Organic Multilayers Research Articles

Fast thermo-osmotic flow through covalent organic framework multilayers for desalination

Fast thermo-osmotic flow through covalent organic framework multilayers for desalination

Enhancing ToF-SIMS OLED Data Analysis with Neural Networks and Mathematical Spectral Mixing.

This study presents a method employing artificial neural networks (ANN) for automated interpretation and depth profiling of organic multilayers using a limited set of time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra. To overcome the challenges of acquiring massive data sets for OLEDs, training data was generated by combining existing ToF-SIMS data sets with mathematically generated spectra. The classification model achieved an impressive 99.9% accuracy in identifying the mixed layers of the OLED dyes. The study demonstrates the synergy of ToF-SIMS and ANN analysis for effective classification and depth profiling of the OLED layers, providing valuable insights for the development and optimization of organic electronic devices.

Time‐of‐flight secondary ion mass spectrometry and X‐ray photoelectron spectroscopy protocol for the analysis of organic multilayers

With the development in the early 2000s of new cluster ion sputtering sources, a reliable analysis of organic multilayers and interfaces has become possible. Nowadays, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and X‐ray photoelectron spectroscopy (XPS) depth profiling are routinely used to investigate organic stacks. However, analysis beams can cause bond scission or beam‐induced degradations that accumulate in buried layers. We developed a correlative protocol that minimises damages related to analysis beams. It uses a shallow angle bevel crater fabricated inside the ToF‐SIMS analysis chamber. With this preparation method, the in‐depth information is displayed over the surface of the bevel crater. XPS profiles and high‐resolution spectra paired with ToF‐SIMS images enable an easy identification of the organic layers and complete understanding of their chemistry. The reduction of beam‐induced degradation is achieved by minimising the acquisition times, therefore beam exposure on materials. Finally, an important advantage of this preparation method is that the analysis can be performed on exactly the same spot by multiple techniques. Several ToF‐SIMS and XPS acquisitions can be carried out with various parameters (investigation of backscattered Arn+ cluster ion fragments, tandem MS imaging…) as well as analysis with other techniques that possess limitations in spatial resolution and/or inaptitude to probe buried layers such as Raman or AFM.

Probing Energy-Level Alignment in Molecular Multilayers by Frequency-Modulation Electrostatic Force Microscopy under Tapping-Mode-Combined Fowler-Nordheim Tunneling Spectroscopy.

The alignment of molecular electronic levels in a molecular multilayer is of crucial importance to realize desired functions for molecular devices. Amplitude-modulation-feedback frequency-modulation electrostatic force microscopy combined with Fowler-Nordheim tunneling spectroscopy is utilized as a probe for the energy-level alignment in an organic multilayer. Bias-dependent electrostatic force spectra were examined for bilayers including a Ru complex as a benchmark multilayer system. Electrostatic properties in the low-bias region were captured well by a single-capacitor model, which indicates weak coupling at the bilayer interface between the Ru complex and self-assembled monolayer. In contrast, in the high-bias region, significant disagreement with the expected electrostatic force was recognized for the bilayers and evaluated as the loss of electrostatic energy through the Fowler-Nordheim tunneling process. Alignment of the lowest unoccupied molecular orbital (LUMO) level of the Ru complex was determined by Fowler-Nordheim emission through resonant tunneling. These results indicate an effective method to probe level alignment at interfaces inside multilayers and to provide the partition factor β that depicts a divided electric field.

Spherical silica particles coated with lamellar nanocomposites based on a hydrophobic functionalized phyllosilicate

The surface of spherical silica particles (monodisperse, 2.6 µm) was modified with inorganic–organic lamellar ordered hybrids for applications as hydrophobic dye supports in cosmetics. The inorganic–organic multilayers comprised a 2:1 phyllosilicate (two sheets of linked SiO4 tetrahedra with one sheet of M2–3(OH)6 octahedra, where M is either magnesium or aluminum), consisting of octyl chains directly bonded to the inorganic sheets via Si–C covalent bonds. Octyltriethoxysilane was allowed to react at room temperature with spherical silica and aluminum acetylacetonate in a mixed aqueous solution of NaOH and NaCl at pH 10. The formation of a 2:1 phyllosilicate grafted with an octyl chain was confirmed by X-Ray powder diffraction, where a lamellar structure with the d001 value of 2.4 nm was displayed. The lamellar structure included the isomorphic substitution of Si by Al and the formation of C–Si–O–Aloct bonds, as shown in 29Si–and 27Al–magic angle spinning (MAS)–nuclear magnetic resonance (NMR) spectra. Further, the 23Na–MAS NMR spectrum indicated the incorporation of Na aquo complex cations into the organophyllosilicate. The hydrated Na ions were exchanged with a cationic dye (methylene blue) to be adsorbed. An anionic dye (Phloxine B), which has frequently been used as cosmetic pigments, was adsorbed onto the resulting hybrid particles when Al3+ was present in the dye solution. The hydrophobic dye supports can be used instead of plastic beads to reduce marine pollution.

