Complex Films Research Articles

Modulation of the LaFeO3 film growth by the terrace width of SrTiO3 substrates

We have investigated the growth of polar LaFeO3 thin films on SrTiO3 (001) substrates with various terrace widths by pulsed laser deposition. It is found that the growth of LaFeO3 films undergoes a transition from a two-dimensional (2D) mode to a three-dimensional (3D) mode due to polarity compensation. Notably, however, the critical thickness of the growth mode transition from 2D to 3D can be modulated by the terrace width of the substrate, i.e., when the film is 30 monolayers thick, it becomes 3D growth on the substrates with narrow terrace width (∼100 nm) while it maintains 2D growth on those with wide terrace width (∼400 nm). Combined with dynamic and kinetic models, we have found that the modulation of the critical thickness from 2D to 3D is rationalized as a result of competition between the dynamic process and the kinetic process. These findings highlight the key influence of substrate surface morphology on the epitaxial growth of complex oxide films, shedding light on the construction of multifunctional artificial low-dimensional structures with polar stackings.

Surface Modification of Biomedical Ti-18Zr-15Nb Alloy by Atomic Layer Deposition and Ag Nanoparticles Decoration.

Superelastic biocompatible alloys attract significant attention as novel materials for bone tissue replacement. These alloys are often composed of three or more components that lead to the formation of complex oxide films on their surfaces. For practical use, it is desirable to have a single-component oxide film with a controlled thickness on the surface of biocompatible material. Herein we investigate the applicability of the atomic layer deposition (ALD) technique for surface modification of Ti-18Zr-15Nb alloy with TiO2 oxide. It was found that a 10-15 nm thick, low-crystalline TiO2 oxide layer is formed by ALD method over the natural oxide film (~5 nm) of the Ti-18Zr-15Nb alloy. This surface consists of TiO2 exclusively without any additions of Zr or Nb oxides/suboxides. Further, the obtained coating is modified by Ag nanoparticles (NPs) with a surface concentration up to 1.6% in order to increase the material's antibacterial activity. The resulting surface exhibits enhanced antibacterial activity with an inhibition rate of more than 75% against E. coli bacteria.

Bacterial cellulose-based dressings with photothermal bactericidal activity and pro-angiogenic ability for infected wound healing

For most traditional wound dressings, it is challenging to simultaneously eliminate bacteria and promote angiogenesis to accelerate the healing process of bacteria-infected wounds. In this work, we develop a multifunctional dressing based on bacterial cellulose (BC) deposited with a tannic acid/Cu2+ ion/Mg2+ ion (TCM) complex film. Overall, the TCM complex exhibits robust interfacial adhesion to modify BC and good photothermal properties to effectively eradicate bacteria in the wound area under near-infrared (NIR) irradiation. The individual components of the TCM complex have several advantageous features for wound healing, such as antibacterial ability and negligible cytotoxicity; in particular, the released Cu2+ and Mg2+ ions are favorable for the proliferation, migration, and tube formation of endothelial cells in vitro. The results of in vivo experiments demonstrated that with the assistance of NIR irradiation, this composite dressing is more effective than traditional gauze or pristine BC dressing in promotion of angiogenesis and collagen deposition without causing remarkable inflammation, thereby accelerating the healing process of bacteria-infected full-thickness skin wounds. This work thus provides a simple and facile way to fabricate multifunctional BC-based dressings that could be potentially used for treating infected wounds.

Contact/Noncontact‐Mode Thermoelectric Characteristics of Polytriarylamine/Lewis Acid Complex Films in Horizontal Device Geometry

Herein, the thermoelectric characteristics of polytriarylamine‐Lewis acid complex films were investigated by employing a horizontal device structure. Poly[N,N′‐bis(4‐butylphenyl)‐N,N′‐bis(phenyl)benzidine] (PolyTPD) is doped with tris(pentafluorophenyl)borane (BCF) via Lewis acid–base reactions by varying the BCF molar ratio (0–300 mol%). The resulting PolyTPD:BCF films are spun on glass substrates and silver electrodes are deposited leading to the horizontal type of organic thermoelectric devices (OTEDs). The OTEDs with the PolyTPD:BCF films are examined by varying temperature differences up to 45 K between two silver electrodes directly contacting hot/cold sources. Both device current and voltage are proportionally increased with the temperature difference, leading to higher powers at larger temperature differences, irrespective of BCF molar ratio. However, the highest current is achieved at 50 mol% owing to the highest electrical conductivity, even though the device voltage is slightly lower at 50 than 20 mol%. The origin of high electrical conductivity is assigned to the formation of radical cations in PolyTPD chains by BCF doping, which is influenced by the reaction time. The device current can be also generated by the illumination of IR radiation (noncontact mode) that is away from the OTEDs with the PolyTPD:BCF films.

