ESA-based in-fiber nanocavity for hydrogen-peroxide detection

A fiber-optic sensor sensitive to hydrogen peroxide has been designed based on the electrostatic layer-by-layer self-assembly method. Prussian blue has been deposited in a polymeric structure formed by Poly(allylamine hydrochloride) and poly(acrylic acid). The concentration that can be detected range between 10/sup -6/-10/sup -3/ M, and recovery of the sensor after immersion into a reductive agent was demonstrated. The response of the sensor is independent of the pH for values that range between 4-7.4. Some rules for estimation of the refractive index of the material deposited and the thickness of the bilayers are also presented.     

Design and fabrication of a novel crystal SiGeC far infrared sensor with wavelength 8-14 micrometer

In this paper, we report the design, fabrication, and performance of a novel crystal SiGeC infrared sensor with wavelength 8-14 /spl mu/m by bulk micromachining technology for portable far infrared ray (FIR) in rehabilitation system application. The working principle of the sensor is based on the change of thermistor's resistance under the irradiation FIR light. The thermistor in the IR detector is made of Si/sub 0.68/Ge/sub 0.31/C/sub 0.01/ thin films for its large activation energy of 0.21 ev and the temperature coefficient (TCR) of -2.74%, respectively. Finite element method package ANSYS has been employed for analyze of the thermal isolation and stress distribution in the IR detector. The dimension of the microbridge fabricated by anisotropic wet etching is 2000 /spl times/ 2000 /spl times/ 25 /spl mu/m/sup 3/. The developed FIR sensor exhibits the thermal conductance of 1.85 /spl times/ 10/sup -1/ WK/sup -1/ and the heat capacity as 7.4 /spl times/ 10/sup -7/ JK/sup -1/ under air ambient at room temperature. The responsivity is 523 VW/sup -1/ in the waveband 8-14 /spl mu/m with nickel absorber under a bias voltage 1.5 V.     

A micromachined wide-bandwidth magnetic field sensor based on all-PMMA electron tunneling transducer

All-PMMA-based tunneling magnetic sensors were fabricated by hot embossing replication with silicon templates. The silicon templates had smooth surfaces, positive profiles, and pyramid-like pits with a high aspect ratio. With this fast (20 min), simple (one-step), and repeatable method, the all-PMMA tunneling sensor platform yielded sharp tunneling tips with 75 /spl mu/m in baseline and 50 /spl mu/m in depth. The sensors were assembled and fixed with measurement circuits, after their electrodes were patterned with modified photolithography and Co film was deposited with e-beam evaporation. A natural frequency response of 1.3 kHz was observed, and a tunneling barrier height of 0.713 eV was tested. Due to the quadratic relation between magnetic force and the field, the sensor field response (7.0/spl times/10/sup 6/ V/T/sup 2/) was also quadratic. The noise voltage at 1 kHz is 0.2 mV, corresponding to a magnet field of 0.46/spl times/10/sup -6/ T. The bandwidth of this sensor is 18 kHz. This new type of sensor platform is promising for the next generation of microsensing applications.     

Surface plasmon resonance detection of metal ions: layer-by-layer assembly of polyelectrolyte sensing layers on a multichannel chip

A single-chip multichannel surface plasmon resonance sensor (SPR) has been used to detect metal ions in aqueous solutions. The equipment was designed around a commercial light-emitting diode and a CCD camera and incorporated no moving parts. The sensing materials were based on molecular architectures of polyelectrolyte films, deposited by the layer-by-layer self-assembly technique. Two bilayer architectures, poly(ethyleneimine) (PEI)/poly(ethylenealt-maleic acid) and PEI/poly(styrenesulfonate), were shown to produce different responses to solutions containing copper, nickel, and iron. The SPR equipment was able to measure concentrations of these metals down to levels of at least 2/spl times/10/sup -5/ M.     

