Comparison of two different carbon nanotube-based surfaces with respect to potassium ferricyanide electrochemistry

This paper describes the electrochemical investigation of two multi-walled carbon nanotube-based electrodes using potassium ferricyanide as a benchmark redox system. Carbon nanotubes were fabricated by chemical vapor deposition on silicon wafer with camphor and ferrocene as precursors. Vertically-aligned as well as islands of horizontally-randomly-oriented carbon nanotubes were obtained by varying the growth parameters. Cyclic voltammetry was the employed method for this electrochemical study. Vertical nanotubes showed a slightly higher kinetic. Regarding the sensing parameters we found a sensitivity for vertical nanotubes almost equal to the sensitivity obtained with horizontally/randomly oriented nanotubes (71.5 ± 0.3 μA/(mM cm²) and 62.8 ± 0.3 μA/(mM cm²), respectively). In addition, values of detection limit are of the same order of magnitude. Although tip contribution to electron emission has been shown to be greatly larger than the lateral contribution on single carbon nanotubes per unit area, the new findings reported in this paper demonstrate that the global effects of nanotube surface on potassium ferricyanide electrochemistry are comparable for these two types of nanostructured surfaces.     

Improvement of R0A product of type-II InAs/GaSb superlattice MWIR/LWIR photodiodes

The effects of atomic hydrogen and polyimide passivation on R₀A product of type-II InAs/GaSb superlattice photo detectors for cut-off wavelength of both 6.5 μm and 12 μm were investigated. Low temperature current–voltage measurement shows that the use of atomic hydrogen during molecular beam epitaxy growth can improve R₀A product by 260% for 6.5 μm cut-off superlattice diodes and by 50% for 12 μm cut-off ones. The R₀A product of polyimide-passivated diodes with 12 μm cut-off is about 80% higher than those un-passivated ones. Wannier–Stark oscillations at higher reverse bias were observed for polyimide-passivated superlattice diodes with 12 μm cut-off. No Wannier–Stark oscillations were observed for un-passivated superlattice diodes, indicating that surface leakage current dominates in un-passivated diodes, while intrinsic dark current mechanisms such as tunneling and diffusion current dominate in polyimide-passivated diodes.     

High operating temperature SWIR p+–n FPA based on MBE-grown HgCdTe/Si(0 1 3)

The characteristics of SWIR (1.6–3 μm) 320 × 256 and 1024 × 1024 focal plane arrays (FPA’s) based on n-type In-doped HgCdTe heteroepitaxial layers are reported. The HgCdTe layers were grown by molecular beam epitaxy on silicon substrates with ZnTe and CdTe buffer layers. p–n junctions were formed by arsenic ion implantation into HgCdTe film. Reverse current in the temperature range from 210 to 330 K was found to be limited by the diffusion mechanism. At the same time in the temperature range from 140 to 210 K the reverse current was dominated by the thermal generation of charge carriers through deep traps located in the middle of the band gap. At 170 K NETD was less than 40 mK.     

Fabry–Pérot cavities based on chemical etching for high temperature and strain measurement

In this paper, two hybrid multimode/single mode fiber Fabry–Pérot (FP) cavities were compared. The cavities fabricated by chemical etching are presented as high temperature and strain sensors. In order to produce this FP cavity a single mode fiber was spliced to a graded index multimode fiber with 62.5 μm core diameter. The Fabry–Pérot cavities were tested as a high temperature sensor in the range between room temperature and 700 °C and as strain sensors. A reversible shift of the interferometric peaks with temperature allowed to estimate a sensitivity of 0.75 ± 0.03 pm/°C and 0.98 ± 0.04 pm/°C for the sensor A and B respectively. For strain measurement sensor A demonstrated a sensitivity of 1.85 ± 0.07 pm/μ? and sensor B showed a sensitivity of 3.14 ± 0.05 pm/μ?. The sensors demonstrated the feasibility of low cost fiber optic sensors for high temperature and strain.     

