Search

In this paper, both steady-state and transient thermal simulations were performed on functional fibers having an embedded electronic chip acting as a heat source. Simulations were conducted for a range of different fiber materials and arbitrary fiber cross-sectional shapes. We show that under steady-state heating conditions, the thermal response for any arbitrary fiber shape and fiber material system was convection dominated regardless of the effective thermal conductivity of the fiber, and that the corresponding temperature rise within the fiber can be predicted analytically allowing for the maximum temperature to be estimated for any known heat load and fiber geometry. In the case of transient heating, we show that for pulsed power operation of the embedded electronic device, the maximum temperature reached in the fiber is always greater than the maximum temperature of the equivalent steady-state average power. However, high peak powers can be safely achieved if the power-on pulse time and duty cycle are selected to limit the maximum temperature reached in the fiber. Based on the results from the transient simulations, a set of criteria was developed to determine whether the operating conditions would be: (1) allowable for the fiber system, thus requiring no transient simulations, (2) requiring a transient simulation to verify that the maximum temperature is acceptable, and (3) the operating conditions are too severe and device operation at these conditions are not practical. Graphical Abstract

We present a design and detailed fabrication of periodic and quasi-periodic plasmonic arrays including infrared scattering, patterning stripe, particle, and hole arrays with large periodicities for longwave IR scattering, and experimental reflectivity and backwards scattering from these metamaterials. We experimentally verify LWIR and other infrared diffraction from sparser arrays and arrays of holes in plasmonic metals. We simulate, using critical coupling analytical models and numerical algorithms, the reflectivity, scattering, etc. of these metamaterial arrays, and compare to the laser-based measurements. We also investigate a hole array in a plasmonic material (Ag).We find plasmonic resonances at both the air-Ag and Ag-substrate interfaces to be present, increasing transmission via the Extraordinary Optical Transmission effect, which may be tuned by an electromagnetic field to shift the resonance position, and in the future may enable novel tunable rectification.

Spectroscopic ellipsometry is demonstrated to be an effective technique for assessing the quality of plasmonic resonances within aluminum nanostructures deposited with multiple techniques. The resonance quality of nanoplasmonic aluminum arrays is shown to be strongly dependent on the method of aluminum deposition. Three-layer metal–dielectric–metal nanopillar arrays were fabricated in a complementary metal-oxide semiconductor facility, with the arrays of nanopillars separated from a continuous metal underlayer by a thin dielectric spacer, to provide optimum field enhancement. Nanostructures patterned in optimized aluminum, which had been deposited with a high-temperature sputtering process followed by chemical mechanical planarization, display different resonance and depolarization behavior than nanostructures deposited by the more conventional evaporation process. Full plasmonic band diagrams are mapped over a wide range of incidence angles and wavelengths using spectroscopic ellipsometry and compared be...

Each year, large ground motions from earthquakes cause infrastructure damage and loss of life worldwide. Here we present a novel concept that redirects and attenuates hazardous seismic waves using an engineered seismic-muffler acting as a cloaking device. The device employs vertically-oriented, sloping-opposing boreholes or trenches to form muffler walls and is designed to: 1) reflect and divert large amplitude surface waves as a barrier, while 2) dissipating body and converted waves traveling from depth upward into the muffler duct. Seismic wave propagation models suggest that a seismic-muffler can effectively reduce broadband ground motion directly above the muffler. 3D simulations are also compared for validation with experimental data obtained from bench-scale blocks containing machined borehole arrays and trenches. Computer models are then scaled to an earth-sized model. Results suggest a devastating seismic energy magnitude 7.0-$\mathrm {M}_{\mathrm {E}}$ earthquake can be reduced to less damaging magnitudes experienced in the muffler vicinity, 4.5- $\mathrm {M}_{\mathrm {E}}$ (surface wave) and 5.7- $\mathrm {M}_{\mathrm {E}}$ (upgoing coupling into the muffler). Our findings imply that seismic-muffler structures significantly reduce the impact of the peak ground velocity of dangerous surface waves, while, seismic transmission upward through the muffler base at depth has marginal effects.

