VUV Detectors Research Articles

Hovhannisyan, M. A., Summary of the Results of Research and Selection of Corundum Crystalsfor Development and Creation of UV and VUV Detectors

The paper summarizes the results of our research conducted on the study of corundum crystals with various activating agents for development and creation of UV and VUV detectors. Corundum crystals with certain parameters were chosen as the optimal converter of UV and VUV radiant energy into the visible region of radiation for creating UV and VUV detectors with high spatial and temporal characteristics, which also have high radiation and thermal resistance.

Vacuum ultraviolet photoconductive detector based on anatase TiO2 thin film deposited on SiO2 substrate

We report on titanium dioxide (TiO2) thin film deposited on a quartz (SiO2) substrate as an improved photoconductive detector for radiation below 200 nm wavelength (vacuum ultraviolet region, VUV). The crystalline film has an anatase phase and an average crystallite size of 10.6 nm. It has a transmission edge at 322 nm and an optical band gap of 3.18 ± 0.02 eV. Under VUV illumination, the TiO2 photoconductive detector exhibited a photocurrent of 5.3 mA at an applied bias voltage of 100 V. The dark current measured without VUV illumination and at the same bias voltage is 8.8 × 10−6 mA, which is 6 orders of magnitude smaller compared to the photocurrent. The photoconductive VUV detector based on TiO2 thin film provides a means of directly measuring VUV radiation compared to detection via the photoluminescence of a scintillator.

Hyphenation of short monolithic silica capillary column with vacuum ultraviolet spectroscopy detector for light hydrocarbons separation

Compared to conventionnal bench top instruments, on-line GC analyzers require specific characteristics. On one hand, for some applications operating with a reactor pressure as high as several tens of bars, sample pressure has to be reduced before GC separation, or specific valves and columns have to be designed to perform separation with high carrier gas inlet pressure. On the other hand, informative detectors such as mass spectrometer are valuable but low maintenance detectors are prefered. To fit these two requirements (sampling at high pressure without decompression stage, and informative detector with low maintenance), short monolithic silica capillary column operated with inlet pressure as high as 60 bar has been hyphenated to VUV detector.Injection and column performance have been first investigated. The system has been optimized by adjusting split ratio at high pressure and by tuning two main VUV detector parameters (“average number” linked to data point averaging and make-up gas pressure) to decrease the limit of quantification. The optimization stage led to a set of experimental parameters which is a good compromise between signal-to-noise ratio and chromatographic efficiency. Finally, the hyphenated monolithic column has be used to partially separate a mixture of methane, ethane, carbon monoxide and carbon dioxide within 15 s, and the VUV deconvolution capabilities have been exploited to overcome coelution and finally separate individual signals.

Flow-modulated comprehensive two-dimensional gas chromatography combined with a vacuum ultraviolet detector for the analysis of complex mixtures

The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC×GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer’s law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120–240nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry (e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC×GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids.Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis.

A high-resolution imaging detector for VUV applications

The VUV (30–1200Å) detector described consists of a compact ‘Micro-Channel-Plate-Wedge-and-Strip anode’ imaging system and of the corresponding data read-out electronics with 32 Mbyte of memory. The performance of this space qualified detector system was measured in the FUV. We obtained a spatial resolution of about 70 μm over the full detector area of ∼7 cm 2. Image distortions are small and can easily be corrected for. Detector efficiency depends on the choice of photo-cathode and ranges between 50% in the FUV up to 90% in the EUV.

真空紫外検出器校正用ビームラインの設計とその特性

真空紫外検出器校正用ビームラインの設計とその特性

Stability of semiconductor photodiodes as VUV detectors

The stability of semiconductor photodiodes originally designed for the visible spectral range has been investigated in the VUV. For silicon photodiodes a strong radiation-induced decrease of the responsitivity was found. The spectral dependence of this effect has been studied in the vicinity of the Si L absorption edge. GaAsP and GaP Schottky diodes show remarkable stability and high quantum efficiency. These photodiodes seem to be suitable as transfer standard detectors in the VUV.

A new type VUV detector with plane electrodes deposited on a crystalline quartz.

A new type VUV detector with plane electrodes deposited on a crystalline quartz has been fabricated and evaluated. The external quantum efficiency of the detector was measured for radiation between 45 nm and 140 nm, and has a maximum value of about four percent at 70 nm. The fundamental absorption edge of the crystalline quartz is found to be at 150 nm. The noise equivalent power for this detector is about 1.25×10-11 W. The detector was employed on trial to measure the helium discharge spectrum, and has given satisfactory results.

Electron–photon coincidence technique for the absolute calibration of VUV detectors

A method is described whereby VUV photon detectors can be accurately calibrated. This method is illustrated by taking the 58.4-nm transition of He as an example. The technique consists of crossing a monoenergetic electron beam with a beam of He atoms. When inelastically scattered electrons which have excited the 2 1P state are detected in coincidence with the 58.4-nm photons emitted in the decay of the excited state, the interaction volume formed by the crossed beams constitutes a standard source of photons. By comparing the number of detected coincidences with the predicted number the calibration can be made. A total detector efficiency of 0.024 + or - 0.003 is obtained for a Galileo 4830 channeltron.