huangpanqi

npj 2D Materials and Applications, Published online: 24 May 2022; doi:10.1038/s41699-022-00310-y

This article reports the epitaxial growth of lead-free 2D Cs₃Cu₂I₅ perovskites, where the strong blue emission with a large Stocks shift and long (microsecond) lifetime is attributed to a radiative transition of self-trapped excitons. The Cs₃Cu₂I₅ photodetector reveals a high responsivity of 3.78 A W^–1 (270 nm, 5 V) with a fast characteristic (τ_rise/τ_decay ≈ 163/203 ms), outperforming congeneric UV sensors.

Abstract

The all-inorganic lead-free Cu-based halide perovskites represented by the Cs−Cu−I system, have sparked extensive interest recently due to their impressive photophysical characteristics. However, successive works on their potential application in light emission diodes and photodetectors rely on tiny polycrystals, in which the grain boundaries and defects may lead to the performance degradation of their embodied devices. Here, 2D all-inorganic perovskite Cs₃Cu₂I₅ single crystals are epitaxially grown on mica substrates, with a thickness down to 10 nm. The strong blue emission of the Cs₃Cu₂I₅ flakes may originate from the radiative transition of self-trapped excitons associated with a large Stocks shift and long (microsecond) decay time. Ultravioelt (UV) photodetectors based on individual Cs₃Cu₂I₅ nanosheets are fabricated via a swift and etching-free dry transfer approach, which reveal a high responsivity of 3.78 A W^–1 (270 nm, 5 V bias), as well as a fast response speed (τ_rise ≈163 ms, τ_decay ≈203 ms), outperforming congeneric UV sensors based on other 2D metal halide perovskites. This work therefore sheds light on the fabrication of green optoelectronic devices based on lead-free 2D perovskites, vital for the sustainable development of photoelectric technology.

Taking advantages of miniaturization and integrability, all-dielectric TiO₂ metalenses are designed based on Fresnel diffraction effect and integrated with molybdenum ditelluride (MoTe₂) photodetectors. Owing to the enhancement of photon utilization efficiency, the corresponding integrated devices exhibit a high responsivity and detectivity of 135.0 A W^{− 1} and 4.05 × 10¹² Jones, respectively. These results accelerate the evolution of metalenses in 2D optoelectronics fields.

Abstract

Atomic layers of group-VI 2D transition metal dichalcogenides (TMDCs) with substantial materials system and unique physicochemical properties have exhibited excellent performances in electronics and optoelectronics. However, photodetectors based on TMDCs suffer from poor sensitivity and optical absorption due to the weak phonon conversion efficiency and optical absorption due to their atomically thin feature. Here, taking advantages of miniaturization and integrability, all-dielectric TiO₂ metalenses are designed based on the Fresnel diffraction effect and integrated with molybdenum ditelluride (MoTe₂) photodetectors. Owing to the enhancement of photon utilization efficiency, the corresponding integrated devices exhibit a high responsivity of 135.0 A W^–1, an excellent external quantum efficiency of 202.0%, and a specific detectivity of ≈4.05 × 10¹² Jones. These results indicate that the optoelectrical properties of 2D materials can be significantly optimized by integration with metalens and will accelerate the evolution of metalens in 2D optoelectronics fields.

An electrically and optically switchable logic operation encryption based on the photoluminescence (PL) ratio of ZnTe is developed. Two PL emissions can be selectively regulated by the electric and optical fields due to different responses of band-edge emission and defect emission. This work provides a design for the creation of logic operation encryption and holds great promise for high-security encryption.

Abstract

Logic operation encryption is emerging as a novel cryptographic mode, protecting logic operation from being attacked and tampered, and is a modern extension of conventional encryption system. However, the existing encryption methods are not conducive to the logic operation encryption due to the complexity, signal mode, and non-adjustability of their design. Herein, an advanced logic operation encryption method is designed via the photoluminescence ratio of ZnTe, and the electrically and optically switchable NAND (Not AND) and NOR (Not OR) encryption based on this method is implemented. Two photoluminescence emissions can be selectively regulated by the gate voltage and excitation laser based on the different responses of band-edge emission and defect emission. This novel approach will shed light on the development of high-security encryption and computer information protection.

This work reports the programmable information encryption by 2D van der Waals rare-earth material ErOCl based on the editable electric-tunable photoluminescence (PL). The correct information encoded in PL outputs can be tactfully decrypted from the PL intensity ratio of two thermal coupling transitions (²H_11/2–⁴I_15/2 and ⁴S_3/2–⁴I_15/2), which has been applied to ASCII codes and images encryption with high-security.

Abstract

High-security encryption has always been important in economic and military fields as well as in daily life. 2D van der Waals (vdW) rare-earth (RE) materials have advantages in photoluminescence (PL) modulation to achieve high-security encryption because of their multiple sharp emission peaks, which will facilitate the multimode regulation for high-security encryption of programmable information. Here, programmable information encryption has been achieved by applying 2D vdW ErOCl via the editable electric-tunable PL. The correct information encoded in PL outputs can be tactfully decrypted from the PL intensity ratio of ²H_11/2–⁴I_15/2 and ⁴S_3/2–⁴I_15/2 transitions. This strategy for ASCII codes and images encryption with high-security is demonstrated. This novel approach, PL modulation of 2D vdW RE material based on programmable electric inputs, will mark a new path to achieve high-security encryption.

