Ray Phaneuf
Motivation
Rapid developments in nanoscience and nanotechnology make it essential to be able to make spectroscopic measurements at the nanometer scale. The existence of quantum confinement effects in nanometer scale structures is a large part of what drives interest in this field; the strong dependence of these effects on individual structure sizes and the potential for strong coupling of levels from closely spaced structures renders the overall performance of assemblies of small structures complex, and difficult to predict. In addition, segregation at interfaces, particularly those to nanostructures will dramatically affect both electronic and transport properties across them. Many of the technologies earmarked for significant growth in the coming decades are critically dependent on credible nanometer-scale measurements and analysis. These certainly include high-density electronics, biosensors, high throughput experimentation, separations, and catalysis. Development of robust, nanoscale measurement tools is critically important if the full potential of these technologies is to be realized.
The spatial resolution available in a spectroscopic measurement depends both on the size of the probe beam, and in the case of incident electrons or holes, on the spreading of the excited region due to either carrier diffusion or energy transfer through a system. In the case of incident visible or UV light, the diffraction limit until recently seemingly prevented resolution at much below 0.1 um. Focused x-ray sources provided insufficient incident flux to make nm scale spectroscopy possible. Electron beams can be focused to sub-nm dimensions, but only at high energies, so that the electrons must undergo a large number of inelastic scatterings to drop into a bound energy level, again leading up until recently to resolution no better than 0.1 um. A number of approaches have been invented in recent years to avoid these limitations. Important examples are: Near-field scanning optical microscopy beats the diffraction limit through the use of an aperture. The advent of ultra-bright third generation synchrotron sources now allows focusing of x-ray beams to a few tens of nm with exceedingly high incident fluxes. The use of the scanning tunneling microscope allows injection of electrons or holes into a structure with 0.1 nm incident beam diameter, and at energies close to resonance with bound levels, greatly reducing their diffusion lengths.
The International Workshop on Nanoscale Spectroscopy was created to serve
as a forum for the exchange of information about applications and new
developments of these techniques in the rapidly growing field of nanoscience
and technology. The first workshop was
held at the
Scope of the Workshop
The development
of powerful new techniques and the modification of existing techniques for the
measurement of spectroscopy with spatial resolution approaching the nanometer
scale in recent years bring forth an unprecedented level of understanding as to
the relationship between size/structure/composition/strain in nanometer sized
structures, and the resultant electronic structure. Briefly put, these techniques make possible
the interrogation of individual nanostructures, or small numbers of coupled
nanostructures, rather than ensembles, so that the above mentioned
relationships and the coupling of energy levels between neighboring structures
can be systematically studied. This
workshop will serve as a forum for scientists from the
One of the focus areas sessions at NSS3 is interfaces
to nanostructures, and how to characterize them. The program includes presentations describing
results of transport though nanotubes/metal interfaces and metal/molecule interfaces,
including vibrational spectroscopy derived from these measurements. These types of measurements will be
instrumental in the understanding of the nature of the transport across these
interfaces. A
crucial issue for application of nanostructures in logic, or sensing
applications is our ability to produce reliable, low impedance contacts to
these structures, to allow transport of signals into and out of them. It has
been recognized at least since the seminal work of Landauer that transport through a nanoscale structure
is determined not merely by its intrinsic conductance but also by the
transmission probabilities across the interfaces bounding it. Recent comparisons of measurements and
calculations of the conductance profile for a simple case, that of single
dithiol molecules between gold contacts show that these transmission
probabilities can dominate the transport, resulting in measured values orders
of magnitude below that for the molecule itself. Measured electrical transport through carbon
nanotubes has also indicated that the barriers formed at the contacts determine
the electrical character of devices based upon these structures. Indeed, this has led to a pronounced
sensitivity the way in which the contacts are formed and subsequently processed,
e.g. annealing in vacuum. Direct
measurement of the electrostatic potential across metallic nanowires by scanned
gate microscopy in fact indicates that the resistance at the contacts can
account for almost the entire potential drop across them. This session will include contributions both
from experimentalists and from theorists doing first principles calculations of
transport through these structures, and should foster a high level of
discussion on this crucial issue.
