Self-formation of dielectric layer containing CoSi2 nanocrystals by plasma-enhanced atomic layer deposition

Dielectric layer containing CoSi₂ nanocrystals was directly fabricated by plasma-enhanced atomic layer deposition using CoCp₂ and NH₃ plasma mixed with SiH₄ without annealing process. Synchrotron radiation X-ray diffraction and X-ray photoelectron spectroscopy results confirmed the formation of CoSi₂ nanocrystal. The gate stack composed of dielectric layer containing CoSi₂ nanocrystals with ALD HfO₂ capping layer together with Ru metal gate was analyzed by capacitance–voltage (C–V) measurement. Large hysteresis of C–V curves indicated charge trap effects of CoSi₂ nanocrystals. The current process provides simple route for the fabrication of nanocrystal memory compatible with the current Si device unit processes.     

Effect of ferric ions on the morphology and size of magnetite nanocrystals synthesized by ultrasonic irradiation

Two‐dimensional plate‐like Fe₃O₄ nanocrystals and nanoparticles could be synthesized by a simple one‐step sonochemical method through ultrasonic irradiation in reverse co‐precipitation solution at low temperature. This technique provided a facile and rapid way to prepare Fe₃O₄nanocrystals with different morphology and size. Magnetite nanoplates were synthesized with only ferrous salt adding into alkali solution, and adding ferric ions with low molar ratio in the metal salts solution would lead to the formation of very small magnetite nanoparticles (∼10 nm). The size of as‐prepared magnetite nanoparticles increased with increasing reaction temperature and showed narrow size distribution, the standard deviation less than 2 nm. This investigation indicated that ferric ions had significant influence on the morphology of Fe₃O₄ nanocrystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optical property studies of CdSe crystalline nanorods synthesized by a solvothermal method

CdSe nanorods are synthesized via a simple solvothermal method at a moderate temperature of 180 °C. The influences of introducing hydrazine hydrate (N₂H₄·H₂O) as the reducing agent, and ammonia (NH₃·H₂O) as the complexing agent and also the reaction temperature, on the morphology and size of the obtained CdSe nanorods are investigated and reported. CdSe nanorods with a mean diameter and length of 25 and 82 nm, respectively, are synthesized and the problem of handling the stacking faults present in the long CdSe nanorods is analyzed. The use of increased quantity of hydrazine hydrate and also prolonged reaction time is found to reduce the stacking faults on the synthesized nanorods. The morphology, phase and the optical properties of CdSe nanoparticles are studied using powder X-ray diffraction, TEM and high-resolution transmission electron microscope (HRTEM), UV–visible absorption spectroscopy and photoluminescence (PL) spectroscopy. The low-resolution TEM images confirm the formation of CdSe nanorods, and also the agglomeration of nanoparticles and the presence of few spherical nanoparticles. The strong PL intensity from the CdSe nanorod at 702 nm confirms a blue shift of 14 nm, when compared with the bulk wurtzite CdSe.     

Fabrication and thermal evolution of nanoparticles in SiO2 by Zn ion implantation

SiO₂ samples were implanted with 45 keV Zn ions at doses ranging from 5×10¹⁵ to 1.0×10¹⁷ ions/cm², and were then subjected to furnace annealing at different temperatures. Several techniques, such as ultra-violet–visible spectroscopy (UV–vis), grazing incidence X-ray diffraction spectroscopy (GXRD) and atomic force microscopy (AFM), have been used to investigate formation of nanoparticles and their thermal evolution. Our results clearly show that Zn nanoparticles could be effectively formed in SiO₂ at doses higher than 5×10¹⁶ ions/cm². The subsequent thermal annealing at oxygen ambient could induce the growth of Zn nanoparticles at intermediate annealing temperature range. While at temperature above 600 °C, Zn nanoparticles could be transformed into ZnO, or even Zn₂SiO₄ nanoparticles. The results have been tentatively discussed in combination with Zn diffusion and migration obtained by Rutherford backscattering spectroscopy (RBS) measurements.     

Size-controlled synthesis of LaAlO3 by reverse micelle method: Investigation of the effect of water-to-surfactant ratio on the particle size

Lanthanum monoaluminate (LaAlO₃) nanoparticles have been synthesized using microreactors made of poly(oxyethylene) nonylphenyl ether (Igepal CO-520)/water/cyclohexane microemulsions. The control of particle size was achieved by varying the water-to-surfactant molar ratio. The synthesized and calcined powders were characterized by thermogravimetry–differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Differential thermal analysis showed that LaAlO₃ phase transformation decreases with increase in water/surfactant (R) value. Pure LaAlO₃ phase was synthesized by annealing at 800 °C for 2 h in air directly from amorphous precursors, without formation of intermediate phase. The average particle size was found to increase with increase in water-to-surfactant ratio (R). FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and calcined powder.     

