Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers create freestanding nanoparticle films without fillers

10.06.2009
Nanoparticle films are no longer a delicate matter: Vanderbilt physicists have found a way to make them strong enough so they don¹t disintegrate at the slightest touch.
­In the last 25 years, ever since scientists figured out how to create nanoparticles ­ ultrafine particles with diameters less than 100 nanometers ­ they have come up with a number of different methods to mold them into thin films which have a variety of interesting potential applications ranging from semiconductor fabrication to drug delivery, solid state lighting to flexible television and computer displays.

Until now these films have had a common problem: lack of cohesion.
Nanoparticles typically consist of an inorganic core coated with a thin layer of organic molecules. These particles are not very sticky so they don¹t form coherent thin films unless they are encapsulated in a polymer coating or mixed with molecules called chemical ³cross-linkers² that act like glue to stick the nanoparticles together.

³Adding this extra material can complicate the fabrication of nanoparticle films and make them more expensive. In addition, the added material, usually a polymer, can modify the physical properties that make these films so interesting,² says James Dickerson, assistant professor of physics at Vanderbilt, who headed the research group that developed freestanding nanoparticle films without any additives.

The properties of the new films and the method that the researchers use to create them is described in the article ³Sacrificial layer electrophoretic deposition of freestanding multilayered nanoparticle films² published online in the journal Chemical Communications on May 27, 2009.

³Our films are so resilient that we can pick them up with a pair of tweezers and move them around on a surface without tearing,² says Dickerson. ³This makes it particularly easy to put them into microelectronic devices, such as computer chips.²

Dickerson considers the most straightforward applications for his films to be in semiconductor manufacturing to aid in the continued miniaturization of digital circuitry and in the production of flexible television and computer screens.

A key component in the transistors in integrated circuits is an insulating layer that separates the gate, which turns current flow on and off, from the channel through which the current flows. Traditionally, semiconductor manufacturers have used silicon dioxide for this purpose. As transistors have shrunk, however, they have been forced to make this layer thinner and thinner until they reached the point where electrons leak through and sap the power from the device. This has led semiconductor manufacturers to retool their process to use ³high-k² dielectric materials, such as hafnium oxide, because they have much higher electrical resistance.

³We have made high-k nanoparticle films that could be cheaper and more effective than the high-k materials the manufacturers are currently using,² Dickerson says.

In addition, the physicist argues that the films have properties that make them ideal for flexible television and computer screens. They are very flexible and don¹t show any signs of cracking when they are flexed repeatedly. They are also made using a technique called electrophoretic deposition (EPD) that is well suited for creating patterned material and is compatible with fluorescent materials that can form the red, green and blue pixels used in flat panel television screens and computer displays.

EDP is a wet method. Nanoparticles are placed in a solution along with a pair of electrodes. When an electric current is applied, it creates an electrical field in the liquid that attracts the nanoparticles, which coat the electrodes. Using colloids, mixtures with particles 10 to 1,000 times larger than nanoparticles, EDP is widely used to apply coatings to complex metal parts such as automobile bodies, prosthetic devices, appliances and beverage containers. It is only recently that researchers like Dickerson have begun applying the technique to nanoparticles.

³The science of colloidal EDP is well known but the particles are substantially larger than the solvent molecules. Many nanoparticles, however, are about the same size as the solvent molecules, which makes the process considerably more complicated and difficult to control,² Dickerson explains.

To get the method to work, in fact, Dickerson and his colleagues had to invent of new form of EDP, which they call sacrificial layer electrophoretic deposition. They added a spun-cast layer of polymer to the electrodes that serves as a pattern that organizes the nanoparticles as they are deposited.
Then, after the deposition process is completed, they dissolve (sacrifice) the polymer layer to free the nanoparticle film.

According to the researchers, films made in this fashion stick together because the electrical field slams the nanoparticles into the film with sufficient force to pack the particles together tightly enough to allow naturally attractive inter-particle forces to bind the particles together.

So far the Dickerson group has used the technique to make films out of two different types of nanoparticles ­ iron oxide and cadmium selenide ­ and they believe the technique can be used with a wide variety of other nanoparticles.

³The technique is liberating because you can make these films from the materials you want and use them where you want,² Dickerson says.

The co-authors on the paper are graduate students Saad A. Hasan and Dustin W. Kavich. The research was funded by a grant from Vanderbilt University.

David F. Salisbury | Vanderbilt University
Further information:
http://www.vanderbilt.edu/News

More articles from Physics and Astronomy:

nachricht Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas

nachricht Calculating quietness
22.09.2017 | Forschungszentrum MATHEON ECMath

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>