The Laboratory for Molecular Robotics at USC offers a seminar series focusing on Nanosystems. We hope to provide a forum for discussing the emerging field of nanoscience and nanoengineering, and for bringing together USC faculty and students with an interest in the area. There are talks by USC and external speakers. The seminars are open to the scientific community, within and outside USC. Times and locations vary. Please refer to the specific seminar announcements. During the academic year 2004-2005 nanotech seminars at USC were primarily recruiting talks and are not included here.
SCHEDULE
Tuesday, March 28, 2006
Prof. Karl Bohringer, University of Washington, Seattle, WA,
"Micromanipulation, Microrobots, and Microfluidics with
Programmable Surfaces",
SSL 150,
3:00-4:30
Abstract
The surface-to-volume ratio increases with decreasing scale, thus,
being able to control and change surface properties with high spatial
and temporal resolution can be a powerful tool in the design,
fabrication, and use of microelectromechanical systems (MEMS). This
presentation introduces "programmable surfaces" as the unifying theme
in a series of recent projects that utilize the modulation of surface
forces, hydrophobicity, and biocompatibility, with applications in
microrobotics, micro-scale self-assembly, and bio-medical microdevices.
Bio Information
Karl Bohringer is an associate professor in Electrical Engineering with
adjunct appointments in Computer Science & Engineering and in
Mechanical Engineering at the University of Washington, Seattle. He
received both his M.S. and Ph.D. degrees in Computer Science from
Cornell University and his Diplom-Informatiker degree from the
University of Karlsruhe, Germany. He was a visiting scholar at the
Stanford Robotics Lab and Transducer Lab and a postdoctoral researcher
at the University of California, Berkeley, before joining the faculty
at the University of Washington.
His current interests include micromanipulation and microassembly, as
well as biomedical implants and bioMEMS for single-cell genomics and
proteomics. His Ph.D. thesis was nominated for the ACM doctoral
dissertation award. He received an NSF postdoctoral associateship in
1997, an NSF CAREER award in 1999, and was an NSF New Century Scholar
in 2000. His work was featured among the Top 100 Science Stories in
Discover Magazine's 2002 "Year in Science". In 2004, he received the
IEEE Robotics and Automation Society Academic Early Career Award and a
sabbatical fellowship from the Japan Society for the Promotion of
Science (JSPS).
Wednesday, February 2, 2005
Prof. Ron Folman, Ben-Gurion University, Israel,
"Matter Wave Quantum Technology: A birth of a new technology at the
extreme of the nano scale",
Gerontology Auditorium,
12:00-1:00
Abstract
We have known about the atom for a long time, but only in 1997 and
2001 when 2 Nobel prizes were given in the field of Atom Optics, did it become
clear that we also know how to manipulate the atoms. The main challenge was to
cool the atoms down to such a temperature, where they could be trapped in one
place, completely isolated, having no thermal energy, and hence could act as a
pure quantum system. We now regularly cool atoms and ions to nano Kelvin
temperatures. This talk will review these cooling methods, and which new science
and technology can emerge from these very cold atoms and ions.
Bio Information
I was Born in 1963 in Israel, and following my biologist father,
spent time also in places like UK, Australia, and even 2 years in LA. I spent 7
years as a pilot for the Israeli Airforce, during which I finished me first
degree. My second and third degree were in elementary particles at the Weizmann
institute of science. I spent several years taking data at the European Nuclear
research Center (CERN), in Geneva. I then changed from elementary particles to
Atom optics, and after a post doc in Innsbruck, became a researcher in
Heidelberg. The focus of my research is the AtomChip.
Friday, July 30, 2004
W. Seth Horne, Department of Chemistry, Ghadiri Lab,
The Scripps Research Institute, La Jolla, CA,
"Non-natural Backbone and Side Chain Modifications in Peptide Based
Supramolecular Designs",
Room HNB 100 (Hedco Neurosciences Auditorium),
10:00-11:00 (with continuing discussion to 11:30)
Abstract
The inherent predisposition toward ordered structure and synthetic
accessibility of polypeptides make this class of compounds a powerful
base for supramolecular designs. Chemical synthesis allows such designs
to expand beyond amino acid side chains found in nature as well as the
peptide backbone itself. In one project exploring such modifications,
we have prepared and studied a variety of peptides incorporating
1,4-disubstituted-1,2,3-triazole e-amino acids as dipeptide surrogates.
