids in an
array format on small bidimensional surfaces, and also to process huge
quantities of information. The most significant achievements worldwide
obtained are presented illustrating the state of the art in this domain.
In order to automate the fluidic process involved in the DNA hybridization
three micromachining techniques, slightly differing from each other have
been approached by the authors team. Reservoirs with volumes ranging from
1nl to 2 ml in different materials
have been obtained by means of reactive ion etching of polyimide,
anisotropic etching of silicon respectively an optimised wet etching of
borosilicate glass as well as a low temperature bonding of borosilicate
glass on silicon nitride. One
obtained device has been tested in a Laser Induced Fluorescence detection
set-up.
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11.
Numerical study of the growth conditions in a MOCVD reactor: application
to the epitaxial growth of CdTe
R.
Tena-Zaera, I. Mora-Seró, C. Martinez-Tomas, V. Muñoz-Sanjosé
A
2-D model to simulate the gas flow in a horizontal MOCVD reactor has been
developed. This model takes into account the conservation equations
coupled with heat transfer and mass transport of the chemical species. For
the mathematical solution a commercial solver, that can be run in a
conventional personal computer, has been used. The influence of different
parameters such as total flow, partial pressures of precursors, reactor
pressure and substrate temperature on the gas flow and growth rate has
been studied. Diisopropyltelluride (DIPTe) and dimethylcadmium (DMCd) have
been used as precursors and H2 as carrier gas. The capabilities
of the used model for the numerical study in a conventional research or
production laboratory will be shown. The main
goal of this paper is both to offer a valuable tool for the numerical
simulation of the MOCVD system and to suggest some practical reflections
for the MOCVD experimental grower in order to facilitate the optimization
process in a reduced time.
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12.
Methylene - blue modified polypyrrole film electrode for optoelectronic
applications
R.
M. Ion , F. Scarlat, Fl. Scarlat, V. I. R. Niculescu
Organic semiconductors
have been the objects of considerable attention in recent years, both as
electrodes and photoelectrods in different applications. Radiation-induced
and electrochemical modification of polypyrrole film by incorporating of
large electro-active organic molecules is investigated in this paper.
Introduction in the polypyrrole (PPy) of methylene blue as counterion has
a strong effect on the electrochemical performance of PPy films. The UV -
VIS spectra of the films (fitted with Gauss type function) are also
evaluated. IR spectra are measured in order to proof the incorporation of
MB into polypyrrole film.
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13.
The effective pair potential calculations of molten NaCl and AgI
S.
Dalgiç
In
this work, we have calculated effective pair potentials for different Z
values of molten NaCl and AgI. We used the Huggins-Mayer potential form
parametrised by Fumi and Tosi for NaCl and the Vashishta-Rahman potential
form for AgI. The interionic interactions in this last system have been
modelled with the use of a semi-empirical rigid ion potential based on the
functional form originally proposed by Vashishta and Rahman in 1978. The
results show excellent agreement with those reported in other works.
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Short
Communications
14.
Grown periodically poled lithium niobate crystal: period stabilization
N.
F. Evlanova, I. I. Naumova, S. A. Blokhin, T. O. Chaplina,
G. D. Laptev, A. A. Novikov
High degree of the period stabilization and homogeneity of the regular
domain structure of the Nd:Mg:LiNbO3 crystals was obtained in
the growth process by the Czochralski method from melt with lithium
dioxide excess, in the direction along the normal to the {
} close packed face.
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Proceedings
of AMS Conference 2002
15. Soft Magnetic
Nanocrystalline alloys
J.
M. Grenèche
During
the last decade, nanocrystalline alloys have received a great interest
because of their unusual structural and magnetic properties. Their soft
magnetic features stimulated the fundamental research. This paper reports
some general structural, microstructural and magnetic aspects of soft
magnetic nanocrystalline alloys and reviews the different tools which are
commonly used to characterize these alloys. The state of art in research
and applications is assessed.
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16.
New ferromagnetic and functionally graded shape memory alloys
C.
