Sreemanth M. Uppuluri

Nanopatterning using NSOM probes integrated with high transmission nanoscale bowtie aperture

Nanoscale ridge aperture antennas have been shown to have high transmission efficiency and confined nanoscale radiation in the near field region compared with regularly-shaped apertures. The radiation enhancement is attributed to the fundamental electric-magnetic field propagating in the TE(10) mode concentrated in the gap between the ridges. This paper reports experimental demonstration of field enhancement using such ridge antenna apertures in a bowtie shape for the manufacture of nanometer size structures using an NSOM (near field scanning optical microscopy) probe integrated with nanoscale bowtie aperture. Consistent lines with width of 59 nm and as small as 24 nm have be written on photoresist using such probes.

Parallel optical nanolithography using nanoscale bowtie aperture array

We report results of parallel optical nanolithography using nanoscale bowtie aperture array. These nanoscale bowtie aperture arrays are used to focus a laser beam into multiple nanoscale light spots for parallel nano-lithography. Our work employed a frequency-tripled diode-pumped solid state (DPSS) laser (lambda = 355 nm) and Shipley S1805 photoresist. An interference-based optical alignment system was employed to position the bowtie aperture arrays with the photoresist surface. Nanoscale direct-writing of sub-100nm features in photoresist in parallel is demonstrated.

Contact optical nanolithography using nanoscale C-shaped apertures

C-shaped ridge apertures are used in contact nanolithography to achieve nanometer scale resolution. Lithography results demonstrated that holes as small as 60 nm can be produced in the photoresist by illuminating the apertures with a 355 nm laser beam. Experiments are also performed using comparable square and rectangular apertures. Results show enhanced transmission and light concentration of C apertures compared to the apertures with regular shapes. Finite difference time domain simulations are used to design the apertures and explain the experimental results.

Three-dimensional mapping of optical near field of a nanoscale bowtie antenna

Ridge nanoscale aperture antennas have been shown to be a high transmission nanoscale light source. They provide a small, polarization-dependent near-field optical spot with much higher transmission efficiency than circularly-shaped apertures with similar field confinement. This provides significant motivations to understand the electromagnetic fields in the immediate proximity to the apertures. This paper describes an experimental three-dimensional optical near-field mapping of a bowtie nano-aperture. The measurements are performed using a home-built near-field scanning optical microscopy (NSOM) system. An aluminum coated Si(3)N(4) probe with a 150 nm hole at the tip is used to collect optical signals. Both contact and constant-height scan (CHS) modes are used to measure the optical intensity at different longitudinal distances. A force-displacement curve is used to determine the tip-sample separation distance allowing the optical intensities to be mapped at distances as small as 50 nm and up to micrometer level. The experimental results also demonstrate the polarization dependence of the transmission through the bowtie aperture. Numerical simulations are also performed to compute the apertures electromagnetic near-field distribution and are shown to agree with the experimental results.

Design, fabrication, and characterization of nanometer-scale ridged aperture optical antennae

We investigate light concentration and field enhancement in nanometer-scale ridged aperture antennae. Resent numerical simulations have shown that nanoscale ridged apertures can concentrate light into nanometer domain. Most importantly, these ridge apertures also provide an optical transmission enhancement several orders of magnitude higher compared to regularly shaped nanoscale apertures. We employ the finite-difference time-domain (FDTD) method to design these apertures and fabricate them in thin metal films. A home-built near field scanning optical microscope (NSOM) is used to map the near-field intensity distribution of the light transmitted through these apertures. It is shown that the ridged apertures can produce a concentrated light spot far beyond the diffraction limit, with transmission enhancement orders of magnitude higher than regularly shaped apertures. Nanolithography applications of these nanoscale ridged aperture antennae are demonstrated.

