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A compact ultrahigh-vacuum molecular-beam deposition system has been developed for the in situ synthesis of organic thin films and multilayers. The system incorporates all the features (heater, thickness monitor, evaporators) necessary for controlled organic thin-film growth. It can be used independently, or it can be docked to the in situ growth system and transferred to other instruments of the PGM beamline, thus allowing extensive film preparation and characterization. A manipulator dedicated to specimen preparation and organic-film deposition with temperature control between 200 K and ∼800 K has been developed. The design and performance of the system are reported with emphasis on a novel solution of masks developed to achieve position-dependent film deposition. To demonstrate the enhanced capabilities of the PGM beamline in the growth and in the characterization of electronic-structure studies of organic molecular films and their heterostructures through synchrotron-based spectroscopies, this paper presents some preliminary results of a study of Fe-phthalocyanine growth on Si substrates and on in situ prepared La0.67Sr0.33MnO3 buffer layers on SrTiO3 single crystal.

The basis of modern optical engineering involves makes finding ways to design predefined optical (and in general – physical) properties of nanoscopic patterns. The boundary parameters of nano-patterns depend on (small) dimensions and the type of nanostructure substance, the external environment, as well as the form and the technical–technological of aspect of production. Fundamental properties of nano-structures can be drastically changed by changing these parameters. We have investigated the optical specificities of molecular dielectric crystal nanofilm under the influence of different confinement conditions. This paper presents a model of crystalline ultrathin molecular film and an analysis of dielectric, i.e. optical properties of these spatially much bounded structures – in their entirety. Using the two-time dependent Green's functions, the energy spectrum, the possible exciton states and their space distribution were determined and the dynamic permittivity was calculated. It was shown that the appearance of localized states in the boundary layers of the film depends on the thickness and the changing values of the system parameters in the boundary areas of the film. These localized states define the schedule and determine the number of resonant absorption peaks in the infrared region of the external electromagnetic radiation (EMR). Analytical analysis of the impact of the boundary parameters on the changes of the dielectric and optical properties of the nanofilm, as compared to the same properties of bulk samples with identical crystalline and chemical structure, is impossible. Thus, a software package (dubbed JOIG_S) has been developed and applied to perform the numerical analysis and plot graphic displays of the relation between microscopic (exciton) and macroscopic (dielectric and optical) properties as a function of the frequency of an external electromagnetic field (EMF), for a specified set of values of the boundary parameters. Optical, i.e. absorption and refraction properties of observed nanostructures demonstrate very narrow and strictly discrete characteristics. Characteristic resonant peaks appear in the dependence of the absorption index on the frequency of external EMF. All peaks fall into infrared region and indicate absorption of corresponding external EM frequencies. The number and distribution of these peaks depend on the number of layers in the film and the perturbation parameters, as a consequence of the quantum size and confinement effects. This proved that the outer environment of the film affects the given fundamental properties of a nano film, i.e. their choice/change directly controls the optical properties of the film. Such an approach could be considered as a kind of optical engineering.

Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have been demonstrated to enhance 2DIR signals by multiple orders of magnitude. We design doubly degenerate in-plane plasmonic normal modes of the symmetric trimer gap-antenna, which have orthogonal dipole moments excited by light of the appropriate polarization, to localize the enhanced field into the antenna's gap. Vibrational excitations serve as sensitive probes of the plasmonic fields. 2DIR spectroscopy of thin molecular films indicates that molecules emitting enhanced signals experience an electric field with a direction independent of the excitation laser pulse polarization. Our results illustrate the trade-off between the large signal amplification in molecules close to the antenna surface by resonant plasmons, where the direction of the enhanced fields follows metal surface boundary conditions, and the associated limitations for the polarization-selective spectroscopy. The ultrafast quantum dynamics reported by the enhanced signals is not affected by its interaction with plasmonic excitation.

Self-assembled layers, and 2D condensed molecular films as their specific cases, are known to be strongly sensitive to external conditions such as temperature, concentration of self-assembling substance(s) in solution, as well as composition of the supporting electrolyte in terms of the kind and concentration of present ions. In this work we have studied effects of a series of four sodium halides on the 2D condensation of 5-fluorocytosine (5-FC) at the hanging mercury drop electrode. This fluorinated nucleobase was selected for the study with respect to its unique 2D condensation properties (previously described in NaCl), showing remarkable capacitance pits in two potential regions (one around the potential of zero charge and the other within highly negative potential region). NaF electrolyte was not able to support 2D condensation of 5-FC, while in NaI and NaBr the 2D condensation was facilitated in comparison with the NaCl electrolyte. Furthermore, we have studied the formation of the 2D condensed film at different temperatures and ac perturbation frequencies to obtaining a complex view into the 5-FC 2D condensation processes. Our results show great importance of the composition of supporting electrolyte, and/or other experimental conditions on the properties of 2D condensed layers.

In this study, we compare and investigate both microscopic molecular packing and mesoscopic morphogenetic behavior in two-dimensional (2D) organized films/three-dimensional (3D) solids of three kin...

Crystal structures of [Dy(dpm)3]2 (1) at 155(2) K (space group P21/n, a = 12.2191(3) A, b = 27.6044(6) A, с = 21.8615(5) A, β = 105.172(1)°, V = 7116.9(3) A3, Z = 4) and Dy(dpm)3 (2) at 200(2) K (space group Pmn21, a = 17.8741(7) A, b = 10.5639(4) A, с = 9.8336(4) A, V = 1856.78(13) A3, Z = 2) are determined. The structure of complex 1 is similar to the previously known dimeric packings [Ln(dpm)3]2 (Ln = La, Pr, Nd, Eu, Gd, Tb). Complex 2 is isostructural to the previously studied molecular complexes Er(dpm)3 and Lu(dpm)3. At room temperature the luminescence quantum yield (QY) of Tb(dpm)3 is found to reach 77% and that of Dy(dpm)3 is 5%, while for the other Lu(dpm)3 complexes, where Ln = Pr, Nd, Sm, Eu, Gd, Ho, Er, Tm, Yb, QY is below 1%. A series of [Tb(dpm)3]2 and Dy(dpm)3 solid solutions is obtained by evaporating mixtures from solutions. Molecular films of these complexes on Si, Cu, Ni, Ti, KBr substrates are obtained by vacuum deposition.

