Utilization of residual CdCl2 in CBD-CdS to realize grain growth in CdTe: A novel route

CdTe films were deposited by thermal evaporation onto chemical bath deposited CdS (CBD-CdS) films. The composite films were subjected to rapid thermal annealing (RTA) to observe simultaneous grain growth in both the CdS and CdTe layers. The films were characterized by measuring the compositional, microstructural and photoluminescence (PL) properties. PL spectra is dominated by the characteristic peaks (∼1.42 eV and ∼1.26 eV) associated with the virgin CdTe film. Additional features located at ∼2.56 eV and ∼1.99 eV could also be detected. The Fourier Transform Infra Red (FTIR) peak at ∼482 cm⁻¹ appeared due to the simultaneous presence of absorption peaks for CdTe stretching mode as well as Cd-S modes. Appearance of the broad peak between 1000 cm⁻¹ and 1165 cm⁻¹ may be an indication of interfacial alloying. Secondary ion mass Spectroscopy (SIMS) measurements were done to observe the compositional uniformity in the film and to measure the interfacial mixing behaviour.     

Synthesis and luminescence of a new phosphorescent iridium(III) pyrazine complex

The synthesis and luminescent study of a new iridium pyrazine complex are reported. The iridium complex [Ir(MDPP)2(acac)] (MDPP=5-methyl-2,3-diphenylpyrazine, acac=acetylacetone) shows strong ¹MLCT (singlet metal-to-ligand charge-transfer) and ³MLCT (triplet metal to ligand charge-transfer) absorption at 386 and 507 nm, respectively. Organic light emitting device (OLED) with a configuration of ITO / NPB (30 nm) / NPB: 7% (wt.) Ir(MDPP)₂(acac) (25 nm) / BCP (10 nm) / Alq₃(30 nm) / Mg : Ag (mass ratio 10 : 1)120 nm / Ag(10 nm) exhibits an external quantum efficiency of 6.02% (power efficiency 9.89 lm W^− 1 ) and a maximum brightness of 78,924 cd m^− 2. The device also shows high color purity with a maximum peak at 576 nm without any shoulder.     

Novel rosette-shaped CdS microparticle with high surface area fabricated by lyotropic liquid crystal templating

Semiconductor CdS microparticle covered with wrinkle-like nanotexture was prepared under ambient condition by using the lyotropic liquid crystal mesophase as a structural template. The prepared CdS microparticle resembles a rosette shape with a diameter of 0.5–1.5 μm and the wrinkle-like nanotexture on its surface. This rosette-shaped CdS consists of small nanocrystals with a diameter of ∼4 nm, and the nanocrystal building block has the zinc-blende crystal structure. The characteristic band-to-band absorption and near band-edge emission are observed in this unique semiconductor particle. Nitrogen gas physisorption measurement reveals that the material has the high BET surface area of 38 m² g⁻¹ and nanoporous nature.     

Conductance measurements of nanoscale regions with in situ transmission electron microscopy

Conductance measurements of nanostructures with simultaneous transmission electron microscopy (TEM) were performed on thin insulating SrF₂ films (3 nm thick) and Fe–SrF₂ granular films (10 nm thick) deposited on tip-shaped Au electrodes. By using a movable counter electrode, nanoscale regions were selected for investigation. Systematic measurements taken during the deformation of the SrF₂ film by the counter-electrode provided a tunnelling barrier height of about 2.5 eV. The conductance of Fe–SrF₂ in nanoscale (∼ 500 nm²) showed the Coulomb staircase like characteristics at room temperature. The staircase period approximately corresponded to the value estimated from the geometry observed by TEM. The feasibility of this method is briefly described.     

Synthesis of carbon nanostructures with unique morphologies via a reduction-catalysis reaction route

Large-scale carbon nanostructures with unique morphologies were successfully synthesized by a reduction-catalysis reaction route. The as-synthesized products, characterized by XRD, SEM and TEM, revealed that hollow carbon nanospheres with diameters in the range of 100–200 nm can be formed at 500 °C while the tetrapod-like carbon nanotubes with bamboo structure can be synthesized with the typical diameters of about 100 nm and length of over 1 μm. Two strong and wide Raman peaks at 1600 cm⁻¹ (G-band) and at 1347 cm⁻¹ (D-band) are observed at room temperature and their mechanism of formation is discussed. These unique carbon nanostructures offer potential applications, such as nanoscale transistors, amplifiers, switches and ballistic rectifiers and so on.     