Characteristics of phosphorescent organic light-emitting devices with interfacial nanolayers of acid molecule-doped tris(4-aminophenyl)amine

Here we report that 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-doped tris(4-aminophenyl)amine (TAPA) can act as an interfacial layer for hole injection in phosphorescent organic light-emitting devices (OLEDs) and deliver improved device stability upon electric fields. The acid-base reaction between TAPA and AMPSA was carried out using 2-methoxy ethanol solvent with various molar ratios (0–300 mol. %). The resulting TAPA:AMPSA layers (1–10 nm thick) were spin-coated on indium-tin-oxide (ITO)-glasses and selectively annealed before the thermal deposition of organic small molecular multilayers in a vacuum. The doping reaction between TAPA and AMPSA gave rise to a new absorption peak at a wavelength of ca. 880 nm. The work function of TAPA:AMPSA layer-coated ITO-glasses increased with the molar ratio, but the highest luminance and efficiency of OLEDs were achieved at 100 mol. % (AMPSA to TAPA). The thickness control and thermal treatment process of TAPA:AMPSA layers (100 mol. %) could further enhance the luminance (from ca. 5000 cd/m2 (t = 10 nm) to 15,500 cd/m2 (t = 2 nm)) with relatively high device stability upon electric field compared to the pristine TAPA layers.

Bevel Structure Based XPS Analysis as a Non-Destructive Chemical Probe for Complex Interfacial Structures of Organic Semiconductors.

The bevel structure of organic multilayers produced by finely controlled Ar gas cluster ion beam sputtering preserves both the molecular distribution and chemical states. Nevertheless, there is still an important question of whether this method can be applicable to organic multilayer structures composed of complex or ambiguous interfaces used in real organic optoelectronic devices. Herein, various bevel structures are fabricated from different types of organic semiconductors using a solution-based deposition technique: complicatedly intermixed electron-donor and electron-acceptor bulk heterojunction structure, thin film structure with an internal donor-acceptor concentration gradient, and multi-layered structure with more than three layers. For these organic material combinations listed above, the bevel structure is fabricated with finely tuned Ar gas cluster ion beam sputtering. The location-dependent X-ray photoelectron spectroscopy (XPS) results obtained for each bevel structure exactly correspond to the XPS depth profiles. This result demonstrates that the bevel structure analysis is a powerful method to distinguish subtle differences in chemical component distributions and chemical states of organic semiconductors even with complex or ambiguous interfaces. Ultimately, due to its reliability as verified by this study, the proposed bevel structure analysis is expected to greatly expand other analytical techniques with a limited spatial or depth resolution.

Phase-shifting electron holography for accurate measurement of potential distributions in organic and inorganic semiconductors.

Phase-shifting electron holography (PS-EH) is an interference transmission electron microscopy technique that accurately visualizes potential distributions in functional materials, such as semiconductors. In this paper, we briefly introduce the features of the PS-EH that overcome some of the issues facing the conventional EH based on Fourier transformation. Then, we present a high-precision PS-EH technique with multiple electron biprisms and a sample preparation technique using a cryo-focused-ion-beam, which are important techniques for the accurate phase measurement of semiconductors. We present several applications of PS-EH to demonstrate the potential in organic and inorganic semiconductors and then discuss the differences by comparing them with previous reports on the conventional EH. We show that in situ biasing PS-EH was able to observe not only electric potential distribution but also electric field and charge density at a GaAs p-n junction and clarify how local band structures, depletion layer widths and space charges changed depending on the biasing conditions. Moreover, the PS-EH clearly visualized the local potential distributions of two-dimensional electron gas layers formed at AlGaN/GaN interfaces with different Al compositions. We also report the results of our PS-EH application for organic electroluminescence multilayers and point out the significant potential changes in the layers. The proposed PS-EH enables more precise phase measurement compared to the conventional EH, and our findings introduced in this paper will contribute to the future research and development of high-performance semiconductor materials and devices.

