Electron Diffraction Resolution Research Articles

Room temperature plasticity and phase transformation of nanometer-sized transition alumina nanoparticles under pressure

A powder of transition alumina nanoparticles (including γ and a so-called δ-type) is compacted at room temperature in a diamond anvil cell (DAC) under pressures ranging from 5 GPa to 20 GPa. Characterization carried out on thin foils prepared by focused ion beam (FIB), from the compacted powder, unambiguously reveals plasticity. High resolution transmission electron microscopy (HRTEM) and electron diffraction also evidence phase transformation of nanoparticles under high pressure and nanoparticles show faceting parallel to the loading direction with a preferential crystallographic orientation of the facets corresponding to {220} planes of γ−Al2O3. It can also be deduced, from the comparison between the DAC experiments and in situ TEM nano-compression tests on single particles performed in a preceding work, that plasticity is driven by slip bands corresponding to {111} slip planes, common for a spinel structure, such as, for instance, γ−Al2O3.We also demonstrate that at ambient temperature the transition alumina phase is also prone to structural change under high pressures with the following sequence γ-Al2O3 → δ* Al2O3, these two phases coexisting, sometimes, in the same nanoparticle after compaction. Plasticity at room temperature in alumina nanoparticles and the subsequent phase transformation under pressure may have strong impacts on the process of alumina nanostructured ceramics.

Formation of metastable phases of ferrous sulfide via pulsed Nd:YAG laser deposition: Experimental and theoretical study

Highly polymorphic ferrous sulfide exhibits attractive optical, semiconducting, magnetic and biocatalytic properties related to its phase modification. Nd:YAG laser ablation of ferrous sulfide (FeS) in vaccum results in noncongruent deposition of nanostructured FeS1-x thin films. Deposits have been carried out on Ta, Al and Cu substrates and achieved thin films were analyzed using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electron diffraction in order to characterize morphology, chemical composition and phase transformation induced by ablative process. Round-shaped and ring-like particles, shapeless agglomerates as well as flat discontinuous areas have been observed for all the coats deposited on various substrates. However, using HRTEM, in agreement with electron diffraction, different phase compositions on various substrates have been detected. Cubic pyrite phase (FeS2) has been detected on Ta substrate. Metastable rhombohedral smythite Fe9S11 and cubic pyrite FeS2 have been found on Al substrate. And cubic pyrite FeS2, metastable rhombohedral smythite Fe9S11 and metastable orthorhombic marcasite FeS2m have been revealed on Cu substrate. The detected crystalline nanograins in all deposits were surrounded by amorphous phase. Furthermore, to gain deep insight into the electronic structure of obtained stable (cubic pyrite) and less known unstable phases (orthorhombic marcasite and rhombohedral smythite) the density functional theory is employed and important characteristics such as band gap values have been calculated.

Study of the precipitation hardening process in recycled Al-Si-Cu cast alloys

AbstractThe formation of extremely small uniformly dispersed particles of a second phase within the original phase matrix during heat treatment changed material properties. Therefore the characterization of precipitation had been investigated using high resolution transmission electron microscopy (TEM) and electron diffraction of thin foils for an AlSi9Cu3 cast alloy. For investigation the hardening effect onto mechanical properties of aluminium cast was used heat treatment, which consisted from solution treatment at 515°C / 4 hours (h), followed by quenching into water with temperature 50°C and artificial aging using different temperatures 170°C and 190°C with different holding time 2, 4, 8, 16, and 32 hours. The observations of microstructure and substructure reveals that precipitation hardening has caused great changes in size, morphology and distributions of structural components, the formation of precipitates of Cu phases, and the change of mechanical properties as well.

On the microscopic structure of a nominal Ag(441) surface

Regularly stepped (vicinal) surfaces provide a convenient means to control the number of defects of a surface. They can easily be prepared by a slight miscut of a low index surface. In the case of an fcc(nn1) surface with small integer n, it is even expected that the large number of steps will dominate the surface properties. We are the first to study the Ag(441) surface with a combination of scanning tunneling microscopy (STM) and high resolution electron diffraction (SPA-LEED). The surface is found to consist of different building blocks, which can be either (331) or (551) microfacets. To unravel the actual morphology, we carried out simulations of the reciprocal space maps (RSMs) in the framework of the simple kinematic approximation.

