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Purpose This study aims to improve the tribological performance of Babbitt alloy under oil lubricant condition. Thus, the surface was treated into oleophobic state by modifying with low surface energy fluorosilane (1H,1H,2H,2H-perfluorodecyltriethoxysilane). It is believed that the oleophobic surface offered excellent wear resistance of Babbitt-based tribo-pairs. Design/methodology/approach By modifying the Babbitt alloy with low surface energy fluorosilane and measuring the oil contact angle, the wetting behavior was evaluated. Using Pin on Disk tribometer, the tribological properties of bare Babbitt and modified Babbitt were quantified. The samples after the friction test were characterized by scanning electron microscope (SEM) and the anti-wear performance was evaluated under dry and oil lubrication conditions. Findings Results showed that oil contact angle of modified Babbitt was109° which was tripled compared to that of prime surface, which indicates the oleophobic behavior was greatly improved. Under dry conditions, the friction coefficient of the modified surface with different load conditions is slightly lower than that of the bare surface, while the friction coefficient of the modified surface under lubrication conditions is significantly decreased compared to that of the bare surface. Interestingly, under low load and high load, the wear rate of the modified Babbitt alloy surface is only 1/4 and 1/3 of that of the bare surface, respectively. Originality/value The work proposed an effective method to improve the Babbitt tribological performances and will lighten future ideas for the Babbitt alloy bearing with high wear resistance, which is beneficial to improve the service life of sliding bearings and has huge promotion and application value in the manufacture of sliding bearings.

Boundary conditions for catalyst performance in the conversion of common precursors such as N2, O2, H2O, and CO2 are governed by linear free energy and scaling relationships. Knowledge of these limits offers an impetus for designing strategies to alter reaction mechanisms to improve performance. Typically, experimental demonstrations of linear trends and deviations from them are composed of a small number of data points constrained by inherent experimental limitations. Herein, high-throughput experimentation on 14 bulk copper bimetallic alloys allowed for data-driven identification of a scaling relationship between the partial current densities of methane and C2+ products. This strict dependence represents an intrinsic limit to the Faradaic efficiency for C–C coupling. We have furthermore demonstrated that coating the electrodes with a molecular film breaks the scaling relationship to promote C2+ product formation., High-throughput experimentation on the reduction of CO2 on copper alloys led to the identification of a scaling relationship between CH4 and C2+ products that can be broken with an organic additive.

We demonstrate the solvent-free amorphous-to-cocrystalline transformations of nanoscale molecular films. Exposing amorphous films to vapors of a haloarene results in the formation of a cocrystalline coating. This transformation proceeds by gradual strengthening of halogen-bonding interactions as a result of the crystallization process. The gas-solid diffusion mechanism involves formation of an amorphous metastable phase prior to crystallization of the films. In situ optical microscopy shows mass transport during this process, which is confirmed by cross-section analysis of the final structures using focused ion beam milling combined with scanning electron microscopy. Nanomechanical measurements show that the rigidity of the amorphous films influences the crystallization process. This surface transformation results in molecular arrangements that are not readily obtained through other means. Cocrystals grown in solution crystallize in a monoclinic centrosymmetric space group, whereas the on-surface halogen-bonded assembly crystallizes into a noncentrosymmetric material with a bulk second-order nonlinear optical response.

The structuring of liquid-liquid and liquid-air interfaces may play an important role in novel microfabrication platforms and biotechnologies, from the spontaneous formation of microfilaments from liquid droplets and the 3D printing of liquids, to the culture of stem cells on emulsions. Understanding the mechanical anisotropy of associated liquid interfaces is essential for the development of such systems. Models of AFM indentation at liquid interfaces, based on the Young-Laplace model, currently do not allow the quantification of interfacial mechanical properties of associated molecular films. This report presents such a model and compares its predictions to interfacial mechanical properties characterised via interfacial shear rheology. An extreme reversal of mechanical anisotropy of liquid-liquid interfaces is observed, upon self-assembly of protein nanosheets, by 5 orders of magnitude. Results indicate that, although interfacial rheology is more sensitive than AFM indentation to the mechanics of molecular films in the low range of interfacial mechanics, AFM indentation allows the quantification of mechanical properties of stiffer molecular films, and remains better adapted to the characterisation of small samples and enables the characterisation of local heterogeneity.

