Orientation Of Crystallites Research Articles

Optimization of Sb2S3 Nanocrystal Concentrations in P3HT: PCBM Layers to Improve the Performance of Polymer Solar Cells.

In this study, polymer solar cells were synthesized by adding Sb2S3 nanocrystals (NCs) to thin blended films with polymer poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) as the p-type material prepared via the spin-coating method. The purpose of this study is to investigate the dependence of polymer solar cells’ performance on the concentration of Sb2S3 nanocrystals. The effect of the Sb2S3 nanocrystal concentrations (0.01, 0.02, 0.03, and 0.04 mg/mL) in the polymer’s active layer was determined using different characterization techniques. X-ray diffraction (XRD) displayed doped ratio dependences of P3HT crystallite orientations of P3HT crystallites inside a block polymer film. Introducing Sb2S3 NCs increased the light harvesting and regulated the energy levels, improving the electronic parameters. Considerable photoluminescence quenching was observed due to additional excited electron pathways through the Sb2S3 NCs. A UV–visible absorption spectra measurement showed the relationship between the optoelectronic properties and improved surface morphology, and this enhancement was detected by a red shift in the absorption spectrum. The absorber layer’s doping concentration played a definitive role in improving the device’s performance. Using a 0.04 mg/mL doping concentration, a solar cell device with a glass /ITO/PEDOT:PSS/P3HT-PCBM: Sb2S3:NC/MoO3/Ag structure achieved a maximum power conversion efficiency of 2.72%. These Sb2S3 NCs obtained by solvothermal fabrication blended with a P3HT: PCBM polymer, would pave the way for a more effective design of organic photovoltaic devices.

Texture Characterization of Duplex Stainless Steel 2205 Using Neutron Diffraction Method

Duplex stainless steel (DSS) is widely used in chemical processes, petrochemical, oil & gas industries, and nuclear technology due to its excellent mechanical properties and exceptional generalized and localized corrosion resistance. In this study, the crystal structure, material phases, and texture characterization of DSS were carried out using the neutron diffraction method. The characterization results show that the duplex has two phases: α (ferrite) and g (austenite), each with a lattice parameter 2.8736 Angstrom and 3.6076 Angstrom, respectively. The sample symmetrization method from triclinic to orthorhombic are used to analyze pole figures. The crystallite orientation in the α and g phases have the opposite direction. The α phase has a crystallite orientation towards {110} <001> or Goss orientation, and the g phase, crystal orientation towards {100} <001> or the cube orientation. The orientation distribution function shows that the orientation strength of ferrite is much stronger than austenite. The crystallite orientation (texture) obtained by the orientation distribution function analysis follows the crystal structure analysis.

Control of physical vapor deposition and architecture of stoichiometric SnSe heterojunction structures for solar cells

Systematic investigations on microstructural development during the physical vapor deposition of SnSe thin films under high vacuum (10−6 mbar) on glass substrates have been carried out, so as to mold the functional properties for fabrication of novel Au/MoO3/p-SnSe/n-CdS/ITO/SLG heterojunction solar cells. Stoichiometric SnSe crystalline target was prepared using a muffle furnace integrated with an indigenously assembled rotation mechanism and its vapors were condensed by subjecting to facile thermal evaporation process, without any extraneous chemical precursors. Effect of substrate temperature, TS (27–350 °C) on morphology, growth mechanism and lattice periodicity was analyzed with the aid of FESEM, AFM and XRD. Fine tuning of TS (= 250 °C) enabled atomically smooth surfaces with appreciable crystallinity and resulted in orthorhombic structure having preferred orientation of crystallites along (111) direction, devoid of other phases. Chemical homogeneity and phase purity were justified by EDAX, XPS and Raman spectroscopy. The values of band gap, electrical resistivity, mobility and concentration of charge carriers are equal to 1.48 eV, 2.36 Ωcm, 6.36 cm2V−1s−1 and 1.25 × 1018 cm−3 respectively. The attained efficiency (1.39%) of the prepared photovoltaic device promises the versatility of SnSe absorber layers towards the enhancement of solar energy conversion.

