Nanocrystalline Morphology Research Articles

Hierarchical Structures from Nanocrystalline Colloidal Precursors within Hybrid Perovskite Thin Films: Implications for Photovoltaics

Originating from stochastic nanocrystalline colloidal precursors with differential chemical compositions, crystalline thin films exhibit hierarchical structures originating at the crystallographic level and scaling up to mesoscale structures, manifested within their nanocrystalline morphology and mesoscale topology. We interlink morphogenetic signatures within thin films to differential precursor chemistry and explain the cooperative impact of structure-defining inorganic and organic counterparts on perovskite hybrids. Understanding the effect of chemical species on the structural characteristics of thin films and leveraging complex assembly processes present facile routes to tuning multiscale morphologies in thin films, pertinent for engineering functional performance metrics within thin-film perovskite photovoltaics.

Effect of the bivalent dopant ionic radius, electronegativity and concentration on the physical properties of the sol–gel-derived ZnO thin films

This study deals with the influence of the concentration and ionic radius of the bivalent dopant on the structural, morphological and optical properties of the sol–gel-derived ZnO thin films. For that, different concentrations of dopants with different radii (Ni2+, Cu2, Fe2+) have been chosen to synthesize many ZnO thin films. The X-ray diffraction confirms that all the obtained films exhibit a pure hexagonal wurtzite structure. Meanwhile, it appears that both the preferential film orientation and the crystal quality are strongly affected when varying the ionic radius or the concentration of dopant. We note also that the lattice parameters decrease when the electronegativity of the dopant increases. This behavior has been explained at the light of a simple schematic model, based on the electrostatic forces involved in chemical bonding. The Scherer formula reveals that the average size of the crystallites is ranged between 20 and 35 nm. On the other hand, as confirmed by the SEM analysis, all the deposited films present a compact, uniform and nanocrystalline morphology. Nonetheless, the optical analysis indicates that the Ni- and Fe-doped films are highly transparent (greater than 90%) in the visible region, while the Cu-doped ones exhibit the lowest transmission (about 76%). Additionally, a blue shift of the bandgap is noticed when doping with Ni or Fe, whereas the doping with Cu induces a red shift.

Structural modifications in Co–Zn nanoferrites by Gd substitution triggering to dielectric and gas sensing applications

The structural modifications in Co–Zn ferrites due to the substitution of Gd3+ ions and their credible use as low loss dielectrics and H2S gas sensors are reported in the present study. The structural modifications lead to the enhancement in physical properties of the ferrites making it suitable for the applications. The nanocrystals of Co0·7Zn0·3Fe2-xGdxO4 (0 ≤ x ≤ 0.1, Δx = 0.025) were obtained using self-ignited citrate sol-gel route of synthesis. The X-ray diffractograms of the ferrites were refined by Rietveld method using the full-proof pdf software. The refinement asserts the creation of mono phase spinel ferrite crystals. The morphology of ferrite crystals analyzed from scanning electron microscopy (SEM) profiles depict that the ferrites exhibit the porous nature. The transmission electron microscopy (TEM) images confirms the nanocrystalline nature of the ferrites with an average dimension of 25 nm and high resolution TEM (HRTEM) confirms the spinel phase created within the ferrites. The frequency variation of dielectric parameters was analyzed to study the relaxation phenomenon in ferrites. The values of dielectric constant, dielectric loss and loss tangent were reported to decline with frequency and the Gd3+composition (x). The a.c. electrical conductivity increases with frequency and decreases with composition ‘x’. The room temperature gas sensing response of the ferrite for the hazardous H2S gas was much higher than that for LPG, SO2, NO2 and H2 gases. The ferrite sample with x = 0.025 exhibits a better sensor performance for H2S gas with small recovery and response time. The nanocrystalline nature, porosity and morphology of the ferrites bear control over response and other parameters.

Assessment of antibacterial and optical features of sol-gel dip coated La doped TiO2 thin films

The effect of Lanthanum ions (La3+) has been investigated on TiO2 thin films with varying La doping percentage from 6 to 10 at.wt. La ions have incorporated into the TiO2 lattice, while no lattice changes in TiO2 has taken place. The band gap of La-doped TiO2 thin films varies with increase in La dopant percentage. SEM images show a nanocrystalline morphology and agglomeration of the grains at high dopant percentage. Higher value of dielectric constant (31.5) and low tangent loss (0.021) are observed. Variation in DC conductivity with change in frequency is recorded by applying Jonscher's power law. AC conductivity is linked with barrier-hopping mechanism. La doped TiO2 thin films show room temperature ferromagnetism. The La doped TiO2 has shown little antibacterial activity.

