A surface plasmon resonance sensor based on a multi-core photonic crystal fiber

A surface plasmon resonance(SPR) sensor based on a multi-core photonic crystal fiber(PCF) is presented in this paper.There is only one analyte channel positioned in the center of the PCF cross section,rather than several closely arranged analyte channels around the central core.So the design of this sensor not only reduces the consumption of gold and samples,but also effectively avoids the interference between neighboring analyte channels.Optical field distributions of this fiber at different wavelengths and the sensing properties of this sensor are theoretically analyzed and discussed using finite element method(FEM).Simulation results confirm that both the thickness of metallic layer and the fiber structural parameters have significant effect on sensing performance.The amplitude sensitivity of the sensor is found to be 1.74×10-5RIU,and the spectral sensitivity is 3300 nm/RIU,corresponding to a resolution of 3.03×10-5 RIU.Finally,in order to achieve PCF-SPR sensing characteristics,an experiment design scheme based on spectroscopic detection method is proposed.     

Concentration sensor based on a tilted fiber Bragg grating for anions monitoring

The ubiquity and importance of anions in many crucial roles accounts for the current high interest in the design and preparation of effective sensors for these species. Therefore, a tilted fiber Bragg grating sensor was fabricated to investigate individual detection of different anion concentrations in ethyl acetate, namely acetate, fluoride and chloride. The influence of the refractive index on the transmission spectrum of a tilted fiber Bragg grating was determined by developing a new demodulation method. This is based on the calculation of the standard deviation between the cladding modes of the transmission spectrum and its smoothing function. The standard deviation method was used to monitor concentrations of different anions. The sensor resolution obtained for the anion acetate, fluoride and chloride is 79 × 10⁻⁵ mol/dm³, 119 × 10⁻⁵ mol/dm³ and 78 × 10⁻⁵ mol/dm³, respectively, within the concentration range of (39–396) × 10⁻⁵ mol/dm³.     

基于氧化锡铟纳米薄膜的圆形晶格光子晶体光纤折射率传感器

为了实现近红外波段的高灵敏度传感,设计并研究了一种基于表面等离子体共振的光子晶体光纤(Surface Plasmon Resonance Photonic Crystal Fiber,SPR-PCF)折射率传感器.该光纤横截面的空气孔排列方式是圆形晶格,呈现出向 日葵形状.光纤包层的外壁淀积了氧化锡铟(Indium T...     

Scalable Microstructured Photoconductive Terahertz Emitters

The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed. Their large active area in the 1 – 100 mm² range allows for using the full power of state-of-the-art femtosecond lasers for excitation of charge carriers. Large fields for acceleration of the photogenerated carriers are achieved at moderate voltages by interdigitated electrodes. This results in efficient emission of single-cycle THz waves. THz field amplitudes in the range of 300 V/cm and 17 kV/cm are reached for excitation with 10 nJ pulses from Ti:sapphire oscillators and for excitation with 5 μJ pulses from amplified lasers, respectively. The corresponding efficiencies for conversion of near-infrared to THz radiation are 2.5 × 10^-4 (oscillator excitation) and 2 × 10^-3 (amplifier excitation). In this article the principle of operation of scalable emitters is explained and different technical realizations are described. We demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes. In particular emitters for linearly, radially and azimuthally polarized radiation are discussed. The success story of photoconductive THz emitters is closely linked to the development of mode-locked Ti:sapphire lasers. GaAs is an ideal photoconductive material for THz emitters excited with Ti:sapphire lasers, which are widely used in research laboratories. For many applications, especially in industrial environments, however, fiber-based lasers are strongly preferred due to their lower cost, compactness and extremely stable operation. Designing photoconductive emitters on InGaAs materials, which have a low enough energy gap for excitation with fiber lasers, is challenging due to the electrical properties of the materials. We discuss why the challenges are even larger for microstructured THz emitters as compared to conventional photoconductive antennas and present first results of emitters suitable for excitation with ytterbium-based fiber lasers. Furthermore an alternative concept, namely the lateral photo-Dember emitter, is presented. Due to the strong THz output scalable emitters are well suited for THz systems with fast data acquisition. Here the application of scalable emitters in THz spectrometers without mechanical delay stages, providing THz spectra with 1 GHz spectral resolution and a signal-to-noise ratio of 37 dB within 1 s, is presented. Finally a few highlight experiments with radiation from scalable THz emitters are reviewed. This includes a brief discussion of near-field microscopy experiments as well as an overview over gain studies of quantum-cascade lasers.     