Thermal treatment-dependent chemical composition of ternary CdS1−xSex nanocrystals grown in borosilicate glass

Variation of the chemical composition of ternary CdS_1−xSe_x nanocrystals grown in borosilicate glass depending on the thermal treatment is studied by resonant Raman spectroscopy. It is shown that only for the nanocrystals with roughly equal content of substitutive S and Se chalcogen atoms (0.4<x<0.6) the nanocrystal composition is independent of the thermal treatment parameters. In other cases an increase of the thermal treatment temperature (625–700 °C) and duration (2–12 h) results in a considerable increase of the predominant chalcogen content in the nanocrystals.     

Synthesis and optical properties of high-purity CoO nanowires prepared by an environmentally friendly molten salt route

CoO nanowires with diameters of 50^_80 nm, and lengths of up to more than 5 μm have been successfully synthesized by a simple environmentally friendly molten salt route, in which the precursor CoCO₃ nanoparticles are decomposed to form high-purity CoO nanowires in NaCl flux. The structure features and morphology of the as-prepared CoO nanowires were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED). The chemical composition and oxidation state of the prepared nanowires were systemically studied by X-ray photoelectron spectra (XPS) and laser Raman spectroscopy. The results indicated that the as-prepared CoO nanowires were composed of pure cubic CoO phase. The growth mechanism of the synthesized nanowires was also discussed in detail based on the experimental results.     

Ordered arrays of high-quality single-crystalline α-Si3N4 nanowires: Synthesis,properties and applications

Ordered arrays of high-quality single-crystalline α-Si₃N₄ nanowires (NWs) have been synthesized via thermal evaporation and detailed characteristics of the NWs have been analyzed by employing scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photospectroscopy (XPS), infrared (IR), photoluminescence (PL) and in situ I–V measurements by STM/TEM holder. The microscopic results revealed that the NWs having diameter in the range of ~30–100 nm and length in microns. Furthermore, the NWs are found to be single crystalline grown along [0 0 1] direction. The elemental composition and valence states of elements are analyzed by EDS and XPS. The room temperature PL spectra exhibit a broad range visible emission band. The electron transport property of a single NW illustrates the symmetric I–V curve of a semiconductor. The possible growth mechanism is also briefly discussed.     

Synthesis and characterization of single-crystalline PrCO3OH dodecahedral microrods and its thermal conversion to Pr6O11

Single-crystalline PrCO₃OH dodecahedral microrods with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Pr₆O₁₁ dodecahedral microrods have been obtained by thermal conversion of PrCO₃OH dodecahedral microrods at 600 °C in air for 6 h. The as-synthesized products were characterized by X-ray powder diffraction, field-emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectra, fourier transform infrared spectroscopy and thermogravimetry–differential thermal analysis. The effect of the reaction parameters on the morphology of the product has been investigated. The dodecahedral microrods with larger size and better crystallinity can be obtained under the higher reaction temperature. The possible formation mechanism of PrCO₃OH microrods was discussed.     

Preparation of Sb2S3 nanomaterials with different morphologies via a refluxing approach

Single-crystalline antimony trisulfide (Sb₂S₃) nanomaterials with flower-like and rod-like morphologies were successfully synthesized under refluxing conditions by the reaction of antimony trichloride (SbCl₃) and thiourea with PEG400 and OP-10 as the surfactants. X-ray diffraction (XRD) indicates that the obtained sample is orthorhombic-phase Sb₂S₃ with calculated lattice parameters a=1.124 nm, b=1.134 nm and c=0.382 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the flower-like Sb₂S₃ is 9–10 μm in size, which is composed of thin leaves with thickness of 0.05–0.2 μm, width of 0.8–2.2 μm and length of 2.5–3 μm, and the rod-like Sb₂S₃ is 45–360 nm in diameter and 0.7–4 μm in length, respectively. UV–Vis analysis indicates that the band gap of Sb₂S₃ nanorods is 1.52 eV, suitable for photovoltaic conversion. A possible mechanism of formation was proposed. The effects of reaction time and surfactants on the growth of nanomaterials with different morphologies were also investigated.     

