Ultrathin Organic Films Research Articles

β-ketoenamine-linked covalent organic frameworks ultrathin film for transparent supercapacitors with enhanced charge storage capability

With the development of electronic products toward optical transparency and intelligent portability, transparent supercapacitors (TSCs) have been considered as one of the ideal and efficient power sources. However, it is still a challenge to explore covalent organic frameworks (COFs) based transparent conductive electrodes (TCEs) with high photoelectric property and capacitive activity. Herein, β-ketoenamine DqTp (DAAQ-TFP, DAAQ = 2,6-diaminoanthraquinone, and TFP = 1,3,5-triformylphluroglucinol) COFs ultrathin films are synthesized for TCEs through the Schiff base reaction of DAAQ and TFP. The DqTp ultrathin films fully expose the redox-active anthraquinone moieties, shorten the ion/electron transport path, accelerate the transport and diffusion rate, and thus enhance charge storage capability. DqTp-1 TCEs possess the excellent optoelectronic property with optical transmittance (T550 nm) of 69.46%, sheet resistance (Rs) of 7.45 Ω sq−1, and remarkable areal capacitance (CA) of 355.67 μF cm−2. The corresponding asymmetric DqTp-1//PANI TSCs (T550 nm = 58.06%) yield a high CA of 64.55 μF cm−2 at 3 μA cm−2 and have a maximum areal energy density of 0.015 μWh cm−2 at 1.95 μW cm−2. After 5000 cycles, the capacitance retention is 96.9%. This work provides key insights into the design and synthesis of transparent redox-active COFs-based TSCs with excellent photoelectric property and enhanced charge storage capability.

Dual-modal biosensor for mercuric ion detection based on Cu2O@Cu2S/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties

In this study, a dual-mode biosensor based on the heterojunction of Cu2O@Cu2S/D-TA COF was constructed for ultra-sensitive detection of Hg2+ using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au–S bonds. In the presence of Hg2+, the formation of T-Hg2+-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant Cu2O@Cu2S probes onto the biosensor. As a p-type semiconductor, Cu2O@Cu2S could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O2 produced by its catalytic decomposition of H2O2 can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu2+/Cu+ redox pairs of Cu2O@Cu2S, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg2+ in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.

50‐2: Ultrathin Cantilever Type Flexible Device with Integrated micro‐OLEDs using Biomedical Implantable Applications

We deposited micro‐scale organic light‐emitting diodes(OLEDs) with a red‐emitting material on an ultrathin organic film and demonstrated a flexible device with a cantilever form factor. This platform satisfied the necessary light irradiation conditions applicable for phototherapeutic applications and also holds potential for biomedical implantable areas such as neurotherapy.

Nano-Tactile Scanner with Dust-Proof and Drip-Proof Structure for High-Resolution Measurement of Skin Surface Textures.

In this study, we have successfully developed a scanner-type measurement device with a built-in nano-tactile sensor for measuring living organisms and skin surface. A complete sensor protection structure for sensitive tactile sensor device has been developed to achieve a sensing system that is capable of measuring texture changes on the skin surface. By using a highly flexible organic ultra-thin film (film adhesive bandage) as the protective structure, it is possible to prevent deterioration of sensor performance and the intrusion of droplets and dust present on the surface to be measured. This system was used in a clinical experiment at the university's medical faculty, and succeeded in accurately extracting changes in the properties of the patient's skin caused by different wiping methods. As a result, the measurement of tactile texture of the skin surface in various states between dry and wet could be accurately done. Finally, in addition to the ability to measure tactile characteristics of the skin surface, a new function has been realized to measure skin hardness distribution caused by skin changes due to blisters, moles, etc.Clinical Relevance- The developed micron scale was the first to explain the changes in the skin surface structure according to the type of skin surface stimulus and the time of its appearance. It is clinically useful to interpret the protective function of the skin and the function of sensory reception.

Chiral Porphyrin Assemblies Investigated by a Modified Reflectance Anisotropy Spectroscopy Spectrometer.