Characterization of Hg0.7Cd0.3Te n- on p-type structures obtained by reactive ion etching induced p- to n conversion

This paper presents transport measurements on both vacancy doped and gold doped Hg_0.7Cd_0.3Te p-type epilayers grown by liquid phase epitaxy (LPE), with N_A=2×10¹⁶ cm⁻³, in which a thin 2 μm surface layer has been converted to n-type by a short reactive ion etching (RIE) process. Hall and resistivity measurements were performed on the n-on-p structures in van der Pauw configuration for the temperature range from 30 K to 400 K and magnetic field range up to 12 T. The experimental Hall coefficient and resistivity data has been analyzed using the quantitative mobility spectrum analysis procedure to extract the transport properties of each individual carrier contributing to the total conduction process. In both samples three distinct carrier species have been identified. For 77 K, the individual carrier species exhibited the following properties for the vacancy and Au-doped samples, respectively, holes associated with the unconverted p-type epilayer with p ≈ 2 × 10¹⁶ cm⁻³, μ ≈ 350 cm²V⁻¹s⁻¹, and p ≈ 6 × 10¹⁵ cm⁻³, μ ≈ 400 cm²V⁻¹s⁻¹; bulk electrons associated with the RIE converted region with n ≈ 3 × 10¹⁵cm⁻³, μ ≈ 4 × 10⁴ cm²V⁻¹s⁻¹, and n ≈ 1.5 × 10¹⁵ cm⁻³, μ ≈ 6 × 10⁴ cm²V⁻¹s⁻¹; and surface electrons (2D concentration) n ≈ 9 × 10¹² cm⁻² and n ≈ 1 × 10¹³ cm⁻², with mobility in the range 1.5 × 10³ cm²V⁻¹s⁻¹ to 1.5 × 10⁴ cm²V⁻¹s⁻¹ in both samples. The high mobility of bulk electrons in the RIE converted n-layer indicates that a diffusion process rather than damage induced conversion is responsible for the p-to-n conversion deep in the bulk. On the other hand, these results indicate that the surface electron mobility is affected by RIE induced damage in a very thin layer at the HgCdTe surface.     

基于PVDF的呼吸信号检测腰带研究

针对人体睡眠状态呼吸信号检测的重要性,基于聚偏氟乙烯(PVDF)的正压电效应,研制了一种呼吸信号检测装置。装置前端由PVDF压电薄膜和可伸缩腰带组成,为获得稳定的呼吸信号,在压电薄膜和腰带间引入弹性结构。针对传感器输出端呼吸信号提取,设计了高品质、灵活的信号处理电路。测试结果表明,该装置检测的呼吸信号波形以周期性形态呈现,稳定性好,满足实际检测需要。     

Time-independent mechanical and physical properties of the ternary 95.5Sn-3.9Ag-0.6Cu solder

The development of a constitutive model for predicting the thermal-mechanical fatigue (TMF) of 95.5Sn-3.9Ag-0.6Cu (wt.%) Pb-free solder interconnects requires the measurement of time-independent mechanical and physical properties. Yield stress was measured over the temperature range of −25–160°C using strain rates of 4.2 × 10⁻⁵ s⁻¹ and 8.3 × 10⁻⁴ s⁻¹. The yield-stress values ranged from approximately 40 MPa at −25°C to 10 MPa at 160°C for tests performed at 4.2 × 10⁻⁵ s⁻¹. The faster strain rate and specimen aging had a limited impact on the yield stress. The true stress/true strain curves indicated that dynamic-recovery and dynamic-recrystallization processes took place in as-cast samples exposed to temperatures of 125°C and 160°C, respectively, while tested at a strain rate of 4.2 × 10⁻⁵ s⁻¹. Aging the sample prior to testing, as well as a faster strain rate, mitigated both phenomena. Dynamic Young’s modulus values ranged from 55 GPa at −50°C to 35 GPa at 200°C, while the coefficient of thermal expansion (CTE) increased from approximately 12 × 10⁻⁶°C⁻¹ to 24 × 10⁻⁶°C⁻¹ for the same temperature range. The aging treatment had little effect on either Young’s modulus or the CTE.     

