This PDF file contains the front matter associated with SPIE Proceedings Volume 9759, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The noble metal nanostructure has attracted significant attention because of their potential applications as sensitive sensor platform blocks for biological and chemical sensing. The unique optical property of the metal nanostructure is originated from localized surface plasmon resonance (LSPR). The fabrication of metal nanostructure is a key issue for sensor applications of LSPR. In this paper, fabrication technique of two-dimensional Ag nanodot array on an indium tin oxide (ITO) glass substrate via the nanoporous alumina mask and the utilization as a platform for LSPR chemical sensor was studied. Well-ordered Ag nanodot array with approximately 65 nm diameter in periodic pattern of 105 nm was fabricated using the nanoporous alumina with through-holes as an evaporation mask. The LSPR of Ag nanodot array on ITO glass substrate was investigated by UV-vis spectroscopy. The LSPR wavelength-shifts owing to the concentration variances of Methylene Blue (MB) adsorbed on Ag nanodot arrays were examined for application of chemical sensor.

Commercially available conventional color printing techniques mainly rely on patterning pigment-based pixels on a substrate. In recent years, structural colors have become increasingly important for their intrinsic advantages such as chemical stability, high resolution and color properties. However, to apply structural color pixels in printing color images for consumer-based demands remains a daunting challenge because such pixels usually require very high resolution patterning at a high speed and low cost. In this paper, we present novel color printing techniques based on micro-patterning of prefabricated nanostructure pixels in RGB primary colors. According to the micro-patterning techniques, the presented techniques are: a) solvent-free optical and thermal patterning of nanostructure pixels, b) photographic exposure through nanostructure color filters and c) inkjet printing of silver on nanostructures. These three presented techniques share some similar characteristics with popular conventional techniques, and can be considered as new-generation printing techniques evolved from their conventional counterparts. The preliminary results suggest that implementing the presented techniques, full-color images can be printed with much improved throughput than other nano-patterning techniques and imply these techniques can potentially be applied towards color production for general consumer use.

Metallic nanoantennas are able to spatially localize far-field electromagnetic waves on a few nanometer length scale in the form of surface plasmon excitations ^1-3. Standard tools for fabricating bowtie and rod antennas with sub-20 nm feature sizes are Electron Beam Lithography or Ga-based Focused Ion Beam (FIB) Milling. These structures, however, often suffer from surface roughness and hence show only a limited optical polarization contrast and therefore a limited electric field localization. Here, we combine Ga- and He-ion based milling (HIM) for the fabrication of gold bowtie and rod antennas with gap sizes of less than 6 nm combined with a high aspect ratio. Using polarization-sensitive Third-Harmonic (TH) spectroscopy, we compare the nonlinear optical properties of single HIM-antennas with sub-6-nm gaps with those produced by standard Ga-based FIB. We find a pronounced enhancement of the total TH intensity of more than three in comparison to Ga-FIB antennas and a highly improved polarization contrast of the TH intensity of 250:1 for Heion produced antennas ⁴. These findings combined with Finite-Element Method calculations demonstrate a field enhancement of up to one hundred in the few-nanometer gap of the antenna. This makes He-ion beam milling a highly attractive and promising new tool for the fabrication of plasmonic nanoantennas with few-nanometer feature sizes.

Any violation of the periodicity of a perfect grating will result in diffuse scattering. In the particular case of a periodic violation the generated stray light shows deterministic, also periodic features that arise as distinct peaks in the stray light spectra, especially so-called Rowland ghosts. In this paper the characteristics of the spurious Rowland ghosts in binary spectrometer gratings are investigated and the potential of a randomization technique in order to suppress the Rowland ghosts is analyzed. Especially in sequential fabrication technologies, e.g. electron beam lithography, the Rowland ghosts originate in a segmentation process that is necessary in order to write large scale gratings. Hence several subareas are subsequentially exposed and stitched together leading to the final full size grating. Due to this stitching approach the subareas induce secondary periodic structures and thus generate the spurious Rowland ghosts in the order of magnitude of <10^-4 compared to the useful diffraction order. A randomization of this segmentation process is investigated both theoretically in rigorous simulations and experimentally by fabricating a purposely designed optical grating. As approach for the randomization in experiment we applied a special multi-pass-exposure. Here the sample is exposed multiple times with an accordingly shifted and dose-reduced subarea in each pass. The achieved simulation results show that a randomization of the subareas effectively reduces the Rowland ghosts. Furthermore the applied randomization technique during grating fabrication was able to suppress one kind of Rowland ghosts completely.

