Average Size Of Nanocrystals Research Articles

Highly dispersed nickel nanoparticles supported on hydrochar for hydrogen-rich syngas production from catalytic reforming of biomass

The synthesis of carbon-based nanomaterials, ideally produced via facile, inexpensive approaches, using sustainable resources as precursors, with modulated structures, morphologies and functionalities is still challenging for energy applications. This work developed a mild one-step hydrothermal synthesis route for the fabrication of highly dispersed metallic nickel nanoparticles on hydrothermal carbons derived from waste biomass. The roles of precursor nickel ion concentration and calcination temperature in modulating the morphology, location and crystalline size of the nickel nanoparticles as well as the metal-support interactions have been delineated. The average grain size of the metallic nickel nanocrystals on the resultant Ni0.5@HCOp nanocatalysts could be tuned to 8–13 nm by varying the preparation conditions. The catalytic abilities of the Ni-based nanocatalysts towards hydrogen-rich syngas production and tar reduction were then tested in a two-stage reactor system using sewage sludge as biomass feedstock. The catalytic tests showed that the Ni0.5@HCOp catalyst calcined at 700 °C was shown to have stronger metal-support interactions compared to other Ni-based nanocomposites, which provided better suppression of coke deposition and resistance of nickel agglomeration during the catalytic gasification process. This highly active catalyst promoted formation of hydrogen-rich syngas, with up to 109.2 g H2/kg sludge, and tar yields as low as 2.12 mg g−1.

Effect of copper on the thermal stability and non-isothermal crystallization behavior of Al86Ni10-xCuxRE4 (x = 0.5–2.5) amorphous alloys prepared by melt spinning

Microstructural features, thermal stability and crystallization kinetics of various melt spun Al-based alloys containing transition metals (TM = Ni, Cu) and Ce-based rare earth metals (MM: Misch Metal) were investigated via X-ray diffractometry (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). It is shown that the extended topological instability of Egami-Waseda model (λ criterion) is a useful tool to predict the crystallization behavior of the prepared alloys. FCC-Al nanoparticles are formed during the initial crystallization process. Calculation of the apparent activation energy using the Kissinger method indicates that partial replacement of nickel by copper decreases the thermal stability. The thermal stability in the presence of copper, however, can be improved by increasing the MM content. On the other hand, TEM studies determine that copper reduces the average size of FCC-Al nanocrystals from ~50 nm in Al86Ni10MM4 to ~35 nm in Al86Ni9Cu1MM4 amorphous alloy. Thermodynamic evaluation of the crystallization process and determination of the local crystallization index reveal that the primary crystallization in amorphous Al-based alloys containing MM, Ni and Cu is a complex diffusion controlled process.

Формирование нанокристаллов в аморфной фазе многокомпонентных систем

AbstractThe effect of the concentration of alloying components on the crystallization of amorphous (Fe_73Si_13B_9)_1 – _ x _– _ y Nb_ x Cu_ y and (Co_70Si_12B_9)_1 – _ x _– _ y Fe_ x Nb_ y alloys has been studied by X-ray diffraction and transmission electron microscopy in a wide composition region. The formation of the bcc structures in both the alloy groups is shown to be substantially dependent on the alloying component concentrations. The bcc phase is found to form in the cobalt-based alloys in the concentration region, where it was not observed before. In the cobalt-based alloys, the bcc phase appears at a niobium concentration higher than 1 at % and the average bcc nanocrystal size varies from 40 nm (at 1 at % Nb) to 14 nm (at 5 at % Nb). In the Fe-based alloys, nanocrystals with the bcc lattice form at the copper concentrations of 0.45–1 at %, and the average nanocrystal size is dependent on the alloy composition and varies in the range 16–24 nm. The causes of the concentration dependence of the formation of nanostructures in these alloys are discussed.

ФОТОЛЮМІНЕСЦЕНЦІЯ НАНОЧАСТИНОК CdSe:Ni ОТРИМАНИХ ХІМІЧНИМ МЕТОДОМ

Cadmium selenide nanocrystals doped with nickel were prepared in water phase chemistry technique with gelatin acting as capping agent. Structures were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), visible absorption and photoluminescence spectroscopies. Influence of component concentrations and technological parameters on nanocrystals average size and properties was studied

Modifications in structural, optical and electrical properties of nanocrystalline CdO: role of sintering temperature

