Metal-organic Films Research Articles

Study of molecular layer deposition of zinc-based hybrid film as photoresist

Molecular layer deposition (MLD) of metal oxide and organic hybrid thin films has great potential to be utilized in extreme ultraviolet photoresist, thanks to its excellent uniformity on the nanometer scale thickness control. Zn has large photoelectron effect cross-section, resulting in lots of secondary electrons, which can break the organic bonds, causing changes in solubility upon the ultraviolet (UV) light exposure. In this work, Zn-based MLD thin films have been demonstrated for their potential to be used as photoresist for extreme ultraviolet (EUV) application. UV light exposure mechanisms have been proposed based on X-ray photoelectron spectroscopy (XPS) analysis.

Towards sustainable, direct printed, organic transistors with biocompatible copolymer gate dielectrics

AbstractWe have investigated the potential of three dielectric materials to meet the future demands of green dielectrics: Polycaprolactone (PCL) thermoplastic, polyvinyl alcohol (PVA)‐carrageenan (CAR) crosslinked biopolymer, and boron nitride nanotubes (BNNTs) as a nano additive in PVA. Metal–insulator–metal (MIM) capacitors and organic thin film transistors (OTFT) were built with bilayer dielectric stacks of PVA‐CAR, PVA‐PCL, and PVA‐BNNT materials to examine their electrical properties. The PVA‐CAR layer uses a cyclic freeze thaw process to crosslink PVA and CAR for superior mechanical and electrical properties to either material alone. The PVA‐CAR MIM capacitors showed a dielectric constant of 23, which was found to be consistent with the extracted OTFT gate dielectric characteristics. Of the OTFT devices tested, PVA‐CAR OTFT showed highest device currents at low applied biases and produced an ON/OFF ratio of 104–105, both values were highest amongst the tested gate dielectrics. This material is therefore extremely promising for green electronics. The PVA‐PCL OTFT had very low leakage current and beneficial hydrophilic properties with comparable electrical properties to the commonly used organic material polytetrafluoroethylene. PVA‐BNNT MIM capacitors showed a low dielectric constant of 0.7, and the high resistivity makes this a promising material for shielding or substrates in high frequency applications. All three materials have the potential to fulfil different niches in a sustainable electronics future.

Measuring the viscosity of films by thermomechanical analysis: application to metal organic precursor films of functional oxides

We have developed a new method to measure the viscosity of micrometric films by thermomechanical analysis with a hemispherical probe of millimetric diameter. The loading curve (displacement vs. time) recorded as the probe tip crosses the whole film at constant load until it touches the substrate is fitted to a theoretical curve shape that has been obtained after solving the problem of liquid flow under the probe tip. The method has been validated by measuring the viscosity of rosin films. It has been applied to analyze the thermal evolution of unstable liquid films that appear on Ba propionate, Ce(III) propionate and a low-fluorine precursor film of YBa2Cu3O6+x. During pyrolysis of the last two films, viscosity first diminishes due to heating and then it increases as solid oxide particles are formed inside the liquid.

Template-free electrodeposition of sponge-like porous polymer interwoven with the bi-metallic metal-organic framework and reduced graphene oxide and application in energy storage device