These building blocks have been incorporated into both linear and cyclic
systems in an effort to explore structural effects of the heterocyclic
backbone modification. The orthogonal reactivity between building blocks
for the amide bond and its triazole replacement provides an alternate
synthetic route to these structures. In another project aimed toward
peptide based materials, we have prepared self-assembling cyclic peptides
bearing 1,4,5,8-naphthalenetetracarboxylic diimide (NDI) modified side
chains in an effort to produce supramolecular aggregates with interesting
electronic properties. Studies in a model system indicate that the peptide
scaffold is capable of templating intermolecular charge transfer between
NDI moieties and that the efficiency of this process depends on structural
factors that are readily addressed synthetically. Recent efforts expand
this result into systems capable of higher order assembly.
Tuesday, April 20, 2004
Prof. Alberto Credi, Department of Chemistry,
University of Bologna, Italy, "Molecular Nanotechnology:
Towards Artificial Molecular Devices and Machines",
Room DRB 140,
10:00-11:00 (with continuing discussion to 11:30)
Abstract
In the context of the challenge offered by the bottom-up approach to
nanotechnology, chemists have been extending the concept of a macroscopic
device to the molecular level [1]. A molecular device can be defined as an
assembly of a distinct number of molecular components (that is, a
supramolecular system) designed to carry out a complex function, resulting
from the cooperation of the simple acts performed by each molecular component.
Of particular interest are molecular-scale devices in which the component
parts can be set in motion upon appropriate stimulation, that is, molecular
machines [1,2]. The energy needed to operate molecular devices and machines
can be provided in form of chemical energy, electrical energy, or light;
however, for several reasons, light stimuli constitute one of the most
convenient ways to power these systems, as well as to monitor their
operations.
Molecular machines are ubiquitous in biological systems. Motor proteins
are extremely complex assemblies, the structures and detailed working
mechanisms of which have been elucidated only in a few cases. Since any
attempt to construct fully artificial systems of such a complexity by using
the bottom-up molecular approach would be hopeless, chemists are trying to
construct much simpler molecular-level machines. In the last few years,
synthetic talent, that has always been the most distinctive feature of
chemists, combined with a device-driven ingenuity evolved from chemists
attention to functions and reactivity, have led to the design and construction
of a great number of very interesting molecular machines [1,2]. Recent
examples studied in our laboratories - based on threaded and interlocked
molecular systems like pseudorotaxanes, rotaxanes and catenanes - will be
presented, and limitations and perspectives of this kind of systems will be
discussed.
References
[1] V. Balzani, A. Credi, M. Venturi, Molecular Devices and Machines
A Journey into the Nano World, Wiley-VCH, Weinheim, 2003.
[2] V. Balzani, A. Credi, F.M. Raymo, J.F. Stoddart, Angew. Chem. Int. Ed. 2000, 39, 3348.
Monday, April 5, 2004
Filippo Marchioni, Department of Chemistry,
University of Bologna, Italy, "Molecular Devices",
Room PHE 223 (Powell Hall),
10:30-11:30 (with continuing discussion to 12:00)
Abstract
A macroscopic device is something invented and constructed for a special
purpose. On going to molecular scale, a molecular-level device can be
defined as an assembly of a discrete number of molecular components
designed to perform a specific function. A molecular-level machine
can be defined as a particular type of molecular-level device in which
the relative positions of component parts change as a result of an external
stimulus. Molecular-level devices and machines operate via electronic
and/or nuclear rearrangements and, like their macroscopic counterparts,
need energy to operate and signal to communicate with the operator. In the
last ten years several prototypes of molecular-level devices and machines
have been studied. Here we show the design, synthesis and operations of
some molecular-level devices and machines, and specifically: (i) molecular
shuttles based on rotaxanes; (ii) molecular clips; (iii) dendrimers for
charge pooling and sensor applications.
