Formation Process Of Thin Films Research Articles

Advanced thin films of indium-tin oxide doping with photosensitive polymer via embossing process

We propose a sol-gel thin film formation process involving nanoimprint lithography. First, indium tin oxide was dissolved in 2-methoxyethanol at a ratio of 5:5 and the mixture were mixed with 10 wt% of a UV-curable. Subsequently, a polydimethylsiloxane sheet prepared by covering a silicon wafer with a polydimethylsiloxane mold was attached to a InSnO thin film to duplicate the nanostructure through UV irradiation exposure. The replicated nanostructured thin films formed about morphological and chemical composition changes on the surface, we progressed to x-ray photoelectron spectroscopy and atomic force microscopy analysis. Furthermore, atomic force microscopy image analysis showed superior patterned grooves for a UV exposure time of 3 min. A suitability test involving the measurement of the transmittance was performed for examining the suitability of the thin film for use in display devices.

Synthesis and Optimization of Cs2B'B″X6 Double Perovskite for Efficient and Sustainable Solar Cells.

Hybrid perovskite materials with high light absorption coefficients, long diffusion lengths, and high mobility have attracted much attention, but their commercial development has been seriously hindered by two major problems: instability and lead toxicity. This has led to lead-free halide double perovskite becoming a prominent competitor in the photovoltaic field. For lead-free double perovskites, Pb2+ can be heterovalent, substituted by non-toxic metal cations as a double perovskite structure, which promotes the flexibility of the composition. However, the four component elements and low solubility in the solvent result in synthesis difficulties and phase impurity problems. And material phase purity and film quality are closely related to the number of defects, which can limit the photoelectric performance of solar cells. Therefore, based on this point, we summarize the synthesis methods of Cs2B'B″X6 double perovskite crystals and thin films. Moreover, in the application of solar cells, the existing research mainly focuses on the formation process of thin films, band gap adjustment, and surface engineering to improve the quality of films and optimize the performance of devices. Finally, we propose that Cs2B'B″X6 lead-free perovskites offer a promising pathway toward developing highly efficient and stable perovskite solar cells.

A Quartz Crystal Microbalance (QCM) Study on the Formation of Aqueous κ-Carrageenan-Chitosan Composite Bilayers with NaCl and Graphene Oxide

Biomaterials and thin biofilms play a fundamental role in the medical, food and pharmaceutical industries. The Quartz crystal microbalance (QCM) measurement technique is one of the attractive techniques which have been used for monitoring the thin-film formation process. In the current work described here, κ-carrageenan and chitosan solutions were used for the layer-by-layer (LBL) deposition of polyelectrolyte multilayers (PEMs) on the gold surface of a 5 MHz AT-cut (thickness-shear mode) quartz crystal in a flow module. A sensitive QCM system was designed to detect 0.1 Hz differences in the resonance frequency (Δf) and 10−7 changes in the energy dissipation (ΔD) values, which are the measures of the deposited mass and the film rigidity, respectively. Negatively charged carrageenan and positively charged chitosan biomolecules in the solutions were used to build up sequential and very thin bilayers on the modified gold surface. The effects of NaCl and graphene oxide (GO) addition on the mass of the deposited films were also investigated. Intermolecular interactions between the biopolymer chains, Na+ cations and GO sheets were explained by interactions between molecules, such as electrostatic forces and hydrogen bondings.

Laser-driven self-organized evolution of 1D- and 2D-Nanostructures from metal thin-films on silicon: Influence of alloying and oxidation

One- and two-dimensional laser-induced periodic surface structure (LIPSS) formation of various metal (Ag, Cu, Fe, Zn, Ti) thin films on silicon wafers is achieved by irradiation with circularly polarized 532 nm nanosecond laser pulses. The occurrence and the evolution of pseudo-1D linear periodic, 2D honeycomb-like structures, and 2D periodic nanoparticle arrays were mapped for each element in dependence on the energy applied, i.e. the effective pulse number, and the metal thin film thickness. Samples series with increasing pulse counts monitor, like snapshots, the progressive pattern evolution. Because the metal thin films are of nanometer thickness only, the co-structuring of the silicon substrate must be taken into account in all cases. Even more complex are LIPSS formations on samples carrying two stacked thin films. The LIPSS formation process of thin films becomes rather complex as soon as co-structuring of the substrate, oxidation of the material, and alloy formation with substrate material or a potential second thin film layer are considered. All these effects affect the morphology of the formed LIPSS patterns.