Reflectance anisotropy spectroscopy (RAS) has been largely used to investigate organic compounds: Langmuir-Blodgett and Langmuir-Schaeffer layers, the organic molecular beam epitaxy growth in situ and in real time, thin and ultrathin organic films exposed to volatiles, in ultra-high vacuum (UHV), in controlled atmosphere and even in liquid. In all these cases, porphyrins and porphyrin-related compounds have often been used, taking advantage of the peculiar characteristics of RAS with respect to other techniques. The technical modification of a RAS spectrometer (CD-RAS: circular dichroism RAS) allows us to investigate the circular dichroism of samples instead of the normally studied linear dichroism: CD-RAS measures (in transmission mode) the anisotropy of the optical properties of a sample under right and left circularly polarized light. Although commercial spectrometers exist to measure the circular dichroism of substances, the "open structure" of this new spectrometer and its higher flexibility in design makes it possible to couple it with UHV systems or other experimental configurations. The importance of chirality in the development of organic materials (from solutions to the solid state, as thin layers deposited-in liquid or in vacuum-on transparent substrates) could open interesting possibilities to a development in the investigation of the chirality of organic and biological layers. In this manuscript, after the detailed explanation of the CD-RAS technique, some calibration tests with chiral porphyrin assemblies in solution or deposited in solid film are reported to demonstrate the quality of the results, comparing curves obtained with CD-RAS and a commercial spectrometer.

Photoelectrochemical biosensing platform based on in situ generated ultrathin covalent organic framework film and AgInS2 QDs for dual target detection of HIV and CEA

In this work, a new photoelectrochemical (PEC) biosensing platform based on an ordered two-dimensional (2D) ultrathin covalent organic framework (COF) film and AgInS2 quantum dots (QDs) has been developed to enable dual-target detection of HIV and CEA. The porous COF film was firstly in situ generated on ITO, displaying super-stable and intense photocurrent with excellent repeatability. Moreover, an effective PEC quenching probe was specifically designed by loading large number of AgInS2 QDs on Au nanoparticles (NPs). After target HIV-induced cyclic amplification process to generate abundant DNA S0, the Au NPs-AgInS2 QDs probe was binded to the COF film through DNA hybridization, enabling PEC signal of the COF film to turn “off” for ultra-sensitive detection of HIV. Furthermore, when CEA as the second target specifically binded to its aptamer, the Au NPs-AgInS2 QDs quenching probe was released, achieving PEC signal “on” of the T-DA COF film for ultra-sensitive detection of CEA. This work opened a unique 2-D COF film-based PEC biosensing platform with excellent signal for rapid detection of dual targets, which can effectively avoid false positives and negatives and shows promising application for early prevention and detection of cancer diseases.

Revealing and Controlling Energy Barriers and Valleys at Grain Boundaries in Ultrathin Organic Films.

In organic electronics, local crystalline order is of critical importance for the charge transport. Grain boundaries between molecularly ordered domains are generally known to hamper or completely suppress charge transfer and detailed knowledge of the local electronic nature is critical for future minimization of such malicious defects. However, grain boundaries are typically hidden within the bulk film and consequently escape observation or investigation. Here, a minimal model system in form of monolayer-thin films with sub-nm roughness of a prototypical n-type organic semiconductor is presented. Since these films consist of large crystalline areas, the detailed energy landscape at single grain boundaries can be studied using Kelvin probe force microscopy. By controlling the charge-carrier density in the films electrostatically, the impact of the grain boundaries on charge transport in organic devices is modeled. First, two distinct types of grain boundaries are identified, namely energetic barriers and valleys, which can coexist within the same thin film. Their absolute height is found to be especially pronounced at charge-carrier densities below 1012 cm- 2 -the regime at which organic solar cells and light emitting diodes typically operate. Finally, processing conditions by which the type or energetic height of grain boundaries can be controlled are identified.

Ultrathin 2D Covalent Organic Framework Film Fabricated via Langmuir-Blodgett Method with a “Two-in-One” Type Monomer

Ultrathin 2D Covalent Organic Framework Film Fabricated via Langmuir-Blodgett Method with a “Two-in-One” Type Monomer

Vapor-solid interfacial reaction and polymerization for wafer-scale uniform and ultrathin two-dimensional organic films

Chemical vapor deposition is a conventional synthesis method for growing large-scale and high-quality two-dimensional materials, such as graphene, hexagonal boron nitride, and transition-metal dichalcogenides. For organic films, solution-based methods, such as inkjet printing, spin coating, and drop and micro-contact printing, are commonly used. Herein, we demonstrate a general method for growing wafer-scale continuous, uniform, and ultrathin (2–5 nm) organic films. This method is based on a copper (Cu) surface-mediated reaction and polymerization of several equivalent bromine (Br)-containing π-conjugated small molecules (C12S3Br6, C24H4O2Br2, and C24H12Br2N4), in which local surface-mediated polymerization and internal π-π interactions among organic molecules are responsible for the dimension and uniformity control of the thin films. Specifically, the growth rate and morphology of thin films were found to be Cu-facet-dependent, and single-crystal Cu(111) surfaces could improve the uniformity of thin films. In addition, the number of Br groups and size of organic molecules were critical for crystallinity and thin-film formation. This method can be used to fabricate heterostructures, such as organic film/graphene, giving room for various functional materials and device applications.