M. Craciunescu, M. Wuttig
The
paper summarizes recent advances in shape memory alloy investigation with
focus on the path used to find new ferromagnetic shape memory alloys and
on the improvement of micro-actuation by thermoelastic control of the
phase transformation in graded shape memory alloy films. The first part of
the paper describes experimental results and theoretical considerations
concerning the search, fabrication and characterization of new Co-based
Heusler-type ferromagnetic shape memory alloys with focus on the CoNiGa
system. It is shown that CoNiGa alloys undergo a reversible thermoelastic
martensitic transformation in a wide temperature range, depending on the
composition and displaying a nickel-like saturation magnetization. The
second part of the paper takes into consideration the case of layered and
functionally graded microlayered films constructed by continuously
changing the temperature during the deposition process of NiTi alloys on
heated Si cantilever-type substrates. It is shown that – depending on
the deposition temperature and sequence of deposition - high actuation can
be achieved. The discussion takes into consideration the martensitic
transformation in layers under constraints from the substrate and/or the
neighboring microlayers. The best actuation can be obtained when
transformation starts and develops gradually from the top microlayer. This
was achieved in NiTi films deposited continuously on heating.
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17.
Spectroscopic characterisation of crystalline phases development from
amorphous precursors
S.
Simon
The
development of LaAl2.03B4O10.5 (124)
lanthanum aluminoborate crystalline phase from amorphous xerogels is
characterised by Magic Angle Spinning Nuclear Magnetic Resonance (MASNMR),
Electron Paramagnetic Resonance (EPR) and Fourier Transform Infrared (FTIR)
spectroscopies. The crystallisation of amorphous xerogels takes place
between 760 and 860 oC. The major changes are evidenced both in
the boron and aluminium surrounding. These structural results are
correlated with those obtained from 27Al and 11B MAS
NMR spectra. The boron environment is changed from three-coordinated in
amorphous samples to tetra-coodinated in the crystalline samples.
Aluminium occurs in amorphous samples as hexa-, penta- and
tetra-coordinated by oxygens while in the crystalline ones it appears
preponderantly penta-coordinated. From FTIR measurements it results, also,
that the local structure dramatically changes when in amorphous matrices
are developed crystalline phases. Three different sites for Fe3+
ions in crystalline samples were identified by EPR measurements.
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18.
MAS NMR and SEM study of local structure changes induced by heat treatment
in La2B4Al2O12
M.
Vasilescu, G. Borodi, S. Simon
Xerogels of
composition La2B4Al2O12,
treated between 200 and 1100°C,
are investigated by magic angle spinning nuclear magnetic resonance (MAS
NMR) and scanning electron microscopy (SEM). The 11B MAS NMR
results indicate the presence of tetra coordinated boron in all
investigated samples. For three coordinated boron, two sites were observed
one of them being present only after heat treatment above 860 °C
when the sample become crystalline. The mean values of the NMR parameters
like chemical shift, asymmetry parameter and quadrupolar coupling constant
are strongly influenced by the heat treatment temperature. SEM results are
correlated with them obtained by NMR.
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19. Structural and magnetic
investigations of transition metal ions in TeO2 based glasses
I. Ardelean,
S. Filip
Electron paramagnetic
resonance (EPR) and magnetic susceptibility measurements are performed on
xMnOm×(100-x)[70TeO2×25B2O3×5PbO]
glasses with MnOm Þ
Cr2O3 (0 < x £
20 mol %), Fe2O3 (0 < x £
20 mol %), MnO (0 < x £
40 mol %) or CuO (0 < x £
40 mol %). The EPR absorption spectra due to paramagnetic ions (Cr3+,
Fe3+, Mn2+ and Cu2+) in vitreous matrix
revealed the structural details of the diamagnetic host, the coordination,
distribution and valence states of the paramagnetic ions, the EPR
parameters being sensitive to the local symmetry, the character of the
chemical bonds, as well as to structural factors. EPR and magnetic
susceptibility data have shown that the magnetic
ions are present in the glasses as isolated species, coupled by
dipole-dipole and negative superexchange interactions. The strength of
interaction that involves magnetic ions was determined as a function of
concentration and the valence states of magnetic-active ions were
revealed. The particular behaviour of the transition metal ions in the
glassy matrix depends on the nature and concentration of the paramagnetic
ions.
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20.
