Orientation Of Crystallites Research Articles

Fluorination of Donor-Acceptor Copolymer Active Layers Enhances Charge Mobilities in Thin-Film Transistors.

Several recent reports have demonstrated that fluorinated analogues of donor/acceptor copolymers surpass nonfluorinated counterparts in terms of performance in electronic devices. Using a copolymer series consisting of fluorinated, partially fluorinated, and nonfluorinated benzotriazole, we confirm that the addition of fluorine substituents beneficially impacts charge transport in polymer semiconductors. Transistor measurements demonstrated a factor of 5 increase in carrier mobilities with the degree of fluorination of the backbone. Furthermore, grazing-incidence X-ray diffraction data indicates progressively closer packing between the conjugated cores and an overall greater amount of π-stacking in the fluorinated materials. It is likely that attractive interactions between the electron-rich donor and fluorinated electron-deficient acceptor units induce very tightly stacking crystallites, which reduce the energetic barrier for charge hopping. In addition, a change in crystallite orientation was observed from primarily edge-on without fluorine substituents to mostly face-on with fluorinated benzotriazole.

In situ electron microscopy tensile testing of constrained carbon nanofibers

Electrospun carbon nanofibers, produced from polyacrylonitrile (PAN) nanofiber precursors, with their superior mechanical properties, are promising candidates for manufacturing advanced polymer composites. Here, we report a series of tensile tests performed in situ under scanning electron microscope (SEM)/transmission electron microscope (TEM) observation, which show that the modulus and strength of electrospun carbon nanofibers can be enhanced through a simple mechanical constraint during the carbonization step in the electrospinning process. The constrained carbon nanofibers of diameter less than 150 nm were nanomanipulated inside the SEM onto a specialized microelectromechanical systems (MEMS) based testing platform and subsequently tested in uniaxial tension until failure. It was identified that both the strength and modulus of the constrained carbon nanofibers with sub-150 nm diameters are on average higher compared to their unconstrained counterparts by ∼22% and ∼31% respectively. Also, by evaluating the internal graphitic order of the constrained carbon nanofibers using TEM-based diffraction methods, we identified that the mechanical constraint during carbonization results in a better degree of orientation in the graphitic crystallites along the fiber axis. Finally, we use Weibull statistics for the deconvolution of the effects of diameter and the mechanical constraint on the tensile properties of carbon nanofibers. The Weibull analysis also showed that the comparatively superior strength of CCNFs is primarily due to better alignment of crystallites with the fiber axis.

Crystal growth patterns in DC and pulsed plated galvanic copper films on (1 1 1), (1 0 0) and (1 1 0) copper surfaces

Copper films for printed circuit board applications have to be fine-grained to achieve even filling of vias. Electroplated Cu films on roll annealed Cu substrates may have unacceptably large epitaxial crystals. Here galvanic films were plated on oriented single-crystal Cu substrates from an additive-free electrolyte, as well as DC plating and pulse reverse (PR) plating with additives. The distribution of crystallite orientations was mapped with XRD and compared with the microstructure determined by SEM. For the additive-free bath on [111] and [100] oriented surfaces a gradual transition from epitaxial to polycrystalline is seen, while films on [110] substrates are persistently epitaxial. Without bath additives, twinning is the main mechanism for the transition to polycrystalline texture. For DC plating, additives (carriers, accelerators and levelers) promote fine-grained films with isotropic grain orientations, with films on [110] substrates being partially isotropic. Plating with carriers and accelerators (no leveler) yields films with many distinct crystallite orientations. These orientations result from up to five steps of recursive twinning. PR plating produces isotropic films with no or very few twins (〈111〉 and 〈100〉 substrates, respectively), while on 〈110〉 oriented surfaces the deposits are about 20% epitaxial.