Present report deals with the synthesis of nanocrystalline cadmium oxide (CdO) using low-cost acetate precursor based modified sol–gel technique. Final product was sintered at different temperatures and studied for their structural, optical and electrical properties. In this present work, we report the sintering temperature-dependent structural, optical and electrical properties of nanocrystalline cadmium oxide (CdO) grown by cost effective sol–gel method. Structural properties of CdO materials were investigated by X–ray diffraction (XRD) which reveals the crystalline phase of the samples without any detectable impurity within the range of measurements. Crystallite size (CS), calculated using Scherer’s formula, is found in the range of nanometer (<100 nm) and increases with increasing sintering temperature. Average crystallite size of all CdO nanocrystals were estimated using the William–Hall (W–H) plots from XRD patterns. Furthermore, transmission electron microscopy (TEM) images were captured to check the crystallinity and particle growth of the samples. The optical properties of nanocrystalline CdO were studied by using UV–Visible (UV–Vis) absorption spectrum. High absorption has been observed for nanocrystalline CdO sintered at lower temperatures. The band gap of nanocrystalline CdO was calculated by using Tauc’s law where band gap increases with increasing sintering temperature. The electrical properties of the samples were studied by performing dielectric and AC conductivity measurements. It is observed that dielectric constant decreases with increase in frequency and sintering temperature. Variation in AC conductivity with light and sintering temperature has been discussed in detail.

Rare earths (Ce, Eu) molar concentration-dependent of the structural and optical properties of CBD-CdS nanofilms

It presents the characterization of rare earths (Eu,Ce)-doped CdS nanofilms that were synthesised by the growth technique chemical bath deposition (CBD) at the reservoir temperature of 70±2°C. The doping of CdS with rare earths is performed by varying the synthesis time from 60 to 135 min. The rare earths molar concentration was range from 0.0≤x≤3.5, which was determined by energy dispersive X-ray spectroscopy. X-ray diffraction (XRD) analysis and Raman scattering reveal that CdS nanofilms showed the zinc blende (ZB) crystalline phase. The CdS average nanocrystal size was ranged from 1.84 to 2.67 nm that was determined by the Debye–Scherrer equation from ZB (111) direction, which was confirmed by transmission electron microscopy. Raman scattering shows that the lattice dynamics is characteristic of bimodal behaviour and the multipeaks adjust of the first optical longitudinal mode for the (Eu,Ce)-doped CdS, which denotes the Raman shift of the characteristic peak about 305 cm−1 of the CdS nanocrystals. The CdS nanofilms exhibit a direct bandgap that slightly decreases with increasing doping, from 2.50 to 2.42 eV, which was obtained by room temperature transmittance. The room-temperature photoluminescence of CdS shows the band-to-band transition at 2.88 eV, which is associated to quantum confinement and a dominant radiative band at 2.37 eV that is called the optical signature of interstitial oxygen. The Eu3+-doped CdS photoluminescence shows the dominant radiative band at 2.15 eV, which is associated to the intra-4f radiative transition of Eu3+ ions that corresponds to the magnetic dipole transition, (5D0→7F1). For the Ce3+-doped CdS the dominant radiative transition, at 2.06 eV, is clearly redshifted, although the passivation of the CdS nanofilms by Ce was approximately by a factor about 21 for the best results.

Enhanced blue photoluminescence of B2O3-CaF2 glass-ceramics containing silver nanoparticles

We report photoluminescence (PL) measurements of B2O3-CaF2 glass-ceramics containing silver nanoparticles (NPs). The samples studied were prepared by the melting-quenching method followed by appropriate heat-treatment to form CaF2 and silver NPs. The techniques of X-rays diffraction (XRD), transmission electron microscopy (TEM), optical absorption and PL were applied to characterize the samples. The average size of the CaF2 nanocrystals was estimated in ≈20 nm while the silver NPs have sizes in the range 2–30 nm. By exciting the samples without silver NPs using light at 290 nm we observed a PL signal at ≈430 nm due to the presence of CaF2 nanocrystals. The experiments with the samples containing silver NPs revealed 1000% intensity enhancement of the blue PL that was attributed to the energy-transfer from the excited silver NPs to the CaF2 nanocrystals.

BCC nanocrystal formation in an amorphous Co-Si-B-Fe-Nb alloy on heating

Crystallization of the amorphous alloys of Co-Si-B-Fe-Nb system has been investigated by X-ray diffraction and transmission electron microscopy. It has been shown that the structure formed upon crystallization significantly depends on niobium concentration. The formation of nanocrystals with a bcc lattice was discovered at considerably lower iron content than it has been observed earlier. When niobium concentration is decreasing, the fraction of the nanocrystalline bcc phase decreases, niobium-free samples are multiphase and do not contain bcc nanocrystals. The average nanocrystal size also depends on niobium content and considerably decreases when niobium concentration is increasing.

