MONDAY, MARCH 7, 2011 Carbon-nanotubes as Ultrafast Photodetectors
Carbon nanotubes are promising elements for optoelectronic components.
However so far there were no electronic methods to analyze the ultra fast
optoelectronic dynamics of the nanotubes. A team of physicists headed by
Professor Alexander Holleitner from the Technische Universitaet Muenchen (TUM)
has now come up with a new method to directly measure the dynamics of
photo-excited electrons in nanoscale photodetectors.
Carbon nanotubes bridging two gold electrodes
Carbon nanotubes have a multitude of unusual properties which make them
promising candidates for optoelectronic components. However, so far it has
proven extremely difficult to analyze or influence their optic and electronic
properties.
A team of researchers headed by Professor Alexander Holleitner, a physicist at
the Technische Universitaet Muenchen and member of the Cluster of Excellence
Nanosystems Munich (NIM), has now succeeded in developing a measurement method
allowing a time-based resolution of the so-called photocurrent in photodetectors
with picosecond precision.
Single-walled carbon nanotubes are promising building blocks for future
optoelectronic devices. With this measurement set-up physicists led by Professor
Alexander Holleitner (Technische Universitaet Muenchen) can resolve the ultra
fast optoelectronic dynamics of carbon-nanotubes. A first laser exites electrons
in the carbon-nanotubes spanning the gap between two gold electrodes while a
second laser measures the resulting photo-current.
"A picosecond is a very small time interval," explains Alexander Holleitner. "If
electrons traveled at the speed of light, they would make it almost all the way
to the moon in one second. In a picosecond they would only cover about a third
of a millimeter."
This new measurement technique is about a hundred times faster than any existing
method. It allowed the scientists headed by Professor Alexander Holleitner to
measure the precise speed of electrons. In the carbon nanotubes the electrons
only cover a distance of about 8 ten-thousandths of a millimeter or 800
nanometers in one picosecond.
At the heart of the photodetectors in question are carbon tubes with a diameter
of about one nanometer spanning a tiny gap between two gold detectors. The
physicists measured the speed of the electrons by means of a special
time-resolved laser spectroscopy process – the pump-probe technique. It works by
exciting electrons in the carbon nanotube by means of a laser pulse and
observing the dynamics of the process using a second laser.
The insights and analytic opportunities made possible by the presented technique
are relevant to a whole range of applications. These include, most notably, the
further development of optoelectronic components such as nanoscale
photodetectors, photo-switches and solar cells.
The studies were funded by the German Research Foundation (Cluster of Excellence
Nanosystems Initiative Munich, NIM) and the Center for NanoScience (CeNS) at
Ludwig-Maximilians-Universitaet Muenchen. Further contributions to the
publication came from physicists of the University of Regensburg (Germany) and
the Swiss Federal Institute of Technology, Zurich.
Femtosecond Transient Absorption Measurements system
Hatteras.
Future nanostructures and biological nanosystems will take
advantage not only of the small dimensions of the objects but of the
specific way of interaction between nano-objects. The interactions
of building blocks within these nanosystems will be studied and optimized on
the
femtosecond time scale - says Sergey Egorov, President and CEO of Del Mar
Photonics, Inc. Thus we put a lot of our efforts and resources into the
development of new Ultrafast
Dynamics Tools such as our Femtosecond Transient Absorption Measurements
system Hatteras. Whether you want to
create a new photovoltaic system that will efficiently convert photon energy
in charge separation, or build a molecular complex that will dump photon energy
into local heat to kill cancer cells, or create a new fluorescent probe for
FRET microscopy, understanding of internal dynamics on femtosecond time scale
is utterly important and requires advanced measurement techniques.
Carbon nanotubes form ultrasensitive biosensor to detect proteins
Sunday, June 27, 2010
A cluster of carbon nanotubes coated with a thin layer of protein-recognizing
polymer form a biosensor capable of using electrochemical signals to detect
minute amounts of proteins, which could provide a crucial new diagnostic tool
for the detection of a range of illnesses, a team of Boston College researchers
report in the journal Nature Nanotechnology.
