Crystallite Distribution Research Articles

Orientation Distribution of Crystalline β-Sheet Domains in Bombyx mori Silk Fiber Studied with Vibrational Sum Frequency Generation Spectroscopy.

Silk fibers have good biocompatibility and mechanical properties, which make them attractive in biomaterial applications as well as textile industries. It is believed that the superior mechanical property is associated with the crystalline β-sheet structure in the fiber; but a deeper understanding of the structure-property relationship is still needed for full exploitation of its physical properties. Especially, accurate information on hydrogen-bonding interactions within β-sheet domains at the nanoscale and their spatial distributions at the mesoscale are critically needed. In this study, we demonstrate the selective detection of crystalline β-sheet domains in Bombyx mori silk fiber using sum frequency generation (SFG) spectroscopy and its use to determine the angular distribution of the β-sheet crystallites with respect to the fiber axis. Numerical simulations of the SFG signal of the amide-I band were carried out using tensors based on the B2 symmetry of the D2 point group and compared with experimental data. This comparison found that the crystalline β-sheet domains are aligned along the fiber axis with a standard deviation of ∼27° and parallel to the fiber surface with a standard deviation of ∼5°. It was also found that the amide bands in the SFG spectra cannot be fully explained with the assumption that the crystalline β-sheet vibrations can be described with the D2 point group. Being able to monitor the amide group vibrations sensitive to both interchain hydrogen bonding and crystallite orientations, SFG analysis has a potential to unveil the structure-mechanical property relationship that may not be readily assessable with other characterization techniques.

Composite nanofibres of CuI‐polystyrene via electrospinning through critical control of solvation conditions

AbstractComposite nanofibres of copper (II) with various polymer matrices have been frequently reported. However, due to the lack of solubility of the Cu(I) moieties, Cu(I) electrospinning has proved more challenging. The objective of this study was to find a route to and prepare nanofibres containing copper iodide. This investigation describes the successful electrospinning of composite nanofibres of copper iodide (CuI) and polystyrene (PS) using a combination of two solvents to provide critical spinning conditions. The electrospinning solution was prepared by combining dimethylformamide (DMF) as the main solvent for PS and triethylamine (TEA) as a cosolvent; this mediates the dissolution of CuI. Electrospinning was accomplished under different parameters such as PS concentration, CuI concentration, and applied voltage. The outcome of the process was colored and smooth nanofibres that underwent analysis using scanning electron microscopy (SEM), energy dispersive X‐ray (EDX), X‐ray diffraction (XRD) and inductively coupled plasma ‐ mass spectrometry (ICP‐MS). The analysis findings emphasized the importance of the electrospinning parameters, specifically the concentration of PS and the applied voltage on successful fiber generation. However with control of these conditions composite nanofibres of CuI‐PS with uniform distribution of nanoscale crystallites of CuI can be successfully produced.

Determination of the average crystallite size and the crystallite size distribution: the envelope function approach EnvACS.

A procedure is presented to exactly obtain the apparent average crystallite size (ACS) of powder samples using standard in-house powder diffraction experiments without any restriction originating from the Scherrer equation. Additionally, the crystallite size distribution within the sample can be evaluated. To achieve this, powder diffractograms are background corrected and long-range radial distribution functions G(r) up to 300 nm are calculated from the diffraction data. The envelope function f env of G(r) is approximated by a procedure determining the absolute maxima of G(r) in a certain interval (r range). Fitting of an ACS distribution envelope function to this approximation gives the ACS and its distribution. The method is tested on diffractograms of LaB6 standard reference materials measured with different wavelengths to demonstrate the validity of the approach and to clarify the influence of the wavelength used. The latter results in a general description of the maximum observable average crystallite size, which depends on the instrument and wavelength used. The crystallite site distribution is compared with particle size distributions based on transmission electron microscopy investigations, providing an approximation of the average number of crystallites per particle.

Crystallographic Texture Evolution in 3D Printed Polyethylene Reactor Blends.

