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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.

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.

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.

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.

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.

Various electrooptic and magnetooptic effects enable the electric and magnetic field control of the holographic information recording. They can become significant if the frequency of light irradiation is close enough to the absorption line of a material. In this paper, these effects are theoretically considered, and the influence of applied external electric (up to 17 kV/cm) as well as magnetic field (0.15T) is experimentally studied on the transmission holographic grating recording in azobenzene-based molecular films at 632.8 and 532 nm. Recording beam polarizations were s-s, p-p, L-L and L-R . Self-diffraction efficiency (SDE) exposure time dependences were measured with and without the applied fields, and maximum SDE values as well as recording energies corresponding to 0.017% SDE were determined. No effect of electric field was found within the measurement accuracy (1-5%). Some trend to recording efficiency increase by magnetic field was observed. This result is in the agreement with the theoretical analysis. Unfortunately, these results are within experimental errors (usually 15-24%).

The organic/inorganic semiconductor interfaces play a key role in determining the functionality of charge injection devices. The energy-level alignment at the interfaces between two in-plane organic materials (F16CuPc and CuPc) and single-crystal black phosphorus was systematically studied by in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). In this work, we reveal that the deposition of F16CuPc onto black phosphorus surface leads to a considerable charge transfer across the interface, resulting in the pronounced increment of work function. As for the molecule–substrate interaction, both F16CuPc and CuPc interact with black phosphorus via van der Waals physisorption, as confirmed by the UPS and XPS measurements. Our results demonstrate the versatile use of organic molecules to tailor the energy levels of black phosphorus based hybrid structures, which can be potentially used to optimize its function in future devices.

We report on the modulation of the electrical properties of graphene-based transistors that mirror the properties of a few nanometers thick layer made of dipolar molecules sandwiched in between the 2D material and the SiO2 dielectric substrate. The chemical composition of the films of quinonemonoimine zwitterion molecules adsorbed onto SiO2 has been explored by means of X-ray photoemission and mass spectroscopy. Graphene-based devices are then fabricated by transferring the 2D material onto the molecular film, followed by the deposition of top source-drain electrodes. The degree of supramolecular order in disordered films of dipolar molecules was found to be partially improved as a result of the electric field at low temperatures, as revealed by the emergence of hysteresis in the transfer curves of the transistors. The use of molecules from the same family, which are suitably designed to interact with the dielectric surface, results in the disappearance of the hysteresis. DFT calculations confirm that the dressing of the molecules by an external electric field exhibits multiple minimal energy landscapes that explain the thermally stabilized capacitive coupling observed. This study demonstrates that the design and exploitation of ad hoc molecules as an interlayer between a dielectric substrate and graphene represents a powerful tool for tuning the electrical properties of the 2D material. Conversely, graphene can be used as an indicator of the stability of molecular layers, by providing insight into the energetics of ordering of dipolar molecules under the effect of electrical gating.

International audience; Magneto-opto-electronic properties are shown for a hybrid device constructed from a spin crossover (SCO) thin film of a Fe[HB(3,5-(Me)2Pz)3]2 molecular material evaporated over a graphene sensing layer. The principle of electrical detection of the light-induced spin transition in SCO/graphene heterostructures is demonstrated. The switchable spin state of the molecular film is translated into a change of conductance of the graphene channel. The low temperature write/erase process of the conductive remnant states is implemented using two distinct excitation wavelengths, in the red (light-induced spin state trapping, LIESST) region for stabilizing the metastable paramagnetic state, and in the near infrared (reverse-LIESST) region for retrieving the stable diamagnetic state. The bistability of the system is confirmed over a significant temperature window through light-induced thermal hysteresis (LITH). This opens new avenues to study the light-induced spin transition mechanisms exploring the coupling mechanisms between SCO systems and 2D materials, providing electrical readings of the molecules/2D substrate interfaces. These results demonstrate how the electronic states of insulating molecular switches can be stored, read and manipulated by multiple stimuli, while transducing them into low impedance signals, thanks to two-dimensional detectors, revealing the full potential of mixed-dimensional heterostructures for molecular electronics and spintronics.

