Vijay Shilpiekandula

Bio: Vijay Shilpiekandula is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Stamping & Interferometry. The author has an hindex of 7, co-authored 17 publications receiving 120 citations.

White-light scanning interferometer for absolute nano-scale gap thickness measurement

Abstract: A special configuration of white-light scanning interferometer is described for measuring the absolute air gap thickness between two planar plates brought into close proximity. The measured gap is not located in any interference arm of the interferometer, but acts as an amplitude-and-phase modulator of the light source. Compared with the common white-light interferometer our approach avoids the influence of the chromatic dispersion of the planar plates on the gap thickness quantification. It covers a large measurement range of from approximate contact to tens of microns with a high resolution of 0.1 nm. Detailed analytical models are presented and signal-processing algorithms based on convolution and correlation techniques are developed. Practical measurements are carried out and the experimental results match well with the analysis and simulation. Short-time and long-time repeatabilities are both tested to prove the high performance of our method.

Review of production of microfluidic devices: Material, manufacturing and metrology

Abstract: Microfluidic devices play a crucial role in biology, life sciences and many other fields. Three aspects have to be considered in production of microfluidic devices: (i) material properties before and after processing, (ii) tooling and processing methodologies, and (iii) measurements for process control. This paper presents a review of these three areas. The key properties of materials are reviewed from both the production and device performance point of views in this paper. The tooling and processing methodologies considered include both the direct tooling methods and the mold based processing methods. The response of material on the production parameters during hot embossing process are simulated for process control and product quality prediction purpose. Finally, the measurements for process control aspect discuss different measurement approaches, especially the defect inspection, critical dimensional measurements, bonding quality characterization and checking functionality. Simulation and experimental results are used throughout the paper to illustrate the effectiveness of such approaches.

White-light scanning interferometer for absolute nano-scale gap thickness measurement

Abstract: A special configuration of white-light scanning interferometer is described for measuring the absolute air gap thickness between two planar plates brought into close proximity. The measured gap is not located in any interference arm of the interferometer, but acts as an amplitude-and-phase modulator of the light source. Compared with the common white-light interferometer our approach avoids the influence of the chromatic dispersion of the planar plates on the gap thickness quantification. It covers a large measurement range of from approximate contact to tens of microns with a high resolution of 0.1 nm. Detailed analytical models are presented and signal-processing algorithms based on convolution and correlation techniques are developed. Practical measurements are carried out and the experimental results match well with the analysis and simulation. Short-time and long-time repeatabilities are both tested to prove the high performance of our method.

High resolution flexural stage for in-plane position and out-of-plane pitch/roll alignment

Abstract: An adjustment structure used in conjunction with an imprinting structure is provided. The adjustment structure includes a sample mount for mounting a sample. An actuator mechanism is coupled to the sample mount, the actuator mechanism producing actuated forces on a X-Y plane to produce movements on a sample mount. A plurality of bladed flexures are positioned on the sample mount. The bladed flexures controls the movements of the sample mount produced by the actuator mechanism so as to allow adjustments in angular alignment about the pitch-roll (ΘX-ΘY) rotation axes or the X-Y plane relative to the sample mount so the imprinting structure can perform its operations on the sample.

Functional Nanomaterials and Nanostructures Enhancing Electrochemical Biosensors and Lab-on-a-Chip Performances: Recent Progress, Applications, and Future Perspective.

Abstract: Electrochemical biosensors and associated lab-on-a-chip devices are the analytical system of choice when rapid and on-site results are needed in medical diagnostics and food safety, for environmental protection, process control, wastewater treatment, and life sciences discovery research among many others. A premier example is the glucose sensor used by diabetic patients. Current research focuses on developing sensors for specific analytes in these application fields and addresses challenges that need to be solved before viable commercial products can be designed. These challenges typically include the lowering of the limit of detection, the integration of sample preparation into the device and hence analysis directly within a sample matrix, finding strategies for long-term in vivo use, etc. Today, functional nanomaterials are synthesized, investigated, and applied in electrochemical biosensors and lab-on-a-chip devices to assist in this endeavor. This review answers many questions around the nanomaterials...

