121,123Sb and 75As NMR and NQR investigation of the tetrahedrite (Cu12Sb4S13) – Tennantite (Cu12As4S13) system and other metal arsenides

This work is motivated by the recent developments in online minerals analysis in the mining and minerals processing industry via nuclear quadrupole resonance (NQR). Here we describe a nuclear magnetic resonance (NMR) and NQR study of the minerals tennantite (Cu₁₂As₄S₁₃) and tetrahedrite (Cu₁₂ Sb₄S₁₃). In the first part NQR lines associated with ⁷⁵As in tennantite and ^121,123Sb isotopes in tetrahedrite are reported. The spectroscopy has been restricted to an ambient temperature studies in accord with typical industrial conditions. The second part of this contribution reports nuclear quadrupole-perturbed NMR findings on further, only partially characterised, metal arsenides. The findings enhance the detection capabilities of NQR based analysers for online measurement applications and may aid to control arsenic and antimony concentrations in metal processing stages.     

On the structure, morphology, and optical properties of chemical bath deposited Sb2S3 thin films

In the present paper, we have reported the room temperature growth of antimony sulphide (Sb₂S₃) thin films by chemical bath deposition and detailed characterization of these films. The films were deposited from a chemical bath containing SbCl₃ and Na₂S₂O₃ at 27 °C. We have analysed the structure, morphology, composition and optical properties of as deposited Sb₂S₃ films as well as those subjected to annealing in nitrogen atmosphere or in air. As-deposited films are amorphous to X-ray diffraction (XRD). However, the diffused rings in the electron diffraction pattern revealed the existence of nanocrystalline grains in these films. XRD analysis showed that upon annealing in nitrogen atmosphere these films transformed into polycrystalline with orthorhombic structure. Also, we have observed that during heating in air, Sb₂S₃ first converts into orthorhombic form and then further heating results in the formation of Sb₂O₃ crystallites. Optical bandgap energy of as deposited and annealed films was evaluated from UV-vis absorption spectra. The values obtained were 2.57 and 1.73 eV for the as-deposited and the annealed films respectively.     

Optical characterization of CdSe/Dy3+-doped silica matrices

Cadmium selenide nanocrystals along with dysprosium ions are doped in silica matrices through sol-gel route. The optical bandgap and size of the CdSe nanocrystals are calculated from the absorption spectrum. The size of the CdSe nanocrystallites is also evaluated from the TEM measurements. The fluorescence intensities are compared for SiO₂-Dy³⁺ and CdSe-doped SiO₂-Dy³⁺. The fluorescence intensity of Dy³⁺ is considerably increased in the presence of CdSe nanocrystals.     

Soft-template synthesis and optical Properties of Sb2S3 semiconductor quasi-nanospheres

The reverse micelle system composed of four phases of Hexamethylene/Triton-100/n-pentanol/water (containing 1 ml 0.1 M Sb³⁺ or 1 ml 0.1 M S²⁻), which ratio is 28:3:1:1, is prepared. Sb₂S₃ quasi-nanospheres with diameters between 160 and 240 nm are synthesized by above reverse micelle soft-template system. The result shows that the fluorescence peaks have a blue shift about 19 nm when it is excited at 219 nm, and the UV–Vis absorption peaks shift about 453 nm (2.74 eV).     

Eu<Superscript>3+</Superscript> doped yttrium oxysulfide quantum structures—structural,optical and electronic properties

Small particles of trivalent europium doped yttrium oxysulfide nanocrystals (ϕ ∼ 7 nm) were synthesized using sol–gel polymer thermolysis. The nanocrystals show significant change in the excitation bands corresponding to fundamental absorption and charge transfer absorption bands. The optical spectra essentially comprise of two parts: fundamental absorption (∼260 nm) and Eu³⁺–X²⁻ ligand (O²⁻/S²⁻) charge transfer (∼290 nm) bands. They show significant blue shifts (0.24–0.30 eV), respectively, with respect to the bulk counterpart. These may be explained by considering possible size dependent changes associated with quantum confinement effect in this large bandgap semiconductor system. FT-IR spectra revealed the difference in chemisorbed species between bulk and nanocrystalline samples. The results of the solid-state photo-induced electrical impedance spectroscopy studies are reported.     

Infrared-to-visible upconversion in Er and Er/Yb activated Sb2O4 nanopowders prepared by sol-gel route

We prepared Er³⁺ doped and Er³⁺/Yb³⁺ codoped Sb₂O₄ nanocrystals by the sol-gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb₂O₄ nanocrystals is very low (the maximum value being 461 cm⁻¹). The upconversion (UC) red emission of the Er³⁺/Yb³⁺ codoped sample is very strong at 975 nm laser diode excitation. The Sb₂O₄ nanocrystals will be a promising luminous material.     

