Deep levels identification

Deep state experiments measure carrier capture or emission rates, processes that are not sensitive to the microscopic structure (such as chemical composition, symmetry, or spin) of the defect. Therefore, the various techniques for analysis of deep states can at best only show a correlation with a particular impurity when used in conjunction with doping experiments. A definitive, unambiguous assignment is impossible without the aid of other experiments, such as high-resolution absorption or luminescence spectroscopy, or electron paramagnetic resonance (EPR). Unfortunately, these techniques are usually inapplicable to most deep levels. However, when absorption or luminescence lines are detectable and sharp, the symmetry of a defect can be deduced from Zeeman or stress experiments (see, for example, Ozeki et al. 1979b). In certain cases the energy of a transition is sensitive to the isotopic mass of an impurity, and use of isotopically enriched dopants can yield a positive chemical identification of a level. 

The presence of a shallow acceptor level in GaN has been attributed to C substituting on an N site by Fischer et al [7], In luminescence experiments on GaN from high temperature vapour phase epitaxy in a C-rich environment donor-acceptor and conduction-band-to-acceptor transitions have been distinguished in temperature dependent experiments. From the separation of both contributions an optical binding energy of 230 meV close to the value of effective mass type acceptors was obtained. Hole concentrations up to 3 x 1017 cm 3 were achieved by C doping with CCU by Abernathy et al [10], In addition Ogino and Aoki [17] proposed that the frequently observed yellow luminescence band around 550 nm should be related to a deep level of a C-Ga vacancy complex. The identification of this band, however, is still very controversial. 

There are some techniques, such as admittance spectroscopy and deep-level transient spectroscopy (DLTS), that are quite powerful in the characterization of deep levels in semiconductors [139]. These techniques have also begun to be used for the characterization of conjugated polymers such as PPV [178] and MEH-PPV [179]. These techniques may permit the determination of several trap parameters such as activation energy, concentration, charge carrier capture cross section, defect donor/acceptor character that can contribute to the chemical identification of the traps. 

The ro-vibronic spectrum of molecules and the electronic transitions in atoms are only part of the whole story of transitions used in astronomy. Whenever there is a separation between energy levels within a particular target atom or molecule there is always a photon energy that corresponds to this energy separation and hence a probability of a transition. Astronomy has an additional advantage in that selection rules never completely forbid a transition, they just make it very unlikely. In the laboratory the transition has to occur during the timescale of the experiment, whereas in space the transition has to have occurred within the last 15 Gyr and as such can be almost forbidden. Astronomers have identified exotic transitions deep within molecules or atoms to assist in their identification and we are going to look at some of the important ones, the first of which is the maser. 

CDC Case Definition An illness with acute onset of fever >101°F followed by a rash characterized by firm, deep seated vesicles or pustules in the same stage of development without other apparent cause. Clinically consistent cases are those presentations of smallpox that do not meet this classical clinical case definition (1) hemorrhagic type, (2) flat type, and (3) variola sine eruptione. Laboratory criteria for diagnosis is (1) polymerase chain reaction (PCR) identification of variola DNA in a clinical specimen, or (2) isolation of smallpox (variola) virus from a clinical specimen (Level D laboratory only confirmed by variola PCR). 

Simultaneous or sequential strokes in different arterial territories, multi-level posterior circulation infarcts, simultaneous infarcts in the three subterritories (superficial anterior, superficial posterior and deep) of the MCA, and hemorrhagic transformation of an ischemic infarct also point to a cardiac origin of the stroke (Arquizan et al. 1997 Ay et al. 1999 Ferro 2003a,b). Occlusion of the carotid artery by a mobile thrombus, early recanalization of an occluded vessel and the identification of microembolism in both MCAs are all highly indicative of a cardiac source of emboli. 

The AFLP has the power of PCR and the solidity of RFLP analysis. As the AFLP is highly reproducible and has a deep enough resolution due to the number of estimable detected fragments this technique allows us to analyze the strains at the intraspecies level. With this technique we can carry out epidemiological studies or can generate a database for routine identification. We proved that its application is very usefiil in the determination of the route of an infection or in the correct identification of pathogenic yeasts. 

The ablation rate of the blue-ice fields surrounding the Elephant Moraine was measured at regular intervals along four surveyed lines that started from the surveyed baseline in Fig. 17.6 and extended up to 1.75 km beyond the edge of the moraine (Faure and Buchanan 1987,1991). At each station a wooden dowel rod was placed into a hole drilled into the ice with an ice sCTew. The holes were 10-15 cm deep and had diameters of 1.0 cm. The level of the ice was recorded by a notch cut into the dowel and the location of each rod was inscribed in order to facilitate future identification. When these stations were revisited 2 years later, the level of the ice was recorded be cutting a second notch into the dowels. The distance between the two... 

Subsequently, a high-sensitivity back-illuminated, deep-depletion CCD-based Raman spectrometer (with 785-nm excitation and a CCD quantum efficiency of 85-90% at this wavelength) was used (instead of the UV spectrometer) for this application in order to improve microconstant determination and, more importantly, to allow qualitative identification of individual microspecies [94]. RS is particularly promising for this work, as it provides high chemical information content in the form of vibrational fingerprints as well as tolerates the presence of water. Just a few years ago, RS could not be considered for this application due to the historically high detection levels and problems with fluorescence. 

---