Bio Information
Filippo Marchioni is finishing a thesis on "Photophysical and electrochemical
characterization of catenanes", under the supervision of Professor Vincenzo
Balzani
in the Department of Chemistry, University of Bologna, Italy. His
research interests are in photophysics, photochemistry and electrochemistry
of supramolecular systems, particularly of catenanes, rotaxanes, dendrimers,
host-guest systems and metal complexes; photocromism; photoinduced energy-
and electron-transfer processes.
Wednesday, February 25, 2004
Prof. Joseph Cline, Department of Chemistry,
University of Nevada at Reno, "Progress toward a practical light-powered
rotary molecular motor",
Room HNB 100 (Hedco Neurosciences Auditorium),
11-12 (with continuing discussion to 12:30)
Abstract
A key component of nanoscale machinery is the controlled positioning
and delivery of mechanical power to nanometer scale structures.
Light-controlled actuation offers numerous advantages over the
chemical fuels that power biological molecular motors. Our group has
designed, modeled, and is synthesizing and testing a rotary
single-molecule motor. The motor consists of a rotor chromophore
which photoisomerizes while mechanically coupled to a base stator
structure. Unidirectionality of rotation is created by
non-equilibrium molecular dynamics on a chiral potential energy
surface for gearing of the rotor and stator. We already have made
measurements of photoisomerization quantum efficiency, thermal and
photochemical stability, and optical properties of an achiral motor
prototype. We also will report our synthetic progress toward the
final motor structure and show the theoretical performance
expectations for the completed motor. Finally, a few speculative
applications will be discussed.
Bio Information
Joe Cline is Professor of Chemistry and Director of the Chemical
Physics Program at the University of Nevada, Reno. He received a
B.S. Degree in Chemistry in 1983 from the University of Virginia and a
Ph.D. in Physical Chemistry from the California Institute of
Technology in 1988. He was a postdoctoral fellow at JILA/University
of Colorado in 1988-1990. Cline's research specialization is in
molecular spectroscopy and molecular reaction dynamics. He has
published extensively in the areas of molecular photodissociation
dynamics, inelastic molecular scattering, and spectroscopic detection
of molecular rotational alignment and orientation. Recently his
research group has turned its focus to the generation and detection of
unidirectional mechanical rotation driven by light absorption.
Wednesday, December 10, 2003
Emil Kartalov, Department of Applied Physics, Quake Lab,
California Institute of Technology, "Single molecule detection and
microfluidic DNA sequencing by synthesis",
Room HNB 100 (Hedco Neurosciences Auditorium),
10-11 (with continuing discussion to 11:30)
Abstract
Fluorescence detection has established itself as one of the main techniques
of investigation of biological and biochemical systems. Extending those
techniques to decrease the sample size to single molecules provides an absolute
standard for bulk sample calibrations, as well as better insights since
individual behavior is observed instead of population averages. We observed
a number of fluorophores, including GFP, at the single molecule level at
room temperature without a laser. Single molecule calibrations were shown
to give a correct estimate of bulk surface densities over four orders of
magnitude, through a optical, non-invasive, non-destructive means. Novel
surface chemistry enabled visualization of single tagged nucleotide
incorporations inside DNA immobilized on a glass surface at the single
molecule level. This technology was later extended to successful
single-molecule DNA sequencing.
At the same time, DMS microfluidic technology was developed to provide the
plumbing control, speed and economy of scale for a broad range of applications.
Novel surface chemistry anchored DNA to the PDMS channels, which allowed
sequencing-by-synthesis to be conducted in the microfluidic environment,
leading to an economy of scale in reagents. Materials, device and architecture
problems were also solved. Finally, all technology was put together and
demonstrated successful microfluidic bulk-fluorescence DNA sequencing. The
same technology can eventually be extended to close the circle to single
molecule detection. Since the architectural flexibility of the underlying
technology provides functional diversity while the surface chemistry
anchors the DNA regardless of the plumbing layout, the surface chemsitry and
microfluidic system by itself is applicable to any DNA studies in microfluidic
environments.