Quantitative crystallographic analysis of individual carbon nanofibers using high resolution transmission electron microscopy and electron diffraction

High resolution transmission electron microscopy (HRTEM) and electron diffraction allow for a thorough crystallographic characterization of the herringbone structure of carbon nanofibers (CNF). A newly developed method for an extended quantitative structural evaluation of single carbon nanofibers is applied. The method is based on quantitative analysis of radial and azimuthal profiles extracted from selected area electron diffraction (SAED) patterns, nano beam electron diffraction (NBED) patterns or power spectra obtained by Fourier transformation of HRTEM images. Precise quantification of structural parameters, in particular cone apex angle, interlayer spacing and undulation of graphene layers is carried out. For the first time a profound interpretation of CNF diffraction patterns is given, proving the rotational disorder of the turbostratic structure and suggesting a random rotation between successive graphene cones. A series of crystallographic analyses along the axis of a single CNF reveal a continuous increase of the interlayer spacing during CNF growth. Additionally, the different techniques HRTEM, SAED, and NBED are evaluated in terms of attainable structural information, precision and applicability to different diameters of CNFs.

A multimethodic approach for the characterization of manganiceladonite, a new member of the celadonite family from Cerchiara mine, Eastern Liguria, Italy

AbstractIn the manganesiferous ores associated with the metacherts of the ophiolitic sequences at the Cerchiara mine, Eastern Liguria (Italy), a new Mn-bearing mineral belonging to the mica group has been recently found and characterized. High resolution transmission electron microscopy and electron diffraction tomography studies confirm that the mineral belongs to the mica group. Unit-cell parameters from the powder diffraction pattern are:a= 5.149(1),b= 8.915(1),c= 10.304(1) Å, β = 102.03(1)°, space groupC2 orC2/m. On the basis of the electron paramagnetic resonance spectroscopic results, the Mn4+content represents a very subordinate fraction of the total Mn, the remaining occurring as Mn3+. The Raman spectrum clearly indicates the presence of OH groups in the structure. Laser-ablation inductively-coupled-plasma mass-spectrometry measurements assess the presence of considerable amounts of Li.Assuming all Mn as Mn3+and 22 negative charges, the empirical formula can be expressed as: (K0.83□0.17)(Mn1.143+Mg0.80Li0.20Fe0.023+)(Si3.89Al0.10)O10[(OH)1.92F0.08] with the sum of the octahedral cations indicating a 'transitional' character between a di- and a tri-octahedral structure. This formula corresponds ideally to the Mn3+analogue of celadonite, thus expanding the range of solid solution in the celadonite family. The ideal end-member formula KMn3+MgSi4O10(OH)2can be easily related to celadonite by the homovalent substitutionVIMn3+→VIFe3+. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association, (IMA 2015-052).

Pulsed Nd:YAG deposition of nanostructured FeS1-x containing meta-stable phases

Pulsed near-IR laser irradiation of ferrous sulfide (FeS) in a vacuum allows a non-congruent ablation and deposition of nanostructured FeS1-x thin films. Deposition has been performed on Al, Ta and Cu unheated substrate and analyzed by scanning (SEM) and high resolution transmission electron microscopy (HRTEM) and electron diffraction. Morphologically, the similar homogeneous, dark, metallic and adhesive appearanceshave been revealed for all the coats deposited on various substrates (by SEM). However, using HRTEM in agreement with electron diffraction, different phase composition on various substrates has been detected. Cubic pyrite phase (FeS2) has been detected on Ta substrate. Cubic pyrite (FeS2) and metastable rhomboedric smythite Fe9S11 have been found in case of Al substrate. Cubic pyrite (FeS2), metastable rhomboedric smythite Fe9S11 and metastable orthorhombic marcasite (FeS2m) revealed HRTEM analysis of the film on Cu substrate. In case of all deposits the detected crystalline nanograins were surrounded by amorphous matrix.

Electron tomography analysis of 3D interfacial nanostructures appearing in annealed Si rich SiC films.