Effect of the Conformation Changes of Polyelectrolytes on Organic Thermoelectric Performances

The relationship between the conformation of a polyelectrolyte and the performance of organic thermoelectric multilayers was studied. The conformational change of a weak polyelectrolyte via controlling assembling pH gave rise to a different thermoelectric behaviour in thin films. Organic thermoelectric multilayers were fabricated by alternately depositing bilayers (BL) of a positively-charged polyaniline (PANi) and multiwalled carbon nanotubes (MWNT), stabilized in poly(acrylic acid) (PAA), via a layer-by-layer assembly technique. The electrical conductivity and See-beck coefficient of PANi/MWNT-PAA nanocomposites were measured by varying assembly pH of PAA solutions. Altering the deposition pH of PAA resulted in different thermoelectric performances. A 40 BL thin film (∼210 nm thick) of PANi/MWNT-PAA assembled at pH 2.5/6.5 exhibited electrical conductivity of 95.2 S/cm and a Seebeck coefficient of 35 µV/K. This translates to a power factor of 11.7 µW/m·K2, which is 50 times higher than that of the same film with all components deposited at pH 2.5. Enhancement of thermoelectric behaviour in PANi/MWNT-PAA nanocomposites is attributed to a conjugated π-π network, together with a tightly packed nanostructure.

Organic Electropolymerized Multilayers for Light-Emitting Diodes and Displays.

In electrochemistry, the carbazole is generally coupled to dimer but not to polymer. This work has reported that organic electropolymerization (OEP) of 4,4',4″-tri(N-carbazolyl)triphenylamine (TCTA) would form a high cross-linked carbazole polymer by its high activity/reversibility and a synchronous viscosity control. It has significantly improved the OEP film quality of both hole-transporting and electroluminescent layers in organic light-emitting diodes. As a result, the conductivity and power efficiency of the organic light-emitting diodes with TCTA are eight and four times of that without TCTA. A prototype display device with a 1.7 in. monochrome passive matrix of 58 ppi under the driving chip is successfully fabricated with accurate pixel size and uniform electroluminescence, which shows a great potential of OEP in the electroluminescent application.

Organic Thermoelectric Multilayers with High Stretchiness.

A stretchable organic thermoelectric multilayer is achieved by alternately depositing bilayers (BL) of 0.1 wt% polyethylene oxide (PEO) and 0.03 wt% double walled carbon nanotubes (DWNT), dispersed with 0.1 wt% polyacrylic acid (PAA), by the layer-by-layer assembly technique. A 25 BL thin film (~500 nm thick), composed of a PEO/DWNT-PAA sequence, displays electrical conductivity of 19.6 S/cm and a Seebeck coefficient of 60 µV/K, which results in a power factor of 7.1 µW/m·K2. The resultant nanocomposite exhibits a crack-free surface up to 30% strain and retains its thermoelectric performance, decreasing only 10% relative to the unstretched one. Even after 1000 cycles of bending and twisting, the thermoelectric behavior of this nanocomposite is stable. The synergistic combination of the elastomeric mechanical properties (originated from PEO/PAA systems) and thermoelectric behaviors (resulting from a three-dimensional conjugated network of DWNT) opens up the possibility of achieving various applications such as wearable electronics and sensors that require high mechanical compliance.

High Throughput Bar-Coating Processed Organic-Inorganic Hybrid Multi-Layers for Gas Barrier Thin-Films.