The charging of solid molecular films grown on grains is an important phenomenon observed in astrochemical processes that take place in interstellar space and is relevant in high altitude environmental physics and chemistry. In this work, we present the temperature dependence study of both the conductivity and the capacitance of amorphous solid water (ASW) films (hundreds of monolayers thick) deposited on a Ru(0001) substrate. These layers subsequently interact with low-energy electrons (5 eV) in the temperature range of 50–120 K under ultra high vacuum (UHV) conditions. The charging of the ASW films was measured via contact potential difference (CPD) detection utilizing an in situ Kelvin probe and found to be sensitive to the substrate temperature during film growth, to the substrate temperature during electron irradiation, and to the film thickness. Internal electric fields exceeding 108 V/m are developed. It is shown that solid water conducts and stores electrons with “memory” of the film’s thermal his...

The molecular orientation of π-conjugated molecules has been reported to significantly affect the performance of organic photovoltaic devices (OPVs) based on molecular films. Hence, the control of molecular orientation is a key issue toward the improvement of OPV performance. In this research, oriented thin films of an n-type molecule, 3,4,9,10-Perylenetetracarboxylic Bisbenzimida-zole (PTCBI), were formed by deposition on in-plane oriented polythiophene (PT) films. Orientation of the PTCBI films was evaluated by polarized UV-vis spectroscopy and 2D-Grazing incidence X-ray diffraction. Results indicated that PTCBI molecules on PT film exhibit nearly edge-on and in-plane orientation (with molecular long axis along the substrate), whereas PTCBI molecules without PT film exhibit neither. OPVs composed of PTCBI molecular film with and without PT were fabricated and evaluated for correlation of orientation with performance. The OPVs composed of PTCBI film with PT showed higher power conversion efficiency (PCE) than that of film without PT. The experiment indicated that in-plane orientation of PTCBI molecules absorbs incident light more efficiently, leading to increase in PCE.

In this work, we studied the effect of an applied electric field on the dissociation of acetic acid (AA) at the interface of the acid and ammonia molecular layers using the ice film capacitor method. The dissociation of AA was monitored by reflection absorption infrared spectroscopy, which measured the changes in the intensities of the vibrational modes of AA and the acetate anion. The extent of field-induced dissociation was found to be dependent on the direction of the applied electric field. Interestingly, the extent of acid dissociation was greater when the field was applied in the opposite direction to that of the proton-transfer motion. This suggested that the reaction was aided by the reorientation of the reagent molecules rather than by electrostatic stabilization of the charge-transfer energy. The effect of molecular size was studied by comparing the results for AA with those of formic acid and propionic acid. The dissociation of smaller acids was more strongly enhanced than that of larger acids,...

A physical insight regarding poly(tetrafluoroethylene) (PTFE) is revealed herein. The driving force for the oriented growth of materials on aligned PTFE is investigated. The growth has been reported in numerous publications for a wide range of deposited materials on aligned PTFE layers since its discovery in 1991 because it is a promising method for preparing ordered molecular films. MD model simulations demonstrate herein that the shallow charged atomic grooves between adjacent PTFE chains trap typical two linear molecules, thus explaining the remarkable degrees of uniaxial orientation in their deposited thin films on the layers. Charge modifications to the model demonstrate for the first time that the negative charge of its fluorine atoms is crucial for the remarkable degrees. Hence, such an orientation is only possible with PTFE.

During the past decades, the development of microelectronic devices based on polymeric active layers experienced considerable progress. The improved understanding of the physics of π-conjugated materials led to the realization of novel devices like photovoltaic cells, thin-film transistors, and light-emitting diodes. The role of Technology-CAD software for molecular films is essentially the same as that for inorganic semiconductors. The obstacles and peculiarities encountered by the underlying numerical simulations however are quite different. We present results obtained with our Kinetic Monte Carlo simulator modeling an organic sandwich structure in situ. The active layer is an intrinsic amorphous Zinc Phthalocyanine film embedded between two gold contacts.

We synthesized a new series of donor–acceptor (D-A) type conjugated copolymers containing two electron-accepting units, namely thienoisoquinoline (TIQO) and benzothiadiazole (BT) (PTIQO-HBT) or fluorinated BT analogs (PTIQO-FBT and PTIQO-FFBT) connected to thiophene-based electron-donating units. The optical and electrochemical properties, planarity of conjugated backbone, molecular crystalline structure, and charge transport characteristics were investigated to comprehensively study the structure–property relationship of these semiconducting copolymers. When the BT unit carries 0, 1, and 2 fluorine, both the highest occupied and the lowest unoccupied molecular orbital energy levels of the conjugated copolymers gradually decrease. DFT calculations showed no significant difference in the energy gap or the copolymer backbone planarity. However, the grazing incidence X-ray diffraction results confirm that the PTIQO-FBT copolymer film has a longer coherence length of π–π stacking between the molecular chains than PTIQO-HBT and PTIQO-FFBT, which may affect the intermolecular charge transport. Organic field-effect transistors (OFETs) employing the three TIQO-based D-A type semiconductor copolymer films as active layer all exhibited ambipolar characteristics that enable both hole and electron transport. Particularly, the PTIQO-FBT based OFETs (hole mobility: 0.030 cm2/V·s, electron mobility: 0.023 cm2/V·s) demonstrate higher performance with well-balanced hole and electron transport, as compared to the other two copolymers in terms of field-effect mobility. Therefore, introducing a single fluorine into the BT unit in the TIQO-based D-A type conjugated copolymers results in the most appropriately controlled ground-state charge transfer for efficient intramolecular charge transport along the polymer backbone, as well as higher molecular film crystallinity.

