Impurities laser spectroscopy

This technique constitutes a good example of high-resolution laser spectroscopy. It has been successfully applied to a variety of systems to examine important aspects, such as the microscopic crystalline structure, the trace impurity distribution, or the degree of structural disorder. 

This molecule is ideal for photodissociation dynamics studies, since it has allowed excited states in the visible region of the spectrum which is more easily accessible with tunable lasers. Both products can in principle be detected using the LIF method, though at the present time only the product distribution of the CN radical has been measured, since NO is often present as an impurity. The spectroscopy is also well studied... 

Laser spectroscopy offers different techniques of increased sensitivity for the detection of tiny concentrations of impurities, pollutant gases, or rare isotopes down to the ultimate level of single-molecule detection. 

For the production of materials for electronic circuits, such as chips, the demands regarding purity of materials, their composition, and the quality of the production processes become more and more stringent. With decreasing size of the chips and with increasing complexity of the electronic circuits, measurements of the absolute concentrations of impurities and dopants become important. The following two examples illustrate how laser spectroscopy can be successfully applied to the solution of problems in this field. 

Applications So far, intracavity laser spectroscopy has been applied primarily to the detection of absorption spectra of gaseous impurities such as NH3 and CH4 in the near-infrared region using a tunable broadband laser. Special DLs designed with an external cavity have also been investigated recently for this purpose. CRS has been applied successfully to trace element detection using the ICP as the atomization system. The detection limits observed are at sub-parts per billion level (e.g., 0.3 ng ml for lead) and comparable to the detection limits achieved with ICP-MS. 

Molecular impurities in solids can now be detected down to the singlemolecule level [15.16]. These molecules and their interaction with their surroundings can be probed by high-resolution laser spectroscopy. The relevance of such techniques in biology is obvious [15.17]. The development of single-molecule detection for the in vitro and in vivo quantification of biomolecular dynamics is essential for the understanding of biomolecular reactions and for the realization of evolutionary biotechnology [15.18]. 

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

Raman spectroscopy has enjoyed a dramatic improvement during the last few years the interference by fluorescence of impurities is virtually eliminated. Up-to-date near-infrared Raman spectrometers now meet most demands for a modern analytical instrument concerning applicability, analytical information and convenience. In spite of its potential abilities, Raman spectroscopy has until recently not been extensively used for real-life polymer/additive-related problem solving, but does hold promise. Resonance Raman spectroscopy exhibits very high selectivity. Further improvements in spectropho-tometric measurement detection limits are also closely related to advances in laser technology. Apart from Raman spectroscopy, areas in which the laser is proving indispensable include molecular and fluorescence spectroscopy. The major use of lasers in analytical atomic... 

When investigating opaque or transparent samples, where the laser light can penetrate the surface and be scattered into deeper regions, Raman light from these deeper zones also contributes to the collected signal and is of particular relevance with non-homogeneous samples, e.g., multilayer systems or blends. The above equation is only valid, if the beam is focused on the sample surface. Different considerations apply to confocal Raman spectroscopy, which is a very useful technique to probe (depth profile) samples below their surface. This nondestructive method is appropriate for studies on thin layers, inclusions and impurities buried within a matrix, and will be discussed below. 

The fluorite in our study consisted of 40 samples from different environments. Concentrations of luminescence impurities in several samples are given in Table 4.6. By using laser-induced time-resolved spectroscopy we were able to detect and ascribe the following emission centers Eu +, Ce ", Gd +, Sm +, Dy3+, Eu +, Pr +, Er +, Tm +, Ho +, Nd +, Mn + and the M-center (Figs. 4.10-4.12). 

The limitations of Raman spectroscopy are its low sensitivity compared to IR absorption and fluorescence interference from impurities in the sample. Raman spectroscopy is a developing technology, and a good amount of research and planning is necessary before deciding whether or not to employ it. The cost of a Raman process analyzer exceeds that of other analyzers. To reduce cost, Raman analyzers often include multichannel capability. Up to four process streams can be analyzed with a single CCD camera by splitting the lasers. 

Colored samples or impurities in polymer samples may absorb laser radiation and re-emit it as fluorescence. The intensity of fluorescence can be as much as 104 times higher than that of Raman scattered light. The fluorescence problem is the major drawback of using Raman spectroscopy. Thus, a Raman spectrum can be completely masked by fluorescence. Three main methods can be used to minimize fluorescence ... 

In an applied perspective, the interest in the spectroscopy of shallow impurities in semiconductors has been linked for a long time with the production of detectors for the medium and far infrared, but the possibility to produce terahertz lasers based on the transitions between discrete shallow levels has aroused a renewed interest in this spectroscopy in silicon. Another new potential field of application is the domain of quantum computing. A large part of the results presented in this book concerns silicon and this reflects the relative volume of investigations devoted to this material. 

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