The nanotube biosensor proved capable of detecting human ferritin, the primary
iron-storing protein of cells, and E7 oncoprotein derived from human
papillomavirus. Further tests using calmodulin showed the sensor could
discriminate between varieties of the protein that take different shapes,
according to the multi-disciplinary team of biologists, chemists and physicists.
Molecular imprinting techniques have shown that polymer structures can be used
in the development of sensors capable of recognizing certain organic compounds,
but recognizing proteins has presented a difficult set of challenges. The BC
team used arrays of wire-like nanotubes approximately one 300th the size of a
human hair coated with a non-conducting polymer coating capable of recognizing
proteins with subpicogram per liter sensitivity.
Central to the function of the sensor are imprints of the protein molecules
within the non-conducting polymer coating. Because the imprints reduce the
thickness of the coating, these regions of the polymer register a lower level of
impedance than the rest of the polymer insulator when contacted by the charges
inherent to the proteins and an ionized saline solution. When a protein molecule
drops into its mirror image, it fills the void in the insulator, allowing the
nanotubes to register a corresponding change in impedance, signaling the
presence of the protein, according to co-author Dong Cai, an associate research
professor of Biology at BC.
The detection can be read in real time, instead of after days or weeks of
laboratory analysis, meaning the nanotube molecular imprinting technique could
pave the way for biosensors capable of detecting human papillomavirus or other
viruses weeks sooner than available diagnostic techniques currently allow. As
opposed to searching for the HPV antibody or cell-mediated immine responses
after initial infection, the nanotube sensor can track the HPV protein directly.
In addition, no chemical marker is required by the lebel-free electrochemical
detection methods.
"In the case of some diseases, no one can be sure why someone is ill," said Cai.
"All that may be known is that it might be a virus. At that time, the patient
may not have detectable serum antibodies. So at a time when it is critical to
obtain a diagnosis, there may not be any traces of the virus. You've basically
lost your chance. Now we can detect surface proteins of the virus itself through
molecular imprinting and do the analysis."
Professor Weisman wrote: Our applications are for carbon nanotube excitation,
mostly with a cw beam but in some experiments with mode-locked pulses.
Del Mar Photonics offered Trestles Ti:Sapphire model with both CW and
femtosecond modes of operation.
Detailed laser specifications are as follows (request
a quote):
Trestles Ti:Sapphire laser with built-in DPSS pump laser Ti:Sapphire oscillator having a tuning range of 710-920 nm; Output power: 30mW (@3W pump, in the whole range);
Spatial mode: TEMoo;
Polarization: linear horizontal;
Repetition rate: 80 MHz;
Pulse duration: <100 fs
Electronic starter with TTL output for mode-locked mode
observation. Output mirrors included.
USB-controlled tuning slit for wavelength tuning
3BRF-TM 3-plate BRF for CW lasers (step motor controlled tuning) Provides CW tuning and 40 GHz linewidth of the Trestles fs
lasers in CW mode; output power @700 nm - >50 mW (3W pump)
3 W pump DPSS laser with control and power supply unit Power: 3 W
Wavelength: 532 nm
Beam size: 2.0 mm
Spatial mode: TEM00
Bandwidth: 30 GHz
Divergence: 0.4 mrad
M squared: < 1.1
Power stability: < 0.4 % RMS
Noise: < 0.4% RMS
Noise bandwidth: 1 Hz - 6 MHz
Pointing stability: < 2 microrads/C
Polarization ratio: 100:1
Polarization direction: horizontal
Coherence length: < 1 cm
Beam angle: < 1 mrad
Umbilical length: 1.5 m
Warm-up time: 10 min
R. Bruce Weisman Professor of Chemistry
Research Statement
Dr. R. Bruce Weisman and his group investigate the spectroscopy and photophysics
of fullerenes and carbon nanotubes. All of these are closed nanoscopic
structures formed from carbon atoms. Fullerenes, such as C60, C70, and their
chemical derivatives, have unusual molecular properties that cause interesting
behaviors following the absorption of light. Time-resolved absorption and
emission methods are used to study radiationless decay, photochemical reactions,
and
energy transfer in fullerenes. Another major research topic is
single-walled carbon nanotube spectroscopy. Following the discovery in Weisman?s
lab of near-infrared nanotube fluorescence, the group has measured and unraveled
the absorption and emission spectra of more than 30 semiconducting nanotube
species. Follow-up projects include detailed elucidation of nanotube electronic
structure, as well as applications in non-invasive biomedical imaging and
analytical nanotechnology.