In this research, an effective template- and binder-free strategy was developed for the design and fabrication of hybrid-structure supercapacitor (HSSC) material based on the novel sponge-like porous polymer enclosed with the bi-metallic metal-organic framework (bi-MMOF) and reduced graphene oxide (RGO) films. For the implementation of this goal, the green, in-situ, and eco-friendly electrochemical deposition technique was employed to modification of the gold surface with the reduced graphene oxide (RGO), poly-dibenzoazepine (PDB) polymer, and Ni/Co bi-metallic metal-organic (bi-MMOF) films, respectively. This procedure was accomplished without the use of any binder, template, pretreatment, and chemical modification of the substrate in an aqueous solution and at room temperature. According to our hypothesis, the synergic effect of conductivity and electrochemical double-layer capacitance (EDLC) of reduced graphene oxide along with the conductivity and pseudocapacitive behaviour of water-stable Ni/Co bi-MMOF, and the high surface area of polymer can be provided enhanced supercapacitor features. The electrochemical surveys indicated the superior performance of the designed nanocomposite with a suitable specific capacitance of 686.0 F g−1 at 1.0 A g−1 and suitable rate performance 554.0 F g−1 at 8.0 A g−1. Also, the assembled symmetric hybrid-structure supercapacitor appeared suitable energy density of 8.4 Wh kg−1 at 200 W kg−1 power density and satisfied specific capacitance of 378.0 F g−1 at 0.5 A g−1 with extraordinary long-life stability (95.1 % capacity retention up to 5000 cycles). These outcomes illustrated the proposed procedure can be shed light on designing new Graphene-Polymer-MMOF configured supercapacitors.

Ultrafast Interfacial Self-Assembly toward Supramolecular Metal-Organic Films for Water Desalination.

Supramolecular metal‐organic materials are considered as the ideal candidates for membrane fabrication due to their excellent film forming characteristics, diverse metal centers and ligand sources, and designable structure and function. However, it remains challenging to rapidly construct highly permeable supramolecular metal‐organic membranes with high salt rejection. Herein, a novel ultrafast interfacial self‐assembly strategy to prepare supramolecular metal‐organic films through the strong coordination interaction between highly active 1,3,5‐triformylphloroglucinol (TFP) ligands and Fe3+, Sc3+, or Cu2+ at the organic–aqueous interface is reported. Benefiting from the self‐completing and self‐limiting characteristics of this interfacial self‐assembly, the new kind of supramolecular membrane with optimized composition can be assembled within 3.5 min and exhibits ultrathin, dense, defect‐free features, and thus shows an excellent water permeance (21.5 L m–2 h–1 bar–1) with a high Na2SO4 rejection above 95%, which outperforms almost all of the non‐polyamide membranes and commercially available nanofiltration membranes. This strong‐coordination interfacial self‐assembly method will open up a new way for the development of functional metal‐organic supramolecular films for high‐performance membrane separation and beyond.

Atomic/Molecular Layer Deposition for Designer's Functional Metal–Organic Materials

AbstractAtomic layer deposition (ALD) for high‐quality conformal inorganic thin films is one of the cornerstones of modern microelectronics, while molecular layer deposition (MLD) is its less‐exploited counterpart for purely organic thin films. Currently, the hybrid of these two techniques, i.e., ALD/MLD, is strongly emerging as a state‐of‐the‐art gas‐phase route for designer's metal–organic thin films, e.g., for the next‐generation energy technologies. The ALD/MLD literature comprises nearly 300 original journal papers covering most of the alkali and alkaline earth metals, 3d transition metals, and lanthanides as the metal component and a variety of aliphatic, aromatic, and natural organic components. Some of these ALD/MLD processes yield in situ crystalline coordination‐polymer‐ or metal–organic‐framework‐like structures. Another attractive aspect is that many of the metal–organics realized through ALD/MLD are fundamentally new materials, and even unaccessible through conventional synthesis. Here, the current state of research in the field is presented, by i) providing a comprehensive account of the ALD/MLD processes so far developed, ii) addressing the constraints/possibilities for growing in situ crystalline metal–organic films, iii) highlighting some intriguing ALD/MLD materials and their application potential, and iv) making a brief outlook to the future perspectives and challenges in the field.