Interests in minimalist device structure design of perovskite solar cells (PSCs) have accelerated the rapid advances of electron transport layer-free PSCs by composition and solvent engineering. Fo...

Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3rd order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor–Acceptor–Donor (D–A–D) architecture with acceptor, AcacBF2, located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert–Mataga plot. As donor strength in the D–A–D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.

Tetrapyrrole complexes adsorbed on magnetic surfaces present an attractive choice for molecular magnetic storage devices as well as spin valves and spin filters. Metalloporphyrins and phthalocyanines molecules arrange in well ordered structures and adopt a flat configuration on ferromagnetic substrates such as Ni, Fe and Co. Electronic and magnetic properties of these molecular films have sensitive dependence on their interface with these substrate, thereby, provide opportunities to control and manipulate the spin of central metal atom by insertion of intermediate graphene layer, oxygen atom or nonmagnetic layers. The current review intends to shed light on recent progress in various strategies to control spin at metal–molecule interfaces.

The structure and reactivity of a molecule in the condensed phase are governed by its intermolecular interactions with the surrounding environment. The multipole expansion of each molecule in the condensed phase indicates that the intermolecular interactions are essentially electrostatic (e.g., ion-dipole, dipole-dipole, dipole-quadrupole, dipole-induced dipole). The electrostatic field is a fundamental language of intermolecular communications. Therefore, understanding the influence of the electrostatic field on a molecule, that is, the mechanisms by which an electrostatic field manipulates a molecule, from the perspective of molecular structure, energy states, and dynamics is indispensable for illustrating and, by extension, controlling the chemistry in molecular systems.In this Account, we describe the recent progress made in manipulation of molecular processes using an external DC electrostatic field. An electrostatic field with unprecedentedly high strength (≤4 × 108 V/m) was applied in a controlled manner across a molecular film sample using the ice film nanocapacitor method. This field strength is comparable in magnitude to that of weak intermolecular interactions such as van der Waals interactions in the condensed phases. The samples were prepared using a thin film growing technique in vacuum to obtain the desired chemically tailored molecular systems. The examples of prepared systems included small molecules and molecular clusters isolated in cryogenic Ar matrices, frozen molecular films in amorphous or crystalline phase, and interfaces of multilayered molecular films. The response of the molecules to the external field was monitored by reflection-absorption infrared spectroscopy. This approach allowed us to investigate a variety of molecular systems with various intermolecular strength and environments under the influence of strong electrostatic fields. The range of observed molecular behaviors includes the manipulation of molecular orientation, intramolecular dynamics, and proton transfer reactions as an example of stereodynamic control of chemical reactivity. These observations improve our understanding of molecular behaviors in strong electric fields and broaden our perspective on electrostatic manipulation of molecules. This information is also relevant to a variety of research topics in physical and biological sciences where electric fields play a role in molecular and biological functions.

The synthesis of a novel expanded π-conjugated system, namely benzotri(7-azaindole), BTAI, is reported. Its C 3h symmetry along with the integration of six complementary donor and acceptor N-H···N hydrogen bonds in the conjugated structure promote the 2D self-assembly on Au(111) over extended areas. Besides, a perfect commensurability with the gold lattice endows the physisorbed molecular film with a remarkable stability. The structural features of BTAI result in two levels of surface chirality: Firstly, the molecules become chiral upon adsorption on the surface. Then, due to the favorable N-H···N hydrogen bond-directed self-assembly, along with the relative molecular rotation with respect to the substrate, supramolecular chirality manifests in two mirror enantiomorphous domains. Thus, the system undergoes spontaneous chiral resolution. LEED and STM assisted by theoretical simulations have been employed to characterize in detail these novel 2D conglomerates with relevant chiral properties for systems with C 3h symmetry.

Strong coupling to the electronic or vibronic transitions of an organic semiconductor has been extensively studied in microcavity structures in which a molecular film is placed between two closely spaced mirrors. Recent experiments suggest that such strong coupling can be used to modify chemical reactions; however, the geometry of conventional microcavity structures makes such studies difficult as they limit the ability of molecules to interact with their local environment. Here, we show that optical strong coupling to a molecular film can be achieved even when such molecules are located on the surface of a dielectric slab. We then show that such molecules on the surface of the slab can undergo facile interactions with molecules in their surrounding environment, and evidence a reversible protonation/deprotonation reaction by exposing a surface-bound porphyrin to an acidic or basic vapor. Although our proof-of-principle measurements do not evidence any change in reaction rates, we believe our structures represent a promising system in which to explore polariton-driven chemical phenomena.

