Columnar Films Research Articles

Quantitative Analysis Method of Conversion of Type of Microscopic Remaining Oil Based on CT Technology

The distribution and mutual conversion of remaining oil during the process of oilfield development constitute an important basis for guiding the exploitation of remaining oil potential. Based on the visual core displacement method of CT scanning technology, CT scanning images of the oil–water phase in core models at different displacement stages were obtained, and the remaining oil types were classified. On this basis, image segmentation technology was employed to establish the transformation analysis method of remaining oil types, and the mutual transformation of microscopic remaining oil types at different displacement stages was clarified. The ability of displacement media to utilize various remaining oils was further clarified. The results demonstrate that there are significant differences in the distribution of remaining oil after the injection of different displacement media. The displacement media can not only spread the continuous-phase oil in large pores to varying degrees but also transform the discontinuous oil into continuous-phase oil in some small pore tubes, showing a “converging” transformation law, thereby enhancing the utilization degree of various remaining oils. Additionally, the surfactant’s unique capabilities of “micellar solubilization, emulsification, and oil carrying” have good adaptability to the discontinuous oil phase and can transform the discontinuous-phase remaining oil into continuous-phase remaining oil, namely columnar–film–cluster–recovery.

In situ growing of ZIF-8 crystals into TiO2 micro columnar films

This study proposes a fast and simple method for the in situ growth of metal-organic frameworks (MOFs) on metal oxide substrates as an alternative to the traditional approaches of using gold substrates and self-assembled monolayers (SAMs). As a case study, zeolitic imidazolate framework 8 (ZIF-8) crystals were grown in micro columnar TiO2 films through simple alternate and successive immersions of the TiO2 films into solutions containing the MOFs precursors. The growth process of the MOF crystals in the interstitial spaces between the TiO2 columns was investigated by varying the metal-to-ligand ratio (1:2, 1:4, and 1:8) and by employing modulating agents such as triethylamine. It was found that the optimal deposition of ZIF-8 occurred when using a higher excess of ligand and the addition of triethylamine after a controlled number of immersion cycles. These results were obtained by using glancing angle X-ray diffraction (GAXRD) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) as characterization techniques. Additionally, a density functional theory (DFT) study as well as Fourier-transform infrared spectroscopy (FTIR) and GAXRD experiments were conducted to elucidate the nucleation process. It was concluded that the starting point is the formation of a covalent bond between the Zn cations and the TiO2 on the metal oxide surface after immersion of the film into a Zinc (II) nitrate solution, allowing for the formation of MOF nuclei once the film is subsequently immersed in the 2-methylimidazole solution. The results demonstrate the feasibility of in situ growth of MOF crystals onto metal oxide structures by a layer-by-layer strategy, offering a promising alternative to conventional methods.

Capillary Force-Assisted CsPbBr3-xIx (x = 0, 1) Columnar Crystal Film for X-ray Detectors with Ultrahigh Electric Field and Sensitivity.

Inorganic halide perovskite thin-film X-ray detectors have attracted great research interest in recent years due to their high sensitivity, low detection limit, and facile fabrication process. The poor crystal quality of the thin film with uncontrollable thickness and low background voltage during detection limits its practical application. Here, a high-quality CsPbBr3-xIx (x = 0, 1) columnar crystal film is prepared by an improved melt-confined method with a porous anodic aluminum oxide (AAO) template, which stabilizes the disorder perovskite systems of CsPbBr2I by stress. The AAO-CsPbBr3-xIx (x = 0) detectors exhibit high detection accuracy and photoelectric conversion capability with an ultrahigh sensitivity of 32,399.5 μC·Gyair-1·cm-2 at 2142.9 V mm-1 under 20 kVp X-rays and 19,217.4 μC·Gyair-1·cm-2 with a higher background electric field of 6666.7 V mm-1 for AAO-CsPbBr3-xIx (x = 1). Moreover, the AAO-CsPbBr3-xIx (x = 1) film detector acquires a lower detection limit of 7.65 nGy·s-1 and a higher X-ray imaging spatial resolution of 1.6 LP/mm and 8.6 nGy·s-1 and 1.4 LP/mm for AAO-CsPbBr3-xIx (x = 0). The facile, high-quality columnar crystal film devices display great potential for low-energy and low-dose X-ray imaging in flat panel detection applications.

