Google News : self assembly, nanoscale electronics, nanowire , FET, microfluidic , porous , electrochemical
15-Jan-2003
An M13 virus directs the deposition of ZnS at peptide sites along the "shaft" portion of the pencil-shaped bacteriophage. M13 virus is approximately 6.5 nm in diameter and 880 nm in length. Annealing removes the virus scaffold to give a solid nanowire. Additionally, as described in a paper in Nano Letters, these viral particles can be engineered to self-assemble higher order structures such as rings
Nanotubes grown on Silicon IC
3-Dec-2003
" Vitaly Podzorov and his colleagues at Rutgers created
single-crystal rubrene OFETs using a gate-insulating layer of parylene,
instead of silicon dioxide, and directly depositing silver contacts
on the crystal to form the source and drain electrodes. Parylene
has a dielectric constant comparable to that of silicon dioxide (~3
versus 3.9) and allows the creation of very thin insulating films without
defects. Though the way the OFET was constructed helped, the major factor
in achieving a record-high mobility of 8 cm2/ V-s was the choice of the
semiconductor, says Podzorov, who has submitted his team’s work to
Applied Physics Letters.
In related work Alberto Morpurgo and his colleagues at Delft used
single crystal tetracene as a semiconductor to achieve a mobility of 0.4
cm2/ V-s, which is the highest mobility
reported for tetracene based transistors so far. Article
, Paper
, 
, 
Optical image of FET transistors constructed by depositing Au electrodes
onto single crystal tetracene overlaying a bulk silicon gate.
image from Delft Institute of Technology
The transistor fabrication is similar one based on a nanowire transistor design developed by Xiangfeng Duan ay Charles Lieber's lab at Harvard. The transistor action is accomplisted by coating a Si nanowire with redox active molecules which supply a stable switchable electric field to the nanowire. On off rations exceed 10-4 and the redox state is stable for up to 20 min.
8 - Aug -2003
A team led by Paul Nealey at the University of Wisconsin's Materials Research Science and Engineering Center (MRSEC) has demonstrated an important step in the push to create precise structures of molecular dimensions. Starting with a block co-polymer with 2 domains which normally self assembles into a randomly ordered state (because the domains is attracted to like domains), they carefully adjusted polymer composition , environmental conditions and surface composition until the block co-polymer forms perfect 20-30 nm wide vertical stripes. press release
21-June-2003
Joonwon Kim at the UCLA Manufacturing Lab has developed a nice demonstration
of a micro-mechanical switch which could be scaled into the nano region.
See his page.
Apparently the ball of mercury can be driven from one position to the other
by using electrostatic potentials between the electrodes. There are quite
a few other interesting projects on the UCLA lab's research
page.
The PennState Nanofabrication facility has demonstrated the use of multiple molecular layers to guide the deposition of metal lines with dimensions smaller than can be obtained with normal lithography. This demonstrates the use of molecular structures to construct precisely positioned structures of potentially exact molecular dimensions.
1) metal lines are deposited
2) coated with multiple layers of resist with precise length
3) entire area is coated with evaporated metal
4) resist is removed leaving metal line with
v 
18-April-2003
S Yi Cui, a graduate student in the Harvard University lab of chemist Charles Lieber, has developed a chemical sensor using silicon nanowires. The nanowires are coated with a a chemical which binds to PSA, a protein which indicates the presence of prostate cancer. This simple arrangement has demonstrated world record sensitivity and is capable of detecting 3 or 4 bound molecules, with instantaneous response times. See the article in Technology Review from 3/2002.
Above is pictured the biomolecule detector developed at
Harvard University which uses nanoscale silicon wires straddling
gold-plated platinum electrodes two to eight micrometers apart atop
a silicon chip. Apparently this technology is being developed into
a commercial device at Nanosys.
The device apparently operates as follows:
1) The silicon nanowires are normally semiconducting, so an applied
voltage across the wire via the electrodes will drive a certain
amount of current through the wire
2) When PSA molecules pass over the nanowire, they bind to the chemical
coating the wire.
3) The bound PSA molecules are bound close enough to the wire to induce
an electric field in the Si-nanowire.
4) The electric field alters the conductivity of the nanowire, shutting
off the current between the electrodes.
The device is extremely sensitive due to the very small size of the
nanowires and the close binding of the PSA protein. This allows
the small electric dipole of the PSA protein to fully permeate the cross-section
of the nanowire, shutting off electron flow completely.