For the successful application of boundary lubrication, detailed investigations about the influence of preparation process on molecular films are needed. In this paper, a specially designed device was used for the film preparation. The scanning electron microscope (SEM) combined with atomic force microscope (AFM) was employed to characterize the surface morphology and nanotribological behavior of molecular films. After the liquid phase deposition, molecular films are randomly and densely distributed over Ti-doped diamond-like carbon (Ti-DLC) substrates. Through rigorous surface treatments, island-like molecular films were finally achieved on substrate surfaces. The surface friction of molecular films is obviously lower than that of Ti-DLC surfaces. Then, pin-on-disk tribotests were performed to study the macrofriction behavior of molecular films under different preparation parameters. Based on the orthogonal experiment, the effect of five preparation parameters (solution weight percent, smearing force and processing time of three smearing steps) on initial friction coefficient of molecular films was investigated. The results indicated that the order of significance levels is as follows: processing time of the second smearing step > solution weight percent > processing time of step 1 > processing time of step 3 > smearing force. For the purpose of friction reduction, the appropriate level ranges are 0.75% (Solution), 2.5 N–15 N (Force), 1 min–10 min (Step 1), 1 min–2 min (Step 2) and 1 min, 2 min, 5 min and 15 min (Step 3). The initial friction coefficient under the optimized conditions is around 0.112, and the equilibrium friction coefficient is around 0.162, which is lower than that of unlubricated Ti-DLC substrates.

Combining 2D materials with functional molecular films enables the fabrication of van der Waals bound organic/inorganic hybrids that are of interest for future device architectures. Recently, the 2D dielectric hexagonal boron nitride (hBN) has received particular attention since exfoliation allows the preparation of crystalline layers which have been utilized as ultrathin dielectrics in electronic devices. Here, we have studied the formation and structure of molecular films of the prototypical organic semiconductors pentacene (PEN) and perfluoropentacene (PFP) on hBN. Special attention was paid to the influence of substrate surface defects on the film formation by comparing molecular films that were grown on hBN substrates of various quality, including single crystals (representing the most ideal surface), briefly ion bombarded substrates, and exfoliated flakes. While X-ray diffraction (XRD) yields precise information about the crystalline structure of films grown on (large) single crystals, it is hardly applicable to analyze the films formed on exfoliated flakes because of their small size. Here, we demonstrate that in the case of flakes detailed structural analyses of the molecular films are possible by combining atomic force microscopy (AFM) with microspot UV/vis spectroscopy and optical polarization microscopy. On well-ordered hBN single crystal surfaces both acenes form very smooth and epitaxial crystalline films where molecules adopt a recumbent orientation (even in 100 nm thick films). By contrast, both materials adopt an upright molecular orientation and different polymorphs on defective hBN surfaces and reveal distinctly different film morphologies. On exfoliated flakes, PFP shows a film structure similar to that on the hBN single crystals, while PEN films exhibit a structure as on defective hBN substrates. In addition, a pronounced decoration of defect steps, which are probably created by the exfoliation process, was observed for PEN leading to the formation of tall and extended fibers where molecules adopt a recumbent orientation. The present study reveals different robustness in film growth on exfoliated hBN flakes for various molecules, which has to be considered in their device integration, especially with regard to their optoelectronic properties such as light absorption or charge transport, which depend critically on the molecular orientation and crystalline order.

Holographic grating recording and relaxation is studied in different azobenzene molecular glassy films by circularly orthogonally polarized 532 nm laser beams L and R. The readout was made by circularly polarized (R or L) 632.8 nm laser beam. Sandwich-type samples (glass-film-glass) were also studied. Maximum diffraction efficiency of 81% has been achieved in sandwich-type AR-173 film. The following relaxation features have been found: after reaching diffraction efficiency (DE) maximum no DE decay took place; DE read out by R-polarized beam was always higher than that by L-polarized beam; in sandwich-type samples DE decayed until zero when read out by R-polarization whereas DE was zero when read out by L-polarization. 50% relaxation times varied from 4 to 44 minutes, and they mainly decreased when grating period was increased. The observed relaxation peculiarities can be understood if one assumes that volume birefringence grating (VBG) is recorded followed by volume density grating (VDG) and surface relief grating (SRG) recording. R-polarization "feels" all gratings whereas L-polarization only VDG and SRG. At large exposures VDG and SRG dominate. These results confirm the conclusion made by J.Mikelsone in her 2018 PhD thesis that birefringence grating recording in azobenzene materials is a neccessary condition for SRG appearance.

