Selective Excitation of Exciton-Polariton Condensate Modes in an Annular Perovskite Microcavity.

Exciton-polariton systems composed of a light-matter quasi-particle with a light effective mass easily realize Bose-Einstein condensation. In this work, we constructed an annular trap in a halide perovskite semiconductor microcavity and observed the spontaneous formation of symmetrical petal-shaped exciton-polariton condensation in the annular trap at room temperature. In our study, we found that the number of petals of the petal-shaped exciton-polariton condensates, which is decided by the orbital angular momentum, is dependent on the light intensity distribution. Therefore, the selective excitation of perovskite microcavity exciton-polariton condensates under all-optical control can be realized by adjusting the light intensity distribution. This could pave the way to room-temperature topological devices, optical cryptographical devices, and new quantum gyroscopes in the exciton-polariton system.

Modulated Structure and Rectification Properties of a Molecular Junction by a Mixed Self-Assembled Monolayer.

The organization of the self-assembled monolayer (SAM) determines its electronic structure and so governs the charge transport process and device performance when adopted into a molecular device. We report a systematic study on the supramolecular structure and rectification performance of the ferrocene (11-ferrocenyl-1-undecanethiol, FUT) based SAM modulated by mixed SAM with inert 1-undecanethiol (C11SH) as diluent. We compared mixed SAMs by two different post assembly strategies, i.e., post assembly of C11SH on FUT SAM and post assembly of FUT on C11SH SAM. The organization and structure of FUT in the mixed SAM were extensively studied by cyclic voltammetry (CV) using the Laviron model. Rectification properties of the mixed SAM obtained using eutectic indium gallium (EGaIn) as the top electrode revealed that the magnitude and stability of the rectification ratio (RR) strongly correlated to not only the amount but also the phase structure and orientation of the FUT in the monolayer, resulting in a tunable RR and increased stability. The mixed monolayer achieved an increased performance relative to pure FUT by post assembling FUT on C11SH SAM, which formed an optimally dense and well-packed monolayer with the FUT head resting on the top of the alkane SAM.

Systematic Modulation of Charge Transport in Molecular Devices through Facile Control of Molecule-Electrode Coupling Using a Double Self-Assembled Monolayer Nanowire Junction.

We report a novel solid-state molecular device structure based on double self-assembled monolayers (D-SAM) incorporated into the suspended nanowire architecture to form a "Au|SAM-1||SAM-2|Au" junction. Using commercially available thiol molecules that are devoid of synthetic difficulty, we constructed a "Au|S-(CH2)6-ferrocene||SAM-2|Au" junction with various lengths and chemical structures of SAM-2 to tune the coupling between the ferrocene conductive molecular orbital and electrode of the junction. Combining low noise and a wide temperature range measurement, we demonstrated systematically modulated conduction depending on the length and chemical nature of SAM-2. Meanwhile, the transport mechanism transition from tunneling to hopping and the intermediate state accompanied by the current fluctuation due to the coexistence of the hopping and tunneling transport channels were observed. Considering the versatility of this solid-state D-SAM in modulating the electrode-molecule interface and electroactive groups, this strategy thus provides a novel facile strategy for tailorable nanoscale charge transport studies and functional molecular devices.

Construction of Large-Area Ultrathin Conductive Metal-Organic Framework Films through Vapor-Induced Conversion.

On account of unique characteristics, the integration of metal-organic frameworks as active materials in electronic devices attracts more and more attention. The film thickness, uniformity, area, and roughness are all fatal factors limiting the development of electrical and optoelectronic applications. However, research focused on ultrathin free-standing films is in its infancy. Herein, a new method, vapor-induced method, is designed to construct centimeter-sized Ni3 (HITP)2 films with well-controlled thickness (7, 40, and 92 nm) and conductivity (0.85, 2.23, and 22.83 S m-1 ). Further, traditional transfer methods are tactfully applied to metal-organic graphene analogue (MOGA) films. In order to maintain the integrity of films, substrates are raised up from bottom of water to hold up films. The stripping method greatly improves the surface roughness Rq (root mean square roughness) without loss of conductivity and endows the film with excellent elasticity and flexibility. After 1000 buckling cycles, the conductance shows no obvious decrease. Therefore, the work may open up a new avenue for flexible electronic and magnetic devices based on MOGA.

Tunable oligo-histidine self-assembled monolayer junction and charge transport by a pH modulated assembly.

Histidine works as an important mediator in the charge transport process through proteins via its conjugate side group. It can also stabilize a peptide's secondary structure through hydrogen bonding of the imidazole group. In this study, the conformation of the self-assembled monolayer (SAM) and the charge transport of the tailor-made oligopeptide hepta-histidine derivative (7-His) were modulated through the pH control of the assembly environment. Histidine is found to be an efficient tunneling mediator in monolayer junctions with an attenuation factor of ß = ∼0.5 Å-1. Successful theoretical model fitting indicates a linear increase in the number of tunneling sites as the 7-His SAM thickness increases, following the deprotonation of histidine. Combined with the ultraviolet photoelectron spectroscopy (UPS) measurements, a modulable charge transport pathway through 7-His with imidazole groups of histidine as tunneling foot stones is revealed. Histidine therefore possesses a large potential for modulable functional (bio)electronic devices.

