WS2 Nanotubes_ WO3-x Nanofibers as Tips for Scanning Probe Microscopy - DOC

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					   Material Sciences                          1


                                  Amouyal Y. and Rabkin E.
             Department of Materials Engineering - Technion, Haifa 32000, Israel

Many physical properties of materials, such as brittleness, corrosion and creep resistance
and high temperature stability are substantially derived from the grain boundary (GB)
atomic structure.
The main obstacle, which still prevents the intermetallic compound NiAl from being largely
used is its low-temperature intergranular brittleness, which stems from relatively high GB
The present research objective is characterizing the GB geometrical degrees of freedom
(DOFs) and measuring its relative free energy.

          The geometry of a GB is defined by 5 macroscopic degrees of freedom:
          Three misorientation parameters of two adjacent grains (the rotation
            of one grain by angle θ around any <hkl> axis of the second grain
            reference system).
          Two parameters of the GB plane inclination (its normal vector N in
            any preferred reference system).

The determination of the 3 misorientation DOFs is carried out by the electron back-scatter
diffraction (EBSD) technique in the scanning electron microscope.
This technique enables acquiring electron diffraction patterns from relatively small surface
areas (~ 0.5 μm). The analysis of two diffraction patterns from the adjacent grains provides
the 3 misorientation DOFs.
The 2 GB plane inclinational DOFs are calculated by measuring the direction of the GB
groove line (the GB plane intersection with the specimen surface), as well as its inclination
to the surface normal. The latter is determined by polishing the specimen surface to a certain
depth, and measuring the horizontal shift of GB groove line. These two GB inclinational
DOFs define the GB normal vector N.
The relative GB free energy is defined as the ratio between GB energy and surface energy,
and is related directly to the dihedral angle of the GB thermal groove.
The atomic force microscopy (AFM) technique is utilized for measuring the GB groove
dihedral angle.
Although the present research is still in progress, preliminary results of one GB can be
presented: The GB misorientation is 310[1 7 0], while its GB plane normal (in one grain’s
reference system) is (3 –4 –1). The GB with these geometrical parameters exhibits a relative
free energy of 0.58±0.02 .
gCombining the EBSD and AFM techniques has been proved to be very promising for the
mesoscopic approach in GB research.
Material Sciences                            2

                     SCANNING PROBE MICROSCOPY

          Ashiri Ifat 1, Gartsman Konstantin 2, Cohen Sidney 2, Tenne Reshef 1
                   Weizmann Institute of Science, Department of Materials and Interface
                         Weizmann Institute of Science, Chemical Services Unit

WS2 nanotubes were the first inorganic fullerene-like (IF) structures to be synthesized.
WS2 nanotubes have a variety of electronic, optical and mechanical properties that
made them suitable for many applications. In this study we tried to use WS 2 nanotubes
/ WO3-x nanofibers as atomic force microscopy (AFM) tips. The commercial silicon
tips that are in use today cannot scan features with aspect ratio higher than 3:1,
however, WS2 nanotubes have both the mechanical properties needed for AFM tip and
the size (diameter: 10-30 nanometer, length: few tens of micrometer) that fit the
requirements of scanning features with high aspect ratio. The process of manufacturing
nanotube tips is based on attaching the WS2 nanotubes / WO3-x nanofibers to silicon
AFM tip. The process is done inside the SEM (scanning electron microscope) by using
a micromanipulators system and epoxy adhesive. The WS2 nanotubes / WO3-x
nanofibers tips are tested in AFM (non contact mode) by imaging a sample with high
aspect ratio features. The WO3-x tip scanned a good image of the sample.
Material Sciences                            3


                      Bakaleinikov L. 1, Berner A. 2 and Kaplan W. D. 2

    Ioffe Physical Technical Institute of Russian Academy of Science, Polytechnical Str. 26,
                                      St. Petersburg, Russia
               Department of Materials Engineering, Technion, Haifa 32000, Israel