Bactericidal effects of negative and positive ions generated in nitrogen on Escherichia coli

The bactericidal effect of both negative and positive ions generated by a dc electrical corona in nitrogen were investigated. Tryptic soy broth agar plates inoculated with Escherichia coli (E. coli) (strain DH5-α) were placed into a custom-built multi-point-to-plane ion generator situated within a glass chamber. Under a nitrogen atmosphere the plates were exposed to either negative or positive ions for various time periods. The plates were then removed and incubated at 37°C for 15 h and the colonies counted. Exposure to either negative or positive ions produced significant reductions (p<0.05) in colony number. Bacterial plates exposed to a constant 200 μA negative current for 30 min demonstrated a 65% reduction in colony number compared to unexposed plates. Increasing the exposure current to 400 μA, further increased the level of disinfection at 30 min to 91%. Exposure to 200 μA current of positive ions produced a 72% reduction after 10 min and virtual sterilisation after 30 min with a 98% reduction in colony number. These results indicate that exposure to negative and particularly positive ions has a lethal effect on E. coli cells. Cell death could be due to a physiological change in the outer membrane as a result of ionic interactions.     

Estimation of martensite feature size in a low-carbon alloy steel by microtexture analysis of boundaries

A methodology for classifying the hierarchy of martensite boundaries from the EBSD microtexture data of low-carbon steel is presented. Quaternion algebra has been used to calculate the ideal misorientation between product α variants for Kurdjumov–Sachs (KS) and its nearby orientation relationships, and arrive at the misorientation angle-axis set corresponding to packet (12 types), block (3 types) and sub-block boundaries. Analysis of proximity of experimental misorientation between data points from the theoretical misorientation set is found to be useful for identifying the different types of martensite boundaries. The optimal OR in the alloy system and the critical deviation threshold for identification of martensite boundaries could both be ascertained by invoking the ‘Enhancement Factor’ concept. The prior-γ grain boundaries, packet, block and sub-block boundaries could be identified reasonably well, and their average intercept lengths in a typical tempered martensite microstructure of 9Cr–1Mo–0.1C steel was estimated as 31 μm, 14 μm, 9 μm and 4 μm respectively.     

Quantum dot nanostructures for multi-band infrared detection

A dual-band (two-color) tunneling-quantum dot infrared photodetector (T-QDIP) structure, which provides wavelength selectivity using bias voltage polarity, is reported. In this T-QDIP, photoexcitation takes place in InGaAs QDs and the excited carriers tunnel through an AlGaAs/InGaAs/AlGaAs double-barrier by means of resonant tunneling when the bias voltage required to line up the QD excited state and the double-barrier state is applied. Two double-barriers incorporated on the top and bottom sides of the QDs provide tunneling conditions for the second and the first excited state in the QDs (one double-barrier for each QD excited state) under forward and reverse bias, respectively. This field dependent tunneling for excited carriers in the T-QDIP is the basis for the operating wavelength selection. Experimental results showed that the T-QDIP exhibits three response peaks at ～4.5 (or 4.9), 9.5, and 16.9 μm and selection of either the 9.5 or the 16.9 μm peak is obtained by the bias polarity. The peak detectivity (at 9.5 and 16.9 μm) of this detector is in the range of 1.0–6.0 × 10¹² Jones at 50 K. This detector does not provide a zero spectral crosstalk due to the peak at 4.5 μm not being bias-selectable. To overcome this, a quantum dot super-lattice infrared photodetector (SL-QDIP), which provides complete bias-selectability of the response peaks, is presented. The active region consists of two quantum dot super-lattices separated by a graded barrier, enabling photocurrent generation only in one super-lattice for a given bias polarity. According to theoretical predictions, a combined response due to three peaks at 2.9, 3.7, and 4.2 μm is expected for reverse bias, while a combined response of three peaks at 5.1, 7.8, and 10.5 μm is expected for forward bias.     

Non-adiabaticity in surface chemical reactions

Chemical reactions at surface may dissipate energy exciting electron-hole pairs in the metal substrate. Direct detection of the chemically induced hot charge carriers may be achieved by measuring the tunnel current in Ta–TaOx–Au tunnel junctions when the Au top electrode is exposed to an atomic hydrogen beam. A current of 1 nA cm^?2 was observed during a hydrogen exposure with a flux of 0.1 ML s^?1. The transient is related to the reaction kinetics and allows us to identify the elementary reaction steps causing the electronic excitations which are monitored by the observed current. Using Pt as top electrode material a markedly different transient is observed. Applying a bias voltage to the sensor allows spectroscopy of the electronic excitations. The experiments provide detailed insights into the non-adiabaticity of various reaction steps at a surface.     