Herein, we demonstrate the preparation of a scalable bar-coated nanocomposite organic-inorganic hybrid film and developed robust barrier films for general purpose packaging. Using combinatory printing of polymers and nanocomposites by bar coating, a facile and effective barrier film fabrication method was developed. Based on a preliminary survey with several material combinations, a rationalized two-fold nanocomposite film was fabricated. The number of layers in the barrier film significantly modified oxygen barrier performance such that, for the 1 wt% ethylene vinyl alcohol (EVOH) intercalated film, the oxygen transmission rate (OTR) of the 5-layer sample was reduced to 31.69% of the OTR of the 3-layer sample (112.8 vs. 35.75 cc/(m² · day)). In addition, fine tuning the amount of EVOH polymer enabled further improvement of oxygen barrier performance. Intercalation of 2 wt% EVOH resulted an OTR improvement from 35.75 in the 1 wt% sample to 11.90 cc/(m² ·day), which is a 4.25-fold enhancement. Overall barrier characteristics proved that our approach could be used for large-area deposited, oxygen resistant, general purpose packaging applications.

ToF-SIMS Depth Profiling of Organic Delta Layers with Low-Energy Cesium Ions: Depth Resolution Assessment.

The advent of cluster ion beams has paved the way to the routine 3D analysis of organic heterojunctions. Alternatively, organic thin layers have also been successfully depth profiled with a low-energy cesium ion beam (Cs+), to exploit the high chemical reactivity of cesium atoms, acting as free-radical scavengers. Despite of this, little is known about the depth resolution associated with low-energy Cs+ sputtering on organic multilayers. In this work, amino acids multilayers, consisting of phenylalanine delta layers alternated with tyrosine spacers, were used as model systems to assess the depth resolution associated with 500eV Cs+ depth profiles. High yields were obtained for quasi-molecular ions from both amino acids, and no significant chemical alteration was noticed under the monoatomic bombardment. A depth resolution as low as 4nm is demonstrated without sensible degradation on a rather long profile depth (300nm). Limited depth resolution (> 10nm) along with high molecular degradation was previously reported on similar systems by combining low-energy Cs+ with Ga+ analysis beam. The use of the Bi3+ analysis beam results in a dramatic improvement of both the characteristic molecular signal intensities and the depth resolution. Even though the analysis beam fluence is very low compared to the sputtering beam fluence, data suggest that further reducing the analysis Bi3+ fluence could improve the depth resolution by ~ 1nm.

Modification of fluorine-doped tin oxide surface: Optimization of the electrochemical grafting of diazonium salt

Fluorine-doped tin oxide (FTO) electrodes were functionalized by electro reduction of in situ generated 4-carboxyphenyl diazonium salt. Several grafting potentials and times were investigated in order to find the optimal grafting conditions. The electrochemical behavior of bare FTO electrodes in the presence of the diazonium, together with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) characterization of the grafted electrodes in the presence of redox probes ferricyanide and ferrocene allowed us to conclude that 10 min grafting under a controlled potential of −0.50 V lead to the formation of a poorly-packed organic multi-layer on the electrode surface. X-ray Photoelectron Spectroscopy (XPS), together with Fourier-Transform Infrared Spectroscopy (FTIR) analyses, further evidenced the presence of carboxylic groups onto modified FTO electrodes.

Soil water repellency: A molecular-level perspective of a global environmental phenomenon

Soil water repellency affects vast regions of agricultural and native land across the globe. Sandy soils are most likely to develop non-wetting characteristics with susceptibility decreasing with clay content. This study uses molecular dynamics simulations combined with laboratory scale experiments to study the interactions and assembly of saturated C16 straight chain alcohol and carboxylic acid molecules on a range of soil surfaces. The development of severe water repellency on sand at low loading levels of palmitic acid (0.75 × 10−6 mol g−1) is explained in terms of favourable H-bonding with silica surfaces and the development of 2–3 layers of lateral aligned organic molecules on the mineral surface. The efficacy of kaolinite in lowering soil water repellency is attributed to the higher surface area of this mineral and favourable surface chemistry, which hinders formation of persistent organic multilayers.

Quasi-phase-matched third harmonic generation in organic multilayers

We report the first realization of quasi-phase-matched (QPM) third harmonic generation in isotropic polymer films. Spin-coated thin films of ethyl-violet molecules dispersed in a polymer host (EV) were used as cubic nonlinear optical media because of their transparency at both the fundamental (1230 nm) and the third harmonic (410 nm) wavelengths. A passive layer of a UV-curable material was formed to compensate the phase shift between the two light waves after propagating through each EV layer. We fabricated a series of samples with 1~4 EV layers (0~3 alternatingly coated passive layers). The third harmonic output power showed a quadratic increase with the number of layers, providing a strong evidence for successful quasi-phase-matching. A conversion efficiency of 0.15% was observed with a 190 fs pulse input.

