Figure 2

(a) A typical heating (red curve) and cooling (blue curve) in a melt-freeze cycle during differential scanning calorimetry (DSC) measurements. This specific sample consists of 17 nm Sn nanocrystals (NCs) dispersed in a polyimide resin matrix. Note that the feature located in the 0–25 °C range of the heating curve is a measurement artifact that occurs when the DSC switches from cooling to heating. (b) The endothermic valley of 17 nm Sn nanocrystals during several different melt-freeze cycles. After the initial melting cycle, a stable and repeatable melting temperature and melting enthalpy are observed. We attribute the elevated melting temperature during the initial cycle to surface stabilization from the organic ligands on the nanocrystal surface. (c) The endothermic valley of 17 nm Sn nanocrystals prepared at varying nanocrystal volume fractions within the polyimide resin matrix. As the nanocrystal volume fraction is changed, the melting enthalpy signature increases proportionately and the melting temperature remains unchanged. (d) The endothermic melting valley for Sn nanocrystals of varying diameters that are embedded in a polyimide resin matrix. As the nanocrystal diameter decreases, both the melting temperature and melting enthalpy decrease. The full-width at half-maximum of the melting valley also increases for smaller nanocrystals.