Electrochemical Characterisation of Copper Thin‐Film Formation on Polycrystalline Platinum

Electrochemically formed thin films are vital for a broad range of applications in virtually every field of modern science and technology. Understanding the film formation process could provide a means to aid the characterisation and control of film properties. Herein, we present a fundamental approach that combines two well‐established analytical techniques (namely, electrochemical impedance spectroscopy and electrogravimetry) with a theoretical approach to provide physico‐chemical information on the electrode/electrolyte interface during film formation. This approach allows the monitoring of local and overall surface kinetic parameters with time to enable an evaluation of the different modes of film formation. This monitoring is independent of surface area and surface concentrations of electroactive species and so may allow current computational methods to calculate these parameters and provide a deeper physical understanding of the electrodeposition of new bulk phases. The ability of this method to characterise 3D phase growth in situ in more detail than that obtained by conventional approaches is demonstrated through the study of a model system, namely, Cu bulk‐phase deposition on a Pt electrode covered with a Cu atomic layer (Cu_ad/Pt).     

Thin‐Film Infrared Spectroscopy of Acetonitrile

Acetonitrile and [D₃]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH₃CN 2252 cm^?1, CD₃CN 2262 cm^?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD₃CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell.     

Dipole Field Guided Orientated Attachment of Nanocrystals to Twin‐Brush ZnO Mesocrystals

Mesocrystals of ZnO were synthesized hydrothermally by using gum arabic as a structure‐directing agent. Their hierarchical structure has a unique twin‐brush form consisting of vertically aligned nanorods in a single‐crystal‐like porous form. The formation mechanism of the twin‐brush ZnO was investigated by quenching a series of samples at different times and examining them by TEM, SEM, and XRD. The alignment of ZnO crystal units can be modulated by adding simple salts such as KCl to change the units from nanorods to nanoplates. This can be explained by screening the dipolar force of the polar crystal. Local cathodoluminescence of twin‐brush ZnO was used to follow the local structure changes.     

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small‐Angle X‐ray Scattering

For the first time, grazing incidence small‐angle X‐ray scattering (GISAXS) analysis is used to characterize the morphology of TiO₂ thin films grown by glancing angle physical vapor deposition (GLAD). According to cross‐section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO₂ columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the tilted geometry of the TiO₂ columns. The patterns also show the existence of two populations of columns in these GLAD‐TiO₂ films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.     

Chemical Solution Deposition of Epitaxial Metal‐Oxide Nanocomposite Thin Films

Epitaixial metal‐oxide nanocomposite films, which possess interesting multifunctionality, have found applications in a wide range of devices. However, such films are typically produced by using high‐vacuum equipment, like pulse‐laser deposition, molecular‐beam epitaxy, and chemical vapor deposition. As an alternative approach, chemical solution methods are not only cost‐effective but also offer several advantages, including large surface coating, good control over stoichiometry, and the possible use of dopants. Therefore, in this Personal Account, we review the chemistry behind several of the main solution‐based approaches, that is, sol‐gel techniques, metal‐organic decomposition, chelation, polymer‐assisted deposition, and hydrothermal methods, including the seminal works that have been reported so far, to demonstrate the advantages and disadvantages of these different routes.     

Morphology of Imidazolium‐Based Ionic Liquids as Deposited by Vapor Deposition: Micro‐/Nanodroplets and Thin Films

The morphology of micro‐ and nanodroplets and thin films of ionic liquids (ILs) prepared through physical vapor deposition is presented. The morphology of droplets deposited on indium‐tin‐oxide‐coated glass is presented for the extended 1‐alkyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C_nC₁im][Ntf₂]; n=1–8) series, and the results show the nanostructuration of ILs. The use of in‐vacuum energetic particles enhances/increases the nanodroplets mobility/coalescence mechanisms and can be a pathway to the fabrication of thin IL films.     

Methylammonium-Mediated Evolution of Mixed-Organic-Cation Perovskite Thin Films: A Dynamic Composition-Tuning Process

Methylammonium-mediated phase-evolution behavior of FA_1−xMA_xPbI₃ mixed-organic-cation perovskite (MOCP) is studied. It is found that by simply enriching the MOCP precursor solutions with excess methylammonium cations, the MOCPs form via a dynamic composition-tuning process that is key to obtaining MOCP thin films with superior properties. This simple chemical approach addresses several key challenges, such as control over phase purity, uniformity, grain size, composition, etc., associated with the solution-growth of MOCP thin films with targeted compositions.     

Biomineralization‐Inspired Preparation of Zinc Hydroxide Carbonate/Polymer Hybrids and Their Conversion into Zinc Oxide Thin‐Film Photocatalysts

The development of ZnO thin films has been achieved through the conversion of zinc hydroxide carbonate thin‐film crystals. Crystallization of this compound is induced by a biomineralization‐inspired method with polymer‐stabilized amorphous precursors. The crystals grow radially on polymer matrices, leading to the formation of zinc hydroxide carbonate/polymer thin‐film hybrids that fully cover the substrate. These hybrids are converted into ZnO and retain their thin‐film morphologies. The resultant ZnO thin films exhibit a preferential crystallographic orientation that is attributed to the alignment of zinc hydroxide carbonate crystals before conversion. In addition, a photocatalytic function of the ZnO thin films has been demonstrated by analyzing the oxidation reaction of 2‐propanol. The biomineralization‐inspired approach reported herein is a promising way to develop ZnO materials with controlled morphologies and structures for photocatalytic applications.     

Low‐Temperature Atomic Layer Deposition of Copper Metal Thin Films: Self‐Limiting Surface Reaction of Copper Dimethylamino‐2‐propoxide with Diethylzinc

A uniform, conformal, pure copper metal thin film was grown at very low substrate temperatures (100–120 °C) on Si(100) substrates by atomic layer deposition involving the ligand exchange of [Cu(OCHMeCH₂NMe₂)₂] with Et₂Zn (see scheme). Patterned copper thin films of Cu nanotubes (diameter 150 nm, length 12 μm) were fabricated.