A novel NO/sub 2/ gas sensor based on Bis[phthalocyaninato] samarium complex/silicon hybrid charge-flow transistor

A new kind of sandwich-like bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] samarium complex Sm[Pc/sup */]/sub 2/(Pc/sup */=Pc(OC/sub 8/H/sub 17/)/sub 8/) is used as film-forming material. Pure Sm[Pc/sup */]/sub 2/ and mixture of Sm[Pc/sup */]/sub 2/ and octadecanol(OA) deposited from both pure water and 10/sup -4/M Cd/sup 2+/ subphases are investigated. It is found that a mixture of 1:3 Sm[Pc/sup */]/sub 2/:OA forms an excellent material for the fabrication of the gas-sensing Langmuir-Blodgett (LB) film by studying the film-forming characteristics. A new gas sensor has been fabricated by incorporating the multilayer LB film into the gate electrode of a metal-oxide-semiconductor field effect transistor, forming an array of charge-flow transistor. On the application of a gate voltage (V/sub GS/), greater than the threshold voltage (V/sub TH/), a delay was observed in the response of the drain current. This is due to the time taken for the resistive gas-sensing film to charge up to V/sub GS/. This delay characteristic was found to depend on the concentration of NO/sub 2/. Results are presented showing that the device can detect reversibly the concentration of NO/sub 2/ gas down to 5 ppm at room temperature.     

Application of some recently synthesized 9, 10-anthraquinone derivatives as new class of ionophores responsive to lead (II) ion

Lead-selective solvent polymeric membrane electrodes, based on some recently synthesized 9, 10-anthraquinone derivatives, are described. The electrode exhibits a good Nernstian response for Pb (II) ions over a wide concentration range of 1.0/spl times/10/sup -6/-1.0/spl times/10/sup -2/ M with a slope of 28.9 mV decade/sup -1/. The potential-pH profile of membrane based on 1-hydroxy-2-({2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}methyl)anthra-9, 10-quinone (A/sub 3/) demonstrated a lack of H/sup +/ interference within a wide pH range (1.5-6.8). The detection limit is 6.7/spl times/10/sup -7/ M. The developed sensor has a very short response time (2.0 s), and it can be used as a working electrode in a flow injection system. The lifetime of the proposed sensor is 120 days (without any considerable divergence in potentials) with good reproducibility (SD=/spl plusmn/0.1 mV). The proposed sensor revealed good selectivity for Pb (II) over a wide variety of other metal ions. It can be used as an indicator electrode in the potentiometric titration of lead ions, with EDTA, oxalate, chromate, and hydroxide ions, and in direct determination of lead in a wastewater sample.     

New polyaniline-based potentiometric biosensor for pesticides detection

A cholinesterase potentiometric sensor based on a glassy carbon electrode modified with processible polyaniline has been developed and explored for the detection of organophosphorus and carbamic pesticides. Acetyl- and butyryl-cholinesterase from various sources were immobilized on the surface of a polyaniline modified electrode by cross-linking with glutaraldehyde. Polyaniline modification made it possible to obtain a reversible pH response of about 86-mV/pH unit and to improve the analytical and operational characteristics of substrate and inhibitor detection. The sensitivity of pesticide detection depends on both the source of the enzyme and its activity and on pesticide hydrophobicity. The detection limits of the pesticides investigated (Trichlorfon, 1.5/spl middot/10/sup -7/ mol/l, Coumaphos, 5/spl middot/10/sup -9/ mol/l, Methiocarb, 8/spl middot/10/sup -7/ mol/l, Aldicarb, 2/spl middot/10/sup -7/ mol/l) were found lower than those obtained with other similar cholinesterase sensors. The possibility for the detection of the trace amounts of pesticides in river waters and grape juice with cholinesterase sensors developed has been established on model samples.     

Disposable biosensor based on a hemoglobin colloidal gold-modified screen-printed electrode for determination of hydrogen peroxide

A disposable reagentless hydrogen peroxide biosensor based on the direct electrochemistry of hemoglobin immobilized on a colloidal gold-modified screen-printed carbon electrode (Hb-Au-SPCE) was proposed. The electrochemical behavior of immobilized Hb at a SPCE was studied for the first time. The electrode reaction of immobilized Hb showed a surface-controlled process with an electron transfer rate constant of (0.40 /spl plusmn/ 0.02) s/sup -1/ determined in the scan rate range from 25 to 200 mV s/sup -1/. The Hb-Au-SPCE exhibited an electrocatalytic activity toward the reduction of hydrogen peroxide with a K/sub M//sup app/ value of 1.8 mM, which was allowed to be used as a disposable sensor for determination of hydrogen peroxide with a linear range from 1.0 /spl times/ 10/sup -5/ M to 3.2 /spl times/ 10/sup -4/ M, a detection limit of 5.5 /spl times/ 10/sup -6/ M at 3/spl sigma/, a high sensitivity, fast response, and good selectivity, accuracy, and reproducibility. The disposable reagentless sensor was stable, low cost, and simple to use for detection of hydrogen peroxide in real samples.     