Hydrothermal synthesis of Bi2Te3 nanowires through the solid-state interdiffusion of Bi and Te atoms on the surface of Te nanowires

Polycrystalline Bi₂Te₃ nanowires were prepared by a hydrothermal method that involved inducing the nucleation of Bi atoms reduced from BiCl₃ on the surface of Te nanowires, which served as sacrificial templates. A Bi–Te alloy is formed by the interdiffusion of Bi and Te atoms at the boundary between the two metals. The Bi₂Te₃ nanowires synthesized in this study had a length of 3–5 μm, which is the same length as that of the Te nanowires, and a diameter of 300–500 nm, which is greater than that of the Te nanowires. The experimental results indicated that volume expansion of the Bi₂Te₃ nanowires was a result of the interdiffusion of Bi and Te atoms when Bi was alloyed on the surface of the Te nanowires. The morphologies of Bi₂Te₃ are strongly dependent on the reaction conditions such as the temperature and the type and concentration of the reducing agent. The morphologies, crystalline structure and physical properties of the product were analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS).     

Morphotropic phase boundary,segregation effect and crystal growth in the NBT–KBT system

Lead-free piezoelectric materials of sodium–potassium bismuth titanate, (1−x)NaBi(TiO₃)₂–xKBi(TiO₃)₂, ceramics and single crystals were prepared and their crystallographic and dielectric properties were measured. Single crystals with dimensions of several centimeters were grown by using the melt growth technique. The morphotropic phase boundary between rhombohedral and tetragonal symmetry determined by X-ray diffraction and Raman spectra was found at x=0.2. No coexistence of rhombohedral/tetragonal phases was found in the NKBT system. Compositions analyses showed that severe phase segregation occurred during the crystallization of the solid solution. From the segregation point, a homogeneous NKBT crystal near the MPB composition is difficult to grow.     

Gain cross-section of 1.06 μm emission in Nd-doped SiO2-LaF3 glass-ceramics prepared by sol-gel method

The room temperature near-infrared emission at 1.06 μm corresponding to the ⁴F_3/2 → ⁴I_11/2 laser transition in Nd³⁺-doped SiO₂-LaF₃ transparent glass-ceramics prepared by sol-gel method has been characterized in terms of the product of emission cross-section and fluorescence lifetime. Stimulated emission cross-sections have been calculated from experimental emission spectra using the Füchtbauer-Ladenburg equation. The precipitation of LaF₃ nanocrystals after heat-treatment, confirmed by X-ray diffraction, induces a significant increment of the 1.06 μm near-infrared emission compared with the as made sample. An enhancement of emission cross-section of about 10% has been achieved with increasing temperature of heat-treatment of the nano-ceramming process from 800 to 1000 °C, which is related to the growth of LaF₃ nanocrystals.     

Hydrothermal synthesis of organic hybrid BaTiO3 nanoparticles using a supercritical continuous flow reaction system

Barium titanate (BaTiO₃: BT) nanoparticles were synthesized by the hydrothermal method in the presence of dispersants using a continuous supercritical flow reaction system. The reactants of TiO₂ sol/Ba(NO₃)₂ mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The dispersant solution such as polyacrylic acid (PAA) and polyoxyethylene(20) sorbitan monooleate (Tween 80) was injected in the cooling process after the reaction. The crystal phase of the obtained particles was identified as perovskite cubic BaTiO₃ by X-ray diffractometry (XRD) and Raman spectroscopy. Raman spectra and thermogravimetric data revealed that PAA and Tween 80 fabricated hybrid BT nanoparicles. Primarily particle size of the BaTiO₃ nanoparticle was determined by means of BET surface area, as small as less than 10 nm irrespective of dispersants. In contrast, dispersed particle size in solution measured by dynamic light scattering (DLS) technique decreased from 282 nm to less than 100 nm depending on the dispersant. Aggregation of BaTiO₃ nanoparticles might be depressed in the presence of dispersants, especially PAA is the most effective among the dispersants examined.     

HRTEM and GIXRD studies of CdS nanocrystals embedded in Al2O3 films produced by magnetron RF-sputtering

In this paper we report on the structural properties of as-grown CdS nanoparticles embedded in Al₂O₃ films produced by a magnetron RF-sputtering technique. Grazing incidence X-ray diffraction together with high-resolution transmission electron microscopy (HRTEM) and electron diffraction were used to study the crystallinity and morphology of the CdS nanocrystals. Depending on the deposition parameters, elongated or spherical nanocrystals were grown. HRTEM shows evidence of the growth of CdS nanocrystals at room temperature with sizes in the range of 3–8 nm, and indicates that the nanocrystals formed in the cubic phase during the early stages of the deposition process. Stress-free films were formed under selected deposition conditions.     