Chemical warfare agents (CWAs) such as nerve and blister agents are expected to pose continuing and growing dangers for the Warfighter in the future. We investigate a novel chemical detection modality, based on a new platform for colorimetric detection of chemical threats incorporated in hollow fibers, which are miniature in two dimensions and extendable (“extrudable”) in the third dimension (along the fiber length). By exploring fibers, and films that can be scaled to a fiber geometry, we will enable a new fiber-based chemical threat detector that can serve in textiles worn by the Warfighter (e.g., uniform), as well as in non-worn textiles and an outlying fence or perimeter for early detection of a threat cloud near an expeditionary shelter, outpost, encampment, or base.

Nanofluidic channels are of great interest for DNA sequencing, chromatography, and drug delivery. However, metrology of embedded or sealed nanochannels and measurement of their fill-state have remained extremely challenging. Existing techniques have been restricted to optical microscopy, which suffers from insufficient resolution, or scanning electron microscopy, which cannot measure sealed or embedded channels without cleaving the sample. Here, we demonstrate a novel method for accurately extracting nanochannel cross-sectional dimensions and monitoring fluid filling, utilizing spectroscopic ellipsometric scatterometry, combined with rigorous electromagnetic simulations. Our technique is capable of measuring channel dimensions with better than 5-nm accuracy and assessing channel filling within seconds. The developed technique is, thus, well suited for both process monitoring of channel fabrication as well as for studying complex phenomena of fluid flow through nanochannel structures.

A lack of inversion symmetry coupled with the presence of time-reversal symmetry endows 2D transition metal dichalcogenides with individually addressable valleys in momentum space at the K and K' points in the first Brillouin zone. This valley addressability opens up the possibility of using the momentum state of electrons, holes, or excitons as a completely new paradigm in information processing. The opportunities and challenges associated with manipulation of the valley degree of freedom for practical quantum and classical information processing applications were analyzed during the 2017 Workshop on Valleytronic Materials, Architectures, and Devices; this Review presents the major findings of the workshop.

Electrically controlled micron-scale liquid lenses have been designed, fabricated and demonstrated, that provide both adjustable focusing and beam steering, with the goal of applying them to optogenetic in vivo mapping of brain activity with single cell resolution. The liquid lens is formed by the interface between two immiscible liquids which are contained in a conically tapered lens cavity etched into a fused silica substrate. Interdigitated electrodes have been patterned along the sidewall of the taper to control the liquid lens curvature and tilt. Microlenses with apertures ranging in size from 30 to 80 μm were fabricated and tunable focusing ranging from 0.25 to 3 mm and beam steering of ± 1 degree have been demonstrated.

Each year, on average a major magnitude-8 earthquake strikes somewhere in the world. In addition, 10,000 earthquake related deaths occur annually, where collapsing buildings claim by far most lives. Moreover, in recent events, industry activity of oil extraction and wastewater reinjection are suspected to cause earthquake swarms that threaten high-value oil pipeline networks, U.S. oil storage reserves, and civilian homes. Earthquake engineering of building structural designs and materials have evolved over many years to minimize the destructive effects of seismic surface waves. However, even under the best engineering practices, significant damage and numbers of fatalities can still occur.

Two scanning electron beam lithography (SEBL) patterning processes have been developed, one positive and one negative tone. The processes feature nanometer-scale resolution, chemical amplification for faster throughput, long film life under vacuum, and sufficient etch resistance to enable patterning of a variety of materials with a metal-free (CMOS/MEMS compatible) tool set. These resist processes were developed to address two limitations of conventional SEBL resist processes: (1) low areal throughput and (2) limited compatibility with the traditional microfabrication infrastructure.