In this study, interactions of Fe3O4 magnetic nanoparticles with serum albumin biomolecules in aqueous solutions were considered. The studies were conducted with the laser correlation spectroscopy and optical analysis of dehydrated films. It was shown that the addition of magnetite to an albumin solution at low concentrations of up to 10−6 g/L led to the formation of aggregates with sizes of up to 300 nm in the liquid phase and an increase in the number of spiral structures in the dehydrated films, which indicated an increase in their stability. With a further increase in the magnetite concentration in the solution (from 10−4 g/L), the magnetic particles stuck together and to albumin, thus forming aggregates with sizes larger than 1000 nm. At the same time, the formation of morphological structures in molecular films was disturbed, and a characteristic decrease in their stability occurred. Most stable films were formed at low concentrations of magnetic nanoparticles (less than 10−4 g/L) when small albumin–magnetic nanoparticle aggregates were formed. These results are important for characterizing the interaction processes of biomolecules with magnetic nanoparticles and can be useful for predicting the stability of biomolecular films with the inclusion of magnetite particles.

We synthesize three fused-ring electron acceptors (m-ITBr, o-ITBr and IT-2Br) based on indacenodithieno[3,2-b]thiophene as the core unit and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile with 1 or 2 bromine substituents as the end-capped unit. The effects of bromine atom number and substituted position on molecular film absorption, energy level, photovoltaic performance, charge transport and film morphology are systematically carried out. Compared with ITIC, m-ITBr, o-ITBr and IT-2Br all show red-shifted film absorption (550–750 nm) and downshifted highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. The PM6:IT-2Br based devices exhibit power conversion efficiency (PCE) of up to 12.92%, which is much higher than the reference devices based on ITIC (8.98%). In addition, all three brominated devices achieve high efficiency over 11% (11.84% for m-ITBr devices and 11.14% for o-ITBr devices). Herein, it is also concluded that bromination on terminal groups plays a vital role in enhancing the photovoltaic performance of IDTT-based FREAs.

Molecular films of octadecyltrichlorosilane (OTS) silanized on silicon substrates were obtained by a succession of fabrication steps consisting in plasma hydroxylation of silicon surface, formation of a water layer adsorbed on hydroxylated surface by substrate exposure to water vapor and OTS vapor deposition. All fabrication steps were realized in the same vacuum chamber to avoid surface contamination and to control the amount of water adsorbed on the hydroxylated surface. It is proved that the amount of water on the substrate surface plays a key role in fabrication of smooth OTS molecular films, large amounts of water on substrates resulting in formation of 3D OTS aggregates. The atomic force microscopy (AFM) investigations of the film surface revealed formation of liquid-expanded and liquid-condensed domains in OTS molecular films. Annealing of the OTS films promotes film dehydration, increases the film hydrophobicity and reduces nanoscopic adhesion and friction forces between silicon AFM tips and film surface.

The uptake and thermal chemistry of cinnamaldehyde on Cu(110) single-crystal surfaces were characterized by temperature-programmed desorption and x-ray photoelectron spectroscopy (XPS). Adsorption at 85 K appears to be initiated by low-temperature decomposition to form styrene, which desorbs at 190 K, followed by the sequential buildup of a molecular monolayer and then a condensed molecular film. Molecular desorption from the monolayer occurs at 410 K, corresponding to a desorption energy of approximately 98 kJ/mol, and further decomposition to produce styrene (again) and other fragmentation products is seen at 550 K. The molecular nature and the quantitation of the low-temperature uptake were corroborated by the XPS data, which also provided hints about the adsorption geometry adopted by the unsaturated aldehyde on the surface. Density functional theory calculations, used to estimate adsorption energies as a function of coverage and coordination mode, pointed to possible η1-O binding, at least at high coverages, and to a stabilizing effect on the surface by the aromatic ring of cinnamaldehyde. Finally, coadsorption of oxygen on the surface was found to weaken the binding of cinnamaldehyde to the Cu substrate at high coverages without enhancing its uptake, but to not modify the decomposition mechanism or energetics in any significant way.

The grain size of the perovskite layer can be tuned by the surface treatment of Ultraviolet ozone (UVO) with β-alanine self-assembled molecular films (SAMs) on the Nickel oxide (NiOx) substrate. The UVO treatment had been used to control the hydroxy (-OH) end-group on NiOx substrate and the condensation reaction of β-alanine SAMs, in which the end-group of the amino group (-NH2) correlates with the nucleation of the perovskite layer. The difference of surface end-group with/without the UVO treatment on the NiOx substrate was revealed by the shift of the oxidation peak of the SAMs layer in the cyclic voltammetry and the electrochemical impedance spectroscopy. It is found that the wettability of NiOx substrate was enhanced by the SAMs treatment time due to the increment of -NH2 end-group and the UVO treatment. Larger grain size of the perovskite layer was achieved on the NiOx substrate with SAMs 15 minutes treatment. Moreover, the optical absorbance of perovskite films in the short wavelength range was enhanced by the assembling time of SAMs. This study provides a method to control the surface morphology of the perovskite active layer in its solar cell device applications.

Molecular semiconductors, as the core component, determine the performance of different devices. It is essential to gain more knowledge of such materials. Hot electron spectroscopy, by applying a ballistic electron emission microscope and hot-electron transistor, has been demonstrated to be the most powerful method. This review concentrates on the achievements in several emerging fields, such as the interfacial energy level alignment and the charge transport characteristics in molecular film. As a versatile technique, hot electron spectroscopy has been found to be helpful in exploring the metal/molecule interface energy, the molecular levels, the electronic transport gap, and even the group structures. In comparison to the traditional techniques, such as ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and scanning tunneling spectroscopy, this method offers in-situ characterizations, which makes the detection much more accurate and convenient. This review contributes to a deep comprehension of the intrinsic characteristics of molecular semiconductors and molecule-based devices.