Design of an Inertially Counterbalanced $Z$ -Nanopositioner for High-Speed Atomic Force Microscopy

Abstract: In many conventional atomic force microscopes (AFMs), one of the key hurdles to high-speed scanning in constant-force contact mode is the low-feedback control bandwidth of the -axis loop. This paper presents the design of a fast -nanoposi-tioner to overcome this limitation. The -nanopositioner has its first resonant mode at 60 kHz and a travel range of 5 m. It consists of a piezoelectric stack actuator and a diaphragm flexure. The flexure serves as a linear spring to preload the actuator and to prevent it from getting damaged during high-speed operations. The -nanopositioner is mounted to an XY-nanopositioner. To avoid exciting the resonance of the XY -nanopositioner, an inertial counterbalance configuration was incorporated in the design of the -nanopositioner. With this configuration, the resonances of the XY-nanopositioner were not triggered. A closed-loop vertical control bandwidth of 6.5 kHz is achieved. High-speed constant-force contact-mode images were recorded at a resolution of 200 200 pixels at 10, 100, and 200 Hz line rates without noticeable image artifacts due to insufficient control bandwidth and vibrations. Images were also recorded at 312- and 400-Hz line rates. These images do not show significant artifacts. These line rates are much higher than the closed-loop bandwidth of a conventional AFM in which this nanopositioner was tested.

A Review of Thickness Measurements of Thick Transparent Layers Using Optical Interferometry

Abstract: Thickness is a typical parameter related to length, of which measurements are conducted in various industrial fields, such as the automotive, aviation, ship-building, semiconductor, and display industries. Among various measurement techniques, optical interferometry is very attractive in terms of reliability owing to the direct realization of the metre. Moreover, the nature of this non-contact method is such that it does not damage samples. In this review, optical interferometric methods for measuring thicknesses of thick transparent layers are introduced through a discussion of basic principles and applications. With consideration of optical layouts and analysis methods of interference signals, monochromatic laser interferometry, low-coherence interferometry, and spectral interferometry are introduced and discussed in chapters 2, 3 and 4, respectively. With regard to spectral interferometry, the two different key technologies of spectrally resolved interferometry and wavelength-scanning interferometry are covered in different subsections of chapter 4.

Near-field radiative heat transfer between two parallel SiO2 plates with and without microcavities

Abstract: Near-to-far-field radiative heat transfer between two macroscopic SiO2 plates—with and without microcavities—was observed using a highly precise and accurate optical gap-measurement method. The experiments, conducted near 300 K, measured heat transfer as a function of gap separation from 1.0 μm to 50 μm and also as a function of temperature differences between 4.1 and 19.5 K. The gap-dependent heat flux was in excellent agreement with theoretical predictions. Furthermore, the effects of microcavities on the plate surfaces were clearly observed and significant enhancement of near-field radiative heat transfer was confirmed between gold-coated microcavities with narrow vacuum separation.

Going far beyond the near-field diffraction limit via plasmonic cavity lens with high spatial frequency spectrum off-axis illumination

Abstract: For near-field imaging optics, minimum resolvable feature size is highly constrained by the near-field diffraction limit associated with the illumination light wavelength and the air distance between the imaging devices and objects. In this study, a plasmonic cavity lens composed of Ag-photoresist-Ag form incorporating high spatial frequency spectrum off-axis illumination (OAI) is proposed to realize deep subwavelength imaging far beyond the near-field diffraction limit. This approach benefits from the resonance effect of the plasmonic cavity lens and the wavevector shifting behavior via OAI, which remarkably enhances the object's subwavelength information and damps negative imaging contribution from the longitudinal electric field component in imaging region. Experimental images of well resolved 60-nm half-pitch patterns under 365-nm ultra-violet light are demonstrated at air distance of 80 nm between the mask patterns and plasmonic cavity lens, approximately four-fold longer than that in the conventional near-field lithography and superlens scheme. The ultimate air distance for the 60-nm half-pitch object could be theoretically extended to 120 nm. Moreover, two-dimensional L-shape patterns and deep subwavelength patterns are illustrated via simulations and experiments. This study promises the significant potential to make plasmonic lithography as a practical, cost-effective, simple and parallel nano-fabrication approach.