Enhancement of optical transmission through planar nanoapertures in a metal film

The optical transmission mechanism through a ridge nano-aperture in a metal film is discussed based on the waveguide theory and FDTD computations. The transmission enhancement through ridge apertures is associated with the TE10 waveguide propagation mode. In terms of near and far field radiator, the ridge aperture can be represented as a combination of an oscillating electric dipole and two magnetic dipoles. The effects of localized surface plasmon (LSP) excited on the edges of ridge nano-apertures made in silver are discussed. The transmission enhancement and field concentration functions of ridge apertures are confirmed by contact lithography experiments.

Concentrating light into nanometer domain using nanoscale ridge apertures and its application in laser-based nanomanufacturing

In this work, we investigate light concentration in nanoscale ridge apertures and its applications in nanomanufacturing. Optical transmission of ridge apertures in a metal film is optimized by numerical design using the finite-difference time-domain (FDTD) method. We show that ridge apertures provide an optical transmission enhancement of several orders of magnitude higher than regularly shaped nanoscale apertures, and also confine the transmitted light to nanoscale dimensions. We fabricated these ridge apertures in metal film coated on quartz substrates by focused ion beam (FIB) milling. These apertures are characterized by nearfield scanning optical microscopy (NSOM). The ridge apertures are also used as a nanoscale light source for nanolithography. Holes with sub-100 nm dimensions are produced in the photoresist with visible and UV laser illuminations. The performance of the ridge apertures is compared with that of regular nanoscale apertures to demonstrate their advantages and promising potentials for many near-field optical applications.

Replication of microstructures in polymers using laser-fabricated glass-ceramic stamps

Recently much research on fabrication of polymer micro structures has been carried out. One of the main advantages of using polymer in micro structure fabrication is the easiness of applying replication processes for mass production. A micro stamping process applying heat and pressure, also referred to as hot embossing lithography, can replicate micro-structures on polymer surfaces. By reforming thermoplastics, many micro features can be transferred directly to polymer surfaces. The micro stamping consists of two main steps: a stamp fabrication step and a replication step. Until now, metal or silicon stamps have been used. In this work, photo-etchable glass-ceramic micro stamps are used, which are micro-machined using an excimer laser processing technique. With the laser process, a glass-ceramic stamp can be fabricated quickly and precisely. In addition, a micro stamping device has been designed and developed for this process. Polyvinylchloride (PVC) is used as the replicating polymer because it has a low glass transition temperature (65 C) and good formability. Many micro structures such as micro channels have been produced. The advantages and the limits of using glass-ceramics stamps and stamping with the PVC material are discussed.

Nanolithography Using High Transmission Nanoscale Ridge Apertures

In this paper, we describe using high transmission nanoscale apertures of C and H shapes for nanolithography applications. We demonstrate that these ridge apertures provide a highly localized and intense light spot that can be used in lithography experiments.Copyright

RLSM: Remote Excimer Laser Micro-Machining Services Model

In this paper, we discuss an Internet based excimer-laser-micro-machining services model that allows multiple users to collaboratively design and fabricate laser micromachining features. This model implements the client-server architecture to support design and editing of features by multiple clients. The client side needs minimum software installation and is made intelligent by incorporating feature verification algorithms to ensure speed and efficiency of the design process. The server side supports solid modeling, solving of geometric constraints, data management and synchronization of clients. JSDT Interface links the server and the client sides. The remote laser micro-machining services model (RLSM) provides a collection of laser micro-machining features such as through-cuts, channels and pockets and different polymer materials such as PMMA, Kapton® , PET and Uplex® for the user to choose from. These design variables from the user are mapped to the corresponding technological parameters for laser micro-machining. The manufacturing feasibility is then assessed with respect to the system capabilities by implementing intelligent algorithms on the client side. In developing this services model we provide a distributed collaborative architecture that incorporates the manufacturing constraints of laser micro-machining in the design stage. The remote service center operation is further integrated with automated path generation for laser micromachining of the features. To our knowledge this is the first attempt towards developing a collaborative environment for design and manufacturing of MEMS components. The importance of such a model in the manufacturing arena is also discussed.Copyright