Wednesday, November 19, 2003
Prof. Ken Nealson, Wrigley Chair in Environmental Studies,
College of Letters, Arts and Sciences, Earth Sciences,
University of Southern California, "The things bacteria do, from
energetics to behavior",
Room HNB 100 (Hedco Neurosciences Auditorium),
10:00-11:00 a.m. (with continuing discussion to 11:30).
Thursday, July 17, 2003
Xinyan Deng, Robotics Laboratory,
University of California at Berkeley, "Virtual Insect Flight Simulator for
a Micromechanical Flying Insect: Modeling, Identification and Biomimetic
Flight Control in Hover",
Room HNB 107 (Hedco Neurosciences Auditorium),
10:30-11:30 a.m.
Abstract
In this talk I will present the design and implementation of a
Virtual Insect Flight Simulator (VIFS), a modeling and simulation tool for
studying real insect flight mechanism and designing a Micromechanical
Flying Insect (MFI). The goal of the MFI project is to build a 10-25mm
(wingtip-to-wingtip) flapping wing micro robot capable of sustained
autonomous flight, and VIFS serves as the link between biological
discoveries and engineering design considerations. It consists of
several modular blocks which model the wing aerodynamics, body dynamics,
thorax actuators, biomimetic sensors, and flight control algorithms.
Biologically inspired wing trajectory parameterization was designed to
sustain body weight and decouple body torques. Controllability is ensured
by considering averaging under high frequency high amplitude forcing.
Position control was achieved through attitude regulation. A nominal
model in hover was identified through linear estimation. Pole placement
feedback control and LQG regulator was designed to stabilize MFI in
hovering, steering and recovering from upside down.
Thursday, May 1, 2003
Prof. Arun Majumdar, Department of Mechanical Engineering,
University of California at Berkeley, "Transport and Mechanics
in Nanostructures", Room HNB 100 (Hedco Neurosciences Auditorium),
12:00-1:00 p.m.
Abstract
When solids and fluids are confined to length scales smaller than
100 nm, one encounters transitions in many aspects of their
behavior. This is because there are several characteristic length
scales related to their behavior that fall in this length scale regime.
In the first part of my talk, I will focus on solids: in particular, on
how energy transport via crystal vibrations and energy dissipation
through electron-vibration coupling can be different at length
scales smaller than 100 nm. It will be apparent that in this regime,
size is a tuning parameter that can be used to control such transport
and dissipative properties. As will be evident, this fundamental
understanding is critical in the development of solid-state energy
conversion devices, which could have impact in the way energy is
utilized and converted in the future. In the second part of the talk,
I will concentrate on the fundamental length scales related to
intermolecular and surface forces in liquids and liquid-solid
interfaces. Part of the discussion will focus on the mechanics of
biological molecules, such as DNA and proteins, and the role of
entropic forces in their mechanical behavior. Next, I will discuss
how the mechanics of biomolecules can be coupled with that of
microstructures to develop biosensors. It will also be evident that
this fundamental knowledge on molecular nanomechanics has
several practical applications in biotechnology.
Bio Information
Dr. Arun Majumdar is a Professor in the Department of Mechanical
Engineering, University of California, Berkeley, where he served as the
vice chair from 1999-2002. He completed his PhD in ME from UC
Berkeley in 1989, after which he was in Arizona State Univ. (1989-92)
and UC Santa Barbara (1992-96) as a faculty in Mechanical Engineering.
He is a recipient of the NSF Young Investigator Award, the ASME
Melville Medal, the ASME Best Paper Award from the Heat Transfer
Division, and the 2001 Gustus Larson Memorial Award from the ASME.
He is currently serving as an editor for the Int. Journal of Heat and Mass
Transfer, and the co-editor-in-chief of Microscale Thermophysical
Engineering. He also serves as the Chair, Board of Advisors, ASME
Nanotechnology Institute; Member, Council on Materials Science and
Engineering, US Dept. of Energy; Member, Chancellor's Advisory
Council on Nanoscience and Nanoengineering at UC Berkeley. He is a
fellow of the ASME and the American Association for the Advancement
of Science (AAAS).