High-sensitivity accelerometer based on cold emission principle

A possibility for fabrication of a high-sensitivity accelerometer is considered. The linear acceleration of a sensor causes displacement of the proof mass electrode. The displacement detector is based on a strong dependence of the tunneling or cold emission current on the gap between the electrodes. The geometry of the electrodes that provides the best sensitivity is determined. The accelerometer with tunneling-emission electrodes is fabricated. At frequencies up to 5 kHz the resolution reaches 10/sup -4/ g/Hz/sup 1/2/ in the tunneling mode and 10/sup -3/ g/Hz/sup 1/2/ in the emission mode.     

An integrated 16/spl times/16 PVDF pyroelectric sensor array

This paper presents a fully integrated PVDF-on-silicon pyroelectric sensor array. The pyroelectric sensor has two main features: a subpixel low noise charge amplifier and a self-absorbing layered structure. The integrated low noise charge amplifier is implemented in a standard CMOS process technology. It is located directly under the sensing structure, maximizing the pixel fill factor. The self-absorbing pyroelectric sensor is a three-layer stack, consisting of a conductive polymer as an absorber layer and front electrode, a thin PVDF film as the pyroelectric material, and a rear metal layer acting as a reflector layer and rear electrode. The manufacture of the pyroelectric sensor array requires five maskless post-CMOS processing steps and is compatible with any n-well, double metal, double polysilicon, CMOS process. The array has an average pixel voltage sensitivity of 2200 V/W at 100 Hz, an NEP of 2.4/spl times/10/sup -11/ W//spl radic/Hz at 100 Hz, and a specific detectivity of 4.4/spl times/10/sup 8/ cm /spl radic/Hz/W at 100 Hz.     

Design and analysis of an integrated optical sensor for scanning force microscopies

In this paper, a novel probe for displacement sensing will be introduced. It is based on a conventional GaAs cantilever, integrated with a Bragg grating as a photo-elastic strain sensor. The deflection of the cantilever is measured directly from the intensity modulation of the reflected light. The principle of the experimental setup and the sensor, as well as the theoretical investigation of the force and displacement sensitivity of the probe, is presented. Finite-element method simulations were performed to get the optimum sensor design. Transfer matrix method simulation of the waveguide grating have been described in detail. In order to enhance the sensitivity, different types of grating structures are discussed. Using this new design, it should be possible to achieve sensitivities, defined as the fractional change in detected optical power per unit displacement of the cantilever, as high as 10/sup -4/ /spl Aring//sup -1/ of cantilever deflection.     

Thinned fiber Bragg gratings as refractive index sensors

In this work, highly sensitive refractive index measurements have been experimentally demonstrated by using thinned fiber Bragg grating (FBG) sensors. When the cladding diameter is reduced, significant changes in the effective refractive index occur due to surrounding medium refractive index modifications, leading to Bragg wavelength shifts. Uniformly thinned FBGs have been obtained by using wet chemical etching in hydrofluoric acid solutions. In order to prove sensor sensitivity, experimental tests have been carried out by using glycerine solutions with well-known refractive indices. Obtained results agree well with the numerical analysis carried out by using the three-layer fiber model. If the cladding layer is completely removed, resolutions of /spl ap/10/sup -5/ and /spl ap/10/sup -4/ for the outer refractive index around 1.450 and 1.333, respectively, are possible. Finally, a novel approach based on the selective etching along the grating region has been analyzed, leading to high-sensitivity refractive index sensors based on intensity measurements.     