In this work, crystallographic texture evolution in 3D printed trimodal polyethylene (PE) blends and high-density PE (HDPE) benchmark material were investigated to quantify the resulting material anisotropy, and the results were compared to materials made from conventional injection molded (IM) samples. Trimodal PE reactor blends consisting of HDPE, ultrahigh molecular weight PE (UHMWPE), and HDPE_wax have been used for 3D printing and injection molding. Changes in the preferred orientation and distribution of crystallites, i.e., texture evolution, were quantified utilizing the wide angle X-ray diffraction through pole figures and orientation distribution functions (ODFs) for 3D printed and IM samples. Since the change in weight-average molecular weight (Mw) of the blend was expected to significantly affect the resulting crystallinity and orientation, the overall Mw of the trimodal PE blend was varied while keeping the UHMWPE component weight fraction to 10% in the blend. The resulting texture was analyzed by varying the overall Mw of the trimodal blend and the process parameters in 3D printing and compared to the texture of conventional IM samples. The printing speed and orientation (defined with respect to the axis along the length of the samples) were used as the variable process parameters for 3D printing. The degree of anisotropy increases with an increase in the nonuniform distribution of intensities in pole figures and ODFs. All the highest intensity major texture components in IM and 3D printed samples (0° printing orientation) of reactor blends are observed to have crystals oriented in [001] or [001̅]. Overall, for the same throughput, 3D printed samples in the 0° orientation showed greater texture evolution and higher anisotropy compared to IM samples. Most notably, an increase in 3D printing speed increased the crystalline distribution closer to the 0° direction, increasing the anisotropy, while deviation from this printing orientation reduced crystalline distribution closer to the 0° direction, thus increasing isotropy. This demonstrates that tailoring material properties in specific directions can be achieved more effectively with 3D printing than with the injection molding process. Change in the overall Mw of the trimodal PE blend changed the preferential orientation distribution of the crystal planes to some degree. However, the degree of anisotropy remained the same in almost all cases, indicating that the effect of molecular weight distribution is not as significant as the printing speed and printing orientation in tailoring the resulting properties. The 3D printing process parameters (speed and orientation) were shown to have more influence on the texture than the material parameters associated with the blend.

Analysis of the turbostratic structures in PAN-based carbon fibers with wide-angle x-ray diffraction

Carbon fiber (CF) is a versatile material renowned for its excellent mechanical, thermal, and electrical properties. Polyacrylonitrile (PAN)-based CFs dominate the market in part due to their high tensile strength, rendering them suitable for structural applications in a wide variety of applications ranging from sporting goods to aerospace. Over five decades of commercial development of PAN-based CF has resulted in a range of varieties with different tensile moduli and tensile strengths. The microstructures, nanostructures, and crystal structures of PAN-based CF all play pivotal roles in the macroscale properties of this material. In particular, the crystal structure and crystallite orientation in CF is closely related to the mechanical properties. The crystal structure of PAN-based CF generally consists of turbostratic carbon, a disordered form of graphite, the characteristics of which can be effectively characterized in a bulk format through wide-angle x-ray diffraction (WAXD). In this work, we employed a three-part approach to the analysis of WAXD patterns collected from four intermediate modulus PAN-based CFs. The approach incorporates a Scherrer analysis, a Debye analysis, and an orientational analysis to provide precise estimates of crystallite sizes, crystallite distributions, and crystallite orientations with the fiber axis. The results presented here suggest that intermediate modulus PAN-based CF mostly consists of small turbostratic crystallites (<4 nm), with larger crystallites having increased orientation with the fiber axis. The results here imply the presence of curvature and/or wrinkling of the turbostratic layers within the CF structure.