Structural and magnetic investigations of manganase ions in 2B2O3×As2O3
glass matrix
I. Ardelean,
M. Flora
Glasses of the xMnO×(100-x)[2B2O3×As2O3]
system with 0 < x £
50 mol % were investigated by means of electron paramagnetic resonance (EPR)
and magnetic susceptibility measurements,. EPR of Mn2+ ions
revealed their distribution on different structural units of 2B2O3×As2O3
glass matrix doped with MnO. Distorted octahedral sites were detected. The
progressive clustering of Mn2+ ions was evidenced for x ³
5 mol %. Magnetic data revealed both 2+ and 3+ valence states for the
manganese ions simultaneously present in the vitreous matrix for x > 1
mol %. The transition from isolated ions (x < 1 mol %) to those
involved in dipole-dipole interactions (x < 5 mol %) and to antiferromagnetically coupled pairs
(x ³
5 mol %) was revealed.
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21. Local structure and metal-metal
interaction in some phosphate glasses
O. Cozar, I.
Ardelean
The local symmetry and
the interactions between metallic ions in some soda-phosphate glasses with
copper, vanadium, molybdenum and tungsten ions were investigated by ESR
spectroscopy. It was evidenced the presence of Cu2+, V4+,
Mo5+ and W5+ ions which are used as spectroscopic
ESR probes. The appearance of other valence states of these ions in the
studied glasses is possible, too. The obtained ESR data suggest different
local symmetry of these ions, which determine specific metal-metal
interaction between them.
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22.
Fast ion conduction in silver molybdenum phosphate glasses
A.
Latia, C. Vancea
Investigation of the
transport phenomena in silver molybdenum phosphate glasses has revealed
that the observed fast ionic transport is due to silver ions. The
structure of these glasses, investigated using infrared spectra, shows
that MoO3 and P2O5 are the glass formers,
the role of the last one being more important as the MoO3
content decreases. The densities of the glasses, measured using the
displacement method show that the addition of Ag2O to the
binary MoO3-P2O5 system causes a constant
increase in the density of the glasses. AC conductivity measurements of
the glasses were conducted in open atmosphere from 5 Hz to 100 kHz by use
of a HP 4142 impedance-meter in the temperature range of 303 - 423 K.
The glasses exhibited high ion conductivities in the range of 10-4
to 10-1 Sm-1 at room temperature. The conductivities
of the glasses increase and the activation energies of the conduction
process decrease with the Ag2O content. The total conductivity
of the glasses was recorded using the two electrodes method. The
investigated glasses have a very similar behavior in direct and
alternative current, respectively, the activation energies being close.
The obtained values for the transport number, very close to unity, shows
that the Ag+ ions are the charge carriers in these glasses, the
contribution of the electronic conductivity being negligible.
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23.
Calcium influence on dissolution rates of potassium phosphate glasses
D. Cacaina, S. Simon
The
dissolution behaviour of xCaO·(90-x)P2O5·10K2O
glasses with 0 £
x £
35% mol% in decationized water, physiological serum and chlorine acid,
considered as simulated biological media was investigated at room
temperature, in static regime. The dissolution behaviour of the samples
depends on the hydrogen concentration in solutions and on glass
composition and local structure. The lowest release rate is observed for
the potassium-phosphate matrix (x = 0) in decationized water. One also
remarks that the dissolution rate is higher in the first four hours, then
decreases up to seven hours and is again intensified in the corrosion
stage from 7 to 24 hours.
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24.
Transverse susceptibility of single-domain
particle systems
A.
Stancu, L. Spinu
Simulations
of the Transverse Susceptibility (TS) signal for single-domain and for
systems of ferromagnetic particles are presented. When calculating the TS
for single domains, details are provided concerning the uniaxial and cubic
anisotropies. For the uniaxial single-domain particles a 2D critical
approach can be used. The TS for cubic anisotropy is essentially a 3D
problem that was solved with a micromagnetic Landau-Lifsith-Gilbert
algorithm. Since the TS experimental method is extensively used in the
laboratories for the anisotropy evaluation, the importance of this study
consists in the fact that it offers a tool for understanding the problems
and errors in the correct interpretation of the TS curves.
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25.
Chain-of-spheres approximation in micromagnetic modelling of magnetic
recording media
D.
