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Structure relaxation and crystallization of the CoW-CoNiW-NiW electrodeposited alloys.

ABSTRACT: The structure of electrolytically deposited nanocrystalline alloys of the CoW-CoNiW-NiW systems under low-temperature heating was investigated by means of high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), and analytical methods such as energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). Structural relaxation and crystallization were investigated at temperatures of 200°C to 300°C. The structural and compositional inhomogeneities were found in the CoW-CoNiW-NiW alloys, while the local changes in composition were found to reach 18 at.%. Nanocrystals in the alloys grew most intensely in the presence of a free surface, and we found their nuclei density to range from 2 × 1023 /m3 to 3 × 1023 /m3. It was determined that the local diffusion coefficient ranged from 0.9 to 1.7 10-18 m2/s, which could be explained by the prevalence of surface diffusion. The data gathered in these investigations can be used to predict the thermal stability of CoW-CoNiW-NiW alloys.

SUBMITTER: Pustovalov EV

PROVIDER: S-EPMC3923096 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Structure relaxation and crystallization of the CoW-CoNiW-NiW electrodeposited alloys.

Pustovalov Evgeny V EV Modin Evgeny B EB Voitenko Oleg V OV Fedorets Aleksander N AN Dubinets Aleksander V AV Grudin Boris N BN Plotnikov Vladimir S VS Grabchikov Sergey S SS

Nanoscale research letters 20140210 1

The structure of electrolytically deposited nanocrystalline alloys of the CoW-CoNiW-NiW systems under low-temperature heating was investigated by means of high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), and analytical methods such as energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). Structural relaxation and crystallization were investigated at temperatures of 20 ...[more]

PMID: 24506913

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Project description:We present the enhanced properties observed in the phase change memory alloy Ge2Sb2Te5 (GST) when doped with arsenic. Although arsenic is known as a toxic element, our observations show that significant improvement can be obtained in GST systems on thermal stability, transition temperature between amorphous and crystalline phases and switching behaviors when doping with arsenic. Though both the GST and arsenic doped GST are amorphous in the as-deposited state, only GST alloy turns to crystalline NaCl-type structure after annealing at 150 °C for 1 h. Results from the resistance versus temperature study show a systematic increase in the transition temperature and resistivity in the amorphous and crystalline states when the arsenic percentage in the GST alloy increases. The crystallization temperature (Tc) of (GST)0.85As0.15 is higher than the Tc observed in GST. Optical band gap (Eopt) values of the as-deposited films show a clear increasing trend; 0.6 eV for GST to 0.76 eV for (GST)0.85As0.15. The decreases in Eopt for the samples annealed at higher temperatures shows significant optical contrast between the as-deposited and annealed samples. Though all (GST)1-xAsx alloys show memory switching behaviors, threshold switching voltages (VT) of the studied alloys show an increasing trend with arsenic doping. For (GST)0.85As0.15, VT is about 5.2 V, which is higher than GST (4.0 V). Higher transition temperature and higher threshold switching values show arsenic doping in GST can enhance the memory device properties by improving the thermal stability and data readability. Understanding the doping effect on the GST is important to understand its crystallization properties. Structure properties of amorphous GST, Ge2Sb2-0.3As0.3Te5 and (GST)0.85As0.15 models were studied using first principles molecular dynamics simulations, compared their partial radial distribution functions, and q parameter order. Arsenic doping into GST features interesting structural and electronic effects revealed by the radial distribution functions, q order parameter and band gap value, in line with the experimental findings.

Dataset Information

Structure relaxation and crystallization of the CoW-CoNiW-NiW electrodeposited alloys.

Publications

Structure relaxation and crystallization of the CoW-CoNiW-NiW electrodeposited alloys.

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