Biomolecule-assisted hydrothermal synthesis of Sb2S3 and Bi2S3 nanocrystals and their elevated-temperature oxidation behavior for conversion into α-Sb2O4 and Bi2O3

We have developed a novel biomolecule-assisted hydrothermal method to prepare Sb₂S₃ and Bi₂S₃ nanocrystals with various sizes and shapes, in which cysteine combined with other sulfur source can exert the synergistic effect on products. The samples were characterized XRPD, TEM, HRTEM, FESEM, and PL techniques. First, we prepared a series of Sb₂S₃ and Bi₂S₃ nanocrystals by simply adjusting the composition of sulfur sources under hydrothermal conditions. Then, we studied the elevated-temperature oxidation behavior of these sulfides in air, which can lead to the formation of α-Sb₂O₄ and Bi₂O₃ samples at 600 °C for 3 h. The optical properties of the α-Sb₂O₄ and Bi₂O₃ samples were also discussed.     

Optical and ESR studies on Fe doped ZnS nanocrystals

Zn_1 − xFe_xS (x=0.0, 0.1, 0.2, 0.4 and 0.6) nanocrystals have been obtained by chemical co-precipitation from homogeneous solutions of zinc and iron salt compounds, with S²⁻ as precipitating anion formed by decomposition of thiophenol. The TEM micrographs show a spherical shape for ZnS nanocrystals and their average size is around 7 nm. The optical absorption spectra indicate a blue shift of the absorption edge with increasing Fe-content. The luminescence of nanoparticles excite at about 370 nm with an emission peak at around 490 nm. At room temperature, ESR signal characteristic of Fe³⁺ was observed in samples of all concentrations.     

Structural and optical properties of amorphous Sb2S3 thin films deposited by vacuum thermal evaporation method

Sb₂S₃ thin films have been deposited by vacuum thermal evaporation onto glass substrates at various substrate temperatures in the range of 30–240 °C. Crushed powder of the synthesized Sb₂S₃ was used as raw material for the vacuum thermal evaporation. The structural investigation performed by means of X-ray diffraction (XRD) showed that the all as-deposited films present an amorphous structure and all the films were highly resistive. The reflectance and transmittance of the films are measured in the incident wavelength range 300–1800 nm. The absorption coefficient spectral analysis revealed the existence of long and wide band tails of the localized states in the low absorption region. The band tails width is calculated and found to be varying between 0.024 and 0.032 eV. The analysis of the absorption coefficient in the high absorption region revealed two direct forbidden band gaps between 1.78–1.98 eV and 1.86–2.08 eV.     

Synthesis of silver nanoparticles and antimony oxide nanocrystals by pulsed laser ablation in liquid media

Pulsed laser ablation in liquid media (PLALM) is a prominent technique for the controlled fabrication of nanomaterials via rapid reactive quenching of ablated species at the interface between the plasma and liquid. Results on nanoparticles and nanocrystals formed by PLALM of silver (Ag) and antimony (Sb) solid targets in different liquid environments (Sodium Dodecyl Sulfate, distilled water) are presented. These experiments were done by irradiating solid targets of Ag and Sb with a nanosecond pulsed Nd:YAG laser output of wavelength 532 nm. Nanoparticles of silver and nanocrystals of antimony oxide (Sb₂O₃) obtained were characterized using UV-Vis spectrometry, Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), X-ray Energy Dispersion Analysis (EDAX) and X-ray diffractometry (XRD). The morphology of nanomaterials formed is studied as a function of surfactant environment. The silver nanoparticles obtained were spherical of size in the order of 10–35 nm in solution of SDS having different concentrations. In case of the Sb target, ablation was performed in two different molarities of SDS solution and distilled water. Nanocrystals of Sb₂O₃ in powder form having cubic and orthorhombic phases were formed in SDS solution and as fibers of nanocrystals of cubic Sb₂O₃ in distilled water.     

Oleylamine‐Assisted Phase‐Selective Synthesis of Cu2−xS Nanocrystals and the Mechanism of Phase Control