Cimpoesu, A. Stancu
The
behavior of prolate spheroidal particles, corresponding to the acicular
particles found in magnetic recording media is analyzed. Both experimental
and theoretical investigations have been carried out to understand and
optimize magnetic materials. A problem is the magnetization reversal mode
for even the simplest system, a particle small enough consisting in a
single magnetic domain.
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26.
Magnetic properties of g-Fe2O3
nanoparticles
D.
Predoi, V. Kuncser, M. Nogues, E. Tronc, J. P. Jolive, G. Filoti, G.
Schinteie
The
g-Fe2O3
nanoparticles
with different surface states are investigated by X-ray Diffraction,
Electron Microscopy, Differential Thermal Analysis and magnetic
measurements in low applied field. The influence of the adsorbed species
(H2O and sulphate complexes) on the inter-particle magnetic
interactions is analysed in relation to both the magnetic states of the
surface and the inter-particle distance.
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27.
Easy axis distribution in modern nanoparticle storage media: a new
methodological approach
V.
Kuncser, W. Keune, M. Vopsaroiu, P. R. Bissell, B. Sahoo, G. Filoti
Easy axis distribution in
metal particle magnetic tapes for linear digital data storage were studied
by Mössbauer spectroscopy and magnetometry, for comparison. Qualitative
and quantitative agreement between the distribution parameters deduced at
room temperature via the two different techniques was found. The proposed
methodology based on the interpretation of the Mössbauer data has the
advantage that it can be applied at different temperatures and for very
thin films. Moreover, angular spin distribution at low temperatures were
obtained by Mössbauer spectroscopy and discussed with respect to the room
temperature results. There was evidenced that the room temperature easy
axis angular distribution contains both static orientation and dynamical
components.
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28.
Study of the interparticle magnetic interaction effect on magnetic
resonance line in ferrofluids
C. N. Marin,
I. Mălăescu, V. Socoliuc
The
dipolar magnetic interaction effect on magnetic resonance line in
ferrofluids is analyzed. Starting from a ferrofluid with magnetite
particles dispersed in kerosene and stabilized with oleic acid, three
samples were obtained by successive dilution with kerosene. Magnetic
resonance and light scattering measurements were performed for each sample
of ferrofluid. The experimental results revealed that the resonance line
has a two-line feature for all samples, the magnetic field at resonance
slowly increases and the magnetic resonance linewidth decreases by
dilution of the samples. In accordance with the light scattering
measurements, this behaviour is interpreted as a magnetic interparticle
interaction and particle agglomeration effect.
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29.
A new method for determination of the effective anisotropy constant of the
particles within ferrofluids
I. Mãlãescu
A new method for
determination of the effective anisotropy constant (magnetocrystalline,
shape and surface), Keff, of the colloidal particles within
ferrofluids, from ferromagnetic resonance measurements and based on the
theoretical values computed for the Lande factor (g) of the ferrite
molecule, is described. Two ferrofluids samples (denoted F1 and F2), with
magnetite particles dispersed in kerosene and stabilized with oleic acid,
were used. In the proposed method only one measurement (magnetic
resonance) is necessary in order to determine Keff. The Lande
factor of the magnetite molecule, having the chemical formula,
, was computed that the weight mean value of the Landé factors
corresponding to the three ions in the tetrahedral positions (A) and in
the octahedral positions (B). The values obtained in this way for Keff
are compared to the ones determined from other measurements.
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30.
Formation of the nanocrystalline cubic (FeNi)23B6
phase in the nickel-rich FeNiZrB alloys and its magnetic behaviour
B.
Idzikowski, A. Szajek
Nickel-rich
amorphous precursor with nominal chemical composition of Ni64Fe16Zr7B12Au1
was produced by melt-spinning technique and then heat-treated at
temperatures ranged from 420 to 465°C for one hour, to form nanostructure.
The transformation from the amorphous state into the nanocrystalline state
was investigated by DSC and XRD techniques. Due to annealing in amorphous
matrix appear grain fraction (5-50 nm in diameter) of magnetically ordered
cubic FexNi23-xB6 phase, as was
identified by XRD measurements. The magnetic behaviour of pure Ni23B6
and Fe23B6 phases was studied theoretically using
the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. Anomalously high magnetic moments of Fe atoms were
found in some nonequivalent positions in the crystal structure.
