Narrow Results

The effect of substrate temperature on the structural, optical and morphological properties of ZnO thin films has been investigated. ZnO thin films were deposited on quartz substrate for various temperatures ranging from room temperature to 250°C by pulsed laser deposition (PLD) technique. Nd:YAG laser (532 nm, 100 mJ, 6 ns, 10 Hz) with corresponding fluence of 6 J/cm² was employed for the ablation of ZnO target. Characterization of the thin films was carried out using X-ray diffraction (XRD), high resolution UV-visible spectrometer, atomic force microscope (AFM) and scanning electron microscope (SEM). From XRD analysis, the amorphous behaviors of films at room temperature and crystalline behavior along the preferred orientation of (002) is exhibited for higher substrate temperature. The transmittances of grown films increase with the increasing substrate temperature. The evaluated values of bandgap energies increase with increasing substrate temperature up to the range of 150°C and then monotonically decrease with the further increase in temperature. AFM and SEM analysis illustrates that the density and height of grains for deposited films increase significantly with increasing substrate temperature.

The effect of annealing temperature on sol–gel deposited ZnO thin films have been studied. The average crystallite size determined from XRD shows that the deposited films are nanocrystalline. FTIR confirms deposition of ZnO thin films. The transmittance of annealed ZnO thin films is greater than 80% in visible region with bandgap ranging from 3.25–3.19 eV. The films annealed at 450°C temperature shows lower resistivity value of 527.241 Ωm. The deposited nanocrystalline films are suitable for biosensing applications due to its higher surface area.

This work presents the influence of changing Ar:N₂ gas ratio on the growth and properties of InAlN films. InAlN films were deposited on $p$-type Si(111) substrates by using magnetron co-sputtering method in 6:12, 10:10, 12:8 and 12:6 Ar:N₂ mixtures at 300${}^{\circ }$C. The surface, structural, electrical and optical properties of the deposited films were evaluated at different Ar:N₂ ratios. The grain size and film thickness were increased by increasing the Ar flow with respect to N₂. Structural characterization by X-ray diffraction (XRD) revealed an improvement in the crystalline quality of the $c$-axis-oriented InAlN film by adjusting the Ar:N₂ ratio to 12:8, however no diffraction peak corresponding to InAlN was detected at 6:12 Ar:N₂ mixture. The surface roughness of InAlN film exhibited an increasing trend whereas the electrical resistivity of the film was decreased by increasing the Ar:N₂ ratio. The bandgap of InAlN film was calculated from the optical reflectance spectra and it was found to change by changing the Ar:N₂ gas ratio. The analysis of results from this work shows that the InAlN film with improved physical properties can be obtained through reactive magnetron co-sputtering method by adjusting the Ar:N₂mixture to 12:8.

In the present paper, the surface modification of low-density polyethylene (LDPE) polymer is done by plasma-etching to tune its surface structure, wettability and optical behavior to make it useful for technical applications. For this purpose, two gasses (N${}_2)$ and (O${}_2)$ are used as the discharge precursors in a home-built plasma reactor. The plasma-treated LDPE surface etch-rate (control other surface properties) is high at the beginning and slows down as the treatment time increases due to surface restructuring. The etched surfaces are analyzed by scanning electron microscopy (SEM), which indicate greater surface changes due to O₂ plasma compared to that of N₂. Also, the surface hardness is slightly low at the first treatment time and increases rapidly at higher exposure durations. Besides, the friction coefficient is significantly changed by plasma treatment, suggesting the formation of cohesive surface skin. The obtained X-ray diffraction (XRD) patterns show that the plasma-treated LDPE samples suffer disordering and structural changes which increase with raising the treatment duration. Surface restructuring is attributed to the combined effects of active species (from plasma) bombardments and surface oxidation. Also, the surface chemistry changes are evaluated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy which reveals chain scission after N₂ plasma treatment. Whereas, the O₂ plasma-treated samples suffer surface oxidation and formation of polar groups which offer some surface oxidation coatings. Furthermore, the surface wettability has been determined by the sessile drop method and shows enhancement upon plasma treatment due to the combined influence of surface chemistry and morphology. Also, the surface free energy (SFE) and adhesion are found to increase with the plasma exposure time due to surface activation. The optical behavior of LDPE is studied using ultraviolet–visible (UV–Vis) spectrophotometer which indicates that the optical bandgap performance depends on the amorphous or crystalline nature of the polymer. Also, the conjugated carbon atoms were examined and correlated to the reduced bandgap. In conclusion, the studied home-built glow discharge plasma reactor could be utilized efficiently to tune polymer surface properties to be used in high technology applications.

It is critical to reduce the bandgap of a ferroelectric photovoltaic (FE-PV) material in order to get the optimal effect of FE-PV. The interface effect of PbO/PbTiO₃ (P/PT) is used in this work to lower the bandgap of PbTiO₃ via the addition of PbO. The bandgaps of (P/PT)_down and ${\text{(P/PT)}}_{\mathrm{\text{up}}1}$, which are two types of polarization structures, fall from 2.63 eV of pure PbTiO₃ to 2.07 eV and 2.08 eV, respectively. Densities of states are calculated for pure PbO, pure PbTiO₃, and P/PT to determine the reason of the bandgap drop. The results indicate that the PbO component of P/PT is critical for both the conduction band minimum (CBM) and valence band maximum (VBM) states. Calculations of the absorption coefficient indicate that P/PT absorbs more light over a wider range of wavelengths in the visible-light region than PbTiO₃.

