NiO Thin Films Research Articles

Single layered Ag/NiO plasmonic nanocoatings: A new green synthesis method for selective solar absorber

This study presents the synthesis of environmentally benign, single-layered spectrally selective Ag/NiO nanocoating absorbers using a green synthesis method. Various characterization techniques, including Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), were used to examine the effects of plasmonic Ag concentration on the structural, chemical composition, and surface morphology of the nanocomposites. The optical properties of the deposited nanocoatings were investigated using a UV–Vis-NIR spectrophotometer in the solar spectrum region (300–2500 nm) and an FT-IR spectrophotometer in the infrared wavelength region (3000–20,000 nm). XRD results confirmed the coexistence of a face-centered cubic phase of Ag and NiO in the Ag/NiO nanocermet thin films. SEM and TEM topography revealed uniformly distributed nanosphere NiO thin films and cubic Ag metal with better dispersibility and crystallization. The RBS spectrum of the samples showed a homogeneous distribution of Ni, Ag, and O atoms throughout the coatings. Ag/NiO nanocoatings deposited with 8 wt% Ag content exhibited excellent solar absorptance (α) = 0.95 and thermal emittance of (ɛ) of 0.08. This enhancement is primarily attributed to the localized surface plasmon resonance (LSPR) effect associated with the embedded Ag nanoparticles, which facilitates more effective utilization of light.

Effects of Li concentration in the precursor solution on NiO thin films deposited using electrostatic spray deposition

Abstract Undoped and Li-added NiO thin films were deposited using electrostatic spray deposition (ESD) techniques. Initially, the NiO thin films displayed minimal contamination, predominantly C and H. The NiO thin films exhibited a flat surface morphology comprising grains of uniform size, approximately 20–30 nm in diameter, and reliable crystal growth, with a full width at half maximum of approximately 0.30 in X-ray diffraction analysis. Moreover, the NiO/ZnO diode demonstrated superior properties when a 5 at. % Li concentration solution was incorporated. The rectification ratio reached approximately 2.3 × 10³ at ± 1.0 V, with an ideality factor of 1.9. Additionally, the NiO/ZnO diodes exhibited remarkable photovoltaic properties even without detailed optimization. These findings underscore the potential of ESD in advancing semiconductor thin-film technology, thereby paving the way for more cost-effective and scalable production methods.

Resistive Switching Characteristics of NiO Thin Films Influenced by Changes in the Diameter of Nanometer-Scale Top Electrodes.

We investigated the forming, set, and reset voltages affected by the area of the top electrodes of a resistive random access memory (RRAM) capacitor fabricated by epitaxial NiO thin films. NiO RRAM capacitors with Au top electrode with a diameter of 100 μm showed typical unipolar switching characteristics. Au top electrodes with diameters of 10, 20, and 30 nm were formed on the surface of epitaxial NiO thin films by e-beam lithography. The forming, set, and reset voltages tended to decrease as the diameter of NiO RRAM capacitors with nanosized Au top electrodes decreased. As the area of the Au top electrodes increases, the volume of space in which the conductive filaments formed within the NiO RRAM capacitors can be formed becomes larger. This causes the conductive filament to be formed at relatively low energy, giving low forming voltages, while increasing the diversity of paths, causing a wide forming voltage distribution.

Electrochemical performance of cobalt-doped NiO thin films synthesized by spray pyrolysis

ABSTRACT In this work, various cobalt-doped NiO thin films have been synthesized via the spray pyrolysis. The cobalt-doped NiO thin films show a cubic phase with preferred orientation along the (111) plane. The scanning electron microscopy images of the cobalt-doped NiO thin films show interconnected flakes with small agglomerated particles. The optical bandgap decreases from 3.30 eV for the undoped NiO thin film to 2.90 eV for 20 mol% cobalt doping, with an increase in cobalt doping concentration in NiO. The electrochemical activities have been tested in 2M KOH electrolyte with cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The highest specific capacitance observed for the 10 mol% cobalt-doped NiO thin film electrode is 760 Fg−1 at a scan rate of 5 mVs−1. The 10 mol% cobalt-doped NiO thin film electrode shows 92% retention in capacitance after 1000 cycles and a low charge transfer resistance of 10 Ωcm2.