Multiscale and multimodal X-ray analysis: Quantifying phase orientation and morphology of mineralized turkey leg tendons

Fibrous biocomposites like bone and tendons exhibit a hierarchical arrangement of their components ranging from the macroscale down to the molecular level. The multiscale complex morphology, together with the correlated orientation of their constituents, contributes significantly to the outstanding mechanical properties of these biomaterials. In this study, a systematic road map is provided to quantify the hierarchical structure of a mineralized turkey leg tendon (MTLT) in a holistic multiscale evaluation by combining micro-Computed Tomography (micro-CT), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD). We quantify the interplay of the main MTLT components with respect to highly ordered organic parts such as fibrous collagen integrating inorganic components like hydroxyapatite (HA). The microscale fibrous morphology revealing different types of porous features and their orientation was quantified based on micro-CT investigations. The quantitative analysis of the alignment of collagen fibrils and HA crystallites was established from the streak-like signal in SAXS using the Ruland approach and the broadening of azimuthal profiles of the small and wide-angle diffraction peaks. It has been in general agreement that HA crystallites are co-aligned with the nanostructure of mineralized tissue. However, we observe relatively lower degree of orientation of HA crystallites compared to the collagen fibrils, which supports the recent findings of the structural interrelations within mineralized tissues. The generic multiscale characterization approach of this study is relevant to any hierarchically structured biomaterials or bioinspired materials from the μm-nm-Å scale. Hence, it gives the basis for future structure-property relationship investigations and simulations for a wide range of hierarchically structured materials. Statement of significanceMany fibrous biocomposites such as tendon, bone, and wood possess multiscale hierarchical structures, responsible for their exceptional mechanical properties. In this study, the 3-dimensional hierarchical structure, the degree of orientation and composition of mineralized tendon extracted from a turkey leg were quantified using a multimodal X-ray based approach combining small-angle X-ray scattering and wide-angle X-ray diffraction with micro-Computed Tomography. We demonstrate that hydroxyapatite (HA) domains are co-aligned with the nanostructure of mineralized tissue. However, the lower degree of orientation of HA crystallites was observed when compared to the collagen fibrils. The generic multiscale characterization approach of this study is relevant to any hierarchically structured biomaterials or bioinspired materials from the micrometer over the nanometer to the Angström scale level.

A study of thickness dependent microstructure of poly (3-hexylthiophene) thin films using grazing incidence x-ray diffraction

ABSTRACT Thin films of poly (3-hexylthiophene), abbreviated as P3HT, are widely used systems of semiconducting polymer for applications in organic electronic devices. We studied the microstructure of spin-coated thin films of P3HT using grazing incidence x-ray diffraction (GID) by combining high-resolution vertical scan with 2D intensity maps obtained using area detector. Microstructure of the films was quantitatively analyzed in terms of relative crystalline density, texture and coherence length. The structure of the films was relaxed by annealing at 110°C. The relaxed microstructure shows strong thickness dependence. Thick film (61 nm) was highly crystalline and textured. For thin film (32 nm), relative crystalline density was very weak but the coherence length of crystallites was larger and the orientation of crystallites was even more strongly textured. For thick film, the strong increase of crystalline density takes place through fresh nucleation and reorientation of crystallites already present in the films. For thin films, the substrate interaction induced very strong alignment of lamellar crystallites through degeneration of off-oriented crystallites and increased lamellar crystalline coherence. The drastic change of microstructure within a small thickness range is an important aspect to be considered while preparing thin film devices.

Structural and optical characteristics determined by the sputtering deposition conditions of oxide thin films.

The influence of film thickness on the structural and optical properties of silicon dioxide (SiO2) and zinc oxide (ZnO) thin films deposited by radio frequency magnetron sputtering on quartz substrates was investigated. The deposition conditions were optimized to achieve stoichiometric thin films. The orientation of crystallites, structure, and composition were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while the surface topography of the samples was analyzed using scanning electron microscopy (SEM). The optical characteristics were measured for samples with the same composition but obtained with different deposition parameters, such as increasing thickness. The optical constants (i.e., the refractive index n, the extinction coefficient k, and the absorption coefficient α) of the SiO2 and ZnO oxide films were determined from the transmission spectra recorded in the range of 190–2500 nm by using the Swanepoel method, while the energy bandgap was calculated from the absorption spectra. The influence of thickness on the structural and optical properties of the oxide films was investigated. Good optical quality and performance were noticed, which makes these thin films worthy of integration into metamaterial structures.