Ultrahigh-vacuum organic molecular-beam deposition system for in situ growth and characterization.

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.

APPLICATION OF SUB-CRITICAL WATER FOR RECOVERY OF TIN AND GLASS SUBSTRATES FROM LCD PANEL E-WASTE

Tin and transparent glass substrate were efficiently recovered from color filter (CF) and thin-film transistor (TFT) glasses in LCD panel wastes using sub-critical water (sub-CW) at various treatment temperatures and reaction time. Treatment for 5 min using sub-CW added with NaOH resulted in a 95% recovery of tin from CF and TFT glasses. The tin oxide did not liquify in the liquid phase instead stayed in the organic multi-layers, which exfoliated together from the CF glass and TFT glass. This is a huge advantage because the organic multi-layers were readily separated by sub-CW and tin was recovered by filtration with ease. Transparent and clean glass was also recovered from LCD panel waste. The amount of tin oxide recovered depended on the sub-CW reaction temperature, reaction time and NaOH concentration. Treatment of smaller CF glass improved the recovery of tin. With this advance, we have showed that sub-CW method is technically feasible for tin oxide recovery in LCD waste.

Fabrication, characterization, electrochemistry, and redox-induced electrochromism of viologen-functionalized silica core-shell nano-composites

Electroactive viologen-functionalized silica core-shell nano-composites have been prepared and characterized using thermogravimetry, field emission transmission electron microscopy, and infrared, UV–vis absorption, and X-ray photoelectron spectroscopy. The viologen monolayer functionalized nano-silica core (nano-SiO2VBen) was obtained via a substitution reaction of propylamine−modified silica nanoparticles (nano-SiO2NH2) with N,N'-di(bromomethylbenzyl)-4,4'-bipyridium dibromide (VBenBr2). The nano-SiO2VBen core was positively charged and could thus act as a support for the construction of the shell layer of viologen multilayers through, alternatively, the electrostatic adsorption of poly(sodium-p-styrenesulfonate) (PSS) and VBenBr2. Dynamic light scattering and morphological studies revealed that the dynamic sizes of the nanoparticles increased in the following order: nano-SiO2NH2, nano-SiO2VBen, and nano-SiO2VBen@(PSS/VBen)n. This was due to the assembly of organic multilayers around the nanoparticles and formation of aggregates. Cyclic voltammograms of nano-SiO2VBen- and nano-SiO2VBen@(PSS/VBen)n-modified electrodes showed two couples of redox waves in the potential range from 0 to −1.2V (vs Hg/Hg2Cl2), corresponding to the redox processes of viologens in the nano-composites. Compared to their precursor of VBenBr2, the nano-SiO2VBen and nano-SiO2VBen@(PSS/VBen)n composites could be more strongly adsorbed on the electrode surface without co-adsorption of the polymeric supporter (Nafion), which can be attributed to a stronger molecular interaction between the present nano-composites and electrode surfaces. Finally, the redox-induced electrochromic properties of VBenBr2 and nano-composites were investigated in the solutions or polymer gel electrolytes, and the results suggest that both viologen organic electrolyte and nano-composites could act as potential candidates for the development of redox-based electrochromic indicators and displays.

Mulifunctional Dendritic Emitter: Aggregation-Induced Emission Enhanced, Thermally Activated Delayed Fluorescent Material for Solution-Processed Multilayered Organic Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) materials emerged as promising light sources in third generation organic light-emitting diodes (OLED). Much effort has been invested for the development of small molecular TADF materials and vacuum process-based efficient TADF-OLEDs. In contrast, a limited number of solution processable high-molecular weight TADF materials toward low cost, large area, and scalable manufacturing of solution processed TADF-OLEDs have been reported so far. In this context, we report benzophenone-core carbazole dendrimers (GnB, n = generation) showing TADF and aggregation-induced emission enhancement (AIEE) properties along with alcohol resistance enabling further solution-based lamination of organic materials. The dendritic structure was found to play an important role for both TADF and AIEE activities in the neat films. By using these multifunctional dendritic emitters as non-doped emissive layers, OLED devices with fully solution processed organic multilayers were successfully fabricated and achieved maximum external quantum efficiency of 5.7%.