Shumin Yang

Large-scale uniform Au nanodisk arrays fabricated via x-ray interference lithography for reproducible and sensitive SERS substrate

Large-scale Au nanodisk arrays on Si substrate are successfully fabricated via x-ray interference lithography and followed by electron-beam vapor deposition. The Au nanodisk arrays exhibit a significant, uniform, and reproducible surface enhancement on Raman scattering signal, which enables the detection of R6G as low as 10(-8) M with an enhancement factor of 10(6). Importantly, the Au nanodisk arrays SERS-active substrates with uniformly high sensitivity also have high reproducibility and stability. The diameters of the nanodisks and the inter-disk distance can be simply optimized to obtain high enhancement in Raman signal by varying exposure time and development time in XIL process. The electric fields of the Au nanodisks with various diameters and inter-disk distance simulated by the finite difference time domain (FDTD) techniques further confirm that the Raman signal enhancement of Au nanodisks is determined by the diameters of nanodisks and the inter-disk distance of nanodisks. The Au/Ag double-layer bimetal nanodisk arrays are also fabricated which show a significant increase in the Raman signal enhancement than that of the Au nanodisk arrays. XIL nanofabrication appears to be a feasible approach to prepare uniform and reproducible SERS-active substrates with high sensitivity for practical SERS applications.

Influence of film thickness and nanograting period on color-filter behaviors of plasmonic metal Ag films

The effects of film thickness and nanograting period on color filter behaviors of the device, fabricated by sub-micrometers patterning on plasmonic silver thin films, have been studied. It is found that color filter properties strongly correlate with film thickness and nanograting period. Based on obtained results, the relationship of the wavelength of transmission minima with film thickness and nanograting period was derived. This equation can predict the transmission minima for a given thickness and period in one-dimensional Ag metallic film nanograting on glass substrate, which could guide to design color filter device with desirable wavelength.

Effect of relative nanohole position on colour purity of ultrathin plasmonic subtractive colour filters

Plasmonic subtractive color filters through patterning periodic nanostructures on ultrathin Ag films deposited on a glass substrate, exhibiting good durability, simple fabrication, and flexible color tunability, have attracted considerable attention due to their tremendous potential applications. While previous studies have mainly focused on their extraordinary physical mechanisms, color purity, which is another key parameter for high quality imaging applications, has been much less investigated. In this work, we demonstrate that the relative position of nanoholes patterned on ultrathin Ag films can largely affect the color purity of plasmonic subtractive color filters. The calculated results agree reasonably well with the experimental data, revealing that the purity of subtractive colors can be improved by changing the nanohole arrays from square lattice to triangular lattice without reducing transmission at visible frequencies. In addition, underlying mechanisms are clarified by systematically analyzing the dominant valley in transmission spectra.

Angle-insensitive plasmonic color filters with randomly distributed silver nanodisks

Plasmonic color filters inherently suffer from angular sensitiveness, which hinder them from practical applications. Here, we present a plasmonic subtractive color filter incorporating two-dimensional randomly distributed silver nanodisks on top of a glass substrate. Due to the elimination of structural periodicity, the proposed plasmonic color filter works via localized surface plasmon resonances (LSPRs) and thus enables excellent angle-insensitive (up to 60°) performance. In addition, uncoupled LSPRs between nanodisks guarantee stability and reproducibility of the color filter. Finally, a palette of colors across the visible region was obtained with the proposed color filters by simply varying the diameter of nanodisks, exhibiting a promising and robust applicability in digital imaging and sensing industries.

Outgassing analysis of molecular glass photoresists under EUV irradiation

A device was designed and assembled to analyze the outgassing of molecular glass (MG) photoresists under extreme ultraviolet (EUV) exposure. The outgassing of the photoresists with different components and different concentrations of tert-butoxycarbonyl (t-Boc), photo-generated acid (PAG), and acid quencher was systematically investigated. Based on experiments, some solutions for reducing the outgassing of MG photoresists were proposed.

Development of broadband X-ray interference lithography large area exposure system

The single-exposure patterned area is about several 10(2) × 10(2) μm(2) which is mainly decided by the mask area in multi-beam X-ray interference lithography (XIL). The exposure area is difficult to stitch to a larger one because the patterned area is surrounded by 0th diffraction exposure areas. To block the 0th diffraction beams precisely and effectively, a new large area exposure technology is developed in the Shanghai Synchrotron Radiation Facility by applying an order-sorting aperture with a new in situ monitoring scheme in the XIL system. The patterned area could be stitched readily up to several square centimeters and even bigger by this technology.

High throughput fabrication of large-area plasmonic color filters by soft-X-ray interference lithography.

Plasmonic color filters in mass production have been restricted from current fabrication technology, which impede their applications. Soft-X-ray interference lithography (XIL) has recently generated considerable interest as a newly developed technique for the production of periodic nano-structures with resolution theoretically below 4 nm. Here we ameliorate XIL by adding an order sorting aperture and designing the light path properly to achieve perfect-stitching nano-patterns and fast fabrication of large-area color filters. The fill factor of nanostructures prepared on ultrathin Ag films can largely affect the transmission minimum of plasmonic color filters. By changing the fill factor, the color can be controlled flexibly, improving the utilization efficiency of the mask in XIL simultaneously. The calculated data agree well with the experimental results. Finally, an underlying mechanism has been uncovered after systematically analyzing the localized surface plasmon polaritons (LSPPs) coupling in electric field distribution.

Plasmonic reflection color filters with metallic random nanostructures

We develop reflective color filters with randomly distributed nanodisks and nanoholes fabricated with hydrogen silsesquioxane and Ag films on silicon substrate. They exhibit high resolution, angle-independence and easily up-scalable fabrication, which are the most important factors for color filters for industrial applications. We uncover the underlying mechanism after systematically analyzing the localized surface plasmon polariton coupling in the electric-field distribution. The agreement of the experimental results with those from the simulation indicates that tunable colors across the visible spectrum can be obtained by simply varying the diameter of the nanodisks, promoting their applications.

Influence of symmetry and duty cycles on the pattern generation in achromatic Talbot lithography

Achromatic Talbot lithography has been proved as a robust and high throughput technique for large area nanopatterning with controllable feature sizes and duty cycles. In this work, the influence of symmetry and duty cycles on the pattern generation has been investigated in detail. Compared with square lattice case, no lattice rotation and spatial frequency multiplication can be observed in hexagonal nanopattern generation. Uniform pattern distribution with a 20 nm feature size has been obtained in square and hexagonal lattices by the masks with 144 nm period and ∼50% duty cycle. For the exposure of mask with a smaller duty cycle, nonuniform dot size distribution has been obtained in the square lattice. While, by using a smaller duty cycle hexagonal lattice mask, a highly uniform periodic hexagonal nanopattern with a 10% duty cycle has been obtained. All the experimental results were consistent with the simulation work.

High sensitivity and homogeneity of surface enhanced Raman scattering on three-dimensional array–film hybrid platform

We design and fabricate a substrate based on a three-dimensional array–film hybrid structure used for surface enhanced Raman scattering (SERS). This substrate exhibits improvements both in sensitivity and homogeneity for the Raman signals. As a result, the substrate increases the Raman signal of Rhodamine 6G by 12.3 times under the same measurement conditions, compared with conventional gold array sitting directly on a silica wafer. The sensitivity of SERS can be easily tuned by changing the thickness of SiO2 separation. Meanwhile, the relative standard deviations are achieved to be less than 10%. This array–film hybrid structure provides a promising approach for future SERS applications.