Kaipeng Liu

Deep sub-wavelength imaging lithography by a reflective plasmonic slab

By utilizing a reflective plasmonic slab, it is demonstrated numerically and experimentally in this paper deep sub-wavelength imaging lithography for nano characters with about 50 nm line width and dense lines with 32 nm half pitch resolution (about 1/12 wavelength). Compared with the control experiment without reflective plasmonic slab, resolution and fidelity of imaged resist patterns are remarkably improved especially for isolated nano features. Further numerical simulations show that near field optical proximity corrections help to improve imaging fidelity of two dimensional nano patterns.

Fabrication of anisotropically arrayed nano-slots metasurfaces using reflective plasmonic lithography

Nanofabrication technology with high-resolution, high-throughput and low-cost is essential for the development of nanoplasmonic and nanophotonic devices. At present, most metasurfaces are fabricated in a point by point writing manner with electron beam lithography or a focused ion beam, which imposes a serious cost barrier with respect to practical applications. Near field optical lithography, seemingly providing a high-resolution and low-cost way, however, suffers from the ultra shallow depth and poor fidelity of obtained photoresist patterns due to the exponential decay feature of evanescent waves. Here, we propose a method of surface plasmonic imaging lithography by introducing a reflective plasmonic lens to amplify and compensate evanescent waves, resulting in the production of nano resist patterns with high fidelity, contrast and enhanced depth beyond that usually obtained by near field optical lithography. As examples, a discrete and anisotropically arrayed nano-slots mask pattern with different orientations and a size of 40 nm × 120 nm could be imaged in photoresist and transferred successfully onto a metal layer through an etching process. Evidence for the pattern quality is given by virtue of the fabricated metasurface lens devices showing good focusing performance in experiments. It is believed that this method provides a parallel, low-cost, high-throughput and large-area nanofabrication route for fabricating nanostructures of holograms, vortex phase plates, bio-sensors and solar cells etc.

Subwavelength focusing of light in the planar anisotropic metamaterials with zone plates

We present here a structure with just a single slit covering the planar anisotropic metamaterial. The metamaterial has hyperbolic dispersion and can be realized using metal-dielectric multilayers. The structure combines the focusing performance of the zone plates and subwavelength resolution of the anisotropic metamaterials so that subwavelength focal spots can be obtained at the focal plane. The relationship between the focal spot size and slit width has been investigated, and a resolution of 36 nm about 1/10 of 365 nm incident wavelength is obtained with a 100 nm wide single slit.

Nanofocusing of circularly polarized Bessel-type plasmon polaritons with hyperbolic metamaterials

A miniature evanescent Bessel beam generator is realized by utilizing the combination of metasurfaces based on a concentric grating and hyperbolic metamaterials composed of alternate metal/dielectric multilayers. After introducing the plasmonic cavity lens, the feature size could be compressed to 62 nm (0.17λ0) at the wavelength of 365 nm with a working distance as large as 100 nm. The theoretical models are verified by a set of experiments, providing a promising way to control light at the nanoscale.

Sub-diffraction demagnification imaging lithography by hyperlens with plasmonic reflector layer

In recent years, hyperlens technology has attracted more attention because of its function of magnification and demagnification. In this study, hyperlens demagnification imaging lithography was experimentally demonstrated with sub-diffraction resolution of about 55 nm line width and about 1.8 demagnification factor at 365 nm. The hyperlens was composed of multiple Ag/SiO2 films and combined with a resist layer and a plasmonic Ag reflector. It was employed to project mask patterns to subwavelength images for nanolithography. It was found that the plasmonic reflector contributes remarkably to improving imaging contrast, fidelity and efficiency by inhibiting the negative influences from the radial electric field components in the resist region. Furthermore, discussions about imaging influences with geometrical parameters are also presented.

Far-Field Super-Resolution Imaging of Nano-transparent Objects by Hyperlens with Plasmonic Resonant Cavity

A plasmonic resonant cavity-based hyperlens is theoretically proposed and demonstrated to achieve far-field phase contrast images of nano-transparent objects. The phase contrast super-resolution imaging is mainly contributed to the excited surface plasmons inside hyperlens and cavity structure surrounding nano-objects, which help to greatly enhance evanescent waves generated by nano-transparent objects and convert weak phase information to light intensity distribution with high contrast at the zoomed imaging plane of hyperlens. As examples, nano-dielectric object imaging is numerically demonstrated with half-pitch resolution about λ/10 and a minimum distinguishable refractive index difference down to 0.15.

Color display and encryption with a plasmonic polarizing metamirror

Abstract Structural colors emerge when a particular wavelength range is filtered out from a broadband light source. It is regarded as a valuable platform for color display and digital imaging due to the benefits of environmental friendliness, higher visibility, and durability. However, current devices capable of generating colors are all based on direct transmission or reflection. Material loss, thick configuration, and the lack of tunability hinder their transition to practical applications. In this paper, a novel mechanism that generates high-purity colors by photon spin restoration on ultrashallow plasmonic grating is proposed. We fabricated the sample by interference lithography and experimentally observed full color display, tunable color logo imaging, and chromatic sensing. The unique combination of high efficiency, high-purity colors, tunable chromatic display, ultrathin structure, and friendliness for fabrication makes this design an easy way to bridge the gap between theoretical investigations and daily-life applications.

Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas

Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanning ±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8 THz to 1.2 THz.

Launching deep subwavelength bulk plasmon polaritons through hyperbolic metamaterials for surface imaging with a tuneable ultra-short illumination depth

Hyperbolic metamaterials (HMMs) composed of multiple nanometal-dielectric films are proposed for launching deep subwavelength bulk plasmon polaritons (BPPs) as uniform, large area surface imaging illumination sources with a skin depth even beyond 10 nm. Benefiting from the coupled plasmon modes over a wide wavevector range in HMMs, the illumination depth could be continually tuned, simply by adjusting the incidence angle of light impinged on a grating structure for BPP excitation. As an example, the illumination depths of 19-63 nm at a light wavelength of 532 nm are demonstrated with SiO2-Ag multifilms. Moreover, the structure holds its deep subwavelength illumination depth for a broad light wavelength range, resembling that of light total internal reflection in a prism with an ultra high refractive index. Furthermore, a fluorescent nanoparticle based micro-zone system was employed for estimating the illumination depth of the HMM structure. The method is believed to provide access for surface imaging features in ultra thin layers especially for bio-samples.

Design of a Structured Bulk Plasmon Illumination Source for Enhancing Plasmonic Cavity Superlens Imaging

A structured bulk plasmon illumination (BPI) source is designed for achieving a uniform high spatial frequency illumination field. By employing the hyperbolic metamaterial (HMM) composed of alternatively stacked metal and dielectric nanolayers, the deep subwavelength bulk plasmon polaritons (BPPs) can be launched. The obtained BPP modes are then utilized as a structured illumination source for improving the imaging resolution. More importantly, the BPI intensity can be improved remarkably by adding an extra Ag layer to the original BPI source. When two nano-slits are illuminated by the BPI source, the imaging resolution of plasmonic cavity superlens is improved obviously. Especially, after adding an extra Ag layer to the original BPI source, one can find the obvious improvement of the image contrast. The proposed BPI source promises some potential in near-field super resolution lithography.