Structure and morphology of calcium-silicate-hydrates cross-linked with dipodal organosilanes

Coupling of organic and inorganic chemistry presents a new degree of freedom in nano-engineering of thermo-mechanical properties of cement-based materials. Despite these vast technological benefits, molecular scale cross-linking of calcium-silicate-hydrate (C-S-H) gel with organic molecules still presents a significant challenge. Herein, we report experimental results on sol-gel synthesis, structure and morphology of nanocrystalline C-S-H cross-linked with dipodal organosilanes. These novel organic-inorganic gels have layered turbostratic molecular structure with similarities to C-S-H precipitating in hydrating cement paste. The organic molecules' chain length controls the interlayer spacing, which shows little to no shrinkage upon dehydration up to 105 °C. However, the structure gets distorted in the basal crystallite plane, in which dimer and trimer Si-polyhedra structures condense on a 2D hexagonal Ca-polyhedra layer. Cross-linked C-S-H gels display plate-like morphology with tendency toward stacking into agglomerates at the larger scale. If successfully realized in cement environment, e.g. high concentration seed, such novel organic-inorganic C-S-H gels could potentially provide cement-based matrices with unique properties unmatched by classical inorganic systems.

High Seebeck coefficient in thermally evaporated Sb-In co-alloyed bismuth telluride thin film

In the present work, we have obtained high magnitudes of the Seebeck coefficient in Sb and In coalloyed bismuth telluride thin film that has been deposited by a simple and cost-efficient thermal evaporation procedure. The films display an exceptional peak Seebeck coefficient of −310 μV/K at the working temperature of 90 °C. In addition to this, a high value of −191.6 μV/K is obtained at room temperature along with appreciable conductivity (6.2 × 103 S/m). The x-ray diffraction (XRD) pattern of the film has been analyzed for probing the crystal profile that depicts a polycrystalline and nanoscale structure. Films’ surface and cross-sectional morphologies are investigated using Field Emission Scanning Electron Microscope (FESEM), where a nanocrystalline morphology of thickness 150 nm is observed. Raman analysis supports the results obtained from XRD and FESEM for nanomorphology and indicates the presence of Te segregates. Atomic composition of the film produced is probed using Energy Dispersive x-ray spectroscopy, which also indicates the presence of excess Te. The Seebeck coefficient of the films shows an enormous enhancement as compared to previously reported work for undoped samples (BST-100S). The magnitudes of the Seebeck coefficient obtained in the present work are among the highest values reported for a bismuth antimony telluride material. These enhancements are attributed to the combined effect of coalloying, the presence of highly mobile (00l) orientations, and confinement effects of a nanocrystalline profile.

Crystallization and electrochemical corrosion behaviors of nanometer amorphous Ni-P alloys

Ni-P alloy coatings with a phosphorus content of 11.65 wt% were deposited by electroless plating. The as-plated nano-amorphous Ni-P alloy coatings were heated in air for 1 h at 200–500 °C. By using an atomic force microscope and the x-ray diffraction method, the nanocrystalline morphology and the crystallization phase identification of the coatings were studied. The corrosion behavior of the coatings in the 3.5 wt% NaCl solution was analyzed using polarization curves and impedance spectroscopy. It was observed that the corrosion behavior of the coatings was affected by the change in the nanocrystalline structure; during the heat treatment, the nanocrystalline structure of the coating alloy undergoes sequential changes from amorphous → the adjustment of amorphous → precipitated phase → crystalline. Meanwhile, the corrosion behavior of the coating alloy has also changed from uniform corrosion controlled by charge transfer → uniform corrosion controlled by diffusion → grain boundary corrosion. The Ni phase and the Ni3P phase developed a compact and dense nanocrystal layer on the surface of the coating alloy, in which the best performance by the corrosion resistant coating can be found.

