From: calendar@ALMADEN.IBM.COM (IBM Almaden Research Center Calendar)
Newsgroups: ba.seminars
Subject: IBM ARC seminars 20 - 24 APR 92
Date: 16 Apr 92 15:35:30 GMT
Article-I.D.: almaden.920416.083530.calendar


                     IBM Almaden Research Center
                           650 Harry Road
                       San Jose, CA 95120-6099

                              CALENDAR

                          April 20-24, 1992


04/20 - GLASS FORMATION, CRYSTALLIZATION KINETICS, AND
VISCOSITY-STRUCTURE RELATIONSHIPS IN MOLTEN SALTS AND MOLECULAR LIQUIDS
Ms. H. Senapati, Department of Chemistry, Arizona State University

Poly. Sci. & Tech. Sem.    Mon., April 20    10:00 a.m.    Room:  E2-450

The two fundamental problems in glass science are (i) the kinetics of
crystallization of supercooled liquids and (ii) the relationship of
molecular structure to the properties of the supercooled liquids and
glasses.  This talk will give attention to both of these areas.
Firstly, we will describe a simple and efficient calorimetric technique
that allows us to directly obtain the Time-Temperature-Transformation
curves for crystal nucleation and growth; furthermore we show how a
multi-step adaptation of the technique can separate nucleation kinetics
from growth kinetics.  As examples we will look at the kinetics of
crystallization in a model glass-forming system Ca(NO3)2 - KNO3 which
gives "fragile" liquids, and two other systems of intermediate
fragility:  the mixed anion system AgI - Ag2 SO4 - Ag2 WO4 and the
hydrogen-bonded system glycerol-water.  We will compare their
crystallization kinetics with those of classical silicate glasses
obtained by traditional microscopy methods.  The second part of the talk
will deal with some intriguing structure-viscosity relationships
observed in supercooled organic liquids.  We will briefly describe the
strong-and-fragile classification of liquids and examine how the
presence of phenyl rings and hydrogen bonding affects the fragility.
Host:  T. Karis


04/20 - MAGNETIC PROPERTIES OF CO/PT AND MAGNETORESISTANCE OF CO/CU
MULTILAYERS SPUTTER-DEPOSITED ON GLASS SUBSTRATES
S. Honda, Department of Physical Electronics, Hiroshima University

Phys. Sci. Sem.    Mon., April 20    10:30 a.m.    Room:  D2-450

1.  Co/Pt Sputtered Multilayers

In order to make clear the origin of perpendicular coercivity in Co/Pt
multilayers, we examined the magnetic properties and the film morphology
of Co/Pt multilayers sputter-deposited on glass substrates with negative
bias voltage.  For OV bias, the film consists of columns grown
perpendicular to the substrate and convex interfaces.  The column
boundaries and the convex interfaces act as the pinning center for the
domain wall motion resulting in the high perpendicular coercivity,
Hc(perpend).  In the -30V  biased multilayers, the columns are fine
and close-paced, and thereby the layer interfaces are smooth and sharp.
So that, Hc(perpend) is very small in these multilayers.  Thus,
Hc(perpend) is strongly affected by the film morphology such as the
column boundaries or the layer interfaces.

In order to throw light on the origin of the perpendicular anisotropy,
we have modulated the bias voltage applied at substrates; VB was
applied only during deposition of Co or Pt layers.  For -30V and -50V
Co bias films, the interface is very sharp and the surface anisotropy
energy Ks becomes large because of the well defined interface
concerned with the Neel surface anisotropy.  However, the volume
anisotropy energy Kv decreases owing to the in-plane compressive
strain in Co layers having negative magnetostriction constant.  On
the other hand, for -50V Pt bias films, the mixing of Co and Pt
occurs over two monolayers at the interfaces.  The anisotropy K??
increases also by the different mechanism from the Co bias films.  The
enhancement arises from the in-plane compressive strain in CoPt alloyed
layers formed at the interfaces.

2.  Magnetoresistance in Bias Sputtered Co/Cu Multilayers

Several researchers showed the magnetoresistance (MR) characteristics
are severely affected by both the film morphology and the interface
structure.  Therefore, we have studied the effects of Ar gas pressure
PAr and VB on both the film structure and the MR in Co/Cu sputtered
multilayers.

