Columnar Films Research Articles

Growth and microstructure of columnar Y-doped SrZrO3 films deposited on Pt-coated MgO by pulsed laser deposition

Direct integration of proton conductor films on Pt-coated substrates opens the way to film-based proton transport devices. Columnar SrZr0.95Y0.05O3−δ (SZY) films with dense microstructure were deposited on Pt-coated MgO(100) substrates at 830 °C by pulsed laser deposition. The optimal window of ambient O2 pressure for good crystallinity of SZY films is from 400 to 600 mTorr. The ambient O2 compresses the plasma plume of SZY and increases the deposition rate. The 10 nm thick Ti adhesion layer on MgO(100) greatly affects the orientation of the sputtered Pt layers. Pt deposited directly on MgO shows a highly (111)-preferred orientation and leads to preferentially oriented SZY films while the addition of a Ti adhesion layer makes Pt show a less preferential orientation that leads to randomly oriented SZY films. The RMS surface roughness of preferentially oriented SZY films is larger than that of randomly oriented SZY films deposited under the same ambient O2 pressure. As the O2 pressure increased, the RMS surface roughness of preferentially oriented SZY films increased, reaching 45.7 nm (2.61% of film thickness) at 600 mTorr. This study revealed the ambient O2 pressure and orientation dependent surface roughness of SZY films grown on Pt-coated MgO substrates, which provides the potential to control the surface microstructure of SZY films for electrochemical applications in film-based hydrogen devices.

A review on the understanding and fabrication advancement of MgB2thin and thick films by HPCVD

MgB2 thin films with superior superconducting properties are very promising for superconducting magnets, electronic devices and coated conductor electric power applications. A clear understanding of flux pinning mechanism in MgB2 films could be a big aid in improving the performance of MgB2 by the enhancement of Jc. The fabrication advancement and the understanding of flux pinning mechanism of MgB2 thin and thick films fabricated by using hybrid physical-chemical vapor deposition (HPCVD) are reviewed. The distinct kind of MgB2 films, such as single-crystal like MgB2 thin films, MgB2 epitaxial columnar thick films, and a-axis-oriented MgB2 films are included for flux pinning mechanism investigation. Various attempts made by researchers to improve further the flux pinning property and Jc performance by means of doping in MgB2 thin films by using HPCVD are also summarized.

Crystalline ZrO2 doping induced columnar structural FePt films with larger coercivity and high aspect ratio

Columnar (001) FePt-ZrO2-C films with large coercivity, small grain size, and high aspect ratio were obtained. By doping ZrO2 into FePt film at high sputtering temperature, tetragonal (002) textured ZrO2 was formed and distributed at the grain boundaries of FePt grains, resulting in the formation of columnar structured FePt films. The perpendicular anisotropy of FePt films was degraded since some (200) FePt grains were formed directly on the (002) textured ZrO2. With a small amount of carbon doping into FePt-ZrO2 35 vol. % films, the perpendicular anisotropy was improved. However, FePt grains were still interconnected. Upon further increasing concentration of ZrO2, (001) textured FePt-ZrO2 40 vol. %-C 5 vol. % films with well isolated grains in average diameter of 5.5 nm and very good columnar structure were obtained.

Dislocation-mediated relaxation in nanograined columnar palladium films revealed by on-chip time-resolved HRTEM testing.

The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications.

The Relevance of Different Oxygen Reduction Pathways of La0.8Sr0.2MnO3 (LSM) Thin Film Model Electrodes

Sr-doped lanthanum manganite (LSM) is a widely used cathode material in solid oxide fuel cells (SOFC). Despite being a poor ion conductor, LSM electrodes can reduce oxygen via two pathways: a “3PB surface path” which includes surface diffusion of oxygen species and oxide ion incorporation at the three phase boundary (3PB), and a “bulk path” based on oxygen diffusion in LSM. In this work, the kinetics of both paths and their dependence on temperature and electrode geometry is investigated by impedance spectroscopy on micropatterned LSM thin film electrodes. Differently shaped and sized macroscopic and microscopic LSM electrodes as well as LSM electrodes with oxygen blocking Pt capping layers are employed to identify two parallel reaction pathways of oxygen reduction. On circular microelectrodes the 3PB surface path carries most of the current in the lower temperature region (below ca. 700°C), while at high temperatures (above ca. 700°C) the bulk path is dominating. The significance of each reduction path also depends on the microstructure of the columnar LSM films which can be changed by varying pulsed laser deposition (PLD) parameters or by annealing. Moreover, relevance of a pseudo-3PB path across edges of the LSM electrodes is discussed.