Conversion of coal fly ash into nanozeolite Na-X by applying ultrasound assisted hydrothermal and fusion-hydrothermal alkaline activation

This research is emphasized on the synthesis of micro-mesoporous nanozeolite Na-X from coal fly ash wastes (CFA) by ultrasound assisted hydrothermal and double stage fusion-hydrothermal alkaline activation. The products from CFA zeolitization were studied with respect to their morphology by scanning electron microscopy (SEM), chemical and phase composition by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), respectively. Their thermal properties were investigated by thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) and surface characteristics by nitrogen adsorption. The effects of the ultrasound agitation and additives on the zeolitization process were studied. Sonicated CFA Na-X zeolites possess nanocrystalline morphology and mixed micro-mesoporous structures with higher external specific surface area as compared to microcrystalline zeolite Na-X prepared by magnetic stirring. CFA nanozeolites of Na-X type are expected to behave excellent adsorption potential and catalytic activity due to the enlarged surface and fine morphology with uniformly distributed particles of iron oxides transferred from the raw material.

Processing of high-grade zeolite nanocomposites from solid fuel combustion by-products as critical raw materials substitutes

High-grade zeolite nanocomposites are synthesized utilizing solid by-products from combustion of coal for energy production in Thermal Power Plants applying alkaline aging, hydrothermal and fusion-hydrothermal activation procedures. The obtained coal ash zeolites were studied with respect to their chemical and phase composition, morphology, surface parameters and thermal properties. It was found that they are distinguished in nanocrystalline morphology and significant content of iron oxide nanoparticles (γ-Fe2O3, α-Fe2O3, γ-Fe3O4) and doping elements (Cu, Co, Mn, V, W, etc.) transferred from the raw coal ash, and therefore they are assumed as nanocomposites. Coal fly ash zeolite nanocomposites are characterized by a mixed micro-mesoporous texture, significant concentration of acidic Brønsted centers due to their high surface insaturation, high chemical and thermal stabilty. This unique combination of compositional and textural properties predetermines the application of these materials as catalysts for thermal oxidation processes, anticorrosion barrier coatings, carbon capture adsorbents, matrices for hosting functional groups, detergents etc. Examples for coal fly ash zeolite applications for substitution of critical raw materials in practice are provided.

Surface-Modified Hollow Ternary NiCo2Px Catalysts for Efficient Electrochemical Water Splitting and Energy Storage.

Generally, a cost-effective electrocatalytic process that offers an efficient electrochemical energy conversion and storage necessitates a rational design and selection of structure as well as composition of active catalytic centers. Herein, we achieved an unprecedented surface morphology and shape tuning to obtain hollow NiCo2Px with a continuum of active sharp edges (spiked) on a hollow spherical surface by means of facile hydrothermal treatments. The highly exposed, branched spike-covered hollow structure of NiCo2Px shows remarkable performance enhancement for hydrogen evolution reaction and oxygen evolution reaction in a wide range of Ph solutions. This catalytic performance was utilized to assemble a water electrolyzer working in an alkaline environment. In particular, this electrolyzer only requires an output voltage of 1.62 V to deliver a current density of 10 mA cm-2 and shows almost no decrease in this value even after a continuous run for 50 h. The new surface-engineered NiCo2Px establishes to be highly active, cost-effective, and robust toward electrochemical energy conversion. Additionally, the charge storage capabilities of spike-covered hollow NiCo2Px structures is also investigated, and it shows a specific capacitance of 682 and 608 F g-1 at a current density of 1 A g-1 with excellent rate capacitance retention. Thus, the importance of surface engineering of nanocrystalline morphologies in design toward the development of a multifunctional electrocatalyst for efficient water splitting and charge storage applications is demonstrated.

Electrodeposition of poly and nanocrystalline Cu-In-Se absorbers for optoelectronic devices

ABSTRACTCoupling semiconductors with electrochemical processes can lead to unusual materials, and attractive, practical device configurations. This work examines the reaction mechanism for single-step electrodeposition approach that creates device quality copper-indium-selenide (CISe) films with either polycrystalline or nanocrystalline morphologies on Cu and steel foils, respectively. The polycrystalline CISe film grows from In3+/Se4+ solution on Cu foil as Cu→ CuxSe→ CuInSe2; it may be used in standard planar pn devices. The nanocrystalline CISe film grown from Cu+/In3+/Se4+ solution follows the CuSe(In)→ CuInSe2→ CuIn3Se5 sequence. The latter approach leads to naturally ordered, space-filling nanocrystals, comprising interconnected 3-dimensional network of sharp, abrupt, p-CISe/n-CISe bulk homojunctions with extraordinary electro-optical attributes. Sandwiching these films between band-aligned contact electrodes can lead to high performance third generation devices for solar cells, light emitting diodes or photoelectrodes for fuel cells. Both approaches produce self-stabilized CISe absorbers that avoid recrystallization steps and can be roll-to-roll processed in simple flexible thin-film form factor for easy scale-up.