In the films prepared at low pressure of 3 mTorr with OV, three well
defined oscillation peaks in MR ratio vs Cu thickness dcu appear with
the period of 12A%, and the maximum value of 46% in MR ratio was
obtained at the first peak.  However, in the films prepared at high
pressure of 10 mTorr, the MR ratio increases monotonically with dcu
until 50A%.  For the -30V bias films prepared at high pressure of
10 mTorr, although the first peak cannot be observed, three
oscillation peaks can be observed also because of well defined
interfaces due to VE.  At the second peak, saturation field and
coercive field are very small compared with OV films and the MR
changes drastically at low field less than 200 Oe.  In this case,
the antiferro-coupling constant J was very small, that is
J = 0.008 erg/cm2.  This suggests that the Co/Cu system sputtered on
glass with -30V is promising for applications to MR sensors.
Host:  R. Farrow


04/23 - MECHANISMS OF HIGH RATE DEPOSITION AND ETCHING OF SILICON IN THE
SI(S)/H2/SIH4-SYSTEM
S. Veprek, Technical University of Munich, Germany

Phys. Sci. Sem.    Thurs., April 23    10:30 a.m.    Room:  J2-609

The mechanism of the plasma induced deposition which includes the
formation of higher silanes will be outlined and the crucial
experiments which support it summarized.  The understanding of the
rate limiting steps allows us to control them and to deposit
amorphous, polycrystalline and epitaxial silicon at high rates.  For
example, a-Si can be reproducibly deposited at rates of 17
Angstroms/sec which has a very low defect density of 3 x 1015/cm3 and
low Urbach edge energy of 45 meV.  Some remarks regarding the
photodegradation and other properties of the material will be
mentioned.

In a very pure hydrogen discharge, one can etch silicon at rates of 100
nm/min.  The influence of electron and ion bombardment and of oxygen
impurities will be summarized.  Controlling the total oxygen impurity in
the range of 5 to 50 parts per million allows one to also control the
anisotropy of the process from almost isotropic to highly anisotropic.
Host:  H. Winters


04/23 - SPECTROSCOPY OF NEUTRAL SILICON CLUSTERS, Si18 - Si41 SMALL
SILICON CLUSTERS OPTICALLY LOOK LIKE SILICON BULK!
Dr. K.-D. Rinnen, Materials Chemistry Research, AT&T Bell Laboratories

Phys. Sci. Sem.    Thurs., April 23    10:30 a.m.    Room:  D2-450

Absorption spectra from 0.94-5.58 eV are obtained for neutral silicon
clusters, Si18 - Si41, using resonant one-file two-color
photodissociation spectroscopy.  The spectra of all clusters are
essentially identical.  Above 3.0 eV, they exhibit six sharp
absorption peaks with cross sections 0.1 - 1.2 angstrom2.  Multiple
photon absorption peaks dominate the spectrum below 3.0 eV.
Comparison of the silicon cluster spectra to those of various forms of
silicon show that they have much in common with the spectra of bulk
diamond lattice crystalline silicon.  Our results are also discussed
in the light of recent results from other workers at AT&T.
Host:  H. Hunziker


04/24 - TRANSFORMATIONAL PARALLEL-PROGRAM DERIVATION
J. A. Yang, Yale University, New Haven, CT

Comp. Sci. Sem.    Fri., April 24    10:30 a.m.    Room:  B2-307

This talk presents a novel parallel-programming methodology based on
transformational program derivation and functional programming.  In a
single framework, it formalizes the process of mapping, scheduling and
optimizing high level functional specifications onto various target
parallel architectures.  We start from verified initial abstract
programs.  Equational transformations are then applied to derive more
concrete programs which yield easily to efficient parallel
implementation.  Because all the derivation steps preserve equalities,
the correctness of the derived programs is established along with the
derivation as a by-product.  A set of metalinguistic constructs which
facilitates the mechanical aspects of the program transformation will
also be discussed.
Host:  H. Ho


04/24 - TOPOLOGY AND NEMATIC ORDERING
D. Rokhsar, Department of Physics, Univ. of California, Berkeley

Phys. Sci. Colloq.    Fri., April 24    10:30 a.m.    Room:  Aud. A

Nematic fluids are composed of rod-like molecules with approximate
head-to-tail symmetry.  At high temperatures the molecular orientations
are disordered, and the fluid is isotropic; at low temperatures the axes
align, resulting in an ordered, anisotropic fluid.  The transition
between these two phases is discontinuous (i.e., has a latent heat), in
contrast with the continuous order-to-disorder transition in a magnet.
A basic qualitative difference between the two systems is that the local
order in a magnet is described by a vector, while the order in a nematic
liquid crystal is described by an axis (i.e., a headless vector).  The
importance of this distinction will be discussed in terms of a lattice
gauge theory for nematics.
Host:  B. Jones

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For further information on individual talks, please contact the host
listed above.

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Xref: sparky ba.seminars:333 ucb.seminars:278 ba.general:1718 ucb.general:246