Nanoscale phase change memory materials.

Phase change memory materials store information through their reversible transitions between crystalline and amorphous states. For typical metal chalcogenide compounds, their phase transition properties directly impact critical memory characteristics and the manipulation of these is a major focus in the field. Here, we discuss recent work that explores the tuning of such properties by scaling the materials to nanoscale dimensions, including fabrication and synthetic strategies used to produce nanoscale phase change memory materials. The trends that emerge are relevant to understanding how such memory technologies will function as they scale to ever smaller dimensions and also suggest new approaches to designing materials for phase change applications. Finally, the challenges and opportunities raised by integrating nanoscale phase change materials into switching devices are discussed.

Size-dependent polar ordering in colloidal GeTe nanocrystals.

The question of the nature and stability of polar ordering in nanoscale ferroelectrics is examined with colloidal nanocrystals of germanium telluride (GeTe). We provide atomic-scale evidence for room-temperature polar ordering in individual nanocrystals using aberration-corrected transmission electron microscopy and demonstrate a reversible, size-dependent polar-nonpolar phase transition of displacive character in nanocrystal ensembles. A substantial linear component of the distortion is observed, which is in contrast with theoretical reports predicting a toroidal state.

Driving oxygen coordinated ligand exchange at nanocrystal surfaces using trialkylsilylated chalcogenides.

A general, efficient method is demonstrated for exchanging native oxyanionic ligands on inorganic nanocrystals with functional trimethylsilylated (TMS) chalcogenido ligands. In addition, newly synthesized TMS mixed chalcogenides leverage preferential reactivity of TMS-S bonds over TMS-O bonds, enabling efficient transfer of luminescent nanocrystals into aqueous media with retention of their optical properties.

Synthesis of metal chalcogenide nanodot arrays using block copolymer-derived nanoreactors.

Soluble metal chalcogenide precursors are used to fabricate arrays of metal chalcogenide nanodots by spin-coating. Nanodots are formed after thermal decomposition of the precursors, which are collected in patterned nanowell arrays. These arrays are derived from block copolymer patterns and may consist of the polymer itself or result from etching to transfer the pattern to an inorganic substrate. Etching provides enhanced control over nanowell shape and the morphology of the resulting metal chalcogenide array.