The controlled guidance of light rays through a mechanically flexible large area polymer optical waveguide sheet is investigated using Zemax OpticStudio software. The geometry and spatial distribution of micro-optical features patterned on the waveguide sheet determines whether the surface acts as a light concentrator or diffuser. To illustrate the concept, incident light is collected over a large center area and then transmitted to the border where it is emitted through an illumination window covered by an array of photo-cells. The efficiencies of the collector and illuminating regions of the hybrid PDMS collector-diffuser waveguide sheet are discussed. Initial analysis of the waveguide design demonstrates an ideal efficiency of over 90% for the concentrating region of the waveguide and over 80% efficiency for the diffusing region of the waveguide. The Zemax simulation of the ideal design of the hybrid concentrator-diffuser waveguide exhibited an efficiency of up to 75%. However this efficiency significantly decreased when examining the waveguide’s performance as a flexible sheet. The necessary design modifications, to mitigate these losses in efficiency, are discussed, and future work will focus on analyzing and optimizing the waveguide design for performance as a fully flexible concentrator-diffuser membrane.

We propose and demonstrate a low cost, large area, and mass production compatible method to fabricate strip-loaded waveguide structures. The structure is fabricated by combination of Atomic Layer Deposition and replication technique without applying any etching process to form the strip. The waveguide was realized in ring resonator configuration which eases the characterization process. The guiding layer is a 200 nm-thick TiO₂ layer integrated with polymer strips to load light in the high index thin film. Due to the characteristic of the applied fabrication technique, achieving a very low propagation losses is expected.

Ridge waveguides in ferroelectric materials like LiNbO3 attended great interest for highly efficient integrated optical devices, for instance, electro-optic modulators, frequency converters and ring resonators. The main challenges are the realization of high index barrier towards the substrate and the processing of smooth ridges for minimized scattering losses. For fabricating ridges a variety of techniques, like chemical and wet etching as well as optical grade dicing, have been investigated in detail. Among them, laser micromachining offers a versatile and flexible processing technology, but up to now only a limited side wall roughness has been achieved by this technique. Here we report on laser micromachining of smooth ridges for low-loss optical waveguides in LiNbO₃. The ridges with a top width of 7 µm were fabricated in z-cut LiNbO₃ by a combination of UV picosecond micromachining and thermal annealing. The laser processing parameters show a strong influence on the achievable sidewall roughness of the ridges and were systematically investigated and optimized. Finally, the surface quality is further improved by an optimized thermal post-processing. The roughness of the ridges were analysed with confocal microscopy and the scattering losses were measured at an optical characterization wavelength of 632.8 nm by using the end-fire coupling method. In these investigations the index barrier was formed by multi-energy low dose oxygen ion implantation technology in a depth of 2.7 μm. With optimized laser processing parameters and thermal post-processing a scattering loss as low as 0.1 dB/cm has been demonstrated.

A method of fabricating large-volume three-dimensional (3D) photonic crystal and quasicrystal templates using holographic lithography is presented. Fabrication is accomplished using a single-beam and single exposure by a reflective optical element (ROE). The ROE is 3D printed support structure which holds reflecting surfaces composed of silicon or gallium arsenide. Large-volume 3D photonic crystal and quasicrystal templates with 4-fold, 5-fold, and 6-fold symmetry were fabricated and found to be in good agreement with simulation. Although the reflective surfaces were setup away from the Brewster's angle, the interference among the reflected s and p-polarizations still generated bicontinuous structures, demonstrating the flexibility of the ROE. The ROE, being a compact and inexpensive alternative to diffractive optical elements and top-cut prisms, facilitates the large-scale integration of holographically fabricated photonic structures into on-chip applications.

