In this paper, we report the optoelectronic properties of multi-layered GeS nanosheet (∼28 nm thick)-based field-effect transistors (called GeS-FETs). The multi-layered GeS-FETs exhibit remarkably high photoresponsivity of Rλ ∼ 206 A W(-1) under 1.5 μW cm(-2) illumination at λ = 633 nm, Vg = 0 V, and Vds = 10 V. The obtained Rλ ∼ 206 A W(-1) is excellent as compared with a GeS nanoribbon-based and the other family members of group IV-VI-based photodetectors in the layered-materials realm, such as GeSe and SnS2. The gate-dependent photoresponsivity of GeS-FETs was further measured to be able to reach Rλ ∼ 655 A W(-1) operated at Vg = -80 V. Moreover, the multi-layered GeS photodetector holds high external quantum efficiency (EQE ∼ 4.0 × 10(4)%) and specific detectivity (D* ∼ 2.35 × 10(13) Jones). The measured D* is comparable to those of the advanced commercial Si- and InGaAs-based photodiodes. The GeS photodetector also shows an excellent long-term photoswitching stability over a long period of operation (>1 h). These extraordinary properties of high photocurrent generation, broad spectral range, and long-term stability make the GeS-FET photodetector a highly qualified candidate for future optoelectronic applications.

Starburst triarylamines 2 and 3 were electropolymerized to form electrochromic thin films. Film from 2 showed intense absorption at 372 nm before voltage was applied. There were two absorption bands at 496 nm and 1000-2000 nm at 0.3 V, and a broad band, which peaked at 807 nm at 0.6 V. Film from 3 showed intense absorption at 372 nm before voltage was applied. There were two absorption bands at 498 nm and 1000-2000 nm at 0.3 V, and a broad band, which peaked at 890 nm at 0.7 V. The switching time studies revealed that thin film from 2 would require 3 s at 0.46 V for switching absorbance at 1600 nm and 1 s for bleaching. It would also require 4 s at 0.66 V for coloration at 800 nm and 2 s for bleaching. On the other hand, thin film from 3 would require 3 s at 0.46 V for switching absorbance at 1500 nm and 1 s for bleaching. It would also require 3.3 s at 0.76 V for switching absorbance at 900 nm and 1.5 s for bleaching. Electropolymerized thin films of 2 and 3 were also used as the surface modification layers to modify the surface of ITO for polymeric light emitting diode (PLED). To evaluate the performance of the modification layer, we selected a device of ITO/modification layer/PVK-Alq 3 -coumarin 6/metal electrode as the standard for comparison. We discovered that co-electropolymerization of the triarylamines 2 or 3 with poly(vinylcarbazole) (PVK) on ITO greatly reduces the turn-on voltage of the PLED devices and their performance is comparable to that of the commercially available PEDOT.

UV Raman scattering studies show longitudinal optical (LO) mode up to fourth order in wurtzite GaN nanowire system. Fröhlich interaction of electron with the long range electrostatic field of ionic bonded GaN gives rise to enhancement in LO phonon modes. Good crystalline quality, as indicated by the crystallographic as well as luminescence studies, is thought to be responsible for this significant observation. Calculated size dependence, incorporating size corrected dielectric constants, of electron-phonon interaction energy agrees well with measured values and also predict stronger interaction energy than that of the bulk for diameter below ∼3nm.