Energy Dispersive X-ray Line Scans Research Articles

In English

The main idea of the work is the development of a cheap and easy method for the manufacture of nanostructured systems based on the Chemical Vapor Deposition (CVD). Beginning with a new class of materials for interference optics in the infrared (IR) range of the spectrum, the evaporation of composites of systems germanium-metal chalcogenide (oxide), in particular, of the Ge-ZnS and Ge-Sb2Se3 systems was studied. They evaporate in vacuum congruently, and upon condensation on substrates form nano-structured thin-film coatings. In the first of these systems, the coating has an X-ray amorphous nature: the formation of a nano-dispersed composite in a Ge-ZnS film is confirmed by the absence of characteristic peaks of Ge and ZnS in X-ray diffraction patterns, but the formation of a characteristic halo takes place. At the same time, upon evaporation and condensation of a sample of the Ge-Sb2Se3 system, a glassy structure is formed; this is confirmed by high-resolution transmission electron microscopy (TEM), where no crystalline regions were found. The energy-dispersive X-ray (EDX) spectroscopy measurements of the coating (about 10 at.% of Ge, 40 at.% of Sb and Se, respectively) indicate a certain deviation from the stoichiometry compared to the initial sample of the system. This may indicate a slightly lower volatility of germanium selenides compared to antimony selenides. The EDX line scans along the cross-section of the coating exhibited strong fluctuations in the concentration of elements, and, consequently, the heterogeneity of the coating in terms of composition. Both coatings have high mechanical strength (group 0). At the same time, their optical properties differ significantly: the refractive indices are 3.00 and 3.66 for the Ge-ZnS and Ge-Sb2Se3 systems, respectively. It is believed that nano-structuring in the above systems is due to the high capability of germanium to amorphize upon condensation on a glass substrate.

Germanium catalyzed vapor–liquid–solid growth and characterization of amorphous silicon oxide nanotubes: comparison to the growth of its nanowires

One-dimensional (1D) nanostructures were grown with a simple technique using continuous-wave laser vaporization of a Ge target containing 5 at.% Si in high-pressure (up to 0.9 MPa) Ar gas atmosphere. A maximum amount (~ 30% of all products) of 1D nanostructures was obtained at 0.9 MPa and these nanostructures were identified as amorphous silicon oxide (SiOx) nanotubes (NTs) and attached with crystalline Ge-rich NPs with elongated prolate-like or sphere-like shapes at their tips by transmission electron microscopy (TEM), high-angle annular dark-field-scanning TEM, and energy dispersive X-ray line scan spectrometry. As the Ar pressure decreased from 0.9 to 0.03 MPa, the average diameters, wall thicknesses, and lengths of the NTs decreased from 57.9 to 22.9 nm, 13.2 to 6.7 nm, and 2.1 to 0.2 µm, respectively, and the tip NP size decreased from 139.0 to 41.7 nm. There was a strong correlation among the diameters, wall thicknesses, and lengths of the NTs and tip Ge NP sizes, indicating the role of molten Ge NPs as catalyst seeds for the precipitation of SiOx in a vapor–liquid–solid growth mechanism at high temperature. The SiOx precipitation quantities from the seed NPs for the NTs were compared with those of amorphous SiOx nanowires (NWs) at 0.1–0.9 MPa to clarify the growth mechanism of the NTs. We argue that smaller precipitation quantities of SiOx than those for the NWs play a critical role in the formation of cap structures with different sizes and shapes from the molten Ge NPs and the growth of the NTs.

A parametric study for the synthesis of graphene–AgAu nanocomposites: performances as electrode material

Reduced graphene oxide (rGO)/AgAu bimetallic nanoparticle nanocomposites were prepared with one step simultaneous reduction of graphene oxide, silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using glucose as a reducing agent. The synthesized nanocomposites were characterized by ultraviolet–visible spectroscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscope with energy dispersive X-ray line scan analysis. The electrochemical performances of nanocomposites were analyzed by cyclic voltammetry and galvanostatic charge–discharge techniques. The effects of synthesis parameters on the structure and the morphology of graphene–AgAu bimetallic nanoparticle nanocomposites were investigated. The results showed that rGO sheets were successfully reduced and decorated homogenously by AgAu bimetallic nanoparticles with small sizes and narrow particle size distribution, also it was determined, synthesis parameters including reducing agent concentration, alkalinity of the reaction media, the presence of stabilizing agent polyvinylpyrrolidone and reaction temperature had significant effect on the particle size, size distribution and the particle structure of graphene nanosheets decorated with bimetallic nanoparticles. The results showed that rGO/AgAu bimetallic nanoparticle nanocomposite proved to be a promising electrode material for supercapacitors application.