We report the experimental measurement of the relationship between the size of particles being moved by optically patterned dielectrophoresis in an Optoelectronic Tweezers (OET) device and the force that they experience. The OET device turns an optical pattern into a pattern of electrical fields through the selective illumination of a photoconductive material. In this work we use a data projector to create the structured illumination which gives a relatively flat optical profile with steep optical gradients and hence steep electrical gradients at the edges of the light patterns created. For a small particle in a constant electrical gradient it would be expected that the force due to dielectrophoresis would scale with the cube of the particle’s radius whereas the forces needed to move it against the viscous fluid scale with the radius so that there would be a an increase of the velocity at which we can move particles with a relationship of the radius squared. As the particles in an OET device are often larger than the area over which the electrical gradients are produced it is not obvious how their forces scale with size. In this paper we show that there is a small size regime where the particle size relationship with force is well described by a linear fit and a regime where it is not. We show that the magnitude of the force is dependent on the light pattern used and that with larger particles and optimized light patterns velocities of around 1mms-1 can be achieved.

We have previously introduced an anisotropic leaky-mode modulator as a waveguide-based, acousto-optic solution for spatial light modulation in holographic video display systems. Waveguide fabrication for these and similar surface acoustic wave devices relies on proton exchange of a lithium niobate substrate, which involves the immersion of the substrate in an acid melt. While simple and effective, waveguide depth and index profiles resulting from proton exchange are often non-uniform over the device length or inconsistent between waveguides fabricated at different times using the same melt and annealing parameters. In contrast to proton exchange, direct writing of waveguides has the appeal of simplifying fabrication (as these methods are inherently maskless) and the potential of fine and consistent control over waveguide depth and index profiles. In this paper, we explore femtosecond laser micromachining as an alternative to proton exchange in the fabrication of waveguides for anisotropic leaky-mode modulators.

Light patterned dielectrophoresis or optoelectronic tweezers (OET) has been proved to be an effective micromanipulation technology for cell separation, cell sorting and control of cell interactions. Apart from being useful for cell biology experiments, the capability of moving small objects accurately also makes OET an attractive technology for other micromanipulation applications. In particular, OET has the potential to be used for efficiently and accurately assembling small optoelectronic/electronic components into circuits. This approach could produce a step change in the size of the smallest components that are routinely assembled; down from the current smallest standard component size of 400×200 μm (0402 metric) to components a few microns across and even nanostructured components. In this work, we have demonstrated the use of OET to manipulate conductive silver nanowires into different patterns. The silver nanowires (typical diameter: 60 nm; typical length: 10 μm) were suspended in a 15 mS/m solution of KCL in water and manipulated by positive dielectrophoresis force generated by OET. A proof-of-concept demonstration was also made to prove the feasibility of using OET to manipulate silver nanowires to form a 150-μm-long conductive path between two isolated electrodes. It can be seen that the resistance between two electrodes was effectively brought down to around 700 Ω after the silver nanowires were assembled and the solution evaporated. Future work in this area will focus on increasing the conductivity of these tracks, encapsulating the assembled silver nanowires to prevent silver oxidation and provide mechanical protection, which can be achieved via 3D printing and inkjet printing technology.

Soft-lithography techniques can be used to fabricate mechanically flexible polydimethylsiloxane (PDMS) optical waveguide sheets that act as large area light collectors (concentrators) and illuminators (diffusers). The performance and efficiency of these optical sheets is determined by the position and geometry of micro-optical features embedded in the sheet or imprinted on its surface, thickness and shape of the waveguide, core and cladding refractive indices, and wavelength of the incident light source. The critical design-for-manufacturability parameters are discussed and a scalable method of fabricating multi-layered PDMS optical waveguides is introduced. To illustrate the concepts a prototype waveguide sheet that acts a combined light collector and illumination panel is fabricated and tested. The region of the waveguide sheet that acts as the light collector consists of two superimposed PDMS layers with slightly different indices of refraction. The top layer is patterned with micro-lenses that focus the incident light rays onto the micro-wedge features that act as reflectors on the bottom of the second layer and, due to total internal reflection, redirect the light rays to the light diffuser region of the waveguide sheet. The bottom face of the diffuser PDMS layer is patterned with angled triangular wedge micro-features that project the light out of the waveguide sheet forming an illuminating pattern. The proposed fabrication technique utilizes precision machined polymethylmethacrylate (PMMA) moulds with negative patterned PDMS inserts that transfer the desired micro-optical features onto the moulded waveguide.

