With the raise of nanotechnology researching, many special physical and chemical properties were found gradually in nanoscale. Among them, the one-dimension nanostructure owns high specific surface area and excellent electron emission properties. Moreover, the two-dimension arrayed nanostructure has the characteristics of photonic crystal and moth-eye effect. Currently, advanced lithographic methods such as electron beam (E-beam) or deep ultraviolet (DUV) lithography and X-ray lithography are adopted to define periodic nanoscale patterns. But these lithographic equipment are too expensive. Moreover, costly etching methods such as inductively coupled plasma reactive ion etching (ICP-RIE) or electron cyclotron resonance reactive ion etching (ECR-RIE) must be used to form arrayed silicon nanostructure with high aspect ratios. The nanoscale array patterns can be defined on the surface of the silicon wafer by the self-assembly of a polystyrene nanosphere. The photo-assisted electrochemical etching (PAECE) has the advantage of forming nanopore, and the aspect ratio of etched nanopores can be as high as 50:1 which is better than ICP-RIE. Therefore, PAECE is very suitable to fabricate nanostructure. This high-cost drawback makes most of academias and small/medium enterprises hard to invest in nanotechnology. This study combines the self-assembly nanosphere lithography (SANSL) process and photo-assisted electrochemical etching to fabricate a nanostructure array with a high aspect ratio on the surface of a silicon wafer.
Experimental results show that the nanosphere array with a nearly perfect arrangement can be obtained in the sample of 1.8 ∗1.8 cm2 by spin coating and vibration coating. Using reactive ion etching (RIE) can transfer the nanosphere array pattern to the silicon nitride layer, and form the etching window of PAECE. The concentration of the HF electrolyte used in PAECE was 2.5 wt%. When PAECE was performed with etching mask can produce deeper and periodic nanopores. The surfactant of SDSS added in the HF electrolyte of PAECE can reduce the contact angle of electrolyte and avoid the phenomenon of hole-reaming. When the voltage of 1 V is used to etch for 12.5 min, the etching depth of the nanopore array structure is about 5.69 £gm and its diameter is about 90 nm, such that the aspect ratio of the pore can reach about 63:1. If the etching voltage was increased, the width of pore will be increased and the depth of pore will be reduced gradually at the same time. When the etching voltage of 2 V is applied to etch for 5 min, the etching height of the nanopillar is about 2 £gm and its diameter is about 100 nm, such that the aspect ratio of the pillar can reach about 20:1. The nanopillar was arranged periodically according to the definition of nanosphere, therefore the arrayed nanopillar can be realized successfully.
Dropping the solution which has biological samples into the gap of nanopillar, it will affect the light which goes through the nanostructure and produce specific parameters of polarization. The results showed that when the DI water was dropped into the nanopillar structure, the degree of polarization (DOP) is 0.981, azimuth is 4.86¢X and ellipticity is 2.83¢X. When the solution which has alkaline lysis plasmid of 5 £gg/ml was dropped into the nanopillar structure, the DOP is 0.957, azimuth is 7.7¢X and ellipticity is 3.99¢X. The result shows that the change of polarization parameter has the relations with the concentration of biological samples in solution. Therefore, the measure system can be combined with nanopillar array to develop the photonic crystal biosensor. This study also applies the developed nanopore nanostructure array to fabricate sub-wavelength antireflection structure of solar cell. Experimental results show that the deeper in structure and then the better in antireflective effect. After performing 1 V PAECE for 5 min, the weighted mean reflectance can be reduced to 1.73% under the wavelength range of 280¡V890 nm. Further coating of a silicon nitride layer on the surface of a nanostructure array reduces the weighted mean reflectance even to 0.878 %. Finally, this study also uses various voltage of PAECE to produce nanostructure array with different surface area for the electrode fabrication of fuel cell. Experimental results show that the larger in surface area of sample and then the better in catalysis effect. Two-staged PAECE of 1.5 V and 1.75 V can yield nanopillar with surface area of 14.2 cm2 , which is about 50.2 times higher than a planar electrode. When the surface of such a nanopillar array is coated with platinum of 1000 Å, the reaction current of nanopillar array is 10.2 mA, which is 72.9 times higher than that obtained by only a planar electrode.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0827109-055027 |
| Date | 27 August 2009 |
| Creators | Huang, Mao-Jung |
| Contributors | Yuang-Cherng Chiou, Chung-Ming Lin, Chii-Rong Yang, Rong-Tsong Lee, Jen-Fin Lin, Yuan-Ching Lin, Yeau-Ren Jeng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0827109-055027 |
| Rights | not_available, Copyright information available at source archive |
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