Stability and formation process of hydrogen-bonded organic porous thin films: A molecular dynamics study

Molecular dynamics simulation using the reactive force field was performed to investigate the stability and formation mechanisms of organic porous thin films made of 1,3,5-tris(4-carboxyphenyl) benzene (BTB) molecules fabricated at the air/water interface. A single-layer honeycomb structure is found to be unstable, whereas thicker films are stable, which is consistent with experimental findings. The slight corrugation of the existing film produces local charge variation that attracts isolated molecules via the Coulomb interaction. When the isolated molecule approaches the film, a hydrogen bond is formed, and then the molecule adjusts the adsorption configuration by itself to maximize both horizontal and vertical intermolecular interactions. The key to the initial hydrogen bond formation is suggested to be the density of the molecules provided in the system as well as the spontaneous alignment of the BTB molecules to the solution/water interface. Our study showed that the BTB film is stable, and the molecules are self-assembled without external forces in the quasi-two-dimensional system. These results suggest that the dominant factor for the film formation at the air/water interface is interactions among BTB molecules and confinement to the two-dimensional space.

Tuneable polarity and enhanced piezoelectric response of ZnO thin films grown by metal–organic chemical vapour deposition through the flow rate adjustment

The formation process of ZnO thin films grown by pulsed-liquid injection metal–organic chemical vapour deposition (PLI-MOCVD) has a major impact on its morphological, structural, electrical and piezoelectric properties, but their correlation has not been elucidated yet nor decoupled from the thickness effects.

Role of solution concentration in formation kinetics of bromide perovskite thin films during spin-coating monitored by optical in situ metrology.

Optoelectronic devices based on metal halide perovskites continue to show a improved performance, and solution-based coating techniques pave the way for large-area applications. However, not all parameters influencing the thin film formation process of metal halide perovskites are identified and entirely rationalised over their full compositional range, thus hampering optimised thin film fabrication. Furthermore, while the perovskite deposition via spin-coating and annealing is an easily accessible technique, more profound insights into the chemical formation process are still lacking. Varying the precursor solution concentration is commonly used to vary the resulting thin film thickness. This study shows that varying the precursor solution concentration also affects the thin film morphology and optoelectronic quality. Hence, we herein investigate the influence of the precursor solution concentration on the formation process of a pure bromide-based triple cation perovskite (Cs0.05MA0.10FA0.85PbBr3) by fiber-based optical in situ measurement. During the spin-coating process, in situ UV-vis and PL measurements reveal formation kinetics are strongly dependent on the concentration. Furthermore, we identify delayed nucleation and retarded growth kinetics for more concentrated precursor solutions. In addition, we quantify the shifting chemical equilibrium of colloidal pre-coordination in the precursor solution depending on concentration. Namely, colloids are pre-organised to a higher degree and higher-coordination lead-bromide complexes tend to form in more concentrated precursor solutions. Thus, the modified solution chemistry rationalises retarded perovskite formation kinetics and highlights the precursor concentration as an influential and optimisable parameter for solution-based thin film deposition.

Impact of band-engineered polymer-interlayers on heterojunction solar cells based on 2D-layered perovskites (Cs3Sb2ClxI9−x)

Thin-film formation process of Cs3Sb2ClxI9−x perovskite in its 2D layered-form is complex and provides a poor control over film-morphology and results in a rough film-surface. Such a surface prompts formation of recombination centers for photogenerated carriers at the interface between the active and carrier-transport layers. We report a process of interface-engineering to decrease recombination loss and thereby improve photovoltaic parameters. Apart from using an inert polymer layer to improve the surface morphology of Cs3Sb2ClxI9−x thin-films, we have introduced transition metal dichalcogenide (TMD) nanoflakes into the polymer; the hybrid interlayer (polymer:TMD) between the active perovskite layer and an electron-transport layer (ETL) could increase the recombination resistance without affecting the series resistance of devices, leading to an increase in photovoltaic properties. We have employed atomic force microscopy and Kelvin probe force microscopy to probe the perovskite surface. Current-voltage characteristics and impedance spectroscopy of the devices were recorded to derive their recombination and series resistances upon the interface-engineering process. Band-diagram of the devices based on Cs3Sb2ClxI9−x/polymer:TMD/ETL have been drawn from scanning tunneling spectroscopy and differential tunnel conductance thereof. The heterojunction devices with a type-II band-alignment at the interfaces have resulted in an enhanced photovoltaic performance in Cs3Sb2ClxI9−x-based solar cells with a PCE of 3.42%.

