No abstract

Graphene based photo-detecting has received great attentions and the performance of such detector is stretching to both ends of high sensitivity and ultra-fast response. However, limited by the current photo-gating mechanism, the price for achieving ultra-high sensitivity is sacrificing the response time. Detecting weak signal within short response time is crucial especially in applications such as optical positioning, remote sensing, and biomedical imaging. In this work, we bridge the gap between ultra-fast response and ultra-high sensitivity by employing a graphene/SiO 2 /lightly-doped-Si architecture with revolutionary interfacial gating mechanism. Such device is capable to detect < 1 nW signal (with responsivity of ~1000 A W -1 ) and the spectral response extends from visible to near-infrared. More importantly, the photoresponse time of our device has been pushed to ~400 ns. The current device structure does not need complicated fabrication process and is fully compatible with the silicon technology. This work will not only open up a route to graphene-based high performance optoelectronic devices, but also have great potential in ultra-fast weak signal detection.

The thermal stability in air of graphene synthesized by either chemical vapor deposition or mechanical cleavage is studied. It is found that single layer graphene prepared by both methods starts to show defects at ~500 °C, indicated by the appearance of a disorder‐induced Raman D peak. The defects are initially sp3 type and become vacancy like at higher temperature. On the other hand, bilayer graphene shows better thermal stability, and the D peak appears at ~600 °C. These results are quite different from those annealing in vacuum and controlled atmosphere. Raman images show that the defects in chemical vapor deposition graphene are not homogeneous, whereas those in mechanical cleavage graphene are uniformly distributed across the whole sample. The factors that affect the thermal stability of graphene are discussed. Our results could be important for guiding the future electronics process and chemical decoration of graphene. Copyright © 2013 John Wiley & Sons, Ltd.

The optical emission efficiency of two dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameter that affects their optoelectronic performance.Optimization of growth parameters of chemical vapor deposition (CVD) to achieve optoelectronics-grade quality TMDs is therefore highly desirable. Here, we present a systematic photoluminescence (PL) spectroscopic approach to assess the intrinsic optical and crystalline quality of CVD grown MoS 2 . We suggest that the intensity ratio between PL measured in air and vacuum could be used as an effective way to monitor the intrinsic optical quality of CVD MoS 2 .Low temperature PL measurements are also used to evaluate the structural defects in MoS 2 by defect-associated bound exciton emission, which is well correlated with the field effect carrier mobilities of MoS 2 grown at different temperatures. This work therefore provides a sensitive, noninvasive method to characterize the optical properties of TMDs, allow tuning of growth parameters for the development of optoelectronic devices.

A new perovskite-like inorganic-organic hybrid compound [Et(n-Pr)P][Cd(dca)] (1) (where [Et(n-Pr)P] is the propyltriethylphosphonium cation and dca is a dicyanamide ligand) was discovered to undergo three reversible phase transitions at 270 K (T), 386 K (T), and 415 K (T), respectively. The variable-temperature single-crystal X-ray structural analyses reveal that these sequential phase transitions originate from the deformations of the [Cd(dca)] frameworks and the concomitant reorientations of the [Et(n-Pr)P] guest cations. It is found that 1 possesses a sensitive nonlinear optical (NLO) switching at T with a large contrast of ∼40 within a narrow temperature range of ∼7 K. Furthermore, 1 shows intriguing photoluminescence (PL) property, and the PL intensity suffers a plunge near T. The multiple phase transitions, switchable NLO and tunable luminescent properties simultaneously exist in this inorganic-organic perovskite-like hybrid compound, suggesting its great potential application in molecular switches and photoelectric field.