Characterization of a newly synthesized organic nonlinear optical crystal: Urea ninhydrin monohydrate

Urea ninhydrin monohydrate (UNM) was synthesized and grown for the first time from aqueous solution employing the slow evaporation method. Single crystal structure was determined by X-ray diffraction data and it reveals that the crystal belongs to centrosymmetric with space group of P2₁/c. The grown crystals were characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and UV–vis–NIR spectroscopy. Preliminary Z-scan measurement indicates that nonlinear refractive index of this crystal is −4.1×10⁻⁸ cm²/W. The etching study was performed to assess the growth pattern of the crystal. Dielectric response of the crystal was analyzed for different frequencies and temperatures.     

Growth and spectroscopic characteristics of Er:YbVO4 crystal

A laser crystal Er³⁺:YbVO₄ has been grown by the Czochralski method with excellent quality. The rocking curve from the (0 0 4) diffraction plane of the as-grown Er³⁺:YbVO₄ crystal was measured and the full-width at half-maximum value was found to be 19.80 in. for the (0 0 4) face. The effective segregation coefficient of Er³⁺ was studied by X-ray fluorescence and the crystal structure was determined by means of X-ray diffraction analysis. The polarized absorption spectra and the fluorescence spectra of Er³⁺:YbVO₄ were measured at room temperature. The spectral parameters were calculated based on the Judd–Ofelt theory, and the intensity parameters Ω₂, Ω₄ and Ω₆ are found to be 5.50×10⁻²⁰, 1.96×10⁻²⁰ and 2.34×10⁻²⁰ cm², respectively. The emission cross-section has been calculated by the Fuechtbauer–Ladenbury method. The spectroscopic parameters of Er³⁺:YbVO₄ are compared with other typical laser hosts.     

Novel mixed–solvothermal synthesis of MoS2 nanosheets with controllable morphologies

MoS₂ nanosheets with controllable morphologies were successfully synthesized via a novel mixed–solvothermal approach based on interfusing organic solvent in the solution. The morphology of the MoS₂ nanosheets was lamellar–like using the mixed water/ethanol/N–Methyl pyrrolidone solvents, whereas that prepared with the mixed water/ethano/ethylene glycol solvents changes to fullerene–like. Because of the structure‐directing ability of organic molecules, the mixed solvents were proposed to be responsible for the formation of such different morphologies. The average size of MoS₂ nanosheets was approximately 90 nm, and the thickness was about 10–20 nm. The results indicated that the crystalline phase and morphology were largely influenced by calcination and reaction system.     

Sublimation crystal growth of yttrium nitride

The sublimation–recombination crystal growth of bulk yttrium nitride crystals is reported. The YN source material was prepared by reacting yttrium metal with nitrogen at 1200 °C and 800 Torr total pressure. Crystals were produced by subliming this YN from the source zone, and recondensing it from the vapor as crystals at a lower temperature (by 50 °C). Crystals were grown from 2000 to 2100 °C and with a nitrogen pressure from 125 to 960 Torr. The highest rate was 9.64×10⁻⁵ mol/h (9.92 mg/h). The YN sublimation rate activation energy was 467.1±21.7 kJ/mol. Individual crystals up to 200 μm in dimension were prepared. X-ray diffraction confirmed that the crystals were rock salt YN, with a lattice constant of 4.88 Å. The YN crystals were unstable in air; they spontaneously converted to yttria (Y₂O₃) in 2–4 h. A small fraction of cubic yttria was detected in the XRD of a sample exposed to air for a limited time, while non-cubic yttria was detected in the Raman spectra for a sample exposed to air for more than 1 h.     

On the Bridgman growth of lead–tin selenide crystals with uniform tin distribution

The application of T–x–y phase diagram for the control of the crystal composition of alloy crystals during Bridgman growth is illustrated using (Pb_1−xSn_x)_1−δSe_1+δ solid solutions as an example. Within the framework of the proposed approach, the axial segregation can be minimised if the feed composition is chosen in the regions of phase diagram where the iso-mole-fraction lines are perpendicular to isotherms. For the system Pb–Sn–Se the component distribution in crystals grown from a melt with δ=0, a Se-rich melt (δ>0) and a metal-rich melt (δ<0) are discussed. Uniform crystals with x=(0.03–0.15)±0.01 can be obtained from Se-rich melt (Se enrichment is 12–5 at%Se, T=1280–1200 K). The use of metal-rich melt allows obtaining crystals with moderate segregation of 3–5 mol% SnSe for x=0.13–0.23 at 3–9 at% of metal enrichment and T=1270–1200 K and for x=0.35–0.45 at 25–35 at% of metal enrichment and T=1120–1050 K.