Trap states generated at grain boundaries often dominate the charge transport behavior of polycrystalline organic field effect transistors (OFETs). While these grain boundaries can be reduced through careful processing, unfortunately they cannot be completely suppressed. In this work, we introduce an approach that renders the grain boundaries inactive. Diels-Alder chemistry, which selectively reacts at the grain boundaries within organic semiconductor thin films, is utilized to attach a dipole-containing molecule in a localized manner. This induced dipole alters the surface potential, shifting the mean energy within the grain boundary and resulting in significantly enhanced device performance. Conductance increases exceed two orders of magnitude with the increase proportional to the amount of grain boundary reacted. In OFETs, this generated a doubling in charge carrier mobility and a reduction in the threshold voltage. The ability to tune the performance and uniformity of fabricated films, regardless of their initial grain size or conductance, represents a significant advance in post-fabrication optimization.

The responses of the N-alkyl diamine groups to variations in pH affect their conformations and surface activities, making them relevant to applications relying on interfacial interactions, such as controlled emulsification and mineral flotation. An in-depth understanding of interfacial self-assembly is crucial. Herein, a molecular-level study was performed to investigate the adsorption and self-assembly of N-dodecylpropane-1,3-diamine (DPDA) at the air-water (A/W) interface using sum frequency generation (SFG) spectroscopy and molecular dynamics (MD) simulations. The SFG spectra of DPDA, acquired under three pH conditions, suggest that the protonation of the DPDA diamine group influences the alkyl chain arrangement at a varying degree at the A/W interface. Analysis of the di-cationic DPDA SFG spectrum at a low pH showed fewer gauche defects at low concentration, as indicated by the relatively higher intensity ratio (I-CH3SS/I-CH2SS) of 18.1 +/- 0.6. The density profiles from MD simulations at different surface areas per molecule and pH conditions, showing varying degrees of packing, support the observation of gauche defects in SFG. With MD simulation, the radial distribution factor for di-cationic species has the highest probability of forming hydrogen bonds compared to mono-cationic and non-ionic species. These g(r) probability results conform with observations obtained from SFG spectroscopy, where we observed a strong hydrogen bond interaction at low pH conditions with di-cationic species, forming tetrahedrally arranged water molecules at the A/W interface. Overall, comprehensive insights will facilitate the visualization of alkyl diamines and their potential derivatives at the A/W interface, enabling a better understanding of their behavior across various applications.

This article reports the superparamagnetic behavior of metal-free nitrogen-doped graphene quantum dots (N-GQDs). The pulsed laser ablation (PLA) method was utilized to synthesize N-GQDs with an average diameter of 3.45 nm and a high doping level (N/C) of 1.4. Magnetic properties of as-synthesized N-GQDs were explored by performing magnetization vs magnetic field (M–H) and magnetization vs temperature (M–T) measurements. M–H plots measured in a temperature range of 2–300 K revealed the superparamagnetic behavior of N-GQDs. The value of saturation magnetization was found to be directly correlated to nitrogen concentration and a saturation magnetization up to 28.7 emu/g was obtained at room temperature (300 K). M–T measurements with zero-field-cooled (ZFC) and field-cooled (FC) conditions were employed to study anisotropy energy barriers and blocking temperature. A variation in the blocking temperature (TB) from 288 to 61 K was observed when the external magnetic field (H) was changed from 0.1 to 0.6 T. The origin of superparamagnetism was attributed to the presence of graphitic nitrogen bonding configuration and defect states. The observed superparamagnetic properties along with the optical properties of N-GQDs create an opportunity for developing materials for biomedical applications and data recording devices.