The crystalline packing of polymers with high tendencies to form amorphous materials has been attained by controlling intermolecular interactions. Block copolymers of aromatic polyamides in which hydrogen-bonding moieties are sparing and mostly substituted easily form amorphous materials because of steric hindrance and weak intermolecular affinities. Block copolymers of aromatic polyamides synthesized from 4-(N-methylamino)benzoic acid, terephthalic acid chloride, and poly(propylene glycol)bis(2-aminopropyl ether) are commonly amorphous, regardless of unit length. Despite these copolymers not having distinct hydrophobic groups along the alkyl chain, aromatic rings in the same plane could be packed by π–π stacking by the method of two-dimensional interfacial molecular films. The hard segment responsible for the c-axis length increased the tilted angle depending on the chain length; as a result, the chain length was not dependent on the long spacing value. Actually, the layered period in organized films of aromatic polyamides did not depend on the segment length and always indicated a constant value. Isothermal crystallization was attempted for block copolymers of aromatic polyamides exhibiting potential packing ability by the method of organized molecular films. The analyzed glass transition temperature of the oligomer corresponding only to the block unit was adopted as the crystallization temperature. All amorphous polyamides used in this study crystallized after 24 h. A monoclinic packing structure and interactions between the few remaining hydrogen-bonding moieties were suggested by a reciprocal lattice analysis. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Using Langmuir and Langmuir-Blodgett techniques molecular films of chlorinated perylene derivatives, namely tetra-n-butyl-1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxylate (PCn for n = 1, 5, 9) have been studied. The Langmuir films of pure compounds and mixed with liquid crystalline 4-octyl-4′-cyanobiphenyl (8CB) were characterized by surface pressure-mean molecular area isotherms. An additive rule reveals miscibility of all the dyes with 8CB but shows different types of intermolecular interaction forces. The pure and mixed Langmuir films were transferred onto quartz plates and characterized spectroscopically. Absorption and fluorescence spectra were recorded for the samples in form of diluted chloroform solution, the dye with 8CB mixtures in monomolecular Langmuir-Blodgett films and in liquid crystal cells. Different tendency to aggregation of the dye with short and long alkyl chains was observed. It is shown that the dye molecule stacking and aggregation of the chlorinated perylene dyes depend on the dye concentration and are related to the torsion of the perylene core.

Hydrophobins are surface-active fungal proteins that adsorb to the water-air interface and self-assemble into amphiphilic, water-repelling films that have a surface elasticity that is an order of magnitude higher than other molecular films. Here we use surface-specific sum-frequency generation spectroscopy (VSFG) and site-directed mutagenesis to study the properties of class I hydrophobin (HFBI) films from Trichoderma reesei at the molecular level. We identify protein specific HFBI signals in the frequency region 1200-1700 cm-1 that have not been observed in previous VSFG studies on proteins. We find evidence that the aspartic acid residue (D30) next to the hydrophobic patch is involved in lateral intermolecular protein interactions, while the two aspartic acid residues (D40, D43) opposite to the hydrophobic patch are primarily interacting with the water solvent.

Emitting dipole orientation (EDO) is an important issue of emitting materials in organic light-emitting diodes (OLEDs) for an increase of outcoupling efficiency of light. The origin of preferred orientation of emitting dipole of spherically shaped iridium-based heteroleptic phosphorescent dyes doped in organic layers is revealed by simulation of vacuum deposition using molecular dynamics (MD) along with quantum mechanical (QM) characterization of the phosphors for a direct comparison with experimental observations of EDO. Consideration of both the electronic transitions in a molecular frame and the orientation of the molecules interacting with the environment at the vacuum/molecular film interface allows quantitative analyses of the EDO depending on host molecules and dopant structures. Interaction between the phosphor and nearest host molecules on the surface, minimizing the non-bonding energy determines the molecular alignment during the vacuum deposition. Parallel alignment of the main cyclometalating ligands in the molecular complex due to host interactions rather than the ancillary ligand orienting to vacuum leads to the horizontal EDO., Comment: 29 pages of the main article in addition to 15 pages of the Supplementary Information including 5 figures, 5 Supplementary figures, and 1 table

The interaction between organic molecules and a metal surface has been intensely discussed these days. In this work, the formation and atomic structure of an inhibitive molecular film are revealed in the combination of molecular dynamics simulation and quantum chemical calculations. Adsorption behavior of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (PAOX) is systematically investigated either in different forms or in different environments. The results indicates that PAOX is a superior corrosion inhibitor, compatible with various environments, for the film effect of protective film formation as well as the solidification effect of aggressive ions binding. Heterocyclic atoms like nitrogen and oxygen are demonstrated to be the reactive sites supported by the Fukui function. Additionally, it shows that the organometallic bond of monomer complex is partly covalent and ionic while N18 in PAOX shares the dominative position in bonding behavior. Notably, weak interactions attributed from water molecules in an inhibi...

A series of enriched gadolinium (Gd, Z = 64) targets was prepared using the molecular plating process for nuclear physics experiments at the Cyclotron Institute at Texas A&M University. After irradiation with 48 Ca and 45 Sc projectiles at center-of-target energies of E cot = 3.8–4.7 MeV/u, the molecular films displayed visible discoloration. The morphology of the films was examined and compared to the intact target surface. The thin films underwent a heavy-ion beam-induced density change as identified by scanning electron microscopy and α-particle energy loss measurements. The films became thinner and more homogenous, with the transformation occurring early on in the irradiation. This transformation is best described as a crystalline-to-amorphous phase transition induced by atomic displacement and destruction of structural order of the original film. The chemical composition of the thin films was surveyed using energy dispersive spectroscopy and X-ray diffraction, with the results confirming the complex chemistry of the molecular films previously noted in other publications.

Oligoacenes have recently received much attention because of their ability to undergo singlet fission, a process which may improve the energy conversion efficiency in organic solar cells. Here, we studied the structural and the electronic properties of triisopropylsilylethynyl-pentacene (TIPS-Pn) adsorbed on Au(111) from monolayer to multilayer coverages using multiexperimental techniques [temperature-programmed desorption, vibrational and electronic high-resolution electron energy loss spectroscopy, and energy- and time-resolved two-photon photoemission (2PPE)]. We demonstrated that well-defined TIPS-Pn molecular films can be prepared via evaporation. TIPS-Pn adopt on Au(111) a molecular adsorption geometry in which the pentacene backbone is oriented parallel to the substrate. We determined the energetic position of several unoccupied and occupied electronic states among others originating from the lowest unoccupied molecular orbital and the highest occupied molecular orbital. Femtosecond time-resolved 2...