Also see related CHEMFET work here
4-April-2003
natural prion assembly
The prion proteins are extremely hardy proteins with a tendency to self-assemble into linear chains 9-11 nm wide. See the article , page and the abstract . The yeast was geneticaly modified to incorporate reactive, surface-accessible cysteine amino acid which bond to gold nano-particles. Subsequent electrochemical processing extended the gold coverage to create wires 100 nm wide. Interestingly, the plating is confined to only those fibers connected to active electrodes.
a selected prion assembly, bonded to gold nanoparticles and plated with
gold and silver.
22-Feb-2003
An article
in EEtimes, discusses the first use of DNA
by Richard
Kiehl at the University of Minnnesota, Nadrian
Seeman and Karin
Musier-Forsyth in directing the assembly of 2 nm sized nanoparticles
into arbitary regular patterns on the surface of a silicon wafer.
In the prototype system, the nanocomponents are simply small gold
clusters that have the ability to act as single-electron memory cells.
The diagram above shows the 2D array of DNA scaffolding (see Seeman's
page),
with gold particles attached at precise periodic positions. Such Lock-and-key
chemistry allows exact self-assembly of dense arrays. See the similar
work from MG
Finn using virus particles.
11-Feb-2003
Pinyung Feng
and others at the University of California, Riverside have synthesized
a large family of semiconducting porous materials. The
new materials reported in Science
are a new class of porous
materials and are made of a divalent anion (sulfur or selenium), a
trivalent cation (gallium or indium), and a tetravalent cation (germanium
or tin). See the press
release
The image above illustrates 4 differnet forms:UCR-20 UCR-21 UCR-22 and
UCR-23
Semiconducting porous structures can possibly be used directly as electronic
components such as
electrochemical sensors, photocatalysts , solid electrolytes for batteries
and adsorbents for gas separation
Additional uses may include LEDs, wires, switches and sensors, or as
a template/component in more complex systems.
22-Jan-2003
In the Jan 17 issue of Science, Joerg Lahann of Robert Langer's lab at MIT and Samir Mitragotri at UCSB along with others report the demonstration of a electrically switchable hydrophobic / hydrophilic surface. See the press release and Science article. The process deposits a monolayer of alkanethiols , MHAE or ( (16-mercapto) hexadecanoic acid (2-chlorophenyl)diphenylmethyl ester) onto a gold surface which can be charged.
In the absence of a surface electric field, the carboxyl group [CO2H] ends of the MHAE molecule form a hydrophilic surface layer. As the surface electric field is increased, the "stalks" of the MHAE bend over and are exposed to create a hydrophobic surface.
From this demonstration, it seems that electronic control of a surface's hydrophobic / hydroplilic properties should be possible at nanometer scales. One can envision a nanoscale array of software configurable switchable surfaces. Possible applications include:
07-Dec-2002
, 
The polymantanes molecules are small diamonds with shapes ranging from rigid cubes to sticks, as well as branching structures. It may be possible to use functionalized versions these as self-asembling building blocks to construct large arrays with atomically precise composition. An article by Merkle describes exactly this kind of usage.
More information on these types of crystal structures can be found
Zeolite
atlas.
Unit diamond cells are known as adamantane, and can be functionalized.
Some of these forms known to act as drugs are shown below and here:
A 3D chime model model.
An article by W. Piekarczyk on CVD diamond growth.
| -1-Aminoadamantane-N,N-d2 | 1-Aminoadamantane-d15 | 1-(N,N-Dimethylamino)adamantane |
 |
 |
 |
It is interesting to note that diamond itself is a semiconductor with high electron mobility. Diamond film transistors have been fabricated by the Diamond Electronics Group at University College London. The Kawarada laboratory has demonstrated diamond based single hole transistors using an AFM based field assisted anodization method to locally control FET conductivity via hydrogen attachment at the 10 nm level, electrolyte controlled diamond FETS and more traditional FETs.
Kawarada's
FET , 
, and transfer function
.
By varying the composition of the protein, they can vary the size
of the cavity from 1.4 to 10 nm. This work is similar
to the work of MG Finn http://www.scripps.edu/chem/finn/research.html
where viral particles directed the deposition of gold particles with atomic
precision.