A second focus area is critical issues in quantum dots, including characterization
of size, shape, composition and correlation to electronic and optical
properties, requiring advanced nanoscale spectroscopies such as optical
near-field spectroscopy. Knowledge gained
from such measurements is needed to feed back into the development of
functionalized quantum dot materials that can enable new technologies such as
spintronics and quantum computing. Additional important issues involve
achieving electronic control of individual quantum dots using local external
fields, for example, with an STM tip or an optical laser pulse. Coherent optical control of the wavefunction
of individual quantum dots using nano-optical techniques could eventually
enable solid state quantum computing.
A third focus area of NSS3 is single molecule
spectroscopies (SMS), which are of great interest at present. There is a
critical need to develop techniques capable of identifying extremely small
concentrations of bio-warfare agents; single molecule identification represents
the ultimate level of this development. From a scientific
viewpoint, the greatest strength of single
molecule spectroscopy lies in our ability to resolve structural and dynamic
heterogeneity masked by conventional ensemble measurements. SMS methods
are particularly suited for the investigation of complex kinetic processes,
determination of structural heterogeneity of complex systems, and materials
characterization on molecular length scales. SMS techniques can be
applied in a host of sample matrices from glassy materials to living cells and
promise to be important in addressing unanswered questions such as the origin of the observed “blinking”
phenomenon in quantum dots and the molecular nature of "hot spots" in surface enhanced Raman scattering.
Participation in this session will include a number of the key researchers in
this field, as listed below.
The development of new
techniques which allow probing of individual nanostructures or small numbers of
nanostructures continues to shed new experimental light on the
interrelationship between synthesis, structure and properties of materials,
enhancing our understanding and driving further development of theoretical
models to explain unexpected observations.
This workshop will serve as a forum for discussion and debate of new and
established scientific ideas, inspired by the measurement made possible by
nanoscale spectroscopic techniques. At
the heart of the excitement of nanoscience is the fact that it provides working
models in which one of the great intellectual feats of the twentieth century,
the development of quantum mechanics, can be tested. The goal of research in nanoscale
spectroscopy is to extend our understanding of fundamental issues in nanoscale
science. These include the relationship between
structure and electronic energy levels at the nanoscale, the coupling of energy
levels in neighboring mesoscale structures, the mechanisms which limit the
coherence length in coupled structures, and how transport occurs across
interfaces between nanostructures. It will serve as a forum for discussion of
new experimental observations, how these can be understood within a theoretical
framework, and how they require the modification of existing models of
phenomena at the nanoscale. NSS3 will
thus promote the process which is the intellectual center of the scientific
method.
The intended impact of NSS3 is
to foster the exchange of information, and new collaborations in the area of
nanoscale spectroscopies. The ideas
exchanged here will accelerate the diffusion of the applications of these
techniques to problems of critical nanoscientific and technological
interest. At present there is no forum
in the
We welcome you to the Third
International Workshop on Nanoscale Spectroscopy and Nanotechnology.
Local Organizing Committee International Program Committee
Ray Phaneuf, Chair, UM Ray Phaneuf, UM
Doug
English, Treasurer, UM Doug
English, UM
Stephan
Stranick, Secretary, NIST Stephan
Stranick, NIST
Dennis Drew, UM Stefan
Heun, TASC-INFM, Trieste
Janice Reutt-Robey, UM Giancarlo Salviati, IMEM-CNR,
Dan Gammon, NRL Italy
Marcello
Colocci, Universita’ di
Firenze, Italy
Yoshio
Watanabe, NTT-Japan
Takashi
Sekiguchi NIMS-Japan
Yoichi Uehara, University of