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.

Aqueous solution-deposited aluminum-gallium-oxide alloy gate dielectrics for low voltage fully oxide thin film transistors

Different to conventional high-κ gate dielectric fabrication that usually generates porosity and pinhole sites when evaporating solvents or impurities in the thin-film formation process, herein, we report a simple aqueous route to deposit aluminum-gallium-oxide (AGO) alloy gate dielectrics. Compared to GaOx dielectric, higher performance and aqueous solution-processed low voltage fully oxide thin film transistors (TFTs) are achieved based on the AGO dielectric films. The solution-processed IZO(300 °C)/AGO TFT with optimal performance shows a good charge carrier saturation mobility of 55.4 cm2 V−1 s−1, an on/off current ratio of ∼104, threshold voltage of 0.1 V, and a low operation voltage of 5 V. Our study represents a significant step toward the development of low-cost, easy-control, and large-area oxide electronics.

딥코팅 공정을 이용하여 제작된 유연 인조혈관의 균일도 향상에 관한 연구

Three-dimensional (3-D) printing, with its capability for producing arbitrary shapes, has shown great potential for usage in patient-specific tissue engineering. However, if artificial tissues are fabricated directly through typical 3-D printing processes, the mechanical properties, particularly for softness or flexibility, significantly differ from those of natural tissues, resulting in inappropriate side effects during surgeries using vascular grafts. However, this can be overcome through the indirect 3-D printing of templates created with a thin-film formation process, such as dip coating. Dip coating is performed in two steps, including dipping/withdrawing a target base template from a polymer solution, and then drying the solvent into a solid thin film on the template. However, it is difficult to form a uniform layer on the arbitrary template because the gravitational flow of the coated solution disturbs the uniformity of the template as the solvent is drying. Therefore, we minimized the flow around the template after dip coating by rapidly removing the solvent removal by dipping the solution-coated template into ethanol. This reduced the solvent removal time and increased the viscosity of the coated solution, thereby alleviating the gravitational flow of the coated solution, and allowing us to successfully fabricate flexible vascular grafts.

Statistical Model of a Thin Film Formation

This paper presents a model of a thin film formation process of an amorphous alloy as a sequential procedure when a conditional unit of substance is randomly thrown onto a substrate at each next step. The islands of a precipitant are generated on the substrate with an increase of number of steps (density defects of substance). We determine the probability distribution of an island area, which shows the maximum informational entropy. An algorithm for computing estimates of parameters of this distribution is obtained. The results of processing experimental data are presented. We demonstrate that the proposed distribution is more consistent with the experimental data than the Pareto distribution.

Thin liquid films formation and evaporation mechanisms around elongated bubbles in rectangular cross-section microchannels

Thin film evaporation is the dominant mechanism of heat transfer in the microchannel flow boiling process. Hence, its understanding is paramount to development of predictive models and more efficient microchannel heat exchangers. Although microchannels mostly have a rectangular cross-section, the existing models are developed for circular cross-section microchannels. The non-uniformity of the liquid film thickness in microchannels with a rectangular cross-section has made prediction of the onset of dryout and heat transfer coefficient greatly challenging. Here, a test device capable of measuring the wall heat flux is utilized to fully characterize the thin film formation and evaporation process. The effects of flow capillary number (Ca) and channel aspect ratio on the liquid film thickness are determined in microchannels with 300 μm width and 300, 150, and 75 μm heights, representing aspect ratios of 1, 2, and 4, respectively. It is shown that the only existing mechanistic model for the elongated bubble regime in microchannels fails to predict the experimental heat transfer coefficient (HTC) both quantitively, by a 50–120% margin, and qualitatively, due to a fundamental difference in evaporation and dryout of a variable versus a uniform film assumed in the model. The results presented here pave the way for development of a more accurate mechanistic model for the thin film evaporation heat transfer mechanism in microchannels with a rectangular cross-section.

