Research Category: Conveyor System
Researchers: Chris Regan|
Location: Lawrence Berkeley National Laboratory, U.S. Department of Energy, United States
In a development that brings the promise of mass production
to nanoscale devices, Lawrence
Berkeley National Laboratory scientists have transformed carbon nanotubes
into conveyor belts capable of ferrying atom-sized particles to microscopic
By applying a small electrical current to a carbon nanotube, they moved indium
particles along the tube like auto parts on an assembly line. Their research
lays the groundwork for the high-throughput construction of atomic-scale
optical, electronic, and mechanical devices that will power the burgeoning field
“We’re not transporting atoms one at a time anymore — it’s more like a hose,”
says Chris Regan of Berkeley Lab’s Materials Sciences Division, who co-authored
the article along with fellow Materials Sciences researchers Shaul Aloni, Ulrich
Dahmen, Robert Ritchie, and Alex Zettl. Aloni, Regan, and Zettl are also
scientists in the University
of California at Berkeley’s Department of Physics, where much of the work
The ability to shuttle a stream of particles to precise locations fills a void
that has stymied the efficient assembly of nanostructures. For years, scientists
have been able to simultaneously deliver millions of atoms to millions of sites
simply by mixing chemicals. Although this fast technique has grown quite
sophisticated, it remains far too blunt to build atomic-scale devices. On the
other end of the spectrum is the ability to manipulate individual atoms, a feat
that came of age in 1990 when IBM researchers spelled out the company logo by
positioning 35 xenon atoms with a scanning tunneling microscope. Although
precise, this technique is painstakingly slow, with no way to swiftly deliver
atoms to the work area.
“It’s either all at once, or excruciatingly serial,” says Regan. “So we combined
incredibly precise localization with something that has higher throughput.”
This middle ground is made possible by carbon nanotubes, which are hollow
cylinders of pure carbon about ten thousand times smaller than the diameter of a
human hair. Since their discovery in the sooty residue of vaporized carbon rods,
these incredibly strong and versatile macromolecules have been engineered into
frictionless bearings, telescoping rods, and the world's smallest
room-temperature diodes. Now, they’re poised to change the way these and other
devices are constructed.
As described in their Nature article, the research team thermally evaporated
indium metal onto a bundle of carbon nanotubes. The amount of evaporated metal
is so small it populates the tubes’ surfaces as isolated indium crystals,
instead of uniformly coating them. The bundle is then placed inside a
transmission electron microscope, where a tungsten tip mounted on the end of a
nanomanipulator approaches one nanotube. After physical contact is made between
the tip and the free end of the nanotube, voltage is applied between the tip and
the other end of the nanotube, creating a circuit. This sends an electrical
current through the nanotube, which generates thermal energy that heats the
Next, if the voltage and thermal energy is carefully controlled, something
strange occurs. Real-time video of the nanotube’s surface captures an indium
particle as it disappears, while the particle to its right grows. Several
seconds later, that newly enlarged particle also disappears, replaced by another
even further to the right. Like squeezing the last bits of toothpaste from a
tube, particles to the left become smaller while those to the right grow.
In this manner, the thermally driven indium atoms inchworm along the nanotube,
momentarily occupying a reservoir where a particle is located, and then moving
to the next, until all of the indium piles up at the end of the nanotube. In the
future, this nano-sized conveyor belt could be aimed anywhere scientists want to
deliver mass atom-by-atom — the makings of a formidable nanoassembly tool.
Moreover, if the voltage is slightly increased, the indium’s temperature
increases, and the metal moves from left to right more quickly.
“It’s the equivalent of turning a knob with my hand and taking macroscale
control of nanoscale mass transport,” Regan says. “And it’s reversible: we can
change the current’s polarity and drive the indium back to its original
In other words, indium can be repeatedly moved back and forth along the nanotube
without losing a single atom. Nothing is lost in transit. This conservation of
mass occurs because the atoms don’t evaporate from the system during their
journey — an advantage in any process meant to deliver valuable material to a
worksite. Instead, the atoms hug the nanotube’s surface as they move, tethered
by a process called surface diffusion.
“In order to build a structure we have to be able transport material to the
construction site, and we’re developing a better way to do that,” Regan says.
“Our nanoscale mass delivery system is simple and reversible. It requires only a
nanotube, a voltage source, and something to transport.”
Note for Carbon Nanotube
Carbon nanotubes (CNTs) are allotropes of carbon. This results in a
nanostructure where the length-to-diameter ratio exceeds 1,000,000. Such
cylindrical carbon molecules have novel properties that make them potentially
useful in many applications in nanotechnology, electronics, optics and other
fields of materials science. They exhibit extraordinary strength and unique
electrical properties, and are efficient conductors of heat. Inorganic nanotubes
have also been synthesized.