Antiferromagnetic standing spin waves generated in NiO thin films by short strain pulses

Antiferromagnetic standing spin waves generated in NiO thin films by short strain pulses

Improved transparency and charge matching of electrochromic devices with Ce-doped NiO counter electrode

The quest for cost-effective and efficient electrochromic electrodes, featuring high color contrast and rapid response times, has sparked increasing interest in research of metal oxides for electrochromic applications. In this study, nickel oxide thin films with various cerium dopant concentrations are synthesized, with the optimized doping concentration identified as 1 at%. X-ray diffraction analysis confirmed that the dopant successfully reduces crystal size and alters the preferred orientation to (111). The 1 % Ce:NiO thin film exhibits enhanced electrochromic performance, with a transmittance modulation increase of 27.4 % at 633 nm, a 27.1 % rise in coloration efficiency and faster response time (tb=9.64 s and tc=6.76 s) compare to the undoped NiO. Importantly, the charge density of 1 % Ce:NiO thin film increases from 4.86 to 8.14 mC cm−2, representing a 67.5 % improvement, which becomes a better charge matching with WO3 in electrochromic devices. The incorporation of Ce into the NiO thin films not only leads to increased transmittance in the bleached state and optical modulation in the electrochromic devices but also contributes to a rise in the optical band gap of the NiO thin films and improved charge balance matching. These results underscore the positive impact of cerium doping on microstructure and electrochromic performance, indicating a promising future for electrochromic devices.

Effect of Al doping on the structural, optical and photocatalytic properties of sol-gel spin-coated NiO thin films

Nanostructured NiO thin films are renowned for their catalytic activity and potential for degradation of industrial effluents. In this study, Al-doped NiO (Ni1-xAlxO with x = 0, 0.02, 0.04, 0.06, and 0.08) thin films were synthesized by sol–gel spin coating, and the influence of Al doping on their physical properties, surface morphology, optical band gap, and photo-catalytic performance was investigated. X-ray diffraction (XRD) analysis confirmed the high crystallinity of the thin films and revealed a pronounced doping effect on parameters such as crystallite size, microstrain, and dislocation density. Scanning electron microscopy (SEM) revealed the formation of spherical nanoparticles with particle sizes ranging from 26 nm to 11 nm. The elemental composition was verified through energy-dispersive x-ray (EDX) analysis. The optical bandgap of the prepared films was determined through UV-visible spectroscopy. The Ni0.98Al0.02O films exhibited the lowest PL intensity, indicating a reduced recombination rate. To assess the photo-degradation capability of the prepared thin film catalysts, industrial effluent Indigo Carmine was employed as a test compound. The Ni0.98Al0.02O sample demonstrated the highest degradation efficiency, achieving about 96% degradation within 2 h of UV–vis light irradiation. Furthermore, the degradation followed pseudo-first-order kinetics.

Third-order non-linear optical switching and threshold limiting of NiO thin films

This study discusses the nonlinear optical properties of as-grown and annealed NiO thin films using the Z-scan technique utilizing the femtosecond laser pulses at a repetition rate of 100 kHz of wavelength 1030 nm with a pulse duration of 370 fs. In open aperture measurements, pristine reveal saturable absorption (SA) with a negative sign of nonlinearity, while annealed samples exhibit reverse saturable absorption (RSA) with a positive sign of nonlinearity. In closed aperture conditions, all samples show prefocal minima and postfocal maxima, indicating self-focusing behavior. The observed RSA phenomena are attributed to the indirect two-photon absorption (TPA) process. The influence of surface plasmon resonance on nonlinear absorption is successfully ruled out due to insufficient excitation energy (1.20 eV) to induce resonance in the samples. The increase in bandgap with annealing temperature, associated with indirect TPA, is elucidated with the shifting of Ni-dx2-y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_{x^2-y^2}$$\\end{document} and Ni-dz2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_{z^2}$$\\end{document} orbitals in the conduction band, under the framework of Density Functional Theory (DFT). The DFT results are correlated with the observed nonlinear SA and RSA processes. The Ni d-d and Ni-d to O-p transitions contribute to the modulation of nonlinearity in the indirect TPA process. The study suggests that the sample annealed at 400 °C exhibits superior optical limiting properties with the highest nonlinear absorption coefficients compared to the other annealed sample, while the as-grown sample is suitable for passive Q-switching applications.