A practical and effective method for reducing differential reflectance spectroscopy noise

Differential reflectance spectroscopy (DRS) is a powerful tool to study processes during thin-film growth, especially that of transition metal dichalcogenides and organic thin films. To satisfy the requirements for in situ and real-time monitoring of film growth, including spectral resolution and sensitivity at the level of monolayers and even sub-monolayers, the most challenging technical task in DRS is to reduce noise to an extremely low level so that the best possible signal-to-noise ratio can be achieved. In this paper, we present a simplified and cost-effective DRS apparatus, with which we show that the measurement noise is mainly composed of thermal drift noise and explore the temperature-dependence of the DRS signal. Based on the results obtained, we propose an easily realized and effective scheme aiming to reduce the noise. Experimental results demonstrate that this scheme is effective in stabilizing reliable signals for a long period of several hours. Significant noise reduction is achieved, with the typical average noise of the DRS system being decreased to 0.05% over several hours. The improved DRS system is applied to study the growth of an organic semiconductor layer for an organic field-effect transistor device. The results indicate that the apparatus proposed in this paper has potential applications in fabrication of devices on the nanoscale and even the sub-nanoscale.

Multistate Switching of Spin Selectivity in Electron Transport through Light-Driven Molecular Motors.

It is established that electron transmission through chiral molecules depends on the electron's spin. This phenomenon, termed the chiral‐induced spin selectivity (CISS), effect has been observed in chiral molecules, supramolecular structures, polymers, and metal‐organic films. Which spin is preferred in the transmission depends on the handedness of the system and the tunneling direction of the electrons. Molecular motors based on overcrowded alkenes show multiple inversions of helical chirality under light irradiation and thermal relaxation. The authors found here multistate switching of spin selectivity in electron transfer through first generation molecular motors based on the four accessible distinct helical configurations, measured by magnetic‐conductive atomic force microscopy. It is shown that the helical state dictates the molecular organization on the surface. The efficient spin polarization observed in the photostationary state of the right‐handed motor coupled with the modulation of spin selectivity through the controlled sequence of helical states, opens opportunities to tune spin selectivity on‐demand with high spatio‐temporal precision. An energetic analysis correlates the spin injection barrier with the extent of spin polarization.

Resonant Plasmon‐Enhanced Absorption of Charge Transfer Complexes in a Metal–Organic Monolayer

AbstractPlasmonic enhancement of absorption in charge‐transfer (CT) complexes formed under NO2 gas adsorption onto 2D hybrid structure, based on the metal–organic monolayer and gold nanoparticles (AuNPs), is demonstrated. By using Langmuir–Blodgett deposition of low‐symmetry zinc phthalocyanine (ZnPc) molecules, the metal–organic monolayer is fabricated with greatly suppressed intermolecular aggregation. Oxidation of the monolayer through coordination of NO2 molecules with axial zinc ions of ZnPc molecules gives rise to the specific absorption band inherited to cation radical ZnPc+. The hybrid AuNPs–ZnPc structure is engineered to maximize exciton–plasmon interaction of CT complexes at the radical form of the metal–organic monolayer. Excellent spectral and spatial overlaps with plasmon resonance boost absorption of CT internal optical transition, so‐called “fingerprint” band, by a factor of six from 0.45% to 2.8% in total. The approach paves the way for efficient plasmonic control over photochemical reactions promoted by charge‐transfer complexes in metal–organic films. In particular, the plasmonic effect is harnessed to improve NO2 gas sensing properties; the experimental study shows a 15‐fold increase of the detection efficiency in the specific band of CT complexes under the gas exposure.

Highly-effective/durable method of mild-steel corrosion mitigation in the chloride-based solution via fabrication of hybrid metal-organic film (MOF) generated between the active Trachyspermum Ammi bio-molecules-divalent zinc cations

This study describes a novel bio-based inhibitor to effectively mitigate the mild-steel (MS) corrosion in the 3.5 wt% NaCl solution. For this purpose, the synergistic effect between the aqueous extract of Trachyspermum Ammi (T.A) seed and divalent zinc cations was thoroughly investigated. The GIXRD, UV–vis, FTIR, and Raman spectroscopy were employed to scrutinize the adsorption of the T.A-Zn2+ complexes on the metal surface. The EIS and potentiodynamic polarization studies also evidenced the outstanding corrosion protection effect of the formed protective layer. EIS results showed 94 % inhibition efficiency in the case of 700:300 ppm Zn:T.A sample.