Improving electrochemical performance of Ni-rich layered cathode material with combining Co-enriched compositional gradient and radial microstructure

Ni-rich complex layered oxides LiNixMnyCozO2 (x > 0.85) with a combined Ni/Co concentration gradient and radially oriented elongated plate-like primary particles were synthesized with hydrothermal microwave-assisted treatment of an as-prepared mixed hydroxide precursor with aqueous solution of Co source and urea followed by a high temperature annealing with a Li source. The radial distribution of plate-like primary crystallites in microwave-treated materials was achieved through Co-enrichment at the surface, which likely triggered the surface-to-bulk growth of plate-like particles rather than isotropic octahedral crystallites. The Co-modified cathode materials demonstrate greatly improved cycling stability (capacity fade per cycle of 0.04 ± 0.01%) compared to unmodified Ni-rich NMCs (capacity fade per cycle of 0.13 ± 0.02%) with similar Ni concentration, as well as good rate capability (215, 210, 199, 189, 178 and 160 mAh/g at C/10, C/5, C/2, 1C, 2C, and 5C rates at 2.7–4.3V vs Li/Li+). Enhanced electrochemical performance is linked to the improved mechanical integrity, which was achieved through radial microstructure organization of the agglomerates triggered by Co concentration gradient, suppressing the intragranular crack formation.

Hollow core mesoporous carbon spheres as catalyst support for improved platinum utilization in phosphoric acid fuel cells

Using a well-known sol-gel technique, monodispersed silica spheres measuring 380 nm in size are generated in situ. These silica spheres serve as a template for the synthesis of hollow core mesoporous shell (HCMS) carbon spheres. Inside the pores of the template, a polymer is synthesized using azoisobutyronitrile and divinylbenzene polymerization route. Polymer carbonization followed by template remotion yielded HCMS carbon spheres. This HCMS carbon is mesoporous and offers uniform Pt crystallite distribution for acid fuel cell applications. As-prepared HCMS carbon is examined by field emission gun SEM, TEM, nitrogen adsorption/desorption isotherm (BET surface area and BJH pore size distribution analysis), and apparent density using Helium pycnometry. The HCMS carbon obtained demonstrates a BET surface area of 623 m2g-1, showcasing a uniform pore size distribution centered at 3.8 nm. This specific characteristic renders it an ideal support material for fuel cell catalysts. The electrochemical studies reveal the key parameters like corrosion resistance, bulk electrical conductivity, the electrochemical surface area of Pt chemically deposited on HCMS carbon, and unit fuel cell performance under phosphoric acid environment. These parameters are compared with the standard carbon powder, Vulcan XC72R and a commercial catalyst to evaluate the HCMS carbons’ suitability for fuel cell applications.

Transparent and highly conductive La-doped strontium stannate thin film growth by PI-MOCVD method on LaAlO3 and MgO substrates of (100), (110), (111) orientations

Wide band gap (4.6 eV) lanthanum doped SrSnO3 semiconductors of high electron mobility have potential applications in transparent oxide semiconductor technologies. However, there is a lack of data on the electrical properties of La:SrSnO3 both in single crystals and in thin films with an orientation other than (001). We show that after applying a modified metalorganic chemical vapor deposition method it is possible to deposit relaxed thick (001), (110) and (111) oriented La:SrSnO3 films on LaAlO3 and MgO substrates. Thin films on LaAlO3 substrates exhibit comparatively high charge carrier mobility values: µ100=71 cm2V−1s−1, µ110=72 cm2V−1s−1 and µ111=67 cm2V−1s−1. In this article, using the results of X-ray diffraction and crystallite orientation distribution modeling, as well as scanning and transmission electron microscopy data, the link between the obtained charge carrier mobility (µ100 ≈ µ110 > µ111) and film's microstructure and morphology is discussed.

Cobalt ferrite as an electromagnetically boosted metal oxide hetero-Fenton catalyst for water treatment

The cobalt ferrite Fenton catalysts were obtained by the flow co-precipitation method. FTIR, XRD, and Mössbauer spectroscopy confirmed the spinel structure. The crystallite size of the as-synthesized sample is 12 nm, while the samples annealed at 400 and 600 °C have crystallite sizes of 16 and 18 nm, respectively. The as-synthesized sample has a grain size of 0.1–5.0 μm in size, while the annealed samples have grain sizes of 0.5 μm–15 μm. The degree of structure inversion ranges from 0.87 to 0.97. The catalytic activity of cobalt ferrites has been tested in the decomposition of hydrogen peroxide and the oxidation of caffeine. The annealing of the CoFe2O4 increases its catalytic activity in both model reactions, with the optimal annealing temperature being 400 °C. The reaction order has been found to increase with increasing H2O2 concentration. Electromagnetic heating accelerates the catalytic reaction more than 2 times. As a result, the degree of caffeine decomposition increases from 40% to 85%. The used catalysts have insignificant changes in crystallite size and distribution of cations. Thus, the electromagnetically heated cobalt ferrite can be a controlled catalyst in water purification technology.

