The Study Of Nano-Patterning Methods And Their Applications

Materials or structures with micro/nano scale often have some unique properties rather than with macro scale. Therefore, the fabrication of micro/nano-scaled materials and structures so as to study their performances has become one of the most popular fields. Various fabrication methods, such as photolithography, e-beam lithography, focused ion beam, scanning probe lithography, nanoimprint lithography and self-assembly methods, arose at the historic moment and developed continuously. However, it is of a great challenge to fabricate micro/nano patterns with wafer-scale except photolithography and nanoimprint lithography. For photolithography, the expensive equipment and complicated exposure system increased the cost and difficulty of fabrication.Basing on the demands of fabricating nanopatterns with wafer-scale and low-cost, we study nanopatterning methods from top-down and bottom-up ways respectively. We introduce the hybrid nanoimprint-soft lithography (HNSL) to fabricate 2-inch wafer-scale nano-patterned sapphire substrate (NPSS) and study the performance enhancement of blue LED grown on such NPSS. Also, we propose a new strategy of maskless lithographic approach to fabricate micro/nano-porous structures by phase separation of polystyrene (PS)/polyethylene glycol (PEG) immiscible polymer blend. It is an extremely facile, low-cost, easily accessible nanofabrication method to obtain the porous structures with wafer-scale.The fabrication of NPSS by HNSL. NPSS has been widely used for fabricating GaN-based light-emitting diodes (LEDs) due to the great enhancement of both the internal quantum efficiency and the light extraction efficiency. At the present time, various state-of-the-art techniques have been employed to fabricate NPSS. Among them, NIL is considered as one of the most potential alternatives. Since sapphire single crystal is mechanically hard and brittle, the traditional imprint process with rigid mold under high pressure can lead to cracking and breakage due to the large warpage of the sapphire substrate. In this paper, we proposed to apply HNSL for fabrication of NPSS. HNSL combined the advantages of both a rigid NIL mold to achieve a high-resolution and a soft lithography stamp to enable conformal contact. It has shown the ability to fabricate nanopatterns with sub-15 nm and on curved surface. Compared to blue LED on flat sapphire substrate, the LED on NPSS shows an enhancement of 43.8% and 40.9% in light output power and external quantum efficiency, respectively. Besides the low cost, high throughput and high resolution of NIL, this method also has the ability of patterning on curved and nonplanar surface so as to be used industrially.The study of phase separation of PS/PEG polymer blend through spin-casting. PS and PEG blend is commonly used phase separation system due to the high miscibility between them. So far there are few reports on fabricating nanopatterns by using the phase separation of PS and PEG. In this paper, we investigate the phase separation of PS and PEG by spin coating and the influence factors such as PS/PEG weight ratios, concentrations and spin speeds which probably affect the morphology of phase separation.PBPSL-the nanopatterning method based on polymer blend phase separation. Basing on the study of phase separation of PS and PEG, we propose a maskless nanopatterning method compatible with traditional nanofabrication process such as etching, metal deposition and lift-off. Nanopatterns with wafer-scale can be produced by PBPSL with low-cost and low requirement for equipments. More importantly, the feature size of nanopatterns fabricated by PBPSL can be tuned easily and conveniently by mofulating the process parameters. Besides, we employ the PMMA/SiO2/PS triple-layer structure of nanopatterns to enlarge the aspect ratio of PS nanopatterns, which benefits the lift-off process with large area.The application of PBPSL in fabricating surface enhanced Raman scattering (SERS) substrates. SERS has been widely used for qualitative and quantitative molecule detection. Hence, it is important for fabricating SERS substrates with high performance, low-cost and wafer-scale. We introduce the PBPSL to fabricate Ag SERS substrate with particle spacing of 36 nm, height of 65 nm and enhancement factor of 1.64×108. Still, the variable coefficient of SERS results is under 5% so that the SERS substrabe can be used practically.The application of PBPSL in fabricating anti-reflection silicon substrate. Silicon substrates with low reflectance are widely used in photoelectric devices such as solar cell. A 4-inch black silicon substrate with<3% reflectance from 450 nm to 950 nm is fabricated by PBPSL. We simulate the reflectance and absorption spectrum of such black silicon structure with COMSOL to understand the mechanism of anti-reflection. Besides, we find that the low reflectance of such black silicon is independent on the angle of incident light by changing the incident angles.The application of PBPSL in fabricating wafer-scale disordered nanopatterned sapphire substrate (DNPSS). A DNPSS is fabricated with 2-inch wafer scale by PBPSL. Standard growth of GaN epitaxial layer is carried out in order to understand the performance of DNPSS. The enhancement in photoluminescence (PL) of LEDs grown on DNPSS is close to that of LEDs grown on NPSS fabricated by HNSL. Although the uniformity in PL of LED grown on DNPSS is less than that of LED grown on NPSS, it is still within the range of process requirements.