A highly-effective/durable metal-organic anti-corrosion film deposition on mild steel utilizing Malva sylvestris (M.S) phytoextract-divalent zinc cations

For the first time, a metal-organic film with high anti-corrosion potency was constructed over the mild steel surface using Malva sylvestris (M.S) and zinc cations (Zn2+). The mild steel panels were immersed in the simulated seawater solution (3.5%wt. NaCl solution) containing different loadings of Zn:M.S inhibitors. The electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements were performed at a different time step up to 240h. The potentiodynamic polarization test was carried out to determine the inhibitor's inhibition mechanisms. The synergistic inhibition impact of the Zn:M.S before and after immersion was analyzed by Ultraviolet-Visible (UV–vis) spectroscopy. The protective film formed on the surface was studied by the Fourier transform infrared (FT-IR), Raman, grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), and contact angle (CA) techniques. The EIS results evidenced that applying various ratios of Zn:M.S resulted in more than 98% corrosion inhibition efficiency (IE), which was stable up to 240h. Meanwhile, the outstanding corrosion resistance of 170kΩ.cm2 in 300:700ppm Zn:M.S was recorded.

Multistate Switching of Spin Selectivity in Electron Transport Through Light-Driven Molecular Motors

It was established that electron transmission through chiral molecules depends on the electron’s spin. This phenomenon, termed the chiral-induced spin selectivity (CISS) effect has been observed in chiral molecules, supramolecular structures, polymers and metal-organic films. Which spin is preferred in the transmission depends on the handedness of the system and the tunneling direction of the electrons. Molecular motors based on overcrowded alkenes show multiple inversions of helical chirality under light irradiation and thermal relaxation. We show here multistate switching of spin selectivity in electron transfer through first generation molecular motors based on the four accessible distinct helical configurations, measured by magnetic-conductive atomic force microscopy. The efficient spin polarization observed in the photostationary state of the right-handed motor coupled with the modulation of spin selectivity through the controlled sequence of helical states opens opportunities to tune spin selectivity on-demand with high spatio-temporal precision. An energetic analysis correlates the spin injection barrier with the extent of spin polarization.

Construction of a high-potency anti-corrosive metal-organic film based on europium (III)-benzimidazole: Theoretical and electrochemical investigations

A series of unique metal–organic films (MOFs) with excellent corrosion protection properties were constructed over the mild steel (MS) surface through covalent bonding between the benzimidazole (BM) molecules and europium (Eu) cations. The corrosion resistance of the MS samples protected by BM:Eu film was evaluated by electrochemical and morphological approaches in 3.5% NaCl solution. The interactions between BM and Eu were investigated by Fourier-transformed infrared (FT-IR) spectroscopy. Also, the π-π*/n-π* electro-transitions in the BM:Eu molecules in NaCl solution were proved by the UV–Vis technique. The FE-SEM images and GIXRD spectra showed the BM:Eu film deposition over the MS surface. Besides, in the presence of BM:Eu the amount of iron oxide drastically decreased. The Tafel curves demonstrated the mixed corrosion inhibition mechanism of the BM:Eu mixture on MS surface in saline solution. Electrochemical impedance spectroscopy (EIS) analysis results evidenced about corrosion inhibition efficiency of about 97% for the MS sample subjected to the 3.5% NaCl solution containing 200:600 ppm BM:Eu inhibitors. In addition, the theoretical insights including quantum mechanics (QM) and molecular dynamics (MD) computations, supported the adsorption of europium/benzimidazole molecules on the MS adsorbent.

