Hongliang Chen

Covalently bonded single-molecule junctions with stable and reversible photoswitched conductivity

Stable molecular switches Many single-molecule current switches have been reported, but most show poor stability because of weak contacts to metal electrodes. Jia et al. covalently bonded a diarylethene molecule to graphene electrodes and achieved stable photoswitching at room temperature (see the Perspective by Frisbie). The incorporation of short bridging alkyl chains between the molecule and graphene decoupled their pielectron systems and allowed fast conversion of the open and closed ring states. Science, this issue p. 1443; see also p. 1394 Stable molecular conduction junctions were formed by covalently bonding single diarylethenes to graphene electrodes. Through molecular engineering, single diarylethenes were covalently sandwiched between graphene electrodes to form stable molecular conduction junctions. Our experimental and theoretical studies of these junctions consistently show and interpret reversible conductance photoswitching at room temperature and stochastic switching between different conductive states at low temperature at a single-molecule level. We demonstrate a fully reversible, two-mode, single-molecule electrical switch with unprecedented levels of accuracy (on/off ratio of ~100), stability (over a year), and reproducibility (46 devices with more than 100 cycles for photoswitching and ~105 to 106 cycles for stochastic switching).

Solution-processable, low-voltage, and high-performance monolayer field-effect transistors with aqueous stability and high sensitivity.

Low-voltage, low-cost, high-performance monolayer field-effect transistors are demonstrated, which comprise a densely packed, long-range ordered monolayer spin-coated from core-cladding liquid-crystalline pentathiophenes and a solution-processed high-k HfO2 -based nanoscale gate dielectric. These monolayer field-effect transistors are light-sensitive and are able to function as reporters to convert analyte binding events into electrical signals with ultrahigh sensitivity (≈10 ppb).

Solution‐Crystallized Organic Semiconductors with High Carrier Mobility and Air Stability

Molecular engineering and chemical self-assembly are combined with materials fabrication to achieve air-stable solution-processable oligothiophene-based field-effect transistors with mobilities up to 6.2 cm(2) V-1 s(-1), which ranks as the highest among oliogthiophene- based semiconducting materials.

Interface‐Engineered Bistable [2]Rotaxane‐Graphene Hybrids with Logic Capabilities

The use of high-quality graphene as a local probe in combination with photo excitation helps to establish a deep mechanistic understanding of charge generation/quenching processes under lying the graphene/environment interface. By combining a non-destructive bottom-up assembly technique with sensitive graphene-based transistors, a bistable [2]rotaxane-graphene hybrid device, which exhibits a symmetric mirror-image photoswitching effect with logic capabilities, is produced.

Interface-modulated approach toward multilevel metal oxide nanotubes for lithium-ion batteries and oxygen reduction reaction

Metal oxide hollow structures with multilevel interiors are of great interest for potential applications such as catalysis, chemical sensing, drug delivery, and energy storage. However, the controlled synthesis of multilevel nanotubes remains a great challenge. Here we develop a facile interface-modulated approach toward the synthesis of complex metal oxide multilevel nanotubes with tunable interior structures through electrospinning followed by controlled heat treatment. This versatile strategy can be effectively applied to fabricate wire-in-tube and tube-in-tube nanotubes of various metal oxides. These multilevel nanotubes possess a large specific surface area, fast mass transport, good strain accommodation, and high packing density, which are advantageous for lithium-ion batteries (LIBs) and the oxygen reduction reaction (ORR). Specifically, shrinkable CoMn2O4 tube-in-tube nanotubes as a lithium-ion battery anode deliver a high discharge capacity of ~565 mAh·g−1 at a high rate of 2 A·g−1, maintaining 89% of the latter after 500 cycles. Further, as an oxygen reduction reaction catalyst, these nanotubes also exhibit excellent stability with about 92% current retention after 30,000 s, which is higher than that of commercial Pt/C (81%). Therefore, this feasible method may push the rapid development of one-dimensional (1D) nanomaterials. These multifunctional nanotubes have great potential in many frontier fields.