Effect of Nd Substitution on Properties of Multiferroic Bismuth Ferrite Synthesized by Sol-Gel Auto-combustion Method

In this work, pure and Nd-doped bismuth ferrite nanocrystals with the general formula of Bi1−x Nd x FeO3 (x = 0, 0.05, 0.1, 0.15, 0.2) were synthesized via the sol-gel auto-combustion method at two different calcination temperatures (550 and 650∘C). Phase analysis and investigating structural, thermal, and magnetic properties and measuring the size of nanoparticles have been done by using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric and differential thermal analysis (TG/DTA), and vibrating sample magnetometry (VSM). For undoped BiFeO3 (BFO), increasing calcination temperature will increase the average size of nanocrystals. On the other hand, the average size of nanoparticles is decreased by increasing the concentration of neodymium in the structure of BFO. By entering neodymium to the structure of bismuth ferrite at the calcination temperature of 550∘C, the ferromagnetic properties decline. However, at 650∘C, ferromagnetic properties are improved which is due to a fall in the number of Fe2+ ions. In this case, by decreasing the Fe2+ ions, remanent and saturation magnetization increase.

The effect of calcination conditions on structural and magnetic behavior of bismuth ferrite synthesized by co-precipitation method

In this paper the effect of calcination conditions on structural properties, particle size, as well as the presence of secondary phases and magnetic characteristics of BiFeO3 nanocrystals have been investigated. Bismuth ferrite nanocrystals were synthesized at room temperature by chemical co-precipitation method. Phase analysis, structural and magnetic features and size of the produced nanopowders were studied via X-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. The formation of the single phase compounds were confirmed by XRD. By analyzing the results from different measurements it was shown that products have the perovskite phase with space group R3C and the average nanocrystal size around 50 nm. The structural studies showed that calcination temperature and duration has crucial roles in disappearing impurities and secondary phases. Magnetic results in an applied field at room temperature indicated that the nanoparticles of bismuth ferrite have weak ferromagnetic order.

Temperature effect on the structure and characteristics of ZnS-based quantum dots

The synthesis of zinc sulfide (ZnS) quantum dots (QDs) by microwave heating in a water-ethanol medium is proposed. The effect of the synthesis temperature (80 °C, 100 °C, 120 °C, and 150 °C) on the QD characteristics is examined. Based on the analysis of X-ray diffraction profiles the conclusion is drawn that the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 2.6-3.7 nm forms in the synthesized QDs. The nanocrystallite size is found to increase with the QD synthesis heating temperature. The analysis of X-ray absorption spectra (XANES) at the zinc K-edge indicates a higher crystallinity of the QD samples prepared at higher synthesis temperatures. The combined analysis of X-ray diffraction profiles, optical diffuse reflectance spectra, and X-ray absorption spectra implies the following possible QD structure: the pure hexagonal ZnS phase of wurtzite type in the bulk of nanoparticles and the amorphous ZnO phase in the surface layer of nanoparticles.

X-ray spectroscopic diagnostics of the structure of quantum dots based on zinc and manganese sulfides and oxides

The microwave synthesis of quantum dots (QDs) based on zinc and manganese sulfides and oxides in a water-ethanol medium is proposed. The sample synthesized is characterized by X-ray diffraction (XRD), photoluminescence, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The XRD analysis shows the presence of the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 4.5 nm and manganese oxide Mn3O4 (hausmannite phase) with an average particle size of 12.5 nm in the sample under study, but does not provide the unambiguous conclusion about the doping of ZnS nanoparticles with Mn atoms. Although the analysis of the zinc and manganese K-edge XANES spectra suggests that the synthesized QD sample is a ZnMnS solid solution (~11%), a significant amount of a by-product (manganese oxide Mn3O4 of the hausmannite phase, ~89%) is formed.

Probing spatial heterogeneity in silicon thin films by Raman spectroscopy

Raman spectroscopy is a powerful technique for revealing spatial heterogeneity in solid-state structures but heretofore has not been able to measure spectra from multiple positions on a sample within a short time. Here, we report a novel Raman spectroscopy approach to study the spatial heterogeneity in thermally annealed amorphous silicon (a-Si) thin films. Raman spectroscopy employs both a galvano-mirror and a two-dimensional charge-coupled device detector system, which can measure spectra at 200 nm intervals at every position along a sample in a short time. We analyzed thermally annealed a-Si thin films with different film thicknesses. The experimental results suggest a correlation between the distribution of the average nanocrystal size over different spatial regions and the thickness of the thermally annealed a-Si thin film. The ability to evaluate the average size of the Si nanocrystals through rapid data acquisition is expected to lead to research into new applications of nanocrystals.