Enhanced ammonia gas sensing performance at room temperature of binder-free NiO, Cu and Co-doped NiO thin films synthesized via the SILAR method

We have comprehensively analyzed the influence of Cu and Co-doping on the structural, compositional, optical, and ammonia sensing characteristics of NiO thin films. The X-ray diffraction analysis revealed that pure NiO, Cu, and Co-doped NiO thin films possess a cubic structure. Remarkably, the Co-dopant caused a transformation in the crystallite size and surface structure of NiO. This alteration ultimately enhanced the sensing capabilities of Co-doped NiO thin films. The presence of Co decreased the amount of energy needed to activate Co-doped NiO, resulting in enhanced sensing capabilities of the doped samples for detecting 50 parts per million of ammonia with a response time of 20 s and recovery time of 16 s and having a percentage response of 76.25 %. The enhanced sensor responsiveness and selectivity of the Co-doped NiO sensor towards ammonia can be attributed to its increased surface area, smaller crystallite sizes, and superior surface properties. The remarkable results of Co-doped NiO thin films exhibited show a potential for use in the production of highly efficient ammonia gas-detecting devices.

Exploring the role of film thickness and oxygen vacancies on the H2S gas-sensing performance of RF magnetron-sputtered NiO thin films

Exploring the role of film thickness and oxygen vacancies on the H2S gas-sensing performance of RF magnetron-sputtered NiO thin films

P-NiO/n-ZnO heterojunctions for visible-blind UV and IR photodetectors: A low-temperature fabrication approach

We investigate the design and characterization of stacked semiconductor structures, specifically p-NiO on n-ZnO, for achieving a multispectral photo-response. This device is fabricated by depositing a thin film of NiO on ZnO using a simple, low-temperature spray pyrolysis technique. The resulting heterojunction device, formed on a glass substrate at 250 °C and annealed at 500 °C, exhibits visible-blind characteristics and demonstrates remarkable stability for ultraviolet (UV) and infrared (IR) detection with a low dark current of 22 nA. The Ag/p-NiO/n-ZnO/Ag device shows enhanced photo-response only at wavelengths of 253 nm and 900 nm with a quick response time (Tr = 4.6 ms and Td = 20.3 ms). The observed photo-current is attributed to defect-mediated charge transport at the interface. These promising results highlight the potential of p-NiO/n-ZnO heterojunction-based device for applications demanding robust performance as visible blind IR and UV photodetectors.

Magnetic field-augmented photoelectrochemical water splitting in Co3O4 and NiO nanorod arrays

Effective charge separation is crucial for improving the sensitivity of photoelectrochemical studies. Here, we provide an immense magnetic field-based electron spin polarization approach for an efficient charge carrier separation. We have fabricated NiO and Co3O4 thin film and nanorod arrays by electron beam evaporation glancing angle method followed by annealing in a two-zone furnace. The photoelectrochemical performance was investigated for NiO and Co3O4 samples in the presence and absence of a magnetic field. The NiO and Co3O4 nanorods array samples exhibit better absorption compared with the thin film samples. The Co3O4 and NiO nanorod arrays showed the highest photocurrent density of 0.12 and 0.55 mA/cm2 in a magnetic field. The superior photoelectrochemical response of NiO and Co3O4 nanorods in a magnetic field could be ascribed to the limitation of non-radiative recombination of carriers manipulated by Lorentz force and spin polarization. Furthermore, the electrochemical impedance spectra of NiO and Co3O4 nanorod arrays in a magnetic field show the least charge transfer resistance. This study sheds light on the interaction process between external fields and radiative/non-radiative recombination of manipulating carriers. Thus, the application of a magnetic field presents an efficient and versatile approach to enhance the performance of photoelectrodes in solar water splitting.