Effect of Si/Al ratio and amount of deposited MFI-type seed crystals on the separation performance of silicalite-1 membranes for ethanol/water mixtures in the presence of succinic acid

Silicalite-1 zeolite membranes were prepared on porous tubular α-Al2O3 supports by a secondary growth method. The influences of the Si/Al ratio and the amount of deposited MFI (silicalite-1 and ZSM-5) seed crystals on membrane pervaporation (PV) performance for the separation of ethanol/water (binary) and ethanol/water/succinic acid (ternary) mixtures were investigated. The prepared membranes were characterized by X-ray diffraction and scanning electron microscopy, and the Si and Al distributions in the membrane layers were determined by energy-dispersive X-ray line scanning. Each silicalite-1 membrane was composed of two layers: an MFI-seed-crystal layer that grew on the support surface, and another gel-derived silicalite-1 top layer that formed on the seed crystal layer. The texture of the MFI seed layer (i.e., the deposited amount and the Si/Al ratio) was found to play an important role in the separation process. When silicalite-1 seed crystals were used, the ethanol separation factor was high in the binary ethanol/water system, but lower in the presence of succinic acid. However, when ZSM-5 seeds were used, the ethanol separation factor in the ternary system improved. These results suggest that silicalite-1 membranes prepared using ZSM-5 seed crystals are effective for the recovery of ethanol in the presence of organic acids.

Characterization of InAs/GaSb type‐II superlattice photodiodes for mid‐wave IR with different mesa sidewall passivation schemes

AbstractWe report on the electrical and material characterization of InAs/GaSb type‐II superlattice (T2SL) mid‐wave infrared (MWIR) photodiodes with different passivation schemes on the mesa‐sidewalls with significant differences in the resulting low temperature dark currents. Devices fabricated by dry etching and passivated with polymerized photoresist, show orders of magnitude lower dark currents as compared to unpassivated devices. The mesa side walls were examined using high resolution transmission electron microscopy (HRTEM) with a special focus on the interface between the superlattice material and the dielectric passivation. Material analysis on nanometer scale at the mesa sidewall interface was performed using energy dispersive X‐ray (EDX) spectrometry. EDX line scans were obtained from interfaces for different passivated and unpassivated devices, using the highly focused electron beam in TEM, to investigate the chemical compositions. The unpassivated and photoresist‐passivated mesas, with different electrical properties, revealed different sidewall morphologies and compositions. An oxygen containing layer was observed in photoresist‐passivated devices covering the whole mesa sidewall. We think this plays a role in reducing surface leakage dark current. In HR‐TEM the mesa sidewall topography reveals preferential etching of one superlattice component as previously observed. Nevertheless, the dielectric material covers the sidewall uniformly (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface treatment of nanoporous silicon with noble metal ions and characterizations

A very large surface to volume ratio of nanoporous silicon (PS) produces a high density of surface states, which are responsible for uncontrolled oxidation of the PS surface. Hence it disturbs the stability of the material and also creates difficulties in the formation of a reliable electrical contact. To passivate the surface states of the nanoporous silicon, noble metals (Pd, Ru, and Pt) were dispersed on the PS surface by an electroless chemical method. GIXRD (glancing incidence X-ray diffraction) proved the crystallinity of PS and the presence of noble metals on its surface. While FESEM (field emission scanning electron microscopy) showed the morphology, the EDX (energy dispersive X-ray) line scans and digital X-ray image mapping indicated the formation of the noble metal islands on the PS surface. Dynamic SIMS (secondary ion mass spectroscopy) further confirmed the presence of noble metals and other impurities near the surface of the modified PS. The variation of the surface roughness after the noble metal modification was exhibited by AFM (atomic force microscopy). The formation of a thin oxide layer on the modified PS surface was verified by XPS (X-ray photoelectron spectroscopy).

Segregation in metastable Fe-Cu nanoparticles

Fe-Cu nanoparticles have been prepared by sputtering and subsequent in-flight sintering. Particles deposited onto amorphous carbon are examined by electron diffraction, energy dispersive x-ray line-scans and electron energy loss spectroscopy using high resolution transmission electron microscopy. The results show that non-sintered particles form a metastable Fe-Cu alloy, whereas the sintered particles undergo a spinoidal decomposition leading to an iron-rich core and a Cu-rich shell. The investigations are carried out on particles of various sizes ranging from 5-50 nm. Within this size range, the sintered particles show similar compositional properties.