Indium-tin oxide/Si contacts with In- and Sn-diffusion barriers in polycrystalline Si thin-film transistor liquid-crystal displays

Indium and tin were used as the diffusion barrier between indium-tin oxide (ITO) and polycrystalline-silicon layers to reduce the contact resistance. The ITO/Si contacts may be adopted in thin-film transistor liquid-crystal displays (TFT-LCD) to reduce the number of fabrication steps. With In and Sn layers, contact-resistance values of 5 × 10⁻³−4×10⁻³ Ωcm² were obtained. These values were higher than those of the conventional ITO/Mo/Al/Si contacts (3×10⁻⁵−4 × 10⁻⁴ Ωcm²) but lower than the values obtained from ITO/Si contacts (about 1×10⁻² Ωcm²). The Sn was stable after annealing, but In diffused into Si and lost its function as the diffusion barrier.     

Irradiation damages in electron beam lithography

 The irradiation damages in the electron beam lithography(EBL)to Al-gate MOS capacitors in the ranges of 10—30keV and 10~(-6)—10~(-3)C·cm~(-2) and the effects of annealing on damages at low temperature(<500℃)are given.The research on damages caused by high electron energy(30keV) and ultra-high dosages(10~(-4)—10~(-3) C·cm~(-2))is important and useful to the EBL.The resolution can be improved by high electron energy.Both the EBL with vapor-development and without development are all operated at ultra-high dosages.After irradiations,the concentrations of inter- face states can increase by about one to two orders of magnitude and the flat-band voltages by about a few to more than ten volts.Under constant exposure dosages,the fiat-band voltages are independent of the changes of electron energies in certain energy ranges.Under constant electron energies the concentrations of interface states are independent of the changes of exposure dosages in certain dosage ranges.After annealing,the flat-band voltages can recover the values before the irradiations for energies and dosages in the ranges of 10—30keV and 1×10~(-6)—6×10~(-3)C·cm~(-2) respectively.The interface state concentrations due to the damages of ultra dosages can not be removed completely.     

Study of interface traps from transient photoconductive decay measurements in passivated HgCdTe

Generation-recombination (g-r) processes in the passivant/HgCdTe interface region are shown to complicate the transient photoconductive (PC) decays. Anomalous PC decays showing delayed peaks are observed and modeled for the first time. These peaks are correlated with the electron and hole traps in the interface region. Activation energy and density of the electron traps in the anodic oxide/n-Hg_0.78Cd_0.22Te interface region are estimated to be 12 meV and 1.1×10¹⁰ cm⁻², respectively. Density of hole traps is estimated to be 2.4×10¹⁰ cm⁻².     

Variable area MWIR diodes on HgCdTe/Si grown by molecular beam epitaxy

Molecular beam epitaxy technique has been used to grow double layer heterostructure mercury cadmium telluride materials on silicon substrates for infrared detection in the mid-wavelength infrared transmission band. Test structures containing square diodes with variable areas from 5.76 × 10⁻⁶ cm² to 2.5×10⁻³ cm² are fabricated on them. The p on n planar architecture is achieved by selective arsenic ion implantation. The absorber layer characteristics for the samples studied here include a full width at half maximum of 100–120 arcsec from x-ray rocking curve, the electron concentration of 1−2 × 10¹⁵ cm⁻³ and mobility 3−5 × 10⁴ cm²/V-s, respectively at 80 K from Hall measurements. The minority carrier lifetime measured by photoconductive decay measurements at 80 K varied from 1 to 1.2 μsec. A modified general model for the variable area I–V analysis is presented. The dark current-voltage measurements were carried out at 80 K and an analysis of the dependence of zero-bias impedance on the perimeter/area ratio based on bulk, surface generation-recombination, and lateral currents are presented. The results indicate state-of-the art performance of the diodes in the midwavelength infrared region.     

Nickel Ohmic Contacts to N-Implanted (0001) 4H-SiC

Samples for transmission line model (TLM) and Hall measurements were fabricated on (0001) 4H-SiC implanted with nitrogen at 1 × 10¹⁸ cm⁻³, 4 × 10¹⁸ cm⁻³, 1 × 10¹⁹ cm⁻³, 4 × 10¹⁹ cm⁻³, and 1 × 10²⁰ cm⁻³. Following high-temperature activation, the activation percentage dropped from ~90% to ~20%, and the Hall mobility decreased from ~100 cm²/V · s to ~20 cm²/V · s as the implant concentration increased from 1 × 10¹⁸ cm⁻³ to 1 × 10²⁰ cm⁻³. The specific contact resistance as a function of Hall concentration is compared with published data for Ni contacts to epitaxial layers. The specific contact resistance as a function of activation temperature was also studied for two fixed implant concentrations of 5 × 10¹⁸ cm⁻³ and 1 × 10²⁰ cm⁻³.     