Hypothesis: The monoalkyl diamine surfactant, N-dodecylpropane-1,3-diamine (DPDA), is expected to exhibit a pH-dependent charge switchability. In response to pH changes, the interfacial self-assembly of DPDA becomes an intermediary constituent that can potentially modify the interfacial interactions and structural assembly of both the oil and water phases. Hence, we hypothesize that as we change the pH, DPDA will respond to it by changing its charge and alkyl tail conformation as well as the conformation of adjacent phases at the molecular level, consequently affecting emulsion formation and stability. A neutral pH, resulting in a mono-cationic dialkyl amine, affects the conformation, driving an ordered self-assembly and stable emulsion. Experiments: The pH-sensitivity and interfacial activity of DPDA were evaluated through pH titration and interfacial tension measurements. Subsequently, a molecular-level study of DPDA, as a pH-sensitive switchable surfactant, was performed at the dodecane-water interface using SFG spectroscopy. The interpretation of the vibrational spectra was further reinforced by determining the gauche defects in the interfacial alkyl chain organization and the extent of hydrogen (H) bonding between the interfacial water molecules. Findings: By adjusting the pH of water, the charge of the adsorbed DPDA molecules, their self-assembly, the organization of interfacial molecules, and ultimately the stability of the emulsion were tuned. At pH 7.0, the SFG spectra of DPDA showed that the interfacial alkyl chains were relatively well-ordered, while water molecules also had stronger H-bonding interactions. As a result, the oil-water emulsion showed improved stability. When water was at a high pH, the water molecules had fewer H-bonding interactions and relatively disordered alkyl chains at the interface, providing desirable conditions for demulsification. These observations were compatible with the observation in bulk emulsion preparation, confirming that alkyl chain packing and water H-bonding interactions at the interface contribute to overall emulsion stability.

Nanoparticles (NPs) can be conjugated with diverse biomolecules and employed in biosensing to detect target analytes in biological samples. This proven concept was primarily used during the COVID-19 pandemic with gold-NP-based lateral flow assays (LFAs). Considering the gold price and its worldwide depletion, here we show that novel plasmonic NPs based on inexpensive metals, titanium nitride (TiN) and copper covered with a gold shell (Cu@Au), perform comparable to or even better than gold nanoparticles. After conjugation, these novel nanoparticles provided high figures of merit for LFA testing, such as high signals and specificity and robust naked-eye signal recognition. Since the main cost of Au NPs in commercial testing kits is the colloidal synthesis, our development with the Cu@Au and the laser-ablation-fabricated TiN NPs is exciting, offering potentially inexpensive plasmonic nanomaterials for various bioapplications. Moreover, our machine learning study showed that biodetection with TiN is more accurate than that with Au.

Measuring Young’s modulus (YM) at a small indentation depth for polymer thin films has been critical in predicting their adhesion properties using atomic force microscopy (AFM). This paper provides adhesion force maps of copolymer thin films composed of methacrylate-based monomers with different bulky substituents added to 2-hydroxyethyl methacrylate (HEMA) using AFM. Then Derjaguin–Müller–Toporov (DMT) fitting model was used to generate YM maps of these copolymers and their homopolymers. For example, using the DMT model, the YM value of 15% phenoxyethyl methacrylate (PhEMA, -OPh): 85% HEMA copolymer is greater than HEMA homopolymer, suggesting that the combination resulted in a stiffer polymer material. The observations indicated that methacrylate-based copolymers with bulky substituents such as -OPh may exhibit higher YM resulting in stiffer polymer thin films.

Nitrogen-doped graphene quantum dots (NGQDs) have gained significant attention due to their various physical and chemical properties; however, there is a gap in the study of NGQDs’ magnetic properties. This work adds to the efforts of bridging the gap by demonstrating the room temperature paramagnetism in GQDs doped with Nitrogen up to 3.26 at.%. The focus of this experimental work was to confirm the paramagnetic behavior of metal free NGQDs resulting from the pyridinic N configuration in the GQDs host. Metal-free nitrogen-doped NGQDs were synthesized using glucose and liquid ammonia as precursors by microwave-assisted synthesis. This was followed by dialysis filtration. The morphology, optical, and magnetic properties of the synthesized NGQDs were characterized carefully through atomic force microscopy (AFM), transmission electron microscopy (TEM)), UV-VIS spectroscopy, fluorescence, X-ray photon spectroscopy (XPS), and vibrating sample magnetometer (VSM). The high-resolution TEM analysis of NGQDs showed that the NGQDs have a hexagonal crystalline structure with a lattice fringe of ~0.24 nm of (1120) graphene plane. The N1s peak using XPS was assigned to pyridinic, pyrrolic, graphitic, and oxygenated NGQDs. The magnetic study showed the room-temperature paramagnetic behavior of NGQDs with pyridinic N configuration, which was found to have a magnetization of 20.8 emu/g.

