Material and electrical characteristics of iron doped Pt-lnAIAs schottky diodes grown by LP-MOCVD

InAlAs lattice-matched to InP is of great importance as a large bandgap material for various InP-based heterostructures device applications. However, growth of good quality InAlAs using metalorganic chemical vapor deposition (MOCVD) is relatively difficult due to the reactive nature of its aluminum sources. In this paper, we present the use of iron as a possible dopant to improve the electrical properties of MOCVD grown InAlAs. Time resolved photoreflectance was used to confirm the increase in trap levels with increased iron doping. The impact of iron doping on the electrical properties of devices was investigated using Pt-Schottky diodes fabricated on undoped and iron doped InAlAs materials. Low frequency noise measurements were also carried out to investigate the impact of iron incorporation on the noise characteristics of the devices. Although noise levels showed marginal difference between undoped and iron doped materials, iron doped InAlAs showed a Lorentzian component in the noise spectra which is not found in undoped materials. An activation energy of ∼0.77 eV was evaluated for traps introduced by iron incorporation using temperature dependent low frequency noise measurements.     

Superconducting instrument systems

Some recently developed superconducting instrument systems which are based upon the use of a highly reliable thin-film superconducting quantum interference device (SQUID) are discussed in detail. These SQUID's, which are shown to have a noise temperature of less than 2 × 10^-4K, are capable of measuring: 1) magnetic flux with a sensitivity of 10^-11Gċcm²rms/√Hz; 2) magnetic field with a sensitivity of 10^-11G rms/√Hz; 3) magnetic field gradient with a sensitivity of 10^-11(G/cm) rms/√Hz. We present construction details and performance data on systems capable of making the above measurements.     

Material and device characterization using a correlation spectrum analyzer

The paper presents the possibilities offered by the Correlation Spectrum Analyzer in the characterisation of semiconductor materials and microelectronic devices. The instrument performs noise analysis in a frequency range from a few mHz to 1 MHz with an extraordinary sensitivity of 1fA/√Hz in current noise measurements and of 20 pV/√Hz in voltage noise measurements. Noise spectra taken in these conditions can be used as a non-destructive-sensitive probe to investigate physical properties of semiconductor materials as well as quantify the noise produced by new devices. As an example of these applications, the text reports on the extraction of noise parameters from a MOSFET operated in strong sub-threshold regime to be inserted in noise models for circuit simulation and on the determination of carrier mobility in single-crystal cadmium telluride (CdTe) samples.     

Coriolis mass-flow meter with integrated multi-DOF active vibration isolation

Vibration isolation of more than 40 dB is achieved for a Coriolis Mass-Flow Meter (CMFM) with integrated Active Vibration Isolation. A CMFM is an active device based on the Coriolis force principle for direct mass-flow measurements independent of fluid properties. The mass-flow measurement is derived from tube displacement measurements. Support excitations can introduce motions that cannot be distinguished from the Coriolis force induced motion, thus introducing a measurement error. Therefore, the measurement stage is passively suspended at 30 Hz in the 3 out-of-plane directions. Active vibration isolation is added to increase the attenuation. In this paper the system model and controller design are presented. Based on the model an on-scale proof of principle is built and the model and controller are validated in multi-DOF. Acceleration feedback and a novel adaptive feedforward control strategy are compared A filtered-reference least-mean-square (FxLMS) adaptive scheme is used to determine the optimal feedforward controller parameters to minimise a squared error signal; the motion of the measurement stage. Both strategies result in an attenuation of 10 – 20 dB at 175 Hz in addition to the 30 dB attenuation obtained by the 30 Hz passive vibration isolation stage. The performance of the feedback strategy is limited by robust stability and the the feedforward performance is limited by sensor noise.     

New experiments on the electrodeposition of iron in porous silicon

We report here the study about the electrodeposition of iron into porous silicon made in p-type (15–25 Ω cm) silicon wafers. Chronoamperometry measurements were performed to show that the iron nucleation does not start only at the bottom of the pores, which is confirmed by the high quality SEM images. The energy band of the heterostructure Si/PS is used to explain the mechanisms involved in the electrodeposition of iron and the porous silicon formation. This new structure (iron and porous silicon), once well controlled might have an influence on the new device developments.     