Fabrication of single-mode Y-branch waveguides in photosensitive polymer with reduced Y-junction residue

Single-mode small-core (～2 μm × 2 μm) Y-branch waveguide structures in photosensitive polymer have been fabricated. Y-branch waveguides are designed by the beam propagation method and Y-branch waveguides are obtained on development after a cross-linkable negative tone epoxy SU-8 2002 polymer is exposed to UV through a photomask. Optical Adhesive NOA 61 is used as under- and over-clad. The fabrication process is optimized to avoid polymer residue at the Y-junction. The average insertion loss obtained for a 7.2 mm 1 × 2 device at chip-level is ～13 dB at 1550 nm.     

Efficient high voltage pulser for piezoelectric air coupled transducer

The design of high voltage pulser for air coupled ultrasound imaging is presented. It is dedicated for air-coupled ultrasound applications when piezoelectric transducer design is used. Two identical N-channel MOSFETs are used together with 1200 V high and low side driver IC. Simple driving pulses’ delay and skew circuit is used to reduce the cross-conduction. Analysis of switch peak current and channel resistance relation to maximum operation frequency and load capacitance is given. PSPICE simulation was used to analyze the gate driver resistance, gate pulse skew, pulse amplitude influence on energy consumption when loaded by capacitive load. Experimental investigation was verified against simulation and theoretical predictions. For 500 pF capacitance, which is most common for piezoelectric air coupled transducers, pulser consumes 650 μJ at 1 kV pulse and 4 μJ at 50 V. Pulser is capable to produce up to 1 MHz pulse trains with positive 50 V–1 kV pulses with up to 10 A peak output current. When loaded by 200 kHz transducer at 1 kV pulse amplitude rise time is 40 ns and fall time is 32 ns which fully satisfies desired 1 MHz bandwidth.     

Picosecond laser cutting and drilling of thin flex glass

We investigate the feasibility of cutting and drilling thin flex glass (TFG) substrates using a picosecond laser operating at wavelengths of 1030 nm, 515 nm and 343 nm. 50 μm and 100 μm thick AF32^®Eco Thin Glass (Schott AG) sheets are used. The laser processing parameters such as the wavelength, pulse energy, pulse repetition frequency, scan speed and the number of laser passes which are necessary to perform through a cut or to drill a borehole in the TFG substrate are studied in detail. Our results show that the highest effective cutting speeds (220 mm/s for a 50 μm thick TFG substrate and 74 mm/s for a 100 μm thick TFG substrate) are obtained with the 1030 nm wavelength, whereas the 343 nm wavelength provides the best quality cuts. The 515 nm wavelength, meanwhile, can be used to provide relatively good laser cut quality with heat affected zones (HAZ) of <25 μm for 50 μm TFG and <40 μm for 100 μm TFG with cutting speeds of 100 mm/s and 28.5 mm/s, respectively. The 343 nm and 515 nm wavelengths can also be used for drilling micro-holes (with inlet diameters of ⩽75 µm) in the 100 μm TFG substrate with speeds of up to 2 holes per second (using 343 nm) and 8 holes per second (using 515 nm). Optical microscope and SEM images of the cuts and micro-holes are presented.     

Pump tuned wide tunable noncritically phase-matched ZnGeP2 narrow line width optical parametric oscillator

A line tunable singly resonant noncritically phase matched narrow band width ZnGeP₂ (ZGP) optical parametric oscillator pumped by the output idler radiation from a KTA OPO based on a 20 mm long KTA crystal pumped from a Q-switched Gaussian shaped Nd:YAG laser beam with a grating having grooves density 85 lines/mm has been demonstrated in the spectral ranges of 3–7 μm. The measured threshold of oscillation energy was 10 μJ. The conversion efficiency was 20.5% and slope efficiency of the ZGP OPO was 20% using a 23 mm long ZGP crystal at 26 mm cavity length. Line width of the generated infrared radiation from ZGP OPO was 37–60 nm.     