The optical and electrical properties of Si rich SiC (SRSC) solar cell absorber layers will strongly depend on interfacial layers between the Si and the SiC matrix and in this work, we analyze hitherto undiscovered interfacial layers. The SRSC thin films were deposited using a plasma-enhanced chemical vapor deposition (PECVD) technique and annealed in a nitrogen environment at 1100 °C. The thermal treatment leads to metastable SRSC films spinodally decomposed into a Si-SiC nanocomposite. After the thermal treatment, the coexistence of crystalline Si and SiC nanostructures was analysed by high resolution transmission electron microscopy (HRTEM) and electron diffraction. From the quantitative extraction of the different plasmon signals from electron energy-loss spectra, an additional structure, amorphous SiC (a-SiC) was found. Quantitative spectroscopic electron tomography was developed to obtain three dimensional (3D) plasmonic maps. In these 3D spectroscopic maps, the Si regions appear as network structures inside the SiC matrix where the a-SiC appears as an interfacial layer separating the matrix and Si network. The presence of the a-SiC interface can be explained in the framework of the nucleation and growth model.

Colloidal CuInSe2 nanocrystals and thin films for low-cost photovoltaics

We report on the synthesis of colloidal CuInSe2 nanocrystals (NCs) using simple solution-based method and its vacuum thermally evaporated films. The tetragonal phase CuInSe2 NCs grow in the shape of nanoparticles with diameter varies between 30 and 40nm according to high resolution transmission electron microscopy and electron diffraction measurements. The deposited films have been annealed for different times (up to 45min) in vacuum and at different temperatures (150–346°C). Optical characterization of the CuInSe2 NCs films using UV–Vis-NIR absorption, transmittance, excitation and photoluminescence measurements were performed. Optical properties of the deposited CuInSe2 films were quantified using developed theoretical model based on transmission and reflectance data. We found a strong dependence of the structural, morphologies and optical absorption coefficient of the prepared films on both annealing temperatures and annealing times. A remarkable enhancement of the optical absorption coefficient (α∼3×105cm−1) of the formed CuInSe2 NCs films with annealing was demonstrated and suggested the potential use of colloidal CuInSe2 for low cost photovoltaics.

Disruption of crystalline structure of Sn3.5Ag induced by electric current

This study presented the disruption of the Sn and Ag3Sn lattice structures of Sn3.5Ag solder induced by electric current at 5–7 × 103 A/cm2 with a high resolution transmission electron microscope investigation and electron diffraction analysis. The electric current stressing induced a high degree of strain on the alloy, as estimated from the X-ray diffraction (XRD) peak shift of the current stressed specimen. The XRD peak intensity of the Sn matrix and the Ag3Sn intermetallic compound diminished to nearly undetectable after 2 h of current stressing. The electric current stressing gave rise to a high dislocation density of up to 1017/m2. The grain morphology of the Sn matrix became invisible after prolonged current stressing as a result of the coalescence of dislocations.

Morphological evolution of hydrothermally derived ZnO nano and microstructures

ZnO nanorods with flowerlike morphologies were synthesized via hydrothermal route. The observations depicted that the as-synthesized flowerlike morphology of ZnO consisted of numerous nanorods. The length of nanorod is in the range of 2–3μm, and the diameter ∼ 150–200nm. The ZnO product was crystallized with hexagonal crystal structure. High resolution transmission microscopy image and electron diffraction pattern revealed a single crystalline nature altogether (0001) direction growth. The photoluminescence spectrum showed a near band edge UV emission peak and defect related blue emission peak in the visible region. Furthermore, the experimental results revealed that the extended reaction period and zinc precursor used in reaction mixture played an inevitable role in the morphological evolution of ZnO nano-/microstructures.

Interlayer Dependence of G-Modes in Semiconducting Double-Walled Carbon Nanotubes

A double-walled carbon nanotube (DWNT), a coaxial composite of two single-walled carbon nanotubes (SWNT), provides a unique model to study interactions between the two constituent SWNTs. Combining high resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and resonant Raman scattering (RRS) experiments on the same individual suspended DWNT is the ultimate way to relate unambiguously its atomic structure, defined by the chiral indices of the coaxial outer/inner SWNTs, and its Raman-active vibration modes. This approach is used to investigate the intertube distance dependence of the G-modes of individual index-identified DWNTs composed of two semiconducting SWNTs. We state the main features of the dependence of the G-mode frequencies on the distance between the inner and outer layers: (i) When the interlayer distance is larger than the nominal van der Waals distance (close to 0.34 nm), a downshift of the inner-layer G-modes with respect to the G-modes in the equivalent SWNTs is mea...