Grayscale lithography is a widely known but underutilized microfabrication technique for creating three-dimensional (3-D) microstructures in photoresist. One of the hurdles for its widespread use is that developing the grayscale photolithography masks can be time-consuming and costly since it often requires an iterative process, especially for complex geometries. We discuss the use of PROLITH, a lithography simulation tool, to predict 3-D photoresist profiles from grayscale mask designs. Several examples of optical microsystems and microelectromechanical systems where PROLITH was used to validate the mask design prior to implementation in the microfabrication process are presented. In all examples, PROLITH was able to accurately and quantitatively predict resist profiles, which reduced both design time and the number of trial photomasks, effectively reducing the cost of component fabrication.

We present an electrically controlled, micron-scale liquid lens that provides adjustable focusing and beam steering, which is being developed for optogenetic in vivo mapping of brain activity with single cell resolution.

In recent years, optical super-resolution by microspheres and microfibers emerged as a new paradigm in nanoscale label-free and fluorescence imaging. However, the mechanisms of such imaging are still not completely understood and the resolution values are debated. In this work, the fundamental limits of super-resolution imaging by high-index barium-titanate microspheres and silica microfibers are studied using nanoplasmonic arrays made from Au and Al. A rigorous resolution analysis is developed based on the object’s convolution with the point-spread function that has width well below the conventional (~λ/2) diffraction limit, where λ is the illumination wavelength. A resolution of ~λ/6-λ/7 is demonstrated for imaging nanoplasmonic arrays by microspheres. Similar resolution was demonstrated for microfibers in the direction perpendicular to the fiber axis with hundreds of times larger field-of-view in comparison to microspheres. Using numerical solution of Maxwell’s equations, it is shown that extraordinary close point objects can be resolved in the far field, if they oscillate out of phase. Possible super-resolution using resonant excitation of whispering gallery modes is also studied.

We have developed a remote detection system consisting of commercially available retroreflective material coated with an analyte-specific colorimetric dye. Quantitative performance modeling predicts that, given the appropriate indicator dye, a system with a 10 cm optic and eye-safe illumination should be capable of detecting small droplets of contamination at kilometer ranges. We have synthesized new colorimetric dyes specific to organophosphate contamination and, with these dyes, demonstrated detection of 1 μl of liquid malathion at over 150 m with less than 20 mW of laser illumination.

Nanochannels are key structures in nanofluidics for a variety of different applications. However, typical nanochannel fabrication methods are ill-suited for full integration with other microfabricated components or devices. Here, nanochannels with an aspect ratio (length to cross-sectional dimension) of greater than 400 000 were demonstrated—where the width (35–40 nm) and height (140–150 nm) of the channels are sufficiently small to elongate macromolecules—at channel lengths on the order of millimeters. These channels were fabricated with a CMOS-compatible toolset, allowing for the batch fabrication of a multitude of channels and with the further potential of full integration with solid-state electronic and photonic devices on the same wafer. Finally, the versatility of the nanochannel fabrication platform was demonstrated by loading the channels with six different liquids, and it was verified that the fluid flow dynamics for each liquid can be well estimated with Washburn's equation.

Achieving enhanced coupling of solar radiation over the full range of the silicon absorption spectrum up to the bandgap is essential for increased efficiency of solar cells, especially thin film versions. While many designs for enhancing trapping of radiation have been explored, detailed measurements of light scattering inside silicon cells is still lacking. Here, we demonstrate experimentally and computationally that plasmonic-assisted localized and traveling modes can efficiently couple red and infrared radiation into ultrathin amorphous silicon (a-Si) layers. Utilizing patterned periodic arrays of aluminum nanostructures on thin a-Si, we perform specular and diffuse reflectivity and transmission measurements over a broad spectrum. Based on these results, we are able to separate parasitic absorption in aluminum plasmonic arrays from enhanced light absorption in the 200 nm thick amorphous silicon layer, as compared to a blank silicon layer. We discover a very efficient near-infrared a-Si absorption mechanism that occurs at the transition from the radiative to evanescent diffractive coupling, analogous to earlier surface-enhanced infrared studies. These results represent a direct demonstration of enhanced radiation coupling into silicon due to large angle scattering and show a path forward to improved ultrathin solar cell efficiency.