Optical coherence tomography based imaging of dental demineralisation and cavity restoration in 840 nm and 1310 nm wavelength regions

In this paper, a study of in-house built optical coherence tomography (OCT) system with a wavelength of 840 nm for imaging of dental caries, progress in demineralisation and cavity restoration is presented. The caries when imaged with the 840 nm OCT system showed minute demineralisation in the order of 5 μm. The OCT system was also proposed to study the growth of lesion and this was demonstrated by artificially inducing caries with a demineralisation solution of pH 4.8. The progress of carious lesion to a depth of about 50–60 μm after 60 hours of demineralisation was clearly observed with the 840 nm OCT system. The tooth samples were subjected to accelerated demineralisation condition at pH of approximately 2.3 to study the adverse effects and the onset of cavity formation was clearly observed. The restoration of cavity was also studied by employing different restorative materials (filled and unfilled). In the case of restoration without filler material (unfilled), the restoration boundaries were clearly observed. Overall, results were comparable with that of the widely used 1310 nm OCT system. In the case of restoration with filler material, the 1310 nm OCT imaging displayed better imaging capacity due to lower scattering than 840 nm imaging.     

Nanosecond-pulsed erbium-doped fiber lasers with graphene saturable absorber

We demonstrate graphene mode-locked nanosecond erbium-doped fiber laser in an all-fiber ring cavity. The clean and robust pulse train was generated at 27 mW pump power. Resultant central wavelength, repetition rate and pulse width was 1560 nm, 388 kHz and 6 ns, respectively. With two stage fiber amplifier, the output power was 553 mW, corresponding to single pulse energy of 1.4 μJ. In addition, the pulse-width can be varied ranging from 3 ns to 20 ns at repetition rate between 200 kHz and 1.54 MHz by changing the length of the laser cavity.     

Antenna length and polarization response of antenna-coupled MOM diode infrared detectors

This work focuses on the fabrication and response of dipole antenna-coupled metal–oxide–metal diode detectors to long-wave infrared radiation. The detectors are fabricated using a single electron beam lithography step and a shadow evaporation technique. The detector’s characteristics are presented, which include response as a function of incident infrared power and polarization angle. In addition, the effect of dipole antenna length on detection characteristics for 10.6 μm radiation has been measured to determine resonant lengths. The response of the detector shows a first resonance at a dipole length of 3.1 μm, a second resonance at 9.3 μm, and third at 15.5 μm. The zeros intermediate to the resonances are also evident.     

InGaAsP/InP photodetectors targeting on 1.06 μm wavelength detection

InP-based InGaAsP photodetectors targeting on 1.06 μm wavelength detection have been grown by gas source molecular beam epitaxy and demonstrated. For the detector with 200 μm mesa diameter, the dark current at 10 mV reverse bias and R₀A are 8.89 pA (2.2 × 10⁻⁸ A/cm²) and 3.9 × 10⁵ Ω cm² at room temperature. The responsivity and detectivity of the InGaAsP detector are 0.30 A/W and 1.45 × 10¹² cm Hz^1/2 W⁻¹ at 1.06 μm wavelength. Comparing to the reference In_0.53Ga_0.47As detector, the dark current of this InGaAsP detector is about 570 times lower and the detectivity is more than ten times higher, which agrees well with the theoretical estimation.     

Evolution of array format of longwave infrared Type-II SLS FPAs with high quantum efficiency

In the remarkably short span of 2 years, longwave infrared focal plane arrays (FPAs) of Type-II InAs/GaSb strained layer superlattice (SLS) photodiodes have advanced from 320 × 256 format to 1024 × 1024 format while simultaneously shrinking the pitch from 30 μm to 18 μm. Despite a dark current that is presently higher than state-of-the-art mercury cadmium telluride photodiodes with the same ∼10 μm cutoff wavelength, the high pixel operability and high (∼50%) quantum efficiency of SLS FPAs enable excellent imagery with temporal noise equivalent temperature difference better than 30 mK with F/4 optics, integration time less than 1 ms, and operating temperature of 77 K or colder. We present current FPA performance of this promising sensor technology.     