Environmentally friendly Cu_2?x S compounds exist in many different mixed phases in nature, while their nanoscale counterparts can be pure phase with interesting localized surface plasmon resonance properties. Because of the complexity of composition and phase, controllable synthesis of Cu_2?x S nanocrystals becomes an important scientific issue in colloidal chemistry. In this work, a hot‐injection method is developed to synthesize Cu_2?x S nanocrystals by injecting a sulfur precursor into a copper precursor using oleylamine and octadecene as solvents. By varying the reaction parameters (temperature, volume ratio of oleylamine/octadecene, molar ratio of Cu/S in the precursors), hexagonal CuS, monoclinic Cu_1.75S, and rhombohedral Cu_1.8S, nanocrystals can be selectively synthesized, providing a platform to illustrate the mechanism of crystal phase control. The crystal phase control of Cu_2?x S nanocrystals is oleylamine‐determined by controlling the molar ratio of Cu/S in the reaction precursors as well as the ratio of Cu_2?x S clusters/Cu⁺ in the subsequent reaction. More importantly, temperature plays an important role in varying the molar ratio of Cu/S and Cu_2?x S clusters/Cu⁺ in the reaction system, which significantly influences the crystal phase of the resulting Cu_2?x S nanocrystals. The understanding into crystal control provides a guideline to realize reproducible phase‐selective synthesis and obtain well‐defined high‐quality materials with precise control.     

Diamond cubic Sn-rich nanocrystals: synthesis, microstructure and optical properties

Diamond cubic Sn-rich nanocrystals were fabricated with radii less than 20 nm by post-growth annealing at T=750 °C of Sn_xGe_1-x alloys grown on Ge(001) by molecular beam epitaxy. The crystal phase of the Sn-rich nanocrystals was determined to be diamond cubic from Fourier transform analysis of high-resolution transmission electron microscopy images. Optical transmittance of these Sn_xGe_1-x/Ge (001) films demonstrated changes in optical absorption that can be attributed to absorption from the nanocrystals. The energy bandgap was measured to be 0.45 eV for nanocrystals arrays in Ge with a mean diameter of 32 nm. PACS 68.37.Lp; 78.67.Hc; 81.07.Ta; 81.16.Dn; 68.65.Hb     

Mechanochemical Synthesis and Characterization of GaN Nanocrystals

A solid-state displacement reaction of Ga₂O₃ with Mg₃N₂ has been used to synthesize GaN nanocrystals by mechanochemical processing. X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) measurements indicated that the nanocrystals had a hexagonal structure and sizes ranging from 4 to 20nm. Optical absorption and transmission measurement showed the bandgap of the nanocrystals was consistent with that of bulk GaN samples (3.43eV). This study demonstrates that mechanochemical processing has significant potential for the synthesis of GaN nanocrystals in a simple and efficient way.     

Synthesis of compositionally controllable Cu<Subscript>2</Subscript>(Sn<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript>)S<Subscript>3</Subscript> nanocrystals with tunable band gaps

In this work, we show that compositionally controlled Cu₂(Sn_1–xGe_x)S₃ nanocrystals can be successfully synthesized by the hot-injection method through careful tuning the Ge/(Sn+Ge) precursor ratio. The band gaps of the resultant nanocrystals are demonstrated to be linearly tuned from 1.45 to 2.33 eV by adjusting the composition parameter x of the Ge/(Sn+Ge) ratio from 0.0 to 1.0. The crystalline structures of the resultant NCs have been studied by the X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), select area electron diffraction (SAED), and Raman spectroscopy. A ligand exchange procedure is further performed to replace the native ligands on the surface of the NCs with sulfur ions. The photoresponsive behavior indicates the potential use of as-prepared Cu₂(Sn_1–xGe_x)S₃ nanocrystals in solar energy conversion systems. The synthesis of compositionally controlled Cu₂(Sn_1–xGe_x)S₃ nanocrystals reported herein provides a way for probing the effect of Ge inclusion in the Cu-Sn-S system thin films.     

Cu addition and its role in thermoelectric properties and nanostructuring in the series compounds (InSb)nCum

We have performed a comparative investigation of the series compounds (InSb)_nCu_m to assess the roles of Cu addition on the thermoelectric properties and nanostructuring in bulk InSb. Detailed temperature dependent transport properties including electrical conductivity, the Seebeck coefficient, and thermal conductivity are presented. The Seebeck coefficients of In₂₀Sb₂₀Cu (m:n = 1:20) are increased by 13 percent in magnitude if compared to those of InSb, which is responsible for the 22 percent enhancement in the highest ZT value at 687 K. Although the magnitudes of κ_L are larger than those of InSb over the entire temperature range, a remarkable reduction in lattice thermal conductivities (κ_L) was observed with measuring temperature elevation. Such changes are mainly due to the precipitation of a large number of Cu₉In₄ nanoparticles with the size of smaller than 5 nm, dispersed in the matrix observed using high resolution transmission electron microscopy (HRTEM) images.     

