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Pyroelectric and photovoltaic effects are vital in cutting-edge broadband sensors and solar energy harvesting. Recent advances revealed great potential of the bulk photovoltaic effect in two-dimensional (2D) materials to surpass the Shockley-Queiseer limit. Moreover, the atomic thickness, high thermal conductivity and room-temperature ferroelectricity endow 2D ferroelectrics with a superior pyroelectric response. Herein, we combined direct pyroelectric-photovoltaic measurements in 2D α-In2Se3. The results reveal a gigantic pyroelectric coefficient of ∼30.7 mC/m2K and a figure of merit of ∼135.9 m2/C. Moreover, a coupled pyroelectric-photovoltaic effect was demonstrated, where the pyroelectric current follows the temperature derivative, while the short-circuit current follows temperature. Finally, we utilized the intercoupled ferroelectricity of In2Se3 to realize a non-volatile, self-powered photovoltaic memory operation, demonstrating stable short-circuit current switching with 103 ON-OFF ratio. The coupled pyroelectric-photovoltaic effect, along with reconfigurable photocurrent, pave the way for a novel integrated thermal and optical response, in-memory logic and energy harvesting. [ABSTRACT FROM AUTHOR]

The increasing interest in realizing the full potential of two-dimensional (2D) layered materials for developing electronic components strongly relies on quantitative understanding of their anisotropic electronic properties. Herein, we use conductive atomic force microscopy to study the anisotropic electrical conductance of multilayer MoS2 by measuring the spreading resistance of circular structures of different radii ranging from 150 to 400 nm. The observed inverse scaling of the spreading resistance with contact radius, with an effective resistivity of ρeff = 2.89 Ω cm, is compatible with a diffusive transport model. A successive etch of the MoS2 nanofilms was used to directly measure the out-of-plane resistivity, i.e., 29.43 ± 7.78 Ω cm. Based on the scaling theory for conduction in anisotropic materials, the model yields an in-plane resistivity of 0.28 ± 0.07 Ω cm and an anisotropy of ∼100 for the ratio between the in-plane and out-of-plane resistivities. The obtained anisotropy indicates that the probed surface area can extend up to 400 times the metal contact area, whereas the penetration depth is limited to roughly 20% of the contact radius. Hence, for contact radius less than 3 nm, the conduction will be limited to the surface. Our investigation offers important insight into the anisotropic transport behavior of MoS2, a pivotal factor enabling the design optimization of miniaturized devices based on 2D materials. [ABSTRACT FROM AUTHOR]

The increasing interest in realizing the full potential of two-dimensional (2D) layered materials for developing electronic components strongly relies on quantitative understanding of their anisotropic electronic properties. Herein, we use conductive atomic force microscopy to study the anisotropic electrical conductance of multilayer MoS2 by measuring the spreading resistance of circular structures of different radii ranging from 150 to 400 nm. The observed inverse scaling of the spreading resistance with contact radius, with an effective resistivity of ρeff = 2.89 Ω cm, is compatible with a diffusive transport model. A successive etch of the MoS2 nanofilms was used to directly measure the out-of-plane resistivity, i.e., 29.43 ± 7.78 Ω cm. Based on the scaling theory for conduction in anisotropic materials, the model yields an in-plane resistivity of 0.28 ± 0.07 Ω cm and an anisotropy of ∼100 for the ratio between the in-plane and out-of-plane resistivities. The obtained anisotropy indicates that the probed surface area can extend up to 400 times the metal contact area, whereas the penetration depth is limited to roughly 20% of the contact radius. Hence, for contact radius less than 3 nm, the conduction will be limited to the surface. Our investigation offers important insight into the anisotropic transport behavior of MoS2, a pivotal factor enabling the design optimization of miniaturized devices based on 2D materials. [ABSTRACT FROM AUTHOR]

It is impossible to imagine modern electronic circuitry without a p–n junction—an essential building block for transistors, rectifiers, amplifiers, photovoltaics, etc. Conventional fabrication processes (ion implantation or chemical diffusion) result in an immutable potential configuration depriving reconfigurability. In contrast, the superior electrostatic tunability, dangling bonds‐ and reconstruction‐free interfaces are some of the key features of 2D based heterostructures, making them promising candidates for cutting‐edge optoelectronic and memory applications. Herein, the intercoupled 2D ferroelectricity of 훼‐In2Se3 is utilized to introduce micron‐scale, non‐volatile electrostatic doping in ambipolar WSe2, enabling reconfigurable p–n junction. The actuation mechanism is based on the strong polarization field along the edge topology of In2Se3. The fabricated device presents stable p–n to n–p switching, a superior rectification ratio of ≈106, and a low leakage current of ≈10−12 A. Furthermore, the switchable short‐circuit current response is utilized to demonstrate a novel self‐powered, non‐volatile memory based on photovoltaic reading. The ferroelectric non‐volatility coupled with the ability to control the device operation using optical and electrical signals paves the way for ultrathin energy‐efficient, multi‐level optoelectronic and in‐memory logic devices. [ABSTRACT FROM AUTHOR]

Stable ferroelectricity at room-temperature down to the monolayer limit, harnessed with strong sensitivity towards visible-to-near-infrared illumination in α-In2Se3, facilitates its potential as versatile building block for developing ultrathin multifunctional photonic integrated networks. Herein, we demonstrated a planar ferroelectric-semiconductor heterojunction (FeS-HJ) field-effect transistor (FET) fabricated out of α-In2Se3 and In2O3, where the ferroelectric-polarization state in α-In2Se3 is utilized to control the device characteristics. The robust in-plane (IP) polarization flipping triggered by out-of-plane (OOP) electrostatic field along with clear anticlockwise hysteresis loop were readily revealed by scanning Kelvin-probe force microscopy (KPFM) and electrical probing. The orthogonally tangled ferroelectric switching was used to manipulate the HJ channel conductance and thereby to realize non-volatile memory (NVM) states. Moreover, gate-tuneable diode-like characteristics and superior photoresponse in HJ compared to its individual constitutes were observed. Utilizing the concurrent ferro-photonic coupling, high bandwidth optical inputs further tailored the outputs into four distinguished current states induced by different polarization directions. Our results pave the way for developing advanced (opto) electronic devices with diverse signal modulation capability to realize next generation low-power neurocomputing, brain-inspired visionary systems, and on-chip optical communications. [ABSTRACT FROM AUTHOR]

Heterostructures based on two-dimensional materials offer the possibility to achieve synergistic functionalities, which otherwise remain secluded by their individual counterparts. Herein, ferroelectric polarization switching in α-In 2 Se 3 has been utilized to engineer multilevel nonvolatile conduction states in a partially overlapping α-In 2 Se 3 -MoS 2 -based ferroelectric semiconducting field effect device. In particular, we demonstrate how the intercoupled ferroelectric nature of α-In 2 Se 3 allows to nonvolatilely switch between n - i and n - i - n type junction configurations based on a novel edge state actuation mechanism, paving the way for subnanometric scale nonvolatile device miniaturization. Furthermore, the induced asymmetric polarization enables enhanced photogenerated carriers' separation, resulting in an extremely high photoresponse of ∼1275 A/W in the visible range and strong nonvolatile modulation of the bright A- and B- excitonic emission channels in the overlaying MoS 2 monolayer. Our results show significant potential to harness the switchable polarization in partially overlapping α-In 2 Se 3 -MoS 2 based FeFETs to engineer multimodal, nonvolatile nanoscale electronic and optoelectronic devices.