Tunable multimodal adhesion of 3D, nanocrystalline CoFe2O4 pollen replicas

3D replicas of sunflower pollen microparticles, comprised of a multicomponent magnetic spinel ferrite (CoFe2O4) with tailorable adhesive properties, have been synthesized for the first time via a conformal layer-by-layer (LbL) surface sol–gel (SSG) deposition process followed by organic pyrolysis and oxide compound formation at a peak temperature of 600 °C–900 °C. These high-fidelity ferrite pollen replicas exhibited multimodal (van der Waals, vdW, and magnetic) adhesion that could be tuned via control of the CoFe2O4 nanoparticle and crystal sizes. The CoFe2O4 pollen replicas exhibited a non-monotonic change in short-range (~10 nm) vdW adhesion with an increase in the peak firing temperature, which was consistent with the counteracting effects of particle coarsening on the size and number of nanoparticles present on the sharp tips of the echini (spines) on the pollen replica surfaces. The longer-range (up to ~1 mm) magnetic force of adhesion increased monotonically with an increase in firing temperature, which was consistent with the observed increases in the values of the saturation and remanent magnetization of CoFe2O4 with an increase in average nanocrystal size. By adjusting the nanocrystal/nanoparticle sizes of the CoFe2O4 pollen replicas, the total force of adhesion (vdW + magnetic) to a magnetic substrate could be increased by a factor of ~3 relative to native pollen grains.

Perovskite solar cells using polymer electrolytes

ABSTRACTThis study deals with the characterization of methylammonium lead iodide (MAPbI3) material and the fabrication of perovskite solar cells using gel polymer electrolyte as the charge transport medium. The crystalline lead–based perovskite has been verified by x-ray diffraction (XRD). The [100], [200], [210], [211], [220], [300] and [222] reflection planes can be observed at 2θ angles of 14.10°, 28.35°, 31.90°, 34.95°, 40.40°, 43.15° and 50.20°, indicating a cubic crystal symmetry for CH3NH3PbI3. EDX spectrum showed a Pb:I ratio of approximately 1:3 as in CH3NH3PbI3. The band gap for lead-based perovskite is 1.45 eV estimated from UV-Vis absorption spectroscopy. The nanocrystalline MAPbI3 have been observed using field emission scanning electron microscopy (FESEM), where the average cuboid size of perovskite nanocrystals is 380 nm. The cell have been fabricated using gel polymer electrolyte with composition 17.02 wt.% PVA–13.93 wt.% TBAI–0.96 wt.% I2– 68.09 wt.% DMF. The cell exhibits a power conversion efficiency (PCE) of 1.28% with open circuit voltage (Voc) 0.58 mV, short circuit current density (Jsc) 3.74 mA cm−2 and fill factor (FF) 59.18%.

Trap emission by nanocrystalline anatase in visible range studied by conventional and synchronous luminescence spectroscopy: Adsorption and desorption of water vapor

We report the spectroscopic study of adsorption and desorption of water vapor on nanocrystalline anatase in air under ambient conditions. We also report the energy level diagram of absorption and emission through the three electronic midgap states of different origin in anatase as determined by absorption spectroscopy, “conventional” PL emission spectroscopy and, for the first time, by synchronous luminescence spectroscopy at 25°C. Under the extrabandgap photoexcitation, visible luminescence from nanocrystalline anatase contains peaks of “blue light” at ca. 450nm and “green light” at ca. 500nm due to the two different midgap states. Photoluminescence in visible range at 25°C is quenched after water vapor adsorption with formation of “hydrated” anatase and increased in “dried” anatase after water desorption. For both “dried” anatase with strong emission of visible light and “hydrated” anatase with weak (quenched) emission, synchronous luminescence spectra are superior to “conventional” PL emission spectra in resolving characteristic emission peaks due to midgap states. Photoexcitation of self-trapped exciton (STE) as intrinsic electronic midgap state in anatase at 420nm results in a strong emission of “green light” at 500nm, which is preferentially quenched upon water vapor adsorption vs. “blue light” at 450nm. Visible PL in anatase decreases when the average nanocrystal size increases within 5–30nm range, suggesting participation of surface midgap states in water adsorption/desorption.