The Role of Silver in Mitigation of Whisker Formation on Thin Tin Films

The mitigating effect of alloying Sn thin films with Ag on the formation of Sn whiskers was investigated by time-resolved investigations employing x-ray diffraction for phase and stress analyses and focused ion beam microscopy for morphological characterization of the surfaces and cross-sections of the specimens. The investigated Sn-6 wt.%Ag thin films were prepared by galvanic co-deposition. The results are compared with those obtained from investigation of pure Sn films and discussed with regard to current whisker-growth models. The simultaneous deposition of Sn and Ag leads to a fine-grained microstructure consisting of columnar and equiaxed grains, i.e. an imperfect columnar Sn film microstructure. Isolated Ag3Sn grains are present at the Sn grain boundaries in the as-deposited films. Pronounced grain growth was observed during aging at room temperature, which provides a global stress relaxation mechanism that prevents Sn whisker growth.

Improved thermoelectric performance of a film device induced by densely columnar Cu electrode

In this study, it was found that the columnar Cu film is similar as a parallel microchannel which can create some sort of channels for the easy transport of electrons and phonons in the device. The p-Bi0.5Sb1.5Te3, n-Bi2Se0.3Te2.7 and Cu films were fabricated by a magnetron sputtering method. These films have been integrated into low-dimension cross-plane devices using mask-assisted deposition technology. The performance of the micro-device with densely columnar Cu film electrode has been tested, which was very superior to that of the device with ordinary structure electrode. For the typical device with 98 pairs of p/n couples, the output voltage and maximum power were up to 120.5 mV and 145.2 μW, respectively, for a temperature difference of 4 K. The device could produce a 14.6 K maximum temperature difference at current of 160 mA. The response time to reach the steady condition was less than 2 S. The results prove that excellent performance of micro-device can be realized by integrating the densely columnar Cu electrode.

Enhancement of thermoelectric properties induced by oriented nanolayer in Bi2Te2.7Se0.3 columnar films

In this paper, it was found that layered and columnar structure can favorably influence the carrier and phonon transport properties of films. The n-Bi2Te2.7Se0.3 columnar film with layered structure was successfully achieved by simple magnetron co-sputtering method at 400 °C deposition temperature, due to the more sufficient growth along the in-plane direction induced by the enhanced mobility of deposited atoms. The layered nanostructure is clear with each layer <25 nm in the columnar film. The properties of the Bi2Te2.7Se0.3 columnar film with layered structure were greatly enhanced in comparison with those of the columnar and the ordinary films synthesized respectively at 350 °C and 250 °C deposition temperature. The layered Bi2Te2.7Se0.3 columnar film with a thermoelectric dimensionless figure-of-merit ZT = 1.27 was obtained at room temperature. The layered column structure was the main reason for the properties enhancement observed in the Bi2Te2.7Se0.3 film. Introduction of such uniquely layered and columnar structure into thermoelectric films is therefore a very promising approach.

고압 수증기하 산화에서 핵연료 피복관내 수소효과 연구

The characteristics of oxidation for the Zry-4 was measured in the 800 o C and high steam pressure (50 bar, 75 bar, 100 bar) conditions, using an apparatus for high pressure steam oxidation. The effect of accelerated oxidation by high-pressure steam was increased more than 60% in hydrogen-charged cladding than normal cladding. This difference between hydrogen charged claddings and normal claddings tends to be larger as the higher pressure. The accelerated oxidation effect of hydrogen charging cladding is regarded as the hydrogen on the metal layer affects the formation of the protective oxide layer. The creation of the sound monoclinic phase in Zry-4 oxidation influences reinforcement of corrosion-resistance of the oxide layer. The oxidation is estimated to be accelerated due to the creation of equiaxial type oxide film with lower corrosion resistance than that of columnar type oxide film. When tetragonal oxide film transformed into the monoclinic oxide film, surface energy of the new monoclinic phase reduced by hydrogen in the metal layer.