TEM Based High Resolution Electron Diffraction Techniques for Three-dimensional Nanostructure Determination

TEM Based High Resolution Electron Diffraction Techniques for Three-dimensional Nanostructure Determination

Micro-structural analysis of NiFe2O4 nanoparticles synthesized by thermal plasma route and its suitability for BSA adsorption.

The paper presents the experimental studies pertaining to the adsorption of bovine serum albumin (BSA) on the nanoparticles of nickel ferrite (NiFe2O4) with a view of correlating the adsorption properties to their microstructure and zeta potentials. Physical properties of two kinds of nickel ferrites, one synthesized by thermal plasma route and the other by chemical co-precipitation method, are compared. Maximum adsorption (231.57μg/mg) of BSA onto nickel ferrite nanoparticles, at body temperature (37°C) was observed at pH-value of 5.58 for the thermal plasma synthesized particles showing its higher adsorption capacity than those synthesized by wet chemical means (178.71μg/mg). Under the same physical conditions the value of zeta potential, obtained for the former, was higher than that of the latter over a wide range of pH values (3.64-9.66). This is attributed to the differences in the specific surface energies of the two kinds of nanoparticles arising from the degree of crystallinity. The paper presents the experimental evidence for the single crystalline nature of the individual nanoparticles, with mean size of 32nm, for the thermal plasma synthesized particles as evidenced from the high resolution transmission electron microscopy and electron diffraction analysis. The measurements also reveal the poor crystalline morphology in the chemically prepared particles (mean size of 28nm) although the X-ray diffraction patterns are not much different. The atomic force microscopy images confirm that the surfaces of plasma synthesized nanoparticles possesses higher surface roughness than that of chemically synthesized one. Presence of adsorbed protein was confirmed by vibrational spectroscopy. The Langmuir adsorption model is found to fit into the experimental data better than the Freundlich adsorption model.

Influence of Cr on the nanoclusters formation and superferromagnetic behavior of Fe-Cr-Nb-B glassy alloys

High resolution imaging and electron diffraction confirm that in the as-quenched state the structure of Fe79.7−xCrxNb0.3B20 (x = 11–13 at. %) melt-spun ribbons is completely amorphous, independent of the Cr content. Energy-dispersive X-ray spectroscopy mapping emphasizes clearly the presence of Fe and Cr clusters varying from approximately 1 to 2–3 nm in size with the increase of Cr content from 11 to 13 at. %. The Fe and Cr atoms segregate the atomic scale to form nanometer sized clusters, influencing strongly the macroscopic magnetic behavior. The Curie temperature of the system, TCsystem, confirmed by the magnetic susceptibility versus temperature measurements, gives the strength of the magnetic interactions between clusters. The inter-cluster interactions are much stronger for lower contents of Cr, the microstructure is less uniform, and TCsystem increases from 290 K for 13 at. % Cr to 330 K for 11.5 at. % Cr. The whole system transforms to a ferromagnetic state through interactions between the clusters. Zero-field cooling and field cooling curves confirm the cluster behavior with a blocking temperature, Tb, of about 250 K. Above Tb, the ribbons behave as a superferromagnetic system, whilst below the blocking temperature a classical ferromagnetic behavior is observed.

Investigation on interfacial adhesion of Ti–6Al–4V/nitride coatings

Both 10-meter ball-on-disk tests and 0.01-meter single pass sliding tests were performed under the same test conditions to compare the adhesion mechanism of titanium alloy Ti–6Al–4V to AISI 52100 steel and two nitride coatings deposited by physical vapor deposition technique (PVD), namely, AlTiN and CrN. The sliding surfaces and the interface region between the transfer layer and the counterface surfaces were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and energy dispersive spectroscopy (EDS). The results revealed that the adhesion of titanium alloy to the counterface materials initiated during the initial stage of sliding in unlubricated sliding contact and resulted in the transfer of titanium alloy to the counterface surfaces. It was found that the transferred Ti–6Al–4V had a layered amorphous structure in which nanocrystalline and polycrystalline oxides were embedded. Severe oxidation of titanium was observed in all the tests. However, Ti–6Al–4V showed less severe oxidation behavior when sliding against CrN. High resolution TEM (HRTEM), electron diffraction, and fast Fourier transform (FFT) investigations carried out at the interface region between the transfer layer and the counterface surfaces revealed the presence of nanocrystalline TiO (C2/m) at the transfer layer interface with steel and AlTiN. However only α-titanium (P63/mmc) was detected at the CrN/transfer layer interface.

