Broadband photoresponse arising from photo-bolometric effect in quasi-one-dimensional Ta2Ni3Se8.

In this paper, we report the synthesis of high-quality Ta2Ni3Se8crystals free of noble or toxic elements and the fabrication and testing of photodetectors on the wire samples. A broadband photoresponse from 405 nm to 1550 nm is observed, along with performance parameters including relatively high photoresponsivity (10 mA W-1) and specific detectivity (3.5 × 107Jones) and comparably short response time (τrise= 433 ms,τdecay= 372 ms) for 1064 nm, 0.5 V bias and 1.352 mW mm-2. Through extensive measurement and analysis, it is determined that the dominant mechanism for photocurrent generation is the photo-bolometric effect, which is believed to be responsible for the very broad spectral detection capability. More importantly, the pronounced response to 1310 nm and 1550 nm wavelengths manifests its promising applications in optical communications. Considering the quasi-one-dimensional structure with layered texture, the potential to build nanodevices on Ta2Ni3Se8makes it even more important in future electronic and optoelectronic applications.

Interface effects of Schottky devices built from MoS2and high work function metals.

Schottky junctions, formed by high work function metals and semiconductors, are important devices in electronics and optoelectronics. The metal deposition in traditional Schottky interfaces usually damages the semiconductor surface and causes defect states, which reduces the Schottky barrier height and device performance. This can be avoided in the atomically smooth interface formed by two-dimensional (2D) metals and semiconductors. For better interface tailoring engineering, it is particularly important to understand various interface effects in such 2D Schottky devices under critical or boundary conditions. Here we report the fabrication and testing of three types of MoS2devices, i.e., using PtTe2, Cr and Au as contact materials. While the Cr/MoS2contact is an ohmic contact, the other two are Schottky contacts. The van-der-Waals interface of PtTe2-MoS2results in a well-defined OFF state and a significant rectification ratio of 104. This parameter, together with an ideality factor 2.1, outperforms the device based on evaporated Au. Moreover, a device in the intermediate condition is also presented. An abrupt increase in the reverse current is observed and understood based on the enhanced tunneling current. Our work manifests the essential role of doping concentration and provides another example for 2D Schottky interface design.

Materials and possible mechanisms of extremely large magnetoresistance: a review.

Magnetoresistance (MR) is a characteristic that the resistance of a substance changes with the external magnetic field, reflecting various physical origins and microstructures of the substance. A large MR, namely a huge response to a low external field, has always been a useful functional feature in industrial technology and a core goal pursued by physicists and materials scientists. Conventional large MR materials are mainly manganites, whose colossal MR (CMR) can be as high as -90%. The dominant mechanism is attributed to spin configuration aligned by the external field, which reduces magnetic scattering and thus resistance. In recent years, some new systems have shown an extremely large unsaturated MR (XMR). Unlike ordinary metals, the positive MR of these systems can reach 103%-108% and is persistent under super high magnetic fields. The XMR materials are mainly metals or semimetals, distributed in high-mobility topological or non-topological systems, and some are magnetic, which suggests a wide range of application scenarios. Various mechanisms have been proposed for the potential physical origin of XMR, including electron-hole compensation, steep band, ultrahigh mobility, high residual resistance ratio, topological fermions, etc. It turns out that some mechanisms play a leading role in certain systems, while more are far from clearly defined. In addition, the researches on XMR are largely overlapped or closely correlated with other recently rising physics and materials researches, such as topological matters and two-dimensional (2D) materials, which makes elucidating the mechanism of XMR even more important. Moreover, the disclosed novel properties will lay a broad and solid foundation for the design and development of functional devices. In this review, we will discuss several aspects in the following order: (I) introduction, (II) XMR materials and classification, (III) proposed mechanisms for XMR, (IV) correlation with other systems (featured), and (V) conclusions and outlook.

Wide-spectrum photodetector constructed on a centimeter-scale flexible SnSe2film using a new one-step strategy.