Tilted columnar metal film as transducer of transverse coherent acoustic phonons in picosecond acoustics

Picosecond acoustics has been widely used to study thin film elasticity, hypersound attenuation, and adhesion of thin films to substrates. A major limitation of the technique is its restriction to only longitudinal waves. Although work has been reported on the ultrafast generation and detection of transverse waves, a general method compatible with thin films deposited on silicon is still missing. In this work, we show that by depositing a tilted columnar metal film and using an optical detection sensitive to light polarization, it is possible to excite and detect optically both types of bulk acoustic waves in thin films. The protocol is first established on metalized glass substrates, then applied to a range of transparent films deposited on silicon (silica, AlN, AlScN, and SiC). In each case, Brillouin oscillations are detected at two frequencies, one being the longitudinal mode, the other the transverse. The film thickness and two sound velocities are measured in each thin film. Transverse coherent phonons as high as 116 GHz are observed in the SiC thin film.

Mechanical and Tribological Properties of Laminated (NbTaMoW)Nx Films.

Laminated (NbTaMoW)Nx films were prepared via co-sputtering. The sputtering variables were a substrate holder rotation speed of 2 and 10 rpm and a nitrogen flow ratio (fN2 = N2/(Ar + N2)) of 0.1, 0.2, and 0.4. The (NbTaMoW)Nx films fabricated at 30 rpm displayed columnar structures. The phase structures of the laminated (NbTaMoW)Nx films varied from multiple body-centered cubic phases to a nanocrystalline and a face-centered cubic phase as the fN2 increased from 0.1 to 0.2 and 0.4. The mechanical and tribological properties of the laminated (NbTaMoW)Nx films were evaluated. The laminated (NbTaMoW)Nx films deposited at an fN2 of 0.4 had hardnesses of 25.2 and 26.1 GPa when prepared at 2 and 10 rpm, respectively, lower than the value of 29.9 GPa for the columnar (NbTaMoW)Nx film prepared at an fN2 of 0.4 and 30 rpm. In contrast, the wear resistances of the laminated (NbTaMoW)Nx films were superior to those of the columnar (NbTaMoW)Nx films.

Corrosion resistance of HiPIMS tungsten and tungsten-aluminium coatings in contact with liquid Sn

Pure‑tungsten and tungsten-aluminium films deposited by high power impulse magnetron sputtering (HiPIMS) on copper‑chromium‑zirconium substrates were investigated as protective coatings against liquid tin corrosion, a critical issue for nuclear fusion applications. The growth of pure‑tungsten coatings was controlled by using a negative substrate bias synchronized to the HiPIMS pulse onset, resulting in columnar films with various degree of compactness and crystallinity according to the set bias amplitude (0, 400 and 800 V). Differently, the co-sputtering of W and Al favored the formation of an amorphous layer with a compact morphology. During liquid tin corrosion experiments at 400 °C for up to 600 min, all produced coatings were not dissolved, but different protective performances were observed after localized liquid tin interaction. Pure-W coated samples suffered from tin penetration after brittle failure of the protective layer. On the contrary, under the same experimental condition, WAl coatings proved to be effective in limiting liquid tin attack.