Made available in DSpace on 2020-12-12T01:30:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-07-01 The combination of organic and inorganic materials at the nanoscale to form functional hybrid structures is a powerful strategy to develop novel electronic devices. The knowledge on semiconductor thin-film polarization brings direct benefits to the hybrid organic/inorganic electronics, becoming primordial for the development of devices such as electromechanical logic gates, solar cells, miniaturized valves, organic diodes, and molecular supercapacitors, among others. Here, we report on the dielectric polarization of ultrathin organic semiconducting films-ca. 5 nm thick metal phthalocyanine ensembles (viz., CuPc, CoPc, F16CuPc)-employed to build up hybrid metal/oxide/molecule heterojunctions. Such hybrid heterostructures are fully integrated into self-rolled nanomembrane-based capacitors and further investigated by impedance spectroscopy measurements as a function of temperature (from 6 to 300 K). The dielectric polarization of the metal phthalocyanines is found to be thermally activated above a specific threshold temperature, which depends on the molecular structure. Below this threshold, the current leakage across the system is suppressed, thus evidencing intrinsic-like polarization mechanisms. The temperature-independent permittivities of the ultrathin molecular films are found to be strongly dependent on the organic/inorganic hybrid interfaces, while the calculated relaxation times are more likely related to each single-molecule polarization. Beyond the advances in determining the temperature dependence of the permittivity for ultrathin phthalocyanine films integrated within solid-state electronics, our results also support the deterministic design of novel functional devices based on nanoscale hybrid organic/inorganic heterojunctions. Brazilian Nanotechnology National Laboratory (LNNano) Brazilian Center for Research in Energy and Materials (CNPEM) Postgraduate Program in Materials Science and Technology (POSMAT) São Paulo State University (UNESP) Postgraduate Program in Materials Science and Technology (POSMAT) São Paulo State University (UNESP)

One common challenge highlighted in almost every review article on organic resistive memory is the lack of areal switching uniformity. This, in fact, is a puzzle because a molecular switching mechanism should ideally be isotropic and produce homogeneous current switching free from electroforming. Such a demonstration, however, remains elusive to date. The reports attempting to characterize a nanoscopic picture of switching in molecular films show random current spikes, just opposite to the expectation. Here, this longstanding conundrum is resolved by demonstrating 100% spatially homogeneous current switching (driven by molecular redox) in memristors based on Ru-complexes of azo-aromatic ligands. Through a concurrent nanoscopic spatial mapping using conductive atomic force microscopy and in operando tip-enhanced Raman spectroscopy (both with resolution

Based on microscopic (exciton) theory of optical properties of perturbed ultrathin molecular films, the absorption, reflection, and transparency indices were formulated and presented in dependence on frequencies of an external electromagnetic field in near IR region. It has been shown that all optical properties depend on the position of the crystal plane with regard to boundary planes of the film. We have determined and analyzed optical properties relations for the whole film structure based on the consideration for multiple reflection, absorption, and transparency in observed multilayered structure. The four-layered dielectric nanofilms with different boundary conditions on surfaces were analyzed and some discrete resonant absorption lines were obtained. Their number, position, and distribution depend on the boundary parameter values, i.e. on the type and the technological process of their preparation/fabrication. Practically monochromatic absorption may occur. Unlike the corresponding bulk-samples, which are total absorbers throughout the near IR, region, in ultrathin films will appear selective and discrete reflection and transparency. These results could provide a great contribution to optical engineering of nanostructures, especially in technology of designing of new electronic and photonic equipment, and for nanoparticles construction for drug carrier/delivery in nanomedicine.

The [1]benzothieno[3,2-b][1]benzothiophene (BTBT) planar system was used to functionalize the phthalocyanine ring aiming at synthesizing novel electron-rich π-conjugated macrocycles. The resulting ZnPc-BTBT and ZnPc-(BTBT)4 derivatives are the first two examples of a phthalocyanine subclass having potential use as solution-processable p-type organic semiconductors. In particular, the combination of experimental characterizations and theoretical calculations suggests compatible energy level alignments with mixed halide hybrid perovskite-based devices. Furthermore, ZnPc-(BTBT)4 features a high aggregation tendency, a useful tool to design compact molecular films. When tested as hole transport materials in perovskite solar cells under 100 mA cm-2 standard AM 1.5G solar illumination, ZnPc-(BTBT)4 gave power conversion efficiencies as high as 14.13 %, irrespective of the doping process generally required to achieve high photovoltaic performances. This work is a first step toward a new phthalocyanine core engineerization to obtain robust, yet more efficient and cost-effective materials for organic electronics and optoelectronics.

International audience; The thermally induced spin-crossover (SCO) phenomenon in transition metal complexes is an entropy-driven process, which has been extensively studied through calorimetric methods. Yet, the excess heat capacity associated with the molecular spin-state switching has never been explored for practical applications. Herein, the thermal damping effect of an SCO film is experimentally assessed by monitoring the transient heating response of SCO-coated metallic microwires, Joule-heated by current pulses. A damping of the wire temperature, up to 10%, is evidenced on a time scale of tens of microseconds due to the spin-state switching of the molecular film. Fast heat-charging dynamics and negligible fatigability are demonstrated, which, together with the solid-solid nature of the spin transition, appear as promising features for achieving thermal energy management applications in functional devices.