Nonlinear elastic response of pan based carbon fiber to tensile loading and relations to microstructure

In this study, wide- and small-angle scattering (WAXS, SAXS) are used to analyze the structure of polyacrylonitrile (PAN) carbon fiber. Wide angle scattering is used to identify lattice parameters such as d-spacings, stacking height of crystalline planes (Lc), average crystallize size (Lc), and various other features (void content, degree of graphitization). Small angle scattering results show orientation and size distributions of pores/amorphous regions. Several analysis techniques were applied to small angle scattering results to ensure accuracy. XRD Data collected is correlated to single fiber mechanical properties and a fiber model is developed. Fiber modulus is heavily related to crystallite dimensions and orientation as well as pore structure. Authors hypothesize that the non-linear elasticity observed in the fiber direction of carbon fibers arises from elastic planar motion within turbostratic carbon. As crystalline regions grow and expand, the lattice structure improves lowering the barriers for (002) quasi-graphene plane motion. This miniscule elastic planar motion can lead to a large nonlinear response to tensile loading especially for high crystallinity carbon fibers and underlying deformation mechanics is addressed considering transverse-isotropy of turbostatic graphite crystals.

Structure and magnetic properties of FeCo nanotubes obtained in pores of ion track templates

A detailed study of structural, electric and magnetic properties of FeCo-alloyed nanotubes (NTs) having a different iron to cobalt ratio with an outer diameter of 110 nm and a length/diameter aspect ratio of more than 100 was carried out. The nanotubes were produced by electrochemical deposition of metal in the pores of PET film template. Ion-track technology was used to produce templates with cylindrical pores. An increase in the deposition potential from U = 1.5 V to U=2.0 V led to a shift in the atomic ratio of metals in the FeCo alloy from 42 to 51 at.% in favour of cobalt as confirmed by energy dispersive analysis. Analysis of structural features by X-ray diffraction and the selected area electron diffraction revealed that at higher deposition potentials the degree of crystallinity of FeCo NTs increases from a nearly random orientation of crystallites at U=1.5 V to a textured polycrystal at U=2.0 V. This was also consistent with a corresponding increase in electrical conductivity. Based on the analysis of hysteresis curves and Mössbauer spectra, the dominant directions of the texture with respect of the NTs axis were established. An axial magnetic anisotropy and rather high magnetic coercivity (∼ 500 Oe for the orientation with the DC magnetic field parallel to tube axes) were observed and attributed to a dominant contribution of the shape anisotropy with a minor crystal anisotropy term due to the textured growth of the nanotubes. It was shown that the technology of electrochemical deposition in the ion-track template pores makes it possible to synthesize the nanotubes and nanowires with the structural and magnetic properties, which have a high interest with the point of view of a fundamental physics and their technological applications.

Influence of Bias Potential Magnitude on Structural Engineering of ZrN-Based Vacuum-Arc Coatings

The creation of the scientific foundations for the structural engineering of ultrathin nanolayers in multilayer nanocomposites is the basis of modern technologies for the formation of materials with unique functional properties. It is shown that an increase in the negative bias potential (from -70 to -220 V) during the formation of vacuum-arc nanocomposites based on ZrN makes it possible not only to control the preferred orientation of crystallites and substructural characteristics but also changes the conditions for conjugation of crystal lattices in ultrafine (about 8 nm) nanolayers.

Structural, morphological and optical properties of atomic layer deposited transition metal (Co, Ni or Fe)- doped ZnO layers

In this work, the feasibility of atomic layer deposition (ALD) to prepare transition metal (Ni-, Co- or Fe-) doped ZnO thin films have been studied. The effects of dopant on the structure, morphology and optical properties of films have been investigated by a number of various techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ellipsometry, UV–Visible spectroscopy, Fourier transformed infrared spectroscopy (FTIR). The effect of substrate (glass, Si with different conductivity type and orientation) on the morphology of layers has also been studied. All layers have a hexagonal wurtzite structure but the preferential orientation of crystallites depends strongly on the dopant. In the case of Ni-doping, the results unambiguously reveal the incorporation of Ni in ZnO lattice. NiO clusters are also possibly formed in Ni:ZnO layers which can explain the observed significant decrease of their transparency. The investigations imply that under the doping scheme and technological conditions used in this study Co and Fe are incorporated only in small amounts in ZnO. Co-doping improves the transparency of ZnO films. The possibility to deposit thin homogeneous films of transition metal (Ni-, Co- or Fe-) doped ZnO by ALD method opens-up new frontiers for implementation of these materials in advanced electronic, magnetic or optical applications.