Post deposition annealing of copper phthalocyanine (CuPc) films develops nano-rod structures on the surface of the film and the length and uniformity of nano-rods depend on the annealing temperature. The proposed methodology combines scanning electron microscopy (SEM) and atomic force microscopy (AFM) with impedance spectroscopy to give new insights into the influence of thermally developed nano structures on the charge carrier mobility of CuPc films. The impedance spectroscopy provides a non-invasive and cost-effective study which finds that the hole mobility of CuPc films improves upon increasing annealing temperature, reaches maximum of (5.3 ± 0.7) × 10–5 cm2V−1 s−1 at 150 °C and reduces at higher temperatures. These results will benefit future strategies for the surface modification of small molecular films for improved charge transport in organic and hybrid devices.

A hallmark of quantum control is the ability to manipulate quantum emission at the nanoscale. Through scanning tunneling microscopy-induced luminescence (STML), we are able to generate plasmonic light originating from inelastic tunneling processes that occur in the vacuum between a tip and a few-nanometer-thick molecular film of C60 deposited on Ag(111). Single photon emission, not of molecular excitonic origin, occurs with a 1/e recovery time of a tenth of a nanosecond or less, as shown through Hanbury Brown and Twiss photon intensity interferometry. Tight-binding calculations of the electronic structure for the combined tip and Ag–C60 system results in good agreement with experiment. The tunneling happens through electric-field-induced split-off states below the C60 LUMO band, which leads to a Coulomb blockade effect and single photon emission. The use of split-off states is shown to be a general technique that has special relevance for narrowband materials with a large bandgap., D. G. de Oteyza acknowledges support from the Alexander von Humboldt Foundation for his research stay at the MPI, hosted by K. Kern, as well as from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 635919) and from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, grant no. MAT2016-78293-C6-1-R).

Perovskite solar cells, as an emerging high-efficiency and low-cost photovoltaic technology1–6, face obstacles on their way towards commercialization. Substantial improvements have been made to device stability7–10, but potential issues with lead toxicity and leaching from devices remain relatively unexplored11–16. The potential for lead leakage could be perceived as an environmental and public health risk when using perovskite solar cells in building-integrated photovoltaics17–23. Here we present a chemical approach for on-device sequestration of more than 96 per cent of lead leakage caused by severe device damage. A coating of lead-absorbing material is applied to the front and back sides of the device stack. On the glass side of the front transparent conducting electrode, we use a transparent lead-absorbing molecular film containing phosphonic acid groups that bind strongly to lead. On the back (metal) electrode side, we place a polymer film blended with lead-chelating agents between the metal electrode and a standard photovoltaic packing film. The lead-absorbing films on both sides swell to absorb the lead, rather than dissolve, when subjected to water soaking, thus retaining structural integrity for easy collection of lead after damage. Using lead-absorbing materials to coat the front and back of perovskite solar cells can prevent lead leaching from damaged devices, without affecting the device performance or long-term operation stability.

An important virtue of polymer-based electronic devices is solution processing that offers large area, cheap roll-to-roll manufacturing. However, all organic electronic devices require a multilayered structure of successive thin layers stacked one on top of the other with defined interfaces and little to no layer intermixing. Solution processing of this type of structure is challenging, requiring careful formulation of the solution and selection of solvents, and is often avoided by turning to molecular films that are deposited by complicated and energy consuming deposition processes. Therefore, self-forming interlayers, where molecules segregate from the semiconducting layer to spontaneously form a distinct thin layer, show great potential for fast and simple processing of polymer-based devices. Until now, self-forming interlayers were demonstrated as a tool to tune the energy-level alignment at either the top or bottom interface in organic devices. Here we show that two judiciously selected additives can be collectively mixed into the active layer blend and each spontaneously migrates to a different interface to self-form interlayers at both organic/contact interfaces. The driving forces for additive migration, surface and interface energy considerations, induce interlayer formation during spin coating and top electrode deposition. Both interlayers modify the interfacial energy level alignment leading to improved device performance. In this case we show that a tri-layer stack composed of electron selective layer/active layer/hole selective layer is formed in one spin coating process. The methodology demonstrated here for organic solar cells is general and versatile, suitable for all polymer electronic devices and can be translated to roll-to-roll fabrication processes such as printing and coating.