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31. Structural relaxation in Fe70Cr10.5P11.5Mn1.5C6.5
amorphous alloy
I.
Mihalca, A. Ercuta
The changes in the Curie
temperature and magnetostriction subsequent to structural relaxation by
isothermally annealing amorphous ribbons of nominal composition Fe70Cr10.5P11.5Mn1.5C6.5
were examined. The alloy is low magnetostrictive in both native and
relaxed states, but significant enhancement, from 0.5 ppm to 10.4 ppm, of
the saturation magnetostriction coefficient was observed. The relaxation
was attributed to free volumes annealing out and short range order
changes, both topological and chemical. A value ~ 0.85 eV of the effective
activation energy resulted from the analysis of the process kinetics.
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32.
Nanocrystalline Ni-Zn ferrites prepared by sol-gel method
M.
Popovici, C. Savii, D. Niznansky, J. Subrt, J. Bohacek, D. Becherescu, C.
Caizer, C. Enache, C. Ionescu
Nanocrystalline
Ni-Zn ferrites have been synthesized in silica matrix by sol-gel
processing and thermal treatment at 1100 oC. Samples with
weight fraction of 20 % Ni1-xZnxFe2O4
in silica matrix were obtained for x = 0.15, 0.35, 0.50, 0.65 and
characterized by X-ray diffraction (XRD), high resolution transmission
electron microscope (HRTEM), Mössbauer spectroscopy (MS) at room
temperature and vibrating sample magnetometry (VSM) measurements. The
cubic spinel structure is proved both by XRD and Mössbauer spectroscopy.
The ferrites embedded in the matrix have nanoparticles in the range 5-13
nm. The obtained composites, display superposed superparamagnetic and
ferrimagnetic behavior, as a function of Zn/Ni ratio. Both lattice
constant parameter and average hyperfine fields vary with the degree of
substitution of nickel ions with zinc ones.
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33.
Preparation and magnetic properties of Ni80Fe20 nanowire
arrays
H.
Chiriac, T. A. Óvári, A. E. Moga, M. Urse
Arrays
of Ni80Fe20 nanowires were prepared by
electrodeposition into nanosized pores of anodic alumina and polycarbonate
membranes, using a two-electrode electrochemical cell. Nanoporous anodic
alumina membranes were prepared in a two-step anodizing process of
aluminium foils. The morphology of the samples was investigated by means
of scanning electron microscopy (SEM). The structural characteristics of
the samples were examined using X-ray diffraction (XRD). Magnetic
measurements were performed at room temperature, using a vibrating sample
magnetometer (VSM) and showed the as-made samples to be magnetically soft.
The magnetization curves are reversible indicating a high saturation field
and low remanence. Magnetic anisotropy along the axis of the wire is
present.
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34.
Non-linear behaviour of the spin transition compounds during
photo-excitation and relaxation
C.
Enachescu, J. Linares, E. Codjovi, K. Boukheddaden, F. Varret
Spin-crossover
solids are photo-excitable materials, which are studied for future
applications as optical memories or numerical display. The spin transition
is a first order phase transition produced by variations of temperature,
pressure or light. Cooperative effects constitute the basic mechanism for
the spin crossover transition. They induce instability in the
thermodynamic competition between the two states of the spin-crossover
molecules: high-spin (HS) and low spin (LS).We investigate here the
photo-excitation process and the relaxation of the photo-excited state in
photo-switchable solids, such as spin transitions systems
[(FexM1-x)(btr)2(NCS)2]
H2O, with M=Co, Ni, Zn. We follow the competition between the
relaxation and the photo-excitation processes (up and eventually down).
The experimental kinetics gives evidence for a non-linear character of the
relaxation at all temperatures, including the tunnelling regime, and for
non-linear behaviours of the photo-excitation rates.
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35.
The quantum efficiency of the photo-excitation in a Fe (II) spin-crossover
compound
C. Enachescu, U. Oetliker, A. Hauser
In
this paper we discuss on the quantum efficiency in spin crossover
compounds. Spin crossover solids are text-book examples of photo
switchable materials that present a thermal spin transition from the
diamagnetic low-spin state, thermodynamically stable at low temperatures,
to the paramagnetic high-spin state becoming the thermodynamically stable
state at elevated temperature. By irradiating them with an appropriate
wavelength, they can pass from the stable low spin state to the metastable
high spin state at temperatures below the thermal transition temperature.
