This paper presents a comprehensive analysis of the electroluminescence (EL) and current distributions in connection with heat transfer (thermal resistance) in high-power “vertical" and "face-up" AlGaInN light emitting diodes (LEDs). The study was carried out using a combination of high-resolution EL mapping techniques giving information on the lateral distributions of near-field light emission intensity and thermal transient measurements for evaluation of thermal resistance of LEDs and its elements. It was shown that poor current spreading at high current density causes increase in thermal resistance.
The foundation of measurement systems for environmental and structural health monitoring based on molecular condensation nuclei (MCN) detector is the measurement of the intensity of light scattered by aerosol particles. Aerosol particles are formed in the condensation chamber around single molecules of detected impurities (harmful and dangerous substances in the case of environmental monitoring and biomarkers in the case of structural health monitoring). The size of an aerosol particle is about 106 times larger than the size of the original impurity molecule. The ability of the aerosol particle to scatter incident light also increases ~1014÷1016 times compared with the original molecule. By measuring the light scattering intensity the concentration of chemical impurities in the air is determined. The paper investigates many aspects of the detection process - the optical scattering by aerosol particles inside the photometer of MCN detector; signal conditioning, processing of light scattering measurements results, determination of the criteria for making a decision about the presence of detected impurities in the environment; multi-component sensing of detected impurities and graphical user interface design. Experimental results of the detection of toxic substances in micro-concentrations in the environment are presented.
Molecular condensation nuclei (MCN) method is used in production engineering and process monitoring and relates to optical metrology methods of measuring the concentrations of various contaminants in the environment. Ultra high sensitivity of MCN method to a class of substances is determined by measuring the optical scattering aerosol particles, at the centers of which are located the detectable impurities molecules. This article investigates the influence of MCN manifestations coefficient (ratio of the concentration of aerosol particles to the concentration of molecules detectable impurities) on the sensitivity of the MCN detector. The MCN method is based on the application of various physicochemical processes to the flow of a gas containing impurities. As a result of these processes aerosol particle that are about 106 times larger than the original molecule of the impurity are produced. The ability of the aerosol particle to scatter incident light also increases ~1014 ÷1016 times compared with the original molecule and the aerosol particle with the molecule of the impurity in the center is easily detected by light scattering inside a photometer. By measuring of the light scattering intensity is determined concentration of chemical impurities in the air. An application nephelometric optical metrology scheme of light scattering by aerosol particles ensures stable operation of reliable and flexible measuring systems. Light scattering by aerosol particles is calculated on the basis of the Mie’s theory as aerosol particle sizes comparable to the wavelength of the optical radiation. The experimental results are shown for detectable impurities of metal carbonyls. Gas analyzers based on the MCN method find application in industries with the possibility of highly toxic emissions into the atmosphere (carbonyl technology of metal coatings and products, destruction of chemical weapons, etc.), during storage and transportation of toxic substances, as well as in the inspection of large-scale objects. There are some perspective areas of use MCN detector: prevention of illegal use of dangerous substances, revealing of their origin and leakage paths by means of marking with special non-radioactive chemical compounds; investigation of large-scale atmospheric circulation with the help of marking substances; nondestructive inspection for highly efficient filters with indicating agent concentration and for the inspection of the devices of high level tightness (heat-exchangers of fast nuclear reactors).
Molecular condensation nuclei (MCN) detector is a specialized optical sensor which provides for monitoring of various chemicals impurity in the environment and diagnosis of diseases in human exhaled air ("electronic nose" biosensor). Structurally MCN detector is included in the highly sensitive gas analyzers based on MCN method. The article describes the fundamental principles, specific features and application fields of the advanced highly sensitive MCN method. The MCN method is based on the application of various physico-chemical processes to the flow of a gas containing impurities. As a result of these processes aerosol particle that are about 106 times larger than the original molecule of the impurity are produced. The ability of the aerosol particle to scatter incident light also increases ~1014÷1016 times compared with the original molecule and the aerosol particle with the molecule of the impurity in the center is easily detected by light scattering inside a photometer. By measuring of the light scattering intensity is determined concentration of chemical impurities in the air. Aerosol particles in the MCN detector are formed in the condensing devices through overgrowth of the molecule detectable impurity by molecules so-called «developer» substance. At the final stage of the analysis in the MCN detector is measured light scattering by aerosol particles which is proportional to the concentration of determined impurities in the environment. For calculations of the scattered radiation is applicable Mie’s theory considering the scattering of light by spherical particles whose size is comparable to the wavelength of light. We have determined that the light scattering by aerosol particles is interferometric and is comparable within an order of magnitude with light scattering by the air inside a photometer. The detection threshold for the target component of the gas analyzer is attained at the spontaneous ionization background level and not at the limiting sensitivity level of the photodetector.
The principal foundations, specific features and application fields of the advanced highly sensitive method of gas
impurities detection - molecular condensation nuclei (MCN) method are discussed. MCN method is based on the
conversion of impurity molecules to condensation nuclei of much larger size followed by the nuclei enlargement in the
supersaturated vapor of specially selected low-volatile organic substances and detection of produced aerosol particles
using an optical (nephelometric) method. The light scattering properties of the aerosol particles and air in the photometer
of an MCN detector as well as sensitivity of the photometer’s photodetector are investigated. We have determined that
the light scattering by aerosol particles is interferometric by nature and is comparable within an order of magnitude with
light scattering by the air inside a photometer. The threshold sensitivity of fotointegrator was reduced a level where the
detection limit for the gas analyzer target component is determined by the background level of spontaneous condensation
and not by the sensitivity of the detector’s photoreceiver.
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