Ultrathin covalent organic framework film as membrane gutter layer for high-permeance CO2 capture

Thin film composite membranes (TFCMs) have displayed attractive CO2 capture performance, in which a critical gutter layer with small transport resistance is needed to prevent the penetration of the top separation layer into the bottom porous support for realizing high CO2 permeance. However, traditional and recently developed gutter layer materials face some issues such as physical aging, thickness-dependent permeability, instability, or poor compatibility. Herein, wholly organic, orientated, two-dimensional covalent organic framework (COF) films, for the first time, are used as the novel gutter layers due to the ideal pore size, intrinsic porosity, small transport resistance, good compatibility with polymer matrix, good anti-aging capability and high stability. Commercial or photo-initiated crosslinked polymer can be deposited compatiblely on the COF gutter layer with a thickness as thin as 55 nm, an ultrathin thickness that traditional gutter layers are challenging to attain. As a result, one optimized TFCM realizes high CO2 capture performance with CO2 permeance of 1843 gas permeation units (GPU) and CO2/N2 separation selectivity of 28.2, which displays unique advantages over other gutter layer-based TFCMs and meets the performance target for CO2 capture (CO2 permeance > 1000 GPU, CO2/N2 selectivity > 20).

Toward Printed Molecular Electronics: Direct Printing of Liquid Metal Microelectrode on Self‐Assembled Monolayers

AbstractDirect printing of conductive material on ultrathin organic films such as molecular monolayers in a non‐invasive and high‐yielding manner can potentially offer a route to unprecedented merging of molecular electronics with printed electronics. This paper reports on an approach to fabricate arrays of molecular tunnel junctions via automated direct printing of liquid‐metal microelectrode comprising eutectic gallium‐indium onto self‐assembled monolayers of n‐alkanethiolates, as a proof‐of‐concept. The printing design enables production of 350 molecular tunneling junctions per chip of 2 cm × 2 cm template‐stripped substrate and 2800 molecular tunneling junctions per batch of 4 in. diameter Si wafer, which exhibit high yields of working junctions (>80%). Printed molecular junctions have uniform geometrical contact area of ≈4.7 × 103 µm2 and guarantees reproducibility in tunneling performance. The junctions exhibit exponential decay of current density (J, A cm−2) as a function of molecular length, obeying the simplified Simmons model, and single, narrow log‐normal distributions of current density (σlog|J| = ≈0.2–0.5). Importantly, there are no significant differences in tunneling decay coefficient and charge injection current density not only between collections of junctions per printed electrode, but also between batches. Results reported herein promise high‐throughput fabrication of molecular‐scale devices via printed molecular electronics.

Parity Effects in the Physicochemical Properties of Self-Assembled Monolayers

Large-area metal/molecule/metal junctions based on self-assembled monolayers (SAMs) of organothiolates are of interest for investigations of charge transport across ultrathin organic films and the fabrication of molecular electronic devices. Several recent reports demonstrate an odd-even dependency in the rate of charge transport through SAMs of the insulating n-alkanethiolates (CH3C n S)1,2 or the redox-active ferrocenylalkanethiolates (FcC n S)3. This parity effect has been attributed to differences in the orientation of the terminal functional group and alkyl chain packing in SAMs consisting of an odd versus even number of methylene repeat units.We have sought experimental evidence for odd-even distinctions in the molecular organization of these SAMs using infrared reflection-adsorption spectroscopy (IRRAS), electrochemistry, and contact angle goniometry. The findings of the investigations will be presented in this talk and the molecular origin of the parity effect of SAM macroscopic properties will be discussed.

