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In addition to draught, plants growing in arid soils face two major challenges: high salinity and iron (Fe) deficiency. Salinity attenuates growth, affects plant physiology and causes nutrient imbalance which is, in fact, one of the major consequences of saline stress. Fe is a micro-nutrient essential for plant development. It is required for several metalloenzymes involved in photosynthesis and respiration and Fe-deficiency is associated to chlorosis and low crop productivity. The role of microbial siderophores in Fe supply to plants is well documented as well as the effect of plant growth promoting rhizobacteria (PGPR) on the Page 1 of 41 http://pedosphere.issas.ac.cn Pedosphere mitigation of saline stress in crop cultures. However, the dual effect of siderophore-producing PGPR both on salt-stress and on Fe limitation is still poorly explored. This review provides a critical perspective on the combined effect of Fe limitation and soil salinization as challenges to modern agriculture and intends to summarize some indirect evidence that argue in favour of siderophore-producing PGPR as bio-fertilization agents in salinized soils. Recent developments as well as future perspectives on the use of PGPR are discussed as clues to sustainable agriculture practices, in the context of present and future climate change scenarios.

During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.

High-temperature characterization of the thermoelectric properties of chalcogenide Ge2Sb2Te5 (GST) is critical for phase change memory devices, which utilize self-heating to quickly switch between amorphous and crystalline states and experience significant thermoelectric effects. In this work, the electrical resistivity and Seebeck coefficient are measured simultaneously as a function of temperature, from room temperature to 600 °C, on 50 nm and 200 nm GST thin films deposited on silicon dioxide. Multiple heating and cooling cycles with increasingly maximum temperature allow temperature-dependent characterization of the material at each crystalline state; this is in contrast to continuous measurements which return the combined effects of the temperature dependence and changes in the material. The results show p-type conduction (S > 0), linear S(T), and a positive Thomson coefficient (dS/dT) up to melting temperature. The results also reveal an interesting linearity between dS/dT and the conduction activation energy for mixed amorphous-fcc GST, which can be used to estimate one parameter from the other. A percolation model, together with effective medium theory, is adopted to correlate the conductivity of the material with average grain sizes obtained from XRD measurements. XRD diffraction measurements show plane-dependent thermal expansion for the cubic and hexagonal phases.

Phase-change memory (PCM) devices are enabled by amorphization-and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses ($ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell. Published by AIP Publishing.