High-precision Characterization Research Articles

High-precision characterization of textured a-Si:H/SnO2:F structures by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) has been applied for the characterization of hydrogenated amorphous silicon (a-Si:H) layers formed on SnO2:F textured structures in an attempt to establish the structural characterization method for a-Si:H solar cells. In particular, an optical model that allows the complete evaluation of microscopically non-uniform a-Si:H/SnO2:F textured structures has been developed for the SE analysis. In order to express the complicated optical response in the textured structures, the optical model incorporates (i) the surface roughness and interface layers calculated using an effective-medium-approximation multilayer model and (ii) the a-Si:H/SnO2:F structure divided into two regions with different thicknesses. Using this optical model, SE spectra obtained experimentally from the a-Si:H/SnO2:F textured structure can be reproduced almost perfectly. The a-Si:H/SnO2:F structure deduced from the SE analysis shows remarkable agreement with that observed from transmission electron microscopy. Moreover, a variety of a-Si:H layers with different thicknesses are expressed from the identical optical model. The SE analysis method developed in this study can be utilized further to perform high-precision and non-destructive characterization of various a-Si:H layers incorporated in large-area a-Si:H modules.

Characterization of an INVS model IV neutron counter for high precision ( [formula omitted]) cross-section measurements

A neutron counter designed for assay of radioactive materials has been adapted for beam experiments at TUNL. The cylindrical geometry and 60% maximum efficiency make it well suited for ( γ , n ) cross-section measurements near the neutron emission threshold. A high precision characterization of the counter has been made using neutrons from several sources. Using a combination of measurements and simulations, the absolute detection efficiency of the neutron counter was determined to an accuracy of ±3% in the neutron energy range between 0.1 and 1 MeV. It is shown that this efficiency characterization is generally valid for a wide range of targets.

Four point bending setup for characterization of semiconductor piezoresistance

We present a four point bending setup suitable for high precision characterization of piezoresistance in semiconductors. The compact setup has a total size of 635 cm(3). Thermal stability is ensured by an aluminum housing wherein the actual four point bending fixture is located. The four point bending fixture is manufactured in polyetheretherketon and a dedicated silicon chip with embedded piezoresistors fits in the fixture. The fixture is actuated by a microstepper actuator and a high sensitivity force sensor measures the applied force on the fixture and chip. The setup includes heaters embedded in the housing and controlled by a thermocouple feedback loop to ensure characterization at different temperature settings. We present three-dimensional finite element modeling simulations of the fixture and discuss the possible contributions to the uncertainty of the piezoresistance characterization. As a proof of concept, we show measurements of the piezocoefficient pi(44) in p-type silicon at three different doping concentrations in the temperature range from T=30 degrees C to T=80 degrees C. The extracted piezocoefficients are determined with an uncertainty of 1.8%.

Hall-Probe Bench for Insertion-Device Characterization at LNLS

A 4.2-m-long Hall-probe bench was developed for high-precision magnetic characterization of insertion devices at the Brazilian Synchrotron Light Laboratory. In this paper, its mechanical and electrical features are described, as well as the procedures applied to improve accuracy and repeatability. Tests used to establish measuring precision were performed in a 2-T planar wiggler, which is 2.8-m long, with periods of 180 mm. The obtained fields were integrated and compared with the rotating-coil measurements.

Creation of a diagnostic complex for the characterization of cryogenic laser-fusion targets using the tomography method with probing irradiation in the visible spectrum

We present our results on developing a diagnostic complex for high-precision characterization of the parameters of laser-fusion microobjects, such as microspheres and cryogenic targets (the microobject size is 1–2 mm). The complex operates based on the principle of tomography. The complex consists of (a) the scanning system providing a set of shadow projections of a microobject in the visible range of radiation and (b) specially developed software for 3D reconstruction of the microobject from the set of projections. The spatial resolution of the optical system is 1 µm for a probing-radiation wavelength of 490 nm. The distinctive features of the diagnostic complex are (1) operation with both free-standing and mounted targets and (2) the possibility of scanning the targets from room to cryogenic temperatures. The operation of the complex was demonstrated in the reconstruction of polystyrene microspheres by a large set (80–90) of shadow projections at room and cryogenic temperatures.