Affection of Post-Nitrogen-Doping of ZnO Columnar Films Photo-Anode on Performance of Dye-Sensitized Solar Cells

ZnO was a promising n-type conductive semiconductor material for dye-sensitized solar cells. Stable and efficient preparation of high quality p-type ZnO films became the main difficulty in current research. In this paper, a nitrogen-doped ZnO columnar film on an indium tin oxide (ITO) substrate was successfully obtained by gas phase method. The absorption of visible light was improved by nitrogen-doped ZnO columnar films. This experiment provided a good strategy for the full utilization of solar energy.

Morphology and Curie temperature engineering in crystalline La0.7Sr0.3MnO3 films on Si by pulsed laser deposition

Of all the colossal magnetoresistant manganites, La0.7Sr0.3MnO3 (LSMO) exhibits magnetic and electronic state transitions above room temperature, and therefore holds immense technological potential in spintronic devices and hybrid heterojunctions. As the first step towards this goal, it needs to be integrated with silicon via a well-defined process that provides morphology and phase control, along with reproducibility. This work demonstrates the development of pulsed laser deposition (PLD) process parameter regimes for dense and columnar morphology LSMO films directly on Si. These regimes are postulated on the foundations of a pressure-distance scaling law and their limits are defined post experimental validation. The laser spot size is seen to play an important role in tandem with the pressure-distance scaling law to provide morphology control during LSMO deposition on lattice-mismatched Si substrate. Additionally, phase stability of the deposited films in these regimes is evaluated through magnetometry measurements and the Curie temperatures obtained are 349 K (for dense morphology) and 355 K (for columnar morphology)—the highest reported for LSMO films on Si so far. X-ray diffraction studies on phase evolution with variation in laser energy density and substrate temperature reveals the emergence of texture. Quantitative limits for all the key PLD process parameters are demonstrated in order enable morphological and structural engineering of LSMO films deposited directly on Si. These results are expected to boost the realization of top-down and bottom-up LSMO device architectures on the Si platform for a variety of applications.

High performance of thick amorphous columnar monolithic film silicon anodes in ionic liquid electrolytes at elevated temperature

The cycling performance of thick (about 7 μm) amorphous columnar monolithic film silicon anodes was studied in ionic liquid based electrolyte solutions. More than 1000 cycles at 60 °C were achieved.

Photoirradiation Caused Controllable Wettability Switching of Sputtered Highly Alignedc-Axis-Oriented Zinc Oxide Columnar Films

This study presents the microstructure morphology and UV photoirradiation coupling effects of the c-axis-oriented zinc oxide (ZnO) columnar films. Highly aligned c-axis-oriented films have been deposited onto glass substrates at room temperature by radio-frequency (RF) magnetron sputtering without introducing any oxygen source under different sputtering powers ranging from 50 to 150 W. Self-assembled ZnO columnar structures that were successfully obtained belong to wurtzite structure, and the corresponding columnar structures and crystalline orientation were confirmed by the FE-SEM and XRD, respectively. All the ZnO columnar films exhibit good transparency with a visible light averaged transmittance over 82%. According to water contact angle (CA) measurement, ZnO columnar films exhibit hydrophobic behavior. After exposing to photoirradiation under ultraviolet (UV) environment, all the ZnO samples showed remarkable transition from hydrophobic to superhydrophilic surfaces and could return to their original hydrophobicity after being placed in the dark. It is demonstrated that the controllable wettability of ZnO columnar films under changing between the UV photoirradiation and dark storage is due to the surface charges accumulation and discharging processes. As a result, this study could provide important applications for many fields such as ZnO-based hybrid sensors/solar cells functional devices with photoirradiation disinfection surfaces accompanied with reversible wettability switches.

Elasticity-dependent self-assembly of micro-templated chromonic liquid crystal films

We explore micropatterned director structures of aqueous lyotropic chromonic liquid crystal (LCLC) films created on square-lattice cylindrical-micropost substrates. The structures are manipulated by modulating the LCLC mesophases and their elastic properties via concentration through drying. Nematic LCLC films exhibit preferred bistable alignment along the diagonals of the micropost lattice. Columnar LCLC films, dried from nematics, form two distinct director and defect configurations: a diagonally aligned director pattern with local squares of defects, and an off-diagonal configuration with zig-zag defects. The formation of these states appears to be tied to the relative splay and bend free energy costs of the initial nematic films. The observed nematic and columnar configurations are understood numerically using a Landau-de Gennes free energy model. Among other attributes, the work provide first examples of quasi-2D micropatterning of LC films in the columnar phase and lyotropic LC films in general, and it demonstrates alignment and configuration switching of typically difficult-to-align LCLC films via bulk elastic properties.