Selected Publications
R. Bruce Weisman and Shekhar Subramoney "Carbon Nanotubes." Interface (Summer,
2006): 42-46.
J. P. Casey, S. M. Bachilo, C. H. Moran, and R. B. Weisman "Chirality-Resolved
Length Analysis of Single-Walled Carbon Nanotube Samples through Shear-Aligned
Photoluminescence Anisotropy." ACS
Nano, 2 (2008): 1738-1746.
J. P. Casey, S. M. Bachilo, and R. B. Weisman "Efficient Photosensitized
Energy Transfer and Near-IR Fluorescence from Porphyrin/SWNT
Complexes." J. Mater. Chem., 18 (2008): 1510-1516.
R. B. Weisman "Optical Spectroscopy of Single-Walled Carbon Nanotubes."
Contemporary Concepts of Condensed Matter Science. Carbon Nanotubes: Quantum
Cylinders of Graphene, 3 (2008): 109-133.
D. A. Tsyboulski, E. L. Bakota, L. S. Witus, J.-D. R. Rocha, J. D. Hartgerink,
and R. B. Weisman "Self-Assembling Peptide Coatings Designed for Highly
Luminescent Suspension of Single-Walled Carbon Nanotubes." J. Am. Chem. Soc.,
130 (2008): 17134-117140.
C. D. Doyle, J.-D. R. Rocha, R. B. Weisman, and J. M. Tour "Structure-dependent
Reactivity of Semiconducting Single-Walled Carbon Nanotubes with Benzene
Diazonium Salts." J. Am. Chem. Soc., 130 (2008): 6795-6800.
D. A. Tsyboulski, S. M. Bachilo, A. B. Kolomeisky, and R. B. Weisman
"Translational and Rotational Dynamics of Individual Single-Walled Carbon
Nanotubes in Aqueous Suspension." ACS
Nano, 2 (2008): 1770-1776.
Robert F. Curl and R. Bruce Weisman "Biography of Richard Errett Smalley." J.
Phys. Chem. C, 111 (2007): 17653-17655.
Christopher J. Gannon, Paul Cherukuri, Boris I. Yakobson, Laurent Cognet, John
S. Kanzius, Carter Kittrell, R. Bruce Weisman, Matteo Pasquali, Howard K.
Schmidt, Richard E. Smalley, and Steven A. Curley "Carbon Nanotube-enhanced
Thermal Destruction of Cancer Cells in a Noninvasive Radiofrequency Field."
Cancer, 110 (2007): 2654-2665.
Laurent Cognet, Dmitri A. Tsyboulski, John-David R. Rocha, Condell D. Doyle,
James M. Tour and R. Bruce Weisman "Stepwise Quenching of Exciton Fluorescence
in Carbon Nanotubes by Single Molecule Reactions." Science, 316 (2007):
1465-1468.