Spectrophotometric determination of optical parameters of lithium niobate films

Lithium niobate films on silicon substrates have been synthesized by high-frequency magnetron sputtering of a target. The spectral dependences of the reflectance in the 300–700nm range at small incidence angles and the angular dependence of p- and s-polarized light for a discrete set of wavelengths from 300 to 700nm with wavelength increments of 50nm, for angles of 1 arc deg, have been obtained using spectrophotometry. The refractive indicies, the film thickness and the extinction coefficients have been determined using a numerical method for solving inverse problems. The initial approximations for the solution of inverse problems have been defined using methods based on the estimation of the interference extrema positions in the reflection spectra. The resultant refractive indicies of the film differ from those typical of LiNbO3 single crystals. These differences are attributed to the structural disorder induced by the predominant crystallite orientation and the absorption in the film.

Novel Polyethylene Fibers of Very High Thermal Conductivity Enabled by Amorphous Restructuring.

High-thermal-conductivity polymers are very sought after for applications in various thermal management systems. Although improving crystallinity is a common way for increasing the thermal conductivity (k) of polymers, it has very limited capacity when the crystallinity is already high. In this work, by heat-stretching a highly crystalline microfiber, a significant k enhancement is observed. More interestingly, it coincides with a reduction in crystallinity. The sample is a Spectra S-900 ultrahigh-molecular-weight polyethylene (UHMW-PE) microfiber of 92% crystallinity and high degree of orientation. The optimum stretching condition is 131.5 °C, with a strain rate of 0.0129 s–1 to a low strain ratio (∼6.6) followed by air quenching. The k enhancement is from 21 to 51 W/(m·K), the highest value for UHMW-PE microfibers reported to date. X-ray diffraction study finds that the crystallinity reduces to 83% after stretching, whereas the crystallite size and crystallite orientation are not changed. Cryogenic thermal characterization shows a reduced level of phonon-defect scattering near 30 K. Polarization Raman spectroscopy finds enhanced alignment of amorphous chains, which could be the main reason for the k enhancement. A possible relocation of amorphous phase is also discussed and indirectly supported by a bending test.

Unique Crystal Orientation of Poly(ethylene oxide) Thin Films by Crystallization Using a Thermal Gradient

Poly(ethylene oxide) (PEO) thin films of different thicknesses (220, 450, and 1500 nm) and molecular masses (4000, 8000, and 20 000 g/mol) have been fabricated by spin-coating of methanol solutions onto glass substrates. All these samples have been recrystallized from the melt using a directional thermal gradient technique. Millimeter-size domains with crystallites uniformly oriented in the direction of the thermal gradient are observed. Futhermore, the crystallites size and orientation distribution are enhanced (e.g., increases and decreases, respectively) when film thickness is decreased, ultimately leading to a single-crystal-like behavior for 220 nm thick PEO films of mass 8000 g/mol. Interestingly, this fine microstructure is partially retained after melting and subsequent cooling back to ambient temperature for the highest molecular weight polymer allowing, in this particular case, to significantly decrease the distribution of crystal orientation obtained after crystallization using the thermal grad...

Structural Effects of Gating Poly(3‐hexylthiophene) through an Ionic Liquid

Ionic liquids are increasingly employed as dielectrics to generate high charge densities and enable low‐voltage operation with organic semiconductors. However, effects on structure and morphology of the active material are not fully known, particularly for permeable semiconductors such as conjugated polymers, in which ions from the ionic liquid can enter and electrochemically dope the semicrystalline film. To understand when ions enter, where they go, and how they affect the film, thin films of the archetypal semiconducting polymer, poly(3‐hexylthiophene), are electrochemically doped with 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, the archetypal ionic liquid. High‐resolution, ex situ X‐ray diffraction measurements and complete pole figures reveal changes with applied voltage, cycling, and frequency in lattice spacing, crystallite orientation, and crystallinity in the bulk and at the buried interface. Dopant ions penetrate the film and enter the crystallites at sufficiently high voltages and low frequencies. Upon infiltrating crystallites, ions permanently expand lamellar stacking and contract pi‐stacking. Cycling amplifies these effects, but higher frequencies mitigate the expansion of bulk crystallites as ions are hindered from entering crystallites. This mechanistic understanding of the structural effects of ion penetration will help develop models of the frequency and voltage impedance response of electrochemically doped conjugated polymers and advance electronic applications.