Nanoparticles of Zn_(1-x)Fe_xS with x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.3 were synthesized using the chemical bath deposition method, using tri-sodium citrate as a complexion agent. These nanoparticles were characterized using XRD, SEM, optical absorbance and photoluminescence. SEM micrographs of the films revealed the combination of Zn_(1-x)Fe_xS nanoparticles with an average particle size D ~ 60.3 to 19.3 nm ± 0.01 nm for x = 0.0 to 0.3. X-ray diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. UV-visible spectrometer measurement showed high absorbance for Fe concentration x ≥ 0.15 in the wavelength range 325–800 nm. However, for x ≤ 0.1, the absorbance of the films decreased with further increase of Fe concentration. From the absorbance data, the direct bandgap values have been calculated to be in the range E_g = 3.5 to 2.23 eV for x = 0.0 to 0.3. The bandgap decreased with the increase of Fe concentration in the films. The photoluminescence spectra of the films showed two emission peaks, the first in the low wavelengths due to band-to-band transition, and the second in the high wavelengths due to the transitions probabilities and to the concentration of Fe ions. Due to the quenching effect, the intensity of PL spectra decreased on further increase of Fe doping.

Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by plasma immersion ion implantation and deposition (PIII-D) at room temperature (RT). During the process of deposition, N₂ flow was changed from 0 to 10 sccm. Lifshitz–van der Waals/acid–base (LW-AB) approach was employed to study the surface electronic state of the films, X-ray photoelectron spectroscopic (XPS) and valence band spectra (VBS) were used to study chemical bonds and electron structure information inside the films. Bandgap of the films were calculated by the data from ultraviolet spectrophotometer. The results showed that synthesized films were n-type semiconductors and doping of nitrogen element will affect the accepted–electron capability of the film. The change tendency of the bandgap coincides with that of the ratio of acidic to alkaline component of the polar acid-alkali surface energy. There was much sp hybrid electronic state existed in the films, which mainly sp²C=C/C=N and sp³C–C/C–N bonds.

Tin oxide (SnO₂) thin films were deposited by radio-frequency (RF) magnetron sputtering on silicon and glass substrates at different oxygen-to-argon gas-flow ratio (O₂-to-Ar = 0%, 10%, 20%, 30% and 50%). All films were deposited at room temperature and fixed working pressures, 10 mTorr. X-ray diffraction (XRD) measurement suggests that all films were crystalline in nature except film deposited only in argon environment. The transparency of all of the films was more than 85% in the visible range except the film deposited only in the argon environment. Atomic force microscopy results showed that the surface of all the films were highly flat and smooth. The optical bandgap, estimated by Tauc plot was increased with oxygen environment. Blue shift was observed in the absorption edge and was accounted to decrease in the oxygen vacancies and dangling bonds.

The development of ferroelectric photovoltaic (FE-PV) materials has been limited for a long time due to their large bandgap. Many strategies for lowering the bandgap have been suggested to promote FE-PV properties. The effects of magnetic ordering and B-site-cation ordering to lower the bandgap of FE-PV are investigated in this paper using first-principles calculations. Results show that the most stable structure of tetragonal Bi₂FeCrO₆ ($t$-Bi₂${\text{FeCrO}}_6)$ is the AS1 structure (Fe/Cr alternate stacking ordering) with C-type antiferromagnetic ordering (defined as AC-$t$-Bi₂FeCrO₆), which has a small bandgap, suggesting that AC-$t$-Bi₂FeCrO₆ is among the FE-PV materials with the highest application potential.

Spinel ferrite ${\text{Ni}}_{0.08}$${\text{Mn}}_{0.90}$${\text{Zn}}_{0.02}$Fe₂O₄ was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050${}^{\circ }$ C, 1100${}^{\circ }$ C and 1150${}^{\circ }$ C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm${}^{-1}$ to 400 cm${}^{-1}$. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 $\mu$m to 0.88 $\mu$m. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity ($H_c)$ and saturation magnetization ($M_s)$. Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature ($T_c)$ and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.

In this work, the structural, electronic and optical properties of Si-doped barium chalcogenide [barium sulfide (BaS)] with different Si concentrations ($0\le x\le 0.25$) are investigated by the first-principles calculations based on the density functional theory (DFT). The band structures, charge densities and complex dielectric functions of the pure as well as Si-doped BaS were presented and analyzed in detail using TB-mBJ approach by WIEN2k package. It is found that silicon concentration can control the bandgap by reducing it to values around 1.4eV and 1.6eV for 12.5% and 6.25% of Si-doped BaS, respectively. The electron charge density indicates the ionic bonding between silicon and sulfur atoms due to the high electronegativity between them. In fact, the results show that the absorption peaks of Si-doped BaS are enhanced compared with pure BaS. These results suggest that the Ba${}_{1-x}$Si_xS original structure displays excellent physical properties thereby revealing that it is a promising material in advanced optoelectronic and solar cell applications.

One avenue toward next-generation spintronic devices is to develop half-metallic ferromagnets with 100% spin polarization and Curie temperature above room temperature. Half-metallic ferromagnets have unique density of states, where the majority spins are metallic but the minority spins are semiconducting with the Fermi level lying within an energy gap. To date, the half-metallic bandgap has been predominantly estimated using Jullière’s formula in a magnetic tunnel junction or measured by the Andreev reflection at low temperature, both of which are very sensitive to the surface/interface spin polarization. Alternative optical methods such as photoemission have also been employed but with a complicated and expensive setup. In this study, we developed and optimized a new technique to directly measure the half-metallic bandgap by introducing circularly polarized infrared light to excite minority spins. The absorption of the light represents the bandgap under a magnetic field to saturate the magnetization of a sample. This technique can be used to provide simple evaluation of a half-metallic film.