Ce–Nd Co-substituted nanospinel cobalt ferrites: An investigation of their structural, magnetic, optical, and apoptotic properties

Abstract In this study, Nd3+ and Ce3+ co-substituted Co ferrite nanoparticles (NPs) were prepared using a sonochemical approach. The simultaneous substitution of Nd3+ and Ce3+ into CoFe2O4 nanoparticles (NPs) affected the structure, magnetic properties, and cation distribution. The structural parameters were investigated and calculated via XRD studies. The nanocrystalline morphology was identified by SEM along with EDX and TEM. The appearance of two vibration bands correlated to the Td and Oh group relevant to the spinel ferrite lattice were confirmed by Fourier-transform infrared spectroscopy (FT-IR). Magnetization analyses were conducted at room temperature (300K; RT) and low (10K) temperatures. Different magnetic parameters including the remanence (Mr), coercivity (Hc), saturation magnetization (Ms), squareness ratio (SQR = Mr/Ms), and magnetic moment ( n B ) were deduced and discussed. The results demonstrated a superparamagnetic (SPM) nature in the x = 0.00 sample at RT. However, the other samples (0.03 ≤ x ≤ 0.20) exhibited ferromagnetic (FM) natures. At 10K, all of the synthesized NPs displayed FM behavior. An enhancement in the Mr, Ms, Hc, and n B was detected at lower Nd3+ and Ce3+ concentrations (x ≤ 0.10). The SQR values at RT were smaller than 0.5, indicating a single domain nature with uniaxial anisotropy in all of the produced ferrites. However, the SQR values were in a range of 0.687–0.769 at 10K, suggesting a multi-magnetic domain at low temperatures. This study also examined the impact of Nd3+- and Ce3+-doped cobalt ferrite nanoparticles on human colon cancer cells (HCT-116) to examine their anti-cancer properties using MTT and morphometric assays. After 48 h of treatment with an optimal dose of Nd3+ and Ce3+, the doped cobalt ferrite nanoparticles demonstrated significant apoptotic effects by decreasing cancer cell viability in a dose-dependent manner. These results could lead to the use of NPs as a drug-screening/potential therapeutic strategy targeting human colorectal cancer.

A facile one-step flash combustion synthesis and characterization on C doped NiO nanostructures

Synthesis of NiO nanostructures in presence of different concentrations of citric acid (CA) was achieved through flash combustion technique. The NiO nanostructures formation was confirmed through X-ray diffraction analysis. At low concentrations of CA no extra peak was observed in XRD patterns, however when the CA concentration was raised to 5 and 10 g, two new extra peaks appeared at 44.6° and 51.9° which may be attributed to the presence of C. The crystallite size was noticed to reduce from 29 to 18 nm with increase in the CA concentration. All observed Raman bands were noticed to be shifted owing to the quantum size effect. EDX and SEM mapping confirm the existence of C. SEM images confirm the cubic nanocrystalline morphology for 0.5 g CA:NiO, however with increasing CA concentration a drastic change in morphology, i.e. from nanocrystals to extended nanosheets, was observed. The energy gap values were determined using Kubelka-Munk theory and found in range of 3.5–4.0 eV. An additional energy gap ∼2 eV was also noticed at higher CA concentration. The values of relative permittivity, εr′, were found in the range of 18–110 for CA concentration upto 5g, however, at 10.0 g CA its value was found to be order of 104 at 2 × 105 Hz.

Electrical Stability of Solution-Processed Indium Oxide Thin-Film Transistors.