Calcite crystal orientation patterns in the bilayers of laminated shells of benthic rotaliid foraminifera

Shells of calcifying foraminifera play a major role in marine biogeochemical cycles; fossil shells form important archives for paleoenvironment reconstruction. Despite their importance in many Earth science disciplines, there is still little consensus on foraminiferal shell mineralization. Geochemical, biochemical, and physiological studies showed that foraminiferal shell formation might take place through various and diverse mineralization mechanisms.In this study, we contribute to benthic foraminiferal shell calcification through deciphering crystallite organization within the shells. We base our conclusions on results gained from electron backscattered diffraction (EBSD) measurements and describe microstructure/texture characteristics within the laminated shell walls of the benthic, symbiontic foraminifera: Ammonia tepida, Amphistegina lobifera, Amphistegina lessonii. We highlight crystallite assembly patterns obtained on differently oriented cuts and discuss crystallite sizes, morphologies, interlinkages, orientations, and co-orientation strengths.We show that: (i) crystals within benthic foraminiferal shells are mesocrystals, (ii) have dendritic-fractal morphologies and (iii) interdigitate strongly. Based on crystal size, we (iv) differentiate between the two layers that comprise the shells and demonstrate that (v) crystals in the septa have different assemblies relative to those in the shell walls. We highlight that (vi) at junctions of different shell elements the axis of crystal orientation jumps abruptly such that their assembly in EBSD maps has a bimodal distribution. We prove (vii) extensive twin-formation within foraminiferal calcite; we demonstrate (viii) the presence of two twin modes: 60°/[001] and 77°/~[6 –6 1] and visualize their distributions within the shells.In a broader perspective, we draw conclusions on processes that lead to the observed microstructure/texture patterns.

The Impact of pH on Structural and Electrical Properties of Er-Substituted ZnFe2O4 Nanoparticles Synthesized via Wet Chemical Route

In this study, erbium-substituted Zn nanoferrites were synthesized by a simple coprecipitation method. The effect of pH on various physical parameters of erbium-substituted Zn nanoferrites was studied. The synthesized ferrite nanoparticles were characterized by XRD, FTIR, and SEM techniques and dielectric measurements. The gravimetric analysis showed the annealing temperature of these ferrites up to 700 °C. The result of XRD revealed the crystal structures of zinc nanoferrites. The FTIR spectra showed the weaker absorption peak due to Er–O stretching vibrations in zinc nanoferrites at pH 11. The SEM analysis showed that synthesized erbium-substituted Zn nanoferrites have a spherical shape with a size range from 42 to 46 nm. Dielectric properties exposed the typical semiconductor behavior of the erbium-substituted Zn nanoferrites. The electric constant at low pH was due to Fe+2 dielectric losses that dominated the sum of intrinsic and extrinsic loss. Increased in dielectric loss is associated with random crystallite orientation and impurities. The ZnFe2O4 nanoparticles with a decrease in dielectric loss revealed the crystallite orientation at pH 8 and 11. Tangent loss revealed the conductivity at higher pH 11 with a decrease in tangent loss.

Strain-Engineering Induced Anisotropic Crystallite Orientation and Maximized Carrier Mobility for High-Performance Microfiber-Based Organic Bioelectronic Devices.

Despite the importance of carrier mobility, recent research efforts have been mainly focused on the improvement of volumetric capacitance in order to maximize the figure-of-merit, μC* (product of carrier mobility and volumetric capacitance), for high-performance organic electrochemical transistors. Herein, high-performance microfiber-based organic electrochemical transistors with unprecedentedly large μC* using highly ordered crystalline poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) microfibers with very high carrier mobilities are reported. The strain engineering via uniaxial tension is employed in combination with solvent-mediated crystallization in the course of drying coagulated fibers, resulting in the permanent preferential alignment of crystalline PEDOT:PSS domains along the fiber direction, which is verified by atomic force microscopy and transmission wide-angle X-ray scattering. The resultant strain-engineered microfibers exhibit very high carrier mobility (12.9 cm2 V-1 s-1 ) without the trade-off in volumetric capacitance (122Fcm-3 ) and hole density (5.8×1020 cm-3 ). Such advantageous electrical and electrochemical characteristics offer the benchmark parameter of μC* over ≈1500Fcm-1 V-1 s-1 , which is the highest metric ever reported in the literature and can be beneficial for realizing a new class of substrate-free fibrillar and/or textile bioelectronics in the configuration of electrochemical transistors and/or electrochemical ion pumps.

