Haifang Yang

Polarization insensitive and omnidirectional broadband near perfect planar metamaterial absorber in the near infrared regime

We present the design, characterization, and experimental demonstration of a polarization insensitive and omnidirectional broadband near perfect planar metamaterial absorber (MA) in the near infrared regime, which does not need to stack multilayer composite structures. Experimental result shows that greater than 80% absorption is obtained across a wavelength range of 0.41 μm, which is in reasonable agreement with the simulation. The electromagnetic response of the MA is theoretically investigated. The broadband planar MA is polarization insensitive and the absorption remains high even at large incident angles.

An all-metallic logic gate based on current-driven domain wall motion

The walls of magnetic domains can become trapped in a ferromagnetic metallic point contact when the thickness of the film and the width of the contact are less than their critical values. The discovery that domain walls can be moved from such constrictions by a sufficiently large current has attracted considerable attention from researchers working on both fundamental research and potential applications. Here we show that Invar nanocontacts fabricated on silica substrates exhibit a sharp drop in resistance with increasing bias voltage at room temperature in the absence of an applied magnetic field. Moreover, when two nanocontacts are combined in an all-metallic comparison circuit, it is possible to perform logical NOT operations. The use of electrical currents rather than applied magnetic fields to control the domain walls also reduces energy consumption and the risk of crosstalk in devices.

Polarization-insensitive and wide-angle plasmonically induced transparency by planar metamaterials

We present the design, characterization, and experimental demonstration of a polarization-insensitive wide-angle plasmonically induced transparency (PIT) planar metamaterial (MM) in the near-infrared regime. A four-level plasmonic system is proposed to explain and analyze the forming mechanisms of the PIT planar MM, whose results agree closely with the simulated and experimental results. This shows that the local asymmetrical nanostructure leading to the plasmon-assisted interaction is the key to producing PIT, but it does not mean that PIT cannot be achieved by the whole symmetrical nanostructure. This work offers a further step in developing optical modulation.

Modulated terahertz responses of split ring resonators by nanometer thick liquid layers

The terahertz responses of planar arrays of split ring resonators with 50nm thin liquid layers introduced in the interspaces between the metal structures have been studied using the terahertz-time domain spectroscopy technique. In our experimental configuration, both the circular current driven and linear polarization induced resonances show redshifted and enhanced transmission. The dielectric functions extracted from an effective medium model indicate that the behavior of the surface and interface charge oscillations is highly sensitive to the interface environment changes. The results suggest that this kind of device may be used for sensing applications.

A polarization insensitive and wide-angle dual-band nearly perfect absorber in the infrared regime

We report the design, characterization, and experimental demonstration of an infrared dual-band metamaterial absorber composed of simple periodically patterned structures. Experimental results show that two distinct absorption peaks of 74% and 96% are obtained, which are in reasonable agreement with the simulations. We demonstrate two absorption resonances that are derived from the mixture of magnetic and electric plasmon resonances. The dual-band absorber is polarization insensitive and the absorption peaks remain high with large angles of incidence for both transverse electric and transverse magnetic polarizations, which provide more efficient absorptions for nonpolarized or oblique incident beams.

Few-layer SnSe2 transistors with high on/off ratios

We report few-layer SnSe2 field effect transistors (FETs) with high current on/off ratios. By trying different gate configurations, 300 nm SiO2 and 70 nm HfO2 as back gate only and 70 nm HfO2 as back gate combined with a top capping layer of polymer electrolyte, few-layer SnSe2 FET with a current on/off ratio of 104 can be obtained. This provides a reliable solution for electrically modulating quasi-two-dimensional materials with high electron density (over 1013 cm−2) for field-effect transistor applications.

Two-color quantum dot laser with tunable wavelength gap

We report on two-color InAs/InP(100) quantum dot lasers with tunable wavelength gap. Two peaks of lasing emission were observed simultaneously, while the high energy peak undergoes continuous blueshift with the increase in the injection current, and the low energy peak is somewhat fixed. Sophisticated studies of the wavelength gap as a function of the laser power prove that the two-peak lasing and shifting is not caused by the effect of Rabi oscillation. Moreover, comparison of electroluminescence and lasing spectra under different injection currents reveal the blueshift of the high energy peak is most likely related to the state-filling effect.

Visible transmission response of nanoscale complementary metamaterials for sensing applications

Metamaterials (MMs) have shown huge potential in sensing applications by detecting their optical properties, which can be designed to operate at frequencies from visible to mid-IR. Here we constructed complementary split ring resonator (CSRR) based metamaterials in nanoscale with unit length of 100 nm and slit width of 30 nm, and observed obvious responses in the visible waveband from 600 to 900 nm. These visible responses show a good tunability with the structures geometry, and are well suited for dielectric detection. We demonstrated good refractive index sensing of CSRR based metamaterials in the visible region under both 0° and 90° polarized incidence. Our results extend the study of CSRR based metamaterials to the visible region, which is expected to deepen the understanding of the response mechanism of CSRRs and benefit their sensing applications in the visible region.

Fabrication of metallic nanostructures by negative nanoimprint lithography

This paper describes a negative nanoimprint lithography (N-NIL) technique for fabricating metallic nanostructures via combining conventional nanoimprint lithography (NIL) with wet chemical etching. Various metallic nanostructures such as gold grating, gold/chromium alternate bimetallic grating and gold nanoelectrode arrays, which are negative replications of the stamp pattern, have been fabricated with N-NIL. This method has demonstrated its advantages on varying the feature size of obtained metallic nanostructures with a single stamp as well as on fabricating bimetallic nanostructures. In addition, it offers a unique path to fabricate micro?nano complex structures in a single imprint process, which compensates the limitation of conventional nanoimprint lithography and maintains the advantages of conventional nanoimprint lithography such as high throughput, low cost and sub-100?nm resolution.

The influences of substrate and metal properties on the magnetic response of metamaterials at terahertz region

The metamaterials (MMs) with planar metal arrays of split ring resonators were fabricated on quartz and silicon substrates; the influences of substrate permittivity and metal conductance on the magnetic responses of in the terahertz region were investigated. The electromagnetic (EM) responses of the metamaterials were characterized by terahertz time-domain spectroscopy. The experimental result reveals that there is a 0.39 THz redshift in the transmission spectra for the magnetic response when the substrate changes from quartz to silicon, which is in consistence with the finite-difference time-domain (FDTD) simulation. Based on the simulation and experimental results, and taking into account the EM properties of substrate materials, a modified L-C model is presented to understand the MM system in terahertz domain.