Microstructure Of Thin Films Research Articles

Impact of oxygen partial pressure on resistive switching characteristics of PLD deposited ZnFe2O4 thin films for RRAM devices

In this paper we show resistive switching characteristics of ZnFe2O4 thin films grown by pulsed laser deposition at various oxygen partial pressures. We discuss how the microstructure, surface roughness, oxidation condition, and resistive switching properties of ZnFe2O4 thin films are influenced by the oxygen partial pressure prevalent in the chamber during the deposition process. The films were deposited at oxygen partial pressure (pO2) of 0.0013, 0.013, 0.13 and 1.3 mbar. The ZnFe2O4 thin film deposited at the lowest pO2 (0.0013 mbar) did not display a resistive switching characteristic. The ZnFe2O4 device deposited at 0.13 mbar yielded the best results. These devices have a low SET variance and a large memory window (more than 2 orders of magnitude) due to an optimum amount of oxygen vacancies/ions contained in the ZnFe2O4 film, which is helpful for better resistive switching, than devices deposited at other oxygen pressures. We also find that the migration of oxygen vacancies is linked to the resistive switching process.

Structural, electrical and energy storage properties of lead-free NaNbO3-BaHfO3 thin films

Lead-free dielectric thin-film capacitors with desirable energy storage density are gathering attention due to the increasing environmental concern and the miniaturization of electronic devices. We here reported the new lead-free dielectric thin films, namely (1-x)NaNbO3-xBaHfO3 (x ≤ 0.15), prepared by a sol-gel method, and presented the dependence of their structural, electrical and energy storage properties on the x level of BaHfO3. The microstructure, leakage current and breakdown strength of pristine NaNbO3 thin films are significantly improved by addition of BaHfO3. As a result, the superior energy storage performances were obtained at x = 0.1 with recoverable energy storage density Wr of 23.1 J/cm3 at 1100 kV/cm, excellent thermal stability from 30 to 210 °C (ΔWr < 4.6%), good fatigue resistance (ΔWr < 2.9% after 104 electrical cycles), and the fast charge-discharge rate (τ = 0.82 μs ).

Effects of Ba2+/Sr2+ ratio on the microstructure, dielectric and ferroelectric properties of Ba x Sr(1−x)TiO3 films prepared by micro-arc oxidation

ABSTRACT BaxSr(1-x)TiO3 (BST) thin films are in situ deposited on a Ti matrix through the micro-arc oxidation technique, using a mixed aqueous solution of Ba(OH)2•8H2O, Sr(OH)2•8H2O and 0.05 M EDTA as the electrolyte. The influence of the Ba2+/Sr2+ ratio on the phase composition, microstructure and properties of the BST thin films is investigated. Ba0.6Sr0.4TiO3, Ba0.5Sr0.5TiO3, and Ba0.4Sr0.6TiO3 thin films have a cubic phase, while Ba0.8Sr0.2TiO3 and Ba0.7Sr0.3TiO3 thin films have a tetragonal phase. When the concentration of Ba2+ in the electrolyte surpasses that of Sr2+, the width of micro-arc holes and the surface roughness of the film grow as the Ba2+ concentration rises. Furthermore, the dielectric and ferroelectric properties of BST films are favorably connected with the surface morphology. When the Ba2+ concentration is 0.06 M, the film has the best compactness and smoothness. In addition, the highest capacitance and lowest dielectric loss are achieved.

Microstructure and residual stress evolution in nanocrystalline Cu-Zr thin films

Grazing incidence X-ray diffraction (GIXRD) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) were employed to study the microstructure evolution and stress development in the nanocrystalline Cu100−X-ZrX (2.5 at% ≤ x ≤ 5.5 at%) alloy thin films. Small Zr additions to Cu led to significant lattice parameter anisotropy in the as-deposited Cu-Zr thin films both due to macroscopic lattice strain and stacking faults in the Cu matrix. Strain free lattice parameters obtained after the XRD stress analysis of Cu-Zr thin films confirmed formation of a supersaturated substitutional Cu-Zr solid solution. For the first time, the study of film microstructure by XRD line profile analysis (XLPA) confirmed progressive generation of dislocations and planar faults with increasing Zr composition in Cu-Zr alloy films. These microstructural changes led to the generation of tensile stresses in the thin films along with considerable stress gradients across the films thicknesses which are quantified by the traditional dψhkl−Sin2ψ and GIXRD stress measurement methods. The origin of tensile stresses and stress gradients in the Cu-Zr film are discussed on the basis of film growth and heterogeneous microstructure with changing Zr composition.

