Move over Elmer's: Nanoglue is thinner, stickier

CHICAGO (Reuters) - A cheap glue that gets stronger at high temperatures might be useful around the house, but make it 100,000 times thinner than a human hair and you have nanoglue, a sticky substance that could help make extremely tiny computer chips, U.S. researchers said on Wednesday.

Developed by researchers at Rensselaer Polytechnic Institute in Troy, New York, nanoglue is made from ultrathin materials that are already commercially available.

"It is really mind-boggling to think about a single layer of molecules improving the adhesion of something," said materials science researcher Ganapathiraman Ramanath, whose work appears in the journal Nature.

"Our work shows the possibility of having organic-based nanolayers that are about a 1,000 times thinner than the thinnest organic-based glues," he said.

Similar toughness has been shown using layers as thin as one-millionth of a meter (yard), but never before with a thickness of only one nanometer -- which is just one billionth of a meter.

"This is a single layer of molecules that are organized like soldiers," Ramanath said in a telephone interview. The glue chain lines up in very orderly fashion all on its own.

"Nature does most of it for you," Ramanath said. "You just have to put the right thing on the top and the right thing on the bottom and it will work."

The glue has a backbone of carbon molecules. On one end of the chain is silica and oxygen and on the other is sulfur. These different end molecules act as hooks that bind with other surfaces.

Ramanath topped off the chain with a thin layer of copper that acts as a protective coating that helps keep the molecules intact.

But when heated to 750 degrees Fahrenheit (400 degrees Celsius) or higher, the copper and silica formed a strong chemical bond and it became much stronger -- increasing its stickiness by five to seven times.

"When you heat it, it becomes a better glue," he said. "That was something we hadn't bargained for."

He said the glue could be used as an inexpensive way to connect any two materials that do not bond well.

And the cost -- at $35 per 100 grams (3.5 ounces) -- would make it a fairly cheap commercial option, he said.

Ramanath and his team are seeking a patent for the material, which he thinks could be used in the development of chips used in any type of microelectronic device.

Modern urethane auto paint (at least in the aftermarket) uses a technology very similar to super glue (isocyanates).

This could be a cool car paint if it could be developed, or heck, any coating for that matter.

Plus, if it’s strong enough to replace welding in some circumstances, it could revolutionize assembly of all sorts of products.

Annealing-induced interfacial toughening using a molecular nanolayer

Self-assembled molecular nanolayers (MNLs) composed of short organic chains and terminated with desired functional groups are attractive for modifying surface properties for a variety of applications. For example, organosilane MNLs are used as lubricants1, in nanolithography2, for corrosion protection3 and in the crystallization of biominerals4. Recent work has explored uses of MNLs at thin-film interfaces, both as active components in molecular devices5, and as passive layers, inhibiting interfacial diffusion6, 7, 8, promoting adhesion9, 10 and toughening brittle nanoporous structures11. The relatively low stability of MNLs on surfaces at temperatures above 350–400 °C (refs 12, 13), as a result of desorption14 or degradation, limits the use of surface MNLs in high-temperature applications. Here we harness MNLs at thin-film interfaces at temperatures higher than the MNL desorption temperature to fortify copper–dielectric interfaces relevant to wiring in micro- and nano-electronic devices. Annealing Cu/MNL/SiO2 structures at 400–700 °C results in interfaces that are five times tougher than pristine Cu/SiO2 structures, yielding values exceeding 20 J m-2. Previously, similarly high toughness values have only been obtained using micrometre-thick interfacial layers15, 16, 17. Electron spectroscopy of fracture surfaces and density functional theory modelling of molecular stretching and fracture show that toughening arises from thermally activated interfacial siloxane bridging that enables the MNL to be strongly linked to both the adjacent layers at the interface, and suppresses MNL desorption. We anticipate that our findings will open up opportunities for molecular-level tailoring of a variety of interfacial properties, at processing temperatures higher than previously envisaged, for applications where microlayers are not a viable option—such as in nanodevices or in thermally resistant molecular-inorganic hybrid devices.

Figures and Tables Check the structure in figure 3. It's strength also appears to involve its hydrogen bonds once the Si-O-Si bond is formed. (lowest figures)

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