AC plasma induced modifications in β-In2S3 thin films prepared by spray pyrolysis

β-In₂S₃ thin films, deposited by spray pyrolysis, were treated in N₂ and air plasmas at 240 and 400 Pa. X-ray diffraction, SEM, and EDS analysis, and optical and electrical studies have been used to characterize the as-prepared and plasma treated thin films. The post-deposition plasma treatments affect the morphology and the optoelectronic properties of the In₂S₃ thin films. The In₂S₃ thin films treated with N₂ plasma at 240 Pa showed an optical band gap, E_g, of 2.16 eV and an electrical conductivity of 2 × 10^− 2 (Ω cm)^− 1.     

Field emission characteristics of carbon nanofibers grown on copper micro-tips at low temperature

Carbon nanofibers (CNFs) were grown on copper micro-tips formed by electroplating. The nickel layer electroplated over the copper micro-tips was used as a catalyst. The CNFs were synthesized by using plasma-enhanced chemical vapor deposition (PECVD) of C₂H₂ and NH₃ at 480 °C. The copper micro-tips were formed by high current pulse electroplating, which played a significant role in characterizing our CNFs. The CNFs grown on the copper micro-tips showed outstanding field emission performance and stability, whose turn-on field, defined as one at the current density of 10 μA/cm², was 1.30 V/μm and the maximum current density reached 5.39 mA/cm² at an electric field of 4.9 V/μm.     

Growth and spectral properties of Er:NaGd(WO4)2 crystal

A high optical quality Er³⁺-doped NaGd(WO₄)₂ single crystal with dimensions of ∅18 × 50 mm³ has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er³⁺ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm.     

Study of annealing-induced changes in CdS thin films using X-ray diffraction and Raman spectroscopy

We have investigated as grown and annealed (300 °C, 400 °C and 500 °C) thin films of CdS grown on GaAs (001) by chemical bath deposition. X-ray diffraction (XRD) shows that the as grown CdS film is polycrystalline and predominantly cubic. A residual compressive stress of the order of 1.45% in the as grown film relaxes on annealing the film at 300 °C. Furthermore, CdS film undergoes a structural phase transition from the metastable cubic phase to the stable hexagonal phase, when, annealed at 500 °C. This is accompanied by significant improvement in crystalline quality of the film. Line shape analysis of the asymmetry of the longitudinal optical phonon shows a disorder-activated mode, which correlates well with the crystalline quality estimated from XRD and photoluminescence measurements. The additional features observed in the Raman spectra ∼ 254 cm^− 1 and 309 cm^− 1 are investigated using temperature dependent Raman spectroscopy and identified as superposition of transverse optical: E₁ (TO) and E₂ phonons at q = 0 and combination mode (two zone-edge E₂ phonons) respectively.     

Growth and characterization of l-phenylalanine nitric acid, a new organic nonlinear optical material

A new organic nonlinear optical material L-phenylalanine nitric acid [2C₉H₁₁NO₂.H⁺. NO₃⁻] (LPN), was synthesized in mixed solvent of deionised water and methanol and single crystals of LPN was grown by slow evaporation method. Transparent crystals upto 2.9 × 0.3 × 0.05 cm³ were obtained. The grown crystals have been subjected to powder X-ray diffraction studies to identify the crystalline nature. Single crystal X-ray diffractometer was utilized to measure unit cell parameters and to confirm the crystal structure. The modes of vibration of different molecular groups present in LPN were identified by FTIR spectral analysis. Transmission spectra reveals that the crystal has low UV cutoff of 295 nm and has a good transmittance in the entire visible region enabling its use in optical applications. Thermal properties of the crystals have been investigated using thermogravimetric (TG) and differential thermal analyses (DTA), which indicate that the material does not decompose before melting. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064 nm.     

Effects of preparation temperature on optical and electrical characteristics of (111)-oriented Cu2O films electrodeposited on (111)-Au film

The (111)-oriented Cu₂O films with a 2.0-eV-bandgap energy were prepared by electrodeposition on a (111)-oriented Au/Si wafer substrate at the preparation temperatures from 298 to 323 K, and the structural, optical, and electrical characterizations were carried out by X-ray absorption spectra measurements, X-ray diffraction, scanning electron microscopic observations, optical absorption spectra, photoluminescence spectra measurements, and Hall effect measurements. The photoluminescence spectra and electrical characteristics changed depending on the temperature. The 1.52-eV-visible light that originated from the copper vacancies weakened with a decrease in the preparation temperature, and the emission of the slight 2.0-eV-visible light due to the recombination of excitons was observed for the Cu₂O film prepared at 298 K. The hole density related to the copper vacancies decreased and the mobility increased with a decrease in the preparation temperature, and the maximum mobility of 21 cm² V⁻¹ s⁻¹ could be obtained at 303 K.     

