Issuu on Google+

Fabrication of Metallic Nanoparticle Array Using Nanosphere Lithography Michael Hoha, S K Sahoob, P S V R V Tejasvib, A Preetib, R Vaibhavb and Dr. V H S Moorthy* a Kaisersslautern University of Technology, Germany. bDepartment of Electronics and Communication, Manipal Institute of Technology, Manipal University, Manipal- 576104, India.

Abstract: Nanosphere lithography1 (NSL) – liquid surface self assembly technique- is an inexpensive, table top and scalable technique for the fabrication of periodic nanostructures of varying size, shape and periodicity. The self assembled mono-dispersed 2D colloidal crystals (polystyrene nanospheres of 450 nm size) on pre-treated Si (100) substrate is used as a mask to create periodic nanostructures of Ag. The polystyrene nanospheres are mono-dispersed on air-DI water interface by using custom-built pipette. A surfactant (Triton X-100/Sodium dodecyl sulphate) is added to the water surface to reduce the surface tension and condense the particles into a closely packed monolayer. Then the hydrophilic Si (100) substrates are introduced beneath the water surface and the water is carefully drained such that the polystyrene film is descended onto the substrate and subsequently left for drying in a clean environment. The resultant self-assembled polystyrene templates are characterized for different defect structures- by optical microscopy and scanning electron microscopy (SEM –JEOL8610) and modifications in the deposition technique are effected to obtain larger domains of hexagonally close packed (hcp) structures of polystyrene nanospheres. On this polystyrene hcp template, an ultrathin film (320 Å) of Ag is deposited by vacuum evaporation technique. The periodic metallic (Ag) nanostructures are obtained by subsequent removal of the under layer hcp structure of polystyrene nanospheres. The periodic nanostructures are characterized by scanning electron microscopy. The periodic structure is characterized by triangular shaped nanoparticles with average size of 120nm and periodicity 450nm.

Different NSL methods     

Rod Coating Spin coating Drop coating Dip coating Lift up method

Characteristic/ Surfactant used

Sodium Dodecyl Sulphate 20% by weight

Sodium Dodecyl Sulphate 20% by weight

Triton X100 1:100 diluted

Triton X100 1:100 diluted

Triton X100 1:100 diluted (Sample 1)

Density of PS nanospheres on airwater interface

~70%

~70%

~70%

~70%

~100%

Sample orientation

Inclined 0 (2.97 )

NonInclined

Inclined 0 (7.758 )

NonInclined

NonInclined

Domain size

8-10 µm

6-7 µm

6-8 µm

8-9 µm

3-4 µm

Packing Density

5.252 5.45/µm

4.42 4.76/µm

5.122 5.31/µm

4.762 5.76/µm

4.5/µm

Line defects

Less

Moderate

Moderate

Less

Moderate

Double layers

Nil

Nil

Very less

Very less

Nil

Triplets/particulates

Very Less

Very Less

Less

Less

Less

2

One of the significant challenges in our experiment was determining the optimum condition for the fabrication of large area, defect-free, periodic nanospheres monolayer template, with repeatability. Parameters like concentration of different surfactants in different solutions, concentration of nanospheres spread, evaporation time, duration of vesseltilting and angle of elevation of the substrate were monitored.

Importance of NSL-a Bottom-Up approach     

Results

Cost- effective Flexible Simple High-throughput Attractive in the present research scenario

Applications of Nanoparticles   

Photonic Crystals Catalysis Plasmonic biosensors

Principle of NSL: COLLOIDAL  

Fig 2: SEM image of a large uniform hcp layer (nanosphere mask- before etching) and Silver nanoparticles post-etching

SELF-ASSEMBLY

Spontaneous organization of colloidal particles into a relatively stable structure through non-covalent interactions Self-assembly at the liquid-gas interface

References: Fig 1: Custom-built micropipette used in Nanosphere Lithography and the procedure of NSL (schematic and experiment)

[1] J. C. Hulteen and R. P. Van Duyne: Nanosphere lithography, J. Vac. Sci. Technol. A 13(3), May/Jun 1995


P12-38