Backscattered electrons (BSE) in SEM represent a powerful tool for obtaining
compositional contrast from samples composed of different phase constituents with a
large difference in the mean atomic number. Unfortunately, in conventional analytical
conditions used for BSE imaging in SEM, the lateral resolution in the BSE images is not
as good as that in secondary electrons images. The purpose of the present research was to
study the lateral distributions of BSE under different analytical conditions and to develop
methods allowing an essential improvement of accuracy of critical dimensions
measurements using BSE.
Monte Carlo (MC) simulations were used for studying the properties of BSE (yield,
energy and angular spectra, radial and lateral distributions). The MC simulations were
performed within the framework of a single inelastic scattering model. The Mott cross-
section for elastic scattering and double differential inelastic cross-sections, based on
experimental data, were used for the simulations. To verify the model and the program
code, calculated BSE yields and energy spectra were compared with those measured
experimentally. In all cases a good agreement between the calculated and experimental
results were found.
Particular attention has been given to studying radial distributions of BSE. It was shown
that calculated BSE radial distributions can be well approximated by a sum of two
Gaussian functions having standard deviations of 1 and 2, where 1>>2. The first
Gaussian distribution describes the radial distribution of BSE that suffer from a large
number of interactions, and the second is connected to BSE which exit the sample after a
small number of interactions. It was shown that energy filtering can drastically improve
the lateral resolution in BSE images. New techniques for exact determination of the
position of A/B phase boundary and for determination of the layer B thickness in triple
A/B/A structures were developed.
Material Sciences                           4


                  Becker S. 1, Shneck R.Z. 1, Makov G. 2 and Venkert A. 2
               Department of Materials Engineering. Ben Gurion University
                                P.O.Box 653 Beer-Sheva
                 Nuclear Research Center, Negev P.O.Box 9001 Beer-Sheva

Dislocation cell structure in highly deformed metals is a well known phenomenon.
However, until now the driving forces, mechanism and structure of dislocation cells and
dislocation walls have only been partially understood. The understanding of dislocation
cells structures formed in various modes of deformation, attracts interest both in basic
scientific understanding and in possible technological implications. Dislocation glide
during the plastic deformation of crystalline materials creates a heterogeneous
microstructure that often consists of misoriented cells or subgrains. These cells or
subgrains tend to rearrange into characteristic patterns. It is believed that glide
dislocations are statistically trapped by forest dislocations and form incidental dislocation
boundaries which subdivide the crystal into a mosaic of cells.

Our objectives were to observe the cell structures in cold rolled aluminum in different
orientations and to evaluate the dependence of the cell structure and dislocation walls
formation on the purity of the aluminum metal and deformation value. Two types of
materials were used; commercial aluminum (99.5%) and high purity aluminum (99.99%).
Specimens from both materials were cold rolled to 5%, 15% and 40% deformation
magnitude. Transmission electron and optical microscopes were used in order to attempt
a direct comparison between dislocation structures in the two different materials. TEM
specimens were prepared from foils using Twin jet electro-polishing or ion milling
techniques. These foils were prepared from the interior part of the specimens in three
different orientations: transverse, longitudinal and rolling.

Well-developed dislocation boundaries and cell structures were observed in pure Al
already in 5% of deformation. In the longitudinal and rolling sections the dislocation cells
are elongated nearly parallel to the rolling direction. In the transverse sections the cells
are equiaxed and perfectly closed. Bimodal size distribution of cells was observed in the
transverse and longitudinal sections. At larger deformations the cells become finer and
subdivisions of cells was observed. In the commercial aluminum similar dislocation
structures developed but the arrangement of the dislocations into cells and sharp
boundaries was hindered.
Material Sciences                          5