Crystallization of Poly(methyl methacrylate) Stereocomplexes under Cylindrical Nanoconfinement

The stereocomplexation of poly(methyl methacrylate) (PMMA) is a unique supramolecular assembling system that has been demonstrated to be valuable in many applications. The crystallization behaviors of stereocomplex PMMA (sc-PMMA) under nanoconfinement, however, have yet to be fully understood. In this work, we fabricate sc-PMMA nanorods using anodic aluminum oxide (AAO) templates with various pore sizes to gain a fundamental understanding of sc-PMMA in confined states. A scanning electron microscope (SEM), a differential scanning calorimeter (DSC), and an X-ray diffractometer (XRD) are used to examine their morphologies, crystallization kinetics, and crystal characteristics. We discover that the crystallization kinetics of sc-PMMA inside the nanopores is significantly different from the bulk state. Also, the preferred orientation of sc-PMMA crystallites is mainly governed by the degree of spatial confinement and the polymer molecular weight. This work provides a deeper understanding of sc-PMMA under nanoconfinement and presents opportunities for the applications of supramolecular nanostructures in miniaturized devices.

Polarized Raman scattering in micrometer-sized crystals of triclinic vanadium dioxide

Triclinic vanadium dioxide VO2 (T) films were produced using cathodic arc deposition. Under certain conditions, the film growth on sapphire substrates Al2O3 (001) is associated with the formation of triclinic monocrystals with lateral sizes of several tens of micrometers. Borders between different crystallites can be determined by Raman mapping analysis. X-ray diffraction measurements revealed that the micrometer-sized monocrystals had two different orientations—epitaxial (002) and non-epitaxial (201). The film was studied by polarized micro-Raman spectroscopy, which can be used to determine the orientation of any single crystallite. The Raman tensor elements of the VO2 (T) phase were determined, and it was shown that though crystallographically triclinic VO2 cell could be fitted by monoclinic one with a high degree of precision, such monoclinic approximation was not valid in terms of Raman spectroscopy. Contrary to the two types of phonons expected for the monoclinic crystal [having five nonzero (four independent) or four nonzero (two independent) Raman tensor elements], all phonons in VO2 (T) have nine (six independent) generally nonzero tensor components.

Quantifying the hydroxyapatite orientation near the ossification front in a piglet femoral condyle using X-ray diffraction tensor tomography

While a detailed knowledge of the hierarchical structure and morphology of the extracellular matrix is considered crucial for understanding the physiological and mechanical properties of bone and cartilage, the orientation of collagen fibres and carbonated hydroxyapatite (HA) crystallites remains a debated topic. Conventional microscopy techniques for orientational imaging require destructive sample sectioning, which both precludes further studies of the intact sample and potentially changes the microstructure. In this work, we use X-ray diffraction tensor tomography to image non-destructively in 3D the HA orientation in a medial femoral condyle of a piglet. By exploiting the anisotropic HA diffraction signal, 3D maps showing systematic local variations of the HA crystallite orientation in the growing subchondral bone and in the adjacent mineralized growth cartilage are obtained. Orientation maps of HA crystallites over a large field of view (~ 3 × 3 × 3 mm3) close to the ossification (bone-growth) front are compared with high-resolution X-ray propagation phase-contrast computed tomography images. The HA crystallites are found to predominantly orient with their crystallite c-axis directed towards the ossification front. Distinct patterns of HA preferred orientation are found in the vicinity of cartilage canals protruding from the subchondral bone. The demonstrated ability of retrieving 3D orientation maps of bone-cartilage structures is expected to give a better understanding of the physiological properties of bones, including their propensity for bone-cartilage diseases.

Critical field anisotropy in the antiferroelectric switching of PbZrO3 films

Antiferroelectrics have been recently sparking interest due to their potential use in energy storage and electrocaloric cooling. Their main distinctive feature is antiferroelectric switching, i.e., the possibility to induce a phase transition to a polar phase by an electric field. Here, we investigate the switching behavior of the model antiferroelectric perovskite PbZrO3 using thin films processed by chemical solution deposition in different geometries and orientations. Both out-of-plane and in-plane switching configurations are investigated. The critical field is observed to be highly dependent on the direction of the electric field with respect to the film texture. We show that this behavior is qualitatively consistent with a phase transition to a rhombohedral polar phase. We finally estimate the importance of crystallite orientation and film texturation in the variations observed in the literature.