We assembled photoresponsive mono- and bilayer systems with well-defined properties from rod-shaped molecules equipped with different photoswitches. Using properly chosen chromophores (diarylethene-based switch and unidirectional light-driven molecular motor), we then selectively targeted layers made of the same types of photoswitches using appropriate monochromatic light. UV-vis analysis confirmed smooth and unrestricted photoisomerization. To achieve this, we synthesized a new class of triptycene-based molecular pedestals adept at forming sturdy Langmuir-Blodgett films on a water-air interface. The films were smoothly transferred to gold and quartz surfaces. Repeated deposition afforded bilayer systems: one layer containing diarylethene-based photoswitches and the other a unidirectional light-driven molecular motor. Structural analysis of both mono- and bilayer systems revealed the molecules to be tilted with carboxylic functions pointing to the surface. At least two different polymorphs differing in monolayer thickness and tilt angle (~40° and ~60°) were identified on the gold surface.

Most photodynamic therapeutics (PDTs) used in cancer treatment require oxygen to work efficiently to terminate cancer cells. These PDTs do not efficiently treat tumors in hypoxic conditions. Rh(III) polypyridyl complexes have been reported to have a photodynamic therapeutic effect in hypoxic conditions when exposed to UV light. UV light can damage tissue and cannot penetrate deep to reach cancer cells. This work proposes the coordination of a BODIPY fluorophore to a rhodium metal center to form a Rh(III)-BODIPY complex that enhances the reactivity of the rhodium under visible light. This complex formation is facilitated with the BODIPY as the highest occupied molecular orbital (HOMO), while the lowest unoccupied molecular orbital (LUMO) is localized on the Rh(III) metal center. Irradiation of the BODIPY transition at ∼524 nm can cause an indirect electron transfer from the orbital of the BODIPY-centered HOMO to the Rh(III)-centered LUMO, populating the dσ* orbital. In addition, photo binding of the Rh complex covalently coordinated to the N (7) position of guanine in an aqueous solution was also observed by mass spectrometry after chloride dissociation upon irradiation with green visible light (532 nm LED). Calculated thermochemistry values of the Rh complex reaction in methanol, acetonitrile, water, and guanine were determined using DFT calculations. All enthalpic reactions and Gibbs free energies were identified as endothermic and nonspontaneous, respectively. This observation supports the chloride dissociation using 532 nm light. This Rh(III)-BODIPY complex expands the class of visible light-activated Rh(III) photocisplatin analogs that may have potential photodynamic therapeutic activity for the treatment of cancers in hypoxic conditions.

Long-distance transmission of oil is usually performed in large-diameter steel pipelines, where water present therein may cause severe internal corrosion. An effective method of mitigating such corrosion is to inject organic corrosion inhibitors (CIs). Their surface adsorption, via heteroatom functionalities, can markedly enhance the corrosion resistance of metals. In this study, three CI model compounds with different head groups but the same alkyl tail length (-C14H29), specifically tetradecyltetrahydropyrimidinium (THP-C14), tetradecylphosphate ester (PE-C14), and tetradecylimidazolinium (IMID-C14), were synthesized, their purities being determined using nuclear magnetic resonance spectroscopy. The critical micelle concentrations (CMCs) of each compound were measured using surface tensiometry (Du Noüy ring) and fluorescence spectroscopy techniques, with differences being found between these indirect and direct methods. In addition, linear polarization resistance was used to determine inhibition efficiencies (IEs) for carbon steel immersed in a 5 wt% NaCl electrolyte saturated with CO2. CI surface saturation concentrations, with maximum IEs, were compared with the determined CMCs. Excellent IEs were observed at concentrations of THP-C14, PE-C14, and IMID-C14 which do not correspond with their CMCs, the differences involved being significantly greater than what was previously reported for tetradecylbenzyldimethylammonium (BDA-C14). These results demonstrate that there is no direct link between CMC and metal surface saturation/corrosion IE that can be made on a generalized basis for the different head groups but with the same tail length CI, indicating that the selection of the appropriate CI concentration for an industrial application should not be based on CMC alone.

