Controllable Modification Of Carbon-based Films For Flexible Functional Devices

With the rapid development of flexible electronics technology, the flexible electronic devices have shown great potential in the application of information, energy, medical, defense and other related fields. However, since the conventional processing techniques such as three-beam (electron, ion and laser) and LIGA (lithography, electroforming and injection) suffer from the bottlenecks of low-yielding and high consumption, and polymer substrates could not match to the fabrication techniques such as ntegrated circuit manufacturing process due to their poor thermal stability. Thus, combinding with the existing micro-/nano-fabrication theores, it is crucial important to develop a simple and efficient, low cost, and high-resolotion fabrication technique for flexible devices. At the same time, in order to achieve widespread application of flexible electronic devices, it is highly desired to achieve a high-performance flexible energy supply componets. The aim of this dissertation is therefore to develop suitable modification strateges for carbon-based films in the application of flexible devices, relying on the atmospheric pressure plasma jet and the electrochemical processing techniques. The patterned nitrogen functionalization of graphene, the controllable welding of polyaniline nanofiber, and the controllable oxidized modification of carbon fiber cloth were systematically investigated by means of Raman spectroscopy (Raman), infrared spectroscopy (FT-IR), X-ray spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).Area selective surface modification of films through low temperature atmospheric pressure plasma jet technique shows obvious advantages, such as nearly room temperature processing conditions, processing without masking and so on, and it is quite suitable for films assembled by temperature sensitive materials. Therefore, we developed a home-made system based on atmospheric pressure cold plasma jet for the controllable modification of graphene and polyaniline nanofiber films.Pattened nitrogen doping of single layer graphene was achieved by using a micro-plasma jet under ambient condition without masking. The results showed that the nitrogen atoms are successfully incorporated into the graphene lattice and they are mainly in the form of pyridine-like nitrogen. This type of nitrogen bonding configuration has two carbon neighbors in a hexagonal ring, which can occur either at the edge of graphene lattice or inside the carbon network where a carbon vacancy is created next to the nitrogen. The two-dimensional spatial distribution of nitrogen doping can be precisely controlled in the range of mm down to 10?m by selecting proper working gas guiding tube. The mechanism of nitrogen incorporating into the graphene lattice was originated form the reaction between N2+ ions and the surface carbon atoms, which can release a huge energy to break the C-C bonds and lead to the formation of new nitrogen group in graphene lattice. Since the chemistry of the micro-plasma jet can be controlled by the choice of the gas mixture, this direct writing process with micro-plasma jet can be a versatile approach for patterned functionalization of graphene with high spatial resolution. This could have promising applications in graphene-based electronics.goining conducting polymer nanofibers into interconnected porous network can result in good mechanical and electrical contacts between nanofibers that can be beneficial for the high performance of Cm based devices. The welding of polyaniline nanofiber loose ends was achieved via cold helium plasma jet ingniated by high voltage pulse power supply. The results showed that the different discharge parameters can truly induce different thermal effects for the polyaniline nanofibers. a uring the experiment, the peak voltage and pulse width were fixed at 6.5 kV and 800 ns, respectively. t hen the pulse frequency reaches at 2.5 ke z, no obvious thermal effect occurs at the surface of the polyaniline nanofibers film except for doping effect. t hen the pulse frequency reaches at 5 ke z, the tip-welding occurs among the polyaniline nanofibers, due to the cross-linking of polyamine chains at the C=N sites. Besides, the doping of film is also happened. t hen the pulse frequency reaches at 7.5 ke z, the polyaniline nanofibers melt to form an integrated film and a clear amorphous development is happened for the materials. Since the cold helium micro-plasma jet launches highly charged ion bullets at mAni nanofiber target with high precision, it is believed that the heating originates from the highly charged ion bullet induces field emission selectively at the sharp nanofiber loose ends. The high the generating frequency, the larger increase in temperature; thus, the polyaniline nanofiber can achieve tip-welding at the loose ends and meting to form integrated films. The nitric acid molecules that generated by the reactions between the cold plasma jet and the surrounding nitrogen and oxygen induces the doping effect. Without shielding gas and There is no mixture gas in the helium and didn't apply shiedling gas around the cold plasma jet, resulting a limited area selective resolution. As this technique can join polyamine nanofiber tips without altering the morphology of the film and protonation property, it can lead to significantly enhanced electrical and mechanical properties. This technique is able to selectively weld and dope regions of the nanofiber film with promising novel device applications.By introducing a combination stratege based on electrochemical oxidation and reduction technique, a carbon cloth electrode with excellent storage capacity and rate performance was prepared. The results showed that micro-cracks, exfoliated carbon fiber shells, and oxygen-containing functional groups (OFGs) were successfully introduced onto the surface of carbon filament after electrochemical activation. The specific surface area increased slightly, while there is a sharp increase in the OFGs, which results in the significant enhancement of the specific capacitance by introducing quantity of extra pseudocapacitance. The electrochemical reduction step is quite important for such efficient activation stratege, because it improve the conductivity of the carbon cloth by the removal of most electrochemical unstable surface OFGs, especially most of the carbonyl group (C=O) that can not contribute revesible pseudocapacitance was disappeared. These all results in a carbon cloth electrode exihibiting an excellent specific capacitance, rate capability and cycle performance. There is a significant enhancement of over two orders of magnitude in capacitance compared to that of the bare CC electrode, reaching up to a maximum areal capacitance of 505.5 mF cm-2 at the current density of 6 mA cm-2 in aqueous H2SO4 electrolyte. Although the activated CC electrode contained a high-level surface oxygen functional groups (?15 at.%), it still exhibited a remarkable charging-discharging rate capability, retaining ?88% of the capacitance when the charging rate increased from 6 to 48 mA cm-2. Moreover, the activated CC electrode exhibited excellent cycling stability with ?97% capacitance remaining after 10000 cycles at a current density of 24 mA cm-2. Symmetrical supercapacitor based on the activated CC exhibited an ideal capacitive behavior and fast charge-discharge properties. The maximum areal capacitance can reach up to 197 mF cm-2 at the current density of 3 mA cm-2 in aqueous H2SO4 electrolyte. Such simple, environment-friendly, and cost-effective strategy to activate CC shows great potential in the fabrication of high-performance flexible supercapacitor, which is suitable for the fexible devices.