Investigation into the effect of substrate material on microstructure and optical properties of thin films deposited via magnetron sputtering technique

This study aims at investigating the effect of the substrate material on growth mechanism and also microstructure of Ta2O5 thin films. For this purpose, atomic force microscopy, scanning electron microscopy, and interferometry analyses were implemented to reveal the influence of silicon wafer and amorphous BK7 glass substrates on the nucleation and growth mechanisms of Ta2O5 thin films deposited via the radio frequency magnetron sputtering technique. Results indicated that those films with finer morphologies had relatively higher nucleation densities. Compared with BK7 glass substrate, crystals formed on the silicon wafer were shown to be finer and had lower mean areas in more nucleation sites. Moreover, optical properties and morphological characteristics of the films on the silicon substrates had much more endurance after the annealing treatment. It was observed that shift in the transmission spectra of the deposited films after the treatment was insignificant, implying high packing density of the films. However, a 6-nm shift in the transmission spectra indicated low density and high porosity of the films. Finally, atomic force microscopy analysis along with the light scattering measurements confirmed the formation of a low-roughness film on the silicon wafer substrates.

Enhanced Ferroelectric, Dielectric Properties of Fe-Doped PMN-PT Thin Films

Fe-doped 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) thin films were grown in Pt/Ti/SiO2/Si substrate by a chemical solution deposition method. Effects of the annealing temperature and doping concentration on the crystallinity, microstructure, ferroelectric and dielectric properties of thin film were investigated. High (111) preferred orientation and density columnar structure were achieved in the 2% Fe-doped PMN-PT thin film annealed at 650 °C. The preferred orientation was transferred to a random orientation as the doping concentration increased. A 2% Fe-doped PMN-PT thin film showed the effectively reduced leakage current density, which was due to the fact that the oxygen vacancies were effectively restricted and a transition of Ti4+ to Ti3+ was prevented. The optimal ferroelectric properties of 2% Fe-doped PMN-PT thin film annealed at 650 °C were identified with slim polarization-applied field loops, high saturation polarization (Ps = 78.8 µC/cm2), remanent polarization (Pr = 23.1 µC/cm2) and low coercive voltage (Ec = 100 kV/cm). Moreover, the 2% Fe-doped PMN-PT thin film annealed at 650 °C showed an excellent dielectric performance with a high dielectric constant (εr ~1300 at 1 kHz).

Microstructure and magnetic properties of FeCoHfN thin films deposited by DC reactive sputtering

The microstructure and electro-magnetic properties of FeCoHfN thin films deposited by reactive sputtering under an in-situ magnetic field have been studied as a function of nitrogen partial pressure (R(N2)). As the (R(N2)) increases, the grain size of α-FeCo phase can be effectively reduced, and the structure of the films changes from an amorphous/nanocrystalline dual-phase structure with ultrafine α-FeCo magnetic nanoparticles isolated by a nonmagnetic insulating layer to a single amorphous structure. The structural transformation and the enrichment of HfN layer improve the resistivity and static and dynamic soft magnetic properties of the films. Higher resistivity is expected to reduce eddy current losses at high frequencies. The critical (R(N2)) when the film shows indications of excellent high-frequency magnetic properties is 8%. The deposited FeCoHfN thin films have high saturation magnetization of 14.9–16.2 kGs, great permeability of 222–322 at GHz, and high ferromagnetic resonance frequency up to 3.5 GHz, showing the promise of high-frequency applications.

Exploitation of electric field assisted optical signal amplification in ferroelectric photorefractive K0.50Na0.50NbO3 thin film

The exploitation of non-linear optical property of potassium sodium niobate [K x Na 1-x NbO 3 (x = 0.50 or KNN-50)] thin film using the two-wave mixing technique in the presence of an external electric field has been performed for the first time. The results show that the presence of external electric field enhances the non-linear optical activity in the KNN-50 medium. For this study, the KNN-50 thin film was prepared on fused quartz substrate by pulsed laser deposition (PLD) technique. XRD study confirms the formation of perovskite phase, and the FESEM image supports the growth of densely packed micro-structured KNN-50 thin film. The band gap of 800 nm thick KNN-50 thin film was found to be 4.1 eV. The electric field assisted nonlinear optical studies are promising, and opens large opportunity of incorporation of these KNN-50 thin films in the development of non-linear optical devices. • The exploitation of non-linear optical property of potassium sodium niobate [K x Na 1-x NbO 3 (x = 0.50 or KNN-50)] thin film using the two-wave mixing technique in the presence of an external electric field has been performed for the first time. • K 0.50 Na 0.50 NbO 3 films were deposited on fused quartz substrate using PLD technique. • XRD study confirms the formation of perovskite phase, and the FESEM image supports the growth of densely packed micro-structured KNN-50 thin film. • Strong non-linear optical property was observed in photorefractive KNN thin films using Two wave mixing technique via the pump-probe set-up. • The obtained results in the present work for KNN thin film are of great significance for its prospective applications in the field of photorefractive devices, electro-optic devices and light modulators .