This report presents recent advances in the design and fabrication of a tunable Fabry-Pérot interferometer (FPI) with subwavelength grating (SWG) reflectors, as well as measurement results and applications. The FPI is designed as wavelength selecting element for highly miniaturized mid-wave infrared spectrometers. The optical resonator of the FPI is built between two highly reflecting mirrors. The mirrors are integrated in a supporting MEMS structure with one electrostatically movable and one fixed mirror carrier. The FPI is fabricated in a bulk micromachining batch process on wafer level from two silicon substrates. The substrates are bonded together with an intermediate SU-8 layer. The reflectors are made of aluminum subwavelength gratings, structured on a thin LP-Si3N4 membrane by nanoimprint lithography. The subwavelength structures build a frequency selective surface with high reflectance and low absorbance in a defined spectral range. Simulations and optimization of the design were done using finite element method with a 3D EM frequency domain solver. Comparison of simulation results and measurements of fabricated reflectors and FPIs are in very good agreement. The FPIs are used in the 5th interference order and can be tuned from 3.5 μm to 2.9 μm electrically. The measured maximum transmittance is between 70 % and 50 % and the measured FWHM bandwidth is lower than 50 nm. The new subwavelength grating reflectors can be integrated in a MEMS batch process more cost-efficient than previously used reflectors of dielectric layer stacks.

While animals have access to sugars as energy source, this option is generally not available to artificial machines and robots. Energy delivery is thus the bottleneck for creating independent robots and machines, especially on micro- and nano- meter length scales. We have found a way to produce polymeric nano-structures with local control over the molecular alignment, which allowed us to solve the above issue. By using a combination of polymers, of which part is optically sensitive, we can create complex functional structures with nanometer accuracy, responsive to light. In particular, this allowed us to realize a structure that can move autonomously over surfaces (it can “walk”) using the environmental light as its energy source. The robot is only 60 μm in total length, thereby smaller than any known terrestrial walking species, and it is capable of random, directional walking and rotating on different dry surfaces.

Conventional optical elements are based on either refractive or reflective optics theory to fulfill the design specifications via optics performance data. In refractive optical lenses, the refractive index of materials and radius of curvature of element surfaces determine the optical power and wavefront aberrations so that optical performance can be further optimized iteratively. Although gradient index (GRIN) phenomenon in optical materials is well studied for more than a half century, the optics theory in lens design via GRIN materials is still yet to be comprehensively investigated before realistic GRIN lenses are manufactured. In this paper, 3D printing method for manufacture of micro-optics devices with special features has been studied based on methods reported in the literatures. Due to the additive nature of the method, GRIN lenses in micro-optics devices seem to be readily achievable if a design methodology is available. First, derivation of ray-tracing formulae is introduced for all possible structures in GRIN lenses. Optics simulation program is employed for characterization of GRIN lenses with performance data given by aberration coefficients in Zernike polynomial. Finally, a proposed structure of 3D printing machine is described with conceptual illustration.

This work reports the fabrication of micron-scale spatially variant photonic crystals (SVPCs) and their use for steering light beams through turns with bending radius R_bend on the order of ten times the optical wavelength λ₀. Devices based on conventional photonic crystals, metamaterials, plasmonics and transformation optics have all been explored for controlling light beams and steering them through tight turns. These devices offer promise for photonic interconnects, but they are based on exotic materials, including metals, that make them impractically lossy or difficult to fabricate. Waveguides can also be used to steer light using total internal reflection; however, R_bend of a waveguide must be hundreds of times λ₀ to guide light efficiently, which limits their use in optical circuits. SVPCs are spatially variant 3D lattices which can be created in transparent, low-refractive-index media and used to control the propagation of light through the self-collimation effect. SVPCs were fabricated by multi-photon lithography using the commercially available photo-polymer IP-DIP. The SVPCs were structurally and optically characterized and found to be capable of bending light having λ₀ = 1.55 μm through a 90-degree turn with R_bend = 10 μm. Curved waveguides with R_bend = 15 μm and 35 μm were also fabricated using IP-DIP and optically characterized. The SVPCs were able to steer the light beams through tighter turns than either waveguide and with higher efficiency.

