Molecule‐Enhanced Surface‐Enhanced Infrared Absorption Spectroscopy (MOSEIRA)

Surface‐enhanced infrared absorption spectroscopy (SEIRA) of methanol, ethanol, 1‐propanol, and 2‐propanol in thin films on planar silver halide (AgX) fibers under slow N₂ flow using 1 sec scans reveals structure in absorbance–time plots. The absorption intensities show extra enhancements (3×) in the absorbance (O? H stretch) ascribed to oligomers present at the AgX surface (molecule enhanced, thus MOSEIRA).This is above those due to amplification (40×, 20 reflections) and enhancement (30×, image dipoles or surface phonon polaritons). In the case of ethanol an excellent initial pentamer spectrum evolves over 8–10 min to a mixture of pentamer, tetramer, and trimer spectra that within another minute forms small oligomers and monomers. We use a new type of cell for infrared spectroscopy containing an AgX planar fiber. The optical configuration leads to a vicinal region at the surface defined by evanescent waves. Within this region are surface‐induced organized species such as ethanol oligomers. The planar AgX fiber supports 20 reflections and transmits light over a wide visible–infrared wavelength range. Short scan times permit the study of volatile substrates or solvents, including the effects of solvent polarity.     

Thin‐Film Metal Hydrides

The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well‐defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye‐catching hydrogen switchable mirror effect, the visualization of solid‐state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin‐metal hydride films are used as model systems to study metal–insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis.     

Thin‐Film Properties of DNA and RNA Bases: A Combined Experimental and Theoretical Study

The structures of the DNA and RNA bases cytosine, uracil, and thymine in thin films with a nominal film thickness of about 20 nm are studied by using X‐ray photoemission spectroscopy (XPS) and Fourier‐transform infrared spectroscopy. The molecules are evaporated in situ from powder on a gold foil. The experimental results indicate that cytosine is composed of two energetically close tautomeric forms, whereas uracil and thymine exist in only one tautomeric form. Additionally, quantum chemical calculations are performed to complement the experimental results. The relative energies of the tautomeric forms of cytosine, uracil, and thymine are calculated using Hartree–Fock (HF), density functional theory (DFT), and post‐HF methods. Furthermore, the assignment of the XPS spectra is supported by using simple model considerations employing Koopmans ionization energies and Mulliken net atomic charges.     

Thin Films that Consist of CuO Mesocrystal Nanosheets: An Application of Microbial‐Mineralization‐Inspired Approaches to Thin‐Film Formation

Thin films of copper oxides can be synthesized on substrates by using approaches that are inspired by microbial mineralization processes. In nature, precipitates of manganese and iron oxides with controlled oxidation states and crystal phases are produced through biomineralization by microorganisms. We have previously reported microbial‐mineralization‐inspired approaches that are comprised of direct and intermediate routes for the controlled syntheses of transition‐metal oxides. Herein, these approaches are applied to the thin‐film formation and coating of copper oxides and a related compound with controlled crystal phases and morphologies. Thin films of CuO, Cu₂O, and Cu₂(OH)₃Cl were selectively synthesized by using direct or intermediate routes. Notably, CuO mesocrystal nanosheets formed a thin film over the whole of the substrate. The resultant CuO mesocrystal nanosheets showed enhanced properties for the electrochemical detection of dopamine. This study shows the potential applicability of microbial‐mineralization‐inspired approaches to thin‐film coatings.     

Harnessing Thin‐Film Continuous‐Flow Assembly Lines

Inspired by nature's ability to construct complex molecules through sequential synthetic transformations, an assembly line synthesis of α‐aminophosphonates has been developed. In this approach, simple starting materials are continuously fed through a thin‐film reactor where the intermediates accrue molecular complexity as they progress through the flow system. Flow chemistry allows rapid multistep transformations to occur via reaction compartmentalization, an approach not amenable to using conventional flasks. Thin film processing can also access facile in situ solvent exchange to drive reaction efficiency, and through this method, α‐aminophosphonate synthesis requires only 443 s residence time to produce 3.22 g h^?1. Assembly‐line synthesis allows unprecedented reaction flexibility and processing efficiency.     