Unlike a semiconductor, where the absorption is limited by the band gap, a “microrectenna array” could theoretically very efficiently rectify any desired portion of the infrared frequency spectrum (25 - 400 THz). We investigated vertical metal-insulator-metal (MIM) diodes that rectify vertical high-frequency fields produced by a metamaterial planar stripe-teeth Al or Au array (above the diodes), similar to stripe arrays that have demonstrated near-perfect absorption in the infrared due to critical coupling [1]. Using our design rules that maximize asymmetry (and therefore the component of the electric field pointed into the substrate, analogous to Second Harmonic Generation), we designed, fabricated, and analyzed these metamaterial-based microrectenna arrays. NbOx and Al2O3 were produced by anodization and ALD, respectively. Smaller visible-light Pt-NbOx-Nb rectennas have produced output power when illuminated by visible (514 nm) light [2]. The resonances of these new Au/NbOx/Nb and Al/Al2O3/Al microrectenna arrays, with larger dimensions and more complex nanostructures than in Ref. 1, were characterized by microscopic FTIR microscopy and agreed well with FDTD models, once the experimental refractive index values were entered into the model. Current-voltage measurements were carried out, showed that the Al/Al2O3/Al diodes have very large barrier heights and breakdown voltages, and were compared to our model of the MIM diode. We calculate expected THz-rectification using classical [3] and quantum [4] rectification models, and compare to measurements of direct current output, under infrared illumination. [1] C. Wu, et. al., Phys. Rev. B 84 (2011) 075102. [2] R. M. Osgood III, et. al., Proc. SPIE 8096, 809610 (2011). [3] A. Sanchez, et. al., J. Appl. Phys. 49 (1978) 5270. [4] J. R. Tucker and M. J. Feldman, Rev. of Mod. Phys. 57, (1985)1055.

Microsphere-assisted ultramicroscopy is a powerful, yet simple, technique to visualize nanometric-scale objects with visible light. In this method, dielectric microspheres are placed in contact with the nanoscale objects, so that the spheres experience object's optical near-fields. The mechanism of imaging is still debated in the literature; however it is likely to involve surface plasmon resonances in metallic nanostructured objects, whispering gallery modes in dielectric microspheres and other factors. In this work we extended this technique from visible to deep-UV range. It is shown that imaging of nanoplasmonic structures at the wavelength of 248 nm can be achieved with ∼ 55 – 60 nm resolution, far beyond the diffraction limit. These results could shed light on the mechanism of super-resolution imaging by microspheres and further advance this technology for practical applications.

Projection optical lithography has had a remarkable history and, most probably, it will have an equally successful future for at least another decade. To date, it has met all the major challenges posed by the semiconductor industry roadmap. In order to do so, it has undergone important transformations, and has greatly expanded the frontiers of the science and engineering of optics. This paper will review the most recent developments, including transitioning to the short wavelengths of 193 nm and 157 nm, moving toward ultrahigh numerical apertures facilitated by liquid immersion, and incorporation of a range of resolution-enhancing techniques such as optical proximity correction and phase-shifting masks.

We present a 'flip chip' technique for testing electronic self-assembled monolayers (SAMs). Metal–SAM–metal junctions with contact areas of approximately (25 nm)2 and smaller have been created and tested. While the approach is similar in spirit to conductive atomic force microscope measurements, it requires only straightforward optical lithography to create the test chips and a simple gravitational-force flexure to close the junction with sub-angstrom scale precision. The junction is formed in a vertical manner, in which the SAM is grown on one or both metal electrodes, and the circuit is closed via the pressure-induced flexing of one chip into another. This method of creating a junction is rapid and facilitates multiple measurements per chip set. We have investigated the electrical transport characteristics of a variety of SAMs using this technique, including aliphatic alkanethiols and aromatic dithiols. Results are consistent with junction contact areas , and elucidate information regarding the role of pressure and defects on SAM transport.