                    SEMICONDUCTOR SURFACES

           Dadosh Tali *, Krahne Roman +, Mahalu Diana +, Sperling Joseph *,
                         Yacoby Amir + and Bar-Joseph Israel +
                         Department of Organic Chemistry
     Department of Condensed Matter PhysicsWeizmann Institute of Science, 76100
                                 Rehovot, Israel

The study of the electrical properties of nano-size objects is of high current interest. In
this small scale structures the quantum size energy and the Coulomb blockade energy are
considerably enhanced and can exceed the thermal energy kT at room temperature. The
dominance of these energy scales makes this system ideal for both studying quantum
phenomena and for constructing practical quantum devices. In this research we combine
the technology available for patterning semiconductor devices with the rich variety of
forming nano-size objects by chemical fabrication to overcome the problem of bridging
the micro and the nano scale. Gold clusters with diameters ranging from one to hundred
nanometers are fabricated and coated by alkane-thiol molecules. The tunnel barrier in
between the macroscopic electrode and the nano-size cluster can be determined by using
coating molecules and linkers of variable length. For the controlled positioning of the
nano-particles in between the electrodes we use the technique of electrostatic trapping as
shown in Figure 1. This structure is the generic design of a single electron transistor
(SET), i.e. a small metal island separated from the connecting leads by tunnel barriers.

Figure. 1: Top view SEM picture of two electrodes separated by a distance of 50 nm. The
bright spot in the center is a captured Au cluster of 60 nm in diameterbright spot in the
center is a captured Au cluster of 60 nm in diameter.
Material Sciences                          6


                    Johansson A1, Gartsman K2, Shahar D1 and Tenne R.3
     Department of Condensed Matter Physics, 2Department of Chemical Services,
     Department of Materials and Interfaces, Weizmann Institute, Rehovot 76100, Israel

Electronic transport properties in inorganic nanotubes are of great interest for both
fundamental understanding of physical phenomena in quasi one dimensional systems as
well as the possibility to fabricate new electronic devices based on these nanotubes. A
study of these properties requires fabrication of ohmic contacts to the nanotubes in order
to allow probing with an electrical current through them. We have developed a technique
for this, using a scanning electron microscope (SEM) not only as an analytical instrument
for observing the nanotubes, but also as a tool for bringing the nanotubes in contact with
micro-electrodes. These electrodes are fabricated by optical lithography on the surface of
an insulating GaAs wafer. The process of placing the nanotubes in the right locations is
done by using manipulators with submicron probes mounted in the sample chamber of
the SEM. The procedure is accurate and fast compared to other known techniques for
handling nanotubes. Once placed in the right location, the WS2 nanotubes are reattaching
to the substrate by van der Waals forces strong enough to allow further lithographic
processing without being displaced. This allows us to add an additional metallic layer on
top of the micro-electrodes and thereby sandwiching the ends of the nanotubes.
Preliminary electrical measurements carried out on the fabricated devices reveal the
semiconducting properties of the WS2 nanotubes.
Material Sciences                           7

                Kauffmann Yaron, Kaplan Wayne D. and Chaim Rachman.

              Department of Materials Engineering, Technion, Haifa, Israel.

In recent years, nano-crystalline materials have attracted considerable interest, since these
ultrafine-grain-sized materials contain a large volume fraction of grain boundaries, which
lead to novel properties, such as increased hardness and ductility. Thus, thorough
investigation of the atomistic structure and the accurate characterization of the
microstructural parameters, such as grain size and internal strains, are of considerable
interest from both scientific and technological viewpoints.