Thickness-dependent leakage current of (polyvinylidene fluoride/lead titanate) pyroelectric detectors

The novel pyroelectric IR detectors have been fabricated using the Polyvinylidene Fluoride (PVDF)/Lead Titanate (PT) pyroelectric bilayer thin films, which were deposited onto Pt(111)/SiO/sub 2//Si(100) substrates by a sol-gel process. The ceramic/polymer structure was constructed of the randomly oriented polycrystalline PT film (/spl sim/1 /spl mu/m) heated at 700/spl deg/C for 1 h and the /spl beta/-phase PVDF film crystallized at 65/spl deg/C for 2 h. The effects of PVDF thin film thickness (100 /spl sim/ 580 nm) on the pyroelectric response of IR detectors were studied. The results show that the depositions of PVDF thin films onto the PT films will cause the leakage current (J) of the detectors decrease from 6.37/spl times/10/sup -7/ A/cm/sup 2/ to 3.86/spl times/10/sup -7/ A/cm/sup 2/. The specific detectivity (D*) measured at 100 Hz decreased from 2.72/spl times/10/sup 7/ cm/spl middot/Hz/sup 1/2//W for detector without PVDF to 1.71/spl times/10/sup 7/ cm/spl middot/Hz/sup 1/2//W for detector with PVDF thickness of 580 nm. By optimizing the ratio of the specific detectivity (D*) to leakage current, D*/J, the detector with PVDF thickness of 295 nm exhibits the best performance.     

A microfabricated biosensor for detecting foodborne bioterrorism agents

A biosensor for the detection of pathogenic bacteria was developed for biosecurity applications. The sensor was fabricated using photolithography and incorporates heterobifunctional crosslinkers and immobilized antibodies. The sensor detected the change in impedance caused by the presence of bacteria immobilized on interdigitated gold electrodes and was fabricated from (100) silicon with a 2-/spl mu/m layer of thermal oxide as an insulating layer. The sensor has a large active area of 9.6 mm/sup 2/ and consists of two interdigital gold electrode arrays each measuring 0.8 /spl times/ 6 mm. Pathogenic Escherichia coli and Salmonella infantis were tested in serially diluted pure culture. Analyte specific antibodies were immobilized to the oxide between the electrodes to create a biological sensing surface. After immersing the biosensor in solution, the impedance across the interdigital electrodes was measured. Bacteria cells present in the sample solution attached to the antibodies and became tethered to the electrode array thereby causing a change in measured impedance. The biosensor was able to discriminate between different cellular concentrations from 10/sup 4/ - 10/sup 7/ CFU/mL (colony-forming units per milliliter) in solution. The sample testing process, including data acquisition, required 5 min. The design, fabrication, and testing of the biosensor is discussed along with the implications of these findings toward further biosensor development.     

Analysis and design of a CMOS angular velocity- and direction-selective rotation sensor with a retinal Processing circuit

This paper implements and analyzes a CMOS angular velocity- and direction-selective rotation sensor with a retinal processing circuit. The proposed rotation sensor has a polar structure and is selective of the angular velocity and direction (clockwise and counterclockwise) of the rotation of images. The correlation-based algorithm is adopted and each pixel in the rotation sensor is correlated with the pixel that is 45/spl deg/ apart. The angular velocity selectivity is enhanced by placing more than one pixel between two correlated pixels. The angular velocity selectivity is related to both the number and the positions of the edges in an image. Detailed analysis characterizes angular velocity selectivity for different edges. An experimental chip consisting 104 pixels, which form five concentric circles, is fabricated. The single pixel has an area of 91/spl times/84/spl mu/m/sup 2/ and a fill factor of 20%, whereas the area of the chip is 1812/spl times/1825/spl mu/m/sup 2/. The experimental results concerning the fabricated chip successfully verified the analyzed characteristics of angular velocity and direction selectivity. They showed that the detectable angular velocity and range of illumination of this rotation sensor are from 2.5/spl times/10/sup -3/ /spl pi//s to 40 /spl pi//s and from 0.91 lux to 366 lux, respectively.     

Optical frequency standards based on the /sup 199/Hg/sup +/ ion

We report on work directed toward the systematic evaluation of an optical frequency standard based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of a single, laser-cooled, trapped /sup 199/Hg/sup +/ ion, whose resonance frequency is 1.06/spl times/10/sup 15/ Hz. For the purpose of the evaluation, a second /sup 199/Hg/sup +/ standard has been constructed. In the cooling-laser system built for the second standard, an injection-locking scheme has been applied to a CW Ti-sapphire laser. We also report optical frequency measurements of the clock transition performed over the past 21 months with the first standard. During this term, the variation of the clock transition frequency is found to be less than /spl plusmn/1/spl times/10/sup -14/.     