FRETTING WEAR BEHAVIOR OF TIN PLATED CONTACTS: INFLUENCE ON CONTACT RESISTANCE

The fretting wear behavior of tin plated copper alloy contacts and its influence on the contact resistance are addressed in this paper. Based on the change in the area of contact zone as well as the wear depth as a function of fretting cycles, a model was proposed to explain the observed low and stable contact resistance. The extent of wear of tin coating and the formation of wear debris as a function of fretting cycles were assessed by scanning electron microscopy (SEM). Energy dispersive X-ray line scanning (EDX), X-ray mapping, and EDX spot analysis were employed to characterize the nature of changes that occur at the contact zone. The study reveals that the fretted area increases linearly up to 8000 cycles due to the continuous removal of the tin coating and attains saturation when the fretting path length reaches a maximum. The observed low and stable contact resistance observed up to 8000 cycles is due to the common area of contact which provides an electrically conducting area. Surface analysis by SEM, EDX, and X-ray elemental mapping elucidate the nature of changes that occurred at the contact zone. Based on the change in contact resistance as a function of fretting cycles, the fretting wear and fretting corrosion dominant regimes are proposed. The interdependence of extent of wear and oxidation increases the complexity of the fretting corrosion behavior of tin plated contacts.

Structural properties of quaternary InAlGaN MQW grown by plasma‐assisted MBE

AbstractQuaternary In0.085Al0.285Ga0.63N/GaN multiple quantum wells (MQW) grown by plasma‐assisted molecular beam epitaxy are characterized by high resolution transmission electron microscopy (HRTEM), geometric phase analysis, and energy dispersive X‐ray (EDX) nano‐analysis. The MQW exhibit sharp well‐defined InAlGaN/GaN interfaces while the GaN/InAlGaN interfaces are more smeared. The InAlGaN quantum wells and the GaN barriers are lattice‐matched. Chemical distribution profiles are extracted from EDX line scans, obtained with a nanoprobe, which are compared to convoluted theoretical profiles, and are in good agreement with the HRTEM observations. Indium clustering occurs after prolonged observation under the electron beam. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nitridation of γ‐TiAl alloys by direct metal–gas reaction at 1000–1300 K

AbstractTwo γ‐TiAl alloys, Ti‐47at%Al‐2at%Nb‐2at%Cr (MJ12) and Ti‐47at%Al‐2at%Nb‐2at%Mn‐0.8at%TiB2 (MJ47), were nitrided by direct metal–gas reaction at 1000–1300 K in 10 cm3s−1NH3. X‐ray diffraction revealed formation of TiN at 1100–1300 K. Knoop microhardness values of the alloys were increased with an increase in the nitridation temperature. Microhardness values of MJ12 and MJ47 with 1300 K nitridation were respectively improved to 1.65 and 1.38 times those of the controls. Nitridation depth at a variety of temperature determined by Rutherford backscattering spectrometry was increased with an increase in the temperature. Ti, Al and N concentrations at a variety of depths analysed by scanning electron microscopy and energy dispersive X‐ray linescanning are also explained. Copyright © 2005 John Wiley & Sons, Ltd.

Structural inhomogeneity of superconducting ex situ MgB2/Cu wires made by the powder-in-tube technique

Single core MgB2 wires have been made by the powder-in-tube (PIT) method using commercial MgB2 powder (Alfa Aesar). Using the two-axial rolling process, composites have been made in a Cu sheath. Energy dispersive x-ray (EDX) mapping and scanning electron microscopy backscattered electron observations prove that there is high element segregation (phase inhomogeneity) for as-rolled and as-sintered wires, although the wire after sintering is more inhomogeneous than the as-rolled (non-sintered) wire. X-ray diffraction diffractograms confirm the presence of isotropy and the absence of texturization in the ‘macroscopic’ phase within the MgB2 cores, despite their thermomechanical history. The observed decrease in the value of Jc in the wire after sintering was attributed to macroscopic cracking and the worsening of the intergrain connectivity. EDX line scans have also shown high anisotropy and high inhomogeneity in the distribution of elements within the MgB2 cores. Inhomogeneity in the final product (wires) has resulted from the high macroscopic inhomogeneity observed in the starting MgB2 powder. The Cu sheath has been shown to be neutral (non-poisoning) for MgB2 cores made ex situ. However, due to its softness, it cannot properly constrain the MgB2 core or give enough support required for adequate grain connectivity.