Doping engineering of NiO–Zn nanofilms for modulation of morphological structure and ultrafast nonlinear optical response at 515 nm

In this work, to investigate the metal doping on the third-order nonlinear optical properties of NiO thin films under femtosecond pulsed laser excitation, pure NiO and 2w,4w,6w,8w Zn doped-NiO nanofilms were prepared by DC-RF co-sputtering technique. Then, the nonlinear absorption properties and nonlinear refractive properties of the five samples were investigated using the femtosecond laser at a wavelength of 515 nm. The experimental results show that the nonlinear absorption and nonlinear refractive properties of NiO are enhanced by the doped metal as well as the effect of defects. In addition, by varying the pump light intensity, we observed the transition of nonlinear absorption from the coexistence of saturated absorption and reverse saturated absorption to reverse saturated absorption. We established a multi-energy level system to interpret the nonlinear absorption and nonlinear refractive results, which broadens the application of NiO thin films in the field of nonlinear optics.

Investigating UV photodetector capabilities of Pd-functionalized NiO thin films with interdigitated Pt electrodes

In this study, Palladium functionalized NiO thin films (Pd/NiO) were successfully deposited using a sputtering technique for the photodetector application. FESEM and EDX analysis were performed to confirm the morphology and the presence of constituent elements in the Pd/NiO films. The defect states and surface chemistry were analyzed using XPS, and PL measurements. The Pd/NiO thin film exhibited excellent responsivity (∼ 62 mA/W) and detectivity (∼ 31.7 × 106 Jones) at a low power density of 200 µW/cm2 in the UV range (∼ 355 nm). Additionally, the low Noise Equivalent Power (NEP) of ∼ 1.78 × 10-9 WHz−1/2 at 200 μW indicates the Pd/NiO photodetector capability to effectively detect light signals even at low optical power for various applications.

Tailored Core-Shell Nanostructure Achieved through Atomic Layer Deposition for Superior Energy Storage Performance Application

A distinctive method was employed to construct ultrathin NiO on phosphorous-doped MnO2 nanosheets, utilizing a straightforward hydrothermal process to form a Mn precursor on Ni-foam followed by phosphorous doping through a simple solid-state annealing process and ALD technique. The impact of phosphorous doping was examined by varying the annealing temperature, resulting in a significant increase in oxygen vacancies and electrochemical performance. Additionally, the atomic layer deposition of NiO not only improved electrochemical performance but also ensured cycling stability without impeding the system. By adjusting the thickness of the NiO thin films over phosphorous-doped MnO2, a notable enhancement in electrochemical performance was achieved, as evidenced by the performance of the solid-state asymmetric device. This hybrid approach is expected to pave the way for novel electrode material designs for high-performance supercapacitors, leveraging electroactive metal oxides through ALD coating.

Preparation of tunable magnesium atom-doped nickel oxide films with short response time and high coloring efficiency by sol-gel method

Nickel oxide, a representative electrochromic material, is commonly employed in environmentally conscious optoelectronic devices, such as multifunctional smart windows. In this paper, novel electrochromic nickel oxide films doped with magnesium atoms were prepared on indium tin oxide (ITO) substrates by sol-gel spin-coating method, and the results of X-ray diffraction and scanning electron microscopy show that the spin-coating is unique in that the existence of a small number of cracks on the surface of the sample is conducive to the enhancement of the electrochemical properties. UV–visible spectrophotometer and electrochemical workstation were used to explore the effect of Mg-atom doping concentration on the electrochromic performance of the nickel oxide thin films, and the results showed that at an annealing temperature of 400 °C, the optical modulation amplitude of the samples with a doping concentration of 4 % reached 43.12 %, and the coloring time and the fading time were reduced to 4.0 s and 3.1 s, respectively, with an increase in the coloring efficiency to 42.25 cm2C−1. In conclusion, Mg doping has an important reference value for the study of electrochromic performance of NiO thin films, and has good prospects for electrochromic applications.

