Issue
Fall
2006
Volume
19
Issue
2
Contact
Cornell University
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At Cornell

G-Line
Watching Atoms Arrange Themselves

Joel Brock and Researchers

Vivid Properties

Plume

Plume of La1-xSrxMnO3 depositing onto a SrTiO3 substrate in the pulsed laser deposition chamber.

Imagine taking a handful of ceramic tiles of various colors and throwing them against a wall. After the dust settles, to your utter amazement you see that the tiles are organized into a beautiful, flawless mosaic design. This scene is unimaginable in everyday life, but it is an accurate microscopic description of a common technique used to grow nearly defect-free crystals of complex materials that exhibit striking physical properties, such as high-temperature superconductivity and colossal magnetoresistance.

To Grow Perfect Crystals of Unusual Materials

Because a high power laser beam is used to vaporize material within a target, this growth technique is called pulsed laser deposition (PLD). The resulting “plume” of material is directed onto a substrate and forms—under the correct conditions—a perfect crystal. PLD is frequently the technique of choice for growing thin films of materials consisting of several different atomic species, because the chemical composition of the deposited film faithfully preserves the chemical composition of the original target. My research peeks behind the curtain to study the microscopic mechanisms by which the atoms (that certainly land at random locations) arrange themselves into a nearly error-free pattern.

To do this, researchers need to be able to make measurements that enable them to “watch” the atoms rearrange themselves. The wavelength of x-rays and their ability to pass through material without being absorbed (think of a chest x-ray) make them ideally suited for structural studies on atomic-length scales. Indeed, most of what is known about the atomic scale structure of materials is based on x-ray measurements. The main challenge is to produce a beam of x-rays with sufficient intensity to obtain a measurable signal from a single atomic layer or less of deposited material. CHESS’s G-line facility was specifically designed to produce the intense x-ray beams needed to perform this type of growth study.

 

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