Highly porous ZnS microspheres for superior photoactivity after Au and Pt deposition and thermal treatment

This work highlights the enhanced photocatalytic activity of porous ZnS microspheres after Au and Pt deposition and heat treatment at 500 °C for 2 h. Microporous ZnS particles of size 2–5 μm with large surface area 173.14 m² g⁻¹ and pore volume 0.0212 cm³ g⁻¹ were prepared by refluxing under an alkaline medium. Photoluminescence of ZnS at 437 nm attributed to sulfur or zinc vacancies were quenched to 30% and 49%, respectively, after 1 wt% Au and Pt loading. SEM images revealed that each ZnS microparticle consist of several smaller ZnS spheres of size 2.13 nm as calculated by Scherrer's equation. The rate of photooxidation of 4-nitrophenol (10 μM) under UV (125 W Hg arc–10.4 mW/cm²) irradiation has been significantly improved by Au and Pt deposition followed by sintering due to better electron capturing capacity of deposited metals and growth of crystalline ZnS phase with less surface defects.     

Influence of pH and HPC concentration on the synthesis of zinc oxide photocatalyst particle from zinc-dust waste by hydrothermal treatment

This work aimed to use the waste zinc-dust from a hot-dip galvanizing plant for the synthesis of nanosized ZnO photocatalyst powder via hydrothermal treatment. ZnO particles with different morphologies and sizes were obtained by varying the solution pH (8–12) and the amount of hydroxypropyl cellulose (HPC) dispersant (0–0.15% (w/v)) under hydrothermal treatment at 170 °C for 8 h. The influence of the preparation conditions on the properties of resultant ZnO particles were evaluated by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, laser light scattering and Brunauer–Emmett–Teller analyses. The solution pH affected the crystallinity, particle morphology and specific surface area of the obtained ZnO, which in turn influenced its photocatalytic activity. The addition of the optimum amount of HPC (0.1% (w/v)) in the starting solution acted as a dispersant to reduce ZnO particle agglomeration but had the opposite effect at higher levels. Moreover, ZnO nanorods with various aspect ratios and a diameter and length range of 20–70 nm and 100–400 nm, respectively, were obtained depending on the amount of added HPC. The photocatalytic activity of the synthesized ZnO powder was improved by the addition of the optimal amount of HPC, and correlated to the particle dispersion and specific surface area.     

Obtaining ultra-long copper nanowires via a hydrothermal process

Ultra-long and uniform copper nanowires with controllable diameters of 30–100 nm, length up to several millimeters (aspect ratio >10⁵) and tunable crystallinity were obtained by hydrothermal processing the complex emulsion of copper (II) chloride and ODA at 120–180 °C. Both XRD pattern and EDX spectrum indicated that the products were pure copper without any observable impurities. It is observed by FESEM that the diameters and aspect ratios of the synthesized copper nanowires were influenced by the concentration of ODA and reaction temperature. HRTEM images and SAED patterns revealed that the crystallinity of copper nanowires were strongly dependent on the synthesis temperatures. Poly- and single-crystal copper nanowires were obtained at 120 °C and 180 °C, respectively.     

Improved efficiency of sol–gel synthesized mesoporous anatase nanopowders in photocatalytic degradation of metoprolol

The structural and morphological properties of mesoporous anatase nanopowders, synthesized by sol–gel method, have been modified by varying the duration of calcination, in order to obtain more efficient photocatalyst than Degussa P25 in the degradation of relatively large pollutant molecules (>1 nm in size). According to X-ray diffraction analysis, the crystallite size was increased from 13 to 17.5 nm with the increase of calcination time from 1 to 7 h. The analysis of nitrogen sorption experimental data revealed that all samples were mesoporous, with a mean pore diameters in the range of ∼5–9 nm. The corrugated pore structure model was employed to evaluate pore structure tortuosity. Nanopowder properties have been related to the photocatalytic activity, tested in the degradation of metoprolol tartrate salt, selective β₁-blocker used in a variety of cardiovascular diseases, with molecular size of 0.610 nm × 1.347 nm. The study has demonstrated that samples calcined for 4 and 5 h have displayed higher photocatalytic performance than Degussa P25, whereas the sample calcined for 3 h has shown comparable activity.     

