The Design, Fabrication And Characteristic Of Some Ultrafine And Nonplanar Nanostrucutes

Ultrafine nanostructure had attracted tremendous scientific and technological interests due to their fascinating properties arising from the strongly confined/correlated states and their strategic importance for the future nanodevice. The decreased size of the nanostructure calls for the technological improvement and innovation for the nanofabrication. Among various nanofabrication methods, electron beam lithography (EBL) is one of the most commonly used technologies due to its ultrahigh spatial resolution, convenient graphical user interface (GUI) and steady performance. However, several limitations of EBL, including the low manufactured efficiency and the complicated process, the instability as the pattern size down to10nanometer as well as lacking of capability for three dimensional (3D) fabrication, have hampered its applications to fabricate ultrafine nanostructure and complex nanodevice.In order to overcome the aforementioned challenges and difficulties in the nanofabrication by EBL, we focused our attentions on the combination of EBL with other nanofabrication technologies. For examples, Combining the magnetic enhanced reactive ion etching (MERIE), the Ion milling (IM) with EBL, we could fabricate the ultrafine nanostructure with the line width down to10nm; we also succeed in fabricating3D nanostructures with the help of the stencil lithography, and realized the controllable surface morphology of nano-plasmonics by transferred printing of PMMA film. In this context, there are four chapters in the dissertation and their contents are outlined as follows.In chapter one, we first briefly introduced the components and operating principles of EBL system and some related nanotechnologies. The advantages and disadvantages of EBL were also summarized. Several successful cases were reviewed, in which the ultrafine and complex nanostructures were fabricated by EBL combined with other techniques such as film deposition, nano-imprint lithography (NIL) and scanning probe lithography (SPL). Lastly, we proposed our creative projects for the research in this subfield.In chapter two, we mainly focused on improving the line-resolution of EBL in order to fabricate ultrafine nanostructures. We first changed the conventional positive EBL resist of polymethyl methacrylate (PMMA) into the negative one with the overexposed dose above3500μC/cm2. While the obtained negative PMMA nano-pattern was used as the Argon IM mask, the line width of the mask could be further reduced after tailored with oxygen plasma MERIE. With this process, we succeed in fabricating a variety of gold nanowires with the smallest width of5nm. The I-V curves of gold nanowires with different widths had been measured and analyzed. We also showed that this method could be successfully applied to fabricate perovskite manganite nanowires and graphene nanoribbons. In this regard, a series of Lao.5Bao.5Mn03(LBMO) nanowires with different width were produced and the behavior of insulate-metal phase transition in LBMO nanowires was found to be extremely different from that existed in the film materials. We also fabricated the field effect transistor (FET) with ultrafine graphene nanoribbons (GNRs) by our proposed method and found that the on-off ratio of FET increased with the decreasing of the GRN width. At the end of this chapter, we investigated the properties of the PMMA resist under different exposure doses and accelerated voltages. The variation of the thicknesses and stabilities of the resist to MERIE and IM etching were well characterized in order to find the appropriate condition for negative PMMA mask.In chapter three, we proposed and demonstrated some novel strategies to fabricate3D nanostructures. A soft stencil lithography technology was presented firstly, in which the patterned PMMA film was used as the deposition mask to construct the nanostructures on uneven substrates. This method started with the spin-coating of PMMA film on silicon substrate covered with silica film. Then the PMMA resist was exposed with EBL and hydrolyzed in KOH solution. After rinsed in water to clean its surface, the patterned PMMA film as a soft stencil was laid on the uneven substrate. Followed by deposited metal or molecular, the PMMA stencil was then removed away in the water, remaining the nanostructures on the uneven substrates. We also applied this method onto various uneven substrates with different features and investigated the fidelity of the produced pattern and the reusability of the stencil. Secondly, we demonstrated the wrinkle/ripple pattern formed on the graphene by heating PMMA-graphene-PDMS and then naturally cooled to the room temperature. We also showed that the wavy and wrinkle pattern of the graphene could be well controlled by the fixed edges and the thickness of the films. At the end of this chapter, combining the PMMA soft stencil lithography and predefined semi-cylinder nanostructure, we fabricated a bridge-like complex3D nanostructure and suggested its potential applications to construct the top gated GNRs FETs and the local modulated spin-device.In chapter four, we reported the fabrication of high quality plasmonic nanostructures with EBL. Firstly, we prepared the gold rod nanostructure based on the IM etching with negative PMMA mask and the template stripped (TS) method. We found that the nanorods produced by TS method had smooth surface and good cathodoluminescence (CL) signal. We then proposed a novel improved method to fabricate plasmonic nanostructures with the ultrasmooth surface. The experiment results indicated that this method could dramatically eliminate the cracks in the final nanostructures, which was frequently occurred in TS method. More importantly, we successfully fabricated plasmonic nanostructures on various capillaries by this method, indicating it was compatible to uneven substrate and might have a potentially important application for the plasma optics. At the end of this chapter, we demonstrated our modified micro-gap stencil lithography, which was capable to decrease the blurring and the damage for the nanostructures in the demolding process. Using this method, we systematically prepared a series of gold nanorods array with different periods and nanorods sizes and investigated their reflection spectrum.