Electron Microscopy Study of Metal Sulfide Nanocrystals Formed in Langmuir–Blodgett Films

The morphology and crystal structure of CdS, ZnS, CdZnS, and PbS nanocrystals formed by sulfidation and the subsequent annealing of the films of behenates of the respective metals using the Langmuir–Blodgett method have been investigated by high-resolution electron microscopy. It has been found that the crystal size is independent of the initial behenate film thickness. The average lateral nanocrystal size ranges from 2 to 4 nm at a film thickness of 2–14 monolayers. It has been shown that annealing in different atmospheres leads to an increase in the average nanocrystal size, morphology variation, and oxidation at the characteristic temperatures. It has been established by analyzing the interplanar spacings that the nanocrystals have hexagonal and/or cubic crystal lattices characteristic of each investigated material.

Properties of silicon nanocrystals with boron and phosphorus doping fabricated via silicon rich oxide and silicon dioxide bilayers

Effects of boron and phosphorus doping on the structural, electrical, and optical properties of silicon nanocrystals in superlattice thin films were investigated. Silicon nanocrystals were fabricated via magnetron sputtering of stoichiometric silicon rich oxide and silicon dioxide bilayers followed by high temperature annealing at 1100 degrees Celsius. The characterization techniques used include: high-resolution transmission electron microscopy with energy filtering, grazing incidence x-ray diffraction, Raman, photoluminescence, and photothermal deflection spectroscopy, as well as electrical measurements. Results showed that phosphorus doping causes the loss of the bilayer structure and an increase in the average size of the silicon nanocrystals due to softening of the silicon dioxide matrix during post-sputter annealing. The result was a decrease in quantum confinement and a redshift in photoluminescence spectrum with an absorption profile similar to crystalline silicon. The undoped (intrinsic) sample maintained its bilayer structure and displayed stronger quantum confinement with higher photoluminescence peak energy and higher absorption coefficient. In-between, the boron doped sample was more similar structurally to the intrinsic sample, although merging between bilayers resulted in an extensive silicon nanocrystalline network. Optically, it displayed different effects due to photoluminescence quenching and free carrier absorption. Finally, both doped samples exhibited a decrease in electrical resistivity.

PVP capped silver nanocubes assisted removal of glyphosate from water—A photoluminescence study

Glyphosate [N-phosphono-methylglycine (PMG)] is the most used herbicide worldwide and it has been reported very recently that Glyphosate is very harmful and can produce lots of diseases such as alzheimer and parkinson’s disease, depression, cancer, infertility including genotoxic effects. As it is mostly present in stable water body and ground water system, its detection and removal is very important. Here, we have shown a fluorescence technique for the removal of glyphosate from water using chemically synthesized polyvinylpyrrolidone (PVP) silver nanocrystals. Transmission Electron Microscopy (TEM) study shows the average size of silver nanocrystals of 100nm approximately with a morphology of cubic shape. Glyphosate does not show absorption in the visible region. But both glyphosate and silver nanocrystals show strong fluorescence in the visible region. So, photoluminescence study has been successfully utilized to detect the glyphosate in water samples and on treating the glyphosate contaminated water sample with silver nanocrystals, the sample shows no emission peak of glyphosate at 458nm. Thus, this approach is a promising and very rapid method for the detection and removal of glyphosate from water samples on treatment with silver nanocubes. NMR spectra further confirms that the silver nanocrystals treated contaminated water samples are glyphosate free.

Characterization of Ag-porous silicon nanostructured layer formed by an electrochemical etching of p-type silicon surface for bio-application

Nanostructured layers composed of silver-porous silicon (Ag-PS) have been formed by an electrochemical etching of p-type (1 1 1) silicon substrate in a AgNO3:HF:C2H5OH solution at different etching times (10 min–30 min). Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) results reveal that the produced layers consist of Ag dendrites and a silicon-rich porous structure. The nanostructuring nature of the layer has been confirmed by spatial micro-Raman scattering and x-ray diffraction techniques. The Ag dendrites exhibit a surface-enhanced Raman scattering (SERS) spectrum, while the porous structure shows a typical PS Raman spectrum. Upon increasing the etching time, the average size of silicon nanocrystallite in the PS network decreases, while the average size of Ag nanocrystals is slightly affected. In addition, the immobilization of prokaryote Salmonella typhimurium DNA via physical adsorption onto the Ag-PS layer has been performed to demonstrate its efficiency as a platform for detection of biological molecules using SERS.