New Manufacturing Process for Granular Texture Management in Polycrystalline BaM Hexaferrites through the Goethite Crystallite Laths Aspect Ratio, and a Specialized Law of Approach to the Magnetic Saturation for Partly Polarized Uniaxial Materials

This study is aimed at the manufacture and the magnetic properties of polycrystalline M-type hexaferrites BaFe12O19 (barium ferrite, or BaM) materials of different magnetic texturing grades, going from a random distribution of the BaM crystallites to their almost complete stacking. Our target is to optimize the value of reduced-remanence magnetization MR/MS, which is among the most significant features of the self-polarized materials. In this study, we focus on the role played by the precursors hematite (isotropic spherical shape) and goethite (anisotropic lath shape). Therefore, 11 samples with a flat cylinder shape are fabricated, with an increasing hematite to goethite ratio. We demonstrate that this ratio drives the texturization of the samples by producing self-polarized materials with different MR/MS from the simple green compaction of the precursors, followed by a heat treatment. Most importantly, our study reveals the orientation of BaM particles after compaction; therefore, MR/MS, is strongly influenced by the aspect ratio of the lath-shaped goethite crystallites. Additionally, we show that finer goethite crystallites yield higher-value MR/MS. We optimize the aspect ratio of the goethite crystallites for an improved BaM texture. The optimization of the morphology of the goethite crystallites leads to an increase in the BaM particles’ orientation and stacking. The salient outcome of this work, which distinguishes it significantly from recent works, is that the particles stacking increases with the value of the shape factor η (defined as the ratio of the diameter of the laths to their length) of the goethite, evidenced by XRD results. The Rietveld refinements of powder diffractograms and the measured magnetic properties reveal a particle-stacking enhancement caused by not only the ratio of hematite: goethite but mainly by an optimal aspect ratio of the goethite crystallites. Based on this study, the BaM materials are further manufactured with a controlled magnetic texture; thus, they are partly self-polarized. They show reduced-remanence magnetization MR/MS varying from 0.5 and 0.81, while the angular dispersion of the BaM particles’ easy axis of magnetization varies from 60° to 10°. The magnetic properties of the samples are further studied in microwave experiments, from which the value of the magnetocrystalline anisotropy field HK = 16.6 kOe is deduced. The first magnetization curves of each sample are obtained using a VSM. A law of approach to the saturation suitable for the case of the uniaxial polycrystalline materials, and for which the particle stacking is only partial, is proposed for the fitting of the magnetization process. It is suggested that by using the proposed law with a known magnetocrystalline anisotropy constant K1, the angular grain-dispersion can be found.

