Systematic study of magnetron sputtered silver-indium tin oxide (Ag-ITO) composite films has been carried out by altering the atomic ratio of silver in the co-sputtered films. The optimal micro-structure characteristic with smooth surface and tight junction between silver and ITO particles could be obtained by tuning Ag atomic ratio. Spectroscopic ellipsometry is applied in order to evaluate the plasmonic properties. Real and imaginary permittivity of the films are retrieved utilizing Drude-Lorentz dispersion model. The cross-over wavelength of the films, optimized to as low as around 1130 nm, exhibits high adjustability on the ratio of silver material and RTP process. Much lower imaginary permittivity as well as tunable real permittivity suggest the potentiality of Ag-ITO composite films as substituted plasmonic materials in the near-infrared region.
Transparent conductive oxides (TCOs, such as Sn:In2O3, Al:ZnO, Ga: ZnO et al) have re-drawn people’s attention as alternative candidates of noble metals (particularly Ag or Au) in the field of plasmonic for the reasons of property tunable and low losses et al. However even for Sn:In2O3 (ITO, reported highest conductivity), the metallic property lies in the near infrared (NIR) range exhibiting the real part permittivity ɛ' was around -3 at communication wavelength of 1.55μm. Under this circumstance, surface plasma polaritons (SPPs) was hard to be exited on the interface between ITO and surrounded dielectric materials with large permittivity. Hence, in order to explore the potential use of TCOs in the applications of silicon photonics (for permittivity of silicon and germanium are 11.6 and 16 at 300K, respectively), we design a hybrid structure of ITO/metal or ITO/metal/ITO as surface plasmonic materials in NIR. The electrical and optical property of hybrid structure was manipulated accordingly by changing the portion of the introduced metal while maintaining a lower loss than bare metals. The highest carrier concentration of the hybrid structure reached 3×10^22cm^-3, definitely the same magnitude of noble metals. Magnetron sputtering and atomic layer deposition (ALD) can be used to deposit the hybrid ITO/metal structure, in which metal represents gold (Au), and iridium (Ir). The normalized radiative decay rate of light emitted by germanium quantum dots reaches a maximum enhancement of ~8-fold with the assistance of ITO/metal hybrid structure according to the finite difference time domain (FDTD) simulation.
Based on the model of microcavity theory and transfer matrix theory, we measured the influence of complex cathode by introducing dielectric layer. Dielectric layer greatly influence the property of microcavity. Complex cathode may have obvious improvement to the trait of microcavity. Both in the instances considering microcavity effect and not considering, we compared the reflectivity, phase of reflection and light outcoupling efficiency of complex cathode with that of single layer metal cathode. To make the model simple, we do not consider complicated effect induced by interface absorbance and combination, we got the greatest improvement to outcoupling efficiency at certain instance. The efficiency of optimum structure is twelve times higher than that of single metal layer cathode. This confirms that dielectric layer can be used to improve the performance of organic metal cavity devices. Based on this kind of structure, unsymmetrical metal may reach great application.
Highly oriented ferroelectric strontium barium niobate (Sr0.6Ba0.4Nb2O6) thin films were prepared on P-type Si(100) substrate by the Sol-Gel process. The XRD patterns of the SBN films show that SBN film prepared by using NbCl5, KOH as raw materials performed a highly c-axis preferred orientation perpendicular to the Si substrate, better than films that was prepared using Nb(OC2H5)5 as starting agents. It may be duo to the existence of the potassium ion that not be filtered out completely during the preparation of the niobium alkoxide. The characteristics of D-F and C-V curves were obtained for SBN/Si film. The film exhibits high dielectric constant. In order to investigate ferroelectric characteristics further, the P-E loops of the SBN/Pt/Si were also measured. The films show better optical properties, transmittance of Sr0.6Ba0.4Nb2O6 films on MgO(001) and SiO2 substrates was more than 60% at the range from 450 to 850nm, refractive index was measured to be 2.14 and 2.12 on the MgO and SiO2 substrate at 633nm respectively.