Experimental Contribution to High-Precision Characterization of Magnetic Forces in Active Magnetic Bearings

Parameter identification procedures and model validation are major steps toward intelligent machines supported by active magnetic bearings (AMB). The ability of measuring the electromagnetic bearing forces, or deriving them from measuring the magnetic flux, strongly contributes to the model validation and leads to novel approaches in identifying crucial rotor parameters. This is the main focus of this paper, where an intelligent AMB is being developed with the aim of aiding the accurate identification of damping and stiffness coefficients of active lubricated journal bearings. The main contribution of the work is the characterization of magnetic forces by using two different experimental approaches. Such approaches are investigated and described in detail. A special test rig is designed where the four pole AMB is able to generate forces up to 1900N. The high-precision characterization of the magnetic forces is conducted using different experimental tests: (i) by using hall sensors mounted directly on the poles (precise measurements of the magnetic flux) and by an auxiliary system, composed of strain gages and flexible beams attached to the rotor, (ii) by measuring the input current and bearing gap variations, monitoring the bearing input signals. Advantages and drawbacks of the different methodologies are critically discussed. The linearity ranges are experimentally determined and the characterization of magnetic forces with a high accuracy of <1% is achieved (percent error is normalized with respect to the instantaneous measured force obtained from the strain gauges signals).

Spatial characterization of fiber Bragg grating structures using transversal pressure

A technique for low cost and high precision characterization of fiber Bragg gratings based structures, using transversal pressure, is presented. It is based on the analysis of the amplitude and wavelength changes of the structure reflection spectrum, while being precisely pressed by an electromechanically actuated arm. The theory and the experimental results, which are in good agreement with the expected ones, are also presented.

High-precision characterization of single-mode optical fiber arrays

A precise method of measuring core center dispersion in single-mode fiber arrays is presented. This approach dispenses with the use of high-precision linear translation stages and is based on a direct comparison of the fiber core center position to a simple lithographically patterned template. Combining image recognition and efficient processing algorithm, the fiber-core center positions of fiber arrays can be determined with precision of order of 0.1 /spl mu/m, in both longitudinal and transversal directions. Complementary information about the position of fibers within v-grooves as well as bending of multifiber arrays can be also obtained.

Characterization of III nitride materials and devices by secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) is an excellent technique to characterize III nitride materials and devices (dopants, impurities, and composition). Using empirical standards, the ion yield trends are derived for III nitride matrices to enable quantitative and high precision characterization of both major and impurity elements. The technique can be employed to investigate the control of purity and doping, determine growth rate and composition, as well as reveal the structure of finished optoelectronic and electronic devices. SIMS is thus a powerful tool for failure analysis, reverse engineering, and concurrent engineering.

High-Precision Characterization of III-Nitride Semiconductor Alloys with Secondary Ion Mass Spectrometry (SIMS)

ABSTRACTSamples of representative AlxGayIn1−x-yN compositions have been studied with secondary ion mass spectrometry (SIMS). First, ionized species of common interest (H, B, C, O, Mg, Si, and Cd) were implanted into the Ill-nitride samples to provide calibrated standards. Depth profiles and conversion factors for quantification of dopants were then obtained using O2+ or Cs+bombardment and positive or negative SIMS to measure B+ and Mg+; H−, B−, C−, O−, and Si−; and CdCs+. In addition calibration curves for quantification of stoichiometry were prepared using MCs+ ions (NCs+, AlCs−, GaCs+, InCs+) for which the ion yields are relatively independent of the matrix composition; and using atomic, dimer, and trimer ions (Al, Ga, In, Al2, Ga2, In2, Al3, Ga3) which are very sensitive to matrix composition. The empirical calibration curves show small non-linearities. Dopant concentrations can be quantified with great sensitivity (detection limits usually below 1 ppm), accuracy (usually better than 10%), and precision (better than 25%). Matrix stoichiometry can be quantified with an accuracy of about 1–3%.