Self-Assembled Monolayers of a Fluorinated Phosphonic Acid as a Protective Coating on Aluminum

Aluminum (Al) placed in hot water (HW) at 90 °C is roughened due to its reaction with water, forming Al hydroxide and Al oxide, as well as releasing hydrogen gas. The roughened surface is thus hydrophilic and possesses a hugely increased surface area, which can be useful in applications requiring hydrophilicity and increased surface area, such as atmospheric moisture harvesting. On the other hand, when using HW to roughen specified areas of an Al substrate, ways to protect the other areas from HW attacks are necessary. We demonstrated that self-assembled monolayers (SAMs) of a fluorinated phosphonic acid (FPA, CF3(CF2)13(CH2)2P(=O)(OH)2) derivatized on the native oxide of an Al film protected the underneath metal substrate from HW attack. The intact wettability and surface morphology of FPA-derivatized Al subjected to HW treatment were examined using contact angle measurement, and scanning electron microscopy and atomic force microscopy, respectively. Moreover, the surface and interface chemistry of FPA-derivatized Al before and after HW treatment were investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS), verifying that the FPA SAMs were intact upon HW treatment. The ToF-SIMS results therefore explained, on the molecular level, why HW treatment did not affect the underneath Al at all. FPA derivatization is thus expected to be developed as a patterning method for the formation of hydrophilic and hydrophobic areas on Al when combined with HW treatment.

Correlation of Plasma Membrane Microviscosity and Cell Stiffness Revealed via Fluorescence-Lifetime Imaging and Atomic Force Microscopy

The biophysical properties of cells described at the level of whole cells or their membranes have many consequences for their biological behavior. However, our understanding of the relationships between mechanical parameters at the level of cell (stiffness, viscoelasticity) and at the level of the plasma membrane (fluidity) remains quite limited, especially in the context of pathologies, such as cancer. Here, we investigated the correlations between cells' stiffness and viscoelastic parameters, mainly determined via the actin cortex, and plasma membrane microviscosity, mainly determined via its lipid profile, in cancer cells, as these are the keys to their migratory capacity. The mechanical properties of cells were assessed using atomic force microscopy (AFM). The microviscosity of membranes was visualized using fluorescence-lifetime imaging microscopy (FLIM) with the viscosity-sensitive probe BODIPY 2. Measurements were performed for five human colorectal cancer cell lines that have different migratory activity (HT29, Caco-2, HCT116, SW 837, and SW 480) and their chemoresistant counterparts. The actin cytoskeleton and the membrane lipid composition were also analyzed to verify the results. The cell stiffness (Young's modulus), measured via AFM, correlated well (Pearson r = 0.93) with membrane microviscosity, measured via FLIM, and both metrics were elevated in more motile cells. The associations between stiffness and microviscosity were preserved upon acquisition of chemoresistance to one of two chemotherapeutic drugs. These data clearly indicate that mechanical parameters, determined by two different cellular structures, are interconnected in cells and play a role in their intrinsic migratory potential.

Archetype-Cation-Based Room-Temperature Ionic Liquid: Aliphatic Primary Ammonium Bis(trifluoromethylsulfonyl)imide as a Highly Functional Additive for a Hole Transport Material in Perovskite Solar Cells

Room-temperature ionic liquids (RTILs) have attracted significant attention owing to their unique nature and a variety of potential applications. The archetypal RTIL comprising an aliphatic primary ammonium was discovered over a century ago, but this cation is seldom used in modern RTILs because other bulky cations (e.g., quaternary ammonium-, pyridine-, and imidazole-based cations) are prominent in current major applications, such as electrolytes and solvents, which require low and/or reversible reactivities. However, although the design of materials should change according to the intended application, RTIL designs remain conventional even when applied in unexplored fields, limiting their functions. Herein, RTIL consisting of an archetypal aliphatic primary ammonium (i.e., n-octylammonium: OA) cation and a modern bis(trifluoromethylsulfonyl)imide (TFSI) anion is proposed and demonstrated as a highly functional additive for a 2,2',7,7'-tetrakis(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), which is the most common hole transport material (HTM), in perovskite solar cells (PSCs). The OA-TFSI additive exhibits prominent functions via permanent reactions of the component ions with the PSC components, thus providing several advantages. The OA cations spontaneously and densely passivate the perovskite layer during the HTM deposition process, leading to both suppression of carrier recombination at the HTM/perovskite interface and hydrophobic perovskite surfaces. Meanwhile, the TFSI anions effectively improve the HTM function most likely via efficient stabilization of the Spiro-OMeTAD radical, enhancing hole collection properties in the PSCs. Consequently, PSC performances involving long-term stability were significantly improved using the OA-TFSI additive. Based on the present results, this study advocates that reconsidering the RTIL design, even when it differs from the current major designs yet is suitable for a target application, can provide functions superior to conventional ones. The insights obtained in this work will spur further study of RTIL designs and aid the development of the broad materials science field including PSCs.