Green synthesis of reduced graphene oxide nanosheets decorated with zinc-centered metal-organic film for epoxy-ester composite coating reinforcement: DFT-D modeling and experimental explorations

Hydrazine is a potent traditional reducing agent of graphene oxide with high deoxygenation capability. However, it has been categorized as a toxic/poisonous substance with serious environmental issues. Due to the hazardous/toxic nature of this substance, numerous researches have been carried out to find sustainable/nontoxic reductants. For the first time, the high quality reduced graphene oxide (rGO) particles were obtained through reduction and covalent-functionalization of GO at the same time with the natural Esfand seed (ES) extract (ESE) that includes some green/harmless reactive nitrogen-rich molecules, e.g., Harmol (C12H10N2O) and Harmalol (C12H12N2O). The rGO-ESE sheets were then modified by metallic zinc ions, and rGO-ESE-Zn(II) sheets were obtained. X-ray diffraction (XRD) analysis revealed the significant increment of GO sheets d-spacing after interaction with ESE-Zn(II). The FT-IR results indicated the disappearance of carbonyl (CO) absorption peak, and significant reduction of COC bond intensity, all affirming the successful GO reduction in the presence of ESE molecules. The C/O ratio calculated based on the EDS data are 0.18 and 0.33 for the rGO-ESE and GO sheets, respectively, indicating the increase in O content after GO reduction proving the ESE adsorption on the GO sheets. Tensile test results depicted the maximum increase of tensile strength (78%), Young's modulus (102%), and fracture energy (83%) of the coating in the presence of rGO-ESE-Zn(II) sheets. FE-SEM analysis revealed the effective toughening mechanisms of the rGO-ESE-Zn(II) sheets in the polymer matrix. Besides, the TGA results evidenced the significant improvement of the epoxy ester coating thermal stability (about 62%) in the presence of rGO-ESE-Zn sheets.

Construction of a zinc-centered metal–organic film with high anti-corrosion potency through covalent-bonding between the natural flavonoid-based molecules (Quercetin)/divalent-zinc: Computer modeling (integrated-DFT&MC/MD)/electrochemical-surface assessments

In the present work, for the first time, a series of unique zinc-centered metal–organic films with high anti-corrosion potency was fabricated on the steel surface through the covalent/non-covalent bonding/interactions between the natural flavonoid based-molecules (Quercetin) and Zn2+/Fe2+ metal-cations. The visualized steel surface micro-scale microstructure by FE-SEM proved that the Quercetin:Zn based metal–organic film covered the metallic surface significantly. Also, the elemental analysis of the protected surfaces via GIXRD, EDS, and mapping experiments illustrated that the metal–organic compounds sufficiently adsorbed. Tafel curves achievements depicted that the Quercetin:Zn based metal–organic film could efficiently protect the iron surface via both O2 reduction/Fe oxidation mechanisms and the outcomes indicated that in the presence of Quercetin (200ppm):Zn (600ppm) inhibitors the most protective film against chloride solution was attained (97% efficiency) after 24h of iron exposure. Additionally, the theoretically derived outcomes applying MC/MD modeling associated with DFT calculations ascertained the interactions followed by adsorption of complexes over the M-Steel.

Effect of zincone ratio on mechanical reliability of aluminum-doped zinc oxide-zincone multilayer thin films grown on flexible substrate using atomic/molecular layer deposition hybrid techniques

The combination of atomic and molecular layer deposition techniques enables the fabrication of various functional organic-inorganic multilayer thin-film structures. The alloys in metal oxide thin films and organic metalcone thin films demonstrate many technical advantages over conventional metal oxide single-layer thin films in terms of mechanical and electrical properties. This study investigates the effect of multilayer thin-film structures, which are fabricated as zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) single thin films and ZnO-zincone and AZO-zincone multilayer thin films, on the mechanical and electrical properties of multilayer thin films. Various multilayer thin films are fabricated with variations in composition ratios between the inorganic and organic materials by controlling the process cycles. To analyze the reliability of thin multilayer films under external deformations, the variations in the electrical resistivity and crack generation of the thin films are measured using micro-tensile specimens. In addition, the variations with respect to the optical transmittance and surface morphology of multilayer thin films are analyzed using various composition ratios, and the results are compared with those obtained from single metal oxide thin films.