CARIOUS AND REMINERALISED ENAMEL;

Objectives: The main purpose of this study was to determine from wherethe demineralisation of crystals occur in enamel during carious process and where the newcrystals will form during remineralization. Material and Methods: Synchrotron x-ray diffractiontechnique was used to determine the crystal orientation and texture of enamel for a Period: of02 years during 2010 and 2011. It was done on extracted teeth. 10 sides of a single tooth wereanalysed and a total of 100 teeth were examined. Sample analysis was done using compositeimaging and powder diffraction using Fit 2D software. Settings: The study was done at QueenMary University of London, Miles End Campus England. Sections of a tooth were taken having1) healthy control enamel 2) natural carious enamel 3) artificially demineralized enamel and4) artificially remineralized enamel. Synchrotron x-ray diffraction was carried out and twodimensional images of the areas of the tooth were collected. A 20μmx20μm beam spot wasused to collect images at high resolution in order to see the changes that occur in a smallregion of interest. First the Fit2D software was used for powder diffraction data processingand later Origin software was used obtain the texture values of the above mentioned areas.Results: Comparison of the side and cuspal both for the control and carious enamel showedthat the carious enamel has a better texture than the control enamel. Also a repetition of thepattern after every 60 to 100um was seen in the cuspal enamel both in the control and cariousenamel respectively. Conclusion: The natural carious enamel showed a better texture andmore orientation from the healthy control enamel. This indicates that the continuous processesof demineralization and remineralization which occur in enamel during caries may have someeffects in increasing the texture of enamel since the mineral left in the carious enamel has ahigher degree of crystallite orientation than the control enamel.

Reprint of: Localization of Cl-35 Nuclei in Biological Solids using Rotational-Echo Double-Resonance Experiments

Chloride ions play important roles in many chemical and biological processes. This paper investigates the possibility of localizing 35Cl nuclei using solid-state NMR. It demonstrates that distances shorter than 3.8Å, between 13C atoms and 35Cl atoms in 10% uniformly labeled 13C L-tyrosine·HCl and natural abundance Glycine·HCl can be measured using rotational-echo (adiabatic passage) double-resonance (RE(AP)DOR). Furthermore the effect of quadrupolar interaction on the REDOR/REAPDOR experiment is quantified. The dephasing curve is plotted in a three dimensional chart as a function of the dephasing time and of the strength of quadrupolar interaction felt by each orientation. During spinning each orientation feels a quadrupolar interaction that varies in time, and therefore at each moment in time we reorder the crystallite orientations as a function of their contribution to the dephasing curve. In this way the effect of quadrupolar interaction on the dipolar dephasing curve can be fitted with a polynomial function. The numerical investigation performed allows us to generate REDOR/REAPDOR curves which are then used to simulate the experimental data.

Monitoring the Crystalline Structure of Sugar Cane Bagasse in Aqueous Ionic Liquids

The use of aqueous ionic liquids as a pretreatment for enhancing enzymatic saccharification of lignocellulosic biomass is well-known, with a focus on lignin and hemicellulose removal. However, in-depth knowledge of changes in cellulose crystallinity during the pretreatment is limited. To this effect, detailed Fourier transform infrared (FT-IR) spectroscopy, cross-polarized magic angle spinning 13C nuclear magnetic resonance (CP/MAS 13C NMR), and X-ray diffraction (XRD) studies on sugar cane bagasse that has been pretreated with aqueous ionic liquids is presented. Secondary derivatives of FT-IR spectra and Gauss deconvolution of XRD patterns were applied to give a detailed understanding of the crystalline changes in sugar cane bagasse cellulose upon pretreatment. The results showed that aqueous ionic liquid pretreatment destroys the semicrystalline region of sugar cane bagasse cellulose, thus disordering the orientation of the cellulose crystallites.