Two-dimensional (2D) materials attached with flexible substrates enable possibilities to apply their superior properties to the rapidly increasing demand for foldable displays and wearable biosensors in the internet-of-things technology. However, previous two-step strategy to construct the flexible devices, namely first obtaining 2D materials elsewhere and then transferring them onto flexible substrates, can cause huge problems, including irreversibly undermining the device performance and limiting the material size. Here we propose a new one-step strategy (other than the liquid phase processing and low temperature synthesis methods), namely directly depositing appropriate 2D materials onto flexible substrates, which involves no transferring and can maintain the crystal quality and properties to the greatest extent. More importantly, this strategy in principle has no limit in the film size, hence removing a main obstacle for the practical use of flexible films, such as complex logic operations and large-area optoelectronic applications. Using this strategy, a centimeter-scale SnSe2film is directly grown on polydimethylsiloxane, which is characterized as a uniform, out-of-plane oriented and semiconducting film that is robust to deformations. Based on the film, a flexible photodetector is fabricated and distinct photoresponse to a broad spectrum of light (405-830 nm) is observed, with remarkable technical parameters.

Topological nature of the node-arc semimetal PtSn4 probed by de Haas-van Alphen quantum oscillations.

Dirac node arc semimetal state is a new topological quantum state which is proposed to exist in PtSn4 (Wu et al 2016 Dirac node arcs in PtSn4 Nat. Phys. 12 667-71). We present a systematic de Haas-van Alphen quantum oscillation study on this compound. Two intriguing oscillation branches, i.e. F 1 and F 2, are detected in the fast Fourier transformation spectra, both of which are characterized to possess tiny effective mass and ultrahigh quantum mobility. And the F 2 branch exhibits an angle-dependent nontrivial Berry phase. The features are consistent with the existence of the node arc semimetal state and shed new light on its complicated Fermi surfaces and topological nature.

Epitaxial thin films of pyrochlore iridate Bi2+xIr2-yO7-δ: structure, defects and transport properties.

While pyrochlore iridate thin films are theoretically predicted to possess a variety of emergent topological properties, experimental verification of these predictions can be obstructed by the challenge in thin film growth. Here we report on the pulsed laser deposition and characterization of thin films of a representative pyrochlore compound Bi2Ir2O7. The films were epitaxially grown on yttria-stabilized zirconia substrates and have lattice constants that are a few percent larger than that of the bulk single crystals. The film composition shows a strong dependence on the oxygen partial pressure. Density-functional-theory calculations indicate the existence of BiIr antisite defects, qualitatively consistent with the high Bi: Ir ratio found in the films. Both Ir and Bi have oxidation states that are lower than their nominal values, suggesting the existence of oxygen deficiency. The iridate thin films show a variety of intriguing transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on temperature, antilocalization corrections to conductance due to spin-orbit interactions, and linear positive magnetoresistance.

Laparoscopic radiofrequency ablation of hepatic cavernous hemangioma. A preliminary experience with 27 patients.

BACKGROUND: Radiofrequency ablation (RFA), currently used extensively for liver tumors, also has been applied successfully to hepatic cavernous hemangioma (HCH) percutaneously. The aim of this study was to assess the feasibility, safety, and efficacy of laparoscopic RFA for patients with HCHs. METHODS: Between March 2001 and March 2004, 27 patients with symptomatic and rapid-growth lesions were treated by laparoscopic RFA using the RF-2000 generator system. The treatment-related complications were observed. All the patients were followed up with helical computed tomography scans and ultrasonography at regular intervals to assess the therapeutic efficacy of laparoscopic RFA. RESULTS: This study assessed 9 men and 18 women with a mean age of 41.6 +/- 8.3 years. Three additional intrahepatic lesions missed preoperatively were found in three patients on intraoperative ultrasound. A total of 27 patients with 50 liver lesions were treated successfully with laparoscopic RFA. The mean maximum tumor diameter was 5.5 +/- 2.0 cm. The mean length of time for RFA per lesion was 20.7 +/- 11.9 min, and the mean blood loss was 134.4 +/- 88.9 ml. Laparoscopic cholecystectomy was performed simultaneously for gallstones in 13 patients and for abutting of gallbladder from hemangioma in 2 patients. In addition, 3 patients also had a laparoscopic deroofing of simple hepatic cysts. Although postoperative low-grade fever and transient elevation of serum transaminase levels were observed in 13 patients, there were no complications related to laparoscopic RFA. During a median follow-up period of 21 months (range, 12-42 months), complete lesion necrosis was achieved for all the patients. CONCLUSIONS: Laparoscopic RFA therapy is a safe, feasible, and effective treatment option for patients with symptomatic and rapid-growth HCHs located on the surface of the liver or adjacent to the gallbladder. Intraoperative ultrasonography is a useful adjunct for detecting additional liver lesions and offering more accurate targeting for RFA.