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).     

Infrared Cavity Ringdown Spectroscopy of Jet‐Cooled Polycyclic Aromatic Hydrocarbons

Infrared absorption spectra of the CH stretching region were observed for naphthalene, anthracene, phenanthrene, pyrene, and perylene using a heated, supersonic, slit‐jet source and cavity ringdown spectroscopy. Band positions and intensities recorded with 0.2‐cm^?1 resolution were compared with previous gas‐phase and argon matrix isolation experiments, as well as theoretical calculations. The largest matrix shift in the absorption maximum (‐7.4 cm^?1) was observed for anthracene, with all others shifted by 3.0 cm^?1 or less. Spectral features in the supersonic jet spectrum were generally narrower than those observed in the Ar matrix, with the largest matrix broadening found for the perylene (80 % increase). Low number densities observed for the larger polycyclic aromatic hydrocarbons (PAHs) suggest that the lower vapor pressure of PAHs with catacondensed four‐membered rings and with five‐membered rings other than perylene will not be detectable using our current configuration.     

Computational Study of the One‐ and Two‐Dimensional Infrared Spectra of a Proton‐Transfer Mode in a Hydrogen‐Bonded Complex Dissolved in a Polar Nanocluster

The signatures of nanosolvation on the one‐ and two‐dimensional (1D and 2D) IR spectra of a proton‐transfer mode in a hydrogen‐bonded complex dissolved in polar solvent molecule nanoclusters of varying size are elucidated by using mixed quantum–classical molecular dynamics simulations. For this particular system, increasing the number of solvent molecules successively from N=7 to N=9 initiates the transition of the system from a cluster state to a bulk‐like state. Both the 1D and 2D IR spectra reflect this transition through pronounced changes in their peak intensities and numbers, but the time‐resolved 2D IR spectra also manifest spectral features that uniquely identify the onset of the cluster‐to‐bulk transition. In particular, it is observed that in the 1D IR spectra, the relative intensities of the peaks change such that the number of peaks decreases from three to two as the size of the cluster increases from N=7 to N=9. In the 2D IR spectra, off‐diagonal peaks are observed in the N=7 and N=8 cases at zero waiting time, but not in the N=9 case. It is known that there are no off‐diagonal peaks in the 2D IR spectrum of the bulk version of this system at zero waiting time, so the disappearance of these peaks is a unique signature of the onset of bulk‐like behavior. Through an examination of the trajectories of various properties of the complex and solvent, it is possible to relate the emergence of these off‐diagonal peaks to an interplay between the vibrations of the complex and the solvent polarization dynamics.     

Deposition and Characterization of Luminescent Eu(tta)3phen‐Doped Parylene‐Based Thin‐Film Materials

Herein, novel host–guest films produced by coarse vacuum cosublimation of the parylene C dimer and Eu(tta)₃phen are prepared and studied. Eu(tta)₃phen sublimation at different temperatures allows films with different concentrations of the Eu complex to be obtained. The films are characterized by Rutherford backscattering spectrometry (RBS), FTIR spectroscopy, X‐ray diffraction (XRD), atomic force microscopy (AFM), and UV/Vis absorption and emission spectroscopy. RBS, FTIR, and XRD reveal the incorporation of Eu(tta)₃phen into the parylene matrix. AFM evidences the very flat film surface, which is particularly advantageous for optical applications. UV/Vis absorption and emission analyses confirm that the optical properties of Eu(tta)₃phen are preserved in the deposited films. Fluorescence measurements evidence the occurrence of an energy‐transfer process between parylene and Eu(tta)₃phen, and this results in an increase in the light emitted by the Eu complex that is as much as five times higher than that emitted by Eu(tta)₃phen alone.     