Ductile polyacrylonitrile fibers with high cellulose nanocrystals loading

Polyacrylonitrile (PAN) fibers containing up to 40 wt% cellulose nanocrystals (CNCs) were processed. Structure, mechanical, and dynamic mechanical properties of these fibers were systematically investigated. The crystallinity, crystal size and crystallite orientation of PAN in PAN and PAN/CNC fibers significantly increases as the draw ratio increases from 4x to 15x. As compared to the control PAN fiber at a draw ratio of 4x, work of rupture increases by a factor of 2 only for 1 wt% CNC loading, and tensile modulus increased by a factor of two at the same draw ratio in fibers containing 40 wt% CNC. Though PAN/CNC 40 wt% fiber is brittle at 4x draw ratio, the elongation at break is significantly improved as fiber was drawn to a draw ratio of 29x and becomes comparable to that for the control PAN fiber at high draw ratio. This is the first study of such a high concentration of nano reinforcement in PAN fibers with good mechanical properties. These results should prove important in reinforcing broader class of polymers with CNCs and other nanomaterials, without making them brittle, which is a common draw back with many reinforcements and fillers.

Effect of PCBM additive on morphology and optoelectronic properties of P3HT-b-PS films

Thin blend films of the diblock copolymer poly(3-hexylthiophene-2,5-diyl)-block-polystyrene (P3HT-b-PS) and phenyl-C61-butyric acid methyl ester (PCBM) are prepared and investigated. The morphology of films with 9, 25, 33, 50, 58 and 67% PCBM weight fraction is determined. The surface topography is probed with optical microscopy and atomic force microscopy whereas the lateral inner structures are determined using grazing incidence small angle neutron scattering (GISANS). Grazing incidence X-ray diffraction (GI-XRD) shows a blend ratio dependence of the P3HT crystallites orientation within the block copolymer films. The thermodynamically favoured P3HT edge-on orientation is suppressed upon increasing the PCBM content from 9% till 33% while it recovers in samples with a PCBM weight fraction above 50%. PCBM tends to interact with the PS block at low PCBM fractions and forms segregated domains at a PCBM weight fraction higher than 50%. The addition of PCBM decreases the degree of lamellar structure order and well-ordered hexagonal packed cylindrical structures emerge in at a PCBM weight fraction of 67%. Absorbance and photoluminescence measurements show the relationship between morphology transformation and optoelectronic properties. The phenomena reported here could provide an alternative view for potential nanotechnology applications.

Electrodeposition of Co and Co composites with carbon nanotubes using choline chloride-based ionic liquids

The paper presents experimental results regarding the electrodeposition and characterization of cobalt and cobalt composites with carbon nanotubes from a choline-chloride-based deep eutectic solvent.Dispersion stability of multi-walled carbon nanotubes (MWCNTs) was excellent in the eutectic solvent used. According to Raman and XRD analysis, the carbon nanotubes were successfully inserted into the metallic matrix. Furthermore, XRD results suggested that the incorporation of CNTs on the deposit promoted a preferred orientation of the Co crystallites on (220) plane. The Co and Co-composites coatings obtained onto a copper substrate are adherent and uniform. Pure Co deposit was formed by sharp edge grains, Co-composites appeared to be less compact and formed by relatively spherical particles connected by MWCNTS. Furthermore, it was found that the presence of MWCNTs contributed to decreasing the deposit's roughness. From corrosion tests, Co-composite films exhibit a comparable or slightly better corrosion performance as compared to pure Co films.