Thursday, February 14, 2002
Prof. Xiang Zhang, Department of Mechanical Engineering,
University of California at Los Angeles, "Exploration of Sub-Wavelength
Photonic Structures", Room SAL 222 (Henry Salvatori Computer Science Bldg.),
12:00-1:00 p.m.
Abstract
Meta-materials with engineered subwavelength
inhomogeneities enable the realization of novel properties that are
unattainable from naturally existing materials. In this talk, I’'l
discuss a recent MURI program that my collaborators and I started
six months ago. Theoretical and preliminary experimental studies
by several Co-PIs of this project have shown that it is possible to
make electromagnetic meta-materials with unprecedented
characteristics such as left-handedness with simultaneous negative
permittivity and permeability, negative lens that focuses
electromagnetic waves far below the diffraction limit, and artificial
magnetism from nonmagnetic materials. These new properties can
lead to many exciting potential applications that are important for
both DoD and commercial sectors. Our MURI team aim at
demonstrating revolutionary properties of meta-materials through
the development of innovative synthesis technologies, theoretical
simulations, experimental characterizations, and device
development. We anticipate that the fundamental discoveries from
this project will have profound impacts in a wide range of
applications such as nanolithography, magnetic resonance image,
microwave and optical communication.
Bio Information
Dr. Xiang Zhang is an Associate Professor and
Director of DoD MURI Center on Scalable and
Reconfigurable Metamaterials at UCLA. He received PhD
from UC Berkeley in 1996 and BS/MS from Nanjing
University, China. He is a receipient of NSF CAREER
award (1997) and ONR Young Investigator award (1999).
Thursday, January 24, 2002
Kwok Hay Ng, Department of Chemistry,
University of California at Irvine, "Metal and Semiconductor
Nanostructures by Electrodeposition", Room EEB 248
(Electrical Enginering Building),
12:00-1:00 p.m.
Abstract
This presentation will be divided in to two parts: (1) Electrochemical
methods for preparing two silver/copper bimetallic archetypes and (2)
Electrochemical/chemical synthesis of Molybdenum Disulfide nanoparticles and
nanowires.
In the first part of the presentation, two electrochemical methods to prepare short-range orderings of two metals (silver and copper) with respect to one another will be discussed. Bimetallic core-shell particles having a silver core and a copper shell were obtained by electrodepositing silver particles first, and then electrodepositing copper using a small overpotential. Silver-copper "oligomers", consisting of a central silver particle surrounded by one or more copper "satellite" particles were obtained by first electrodepositing silver particles, assembling an n-alkane thiolate molecular layer on the surfaces of these particles from ethanolic solution, and then electrodepositing copper using a low overpotential. The structures of both types of bimetallic particles were determined using scanning electron microscopy in conjunction with spatially resolved x-ray fluorescence elemental analysis.
In the second part of the talk, preparation of molybdenum disulfide particles and wires will be discussed. MoOx particles were deposited electrochemically from MoO42- ions in an electrolyte solution. The metal oxide particles were then converted into MoS2 particles by heating in a tube furnace with H2S gas at 500oC. MoS2 nanowires can be prepared by step edge decoration before the gas phase conversion. Transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) confirmed the crystalline structure and the stoichiometric ratio of molybdenum to sulfur. Photoluminescence spectroscopic analysis showed an emission peak around 2 eV. When the experiment was repeated with smaller crystalline sizes, the center of the PL peak shifted to higher energies qualitatively in accordance with the predictions of the effective mass, strong confinement model.
Thursday, February 15, 2001
Dr. Fernando Teran-Arce, Department of Physics,
Northwestern University, "Mechanical properties of surfaces studied by
AFM nanoindentation", PHE 223 (Neustadt Conference Room, Powell Hall),
12:30-1:30 p.m.