We demonstrate visible pump soft X-ray probe near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements at the carbon K edge on thin molecular films in the laboratory. This opens new opportunities through the use of laboratory equipment for chemical speciation. We investigate the metal-free porphyrin derivative tetra(tert-butyl)porphyrazine as an ideal model system to elucidate electronic properties of tetrapyrroles like chlorophyll or heme. In contrast to measurements in gas or liquid state, the investigation of thin films is of high interest in the field of optoelectronic and photovoltaic devices though challenging due to the low damage thresholds of the samples upon excitation. With a careful pre-characterization using optical techniques, successful measurements were performed using a NEXAFS spectrometer based on a laser-produced plasma source and reflection zone plates with a resolving power of 1000 and a time resolution of 0.5 ns. In combination with density functional theory calculations, first insights into a long-lived excitonic state are gained and discussed. Deutsche Forschungsgemeinschaft 313838950 LASERLAB Europe 654148 Ministerio de Ciencia e Innovación PGC2018-101689-B-I00

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 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.

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.

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.

2D organic materials with in-plane van der Waals forces among molecules have unique characteristics that ensure a brilliant future for multifunctional applications. Soluble organic semiconductors can be used to achieve low-cost and high-throughput manufacturing of electronic devices. However, achieving solution-processed 2D single-crystalline semiconductors with uniform morphology remains a substantial challenge. Here, the fabrication of 2D molecular single-crystal semiconductors with precise layer definition by using a floating-coffee-ring-driven assembly is presented. In particular, bilayer molecular films exhibit single-crystalline features with atomic smoothness and high film uniformity over a large area; field-effect transistors yield average and maximum carrier mobilities of 4.8 and 13.0 cm2 V−1 s−1, respectively. This work demonstrates the strong potential of 2D molecular crystals for low-cost, large-area, and high-performance electronics.

The paper presents preliminary results of studies of the temporal dependence of refractive index, current-voltage characteristics, the dependence of resistance on voltage, and dynamics of resistance variations in time for biomolecular films during dehydration. The experimental results demonstrated the efficiency of the use of refractometry in the regime of total internal reflection for determining optical and physical properties of self-assembled molecular films in biomolecular electronics.

The functionalities offered by single-molecule electrical junctions are yet to be translated into monolayer or few-layer molecular films, where making effective and reproducible electrical contact is one of the challenging bottlenecks. Here we take a significant step in this direction by demonstrating that excellent electrical contact can be made with a monolayer biphenyl-4,4'-dithiol (BPDT) molecular film, sandwiched between gold and graphene electrodes. This sandwich device structure is advantageous, because the current flows through the molecules to the gold substrate in a 'cross-plane' manner, perpendicular to the plane of graphene, yielding high-conductance devices. We elucidate the nature of the cross-plane graphene/molecule/Au transport using quantum transport calculations and introduce a simple analytical model, which captures generic features of the current-voltage characteristic. Asymmetry in junction properties results from the disparity in electrode electrical properties, the alignment of the BPDT HOMO-LUMO energy levels and the specific characteristics of the graphene electrode. The experimental observation of scalability of junction properties within the junction area, in combination with a theoretical description of the transmission probability of the thiol-graphene contact, demonstrates that between 10% and 100% of the molecules make contact with the electrodes, which is several orders of magnitude greater than that achieved to date in the literature.

Contamination control engineers provide critical plans to monitor, mitigate, and reduce the impact of molecular and particulate contamination on spacecraft systems. Witness monitoring programs are dependable methods that utilize strategically placed witness samples on space flight hardware to monitor particulate and molecular contaminants during the assembly, integration, and test (AI&T) phases. Traditionally, optical characterization of these witness plates is the tool to determine the presence of molecular films on space flight hardware in the AI&T environment. Once a visual inspection or optical measurement identifies the presence of a contaminant, analysts collect tape lifts and wipe samples from the witness plate for analysis in an analytical lab with a potential contaminant identified within 24 hours. To speed up this process and reduce the impact to project schedule and cost the use of a non-invasive and in situ method for optical witness plate program with portable Raman spectroscopy to detect molecular contamination on spacecraft was explored.

Contamination control engineers are constantly challenged by time-consuming processes during the system assembly, integration and test phase for spacecraft. Hardware components, subassemblies, and integrated systems must be visually inspected throughout the process, and any signs of contamination found are usually analyzed by processes that can take days to complete. Portable Raman spectroscopy is a promising technology for spacecraft integration, where it may be possible to probe hardware or witness surfaces and identify contaminants throughout the assembly, integration and test phase. This study explored detection of five common spacecraft contaminants with portable Raman spectroscopy: silicone, hydrocarbon, fluorocarbon, ester, and a glycol polymer. It was found portable Raman spectroscopy can provide a quick-look capability which can be followed by more detailed contaminant quantification analysis techniques. In this way, portable Raman spectroscopy can aid contamination control engineers in providing actionable information to projects earlier in the assembly, integration and test phase of the project lifecycle.