In this research we chose to investigate a basic model system of nano-crystalline gold.
We tried to quantitatively characterize different microstructural parameters, such as the
presence and distribution of micro-strains in the nano-grains and the influence of grain
size on such micro-strains.
To achieve this goal, it is necessary to combine “traditional” (X-ray diffraction - XRD)
and “non-conventional” (High-Resolution Transmission Electron Microscopy - HRTEM
assisted by quantitative image analysis) methods for measuring and mapping the micro-
strain fields in the nano-scale.
There are a number of techniques to measure strains directly from HRTEM micrographs.
The simplest and most inaccurate is line-scan contrast analysis. A fully quantitative but
application limited technique is full atomic column position retrieval from HRTEM
images. A number of other methods, which are more accurate, were studied and
evaluated on simulated images as well as on experimental micrographs.
This presentation will include a comparison of the different HRTEM-based techniques,
their advantages and disadvantages, and a potential scheme to include atomistic computer
simulations (i.e. Molecular Dynamics) in the strain measurement procedure.
Material Sciences                           8

                     IN COPPER METALLIZATION

             Kohn Amit 1, Eizenberg Moshe 1 and Shacham-Diamand Yosi 2
                Department of Materials Engineering, Technion, Haifa,Israel
         Department of Physical Electronics, Tel-Aviv University, Ramat-Aviv, Israel

The application of Cu metallization in ULSI devices requires the development of efficient
ultra thin diffusion barriers. Electroless is a potential deposition method as it is a
selective, low temperature process readily integrated with electrochemical copper
deposition, which is the current Cu deposition method.
In electroless deposition, reaction kinetics can be dominant, resulting in a nanocrystalline
or amorphous structure of the metallic layer. This microstructure improves the quality of
the diffusion barrier by eliminating direct, fast diffusion paths via the grain boundaries.
For electroless Co, this modification of the microstructure is achieved by the
incorporation of P and W. Additionally, under equilibrium conditions, the solubility of P
and W in Co is by more than one order of magnitude lower than the amounts
incorporated in the electroless deposited films. Therefore, we expect the impurities to
enrich the Co grain boundaries after thermal treatment.
Co0.9P0.08W0.02 was evaluated as a potential barrier by electrical measurements of MOS
devices. This diffusion barrier was found to be effective up to 450C compared to
sputtered Co, which is a poor barrier, attributed to grain boundaries’ diffusion.
In order to understand the mechanism responsible for the improved barrier properties,
TEM and XRD studies were performed to characterize the microstructure of the as-
deposited films and after thermal anneals up to 700C.
The as-deposited film was found to be a solid solution of nano-crystalline hcp Co. After
thermal anneal, we observed microstructural evolution of grain growth along a preferred
basal plane orientation, formation of Co2P precipitates and a delayed phase
transformation from hcp to fcc Co. An additional phenomenon was the observation of
periodicity in the phosphorus concentration perpendicular to the substrate after annealing
at 400C. A possible reason for this observation is precipitation of Co2P on a plane of
coherency, the hcp basal plane.
We conclude that the improved barrier behaviour is attributed to the so-called solute
effect. The impurities (phosphides and tungsten) partially reside at the grain boundaries,
excerting a blocking effect on Cu diffusion.
Material Sciences                            9


                Perets S.1, Arbel A.1, Ariely S 3, Venkert A.2and Shneck R.Z.1

                 Departmentof Materials Engineering. Ben Gurion University
                                 P.O Box 653 Beer- Sheva.
                  Nuclear Research Center, Negev P.O Box 9001 Beer Sheva.
                                   Israel Electric Company.

A wealth of data has been acquired concerning the creep and creep-fatigue properties of
ferritic steels and their microstructural evolution at high temperatures and long term
creep. The mechanical data was acquired in accelerate laboratory tests in conditions of
high stresses and tempratures in relation to actual service conditions.
The purpose of this work is to evaluate the microstructural changes and their influence on
the mechanical properties of a steam pipe that was made of P-22 (2.25%Cr-1%Mo) steel
after 30 years of service at 5400C. This approach is sought to extend the predictions to the
residual life of serviced components, based on the damage accumulated during the long
service time.
Longitudinal and transverse creep specimens were machined from the steam pipe.
Accelerated creep tests to fracture were preformed in a range of temperatures and
stresses, the results of those experiments were compared to the Larson-Miller curve of P-
22 steel. Similar comparative specimens were prepared from type P-22 steel in its as-
received condition. Optical microscopy as well as scanning and transmition electron
microscopy were used to study the microstucture of the as received steel after 30 years of
service and after the accelerated creep tests.
The high-temperature service led to spherodization of the original lamellar carbides in the
pearlitic grains. Smaller spherical carbides formed, during service, in the original ferritic
grains. Carbide free zones (CFZ) were formed along the boundaries of the original ferrite
grains. TEM observations indicated precipition of carbides at the grain boundaries of the
ferrite and pearlite grains and occational pre-cracking around the boundary carbides; no
other indications of damage was discerned in the service pipe.
Material Sciences                         10