The evolution of electronic structure of manganese phthalocyanine on Bi2Te3 shows a transition to a bulk-like aspect abruptly after completion of the first layer. This allows the inference that, in the first layer, there is charge transfer and electronic hybridization involving the occupied Mn-derived d orbitals of the molecule into the conduction band of the substrate. The charge transfer coupling is seen using angle-resolved ultraviolet photoelectron spectroscopy by monitoring the evolution of work function and band structure with increasing molecular film thickness. The electronic structure in the second layer is more bulk-like as indicated by the reappearance of well-known low energy d orbitals that were depopulated in the first layer. Scanning tunneling microscopy shows that the transition to bulk like behavior is also reflected in film structure as a transition from a unique disordered monolayer to a locally ordered and dense second layer. These observations are relevant to ongoing efforts to control topological insulator interfaces especially for spintronics applications.

We demonstrate the read-out of the conformational state of photoswitchable molecules, without modifying that state by the read-out process itself. The ring-opening and ring-closing reactions change not only the absorption spectrum of a molecular layer but also its index of refraction. A thin layer of a dithienylethene derivative was combined with well-designed gold nanostructures. The particle plasmon resonance of these nanostructures is extremely sensitive to the photoinduced change in the environment and can therefore be used to probe the state of the photochromic switch. The probing wavelength now interrogates the plasmonic structure, not the molecular film, and can thus be conveniently placed in a transparent spectral range, e.g., the near-infrared. We find good agreement between experiments and numerical simulations with regard to spectral signatures of the plasmon resonance.

Generating well-defined molecular structures at inorganic/organic interfaces and within molecular films is fundamental for charge carrier transport and thus the performance of organic molecule-based (opto)electronic devices. Here we show by means of low-energy electron diffraction that tetrafluorotetracyanoquinodimethane (F4TCNQ) grows in an epitaxial fashion on the Au(111) surface, resulting in a unit cell which consists of one molecule. In this well-ordered crystalline films we found the formation of an extended space charge region and a dispersing unoccupied electronic molecular state using energy- and angle-resolved two-photon photoemission. The latter finding is a clear proof for band formation in the crystalline molecular structure. We suggest that the high electron affinity of F4TCNQ and a bandlike electron transport are responsible for the formation of the space charge region. Using F4TCNQ as a hole injection layer may open the opportunity to manipulate the hole injection barrier in a controlled w...

Understanding the role of appended alkyl side chains is a key issue to enhance photovoltaic performance because the side chains control molecular solubility, film crystallinity, and morphology. For this purpose, we synthesized three new planar aromatic backbone molecules ( Eh-Hex , Eh-Eh and Oct-Eh ), where the appended alkyl side chains on the aromatic core unit were either 2-ethylhexyl (Eh) or n-octyl (Oct) and those on the side ends were either Eh or hexyl (Hex). Characterization of the molecular films revealed that all of the molecules were crystalline with mainly edge-on orientation, while the Eh-Hex and Eh-Eh molecules having Eh groups on the core units manifested higher crystallinity than the molecule ( Oct-Eh ) having Oct groups on the core units. Of the small molecule:PC 71 BM blend films, only the Eh-Hex case exhibited both good intermolecular packing and uniformly distributed nanoscopic networks of molecular channels, maintaining extensive interfacial contacts between the Eh-Hex and PC 71 BM domains. On the other hand, the Eh-Eh molecules showed poor miscibility with PC 71 BM, and the Oct-Eh molecules displayed excessive miscibility with PC 71 BM. These morphological differences resulted in significant differences in the photovoltaic performance of the devices using small molecule:PC 71 BM blend films. Inverted-type photovoltaic devices fabricated using the Eh-Hex :PC 71 BM blend had the highest power conversion efficiency among the three molecule-based devices. Overall, this work demonstrated that both the type of alkyl side chain and its position are crucial factors controlling the balance of interactions between small molecules and PC 71 BM molecules, which can significantly alter blend morphology and photovoltaic performance.

Molecular films of quinonoid zwitterions, of the general formula C6H2([horiz bar, triple dot above]O)2([horiz bar, triple dot above]NHR)2, have been shown to display electronic properties highly dependent on the nature of the N-substituent R when deposited on gold substrates. The different spacing and organization of the molecules can lead to molecular films with semi-metal or dielectric behavior. With the long term goal to establish how packing effects in the solid state correlate with properties as thin films, we first attempted to identify by X-ray diffraction analysis candidate molecules showing suitable packing arrangements in the crystalline state. To this end, we have prepared a series of new functionalized, enantiopure or sterically-hindered quinonoid zwitterions and established the crystal structure of those with R = CH2–CH2–Ph (6), CH2–CH2–CH2–Ph (7), CH2–CH2–CH2–CH2–Ph (8), CH2–CH2–CH(Ph)–Ph (9), CH(CH3)–Ph (12), CH(CH2–CH3)–Ph (13), CH2–((4–CH3)–C6H4) (15), CH2–((4–NH2)–C6H4) (19) and CH2–CH2–((3,4–(OCH3)2)–C6H3) (24). An analysis of the crystal packing of three molecules, 5, 13 and 15, selected as illustrative examples for comparisons, was carried out and it was unexpectedly found that these chemically very similar molecules gave rise to different packing in the bulk, with resulting thin films showing different electronic properties. Various methods have been used for the characterization of the films, such as synchrotron radiation-based FTIR spatial spectra-microscopy, which provided an anchoring map of zwitterion 15 on a patterned substrate (Au/SiO2) showing its selective anchoring on gold. This is one of the best examples of preferential anchoring of a zwitterion and the sole example of spatial localization for a quinonoid zwitterion thin film. We have also used combined photoemission and inverse photoemission spectra and the data were compared to occupied and unoccupied DFT density state calculations.