Spontaneous pattern formation is an energetically favorable process and is shown in nature in molecular-scale assembly, biological association, and soft material organizations. The opposite regime, the artificial process, which is widely applied to the fabrication of semiconducting devices, such as lithographic techniques, requires enormous amounts of energy. Here, we propose a concept of tuning the properties of semiconducting MoS2 and WSe2 devices using the spontaneous pattern formation of adjacent molecular films. The film used was a 10 nm thick ultrathin film of a molecular electron dopant, which exhibited spontaneous pattern formation and dynamically transformed the morphology of tiny holes, a network, a maze, and dots on substrates, including SiO2, MoS2, and WSe2. These patterns were exhibited only when the film came in contact with water and was tuned with temperature and time. The specific lengths of the patterns were less than 200 nm, which is sufficiently smaller than the exfoliated ∼10 μm semiconducting MoS2 and WSe2 flakes. The properties of the field-effect devices of MoS2 and WSe2 were found to be modified according to the pattern formation process of the ultrathin molecular film on the device. This concept applies the spontaneous patterning phenomena shown in nature to the fabrication and optimization of electronic devices by using molecular films and their responses to the external environment.

In the following article, we have considered problems and ways of transition from semiconductor to biomolecular electronics. We have used experimental studies of biomolecular materials to achieve goals for biomolecular electronics and communications. The paper studies a joint use of laser correlation spectroscopy and visual microscopic methods for investigation of self-assembling of proteins at transition from the liquid state to films. Furthermore, we have presented preliminary results of studies of molecular solutions. Finally, it is shown that structure evolution of drying out protein solution is a complex multi-stage process, which depends on external conditions.

The evaluation of thickness, refractive index, and optical properties of biomolecular films and self-assembled monolayers (SAMs) has a prominent relevance in the development of label-free detection techniques (quartz microbalance, surface plasmon resonance, electrochemical devices) for sensing and diagnostics. In this framework Spectroscopic Ellipsometry (SE) is an important player. In our approach to SE measurements on ultrathin soft matter, we exploit the small changes of the ellipsometry response (\(\delta \varDelta \) and \(\delta \varPsi \)) following the addition/removal of a layer in a nanolayered structure. So-called \(\delta \varDelta \) and \(\delta \varPsi \) difference spectra allow to recognize features related to the molecular film (thickness, absorptions) and to the film-substrate interface thus extending SE to a sensitive surface UV-VIS spectroscopy. The potential of ellipsometry as a surface spectroscopy tool can be boosted when flanked by other characterizations methods. The chapter deals with the combined application of broad-band Spectroscopic Ellipsometry and nanolithography methods to study organic SAMs and multilayers. Nanolithography is achieved by the accurate removal of molecules from regularly shaped areas obtained through the action of shear forces exerted by the AFM tip in programmed scans. Differential height measurements between adjacent depleted and covered areas provide a direct measurement of film thickness, which can be compared with SE results or feed the SE analysis. In this chapter we will describe the main concepts behind the SE difference spectra method and AFM nanolithograhy. We will describe how SE and AFM can be combined to strengthen the reliability of the determination of thickness and, as a consequence, of the optical properties of films. Examples will be discussed, taken from recent experiments aimed to integrate SE and AFM nanolithography applied to SAMs and nano layers of biological interest. By analysing in detail the changes of the spectroscopic features of compact versus non-compact layers and correlating such changes with the post-lithography AFM analysis of surface morphology SE unravels the specific versus unspecific adsorption of biomolecules on gold surfaces functionalized with suitable SAMs.

Molecular communication systems became a promising paradigm of modern nanonetworks. Quantum carrier transfer creates communication channels between parts of a molecule and/or connects a few domains inside a molecular metamaterial network. This manuscript presents our studies of such channels activated by means of modulated laser beam irradiation resulting in molecular fluorescence, probably at a shifted frequency. The acquisition system for the electromagnetic field generated by a molecule based on the novel dynamic pin-photo diode is characterized by a high sensitivity and a low noise level due to the signal amplitude-time function integration.