Pure Cubic‐Phase Hybrid Iodobismuthates AgBi2I7 for Thin‐Film Photovoltaics

Bismuth‐based hybrid perovskites are candidates for lead‐free and air‐stable photovoltaics, but poor surface morphologies and a high band‐gap energy have previously limited these hybrid perovskites. A new materials processing strategy to produce enhanced bismuth‐based thin‐film photovoltaic absorbers by incorporation of monovalent silver cations into iodobismuthates is presented. Solution‐processed AgBi₂I₇ thin films are prepared by spin‐coating silver and bismuth precursors dissolved in n‐butylamine and annealing under an N₂ atmosphere. X‐ray diffraction analysis reveals the pure cubic structure (Fd3m) with lattice parameters of a=b=c=12.223 Å. The resultant AgBi₂I₇ thin films exhibit dense and pinhole‐free surface morphologies with grains ranging in size from 200–800 nm and a low band gap of 1.87 eV suitable for photovoltaic applications. Initial studies produce solar power conversion efficiencies of 1.22 % and excellent stability over at least 10 days under ambient conditions.     

Sol Processing of Conjugated Carbon Nitride Powders for Thin‐Film Fabrication

The chemical protonation of graphitic carbon nitride (CN) solids with strong oxidizing acids, for example HNO₃, is demonstrated as an efficient pathway for the sol processing of a stable CN colloidal suspension, which can be translated into thin films by dip/disperse‐coating techniques. The unique features of CN colloids, such as the polymeric matrix and the reversible hydrogen bonding, result in the thin‐film electrodes derived from the sol solution exhibiting a high mechanical stability with improved conductivity for charge transport, and thus show a remarkably enhanced photo‐electrochemical performance. The polymer system can in principle be broadly tuned by hybridization with desired functionalities, thus paving the way for the application of CN for specific tasks, as exemplified here by coupling with carbon nanotubes.     

Enhanced Performance of Benzothieno[3,2‐b]thiophene (BTT)‐Based Bottom‐Contact Thin‐Film Transistors

Three new benzothieno[3,2‐b]thiophene ( BTT ; 1 ) derivatives, which were end‐functionalized with phenyl ( BTT‐P ; 2 ), benzothiophenyl ( BTT‐BT ; 3 ), and benzothieno[3,2‐b]thiophenyl groups ( BBTT ; 4 ; dimer of 1 ), were synthesized and characterized in organic thin‐film transistors (OTFTs). A new and improved synthetic method for BTT s was developed, which enabled the efficient realization of new BTT ‐based semiconductors. The crystal structure of BBTT was determined by single‐crystal X‐ray diffraction. Within this family, BBTT , which had the largest conjugation of the BTT derivatives in this study, exhibited the highest p‐channel characteristic, with a carrier mobility as high as 0.22 cm² V^?1 s^?1 and a current on/off ratio of 1×10⁷, as well as good ambient stability for bottom‐contact/bottom‐gate OTFT devices. The device characteristics were correlated with the film morphologies and microstructures of the corresponding compounds.     

A Fast Deposition‐Crystallization Procedure for Highly Efficient Lead Iodide Perovskite Thin‐Film Solar Cells

Thin‐film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low‐cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two‐step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one‐step, solvent‐induced, fast crystallization method involving spin‐coating of a DMF solution of CH₃NH₃PbI₃ followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution‐processed thin films yielded an average power conversion efficiency of 13.9±0.7 % and a steady state efficiency of 13 % under standard AM 1.5 conditions.     

