Lattice-Matched Metal-Semiconductor Heterointerface in Monolayer Cu2Te

Effects of strain and thickness on the mechanical, electronic, and optical properties of Cu2Te

Two-dimensional transition-metal chalcogenides (TMCs) have attracted considerable attention because of their exceptional photoelectric properties, finding applications in diverse fields such as photovoltaics, lithium-ion batteries, catalysis, and energy conversion and storage. Recently, experimentally fabricated monolayers of semiconducting Cu2Te have emerged as intriguing materials with outstanding thermal and photoelectric characteristics. In this study, we employ first-principles calculations to investigate the mechanical, electronic, and optical properties of monolayer Cu2Te exhibiting both λ and ζ structures, considering the effects of thickness and strain. The calculations reveal the robust mechanical stability of λ-Cu2Te and ζ-Cu2Te under varying thickness and strain conditions. By applying -5% to +5% strain, the band gaps can be modulated, with ζ-Cu2Te exhibiting an indirect-to-direct transition at a biaxial strain of +5%. In addition, a semiconductor-to-metal transition is observed for both ζ-Cu2Te and λ-Cu2Te with increasing thickness. The absorption spectra of λ-Cu2Te and ζ-Cu2Te exhibit a redshift with an increase in the number of layers. These computational insights into Cu2Te provide valuable information for potential applications in nano-electromechanical systems, optoelectronics, and photocatalytic devices and may guide subsequent experimental research efforts.

Advances of Zn Metal-Free "Rocking-Chair"-Type Zinc Ion Batteries: Recent Developments and Future Perspectives

Aqueous zinc ion battery (AZIBs) has attracted the attention of many researchers because of its safety, economy, environmental protection, and high ionic conductivity of electrolytes. However, the battery greatly suffers from zinc dendrite produced by zinc metal anode leading to poor cycle life and even unsafe problems, which limit its further development for various important applications. It is known that the success of the commercialization of lithium-ion batteries (LIBs) is mainly due to replacement of lithium metal anode with graphite, which avoids the formation of Li dendrite. Therefore, it is an important step to develop aqueous zinc ion anode to replace conventional zinc metal one with zinc-metal free anode material. In this review, the working principle and development prospect of "rocking-chair" AZIBs are introduced. The research progress of different types of zinc metal-free anode materials and cathode materials in "rocking-chair" AZIBs is reviewed. Finally, the limitations and challenges of the Zn metal-free "rocking-chair" AZIBs as well as solutions are deeply discussed, aiming to provide new strategies for the development of advanced zinc-ion batteries.

Engineering Atomic-Scale Patterning and Resistive Switching in 2D Crystals and Application in Image Processing

The ultrathin thickness of 2D layered materials affords the control of their properties through defects, surface modification, and electrostatic fields more efficiently compared with bulk architecture. In particular, patterning design, such as moiré superlattice patterns and spatially periodic dielectric structures, are demonstrated to possess the ability to precisely control the local atomic and electronic environment at large scale, thus providing extra degrees of freedom to realize tailored material properties and device functionality. Here, the scalable atomic-scale patterning in superionic cuprous telluride by using the bonding difference at nonequivalent copper sites is reported. Moreover, benefitting from the natural coupling of ordered and disordered sublattices, controllable piezoelectricity-like multilevel switching and bipolar switching with the designed crystal structure and electrical contact is realized, and their application in image enhancement is demonstrated. This work extends the known classes of patternable crystals and atomic switching devices, and ushers in a frontier for image processing with memristors.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

A Fast-Response Ultraviolet Phototransistor with a PVK QDs/ZnO Nanowire Heterostructure and Its Application in Pharmaceutical Solute Detection

The sensitivity and photoelectric noise of UV photodetectors are challenges that need to be overcome in pharmaceutical solute detection applications. This paper presents a new device concept for a CsPbBr3 QDs/ZnO nanowire heterojunction structure for phototransistors. The lattice match of the CsPbBr3 QDs and ZnO nanowire reduces the generation of trap centers and avoids carrier absorption by the composite center, which greatly improves the carrier mobility and high detectivity (8.13 × 10¹⁴ Jones). It is worth noting that by using high-efficiency PVK quantum dots as the intrinsic sensing core, the device has a high responsivity (6381 A/W) and responsivity frequency (300 Hz). Thus, a UV detection system for pharmaceutical solute detection is demonstrated, and the type of solute in the chemical solution is estimated by the waveform and the size of the output 2f signals.