Fluorine—its chemical and physical properties—plays a critical role in the development of advanced photolithography. It is widely expected that, when in a few years the critical dimensions in microelectronic devices will be less than ∼70 nm, the patterning technology of choice will be based on 157 nm light generated from molecular fluorine laser medium. Lithography at 157 nm also requires major advances in areas of fluorine science, from the growth of near-perfect calcium fluoride crystals for lenses to fluorine doping of fused silica for masks to the synthesis of fluoropolymers that would serve as pellicles, photoresists, and immersion liquids. With the expected resolution of these issues, the prospects are excellent that photolithography will continue as the main semiconductor patterning technology for at least another decade.

Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. 1-3 Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. 4 Monolayers of Ag nanoparticles with diameter d < 300 nm have shown strong plasmonic resonances when coated in thin polymer layers with thicknesses < d. 5 We study experimentally the diffuse vs. specular scattering from monolayer arrays of Ag nanoparticles (spheres and prisms with diameters in the range 50 – 300 nm) coated onto the front side of thin (100 nm < t < 500 nm) silicon films deposited on glass and flexible polymer substrates, the latter originating in a roll-to-roll manufacturing process. Ag nanoparticles are held in place and aggregation is prevented with a polymer overcoat. We observe interesting wavelength shifts between maxima in specular and diffuse scattering that depend on particle size and shape, indicating that the nanoparticles substantially modify the scattering into the thin silicon film.

Tunable, narrow-wavelength spectral filters with a ms response in the mid-wave/long-wave infrared (MW/LWIR) are an enabling technology for hyperspectral imaging systems. Few commercial off-the-shelf (COTS) components for this application exist, including filter wheels, movable gratings, and Fabry-Perot (FP) etalon-based devices. These devices can be bulky, fragile and often do not have the required response speed. Here, we present a fundamentally different approach for tunable reflective IR filters, based on coupling subwavelength plasmonic antenna arrays with liquid crystals (LCs). Our device operates in reflective mode and derives its narrow bandwidth from diffractive coupling of individual antenna elements. The wavelength tunability of the device arises from electrically-induced re-orientation of the LC material in intimate contact with antenna array. This re-orientation, in turn, induces a change in the local dielectric environment of the antenna array, leading to a wavelength shift. We will first present results of full-field optimization of micron-size antenna geometries to account for complex 3D LC anisotropy. We have fabricated these antenna arrays on IR-transparent CaF2 substrates utilizing electron beam lithography, and have demonstrated tunability using 5CB, a commercially available LC. However, the design can be extended to high-birefringence liquid crystals for an increased tuning range. Our initial results demonstrate

This paper outlines the critical issues facing the implementation of 157-nm lithography as a sub-100-nm technology. Special emphasis is placed on 157-nm photoresist options, including ultrathin resists and thicker resists with new chemistries. The status of other issues is also presented, such as mask materials, pellicles, optical materials, and coatings.

We present results of the study of 193 nm laser-induced densification of fused silica as a function of incident laser fluence and pulse count. We describe an internally self-consistent experiment involving the simultaneous irradiation of 12 samples of two different grades, at fluences varying by two orders of magnitude and pulse counts exceeding 1.5 × 109. We are able to establish the existence of a dose-rate dependence of the densification phenomenon and to characterize the empirical rate constants as a function of fluence for two different grades of fused silica.

A new, relatively inexpensive, easy-to-use instrument has been developed for measuring the thermal conductivity of thin films based on a differential photoacoustic method. Measurements made on silicon dioxide and silicon nitride are consistent with those reported previously for a different technique. In addition, the room temperature thermal conductivity of conventional polymer thin films and plasma deposited thin films has been determined relative to thermally grown silicon dioxide. Knowledge of the thermal conductivity of thin films, which is critical for many applications, can now be obtained for any thin film which can be deposited on a high thermal conductivity substrate.

Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. Such Ag stripes are combined with 200 nm long and 60 nm wide “teeth”, which act as nanoantennas, and form vertical rectifying metal-insulator-metal (MIM) nanostructures on metallic substrates coated with thin oxides, such as Nb/NbOx films. We characterize experimentally and theoretically the visible and near-infrared spectra of these “stripeteeth” arrays, which act as microantenna arrays for energy harvesting and detection, on silicon substrates. Modeling the stripe-teeth arrays predicts a substantial net a.c. voltage across the MIM diode, even when the stripe-teeth microrectenna arrays are illuminated at normal incidence.

Suspensions of Au and Ag plasmonic nanoparticles, irradiated with 532-nm, ns-long pulses, exhibit nonlinear absorption, nonlinear scattering and saturable absorption. Laser-induced damage is suppressed by >100x when the solvent is toluene instead of water.

Diffractive waveplates and equivalent metasurfaces provide a promising path for applications in thin film beam steering, tunable lenses, and polarization filters. However, fixed metasurfaces alone are unable to be tuned electronically. By combining metasurfaces with tunable liquid crystals, we experimentally demonstrate a single layer device capable of electrically switching a diffractive waveplate design at a measured peak diffraction efficiency of 35%, and a minimum switching voltage of 10V. Furthermore, the nano-scale metasurface aligned liquid crystals are largely independent of variations in wavelength and temperature. We also present a computational analysis of the efficiency limits of liquid crystal based diffractive waveplates, and compare this analysis to experimental measurements.

The trend in microelectronics toward printing features 0.25 /spl mu/m and below has motivated the development of lithography at the 193-nm wavelength of argon fluoride excimer lasers. This technology is in its early stages, but a picture is emerging of its strengths and limitations. The change in wavelength from 248 to 193 nm will require parallel progress in projection systems, optical materials, and photo-resist chemistries and processes. This paper reviews the current status of these various topics as they have been engineered under a multiyear program at MIT Lincoln Laboratory. >

A review of recent efforts to develop photoresist materials and processes for 193 nm (ArF excimer laser) photolithography is reported. Three categories of resist processes are discussed: (1) conventional single layer, (2) bilayer and (3) surface-imaged resist processes. To date, materials have been developed for each process which exhibit resolution to less than 0.25 μm with sensitivities of less than 50 mJ/cm2.

The photoresist processes used for lithography at wavelengths from the deep UY to the soft x ray will need to accommodate the strong resist film absorbance inherent in this wavelength range. Already silylation processes have been demonstrated as manufacturable near-surface-imaged resists in the deep UV. In addition other chemistries are being developed that take advantage of near-surface or at-the-surface imaging. Together these new approaches to imaging will provide not only greater wavelength flexibility but have potential for improved exposure and focus tolerances as well. These attributes will become important as device dimensions are reduced from 0.35 down to 0.1 µm.

Noncontact detection of the homemade explosive constituents urea nitrate, nitromethane and ammonium nitrate is achieved using photodissociation followed by laser-induced fluorescence (PD-LIF). Our technique utilizes a single ultraviolet laser pulse (approximately 7 ns) to vaporize and photodissociate the condensed-phase materials, and then to detect the resulting vibrationally-excited NO fragments via laser-induced fluorescence. PD-LIF excitation and emission spectra indicate the creation of NO in vibrationally-excited states with significant rotational energy, useful for low-background detection of the parent compound. The results for homemade explosives are compared to one another and 2,6-dinitrotoluene, a component present in many military explosives.