Direct Nanoscale Visualization of the Electric-Field-Induced Aging Dynamics of MAPbI3 Thin Films

Perovskite solar cells represent the most attractive emerging photovoltaic technology, but their practical implementation is limited by solar cell devices' low levels of operational stability. The electric field represents one of the key stress factors leading to the fast degradation of perovskite solar cells. To mitigate this issue, one must gain a deep mechanistic understanding of the perovskite aging pathways associated with the action of the electric field. Since degradation processes are spatially heterogeneous, the behaviors of perovskite films under an applied electric field should be visualized with nanoscale resolution. Herein, we report a direct nanoscale visualization of methylammonium (MA⁺) cation dynamics in methylammonium lead iodide (MAPbI₃) films during field-induced degradation, using infrared scattering-type scanning near-field microscopy (IR s-SNOM). The obtained data reveal that the major aging pathways are related to the anodic oxidation of I^- and the cathodic reduction of MA⁺, which finally result in the depletion of organic species in the channel of the device and the formation of Pb. This conclusion was supported by a set of complementary techniques such as time-of-flight secondary ion mass spectrometry (ToF-SIMS), photoluminescence (PL) microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) microanalysis. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved field-induced degradation dynamics of hybrid perovskite absorbers and the identification of more promising materials resistant to the electric field.

Deposition Kinetics of Thin Silica-Like Coatings in a Large Plasma Reactor

An industrial size plasma reactor of 5 m³ volume was used to study the deposition of silica-like coatings by the plasma-enhanced chemical vapor deposition (PECVD) method. The plasma was sustained by an asymmetrical capacitively coupled radio-frequency discharge at a frequency of 40 kHz and power up to 7 kW. Hexamethyldisilioxane (HMDSO) was introduced continuously at different flows of up to 200 sccm upon pumping with a combination of roots and rotary pumps at an effective pumping speed between 25 and 70 L/s to enable suitable gas residence time in the plasma reactor. The deposition rate and ion density were measured continuously during the plasma process. Both parameters were almost perfectly constant with time, and the deposition rate increased linearly in the range of HMDSO flows from 25 to 160 sccm. The plasma density was of the order of 10¹⁴ m⁻³, indicating an extremely low ionization fraction which decreased with increasing flow from approximately 2 × 10⁻⁷ to 6 × 10⁻⁸. The correlations between the processing parameters and the properties of deposited films are drawn and discussed.

Investigation of psoriasis skin tissue by label-free multi-modal imaging: a case study on a phototherapy-treated patient

Background: Psoriasis is a systemic inflammatory disease characterized by epidermal proliferation in the skin. Altered lipid metabolism is considered to be a central factor in the psoriatic etiopathogenesis. Thus, it is necessary to visualize chemical specificity of the samples for better medical diagnosis and treatment. Here, we investigate its role in the development of psoriatic lesions, before and after ultraviolet phototherapy, in a case study.

Methods: The distribution and morphology of different lipids and fibrous proteins in psoriatic (lesional) tissues were visualized by two complementary label-free imaging techniques: 1) non-linear microscopy (NLM), providing images of lipids/proteins throughout the skin layers at submicrometer resolution; and 2) mass spectrometry imaging (MSI), offering high chemical specificity and hence the detection of different lipid species in the epidermal and dermal regions. A conventional method of histological evaluation was performed on the tissues, with no direct comparison with NLM and MSI.

Results: Psoriatic tissues had a higher lipid content, mainly in cholesterol, in both the epidermal and dermal regions, compared to healthy tissues. Moreover, the collagen and elastin fibers in the psoriatic tissues had a tendency to assemble as larger bundles, while healthy tissues showed smaller fibers more homogeneously spread. Although phototherapy significantly reduced the cholesterol content, it also increased the amounts of collagen in both lesional and non-lesional tissues.

Conclusion: This study introduces NLM and MSI as two complementary techniques which are chemical specific and can be used to assess and visualize the distribution of lipids, collagen, and elastin in a non-invasive and label-free manner.

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