Effects of Kr and Xe ion irradiation on the structure of Y2O3 nanoprecipitates in YBCO thin film conductors

ABSTRACT

The response of Y₂O₃ nanoprecipitates in a 1-µm YBa₂Cu₃O_7-x layer from a superconducting wire Ag/YBCO/buffer metal oxides/Hastelloy to 107?MeV Kr and 167?MeV Xe ion irradiation was investigated using a combination of transmission electron microscopy, diffraction and X-ray energy-dispersive spectrometry. The direct observation of the radiation-induced tracks in Y₂O₃ nanocrystals is reported for the first time to the authors’ best knowledge. Structureless damaged regions of 5–9?nm (average 8?nm) in diameter were observed in Y₂O₃ nanocrystals when the electronic stopping power S_e was about or higher than 4.7 keV/nm. This value of S_e is the upper estimate of the minimum electronic stopping power to create damage in yttria nanocrystals. The electron diffraction patterns, high-resolution transmission electron microscopy, high-resolution scanning transmission electron microscopy, Fourier transform patterns from areas extending a few nanometres around the tracks show that yttria and YBCO keep their respective cubic and orthorhombic pristine structures.     

The fine structure of FCC nanocrystals in Al-and Ni-based alloys

The structural perfection of nanocrystals in alloys of different chemical composition is studied by x-ray diffraction and high-resolution electron microscopy. In all the alloys studied, crystallization of the amorphous phase produces a nanocrystalline structure. The nanocrystal size depends on the chemical composition of the alloy and varies in aluminum-based alloys from 5 nm in Al₈₉Ni₅Y₆ to 12 nm in Al₈₂Ni₁₁Ce₃Si₄. Nanocrystals in nickel-based alloys vary in size from 15 to 25 nm. Al nanocrystals are predominantly defect-free, with microtwins observed only in some nanocrystals. The halfwidth of the diffraction lines is proportional to sec θ, which implies the small grain size provides the major contribution to the broadening. Nanocrystals in nickel alloys contain numerous twins, stacking faults, and dislocations.     

The size effect of Ba0.6Sr0.4TiO3 thin films on the ferroelectric properties

Barium strontium titanate (BST) thin films were prepared by RF magnetron sputtering. The dielectric constant-voltage curves and the hysteresis loops of BST thin films with different grain sizes and film thicknesses were investigated. When the grain size increases from 12 nm to 35 nm, remarkable increases in dielectric constant and tunability were observed. Above 12 nm, the BST films exhibited size effects, i.e. a decrease in maximal polarization (P_m) and an increase in coercive electric field (E_c) with reduction in grain size. In our investigation, the dielectric constant, tunability and maximal polarization increased as the film thickness increased. Furthermore, the size dependence of the dielectric constant and tunability of Ba_0.6Sr_0.4TiO₃ thin films is determined by that of the maximal polarization and the coercive electric field.     

Synthesis of RGO/Cu8S5/PPy Composite Nanosheets with Enhanced Peroxidase‐Like Activity for Sensitive Colorimetric Detection of H2O2 and Phenol

In this paper, a novel strategy for the fabrication of reduced graphene oxide (rGO)/Cu₈S₅/polypyrrole (PPy) composite nanosheets with Cu₈S₅ nanoparticles and PPy layer anchored on the surface of rGO as peroxidase‐like nanocatalyst is reported. During the synthesis, graphene oxide (GO)/CuO composite nanosheets are prepared first and used as templates, then the sulfuration of CuO and polymerization of pyrrole are accompanied with the reduction of GO, resulting in ternary rGO/Cu₈S₅/PPy composite nanosheets. The synthesized Cu₈S₅ nanoparticles with a diameter in the range from tens to hundreds of nanometers are dispersed within PPy decorated rGO nanosheets. The resultant ternary rGO/Cu₈S₅/PPy composite nanosheets exhibit a higher peroxidase‐like catalytic activity toward the oxidation of 3,3′,5,5′‐tetramethylbenzidine in the presence of H₂O₂ than GO/CuO and rGO/CuS composite nanosheets, revealing a synergistic effect on their activity. The as‐prepared rGO/Cu₈S₅/PPy platform provides a simple colorimetric approach for the detection of H₂O₂ and phenol with a high sensitivity. This work offers a new way for the fabrication of rGO‐based nanocomposite with superior enzyme‐like activity, which displays great potential applications in biocatalysis and environmental monitoring.     

Structural and optical properties of Cu2ZnSn(S,Se)4 films obtained by magnetron sputtering of a Cu2ZnSn alloy target

Results of the study of structural and optical properties of Cu₂ZnSn(S,Se)₄ thin films obtained by sulfitation (selenization) of Cu₂ZnSn films which were sputtered by target direct current magnetron sputtering using a stoichiometric Cu₂ZnSn (99.99%) target are presented. It has been found that Cu₂ZnSn(S,Se)₄ thin films are polycrystalline with a grain size of ~60 nm. The optical bandgap of Cu₂ZnSnS₄ (E ^op _g = 1.65 eV) and Cu₂ZnSnSe₄ (R ^op _g = 1.2 eV) thin films have been determined.