Ferromagnetic high-permeability alloy alone can provide sufficientlow-frequency and eddy-current shieldings for biomagnetic measurements

A low cost, two-shell ferromagnetic shielded room large enough for a person to enter and prepare experiments was constructed for biomagnetic measurements. No aluminium or copper shell was used for eddy-current shielding. A high-permeability nickel-iron-molybdenum alloy (1.57 mm thick) was used for both ferromagnetic and eddy-current shieldings. The shielding factor was 60 dB at DC and 40 dB between 0.1 Hz and about 3 Hz. The eddy-current shielding due to the alloy alone provided a shielding factor of 55 dB at 30 Hz and 66 dB at 60 Hz. The shielding factor was sufficiently high in all the frequency range for biomagnetic measurements with a first-order superconducting gradiometer     

Field Measurements with a 5.25 GHz Broadband MIMO-OFDM Communication System

Theoretical capacity calculations and corresponding simulations show significant capacity/throughput gains from MIMO systems. Whether these gains are achievable in a real system, deployed in a practical environment, depends on a variety of factors, such as the choice of the communication algorithms, analog impairments and the "quality" of the wireless channel to sustain MEMO communications. In this paper, a 5.25 GHz broadband MIMO-OFDM testbed is described along with field measurements conducted with it. The MIMO-OFDM communication algorithms and also the impact of analog impairments on the performance of the system are described. Detailed system calibration results are described which serve as a baseline for results of field measurements. The results of wireless measurements are compared with the theoretical capacity, computed with the channel estimates obtained during the demodulation process. The average achievable capacity in the indoor wireless environment is shown to be 9.97 bps/Hz (bits per sec per Hz) while the capacity loss due to analog impairments and the choice of algorithms is about 2.33 bps/Hz. Also, field measurements conducted with the system in various environments are presented comparing the average throughput/capacity achieved in each of these environments.     

A CMOS uncooled heat-balancing infrared imager

In this paper, we report the fabrication, design, and testing of an uncooled 8×8 infrared imager based on an active pixel heat balancing technique. The imager is fabricated using a commercial CMOS process plus a simple electrochemical etch stop releasing step. The basic active pixel detector structure consists of a simple cascode CMOS amplifier in which the PMOS devices are built inside a thermally isolated floating n-well. The intrinsic coupling of the cascode currents with the self-heating of the well forms an electrothermal feedback loop that tends to maintain the well temperature constant, By employing the heat balance between incoming infrared radiation and the PMOS device power dissipation, the responsivity of the detector is controlled by the cascode biasing current. Measurements show responsivities between 0.3-1.2×10⁶ V/W when the infrared source is chopped at 20 Hz and a detectivity D*=3×10⁷ cm√(Hz)W^-1 at 30 Hz. Noise measurements suggest that a D* of 10⁸ cm√(Hz)W^-1 is achievable in this design     

A fiber Bragg grating sensor system for simultaneously static and dynamic measurements with a wavelength-swept fiber laser

A novel fiber Bragg grating (FBG) sensor system for static and dynamic measurements with a wavelength-swept fiber laser is proposed and demonstrated. In this system, both static and dynamic perturbation of each FBG in the sensor arrays can be interrogated simultaneously. The experiments demonstrated the strain resolutions of /spl sim/1 /spl mu//spl epsiv/ and 3.4 n/spl epsiv///spl radic/Hz at 500 Hz for static and dynamic measurements, respectively.     

Iron oxide nanoparticles synthesized by controlled bio-precipitation using leaf extract of Garlic Vine (Mansoa alliacea)

Iron (III) oxide nanoparticles were synthesized through green chemistry by the controlled reduction of hepta hydrous iron sulphate using the leaf extract of Garlic Vine. The crystalline phase of trivalent iron embedded in the primitive lattice of hexagonal β-Fe₂O₃ was obtained under the space group P3 (143). The scattered lines and considerably broadened peaks in the x-ray diffraction pattern indicate that the samples formed are crystallites of nano regime rather than bulk or amorphous in nature. Further, the size and the microstrain of the nanocrystallites were estimated through Hall Williamson analysis. The abundance of elemental iron present in the sample was estimated through Atomic Absorption Spectroscopy, whilst the UV visible analysis and FT-IR measurements, in accordance with XRD result, endorsed the formation of iron (III) oxide nanocrystals with iron predominantly occupying the octahedral sites. The band gap energy (2.84 eV) corresponds to the best fit is found to be for indirect allowed semiconducting transition between valance and conduction bands. Further, the TGA measurements were performed to identify the presence of capped polymer over the surface of nanoparticles, the organic decomposition temperature and phase transformation of meta-stable β-Fe₂O₃ to stable α-Fe₂O₃ at temperature above 500 °C.     

