Defects as a factor limiting carrier mobility in WSe2： A spectroscopic investigation

The electrical performance of two-dimensional transition metal dichalcogenides （TMDs） is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe2 devices. Low-temperature photoluminescence （PL） spectra of electron-beam-lithography- processed WSe2 exhibit a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an electron-beam-free transfer-electrode technique, we successfully prepared a backgated WSe2 device containing a limited amount of defects. A maximum hole mobility of approximately 200 cm2.V -1.s-1 was achieved because of the reduced scattering sources, which is the highest reported value for this type of device. This work provides not only a versatile and nondestructive method to monitor the defects in TMDs but also a new route to approach the room-temperature phonon-limited mobility in high-performance TMD devices.

Interfacial amplification for graphene-based position-sensitive-detectors

Position-sensitive-detectors(PSDs)based on lateral photoeffect have been widely used in diverse applications1–9,including optical engineering,aerospace and military fields.With increasing demand in long distance,low energy consumption,and weak signal sensing systems,the poor responsivity of conventional PSDs has become a bottleneck limiting their applications,for example,silicon p–n or p–i–n junctions2–5,or other materials and architectures6–10.Herein,we present a high-performance graphene-based PSDs with revolutionary interfacial amplification mechanism.Signal amplification in the order of~10^(4) has been demonstrated by utilizing the ultrahigh mobility of graphene and long lifetime of photo-induced carriers at the interface of SiO_(2)/Si.This would improve the detection limit of Si-based PSDs fromμW to nW level,without sacrificing the spatial resolution and response speed.Such interfacial amplification mechanism is compatible with current Si technology and can be easily extended to other sensing systems11,12.

The oscillatory damped behavior of double wall carbon nanotube oscillators in gaseous environment

The mechanical oscillatory behaviors of multiwall carbon nanotube oscillators in gaseous environment are investigated using the molecular dynamics method. The effects of ambient gas and temperature on intertube frictional force and oscillation frequency are analyzed. It is found that the intertube frictional force increases with the ambient gas density and temperature. Higher gas density and higher tem- perature cause a more rapid decay in the oscillation amplitude and an increase of the oscillation fre- quency. Compared to the vacuum environmental condition, the collision between gas atoms and the nanotube walls is a main ingredient leading to the increase of the energy dissipation. Gas damping may be the main reason for the failure of carbon nanotube oscillators working in gas environment. The am- bient temperature also has an important effect on oscillations and low temperature is advantageous to sustain oscillations.