Antisite disorder and phase segregation in Mn2NiSn

A systematic study of crystal structure, local structure, magnetic and transport properties in quenched and temper annealed Ni2−xMn1+xSn alloys indicate the formation of Mn3Sn type structural defects caused by an antisite disorder between Mn and Sn occupying the Y and Z sublattices of X2YZ Heusler structure. The antisite disorder is caused by the substitution of Ni by Mn at the X sites. On temper annealing, these defects segregate and phase separate into L21 Heusler and D019 Mn3Sn type phases.

Nanoscale Chemical Imaging of Coadsorbed Thiolate Self-assembled Monolayers on Au(111) by Tip-Enhanced Raman Spectroscopy

Self-assembled monolayers (SAMs) of thiolates on metal surfaces are of key importance for engineering surfaces with tunable properties. However, it remains challenging to understand binary thiolate SAMs on metals at the nanoscale under ambient conditions. Here we employ tip-enhanced Raman spectroscopy (TERS) and density functional theory (DFT) calculations to investigate local information of binary SAMs on Au(111) coadsorbed from an equimolar mixture of p-cyanobenzenethiol (pCTP) and p-aminothiophenol (pATP), including chemical composition, coadsorption behavior, phase segregation, plasmon-induced photocatalysis, and solvation effects. We found that upon competitive adsorption of pCTP and pATP on Au(111) from a methanolic solution, the coadsorption initially occurs randomly and homogeneously; eventually, pATP is replaced by pCTP through gradual growth of pCTP nanodomains. TERS imaging also allows for visualization of the plasmon-induced coupling of pATP to p,p’-dimercaptoazobenzene (DMAB) and the solvation-induced phase segregation of the binary SAMs into nanodomains, with a spatial resolution of ~9 nm under ambient conditions. According to DFT calculations, these aromatic thiolates differing only in their functional groups, -CN versus –NH2, show different adsorption energy on Au(111) in vacuum and methanol, and thus the solvation effect on adsorption energy of these thiolates in methanol can determine the dispersion state and replacement order of the binary thiolates on Au(111).

Phase Segregation via Etching-Induced Cation Migration in CoSx-ZnS Nanoarchitectures for Solar Hydrogen Evolution

Low charge carrier mobility limits the development of highly efficient semiconductor-based photocatalysis. Heterointerface engineering is a promising approach to spatially separate the photoexcited charge carriers and thus enhance photocatalytic activity....

Alloying and Phase Transformation of Fe/FeNi Core/Alloy Nanoparticles at High Temperatures

This work explores how to form and tailor the alloy composition of Fe/FexNi1-x core/alloy nanoparticles by annealing a pre-formed particle at elevated temperatures between 180 – 325 oC. This annealing allowed for a systematic FeNi alloying at a nanoparticle whose compositions and structure began as a alpha-Fe rich core, and a thin gamma-Ni rich shell, into mixed phases resembling gamma-FeNi3 and gamma-Fe3Ni2. This was possible in part by controlling surface diffusion via annealing temperature, and the enhanced diffusion at the many grain boundaries of the nanoparticle. Lattice expansion and phase change was characterized by powder X-ray diffraction (XRD), and composition was monitored by X-ray photoelectron spectroscopy (XPS). Of interest is that no phase precipitation was observed (i.e., heterostructure formation) in this system and the XRD results suggest that alloying composition or alloy gradient is uniform. This uniform alloying was considered using calculations of bulk diffusion and grain boundary diffusion for Fe and Ni self-diffusion, as well as Fe-Ni impurity diffusion is provided. In addition, alloying was further considered by calculations for Fe-Ni mixing enthalpy (Hmix) and phase segregation enthalpy (HSeg) using the Miedema model, which allowed for the consideration of alloying favorability or core-shell segregation in the alloying, respectively. Of particular interest is the formation of stable metal carbides compositions, which suggest that the typically inert organic self-assembled monolayer encapsulation can also be internalized.

Additive Effect on the Structure of PEDOT:PSS Dispersions and Its Correlation with the Structure and Morphology of Thin Films

We reported on the interaction between poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and high-boiling-point additives in PEDOT:PSS aqueous dispersions and in the final polymer films with the aim of stablishing correlations between the structure of both inks and solid thin films. By Small-Angle X-ray Scattering (SAXS) using synchrotron radiation, it was found that the structural changes of dispersions of PEDOT:PSS with high-boiling-point additives can be explained as a two-step mechanism depending on the additive concentration. A compaction of PEDOT:PSS grains was observed at low concentrations while a swelling of the grains together with a phase segregation between PEDOT and PSS segments was evidenced at larger concentrations. Thin films’ morphology and structure were investigated by atomic force microscopy (AFM) and synchrotron Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) respectively. Our two-step model provides an explanation for the small and sharp domains of PEDOT:PSS thin films observed for low-additive concentrations (first step) and larger domains and roughness found for higher-additive concentrations (second step). A reduction of the ratio of PSS in PEDOT:PSS thin films upon the presence of additives was also observed. This can be related to a thinning of the PSS shells of PEDOT:PSS grains in the dispersion. The results discussed in this work provide the basis for a controlled tuning of PEDOT:PSS thin films structure and the subsequent electrical properties.

Horizontal wellbore production profile evaluation by distributed fiber-optic temperature surveillance

The main goal of the paper is demonstration of permanent downhole long-term monitoring capabilities for oil and gas production profile along horizontal wellbore in case of natural flow. The informational basis of the results obtained is the data of long-term temperature and acoustic monitoring in the borehole using a distributed fiber-optic sensor (DTS + DAS). Materials and methods. At the same time, flowing bottom-hole pressure and surface rates were monitored at the well for rate transient analysis, as well as acoustic cross-well interference testing [1], based on the results of which “well-reservoir” system properties were evaluated, the cross-well reservoir properties of the were estimated, and the possibility of cross-well testing using downhole DTS-DAS equipment was justified. The research results made it possible to assess reliability of DTS-DAS long-term monitoring analysis results in case of multiphase inflow and multiphase wellbore content. In particular, DTS-DAS results was strongly affected by the phase segregation in the near-wellbore zone of the formation. Conclusions. In the process of study, the tasks of inflow profile for each fluid phase evaluation, as well as its changes during the well production, were solved. The reservoir intervals with dominantly gas production have been reliably revealed, and the distribution of production along the wellbore has been quantified for time periods at the start of production and after production stabilization.