International audience; Localized and delocalized plasmons in metallic nanostructures are associated with a strongly confined electromagnetic field, inducing an enhanced interaction with emitters located in the close environment of the metal. When the plasmon/emitter interaction overtakes the damping in the system, the system enters into strong coupling regime leading to light-matter hybridization [1]. This strong coupling has been observed with a large number of materials, in particular disordered materials which are constituted by a collection of independent emitters (molecules, semiconductor quantum dots...). The spatial and dynamic properties of an assembly of molecules in strong coupling are drastically modified compared to the same molecules in weak coupling [2]. We will present our ongoing research on strong coupling between plasmons and molecular emitters. If we take into account the microscopic structure of the molecular film, collective effects between the delocalized plasmon and the set of molecules occurs. The excitations are not localized in a single emitter anymore but delocalized on a large number of molecules due to the formation of an extended hybridized state over several microns which modifies various properties of molecular materials like conductivity or reactivity [3]. However, the extension of the coherent state is limited by the reduced plasmon propagation length, due to metal losses. We will show that the coherence length can be extended using a low loss surface plasmon in a symmetrical structure leading to Long Range Surface Plasmon (LRSP) [4, 5] (Fig. 1a). Simulations using a transfer matrix method are performed to optimize the parameters of the LRSP formation and its interaction with the aggregated dye and compared to experiments. After the demonstration of strong coupling between aggregated dyes and long range plasmon (Fig. 1b), we will evaluate the extension of the coherent polaritonic mode in the structures. A coherence length up to several tens of microns can be achieved. The parameters of these modes will be discussed to optimize the interaction with the organic material. Figure 1: a) Schematic of the sample structure for surface plasmon long range generation; b) Experimental relation dispersion of plasmon strongly coupled with molecular emitters.

The electroluminescence of organic films is the central aspect in organic light emitting diodes (OLEDs) and widely used in current display technology. However, its spatial variation on the molecular scale is essentially unexplored. Here, we address this issue by using scanning tunneling microscopy (STM) and present an in-depth study of the electroluminescence from thin C60 films (

Nano-devices with embedded molecular films appear as promising nano communications tools. In general, processing in such hybrid nano-device consists of initial energy of both activated electronic and atomic subsystems of an embedded molecular species, followed by intra- and inter-molecular nanoscale signals generation and reception of the transmitted signal at remote site. Actually, electromagnetic radiation can establish wireless nano communication in Visible, Infrared, and Microwave frequency ranges. In this manuscript, we estimate some properties of a microelectronics receiver in such systems, presented by novel dynamic operation pin photodetector, possesses signal integration, and required for receiving and demodulation of an electromagnetic wave. Revealed both theoretical and experimental characteristics of a photodetector have allowed designing dynamic process scenarios, as well as its possible applications inside a nano network.

We demonstrate a technique for growing fine molecular films on a monolayer scale. We achieve layer-by-layer growth under thermally equilibrium condition by precisely controlling the conditions of an ultra-slow deposition technique. This technique is applicable to various kinds of p-type and n-type organic semiconductors and makes it possible to form a hetero-molecular interface (p-n junction) with molecular level flatness. The technique was used to produce a molecular superlattice, which enables the well-controlled design of energy level alignments in organic semiconductors.

We demonstrate a dual sensor concept for lab-on-a-chip in-liquid sensing through integration of surface acoustic wave resonance (SAR) sensing with electrochemical impedance spectroscopy (EIS) in a single device. In this concept, the EIS is integrated within the building blocks of the SAR sensor, but features a separate electrical port. The two-port sensor was designed, fabricated, and embedded in a soft polymer microfluidic delivery system, and subsequently characterized. The SAR-EIS tandem sensor features low cross-talk between SAR and EIS ports, thus promoting non-interfering gravimetric and impedimetric measurements. The EIS was characterized by means of the modified Randle's cell lumped element model. Four sensitive parameters could be established from the tandem sensor readout, and subsequently employed in a proof of principle study of liposome layers and their interaction with Ca2+ ions, leading to transformation into molecular film structures. The associated shift of the sensing quantities is analysed and discussed. The combination of impedimetric and gravimetric sensing quantities provides a unique and detailed description of physicochemical surface phenomena as compared to a single mode sensing routine. Keywords: Surface acoustic wave, Resonator, Electrochemical impedance spectroscopy, Sensor, Microfluidics, IDE