Thermally reduced graphene oxide acting as a trap for multiwall carbon nanotubes in bi-filler epoxy composites

The effect of thermally reduced graphene oxide (TRGO) on the electrical percolation threshold of multi wall carbon nanotube (MWCNT)/epoxy cured composites is studied along with their combined rheological/electrical behavior in their suspension state. In contrast to MWCNT and carbon black (CB) based epoxy composites, there is no prominent percolation threshold for the bi-filler (TRGO–MWCNT/epoxy) composite. Furthermore, the electrical conductivity of the bi-filler composite is two orders of magnitude lower (∼1 × 10⁻⁵ S/m) than the pristine MWCNT/epoxy composites (∼1 × 10⁻³ S/m). This result is primarily due to the strong interaction between TRGO and MWCNTs. Optical micrographs of the suspension and scanning electron micrographs of the cured composites indicate trapping of MWCNTs onto TRGO sheets. A morphological model describing this interaction is presented.     

Influence of carbon precursors on thermal plasma assisted synthesis of SiC nanoparticles

Nanosized SiC was synthesized by solid state method using silicon and carbon powders followed by non-transferred arc thermal plasma processing. X-ray diffraction (XRD) analysis revealed that activated carbon has highest reactivity while graphite has lowest activity in the crystallization of SiC through solid state method. The reactivity was dependent on surface area of carbon source and activated carbon with highest surface area (590.18 m² g⁻¹) showed highest reactivity, whereas graphite with least surface area (15.69 m² g⁻¹) showed lowest reactivity. The free silicon content was decreased with increasing reaction time as well as carbon mole ratio. Scanning electron microscope (SEM) study showed that the shape and size of synthesized SiC depends on the shape and size of carbon source. SiC nanoparticles within 500 nm were formed for carbon black while bigger particles (∼5 μm) were formed for activated carbon and graphite. Plasma processing of these solid–solid synthesized SiC resulted into the formation of well dispersed, ultrafine SiC nanoparticles (30–40 nm) without any structural modification. Thermal plasma processing resulted into the increase in crystallite size of SiC.     

Effects of aluminum substitution on photocatalytic property of BiVO4 under visible light irradiation

Novel visible-light-driven Al/BiVO₄ photocatalysts were synthesized via a facile hydrothermal method for the first time. The samples were characterized by X-ray diffraction, N₂-sorption, UV–vis diffuse reflectance spectra, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transformed infrared spectra and X-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of methylene blue under visible light irradiation (400 nm < λ <580 nm) and was compared with that of single-phase BiVO₄. The results revealed that the introduction of Al can improve photocatalytic performance greatly and different concentration of Al resulted in different photocatalytic activity. The highest activity is obtained by the sample with a doping concentration of 12 at%. The reason for the enhanced photocatalytic activities of Al/BiVO₄ samples was also discussed in this paper.     

CdS nanoparticles incorporated onion-like mesoporous silica films: Ageing-induced large stokes shifted intense PL emission

CdS nanoparticles (NPs) were generated in onion-like ordered mesoporous SiO₂ films through a modified sol–gel process using P123 as a structure directing agent. Initially Cd²⁺ doped (12 equivalent mol% with respect to the SiO₂) mesoporous SiO₂ films were prepared on glass substrate. These films after heat-treatment at 350 °C in air yielded transparent mesoporous SiO₂ films having hexagonally ordered onion-like pore channels embedded with uniformly dispersed CdO NPs. The generated CdO NPs were transformed into CdS NPs after exposing the films in H₂S gas at 200 °C for 2 h. The as-prepared CdS NPs incorporated mesoporous SiO₂ films (transparent and bright yellow in color) showed a band-edge emission at 485 nm and a weak surface defect related emission at 530 nm. During ageing of the films in ambient condition the band-edge emission gradually weakened with time and almost disappeared after about 15 days with concomitant increase of defect related strong surface state emission band near 615 nm. This transformation was related to the decay of initially formed well crystalline CdS to relatively smaller and weakly crystalline CdS NPs with surface defects due to gradual oxidation of surface sulfide. At this condition the embedded CdS NPs show large Stokes shifted (∼180 nm) intense broad emission which could be useful for luminescent solar concentrators. The detailed process was monitored by UV–Visible, FTIR and Raman spectroscopy, XPS, XRD and TEM studies. The evolution of photoluminescence (PL) and life times of CdS/SiO₂ films were monitored with respect to the ageing time.     