Epitaxial Design of Complex Nickelates as Electrocatalysts for the Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) is a crucial process in electrochemical water splitting, a promising technology to renewably yield hydrogen gas from water. Designing and developing earth‐abundant, efficient, and stable OER electrocatalysts to replace the most widely used but scarce RuO2 and IrO2 are thus of critical interest. Recently, ABO3‐structured perovskite oxides, especially rare‐earth nickelates, are extensively studied for their potential use as OER electrocatalysts. In particular, the epitaxial synthesis of complex oxide thin films allows flexible and precise control over the materials so that their structure–stability–property relationships can be established. Using nickelate thin films as model systems, this review illustrates how epitaxial design allows researchers to test different hypotheses and proposed descriptors, as well as formulate new design principles. Following a brief introduction to the background of OER mechanisms, proposed activity descriptors, and synthesis methods, various epitaxial design strategies are surveyed including strain tuning, composition control, surface termination/orientation selection, defect engineering, and interface design. These have led to precise control over the atomic structures and electronic properties of nickelates which in turn determine their electrochemical performance. Finally, the remaining challenges and perspectives toward a deeper understanding and use of complex oxides as OER catalysts are discussed.

Electrically Amplified Circularly Polarized Luminescence by a Chiral Anion Strategy

AbstractThe development of circularly polarized electroluminescence (CPEL) is currently hampered by the high difficulty and cost in the syntheses of suitable chiral materials and the notorious chirality diminishment issue in electrical devices. Herein, diastereomeric IrIII and RuII complexes with chiral (±)‐camphorsulfonate counteranions are readily synthesized and used as the active materials in circularly polarized light‐emitting electrochemical cells to generate promising CPELs. The addition of the chiral ionic liquid (±)‐1‐butyl‐3‐methylimidazole camphorsulfonate into the active layer significantly improves the device performance and the electroluminescence dissymmetry factors (≈10−3), in stark contrast to the very weak circularly polarized photoluminescence of the spin‐coated films of these diastereomeric complexes. Control experiments with enantiopure IrIII complexes suggest that the chiral anions play a dominant role in the electrically‐induced amplification of CPELs.

Electrically Amplified Circularly Polarized Luminescence by a Chiral Anion Strategy.

The development of circularly polarized electroluminescence (CPEL) is currently hampered by the high difficulty and cost in the syntheses of suitable chiral materials and the notorious chirality diminishment issue in electrical devices. Herein, diastereomeric IrIII and RuII complexes with chiral (±)-camphorsulfonate counteranions are readily synthesized and used as the active materials in circularly polarized light-emitting electrochemical cells to generate promising CPELs. The addition of the chiral ionic liquid (±)-1-butyl-3-methylimidazole camphorsulfonate into the active layer significantly improves the device performance and the electroluminescence dissymmetry factors (≈10-3 ), in stark contrast to the very weak circularly polarized photoluminescence of the spin-coated films of these diastereomeric complexes. Control experiments with enantiopure IrIII complexes suggest that the chiral anions play a dominant role in the electrically-induced amplification of CPELs.

Multifunctional Anti‐Corrosive Interface Modification for Inverted Perovskite Solar Cells

AbstractThe interface stability and non‐radiative recombination loss of the cathode interface greatly limit the stability and performance of inverted perovskite solar cells (PSCs). Here, an efficient multifunctional anti‐corrosive interface modification strategy based on 2,2′‐(1,3‐phenylene)‐bis[5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole] (OXD‐7) is proposed to overcome the cathode interface issues. OXD‐7 molecules chemically coordinate to the Ag electrode and form a chemically stable complex film of OXD7‐Ag, which suppresses halide ion migration and thus enhances the corrosion resistance of the electrode as well. In addition, the trap density of perovskite film, PCBM/Ag interfaces contact, the built‐in potential, moisture resistance, as well as the unfavorable interface exciton dissociation elimination of the devices, are also improved with the OXD‐7 arrangement upon PCBM film, which correspondingly enhances the device performance and stability. Bidirectional halide ion migration and the ITO corrosion are observed, which is also suppressed by the OXD‐7 modification. The high power conversion efficiency (PCE) of 21.84% and the high fill factor (≈84.63%) is obtained via this strategy, which is one of the highest PCEs and FFs based on solution‐process MAPbI3/PCBM heterojunctions. The PCE can maintain ≈80% of its initial value after 1080 h at 85 °C with OXD‐7 modification.