Comparative Morphological and Crystallographic Analysis of Electrochemically- and Chemically-Produced Silver Powder Particles

Silver powders chemically synthesized by reduction with hydrazine and those produced by electrolysis from the basic (nitrate) and complex (ammonium) electrolytes were examined by X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis of the produced particles. Morphologies of the obtained particles were very different at the macro level. The needle-like dendrites, as well as the mixture of irregular and regular crystals, were formed from the nitrate electrolyte, while the highly-branched pine-like dendrites with clearly noticeable spherical grains were formed from the ammonium electrolyte. The agglomerates of spherical grains were formed by reduction with hydrazine. In the particles obtained from the nitrate electrolyte, Ag crystallites were strongly oriented in the (111) plane. Although morphologies of Ag particles were very different at the macro level, the similarity at the micro level was observed between chemically-synthesized particles and those obtained by electrolysis from the ammonium electrolyte. Both types of particles were constructed from the spherical grains. This similarity at the micro level was accompanied by the similar XRD patterns, which were very close to the Ag standard with a random orientation of Ag crystallites. For the first time, morphologies of powder particles were correlated with their crystal structure.

Effect of the inclusion of galium in normal cadmium chloride treatment on electrical properties OF CdS/CdTe solar cell

The inclusion of gallium into the well-known CdCl2 post-growth treatment shows drastic improvement in both CdTe material and electrical properties of the fully fabricated CdS/CdTe-based solar cell as compared with the regular CdCl2 treatment. The optical, morphological, compositional and electronic properties the glass/FTO/n-CdS/n-CdTe/p-CdTe were explored after post-growth treatment of glass/FTO/n-CdS/n-CdTe/p-CdTe with CdCl2 and CdCl2:Ga treatments at 430 °C for 20 min. Morphological analysis show grain growths within the ranges of (100–2000) nm and (200–2600) nm for CdCl2 and CdCl2:Ga treatments as compared with the as-deposited glass/FTO/n-CdS/n-CdTe/p-CdTe layer with grain size within the ranges of (100–250) nm. Structurally, the preferred orientation of the as-deposited CdTe remains (111)C after both CdCl2 and CdCl2:Ga treatments of glass/FTO/n-CdS/n-CdTe/p-CdTe with randomisation of crystallite orientation observed after CdCl2:Ga with an increase in the diffraction intensities of the (220)C and (311)C CdTe peaks. The multilayer structure glass/FTO/n-CdS/n-CdTe/p-CdTe utilised in this work was grown using electrodeposition technique. The glass/FTO/n-CdS/n-CdTe/p-CdTe sample was divided into three sets; the first and second sets were treated with CdCl2 and CdCl2:Ga respectively, while the third set was left as-deposited. Both the CdCl2 and CdCl2:Ga sets were heat treated in air at 430 °C for 20 min, etched to improve metal/semiconductor interface and metallised with 100 nm Au contacts. The current-voltage measurements show comparative improvements in the open-circuit voltage, short-circuit current density, fill factor and the solar cell efficiency of the CdCl2:Ga treated glass/FTO/n-CdS/n-CdTe/p-CdTe as compared with the CdCl2 treated structure. A conversion efficiency of ∼11% was achieved with the CdCl2:Ga treatment while ∼7% was achieved with the CdCl2 treatment of similar glass/FTO/n-CdS/n-CdTe/p-CdTe device structure. This observation shows that the inclusion of gallium further improves CdCl2 treatment of CdS/CdTe-based solar cell due to its unique features of improving the stoichiometry of the CdTe layer.

Orientation Processes in Crystalline and Amorphous Regions of Polypropylene During Yarn Spinning

The influence of the spinneret draw ratio and subsequent solid-state stretching of polypropylene multifilament yarns (PMY) on changes in the orientation of crystallites and molecular chains in the polymer amorphous regions was studied using x-ray structure analysis. It was shown that crystallites and molecular chains of amorphous polypropylene (PP) became significantly more oriented already for a yarn spinneret draw ratio of 2400% and changed little if it was increased further. Additional solid-state stretching of yarns at elevated temperature had practically no effect on the orientation of PP crystallites but did halve the misorientation angle of molecular chains in the polymer amorphous regions. This phenomenon suggested that the substantial decrease of the elongation at break and increase of PMY physicomechanical parameters could be attributed to distribution of the applied load onto a larger number of continuous chains.

