Zongming Bao

A MEMS IR thermal source for NDIR gas sensors

A MEMS thermal emitter based on heating thin film resistors has been studied for the MEMS infrared gas sensor as an infrared (IR) source. The IR source, with an effective emitting area of 1.6 times 1.6 mm2, is fabricated using heated platinum thin film resistors deposited on a Si3N4/Si02 membrane. IR radiation power of the emitter is up to 60mW with the effective blackbody temperature ranged from 300 to 850K. Moreover, it has very good dynamic parameters a modulation frequency as high as 100Hz and a response time of 23ms. The properties of the source demonstrate the potential applications to meet the performance, size and low-cost requirements of the mass market

Transmission enhancement properties of double-layered metallic hole arrays

We report experimental results on enhanced light transmission through double-layered (Ag/Au) metallic hole arrays within a skin-depth. Zero-order transmission spectrums are characterized as a function of Ag films thickness, which extends from \delta/15, \delta/6 to approximately \delta, where \delta is a skin-depth. In contrast with other reported results (Refs.[11-13]) in single-layered metallic hole arrays, our experimental results show much more dramatic properties of transmission process dependent on sub- thickness. It is shown that there is no negligible transmission enhancement at \delta/16. At \delta/6, much higher transmission efficiency can be achieved. With films thickness being close to \delta, the transmission efficiency declines contrarily. Simultaneously, the corresponding resonant peak also slightly moves toward the shorter wavelength. It is proposed that the coupling of surface plasmon polaritons (SPPs) at Ag/Au interface within is involved in the process.

A novel NDIR CO 2 sensor using a mid-IR hollow fiber as a gas cell

A novel CO2 non-dispersive infrared (NDIR) sensor using the mid-infrared (mid-IR) hollow fiber as a gas cell has been demonstrated. The mid-IR hollow fiber is chosen for its optimum transmission band (bandgap) overlap with CO2 fundamental absorption spectrum around 4.26 µm to serve as a filter. A comparison with the system using a smooth metal cell is presented. The signal noise suggests that a measurement resolution better than 5 ppm concentration is achievable using this mid-IR hollow fiber. The response time of the system using hollow fiber can be in the order of shorter than 10s with the sensitivity of 1.82 mv/ppm.

Effect of the ratio of hole radius to lattice spacing on transmission characteristics for metal/dielectric photonic crystal

In this work, the effect of the ratio of hole radius to lattice spacing (r/a0) on transmission characteristics for the metal/dielectric photonic crystal (MDPC) is investigated. The relationship between the photonic band gap (PBG) dependent on r/a0 is discussed. This is because the characteristics of the PBG dependent on r/a0 affect transmission characteristics for MDPC. The plane wave method (PWM) is used to simulate the PBG by changing r/a0 from 0.2 to 0.3. For hexagonal arrays, we find that with r/a0 being 0.25, the desired PBG structure is achieved. The experimental study for hexagonal air holes arrays residing in the Au@SiO2@Si structure by changing r/a0 from 0.2 to 0.3 is presented. The result shows that with r/a0 being 0.25, a narrow bandwidth and high efficiency transmission is achieved. It is demonstrated that the distinct effect of r/a0 on transmission characteristics for MDPC structure.

Enhanced middle-infrared light transmission through Au/SiO x N y /Au aperture arrays

The enhanced middle-infrared light transmission through Au/SiO x N y /Au aperture arrays by changing the refractive index and the thickness of a dielectric layer was studied experimentally. The results indicated that the transmission spectrum was highly dependent on the refractive index and the thickness of SiO x N y . We found that the transmission peaks redshifted regularly along with the refractive index from 1.6 to 1.8, owing to the role of surface plasmon polaritons (SPP) coupling in the Au/SiO x N y /Au cascaded structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO 2.1 N 0.3 /Au cascaded structure with small refractive index (1.6) than in Au/ SiO 0.6 N1/Au cascaded structure with large refractive index (1.8). When the thickness of SiO x N y changes from 0.2 to 0.4 µm, the shape of transmission spectrum exhibits a large change. It was found that a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO x N y /Au cascaded structure with a thin dielectric film (0.2 µm), with the increase of SiO x N y films thickness, the transmission peak gradually widened and disappeared finally. This effect is useful in applications of biochemical sensing and tunable integrated plasmonic devices in the middle-infrared region.

Tunable photonic crystals based on photoinduced deformations of crosslinked liquid-crystalline polymers

A novel tunable three-dimensional (3D) photonic crystals is demonstrated based on the photoinduced deformation of the azobenzene crosslinked liquid-crystalline polymers(CLCPs). A nanoimprinting approach is utilized to create a robust CLCPs 3D photonic crystal structure. The dynamical modulated performance of the photonic crystals induced by ultraviolet and visible are measured and analyzed. It is shown that the tunable photonic crystals is reversible and stable.

Effect of refractive index of dielectric on transmission properties for metal/dielectric/metal photonic crystal

The effect of refractive index of dielectric on transmission properties for metal/dielectric/metal photonic crystal (M/D/MPhC) by changing a thin dielectric layer was studied experimentally. We measured zero-order transmission spectra of three different M/D/MPhC samples in the middle-infrared region and found that the transmission peaks shifted regularly along with the refractive index change, owing to the role of surface plasmon polaritons (SPP) coupling in the M/D/MPhC. The position of transmission peak for M/D/MPhC is not only determined by the periodic structure on top Au film but is also affected by the refractive index of intermediate dielectric. By analyzing the relationship between transmission peaks and effective refractive index of a thin dielectric layer sandwiched by two gold layers, we find that the transmission properties for M/D/MPhC depend strongly on both the material property and the refractive index of dielectric being sandwiched by two metal films. The transmission peak sensitive nature to the refractive index of a thin dielectric layer in M/D/MPhC is promising in applications of biochemical sensing and tunable integrated plasmonic devices.

Study of the heavy metal gettering effect of porous silicon on SOI structure

Gettering of copper and nickel in FIPOS SOI structures has been investigated using XTEM and SIMS for the first time in this paper. A transition region with dendrite porous oxidized Si exists at the interface between the Si oxidized porous layer (PS) and the substrate Si. This transition region may provide effective gettering sites for Cu and Ni which can diffuse from the top Si layer to the substrate during the SOI formation. In addition, Cu segregates to the transition region more readily.