Mixed halide lead perovskite such as methylammonium lead iodide bromides MAPb(BrxI1-x)3 have emerged as one of the most promising materials of future solar cells, offering high power conversion efficiencies and bandgap tunability. Among other factors, the reversible phase segregation under even low light intensities is still limiting their potential use. During this process, the material segregates locally into iodide-rich and bromide-rich phases, lowering the effective bandgap energy. While several studies have been done to illuminate the mechanism and suppression of phase segregation, fundamental aspects remain unclear. Phase compositions after segregation vary extensively between different studies and the exact amounts of phases often remain unmentioned. For iodide-rich phases, the end-point compositions at around x=0.2 are widely accepted but the proportion of the phase is difficult to measure. In this report, we observe the phase segregation using spectroscopic ellipsometry, a powerful, nondestructive technique that has been employed in the study of film degradation before. We obtained dynamic ellipsometric measurements from x=0.5 mixed halide lead perovskite thin films protected by a polystyrene layer under green laser light with a power density of ~11 W/cm2. Changes in the bandgap region can be correlated to the changes in composition caused by phase segregation, allowing for the kinetics to be observed. Time constants between 1.7(± 0.7)×10-3 s-1 for the segregation and 1.5(± 0.6)×10-4 s-1 for recovery were calculated. We expect ellipsometry to serve as a complementary technique to other spectroscopies in studying mixed-halide lead perovskites phase segregation in the future.

HYPOTHESIS:We hypothesize that varying the chemical structure of the monomeric unit in a polymer will affect the surface structure and interfacial molecular group orientations of the polymer film leveraging its response to solvents of different chemical affinities.EXPERIMENTS:Poly (2-methoxy ethyl methacrylate) and poly (2-tertbutoxy ethyl methacrylate) thin films exposed to either deuterated water (D2O) or deuterated chloroform (CDCl3) were studied by sum frequency generation (SFG) spectroscopy, contact angle goniometry, and atomic force microscopy (AFM) at the polymer-solvent interface, supported with molecular simulation studies.FINDINGS:SFG spectral analysis of the polymer thin films corroborated molecular re-organization at the surface when exposed to different chemical environments. The AFM height images of the polymer surfaces were homogeneously flat under CDCl3 and showed swollen regions under D2O. Following the removal of D2O, the exposed areas have imprinted, recessed locations and exposure to CDCl3 resulted in the formation of aggregates. The chemical affinity and characteristics of the solvents played a role in conformational change at the polymer surface. It had direct implications to interfacial processes involving adsorption, permeation which eventually leads to swelling, deformation or aggregation, and possibly dissolution.

New glass systems of bismuth borate with various concentrations of cadmium oxide are prepared based on the melt‐quenching method. The X‐ray diffraction (XRD) reveals a fully amorphous structure of the prepared glasses (S1–S4), and the UV–vis results display good transparency (>50%) in the visible and near‐UV region. In addition, the radiation shielding properties (mass attenuation coefficient, half‐value layer, tenth value layer, mean free path, effective atomic number, and electron density) of the new glass system are determined at selected energies experimentally and by using MCNP5 simulation code and XCOM computer program. Based on the calculated relative difference, the obtained values from MCNP5 and XCOM are in good agreement with the experimental data. The mean free path of the current systems (particularly S4) shows optimistic results when compared with the barite and chalcocite concretes.

