Dark spot formation

Sato, H. Manufacture of organic electroluminescent (EL) displays with suppressed leak and dark spot formation. Jpn. Kokai Tokkyo Koho JP 2005149811,2005. 

Figure 12.13. Image depicting the formation of precipitates, seen as small dark spots, in a palladium precursor solution after 1 day of storage. The image shown was taken of a drop of precursor solution that was dispensed onto a microscope slide and covered with a glass cover slide.

Si02 layers pre-implanted with 140keV Si ions, and those with embedded Si nanociystals (Si-ncs) have been irradiated with 130 MeV Xe ions, HREM and photoluminescence spectroscopy wo e used for the characterizations. In the Si-implanted layers HREM revealed the 3-4 nm-size dark spots, whose number and size grew with increase in Xe ion dose. Photoluminescenoe showed the presence of two bands - at 780 nm and at 670 nm. The intensity and position of the bands depended on the dose. Changes of the spectra and the results of passivation were interpreted as transformation of Si-ncs (-780 nm) into damaged Si-ncs (-670 nm) and vice versa. It is concluded, that electronic losses are responsible for the formation of new Si-ncs, whereas elastic losses introduce the defects. 

Kralchevsky, P.A. Nikolov, A.D. Wasan, D.T. Ivanov, LB. Formation and expansion of dark spots in stratifying foam films. Langmuir 1990, 6 (6), 1180-1189. 

Fig, 8.GB shows a small metastable pit observed with the optical microscope. The formation of tlie pit is accompanied by a spike in the current (with an amplitude of only 80nA), indicating an electrochemical reaction. About three seconds later, the pit abruptly passivates and the electrical current drops to its noise level. The pit remains seen as a dark. spot. 

Extrinsic degradation is attributed to chemical reactions of the active materials with its environment. The most common cause of degradation is the contact with oxygen and water in the presence of light, which leads to a rapid decrease of performance of the diodes, resulting from a modification of the structure of the active material, which is furthermore accelerated by electrical stress. The degradation onset corresponds to a formation of dark spots [33], which are nonemis-sive areas of the device surface. Most of the devices should therefore be protected by an encapsulation to prevent the contact with ambient air. A properly protected encapsulated diode will not develop chemical reactions that affect its lifetime. An alternative approach is the use of metal oxide layers combined with high work function and air-stable metals such as A1 or Au to replace the usual transport layers (PEDOTPSS or LiF) to fabricate diodes that can be used without encapsulation [34]. 

Transmission electron microscopy (TEM) was used to determine the size and size distribution of the AuNPs. The nanoparticles are observed as dark spots because of their higher density as compared with the organic ligand. The TEM micrographs show the formation of long nanofibres consisting of AuNPs (Fig. 11a). 

Figures. A microtitre plate-adapted format of a manually prepared 9 -spot membrane. Dark spots indicate stained (blue) free amino functionalities, light spots have turned to yellow after coupling with an Fmoc-amino acid HOBt ester.

Procedure I. The test solution should be made as neutral as possible (if necessary by preliminary treatment with ammonia or zinc oxide). A drop of the clear solution is placed on a dark spot plate or black watch glass and stirred with 8 drops of the reagent solution. The formation of a yellow turbidity or precipitate indicates the presence of sodium. 

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