                      YTTRIUM AND PRASEODYMIUM

                               Popov I. *, Shechtman D. **

      *Faculty of Natural Science, Hebrew University of Jerusalem, E.Safra Campus
                              Givat Ram, Jerusalem 91904
     ** The Department of Materials Engineering, TECHNION – Israel Institute for
                       Technology, Technion City 32000, Haifa

We studied microstructure and properties of rapidly solidified magnesium-based
materials. Mg-Zn based alloys containing Rare Earth (RE) elements (Y, Ce, Pr and Nd)
have been prepared by melt spinning technique, at the cooling rates of 106-107 K/sec.
Their structure has been examined by electron microscopy and X-ray diffraction analysis,
while DTA has been used to test their heating behavior. Effect of heat treatment on the
structural features of these materials has also been studied.
We found that upon applied melt spinning conditions, Mg-Zn-RE alloys formed as
filament-like ribbons of tens microns thickness. These ribbons have specific fine
crystalline microstructure consisting mainly of Mg-Zn solid solution matrix and 20-500
nm size separate precipitates of intermetallic phases enriched by Zn and REs. Upon
heating all the alloys passed the only endothermic process at around 5700C.

Based on these results we will try to re-construct a possible solidification processes
caused the formation of the observed microstructural features. Microsegregation of heavy
elements in both melt and solid states as well as their diffusivity in the solidification
temperature range will be discussed. The role of temperature and cooling rate distribution
across the melt puddle will be considered as the factors, which determine the filament-
like morphology of ribbons and causing some periodicity at the microscopic level of their
Material Sciences                                         11


 Rosenfeld Hacohen Y. *, Popovitz-Biro R. *, Grunbaum E. *, Prior Y. ** and Tenne R. *

     *Department of Material and Interfaces, and **Department of Physical Chemistry,
                         The Weizmann Institute of Science, Rehovot 76100.

The research into carbon fullerenes[1] and nanotubes[2] paved the way to the discovery of
these morphologies in other layered materials, such as WS2[3-4], other chalcagonides[5]
and oxides[6-7]. Since NiCl2 crystallizes in a hexagonal lattice in which each Ni atom is
surrounded by a 6 Cl atoms in an octahedral coordination[8], it was hypothesized that
inorganic fullerene - like structures (IF) of NiCl2 with closed cage octahedral shape and
related nanotubes may form. The first synthesis of IF - MCl2 (M=Ni,Cd) and nanotubes
were made via evaporation-sublimation/condensation process at elevated temperatures[9-
Pulsed laser photons are absorbed in the target by an electronic transitions, followed by
internal conversion processes to a vibrational energy. The interaction of laser light with
matter can formally be divided into three parts; absorption, energy transport and ablation.
Historically, laser ablation was the first technique used to generate fullerene clusters in
the gas phase[1].
In this research the ablation of the NiCl2 target took place inside a quartz reactor that was
inserted through a horizontal cylindrical high temperatures furnace. A 140mW laser of a
532 nm wavelength and 8ns pulse duration was used at 25Hz pulse rate. In order to
stabilize the NiCl2 stochiometry of the ablated material a CCl4 gas was added to the
carrier He gas. The vaporized nanoparticles condensed and recoiled into a 940ºC region
and flushed buck by a 100-170 cm3 min-1 flow of gasses.
Transmission electron microscopy revealed that a high percentage of NiCl 2 whiskers
were grown with a small portion of opened nested nanotubes. In most of the cases a ball
like particle of NiCl2/amorph carbon was attached to one end of the tubes. This suggests
that a VLS – growth mechanism is evolved at this type of synthesis[11]. Detailed
knowledge of the growth mechanism is still lacking, but we envisage three stages for the
growth: i) melting of Ni/NiCl2 above the eutectic temperature and super saturation with
respect to the Cl2 gas; ii) crystal nucleation at the surface of the droplet; iii) axial growth
of a NiCl2 nanotube by pushing back (or forward) the interface along a preferred