Microstructured Ultrathin Organic Semiconductor Film via Dip-Coating: Precise Assembly and Diverse Applications

ConspectusOrganic semiconductors (OSCs) have led to considerable progress in various fields owing to their intrinsic flexibility, adjustable chemical structures, multifunctionalities, and low processing cost. The optoelectronic properties of OSCs greatly depend on their aggregation state in molecular assemblies. To obtain ideal and reliable optoelectronic performances, a highly controlled assembly method for modulating OSC packing structures is indispensable. In particular, ultrathin OSC microstructures consisting of one to several molecular layers, known as microstructured ultrathin organic semiconductor films (MUOSFs), are of great importance for both fundamental research and applications of OSCs. However, most reported film thicknesses or molecular layer numbers of ultrathin OSC films/microstructures are “average values” rather than “real values” and are not molecularly precise. The lack of an effective and general assembly strategy seriously hinders the progress of MUOSFs. In this Account, we summarize our recent progress in exploring the assembly strategy, the underlying mechanism, and diverse applications of MUOSFs prepared via dip-coating under optimized conditions.Dip-coating, with an intrinsic three-phase contact line, has a great advantage to precisely assemble ultrathin OSC films/microstructures. As an evaporation-controlled method, the assembly processes used in dip-coating are susceptible to multiple factors, such as pulling speed, molecular structures, and solution properties. Under the guidance of our proposed “Balance Principle” for adjusting these factors, uniform and continuous MUOSFs can be obtained over a large area. Under optimized conditions, the number of molecular layers of MUOSFs can be customized with monolayer precision, which is significant for investigating the charge transport mechanism of OSCs. At the same time, the ultrathin and partial coverage characteristics of MUOSFs are beneficial to fabricate flexible and transparent devices for wearable electronics. Notably, the morphologies and coverage of ultrathin microstripes can be well tuned by the pulling speed, which is highly desired for high-performance bio/chemical sensors, because the large specific surface area provides abundant reactive sites.The feasibility and generality of our assembly method demonstrate that dip-coated MUOSFs have excellent advantages for fundamental research and applications of OSC materials, based on which many promising future works around MUOSFs can be extended to more related fields by engineering molecular orientations, packing structures, film morphologies, coverage, etc. The work on the assembly and applications of MUOSFs might offer the potential to promote the progress of organic electronics.

Morphological Transitions in Organic Ultrathin Film Growth Imaged by In Situ Step-by-Step Atomic Force Microscopy

In situ atomic force microscopy (AFM) allowed us to investigate the evolution at the early stages of the growth of organic thin films. An ultrahigh-vacuum atomic force microscope, integrated with a...

Molecular Layer Deposition of “Magnesicone”, a Magnesium-based Hybrid Material

Molecular layer deposition (MLD) offers the deposition of ultrathin and conformal organic or hybrid films which have a wide range of applications. However, some critical potential applications require a very specific set of properties. For application as desiccant layers in water barrier films, for example, the films need to exhibit water uptake and swelling and be overcoatable. For application as a backbone for a solid composite electrolyte for lithium ions on the other hand, the films need to be stable against lithium and need to be transformable from a hybrid MLD film to a porous metal oxide film. Magnesium-based MLD films, called magnesicone, are promising on both these aspects, and thus, an MLD process is developed using Mg(MeCp)(2) as a metal source and ethylene glycol (EG) or glycerol (GL) as organic reactants. Saturated growth could be achieved at 2 to 3 angstrom/cycle in a wide temperature window from 100 to 250 degrees C. The resulting magnesicone films react with ambient air and exhibit water uptake, which is in the case of the GL-based films associated with swelling (up to 10%) and in the case of EG-based magnesicone with Mg(CO)(3) formation, and are overcoatable with an ALD of Al2O3. Furthermore, by carefully tuning the annealing rate, the EG-grown films can be made porous at 350 degrees C. Hence, these functional tests demonstrate the potential of magnesicone films as reactive barrier layers and as the porous backbone of lithium ion composite solid electrolytes, making it a promising material for future applications.