Stoichiometric and non-stoichiometric films in the Si–O–N system: mechanical,electrical, and dielectric properties

A novel low-temperature (600–850 °C), chemical vapor deposition method, involving a simple reaction between disiloxane (H₃Si–O–SiH₃) and ammonia (NH₃), is described to deposit stoichiometric, Si₂N₂O, and non-stoichiometric, SiO_xN_y, silicon oxynitride films (5–500 nm) on Si substrates. Note, the gaseous reactants are free from carbon and other undesirable contaminants. The deposition of Si₂N₂O on Si (with (1 0 0) orientation and a native oxide layer of 1 nm) was conducted at a pressure of 2 Torr and at extremely high rates of 20–30 nm min⁻¹ with complete hydrogen elimination. The deposition rate of SiO_xN_y on highly-doped Si (with (1 1 1) orientation but without native oxide) at 10⁻⁶ Torr was ∼1.5 nm min⁻¹, and achieved via the reaction of disiloxane with N atoms, generated by an RF source in an MBE chamber. The phase, composition and structure of the oxynitride films were characterized by a variety of analytical techniques. The hardness of Si₂N₂O, and the capacitance–voltage (C–V) as a function of frequency and leakage current density–voltage (J_L–V) characteristics were determined on MOS (Al/Si₂N₂O/SiO/p-Si) structures. The hardness, frequency-dispersionless dielectric permittivity (K), and J_L at 6 V for a 20 nm Si₂N₂O film were determined to be 18 GPa, 6 and 0.05–0.1 nA cm⁻², respectively.     

Molecule counting with alkanethiol and DNA immobilized on gold microplates for extended gate FET

Several molecule counting methods based on electrochemical characterization of alkanethiol and thiolated single-stranded oligonucleotide (HS-ssDNA) immobilized on gold microplates, which were used as extended gates of field effect transistors (FETs), have been investigated in this paper. The surface density of alkanethiol and DNA monolayers on gold microplates were quantitatively evaluated from the reductive desorption charge by using cyclic voltammetry (CV) and fast CV (FCV) methods in strong alkali solution. Typically, the surface density of 6-hydroxy-1-hexanethiol (6-HHT) was evaluated to be 4.639 molecules/nm², and the 28 base-pair dsDNA about 1.226–4.849 molecules/100 nm² on Au microplates after post-treatment with 6-HHT. The behaviors on surface potential and capacitance of different aminoalkanethiols on Au microplates were measured in 0.1 mol/L Na₂SO₄ and 10 mmol/L Tris–HCl (pH = 7.4) solutions, indicating that the surface potential increases and the double-layer capacitance decreases with the length of carbon chain increased for the thiol monolayers, which obey a physics relationship for a capacitor. Comparably, a simple sensing method based on the electronic signals of biochemical reaction events on DNA immobilization and hybridization at the Au surface of the extended gate FET (EGFET) was developed, with which the surface density of the hybridized dsDNA on the gold surface of the EGFET was evaluated to be 1.36 molecules per 100 nm², showing that the EGFET is a promising sensing biochip for DNA molecule counting.     

On the synthesis and dielectric studies of (1 − x)Bi(Mg1 / 2Zr1 / 2)O3 − xPbTiO3 piezoelectric ceramic system

Scandium free piezoelectric ceramics of the composition (1 − x)Bi(Mg_1 / 2Zr_1 / 2)O₃ − xPbTiO₃ (BMZ − xPT) were fabricated by the solid state reaction method. Dielectric and structural properties were measured and phase diagram was constructed from the temperature dependent dielectric and impedance data. The morphotropic phase boundary (MPB) was found to be located in the range 0.55 < x < 0.60 with paraelectric–ferroelectric phase transition temperature, T_C (∼ 280 °C). The ceramics near the MPB showed high room temperature dielectric constant (∼ 1387). The room temperature values of the remanent polarization (P_r) and coercive filed (E_C), were ∼ 29 μC/cm² and ∼ 23 kV/cm, respectively.     

