Optical properties of nanostructured InSe thin films

Thin films of InSe were prepared by thermal evaporation technique. The as-deposited films have nano-scale crystalline nature and the annealing enhanced the degree of crystallinity. The optical properties of nanocrystalline thin films of InSe were studied using spectrophotometric measurements of transmittance, T, and reflectance, R, at normal incidence of light in the wavelength range 200–2500 nm. The optical constants (refractive index, n, and absorption index, k) were calculated using a computer program based on Murmann's exact equations. The calculated optical constants are independent of the film thickness. The optical dispersion parameters have been analysed by single oscillator model. The type of transition in InSe films is indirect allowed with a value of energy gap equals to 1.10 eV, which increased to 1.23 eV upon annealing.     

Mechanical and magnetic properties of nanostructured CoNiP films

The electroplating technique is especially interesting due to its low cost, high throughput and high quality of deposit. Magnetic thin films are extensively used in various electronic devices including high-density recording media and micro electromechanical (MEMS) devices. Due to these potential applications, deposition of magnetic film draws special attention and it needs a cost-effective process. Electro-deposition being cost-effective, in the present work cobalt-based magnetic films were deposited electrochemically and deposition characteristics were studied. Effect of concentration of organic additives such as urea and thiourea in the presence of sodium hypophosphite was studied. Surface characterisation was carried out using X-ray diffractometer (XRD) and scanning electron microscope (SEM). Elemental compositions of the films were studied using atomic absorption spectrometer (AAS) and showed phosphorous content was less than 1%. Samples were subjected to vibrating sample magnetometer (VSM) and studies showed that organic additive has altered magnetic properties of these films. The reason for change in magnetic properties and structural characteristics because of the additives were discussed. Mechanical properties such as residual stress, hardness and adhesion of the films were also examined and reported.     

Structure and physical-mechanical properties of nanostructured thin films

The structure and mechanical properties of nanostructured thin films based on carbides, nitrides, and borides of transition metals are described. The mechanisms of localized deformation of the films during indentation are compared. It is shown that the tendency of a material to form shear bands during deformation can be predicted using the parameter H³/E², which describes the resistance of the material to plastic deformation. The columnar structure of the films is found to play an important role during deformation, which proceeds via slipping of columnar structural elements along the direction of an applied load.     

Room temperature magnetic properties of ZnO nanostructured films

The ZnO nanorod array films have been epitaxially deposited on indium tin oxide (ITO) glass along 〈0001〉 direction. It is found that the film is grown in a two-step process including nanoparticle film nucleation and oriented rod growth. The as-prepared ZnO film shows a dominant diamagnetic signal and a weak ferromagnetic signal at room temperature. The room temperature ferromagnetism deteriorated by annealing in air or N₂. The photoluminescent spectra revealed that the intensity of ZnO defect band decreases after annealing. Thus, the decreased ferromagnetism is likely to have resulted from the decrease of oxygen vacancies and defects in the as-prepared film. Moreover, ZnO deposited at various times showed that defects located at or near the interface between the substrate and the film play a major role in ferromagnetism. It suggests that ferromagnetism can be tuned by changing the defects in ZnO.     

Photoelectric properties of CdS films with nanostructured surfaces

The results from studying the photoelectric properties of CdS films with nanostructured surfaces and synthesized via pyrolysis of thiourea coordination compounds are presented. It is shown that the photocurrent limiting effect is observed in the studied structures at higher intensities of the excitation light. This effect, which is attributable to the optical smoothing of nonuniform barrier relief, could find practical application in optoelectronics.     

Growth kinetics and properties of nanostructured hafnium diboride films

The composition, structure, substructure, and physicomechanical properties of hafnium diboride films deposited by nonreactive rf magnetron sputtering are studied by X-ray diffraction (including photographic recording) and electron microscopy. The results obtained are analyzed, and the film growth kinetics is revealed.     

Spectral and luminescence properties of gadolinium gallium garnet epitaxial films doped with terbium

Gadolinium gallium garnet single-crystal films containing terbium are grown through liquid-phase epitaxy from a supercooled solution melt in the PbO-B₂O₃ system. The optical absorption spectra in the wavelength range 0.2–10.0 μm and the luminescence spectra excited by synchrotron radiation with energies in the range 3.5–30.0 eV are investigated at temperatures of 10 and 300 K. It is revealed that the optical absorption spectra contain an absorption band with the maximum at a wavelength λ ≈0.260 μm, which corresponds to the spin-allowed electric dipole transition between the electronic configurations 4f ⁸(⁷ F ₆) → 4f ⁷(⁸ S)5d of the Tb³⁺ ions. The narrow low-intensity absorption bands attributed to the 4f → 4f transitions from the ⁷ F ₆ ground level to the ⁷ F _0–5 multiplet levels of the Tb³⁺ ions are observed in the wavelength range 1.7–10.0 μm. In the luminescence spectra measured at a temperature of 10 K, the highest intensity is observed for a band with the maximum at a wavelength λ ≈ 0.544 μm, which is associated with the ⁵ D ₄ → ⁷ F ₅ radiative transition in the Tb³⁺ ion.     