Microstructure and properties of Ti2AlN thin film synthesized by vacuum annealing of high power pulsed magnetron sputtering deposited Ti/AlN multilayers

The (002) texture, compactness, and smoothness Ti 2 AlN thin films render them promising for many potential applications, especially in the surface modification of wear-resistant components. In this study, Ti 2 AlN thin films were fabricated by the vacuum annealing of Ti/AlN multilayers deposited by high power pulsed magnetron sputtering (HPPMS). The influence of the multilayer modulation ratio and modulation period of Ti/AlN on the microstructure and properties of the Ti 2 AlN thin film were explored. The results indicate that a Ti/AlN modulation ratio close to 6:4 and period less than 30 nm are appropriate for yielding high-quality crystallized Ti 2 AlN thin films. The microstructure of the Ti 2 AlN thin film is (002) textured, nanocrystalline, smooth, and compact, which benefits from the HPPMS technique. The Ti 2 AlN thin film adheres well to the substrate and has a hardness of 32.5 ± 2.1 GPa and has a friction coefficient of 0.15 while tested with a Si 3 N 4 friction pair. • The modulation ratio and period are critical for Ti 2 AlN thin film synthesis. • HPPMS improves the (002) texture and compactness of the Ti 2 AlN thin film. • HPPMS enhances the adhesion, hardness and wear resistance of the Ti 2 AlN thin film.

Influence of coating thickness on the microstructure, composition and optical properties of aluminum nitride thin films grown on silicon substrates via low-temperature PEALD

Within the framework of the study, fine-grained nanocrystalline aluminum nitride films were obtained using the PEALD method at the temperature of 250 °С and the number of deposition cycles from 80 to 500 on single-crystal silicon substrates. Low-temperature synthesis processes were carried out in the self-limited growth regime of the PEALD method at the constant growth rate of ∼0.115 nm/cycle. The obtained samples were studied by ellipsometry, FTIR-spectroscopy, X-ray diffraction analysis, Auger spectroscopy, Scanning electron and Atomic force microscopy. It was found that the samples in the IR-absorption spectra and ω/2θ-scans had bands and reflections characteristic for wurtzite AlN with hexagonal structure. It was shown that an increase in the coating thickness led to an increase in the crystallinity and optical density of the film material, the crystallites size, and values of the root-mean-square (RMS) roughness. In this case, significant changes in the crystal lattice parameter and relaxation of internal mechanical stresses within the obtained values of the AlN layers thicknesses were not observed.

Microstructure and electrical properties of La2Ti2O7 thin films on SrTiO3 substrates

La2Ti2O7 has recently received extensive interest due to its attractive ferroelectric and photocatalytic properties. Here, high-quality La2Ti2O7 thin films on (110) SrTiO3 substrates are prepared via oxidation of LaTiO3 thin films that are fabricated by pulsed-laser deposition. X-ray diffraction analyses reveal that the La2Ti2O7 thin film grows epitaxially on the (110) SrTiO3 substrate and has a good crystallinity. Atomic force microscopy investigations suggest that the surface of La2Ti2O7 thin film turns into a stepped and terraced structure after the annealing. X-ray photoelectron spectroscopy analyses indicate that the La2Ti2O7 thin film has a high purity and contain only Ti4+ ions (i.e., without Ti3+ ions). The band gap of the La2Ti2O7 film is measured to be ∼3.2 eV by UV–visible spectra. Atomic and electronic structures of the La2Ti2O7/SrTiO3 heterointerface have been studied by a combination of transmission electron microscopy and first-principles calculations. The La2Ti2O7/SrTiO3 heterointerface is atomically abrupt and coherent. Electronically, this heterointerface contributes to the decrease of band gap of La2Ti2O7 near the interface. The reduction of spontaneous polarization in La2Ti2O7 is localized in two layers of TiO6 octahedra near the interface due to the discontinuous Ti-O bonds between the perovskite layers of La2Ti2O7.