We investigated the electrical stability of bottom-gate/top-contact-structured indium oxide (In₂O₃) thin-film transistors (TFTs) in atmospheric air and under vacuum. The solution-processed In₂O₃ film exhibits a nanocrystalline morphology with grain boundaries. The fabricated In₂O₃ TFTs operate in an n-type enhancement mode. Over repeated TFT operation under vacuum, the TFTs exhibit a slight increase in the field-effect mobility, possibly due to multiple instances of the "trapping and release" behavior of electrons at grain boundaries. On the other hand, a decrease in the fieldeffect mobility and an increase in the hysteresis are observed as the measurement continues in atmospheric air. These results suggest that the electrical stability of solution-processed In₂O₃ TFTs is significantly affected by the electron-trapping phenomenon at crystal grain boundaries in the In₂O₃ semiconductor and the electrostatic interactions between electrons and polar water molecules.

Exploration of thermoacoustics behavior of water based nickel ferrite nanofluids by ultrasonic velocity method

Magnetic nanofluids (commonly known as ferrofluids) have captured the great attention of the researchers due to their various kinds of applications such as heat transfer, hyperthermia treatments, targeted drug delivery etc. The present experimental investigations deal with the thermoacoustic behaviour of the water based nanofluids of nickel ferrites. The magnetic nickel ferrite nanoparticles were produced by the simple and inexpensive chemical co-precipitation route. The prepared nanoparticles were exposed to different characterization tools for structural, morphological, compositional and magnetic properties analysis. X-ray diffraction analysis with Rietveld refinement confirmed the single phasic nature with nanometric crystallite size of the prepared nanoparticles. Scanning electron microscope images revealed the spherical and nanocrystalline morphology of the prepared nanoparticles. The M-H plot recorded at room temperature revealed the superparamagnetic nature of the nanoparticles. Further, the co-precipitated nickel ferrite nanoparticles with different concentrations were utilized for the preparation of the water based magnetic nanofluids. Colloidal stability of the prepared nanofluids was analyzed by UV–Vis spectroscopy technique and it revealed the stability over 11 days without separation in phase. The temperature dependent thermoacoustic properties of the prepared nanofluids were analyzed through Ultrasonic Interferometer. The interaction between particle–particle and particle–fluid are explained on the basis of thermo-acoustic parameters.

Ball milling for the formation of nanocrystalline intermetallic compounds from Ni-Ti elemental powders

Abstract In the present research work nickel (Ni) and titanium (Ti) elemental powder with an ostensible composition of 50% of each by weight were mechanically alloyed in a planetary high energy ball mill in diverse milling circumstances (10, 20, 30 and 60 h). The inspection exposed that increasing milling time leads to a reduction in crystallite size, and after 60 h of milling, the Ti dissolved in the Ni lattice and the NiTi (B2) phase was obtained. The lattice strain of ball milled mixtures augmented from 0.15 to 0.45 at 60 h milling. With increase in milling time the morphology of pre-alloyed powder changed from lamella to globular. Annealing of as-milled powders at 1100 K for 800 s led to the formation of NiTi (B19′), grain growth and the release of internal strain. The result indicated that this technique is a powerful and highly productive process for preparing NiTi intermetallic compounds with a nano-crystalline structure and appropriate morphology.

Boron-doped TiO2 (B-TiO2) Thin Films Grown Using Sol-Gel Spin Coating Method


 
 
 
 In this study, the effect of modifying boron doping concentration on the optical properties, electrical properties and microstructural images of TiO2 thin films was investigated by the sol-gel technique by grinding TiO2 powder with a boron compound at a wavelength range of 250 nm to 850 nm. The SEM micro-images revealed the homogenous, continuous and nanocrystalline surface morphology: 10% is the tolerable amount of boron doping concentration into the TiO2 for achieving sphere-like nanostructures materials with low agglomeration. The XRD spectra of the B-TiO2 films showed anatase peaks of greater intensities when compared to the pure TiO2 film. All the films illustrate extinction coefficient in the visible region of solar spectra corresponding to the low absorption, and absorption peaks established in the ultraviolet region near 330nm with the optical transmittance varied from over 52 - 96% in the UV-Vis wavelength range. Diffuse reflectance absorption spectra analysis indicated that the incorporation of B into TiO2 material results in a substantial red shift and the absorption extends significantly into the visible range. The optical band gap energy values of the thin films were found to be 3.38, 3.35, 3.28, 3.26, and 3.36eV. This showed a low probability of raising the electron across the mobility gap with the photon energy in the visible region. The refractive index values varied between 1.891 and 1.922 depending on the percentage content of boron. Moreover, the imaginary part of the dielectric constant increase slowly, whereas the real part increases sharply and the optical conductivity was found to increase with the increase in boron addition.
 