As next generation immersion lithography, combined with double patterning, continues to shrink feature sizes, the industry is contemplating a move to non-chemically amplified resists to reduce line edge roughness. Since these resists inherently have lower sensitivities, the transition would require an increase in laser exposure doses, and thus, an increase in incident laser fluence to keep the high system throughput. Over the past several months, we have undertaken a study at MIT Lincoln Laboratory to characterize performance of bulk materials (SiO 2 and CaF 2 ) and thin film coatings from major lithographic material suppliers under continuous 193-nm laser irradiation at elevated fluences. The exposures are performed in a nitrogen-purged chamber where samples are irradiated at 4000 Hz at fluences between 30 and 50 mJ/cm 2 /pulse. For both coatings and bulk materials, in-situ laser transmission combined with in-situ laser-induced fluorescence is used to characterize material performance. Potential color center formation is monitored by ex-situ spectrophotometry. For bulk materials, we additionally measure spatial birefringence maps before and after irradiation. For thin film coatings, spectroscopic ellipsometry is used to obtain spatial maps of the irradiated surfaces to elucidate the structural changes in the coating. Results obtained in this study can be used to identify potential areas of concern in the lens material performance if the incident fluence is raised for the introduction of non-chemically amplified resists. The results can also help to improve illuminator performance where such high fluences already occur.

Two new techniques for forming dense plasmonic nanoarrays utilizing 157-nm interference lithography on a 90-nm pitch grid include 1) convective assembly of Au nanoparticles into pre-patterned PMMA templates and 2) direct patterning of Ag nanocones.

We have implemented a space-invariant interference lithography tool for 157 nm F2 lasers, capable of creating dense line and space patterns with a spatial period of 91 nm. No gratings or curved optics are required, allowing a simple and inexpensive tool for resist and process development at 157 nm. Initial patterning of several commercial and experimental resists has resulted in high contrast features with little line edge roughness and good cross-sectional profiles, indicating that the fundamental performance of acid-catalyzed resists patterned at 157 nm may meet lithography requirements for sub-50 nm features.

A variable -transmittance apodizing filter has been designed and demonstrated at 157 nm. The Gaussian transmission function is created by flowing oxygen gas, which is absorptive below 185 nm, between the two spherical surfaces of meniscus lenses. By varying the oxygen partial pressure, the degree of apodization can be controlled.

In studies of surface-enhanced Raman scattering (SERS), individual metal nanoparticle and particle assemblies introduce enhancement of electromagnetic fields. However, the contributions to enhancement due to the substrate supporting the particles are yet to be studied analytically. In this communication, we present an analytical method to investigate the effect of a substrate with realistic layers in SERS. The proposed method quantifies the effect of a substrate on the electric field on the nanoparticles surface in SERS experiments. By applying the proposed method, optimal constructions of a substrate can be obtained to maximize the surface electric field while a poorly constructed one can be avoided. The maximization can lead to a high Raman enhancement factor. The method is verified using numerical simulations. Published version

A silylation process based on laser induced crosslinking has been developed using novolac, novolac/ diazoquinone blends and chemically amplified resists. Dimethylsilyldimethylamine was used as a silylating reagent. The diffusion characteristics show a change at the polymer glass transition temperature. The profile of diffused silicon is anisotropic, and diffusion in unexposed regions of the film is affected by the extent of exposure in adjacent regions of the film.

MIT Lincoln Laboratory has developed a concept that could enable remote (10s of meters) detection of trace explosives' residues via a field-portable laser system. The technique relies upon laser-induced photodissociation of nitro-bearing explosives into vibrationally excited nitric oxide (NO) fragments. Subsequent optical probing of the first vibrationally excited state at 236 nm yields narrowband fluorescence at the shorter wavelength of 226 nm. With proper optical filtering, these photons provide a highly sensitive explosives signature that is not susceptible to interference from traditional optical clutter sources (e.g., red-shifted fluorescence). Quantitative measurements of trace residues of TNT have been performed demonstrating this technique using a breadboard system, which relies upon a pulsed optical parametric oscillator (OPO) based laser. Based on these results, performance projections for a fieldable system are made.