ZnO were deposited on sapphire and silicon substrates by RF magnetron sputtering from a metallic zinc target. The structural and optical propertied of ZnO films were studied by X-ray diffraction, and UV-VIS-NIR scanning spectrophotometer. XRD measurements show ZnO films had a preferential orientation along the c-axis. Only one peak, (002) phase, appears on the diffraction spectra. The transmittance spectra indicate that ZnO films possessed a transmittance of about 80% in the visible region and a sharp absorption edge at wavelength of about 390nm. The refractive index n and the extinction coefficient k are all sensitive to the oxygen partial pressure and the substrate temperature. Furthermore, based on the ideal five layers symmetrical waveguide films, the relationships of the loss and the thickness of the waveguide layer and the buffer layer were analyzed using ZnO as waveguide layer and SiO2 as buffer layer.
Dense and crack-free SBN thin films with the preferred c-axis orientation were successfully fabricated by the sol-gel method on Si(100) substrates with a MgO buffer layer. It was found that introducing the MgO buffer layer could effectively promote the formation of TTB SBN phase from SN and BN phases at lower temperature. Effects of annealing temperature and thickness of MgO buffer layer on the structural and morphological properties of SBN thin films were investigated. The SBN film with MgO buffer layer showed excellent epitaxy and densely packed grain morphology. The capacitance-voltage (C-V) properties of SBN films deposited on silicon substrates were found completely different from those of the films deposited on MgO-buffered silicon substrates, the C-V curves of SBN/Si films and SBN/MgO/Si films represent typical shapes of asymmetric and butterfly, respectively, indicating the improvement of the electrical properties and ferroelectric properties of the SBN films by introducing the MgO buffer layer.
Microcavity structures are widely utilized as resonators in many optoelectronic devices to improve their optical performance. We present an analytic approach to study the angle-dependent properties in active microcavities with dielectric Bragg reflectors. Based on the hard mirror (HM) model and paraxial propagation approximation, the angle dependent resonance properties can be expressed analytically in virtue of the cavity parameters and incident angle. Making use of these expressions, we found both the position of the active layer and the configuration of dielectric Bragg mirrors contribute to the angular characteristics of resonance in the active microcavity. The varying trend of the standing wave effect, intracavity electrical field and the degradation of quantum efficiency due to different incident angle are discussed in detail. It's found that there exists an optimal cavity configuration where the enhanced intracavity resonance can keep high value within a broader incidence range. Then further performance optimization of the whole devices can be performed.
Soluble poly(phenylene vinylene)(PPV)-type polymers have been applied widely as active layers in many optoelectronic devices, such as light-emitting diodes and organic lasers. In such devices their physical thickness are commonly about 100~200 nanometers for the desirable charge transport characteristics and optical interference effects. In this work, poly[(2-methoxy,5-octoxy) 1,4-phenylenevinylene] (MO-PPV) thin films have been prepared from their chloroform solutions of different concentrations. Then their UV-VIS absorption (Abs), photoluminescence (PL) and selective-excitation photoluminescence (SEPL) spectra have been measured at room temperature. A long wavelength emission component near 630 nm has been identified as S2→S0 vibronic band through gaussian decomposition method and confirmed by experiments. The effect of annealing on the optical properties of MO-PPV thin films is also studied. The results show that there exists an optimal treatment temperature under which the maximal excitation intensity can arrive. It can be attributed to the different morphologies in films. In addition, an experimental research about the active polymer photonic well structures of MO-PPV/PMMA pairs has been carried out.
A novel micro fluid oscillator with a boron diffused resistor is proposed in this paper. The actuation principle is based on the combination of Marangoni effect. The contemporary microfabrication technique enables us to fabricate microheater tiny enough to control temperature so quickly and precisely in micro length scale. The devices exhibiting the Marangoni effect in square channels were designed and fabricated from one silicon substrate and two quartz substrates. And the three substrates were aligned, bonded and packaged for testing. In this actuator there is a pair of micro-heaters to produce a thermal gradient along the slit. The driving wattage is about 0.1W and the resistors can make a temperature difference about 100 degrees during 0.1s with a pulsewidth of 20us for 0.1A current pulses. Then the movement is driven towards the lower temperature direction by the interfacial tension of the air-liquid interface. This micro fluid actuator can play important role in many liquid micro-systems such as in micromotor and micro valve.