 
 
 

Wafer-Scale Black Arsenic–Phosphorus Thin-Film Synthesis Validated with Density Functional Perturbation Theory Predictions

Herein we report the wafer-scale synthesis of thin-film black arsenic–phosphorus (b-AsP) alloys via two-step solid-source molecular beam deposition (MBD) and subsequent hermetic thermal annealing. We characterize our thin films with a variety of compositional and structural metrology techniques. X-ray photoelectron spectroscopy and energy dispersive spectroscopy determine compositions of As0.78P0.22 for our thin films, while X-ray reflectivity measurements indicate film thicknesses of 6–9 nm. High-resolution transmission electron spectroscopy images reveal a nanocrystalline morphology with orthorhombic b-AsP grains on the order of ∼5 nm. Raman scattering spectroscopy is employed to characterize the vibrational spectra of our thin films, and the results obtained are in agreement with previously reported b-AsP spectra. Evidence of uniform wafer-scale growth is substantiated by Raman mapping. We simulate crystal structure, band gaps, and Raman spectra from first-principles DFT-based computations and find exc...

Effective removal of automobile exhausts over flower-like Ce1−xCuxO2 nanocatalysts exposed active {100} plane

This work elucidates the synthesis and characterization of copper ions incorporated ceria (Ce1−xCuxO2) nanocatalysts with 3D flower-like and nanocrystalline morphology for the purification of automobile exhausts. XRD and Raman results confirm the presence of copper ions in ceria. The 3D flower-like and nanocrystalline morphology exhibited by these catalysts were seen by FESEM images. HRTEM and SAED results confirm that (100) plane is dominantly presented in 3D flower-like Ce1−xCuxO2 catalysts when compared to nanocrystalline morphology. The textural properties of synthesized catalysts was done with the help of N2 sorption study, which confirms that flower-like Ce1−xCuxO2 catalysts show high surface area and pore volume. The existence of Ce3+, Ce4+, Cu+ and Cu2+ ions in the catalyst were examined by XPS and DR UV–Vis techniques. Oxygen storage capacity (OSC) of the catalysts was studied by H2-TPR analysis. These characterization results elucidate the presence of dominant active sites (Ce3+, Ce4+, Cu+ and Cu2+) and {100} plane in the flower-like morphology compared to nanocrystalline. The catalytic activity of synthesized Ce1−xCuxO2 catalysts was tested for removal of CO, HCx and NO gases from automobile emission with respect to the copper content and morphology. The obtained results indicate that the presence of optimum amount of copper in ceria with flower-like morphology is essential for the removal of CO, HCx and NO at low temperature via redox process, which is due to the presence of active sites on the dominant {100} plane.

Oligomerization of light olefins over ZSM-5 and beta zeolite catalysts by modifying textural properties

The oligomerization of ethene and 1-hexene was performed under 35 bar and 200 °C over NiH- and H-forms of ZSM-5 and beta zeolite catalysts which had similar Si/Al and Ni content, but different textural properties. Among the H-zeolites, H-ZSM-5 and H-beta composed of nanometer scale (ca. 10 nm) sheet-like crystals, as well as intercrystalline mesoporosity (ca. 5 nm), were found to be much more efficient for the oligomerization of 1-hexene to liquid fuel range products higher than C10 (C10 + ). In the oligomerization of ethene, identically prepared ZSM-5 and beta zeolites but with further exchange with Ni ion, also showed higher activity with remarkable C10+ product selectivity (>80%) after a single stage oligomerization, as compared to the corresponding cation form of ZSM-5 and beta zeolites without nanocrystalline and mesoporous morphology (conversion < 50% and C10+ selectivity < 30%). These results demonstrate that both small crystal size and the mesoporosity of the zeolite catalyst are critical factors for improving the diffusion limitation during the oligomerization of light olefins. This improvement was accompanied by a shift in major oligomeric product selectivity toward C10+ hydrocarbons.