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Recently, emerging two-dimensional (2D) germanium selenide (GeSe) has drawn lots of attention due to its in-plane anisotropic properties and great potential for optoelectronic applications such as in solar cells. However, methods are still sought to enhance its interaction with light to enable practical applications. Herein, we numerically investigate the localized plasmon response of monolayer GeSe nanoribbon arrays systematically, and the results show that localized surface plasmon polaritons in the far-infrared range with anisotropic behavior can be efficiently excited to enhance the light-matter interaction. We further show that the plasmon response of monolayer GeSe nanoribbons could be tuned effectively through the nanoribbon width, local refractive index, substrate thickness and carrier concentration, pointing out the ways for controlling the localized plasmon response. In the case of monolayer GeSe nanoribbons on a substrate of finite thickness, a Fabry-Pérot-like (FP-like) quantitative model has been proposed to explain the overall spectral response originating from overlapped FP and plasmon modes, and it matches well with the simulation results. All in all, we investigate the plasmon response of the novel 2D GeSe nanoribbons thoroughly for the first time, bringing opportunities for potential applications of novel polarization-dependent optoelectronic devices.

Nonlinear plasmons are becoming an appealing and intriguing research area due to their remarkable light concentration and manipulation abilities. In this work, the nonlinear absorption (NLA) phenomena of polarized nanoantenna arrays coupled with the low dimensional topological insulator Bi2Se3 are studied at different excitation wavelengths. Our experimental results indicate that a significant enhancement in the linear absorption coefficient is achieved by localized surface plasmon (LSP) resonance, with enhancement factors that are 10- and 8-fold in magnitude for the cases of 800 nm (y polarization) and 970 nm (x polarization), respectively. Moreover, by polarization sensitive studies under 800 nm laser excitation, this new Bi2Se3-Au nanoantenna hybrid-structure exhibits adverse absorption responses of enhancement and suppression compared to pure Bi2Se3 film, providing excellent potential for applications in information converters. In particular, under 800 nm pump light (10 GW cm-2), the transmittance intensity of 450 nm or 1064 nm continuous wave (CW) probe light alters back and forth when the polarization direction changes by 90°. Thus, "ON" and "OFF" modes of this Bi2Se3-Au nanoantenna hybrid structure-based switch are achieved by using 450 nm and 1064 nm light, respectively, with a corresponding modulation depth of 3.4% and 21.9%, which can be applied in versatile photonic devices.

Broadband, ultrafast and scalable topological insulator Sb2Te3/STO heterostructure photovoltaic detectors were fabricated by molecular beam epitaxy.

Topological insulators (TIs) are new states of quantum matter in which the spin-momentum-locked surface states reside in the bulk insulating gap and have triggered extensive investigations on fundamental properties and potential applications. Herein, we report scalable, broadband photovoltaic detectors based on the topological insulator Sb2Te3/strontium titanate (STO) heterostructure. Large-scale (2 mm × 5 mm), high crystalline quality p-type Sb2Te3 films were fabricated on an n-type STO substrate by the molecular beam epitaxy (MBE) method. The Sb2Te3/STO heterostructures exhibited pronounced photovoltaic behavior in a wide range of temperatures as a result of a strong built-in field at the hetero-interface. Superior performances of broadband (from visible to infrared, 405 nm–1550 nm) and ultrafast (rise time ∼30 μs, fall time ∼95 μs) photoresponses were achieved under ambient conditions. The prominent repeatability and stability indicated that our photodetectors can operate effectively in harsh circumstances. These results show that stacking the topological insulator thin films on a strongly correlated oxide substrate using the MBE approach holds great promise for high performance optoelectronic applications.

A series of donor–acceptor (D–A) polymers based on furan-bridged benzodithiophene and different acceptor blocks were designed and synthesized. By incorporating various acceptors with differing electron-withdrawing abilities into the same polymer backbone, we were seeking to reveal the correlation between molecular structures and the corresponding film morphology as well as photovoltaic performance. The experimental results and theoretical calculations indicate that the selection of acceptor units has significant impacts on the polymer energy levels and backbone coplanarity, leading to differing intermolecular packing. By using atomic force microscopy and transmission electron microscopy, we also observed that the size and topology of the alkyl-chains on acceptors can tune the polymer solubility and result in different film morphology. As a result of optimized morphology, we demonstrated power conversion efficiencies over 5% for the new polymer based devices, which are among the highest efficiencies of reported furan bridged D–A polymers.