Development of solution-processed methods for graphene synthesis and device fabrication.

摘要

Various solution-processed methods have been employed in this work. For the synthesis of graphene, a chemical exfoliation method has been used to generate large graphene flakes in the solution phase. In addition, chemical or electro polymerization has been used for synthesizing polyanthracene, which tends to form graphene nanoribbon through cyclodehydrogenation. For the device fabrication, graphene oxide (GO) thin films were deposited from solution phase on the vapor-silanzed aminosilane surface to make semiconducting active layer or conducting electrodes. Gold nanoparticles (AuNPs) were selectively self-assembled from solution phase to pattern nanowires.;A novel macromolecular surfactant dicholesteryldithienothiophene (ChDTT) was synthesized by Dr. Janusz Kowalik in Dr. Tolbert's group. By simple sonication of expandable graphite in solutions containing ChDTT, graphene sheets with sizes exceeding 50 micrometers were observed. The new surfactant is more efficient than poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV), and can be cleanly removed by thermal treatment. Using this surfactant, graphene flakes can be extracted directly from highly oriented pyrolytic graphite (HOPG) without additional chemical, mechanical, or thermal treatment, producing larger flakes of higher quality.;In the work of making reduced-GO (rGO) devices, we present a process to pattern and deposit both GO thin film or few-layer GO by a combination of conventional lithography, vapor silanization, GO self-assembly (or spin-coating), and lift-off. We explored an effective method to deposit 3-aminopropyltriethoxysilane (APTES) through a vapor phase and were able to generate a surface with a higher ratio of free amine. The transfer characteristics of GO film self-assembled on vapor-silanized APTES proved that we can precisely deposit continuous few-layer GO with 1∼3 layers. Besides, the under-layer amine corrected the intrinsic p-doping effect of rGO in air. On the other hand, we also showed that the vapor-silanized APTES layer can form strong electrostatic attraction and further increase film thickness to reach higher conductivity. Devices bearing rGO source-drain showed superior performance than gold electrodes.;A flow type vacuum reactor equipped with an evaporator and carrier gas flow system was used to perform the vapor-silanization of 3-Aminopropyltriethoxysilane (APTES). We altered the APTES vapor concentration, reaction time, and reaction temperature to seek the high quality APTES monolayer. It was found that vapor-silanization performed under 150°C can generate an APTES layer with high free amine content and that is uniform in morphology. A continuous GO thin film can be deposited on an APTES layer in 10 minutes by the self-assembly of the GO flakes. Similarly, highly dense AuNPs arrays can also be immobilized on the surface.;Thermochemical nanolithography, which in this case involves use of a heated nanoprobe to pattern a protected reactive self-assembled monolayer (SAM), is used to perform controlled patterning and assembly of gold nanoparticles (AuNPs). When the cantilever heater was operated at an appropriate condition, the SAM was ablated to produce positive tone AuNP features. We show AuNP features ranging from large densely covered squares to single particle wide lines and features. This method can be performed on a wide variety of substrates by simply choosing an appropriate surface reactive group for the SAM layer.