For the compound [Fe(pic)3]Cl2·EtOH, the question
regarding the quantum efficiency of the photo-conversion process that is
the number of molecules converted by one single photon and its possible
dependency on irradiation intensity gave rise to a controversy. The
experimental results presented in this paper demonstrate that the quantum
efficiency of the photo-conversion at 11 K is on the order of unity, with
no noticeable dependency of the quantum efficiency on light intensity. It
does, however, depend to a small extent on the fraction of complexes
already converted to the high-spin state.
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36.
Stress and temperature effect on the FMR response of nearly zero
magnetostrictive amorphous microwires
F. M. Tufescu, T. A. Óvári, H. Chiriac, A. Stancu
Results on the
ferromagnetic resonance (FMR) investigation of the effect of applied
tensile stresses and different temperatures during measurements on the
surface magnetic anisotropy of Co68.25Fe4.5Si12.25B15
amorphous glass-covered microwires are reported. Axial stresses determine
a decrease of the resonance field and an increase of the absorption
intensity that correspond to the resonance peak, indicating a
reinforcement of the circumferential magnetoelastic anisotropy from the
microwire’s surface region. An increase of the temperature during
measurements up to 160 °C
leads to a significant increase of the resonance field that corresponds to
a decrease of the circumferential magnetoelastic anisotropy.
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37.
Spin dynamics investigated by magnetic resonance in colossal
magnetoresistive materials
L.
V. Giurgiu
The spin dynamics in
colossal magnetoresistive manganites La2/3Ca1/3Mn1-xDixO3
(Di = Al, In;
x ≤
0.05) has been analysed by ESR spectroscopy. The effect of the partial
substitution of Mn by closed shell ions was evidenced. The temperature and
x dependence of the resonance linewidth and integral intensity of the ESR
signal have been investigated and disscused in terms of the bottlenecked
spin relaxation and small polaron hoping models. The exchange coupling
integral between Mn3+ and Mn4+ ions shows a decrease
with increasing x due to the weakening of the double exchange interaction
upon doping. A strong variation of the polaron activation energy with the
doping level was also found and discussed in terms of the Mn - O
distortion and the Mn3+ content.
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38.
Effects of In doping investigated by ESR in colossal magnetoresistive
manganite La2/3Ca1/3MnO3
O.
Raita, M. N. Grecu, X. Filip, Al. Darabont, D. Gavre, J. Blasco, L. V.
Giurgiu
The effects of the
substitution for Mn with In in the colossal magnetoresistive manganites La2/3Ca1/3Mn1-xInxO3
(x £
0.05) have been investigated by ESR. The temperature and x
dependence of the resonance linewidth have been investigated and discussed
in terms of the spin–spin (exchange) interaction scenario. In the
paramagnetic regime, the exchange coupling integral, J, between Mn3+and
Mn4+ spins shows a decrease with increasing x. It could arise
from the weakening of the double - exchange interaction upon doping, which
reduces the exchange field at the Mn sites. The high temperature limit of
the ESR linewidth does not depend on the doping level.
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39.
Modeling the multi-crystalline SIlicon ingot solidification process in a
vertical square furnace
F. Barvinschi, C. Stelian, Y. Delannoy, N. Mangelinck, T.
Duffar
Large-scale production of multi-crystalline silicon for high-efficient
solar cells is a very important task of today’s photovoltaic technology.
The efficiency of crystalline silicon solar cells depends on both the
crystallization process and the solar cell processing sequence. As far as
the crystallization process is concerned, it is very important to know the
temperature distribution during the solidification of silicon ingots, to
predict the solidification structure obtained and thus the materials
properties. In this study the transient 2D and stationary 3D numerical
simulation of the solidification process of large square mc-Si ingots is
investigated, by using the software FIDAP and FluentTM. Some
geometrical approximations of the real furnace and specific approaches for
the radiation modelling are used in order to solve the difficulties
related to numerical analysis. The
results are compared to the experimental data, in order to calibrate the
numerical model.