Composition, structure, and properties of tantalum boride nanostructured films

The structure, as well as the phase and elemental compositions, of tantalum diboride-based nanostructured films deposited by rf magnetron sputtering under various conditions are studied by X-ray diffraction, electron microscopy, and secondary ion mass spectrometry. The physicomechanical properties of the films (hardness, as well as elastic and plastic properties) are determined. The maximum hardness and elastic modulus of the synthesized films are 42 are 240 GPa, respectively. The grain size is found to influence the physicomechanical and electrical properties of the films.     

Magnetic properties of terbium dihydrides

Magnetization measurements of terbium dihydride samples with different hydrogen concentration, TbH_1.92, TbH_1.99, TbH_2.03 and TbH_2.09, in the temperature range from 1.8 to 300 K and at an applied field of 1 kOe are reported. Two first-order antiferromagnetic transitions have been registered in the narrow temperature range between 15–18 K for all hydride compositions. Isothermal magnetization ($\sigma {\left(H\right)}_{T=\mathrm{const}}$) measurements at several temperatures in the vicinity of magnetic transitions have been carried out and used for the magnetic-entropy change, $\Delta S_{\sigma }$, calculations. The magnetic-entropy changes have negative values, and in an applied magnetic field of 5 T they reach 2.5 J/kg K, which is only about 26% of the $\Delta S_{\sigma }\left(H\right)$ value expected from thermal measurements. A much larger magnetic field must be applied for terbium hydrides to be used as refrigerant materials for low-temperature needs.     

Magneto-optical properties of terbium glass

Dispersion of the Verdet Constant of Tb-glass is investigated.The cause of thisdispersion is dicussed by a comparison with the dispersion of refractive index.Relationship be-tween the Verdet constant and Tb~(3 ) concentration is summaried and can be used to estimatethe Verdet constant of Tb~(3 )-materials.     

Effect of thickness on the optoelectronic properties of electrodeposited nanostructured SnS films

The present study focuses on the effect of film thickness on the physical properties of tin mono-sulfide (SnS) nanostructures deposited through an electrodeposition technique. The SnS films were characterized using X-ray diffraction (XRD) analysis, which confirmed the formation of polycrystalline orthorhombic SnS thin films. The crystallite size and lattice parameters were estimated from the XRD patterns. The effect of the deposition voltage on the surface morphology of the deposited films was evaluated by field emission electron microscopy (FESEM). The FESEM images revealed that the nanostructures possess plate-like and bulky pyramid morphologies. Also, optical plots of the thin films were considered, which determined the direct band gap energies of the samples as 1.42–1.50 eV. Finally, Mott–Schottky measurements indicated that the samples have p-type conductivity and the carrier concentrations of the SnS films improve with the increase of their thicknesses.     

Structural and optical properties of electrohydrodynamically atomized TiO2 nanostructured thin films

In this paper, we report an alternate technique for the deposition of nanostructured TiO₂ thin films using the electrohydrodynamic atomization (EHDA) technique using polyvinylpyrrolidone (PVP) as a stabilizer. The required parameters for achieving uniform TiO₂ films using EHDA are also discussed in detail. X-ray diffraction results confirm that the TiO₂ films were oriented in the anatase phase. Scanning electron microscope studies revealed the uniform deposition of the TiO₂. The purity of the films is characterized by using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), confirming the presence of Ti–O bonding in the films without any organic residue. The optical properties of the TiO₂ films were measured by UV-visible spectroscopy, which shows that the transparency of the films is nearly 85% in the visible region. The current–voltage (I–V) curve of the TiO₂ thin films shows a nearly linear behavior with 45 mΩ?cm of electrical resistivity. These results suggest that TiO₂ thin films deposited via the EHDA method possess promising applications in optoelectronic devices.     

Dielectric and relaxation properties of thermally evaporated nanostructured bismuth sulfide thin films

Nanostructured bismuth sulfide thin films were prepared onto glass substrates with particle size of 21 nm by thermal evaporation using readily prepared bismuth sulfide nanocrystallite powder. The X-ray diffraction pattern revealed that bismuth sulfide thin films exhibit orthorhombic structure. The existence of quantum confinement effect was confirmed from the observed band gap energy of 1.86 eV. AC and DC electrical conductivity of Al/BiSnc/Al structures was investigated in the frequency range 0.5-100 kHz at different temperatures (303-463 K) under vacuum. The AC conductivity (σ_ac) is found to be proportional to angular frequency (ω^s). The obtained experimental result of the AC conductivity showed that the correlated barrier hopping model is the appropriate mechanism for the electron transport in the nanostructured bismuth sulfide thin films. DC conduction mechanism in these films was studied and possible conduction mechanism in the bismuth sulfide thin films was discussed.     