Enhanced cross-interfacial growth by thickening transition layers and tailoring grain size of columnar nanotwinned Cu films

Electrodeposited <111>-oriented nanotwinned Cu (NT-Cu) films consist of micron-scale columnar grains and they are thermally stable up to 400 °C. By adding nanoscale equiaxed Cu grains at the bottom of the NT-Cu films, anisotropic large grain growth could be triggered below 200 °C. The grains grew over 50 μm in bonded Cu–Cu films with 5.7 μm thick. Two main factors are identified for the low thermal stability and large grain growth behavior. The grain refining and transition layer thickening are effective to lower the thermal stability of the NT-Cu and reduce the required temperature for recrystallization and grain growth in the NT-Cu film. By increasing the fine-grained layer and refining the grain size of the columnar twinned grains, anisotropic grain growth can occur at 150 °C. The low thermal stability NT-Cu can be employed to completely eliminate the bonding interface at low temperatures in Cu–Cu joints. However, when the fine-grained layer is thicker than a threshold value, normal grain takes place and the bonding interface remains. The mechanism of anisotropic large grain growth was also proposed.

Dielectric ultracapacitors based on columnar nano-grained ferroelectric oxide films with gradient phases along the growth direction

Dielectric ultracapacitors based on columnar nano-grained ferroelectric oxide films with gradient phases along the growth direction

Characterization of columnar BiFeO3 thick films prepared by magnetic field-assisted pulsed laser deposition

Polycrystalline BiFeO3 thick films were prepared on Pt/TiO2/SiO2/Si substates by using magnetic field-assisted pulsed laser deposition. Columnar BiFeO3 thick films were successfully obtained with a thickness of 1.8 μm, owing to an oblique incoming flux and high deposition rate by the confinement of the plume under a magnetic field. In the columnar BiFeO3 thick films, a saturated P-E hysteresis loop was obtained at RT, and the remanent polarization (P r ) and coercive field (E c ) were 42 μC cm−2 and 380 kV cm−1, respectively. Also, the piezoelectric response measured by atomic force microscopy showed a butterfly-shaped curve, and the piezoelectric d 33 coefficient was about 50 pm V−1.

Exploring tribological characteristics of ZrN-MoSN composite films fabricated via RF magnetron sputtering: Insights from microstructure and performance analysis

Achieving the stringent demands of sustainable tribological industrial applications poses a significant challenge, particular in optimizing the self-lubricant performance of nitride-based films. This paper tackled this challenge by designing and depositing a series of ZrN-MoSN composite films with varying (Mo + S)/Zr ratios, employing RF magnetron sputtering, aimed to enhance the tribological properties through utilizing the high loading capacity of the ZrN matrix and the exceptional self-lubricating attributes of Mo-S-N additives. After conducting thorough investigations on the microstructure, and tribological properties, the results revealed that the dense columnar structured ZrN-MoSN composite films displayed a polycrystalline composition comprising fcc-ZrN and hcp-MoS2 phases, intertwined with amorphous phases of Mo(SN)x and MoS2(N2). (Mo + S)/Zr ratios below 1.08 exhibited a minor impact on the room temperature (RT) tribological properties, while higher ratios led to degradation on RT average friction coefficient (COF) and wear rate (WR). However, the synergistic effect of ZrN matrix and the tribo-phases of layered MoO3 and hard ZrO2 contributed to the significant enhanced 500 °C tribological properties, particularly with an optimized (Mo + S)/Zr ratio of 0.43.

Molten pool free surface solidification behavior in laser remelted near-β titanium alloy

Free surface solidification (FSS) is a common physical phenomenon that has been found by various studies in metallurgy field while targeted studies are rare. This work investigated special structure and formation mechanism of surface grains generated by free surface solidification through laser remelting a near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55,511). A thin layer crystal film covers molten pool surface through two-dimensional constrained solidification, which can be classified into flake-like crystal film located at molten pool edge and lotusleaf-like crystal film at molten pool center. Numerous cells grow from overflowing melt chill zone around molten pool edge and undergo two-dimensional constrained growth on surface, forming flake-like crystal films. TiNx particles formed from surface melt and N2 reaction can act as heterogeneous crystal nuclei, forming lotusleaf-like crystal films, whose secondary dendrite arm growth direction transforms from 〈100〉 of primary dendrite arm to 〈110〉. Equiaxed lotusleaf-like crystal films and columnar flake-like crystal films have a competitive growth relationship. Inward growth cells growing from two kinds crystal films form flake-like surface grains and central surface grains, respectively. This study can provide FSS theoretical guidance for laser additive manufacturing and surface modification.