A
2 input sorter
A
three input sorter
The memory is based on a 1:1000 fluidic de-multiplexer where an input stream can be routed to any of 1000 output streams. The device works analogously to an electronic demultiplexer by using 11 binary coded pairs of control channels to open or close gates (fluidic valves) to route the input channel to a selected output channels. These output channels are connected to load fluidic chambers which serve as a fluidic analogy to memory elements. The current cells are quite large (500,000 um^2) by microlithography standards, but there is good reason to expect successful scaling to the nanoscale.
This debut of LSI fluidic processors is an important step generally in the development of nanoscale devices, but may be particularly important for the development of electronic devices. Fluidic devices may serve as chemical workspaces to construct molecular devices by supplying precise delivery of reagents to reactor chambers or workfaces. They may be used to sort and route nanoscale suspended materials with exact precision. Fluidic devices may also serve directly to implement hybrid electronic devices based on electrochemical switches and electrochemical memory cells.
See Stephen Quake's lab
and a paper
describing the soft lithography technique used in the devices above. Another
paper
describes a cell-sorter using fluidic valves controlled by a imaging
system.
The HP team of Stan Williams and others announced the
development of a 64 - bit memory based on reversible IV cycles of
molecular films.
Press
release
Close-up of a single 64-bit memory.
A bit can be stored at each of the intersections of the
eight vertical and eight horizontal wires. In operation, a
junction is selected by applying a voltage between a selected horizontal
and a selected vertical wire. At the junctions is a molecular
film . When a current flows through the film, the film changes it's state
from conducting to non conducting (or visa versa). Each junction
is selected and programmed to a conducting or non-conducting state, after
which it can be read as a memory bit.
May-2002
The Chemical Sensors Research Group
at Warsaw University of Technology is developing chemical controlled sensors
and FETs (Field Effect Transistors). The device below is called a CHEMFET
because it's conductance is a function of the chemical environment. It's
operation is detailed here.
These devices can be selectively targeted towards detection of arbitrary
chemical signals. If an array of these devices can be arranged into
an arbitrary pattern, the array will "calculate" an arbitrary function
of the chemical environment. Such devices operating at the molecular level
can potentially be used to "program" higher performance electronic or electromechanical
switches.
Another paper by Carmen Bartic illustrates the response of such a device to pH.
Researchers at Scripps Research Institute, MG Finn and others have inserted cysteine at a single point in viral cowpea mosaic virus RNA which directs the binding of gold and numerous other groups at specific locations on the viral protein surface. Functional groups include biotin, sugars and organic molecules. The viral particles can be harvested in gram quantities from infected plants.
Cyroelectron microscopy shows 60 gold clusters attached
at designed points about the CPMV coat protein structure
The locations encoded by the cysteine can in principle be used to direct assembly of molecular components into nanoscale electronic devices with exact periodic positions. Cyclic molecular attachments using dendrimer like techniques could enable fully specified structures to be constructed. This is in contrast to lithographic methods of defining surface periodicity which are inherently noisy. Even small amounts of variation can disrupt behavior of charge sensitive devices (such as extended molecular orbitals), so the nature of exact viral attachment points may enable certain classes of electronic devices to be developed.
The viral particle are 30 nm in diameter and can themselves self-assemble in to larger crystal structures.
The work is described as Virus-Based Chemistry by Finn,
John
E. Johnson of Department of Molecular Biology, TSRI and Mark
A Young of Montana State University.
Check out the review paper on sub 10 nm electronics Electronics Below 10 nm
A Single electron transistor as a self latching memory
and switch
A Voltage vs Current sweep shows the memory action. After the input voltage exceeds a certain threshold, the device accepts a single electron. The charge maintains the "on" state of the switch until the charge leaks away or is withdrawn by a reverse voltage.
A regular array of these or similar devices exhibits neuron like behavior when voltage is raised a a selected point in the network.
Andre DeHon's nanofet array and Seth Goldstein's diode arrays papers presented at the First Workshop on Non-Silicon Computation mark the beginning of molecular architecture development. These architectures apply basic programmable logic concepts to develop molecular computing fabrics and illustrate the universal computing ability of 2 D arrays of diodes and FETs based on crossed nanowire junctions. These simple devices (diodes and FETs) have already been demonstrated and random arrays assembled, although production of precise regular arrays remains to be demonstrated.