Photodegradation and oxidizing action of peroxotitanium complex film

Photodegradation and accompanying oxidizing action of peroxotitanium complex (PTC) film were investigated, which made from PTC aqueous solution containing 61.3 mol % peroxo groups (O-O) to total Ti. The apparent activation energy (Ea) of the PTC degradation was revealed to be 132 kJ·mol−1 (λ = 905 nm), according to Arrhenius plot of the degradation rate constant of PTC aqueous solution with microwave hydrothermal treatment at 100–180 °C. The PTC films were slowly decomposed by light irradiation of UV lamp, visible light LED or light bulb, and simultaneously oxidatively decomposed methylene blue dissolved in water. The oxidation reaction occurred even under the light of long wavelength around 900 nm closed to the Ea. Furthermore, the utilization efficiency of active oxygen generated by the photodegradation to the oxidation reaction of acetaldehyde gas was estimated to be 66 and 80 % under UV light (2.00 mW·cm−2) and LED visible light (1.50 mW·cm−2), respectively.

Synthesis, Characterization and Electrochemical Studies on the Corrosion Inhibition Properties of Schiff Bases for Mild Steel in 1 M HCl Solution

Schiff bases (SBL1 and SBL2), non-toxic compounds were synthesized, characterized and investigated as alternative anticorrosive additives for inhibition of mild steel corrosion in I M HCl acid medium. Corrosion of the steel was monitored by Potentiodynamic Polarization (PDP), Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS) and Weight Loss (WL) techniques. The novel Schiff base ligands obtained were characterized by Ultraviolet-visible and Fourier-Transform Infrared Spectroscopy. The elemental analysis data for the Schiff base ligands were used to confirm the formula of SBL1 as C17H20N2O2 and SBL2 as C24H21N5O2. Fourier-Transform Infrared spectroscopy suggest that the formation of a complex film on the mild steel surface was due to the adsorption of SBL1 and SBL2. The adsorption process was spontaneous and consistent with the mechanism of physical adsorption as best approximated by the Langmuir adsorption isotherm. Maximum inhibition efficiency was obtained at maximum concentration of 100 ppm for both SBL1 and SBL2 with SBL2 possessing the higher inhibition efficiency (86.21%) more than SBL1 (76.92%). Effectiveness of SBL1 and SBL2 reduced with increase in time and progressed with increase in concentration of SBL1 and SBL2. PDP measurements showed that SBL1 and SBL2 acted as a mixed type inhibitor. EIS measurement reveals that the corrosion process was controlled by charge transfer process. Values of the inhibition efficacy obtained from the different techniques were comparable. SEM micrographs of mild steel surface indicated good surface protection of SBL1 and SBL2.

Clindamycin phosphate and bone morphogenetic protein-7 loaded combined nanoparticle-graft and nanoparticle-film formulations for alveolar bone regeneration – An in vitro and in vivo evaluation

Commonly utilized techniques for healing alveolar bone destruction such as the use of growth factors, suffering from short half-life, application difficulties, and the ability to achieve bioactivity only in the presence of high doses of growth factor. The sustained release of growth factors through a scaffold-based delivery system offers a promising and innovative tool in dentistry. Furthermore, it is suggested to guide the host response by using antimicrobials together with growth factors to prevent recovery and achieve ideal regeneration. Herein, the aim was to prepare and an in vitro - in vivo evaluation of bone morphogenetic protein 7 (BMP-7) and clindamycin phosphate (CDP) loaded polymeric nanoparticles, and their loading into the alginate-chitosan polyelectrolyte complex film or alloplastic graft to accelerate hard tissue regeneration. PLGA nanoparticles containing CDP and BMP-7, separately or together, were prepared using the double emulsion solvent evaporation technique. Through in vitro assays, it was revealed that spherical particles were homogeneously distributed in the combination formulations, and sustained release could be achieved for >12 weeks with all formulations. Also, results from the micro-CT and histopathological analyses indicated that CDP and BMP-7 loaded nanoparticle-film formulations were more effective in treatment than the nanoparticle loaded grafts.

