An influence of crystal structure and interface formation on the electrical properties of nanoparticle printed thin films
The creation of inexpensive electronic devices through the direct printing of organic semiconductors is of interest for the clear advantages associated with device cost reduction through mass production using cheap substrates. However, the low inherent carrier mobility of organics places fundamental limitations on both the performance and types of devices that can be created with this approach. As a substitution for organics, printing of inorganic nanoparticles followed by subsequent sintering to form conductive films has been proposed. However, the high required sintering temperatures have restricted their usage. Here, core-shell nanoparticles are proposed to reduce the sintering temperature of inorganic nanoparticles, with three semiconductor (or metal)-metal core-shell nanoparticle systems investigated; Ge-Ag, SnO2-Ag, and Cu-Ag. These were chosen because (1) silver exhibits a high surface self-diffusion, (2) silver has a low solubility in the core materials, and (3) silver dewets on the core materials. Due to the difficulty of synthesizing Ge-Ag and SnO 2-Ag core-shell nanoparticle systems, alternate approaches were taken to analyze the thermal behavior of these systems. The thermal behavior of pure Ge nanoparticles was investigated, as first approach to determine the feasibility of using simple inorganic particles in printed electronics. Based on in situ transmission electron microscopy (TEM) annealing experiments mass transport temperature was at ≈ 200 °C. Additionally, it was found that different synthesis routes and sintering conditions lead to differences in the crystal structure of the Ge nanoparticles. As a proof of principle experiment to predict the sintering behavior of SnO2-Ag core-shell nanoparticles, the annealing behavior of a SnO2/Ag/SnO2 trilayer was examined. Ag layer pinch off and the formation of both Ag rods and islands was observed. This implies that a potential SnO2-Ag core-shell nanoparticle system would exhibit sintering at lower temperatures than clean SnO2 nanoparticle system. Finally, from the investigation of the sintering behavior of Ag-Cu core-shell nanoparticles, it was determined conclusively that the Ag shell leads to accelerated sintering of the copper, thereby validating the general principle. Based on the results, the use of core-shell nanoparticles is a viable route to fabricate thin films using inorganic nanoparticles in printed electronics through the use of lower sintering temperatures.
Stach, Purdue University.
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