Nanometer-scale order in amorphous Ge2Sb2Te5 analyzed by fluctuation electron microscopy

Abstract

The phase change material Ge2Sb2Te5 is widely investigated for use in nonvolatile memories. It has been reported that the crystallization speed depends on the thermal history, indicating that structural differences exist between amorphous states. The authors apply fluctuation electron microscopy to quantify differences in the nanometer-scale structural order between several amorphous states of Ge2Sb2Te5. All as-deposited films are found to contain ordered regions. Thermal annealing below the crystallization threshold increases the nanoscale order, and such samples crystallize slightly more rapidly. The authors hypothesize that the nanoscale ordered regions act as the nuclei for crystallization, with the largest regions being the most significant.

Fluctuation Transmission Electron Microscopy: Detecting Nanoscale Order in Disordered Structures

“…[14] The variance values are higher near the Bragg conditions of crystalline (fcc) Ge 2 Sb 2 Te 5 , whereas they are lower at other k values. Such prominent peaks in V(k) would not be produced by a random arrangement of atoms.…”

“…This nanostructural change detected by FTEM directly correlates with an increase or decrease, respectively, in the crystallization speed of the material. Note that in chalcogenide materials, these results may vary with the details of the thermal history, [1,14] composition, [30] or deposition conditions (Figure 2). [14] 5.3.…”

Time Resolved Investigation of Fast Phase- Change Phenomena in Rewritable Optical Recording Media

“…In contrast to the reliability and high-speed-performance of DVD media, the mechanism of rapid phase change, especially crystallization from the amorphous phase is still not fully understood, in spite of a lot of investigation using transmission electron microscopy (Park et al, 1999;Naito et al, 2004), fluctuation electron microscopy (Kwon et al, 2007), optical (Wei & Gan, 2003), electronic (Lee et al, 2005), and structural (Yamada & Matsunaga, 2000;Kolobov et al, 2004;Kohara et al, 2006) studies. We therefore developed the X-ray pinpoint structural measurement system , which enables the 40 picosecond time resolved pump and probe X-ray diffraction experiment using 100 nm scale SR beam.…”

A Trial on Detecting Fluctuations in Bulk Metallic Glass Beams by Strain Contrast Variation Method–Use of High Energy Small-Angle Scattering

“…14) Such heterogeneity has been examined by electron microscopy, 5) XAFS, 6) smallangle scattering, 79) diffraction 8) and inelastic scattering. 10) Recent works using fluctuation microscopy 11) are quite powerful for its sensitivity to the local heterogeneity in atomic structures. Yet, it is desirable to seek an approach which detects chemical and mechanical/volumetric heterogeneity as an ensemble average, because bridging atomistic short-range order as observed by electron high resolution microscopy or XAFS and nanoscopic fluctuations in composition/structure is not easy.…”