Growth atmosphere

Small amounts of tritium were added to the hydrogen growth atmosphere of some crystals. Radiation detectors fabricated from these crystals measure the energy distribution of the electrons created in the tritium decays inside the crystal (Hansen et al., 1982). These studies set a lower limit of the hydrogen concentration at a value between 1014 cm 3 and 1015 cm-3. 

More than for Cz, upscaling is limited by physical reasons. The RF threshold voltage of the inert growth atmosphere (Ar) limits the maximum crystal diameter. For rising diameters, more and more RF power is needed and finally, arcing occurs at the slit of the RF inducting coil. 

Artificially-grown materials can be contaminated by FAs for several reasons. The first one is the initial purity of the starting material for instance, the LHeT spectra of high-purity intrinsic silicon samples with RT resistivities 104flcm show the presence of residual boron and phosphorus at concentrations x 1012 cm 3 (see Fig. 7.7). Polycrystalline silicon also contains carbon as a residual impurity, which is transferred into the single crystal [45]. In bulk crystal growth, the impurities can come from the growth atmosphere,... 

We tried to obtain YAG optical ceramics doped with other d ions and to investigate properties of the samples. Ti ion can be a possible d dopant for YAG, and absorption and luminescence spectra of Ti were reported to resemble Ti3 spectra in sapphire It was found that Ti distribution in YAG depends strongly on crystal growth atmosphere, with appearance of precipitates in some cases. The situation can change in case of ceramics. So we decided at the beginning to investigate YAG Ti ceramics as well as YAG with less usual d dopant - Zr. ... 

Bi4Ge30 2 crystals will only be really colorless when the raw materials Bi203 and Ge20 have a high purity (5-6N). The growth atmosphere has to be oxygen, otherwise the Pt crucible will be attacked. 

The above rate law has been observed for many metals and alloys either anodically oxidized or exposed to oxidizing atmospheres at low to moderate temperatures—see e.g. [60]. It should be noted that a variety of different mechanisms of growth have been proposed (see e.g. [61, 62]) but they have in common that they result in either the inverse logaritlnnic or the direct logarithmic growth law. For many systems, the experimental data obtained up to now fit both growth laws equally well, and, hence, it is difficult to distinguish between them. 

At atmospheric pressure and at its melting point, urea decomposes to ammonia, biuret (1), cyanuric acid (qv) (2), ammelide (3), and triuret (4). Biuret is the main and least desirable by-product present in commercial urea. An excessive amount (>wt%) of biuret in fertiliser-grade urea is detrimental to plant growth. 

During the vapor deposition process, the polymer chain ends remain truly aUve, ceasing to grow only when they are so far from the growth interface that fresh monomer can no longer reach them. No specific termination chemistry is needed, although subsequent to the deposition, reaction with atmospheric oxygen, as well as other chemical conversions that alter the nature of the free-radical chain ends, is clearly supported experimentally. 

For some high growth-rate biomass species, the carbon dioxide concentration in the air among the leaves of the plant often is considerably less than that in the surrounding atmosphere. Photosynthesis may be limited by the carbon dioxide concentrations under these conditions when wind velocities are low and insolation is high. 

Fig. 4. Sihcon dioxide growth rate using a (100) sihcon substrate where the sohd lines represent a dry oxygen and the dashed lines a steam atmosphere.

Optimism about economic growth in the period 1960—1975 led to a large number of reactor orders. Many of these were canceled even after partial completion in the period after the 1974 oil crisis, as the result of a reduction in energy demand. Inflation, high interest rates, long constmction periods, and regulatory delays resulted in severe cost overmns. Moreover, the reactor accidents of TMI and, later, Chernobyl produced an atmosphere of pubHc concern. 

Confirmation of the destmetion of ozone by chlorine and bromine from halofluorocarbons has led to international efforts to reduce emissions of ozone-destroying CPCs and Halons into the atmosphere. The 1987 Montreal Protocol on Substances That Deplete the Ozone Layer (150) (and its 1990 and 1992 revisions) calls for an end to the production of Halons in 1994 and CPCs, carbon tetrachloride, and methylchloroform byjanuary 1, 1996. In 1993, worldwide production of CPCs was reduced to 50% of 1986 levels of 1.13 x 10 and decreases in growth rates of CPC-11 and CPC-12 have been observed (151). 

Even higher organisms can be used for the production of labeled compounds. Plants, tobacco, or Canna indica for example, when grown in an exclusive atmosphere of radioactive carbon dioxide, [ 002], utilize the labeled precursor as the sole source of carbon for photosynthesis. After a suitable period of growth, almost every carbon atom in the plant is radioactive. Thus, plants can serve as an available source of C-labeled carbohydrates (9). 

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