Place Setting: Physics Lab, Olin Hall

Physics

One imagines scientists spending their days conducting important laboratory experiments, but Melissa Eblen-Zayas, assistant professor of physics, who came to Carleton in fall 2005, had to wield screwdrivers and wrenches before she could get on with the weightier aspects of her research. “During my first couple of years here, I spent most of my time building the equipment,” says Eblen-Zayas, an experimental condensed matter physicist (one who studies the properties of solids and liquids). “It’s been great to move beyond the building-the-lab stage to actually growing the materials and starting to think about the physics.”

Interested in studying a group of materials that have unusual electronic and magnetic properties, Eblen-Zayas makes samples of the materials, then tests how well the samples conduct electrical current or respond to magnetic fields. Her current focus is on materials that exhibit an intrinsic property known as colossal magnetoresistance (CMR): at certain low temperatures such materials dramatically change their electrical resistance in the presence of a large magnetic field.

So far, 18 Carleton students (primarily physics and chemistry majors)—some of whom have worked full time in the lab during the summer—have assisted her in both building the equipment and preparing materials.

During a recent tour of her lab, Eblen-Zayas gave us a quick course in the physical properties of matter—and a much-needed refresher in the periodic table of the elements.

  1. Melissa Eblen-Zayas: “Condensed matter physics has more practical impact on how we live than any other subfield of physics—from alternative energy technologies to data storage and processing to medical technologies,” says Eblen-Zayas. “The transistors in your computers, the LEDs in various displays, the magnetic memory devices for iPods and other technologies are all based on condensed matter physics.”
  2. Tom Brenner ’09 (Plymouth, Minn.): Brenner—who is interested in renewable energy and is now in graduate school at the Colorado School of Mines—worked in the lab for three years. Last spring he presented a poster at the American Physical Society on preliminary results of the first samples grown in Carleton’s lab. “Tom had little knowledge when he started working in the lab,” says Eblen-Zayas, “but when he left, I regarded him as more of a colleague than a student.” Here, Brenner is checking for shorts in the electrical leads, which could affect the output of the cryostat (see #8).
  3. Brian Schuster ’11 (Owings Mills, Md.): Schuster, who earns credit for working in the lab two days a week and is interested in engineering, is monitoring pressures of different gases within the ultra-high vacuum chamber (see #6) to ensure that oxygen levels remain consistent. “Too little or too much, and we don’t get the product we’re looking for,” says Schuster. “I’ve learned stuff in the lab that I wouldn’t have learned in the classroom alone—things as basic as how to solder and as complicated as the theory behind CMR.”
  4. Sputtering chamber: In this machine, a target material is bombarded with ions through a process called sputtering. When the ions collide with the target, little bits of the material are deposited as a thin film on a crystal substrate that sits at the top of the chamber. Eblen-Zayas and her students are trying to grow alternating layers of thin films (only a few atoms thick) of magnetic and nonmagnetic materials, which are necessary to produce giant magnetoresistance (GMR) responses—a physical effect in which the human-made material’s electrical resistance decreases significantly in the presence of a weak external magnetic field and increases in the absence of one. GMR-based technology has made it possible to miniaturize computer hard disks in recent years.
  5. Crane: This crane lifts the stainless steel lid of the sputtering chamber, which weighs about 150 pounds.
  6. Ultra-high vacuum (UHV) chamber: When materials do not occur naturally, this machine is used to synthesize them. “We start out with individual elements and we cook them together to get a material that has particular intrinsic properties,” says Eblen-Zayas. “In this case, we’re putting together europium and oxygen to get europium oxide (EuO) [which exhibits the property of colossal magnetoresistance].”
  7. Aluminum foil: “When we’re baking the UHV chamber, we wrap it in aluminum foil to achieve the uniform high temperatures that ultimately help to create the vacuum,” says Eblen-Zayas. “When the gas molecules heat up, they move around instead of sticking to the walls of the chamber and it’s easier to pump them away.”
  8. Cryostat: This cryostat can measure the electrical resistance of samples exposed to temperatures down to 10 K (Kelvin). (For comparison’s sake: 300 K is room temperature; 272 K is the temperature at which water freezes.) The large decrease in electrical resistance in europium-rich europium oxide (Eu-rich EuO) occurs at temperatures in the range of 70 to 140 K. Eu-rich EuO samples are about 100 nanometers thick, or about 1,000 times smaller than the diameter of a human hair. “We can see our samples [without a microscope] because they appear slightly bluish,” says Eblen-Zayas.
  9. Sample transport box: Eblen-Zayas and her students use this tackle box to carry samples to more advanced facilities at the University of Minnesota, where they collaborate with physicists and use additional equipment to expand their research.
  10. Mascot: A plastic figure of android Lieutenant Commander Data from Star Trek resides in the lab. “When you’re doing experimental work, there is a high probability that things will go wrong,” says Eblen-Zayas. “So even if our data aren’t working, we still have Data.”

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