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A model sliding potential, based on Prandtl–Tomlinson type models, is proposed for analyzing the temperature- and velocity-dependences of sliding processes at the interface between a tip and an adsorbed molecular layer. The proposed simple periodic potential has a parabolic form up to a critical distance, corresponding to the onset of detachment, at which point it becomes flat. The simplicity of the model will enable it to be used to analyze complex molecular interfaces, such as molecular films, mechanically induced chemical reactions or biological interfaces such as muscles or transport molecules. A simple analytical model is presented for the resulting velocity- and temperature-dependences of the friction force for the sliding of a compliant atomic force microscopy tip over an array of molecular species adsorbed on a surface, when only considering transitions of the tip in the forward direction (overall sliding direction). The validity of the analysis is tested by using kinetic Monte Carlo (kMC) simulations of the sliding over the molecular potential. This simulation provides excellent agreement with the analytic model, except for some slight differences that arise from the way in which the simulations calculate the lateral force compared to the analytical model. However, significant deviations are found between the kMC simulations and the analytical model when the possibility of both forward and reverse transitions are included, in particular at high sliding velocities and low temperatures. The origin of these effects are discussed in the manuscript, but result in superlubricious behavior, that is, vanishing friction, in particular at low sliding velocities.

Ultrathin molecular films deposited on a substrate are ubiquitously used in electronics, photonics, and additive manufacturing methods. The nanoscale surface instability of these systems under uniaxial compression is investigated here by molecular dynamics simulations. We focus on deviations from the homogeneous macroscopic behavior due to the discrete, disordered nature of the deformed system, which might have critical importance for applications. The instability, which develops in the elastoplastic regime above a finite critical strain, leads to the growth of unidimensional wrinkling up to strains as large as 0.5. We highlight both the dominant wavelength and the amplitude of the wavy structure. The wavelength is found to scale geometrically with the film length, λ∝L, up to a compressive strain of ε≃0.4 at least, depending on the film length. The onset and growth of the wrinkling under small compression are quite well described by an extended version of the familiar square-root law in the strain ε observed in macroscopic systems. Under large compression (ε≳0.25), we find that the wrinkling amplitude increases while leaving the cross section nearly constant, offering a novel interpretation of the instability with a large amplitude. The contour length of the film topography is not constant under compression, which is in disagreement with the simple accordion model. These findings might be highly relevant for the design of novel and effective wrinkling and buckling patterns and architectures in flexible platforms for electronics and photonics.

Growth of molecular thin films with desired orders and orientations has become technologically relevant as the electronic industries seek new opportunities and applications. However, the delicate balance of interfacial and intermolecular forces and their complex influence on thin-film growths still require more understanding. Here, the effects of a hydrophobic self-assembled monolayer (SAM) surface on the crystallization of four common solvents—acetonitrile, ethanol, methanol, and water—are investigated. Despite the absence of significant substrate–molecule forces, unexpected oriented growth is observed for these molecules except water. Acetonitrile and ethanol form a sustaining vertical assembly order with long-range crystalline structures. Coincident epitaxy with small lattice mismatches is found to be essential to these orderings, which are energetically favored but without a dominant azimuthal orientation. In contrast, a preferred in-plane registry of methanol overlayers is observed for an ultrathin nominal thickness and becomes lost in slightly thicker films. Such thickness-dependent ordering of methanol assemblies can be explained with semi-commensurate epitaxy with a tensile strain of ~6.6% along hydrogen-bonded chains, whose quick relief results in the loss of order and even the phase. These rich observations suggest that SAM surfaces offer good opportunities for selective crystallization of molecular films worthy of further investigations.