Molecular cocrystals: design, charge-transfer and optoelectronic functionality.

Organic cocrystals, formed by a combination of electron-rich donors and electron-poor acceptors, play an important role in tailoring the optoelectronic properties of molecular materials. Charge transfer interactions in cocrystals not only endow them with an ordered three-dimensional (3D) supramolecular network in different constituent units, but also render them ideal scaffolds to control the intermolecular interactions in multicomponent solids. In this perspective, we firstly introduce preparation methods, molecular packing modes and charge transfer in organic cocrystals. Then, we focus on the novel and promising optoelectronic properties of organic cocrystals based on charge transfer interactions. Finally, we briefly discuss the outlook for the future development of these multicomponent crystalline materials.

Prediction of gap asymmetry in differential micro accelerometers.

Gap asymmetry in differential capacitors is the primary source of the zero bias output of force-balanced micro accelerometers. It is also used to evaluate the applicability of differential structures in MEMS manufacturing. Therefore, determining the asymmetry level has considerable significance for the design of MEMS devices. This paper proposes an experimental-theoretical method for predicting gap asymmetry in differential sensing capacitors of micro accelerometers. The method involves three processes: first, bi-directional measurement, which can sharply reduce the influence of the feedback circuit on bias output, is proposed. Experiments are then carried out on a centrifuge to obtain the input and output data of an accelerometer. Second, the analytical input-output relationship of the accelerometer with gap asymmetry and circuit error is theoretically derived. Finally, the prediction methodology combines the measurement results and analytical derivation to identify the asymmetric error of 30 accelerometers fabricated by DRIE. Results indicate that the level of asymmetry induced by fabrication uncertainty is about ±5 × 10(-2), and that the absolute error is about ±0.2 µm under a 4 µm gap.

A Robust Nonvolatile Resistive Memory Device Based on a Freestanding Ultrathin 2D Imine Polymer Film.

Here, the synthesis of a wafer-scale ultrathin 2D imine polymer (2DP) film with controllable thickness from simple benzene-1,3,5-tricarbaldehyde (BTA) and p-phenylenediamine (PDA) building blocks is reported using a Schiff base polycondensation reaction at the air-water interface. The synthesized freestanding 2DP films are porous, insulating, and more importantly, covalently linked, which is ideally suited for nonvolatile memristors that use a conductive filament mechanism. These devices exhibit excellent switching performance with high reliability and reproducibility, with on/off ratios in the range of 102 to 105 depending on the thickness of the film. In addition, the endurance and data retention capability of 2DP-based nonvolatile resistive memristors are up to 200 cycles and 8 × 104 s under constant voltage stress at 0.1 V. The intrinsic flexibility of the covalent organic polymer enables the fabrication of a flexible memory device on a polyimide film, which exhibits as reliable memory performance as that on the rigid substrate. Moreover, the 2DP-based memory device shows outstanding thermal stability and organic solvent resistance, which are desirable properties for applications in wearable devices.

Low-Voltage Organic Single-Crystal Field-Effect Transistor with Steep Subthreshold Slope.

Anodization is a promising technique to form high- k dielectrics for low-power organic field-effect transistor (OFET) applications. However, the surface quality of the dielectric, which is mainly inherited from the metal electrode, can be improved further than other fabrication techniques, such as sol-gel. In this study, we applied the template stripping method to fabricate a low-power single-crystalline OFET based on the anodized AlO x dielectric. We found that the template stripping method largely improves the surface roughness of the deposited Al and allows for the formation of a high-quality AlO x high- k dielectric by anodization. The ultraflat AlO x/SAM dielectric combined with a single-crystal 2,6-diphenylanthracene (DPA) semiconductor produced a nearly defect-free interface with a steep subthreshold swing (SS) of 66 mV/decade. The current device is a promising candidate for future ultralow-power applications. Other than metal deposition, template stripping could provide a general approach to improve thin-film quality for many other types of materials and processes.

Temperature- and Component-Dependent Degradation of Perovskite Photovoltaic Materials under Concentrated Sunlight.

We report on accelerated degradation testing of MAPbX3 films (X = I or Br) by exposure to concentrated sunlight of 100 suns and show that the evolution of light absorption and the corresponding structural modifications are dependent on the type of halide ion and the exposure temperature. One hour of such exposure provides a photon dose equivalent to that of one sun exposure for 100 hours. The degradation in absorption of MAPbI3 films after exposure to 100 suns for 60 min at elevated sample temperature (∼45-55 °C), due to decomposition of the hybrid perovskite material, is documented. No degradation was observed after exposure to the same sunlight concentration but at a lower sample temperature (∼25 °C). No photobleaching or decomposition of MAPbBr3 films was observed after exposure to similar stress conditions (light intensity, dose, and temperatures). Our results indicate that the degradation is highly dependent on the hybrid perovskite composition and can be light- and thermally enhanced.