Engineering of a highly stable metal-organic Co-film for efficient electrocatalytic water oxidation in acidic media

Water oxidation is traditionally performed over IrO2 and RuO2 owing to their high stability at low pH compared to molecular O2 evolution catalysts. The low stability of molecular complexes in acids limits their industrial exploitation as anodes in water-splitting devices, where high current densities and proton conductivity are required. Herein, an existing Co(1,10-phenanthroline)2 complex film is engineered to improve its pH-stability via extra OH substituents on the ligand, i.e. 1,10-phenanthroline-4,7-diol. This novel Co(1,10-phenanthroline-4,7-diol)2 complex film is active for water oxidation at low overpotentials and stable at low pH. Since the calculated water oxidation overpotentials of both complexes are similar, the difference in water oxidation activity is attributed to a smaller charge transfer resistance, which originates from a different anchoring style to the electrode via the OH groups of the ligand. This result is supported by electrochemical impedance measurements. The high pH-stability of the Co(1,10-phenanthroline-4,7-diol)2 film is computationally rationalized by a high crystal formation energy observed in DFT calculations. In summary, an acid-stable and active cobalt-based metal-organic film is reported that competes well with most reported earth-abundant catalysts for water oxidation under similar conditions.

Surface-Initiated ARGET ATRP of Antifouling Zwitterionic Brushes Using Versatile and Uniform Initiator Film.

In this study, we developed a uniform initiator layer that can be formed on various surfaces, and formed site-selectively, for the subsequent antifouling polymer brush formation. Initially, metal-organic films composed of tannic acid (TA) and FeIII ions (TA-FeIII) were formed on various surfaces, followed by functionalization with an aryl azide-based initiator (ABI) under photoreaction. In particular, combination with a photolithographic technique enabled the presentation of initiators only on the intended region within a single-surface platform. A resultant initiator film (TF-ABI) was formed under mild reaction conditions and meets the uniformity and transparency requirements concurrently. Subsequently, we showed that TF-ABI can be further utilized to form a polymer brush by proceeding with surface-initiated polymerization using a zwitterionic monomer, namely, sulfobetaine acrylamide (SBAA). Instead of applying a classical, yet air-sensitive atom transfer radical polymerization (ATRP) technique, we utilized an activator regenerated by electron transfer (ARGET) ATRP under air conditions without a cumbersome deoxygenation step. Overall, our initiator layer allowed the antifouling poly(SBAA) brush to be used on various surfaces, and enabled their pattern generation.

Electroreduction of a CoIIcoordination complex producing a metal–organic film with high performance toward electrocatalytic hydrogen evolution

Remarkable, high stability, simple, and inexpensive noble metal-free materials as electrocatalysts with the best TOF (312 900 s−1, corrected by Faraday efficiency) for H2production.

Enhancing light absorption in organic semiconductor thin films by one-dimensional gold nanowire gratings

The interaction of metallic plasmonic nanostructures and organic semiconductor thin films plays a crucial role in engineering light harvesting and energy transfer processes, e.g., for optoelectronic applications. Plasmonic resonances of the metal structures can be used to increase the light emission or absorption of organic molecules. Here small molecules are employed since they can form organic layers with a defined crystalline order and orientation of the transition dipole. Extinction measurements combined with numerical simulations of a hybrid system consisting of a gold nanowire grating and a thin film of diindenoperylene (DIP) are reported. The experimental results are compared to the simulations and indicate an enhanced absorption in the wavelength region corresponding to the transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital of DIP. This enhancement is found to be related to the localized field enhancement near the individual nanostructures as well as to grating-induced effects. Notably, the hybrid system also exhibits parallel lattice resonances, which have recently been discussed for two-dimensional (2D) gold nanostructure arrays. In this study a hybrid plasmonic-organic small molecule system exhibiting these modes is investigated. The results for this model system show a way to modify the optical properties of plasmonic nanostructures by collective effects to achieve stronger light-matter interaction in a wide range of hybrid plasmonic systems.