This work reports a detailed study of the processing and photo-patterning of two chalcogenide glasses (ChGs) − arsenic trisulfide (As₂S₃) and a new composition of germanium-doped arsenic triselenide Ge5(As2Se3)95 − as well as their use for creating functional optical structures. ChGs are materials with excellent infrared (IR) transparency, large index of refraction, low coefficient of thermal expansion, and low change in refractive index with temperature. These features make them well suited for a wide range of commercial and industrial applications including detectors, sensors, photonics, and acousto-optics. Photo-patternable films of As₂S₃ and Ge₅(As₂Se₃)₉₅ were prepared by thermally depositing the ChGs onto silicon substrates. For some As₂S₃ samples, an anti-reflection layer of arsenic triselenide (As₂Se₃) was first added to mitigate the effects of standing-wave interference during laser patterning. The ChG films were photo-patterned by multi-photon lithography (MPL) and then chemically etched to remove the unexposed material, leaving free-standing structures that were negative-tone replicas of the photo-pattern in networked-solid ChG. The chemical composition and refractive index of the unexposed and photo-exposed materials were examined using Raman spectroscopy and near-IR ellipsometry. Nano-structured arrays were photo-patterned and the resulting nano-structure morphology and chemical composition were characterized and correlated with the film compositions, conditions of thermal deposition, patterned irradiation, and etch processing. Photo-patterned Ge₅(As₂Se₃)₉₅ was found to be more resistant than As₂S₃ toward degradation by formation of surface oxides.

We report fabrication and optical properties of ultra-thin polarization-invariant electromagnetic absorber metasurface for infra-red spectral. The absorber structure, which uses three-dimensional architecture is based on single-turn metallic helices arranged into a periodic square lattice on a metallic substrate, is expected to exhibit total resonant absorption due to balanced coupling between resonances of the helices. The structure was designed using numerical simulations aiming to tune the total absorption resonance to infra-red wavelength range by appropriately downscaling the unit cell of the structure, and taking into account dielectric dispersion and losses of the metal. The designed structures were subsequently fabricated using femtosecond direct laser write technique in a dielectric photoresist, and subsequent metallisation by gold sputtering. In accordance with the expectations, the structure was found to exhibit resonant absorption centred near the wavelength of 6 - 9 µm, with peak absorption in excess of 82%. The absorber metasurface may be applied in various areas of science and technology, such as harvesting infra-red radiation in thermal detectors and energy converters.

Tunable liquid lens arrays can produce three dimensional images by using electrowetting principle that alters surface tensions by applying voltage. This method has advantages of fast response time and low power consumption. However, it is challenging to fabricate a high fill factor liquid lens array and operate three dimensional images which demand high diopter. This study describes a hybrid structure lens array which has not only a liquid lens array but a solid lens array. A concave-shape lens array is unavoidable when using only the liquid lens array and some voltages are needed to make the lens flat. By placing the solid lens array on the liquid lens array, initial diopter can be positive. To fabricate the hybrid structure lens array, a conventional lithographic process in semiconductor manufacturing is needed. A negative photoresist SU-8 was used as chamber master molds. PDMS and UV adhesive replica molding are done sequentially. Two immiscible liquids, DI water and dodecane, are injected in the fabricated chamber, followed by sealing. The fabricated structure has a 20 by 20 pattern of cylindrical shaped circle array and the aperture size of each lens is 1mm. The thickness of the overall hybrid structure is about 2.8mm. Hybrid structure lens array has many advantages. Solid lens array has almost 100% fill factor and allow high efficiency. Diopter can be increased by more than 200 and negative diopter can be shifted to the positive region. This experiment showed several properties of the hybrid structure and demonstrated its superiority.