     

CuO–ZnO Micro/Nanoporous Array‐Film‐Based Chemosensors: New Sensing Properties to H2S

CuO–ZnO micro/nanoporous array‐films are synthesized by transferring a solution‐dipped self‐organized colloidal template onto a device substrate and sequent heat treatment. Their morphologies and structures are characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectrum analysis. Based on the sensing measurement, it is found that the CuO–ZnO films prepared with the composition of [Cu²⁺]/[Zn²⁺]=0.005, 0.01, and 0.05 all show a nice sensitivity to 10 ppm H₂S. Interestingly, three different zones exist in the patterns of gas responses versus H₂S concentrations: a platform zone, a rapidly increasing zone, and a slowly increasing zone. Further experiments show that the hybrid CuO–ZnO porous film sensor exhibits shorter recovery time and better selectivity to H₂S gas against other interfering gases at a concentration of 10 ppm. These new sensing properties may be due to a depletion layer induced by p–n junction between p‐type CuO and n‐type ZnO and high chemical activity of CuO to H₂S. This work will provide a new construction route of ZnO‐based sensing materials, which can be used as H₂S sensors with high performances.     

Inactivation of Escherichia coli on Immobilized CuO/CoFe2O4‐TiO2 Thin‐Film under Simulated Sunlight Irradiation

Composite photocatalysts of CuO/CoFe₂O₄‐TiO₂ were successfully synthesized by a sol‐gel method and fixed on ordinary tiles. The photosterilization of Escherichia coli was examined on CuO/CoFe₂O₄‐TiO₂ thin films under a xenon lamp irradiation. The film was characterized by XRD, and the morphology was observed by SEM. Disinfection data indicated that CuO/CoFe₂O₄‐TiO₂ composite photocatalysts have the much better photocatalytic activity than CuO/CoFe₂O₄ and TiO₂. The optimized composition of the nanocomposites has been found to be m_CuO/CoFe2O4:m_TiO2=3:7, with loadings ranging from 790 to 1400 mg/m². The photocatalytic inactivated rate of E. coli (10⁵ CFU/mL) reached 98.4% under the xenon lamp of 150 W within 30 min.     

Thin‐Film Transformation of NH4PbI3 to CH3NH3PbI3 Perovskite: A Methylamine‐Induced Conversion–Healing Process

Methylamine‐induced thin‐film transformation at room‐temperature is discovered, where a porous, rough, polycrystalline NH₄PbI₃ non‐perovskite thin film converts stepwise into a dense, ultrasmooth, textured CH₃NH₃PbI₃ perovskite thin film. Owing to the beneficial phase/structural development of the thin film, its photovoltaic properties undergo dramatic enhancement during this NH₄PbI₃‐to‐CH₃NH₃PbI₃ transformation process. The chemical origins of this transformation are studied at various length scales.     

(110)‐Oriented ZIF‐8 Thin Films on ITO with Controllable Thickness

(110)‐oriented zeolitic imidazolate framework (ZIF)‐8 thin films with controllable thickness are successfully deposited on indium tin oxide (ITO) electrodes at room temperature. The method applied uses 3‐aminopropyltriethoxysilane (APTES) in the form of self‐assembled monolayers (SAMs), followed by a subsequent adoption of the layer‐by‐layer (LBL) method. The crystallographic preferential orientation (CPO) index shows that the ZIF‐8 thin films are (110)‐oriented. A possible mechanism for the growth of the (110)‐oriented ZIF‐8 thin films on 3‐aminopropyltriethoxysilane modified ITO is proposed. The observed cross‐sectional scanning electron microscopy (SEM) images and photoluminescent (PL) spectra of the ZIF‐8 thin films indicate that the thickness of the ZIF‐8 layers is proportional to the number of growth cycles. The extension of such a SAM method for the fabrication of ZIF‐8 thin films as described herein should be applicable in other ZIF materials, and the as‐prepared ZIF‐8 thin films on ITO may be explored for photoelectrochemical applications.     

Axis‐Oriented,Continuous Anatase Titania Films with Exposed Reactive {100} Facets

Homogeneous TiO₂ single crystals with high exposure of {100} reactive facets were constructed as a seed monolayer on transparent conductive substrates with the desired orientation of reactive facets. A secondary growth process was subsequently carried out on the monolayer seed film to form an axis‐oriented continuous reactive film. Performing secondary growth with different precursors led to optimized conditions for high‐performance photoelectrochemical activity of anatase TiO₂ films. Experimental techniques such as UV/Vis absorption spectroscopy, X‐ray diffraction, high‐resolution SEM, and photoelectrochemistry were used to characterize the structural, optical, and photoelectrochemical properties of the as‐synthesized films. As a photoanode in a photoelectrochemical cell, the axis‐oriented reactive film shows a maximum photocurrent density of 0.3 mA cm^?2, as opposed to 0.075 mA cm^?2 for non‐axis‐oriented (randomly oriented) TiO₂ film.     

Oriented Monolayer Film of Gd2O3:0.05 Eu Crystallites: Quasi‐Topotactic Transformation of the Hydroxide Film and Drastic Enhancement of Photoluminescence Properties

Caught on film : A semitransparent and intensely luminescent monolayer film of oriented Gd₂O₃:0.05 Eu platelet crystallites is fabricated by annealing the precursor hydroxide film (see scheme). The photoluminescence properties of the as‐transformed film are greatly improved over those of the hydroxide film, and are much more pronounced than those of the corresponding Gd₂O₃:0.05 Eu powder.