 1    H.W. Kroto, J.R. Heath, S.C. O’brien, R.F. Curl, R.E. Smalley, Nature 318,162 (1985)
 2    S. Iijima, Nature 354, 56 (1991)
 3    R. Tenne, L. Margulis, M. Genut, G. Hodes, Nature 360, 444 (1992)
 4    Y. Feldman, E. Wasserman, D.J. Srolovitz and R. Tenne, Science, 267, 222 (1995)
 5    M. Nath and C. N. R. Rao, J. Am. Chem. Soc 123(20), 4841-4842(2001)
 6    M.E. Spahr, P. Bitterli, R. Nespar, Angew.Chem.Int.Ed 37, 1263 (1998)
 7    S. Avivi, Y. Mastai, A. Gedanken, J.Am.Chem.Soc 122, 4331 (2000)
 8    L. Pauling, Proc of the Nat.Acad.of Sci 15, 709 (1929)
 9    Y. Rosenfeld Hacohen; E. Grunbaum, R. Tenne, J. Sloan, J.L. Hutchison,. Nature 395, 336-337, (1998)
10    R. Popovitz-Biro, A. Twersky, Y. Rosenfeld Hacohen and R. Tenne, AIP Conf. Proc. 544, 441-447. (2000) (Electronic
      Properties of Novel Materials-Molecular Nanostructures)
11    R.S. Wagner and W.C. Ellis, Vapor-liquid-Solid Mechanism of single Crystal Growth, Applied Phys. Lett, 4, (5) , 89-90,
Material Sciences                         12


Rosentsveig R.*, Margolin A.*, Feldman Y.**, Popovitz-Biro R.* and Tenne R.*

       Department of Materials and Interfaces* and Unit of Chemical Services**
              The Weizmann Institute of Science, Rehovot 76100, Israel

Recently, large quantities (grams) of multi-walled WS2 nanotubes were obtained in a one
step synthesis, using a fluidized-bed reactor that was used for the synthesis of inorganic
fullerene-like(IF) WS2 nanoparticles, but under modified conditions [1]. In this process
nanowhiskers of WO3-x and subsequently WS2 nanotubes were produced in a single
process using commercially available WO3 nanoparticles as precursors. Very long
(hundreds of micrometers) open ended nanotubes appear either as bundles in the bulk of
IF-WS2 product, or as thin foils attached to the walls of the reactor. Transmission electron
microscopy (TEM ) analysis of a broken area in a ribbon, obtained during the detachment
of a thin foil from the reactor wall, showed long and uniform nanotubes which are mostly
4 -7 layers thick. To further analyze the structure of the ribbons, one such ribbon was
embedded in a polymer matrix and subsequently cross-sectioned by ultramicrotome.
TEM of such section reveals clearly well aligned nanotubes. The observed nanotubes are
close packed and their circular cross section was somewhat distorted, probably during the
microtomy. Isolated WS2 nanotubes and bundles thereof, mixed with fullerene-like
particles, were also found in the center of the reactor, consisting of 300µm long
nanotubes of rather perfect shape. The flawless structure of a typical nanotube is
appreciated from the high resolution TEM image showing WS2 layers separated by 6.2Å,
in the nanotube walls. In contrast to the nanotubes in the foils, these isolated nanotubes
have been shown to be of perfectly circular in cross-section, by tilting the sample along
the tube axis. The nanotubes consist of coaxial-cylinders build up of hexagonal sheets.
All nanotubes in this study were found to be chiral. The helicity angles of the nanotubes
were determined from the electron diffraction (ED) pattern [2]. In order to gain
understanding of the nanotubes growth mechanism, partially reduced or sulfidized
intermediates were isolated from interrupted process [3]. Such intermediate
nanowhiskers, encapsulated by WS2 layers, were shown to be W18O49 phase from the ED