Nanotubes are members of the fullerene structural family, which also includes
buckyballs. Whereas buckyballs are spherical in shape, a nanotube is
cylindrical, with at least one end typically capped with a hemisphere of the
buckyball structure. Their name is derived from their size, since the diameter
of a nanotube is in the order of a few nanometers (approximately 1/50,000th of
the width of a human hair), while they can be up to several millimeters in
length. Nanotubes are categorized as single-walled nanotubes (SWNTs) and
multi-walled nanotubes (MWNTs).
The nature of the bonding of a nanotube is described by applied quantum
chemistry, specifically, orbital hybridization. The chemical bonding of
nanotubes are composed entirely of sp2 bonds, similar to those of graphite. This
bonding structure, which is stronger than the sp3 bonds found in diamond,
provides the molecules with their unique strength. Nanotubes naturally align
themselves into "ropes" held together by Van der Waals forces. Under high
pressure, nanotubes can merge together, trading some sp² bonds for sp³ bonds,
giving great possibility for producing strong, unlimited-length wires through
high-pressure nanotube linking. Carbon Nanotubes are said to have the strength
of diamonds and research is being made into weaving them into clothes to create
stab and bulletproof clothing. The Nanotubes would effectively stop the bullet
from penetrating the body but the force and velocity of the bullet would be
likely to cause broken bones and internal bleeding.
Carbon nanotubes are the strongest and stiffest materials on earth, in terms of
tensile strength and elastic modulus respectively. This strength results from
the covalent sp² bonds formed between the individual carbon atoms. In 2000, a
multi-walled carbon nanotube was tested to have a tensile strength of 63
gigapascals (GPa). Since carbon nanotubes have a low density for a solid of
1.3-1.4 g/cm³, its specific strength of up to 48,000 kN·m/kg is the best of
known materials, compared to high-carbon steel's 154 kN·m/kg.
Under excessive tensile strain, the tubes will undergo plastic deformation,
which means the deformation is permanent. This deformation begins at strains of
approximately 5% and can increase the maximum strain the tube undergoes before
fracture by releasing strain energy.
CNTs are not nearly as strong under compression. Because of their hollow
structure and high aspect ratio, they tend to undergo buckling when placed under
compressive, torsional or bending stress.
The strength and flexibility of carbon nanotubes makes them of potential use in
controlling other nanoscale structures, which suggests they will have an
important role in nanotechnology engineering. The highest tensile strength an
individual multi-walled carbon nanotube has been tested to be is 63 GPa. Bulk
nanotube materials may never achieve a tensile strength similar to that of
individual tubes, but such composites may nevertheless yield strengths
sufficient for many applications. Carbon nanotubes have already been used as
composite fibers in polymers to improve the mechanical, thermal and electrical
properties of the bulk product.
Note for Conveyor Belt
A belt conveyor consists of two or more pulleys, with a continuous loop of
material - the conveyor belt - that rotates about them. One or both of the
pulleys are powered, moving the belt and the material on the belt forward. The
powered pulley is called the drive pulley while the unpowered pulley is called
the idler. There are two main industrial classes of belt conveyors; Those in
general material handling such as those moving boxes along inside a factory and
bulk material handling such as those used to transport industrial and
agricultural materials, such as grain, coal, ores, etc. generally in outdoor
locations. Generally companies providing general material handling type belt
conveyors do not provide the conveyors for bulk material handling. In addition
there are a number of commercial applications of belt conveyors such as those in
The belt consists of one or more layers of material they can be made out of
rubber. Many belts in general material handling have two layers. An under layer
of material to provide linear strength and shape called a carcass and an over
layer called the cover. The carcass is often a cotton or plastic web or mesh.
The cover is often various rubber or plastic compounds specified by use of the
belt. Covers can be made from more exotic materials for unusual applications
such as silicone for heat or gum rubber when traction is essential.
Material flowing over the belt may be weighed in transit using a beltweigher.
Belts with regularly spaced partitions, known as elevator belts, are used for
transporting loose materials up steep inclines. Belt Conveyors are used in
self-unloading bulk freighters and in live bottom trucks. Conveyor technology is
also used in conveyor transport such as moving sidewalks or escalators, as well
as on many manufacturing assembly lines. Stores often have conveyor belts at the
check-out counter to move shopping items. Ski areas also use conveyor belts to
transport skiers up the hill. A wide variety of related conveying machines are
available, different as regards principle of operation, means and direction of
conveyance, including screw conveyors, vibrating conveyors, pneumatic conveyors,
the moving floor system, which uses reciprocating slats to move cargo, and
roller conveyor system, which uses a series of powered rollers to convey boxes
The longest belt in the world is in Western Sahara. It is 100 km long, from the
phosphate mines of Bu Craa to the coast south of El-Aaiun. The longest single
belt conveyor runs from Meghalaya in India to Sylhet in Bangladesh. It is 17
miles long and conveys limestone and shale. The Conveyor belt was manufactured
in about 300 meter lengths and was joined together and installed on the conveyor
at site. The job was carried out by NILOS India Pvt. Ltd. in Chennai India.