Crystal growth and scintillation characteristics of the Nd doped LiLuF4 single crystals

Sixty millimeter diameter single crystal of Nd³⁺ doped LiLuF₄ was successfully grown by the Czochralski technique. No remarkable absorption due to unfavorable impurities was observed from optical absorption measurements in the vacuum ultra-violet spectral region. The high crystallinity and homogeneous luminescence characteristics were found from X-ray rocking curve and cathode-ray luminescence respectively. X-ray excited luminescence spectrum was measured and the significant 4f²5d-4f³ luminescence at 182 nm was observed in the grown crystal. The pulse height spectrum was taken upon γ-ray irradiation. As a result, the grown crystals demonstrated sufficient response to the γ-ray showing the light yield of 420 ± 30 photons/MeV. The decay curve under α-ray irradiation was also investigated and described by two component decay kinetics which consists of the decay constants of 34 and 450 ns.     

Transparent p-AgCoO2/n-ZnO diode heterojunction fabricated by pulsed laser deposition

Transparent diode heterojunction on ITO coated glass substrates was fabricated using p-type AgCoO₂ and n-type ZnO films by pulsed laser deposition (PLD). The PLD of AgCoO₂ thin films was carried out using the pelletized sintered target of AgCoO₂ powder, which was synthesized in-house by the hydrothermal process. The band gap of these thin films was found to be ∼ 3.89 eV and they had transmission of ∼ 55% in the visible spectral region. Although Hall measurements could only indicate mixed carrier type conduction but thermoelectric power measurements of Seebeck coefficient confirmed the p-type conductivity of the grown AgCoO₂ films. The PLD grown ZnO films showed a band gap of ∼ 3.28 eV, an average optical transmission of ∼ 85% and n-type carrier density of ∼ 4.6 × 10¹⁹ cm^− 3. The junction between p-AgCoO₂ and n-ZnO was found to be rectifying. The ratio of forward current to the reverse current was about 7 at 1.5 V. The diode ideality factor was much greater than 2.     

Melt growth and characterization of Mg2Si bulk crystals

We have grown Mg₂Si bulk crystals by the vertical Bridgman method using a high-purity Mg (6N-up) source. The grown crystals were single-phase Mg₂Si and had well-developed grains (1-5 mm³). Laue observations and SEM-EDX observations confirmed that crystalline quality in the grains was single crystal with stoichiometric composition. Electron concentration of the single crystalline specimens grown from 6N-up-Mg was 4.0 × 10¹⁵ cm^− 3 at room temperature (RT). This value is more than one order of magnitude lower than that of specimens grown from 4N-Mg [(5-7) × 10¹⁶ cm^− 3]. The Hall mobility of 14,500 cm²/Vs was observed at 45 K in the crystals grown from 6N-up-Mg. We also found that Al impurity plays an important role in the crystals grown from a low-purity Mg source. From the optical absorption measurement, we estimated that the indirect energy gap was about 0.66 eV at 300 K and about 0.74 eV at 4 K.     

Preparation and electrochemical performance of manganese oxide/carbon nanotubes composite as a cathode for rechargeable lithium battery with high power density

Manganese oxide/carbon nanotubes (MO/CNTs) composite was prepared by hydrothermally reducing KMnO₄ with CNTs, where the used CNTs are of dual role, i.e., they serve as reductant during reaction and the remaining CNTs act as conducting agent in the composite. This composite was characterized by X-ray diffraction and scanning electron microscopy techniques. In addition, the electrochemical performances of the composite were investigated, which suggested an excellent rate-capability of this material; e.g., it delivered a high discharge capacity as 131 mAh g^− 1 at a high current density of 4 A g^− 1 (20 C), and high capacity at low discharge current density, e.g., about 209 mAh g^− 1 at 0.2 C rate. Therefore, such a MO/CNTs composite is promising in high power application of lithium battery and electrochemical capacitor.     