Frequency-modulated multimode laser diode for fiber Bragg gratingsensors

A demodulation scheme for fiber Bragg grating (FBG) sensors is presented. It is based on the generation of an electrical carrier by using a modulated multimode laser diode to illuminate the fiber grating. The change in Bragg wavelength is measured by tracking the phase of the carrier at the detector output in either an open- or a closed-loop scheme. A theoretical analysis of the interrogation technique in terms of linearity and dynamic range is presented. Experimental data were obtained for both strain and temperature measurements. Sensitivities of 0.7 μϵ/√Hz and 0.05°C/√Hz were obtained over a dynamic range of ≈60 dB. The application of this demodulation scheme to a multiplexed sensing system is also demonstrated     

Magnetocardiography using HTS rf SQUIDs with coplanar resonators

We have employed HTS rf washer SQUIDs with coplanar resonators for magnetocardiography measurements. The white field noise of such a magnetometer (rf washer SQUID, 3.5 mm in diameter, flip-chip mounted on a flux concentrator 13 mm in diameter) inside a 4 layer μ-metal shielding was 16 fT/√Hz. MCG measurements were performed with a magnetometer in the Berlin magnetically shielded room (BMSR) and with a first order gradiometer in a standard shielded room in Jülich (JMSR). The results are compared regarding the fragmentation score, which is supposed to be a risk marker for sudden cardiac death. Despite different environments, score values determined with the magnetometer and the gradiometer were almost identical.     

Phosphorus gettering of iron by screen‐printed emitters in monocrystalline Czochralski silicon wafers

In this paper, we demonstrate single‐sided screen‐printed emitters in thin monocrystalline Czochralski silicon (Cz‐Si) wafers with an improved gettering of iron compared with conventional double‐sided POCl₃ emitters. The phosphorus dopant pastes used have to be chosen carefully to provide a sufficiently low emitter sheet resistance and to avoid iron contamination. The iron concentration is determined in a non‐destructive way from the minority carrier lifetime obtained by quasi‐steady‐state photoconductance measurements, down to levels not yet demonstrated for screen‐printed emitters. In addition, the well‐known metastable boron–oxygen complexes in Cz‐Si have been transferred into a stable state by light‐induced degradation prior to these measurements. Copyright © 2012 John Wiley & Sons, Ltd.     

双通道石英增强光声光谱测声器的设计及实验研究

设计了一款拥有双谐振腔的新型石英增强光声光谱测声器。通过开展多气体浓度的快速测量实验,研究了系统的灵敏度及可靠性。实验结果显示该种新颖的谐振腔结构并未引入新的噪声。双谐振腔的设计大大增强了石英音叉与谐振腔之间的声耦合强度,这一强耦合使传感器的响应时间下降至约5 ms,且上下两通道单独工作时的归一化噪声等效吸收系数分别达到7.8*10-9 cm-1W/√Hz和8.1*10-9 cm-1W/√Hz。另外,这一配置提供了两个相互独立的气体检测通道,为不同波长特别是波长间隔较大的两路激光光信号的相加或相消提供了一种可行性方案,也必将对多组分混合气体的快速在线检测的发展起到极大的推动作用。     

Outdoor BLAST measurement system at 2.44 GHz: calibration andinitial results

There are ever increasing demands for additional capacity in wireless communications to handle voice, data, and wideband Internet applications. These demands are constrained by the bandwidth that was allocated to wireless communications. The spectral efficiencies in present day wireless systems hover around 1 bit/s/Hz. Bell-labs Layered Space-Time (BLAST) is a communication technique for achieving very high spectral efficiencies in highly scattering environments using multiple transmit and receive antennas. A measurement campaign was undertaken to assess the BLAST gains in spectral efficiency in the suburban outdoor environment for stationary subscribers. The measurements employed directive antennas to better control interference from adjacent cells. The measurements were performed over a narrow band at 2.44 GHz with five transmitting and seven receiving antennas, respectively. Extensive calibration methods, assisted by simulations, were developed to assure accurate results for the BLAST capacities of the measured remote subscriber sites. Initial results indicate that BLAST capacities of C _B⩾38 bits/s/Hz at 20% of the measured locations and C_B⩾24 bits/s/Hz at 50% of these locations are feasible, for reasonable link parameters and negligible interference     