The microstructural evolution of sputtered ZnO epitaxial films to stress-relaxed nanorods

Epitaxial ZnO thin films and nanorods were grown on c-sapphire substrate by reactive sputtering of Zn in Ar-O2 atmosphere at substrate temperatures ranging from near room temperature to 700 °C. Scanning electron microscopy showed that with increase in substrate temperature, the morphology transformed from columnar films to vertically aligned ZnO nanorods. High resolution x-ray diffraction revealed improvement in crystalline and epitaxial quality with increase in substrate temperature, along with the decrease of edge dislocation density from 5 × 1012 cm−2 to 8 × 1010 cm−2. The films grown near room temperature showed large hydrostatic strain (∼6 × 10−3) and compressive intrinsic biaxial stress (-0.8 GPa), which decreased substantially with increase in substrate temperature, due to the desorption of excess oxygen and reduction in edge dislocation density. Above the substrate temperature of 500 °C, the intrinsic biaxial stress reversed from compressive to mildly tensile in the case of nanorods, due to the intrinsic tensile stress, originating from crystallite coalescence. Raman measurements correlate well with the changes in biaxial stress and confirm the improvements in crystallinity and epitaxial quality of nanorods grown at higher temperatures. Room temperature photoluminescence of the ZnO films showed weak near-band-edge emission, which enhanced drastically in the case of nanorods due to their superior microstructure and epitaxial quality.

Synthesis and characterization of dense, rare-earth based high entropy fluorite thin films

High entropy oxides (HEOs) with 5 or more cations in equimolar proportions that result in a phase-pure material, are a new class of materials attracting a lot of attention in recent years. HEOs exhibit interesting optical, electrochemical, magnetic and catalytic properties. To get a comprehensive understanding of the physics behind the complex interactions taking place in these materials, it is important to evaluate the material in (near-fully) dense forms, such as pellets or thin films. The fluorite structured high entropy oxide, (CeLaSmPrY)O2−x has been investigated only in the powder form and there are no studies on the dense form of fluorite (CeLaSmPrY)O2−x. One of the main reasons is that (CeLaSmPrY)O2−x undergoes a structural transition from fluorite to bixbyite (at 1000 °C) and typically temperatures above the transition (>1200 °C) are required for achieving high densities via conventional sintering. In this study, we synthesize dense films of fluorite structured (CeLaSmPrY)O2−x by sol-gel as well as pulsed laser deposition processes. The films synthesized via sol-gel process exhibit equiaxed grains and polycrystalline morphology, whereas columnar and epitaxial films are obtained using pulsed laser deposition. Thus, microstructural tuning of dense fluorite (CeLaSmPrY)O2−x films has been demonstrated while maintaining the basic characteristics of the HEO as observed in the powder form, therefore, paving the way towards more comprehensive studies for possible applications.

Radio-frequency magnetron sputter deposition of ultrathick boron carbide films

The deposition of thick B4C films with low residual stress by conventional direct-current magnetron sputtering is accompanied by the formation of dust particulates contaminating the target, chamber, and substrates and leading to the formation of nodular defects in films. Here, we demonstrate that the formation of particulates is greatly reduced during radio-frequency magnetron sputtering (RFMS). We systematically study properties of B4C films deposited by RFMS with a substrate temperature of 330 °C, a target-to-substrate distance of 10 cm, Ar working gas pressure in the range of 4.5–12.0 mTorr (0.6–1.6 Pa), and substrate tilt angles of 0°–80°. All films are x-ray amorphous. A columnar structure develops with increasing either Ar pressure or substrate tilt. For columnar films, the column tilt angle decreases with increasing Ar pressure, which we attribute to a corresponding increase in the width of the distribution of impact angles of deposition flux. In contrast to the Keller–Simmons rule, the deposition rate increases with increasing Ar pressure, which suggests a better coupling of the RF energy to the plasma processes that lead to target sputtering at higher pressures. There is a critical substrate tilt angle above which the total residual stress is close to zero. This critical substrate tilt angle is ∼0° for an Ar pressure of 12 mTorr (1.6 Pa). The lower residual stress state, necessary for depositing ultrathick films, is characterized by a larger concentration of nanoscale inhomogeneities and decreased mechanical properties. Based on these results, RFMS deposition of 60-μm-thick B4C films is demonstrated.