We demonstrate the efficient formation of carbon–nitrogen bonds starting from CH4 and NH3 on a metal surface at cryogenic temperatures. Electrons in the energy range of 1–90 eV are used to initiate chemical reactions in mixed molecular films of CH4 and NH3 at ∼15 K, and the products are detected by performing temperature programmed desorption (TPD). Extensive dehydrogenation occurs at all energies giving the products CH2NH and HCN in preference to CH3NH2. This is likely to do with the energetics of the reactions and the subsequent stability of these species in the condensed film. Thermal processing of the irradiated mixture favours dehydrogenation as indicated by the results of using different desorption rates. Electron impact excitation and subsequent dissociation into radicals is the reaction-initiating step rather than ionization of CH4 and NH3, as inferred from the yield of products as a function of electron energy. This could give insight into the important catalytic process of the industrial scale synthesis of HCN from CH4 and NH3 over Pt. This may also be a relevant pathway in the astrochemical environment where CN and HCN are abundant and low-energy electrons are found ubiquitously.

Covalently-assembled monolayers of functionalized Zn-porphyrin complex (5,10,15,20-tetra(4-pyridyl)-porphyrin, Zn-TPyP) are employed as the template layer for fabricating heterogeneous molecular dyads composed of opto-active metallo-terpyridyl complexes on SiOx substrates. Metallo-linkers such as Cu2+ and Pd2+ are exploited to connect the Zn-porphyrin template layer with the metallo-terpyridyl complexes (M–PT, M = Fe2+, Ru2+, Os2+, while PT = 4′-pyridyl terpyridyl) using a wet chemical “layer-by-layer” (LBL) technique. Formation of both the template and dyad layers over the SiOx substrates were probed by atomic force microscopy (AFM) and UV-vis absorption techniques. The molecular films were used for comparison and to study the effect of different metallo-linkers based on the changes in the characteristics of the Soret bands of Zn-TPyP and the metal-to-ligand charge-transfer (MLCT) bands of terpyridyl complexes. Besides, detailed electronic structure calculations based on first-principles density functional theory (DFT) and time-dependent DFT (TDDFT) have been performed for understanding experimentally observed photophysical properties of the surface-confined dyads.

The molecular arrangement and the interfacial electronic properties of cobalt phthalocyanine (CoPc) on the deactivated B-Si(111)-$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\phantom{\rule{0.16em}{0ex}}R{30}^{\ensuremath{\circ}}$ surface are analyzed using scanning tunneling microscopy and spectroscopy as well as photoemission studies. Our data demonstrate that for low coverages of CoPc the molecules lie flat with the ${p}_{z}$ orbital of the Si surface atom forming a hybrid state with the ${d}_{{z}^{2}}$ orbital of the transition metal. This hybridization is observed in a broadening of the corresponding Si $2p$ core level photoemission spectra and in an additional contribution to the valence band spectra. Furthermore, this additional hybridization state is detected in the tunneling spectra. For higher CoPc coverages, the CoPc molecules are tilted with respect to the Si surface forming highly ordered organic molecular films. The spectroscopic data of the thick film demonstrates that the electronic properties resemble those of pure CoPc.

Layer-by-layer (LbL) assembly is a nanoscale technique with great versatility, simplicity and molecular-level processing of various nanoscopic materials. Weak polyelectrolytes have been used as major building blocks for LbL assembly providing a fundamental and versatile tool to study the underlying mechanisms and practical applications of LbL assembly due to its pH-responsive charge density and molecular conformation. Because of high-density uncompensated charges and high-chain mobility, weak polyelectrolyte exponential multilayer growth is considered one of the fastest developing areas for organized molecular films. In this article, we systematically review the current status and developments of weak polyelectrolyte-based multilayers including all-weak-polyelectrolyte multilayers, weak polyelectrolytes/other components (e.g. strong polyelectrolytes, neutral polymers, and nanoparticles) multilayers, and exponentially grown weak polyelectrolyte multilayers. Several key aspects of weak polyelectrolytes are highlighted including the pH-controllable properties, the responsiveness to environmental pH, and synergetic functions obtained from weak polyelectrolyte/other component multilayers. Throughout this review, useful applications of weak polyelectrolyte-based multilayers in drug delivery, tunable biointerfaces, nanoreactors for synthesis of nanostructures, solid state electrolytes, membrane separation, and sensors are highlighted, and promising future directions in the area of weak polyelectrolyte-based multilayer assembly such as fabrication of multi-responsive materials, adoption of unique building blocks, investigation of internal molecular-level structure and mechanism of exponentially grown multilayers, and exploration of novel biomedical and energy applications are proposed.

Quasicrystalline surfaces are potential templates for highly ordered but aperiodic molecular self-assemblies. Here, we report on the adsorption of ${\mathrm{C}}_{60}$ molecules on a two-dimensional oxide quasicrystal (OQC) and its $\ensuremath{\sigma}$-phase approximant at room temperature and $150\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The molecular films have been characterized by means of scanning tunneling microscopy and low-energy electron diffraction. A weak interaction of the molecules with the dodecagonal oxide template is found, resulting in a low desorption temperature of $510\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. For low temperatures specific adsorption sites within the tiling of the OQC and the $\ensuremath{\sigma}$-phase approximant have been identified as preferred nucleation sites. The narrow spacing between these sites introduces repulsive interaction between ${\mathrm{C}}_{60}$ molecules and restricts the epitaxial growth to small patches. At room temperature, ${\mathrm{C}}_{60}$ nucleates in hcp islands of almost arbitrary rotational orientation on the OQC. A slight orientational preference for hexagonal islands with a ${15}^{\ensuremath{\circ}}$ rotation against the OQC tiling is discussed as a consequence of the preferential adsorption on the quadratic tiles.