Al2O3 films have been deposited at 85 °C by atomic layer deposition onto single 100 nm thick tris-(8-hydroxyquinoline) aluminium (AlQ3) films made onto silicon wafers. It has been found that a thick ALD-deposited Al2O3 layer (> 11 nm) greatly prevents the photo-oxidation of AlQ3 films when exposed to continuous UV irradiation (350 mW/cm2). Thin Al2O3 thicknesses (< 11 nm) on the contrary yield lower barrier performances. Defects in the Al2O3 layer have been easily observed as non-fluorescent AlQ3 singularities, or black spots, under UV light on the system Si/AlQ3/Al2O3 stored into laboratory conditions (22 °C/50% Relative Humidity (RH)) for long time scale (~ 2000 h). Accelerated aging conditions in a climatic chamber (85 °C/85% RH) also allow faster visualization of the same defects (168 h). The black spot density grows upon time and the black spot density occurrence rates have been calculated to be 0.024 h− 1·cm− 2 and 0.243 h− 1·cm− 2 respectively for the two testing conditions. A detailed investigation of these defects did show that they cannot be ascribed to the presence of a detectable particle. In that sense they are presumably the consequence of the existence of nanometre-scaled defects which cannot be detected onto fresh samples. Interestingly, an additional overcoating of ebeam-deposited SiO2 onto the Si/AlQ3/Al2O3 sample helps to decrease drastically the black spot density occurrence rates down to 0.004 h− 1·cm− 2 and 0.04 h− 1·cm− 2 respectively for 22 °C/50% RH and 85 °C/85% RH testing conditions. These observations highlight the moisture sensitivity of low temperature ALD-deposited Al2O3 films and confirm the general idea that a single Al2O3 ALD film performs as an ultra-high barrier but needs to be overprotected from water condensation by an additional moisture-stable layer.

Low-energy electron diffraction (LEED) is a widely employed technique for the structural characterization of crystalline surfaces and epitaxial adsorbates. For technical reasons the accessible reciprocal space is limited at a given primary electron energy E. This limitation may be overcome by sweeping E to observe higher diffraction orders decisively enhancing the quantitative examination. Yet, in many cases, such as molecular films with rather large unit cells, the adsorbate reflexes become less pronounced at energies high enough to observe substrate reflexes. One possibility to overcome this problem is an intentional inclination of the sample surface during the measurement at the expense of the quantitative interpretability of then severely distorted diffraction patterns. Here, we introduce a correction method for the axially symmetric distortion in LEED images of tilted samples. We provide experimental confirmation for micro-channel plate LEED and spot-profile analysis LEED instruments using the (7×7) reconstructed surface of a Si(111) single crystal as a reference sample. Finally, we demonstrate that the correction of this distortion considerably improves the quantitative analysis of diffraction patterns of adsorbates since substrate and adsorbate reflexes can be evaluated simultaneously. As an illustrative example we have chosen an epitaxial monolayer of 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111) that is known to form a commensurate superstructure.

In this work, we studied properties of Langmuir and Langmuir-Blodgett molecular films formed by mixture of arachidic acid with nematic liquid crystal mixture having the negative dielectric anisotropy. The Langmuir films were characterised by surface pressure versus mean molecular area isotherms (π–A isotherms) and subsequently were transferred at a particular surface pressure onto hydrophillic and hydrophobic quartz substrates forming monolayer and multilayer Langmuir-Blodgett films. Miscibility of the compounds in the Langmuir films was determined. Absorption spectra of the Langmuir-Blodgett films were recorded in UV-Vis region in order to reveal organisation of the molecules. Morphology of deposited films was visualised using atomic force microscope (AFM) working in tapping mode. Finally, Langmuir-Blodgett films were deposited onto glass plates covered with indium tin oxide (ITO, transparent and conductive electrodes) and were used as aligning layers in laboratory model of Vertical Alignment-type liquid...

Localized and delocalized plasmons in metallic nanoparticles are associated with a strongly confined electromagnetic field, inducing an enhanced interaction with emitters located in the close environment of the metal. When the plasmon/emitter interaction becomes predominant compared to the damping in the system, the system is in strong coupling regime leading to light matter hybridization. This strong coupling has been observed with a large number of materials, in particular disordered materials. These materials are constituted by a collection of independent emitters (molecules, semiconductor quantum dots...). The hybrid light/matter state can be described by considering a homogeneous absorbing system using coupled oscillator model. But if the microscopic structure of the molecular film close to a metallic film is considered, collective effects between the delocalized plasmon and the set of molecules are present. The spatial and dynamic properties of a set of molecules in strong coupling are dramatically modified compared to the same molecules in weak coupling (the usual configuration of emission). The excitations are not localised in a single particle anymore but delocalised on a large number of particles due to the formation of an extended hybridised state on several microns. We will describe some properties of disordered systems strongly coupled to surface plasmons and experimental demonstrations of the collective phenomena associated with the strong coupling. In particular we will present an experimental study of the coherent character of the emission of different emitters with a Young’s interferences setup. The system studied consists of J-aggregated dye (TDBC) in interaction with a surface plasmon on silver. The extension of the coherent state will also be discussed.