Nature Electronics, Published online: 30 May 2022; doi:10.1038/s41928-022-00766-2

Nanopatterning bridges the microstructure of 2D materials and integrated chip devices, essentially enabling and prompting their successful application in industry. A critical summary on the recent development of key nanopatterning technologies of 2D materials, with the aim of realizing large-scale device integration, is provided. This contribution offers a pioneering reference and guidelines to promote 2D materials from laboratory research to practical use.

Abstract

With the reduction of feature size and increase of integration density, traditional 3D semiconductors are unable to meet the future requirements of chip integration. The current semiconductor fabrication technologies are approaching their physical limits based on Moore's law. 2D materials such as graphene, transitional metal dichalcogenides, etc., are of great promise for future memory, logic, and photonic devices due to their unique and excellent properties. To prompt 2D materials and devices from the laboratory research stage to the industrial integrated circuit-level, it is necessary to develop advanced nanopatterning methods to obtain high-quality, wafer-scale, and patterned 2D products. Herein, the recent development of nanopatterning technologies, particularly toward realizing large-scale practical application of 2D materials is reviewed. Based on the technological progress, the unique requirement and advances of the 2D integration process for logic, memory, and optoelectronic devices are further summarized. Finally, the opportunities and challenges of nanopatterning technologies of 2D materials for future integrated chip devices are prospected.

Nature, Published online: 04 May 2022; doi:10.1038/s41586-022-04514-6

Nature, Published online: 04 May 2022; doi:10.1038/s41586-022-04523-5

Inspired by the structure of cell membranes, including aquaporins for fast water transport and hydrophilic polymers for fouling resistance, a membrane is fabricated by assembling chitosan-modified graphene nanomesh. This cell membrane-inspired functionalized graphene nanomesh membrane is endowed with high water-permeance and superior antifouling when separating surfactant-stabilized oil-in-water emulsions.

Abstract

Graphene exhibits fascinating prospects for preparing high-performance membranes with fast water transport, due to its low friction with water and extreme thinness. However, for graphene-assembled membranes, each molecule passing through the membrane should bypass many graphene sheets, which lengthens the molecular pathways and increases the mass transfer resistance. Herein, a graphene nanomesh (GNM) membrane is fabricated that is inspired by cell membranes, including aquaporins with their hydrophilic gate for selective transport and hydrophobic channel for low friction with water, thus resulting in fast water transport, as well as hydrophilic polymer brushes on the membrane surface for fouling resistance. GNM is synthesized by etching nanopores on graphene oxide (GO) nanosheets to significantly shorten the water transport channels, whereas the hydrophobic graphene sheets lead to low water friction; in combination, ultra-fast, selective water flux is achieved. Also, hydrophilic polymer chitosan is utilized to modify GNM to construct a hydration layer, which suppresses foulants from touching the membrane surface. Accordingly, the permeance of the cell membrane-inspired graphene nanomesh membrane reaches almost 4000 L m^–2 h^–1 bar^–1, which is about 260 times the permeance in a GO membrane, and the membranes show superior antifouling properties for separating various surfactant-stabilized oil-in-water emulsions.

Recent advances in emerging 2D-material-based integrated memory devices are reviewed in terms of working principles, device architectures, array integration, and specific brain-inspired applications. Future challenges and promising research lines toward reliable, practical neuromorphic computing chips are highlighted.

Abstract

With the advent of the Internet of Things and big data, massive data must be rapidly processed and stored within a short timeframe. This imposes stringent requirements on memory hardware implementation in terms of operation speed, energy consumption, and integration density. To fulfill these demands, 2D materials, which are excellent electronic building blocks, provide numerous possibilities for developing advanced memory device arrays with high performance, smart computing architectures, and desirable downscaling. Over the past few years, 2D-material-based memory-device arrays with different working mechanisms, including defects, filaments, charges, ferroelectricity, and spins, have been increasingly developed. These arrays can be used to implement brain-inspired computing or sensing with extraordinary performance, architectures, and functionalities. Here, recent research into integrated, state-of-the-art memory devices made from 2D materials, as well as their implications for brain-inspired computing are surveyed. The existing challenges at the array level are discussed, and the scope for future research is presented.

Huge achievements have been made in graphene chemical vapor deposition (CVD) growth. This review systematical summarizes the current progresses in four research directions, including theoretical study of graphene CVD growth, direct growth on insulating substrates, low temperature growth, layer number, and stacking-angle controlled growth. Finally, the future research directions of graphene are discussed.