Extremely Low Frequency (ELF) Propagation Measurements Along a 4900-km Path

Extremely low frequency (ELF) electromagnetic wave propagation was investigated by measuring the amplitude of a CW signal transmitted from the Sanguine site in North Carolina to receiving sites located in New York State, Labrador, and Iceland. The attenuation factor α and the reciprocal of the excitation factorh_{i} (sigma_{e}S_{0})^{1/2}were determined. Data for daytime, nighttime, and sunrise transition paths were obtained. The attenuation factors obtained for 78 and 156 Hz are compared with the value of α obtained from measurements of atmospherics. The attenuation values at 78 Hz of 1.29 and 1.01 dB/1000 km, and a value of 0.75 dB/1000 km at 45 Hz, obtained by interpolation of results of this and other experiments, were used in Sanguine systems analysis.     

Characterization of the iron and nickel impurities in gaas0.6p0.4

Characterization of nickel and iron impurity centers in GaAs_0.6P_0.4 has been made using the technique of capacitance transients on reverse biased zinc-diffused p⁺n diodes. Both the nickel and iron levels have been identified by thermal hole emission having activation energies of 0.3eV and 0.58eV, respectively. Relative photoresponse measurements resulted in a threshold for optical hole emission of 0.3eV and 0.58eV, therefore, confirming the thermal hole emission measurements. Capture studies for nickel and iron centers indicated a relatively large capture cross-section and a strong electric field dependence. This work is supported by the National Science Foundation, Grant ENG76-80128.     

A Self-Mixing NMOS Channel-Detector Optimized for mm-Wave and THZ Signals

A self-mixing terahertz signal detector combined with a low noise amplifier and a properly balanced - folded dipole or slot antenna for concentrating millimeter wave signals to NMOS detectors is described. The detector was optimized to 300 GHz signals. The noise equivalent power (NEP) was estimated to 320 pW/√Hz while the total output referred noise of 2.1 μV/(Hz)^1/2 was measured at amplifier gain of 46 dB. This was achieved by using NMOS mixer devices optimized for resistive mixing that operate in a linear region of operation where the channel voltage is set close to zero by means of regulating the virtual ground level. The NMOS device, which is positioned at the antenna connections, has a minimum channel length that permits a far more precise calculation of the coupling devices. A position like termination of the two symmetrical detector devices was distributed between an antenna area and the amplification stage. The detectors were fully integrated using the 250 nm CMOS technology. Good matching was found between mathematically analyzed and simulated noise performances and prototypes measurements, where comparable measurements were performed on a THz array which consists of four pixels with folded dipole antennas or those with slot type antennas.     

Nonlinear modeling of the dynamic effects of arterial pressure and CO2 variations on cerebral blood flow in healthy humans

The effect of spontaneous beat-to-beat mean arterial blood pressure fluctuations and breath-to-breath end-tidal CO2 fluctuations on beat-to-beat cerebral blood flow velocity variations is studied using the Laguerre-Volterra network methodology for multiple-input nonlinear systems. The observations made from experimental measurements from ten healthy human subjects reveal that, whereas pressure fluctuations explain most of the high-frequency blood flow velocity variations (above 0.04 Hz), end-tidal CO2 fluctuations as well as nonlinear interactions between pressure and CO2 have a considerable effect in the lower frequencies (below 0.04 Hz). They also indicate that cerebral autoregulation is strongly nonlinear and dynamic (frequency-dependent). Nonlinearities are mainly active in the low-frequency range (below 0.04 Hz) and are more prominent in the dynamics of the end-tidal CO2-blood flow velocity relationship. Significant nonstationarities are also revealed by the obtained models, with greater variability evident for the effects of CO2 on blood flow velocity dynamics.     

Thermal lens study of the Tris(2,2’-bipyridyl)iron(Ⅱ) tetrafluoroborate

Experimental results of thermal lens measurements for Tris(2,2’-bipyridyl)iron(II) tetrafluoroborate solution are reported using the dual beam technique. The temporal evaluation of thermal lens was observed at input pump power of I=47 mW. The thermal lens effect was observed with increasing the pump power intensity as well. The evolution time of thermal lens and the fitting of the experimental transient curve were useful to evaluate the parameters of the Tris(2,2’-bipyridyl)iron(Ⅱ) tetrafluoroborate solution.