Janus particles have recently garnered significant attention for their distinct properties compared to particles that are homogeneously functionalized. Moreover, high aspect ratio Janus particles that are rod-like or planar (i.e., nanosheets) are especially intriguing considering their interfacial properties as well as their ability to assemble into higher order and hybrid structures. To date, major challenges facing the exploration and utilization of 2D Janus particles are scalability of synthesis, characterization of tailored chemical functionalization, and ability to introduce a diverse set of functionalities. Herein, a facile method to access Janus 2D graphene oxide (GO) nanosheets by combining a Pickering-type emulsion and grafting-from polymerization via ATRP is reported. Janus GO nanosheets bearing PMMA on one face as well as the symmetrically functionalized analogue are prepared, and the chemical, thermal, structural, surface, and interfacial properties of these materials are characterized. Time-of-flight secondary ion mass spectrometry coupled with Langmuir-Blodgett films is shown to be an ideal route to conclusively establish asymmetric functionalization of 2D materials. This work not only provides a facile route for the preparation of Janus nanosheets but also demonstrates the direct visualization of polymer grown from the surface of GO.

In this work, we discovered a very efficient method of crystallization of thermally evaporated rubrene, resulting in ultrathin, large-area, fully connected, and highly crystalline thin films of this organic semiconductor with a grain size of up to 500 μm and charge carrier mobility of up to 3.5 cm2 V–1 s–1. We found that it is critical to use a 5 nm-thick organic underlayer on which a thin film of amorphous rubrene is evaporated and then annealed to dramatically influence the ability of rubrene to crystallize. The underlayer property that controls this influence is the glass transition temperature. By experimenting with different underlayers with glass transition temperatures varying over 120 °C, we identified the molecules leading to the best crystallinity of rubrene films and explained why values both above and below the optimum result in poor crystallinity. We discuss the formation of different crystalline morphologies of rubrene produced by this method and show that field-effect transistors made with films of a single-domain platelet morphology, achieved through the aid of the optimal underlayer, outperform their spherulite counterparts with a nearly four times higher charge carrier mobility. This large-area crystallization technique overcomes the fabrication bottleneck of high-mobility rubrene thin film transistors and other related devices and, given its scalability and patternability, may lead to practical technologies compatible with large-area flexible electronics.

Since CH3NH3PbI3 perovskites are discovered as a viable active material for next‐generation photovoltaic devices, their instability in humid environments is a constant challenge. Therefore, understanding the exact spatially resolved degradation process is a crucial need before being able to improve the stability and durability of these exceptional materials. In this work, it is demonstrated that the CH3NH3PbI3 perovskite will eventually degrade irreversibly at high humidity through a slow leaching and vaporization process of CH3NH2. Deuterium oxide (D2O) is used as a humidity source instead of H2O to distinguish the exogenous water diffusing into the perovskite from moisture embedded during sample fabrication. The degradation process of CH3NH3PbI3 perovskite is examined in situ by using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and an argon ion cluster beam for layer‐by‐layer in situ sputtering and then compared to their corresponding solar cell performances. 3D images are constructed from the layer‐by‐layer spatially resolved elemental distribution analysis and the D2O moisture penetration through the sample. It is observed that the H/D exchange on the organic methylammonium ion is the first indication for moisture uptake in a given volume element. The intermediate products of interaction with moisture are also analyzed by ToF‐SIMS and X‐ray photoelectron spectroscopy. The initial products of this deuterium exchange reaction are CH3NH2D, CH3NHD2, and CH3ND3. In the following, the D2O molecule stepwise replaces the methylammonium, which leads to evaporation of the organic molecules and eventually to erosion of the perovskite along with drastic changes in morphology, crystallography, and photovoltaic performance.

A simple-prepare, single-use and cost-effective, in vitro biosensor for the detection of TAR DNA-binding protein 43 (TDP-43), a biomarker of neuro-degenerative disorders, was designed, manufactured and tested. This study reports the first biosensor application for the detection of TDP-43 using a novel biosensor fabrication methodology. Bioconjugation mechanism was applied by conjugating anti-TDP 43 with N-succinimidyl S-acetylthioacetate (SATA) producing a thiol-linked anti-TDP 43, which was used to directly link with gold electrode surface, minimizing the preparation steps for biosensor fabrication and simplifying the biosensor surface. The effectiveness of this bioconjugation mechanism was evaluated and confirmed by FqRRM12 protein, using nuclear magnetic resonance (NMR). The surface coverage of the electrode was analyzed by Time-of-Flight-Secondary Ion Mass Spectrometry (TOF-SIMS). Differential pulse voltammetry (DPV) was acted as the detection transduction mechanism with the use of [Fe(CN)6]3−/4-redox probe. Human TDP-43 peptide of 0.0005 μg/mL to 2 μg/mL in undiluted human serum was analyzed using this TDP-43 biosensor. Interference study of the TDP-43 biosensor using β-amyloid 42 protein and T-tau protein confirmed the specifity this TDP-43 biosensor. This bioconjugation chemistry based approach for biosensor fabrication circumvents tedious gold surface modification and functionalization while enabling specific detection of TDP-43 in less than 1 hr with a low fabrication cost of a single biosensor less than $3.

The smooth surface of crystalline rubrene films formed through an abrupt heating process provides a valuable platform to study organic homoepitaxy. By varying growth rate and substrate temperature, we are able to manipulate the onset of a transition from layer-by-layer to island growth modes, while the crystalline thin films maintain a remarkably smooth surface (less than 2.3 nm root-mean-square roughness) even with thick (80 nm) adlayers. We also uncover evidence of point and line defect formation in these films, indicating that homoepitaxy under our conditions is not at equilibrium or strain-free. Point defects that are resolved as screw dislocations can be eliminated under closer-to-equilibrium conditions, whereas we are not able to eliminate the formation of line defects within our experimental constraints at adlayer thicknesses above ∼25 nm. We are, however, able to eliminate these line defects by growing on a bulk single crystal of rubrene, indicating that the line defects are a result of strain built into the thin film template. We utilize electron backscatter diffraction, which is a first for organics, to investigate the origin of these line defects and find that they preferentially occur parallel to the (002) plane, which is in agreement with expectations based on calculated surface energies of various rubrene crystal facets. By combining the benefits of crystallinity, low surface roughness, and thickness-tunability, this system provides an important study of attributes valuable to high-performance organic electronic devices.