Made available in DSpace on 2022-04-28T19:42:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-02 Langmuir monolayers can be assembled from molecules that change from a low-energy orientation occupying a large cross-sectional area to a high-energy orientation of small cross-sectional area as the lateral pressure grows. Examples include cyclosporin A, amphotericin B, nystatin, certain alpha-helical peptides, cholesterol oxydation products, dumbbell-shaped amphiphiles, organic– inorganic nanoparticles and hybrid molecular films. The transition between the two orientations leads to a shoulder in the surface pressure-area isotherm. We propose a theoretical model that describes the shoulder and can be used to extract the energy cost per molecule for the reorientation. Our two-state model is based on a lattice–sublattice approximation that hosts the two orientations and a corresponding free energy expression which we minimize with respect to the orientational distribution. Inter-molecular interactions other than steric repulsion are ignored. We provide an analysis of the model, including an analytic solution for one specific lateral pressure near a point of inflection in the surface pressure-area isotherm, and an approximate solution for the entire range of the lateral pressures. We also use our model to estimate energy costs associated with orientational transitions from previously reported experimental surface pressure-area isotherms. Department of Physics North Dakota State University Department of Physics Institute of Biosciences Humanities and Exact Sciences São Paulo State University (UNESP) Department of Physics Institute of Biosciences Humanities and Exact Sciences São Paulo State University (UNESP)

The methods of decreasing the surface wear in tribounits and increasing the service life of agricultural machines by modifying tribounits by fluocarbon surfactants are considered, and the technology of application of a protective molecular film, electrolytic fluorination, and copolymerization reaction are discussed.

Mitigating molecular contamination during the assembly, integration, and testing of space systems requires quantitative and qualitative methods to detect the presence of molecular films on sensitive surfaces. Atomic layer deposition (ALD) is a self-limiting deposit of a variety of films layer by layer in the vapor phase on multiple types of substrates. The controlled layer-by-layer deposition enables the user to change orientation, morphology, and grain size in films, which directly impacts optical and electronic responses. In this study, the authors demonstrate the ability to use ALD-grown metal oxide thin films coupled with a Raman spectrometer to provide early detection of molecular films on witness surfaces during the assembly, integration, and testing of space flight hardware.

The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [ZnII (LN2O2 )H2 O] (1) and [GaIII (LN2O3 )] (2). These species were deposited as multilayer Langmuir-Blodgett films and characterized by IR reflection absorption spectroscopy and UV/Vis spectroscopy. Scanning electron microscopy images, potentiodynamic polarization experiments, and electrochemical impedance spectroscopy were used to assess corrosion mitigation. Both metallosurfactants demonstrate superior anticorrosion activity due to the presence of redox-inactive 3d10 metal ions that enhance the structural resistance of the ordered molecular films and limit chloride mobility and electron transfer.

Chitosan-derived molecular films self-assembled on the gold surface were characterized using electrochemical methods combined with quartz crystal microbalance, atomic force microscopy and surface enhanced infrared absorption spectroscopy. We have observed potential-dependent structural transitions, which involved a reorientation of the oligosaccharide molecules and either depletion or accumulation of water molecules within the film. The nature of water accumulated within the chitosan-derived film varies with the potential but it is dominated by hydrogen-bonded species. The content of water entrapped within the oligosaccharide film can be controlled by the potential applied to the electrode, which means that its hydration/dehydration can be triggered by an electric field.

Extension of surface-enhanced two-dimensional infrared spectroscopy (SE-2DIR) to dual-frequency experiments allows studying dynamics and energy transport in thin molecular films by tagging and prob...

Here we report molecular films terminated with diazonium salts moieties at both ends which enables single-molecule contacts between gold and silicon electrodes at open circuit via a radical reaction. We show that the kinetics of film grafting is crystal-facet dependent, being more favorable on ⟨111⟩ than on ⟨100⟩, a finding that adds control over surface chemistry during the device fabrication. The impact of this spontaneous chemistry in single-molecule electronics is demonstrated using STM-break junction approaches by forming metal-single-molecule-semiconductor junctions between silicon and gold source and drain, electrodes. Au-C and Si-C molecule-electrode contacts result in single-molecule wires that are mechanically stable, with an average lifetime at room temperature of 1.1 s, which is 30-400% higher than that reported for conventional molecular junctions formed between gold electrodes using thiol and amine contact groups. The high stability enabled measuring current-voltage properties during the lifetime of the molecular junction. We show that current rectification, which is intrinsic to metal-semiconductor junctions, can be controlled when a single-molecule bridges the gap in the junction. The system changes from being a current rectifier in the absence of a molecular bridge to an ohmic contact when a single molecule is covalently bonded to both silicon and gold electrodes. This study paves the way for the merging of the fields of single-molecule and silicon electronics.