The current method for the prediction of molecular contamination build up in systems such as the James Webb Space Telescope and other large astronomical satellites is based on a monotonic linear model of accumulation. Recent long term observations carried out at Northrop Grumman show that the linear monotonic model over predicts thickness of the molecular film. This paper reviews the long term observations of contaminant film thickness accumulation made at Northrop Grumman facilities. The formulation of a semi-empirical method for the prediction of film thickness evolution consistent with both observation and first principles is discussed in detail. The paper concludes with a validation of the predictions of the semi-empirical model. The increased accuracy of the semi-empirical method holds the promise of improved and more effective means of contamination control, thus reducing mission cost and risk.

Based on microscopic (exciton) theory of optical properties of symmetrically perturbed ultrathin molecular films, the absorption, reflection and transparency indices were formulated and presented in the function of frequencies of external electromagnetic field in near infrared (IR) region. It has been showed that all optical properties depend on the position of the crystal plane with regard on boundary planes of the film. We have determined and analyzed optical properties relations for the whole film structure based on the consideration for multiple reflection, absorption and transparency in those multilayered structure. The three-layered dielectric nanofilms with different boundary conditions on surfaces were analyzed and some discrete resonant absorption lines were obtained. Their number, position and distribution depend on the boundary parameter values, i.e. on the type and the technological process of their preparation/fabrication. Practically monochromatic absorption may occur. Unlike the corresponding bulk-samples which are total absorbers throughout the near IR region, in ultrathin films will appear selective and discrete reflection and transparency too. These results could give a great contribution in optical engineering of nanostructures, especially in technology of designing of new electronic and photonic equipment, and for nanoparticles construction for drug carrier/delivery in nano-medicine.

It has recently been demonstrated that nanoscale molecular films can spontaneously assemble to self-generate intrinsic electric fields that can exceed 108 V/m. These electric fields originate from polarization charges in the material that arise because the films self-assemble to orient molecular dipole moments. This has been called the spontelectric effect. Such growth of spontaneously polarized layers of molecular solids has implications for our understanding of how intermolecular interactions dictate the structure of molecular materials used in a range of applications, for example, molecular semiconductors, sensors, and catalysts. Here we present the first in situ structural characterization of a representative spontelectric solid, nitrous oxide. Infrared spectroscopy, temperature-programmed desorption, and neutron reflectivity measurements demonstrate that polarized films of nitrous oxide undergo a structural phase transformation upon heating above 48 K. A mean-field model can be used to describe quantitatively the magnitude of the spontaneously generated field as a function of film-growth temperature, and this model also recreates the phase change. This reinforces the spontelectric model as a means of describing long-range dipole-dipole interactions and points to a new type of ordering in molecular thin films.

Small molecules with different film-forming properties and electron traps were synthesized and characterized in the meantime. An electrical memory device with the indium-tin-oxide (ITO)/Small-Molecule/Al sandwich structure was fabricated and its electrical performance was investigated. WORM storage devices with different threshold voltages were obtained, some of which present “ternary” property. The relationship between turn-on voltage and the energy barrier between active materials and electrodes was revealed by the cyclic voltammetry measurement. The molecular film-forming properties and electron traps are responsible for device performances collectively, which could be elucidated unambiguously from UV–vis absorption spectra and X-ray diffraction patterns.

An array of optoelectronic applications requires micro- and nanoscale patterning of molecular organic films. A subtractive patterning technique is developed to define micron-sized features of nanometer range thickness on a variety of hole transporting and hole blocking materials. Lateral resolution of patterned features is controlled by micron-scale stamp shapes, while the removal of the patterned nanoscale film thicknesses (sub-10 nm to over 40 nm) is correlated to strength of interfacial and intermolecular forces. Using this process, a multi-color organic light-emitting device is fabricated, demonstrating the ability of contact patterning to manipulate organic molecular films on the micro- and nanoscales.

The presence of self-assembled monolayers at an electrode introduces capacitance and resistance contributions that can profoundly affect subsequently observed electronic characteristics. Despite the impact of this on any voltammetry, these contributions are not directly resolvable with any clarity by standard electrochemical means. A capacitive analysis of such interfaces (by capacitance spectroscopy), introduced here, enables a clean mapping of these features and additionally presents a means of studying layer polarizability and Cole-Cole relaxation effects. The resolved resistive term contributes directly to an intrinsic monolayer uncompensated resistance that has a linear dependence on the layer thickness. The dielectric model proposed is fully aligned with the classic Helmholtz plate capacitor model and additionally explains the inherently associated resistive features of molecular films.

The structure of thin molecular films of copper phthalocyanine (CuPc) on crystalline GaAs(001) and glass substrates has been studied by the method of reflectance anisotropy spectroscopy. It is shown that, using this method, it is possible to determine the orientational anisotropy in CuPc layers. It is established that the GaAs crystal surface produces orienting action on the molecular structure of CuPc films, while a glass substrate does not exhibit this effect. A model of the anisotropic reflection of light is considered that provides satisfactory description of the orientation-related features in the spectra of thin CuPc films as dependent on their thicknesses.

