Yong-Yuan Zhu

Magnetic and transport properties of (Mn, Co)-codoped ZnO films prepared by radio-frequency magnetron cosputtering

(Mn, Co)-codoped ZnO films have been synthesized on c-sapphire (0001) by a radio-frequency magnetron sputtering system in which two targets were sputtered together. X-ray-diffraction measurements indicate that the films are highly c-axis oriented. X-ray photon spectra show that the doped Mn and Co ions in (Mn, Co) ZnO films are both in the divalent states. The films show ferromagnetic behavior with a coercivity of about 90 Oe and a saturation moment of 0.11μB∕(0.3Mn2++0.7Co2+) at 300 K. In the lower temperatures between 5 and 20 K, a relatively large positive magnetoresistance over 10% was observed for (Mn0.03,Co0.07)Zn0.90O film. The number of carrier concentration is experimentally established to be 1.5613×1018cm−3 and the mobility to be 2.815cm2V−1s−1 for (Mn0.03,Co0.07)Zn0.90O film by Hall measurements at 300 K. The origins of the room-temperature magnetism and the large positive magnetoresistance are also discussed.(Mn, Co)-codoped ZnO films have been synthesized on c-sapphire (0001) by a radio-frequency magnetron sputtering system in which two targets were sputtered together. X-ray-diffraction measurements indicate that the films are highly c-axis oriented. X-ray photon spectra show that the doped Mn and Co ions in (Mn, Co) ZnO films are both in the divalent states. The films show ferromagnetic behavior with a coercivity of about 90 Oe and a saturation moment of 0.11μB∕(0.3Mn2++0.7Co2+) at 300 K. In the lower temperatures between 5 and 20 K, a relatively large positive magnetoresistance over 10% was observed for (Mn0.03,Co0.07)Zn0.90O film. The number of carrier concentration is experimentally established to be 1.5613×1018cm−3 and the mobility to be 2.815cm2V−1s−1 for (Mn0.03,Co0.07)Zn0.90O film by Hall measurements at 300 K. The origins of the room-temperature magnetism and the large positive magnetoresistance are also discussed.

Enhanced optical transmission through metal films with rotation-symmetrical hole arrays

The transmission of light through metal surface with subwavelength holes are influenced by many factors, and the rotational symmetry of hole arrays can be one of them. In this paper, we fabricated the hole lattices in metal films with different symmetry and measured the transmission spectra from the visible to near-infrared region. It is found that both the spectrum shape and the transmission efficiency are strongly dependent on the rotational symmetry. The spectrum shape is governed by the reciprocal vectors. And the higher is the symmetry order, the larger the peak efficiency. The results provide us with new insight into the unusual effect.

Tunable negative refractions in two-dimensional photonic crystals with superconductor constituents

In this paper, a two-dimensional square photonic crystal (PC) with superconductor cylinders is proposed to realize tunable negative refraction. Based on the dependence of the superconductors’ permittivity on temperatures, photonic band structures thus negative refraction could be tuned by temperatures, whereby the refractive angle could be scanned from positive to negative. The feasibility of the PC operating in infrared and visible regions was discussed. The tunability resulted from the lattice, superconductors, operating frequency, and incident angle may lead the PC to great promise in photoelectronics and superconductor electronic applications.

Piezoelectric–piezomagnetic multilayer with simultaneously negative permeability and permittivity

We study the propagation of an electromagnetic (EM) wave in piezoelectric–piezomagnetic multilayers, in which the incident EM wave excites high frequency acoustic waves and couples strongly with them through piezoelectric and piezomagnetic effects, creating dielectric polariton and magnetic polariton simultaneously. The dispersion abnormality appears at some frequency ranges where simultaneous negative permittivity and permeability can be achieved. Theoretical analysis and numerical simulation proved that this structure forms a kind of “left-handed” material.

Effect of electro-optic modulation on coupled quasi-phase-matched frequency conversion.

The electro-optic effect can be employed to modulate the refractive index of an optical superlattice. In coupled quasi-phase matched processes, this modulation will introduce quasi-phase mismatches and result in energy redistribution among the optical waves. Numerical results indicate that an efficient third harmonic in a periodic or quasi-periodic superlattice can be achieved by varying the external dc electric field. This method provides a simple and convenient way to control the efficiencies of frequency conversion.

Detection of defects on the surface of a semiconductor by terahertz surface plasmon polaritons.

We propose a new method for detecting small defects on the surface of a semiconductor by analyzing the transmission spectrum of terahertz surface plasmon polaritons. The field distributions caused by the detection of defects of different sizes are simulated. Experimentally, using a terahertz time domain spectrometer, we measure the transmission spectrum of terahertz surface plasmon polaritons passing through particles on the surface of an intrinsic InSb wafer. Our results show that the measured temporal waveform and frequency spectra are distinctly changed due to the presence of the particles, thereby confirming the effectiveness of this method for detecting defects. For increased detection efficiency, the frequency of the surface plasmon polaritons has to be slightly lower than the plasma frequency of the semiconductor. In comparison with traditional methods, our approach offers the merits of detecting both on-surface and subsurface defects, which is critical in monitoring the quality of semiconductor wafers.

Compact Spectrometer Based on a Frosted Glass

We demonstrate a spectrometer based on multiple interference and scattering in an ordinary frosted glass featuring random structures. The probe signal disperses through the frosted glass generating wavelength-dependent speckle patterns, which are detected by a charge coupled device chip and used to reconstruct the input spectrum after calibration. We consider an underdetermined system of linear equations as a model for signal spectrum estimation. Smoothing regularization algorithm is designed for solving the system of equations. Experimental results show that the reconstruction range of the spectrometer at least includes the entire visible band and some part of the ultraviolet band. In comparison with conventional miniature spectrometers, the frosted glass spectrometer consequently has the merits of static measurement, low cost, small size, high throughput, and wide spectral range, which may find applications in a wide range of applications.

Investigation of terahertz surface plasmon modulation with optical injection of free carriers

Abstract. Optical modulation of terahertz surface plasmon polaritons (THz SPPs) propagating in an intrinsic indium antimonide surface is demonstrated in this paper. The modulation is mediated by the modification of free carrier density with optical illumination. Simulation and experimental results show that a THz modulator can be realized by tuning the propagation lengths of THz SPPs, which could be controlled to be larger or shorter than the distance of two razor blades used for the coupling of the THz wave and the THz SPPs. In comparison with conventional THz modulation approaches, this method of manufacturing is simpler and the switching bandwidth is wider. The maximum modulation frequency of the modulators is anticipated to be above gigahertz, thus leading to the possibility of communication applications using the THz baseband.

Terahertz surface plasmon on semiconductor and thin dielectric surfaces

We theoretically study the properties of terahertz (THz) surface plasmon (SP) propagating on semiconductor and thin dielectric surfaces by employing numerical calculations. The results show that the major energy of THz SP can be confined in the thin film on the surface of an InSb semiconductor. At the same time, the magnetic field dispersion curves and absorption coefficients of the structures are studied. We find that the absorption coefficient is related to the permittivity of the dielectric films. Therefore, we can sensitively detect a thin dielectric sample by broadband terahertz spectroscopy.

Optical modulation of terahertz surface plasmon propagated on surfaces of semiconductors

Optical modulation of terahertz surface plasmon polaritons propagating in semiconductor surfaces is proposed in the paper. The maximum modulation frequency is estimated to be at GHz order.