Determination of optical properties in nanostructured thin films using the Swanepoel method

We present the methodological framework of the Swanepoel method for the spectrophotometric determination of optical properties in thin films using transmittance data. As an illustrative case study, we determined the refractive index, thickness, absorption index, and extinction coefficient of a nanostructured 3 mol% Y₂O₃-doped ZrO₂ (yttria stabilized zirconia, 3YSZ) thin film prepared by the sol-gel method and deposited by dipping onto a soda-lime glass substrate. In addition, using the absorption index obtained with the Swanepoel method, we calculated the optical band gap of the film. The refractive index was found to increase, then decrease, and finally stabilize with increasing wavelength of the radiation, while the absorption index and extinction coefficient decreased monotonically to zero. These trends are explained in terms of the location of the absorption bands. We also deduced that this 3YSZ thin film has a direct optical band gap of 4.6 eV. All these results compared well with those given in the literature for similar thin films. This suggests that the Swanepoel method has an important role to play in the optical characterization of ceramic thin films.     

Substrate-dependent structure, microstructure, composition and properties of nanostructured TiN films

Titanium nitride films of a thickness of ∼1.5 μm were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate.     

Multiferroic properties in terbium orthoferrite

Multiferroic properties in a polycrystalline terbium orthoferrite are investigated. Different thermomagnetic behaviors are observed in different magnetic fields, which is attributed to the suppression of the low temperature magnetic phase by an external magnetic field. Further studies reveal that the ferroelectricity originates from the spin configuration below3.5 K. In addition, the magnetic field control of electric polarization and dielectric constant is observed, which suggests a magnetoelectric effect in TbFeO3. The origin of ferroelectricity in this rare-earth orthoferrite is discussed.     

Effect of nanostructured AlN coatings on the oxidation-resistant properties of optical diamond films

Diamond film is an ultra-durable optical material with high thermal conductivity and good transmission in near-infrared and far-IR (8-14 μm) wavebands. CVD diamond is subjected to oxidation at temperature higher than 780 °C bared in air for 3 min, while it can be protected from oxidation for extended exposure in air at temperature up to 900 °C by a coating of aluminum nitride. Highly oriented AlN coatings were prepared for infrared windows on diamond films by reactive sputtering method and the average surface roughness (R_a) of the coatings was about 10 nm. The deposited films were characterized by X-ray diffraction (XRD) and atom force microscope (AFM). XRD confirmed the preferential orientation nature and AFM showed nanostructures. Optical properties of diamond films coated AlN thin film was investigated using infrared spectrum (IR) compared with that for as-grown diamond films.     

Physical and chemical properties of nanostructured CoO-AlOx granular films

A series of nano CoO-AlO_x granular films were prepared by Ar-O₂ reactive rf sputtering and their resistive and magnetoresistive properties were measured for studying the spin-dependent properties. Transmission electron microscopy and X-ray photoelectron spectroscopy are also utilized to investigate the structures and chemical states of these samples. Based on our results, the particles of CoO with radius around 2 nm could be magnetic at room temperature and provide a large tunneling magnetoreststance of −6% through the AlO_x barrier.     

Structure and optical properties of nanostructured zinc oxide films with different growth temperatures

ZnO films were prepared by pulsed laser deposition (PLD) on glass substrate with temperature ranging from room temperature (RT) to 500 °C. All the films formed the hexagonal wurtzite structure and showed the c-axis (0 0 2) preferred orientation. The films deposited at 200 °C showed the narrowest full width at half maximum of both X-ray diffraction (XRD) and rocking curve, largest height grain size, smallest macrostress and least point defects. Meanwhile, it was found that the films deposited at 350 °C displayed the most intense diffraction peak in XRD and a strong UV emission while it showed the most intense defect-related green emission, fastest growth rate and larger macrostress. In addition, the cross section images showed all films grew with a columnar form along (0 0 2) orientation.     

Influence of polyethylene glycol-300 addition on nanostructured lead sulfide thin films properties

The concentration of polyethylene glycol-300 was found to play a crucial role in the formation of nanoparticles in PbS-chemical bath deposition process. We report here an endeavor to set up a relation between the variation of lead sulfide (PbS) nanocrystalline thin film properties, grown by (CBD) process at room temperature on corning glass and Si(100) substrates, with amount fluctuations of polyethylene glycol-300 in the solution. The transmittance of the films, for a fixed reaction time, increased up to ∼ 80% with the increase of % polyethylene glycol-300 in the solution, indicating the formation of very thin films due to the decrease of reaction rate with the increase of the concentration of polyethylene glycol-300. The optical band gaps were found to strongly rely on the composition of the bath deposition and increase with the increase of the polyethylene glycol-300 amount in the solution. Particle sizes between 2.8 and 8.7 nm were obtained by varying the % of polyethylene glycol-300 from 0.2 to 1.5. The concentration of polyethylene glycol-300 not only affects the reaction rate but also the morphology of the obtained films. PbS nanoparticles were found to be oriented preferentially along the < 200> plane. The absorption shifts towards short wavelength indicating a blue-shifting as a consequence of quantum confinement.