Nd:YAG infrared laser as a viable alternative to excimer laser: YBCO case study

We report on the growth and characterization of epitaxial YBa_{2}Cu_{3}O_{7-delta } (YBCO) complex oxide thin films and related heterostructures exclusively by Pulsed Laser Deposition (PLD) and using first harmonic Nd:Y_{3}Al_{5}O_{12} (Nd:YAG) pulsed laser source (lambda = 1064 nm). High-quality epitaxial YBCO thin film heterostructures display superconducting properties with transition temperature sim 80 K. Compared with the excimer lasers, when using Nd:YAG lasers, the optimal growth conditions are achieved at a large target-to-substrate distance d. These results clearly demonstrate the potential use of the first harmonic Nd:YAG laser source as an alternative to the excimer lasers for the PLD thin film community. Its compactness as well as the absence of any safety issues related to poisonous gas represent a major breakthrough in the deposition of complex multi-element compounds in form of thin films.

Resistance fluctuation spectroscopy of phase transitions in (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)NiO3 thin films

The study of phase transitions is crucial to understanding the physics of materials and utilizing them for technological applications. This article presents a detailed analysis of the electronic transport properties of high entropy oxide thin films. We observe an increase in resistance fluctuations across a first-order phase transition. We show that the noise arises from an electronic phase separation accompanying the spin ordering due to the formation of domains of localized and delocalized charges. We conclude that due to charge disproportionation, the charge carriers form domains of localized and delocalized electrons in this system. Our study establishes the existence of multiple states with near equal energy in such complex oxide thin films.

Reusable, Ultrasensitive, Patterned Conjugated Polyelectrolyte-Surfactant Complex Film with a Wide Detection Range for Copper Ion Detection.

Conjugated polyelectrolytes (CPEs) are emerging as promising materials in the sensor field because they enable high-sensitivity detection of various substances in aqueous media. However, most CPE-based sensors have serious problems in real-world application because the sensor system is operated only when the CPE is dissolved in aqueous media. Here, the fabrication and performance of a water-swellable (WS) CPE-based sensor driven in the solid state are demonstrated. The WS CPE films are prepared by immersing a water-soluble CPE film in cationic surfactants of different alkyl chain lengths in a chloroform solution. The prepared film exhibits rapid, limited water swellability despite the absence of chemical crosslinking. The water swellability of the film enables the highly sensitive and selective detection of Cu2+ in water. The fluorescence quenching constant and the detection limit of the film are 7.24 × 106 L mol-1 and 4.38 nM (0.278 ppb), respectively. Moreover, the film is reusable via a facile treatment. Furthermore, various fluorescent patterns introduced by different surfactants are successfully fabricated by a simple stamping method. By integrating the patterns, Cu2+ detection in a wide concentration range (nM-mM) can be achieved.

Role of Ta in improving corrosion resistance of titanium alloys under highly reducing condition

Great improvement on corrosion resistance was achieved by adding small amount of Ta into ASTM Gr13 titanium alloy. Main contribution to the improved corrosion resistance originated from the stabilized passive film in terms of the prolonged time to passivity loss. OCP results showed that the OCP transition from the passive state to corroding one prolonged with the Ta content. This behavior was also supported by EIS results, where the loop shrinkage denoting the passivity loss was retarded and/or inhibited by the Ta addition. Microstructural analysis revealed that the added Ta functioned as both substitution element and solid solution one, leading to the growth of the precipitates including β-Ti phase and formation of the complex structured passive film. Especially, the prominent stability of the passive film observed for Gr13–1.0% Ta was ascribed to the high content of the Ta oxide in the passive film, meaning that the complex oxide film required the minimum amount of the Ta oxide to obtain the excellent stability of the passive film against the high concentrated acid solution.

Composition tuning of Mg/Ir ratio and crystallization of a spinel-related structure in Mg-Ir-O films by pulsed-laser deposition

Pulsed-laser deposition is one of widely used methods to fabricate complex oxide thin films. In pulsed-laser deposition processes, composition of films is regulated by balance of supply and re-evaporation via various conditions such as laser pulses for target ablation, composition of target, substrate temperature, and oxidizing atmosphere. In this study, we report an experimental scheme to tune Mg/Ir composition ratio in Mg-Ir-O films fabricated by pulsed-laser deposition. In contrast to usual situations of oxide films, it was difficult to attain the composition of Mg/Ir ∼ 1 in the Mg-Ir-O films by ablating a target of Mg/Ir ∼ 1. By examining three targets with different Mg/Ir ratios, various laser fluences, substrate temperature, and oxygen partial pressure, a wide range of Mg/Ir composition ratio was regulated in the Mg-Ir-O thin films. We discovered a spinel-related crystalline phase in the Mg-Ir-O films controlled in Mg-rich compositions.

