Ge 2 Sb 2 Te 5 films were deposited by RF magnetron sputtering on Si(100)/SiO 2 substrates. N + ion was implanted into Ge 2 Sb 2 Te 5 films. Two obvious steps were observed in the resistance-temperature curve of the Ge 2 Sb 2 Te 5 -N film with a minor nitrogen implant dose. The two steps may change into one step because the phase transition from FCC to hexagonal structure was suppressed by nitrogen implantation if the nitrogen implant dose is higher than 4.51 × 10 16 cm −2 . The favourite nitrogen implant dose is about 6.44 × 10 15 to 1.92 × 10 16 cm −2 in our study. This phenomenon is very important for multilevel storage. Three-level storage with Ge 2 Sb 2 Te 5 -N media for chalcogenide random access memory (C-RAM) can be performed easily, and hence, the capacity of C-RAM will be dramatically increased.
Several factors including the culture temperature, bivalent ion, and osmotic stress were gradually optimized for preparing efficient competent cells. The effect of culture temperature on the transformation efficiency (TrE) of DH5α was tested with 100 mM CaCl. The lower culture temperature at 18 °C resulted in higher TrE of 2.5 × 10 cfu/μg, which was about 3.5 times of that obtained at 37 °C. Bivalent ions including Ca, Mn, Mg, and Ni were tested independently or combinatorially at a total concentration of 100 mM. Ni showed a significantly inhibition on the TrE, and various concentration combinations of Ca, Mg, and Mn were tested. The TrE was improved up to 1.8 ± 0.4 × 10 cfu/μg, when a combination of 25 mM Ca, 50 mM Mg, and 25 mM Mn was applied. Further supplement of 0.8% (w/v) PEG lead to a slight decrease in the TrE, whereas supplement of 25 mM sucrose contributed to another increase in the TrE by 17% up to 2.1 ± 0.3 × 10 cfu/μg. These results indicated that the culture temperature and bivalent ion were important factors affecting the TrE of A chemical method for preparing efficient competent cells of was provided.
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