Graded refractive index Silicon Oxy-nitride thin films were deposited by RF magnetron reactive sputtering at different N2/O2 flow ratio. The effects of gas flow ratio on the refractive index, extinction coefficient and composition were studied using UV-VIS spectrophotometer, XPS and FTIR characterization methods. A simple and accurate method is presented for determination of the optical constants and physical thickness of thin films. Which was consisted in fitting the experimental transmission curve with the help of the physical model. The relationship between composition and optical gap and dispersion energy was analyzed using Wemple DiDomenico single-oscillator model. As a result, the samples’ refractive index can be controlled from 1.92 to 1.46 by adjusting the gas flow ratio, and the optical gap lies between 5eV~6.5eV.
Novel organic light-emitting diodes (OLEDs) using polymidy, fluorene-based cardo perylere polyimide (PFB5) were fabricated. EL properties of single-layer light-emitting diodes (LED) of indium-tin-oxide (ITO)/PFB5+/Al and ITO/PFB5+PBD/Al and multi-layer devices of ITO/PFB5/PBD/Al,ITO/PFB5/Alq/Al were characterized. In the pure PFB5 single layer device, the EL spectrum has a broad band and the peak wavelenght at 420nm, 450nm, and 545nm respectively. However, the EL emission fromthe single layer deviec of PFB5 blend PBD or multi-layer devices has the greatly narrow band and the peak wavelength at 545nm. Furthermore, the EL efficiency is improved significantly in these EL devices.
Semiconducting ferroelectric antimony sulphoiodide (SbSI) microcrystallite doped organically modified TiO2 thin films were successfully fabricated with the sol-gel process. Ferroelectric SbSI crystallites have some attractive properties, including high dielectric permittivity, high electro-optical coefficient and high photoconductivity. SbSI is also an intrinsic semiconductor with a relatively narrow eneryg gap. The Bohr radius of the SbSI crystal was calculated larger than other semiconductors due to its large dielectric constant. If the crystal size is smaller than its Bohr radius and the microcrystallite are dispersed in a suitable matrix, a dramatic improvement of the nonlinear three-order nonlinearity will be achieved due to the quantum confinement effect. The SbSI quantum dot composites were proved to be good candidates for nonlinear and electro-optical devices. Glycidopropyltrimetroxysilane modified TiO2 was chosen as the matrix and SbSI was synthesized in situ by using SbI3, SC(NH2)2. The materials in thin film were heat-treated in different conditions and the size of the microcrystallite was characterized by the XRD. A value of 3.5pm/V of effective transverse electro-optical coefficient reff for the nano-composite containing 8 wt percent of antimony sulfide iodide was measured. The third-order nonlinear optical susceptibility of the SbSI quantum dot thin film was measured by degenerate four-wave mixing at 532nm using a frequency double Nd:YAG laser beams with a pulse width of around 10ns, the x(3) value of 3 μm sample was measured to be 6 × 10-11 esu.
The Bi2S3 microcrystallite doped thin films and glass lumps have been successfully prepared by the sol-gel process, the size of the microcrystallite in glass heated for different times at 400 degree(s)C was decided by the method of HRTEM. The optical transmission valley shifted towards longer wavelengths with longer heat-treatment time at 500 degree(s)C in the Bi2S3 doped thin films, showing the experimental evidence of quantum size effects. The red-shift of emission peaks in luminescence spectrum excited with longer wavelength is attributed to the broad distribution of particle size in Bi2S3 doped glass. The nonlinear refractive index of the Bi2S3 quantum dots glass which is studied by the method of Z- scan gives n2 equals 3.3089 X 10-9 esu. The optical second generation (SHG) of the Bi2S3-doped glass also is observed using a Nd:YAG colliding mode locked laser.
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