Presentations
"Quantitative Analysis of Bulk SWCNT Samples using Near-IR Fluorimetry,” Focus
Session on Development of Purity Evaluation Criteria and Quality Assurance
Standards for Carbon Nanotubes,." Materials Research Society Meeting, Boston,
Massachusetts. (November 30, 2008)
"Near-infrared Fluorescence of Single-Walled Carbon Nanotubes: a
Tool for Developing Medical Applications." Nanomedicine Summit
08, Cleveland, Ohio. (September 25, 2008)
"Single-walled Carbon Nanotubes: Physical Properties and Biomedical
Applications." Howard Hughes Medical Institute Summer Lecture Series,
Harvey Mudd College, Claremont, California. (July 16, 2008)
"Near-IR Fluorescence of Single-Walled Carbon Nanotubes: A
Tool for Developing Medical Applications." Carbon Nanotube
Biology, Medicine, and Toxicology Symposium, Montpelier, France. (June 28, 2008)
"Qualitative and Quantitative Analysis of Bulk SWNT Samples using Near-IR
Fluorimetry." Workshop on Metrology, Standardization, and Industrial Quality of
Nanotubes, Montpelier, France. (June 28, 2008)
Editorial Positions
Associate Editor, Applied Physics A, Springer-Verlag,, (2008).
Theses
Paul Cherukuri, Ph.D. "Biomedical Studies of Single-Walled Carbon Nanotubes
Using Near-Infrared Fluorescence." (2007).(Thesis or Dissertation Director)
Dmitry Tsyboulski, Ph.D. "Spectroscopic and Optical Imaging Studies of Fullerene
Complexes and Single-Walled Carbon Nanotubes." (2006).(Thesis or Dissertation
Director)
Eric Booth,
PhD. "Photophysical Studies of Selected C84 Isomers, C80
Species, Aqueous C60 Colloid, and a C60-Amino Acid Derivative." (2005).(Thesis
or Dissertation Director)
Awards Elected Fellow, American Physical Society. (2008).
Paul Frison Accelator Award for Applied NanoFluorescence, Houston Business
Journal. (2007).
Institute of Physics in Ireland Lecturer, . (2005).
Del Mar Photonics is involved in research of CNTs, graphene
nanoplatelets and graphene materials, develops advanced multifunctional
materials for variety of applications as well as research instrumentation for
characterization of the above.
We currently we can offer:
1) Graphene nanoplatelets: the stack of multi-layer graphene sheets with high
aspect ratio, diameter: 0.5-20 µm,
thickness: 5-25 nm.
2) Graphene materials: Graphene Powder, Graphene Oxide Powder, Graphene
Suspension.
3) Carbon Nanotubes.
Contact our application team to discuss your requirements for high-performance nanocomposite materials, display materials, sensing
materials, ultracapacitors, batteries, energy storage and other area to improve
electrical, thermal, barrier, or mechanical properties by using low-cost
nano-additive.
Graphene nanoplatelets are the stack of multi-layer
graphene sheets including platelet morphology, with characteristics as follows:
The high performance composite additives in PPO, POM, PPS, PC, ABS,
PP, PE, PS, Nylon and rubbers.
To improve composite tensile strength, stiffness, corrosion resistance, abrasion
resistance and anti-static and lubricant properties.
Mechanical properties modifications.
Conductivity modification.
Fuel tank coating.
In electronic enclosures add electrical conductivity to polymers at low
densities of 3 to 5 wt%.
Adding EMI or RFI shielding capabilities to a variety of polymers.
Automotive parts: a composite with nanoplatelets can be painted
electrostatically, thereby saving costs.
Aerospace: graphite has long been used in aerospace composites. Nanoplatelets
can be combined with other additives to reinforce stiffness, add electrical
conductivity, EMI shielding, etc.
Appliances: fortified polymers provide superior thermal and electrical
conductivity, thereby saving the costs of separate heat dissipation mechanisms.
Sporting goods: graphite-based composites are stronger and stiffer and lighter
than comparable materials.
Coatings and paints: graphene nanoplatelets can be dispersed in a wide variety
of materials to add electrical conductivity and surface durability.
Batteries: graphene nanoplatelets increase the effectiveness of Lithium-ion
batteries when used to formulate electrodes.
Fuel cells: both bi-polar plate and electrode efficiencies can be improved.
Del Mar Photonics develops advanced instrumentation for research of CNTs,
graphene nanoplatelets and graphene materials including lasers for broadband
spectroscopy, femtosecond transient absorption and fluorescence measurements.