Effect of oxygen partial pressure on the behavior of Ga-doped ZnO/p-Si heterojunction diodes fabricated by reactive sputtering

A systematic investigation of Ga-doped ZnO (GZO) films deposited by radio frequency reactive magnetron co-sputtering of Zn and GaAs has been carried out toward the realization of n-GZO/p-Si heterojunction diodes. X-ray diffraction and X-ray photoelectron spectroscopy studies of these films have shown a strong dependence of the c-axis orientation of crystallites, Ga/Zn ratio, oxygen vacancies and chemisorbed oxygen species on the partial pressure (percentage) of oxygen in the Ar-O2 sputtering atmosphere. The GZO films deposited at low O2 percentage (≤ 6%) exhibit Ga/Zn ratio ~ 0.03 and consequently high conductivity ~ 103 Ω−1 cm−1 with carrier concentration > 1020 cm−3, leading to the formation of non-rectifying contact with p-Si. A significant finding of the present study is that the doping level and conductivity of GZO layer can be controlled by O2 percentage in sputtering atmosphere, which has been utilized to fabricate heterojunction diodes with GZO films deposited above 6% O2, which possess low Ga/Zn ratio ~ 0.01 and carrier concentration ≤1019 cm−3. In particular, the diode fabricated with 8% O2 displays ideality factor ~ 7 and reverse saturation current ~ 2 × 10–6 A, along with improved turn-on-voltage and series resistance. The nearly complete c-axis orientation, absence of oxygen vacancies and presence of chemisorbed oxygen at the grain boundaries in GZO layer appear to facilitate improved diode performance.

Dichroic Fourier Transform Infrared Spectroscopy Characterization of the β-Sheet Orientation in Spider Silk Films on Silicon Substrates.

Orientation analysis of the β-sheet structure within films of the established recombinant spider silk protein eADF4(C16) was performed using a concept based on dichroic transmission- and attenuated total reflection-Fourier transform infrared spectroscopy, lineshape analysis, assignment of amide I components to specific vibration modes, and transition dipole moment directions of β-sheet structures. Based on the experimental dichroic ratio R, the order parameter S of β-sheet structures was calculated with respect to uniaxial orientation. Films of eADF4(C16) were deposited on untexturized (Si) and unidirectionally scratched silicon substrates (Si-sc) and post-treated with MeOH vapor. Freshly cast thin and thick eADF4(C16) films out of hexafluoroisopropanol featured β-sheet contents of ≈6%, which increased to >30% after MeOH post-treatment in dependence of time. Pseudo-first order folding kinetics were obtained, suggesting a transition from an unfolded to a folded state. In MeOH post-treated thin films with diameters in the nanometer range, a significant orientation of β-sheets was obtained regardless of the texturization of the silicon substrate (Si, Si-sc). This was rationalized by dichroic ratios of the amide I component at 1696 cm-1 assigned to the (0, π) mode of antiparallel β-sheet structures, whose transition dipole moment M is located in parallel to both β-sheet plane and chain direction. The calculated high molecular order parameter S ≈ 0.40 suggested vertically (out-of-plane) oriented antiparallel β-sheet stacks with tilt angles of γ ≈ 39° to the surface normal. Microscale (thick) films, in contrast, revealed low order parameters S ≈ 0. Scanning force microscopy on thin eADF4 films at silicon substrates showed dewetted polymer film structures rather at the micro-scale. These findings give new insights in the role of the β-sheet crystallite orientation for the mechanical properties of spider silk materials.

Transmission electron microscopy investigation of the dislocation structure in a Ti-6Al-4V alloy subjected to an early stage of cyclic deformation

A detailed investigation was conducted of the dislocation structure formed within both the α and β phase of a Ti-6Al-4V alloy subjected to an early stage of cyclic deformation. The cyclic loading-unloading was carried out in tension between applied stress levels of 1100 and 100 MPa, the macroscopic yield stress (σ02) being about 1205 MPa, at a strain rate of 2×10−3 s−1 to 300 cycles, as part of an in-situ synchrotron experiment. The dislocation type, arrangement and density were examined post-mortem using transmission electron microscopy, complemented by the automatic determination of individual crystallite orientations through precession-enhanced nanobeam diffraction. The deformation took place entirely through dislocation glide and no evidence of deformation twinning was found within either of the constituent phases. The dislocation structure within the α phase was fairly similar to that formed during monotonic straining and no presence of periodic planar dislocation networks suggested in the literature was detected. Prismatic and basal slip were the dominant observed deformation modes, based on the calculated Schmid factor and critical resolved shear stress values reported in the literature. The <a>−type dislocations present after straining typically displayed a large screw component, with a majority of them having a pure screw character. There was also limited presence of <c+a> dislocations within the α phase and these were largely of a mixed type. Burgers vectors of the dislocations remaining after deformation within the β phase were also largely associated with the potential slip systems having high Schmid factor values and these dislocations mainly displayed a large screw component.