Resistive RAM is a promising, relatively new type of memory with fast switching characteristics. Metal chalcogenide films have been used as the amorphous semiconductor layer in these types of devices. The amount of cr...Resistive RAM is a promising, relatively new type of memory with fast switching characteristics. Metal chalcogenide films have been used as the amorphous semiconductor layer in these types of devices. The amount of crystallinity present in the films may be important for both reliable operation and increased longevity of the devices. Germanium sulfide films can be used for these devices, and a possible way to tune the crystalline content of the films is by substituting Sn for some of the Ge atoms in the film. Thin films of GexSnySz containing varying amounts of tin were deposited in a plasma enhanced chemical vapor deposition reactor. Films with 2%, 8%, 15%, 26%, and 34% atomic percentage Sn were deposited to determine crystallinity and structural information with XRD and Raman spectroscopy. Based on these depositions it was determined that at about 8% Sn content and below, the films were largely amorphous, and at about 26% Sn and above, they appeared to be largely crystalline. At 15% Sn composition, which is between 8% and 26%, the film is more a mixture of the two phases. Based on this information, current-voltage (IV) curves of simple memory switching devices were constructed at 5% Sn (in the amorphous region), at 25% Sn (in the crystalline region), and at 15% (in the mixed region). Based on the IV curves from these devices, the 15% composition gave the best overall switching behavior suggesting that a certain degree of order in the semiconductor layer is important for RRAM devices.展开更多
The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere(NH).However,we reported here a pervasive an...The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere(NH).However,we reported here a pervasive and continuous vegetation greening and no weakened land carbon sink in the maturation phase of the 2015/2016 El Niño event over the NH(mainly in the extra-tropics),based on multiple evidences from remote sensing observations,global ecosystem model simulations and atmospheric CO_(2)inversions.We discovered a significant compensation effect of the enhanced vegetation growth in spring on subsequent summer/autumn vegetation growth that sustained vegetation greening and led to a slight increase in the land carbon sink over the spring and summer of 2015(average increases of 23.34%and 0.63%in net ecosystem exchange from two independent datasets relative to a 5-years average before the El Niño event,respectively)and spring of 2016(6.82%),especially in the extra-tropics of the NH,where the water supply during the pre-growing-season(November of the previous year to March of the current year)had a positive anomaly.This seasonal compensation effect was much stronger than that in 1997 and 1998 and significantly alleviated the adverse impacts of the 2015/2016 El Niño event on vegetation growth during its maturation phase.The legacy effect of water supply during the pre-growing-season on subsequent vegetation growth lasted up to approximately six months.Our findings highlight the role of seasonal compensation effects on mediating the land carbon sink in response to episodic extreme El Niño events.展开更多
文摘Resistive RAM is a promising, relatively new type of memory with fast switching characteristics. Metal chalcogenide films have been used as the amorphous semiconductor layer in these types of devices. The amount of crystallinity present in the films may be important for both reliable operation and increased longevity of the devices. Germanium sulfide films can be used for these devices, and a possible way to tune the crystalline content of the films is by substituting Sn for some of the Ge atoms in the film. Thin films of GexSnySz containing varying amounts of tin were deposited in a plasma enhanced chemical vapor deposition reactor. Films with 2%, 8%, 15%, 26%, and 34% atomic percentage Sn were deposited to determine crystallinity and structural information with XRD and Raman spectroscopy. Based on these depositions it was determined that at about 8% Sn content and below, the films were largely amorphous, and at about 26% Sn and above, they appeared to be largely crystalline. At 15% Sn composition, which is between 8% and 26%, the film is more a mixture of the two phases. Based on this information, current-voltage (IV) curves of simple memory switching devices were constructed at 5% Sn (in the amorphous region), at 25% Sn (in the crystalline region), and at 15% (in the mixed region). Based on the IV curves from these devices, the 15% composition gave the best overall switching behavior suggesting that a certain degree of order in the semiconductor layer is important for RRAM devices.
基金This study was financially supported by the National Key Research and Development Program of China(Grant No.2022YFF0801802)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0306)+2 种基金the National Natural Science Foundation of China(Grant No.42171050)the China Postdoctoral Science Foundation(Grant No.2023M730281)the State Key Laboratory of Earth Surface Processes and Resource Ecology of Beijing Normal University(Grant No.2023-KF-07).
文摘The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere(NH).However,we reported here a pervasive and continuous vegetation greening and no weakened land carbon sink in the maturation phase of the 2015/2016 El Niño event over the NH(mainly in the extra-tropics),based on multiple evidences from remote sensing observations,global ecosystem model simulations and atmospheric CO_(2)inversions.We discovered a significant compensation effect of the enhanced vegetation growth in spring on subsequent summer/autumn vegetation growth that sustained vegetation greening and led to a slight increase in the land carbon sink over the spring and summer of 2015(average increases of 23.34%and 0.63%in net ecosystem exchange from two independent datasets relative to a 5-years average before the El Niño event,respectively)and spring of 2016(6.82%),especially in the extra-tropics of the NH,where the water supply during the pre-growing-season(November of the previous year to March of the current year)had a positive anomaly.This seasonal compensation effect was much stronger than that in 1997 and 1998 and significantly alleviated the adverse impacts of the 2015/2016 El Niño event on vegetation growth during its maturation phase.The legacy effect of water supply during the pre-growing-season on subsequent vegetation growth lasted up to approximately six months.Our findings highlight the role of seasonal compensation effects on mediating the land carbon sink in response to episodic extreme El Niño events.