Metal deposition onto organic materials results in a myriad of issues at the metal-on-organic interface, necessitating a highly adaptable interlayer. A single cysteamine-based monolayer on evaporated tetracene thin films is demonstrated to be highly multifunctional, inhibiting metal penetration and increasing contact wetting for the silver-on-organic interface. Cross sections of the monolayer-coated sample, imaged via transmission electron microscopy, show that silver penetration decreased by up to 40% compared to untreated tetracene. Substantial morphology differences are observed between treated and untreated samples; metal poorly wets untreated samples, forming nanoparticle clusters, while monolayer-coated samples are uniform. Scanning electron microscopy indicates that the monolayers prevent contact discontinuities (hundreds of nanometers in size) that were observed on untreated samples with thin (20 nm) silver contacts. Monolayers do not add any significant barrier to charge transport compared to untreated samples, with conductivity values measured to be near identical. When these are combined with earlier reports of cysteamine improving contact adhesion and durability, monolayers can effectively address most of the issues plaguing metal-on-organic devices.

HYPOTHESIS:Surfactants are commonly used as corrosion inhibitors for oil-and-gas pipelines. The alkyl chain of surfactants and their overall conformation contributes to the adsorption, flotation, and foam separation in the inhibition process. We hypothesize that the conformation of shorter alkyl chains and chemical nature of surfactants has an effect on the ordering of water molecules at the air-water interface which is not yet well understood. EXPERIMENTS:Alkyl (C4, C6, C8, C10, and C12) dimethylbenzylammonium bromides (Quats) were synthesized. Aqueous solutions at 0% and with different salt concentrations were studied at the air-liquid interface using sum frequency generation spectroscopy. Surface tension and pH measurement were also conducted for comparison. FINDINGS:Surfactant solutions at 0%, 1%, and 10% salt showed a zigzag trend for the number of gauche defects. At 0% salt, an increasing trend of OH band intensity at 3182 cm-1 was observed from C6 to C12 SFG spectra. Yet, C4 showed a more prominent SFG signal from strongly hydrogen-bonded water molecules compared to C6. The headgroup's chemical nature was found to play a role in the ordering of water molecules for a C4 alkyl chain length. The OH band intensity decreases with increasing ionic strength.

Understanding interfacial phenomena is important in processes like corrosion, catalysis, and electrochemical reactions. Specifically, in corrosion inhibition, the assembly of adsorbed surfactants at metal-water interfaces in well-packed, ordered layers is desired. We provide direct evidence of the role of alkyl tails of surfactants in the formation of ordered adsorbed layers at metal-water interfaces. We have employed surface-specific sum frequency generation (SFG) spectroscopy to probe the in situ adsorption and self-assembly of cationic surfactants, alkyldimethylbenzyl ammonium bromides of tail lengths n = 4 (C4) and 12 (C12), without any applied potential or stimulus, at the gold-water interface. Our SFG measurements show that C12 Quat adsorbs as an ordered monolayer, whereas C4 Quat adsorbs in a disordered monolayer. All-atom molecular dynamics (MD) simulations of these surfactants corroborate with SFG results. These findings provide new insights on how hydrophobic interactions between alkyl tails of surfactants affect their self-assembly at metal-water interfaces.

The current study is aimed to investigate the gamma ray and neutron shielding properties of the bismuth borate glass system with various concentration of cadmium oxide (0, 5, 10 and 15 mol%). The XRD spectra confirms the amorphous state of the prepared samples. A number of physical and mechanical properties (molar volume, oxygen molar volume, oxygen packing density, Poisson's ratio, optical absorption and dissolution rates) have been determined. The mass attenuation coefficients were estimated at different energy levels by using XCOM and EXABcal programs. The gamma and neutron beam shielding properties are evaluated through the calculation of several parameters such as equivalent number, specific gamma ray constant, gamma dose rate, specific absorbed fraction of energy and total neutron removal cross-section. Comparing with the standard gamma ray shielding materials, the new composition exhibits promising properties in terms of mass attenuation, halve value layer and mean free path. The glass with the highest concentration of CdO was found to be good shielding material for neutrons compared with some standard shielding materials (water, graphite, ordinary concrete and hematite-serpentine concrete).