[1]    Feldman, Y.; Zak, A.; Popovitz-Biro, R.; Tenne, R. Solid State Sci. 2000, 2, 663.
[2]    Margulis, L.; Dluzewski, P.; Feldman, Y.; Tenne, R. J. Microsc. 1996, 181, 68.
[3]    Frey, G.L.; Rothschild, A.; Sloan, J.; Popovitz-Biro, R. Tenne, R. J. Solid State
       Chem.2001, 162, 300.
Material Sciences                       13


                                    Yossi Rosenwaks

               Department of Physical Electronics, Faculty of Engineering,
                    Tel-Aviv University, Ramat-Aviv 69978, Israel

Scanning probe microscopy has opened new opportunities to image semiconductors
electronic properties with unprecedented spatial resolution.    The recently developed
Kelvin probe force microscopy (KPFM) technique has already been demonstrated as a
powerful tool for measuring nanoscale electronic properties and has found many diverse
applications in recent years.
In this talk several novel applications of the KPFM technique recently developed and
demonstrated by our group will be presented.          The first application is a direct
measurement of minority carrier diffusion lengths, which is based on measuring the
surface photovoltage between the KPFM tip and the surface of a uniformly illuminated
semiconductor junction. The second application, called near-field surface photovoltage
(NFSPV), combines the measurement of contact potential difference (CPD) with near-
field optical excitation. The second part of the talk will describe a novel high voltage
atomic force microscope recently developed in our group.        Current scanning probe
instrumentation does not permit applying high voltages (in the kV range) between AFM
tip and sample. We will describe a high voltage AFM (Patent pending) that allows us to
apply voltages as high as 15 kV across an AFM measured sample. The use of the method
for nanoscale domain inversion in bulk ferroelectrics will be described, and possible
other applications will be discussed.
Material Sciences                         14

                                 PbSe ON GaAs(100)

                           Shandalov Michael and Golan Yuval

          Dept. of Materials Engineering, Ben-Gurion University of the Negev
                              Beer-Sheva 84105, ISRAEL

Chemical bath deposition from solution offers a simple and cost-effective route for the
fabrication of high quality semiconductor thin films, without the need for high deposition
temperatures, stringent vacuum or plasma generators. Chemical deposition is particularly
advantageous for the synthesis of nanocrystalline semiconductors (typically in a size
range of up to 10-15 nm), in which the energy bandgap, Eg, can be adjusted by
controlling the grain size of the films due to the quantum size effect. This option allows
us to tune the energy gap of the active semiconducting layers to a desirable range in, e.g.,
devices used for light emission and detection.
Lead selenide (PbSe) semiconductor thin films are widely used in IR detector
applications, as well as for other photonic applications. We have used chemical bath
deposition for the synthesis of highly oriented PbSe thin films. Controlled release of the
reaction precursors was achieved by KOH complexation of Pb2+ ions in the presence of a
selenosulfate source for selenium, and low deposition temperature (0ºC). In this work, we
will present the deposition mechanism and experimental procedure for synthesizing high
quality nanocrystalline PbSe thin films, followed by the results of a detailed structural
characterization study of highly oriented PbSe thin films grown on GaAs(100) substrates.
Cross-sectional and plan view TEM and HRTEM, electron diffraction, EDS chemical
analysis in the TEM as well as intermittent contact AFM were used in order to study the
morphology, crystal structure and chemical composition of the films.
Material Sciences                         15


                          Zenou V.Y., Livne Z. and Venkert A.

