These multi-layer PV devices are typically configured to include an active layer, which is typically a cooperating sandwich of p-type, intrinsic i-typeand n-type semiconductors. With appropriately located electrical contacts being included, the structure forms a working PV cell.
Inductively coupled plasma An inductively coupled plasma is a plasma that is energized ionized by inductively heating the gas with an electromagnetic coiland contains a sufficient concentration of ions and electrons to make the gas electrically conductive. In these plasmas the positive ions are almost all singly charged and there are few negative ions, so there are nearly equal amounts of ions and electrons in each unit volume of plasma.
An inductively coupled plasma ICP for spectrometry is sustained in a torch that consists of three concentric tubes, usually made of quartzalthough the inner tube injector can be sapphire if hydrofluoric acid is being used. The end of this torch is placed inside an induction coil supplied with a radio-frequency electric current.
A flow of argon gas usually 13 to 18 liters per minute is introduced between the two outermost tubes of the torch and an electric spark is applied for a short time to introduce free electrons into the gas stream.
These electrons interact with the radio-frequency magnetic field of the induction coil and are accelerated first in one direction, then the other, as the field changes at high frequency usually The accelerated electrons collide with argon atoms, and sometimes a collision causes an argon atom to part with one of its electrons.
The released electron is in turn accelerated by the rapidly changing magnetic field. The process continues until the rate of release of new electrons in collisions is balanced by the rate of recombination of electrons with argon ions atoms that have lost an electron.
The temperature of the plasma is very high, of the order of 10, K. The plasma also produces ultraviolet light, so for safety should not be viewed directly.
The ICP can be retained in the quartz torch because the flow of gas between the two outermost tubes keeps the plasma away from the walls of the torch.
A second flow of argon around 1 liter per minute is usually introduced between the central tube and the intermediate tube to keep the plasma away from the end of the central tube.
A third flow again usually around 1 liter per minute of gas is introduced into the central tube of the torch. This gas flow passes through the centre of the plasma, where it forms a channel that is cooler than the surrounding plasma but still much hotter than a chemical flame.
Samples to be analyzed are introduced into this central channel, usually as a mist of liquid formed by passing the liquid sample into a nebulizer. To maximise plasma temperature and hence ionisation efficiency and stability, the sample should be introduced through the central tube with as little liquid solvent load as possible, and with consistent droplet sizes.
A nebuliser can be used for liquid samples, followed by a spray chamber to remove larger droplets, or a desolvating nebuliser can be used to evaporate most of the solvent before it reaches the torch.
Solid samples can also be introduced using laser ablation. The sample enters the central channel of the ICP, evaporates, molecules break apart, and then the constituent atoms ionise.
At the temperatures prevailing in the plasma a significant proportion of the atoms of many chemical elements are ionized, each atom losing its most loosely bound electron to form a singly charged ion.
The plasma temperature is selected to maximise ionisation efficiency for elements with a high first ionisation energy, while minimising second ionisation double charging for elements that have a low second ionisation energy.
Mass spectrometry For coupling to mass spectrometrythe ions from the plasma are extracted through a series of cones into a mass spectrometer, usually a quadrupole. The ions are separated on the basis of their mass-to-charge ratio and a detector receives an ion signal proportional to the concentration.
The concentration of a sample can be determined through calibration with certified reference material such as single or multi-element reference standards.
ICP-MS also lends itself to quantitative determinations through isotope dilutiona single point method based on an isotopically enriched standard. Other mass analyzers coupled to ICP systems include double focusing magnetic-electrostatic sector systems with both single and multiple collector, as well as time of flight systems both axial and orthogonal accelerators have been used.
Applications[ edit ] One of the largest volume uses for ICP-MS is in the medical and forensic field, specifically, toxicology. Another primary use for this instrument lies in the environmental field. Such applications include water testing for municipalities or private individuals all the way to soil, water and other material analysis for industrial purposes.
The trace elements from the glass can be used to match a sample found at the crime scene to a suspect. In recent years, industrial and biological monitoring has presented another major need for metal analysis via ICP-MS. Individuals working in plants where exposure to metals is likely and unavoidable, such as a battery factory, are required by their employer to have their blood or urine analyzed for metal toxicity on a regular basis.
This monitoring has become a mandatory practice implemented by OSHAin an effort to protect workers from their work environment and ensure proper rotation of work duties i.
Regardless of the sample type, blood, water, etc. Very high concentrations of salts, e. This can be avoided by diluting samples whenever high salt concentrations are suspected, though at a cost to detection limits. ICP-MS is also used widely in the geochemistry field for radiometric dating, in which it is used to analyze relative abundance of different isotopes, in particular uranium and lead.
ICP-MS is more suitable for this application than the previously used thermal ionization mass spectrometryas species with high ionization energy such as osmium and tungsten can be easily ionized.
For high precision ratio work, multiple collector instruments are normally used to reduce the effect noise on the calculated ratios. In the field of flow cytometrya new technique uses ICP-MS to replace the traditional fluorochromes.
Briefly, instead of labelling antibodies or other biological probes with fluorochromes, each antibody is labelled with a distinct combinations of lanthanides. When the sample of interest is analysed by ICP-MS in a specialised flow cytometer, each antibody can be identified and quantitated by virtue of a distinct ICP "footprint".
In theory, hundreds of different biological probes can thus be analysed in an individual cell, at a rate of ca.This has been the main motivation and passion for us to write this book.
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Atomic absorption spectroscopy is an element specific spectroscopic monitoring system that can determine the presence of specific elements when they exist at high temperature in a .