In this work we present a detailed surface science characterization of L-arginine adsorption on the Cu(1 1 0) surface in a submonolayer regime. Arginine (ARG) is one of the main components of the tripeptide RGD (arginine-glycine-aspartic acid) commonly used as a linker/binder when engineering biomedical devices such as integrin receptors. We replaced the traditional Knusden cell sublimation method to obtain molecular films by dosing arginine directly from an aqueous solution through an electrospray ionization device (ESI). X-ray Photoelectron Spectroscopy (XPS) evidenced the co-existence of different adsorbed molecular species. In addition, Scanning Tunneling Microscopy (STM) data show that the arginine molecules form short and well-separated lines, constituted of dimers of molecules on the surface. Density Functional Theory (DFT) calculations helped clarifying these experimental findings, bringing strong evidences that ARG molecules adsorb in an ionic and a neutral form, with varied binding modes between N atoms and Cu atoms from the surface. These different N Cu bonds lead to the establishment of intermolecular H-bonds, responsible for the dimerization process.

The correlations detected by the mutual information in the propensities of a molecular viscous liquid are studied by molecular-dynamics simulations. Dynamic heterogeneity is evidenced and two particle fractions with different mobility and relaxation identified. The two fractions exhibit the scaling of their relaxation in terms of the rattling amplitude of the particle trapped in the cage of the first neighbours 〈u2〉 . The scaling master curve does not differ from the one found for bulk systems, thus confirming identical results previously reported in other systems with strong dynamic heterogeneity as thin molecular films. The excitation of planar and globular structures at short and long times with respect to structural relaxation, respectively, is revealed. Some of the globular structures are different from the ones evidenced in atomic mixtures. States with equal 〈u2〉 are found to have identical time dependence of several quantities, referring to both bulk and the two fractions with heterogeneous dynamics, at least up to the structural relaxation time $ \tau_{\alpha}$.

The bottom-up approach in designing and synthesis of materials using nanoparticles of different size-, shape- or chemical composition is an extreme challenge. However, in this way, new task-specific or general use nanocomposites can be obtained. This work presents, the investigations of the preparation procedures and molecular stability of Langmuir films based on cellulose nanocrystals (CNC) and different liquid crystals. The CNC-based nanocomposite with the 5CB, 5OCB, 5FCB, and 5PCH liquid crystals, have been obtained by the modified Langmuir technique. The investigations of the Langmuir monolayers gives an excellent model system for studying intermolecular interactions at the interface, which allows analyzing the ordering, sorption, desorption, association and phase separation phenomena determining physical and chemical properties of studied systems. The process of self-assembly and molecular organization on the air-liquid interphase was studied for different compositions of LC/CNC films. The compressibility profiles and the mean molecular area have been calculated. The stability of prepared monolayers has been studied to investigate the sorption and desorption processes. The morphology of the prepared systems was determined by Brewster Angle Microscopy (BAM), and the influence of the CNC on LC organization in molecular monolayers on the air-liquid interphase has been studied.

Adsorbed molecular films provide two-dimensional systems that show various emergent phenomena that are not observed in bulk counterparts. We have measured the elasticity of thin neon films adsorbed on porous glass down to 1 K by the torsional oscillator technique. The shear modulus of a neon film anomalously increases at low temperatures with excess dissipation. This behavior indicates a crossover from a soft (fluidlike) state at high temperatures to a stiff (solidlike) state at low temperatures. The temperature dependence of the anomaly is qualitatively similar to that of the elastic anomaly of helium films found in our recent study. The dissipation peak temperature, however, becomes constant at about 5 K, contrary to the case of helium, in which it decreases to 0 K at a critical coverage of a quantum phase transition between a gapped localized phase and a mobile (superfluid) phase. It is concluded that neon films behave as a classical system that does not show a quantum phase transition or superfluidity, although the films may be strongly supercooled to temperatures much lower than the bulk triple point, 24.6 K. Our results suggest that the elastic anomaly is a universal phenomenon of atomic or molecular films adsorbed on disordered substrates., 7 pages, 6 figures

Natural liquids can contain self-aligned molecules (such as liquid crystals and biological membranes) which give them unique properties of anisotropic diffusion, coupling between the molecular orientation and flow, etc. Here, we describe the observation of new phenomena in those materials: long-distance transport and molecular orientation waves that are induced by pulses of spatially localized electrical potential. As a result, the morphological properties of the material are significantly altered well beyond the reach of the electrical field. The local dielectric torque-induced reduction of the effective molecular volume and corresponding pressure gradients are in the origin of these phenomena. Our observations are made for electric fields that are an order of magnitude smaller than those present in biological membranes. Thus, this discovery may have important impact on the understanding of the operation of these membranes and on the dynamics of action potential propagation in neural cells. The corresponding possible influence of observed excitation mechanisms on the ionic gates and the role of myelin sheath are discussed.

Experimental data from second-order nonlinear optical spectroscopies (SFG, DFG, and SHG) provide parameters relevant to the physical chemistry of interfaces and thin films. We show that there are in general 2 N or 2 N-1 equivalent sets of parameters to fit an experimental curve comprising N resonant features, of vibrational or electronic origin for example. We provide the algorithm to calculate these sets, among which the most appropriate has to be selected. The main consequences deal with the existence of “ghost resonances”, the need of a critical analysis of fit results, and the procedure to search for better sets of parameters coherent with applied constraints. For the past several years, infrared-visible sum-frequency generation (SFG) has become a widely used investigation technique for the chemical analysis of interfaces and surfaces. A lot of technical work has been done to improve the experimental set-ups dedicated to the production and detection of SFG photons. In the nonlinear SFG process, two monochromatic light sources (frequencies ω1 and ω2) create a second-order polarization when interacting with a material. At the lowest-order (i.e., dipolar) approximation, this polarization is proportional to the product of the incoming electric fields through the second-order susceptibility tensor � (2) , which accounts for the material’s properties. The macroscopic polarization and susceptibility account for spatial averages of microscopic second-order dipole moments and hyperpolarisabilities (� ), respectively. The secondorder polarization may oscillate at the sum (ω1 + ω2, SFG) or the difference (|ω1 - ω2|, DFG) of the incoming frequencies, acting as a coherent source of new beams at these frequencies. As such processes have a low cross section, they require the beams to have a high energy density, implying the use of short pulsed lasers. Infrared-visible SFG/DFG spectroscopy uses one beam in the visible range, usually with fixed frequency, which makes the detection of the few SFG photons easier, and a tunable (or broadband) one in the infrared (IR) frequency range. The SFG/DFG process becomes resonant (and therefore amplified) when the energy of the infrared beam matches that of an IR and Raman active vibrational transition of the material, making it a vibrational spectroscopy. The main advantage of the nonlinear vibrational spectroscopies as compared to the linear ones (e.g., IR absorption, Raman spectroscopy) lies in a fundamental property of second-order nonlinear optical (NLO) processes, which vanish within media possessing an inversion symmetry. The direct consequence is that SFG/DFG in centrosymmetric materials is only produced where the symmetry is broken, i.e. at the interface between two media. SFG/DFG spectroscopy is therefore intrinsically specific of interfaces. This has led to the continuous spreading of this spectroscopic tool over time and its application to various kinds of interfacess molecular monolayers adsorbed at the surface of liquids, 1 solids 2 and nanoparticles, 3‐6 the surface of liquids, 7 thin molecular films 8 sunder diverse environments, for example in vacuum, 9