Grain engineering of high energy density BaTiO3 thick films integrated on Si

Ferroelectric (FE) ceramics with a large relative dielectric permittivity and a high dielectric strength have the potential to store or supply electricity of very high energy and power densities, which is desirable in many modern electronic and electrical systems. For a given FE material, such as the commonly-used BaTiO3, a close interplay between defect chemistry, misfit strain, and grain characteristics must be carefully manipulated for engineering its film capacitors. In this work, the effects of grain orientation and morphology on the energy storage properties of BaTiO3 thick films were systematically investigated. These films were all deposited on Si at 500 °C in an oxygen-rich atmosphere, and their thicknesses varied between ~500 nm and ~2.6 μm. While a columnar nanograined BaTiO3 film with a (001) texture showed a higher recyclable energy density Wrec (81.0 J/cm3vs. 57.1 J/cm3 @3.2 MV/cm, ~40% increase) than that of a randomly-oriented BaTiO3 film of about the same thickness (~500 nm), the latter showed an improved energy density at a reduced electric field with an increasing film thickness. Specifically, for the 1.3 μm and 2.6 μm thick polycrystalline films, their energy storage densities Wrec reached 46.6 J/cm3 and 48.8 J/cm3 at an applied electric field of 2.31 MV/cm (300 V on 1.3 μm film) and 1.77 MV/cm (460 V on 2.6 μm film), respectively. This ramp-up in energy density can be attributed to increased polarizability with a growing grain size in thicker polycrystalline films and is desirable in high pulse power applications.

Nanostructured Semi-Transparent TiO2 Nanoparticle Coatings Produced by Magnetron-Based Gas Aggregation Source

A novel strategy to produce semi-transparent TiO2 nanoparticle-based coatings is investigated. This two-step strategy utilizes a magnetron-based gas aggregation source of Ti nanoparticles that are subsequently annealed in air at the temperature of 450 °C. It is shown that by using this technique, it is possible to fabricate highly porous and patterned TiO2 nanoparticle coatings with an optical band gap of around 3.0 eV on the substrate materials commonly used as transparent electrodes in photovoltaic applications or for water-splitting. In addition, it is shown that the morphology of the resulting coatings may be varied by changing the angle between the direction of the substrate and the incoming beam of nanoparticles. As demonstrated, the tilting of the substrate leads to the formation of columnar nanoparticle films.

Influence of HiPIMS pulse widths on the deposition behaviour and properties of CuAgZr compositionally graded films

In this work, the influence of different pulse widths (25, 50 and 100 μs) during high power impulse magnetron sputtering (HiPIMS) of copper, silver and zirconium was investigated in terms of plasma properties and properties of combinatorial composition gradient CuAgZr film libraries. In situ plasma diagnostics via optical emission spectroscopy (OES), time-of-flight mass spectrometry (TOFMS), and modified quartz crystal microbalance (m-QCM), followed by film ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations allowed to determine the effect of deposition parameters on the thin films' microstructural changes. Changing the pulse width, while keeping the duty cycle constant, modified the discharge composition in the target region and the ionised fraction of the sputtered species in the substrate region. The maximum Cu ionised fraction (19 %) was found for 50 μs, resulting in compact and smooth morphology for Cu-rich films, whereas short 25 μs pulses provided porous columnar films with rough surfaces, as the result from Ar+ bombardment. For Ag-rich films, Ag segregation allowed the deposition of dense layers, regardless of the used pulse width.Furthermore, low Ag (<10 at.%) CuAgZr films produced via HiPIMS and direct-current magnetron sputtering (DCMS) were compared in terms of structural and mechanical property changes as a function of Zr contents. For the studied chemical composition range, a linear relationship between Zr content, XRD phase shift and mechanical properties was observed for HiPIMS films, in contrast to DCMS's more abrupt transitions. An increase in hardness and elastic modulus (up to 44 % and 22 %, respectively) was found for the HiPIMS films compared to DCMS ones. The obtained results highlight HiPIMS's flexibility in providing a wide range of tailoring possibilities to meet specific application requirements, such as crystalline microstructure, density and associated mechanical properties.