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40.
Identification of nonlinearties in anelastic polycrystalLine materials
using Volterra - Fourier Transform
Gh.
E. Drăgănescu, A. Ercuţa
A nonlinear rheological model built on the basis of
structural properties of polycrystalline solids is presented. A Fourier -
Volterra series method of model parameters identification from the
experimental data is proposed.
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41.
Manganase activated (2-x)ZnO×xCdO×1.1SiO2
phosphors obtained by solid state synthesis
C.
Enache, R. Turcin, C. Savii, M. Popovici, R. M. Jurca, V. Socoliuc
The
aim of the work was to study the evolution of luminescence emission
properties of some Mn2+ activated phosphors in the ZnO – CdO
– SiO2 system in correlation with both the cadmium oxide/zinc
oxide mole ratio and the activator concentration. A number of phosphors
corresponding to the mole target composition of (2-x)ZnO×xCdO×1.1SiO2:yMn,
where 0 £
x £
0.15, and y = 0.021; 0.042; 0.085, were obtained by firing the mixed
powders of precursors (oxides and carbonates), at 1250 ºC or 1350 ºC
temperatures, in air, for 60 minutes. Thermal analysis technique was used
in order to elucidate the oxide system behaviour during thermal treatment.
Structural and optical properties were investigated by X-ray diffraction
and spectrofluorometry techniques All obtained samples show a green
luminescence emission, as it was expected for manganese-activated
willemite. The emission intensity of the synthesised phosphors seems to be
influenced by host matrix composition and activator amount, as well. It
was observed that, in the domain of relatively low CdO/ZnO mole ratio,
regardless the activator concentration, the emission intensity is
favourable influenced by CdO content, the maximum being reached for the
composition 1.975ZnO×0.025CdO×1.1SiO2×0.085Mn.
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42.
Microstructural evolution and thermo-mechanical response of Ni ion
irradiated TiNi SMA thin films
T. B. Lagrange, R. Gotthardt
The
present study focuses on the effect of 5 MeV Ni ion irradiation of
plastically strained (e
~ 4 %) martensitic TiNi thin films, which is used as a processing
technique for a novel out of plane bending actuator. Conceptually, the
frustration of the martensitic transformation due to ion beam damage in a
2 mm
surface layer of a 6 mm
thick film will create a sharp differential latent strain on reverse
transformation. This latent strain causes a two-way bending motion during
cyclic heating and cooling, and in addition, this thermal actuator can be
used to do useful mechanical work on both heating and cooling. To better
understand the behaviour of these ion irradiated thin films, TEM
observations and motion experiments were conducted.
Results are presented and discussed as they relate to the ion
induced microstructure and its influence on the martensitic transformation
and the shape memory effect.
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43.
Computer simulation of magnetization curves in magnetic thin films
M. Volmer, J. Neamtu
Computer
simulation based on Stonner-Wolfarth model is used to investigate
magnetization flop in magnetic thin films of Ni80Fe20
(Py) and magnetic multilayers with the structure Py/Cu/Py. The results of
computer simulations are compared with the magnetic measurements made with
a commercial Vibrating Sample Magnetometer (VSM).
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44.
Thermoionic Vacuum Arc – a new method of thin film deposition
R. Vladoiu, G.
Musa, I. Mustata
New equipment for the technology of thin film
deposition using thermoionic vacuum arc is presented. Advantages of this
system are underlined: extended application possibilities for the increase
of the microhardness of the pieces, decrease of the friction of moving
pieces, change of the chemical reactivity of the pieces (corrosion
resistant components). The new technique can be used for the development
of nanostructural materials.
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45.
Optical and electronic properties of metal doped polymers for integrated
optics
M.
Bulinski, V. Kuncser, D. Cristea, C. Plapcianu, S. Krautwald, H. Franke,
F. E. Wagner, G. Filoti
The
electronic mechanism responsible for the optical behavior of the mixed Fe
and Sn doped polymers were studied in comparison with the correspondent
single doped (Fe or Sn) ones.
Optical absorption as well as 57Fe and 119Sn Mössbauer
measurements were performed on different UV exposed films. The new data
provided the role of each element from the pair on the involved electronic
mechanism induced by irradiation.
