Fabricating Functional Structures Based On Patterned LB Monolayer

The fabrication of surface patterning with micro-structures has attracted much attention due to its important role on building nano-devices. So far, various approaches, including photolithography, nano-imprint lithography (NIL), electron-beam lithography (EBL), micro-contact printing (μCP) and many other methods have been proposed to fabricate the patterned surface. However, scientists are still searching for a low cost and efficient method for fabricating surface pattern over large area.Langmuir-Blodgett (LB) technique makes great contribution in the miniaturization of information technology due to its distinct features:the relative low cost, few defects, and large area. Usually, the films fabricated by LB technique are continuous and compact. Additionally, for some special molecules, it is also possible to obtain the patterned film by LB technique under certain optimal experimental conditions. The mold is not necessary for fabricating patterned film by LB technique, which greatly reduces the cost. Therefore, the technique for fabricating patterned surface without the mold shows great significance and promising in constructing nano-devices.In this thesis, we use the simple and inexpensive LB technique to fabricate patterned surface over large area, which can be used as the templates to induce the site-selective patterning organic functional materials or fabricate antireflective surface. The corresponding sections of the study are described as follows: We used LB technique to fabricate stripe and domain monolayer structure, which are composed of different phases of DPPC and stearic acid molecules, respectively. The periodicity of the domain and stripe structures can be controlled by adjusting transfer parameters, such as transfer speed and the concentration of sub-phase. Firstly, we use these two patterned structures as the templates to induce the site-selective patterning of luminescent materials in gas phase. The organic luminescent pattern with nano/micro structure was fabricated successfully, and the corresponding simulation work was accomplished by the molecular dynamics method. As well known, the diffusion length of dye molecules on the different phases of monolayer is different. Thus, if there is no selectivity on the patterned monolayer, dye molecules will form the particles in different size on two different phases of the monolayer, which will lead to form the luminescent pattern with different luminescent intensity. It is likely to provide a new method to pattern the organic luminescent materials, which have size tunable optical properties.Secondly, we used the stripe structures fabricated by LB technique as a template to direct the anisotropic growth of organic semiconductors in gas phase. The molecular orientation and the density of grain boundaries can be well controlled, which results in the thin film transistors with high anisotropic field effect mobility. It is a general method to control the density of grain boundaries. At the same time, it can increase the density of grain boundaries along the direction perpendicular to the stripes, which exhibits potential applications in increasing the sensitivity of chemical sensors based on OFETs.Thirdly, we used the LB domain structure as a mask to fabricate pyramidal structures on single crystal silicon surface by chemical etching. By means of the etched pyramidal structures, the surface reflectance of silicon is reduced to below 6% in the wavelength between 400 and 2400 nm. The pyramidal structures can be transferred onto the polymer surface by soft nano-imprint lithography process, which can greatly reduce the surface reflectance of PMMA. This method combines the merits of simplicity and scalability of self-assembly and low cost of chemical etching together. Fourthly, in order to further explore the applications of the patterned LB monolayer in other areas, we used the pre-patterned substrate to adjust the formation of DPPC stripes. The gradient stripes in micro area with the structure similar to butterfly micro-structure were obtained by transferring DPPC stripes on the Au-line-array patterned silicon substrate. The formation of these two structures was studied in details. These two structures show potential applications in studying biological recognition and fabricating biomimetic structures.In conclusion, we used LB technique to fabricate stripe and domain monolayer. Subsequently, the obtained monolayer was served as templates to induce the site-selective assembly of organic functional materials in gas phase and the anisotropic chemical etching in KOH solution, which is a simple and low cost method to fabricate functional structures over large area.