Abstract

Graphene, since the first successful exfoliation of graphite, has continuously attracted attention due to its remarkable properties and applications. Recently, the research focus on graphene synthesis has been directed to the controllable synthesis of large-area and high-quality graphene. In the last decade, there has been great progress in the chemical vapor deposition (CVD) growth of graphene. Theoretical investigations have led to an enhanced understanding of puzzles on hydrocarbon species stability, key reaction pathways, the role of hydrogen gas, the morphology of graphene islands, and the alignment of graphene on substrates. Experimentally, high-quality graphene is epitaxially grown on both insulating and metal substrates. Progress has also been reported on low-temperature graphene growth and on controlling the thickness and stacking of graphene layers. In this review, the authors summarize the previous theoretical and experimental studies on graphene CVD growth and discuss the future challenges on the growth of graphene i) on insulating substrates, ii) at low temperature, iii) with controllable thickness, and iv) with selected stacking twist angles. The authors assert that the key to the continuous advancement of graphene growth is the synergy of experimental and theoretical investigations.

Contrast nonlinear Edelstein magnetization responses in different ferroelectric In₂Se₃ bilayer stacking patterns are demonstrated. The largely tunable electronic band structure of In₂Se₃ bilayers provides a fascinating semiconducting platform for exploring the interplay among spintronics, orbitronics, nonlinear optics, and ferroelectrics in a single platform.

Abstract

Magnetization generation and accumulation in intrinsically nonmagnetic materials is one of the key routes to various exotic applications, especially realizing fast information storage and memory devices. Among the various approaches for magnetization injection, light irradiation is advantageous for its noncontacting and non-invasive nature, and has been receiving great attention during the past few decades. In the current work, a quadratic response theory and first-principles calculations are applied to reveal photoinduced magnetization in recently discovered 2D In₂Se₃ bilayers. The ferroelectric In₂Se₃ bilayers can be (meta-) stabilized in versatile stacking patterns, exhibiting largely tunable electronic band structure, and optical feature. Hence, it is suggested that under circularly polarized light illumination, the system can show different photoinduced magnetization responses with large contrast in different stacking patterns. The magnetizations are composed by both spin and orbital angular momentum contributions, which can reach as large as 1μ_B under a laser with intermediate intensity (≈10⁹ W cm^–2). This magnitude can be easily observed and furthermore manipulated in the state-of-the-art experimental techniques. The proposal suggests a candidate material platform to explore the interplay among spintronics, orbitronics, nonlinear optics, and ferroelectrics in a single platform.

This manuscript reports dynamic, unclonable cryptographic primitives based on plasmonic fluorescence blinking that can generate a large number of temporally varying codes in a single device—a key requirement toward their applications in modern anti-counterfeiting and communication systems. It opens a new field of investigation into dynamic encryption and provides new insight for future anti-counterfeiting research.

Abstract

Merging cryptographic primitive technologies and physical unclonable functions (PUFs) have become a new paradigm of one-way encryption. Herein, the authors report a dynamic PUF cryptographic primitive based on plasmonic fluorescence blinking from single or a few dye molecules embedded within the nanogaps of plasmonic patch nanoantennas. This cryptographic primitive carries two sets of high-capacity optical codes: the fluorescence blinking of the embedded dye molecules and multi-color light scattering enabled by the plasmonic nanoantennas. The former allows the generation of temporal binary codes from a large number of individual plasmonic patch nanoantennas by holding either “1” (bright state) or “0” (dark state), while the latter provides a permanent color-based novenary code that acts as a decryption channel for authentication. Benefiting from the high electromagnetic field localized within the nanogaps and the large Purcell enhancement of the plasmonic nanoantennas, the fluorescence blinking is readily detectable by a common fluorescence microscope with a mercury arc lamp as a low-power excitation source. The developed dynamic PUF codes are robustly and accurately authenticated by a self-programmed computer vision algorithm. This study revolutionizes the conventional static PUF encryption to nanophotonics-based dynamic encryption, opening a new avenue for next-generation advanced anti-counterfeiting.

D. Yagodkin, K. Greben, A. Eljarrat, S. Kovalchuk, M. Ghorbani-Asl, M. Jain, S. Kretschmer, N. Severin, J. P. Rabe, A. V. Krasheninnikov, C. T. Koch, K. I. Bolotin

A new excitonic state is observed in 2D semiconductors after electron beam functionalization. The state is bright, has a very narrow photoluminescence peak at cryogenic temperatures, and survives up to room temperature. It is shown that this state is not related to intrinsic defects in transition metal dichalcogenides but is associated with molecules on the surface of the material.

A new localized excitonic state is demonstrated in patterned monolayer 2D semiconductors. The signature of an exciton associated with that state is observed in the photoluminescence spectrum after electron beam exposure of several 2D semiconductors. The localized state, which is distinguished by non-linear power dependence, survives up to room temperature and is patternable down to 20 nm resolution. The response of the new exciton to the changes of electron beam energy, nanomechanical cleaning, and encapsulation via multiple microscopic, spectroscopic, and computational techniques is probed. All these approaches suggest that the state does not originate from irradiation-induced structural defects or spatially non-uniform strain, as commonly assumed. Instead, it is shown to be of extrinsic origin, likely a charge transfer exciton associated with the organic substance deposited onto the 2D semiconductor. By demonstrating that structural defects are not required for the formation of localized excitons, this work opens new possibilities for further understanding of localized excitons as well as their use in applications that are sensitive to the presence of defects, e.g. chemical sensing and quantum technologies.