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46.
Strontium-doped LaCoO3 perovskites in solid oxide fuel cells
V. V. Srdic, L. Nikolic,
V. Pejovic
Cathode-electrolyte
structures, for solid oxide fuel cells, are prepared by deposition of
porous (La,Sr)CoO3 film on the surface of dense
nanocrystalline 3 mol% Y2O3 stabilized zirconia
electrolyte. The perovskite powder is prepared by a wet-chemical synthesis
technique using metal-nitrates, mixed with a resin and organic solvents to
form a paste that is deposited as a thick film by screen-printing
technique. The characteristics of the synthesized powders, sintered
samples and cathode-electrolyte structures are investigated.
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47.
Synthesis of LiMn2O4 by glycine-nitrate method
D. Jugović,
N. Cvjetićanin, V. Kusigerski, S. Mentus
Glycine-nitrate method
was used to synthesize lithium manganese oxides. For the molar ratio of
lithium-to-manganese in precursor solution equal to 1:2 spinel LiMn2O4
was obtained. For molar ratio of 1:1 a mixture of Li2MnO3
and spinel phase different from LiMn2O4 was
observed.
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48.
Conduction electron spin resonance of Pt-nanoparticles in porous Al2O3
membranes
D. Gavre, G.
Mihailescu, O. Raita, E. Indrea, S. Pruneanu, J. Rahmer, L. V. Giurgiu
An electron spin resonance (ESR) investigation of Pt-nanoparticles
electrodeposited in the channels of porous Al2O3
membranes has been performed in the temperature range 6 – 50 K. Pt –
particle mean size was evaluated by means of Kawabata theory that relates
ESR linewidth to metal particle size. A comparison with the effective
crystallite mean size obtained from the X – ray diffraction analysis is
given.
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49.
Identification of the generalised preisach
model parameters for systems with magnetostatic interactions
M.
Cerchez, L. Stoleriu, Al. Stancu
This
paper presents the testing of a recently developed Preisach identification
algorithm. The algorithm uses the properties of the Integral Generalized DM
plot that is very sensitive to interactions and thus produces a more
accurate choice of parameters. The parameters obtained in the
identification produce simulations that fit first and second order
magnetization processes with reasonable precision.
For some of the metal particle recording media studied with
negative DM
curves, a good fit can only be obtained using negative mean field
interactions. This is different from most acicular systems where a
positive mean term is usually required.
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50.
A Preisach-Néel model with thermal variable variance: sensibility to the
parameters
I. D. Borcia, L. Spinu, Al. Stancu
We performed simulations of magnetization curves in
field, remnant and also with variable temperature. The simulations were
done using a Preisach-Néel model for nanoparticulate media. The model
includes the reversible and the irreversible part of the magnetization.
There are taken into account the variations of the Preisach distribution
due to the mean field and to the thermals effects as well as the movements
of the thermal boundary in processes with variable field and temperature.
Because the identification problem is a very important point in our
simulations, the study of the model sensibility to the parameters can
allow for choosing a better identification procedure.
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51.
Bar-configuration in Hall measurements with GaAs
R. V. Ghita,
C. Logofatu, C. Negrila, M. F. Lazarescu, A. S. Manea, V. Ciupina
The electrical and
transport properties of GaAs crystals such as resistivity (r),
mobility (m)
and carrier concentration (n) depend on the purity and defects of a
particular crystal. These parameters are normally obtained by performing a
simple Hall effect analysis in a bar configuration.
The technical procedure is connected with the design of appropriate
contacts for Hall bar configuration. In order to ensure good ohmic
contacts on GaAs, thin metal layers of Au-Ge-Ni have been deposited in
high vacuum followed by heat treatment in low vacuum. Hall effect
measurement is important for checking the quality of the GaAs wafers. We
analyzed various GaAs wafers with (100) and (110), orientation obtained by
LEC and HB methods. The resistivity of the wafers varied from low
resistivity, n-type doped crystals (n = 1018 cm-3),
to high resistivity crystals (n = 1014 cm-3). This
paper presents the data of Hall characterization of wafers cut from GaAs
crystals grown by different methods (LEC, HB).
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