Infrared Spectroscopy of a Wilkinson Catalyst in a Room‐Temperature Ionic Liquid

Homogeneous catalysis in room‐temperature ionic liquids (ILs) constitutes a most interesting field of research with high potential in technical applications. As concerns the hydrogenation of unsaturated hydrocarbons, Wilkinson’s compound RhCl(PPh₃)₃ represents a catalyst that provides high selectivity and activity. Herein, we demonstrate the application of infrared spectroscopy to the quantitative analysis of the Wilkinson catalyst in the IL 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). Our study demonstrates for the first time the quantitative, accurate and reproducible determination of the concentration of a rhodium catalyst by means of IR spectroscopy and, moreover, allows the investigation of intermolecular interactions. Spectral features, located mainly in the fingerprint region of the IR spectrum, are identified revealing the influence of the dissolved catalyst on the IL’s vibrational structure. In particular, the ring‐bending mode of the imidazolium ring shows a frequency shift as a function of catalyst concentration, probably due to hydrogen‐bond formation between the IL cation and the Rh complex. The results show the potential of IR spectroscopy both for application as a quick process control technology in catalytic processes and as a tool for better understanding of IL–catalyst interactions.     

Oxidation‐State Analysis of Ceria by X‐ray Photoelectron Spectroscopy

Three different methods to determine the oxide‐phase concentration in mixed cerium oxide by hard X‐ray photoelectron spectroscopy are applied and quantitatively compared. Synchrotron‐based characterization of the O 1s region was used as a benchmark to introduce a method based on the weighted superposition of the Ce 3d spectra of the pure Ce³⁺ and Ce⁴⁺ phases, which was shown to lead to reliable and highly accurate determination of the mean oxidation state in mixed cerium oxides. The results obtained reveal a linear relation between the third distinct final state (u′′′) satellite peak intensity of the Ce⁴⁺ phase and the Ce⁴⁺ concentration by proper inclusion of Ce³⁺‐related plasmon satellite peaks, which contradicts previous claims of nonlinear behavior. In contrast, quantitative conventional peak‐fitting procedures were shown to be well suited for the Ce 2p region due to its relatively simple structure. Additional satellite features observed in the Ce 3d spectrum of CeO₂ were proposed to originate from plasmon contributions.     

Ionization‐Induced Solvent Migration in Acetanilide‐Methanol Clusters Inferred from Isomer‐Selective Infrared Spectroscopy

We present the resonance‐enhanced multiphoton ionization, infrared‐ultraviolet hole burning (IR‐UV HB), and IR dip spectra of the trans‐acetanilide–methanol (AA–MeOH) cluster in the S₀, S₁, and cationic ground state (D₀) in a supersonic jet. The IR‐UV HB spectra demonstrate the co‐existence of two isomers in S_0,1, in which MeOH binds either to the NH or the CO site of the peptide linkage in AA, denoted as AA(NH)–MeOH and AA(CO)–MeOH. When AA(CO)–MeOH is selectively ionized, its IR spectrum in D₀ is the same as that measured for AA⁺(NH)–MeOH. Thus, photoionization of AA(CO)–MeOH induces migration of MeOH from the CO to the NH site with 100% yield.     

Simultaneously Probing Two Ultrafast Condensed‐Phase Molecular Symmetry Breaking Events by Two‐Dimensional Infrared Spectroscopy

In condensed phases, a highly symmetric gas‐phase molecule lowers its symmetry under perturbation of the solvent, which is vital to a variety of structural chemistry related processes. However, the dynamical aspects of solvent‐mediated symmetry‐breaking events remain largely unknown. Herein, direct evidence for two types of solvent‐mediated symmetry‐breaking events that coexist on the picosecond timescale in a highly symmetric anion, namely, hexacyanocobaltate, is presented: 1) an equilibrium symmetry‐breaking event in which a solvent‐bound species having lowered symmetry undergoes a population exchange reaction with the symmetry‐retaining species; 2) a dynamic symmetry‐breaking event that is composed of many dynamic population‐exchange reactions under fluctuating solvent interactions. Ultrafast two‐dimensional infrared spectroscopy is used to simultaneously observe and dynamically characterize these two events. This work opens a new window into molecular symmetry and structural dynamics under equilibrium and non‐equilibrium conditions.