Improvement of the /spl mu/-Hall magnetic sensor sensitivity at low frequency

We have developed a configuration for precision magnetic measurements associating a /spl mu/-Hall sensor, a modulated ferromagnetic antenna, and an analog electronic circuitry. This association is not only able to remove the 1/f noise of the Hall sensor, but also to achieve an ultimate noise level even lower than thermal white noise of the Hall sensor. The system main characteristics are the following: bandwidth 645 Hz, noise level white and lower than 10 nT//spl radic/Hz above 0.1 Hz, slew rate 10/sup -1/ T/s and system dynamic 84 dB in a 1-Hz bandwidth. The performances of the modulated sensor are compared to those of a dc operated sensor.     

Development of advanced-type multi-functional electronic personal dosemeter

An advanced-type small, light, multi-functional electronic personal dosemeter has been developed using silicon semiconductor radiation detectors for dose management of workers at nuclear power plants and accelerator facilities. This dosemeter is 62 x 82 x 27 mm(3) in size and approximately 130 g in weight, which is capable of measuring personal gamma ray and neutron dose equivalents, Hp(10), simultaneously. The neutron dose equivalent can be obtained using two types of silicon semiconductors: a slow-neutron sensor (<1 MeV) and a fast-neutron sensor (>1 MeV). The slow neutron sensor is a 10 x 10 mm(2) p-type silicon on which a natural boron layer is deposited around an aluminium electrode. The fast neutron sensor is also a 10 x 10 mm(2) p-type silicon crystal on which an amorphous silicon hydride is deposited. The neutron energy response corresponding to the fluence-to-dose-equivalent conversion coefficient given by ICRP Publication 74 has been evaluated using a monoenergetic neutron source from 250 keV to 15 MeV at the Fast Neutron Laboratory of Tohoku University. As the result, the Hp(10) response to neutrons in the energy range of 250 keV and 4.4 MeV within +/-50% difference has been obtained.     

High-potential magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media

The magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media, including higher energy terms, was studied as a function of film composition and seed layer materials. All series of CoPtCr films with various Cr content, deposited on Ru seed layers, show maximum values of total anisotropy K/sub u/ at 25-30 at%Pt. The maximum value for CoPt(Cr=0) films reaches /spl sim/15/spl times/10/sup 6/ erg/cm/sup 3/. The addition of SiO/sub 2/ to the CoPtCr films reduces the grain K/sub u/, however the grain K/sub u/ maintains a large value of 8/spl times/10/sup 6/ erg/cm/sup 3/ even when 10at%SiO/sub 2/ is added to (Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/, for instance, which indicates the high-potential thermal stability. Theoretical calculations for media designs of 400 Gbits/in/sup 2/ revealed that the ratio of the high-energy anisotropy term K/sub u2/ to K/sub u1/(K/sub u/=K/sub u1/+K/sub u2/) is required to be 0.2-0.35 to enhance the energy barrier for the remanent state, without a notable change in switching field. The films deposited on Ru seed layers were found to show negligibly small K/sub u2/ values, however, the values of K/sub u1/ and K/sub u2/ vary significantly with the seed layer material used. K/sub u1/ decreases almost linearly as the K/sub u2/ value increases. It is concluded that CoPtCr films have a sufficient potential in the values of K/sub u1/ and K/sub u2/ for high-density perpendicular media.     

Cryogenic dual-mode resonator for a fly-wheel oscillator for a caesium frequency standard

A dual-mode, sapphire-loaded cavity (SLC) resonator has been designed and optimized with the aid of finite element software. The resonance frequency was designed to be near the frequency of a Cs atomic frequency standard. Experimental tests are shown to agree very well with calculations. The difference frequency of two differently polarized modes is shown to be a highly sensitive temperature sensor in the 50 to 80 K temperature range. We show that an oscillator based on this resonator has the potential to operate with fractional frequency instability below 10/sup -14/ for measurement times of 1 to 100 seconds. This is sufficient to operate an atomic clock at the quantum projection noise limit.