10.6 μm Infrared light photoinduced insulator-to-metal transition in vanadium dioxide

Vanadium dioxide has excellent phase transition characteristic. Before or after phase transition, its optical, electrical, magnetic characteristic hangs hugely. It has a wide application prospect in many areas. Now, the light which can make vanadium dioxide come to pass photoinduced phase transition range from soft X-ray to medium infrared light (6.9 μm, 180 meV). However, whether 10.6 μm (117 meV) long wave infrared light can make vanadium dioxide generate photoinduced phase transition has been not studied. In this paper, we researched the response characteristic of vanadium dioxide excited by 10.6 μm infrared light. We prepared the vanadium dioxide and test the changes of vanadium dioxide thin film’s transmittance to 632.8 nm infrared light when the thin film is irradiate by CO₂ laser. We also test the resistivity of vanadium dioxide. Excluding the effect of thermal induced phase transition, we find that the transmittance of vanadium dioxide thin film to 632.8 nm light and resistivity both changes when irradiating by 10.6 μm laser. This indicates that 10.6 μm infrared light can make the vanadium dioxide come to pass photoinduced phase transition. The finding makes vanadium has a potential application in recording the long-wave infrared hologram and making infrared detector with high resolution.     

Threshold curves obtained under various gaseous conditions for free radical generation by burst ultrasound – Effects of dissolved gas,microbubbles and gas transport from the air

To understand the underlying concepts required for the determination of thresholds for free radical generation, effects of gas dissolution in and microbubble addition to sonicated solutions were investigated. Four solutions with different gaseous conditions, air-saturated and degassed solutions with and without microbubbles of 20 μm in diameter with shells, were studied in the presence of an air–liquid interface. These test solutions were exposed to 1 MHz ultrasound of 0.06 MPa_p-p at various pulse durations (PDs) from 0.1 to 5 ms and pulse repetition frequencies from 0.1 to 2 kHz. Generation of free radicals was evaluated using the electron spin resonance (ESR) spin trapping method and starch–iodine method. Thresholds of duty ratio (DR) corresponding to temporal average intensity of ultrasound for free radical generation were significantly greater in degassed solutions than in air-saturated solutions. Microbubbles had no significant effects in air-saturated solutions but caused a slight decrease in the threshold in degassed solutions. In all of these results, the DR of a threshold curve against pulse repetition period (PRP) was not constant but linearly decreased with it, suggesting that a balance between bubble growth and shrinkage during the ON and OFF times of burst ultrasound is the primary parameter for the interpretation of thresholds. The effect of an air–liquid interface of the solution was also examined, and it was revealed that gas transport from the air is a predominant factor determining the amount of free radicals.     

Analytical modeling and ATLAS simulation of N+-InP/n0-In0.53Ga0.47As/p+-In0.53Ga0.47As p-i-n photodetector for optical fiber communication

In this paper we report an analytical modeling of N⁺-InP/n⁰-In_0.53Ga_0.47As/p⁺-In_0.53Ga_0.47As p-i-n photodetector for optical fiber communication. The results obtained on the basis of our model have been compared and contrasted with the simulated results using ATLAS? and experimental results reported by others. The photodetector has been studied in respect of energy band diagram, electric field profile, doping profile, dark current, resistance area-product, quantum efficiency, spectral response, responsivity and detectivity by analytical method using closed form equations and also been simulated by using device simulation software ATLAS? from SILVACO® international. The photodetector exhibits a high quantum efficiency ～90%, responsivity ～1.152–1.2 A/W in the same order as reported experimentally by others, specific detectivity ～5 × 10⁹ cm Hz^1/2 W^?1at wavelength 1.55–1.65 μm, dark current of the order of 10^?11 A at reverse bias of 1.5 V and 10^?13–10^?12 A near zero bias. These values are comparable to those obtained for practical p-i-n detectors. The estimated noise equivalent power (NEP) is of the order of 2.5 × 10^?14 W.