This paper aims to describe a slanted liquid microlens array using diffusers. Ordinary liquid microlens has vertical side walls. The shape of it, however, has several weaknesses such as a low value of diopter and a difficulty in evaporating electrode. The diffuser causes UV light to spread slantly not straightly. This research shows a result of a slanted liquid micro lens having side walls with an angle of 74 degrees and verifies a high value of diopter and a well-filmed electrode. In order to achieve a high percentage of fill factor, it also presents matching values for refractive indices of the two media, oil and chamber.

Nanoimprint Lithography is a promising high-throughput technology for the fabrication of optical nanostructures over large areas in the centimeter range. However, there are limitations (cost, proprietary and tool specific) of the commercial transfer resist. In this work, the photo-resist AZ1518 is investigated as a viable nanoimprint resist mask with a tefloncoated silicon mold. The results are comparable with a commercial nanoimprint resist. To our knowledge, the application of a conventional photoresist as the nanoimprint mask with teflon-coated mold is novel, providing a critical solution for cost-effective, flexible and high-throughput fabrication of optical nanostructures over large areas. Periodic gratings with lateral width of 100 nm and 200 nm pitch have been fabricated using this approach. The nanoimprint process parameters (pressure and temperature) are optimized to improve the release of the mold from the resist. In addition, the Teflon-coated mold improves the release process to avoid tearing of the mask.

Liquid-filled square lens array has been developed for an alternative to solid lens array because of its advantage in variable focus length. In addition, the square lens array has advantage with high fill factor compared to liquid circular lens array which is another alternative. However, one of the main limitations of conventional square lens array is the distortion. In this paper, distortion-free liquid square lens array is proposed. The partition walls of the proposed square lens array is fabricated into hemispherical shape to reduce the distortion, and then additional vertical walls are set up on the hemispherical structures to unify the height of partition walls and divide chamber sections. UV lithography techniques are used to fabricate this structure, and diffuser which has an angle of 80 degrees is used in the process. Photoresist is exposed to scattered ultraviolet rays which pass through the diffuser, and hemispherical lens-shaped structures of photoresist remains after development process. Supplementary vertical partition walls are obtained by additional photoresist patterning process on the structure. In this structure, the interface between oil and water comes into contact with the surface of the hemispherical walls, and the refractive index of oil and the walls are equally matched to maximize the part which acts as lens in the chamber. The proposed liquid square lens array can provide us with aberration-free 3D images with high fill factor.

Wire-grid polarizers (WGPs) are composed of 1-D nanoscale periodic structures and are widely used in liquid crystal display devices to enhance the brightness and improve the utilization rate of the backlight source. This paper proposes the design and application of a WGP device for an microelectromechanical system physical force sensor derived through an optical measurement method. Infrared (IR) light was served as the signal source, with the initial angle set incident to the WGP, which was fabricated on microstructures such as cantilever beam, thin-film or bridge structures. According to the operation principle, when a physical force affects the microstructures, the incident angle of the signal light changes, which easily produces different transmission signal values for detection by an IR photodetector. Therefore, the proposed system can be used for optical contactless sensing in physical force sensing modules. Furthermore, the WGP structure introduced in this paper was defined using laser interference lithography and deposited with Al by E-beam evaporation.

Conventionally, poly (dimethylsiloxane) lens array is fabricated by replica molding. In this paper, we describe simple method for fabricating lens array with expanding property of PDMS. The PDMS substrate is prepared by spin coating on cleaned glass. After spin coating PDMS, substrate is treated with O2 plasma to promote adhesion between PDMS substrate and photoresist pattern on it. Positive photoresist az-4330 and AZ 430K developer is used for patterning on PDMS. General photolithography process is used to patterning. Then patterned PDMS substrate is dipped to 1- Bromododecane bath. During this process, patterned photoresist work as a barrier and prevent blocked PDMS substrate from reaction with 1-Bromododecane. Unblocked part of PDMS directly react with 1-Bromododecane and results in expanded PDMS volume. The expansion of PDMS is depends on absorbed 1-Bromododecane volume, dipping time and ratio of block to open area. The focal length of lens array is controlled by those PDMS expansion factors. Scale of patterned photoresist determine a diameter of each lens. The expansion occurs symmetrically at center of unblocked PDMS and 1-Bromododecane interface. As a result, the PDMS lens array is achieved by this process.