Design of a Photoactive Hybrid Bilayer Dielectric for Flexible Nonvolatile Organic Memory Transistors

Organic field-effect transistors (OFETs) featuring a photoactive hybrid bilayer dielectric (PHBD) that comprises a self-assembled monolayer (SAM) of photochromic diarylethenes (DAEs) and an ultrathin solution-processed hafnium oxide layer are described here. We photoengineer the energy levels of DAE SAMs to facilitate the charging and discharging of the interface of the two dielectrics, thus yielding an OFET that functions as a nonvolatile memory device. The transistors use light signals for programming and electrical signals for erasing (≤3 V) to produce a large, reversible threshold-voltage shift with long retention times and good nondestructive signal processing ability. The memory effect can be exercised by more than 10(4) memory cycles. Furthermore, these memory cells have demonstrated the capacity to be arrayed into a photosensor matrix on flexible plastic substrates to detect the spatial distribution of a confined light and then store the analog sensor input as a two-dimensional image with high precision over a long period of time.

High-Efficiency Selective Electron Tunnelling in a Heterostructure Photovoltaic Diode

A heterostructure photovoltaic diode featuring an all-solid-state TiO2/graphene/dye ternary interface with high-efficiency photogenerated charge separation/transport is described here. Light absorption is accomplished by dye molecules deposited on the outside surface of graphene as photoreceptors to produce photoexcited electron-hole pairs. Unlike conventional photovoltaic conversion, in this heterostructure both photoexcited electrons and holes tunnel along the same direction into graphene, but only electrons display efficient ballistic transport toward the TiO2 transport layer, thus leading to effective photon-to-electricity conversion. On the basis of this ipsilateral selective electron tunnelling (ISET) mechanism, a model monolayer photovoltaic device (PVD) possessing a TiO2/graphene/acridine orange ternary interface showed ∼86.8% interfacial separation/collection efficiency, which guaranteed an ultrahigh absorbed photon-to-current efficiency (APCE, ∼80%). Such an ISET-based PVD may become a fundamental device architecture for photovoltaic solar cells, photoelectric detectors, and other novel optoelectronic applications with obvious advantages, such as high efficiency, easy fabrication, scalability, and universal availability of cost-effective materials.

Photocontrol of charge injection/extraction at electrode/semiconductor interfaces for high-photoresponsivity organic transistors

Charge injection typically occurring at the electrode/semiconductor interface in organic field-effect transistors (OFETs) is of great importance to the device performance and stability. Therefore, the chemical modulation of electrode/semiconductor heterojunctions provides a promising approach to enhance the performance and even incorporate new functionalities. In this study, we develop an efficient route for constructing optically switchable OFETs featuring a photochromic spirothiopyran (SP) self-assembled monolayer (SAM)-functionalized electrode/semiconductor interface. The photoisomerization of SPs induces a reversible change in the dipole moment of SP-SAMs, which affects the work function of gold electrodes. This change in the electrode work function enables the tuning of the contact resistance between organic semiconductors and metal electrodes. Consequently, the channel conductance of these devices is modulated in a nondestructive manner, thus leading to a new type of cost-effective OFET-based photodetector with high photosensitivity. These results help us to better understand interfacial phenomena and offer novel insights into developing a new generation of multifunctional interfaces and ultrasensitive OFET-based sensors by interface engineering.

The shift of the magnetic transition temperature in perovskite manganese oxides caused by magnetostriction

Abstract Magnetization, thermal expansion and resistance measurements were performed on the perovskite manganese La 2/3 Ca 1/3 MnO 3 and (Nd 0.6 Th 0.4 ) 2/3 Sr 1/3 MnO 3 . The results indicate that spontaneous magnetostriction through spin–lattice coupling leads to anomalous thermal expansion and lattice striction. For La 2/3 Ca 1/3 MnO 3 , the temperature corresponding to the maximum of resistance and Curie temperature shifts to higher temperature under an applied field. As for (Nd 0.6 Tb 0.4 ) 2/3 Sr 1/3 MnO 3 , the temperature corresponding to the maximum of resistance shifts up to higher temperature with the applied field, but the paramagnetic Curie temperature does not. We suggest that the shift of the magnetic transition temperature in perovskite manganese oxides due to the spontaneous magnetostriction and forced magnetostriction.