Confined Crystals of the Smallest Phase-Change Material

• Published in: Nano letters Vol. 13; no. 9; pp. 4020 - 4027
• Main Authors: Giusca, Cristina E, Stolojan, Vlad, Sloan, Jeremy, Börrnert, Felix, Shiozawa, Hidetsugu, Sader, Kasim, Rümmeli, Mark H, Büchner, Bernd, Silva, S. Ravi P
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11.09.2013
• Subjects: Amorphous materials; Chemical synthesis methods; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Data storage; Devices; Electronics; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Letter; Materials science; Methods of nanofabrication; Miniaturization; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Nanotubes; Nanowires; Phase transformations; Physics; Specific phase transitions; Structural transitions in nanoscale materials; electron microscopy; carbon nanotubes; Phase-change materials; scanning tunneling microscopy; GeTe; Optical storage; Crystalline phase; Phase transformations; High density; Memory; Data storage; Carbon nanotubes; Template reaction; Heat treatments; Experimental design; PCM material; Miniaturization; Nanowires; Nanostructured materials; Crystal structure
• ISSN: 1530-6984; 1530-6992; 1530-6992
• DOI: 10.1021/nl4010354

The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.