We report a low-cost and high-throughput process for the realization of two-dimensional arrays of deep sub-wavelength features using silica and polystyrene spheres. The pattern size in this method is a weak function of sphere size, and hence excellent size uniformity is achievable. Also, the period and diameter of the holes and pillars formed with this technique can be controlled precisely and independently. Moreover, the patterns can be formed in conventional negative and positive photoresists, and hence this approach is compatible with a wide range of existing processing methods. Although we achieved hole sizes of ∼250 nm with a broadband UV source centered at 400 nm, our simulation results show that patterns as small as 180 nm should be achievable at a wavelength of 365 nm.

We present spatial mapping of optical force generated near the hot spot of a metal-dielectric-metal bowtie nanoantenna at a wavelength of 1550 nm. Maxwell's stress tensor method has been used to simulate the optical force and it agrees well with the experimental data. This method could potentially produce field intensity and optical force mapping simultaneously with a high spatial resolution. Detailed mapping of the optical force is crucial for understanding and designing plasmonic-based optical trapping for emerging applications such as chip-scale biosensing and optomechanical switching.

Large area periodic nanostructures exhibit unique optical and electronic properties and have found many applications, such as photonic band-gap materials, high dense data storage, and photonic devices. We have developed a maskless photolithography method—Nanosphere Photolithography (NSP)—to produce a large area of uniform nanopatterns in the photoresist utilizing the silica micro-spheres to focus UV light. Here, we will extend the idea to fabricate metallic nanostructures using the NSP method. We produced large areas of periodic uniform nanohole array perforated in different metallic films, such as gold and aluminum. The diameters of these nanoholes are much smaller than the wavelength of UV light used and they are very uniformly distributed. The method introduced here inherently has both the advantages of photolithography and self-assembled methods. Besides, it also generates very uniform repetitive nanopatterns because the focused beam waist is almost unchanged with different sphere sizes.

Fabrication of a large area of periodic structures with deep sub-wavelength features is required in many applications such as solar cells, photonic crystals, and artificial kidneys. We present a low-cost and high-throughput process for realization of 2D arrays of deep sub-wavelength features using a self-assembled monolayer of hexagonally close packed (HCP) silica and polystyrene microspheres. This method utilizes the microspheres as super-lenses to fabricate nanohole and pillar arrays over large areas on conventional positive and negative photoresist, and with a high aspect ratio. The period and diameter of the holes and pillars formed with this technique can be controlled precisely and independently. We demonstrate that the method can produce HCP arrays of hole of sub-250 nm size using a conventional photolithography system with a broadband UV source centered at 400 nm. We also present our 3D FDTD modeling, which shows a good agreement with the experimental results.

We report on a photon detector aimed at low light detection, which is based on the combination of small sensing volumes and large absorbing regions. Fabricated devices show stable gain values in the range of 1000-10 000 at bias voltages of ϳ1 V at 1.55 m at room temperature. Submicron devices show dark current less than 90 nA and unity gain dark current density values less than 900 nA/ cm 2. The noise equivalent power ͑NEP͒ is measured to be 4 fW/ Hz 0.5 at room temperature without any gating, which is similar to NEP of current InGaAs/ InP avalanche photodetectors in gated operation.