Abstract
The atomic force microscope (AFM) can be used to perform
nanoindentations. The resulting indentation curves serve
to characterize at the nanometer scale the elastic and strength properties
of materials. Furthermore, one can follow in situ the recovery
of the surface after the indentation. Nanoindentations on surfaces of
an ionic crystal, MgO(100), and a Langmuir-Blodgett film of a fatty acid
(C21) have been carried out. In both cases, force vs. distance curves
show characteristic discontinuities associated with the depth of atomic
or molecular layers being expelled by the tip. Indentation curves
extracted from the force plots show two regions. One of them corresponds
to elastic deformation of the surface. The other one starts with the
onset of discontinuities and corresponds to plastic deformation. The
Young's modulus and the critical shear stress of the materials have been
obtained from these indentation curves. In the case of MgO, it was found
that relative humidity, RH, plays a fundamental role in the kinetics of
surface recovery after the indentation.
Thursday, May 4, 2000
Prof. Harry Atwater, Department of Applied Physics, Caltech,
12 noon.
Friday, April 28, 2000
Bjorn Marsen, Department of Physics, University of Hawai, 10:30 a.m.
Friday, March 31, 2000
Brandon Weeks, Department of Chemistry, Cambridge University, U.K,
"Applications of high pressure scanning tunneling microscopy",
HNB 100, 11 a.m.
Abstract
One of the most popular approaches to characterize catalytic surfaces is
the use of high-pressure isolation chambers. The chamber allows samples
that have been prepared and characterized by traditional ultra-high vacuum
(UHV) techniques to be exposed to high pressures and temperatures. Data
obtained under high vacuum is then related to the structure under 'real'
conditions. However, this technique still presents a problem: Are the
structures observed under UHV similar to those formed in the reaction
chamber, or have the surfaces rearranged during transfer?
STM is an ideal tool for in-situ studies since it is capable of imaging in
both vacuum and high pressure, low (4 K) and high temperatures (>1000 K).
However, very few instruments have been built that utilized the unique
range of STM because of the difficulty in designing such an instrument. A
novel instrument will be described which can be operated at pressures up
to 60 bar and temperatures in excess of 700 K. The challenges of
implementing such an instrument will also be discussed along with
preliminary results.
Friday, February 11, 2000
Prof. Young Kuk, Department of Physics and Center for Science in Nanometer
Scale, Seoul National University, Korea,
"New concept of memory based on scanning probe microscopy", EEB248, 10:30 am.
Abstract
In present technology, data are stored in the form of small magnetic dipoles,
capacitors and electrical charge traps. They can be read by measuring the
stored energy
in them. Many expect that the reading and writing mechanisms will not
change for the
next 10 years. However, with down-sizing of recorded bits, developing new
types of
media, reading and writing devices, new concepts are demanded.
This demand may be
met by exploring new or existing but not-used, physical principles.
New direction for
reading sub-0.05 um magnetic and trap recording bits will be introduced.
Monday, January 24, 2000
Prof. Claudio Nicolini, Director of the Institute for Biophysics, University
of Genoa, Italy, President of the EL.B.A. Foundation,
"Bionanotechnology", HNB 107, 10:30 am.
Thursday, January 20, 2000
Scott Paulson, Department of Physics, University of North Carolina.
"Molecular Manipulation and Carbon Nanotube Electronics", PHE 223, noon.
Abstract
An advanced interface that allows for facile manipulation
of macromolecules has been developed. This interface has allowed
for studies of mechanical/frictional properties of objects on the ~10
nm length scale, the development of a precise AFM based
lithography, and the electrical response of carbon nanotubes to
mechanical strain. Basic properties of carbon nanotubes and their
electronic properties will be discussed, and we show that
nanotubes are robust electrical conductors even while being
deformed to the point of fracture. Theoretical explanations of this
behavior, as well as the nature of the junction between ends of a
broken nanotube will also be presented.
Thursday, September 9, 1999
Dr. Bruce Weiller, The Aerospace Corporation,
Mechanics and Materials Technology Center,
"Space Applications of Micromachined Chemical Sensors", room TBA, noon.