Highly oriented, multilayer molecular films of picene and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) molecules with the long axis parallel to the substrate (parallel configuration, hereafter) were fabricated on their characteristic bulklike monolayer. These molecules form a dense monolayer with a bulklike molecular arrangement on metal surfaces such as Au(111), which allows further stacking of parallel molecules. Indeed, upon adsorption of picene and DNTT on these dense monolayers, growth of straight islands of multilayer without the dendritic layer was observed. Particularly, in the case of picene, one-dimensional islands with lengths over 100 μm were formed and aligned in 3-fold symmetric directions of the substrate, which was not observed in the case of DNTT. X-ray diffraction measurements revealed the presence of [201̅] and [211̅] planes and the absence of the [001] diffractions, indicating that the one-dimensional islands of picene indeed consist of parallel molecules. The formation of huge crystalline islands in the case of picene, in contrast to the case of DNTT, is likely induced by the stronger intermolecular force, as suggested from the calculation of the vibrational energy.

Electronic symmetry breaking by charge disproportionation results in multifaceted changes in the electronic, magnetic and optical properties of a material, triggering ferroelectricity, metal/insulator transition and colossal magnetoresistance. Yet, charge disproportionation lacks technological relevance because it occurs only under specific physical conditions of high or low temperature or high pressure. Here we demonstrate a voltage-triggered charge disproportionation in thin molecular films of a metal–organic complex occurring in ambient conditions. This provides a technologically relevant molecular route for simultaneous realization of a ternary memristor and a binary memcapacitor, scalable down to a device area of 60 nm2. Supported by mathematical modelling, our results establish that multiple memristive states can be functionally non-volatile, yet discrete—a combination perceived as theoretically prohibited. Our device could be used as a binary or ternary memristor, a binary memcapacitor or both concomitantly, and unlike the existing ‘continuous state’ memristors, its discrete states are optimal for high-density, ultra-low-energy digital computing. Charge disproportionation in thin molecular films of a metal–organic complex enables the realization of a ternary memristor and binary memcapacitor.

We have studied the circular dichroism (CD), in the ultraviolet and visible regions, of the transparent, chiral molecule 1,1’-Bi-2-naphtol (BINOL) in 1.5 μm thick films. The initial transparent film shows an additional negative cotton effect in the CD compared to solution. With time under room temperature the film undergoes a structural phase transition. This goes hand in hand with a cotton effect at the low energy absorption band which inverts with opposite propagation direction of light through the film which is revealed as a polarity reversal of ellipticity (PRE). After completion of the phase transition the film exhibits circular differential scattering throughout the visible range which also shows PRE. The structure change was studied with Raman, microscopy under cross polarization conditions and nonlinear second-harmonic generation circular dichroism (SHG-CD). The superposition of the optical activity of individual molecules and isotropy effects makes an interpretation challenging. Yet overcoming this challenge by finding a suitable model structural information can be derived from CD measurements.

Hydrocarbon films confined between smooth mica surfaces have long provided an experimental playground for model studies of structure and dynamics of confined liquids. However, fundamental questions regarding the phase behavior and shear properties in this simple system remain unsolved. With ultrasensitive resolution in film thickness and shear stress, and control over the crystallographic alignment of the confining surfaces, we here investigate the shear forces transmitted across nanoscale films of dodecane down to a single molecular layer. We resolve the conditions under which liquid–solid phase transitions occur and explain friction coefficients spanning several orders of magnitude. We find that commensurate surface alignment and presence of water at the interfaces each lead to moderate or high friction, whereas friction coefficients down to [Formula: see text] are observed for a single molecular layer of dodecane trapped between crystallographically misaligned dry surfaces. This ultralow friction is attributed to sliding at the incommensurate interface between one of the mica surfaces and the laterally ordered solid molecular film, reconciling previous interpretations.

Thin molecular films under model conditions are often exploited as benchmarks and case studies to investigate the electronic and structural changes occurring on the surface of metallic electrodes. Here we show that the modification of a metallic surface induced by oxygen adsorption allows the preservation of the geometry of a molecular adlayer, giving access to the determination of molecular orbital symmetries by means of near-edge x-ray absorption fine structure spectroscopy, NEXAFS. As a prototypical example, we exploited Nickel Tetraphenyl Porphyrin molecules deposited on a bare and on an oxygen pre-covered Cu(100) surface. We find that adsorbed atomic oxygen quenches the charge transfer at the metal-organic interface but, in contrast to a thin film sample, maintains the ordered adsorption geometry of the organic molecules. In this way, it is possible to disentangle {\pi}* and {\sigma}* symmetry orbitals, hence estimating the relative oscillator strength of core level transitions directly from the experimental data, as well as to evaluate and localize the degree of charge transfer in a coupled system. In particular, we neatly single out the {\sigma}* contribution associated with the N 1s transition to the mixed N 2px,y-Ni 3dx2-y2 orbital, which falls close to the leading {\pi}*-symmetry LUMO resonance.