Parylene-based polymeric dielectric top-gate organic field-effect transistors exposed to a UV/ozone environment

Abstract Organic field-effect transistors (OFETs) structured with a top-gate configuration have several advantages, such as better charge-carrier injection, easy gate line designing, and encapsulation or protection of devices, over those configured with a bottom-gate architecture. In particular, Poly (para-xylylene) (Parylene) -based polymer and its derivatives are considered suitable insulating materials for these transistors, due to thin film formation through a low-temperature vapor deposition process, superior barrier properties, and excellent dielectric characteristics. In this study, we analyzed two types of Parylene dielectrics (Parylene-C and Parylene -AF) considering their thin film formation process, surface, insulating, and OFET operation characteristics. Furthermore, we investigated the durability of the top-gate based OFETs composed of two polymer dielectrics while it was exposed to a UV/ozone environment. Also, we could fabricate UV/ozone durable top-gate OFETs composed by a bilayer with both Parylene dielectrics. We expect, therefore, that these results will help the selection and use of versatile dielectric layers for top-gate based OFETs.

Molecular engineering of a conjugated polymer as a hole transporting layer for versatile p–i–n perovskite solar cells

Along with the development of perovskite materials, which have enormous potential for optoelectronics such as solar cells and light-emitting diode devices, numerous organic semiconductor polymers, which have been critically adopted into the hole and electron transporting layers, have been synthesized and studied. In n–i–p-structured perovskite solar cells, various outstanding polymer materials have been successfully applied. However, in p–i–n-structured solar cells, the hydrophobic nature of the polymers makes the sequential deposition of a perovskite thin film difficult. Several destructive methods have been proposed; however, a more efficacious and fundamental method is urgently needed. Here, we present a nondestructive polymer hole-transporting layer (HTL) thin-film formation process based on molecular engineering via a simple solvent process. When we used various solvents with different volatilities, perovskite film formation was achieved on polymer thin films formed from highly volatile solvents. In addition, we elucidated the structure and orientation of the molecules in the films and revealed that the molecular structure of face-on orientation for the horizontally aligned hydrophobic alkyl groups induced a lower surface energy of the film, as determined by grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. Furthermore, the tilt angle of the molecules, which was calculated from the results of quantitative near-edge X-ray absorption fine structure (NEXAFS) analysis, was found to correlate with the surface energy. This result provides guidance for polymer-orientation and surface-energy studies, and perovskite solar cells fabricated using the polymer HTL demonstrated good durability and flexibility. We expect that our approach represents a new route for fabricating p–i–n-structured solar cells and that numerous valuable p-type conjugated polymers will be developed via our proposed molecular engineering process.

(Invited) Impact of Stoichiometry and Interface Configuration on the Time Stability and the Speed-Limiting Step in Memristive SrTiO3 Cells

Resistive switching oxides are promising candidates for future non-volatile memory and for functional units of neuromorphic computing. Epitaxial SrTiO3 thin films can be regarded as model system for resistive switching thin films due to their well-known defect chemistry and the absence of grain boundaries. We have recently shown that so-called eightwise switching in SrTiO3 can be attributed to the release and reincorporation oxygen at the interface to a Pt electrode [1,2]. In the light of this knowledge, we studied in detail the impact of the Sr/Ti stoichiometry on the filament formation process, the filament stability [3] and the switching kinetics. We observed that Sr rich thin films exhibit an improved retention of the low resistive state (LRS) at low current compliance values with respect to the stoichiometric thin films. In order to identify the underlying processes, we investigated the filament formation process of SrTiO3 thin films with different stoichiometry by photoelectron emission microscopy. Stoichiometric thin films form a stable LRS state as soon as the current compliance is sufficient to trigger SrO segregation at the surface [4]. We attribute this to the impeded reoxidation of the oxygen deficient filament by the presence of the SrO at the surface. We could mimic this effect by intentionally depositing additional SrO, or other oxygen blocking layers such as Al2O3 on the surface of stoichiometric thin films and were thereby able to improve the memory window as well as the LRS retention. We furthermore investigated the switching kinetics of the SET process for different Sr/Ti stoichiometries and interface layers. We compared these results to analytical models for the switching kinetics based on ion movement, modeled by the Mott-Gurney-Law, and an oxygen exchange reaction at the interface, modeled by the Butler-Volmer-Equation, as the rate-determining steps in combination with simulated temperature and electrical potential data from finite element simulations, as shown in Figures 1 ((a) stoichiometric, (b) Sr rich). For stoichiometric SrTiO3 cells, oxygen transfer at the oxide-metal interface is determined as the rate-determining step. In contrast, for Sr-rich STO cells we propose oxygen diffusion within the SrO layer at the metal-STO interface as rate-limiting. We will discuss possible reasons for the different rate-determining steps, such as different vacancy concentrations and exchange probabilities.