Fabrication and characterization of copper oxide (CuO)–gold (Au)–titania (TiO2) and copper oxide (CuO)–gold (Au)–indium tin oxide (ITO) nanowire heterostructures

Nanoscale heterostructures composed of standing copper oxide nanowires decorated with Au nanoparticles and shells of titania and indium tin oxide were fabricated. The fabrication process involved surfactant-free and wet-chemical nucleation of gold nanoparticles on copper oxide nanowires followed by a line-of-sight sputtering of titania or indium tin oxide. The heterostructures were characterized using high resolution electron microscopy, diffraction, and energy dispersive spectroscopy. The interfaces, morphologies, crystallinity, phases, and chemical compositions were analyzed. The process of direct nucleation of gold nanoparticles on copper oxide nanoparticles resulted in low energy interface with aligned lattice for both the components. Coatings of polycrystalline titania or amorphous indium tin oxide were deposited on standing copper oxide nanowire–gold nanoparticle heterostructures. Self-shadowing effect due to standing nanowire heterostructures was observed for line-of-sight sputter deposition of titania or indium tin oxide coatings. Finally, the heterostructures were studied using Raman spectroscopy and ultraviolet–visible spectroscopy, including band gap energy analysis. Tailing in the band gap energy at longer wavelengths (or lower energies) was observed for the nanowire heterostructures.

TEM preparation methods and influence of radiation damage on the beam sensitive CaCO3 shell of Emiliania huxleyi

The ultrastructure of biologically formed calcium carbonate crystals like the shell of Emiliania huxleyi depends on the environmental conditions such as pH value, temperature and salinity. Therefore, they can be used as indicator for climate changes. However, for this a detailed understanding of their crystal structure and chemical composition is required. High resolution methods like transmission electron microscopy can provide those information on the nanoscale, given that sufficiently thin samples can be prepared. In our study, we developed sample preparation techniques for cross-section and plan-view investigations and studied the sample stability under electron bombardment. In addition to the biological material (Emiliania huxleyi) we also prepared mineralogical samples (Iceland spar) for comparison. High resolution transmission electron microscopy imaging, electron diffraction and electron energy-loss spectroscopy studies revealed that all prepared samples are relatively stable under electron bombardment at an acceleration voltage of 300kV when using a parallel illumination. Above an accumulated dose of ∼105e/nm2 the material – independent whether its origin is biological or geological – transformed to poly-crystalline calcium oxide.

The stabilization of a single domain in free-standing ferroelectric nanocrystals

High resolution electron microscopy, electron diffraction and electron holography were used to study individual free-standing ∼30 nm barium titanate nanocrystals. Large unidirectional variations in the tetragonal distortion were mapped across the smaller nanocrystals, peaking to anomalously large values of up to 4% at the centers of the nanocrystals. This indicated that the nanocrystals consist of highly strained single ferroelectric domains. Simulations using an effective Hamiltonian for modeling a nanocrystal under a small depolarizing field and negative pressure qualitatively confirm this picture. These simulations, along with the development of a phenomenological model, show that the tetragonal distortion variation is a combined effect of: (i) electrostrictive coupling between the spontaneous polarization and strain inside the nanocrystal, and (ii) a surface-induced effective stress existing inside the nanodot. As a result, a ‘strain skin layer’, having a smaller tetragonal distortion relative to the core of the nanocrystal, is created.

Coupled Vibrations in Index-Identified Carbon Nanotubes

ABSTRACTCombining high resolution transmission electron spectroscopy, electron diffraction, and resonant Raman spectroscopy experiments on the same suspended (free-standing) individual carbon nanotubes is the ultimate approach to relate unambiguously the structure and the intrinsic phonon features of these nano-systems.By using this approach, the effect of coupling between nanotubes on the phonons is investigated in two model nano-systems: (i) a bundle of two non-identical SWNTs (inhomogeneous dimer), (ii) double-walled carbon nanotubes.