Modification of the diamond film electrode with photochemistry for phenol degradation

The degradation of phenols has become urgent issues. In this paper, the diamond film electrode modified by photochemistry is chosen as the research object for phenol degradation. The boron-doped diamond films, which are modified and unmodified, are characterized by the X-ray photoelectron spectroscopy (XPS). Cyclic voltammograms are used to test the electrochemical window. It is found that the current value of tantalum/boron-doped diamond (Ta/BDD) electrode with amino modification increases two orders of magnitude in degrading the nitro-phenol, when the amino-modified rate is only 1.9%. The current value is enhanced from −4.0 × 10⁻⁴A-4.0 × 10⁻⁴ A to −4.0 × 10⁻²A-4.0 × 10⁻²A. In addition, in order to understand the excellent characteristics of Ta/BDD electrode modified by photochemistry for phenol degradation, the efficiency of degradation is also discussed.     

Zn-doping in OMVPE Grown lnP:Zn/lnGaAs/lnPp-i-n double heterojunctlons with lnGaAs:Zn contacting layers

We report on the control of zinc in organometallic vapor phase epitaxial (OMVPE) grown InP:Zn/InGaAs/InPp- i- n double heterojunctions with InGaAs:Zn contacting layers. As a function of diethylzinc (DEZn) flow, we measure net acceptor concentrations for the InP:Zn p-layer in the range 2 × 10¹⁷≤N _a−N _d≤ 9 × 10¹⁷ cm⁻³. A 435°C post-growth anneal for 300 sec increases the net acceptor concentrations by a factor of 3.6 − to 6 × 10¹⁷≤N _a−N _d≤ 3 × 10¹⁸ cm⁻³. When the annealed value ofN _a − N_din the InP:Zn layer is 6 × 10¹⁷ cm⁻³ , secondary ion mass spectrometry (SIMS) measurements show abrupt Zn-doping transitions at the heterojunction interfaces. In contrast, when the annealed value ofN _a − N_din the InP:Zn layer is near the saturation value of 3 × 10¹⁸ cm⁻³, SIMS measurements show significant movement of Zn into the nominally undoped InGaAs instrinsic layer. Increasedp-i-n diode capacitance is associated with the Zn movement.     

Intense Terahertz Radiation from InAs Thin Films

Terahertz (THz) radiation from InAs thin films grown by molecular-beam epitaxy on closely lattice-matched p-type GaSb (100) substrates and lattice-mismatched semi-insulating GaAs (100) substrates was investigated. The THz radiation intensity was measured from InAs films with thicknesses between 100 nm and 1.5 μm excited by a femtosecond laser pulse with a wavelength of approximately 780 nm. The radiation intensity increased as the InAs film thickness increased and it exceeded that from a bulk n-type InAs substrate with an electron concentration of 2.3 × 10¹⁶ cm⁻³ when the InAs film thickness was greater than about 500 nm. In addition, the THz intensity from a 1-μm-thick InAs film was greater than that from a bulk p-type InAs substrate. We ascribe this enhanced THz intensity to the wave reflected from the lower interface between the InAs film and the layer grown beneath it. We confirmed this by observing an increased pulse width due to constructive overlap of the reflected wave. The results demonstrate that InAs thin films are promising materials for THz emitting devices.     

Printable Ferroelectric PVDF/PMMA Blend Films with Ultralow Roughness for Low Voltage Non‐Volatile Polymer Memory

Here, a facile route to fabricate thin ferroelectric poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) blend films with very low surface roughness based on spin‐coating and subsequent melt‐quenching is described. Amorphous PMMA in a blend film effectively retards the rapid crystallization of PVDF upon quenching, giving rise to a thin and flat ferroelectric film with nanometer scale β‐type PVDF crystals. The still, flat interfaces of the blend film with metal electrode and/or an organic semi‐conducting channel layer enable fabrication of a highly reliable ferroelectric capacitor and transistor memory unit operating at voltages as low as 15 V. For instance, with a TIPS‐pentacene single crystal as an active semi‐conducting layer, a flexible ferroelectric field effect transistor shows a clockwise I–V hysteresis with a drain current bistability of 10³ and data retention time of more than 15 h at ±15 V gate voltage. Furthermore, the robust interfacial homogeneity of the ferroelectric film is highly beneficial for transfer printing in which arrays of metal/ferroelectric/metal micro‐capacitors are developed over a large area with well defined edge sharpness.     