, 
Seth Goldstein's diode matrix and nanofabric
, 
Andre's DeHon's nanowire switch and array
In Science a paper by Mohamed Eddaoudi, M. O'Keeffe, and Omar M. Yaghi and others describes the synthesis of Zn0 Metal Organic Frameworks with the lowest reported density for any crystalline material known to date. (.21 g/cm) This material is exceptional in other aspects. The material is a regular cubic framework of Oxygen terminated organic spacers and ZnO hubs as shown below. It is stable to 400 deg C.
The Metal Organic Framework is called Isoreticular because it's unit cell "generates" a regular 3D network. In a real sense the ZnO hubs (in blue tetrahedrons) segment space into an XYZ grid of 1-2 nm sized cubes . The interior of the unit cube is empty and it allows the entry of gas and solvent molecules. In a system designed to transport molecular payloads precisely, the periodic energy potential imposed by the lattice can potentially be used to move molecules in a "clocked" and exact fashion.
The makeup of the spacers or links is apparently quite variable. 16 variations are reported in the Science paper. Those synthesized are based on O2 terminated (carboxylate) struts composed of single, multiple or fused benzene rings. They report functionalized links including Br, NH3, and O-R ligands. Gross control over array dimensions, molecular transport and adsorption can be obtained as a function of the link type. These links are similar to those recently demonstrated to act as molecular FETs
One can imagine using this framework to guide the secondary synthesis of molecular electronic devices. For instance, it would seem reasonable to attach a gold atom to a thiol attached to a link. Electric field directed electrodeposition might allow the construction of nanowires in a periodic controlled fashion. It may be possible to cut links and replace them with other material. It may be possible to synthesize hetrogeneous layered or otherwise periodic cycles of links.
Key to any framework modification, is the ability for
materials to move throughout the lattice. These new MOFs have exceptional
open space allowing much opportunity for molecular transport. This movement
would normally be diffusion controlled, but could be influenced by the
application of directed electric fields to orient links and their attached
molecules. Thus it seems that periodic electric fields could "surf"
molecular payloads to any specific part of the lattice by inducing molecular
movement one unit cell per clock period (of the electric field). This could
enable the physical analog of electronic multiplexers, memories and
gates. Conversely, the presence of ions and molecules in unit cells could
alter the transport properties of neighboring cells. These actions mimic
electronic logic circuits, and may pave the way to nano-molec-tronics (Huh?)
as opposed to nano-elec-tronics. Certainly, the ability to construct and
decorate these cubes and possibly to direct material to specific xyx coordinates
with atomic precision will present opportunities
People/Organizations
| Academia | |
| architecture | Goldstein, Likarev |
| Exact Molecular Arrays | Yaghi , Finn , Seeman, Feng , Kiehl , |
| switches | Lieber , Reed , Heath/Williams ,Gimzewski , McEuen , Likarev, Deeker , Chou |
| assembly | Craighead , |
| electro chemical devices | ASU, , , |
| molecular scale fluidics | Thorsen, Quake , |
| nanowires, | Yang , |
| electro-deposition, polymerization | Schindler , Mallouk , , |
| molecular optics | Dalton , Drain |
| Switchable surface properties | Langer , |
| nems | Roukes |
| structure | Michl |
| porphyrin like devices | Holten , Bocian , Lindsey |
| transport | ASU , Ga Tech , Seminario , Di Ventra |
| Simulations | ncsu , , |
.
Transfer interrupted!/tr> |
|
| Switches | IBM , HPLabs , nanosys, Molecular Electronics Corp , |
| Material | Covalent Materials , nanolayers , molecular nanosystems , |
| Memory | Rolltronics , Nantero |
| Architecture | Cell Matrix |
| nanopatterned
directed assembly |
?? |
| Fludics | Fluidigm , |
.
| Info | |
| News | Physics News , VJnano , ACS news , Nanonews , CEN nanoarchive , EET , Foresight , , , |
| Events | |
| Reviews | molecular-electronics, C&EN , Electronics Below 10 nm |
| Mags | Sci-Am , Reed , Tech Review , Science , Nano Letters , MRS , Materials Today , |
| Books | Molecular
Electronics , quantum
computation , chemistry
, electron
transport ,
Feynman and Computation |
| Tutorials | qubits , quantum physics , self_assembly |
Transfer interrupted!nt> |
viewer ,editor , structure , tink , molecular electronic simulation , molspice , circuit simulator |
| Reaction Software | AOCR , open dir page , , |
| Table | |