Hexamethylenetetramine additive with zincophilic head and hydrophobic tail for realizing ultra-stable Zn anode

Aqueous zinc batteries are regarded as one of the promising next-generation energy storage batteries due to their high safety and low cost, however, one of the most important problems limiting their commercialization is the cyclic stability of the zinc anode. Therefore, in this work, we first employed hexamethylenetetramine (HMT) as the electrolyte additive to in-situ construct a Zn-HMT complex film to stabilize the zinc anode. After adding the HMT, its zincophilic head will be prior to adsorbing on the zinc foil to form Zn-HMT complex film and then introduce uniform zinc deposition, and simultaneously the formed Zn-HMT complex with hydrophobic alkyl tail will repel the H2O from combining with Zn2+ to form Zn4SO4(OH)6·nH2O by-product as well as the hydrogen evolution reaction (HER). As a result, the HMT-based electrolyte promotes ultra-stable zinc anode cycling for as long as 2000 h with extremely high average Coulombic efficiency (99.51 %). When applied in the Zn-V2O5 full cell, it also demonstrates outstanding electrochemical performances with a reversible capacity as high as 197.8 mAh/g after 500 cycles. This work provides a simple and effective method for the implementation of high-safety and high-stable aqueous zinc-ion batteries.

Towards ductile single-step polyelectrolyte complex films by means of plasticization

Polyelectrolyte complexes (PECs) show great promise as functional coatings, including as oxygen barrier coatings for food packaging, but the brittleness of dry PECs limits their application. In this work, the possibility of plasticizing polyethylenimine/poly(4-styrenesulfonic acid) (PEI/PSS) films was investigated. Three different classes of plasticizers were chosen: salt, polyols, and ionic liquids (ILs). They were successfully incorporated in the evaporation-based single-step method. Potassium bromide or sorbitol plasticized films all showed crystallization upon evaporation, while films plasticized by glycerol, polyethylene glycol, and imidazole-based ILs all showed a clear brittle-to-ductile transition in their mechanical properties. The hydrophilicity of polyols and the amphiphilicity of these ILs allowed them to form homogenous casting solutions, but also increased their water sensitivity. The ionic nature of ILs make them more efficient as plasticizers since they can replace part of the PE-PE ionic-crosslinks, resulting in a more flexible network. Overall, this work demonstrates that ductile PEC films can be formed in a single step with controlled mechanical properties through plasticization.

Conductivity in Thin Films of Transition Metal Coordination Complexes.

Two coordination complexes have been made by combining the dithiolene complexes [M(mnt)2]2- (mnt = maleonitriledithiolate; M = Ni2+ or Cu2+) as anion, with the copper(II) coordination complex [Cu(Stetra)] (Stetra = 6,6'-bis(4,5-dihydrothiazol-2-yl)-2,2'-bipyri-dine) as cation. The variation of the metal centers leads to a dramatic change in the conductivity of the materials, with the M = Cu2+ variant (Cu-Cu) displaying semiconductor behavior with a conductivity of approximately 2.5 × 10-8 S cm-1, while the M = Ni2+ variant (Ni-Cu) displayed no observable conductivity. Computational studies found Cu-Cu enables a minimization of reorganization energy losses and, as a result, a lower barrier to the charge transfer process, resulting in the reported higher conductivity.

Luminescent mechanism analyzing and metal-ion sensing of Eu(III)-organic ligands complex doped gelatin-based films and hydrogels

A series of gelatin-based composite films (gf) were prepared by doping Eu(TTA)3(H2O)2, Eu(TTA)3bipy, or Eu(TTA)3phen respectively into type-E or -B gelatin film substrate. All of B-gf and the E-gf doped Eu(TTA)3phen were realized with red luminescence under 365 nm excitation, while only slight blue luminescence originated from gelatin substrate can be observed in E-gf doped Eu(TTA)3(H2O)2 or Eu(TTA)3bipy. A UV-absorption competition between substrate and dopant was confirmed to decide the luminescent properties of gf. Weaker UV absorption of B-gelatin ensures that Eu(TTA)3, regardless of ancillary ligand, can obtain sufficient excitation energy for luminescence emission. While only Eu(TTA)3phen possesses a strong enough ability to absorb UV against E-gelatin. Based on the optimal matching principle of substrate and dopant, luminescent gelatin-based hydrogel (gh) doped Eu(TTA)3phen was prepared. A ‘dual effect’ mechanism was proposed for explaining metal-ion sensing applications. Among various metal ions, furthermore, both B and E types of Eu(TTA)3phen@gh exhibited similar significant luminescence quenching for Fe3+ with a detection limit of about 1.15 μmol/L.