In Ukrainian

The study of the microstructure of nanocrystalline substances by the method of powder diffractometry based on the physical broadening of diffraction lines involves the use of diffraction data of standard polycrystalline samples, preferably, one nature with the test samples with the size of crystallites exceeding 100 nm. In the absence of such standards, researchers resort to the existing dependence of the width of diffraction peaks on the angle of diffraction for the standard sample or the construction of theoretical instrumental profiles due to the collimation parameters of x -rays used. In this paper a comparative study of the microstructure of nanocrystalline titanium oxide (anatase), tin oxide iron oxide (magnetite), synthesized in various ways, using several methods of analysis of powder diffractograms, was carried out. To evaluate the average crystallite sizes of the studied oxides, the Sherer equation with a graphical method of determining the width of instrumental profile and the influence of dublet radiation was chosen. Methods of profile analysis of diffraction spectra, such as a method of whole profile modeling of powder diffractograms (WPPM) and the chord method, were used to construct crystallite size distribution functions and determine the average size of crystallites of the oxides. Modeling of instrumental diffraction profiles of titanium, tin and iron oxides was performed using X -rays collimation parameters determinated using a polycrystalline silicon as standard and pseudo -Voigt function, which best describes the form of diffraction peak. The crystallite size distribution functions were constructed by means of WPPM and chords methods based on the instrumental profiles. It has been found that the values of average size of the crystallites, obtained by the methods of Sherer, WPPM and chords, differ within the one order of magnitude for each oxide. Thus, for titanium oxide this value is within 12-18 nm, for tin oxide within 7-10 nm, the iron oxide of iron within 9-12 nm. Analysis of size crystallite distribution functions and average sizes of the crystallites of the studied oxides showed the advisability of using different methods of studying microstructure to clarify the true type of the size crystallites distribution and establish its connection with the conditions and the synthesis method.

Mesoscale structural gradients in human tooth enamel

The outstanding mechanical and chemical properties of dental enamel emerge from its complex hierarchical architecture. An accurate, detailed multiscale model of the structure and composition of enamel is important for understanding lesion formation in tooth decay (dental caries), enamel development (amelogenesis) and associated pathologies (e.g., amelogenesis imperfecta or molar hypomineralization), and minimally invasive dentistry. Although features at length scales smaller than 100 nm (individual crystallites) and greater than 50 µm (multiple rods) are well understood, competing field of view and sampling considerations have hindered exploration of mesoscale features, i.e., at the level of single enamel rods and the interrod enamel (1 to 10 µm). Here, we combine synchrotron X-ray diffraction at submicrometer resolution, analysis of crystallite orientation distribution, and unsupervised machine learning to show that crystallographic parameters differ between rod head and rod tail/interrod enamel. This variation strongly suggests that crystallites in different microarchitectural domains also differ in their composition. Thus, we use a dilute linear model to predict the concentrations of minority ions in hydroxylapatite (Mg2+ and CO32-/Na+) that plausibly explain the observed lattice parameter variations. While differences within samples are highly significant and of similar magnitude, absolute values and the sign of the effect for some crystallographic parameters show interindividual variation that warrants further investigation. By revealing additional complexity at the rod/interrod level of human enamel and leaving open the possibility of modulation across larger length scales, these results inform future investigations into mechanisms governing amelogenesis and introduce another feature to consider when modeling the mechanical and chemical performance of enamel.

Uneven crystallization of lead halide perovskite in the carbon-electrode based, low-temperature mesoscopic perovskite solar cells

Crystallization of perovskite is monitored in carbon-electrode based, low-temperature, mesoscopic perovskite solar cells. Crystallographic and morphological properties of the perovskite are examined through changes in the film thickness of carbon-electrode or the volume of perovskite precursor. It is observed that, when a relatively thin carbon-electrode or large volume of perovskite precursor is used, perovskite crystallites mainly form on the device surface, leaving the bottom part of the device un-wetted. However, if a thicker carbon-electrode or less perovskite precursor is used, crystallization could be seen in the whole porous skeleton, and relative uniform distribution of perovskite crystallites is achieved. As such, uneven crystallization is observed. Such behavior is due to solvent evaporation on the surface, which facilitates nucleation processes on the surface, while retards crystallization on the bottom due to the Ostwald ripening effect. Charge transfer/recombination processes and photo-to-electric power conversion properties are studied. As expected, uneven crystallization results in retarded charge transfer and increased risk of recombination, and poor power conversion efficiency, for example, ∼3%. In contrast, uniform crystallization accelerates charge transfer and reduces recombination risk, and increases the efficiency to higher than 11% (AM1.5G, 100 mW/cm2).

Mechanical ordering of pigment crystallites in oil binder: can electron paramagnetic resonance reveal the gesture of an artist?

