Nano-scale Grating Structure Research Articles

Resonant Subwavelength and Nano-Scale Grating Structures for Biosensing Application: A Comparative Study.

Resonant-based sensors are attractive optical structures due to the easy detection of shifts in the resonance location in response to variations in the analyte refractive index (RI) in comparison to non-resonant-based sensors. In particular, due to the rapid progress of nanostructures fabrication methods, the manufacturing of subwavelength and nano-scale gratings in a large area and at a low cost has become possible. A comparative study is presented involving analysis and experimental work on several subwavelength and nanograting structures, highlighting their nano-scale features’ high potential in biosensing applications, namely: (i) Thin dielectric grating on top of thin metal film (TDGTMF), which can support the excitation of extended surface plasmons (ESPs), guided mode resonance, or leaky mode; (ii) reflecting grating for conventional ESP resonance (ESPR) and cavity modes (CMs) excitation; (iii) thick dielectric resonant subwavelength grating exhibiting guided mode resonance (GMR) without a waveguide layer. Among the unique features, we highlight the following: (a) Self-referenced operation obtained using the TDGTMF geometry; (b) multimodal operation, including ESPR, CMs, and surface-enhanced spectroscopy using reflecting nanograting; (c) phase detection as a more sensitive approach in all cases, except the case of reflecting grating where phase detection is less sensitive than intensity or wavelength detection. Additionally, intensity and phase detection modes were experimentally demonstrated using off-the-shelf grating-based optical compact discs as a low-cost sensors available for use in a large area. Several flexible designs are proposed for sensing in the visible and infrared spectral ranges based on the mentioned geometries. In addition, enhanced penetration depth is also proposed for sensing large entities such as cells and bacteria using the TDGTMF geometry.

Resonant Subwavelength and Nano-Scale Grating Structures for Biosensing Application: A Comparative Study

Resonant Subwavelength and Nano-Scale Grating Structures for Biosensing Application: A Comparative Study

Resonant-Like Field Enhancement by Nanoscale Grating-Coupled Propagating Surface Plasmons and Localized Surface Plasmons in the Mid-Infrared Range: Implications for Ultrafast Plasmonic Electron Sources

We investigated electron emission induced by an intense mid-infrared (MIR) field from a nanoscale aluminum-coated grating. The total photoelectron yields clearly show a resonant-like behavior when frustrated diffraction occurs near the Wood anomaly. This result indicates that a strong near field, which is formed by the localized surface plasmons (LSPs) at the ridge of the grating, can be enhanced by resonantly produced propagating surface plasmons (PSPs) owing to the phase matching between the diffracted light and PSPs. The observed photoelectron spectra can be reproduced well by a simple one-dimensional (1D) model of a near field that contains two parameters: the field enhancement factor, α, and the ridge radius, r0. In addition, we show that the resonant-like photoemission was attributed to the interference of the near fields produced by the LSPs and PSPs in the nanoscale grating structure. These results demonstrate that the nanoscale structure is useful for ultrafast plasmonic electron sources.

Metrology of nanoscale grating structures by UV scatterometry.

In this contribution we demonstrate goniometric scatterometry measurements of gratings with linewidths down to 25 nm on silicon wafers with an inspection wavelength of 266 nm. For each sample, measurements have been performed in four different configurations and the obtained data have been evaluated in parallel. As results we present the reconstruction of the complete cross-section profile. We introduce a novel geometry parameterization which overcomes some limitations of the default parameterization. A co-variance analysis of the parameters is offered to indicate the soundness of the results. A qualitative comparison with cross-section scanning electron microscope (SEM) images shows excellent agreement.

Design of color filter based on dielectric thin film with nano-scale grating structure

In order to improve the light reflectance efficiency and to decrease the overlay of tricolor output spectra of a color filter, based on dielectric thin film with nano-scale grating structure, three primary color filters (Red, Green and Blue) located at 635nm, 530nm and 455nm are proposed. The design is obtained by adjusting the geometrical parameters after analyzing the reflection response of the proposed grating structure with various fill factor f, groove depth d and period p for the normal incidence TE-polarized light based on rigorous couple-wave analysis method. The reflectance curve shows that high reflectance and low sideband level with full width at half maximum is 50nm, 46nm and 42nm. It indicates that the proposed color filter will be readily exploited for upgrading the performance of various types of displays, image sensors and biomedical imaging technologies applications.