Stereostructural Effects in the Electrochemical Properties of Self-Assembled Monolayers

Large-area metal/molecule/metal junctions based on self-assembled monolayers (SAMs) of organothiolates are of interest for the investigation of charge transport across ultrathin organic films and the fabrication of molecular electronic devices such as diodes and switches. Several reports demonstrate an odd-even dependency in the rate of charge transport across SAMs of the redox-active ferrocenylalkanethiolates Fc(CH2) n S1, 2 and insulating n-alkanethiolates CH3(CH2) n S3-6. This parity effect is attributed to small changes in the orientation of the terminal functional group (ferrocene or methyl) and in the alkyl chain packing in SAMs consisting of an odd versus even number of methylene repeat units (n odd or n even). These odd-even differences ultimately impact device performance. For instance, junctions comprising gold-supported Fc(CH2) n S SAMs (Figure 1) of n even present lower leakage currents and rectify current, while those of n odd do not.1, 2 We have sought experimental evidence for odd-even distinctions in the molecular organization of these SAMs using electrochemistry,7 infrared reflection-absorption spectroscopy (IRRAS), contact angle goniometry, and surface stress measurements8. The findings of these investigations will be presented in this talk.

2D/3D Metallic Nano-objects Self-Organized in an Organic Molecular Thin Film.

We present the fabrication and investigation of the properties of nanocomposite structures consisting of two-dimensional (2D) and three-dimensional (3D) metallic nano-objects self-organized on the surface and inside of organic molecular thin-film copper tetrafluorophthalocyanine (CuPcF4). Metallic atoms, deposited under ultrahigh vacuum (UHV) conditions onto the organic ultrathin film, diffuse along the surface and self-assemble into a system of 2D metallic overlayers. At the same time, the majority of the metal atoms diffuse into the organic matrix and self-organize into 3D nanoparticles (NPs) in a well-defined manner. The evolution of the morphology and electronic properties of such structures as a function of nominal metal content is studied under UHV conditions using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), and photoelectron spectroscopy (PES) techniques. Using HR-TEM, we have observed the periodicity of atomic planes of individual silver NPs. The steady formation of agglomerates from individual single nanocrystallites with intercrystallite boundaries is observed as well. PES reveals generally weak chemical interactions between silver and the organic matrix and n-doping of CuPcF4 at the initial stages of silver deposition, which is associated with charge transfer from the 2D wetting layer on the basis of core-level spectra shift analysis.

Persistence of the Co-tetra-phenyl-porphyrin HOMO-LUMO features when a single organic layer is grown onto Cu(1 1 0)-(2 × 1)O

Ultra-thin organic films must be screened when deposited onto freshly prepared metal surfaces in view of preserving the molecular physical-chemical properties. A current promising strategy prescribes the oxidation of the substrate and, when possible, the creation of a single oxide layer. This strategy was successfully exploited with metal-tetra-phenyl porphyrins (M-TPP) on Fe(0 0 1)-p(1 × 1)O. Here, our study is extended to the oxidized Cu(1 1 0)-(2 × 1)O. Having free coordination sites, the Co-TPP is perturbed when deposited onto the freshly prepared copper surface and the HOMO-LUMO levels quenched, as reported in the literature. Here, we prove that the oxide copper surface reduces the molecule-substrate interaction and photoemission spectroscopy is able to reveal the characteristic electronic features of the molecules.

Covalent organic framework-based ultrathin crystalline porous film: manipulating uniformity of fluoride distribution for stabilizing lithium metal anode

In situ formed LiF grains are confined and evenly distributed throughout a covalent organic framework (COF) film, which exhibits cooperative effectiveness to greatly stabilize the lithium metal.

Low-Cost Localized Surface Plasmon Resonance Biosensing Platform with a Response Enhancement for Protein Detection.

There are many potential applications for biosensors that can provide real-time analysis, such as environmental monitoring and disease prevention. In this study, we investigated a simple strategy for real-time protein detection, which had the advantages of affordability, fast response, portability, and ease of use. A robust quantification of protein interaction was achieved by combining capillary localized surface plasmon resonance (LSPR) sensors and complementary metal–oxide–semiconductor (CMOS) image sensors. Gold nanoparticles were modified on the inner wall of the capillary, which was used as a microfluidic channel and sensing surface. We functionalized one of the LSPR sensors using ligand bound to gold nanoparticle. Our proposed biosensing platform could be easily multiplexed to achieve high throughput screening of biomolecular interactions, and it has the potential for use in disposable sensors. Moreover, the sensing signal was enhanced by the extinction effect of gold nanoparticles. The experimental results showed that our device could achieve qualitative identification and quantitative measurement of transferrin and immunoglobulin G (IgG). As a field-portable and low-cost optical platform, the proposed LSPR biosensing device is broadly applicable to various protein binding tests via a similar self-assembly of organic ultrathin films.