Autumn 2005-2006 Schedule
From Nanometers to Meters: New Materials and Processing Technologies for Large-Area Multi-Functional Systems
November 11, 2005; 3:30pm
Presented by:
Prof. Alberto Salleo
Department of Materials Science and Engineering
Stanford University
Applications that require functional systems (e.g. logic, detectors, sensors) to be spread over large-areas are difficult to manufacture with conventional microelectronics technology. Consequently, there is an opportunity to develop new materials systems and processing technologies to address this shortcoming. One requirement that is often considered as crucial is the ability to process materials on flexible substrates. The spectrum of materials that are being investigated includes low-temperature a-Si:H, micro and nano-structured crystalline silicon and organic semiconductors in the form of thermally evaporated or solution processed thin films. In the first part of this presentation I will focus on a particular class of solution processable semiconductors: organic polymers. Charge transport in these materials is still poorly understood. I will show that for semicrystalline polymer films charge transport is described by the multiple trapping and release model (MTR). Furthermore, the MTR model allows to correlate processing, micro-structure and performance in these films, providing guidelines for performance optimization. Interestingly, the MTR model does not apply to all families of organic polymer semiconductor providing further evidence that micro-structure and charge transport mechanisms are intimately related. In the second part of my talk I will present some promising materials systems and processing techniques that may be applied to large-area systems and are of general interest to materials scientists.
Spin Torque and Nanorings
November 4, 2005; 3:30pm
Presented by:
Prof. Chia-Ling Chien
Department of Physics and Astronomy
The Johns Hopkins University
Magnetic nanostructures, in which spin transport, interplay of materials, and small entities are important, have been at the forefront of nanomaterials and nanotechnology. A number of new phenomena have been discovered in magnetic nanostructures and some have led to important devices. In this presentation, some new aspects of spin torque and arrays of magnetic nanorings will be described. The spin torque effect offers the prospects of switching magnetic entities in multilayers and in single layers by a spin-polarized current. Nanoring magnets have the attributes of several unique magnetic configurations including the vortex state with two chiralities and the onion state. We have developed a new method for fabricating a large number (109) of small nanorings (100 nm in diameter) over a macroscopic area (5 cm x 5 cm) with a high areal density (45 rings/µm2). The switching characteristics of Co nanorings, both symmetrical and asymmetrical, will be described.
Nanocrystal Electrical Transport and Self-Assembly
October 28, 2005; 3:30pm
Presented by:
Prof. Yi Cui
Department of Materials Science and Engineering
Stanford University
Colloidal nanocrystals represent an important type of nanomaterials for electronics, photonics and energy conversion. Understanding the electronic coupling characteristics of self-assembled nanocrystal materials is essential for these applications. Here I present my recent research in studying coupling in different forms of self-assembled nanocrystal systems. First, semiconductor nanotetrapods are unique self-assembled systems of quantum dots and rods. I have demonstrated by single electron transistor measurements that either ionic or covalent bonding-type of coupling can exist when the interaction between the quantum dot at the junction and the arm rods is weak or strong, respectively. Second, I have developed a facile fluidic method for organizing nanocrystals into large-scale device arrays, which incorporates a controlled number of nanocrystals at lithographically precise locations on a chip and within a circuit. The method provides interesting systems for studying chemically-tunable coupling phenomena.
Why Are There So Few Magnetic Ferroelectrics?
October 21, 2005; 3:30pm
Presented by:
Prof. Nicola A. Spaldin
Materials Department
University of California Santa Barbara
Multiferroic magnetoelectrics are materials that
are both ferromagnetic and ferroelectric in the
same phase. As a result they have a spontaneous
magnetization which can be switched by an applied
magnetic field, a spontaneous polarization which
can be switched by an applied electric field, and
often some coupling between the two. Very few exist
in nature, or have been synthesized in the laboratory,
but there is some incentive to produce new multiferroics
for specific technological applications.
In this talk we use the study of multiferroics
to illustrate the utility of theoretical and computational
methods in the design of new technologically relevant
materials. First we determine the fundamental physics
behind the scarcity of ferromagnetic ferroelectric
coexistence, and show that in general the transition
metal d electrons, which are essential for magnetism,
reduce the tendency for off-center ferroelectric
distortion. Then we identify the chemistry behind
the additional electronic or structural driving
forces that must be present for ferromagnetism
and ferroelectricity to occur simultaneously. Finally
we describe the successful prediction and subsequent
synthesis of new multiferroic materials.
Aberration-Corrected Electron Microscopy: What are the New Perspectives for Materials Science?
October 14, 2005; 3:30pm
Presented by:
Dr. Christian Kisielowski
Staff Scientist and principle Investigator
National Center for Electron Microscopy (NCEM)
Lawrence Berkeley National Lab
Berkeley, CA
Ongoing technological advancements of electron
microscopy will reshape the way electron scattering
is utilized to investigate structure and composition
of materials down to the atomic level. It is foreseeable
(and partly established) that electron microscopes
will have the ability to image single atoms of
most elements of the periodic table of elements
and to tie the spatial information to spectroscopy,
which probes for chemical constituents and local
bonding. Therefore, a three-dimensional materials
characterization can reach towards atomic resolution
and it is feasible to solve the long-standing problem
of information loss that comes from projecting
the 3D materials structure into a 2D image plane.
This talk highlights how much materials science
already benefits from recent advancement of instrumentation.
Application examples include a characterization
of a dislocation in GaAs in terms of displacement
fields and impurity segregation, investigations
of strain relaxation processes in FePt nanoparticles,
and investigations of local band gap fluctuations
that are induced by indium clusters in GaN/InGaN/GaN
quantum wells. The given examples also point to
current limitations that will be removed by the
next generation of fully aberration corrected microscopes,
which are currently developed within the DoE’s
TEAM-Project.
Moore's Law and Magnetic Recording Areal Density – A Nano Processing Perspective
October 7, 2005; 3:30pm
Presented by:
Dr. Robert E. Fontana, Jr.
2005 IEEE Magnetics Society Distinguished Lecturer
San Jose Research Center
Hitachi Global Storage Technologies
This talk examines the growth of magnetic recording storage density (disk drive capacity) from the perspective of thin film nano processing. Over the past 25 years, Moore’s Law scaling has characterized the progress of the magnetic recording industry with magnetic recording storage densities increasing by a factor of 10,000 to densities of 120 Gbit/in². Today, typical disk drive capacities are 40 GB with a cost of $2.00/GB. These economies of capacity and cost have been accomplished by the ability to fabricate thin film heads, the transducers that write and read magnetic transitions on a disk surface, at nano scale dimensions. The critical structures in the thin film heads are now 100 nm in length, 30 nm in thickness, and formed from 4 to 5 layers of thin magnetic and metallic films, each in the 1 nm to 10 nm thickness range.
This talk describes the processes to form these sensor dimensions, shows that future areal density growth rates in the magnetic recording will be sustained by minimum feature processing and will be limited by the semiconductor lithography roadmap, and compares semiconductor and thin film head processing strategies for achieving smaller device sizes. The talk will describe, in detail, a subtractive nano processing module that is practiced in our laboratory for the formation of nano wires with sub 50 nm features.
Lastly, comparisons between solid state non-volatile memory (NAND) areal efficiency and magnetic recording areal density increases will be made with a prediction of sustained annual density improvements of 25% to 35%. The magnetic recording industry anticipates products achieving > 360 Gbit/in² magnetic recording densities in 3 years (2008) with 40 nm minimum features. NAND flash anticipates products with > 100 Gbit/in² areal efficiency in 2 years (2007) with 50 nm minimum features.