Conveyors are used as components in automated distribution and warehousing. In
combination with computer controlled pallet handling equipment this allows for
more efficient retail, wholesale, and manufacturing distribution. It is
considered a labor saving system that allows large volumes to move rapidly
through a process, allowing companies to ship or receive higher volumes with
smaller storage space and with less labor expense.
Rubber Conveyor Belts are commonly used to convey items with irregular bottom
surfaces, small items that would fall in between rollers, or bags of product
that would sag between rollers. Belt conveyors are generally fairly similar in
construction consisting of a metal frame with rollers at either end of a flat
metal bed. The belt is looped around each of the rollers and when one of the
rollers is powered (by an electrical motor) the belting slides across the solid
metal frame bed, moving the product. In heavy use applications the beds which
the belting is pulled over are replaced with rollers. The rollers allow weight
to be conveyed as they reduce the amount of friction generated from the heavier
loading on the belting. Belt conveyors can now be manufactured with curved
sections which use tapered rollers and curved belting to convey products around
a corner. These conveyor systems and are commonly used in postal sorting offices
and airport baggage handling systems.
Note for Transmission Electron Microscopy
Transmission electron microscopy (TEM) is a microscopy technique whereby a beam
of electrons is transmitted through an ultra thin specimen, interacting with the
specimen as it passes through it. An image is formed from the electrons
transmitted through the specimen, magnified and focused by an objective lens and
appears on an imaging screen, a fluorescent screen in most TEMs, plus a monitor,
or on a layer of photographic film, or to be detected by a sensor such as a CCD
camera. The first practical transmission electron microscope was built by Albert
Prebus and James Hillier at the University of Toronto in 1938 using concepts
developed earlier by Max Knoll and Ernst Ruska.
Theoretically the maximum resolution that one can obtain with a light microscope
has been limited by the wavelength of the photons that are being used to probe
the sample and the numerical aperture of the system. Early twentieth century
scientists theorized ways of getting around the limitations of the relatively
large wavelength of visible light (wavelengths of 400–700 nanometers) by using
electrons. Like all matter, electrons have both wave and particle properties (as
theorized by Louis-Victor de Broglie), and their wave-like properties mean that
a beam of electrons can be made to behave like a beam of electromagnetic
radiation. Electrons are usually generated in an electron microscope by a
process known as thermionic emission from a filament, usually tungsten, in the
same manner as a light bulb, or by field emission. The electrons are then
accelerated by an electric potential (measured in V, or volts) and focused by
electrostatic and electromagnetic lenses onto the sample. The beam interacts
variously with the sample due to differences in density or chemistry. The beam
that is transmitted through the sample contains information about these
differences, and this information in the beam of electrons is used to form an
image of the sample.
Just as details of a light microscope sample can be enhanced by the use of
stains, staining can be used to enhance differences in a sample for electron
microscopy. Compounds of heavy metals such as osmium, lead or uranium can be
used to selectively deposit heavy atoms in areas of the sample and to enhance
structural detail by the dense nuclei of the heavy atoms scattering the
electrons out of the optical path. The electrons that remain in the beam can be
detected using a photographic film, or fluorescent screen among other
technologies. So areas where electrons have been scattered in the sample can
appear dark on the screen, or on a positive image due to this scattering.
The TEM is used heavily in both material science/metallurgy and the biological
sciences. In both cases the specimens must be very thin and able to withstand
the high vacuum present inside the instrument.
For biological specimens, the maximum specimen thickness is roughly 1 micrometre.
To withstand the instrument vacuum, biological specimens are typically held at
liquid nitrogen temperatures after embedding in vitreous ice, or fixated using a
negative staining material such as uranyl acetate or by plastic embedding.
Typical biological applications include tomographic reconstructions of small
cells or thin sections of larger cells and 3-D reconstructions of individual
molecules via Single Particle Reconstruction.
In material science/metallurgy the specimens tend to be naturally resistant to
vacuum, but must be prepared as a thin foil, or etched so some portion of the
specimen is thin enough for the beam to penetrate. Preparation techniques to
obtain an electron transparent region include ion beam milling and wedge
polishing. The focused ion beam (FIB) is a relatively new technique to prepare
thin samples for TEM examination from larger specimens. Because the FIB can be
used to micro-machine samples very precisely, it is possible to mill very thin
membranes from a specific area of a sample, such as a semiconductor or metal.
Materials that have dimensions small enough to be electron transparent, such as
powders or nanotubes, can be quickly produced by the deposition of a dilute
sample containing the specimen onto support grids. The suspension is normally a
volatile solvent, such as ethanol, ensuring that the solvent rapidly evaporates
allowing a sample that can be rapidly analysed.
Berkeley Lab is a U.S.
Department of Energy national laboratory located in Berkeley, California. It
conducts unclassified scientific research and is managed by the University of
In figure 1, Someday, nanoscale conveyor belts could expedite
the atom-by-atom construction of the world’s smallest devices
In figure 2, A glimpse into the factory of the future. Four images, each taken
60 seconds apart, portray the rightward march of indium atoms along a carbon
nantoube subjected to about two volts