Study of optical and structural properties of Cu2ZnSnS4 thin films

Cu₂ZnSnS₄ is a promising semiconductor to be used as absorber in thin film solar cells. In this work, we investigated optical and structural properties of Cu₂ZnSnS₄ thin films grown by sulphurization of metallic precursors deposited on soda lime glass substrates. The crystalline phases were studied by X-ray diffraction measurements showing the presence of only the Cu₂ZnSnS₄ phase. The studied films were copper poor and zinc rich as shown by inductively coupled plasma mass spectroscopy. Scanning electron microscopy revealed a good crystallinity and compactness. An absorption coefficient varying between 3 and 4 × 10⁴cm^− 1 was measured in the energy range between 1.75 and 3.5 eV. The band gap energy was estimated in 1.51 eV. Photoluminescence spectroscopy showed an asymmetric broad band emission. The dependence of this emission on the excitation power and temperature was investigated and compared to the predictions of the donor-acceptor-type transitions and radiative recombinations in the model of potential fluctuations. Experimental evidence was found to ascribe the observed emission to radiative transitions involving tail states created by potential fluctuations.     

Thin film passivation of organic light emitting diodes by inductively coupled plasma chemical vapor deposition

The characteristics of an SiN_x passivation layer grown by a specially designed inductively coupled plasma chemical vapor deposition (ICP-CVD) system with straight antennas for the top-emitting organic light emitting diodes (TOLEDs) are investigated. Using a high-density plasma on the order of ∼ 10¹¹ electrons/cm³ formed by nine straight antennas connected in parallel, a high-density SiN_x passivation layer was deposited on a transparent Mg-Ag cathode at a substrate temperature of 40 °C. Even at a low substrate temperature, single SiN_x passivation layer prepared by ICP-CVD showed a low water vapor transmission rate of 5 × 10^− 2 g/m²/day and a transparency of ∼ 85% respectively. In addition, current-voltage-luminescence results of the TOLED passivated by the SiN_x layer indicated that the electrical and optical properties of the TOLED were not affected by the high-density plasma during the SiN_x deposition process.     

Effect of nitrogen ion implantation on the sprayed ZnSe thin films

The ZnSe thin films were deposited onto glass substrates by the spray pyrolysis method using mixed aqueous solutions of ZnCl₂ and SeO₂ at the substrate temperature 430 °C. These films were implanted with 130 keV nitrogen ions to various doses from 1 × 10¹⁶ to 1 × 10¹⁷ ions/cm². We have analysed the properties of the nitrogen ion-implanted ZnSe thin films using X-ray diffraction and optical transmittance spectra. The values of optical bandgap have been determined from the absorption spectra. The bandgap of the N⁺ doped films decreased from 2.70 eV for undoped film to 2.60 eV for maximum doping probably due to band-tailing, whereas the absorption coefficient values increased with the increase of the implantation dose.     

Optical and structural properties of CuSbS2 thin films grown by thermal evaporation method

Structural, optical and electrical properties of CuSbS₂ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuSbS₂ thin films were carried out at substrate temperatures in the temperature range 100-200 °C. The structure and composition were characterized by XRD, SEM and EDX. X-ray diffraction revealed that the films are (111) oriented upon substrate temperature 170 °C and amorphous for the substrate temperatures below 170 °C. No secondary phases are observed for all the films. The optical absorption coefficients and band gaps of the films were estimated by optical transmission and reflection measurements at room temperature. Strong absorption coefficients in the range 10⁵-10⁶ cm^− 1 at 500 nm were found. The direct gaps Eg lie between 0.91-1.89 eV range. It is observed that there is a decrease in optical band gap Eg with increasing the substrate temperature. Resistivity of 0.03-0.96 Ω cm, in dependence on substrate temperature was characterized. The all unheated films exhibit p-type conductivity. The characteristics reported here also offer perspective for CuSbS₂ as an absorber material in solar cells applications.     

Electrical, optical, and structural properties of InZnSnO electrode films grown by unbalanced radio frequency magnetron sputtering

We have investigated the electrical, optical, structural, and annealing properties of indium zinc tin oxide (IZTO) films prepared by an unbalanced radio frequency (RF) magnetron sputtering at room temperature, in a pure Ar ambient environment. It was found that the electrical and optical properties of unbalanced RF sputter grown IZTO films at room temperature were influenced by RF power and working pressure. At optimized growth condition, we could obtain the IZTO film with the low resistivity of 3.77 × 10^− 4 Ω cm, high transparency of ~ 87% and figure of merit value of 21.2 × 10^− 3Ω^− 1, without the post annealing process, even though it was completely an amorphous structure due to low substrate temperature. In addition, the field emission scanning electron microscope analysis results showed that all IZTO films are amorphous structures with very smooth surfaces regardless of the RF power and working pressure. However, the rapid thermal annealing process above the temperature of 400 °C lead to an abrupt increase in resistivity and sheet resistance due to the transition of film structure from amorphous to crystalline, which was confirmed by X-ray diffraction examination.     

