Nanoimprint lithography is conventionally used to transfer a pattern from a mold to a deformable and curable
resist layer. Here we report a nanoimprinting technique to selectively transfer components of a pre-assembled
nanostructure to a new substrate, while retaining the advantages of nanoimprint lithography such as low cost and high
throughput. We use this technique to study metal particle roughness in Au "nanofinger" substrates, along with the
effects of annealing to reduce roughness, and the impact of annealing on the Surface Enhanced Raman Scattering
(SERS) signal. The nanofinger substrates consist of Au-coated polymer pillars arranged to collapse into a designed
assembly. Upon exposure to a volatile liquid and subsequent drying, microcapillary forces pull the pillars and their
metal caps together into the designed structure. Successful transfer was achieved using the concept of template stripping
via cold welding using a normal nanoimprinting process with no resist layer but under appropriate pressure to ensure
even and complete transfer of all the nanostructures. Particle roughness was not found to be a significant factor in SERS
from naonfinger substrates as annealing did not increase the observed Raman intensity.
At last meeting, we reported a new type of surface-enhanced Raman Spectroscopy (SERS) substrates based on metal
(Au or Ag) coated Si nanocones fabricated by a Bosch etching process. The substrate showed reliable SERS
performance with an analytical enhancement factor greater than 6 × 107 for trans-1,2-bis(4-pyridyl)-ethylene (BPE)
molecules. However, the process is limited to single crystalline silicon material, also silicon can absorb both incident
and scattered light, making it difficult to investigate the SERS enhancement mechanism. To further improve the
sensitivity of the SERS substrate, we have recently developed a process to duplicate the Si nanocones by a cross-linked
polymer using 3-D nanoimprint lithography (NIL). The SERS substrate made by NIL demonstrated better enhancement
factors for both 633 nm excitation and 785 nm excitation with analytical enhancement factors of over 1011
demonstrated. We will report the rational engineering of the nanocone based SERS substrate and the fundamental
understanding of the enhancement mechanism.
We created novel SERS substrates by metalizing (Ag or Au) Si nanograss fabricated by a Bosch process on single
crystalline silicon. We demonstrated that the fabricated SERS substrates are highly sensitive. The sensitivity of the
substrates depends on the target molecules, the excitation laser wavelengths and the metal coating on the silicon
nanograss. With the optimal excitation condition at 633 nm, an enhancement factor of 6 × 107 can be achieved for trans-
1,2-bis(4-pyridyl)-ethylene (BPE) molecules on the gold coated silicon nanograss substrate.
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