Anion and Cation Co-Doping of NiO for Transparent Photovoltaics and Smart Window Applications

Materials engineering based on metal oxides for manipulating the solar spectrum and producing solar energy have been under intense investigation over the last years. In this work, we present NiO thin films double doped with niobium (Nb) and nitrogen (N) as cation and anion dopants (NiO:(Nb,N)) to be used as p-type layers in all oxide transparent solar cells. The films were grown by sputtering a composite Ni-Nb target on room-temperature substrates in plasma containing 50% Ar, 25% O2, and 25% N2gases. The existence of Nb and N dopants in the NiO structure was confirmed by the Energy Dispersive X-Ray and X-Ray Photoelectron Spectroscopy techniques. The nominally undoped NiO film, which was deposited by sputtering a Ni target and used as the reference film, was oxygen-rich, single-phase cubic NiO, having a visible transmittance of less than 20%. Upon double doping with Nb and N the visible transmittance of NiO:(Nb,N) film increased to 60%, which was further improved after thermal treatment to around 85%. The respective values of the direct band gap in the undoped and double-doped films were 3.28 eV and 3.73 eV just after deposition, and 3.67 eV and 3.76 eV after thermal treatment. The changes in the properties of the films such as structural disorder, direct and indirect energy band gaps, Urbach tail states, and resistivity were correlated with the incorporation of Nb and N in their structure. The thermally treated NiO:(Nb,N) film was used to form a diode with a spin-coated two-layer, mesoporous on top of a compact, TiO2 film. The NiO:(Nb,N)/TiO2heterojunction exhibited visible transparency of around 80%, showed rectifying characteristics and the diode’s parameters were deduced using the I-V method. The diode revealed photovoltaic behavior upon illumination with UV light exhibiting a short circuit current density of 0.2 mA/cm2 and open-circuit voltage of 500 mV. Improvements of the output characteristics of the NiO:(Nb,N)/TiO2 UV-photovoltaic by proper engineering of the individual layers and device processing procedures are addressed. Transparent NiO:(Nb,N) films can be potential candidates in all-oxide ultraviolet photovoltaics for tandem solar cells, smart windows, and other optoelectronic devices.

NiO thin films fabricated using spray-pyrolysis technique: structural and optical characterization and ultrafast charge dynamics studies

Nickel (II) oxide, NiO, is a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displays antiferromagnetic order at room temperature. NiO has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the fabrication of polycrystalline NiO using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. The composition and structure of the NiO thin films were then studied using x-ray diffraction, and atomic force and scanning electron microscopies (SEM). The phononic and magnonic properties of the NiO thin films were also studied via Raman spectroscopy, and the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that the NiO samples display the same phonon and magnon excitations expected for single crystal NiO at room temperature, and that electron dynamics in our system is like those of previously reported NiO mono- and polycrystalline systems synthesized using different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthesize strongly correlated materials for a large set of applications.

Study of the effects of heating on the physical, optical, and electrical properties of NiO thin films synthesized using a low-cost sol-gel method

Developments in low-cost techniques for growing high-quality nickel oxide thin films (NiOTFs) are critical enablers for the fabrication of NiO-based devices, particularly solar cells, light-emitting diodes, lasers, and many other applications. In this study, it has been demonstrated that the optical, electrical, and structural characteristics of NiOTFs coated on glass substrate employing a low-cost solution method are strongly influenced by post-thermal annealing treatments in ambient air. A comprehensive study was carried out on the characteristics of the deposited NiOTFs. X-ray diffraction (XRD) measurements indicate the enhancement of the crystal quality of films after annealing. There is a noticeable change and improvement in coated NiOTFs with heat treatment at 300 and 600 ℃ due to clear shifts in density. During the heating temperature increment, the energy of the band gap was shifted from 3.63 to 3.44 eV, and the electrical resistance of the NiOTFs varied from 1020 to 700 Ω-cm. Furthermore, the results indicate that the low-cost sol-gel (SG) deposition technique has a greater potential for producing high-quality p-type NiOTFs with minimal defects for electronic device applications.

Effect of morphology on the electrochemical performance of NiO thin films

Effect of morphology on the electrochemical performance of NiO thin films