Performance of pentacene-based organic field effect transistors using different polymer gate dielectrics

Pentacene-based organic field effect transistors（OFETs） are fabricated using poly（methyl methacrylate）（PMMA） and polyimide（PI） as gate dielectrics,respectively.The fabricated OFETs exhibit reasonable device characteristics.The field-effect mobility,threshold voltage,and on/off current radio are determined to be 3.214 ×10^-2 cm^2 /Vs,-28 V,and 1 ×10^3 respectively for OFETs with PMMA as gate dielectrics,and 7.306×10^-3cm^2 /Vs,-21 V,and 2 ×10^2 for OFETs with PI.Furthermore,the dielectric properties of gate insulator layer are tested and the dipole effect at the semiconductor/dielectrics interface is also analyzed by a model of energy level diagram.     

Passivation of infrared photodiodes with alcoholic sulfide solution

The effect of passivation with the solution of sodium sulfide (Na₂S) in isopropyl alcohol on the room-temperature performance of the GaInAsSb/GaAlAsSb and InAs/InAsSbP photodiodes is investigated. After such a treatment the dark current density of the GaInAsSb/GaAlAsSb photodiodes at a reverse bias of 0.1 V is reduced from 5.5 × 10⁻² to 2.1 × 10⁻³ A/cm² and a zero-bias resistance-area product (R ₀ A) is improved from 1.0 to 25.6 Ω cm². For the InAs/InAsSbP photodiodes, the dark current density at U = −0.1 V is decreased from 1.34 to 8.1 × 10⁻¹ A/cm², while the R ₀ A value increases from 4.4 × 10⁻² to 7.3 × 10⁻² Ω cm². The method offers long-term stability of the photodiode performance.     

Effect of barrier layers on BaTiO3 thin film capacitors on Si substrates

The choice of the bottom electrode or barrier layer plays an important role in determining the electrical and structural properties of metal/ferroelectric/metal thin film capacitors. A substantial improvement of the electrical and structural properties of the capacitors was found by using RuO₂ as a bottom electrode. Electrical measurement on a capacitor with a structure of BaTiO₃(246 nm)/RuO₂ (200 nm)/SiO₂/Si, where the BaTiO₃ thin film was deposited at room temperature, showed a dielectric constant of around 15, leakage current density of 1.6 × 10⁻⁷A/cm² at 4 V, a dc conductivity of 9.8 × 10¹⁴S/cm, and a capacitance per unit area of 5.6 × 10⁴pF/cm². A similar structure but with polycrystalline BaTiO³ (273 nm) as the dielectric deposited at 680°C showed a dielectric constant of 290, leakage current density of 1.7 × 10⁻³A/cm² at 4 V, a dc conductivity of 1.2 × 10⁻⁸ S/cm, and a capacitance per unit area of 9.4 × 10⁵ pF/cm². Scanning electron microscopy analysis on the films showed differences in the microstructure due to the use of different bottom electrode materials, such as RuO₂ or Pd.     

Pd/Sb(Zn) and Pd/Ge(Zn) ohmic contacts on p-type indium gallium arsenide: The employment of the solid phase regrowth principle to achieve optimum electrical and metallurgical properties

The development of two metallizations based on the solid-phase regrowth principle is presented, namely Pd/Sb(Zn) and Pd/Ge(Zn) on moderately doped In_0.53Ga_0.47As (p=4×10¹⁸ cm⁻³). Contact resistivities of 2–3×10⁻⁷ and 6–7×10⁻⁷ Ωcm², respectively, have been achieved, where both systems exhibit an effective contact reaction depth of zero and a Zn diffusion depth below 50 nm. Exhibiting resistivities equivalent to the lowest values of Au-based systems in this doping range, especially Pd/Sb(Zn) contacts are superior to them concerning metallurgical stability and contact penetration. Both metallizations have been successfully applied for contacting the base layer of InP/In_0.53Ga_0.47As heterojunction bipolar transistors.