Is it possible to reconstruct the gesture of an ancient artist applying a paint layer, considering that the orientation distribution of crystallites of an inorganic pigment remains definitively imprinted on the support after drying of the layer? If the pigment contains paramagnetic transition metal ions whose magnetic interactions are themselves anisotropic, then the shape of the electron paramagnetic resonance (EPR) spectrum should reflect the distribution of grain orientations. We have demonstrated this effect in the case of Egyptian blue CaCuSiO, a pigment used for at least 3 millennia in antiquity, by reconstructing the probability density of crystallite orientations under various modes of application, such as brush painting, dabbing and droplet deposition.

Interplay of electrode geometry and bias on charge transport in organic heterojunction gas sensors

Modulation of charge transport in an organic heterojunction sensor is a promising strategy to enhance its gas sensing properties. Herein, a heterostructure consisting of a bilayer assembly of perfluorinated copper phthalocyanine and lutetium bis-phthalocyanine is investigated for ammonia sensor development in two different electrode geometries and in a wide range of applied bias. The microstructure of the heterostructure retains the bulk electronic and structural properties of the individual components and shows granular distribution of phthalocyanine crystallites on the surface. The charge transport of the heterojunction devices depends on the electrode geometry and the applied bias. Notably, interfacial charge transport gets faster, while bulk charge transport remains constant with increasing bias in both devices. But, the small gap between the electrodes fastens the bulk and the interfacial charge transport by 75 and 5 times, respectively, compared to the big gap electrodes. The implication of faster charge transport in the small gap electrodes-based sensor is demonstrated on its ammonia sensing properties, exhibiting higher response and shorter response time. Moreover, the response of the sensor exponentially increases with increasing bias. The high sensitivity and stability of the sensor at different relative humidity make it a suitable NH3 sensor for real environment applications.

Supercritical impregnation of chitosan sponges with 17β-estradiol

Chitosan sponges with open porous structures have great potential as drug delivery matrices for constructing transdermal patches. Supercritical solvent impregnation (SSI) is an advantageous green technique for the inclusion of hydrophobic drugs into porous matrices. In this work SSI of chitosan sponges with 17β-estradiol (E2) using a supercritical scCO2 /ethanol medium under static conditions was investigated. In the SSI study, the influence of such operating parameters as temperature (35 and 65 °C), pressure (15–120 MPa, which corresponds to density of CO2 815–1142 kg m-3.), and a molar fraction of the drug (from 2.3 ×10-3 mol% to 8.9 ×10-3 mol% from CO2 amount) in the reactor on the loading capacity and the efficiency of the uptake was evaluated. It was revealed that hormone loading increased linearly with the initial concentration of E2 and CO2 density in the reactor. The developed processing parameters for SSI made it possible to vary the loading of E2 into the chitosan sponges in a wide range from a few to hundreds of µg per mg of the matrix, which corresponds to the adequate doses range of the hormone used in transdermal delivery. The successful inclusion of E2 into the polymer matrices was proven by UV spectroscopy, powder X-ray diffraction, fluorescence microscopy, and scanning electron microscopy. It was found that SSI method provides a strong micronization and a uniform distribution of E2 crystallites in the sponge volume, which may positively affect the bioavailability of the drug.

Modification of crystallization behavior, mechanical strength and optical property of Ge–S binary chalcogenide glass ceramics by trace CsCl incorporation

In present work, we discovered that nano-crystallization behavior of Ge–S binary chalcogenide glass can be remarkably improved by incorporating trace amount of CsCl as nucleating agent. After implementing an annealing process, the resultant Ge-S-CsCl chalcogenide glass ceramics (GSC ChGCs) possess fine distribution of crystallites belonging to GeS2 and GeS mixture phase which could enhance mechanical strength and narrow bandgap energy of the original glass. By utilizing femtosecond Z-scan method, nonlinear optical properties of the GSC ChGCs were investigated in a spectral range from 750 to 900 nm. The results showed that the nonlinear absorption attribute of the GSC ChGCs can be enhanced by the crystallinity increase which led to the maximum two-photon absorption coefficient of 19.57 cm/GW at excitation wavelength of 750 nm, increased by 78% as compared to the original glass. This indicates the current GSC ChGCs a promising candidate for the optical limiting devices.