Field emission from oriented tin oxide rods

Tin oxide (SnO₂) films were grown on silicon substrates by a wet chemical route. It was found from scanning electron microscopy investigations that oriented SnO₂ rods normal to the substrates were obtained. Field emission studies were carried out in diode configuration in an all metal ultra high vacuum chamber at a base pressure ∼ 1.33 × 10^− 8 mbar. The ‘onset’ field required to draw 0.1 μA/cm² current density from the emitter cathode was found to be ∼ 3.4 V/μm for SnO₂ rods. The field emission current and applied field follows the Folwer-Nordheim relationship in low field regime. The observed results indicate that the field emission characteristics of chemically grown SnO₂ structures are comparable to the vapor grown nanostructures.     

Synthesis, growth, and characterization of nonlinear optical material l-arginine iodate crystal

Single crystals of nonlinear optical l-arginine iodate (l-Arg·2HIO₃) (C₆H₁₄N₄O₂·2HIO₃), were successfully grown for the first time by the temperature-lowering method and also by the slow evaporation method at a constant temperature (30 °C) from its aqueous solution at pH value of 6. Crystals were of average dimensions 3 × 2.5 × 1.0 cm³ by optimizing the growth parameters. Initially, solubility studies were carried out for four different solvents such as water, water-methanol, water-ethanol, and water-acetone. Among the four solvents, the solubility of l-Arg·2HIO₃ was found to be the highest in water and hence crystallization of l-Arg·2HIO₃ was carried out from aqueous solution. Morphology studies reveal that the crystals grow with reasonable growth rate along the [100], [001], [110¯] and [011] direction. As-grown crystals were characterized by density measurement, X-ray powder diffraction studies, infrared spectrophotometer, UV-Vis spectrometer, laser induced damage threshold studies and nonlinear optical study.     

Fabrication of transparent conducting amorphous Zn-Sn-In-O thin films by direct current magnetron sputtering

Amorphous ZnO-SnO₂-In₂O₃ films were grown by direct current magnetron sputtering from vacuum hot pressed ceramic oxide targets of Zn:In:Sn cation ratios 1:2:1 and 1:2:1.5 onto glass substrates. X-ray diffraction analysis showed that the microstructure remained amorphous during annealing at 200 °C for up to 5 hours. By monitoring the electrical resistivity, oxygen content and substrate temperature were optimized during deposition. The optimal films were characterized by Hall Effect, work function and optical spectroscopy measurements. Films of 1:2:1 composition showed the lowest resistivity (7.6 × 10^− 4 Ω-cm), when deposited onto substrates preheated to 300 °C. Transmissivity of all films exceeded 80% in the visible spectral region. The energy gap was 3.52-3.74 eV, and the work function ranged 5.08-5.22 eV, suitable for cathode applications in organic light emitting diodes. Overall, the film characteristics were comparable or superior to those of amorphous tin-doped indium oxide and zinc-doped indium oxide films and may serve as viable, lower-cost alternatives.     

Enhanced conductivity of pulsed laser deposited n-InGaZn6O9 films and its rectifying characteristics with p-SiC

Wide band gap InGaZn₆O₉ films of thickness ~ 350 nm were deposited on sapphire (0001) at room temperature by using the pulsed laser deposition technique. The transparent films showed the optical transmission of > 80% with the room temperature Hall mobility of ~ 10 cm²/V s and conductivity of 4 × 10² S/cm at a carrier density > 10²⁰ cm^− 3. The electrical properties as a function of deposition temperatures revealed that the conductivity and mobility almost retained up to the deposition temperature of 200 °C. The films annealed in different atmospheres suggested oxygen vacancy plays an important role in determining the electrical conductivity of the compound. Room temperature grown heterostructure of n-InGaZn₆O₉/p-SiC showed a good rectifying behavior with a leakage current density of less than 10^− 9 A/cm², current rectifying ratio of 10⁵ with a forward turn on voltage ~ 3 V, and a breakdown voltage greater than 32 V.     

Structure evolution on annealing of copper-doped carbon film

Thin copper-doped (8 at.% Cu) carbon film was deposited by direct current magnetron sputtering of composite graphite/copper target in argon plasma. The evolution of film structure on annealing at 600 °C in a vacuum has been studied by transmission electron microscopy and electron diffraction. The as-deposited film was amorphous with copper atoms uniformly distributed over the film volume. Annealing resulted in precipitation of copper particles within carbon film followed by the decrease in the density of copper particles and increase in particle average size with annealing time due to diffusion coalescence within the ensemble of copper particles. The coalescence occurred by the mixed mechanism of bulk and surface diffusion of copper atoms within carbon film that contained a large number of structural defects. As a result, the mean radius of copper particles in ensemble changed as R¯⁵ ∼ t.