Kim et al. Nanoscale Research Letters 2012, 7:49 http://www.nanoscalereslett.com/content/7/1/49 Page 3 of 6 Figure 3 DSC (a) and TGA (b) curves of the Ag nanopaste. a similar particle shape and size compared to the as- dried one. However, when the printed Ag nanopaste was sintered at 200°C for 30 min, the clusters were built via interconnections, resulting from interparticle necking that occurred after the drying of the dispersing agent and decomposition of the organic solvent. Therefore, this microstructural evolution matched well with the thermal analysis results, as shown in Figure 3. Above a sintering temperature of 200°C, the surface of the sin- tered Ag nanopaste drastically changed from discrete and spherical Ag nanoparticles to continuous and con- solidated ones. Figure 5 plots the variation in the apparent density of the Ag nanopaste as a function of sintering temperature. Except at 300°C, the average apparent density did not change much which was approximately 6.32 g/cm3 within the standard deviation of 0.22. At 300°C, the film of the Ag nanopaste as the result of volume shrinkage appeared after the interparticle neck growth, as shown in Figure 4d [14]. Because the apparent density was calcu- lated from the values of the measured mass and volume, any change in mass or volume would consequently affect the density. Although some pores were observed inside the film of the Ag nanopaste, the main parameter was the volume shrinkage of the screen-printed Ag film com- pared to the mass decrement caused by the solvent eva- poration. In this case, although the mass of the Ag nanopaste was reduced by solvent evaporation that resulted in observable pores inside the film, the dominat- ing factor was still the volume shrinkage of the screen- printed Ag film. Therefore, the volume shrinkage led to the increase of apparent density. Figure 4 FE-SEM micrographs of the screen-printed Ag nanopaste sintered at various temperatures. (a, e) 150°C, (b, f) 200°C, (c, g) 250°C, and (d, h) 300°C.