AsianScientist (Nov. 26, 2012) – Phase change materials are highly attractive for their use in data storage applications such as optical media and solid state memory. However, large amounts of energy are required to induce phase switching between amorphous and crystalline stages using conventional phase change materials such as Ge-Sb-Te (GST).
Dr. Song Wendong and colleagues at the A*STAR Data Storage Institute (DSI) have developed novel phase change materials using the elements iron (Fe) and tellurium (Te), whose phase change properties were previously unknown.
First, they first deposited the Fe-Te materials by laser molecular beam epitaxy (MBE) onto a silicon substrate to a thickness of ~50 nanometers. Next, they characterised the compositions and crystal structures of the samples by x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD), respectively.
To test the phase change properties of the materials, the researchers used a pulsed laser beam to detect a reflectivity change at the temperature where the materials switched from an amorphous to a crystalline state.
Not only do the Fe-Te materials exhibit a low crystallization temperature of 180 ˚C which helps to reduce energy requirements, the crystallization temperature could also be adjusted by altering the ratio of Fe to Te.
More interestingly, the materials exhibit a unique optical property of higher reflectivity in the amorphous state versus the crystalline state. In conventional phase change materials such as Ge-Sb-Te (GST), the optical reflectivity at the visible range is higher in the crystalline state versus the amorphous state.
“We found that Fe-Te materials exhibit not only an anomalous optical property, but also an anomalous electrical property that has lower resistivity at amorphous than crystalline state,” said Song.
These upside-down properties may be useful in the search for the next generation of data storage materials.
“Since this material exhibits anomalous optical and electrical properties, it may also have an application in spintronics and semiconductor devices,” said Song.
The article can be found at: Fu XT et al. (2012) Anomalous phase change characteristics in Fe-Te materials.
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Copyright: Asian Scientist Magazine; Photo: Song Wendong.
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