Probing the Melting Transitions in Phase-Change Superlattices via Thin Film Nanocalorimetry.

Phase-change superlattices with nanometer thin sublayers are promising for low-power phase-change memory (PCM) on rigid and flexible platforms. However, the thermodynamics of the phase transition in such nanoscale superlattices remain unexplored, especially at ultrafast scanning rates, which is crucial for our fundamental understanding of superlattice-based PCM. Here, we probe the phase transition of SbTe (ST)/GeSbTe (GST) superlattices using nanocalorimetry with a monolayer sensitivity (∼1 Å) and a fast scanning rate (10 K/s).

Approaching the size limit of organometallic layers: synthesis and characterization of highly ordered silver-thiolate lamellae with ultra-short chain lengths.

Approaching the ultimate limits of material sizes provides a route for designing new functional materials with extraordinary properties. We report the first systematic synthesis and characterization study of a wide range of highly ordered silver alkanethiolate (AgSCH or AgSCn, n = 1-16) aliphatic lamellae. Single crystalline multilayer AgSCn are synthesized by a modified solution reaction method.

Size effect and odd-even alternation in the melting of single and stacked AgSCn layers: synthesis and nanocalorimetry measurements.

We report a systematic study of melting of layered lamella of silver alkanethiolates (AgSCn). A new synthesis method allows us to independently change the thickness of the crystal in two ways-by modulating chain length (n = 7-18) and by stacking these crystals to a specific layer number (m = 1-10). This method produces magic size lamella, having a well-spaced discrete melting point, Tm, distribution.

Synthesis and characterization of single-layer silver-decanethiolate lamellar crystals.

We report the synthesis of silver-decanethiolate (AgSC10) lamellar crystals. Nanometer-sized Ag clusters grown on inert substrates react with decanethiol vapor to form multilayer AgSC10 lamellar crystals with both layer-by-layer and in-plane ordering. The crystals have strong (010) texture with the layers parallel to the substrates.

Self-assembly and ripening of polymeric silver-alkanethiolate crystals on inert surfaces.

We characterize and compare the reaction of alkanethiol with Ag continuous planar thin films and Ag islands on inert substrates. Ag islands generate a significantly larger (3-fold) amount of alkanethiolate than continuous Ag films at comparable conditions. The reaction with planar Ag thin films produces alkanethiol self-assembled monolayers (SAMs), whereas the reaction with Ag islands yields two dissimilar products depending on the size of the islands.

Glass transition in ultrathin polymer films: calorimetric study.

The ultrasensitive differential scanning calorimetry is used to observe the glass transition in thin (1-400 nm) spin-cast films of polystyrene, poly (2-vinyl pyridine) and poly (methyl methacrylate) on a platinum surface. A pronounced glass transition is observed even at a thickness as small as 1-3 nm. Using the high heating (20-200 K/ms) and cooling (1-2 K/ms in glass transition region) rates which are typical for this technique, we do not observe appreciable dependence of the glass transition temperature over the thickness range from hundreds of nanometers down to 3 nm thick films.