Electronic Design

Simulations Prove Viability Of 6-nm Liquid Jets

While the airline companies are announcing larger and larger widebodies, the electronics industry is going smaller and smaller—with jets as small as a few nanometers in diameter.

Researchers at the Georgia Institute of Technology in Atlanta have an-nounced that it may be possible to produce liquid jets with 6-nm diameters. These diminutive devices could be used to produce miniscule electronic circuitry, inject genes into cells, etch tiny features, and even serve as fuel injectors in microscopic engines.

Uzi Landman and Michael Moseler, members of Georgia Tech's Center for Computational Materials Science, led the effort. They used molecular dynamics simulations to observe how approximately 200,000 propane molecules would behave when compressed within a miniature reservoir and then injected out of a narrow, gold nozzle. These simulations, operating on an IBM SP-2 parallel processing computer, recorded the dynamics of the fluid molecules on the femtosecond timescale over periods of several nanoseconds each.

The scientists applied 500 Mpascals (5000 atmospheres) of pressure to the jets. But the simulations revealed that the jets would rapidly clog up during this process. A film measuring several molecules thick rapidly formed on the nozzle's outer surface. Countering this, the team heated the nozzle's outer surface and evaporated the film. Alternatively, the researchers speculate that they may be able to apply a molecule-resistant coating to the nozzle's outer surface in future applications. Once they were able to maintain the propane's flow, the researchers noted a number of significant properties.

Jets exiting the nozzle into a simulated vacuum reach speeds of up to 400 m/s. The friction caused by the pressurized fluid's movement through the nozzle heats the propane and turns it into a very hot fluid. Once it exits the nozzle, molecule evaporation cools the jets and reduces their diameter by about 25%. The jets' shape is affected by instabilities caused by thermal fluctuations as well. Each jet forms a series of "necks" that cause it to resemble "links of sausage" connected to one another. Ultimately, one of the necks pinches off, and a droplet of propane separates itself from the jet.

Despite these changes, the jets remain intact. They even propagate as a whole over shorter distances than macroscopic jets would under similar conditions. Landman and Moseler observed jets that extended 150 to 200 nm, compared to deterministic Navier-Stokes calculations that predict jets that are 500 nm long. According to the scientists, these observations matched their predictions. The team modified the hydrodynamic equations to include the effect of stress fluctuations.

During the research's second stage, the team tried to reconcile its observations with the predictions of traditional fluid dynamics equations, such as Navier-Stokes. These equations didn't account for the effect of thermally induced fluctuations, which have a significant effect on the nanojets' stability. By reformulating the hydrodynamic equations, Landman and Moseler were able to describe what they observed in their atomistic equations. Now, other researchers can use these modified equations to predict the behavior of nanojets of different materials under other conditions.

Next, the team hopes to experimentally create nanojets and use them to apply patterns that could replace current lithographic processes in the manufacture of nanoscale miniaturized circuits. According to Landman, these jets also could be used as "gene guns" to insert genetic materials into cells without damaging them.

For more information, contact Landman at (404) 894-3368, or go to http://gtresearchnews.gatech.edu.

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