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Abstract: The effects of nitrogen doping on the chemical bonding state, microstructure, electrical property and thermal stability of Ge15Sb85 film were investigated in detail. The doped N atoms tend to bond with Ge to form Ge3N4, as proved by X-ray photoelectron spectroscopy analyses. X-ray diffraction patterns showed that both undoped and N-doped Ge15Sb85 films crystallize into a hexagonal phase very similar to Sb. The thickness reduction upon crystallization for undoped and N-doped Ge15Sb85 films is less than 5%. The crystalline resistivity, crystallization temperature, and thermal stability of amorphous state all increase after nitrogen doping, while the grain size decreases. By adding 7.0at.% N into the Ge15Sb85 film, the crystalline resistivity increases twelve times and the crystallization temperature increases about 50°C. The maximum temperature for 10-year retention of amorphous Ge15Sb85 film is estimated to be 147°C and that of N-doped films is even higher, which will promise better data retention of phase-change random access memory especially in the high-temperature application. [Copyright &y& Elsevier]

Abstract: The characteristics of Si-doped Sb2Te3 thin films were investigated using differential scanning calorimetry (DSC), four-point probe technique, X-ray diffraction (XRD) analysis and high resolution transmission electron microscopy (HRTEM). It is found that the as-deposited Sb2Te3 film in our study is partly crystallized. Silicon doping increases the crystallization temperature and resistivity of Sb2Te3 film significantly. XRD and HRTEM analyses indicated that some of the doped Si atoms substitute for Sb or Te in the lattice, while others exists at the grain boundaries in the form of amorphous phase, which may be responsible for grain size reduction and high crystalline resistivity of Si-doped specimens. Compared with the conventional Ge2Sb2Te5 film, Si-doped Sb2Te3 films exhibit lower melting temperature and higher crystalline resistivity, which is beneficial to RESET current reduction of phase-change random access memory (PRAM). These results show the feasibility of Si-doped Sb2Te3 films in PRAM application. [Copyright &y& Elsevier]

Abstract: The effects of Si doping on the structural and electrical properties of Ge2Sb2Te5 film are studied in detail. Electrical properties and thermal stability can be improved by doping small amount of Si in the Ge2Sb2Te5 film. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phase-transition temperature from face-centered cubic (fcc) phase to hexagonal (hex) phase, however, decreases the melting point slightly. The crystallization activation energy reaches a maximum at 4.1at.% and then decreases with increasing dopant concentration. The electrical conduction activation energy increases with the dopant concentration, which may be attributed to the increase of strong covalent bonds in the film. The resistivity of Ge2Sb2Te5 film shows a significant increase with Si doping. When doping 11.8at.% of Si in the film, the resistivity after 460°C annealing increases from 1 to 11mΩcm compared to the undoped Ge2Sb2Te5 film. Current–voltage (I–V) characteristics show Si doping may increase the dynamic resistance, which is helpful to writing current reduction of phase-change random access memory. [Copyright &y& Elsevier]

Catalytic steam reforming of acetic acid can be divided into two steps, i.e. acetic acid decomposition followed by water gas shift. While theoretical studies have been devoted to these two individual reactions, the role of water and its derivatives in the reforming process, especially in CH 3 COOH decomposition, remains largely unknown. In this study, a thorough investigation of the effects of the solvent water and its derived O*/OH* species on some key dehydrogenation steps on Ni(111) is carried out using density functional theory. The involved dehydrogenation species include O−H bond scission species H 2 O*, CH 3 COOH*, trans -COOH* and C−H bond scission species CH 3 CO*, CH 3 C*, CH 2 C*. The results show that the pre-adsorbed O*, OH*, and H 2 O* species not only affect the adsorption stability of these species, but also influence their dehydrogenation reactivity. O* and OH* species can both enhance the O−H bond scission, and the promotional effect of O* is superior to OH*. Nevertheless, H-abstraction from C−H bond by O* and OH* are both hindered except for CH 3 CO* dehydrogenation in the presence of OH*. Furthermore, the solvent water notably weakens O−H bonds, yet exhibits negligible effect on the C−H bond breakage. Analogously, the solvent effect of CH 3 COOH* on O−H bond scission is also investigated. [ABSTRACT FROM AUTHOR]