In this paper, nanosegmented floating-gate memories consisting of a uniform set of identical organic dye molecules were fabricated and evaluated for potential use as programmable charge storage and charge retention elements in a future flash-memory technology. Viability of molecular thin films to serve as an energetically uniform set of ~1 nm in size charge-retaining sites is tested on a series of molecular materials, the best performing of which are thermally evaporated thin films of 3,4,9,10- perylenetetracarboxylic bis-benzimidazole. The initial results show device durability over 105 program/erase cycles, with hysteresis window of up to 3.3 V, corresponding to charge-storage density as high as 5 × 1012 cm-2. Data shows that charge retention is improved for molecular films with lower carrier mobility, which for the first time experimentally confirms in a coherent material set that inhibiting charge transport by nanosegmented floating-gate structures benefits the memory retention.

In a comparison between a bare diindenoperylene (DIP) film and a DIP film spin-coated with a layer of gold nanoparticles, we have investigated the influence of plasmon resonances in the gold particles on spectroscopic properties of the molecular film. Under off-resonant excitation with a laser at 633 nm, the bare DIP film showed only weak photoluminescence (PL) and Raman signals, but after spin-coating gold nanoparticles on such a DIP film, we found an enhancement of both the PL and Raman signals by a factor of about 3, whereas no enhancement could be observed when the same sample was excited with laser light of 488 nm. This difference reveals that at 633 nm, plasmon resonances in the gold nanoparticles are excited, leading in turn to an enhancement of PL and Raman signals of the weakly absorbing DIP film via coupling between plasmons in the gold particles and exciton–polaritons in the molecular film. For the laser at 488 nm, due to a much larger absorption coefficient of DIP, excitons in the molecular film are directly excited, out-weighing the influence of an off-resonant coupling to the plasmon resonances in the gold particles occurring at much lower energy.

For the development of micro- and nano-technology, it has been strongly desired to understand thermo-fluid phenomena inside or around micro- and nano-devices. An optical measurement technique based on the absorption and the emission of photons by molecules is useful for experimental analyses of thermo-fluid phenomena of micro and nanoflows. The pressure-sensitive paint (PSP) technique is a potential diagnostic tool for pressure measurements of micro/nano gas flows because it works as a so-called “molecular sensor”. However, the micro-scale measurement of PSP has been limited by the aggregation of the luminescent molecules and their thick film due to the use of a polymer binder. In our previous work, we adopted the Langmuir–Blodgett (LB) technique to fabricate pressure-sensitive molecular film (PSMF) with ordered molecular assemblies, and investigated properties of PSMF. In this study, a novel approach to enhance the luminescent intensity of PSMF is proposed, and the pressure distribution in a micro-nozzle is successfully measured by using PSMF. Moreover, we compared the pressure distribution measured by PSMF with that numerically analyzed by the direct simulation monte carlo (DSMC) method, showing good agreement with each other.

Molecular film contamination is known to degrade the optical performance of space system components, including solar arrays and thermo-optical, second surface mirrors. In the form of a contaminant film, the resulting performance loss rate can be evaluated using traditional models for absorption and reflection. In recent years, however, some space-borne optical sensors have suffered severe and rapid performance degradation due to the formation of contaminant droplets that fog interior lenses, mirrors, and windows. Optical system analysts tasked with predicting the loss of throughput due to molecular film contamination have not addressed the impact of droplets in great depth. This paper investigates the conditions leading to the formation of films or droplets resulting from the outgassing products of typical spacecraft materials. A simplified view of surface energy and the wetting parameter are used to show that typical outgassed contaminants and optical substrates favor the formation of droplets. Therefore, analysis of throughput losses due to the scattering of droplets is critical. The droplets can be converted into films or extended islands when exposed to vacuum ultraviolet (VUV) radiation. This observation shows why droplets are rarely observed on external thermal control mirrors and solar arrays but might be considered highly likely in a low-VUV environment.

We present a new nonlinear optical technique to probe chirality, i.e., lack of reflection symmetry, of surfaces and thin molecular films. The technique is based on second-harmonic generation and focusing of circularly polarized light at normal incidence on the sample. Because of the high symmetry of the experimental arrangement, the technique provides an unambiguous probe of chirality in the sense that it avoids false chiral signatures arising from possible in-plane anisotropy of the sample. The technique is verified by using two Langmuir−Blodgett thin films, one chiral and anisotropic, the other achiral and anisotropic, where the latter acted as a reference. Due to the focusing condition, the technique is also naturally applicable to nonlinear chiral microscopy of surfaces and interfaces.