We explore a new glassy material for radiation shielding applications. Novel transparent and non-toxic Bi2O3–B2O3 glasses including different concentrations of CdO were prepared by the conventional melt quenching method. The prepared samples were characterized and analyzed by using various analytical tools (XRD, FTIR, Raman, DSC, and UV-Vis-NIR). Ab initio molecular dynamics simulations were carried out to create structural models of the materials, and these were compared to our measurements. To the best of our knowledge, this is the first study to compare the vibrations obtained experimentally with the vibrational density of states obtained from an ab initio computer model for these materials. The radiation shielding properties were measured for the photon energy range (10−3–105 MeV): both mass attenuation coefficient (μ/p) and effective atomic number (Zeff) showed a gradual increase with an increase in the CdO content. The mean-free-path, tenth value layer, half-value layer, and electron density for all prepared glasses were estimated. Promising results were achieved with the new glasses for radiation shielding purposes such as nuclear reactor and medical applications. The structural, electronic, and vibrational properties of the computer models revealed a topologically disordered, but chemically ordered network, and our vibrational computations provide direct insight into several Raman peaks observed for the materials.

Hypothesis: Copolymers are developed to enhance the overall physical and chemical properties of polymers. The surface nature of a copolymer is relevant to creating efficient materials to improve adhesion and biocompatibility. We hypothesize that the improved adhesion, as a surface property, is due to phase separation, surface segregation, and the overall molecular organization of different polymer components at the copolymer surface. Experiments: The surface structure of a copolymer composed of 2-hydroxyethyl methacrylate (HEMA) monomer and 2-phenoxyethyl methacrylate (PhEMA) monomer was analyzed in comparison to the polyHEMA and polyPhEMA homopolymers using atomic force microscopy (AFM) and sum frequency generation (SFG) spectroscopy. Findings: The contrast in the phase images was due to the variance in the hydrophobic level provided by the hydroxyl and phenoxy modified monomers in the copolymer. The distribution of the adhesion values, supporting the presence of hydrophobic moieties, across the polymer surface defined the surface segregation of these two components. SFG spectra of the copolymer thin film showed combined spectral features of both polyHEMA and polyPhEMA thin films at the polymer surface. The tilt angles of the alphamethyl group of homopolymers using the polarization intensity ratio analysis and the polarization mapping method were estimated to be in the range from 48 degrees to 66 degrees. (C) 2020 Elsevier Inc. All rights reserved.

Sum frequency generation (SFG) * Equal contributors. spectroscopy was used to deduce the orientation of the terminal methyl (CH3) group of self-assembled monolayers (SAMs) at the air–solid and air–liquid interfaces at surface concentrations as low as 1% protonated molecules in the presence of 99% deuterated molecules. The SFG spectra of octadecanethiol (ODT) and deuterated octadecanethiol (d37 ODT) SAMs on gold were used for analysis at the air–solid interface. However, the eicosanoic acid (EA) and deuterated EA (d39 EA) SAMs on the water were analyzed at the air–liquid interface. The tilt angle of the terminal CH3 group was estimated to be ∼39 ° for a SAM of 1% ODT : 99% d37 ODT, whereas the tilt angle of the terminal CH3 group of the 1% EA : 99% d39 EA monolayer was estimated to be ∼32 °. The reliability of the orientational analysis at low concentrations was validated by testing the sensitivity of the SFG spectroscopy. A signal-to-noise (S/N) ratio of ∼60 and ∼45 was obtained for the CH3 symmetric stretch (SS) of 1% ODT : 99% d37 ODT and 1% EA : 99% d39 EA, respectively. The estimated increase in S/N ratio values, as a measure of the sensitivity of the SFG spectroscopy, verified the capacity to acquire the SFG spectra at low concentrations of interfacial molecules under ambient conditions. Overall, the orientational analysis of CH3 SS vibrational mode was feasible at low concentrations of protonated molecules due to increased S/N ratio. In support, the improved S/N ratio on varying incident power density of the visible beam was also experimentally demonstrated.