Abstract
We have been developing chemical microsensors for the detection of chemicals
important in the following areas: propellants, rocket exhaust plumes,
contaminants for spacecraft electronic and optical components,
and manned space flight. In earlier work, we developed chemical microsensors
for the detection of hydrogen, O atoms, ozone, and HCl. The HCl sensor has
potential for solid rocket motor exhaust plume detection. It is
based on the use of phthalocyanines on a 3x3 mm hot plate sensor substrate.
Recently we have developed a micromachined version of this sensor using a
novel combination of chemical and laser micromachining. An IR microscope
was used for thermal imaging of the micro hot plate. The device has very
high thermal efficiency, a fast response time, and consumes very little power.
Data will be presented on the characterization of phthalocyanine sensor
films and the micro hot plate device.
Friday, April 23, 1999
Prof. Mauro Ferrari, Director, Biomedical Engineering Center,
Ohio State University, "Therapeutic Applications of BioMEMS and
Biomedical Nanotechnologies: A View from the Trenches", HNB 107, noon.
Abstract
We will review the historical antecedents, and the main components of the
current wave of interest in therapeutic applications of BioMEMS and
biomedical nanotechnology. These will include nerve/spinal reconstruction
templates, micromachined tissue engineering scaffolds, and cell
transplantation microsystems. The main emphasis of the lecture will be in
drug delivery, and focusing on the potential advantages that
BioMEMS/BioNEMS have over competitive technologies, such as liposomes, and
polymer-based biodegradable microspheres.
Friday, March 26, 1999
Paul Rothemund, Computer Science Department, USC,
"Programmed self-assembly using lateral capillary forces", HNB 107, noon.
Abstract
Self-assembly plays a ubiquitous role in the organization of matter
from atoms and molecules to cells and galaxies. Yet it remains
poorly understood in both theory and practice. Recent investigations
of DNA computing have highlighted a fundamental connection between
self-assembly and computation. Concurrently, a mesoscale system
suitable for studying self-assembly has been developed that uses
surface tension to mediate the assembly of plastic tiles based on
shape complementarity and likeness of wetting. These developments
have stimulated us to explore programmed self-assembly. We decorate
tiles with wetting codes that create different binding interactions
of similar energy. We use these interactions to generate three
self-assembled structures of increasing complexity: a periodic
'checkerboard' tiling, an aperiodic Penrose tiling, and a cellular
automaton that produces Sierpinski triangle-like patterns.
A comparison of these physical structures to mathematically ideal
ones reveals that energetic, kinetic and mechanistic details of the
self-assembly have a great effect on the quality of the structures
produced.
Friday, February 26, 1999
Prof. Clifford Kubiak, Chemistry Department, UC S. Diego,"Conductance
Spectroscopy of Organic Molecules on Au(III):
Chemically Gating Current Flow Through Nanostructures", EEB 248, noon.
Abstract
The use of chemical self-assembly in two dimensions to assemble 2D super
lattices consisting of tens of thousands of single crytstal gold clusters
linked by molecular interconnects into structures having overall dimensions
of microns will be described. These 2D super lattices have also been
assembled between a pair of metal contacts separated by 300 nm so that
electrical responses of the linked cluster networks can be measured.
Transport is found to be limited by the resistances of individual
molecules, which are found to be on the order of megaohms. Measurement of
the conductance spectra of individual poly(phenyl) thiol, dithiol,
isocyanide, and diisocyanide molecules by STM I(V) measurements show that a
significant potential drop between the molecule and substrate must be taken
into account. These studies also show that the Fermi energy of a gold
metal/molecule junction can be located relative to the highest occupied
molecular orbital (HOMO) by analysis of the I(V) conductance spectra. A
key finding is that the conductance spectra are very sensitive to the
functional groups present on the molecule. Finally, it will be shown that
"gating" current flow through molecules via charge transfer interactions
can dramatically alter electrical resistance. Chemical gating can also be
achieved leading to ultra-sensitive sensor applications.
Friday, January 22, 1999
Prof. Ari Requicha, USC, "Molecular robotics research at USC", PHE 223, 12 noon.