Effect of swift heavy ion beam irradiation on Au–polyaniline composite films

In this paper, two-step electrochemical synthesis method is reported for the fabrication of Au–polyaniline (Au–PANI) composite film. Initially, PANI film was electrochemically synthesized by using chronopotentiometery with optimized process parameters on platinum electrode. The synthesized PANI film acts as working electrode for the decoration of Au particles on the surface of PANI film by using cyclovoltammetry (CV) technique. Later, these films were irradiated under high vacuum (∼5 × 10⁻⁶ Torr) at room temperature with 40 MeV C⁵⁺ ion beam at various fluences ranging from 1 × 10¹¹ to 1 × 10¹³ ions/cm². The Au–PANI composite films were characterized before and after irradiation by using micro-Raman, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The characteristic peaks of the Raman spectrum of Au–PANI composite films were reduced after irradiation. XRD spectra exhibited the decrease in the peak intensity. Moreover, interchain distance, interplanar distance, micro strain, dislocation density and distortion parameters were calculated. The analysis revealed a significant variation in these parameters with an increase in the ion fluence, which is in line with the Raman analysis. SEM shows the formation of clusters with porous structure after irradiation.     

Deposition and DC electrical characterisation of rf magnetron sputtered silicon nitride thin films

Silicon nitride (Si₃N₄) is an important insulator, frequently used in VLSI technology and for encapsulation. Conventionally it is prepared by low pressure and plasma-enhanced chemical vapour deposition, but may also be successfully deposited by RF sputtering. In the present work the sputtering process was characterised, together with some measurements on the high-field DC electrical properties in sandwich samples with Au electrodes. Films were Ar-sputtered using a Si₃N₄ sputtering target at gas pressures up to 2.12 Pa and RF discharge powers of 60–200 W. The deposition rate R was in the range 0.03–0.19 nm s^− 1 and was directly proportional to the discharge power and varied linearly with the pressure. Au electrodes formed sandwich structures with thicknesses of 50 nm–1 μm. Conductivity was essentially ohmic below 300 nm, while for the thicker films space-charge limited conductivity, dominated by an exponential distribution of traps, was observed. A mobility value of μ = 2.89 × 10^− 6 m² V^− 1 s^− 1 was derived from temperature measurements, and further analysis of the J–V data indicated a thermally generated electron concentration of 3.23 × 10¹⁹ m^− 3 and a trap concentration of 1.57 × 10²⁴ m^− 3. It was concluded that this method is suitable for the deposition of thin films, which have similar electrical properties to those prepared by chemical vapour deposition methods.     

The fabrication of SnSe/Ag nanoparticles on TiO2 nanotubes

SnSe and silver (Ag) nanoparticles were sequentially deposited on TiO₂ nanotube (NT) by pulsed electrochemical deposition and polyol chemistry process, respectively. The morphological observation under scanning electron microscope (SEM) showed that the average size of SnSe was about 30 nm and the Ag was about 5 nm. Transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) examination indicated that Ag nanoparticles exhibited a well-defined crystallinity. However, SnSe nanoparticles were amorphous and they turned to crystalline after being annealed at 300 °C in the atmosphere. The photocatalytic behavior of SnSe/Ag-TiO₂ NT was evaluated by UV–vis diffuse reflectance spectra (DRS). The results showed that the deposition of SnSe and Ag nanoparticles increased light absorption intensity in the wavelength range of visible light, which implied that the SnSe/Ag-TiO₂ NT is a promising ternary hybrid material in photocatalysis.     

Electrical properties of lead zirconate titanate thick films prepared by hybrid sol–gel method with multiple infiltration steps

High-quality ferroelectric thick films are required for various piezoelectric applications including high-frequency transducers and microelectromechanical systems. In this work, we report the fabrication of dense crack-free lead zirconate titanate (PZT) thick films on Pt-coated Si substrates using commercial PZT powder dispersed in a sol–gel precursor solution without viscous additives. Preannealed films were infiltrated with the same solution and heat treated at 500 °C. Dielectric and ferroelectric properties of the films are found to be strongly dependent on the number of infiltration steps reaching sufficiently high values: dielectric constant ∼2270 and remanent polarization ∼35 μC cm⁻². Moderate coercive field of 60 kV cm⁻¹ and low dielectric loss ∼0.04 are observed in these films. Effective longitudinal piezoelectric coefficient d₃₃ also depends on the number of infiltrations demonstrating remanent value of ∼80 pm V⁻¹ for eight infiltration steps. The results show the suitability of hybrid sol–gel method for the fabrication of PZT thick films for dielectric and piezoelectric applications.