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Two-dimensional colloidal nanostructures - Synthesis and electrical transport

Final Report Summary - 2D–SYNETRA (Two-dimensional colloidal nanostructures - Synthesis and electrical transport)

Novel nanoscaled electrical devices rely on the design of tailored architectures. For this purpose nanoparticles are intensively investigated. So far, electrical characterizations concentrated mainly on thin films, but it is still a challenge to establish reliable, high quality assemblies of nanocomponents.

In a first approach, we developed truly two-dimensional continuous materials made of lead sulfide by the comparatively fast, inexpensive, and scalable colloidal synthesis method. We studied the synthesis mechanisms and the materials’ properties, in particular regarding their opto-electrical transport. We investigated the formation mechanism of such nanosheets, developed methodologies to tune their geometrical properties, and we studied the (photo-) electrical properties of individual nanosheets.

In a second approach, we investigated two-dimensional monolayer films composed of individual nanocrystals. We used the Langmuir-Blodgett method to deposit highly ordered monolayers of monodisperse nanoparticles. Such structures show interesting transport properties governed by Coulomb blockade effects known from individual nanoparticles. This leads to semiconductor-like behavior in metal nanoparticle films. The understanding of the electrical transport in such “multi-tunnel devices” is still very limited. Thus, we investigated this concept in detail. Beside improvement of quality and exchange of material we will tune the nanoparticles’ size and shape in order to gain a deeper understanding of the electrical properties of supercrystallographic assemblies. In such films, the Coulomb charging energy takes over the role of the semiconductor band gap. Thus, it is possible to influence the current through the films by a the voltage applied at a remote electrode (gate).

Nanosheets and monolayers of nanoparticles truly follow the principle of building devices by the bottom-up approach and allow electrical transport measurements in a 2D regime. Highly ordered nanomaterial systems possess easy and reliable to manipulate electronic properties what makes them interesting for future (inexpensive) electronic devices.

Based on our experiences and investigations and with the integrated physico-chemical approach with different expertise we will investigate the electrical transport mechanisms in modern nanoparticle superstructures.