Effect of post-deposition annealing in oxygen atmosphere on LiCoMnO4 thin films for 5 V lithium batteries

Thin-film batteries are a promising microscale high-capacity energy sources for future micro devices. One possible way to increase the energy density is to use a cathode made of spinel LiCoMnO4, which has a theoretical specific energy of 475 Wh/kg and operates at about 5 V. However, one problem of this material is the loss of oxygen in the lattice during the thin-film formation process, which causes the loss of capacity at 5 V and the appearance of unexpected peak at around 4 V. In the study reported here, the effect of oxygen loss on the thin-film battery performance was investigated using post-deposition annealing of the thin-films under an oxygen flow at different temperatures and for different periods of time. The crystallinity and oxygen deficiency were characterized by the intensity of the X-ray diffraction (XRD) peaks and their shift in position. A clear correlation was found between the discharge capacity and the XRD peak shift (or oxygen content of the thin films). Based on these results, the optimum combination of conditions for post-deposition annealing of the LiCoMnO4 thin films was determined to be a temperature of 600 °C for 6 h under an oxygen atmosphere.

Nanoporous alumina thin films with interpenetrated structure via alternating voltage anodization

Ordered nanoporous alumina thin films with interpenetrated structures were prepared via alternating voltage (AV) anodization of Al foils in oxalic acid aqueous solutions. Anodization at different time periods was systematically investigated to better understand the formation process of this unique structure. Meanwhile, the corresponding current-time transient curves were recorded to monitor the formation process. Based on the obtained results, the possible formation process of porous alumina thin films with interpenetrated structure was discussed.

Record Efficiency Stable Flexible Perovskite Solar Cell Using Effective Additive Assistant Strategy.

Even though the power conversion efficiency (PCE) of rigid perovskite solar cells is increased to 22.7%, the PCE of flexible perovskite solar cells (F-PSCs) is still lower. Here, a novel dimethyl sulfide (DS) additive is developed to effectively improve the performance of the F-PSCs. Fourier transform infrared spectroscopy reveals that the DS additive reacts with Pb2+ to form a chelated intermediate, which significantly slows down the crystallization rate, leading to large grain size and good crystallinity for the resultant perovskite film. In fact, the trap density of the perovskite film prepared using the DS additive is reduced by an order of magnitude compared to the one without it, demonstrating that the additive effectively retards transformation kinetics during the thin film formation process. As a result, the PCE of the flexible devices increases to 18.40%, with good mechanical tolerance, the highest reported so far for the F-PSCs. Meanwhile, the environmental stability of the F-PSCs significantly enhances by 1.72 times compared to the device without the additive, likely due to the large grain size that suppresses perovskite degradation at grain boundaries. The present strategy will help guide development of high efficiency F-PSCs for practical applications.

The phase formation process of Bi0.5(Na0.8K0.2)0.5TiO3 thin films prepared using the sol-gel method

Lead-free Bi0.5(Na0.8K0.2)0.5TiO3 (abbreviated as BNKT) thin films were grown on Pt(111)/Ti/SiO2/Si substrates using a sol-gel/spin coating technique and were then annealed at different temperatures (350°C, 550°C, 750°C and 850°C). Analysis of the XRD patterns and FT-IR spectra were used to determine the main reactions and the phase formation process of BNKT thin films during the sol-gel process. The results show that the dielectric constant of the thin films attains a maximum at a set temperature and then decreases at higher annealing temperatures, which can be attributed to phase formation and transformation. Moreover, the morphologies of the BNKT thin films improve with the increase in grain size and the formation of distinct grain boundaries. Furthermore, through increasing the pH of the precursor solutions, the size of the sol-gel colloidal particles increases slightly and the grains formed from the corresponding solutions tend to be small and uniform.