Noticeable red emission and Raman active modes in nanoscale gadolinium oxyfluoride (Gd4O3F6) systems with Eu3+ inclusion

Eu3+ doped gadolinium oxyfluoride (Gd4O3F6, GOF) nanoscale systems have been synthesized following a modified Pechini method. While exhibiting a tetragonal crystal structure, the GOF nanosystem gave an average crystallite size (d) of ~21–26 nm. The Lotgering factor (LF), which is a measure of orientation of crystallites along the preferred direction was found to vary between 0.22 and 0.48. In the photoluminescence spectra, ~595 and ~613 nm peaks were identified as magnetically driven (5D0 → 7F1) and electrically driven (5D0 → 7F2) transitions with latter (red emission) being strongly manifested with Eu3+ doping concentration and intrinsic defects. Moreover, several Raman active modes have been probed in the Raman spectra with low frequency peaks (<300 cm−1) and moderate frequency peaks (~481 and 567 cm−1) assigned to observable vibration of heavy atom Gd–Gd pairs and Gd–O groups, respectively. Apart from manifestation of phononic features, inclusion of Eu3+ in the host lattice would bring new insight on improving the red emission response prior to concentration quenching.

Effects of ultra-high temperature treatment on the microstructure of carbon fibers

The microcrystalline structure and microvoid structure in carbon fibers during graphitization process (2300−2700 °C) were characterized employing laser micro-Raman scattering (Raman), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy (HR-TEM). The crystalline sizes (L a, L c) increased and interlayer spacing (d 002) decreased with increasing heat treatment temperature (HTT). The microvoids in the fibers grew up and contacted to the neighbors with the development of microcrystalline. In addition, the preferred orientation of graphite crystallite along fiber axis decreased and microvoids increased. The results are crucial for analyzing the evolution of microstructure of carbon fibers in the process of heat treatment and important for the preparation of high strength and high modulus carbon fibers.

Influence of metal electrodes on c‐axis orientation of AlN thin films deposited by DC magnetron sputtering

Nanocrystalline aluminum nitride (AlN) thin films were deposited on two types of metallic seed layers on silicon substrates, (111) textured Pt and (110) Mo, by reactive DC magnetron sputtering at low temperature (200 °C). Both textured films of Pt and Mo promote nucleation, thereby improving the crystallinity and epitaxial growth condition for AlN thin films. The deposited films were examined by X‐ray diffraction, scanning electron microscopy and atomic force microscopy techniques. The results indicated that the preferred orientation of crystallites greatly depends upon the kinetic energy of the sputtered species (target power) and seed layers used. Furthermore, AlN thin films with c‐axis perpendicular to the substrate grew on both types of metal electrodes at all power levels larger than 100 W. By comparing the structural properties and compressive stresses at perfect c‐axis orientation conditions, it is evident that AlN films deposited on (110) oriented Mo substrates exhibited superior properties as compared with Pt/Ti seed layers. Furthermore, less values of compressive stresses (−3 GPa) as compared with Pt/Ti substrates (−7.08 GPa) make Mo preferentially better candidate to be employed in the field of suspended Micro/Nano ‐ electromechanical systems (MEMS/NEMS) for piezoelectric devices. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Synchrotron X-ray diffraction to understand crystallographic texture of enamel affected by Hunter syndrome

ObjectiveTo determine whether Hunter syndrome (MPS II) affects the crystallographic texture (preferred orientation) of enamel. DesignSynchrotron X-ray diffraction, being a state of the art technique, has been used to determine the enamel crystallite orientation in enamel affected by Hunter syndrome (MPS II). The incisal, lingual and cervical regions of the MPS II affected tooth were observed and compared to healthy tooth. ResultsIt was observed that there is a loss of organization of crystallites in deciduous incisal enamel affected by Hunter syndrome (MPS II) as compared to healthy deciduous enamel tissue. Generally it was observed that, in contrast to the healthy enamel, the enamel affected by MPS II possessed a lower crystallographic preferred orientation, with a more uniform spatial distribution; however, the enamel at the incisal tip was relatively unaffected. ConclusionHunter syndrome affects the enamel texture in the lingual and cervical regions of the tooth.