Single-Shot Fabrication of Waveguide Ternary Gratings with Narrow-Band Optical Response

Single-shot fabrication of three sets of nano-scale grating structures with different periods is reported, which are constructed on a glass substrate coated with a waveguide layer made of 200-nm-thick indium tin oxide (ITO). Multiple waveguide resonance modes are observed in the visible spectral range with a bandwidth as narrow as 10 nm. Angle-resolved tuning properties of these resonance modes enable simultaneous three-color optical response of the nanodevice to cover the whole visible spectrum. This implies very simple methods for the potential design and realization of flexible optoelectronic devices.

Motif Parameters Based Characterization of Line Edge Roughness of a Nanoscale Grating Structure

Motif parameters were introduced to characterize line edge roughness (LER) of a nanoscale grating structure. Firstly with electron beam lithography employed the expected nano-scale grating structure with linewidth of 16 nm was fabricated on positive resist. Then the line edge profiles of the structure were extracted and their LERs were characterized. The results showed that the evaluation method is rather simple, effective and recommendable.

Injection Molding Nanoscale Features with the Aid of Induction Heating

During injection molding of micron or submicron scale features, incomplete filling frequently occurs, resulting from premature freezing of the polymer melt in contact with a cold mold. In order to overcome the filling difficulty without increasing the total cycle time, the mold surface temperature was raised rapidly by induction heating. A prototype mold insert with cooling channels was fabricated and integrated with a nickel stamp having nanoscale-grating structures. The nickel stamp surface was successfully heated from 25 to 258°C in 2.7 sec. Four different mold surface temperatures, 100, 150, 200 and 250°C, were tested to determine if the nanograting structures can be replicated with an optical quality cyclic olefin copolymer. Experimental results indicate that the nanocavities were successfully filled when the surface temperature reached 250°C, but mold release caused drag damages on the nanogratings. Further, coupled thermoelectromagnetic analyses were carried out to simulate the induction heating process of the nanostructured mold insert. The predicted surface temperature responses in general agree with the experimental ones and the simulation model can be used in the further development of process control and mold design in micro/nano molding.

Optical and electrical properties of nanostructured metal-silicon-metal photodetectors

We report an experimental evaluation of the performance of silicon (Si) photodetectors incorporating one-dimensional (1-D) arrays of rectangular and triangular-shaped nanoscale structures within their active regions. A significant (/spl sim/2/spl times/) enhancement in photoresponse is achieved in these devices across the 400- to 900-nm spectral region due to the modification of optical absorption properties that results from structuring the Si surface on physical optics scales smaller than the wavelength, which both reduces the reflectivity and concentrates the optical field closer to the surface. Both patterned (triangular and rectangular lineshape) and planar Ni-Si back-to-back Schottky barrier metal-semiconductor-metal photodetectors on n-type (/spl sim/5/spl times/10/sup 14/ cm/sup -3/) bulk Si were studied. 1-D /spl sim/50-250-nm linewidth, /spl sim/1000-nm depth, grating structures were fabricated by a combination of interferometric lithography and dry etching. The nanoscale grating structures significantly modify the absorption, reflectance, and transmission characteristics of the semiconductor: air interface. These changes result in improved electrical response leading to increased external quantum efficiency (from /spl sim/44% for planar to /spl sim/81% for structured devices at /spl lambda/=700 nm). In addition, a faster time constant (/spl sim/1700 ps for planar to /spl sim/600 ps for structured at /spl lambda/=900 nm) is achieved by increasing the absorption near the surface where the carriers can be rapidly collected. Experimental quantum efficiency and photocurrents results are compared with a theoretical photocurrent model based on rigorous coupled-wave analysis of nanostructured gratings.