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Chileans in the lab, February 2010

Francisco Martinez

Francisco's project is to make a sensor to control a laser beam. The laser is part of a new atom-trapping apparatus in the lab of Prof. Cheng Chin. Kathy Anne Soderberg is the postdoc working directly with Francisco. Francisco has just finished a second version of the sensor. The picture at right shows them measuring the response to the small red light in the foreground.

Tiaren Garcia

Prof. Guyot-Sionnest is working to create electron channels using narrow columns of nanoparticles. These particles have tunable sizes in the range of 5-7 nm and are made of semiconductors such as cadmium selenide. If the particles are stacked into narrow pores like those shown in Tiaren's sketch at right, electrons can traverse the column by passing from particle to particle. Slight changes in the particles or in external electric fields or light should have a big effect on the electric current. Before measureing the currents, the purity of the nanoparticles must be assayed by measuring their optical absorption. Tiaren's graphs at left show the measured optical optical absorption of two samples with different sized nanoparticles. The light lines underneath show postulated contributions from different electronic energies.

Ruben Meza

Ruben is pointing to a polymer gel that he is making in Prof. Lee's lab. Working with Niels Anderson, Ruben is testing how a rigid film attached to a gel wrinkles when it is squeezed. Strong gels make fine wrinkles; weak gels make coarse ones. To test the predictions of wrinkle size vs gel strength, Ruben measures the strength of each gel sample, pictured at right, in a rheometer, right, also used by Franco Tapia. The vertical rod pushes down on the gel sample. A graph of the measurements appears on the screen in the background.

Franco Tapia

Working with postdoc Eric Brown in Prof. Jaeger's lab, Franco is measuring how a suspension of colloidal particles can exert strong counterforces when suddenly pushed. Franco is about to drop a steel ball into a jar of cornstarch. If the ball is dropped from very high, the cornstarch stops it quickly. If dropped from just above the surface, the ball sinks steadily instead. Franco and Eric hope to explain the stopping power quantitatively by using geometrically regular colloidal suspensions and measuring their stress-strain properties with a rheometer.

Gustavo Castillo

Gustavo is checking the top of the granular drop tower in Prof. Jaeger's lab. A fine stream of submillimeter-sized particles, shown at the right, is falling into the tower, accelerating and interacting. Fast photography of the falling stream reveals bunching and stretching phenomena not seen in other situations. Working with PhD student Scott Waitrusaitis, Gustavo will apply external electric fields to the stream, so they can judge whether static charges on the particles might contribute to their interactions.

Sebastian Cespedes

Sebastian's experiment is about the wispy iridescence seen under the microscope lens at left. It is a film of 5-nanometer gold particles just three particles thick. Sebastian compresses the films using the white slider in the foreground and measure the resulting rise in surface pressure. Sebastian, shown at right with his boss Brian Leahy is working in Dr. Binhua Lin's lab. He is measuring films like this to gauge their mechanical strength. They are trying iron as well as gold, and incorporating extra surfactants at the surface to spread the particles apart. So far these variations are making the films fragile and brittle compared to the original gold trilayers.

Tania Sauma

Tania is working with Prof. Witten on a fluid capillary problem inspired by Prof. Ismagilov. He invented the slip-chip, a capillary fluid device made of sliding glass plates with wells cut into them as Tania is showing. The surfaces are coated with oil. When the upper plate's well lies above the lower well, they trap a body of water via capillary forces. When the two wells slide a part, it cuts the water in two, via a scissoring motion. Tania is using numerical calculations in Matlab to design the well shape that gives the cleanest scissoring of the liquid.