The development of many photonic devices, such as photonic integrated circuit, optical sensors, and photovoltaic devices, demands low-cost and reliable fabrication technologies to fabricate sub-wavelength features. Here, we report a programmable nanoreplica molding process, which is capable of producing photonic devices with a variety of submicrometer patterns. The process utilizes a stretchable plastic mold to generate the desired periodic pattern using a UVcurable polymer on plastic substrates. During the replica molding process, a uniaxial force is applied to the mold and results in changes of the periodic structure, which locates on the surface of the mold. The geometry of the replicated pattern, including the lattice constant and arrangement, is determined by the magnitude and direction of the force. As an example, we present a plasmonic crystal device with surface plasmon resonances carefully tuned by using the uniaxial force. This unique process offers an inexpensive route to generate various periodic nanostructures rapidly.

Mac(metal assisted chemical) etching is a simple, low-cost and anisotropic etching method to make Si NWs (silicon nanowires). In this method, smaller surface area is damaged compared to dry etching process, either. Mac etching uses a combination of an oxide removal acid (e.g. HF), an oxidant (e.g. H₂O₂) with a noble metal (e.g. Au, Ag, Pt, etc.) as the catalyst. Typically, the Si beneath the noble metal is etched faster than the Si without noble metal coverage by electron transfer mechanism at the noble metal /solution and the noble metal/Si interface. While Mac etching to build Si NWs, unwanted etching occurs in the bulk silicon layer resulting from excess hole diffusion caused by the increase in hole concentration at the nearby metal layers. In this study, we explored the ratio of oxidant to oxide removal acid in the Mac etching solution that is most effective in etching the Si underneath the noble metal layer suppressing the unwanted etching. At the optimized ratio, Si NWs were fabricated at a faster rate with good uniformity.

The nanomasking fabrication technique has been shown to be capable of producing many sub-10 nm gaps between metallic structures over a wafer-scale area. This provides the opportunity to utilize the technique in spectroscopy signal enhancement applications. Here we describe a device designed via nanomasking that holds potential as a surface enhanced Raman spectroscopy (SERS) substrate for biosensing or other applications. The high density of plasmonic hotspot nanogaps improves the feasibility of these types of patterns for signal enhancement, as it provides ease of use and increased speed of sample deposition for taking spectrum. The ability to fabricate these patterns with high repeatability at mass production scale is another benefit of nanomasking-fabricated spectroscopy substrates. This work demonstrates tests of fabricated devices for use in a custom Raman spectroscopy system as a potential source of signal enhancement. Also, theoretical enhancement results are calculated for comparison via computational electromagnetic studies.

We report the fabrication of designed defects and regions in photonic crystal templates with differing filling fractions using a spatial light modulator. For the hexagonal lattice, phase patterns with local variance of diffraction efficiency are created using phase tiles from other phase patterns with known diffraction efficiencies. Six-fold symmetric phase patterns are used to generate six beams with locally specified phases. Fourier transform simulations of designed phase patterns are used to guide the filtering process and also give insight into the interference pattern in the 4f plane. Photonic crystal templates are fabricated using exposure of photoresist to the interference patterns generated from the phase patterns with local diffraction efficiency variance displayed on a spatial light modulator. It is shown that local control of filling fraction is achievable using this method. For the square lattice, line defects in polymer lattices are produced using line phase defects in a checkerboard phase pattern. The shifting of the lattice due to the defect phase is investigated. The shifting of lattice around the defects in 2+1 interference is less than that produced by 4+1 interference due to the alternative shifting in lattice in the 2+1 interference. By 45 degree defect orientation and 2+1 interference, the defect orientation can be aligned with the background lattice, the shifting is alternative in lattice, and the shifting is only in one side of the defects, in agreement with the theory prediction.