Spatially-resolved Detection Research Articles

DEPFET Macropixel Detectors for MIXS: First Electrical Qualification Measurements

The Mercury Imaging X-ray Spectrometer (MIXS) is one of the instruments on board the Mercury Planetary Orbiter of the fifth European Space Agency (ESA) cornerstone mission BepiColombo. This spectrometer comprises two instruments and allows imaging X-ray spectroscopy of the Mercurian surface. The focal plane arrays for the energy and spatial resolved detection of X-rays are based on depleted P-channel FET (DEPFET) macropixel detectors. We report on the first electrical qualification measurements of DEPFET macropixel flight hardware, which are done at room temperature. The measurement of the transistor properties of all DEPFET pixels allows the selection of 100% electrically defect-free devices at an early stage directly after completion of the production process. Additionally, these measurements allow to investigate topics such as the homogeneity of transistor parameters across the detector matrix, to monitor die-to-die variations for matrices from the same wafer, and to investigate the differences between dies from different wafers in order to learn about the stability and reproducibility of the production process. The test results demonstrate good homogeneity and yield for the investigated detector matrices from the first production batch.

Spatially resolved atomic absorption analysis

Previous research carried out in our laboratories has shown that all the key parameters of electrothermal atomic absorption spectrometry, gas phase temperature, intensity of the probing beam and number density of absorbing species, are generally highly non-uniform over the absorption volume. Further, it was shown that, when using conventional detection systems based on a photomultiplier tube or a photodiode that can only detect radiation spatially integrated over their working area, absorbance measurements are subject to photometric errors when the absorbing layer is spatially non-uniform. This error is eliminated when using spatially-resolved detection of transmitted intensities with a linear solid state detector (photodiode array, linear CCD). The photometric error of the conventional detection systems does result in an analytical error, if analyte distributions in the absorption volume produced from an aqueous standard solution and the unknown sample are different. Such a differing distribution could be created under the influence of the sample matrix on the analyte gas phase distribution. An atomic absorption spectrometer is described in the paper that allows spatially and temporally resolved detection of both specific and non-specific absorbances. The effect of sample matrix on the analyte gas phase distribution is investigated when atomizing some environmental samples and, for the first time, the results of spatially-resolved atomic absorption determination of cadmium and lead in these samples are presented. It is shown that the influence of the matrix on the analyte distribution is significant, resulting in a significant analytical error. By avoiding such errors, the benefits of atomic absorption analysis with spatial resolution over conventional AAS are directly demonstrated.

Development and characterization of a titanium dioxide-based semiconductor photoelectrochemical detector

The development and characterization of a flow-through semiconductor-based titanium dioxide photoelectrochemical detector for flow injection analysis and liquid chromatography is described. The detector is nonselective, responding to a variety of organic analytes including amines, aromatic alcohols, hydroquinones, aldehydes, and furans with redox potentials less positive than the valence band edge of the titanium dioxide semiconductor. An investigation of the illuminated photoelectrochemistry and dark semiconductor electrochemical properties of the detector was carried out as a function of solvent system, electrochemical potential, and TiO{sub 2} production variables. Illumination intensity, titanium oxidation temperature, and electrode potential controlled the magnitude of the photoelectrochemical currents. Duration of thermal oxidation and the amount of hydrogen doping determined the ratio of the light to dark current for the analyte. Linearity over 2 orders of magnitude and detection limits in acelonitrile of 40 and 140 pmol, for p-aminoacetanilide and diethylamine, respectively, were demonstrated. Illumination of the semiconducting TiO{sub 2} wire electrode along a cylindrical electrochemical cell indicated the possible application of this spatially-resolved detection technique to whole column detection chromatography. 51 refs., 9 figs., 2 tabs.

Deposition Rate Monitoring using Laser Induced Fluorescence

ABSTRACTUltra thin films (< 10 nm) prepared using sputtering or other deposition techniques are becoming more technologically important, with promise of increased importance in the future, particularly in certain magnetic structures. For example, giant-magnetoresistive structures may incorporate individual layers having a thickness < 1 nm. Such a small thickness is commonly associated with relatively short deposition times (∼10 s) and may place limits on the reproducibility and accuracy of the conventional techniques for in situ thickness monitoring or integrated rate monitoring. Experiments have been performed to use laser induced fluorescence (LIF) as a rate monitoring technique for ultra thin films. An RF diode sputtering system was combined with a YAG-pumped, frequency-doubled dye laser to monitor the deposition rale of copper over a range of conditions. When coupled with an absolute calibration reference, the LIF signal gave a reproducible, well-behaved output over a range of pressure and temperature. The technique is potentially advantageous for depositions where rapid (∼1 s) measurements are needed. LIF is also projected to be a valuable tool for detecting very low deposition rates, and it offers the potential of sensitive, real time, spatially-resolved detection in time regimes extending to the nanosecond regime.

Spatially resolved detection of antibody—antigen reaction on solid/liquid interface using total internal reflection excited antigen fluorescence and charge-coupled device detection

Spatially-resolved detection of antibody—antigen reactions at the solid/liquid interface was investigated by total internal reflection excited fluorescence from large area flat surfaces. Anti-HSA immunoglobulin G(IgG) antibody was immobilized at four spatially distinct spots. Binding of fluorescein-labeled human serum albumin (HSA) from the solution to immobilized antibody was detected by a cooled charge-coupled device (CCD) as a change in the fluorescence intensity. A two-dimensional representation of the fluorescence was obtained during the binding reaction time of 25 mins. The contributions from bound and free antigen to the total signal were evaluated. The influence of the scattered excitation light and the normalization of fluorescence signal with respect to the two-dimensional incident light intensity distribution are discussed.