Deposition of yttria-stabilized zirconia thin films by high power impulse magnetron sputtering and pulsed magnetron sputtering

Yttria-stabilized zirconia (YSZ) thin films were reactively sputter-deposited by high power impulse magnetron sputtering (HiPIMS) and pulsed direct current magnetron sputtering (DCMS). The use of substrate bias voltage was studied in both modes of deposition as a process parameter to promote the growth of dense and less columnar films. Films were deposited on both Si(100) and NiO–YSZ fuel cell anodes. The texture, morphology and composition of the deposited films were investigated with regard to their application as thin electrolytes for solid oxide fuel cells (SOFCs). Independent of the deposition mode the films were found to be stoichiometric. The application of substrate bias voltage had opposite effects on texture and crystallinity of films deposited by pulsed DCMS and HiPIMS. Films deposited by pulsed DCMS became highly crystalline and <220> textured at high bias voltage whereas bias applied to HiPIMS deposited films disrupted crystal growth leading to deterioration of crystallinity. Comparing film morphology, it was found that pulsed DCMS films were columnar and contained voids regardless of the applied substrate bias. When depositing by HiPIMS a window of operation at a bias voltage of −25V to −50V was found in which it is possible to deposit non-columnar thin films without voids and cracks as desired for SOFC applications.

New Structure of Cathode Function Layer of SOFC By Nanoporous Columnar YSZ Films

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Enhancement of the photocatalytic property of TiO2 columnar nanostructured films by changing deposition angle

Isolated and inclined columnar nanostructured TiO2 films were obtained by sputtering titanium with glancing angle deposition method and subsequently annealing in air. Compared with flat film, TiO2 film fabricated with this method has higher porosity; compared with TiO2 powder, it overcomes the obstacles of immobilization and recycling. The TiO2 photocatalysis was evaluated by the degradation of methyl orange under UV light. It was indicated that the photocatalytic performance increased with deposition angle, which changed the porosity of the films. The relationship between deposition angle (the angle between the target and substrate surface) and the TiO2 columnar inclination angle (the angle between TiO2 columnar and substrate normal) was discussed.

New Structure of Cathode Function Layer of SOFC by Nanoporous Columnar YSZ Films

The Solid Oxide Fuel Cell (SOFC) is an electrochemical device operated at high temperature(500-900℃), it transforms the chemical energy stored in fuels into electrical energy and heat. The first element of fuel cell industry is reduce the SOFC to 400-600℃. We realize the nanoscale interface to enhance the conductivity effect by nanostructure of the electrode function, thereby we find a new way to explore new cathode functional layer materials and new structure.

The role of aluminum distribution on the local corrosion resistance of the microstructure in a sand-cast AM50 alloy

Abstract Site-specific analytical electron microscopy was performed on a corroded sand-cast AM50 alloy. Areas close to partially divorced eutectic were the regions with less corrosion damage. The corrosion product layer in these areas consisted of a columnar section of predominantly amorphous MgO. At the alloy interface, an aluminum-rich layer was identified. Electron energy-loss spectroscopy suggests this layer is metallic in character. The corrosion product film on the primary α-Mg grains possessed a bi-layer morphology: a thin columnar film and a thicker, porous sub-layer. The formation of the Al-rich layer depends on the Al content in solid solution at a specific location.

Tuning properties of columnar nanocomposite oxides

One major challenge for engineering functional nanocomposites is how to tune the geometry structure and control the chemical composition. We demonstrate here that columnar nanocomposite films can be grown by using alternate deposition of La2/3Sr1/3MnO3 and V2O3 on LaAlO3 (111). A solid state reaction, rather than simple spinodal decomposition, dictates the nanocomposite structure, chemical composition, and functionality. By controlling the deposition time ratio of the two compounds, the physical properties of the composite films can be tuned, thus providing a flexible way to tailor nanocomposites for advanced functionality.