Crown-ether (CR) ring molecules are known as host molecules for capturing guest species inside the ring. So far CR molecular films have only been grown by drop-casting a CR solution on an inert sub...

This paper focuses on the formation of high-density, low-defect monolayers of triphosphasumanene trisulfides, which are newly synthesized electronic and geometric Janus-type molecules, in a flat-on conformation. Although the molecules stack easily because of the developed π-conjugated plane, their application as a metal coating in a flat-on conformation via an interfacial molecular film enables the work function to be tuned. Surface pressure-area isotherms of the triphosphasumanene trisulfides show a two-dimensional phase transition at the air/water interface. Atomic force microscopy observations of the transferred monolayer and in- and out-of-plane X-ray diffraction patterns of the corresponding multilayers reveal that this phase transition occurs from the flat-on to the end-on conformation. The X-ray diffraction patterns obtained in the two directions completely reversed before and after the phase transition, indicating that the molecular arrangement that is generated by layers of molecular films and resultant molecular stacking is similar. The flat-on conformation of the molecules was evident from the out-of-plane X-ray diffraction and polarized infrared spectroscopy results, which indicate that a large, low-defect monomolecular film is obtained using a toluene solution with a small diffusion coefficient. The spectroscopic results reveal triphosphasumanene trisulfide aggregation in the organized molecular film, suggesting high-density molecular packing.

An elastic recoil detection analysis (ERDA) system in air for hydrogen analysis was developed in the Wakasa Wan Energy Research Center. This system uses a thin silicon–nitride window to separate the air and vacuum regions, and the beam is irradiated through the window. Elements scattered by the beam enter the vacuum region through the same window, and are detected by an ERDA detector located there. The hydrogen sensitivity of the system was investigated by analyzing high molecular films. We used a helium beam and a stopper foil in front of the ERDA detector to ensure that only hydrogen was detected. Hydrogen energy spectra for the high molecular films and background were obtained.

Collective molecular physical properties can be enhanced from their intrinsic characteristics by templating at material interfaces. Here we report how a black phosphorous (BP) substrate concatenates a nearly-free-electron (NFE) like conduction band of a C60 monolayer. Scanning tunneling microscopy reveals the C60 lowest unoccupied molecular orbital (LUMO) band is strongly delocalized in two-dimensions, which is unprecedented for a molecular semiconductor. Experiment and theory show van der Waals forces between C60 and BP reduce the inter-C60 distance and cause mutual orientation, thereby optimizing the π-π wave function overlap and forming the NFE-like band. Electronic structure and carrier mobility calculations predict that the NFE band of C60 acquires an effective mass of 0.53–0.70 me (me is the mass of free electrons), and has carrier mobility of ~200 to 440 cm2V−1s−1. The substrate-mediated intermolecular van der Waals interactions provide a route to enhance charge delocalization in fullerenes and other organic semiconductors., Fullerenes are promising organic semiconducting materials for electronic applications, but of low conductivity due to limited intermolecular hybridization. Cui et al. show a black phosphorous substrate organizes C60 monolayers to form delocalized semiconducting band with tens times enhanced conductivity.

The paper deals with the cholesterol–cyclosporine A (Chol–CsA) monolayers at the air/water interface investigated using the Langmuir trough coupled with the Brewster’s angle microscopy. The compressed films were transferred onto the PEEK polymer support by means of the Langmuir–Blodgett technique. To improve molecules adhesion and organization the PEEK surface was treated with air plasma before thin films deposition. The obtained surfaces were characterized by means of atomic force microscope (AFM). Then, the wettability of the supported monolayers was determined by the contact angle measurements. Finally, the surface free energy and its components were evaluated from the theoretical approach proposed by van Oss et al. The obtained results reveal correlation between properties of the Langmuir monolayers at the air/water interface and those of the Langmuir–Blodgett films on PEEK. This was found to be helpful for understanding the wettability of organized molecular films on the polymer support as far as biocompatibility improve is concerned. The preparation of films with defined polarity and various compositions is an important step in the development of polymer surfaces with increased biofunctionality. It is believed that the results presented in this paper can be exploited in the in vivo studies.