Effect of Bi doping on the structural and optical properties of NiO thin films

Nickel Oxide (NiO) based thin films have drawn widespread attention in optoelectronics applications because of their superior optical and electrical properties. Herein, the effect of Bi doping on the microstructure, phase evolution, composition, electrical and optical properties of NiO thin films are reported. Bi-doped NiO (0–7.5 %) thin films were deposited on glass substrates by the cost-effective spin coating technique. The X-ray diffraction studies showed that the undoped and 2.5 % Bi-doped films develop cubic structure and 5.0 % and 7.5 % of Bi doped films formed an amorphous nature. A systematic decrease in the grain size as well as surface roughness with Bi doping was noticed through AFM analysis. The films are highly transparent (80 %) and the optical band gap increases from 3.45 eV for undoped NiO to 3.99 eV for 7.5 % Bi-doped NiO thin film. The nonlinear optical susceptibility values are found to be in the range of 0.034 × 10-11 to 2.72 × 10-11 esu.

Acceptor Modulation Strategies for Improving the Electron Transport in High-Performance Organic Field-Effect Transistors.

High-performance ambipolar and electronic type semiconducting polymers are essential for fabricating various organic optoelectronic devices and complementary circuits. This review summarizes the strategies of improving the electron transport of semiconducting polymers via acceptor modulation strategies, which include the use of single, dual, triple, multiple, and all acceptors as well as the fusion of multiple identical acceptors to obtain new heterocyclic acceptors. To further improve the electron transport of semiconducting polymers, the introduction of strong electron-withdrawing groups can enhance the electron-withdrawing ability of donors and acceptors, thereby facilitating electron injection and suppressing hole accumulation. In addition, the relationships between the molecular structure, frontier molecular orbital energy levels, thin film morphology, microstructure, processing conditions, and device performances are also comprehensively discussed. Finally, the challenges encountered in this research area are proposed and the future outlook is presented.

Multichromic Vanadium Pentoxide Thin Films Through Ultrasonic Spray Deposition

Vanadium pentoxide (V2O5) is a highly promising material for optoelectronic applications due to its wide optical band gap, significant thermal/chemical stability, and intriguing multichromic properties. Nonetheless, the production of uniform and crack-free V2O5 thin films over large areas via conventional deposition methods remain to be a challenge. In this work, we demonstrate deposition of microscopically uniform, large area (15 cm × 15 cm), nanocrystalline and multichromic V2O5 thin films onto fluorine-doped tin oxide (FTO) coated glass substrates via ultrasonic spray deposition (USD) method. Thin-film formation behavior, microstructural and optoelectronic properties of the deposited films were investigated as a function of post-deposition annealing temperature. Electrochromic performance of the fabricated films up to an area of 15 cm × 15 cm was monitored using cyclic voltammetry (CV), where 3 different coloration states of V2O5 were observed under different applied potentials. Electrochromic devices fabricated with the deposited V2O5 thin films were found to be stable up to 1000 cycles. Results presented herein provide a new roadmap for the large area deposition of V2O5 through USD method, which can be readily extended to a vast number of other functional metal oxide systems.

Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

In Situ X-ray Measurements to Follow the Crystallization of BaTiO3 Thin Films during RF-Magnetron Sputter Deposition

Here, we report on adding an important dimension to the fundamental understanding of the evolution of the thin film micro structure evolution. Thin films have gained broad attention in their applications for electro-optical devices, solar-cell technology, as well storage devices. Deep insights into fundamental functionalities can be realized via studying crystallization microstructure and formation processes of polycrystalline or epitaxial thin films. Besides the fundamental aspects, it is industrially important to minimize cost which intrinsically requires lower energy consumption at increasing performance which requires new approaches to thin film growth in general. Here, we present a state of the art sputtering technique that allows for time-resolved in situ studies of such thin film growth with a special focus on the crystallization via small angle scattering and X-ray diffraction. Focusing on the crystallization of the example material of BaTiO3, we demonstrate how a prototypical thin film forms and how detailed all phases of the structural evolution can be identified. The technique is shaped to enable a versatile approach for understanding and ultimately controlling a broad variety of growth processes, and more over it demonstrate how to in situ investigate the influence of single high temperature sputtering parameters on the film quality. It is shown that the whole evolution from nucleation, diffusion adsorption and grain growth to the crystallization can be observed during all stages of thin film growth as well as quantitatively as qualitatively. This can be used to optimize thin-film quality, efficiency and performance.