Scalable Edge-Oriented Metallic Two-Dimensional Layered Cu2Te Arrays for Electrocatalytic CO2 Methanation

Copper-based nanomaterials are compelling for high-efficient, low-cost electrocatalytic CO₂ reduction reaction (CO₂RR) due to their exotic electronic and structural properties. However, controllable preparation of copper-based two-dimensional (2D) materials with abundant catalytically active sites, that guarantee high CO₂RR performance, remains challenging, especially on a large scale. Here, an in situ vertical growth of scalable metallic 2D Cu₂Te nanosheet arrays on commercial copper foils is demonstrated for efficient CO₂-to-CH₄ electrocatalysis. The edge-oriented growth of Cu₂Te nanosheets with tunable sizes and thicknesses is facilely attained by a two-step process of chemical etching and chemical vapor deposition. These active sites abounding on highly exposed edges of Cu₂Te nanosheets greatly promote the electroreduction of CO₂ into CH₄ at a potential as low as -0.4 V (versus the reversible hydrogen electrode), while suppressing hydrogen evolution reaction. When a flow cell is employed to accelerate the mass transfer, the faradaic efficiency reaches ∼63% at an applied current density of 300 mA cm^-2. These findings will provide great possibilities for developing scalable, energy-efficient Cu-based CO₂RR electrocatalysts.

Understanding Micro and Atomic Structures of Secondary Phases in Cu-Doped SnTe

Highly efficient thermoelectric materials require, including point defects within the host matrix, secondary phases generating positive effects on lowering lattice thermal conductivity (κ_L ). Amongst effective dopants for a functional thermoelectric material, SnTe, Cu doping realizes the ultra-low κ_L approaching the SnTe amorphous limit. Such effective κ_L reduction is first attributed to strong phonon scattering by substitutional Cu atoms at Sn sites and interstitial defects in the host SnTe. However, other crystallographic defects in secondary phases have been unfocused. Here, this work reports micro- to atomic-scale characterization on secondary phases of Cu-doped SnTe using advanced microscopes. It is found that Cu-rich secondary phases begin precipitation ≈1.7 at% Cu (x = 0.034 where Sn_{1- x} Cu_x Te). The Cu-rich secondary phases encapsulate two distinct solids: Cu₂ SnTe₃ ( F 4 ¯ 3 m $F\bar{4}3m$ ) has semi-coherent interfaces with SnTe ( F m 3 ¯ m $Fm\bar{3}{\rm{m}}$ ) such that they minimize lattice mismatch to favor the thermoelectric transport; the other resembles a stoichiometric Cu₂ Te model, yet is so meta-stable that it demonstrates not only various defects such as dislocation cores and ordered/disordered Cu vacancies, but also dynamic grain-boundary migration with heating and a subsequent phase transition ≈350 °C. The atomic-scale analysis on the Cu-rich secondary phases offers viable strategies for reducing κ_L through Cu addition to SnTe.

High-Performance Memristors Based on Ultrathin 2D Copper Chalcogenides

Copper chalcogenides represent a class of materials with unique crystal structures, high electrical conductivity, and earth abundance, and are recognized as promising candidates for next-generation green electronics. However, their 2D structures and the corresponding electronic properties have rarely been touched. Herein, a series of ultrathin copper chalcogenide nanosheets with thicknesses down to two unit cells are successfully synthesized, including layered Cu₂ Te, as well as nonlayered CuSe and Cu₉ S₅ , via van der Waals epitaxy, and their nonvolatile memristive behavior is investigated for the first time. Benefiting from the highly active Cu ions with low migration barriers, the memristors based on ultrathin 2D copper chalcogenide crystals exhibit relatively small switching voltage (≈0.4 V), fast switching speed, high switching uniformity, and wide operating temperature range (from 80 to 420 K), as well as stable retention and good cyclic endurance. These results demonstrate their tangible applications in future low-power, cryogenic, and high temperature harsh electronics.

Achieving Ultralow Lattice Thermal Conductivity and High Thermoelectric Performance in GeTe Alloys via Introducing Cu2Te Nanocrystals and Resonant Level Doping

The binary compound of GeTe emerging as a potential medium-temperature thermoelectric material has drawn a great deal of attention. Here, we achieve ultralow lattice thermal conductivity and high thermoelectric performance in In and a heavy content of Cu codoped GeTe thermoelectrics. In dopants improve the density of state near the surface of Femi of GeTe by introducing resonant levels, producing a sharp increase of the Seebeck coefficient. In and Cu codoping not only optimizes carrier concentration but also substantially increases carrier mobility to a high value of 87 cm² V^-1 s^-1 due to the diminution of Ge vacancies. The enhanced Seebeck coefficient coupled with dramatically enhanced carrier mobility results in significant enhancement of PF in Ge_1.04-x-yIn_xCu_yTe series. Moreover, we introduce Cu₂Te nanocrystals' secondary phase into GeTe by alloying a heavy content of Cu. Cu₂Te nanocrystals and a high density of dislocations cause strong phonon scattering, significantly diminishing lattice thermal conductivity. The lattice thermal conductivity reduced as low as 0.31 W m^-1 K^-1 at 823 K, which is not only lower than the amorphous limit of GeTe but also competitive with those of thermoelectric materials with strong lattice anharmonicity or complex crystal structures. Consequently, a high ZT of 2.0 was achieved for Ge_0.9In_0.015Cu_0.125Te by decoupling electron and phonon transport of GeTe. This work highlights the importance of phonon engineering in advancing high-performance GeTe thermoelectrics.