Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (∼70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m(-1) and 0.08 S m(-1), respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m(-1) and 137 S m(-1) for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 μV K(-1) and 335 μV K(-1) for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.
BACKGROUND: Tea (Camellia sinensis L.) bushes are periodically (at 3-4 year intervals) pruned (cut from top) to maintain vegetative growth stage and constant height. Plant residues (prunings litter) generated after pruning are generally left in the field as a potential source of organic matter in soil. Organic carbon (C) sequestration due to pruning litter incorporation is expected to increase microbial activity in soil. Being an evergreen plant, tea bushes assimilate atmospheric carbon dioxide (CO 2 ) throughout the year; however, the relation between decomposition of pruning litters and net CO 2 flux for tea plantation have not been studied before. The objective of this experiment was to evaluate the relation between organic C accumulation and microbial respiration in pruning litters incorporated soil and its subsequent effect on the net CO 2 flux from the atmosphere to tea plantation.
RESULTS: Tea bushes assimilated 1878.2-2371.2 kg CO 2 ha −1 from the atmosphere within December to November; however, pruned bushes assimilated 1451.7-1840.8 kg CO 2 ha −1 within the same period. Decomposition of pruning litters added organic matter in soil, which was mostly accumulated in larger soil aggregates having 2.0-0.25 mm size. Such organic matter accumulation significantly increased microbial respiration in those aggregates, which in turn increased the overall rate of CO 2 emission from soil to the atmosphere. CONCLUSION: Decomposition of pruning litters leads to emission of 426.5-530.4 kg CO 2 ha −1 from soil. Hence, pruned areas recorded relatively lower (16.0-27.4%) net CO 2 flux from the atmosphere to tea ecosystem as compared to unpruned tea bushes.
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