Transmittance predictions for transparent alumina ceramics based on the complete grain size distribution or a single mean grain size replacing the whole distribution

A simple method, based on the equivalent composite model or the dense polycrystalline model, is proposed for predicting the in-line transmittance in ceramics with a grain size distribution of birefringent crystallites. It is shown that the transmittance predictions based on the Rayleigh-Gans approximation are indistinguishable from those based on Mie theory, so that the latter can be replaced by the former. Based on normal distributions of different position and width it is shown that size distributions with smaller mean sizes lead to higher transmittance, whereas the effect of the distribution width on the transmittance is comparatively weak (with the narrowest distribution being the most favorable for high transmittance). The key result of this paper is the fact that for the distributions investigated (normal and log-normal) the transmittance prediction based the whole grain size distribution can be replaced by a transmittance prediction based on the geometric mean of the intensity-weighted distribution.

Cuprous Oxide Nanoparticles: Synthesis, Characterization, and Their Application for Enhancing the Humidity-Sensing Properties of Poly(dioctylfluorene).

In this paper, we report on the synthesis—via the wet chemical precipitation route method—and thin film characteristics of inorganic semiconductor, cuprous oxide (Cu2O) nanoparticles, for their potential application in enhancing the humidity-sensing properties of semiconducting polymer poly(9,9-dioctylfluorene) (F8). For morphological analysis of the synthesized Cu2O nanoparticles, transmission electron microscope (TEM) and scanning electron microscope (SEM) micrographs are studied to investigate the texture, distribution, shape, and sizes of Cu2O crystallites. The TEM image of the Cu2O nanoparticles exhibits somewhat non-uniform distribution with almost uniform shape and size having an average particle size of ≈24 ± 2 nm. Fourier transformed infrared (FTIR) and X-ray diffraction (XRD) spectra are studied to validate the formation of Cu2O nanoparticles. Additionally, atomic force microscopy (AFM) is performed to analyze the surface morphology of polymer-inorganic (F8-Cu2O) nanocomposites thin film to see the grain sizes, mosaics, and average surface roughness. In order to study the enhancement in sensing properties of F8, a hybrid organic–inorganic (F8-Cu2O) surface-type humidity sensor Ag/F8-Cu2O/Ag is fabricated by employing F8 polymer as an active matrix layer and Cu2O nanoparticles as a dopant. The Ag/F8-Cu2O/Ag device is prepared by spin coating a 10:1 wt% solution of F8-Cu2O nanocomposite on pre-patterned silver (Ag) electrodes on glass. The inter-electrode gap (≈5 μm) between Ag is developed by photolithography. To study humidity sensing, the Ag/F8-Cu2O/Ag device is characterized by measuring its capacitance (C) as a function of relative humidity (%RH) at two different frequencies (120 Hz and 1 kHz). The device exhibits a broad humidity sensing range (27–86%RH) with shorter response time and recovery time, i.e., 9 s and 8 s, respectively. The present results show significant enhancement in the humidity-sensing properties as compared to our previously reported results of Ag/F8/Ag sensor wherein the humidity sensing range was 45–78%RH with 15 s and 7 s response and recovery times, respectively. The improvement in the humidity-sensing properties is attributed to the potential use of Cu2O nanoparticles, which change the hydrophobicity, surface to volume ratio of Cu2O nanoparticles, as well as modification in electron polarizability and polarity of the F8 matrix layer.

Interface stress in nanocrystalline materials

Abstract Based on a generalization of a capillary equation for solids, we develop a method for measuring the absolute value of grain-boundary stress in polycrystalline samples having a large interface-to-volume ratio. The grain-boundary stress in nanocrystalline Pd is calculated from X-ray diffraction measurements of the average grain size and the residual-strain-free lattice spacings, yielding a value of 1.2 ± 0.1 N /m. The random distribution of crystallite orientations in the sample in conjunction with calorimetric data for the area-averaged interfacial energy and knowledge of the grain-boundary misorientation distribution function suggest that this value is characteristic of random high-angle grain boundaries in Pd.