           Nuclear Research Center-Negev, P.O.Box 9001, Beer-Sheva, Israel

Maraging steels have an unusually high combination of strength and toughness. Their
ability to meet the high requirements of the aerospace industry as well as other numerous
industrial applications has been successfully proven. The structure of these steels is
essentially martensitic in which the nickel is the effective alloying element. Unlike the
brittle martensite of the conventional carbon steels, the maraging steels martensite is soft
and can readily be machined and formed. Aging of the martensite will result in a
considerable strengthening due to precipitation and an order-disorder reaction.
The microstructure evolvement of solution treated 18% Ni maraging steel, before and
after aging treatment for 3 hour at 510˚C, was investigated. The structure was examined
using optical microscopy (OM), scanning electron microscopy (SEM), transmission
electron microscopy (TEM) and x-ray diffraction (XRD) combined with Reitveld
analysis. In addition, hardness measurements were performed in the samples. The
microstructure of 18% Ni maraging steel showed equi-axial grains of 10μm, which
consisted of small packets of lath martensite. The widths of the layers of lath martensite
varied between 100nm to 250nm. We determined from the selected area diffraction
patterns, which were taken from the martensite, that the structure was α-Fe. Few,
relatively large (2-3 μm) Ti consisting precipitates were randomly spread within the
The 3 hour aging resulted in the segregation of elongated Fe2Mo (20nm in width) and
very small randomly oriented, needle-like (30-40nm long and 7nm wide) FeMo
precipitates inside the martensitic laths. X-ray diffraction showed that the aging caused
reduction of the lattice parameter of the bcc cell from 2.8748A to 2.8690A.
The hardness of the steel increased from 35RC to 58RC due to the aging processes.
No retained austenite was observed in the samples.
Material Sciences                        16


                                Zilberov A, Bamberger M.
                         Department of Materials Engineering
                  Technion- Israel Institute of Technology, Haifa, Israel

AZ91D containing 8,3 to 9.7 %wt. Al is the most commonly used Mg based alloy for
pressure die casting, due to its very good castability. Its low creep resistance, however,
limits its application at temperature below 120 C0.
For this reason the development of a new Mg based alloy with enhanced creep resistance
at elevated temperatures and with castability making it suitable for pressure die casting
and lending structural stability is of a great current interest.
 It was found that promising candidates alloys providing the above mentioned properties
are Mg-Zn-Ca alloys.
The purpose of the present research is microstructural characterization of alloys with the
next chemical composition:

1. Alloy1: 3.2% wt. Zn, 1.58% wt. Ca, 94.73% wt. Mg
2. Alloy2: 8.10% wt. Zn, 1.72%wt. Ca, 89.57% wt. Mg
3. Alloy3: 9.82% wt. Zn, 5.67%wt. Ca, 83.58% wt. Mg

 The microstructure and composition was determined by Scanning Electron Microscope
(SEM) equipped with Energy Dispersive Spectrometer (EDS)
The X-ray diffraction (XRD) was used for phase identification.
Differential Thermal Analyze (DTA) is used to determine temperatures of phase
 The next microstructures were found:

   1. Alloy 1: grains consist of solid solution of Ca and Zn in the Mg matrix; grain
      boundary phase enriched by Zn and Ca; spherical phase enriched by Zn and Ca
   2. Alloy 2: grains consist of solid solution of Ca and Zn in the Mg matrix; two types
      of grain boundary phase (black and white) enriched by Zn and Ca;
   3. Alloy 3: grains consist of solid solution of Ca and Zn in the Mg matrix; grain
      boundary phase enriched by Zn and Ca;

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