Al L2,3 near edge structure captures the dopant activation and segregation in Al-doped ZnO films

Aluminum-doped zinc oxide (AZO) films have been synthesized using reactive high power impulse magnetron sputtering (HiPIMS) in a wide range of Al contents, 0.6–14.7 at.%. The film structure and microstructure investigated by X-ray diffraction and transmission electron microscopy evolves from nanocrystalline columnar film towards ultrafine nanocrystalline films of wurtzite ZnO structure upon increasing the Al content. Electrical properties measured by 4-point probe and Hall effect setups revealed that effective doping maybe achieved up to 3 at.% Al by using HiPIMS. Most importantly, optical transmittance and electronic structure measurements at the Al L2,3 of electron energy loss near edge structure (ELNES) contain signatures of dopant activation, and dopant segregation that may serve to investigate on the origin of electrical properties degradation and to optimize the electrical properties of AZO films.

Delayed Fluorescence by Triplet-Triplet Annihilation from Columnar Liquid Crystal Films.

Delayed fluorescence (DF) by triplet–triplet annihilation (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO–LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF. In contrast to the DF from the monomeric imidoester in solution, DF of the imide occurs from dimeric aggregates in the blend films, assisted by the imidoester. Thus, the close contact of intimately stacked molecules of the two different species in the columnar mesophase leads to a unique mesophase-assisted aggregate DF. This constitutes the first observation of DF by TTA from the columnar liquid crystalline state. If the imide is dispersed in films of polybromostyrene, which provides an external heavy-atom effect facilitating triplet formation, DF is also observed. Organic light-emitting diodes (OLEDs) devices incorporating these liquid crystal molecules demonstrated high external quantum efficiency (EQE). On the basis of the literature and to the best of our knowledge, the EQE reported is the highest among nondoped solution-processed OLED devices using a columnar liquid crystal molecule as the emitting layer.

Influence of the Template Layer on the Structure and Ferroelectric Properties of PbZr0.52Ti0.48O3 Films.

The microstructure of the PbZr0.52Ti0.48O3 (PZT) films is known to influence the ferroelectric properties, but so far mainly the effect of the deposition conditions of the PZT has been investigated. To our knowledge, the influence of the underlying electrode layer and the mechanisms leading to changes in the PZT microstructure have not been explored. Using LaNiO3 (LNO) as the bottom electrode material, we investigated the evolution of the PZT microstructure and ferroelectric properties for changing LNO pulsed-laser deposition conditions. The explored deposition conditions were the O2 pressure, total pressure, and thickness of the electrode layer. Increasing both the O2 pressure and the thickness of the electrode layer changes the growth of PZT from a smooth, dense film to a rough, columnar film. We explain the origin of the change in PZT microstructure as the increased roughness of the electrode layer in relaxing the misfit strain. The strain relaxation mechanism is evidenced by the increase in the crystal phase with bulk LNO unit cell dimensions in comparison to the crystal phase with substrate-clamped unit cell dimensions. We explain the change from a dense to a columnar microstructure as a result of the change in the growth mode from Frank–van der Merwe to Stranski–Krastanov. The ferroelectric properties of the columnar films are improved compared to those of the smooth, dense films. The ability to tune the ferroelectric properties with the microstructure is primarily relevant for ferroelectric applications such as actuators and systems for energy harvesting and storage.