Fabrication and Characterization of Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; Dopant Al Thin Films Prepared by DC Reactive Plasma Sputtering Technique

The development of niobium oxide (Nb2O5) thin films is an important work as a result of wide applications of this oxide in the field of material science and thin-film applications. In this study, thin-film microstructures of aluminum (Al)-doped Nb2O5 were prepared by DC plasma sputtering on glasses substrate. The ratio of doping was (0.5, 1, and 1.5) wt. % Al. The obtained samples were thermally treated at 450 °C. Characterized and analyzed the physical properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and UV-Visible spectroscopy for optical properties investigation. Results showed that the average crystalline size of Nb2O5:0.5%Al film was found at 26.47 nm and the structure was a monoclinic phase for all samples. The distribution of grain size was found lower than 36.3 nm and uninformed particles on the surface. The analyzed optical properties showed the absorption decreased from 0.46 to 0.05 with increasing the wavelength and Low energy gap values decreased from 3.10 eV for Nb2O5 samples to 2.84 eV for 1.5%Al samples. In general, the doping by aluminum improved the physical properties of Nb2O5 films.

The low temperature pyrolysis preparation of In2S3 thin film and its application in Sb2S3 thin film solar cells

In2S3 thin films were successfully prepared by the low temperature pyrolysis of indium-butyldithiocarbamate (In-BDCA) complex at 200 °C for 30 min and first applied as the electron transport layer in Sb2S3 thin film solar cells. The influence of the In-BDCA complex content in the precursor solution on the microstructure of the In2S3 thin films was investigated and the photovoltaic performance of the corresponding Sb2S3 thin film solar cells was evaluated. The result revealed that In2S3 thin film with 2:1 possessed compact and full-coverage surface morphology and its thickness was 25 nm. The corresponding Sb2S3 thin film solar cells achieved the photoelectric conversion efficiency (PCE) of 2.87% with the open-circuit voltage (Voc) of 0.60 V, short-circuit current density (Jsc) of 10.38 mA cm−2, fill factor (FF) of 46.40%. When the preparation temperature of Sb2S3 thin films increased from 200 °C to 300 °C, the corresponding Sb2S3 thin film solar cells achieved the PCE of 4.03% with the Voc of 0.66 V, Jsc of 12.56 mA cm−2, FF of 48.63%. This result demonstrated that the In2S3 thin film can be applied as the efficient electron transport layer in Sb2S3 thin film solar cells.

Optical Absorption in Si:H Thin Films: Revisiting the Role of the Refractive Index and the Absorption Coefficient

This paper reports on absorption properties of thin films of hydrogenated amorphous and microcrystalline silicon considered for absorption-based applications, such as solar cell, photodetectors, filters, sensors, etc. A series of four amorphous and four microcrystalline samples PECVD deposited under varied hydrogen dilution was under consideration. Various absorption metrics, based separately on the absorption coefficient and the refractive index (single pass absorption, optical path length, classical light trapping limit) or direct absorptance calculated by the Yablonovitch concept based on a mutual role of them were examined and compared. Differences in absorption abilities are related to the evolving thin film microstructure.

Impact of Ar:O2 gas flow ratios on microstructure and optical characteristics of CeO2-doped ZnO thin films by magnetron sputtering

In this study, a radio frequency magnetron sputtering technique was applied to deposit eminently oriented ZnO thin films on stainless steel (SS316L). The effect of different ratios (Ar:O2) of gas flow ((20:0), (15:5), (10:10), (5:15), (0:20)) on optical and structural properties of CeO2-doped ZnO thin films has been examined. The increase in grain size of thin films was observed with a partial increase in the Ar:O2 sputtering gas at substrate temperature of 673 K. The average surface roughness of the thin films has increased with sputtering gas. The photoluminescence peak exhibited a broad green-yellow band spiked at 467 nm for all the samples of CeO2-doped ZnO thin films and a wide band of visible light focused in the 500–600 nm range. Intensity reduction of deep level emission peaks of ZnO films was observed. The refractive index of undoped and CeO2-doped ZnO thin films with various sputtering gas ratios (Ar:O2) were also investigated. The optimized argon gas flow rate findings allow us to choose the deposition conditions for CeO2-doped ZnO thin films for solar thermal applications.