Inverse photoresponse is discovered from phototransistors based on molybdenum disulfide (MoS ). The devices are capable of detecting photons with energy below the bandgap of MoS . Under the illumination of near-infrared (NIR) light at 980 and 1550 nm, negative photoresponses with short response time (50 ms) are observed for the first time. Upon visible-light illumination, the phototransistors exhibit positive photoresponse with ultrahigh responsivity on the order of 10 -10 A W owing to the photogating effect and charge trapping mechanism. Besides, the phototransistors can detect a weak visible-light signal with effective optical power as low as 17 picowatts (pW). A thermally induced photoresponse mechanism, the bolometric effect, is proposed as the cause of the negative photocurrent in the NIR regime. The thermal energy of the NIR radiation is transferred to the MoS crystal lattice, inducing lattice heating and resistance increase. This model is experimentally confirmed by low-temperature electrical measurements. The bolometric coefficient calculated from the measured transport current change with temperature is -33 nA K . These findings offer a new approach to develop sub-bandgap photodetectors and other novel optoelectronic devices based on 2D layered materials.

We report a study of enhancing the magnetic ordering in a model magnetically doped topological insulator (TI), Bi(2-x)Cr(x)Se(3), via the proximity effect using a high-TC ferrimagnetic insulator Y(3)Fe(5)O(12). The FMI provides the TI with a source of exchange interaction yet without removing the nontrivial surface state. By performing the elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally observed an enhanced TC of 50 K in this magnetically doped TI/FMI heterostructure. We have also found a larger (6.6 nm at 30 K) but faster decreasing (by 80% from 30 to 50 K) penetration depth compared to that of diluted ferromagnetic semiconductors (DMSs), which could indicate a novel mechanism for the interaction between FMIs and the nontrivial TIs surface.

Electronics based on solution-processable materials are promising for applications in many fields which stimulated enormous research interest in liquid-drying and pattern formation. However, assembling of structure with submicrometre/nanometre resolution through liquid process is very challenging. We show a simple method to rapidly generate polymer structures with deep-submicrometre-sized features over large areas. In this method, a solution film is dried on a substrate under a suspended flexible template with groove/ridge surface topography. Upon solvent evaporation, the solution splits in the grooves and forms capillary bridges between the template and substrate, which are firmly pinned by the edges of the template grooves. This groove pinning stabilizes the contact lines, thereby allowing the formation of fine patterned structures with high aspect ratios which were used to fabricate various functional materials and electronic devices. We also produced secondary self-assembled nano-stripe patterns with resolutions of about 50 nm on the primary lines.

Heterojunction based on two-dimensional (2D) layered materials is an emerging topic in the field of nanoelectronics and optoelectronics. Here, molybdenum sulfide (MoS)-based Schottky diodes were fabricated using the field-effect transistor configuration with asymmetric metal contact structure. Gold and chromium electrodes were employed as drain and source electrodes to form Ohmic and Schottky contact with MoS, respectively. The devices exhibited electrical rectifying characteristic with the current rectifying ratio exceeding 10 and an ideal factor of 1.5. A physics model of the band diagram was proposed to analyze the gate-tunable rectifying behavior of the device. The dynamic rectification based on the diode circuit was further realized with the operating frequency up to 100 Hz. The devices were also demonstrated to show different sensitivities to the light under external biases in the opposite directions, with the highest photoresponsivity reaching 1.1 × 10 A/W and specific detectivity up to 8.3 × 10 Jones at a forward drain bias of 10 V. This kind of 2D material-based Schottky diodes have the advantage of simplicity in design and fabrication, as well as superior electrical rectifying and photosensing characteristics, which have great potential for future integrated electronic and optoelectronic applications.

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