Tuning 2D Magnetism in Cobalt Monoxide Nanosheets Via In Situ Nickel-Doping

Physics of 2D Materials for Developing Smart Devices

Rapid industrialization advancements have grabbed worldwide attention to integrate a very large number of electronic components into a smaller space for performing multifunctional operations. To fulfill the growing computing demand state-of-the-art materials are required for substituting traditional silicon and metal oxide semiconductors frameworks. Two-dimensional (2D) materials have shown their tremendous potential surpassing the limitations of conventional materials for developing smart devices. Despite their ground-breaking progress over the last two decades, systematic studies providing in-depth insights into the exciting physics of 2D materials are still lacking. Therefore, in this review, we discuss the importance of 2D materials in bridging the gap between conventional and advanced technologies due to their distinct statistical and quantum physics. Moreover, the inherent properties of these materials could easily be tailored to meet the specific requirements of smart devices. Hence, we discuss the physics of various 2D materials enabling them to fabricate smart devices. We also shed light on promising opportunities in developing smart devices and identified the formidable challenges that need to be addressed.

Significant enhancement in the magnetic properties of Cr2Te3 nanosheets by atom substitution doping

Ferromagnetic Cr2Te3 nanocrystals, with their high spin-orbit coupling and low symmetry, have attracted considerable attention as rare-earth-free magnetic nanomaterials due to their potential to achieve high magnetic anisotropy. However, their relatively low values of remanence (Mr) and saturation (MS) magnetisation limit their energy product, making them unsuitable for practical applications. Herein, we report a straightforward one-pot heat-injection technique for the synthesis of high-remanence hexagonal Cr2Te3 nanosheets by heterogeneous doping with atoms of M (M = V, Mn and Se). The doped materials provide enhanced Mr and MS at an unchanged Curie temperature (TC), resulting in excellent hard magnetic properties. With Mn doping, the Mr of the matrix increases significantly, reaching 18.38 emu g-1 at 5 K, far exceeding the original undoped Cr2Te3 nanosheets. The nearly square hysteresis loop makes it valuable for many low temperature applications. These results provide a valuable case for tuning the magnetism of ferromagnetic Cr2Te3 by substitutional doping.

Robust Ferrimagnetism and Ferroelectricity in 2D ɛ-Fe2O3 Semiconductor with Ultrahigh Ordering Temperature

2D single-phase multiferroic materials with the coexistence of electric and spin polarization offer a tantalizing potential for high-density multilevel data storage. One of the current limitations for application is the scarcity of the materials, especially those combine ferromagnetism and ferroelectricity at high temperatures. Here, robust ferrimagnetism and ferroelectricity in 2D ɛ-Fe2O3 samples with both single-crystalline and polycrystalline form are demonstrated. Interestingly, the polycrystalline nanosheets also exhibit easily switchable ferroelectric polarizations comparable to that of single crystals. The existence of grain boundary does not hinder the switching and retention of ferroelectric polarization. Furthermore, the ɛ-Fe2O3 nanosheets show ferrimagnetic and ferroelectric Curie temperatures up to 800 K, which reaches record highs in 2D single-phase multiferroic materials. This work provides important progress in the exploration of 2D high-temperature single-phase multiferroics for potentially compact high-temperature information nanodevices.

Van der Waals Epitaxial Growth of Ultrathin Indium Antimonide on Arbitrary Substrates through Low-Thermal Budget

III-V semiconductors possess high mobility, high frequency response, and detection sensitivity, making them potentially attractive for beyond-silicon electronics applications. However, the traditional heteroepitaxy of III-V semiconductors is impeded by a significant lattice mismatch and the necessity for extreme vacuum and high temperature conditions, thereby impeding their in situ compatibility with flexible substrates and silicon-based circuits. In this study, a novel approach is presented for fabricating ultrathin InSb single-crystal nanosheets on arbitrary substrates with a thickness as thin as 2.4 nm using low-thermal-budget van der Waals (vdW) epitaxy through chemical vapor deposition (CVD). In particular, in situ growth has been successfully achieved on both silicon-based substrates and flexible polyimide (PI) substrates. Notably, the growth temperature required for InSb nanosheets (240 °C) is significantly lower than that employed in back-end-of-line processes (400 °C). The field effect transistor devices based on fabricated ultrathin InSb nanosheets exhibit ultra-high on-off ratio exceeding 108 and demonstrate minimal gate leakage currents. Furthermore, these ultrathin InSb nanosheets display p-type characteristics with hole mobilities reaching up to 203 cm2 V-1 s-1 at room temperatures. This study paves the way for achieving heterogeneous integration of III-V semiconductors and facilitating their application in flexible electronics.

Recent Advances of Emerging Metal-Containing Two-Dimensional Nanomaterials in Tumor Theranostics

In recent years, metal-containing two-dimensional (2D) nanomaterials, among various 2D nanomaterials have attracted widespread attention because of their unique physical and chemical properties, especially in the fields of biomedical applications. Firstly, the review provides a brief introduction to two types of metal-containing 2D nanomaterials, based on whether metal species take up the major skeleton of the 2D nanomaterials. After this, the synthetical approaches are summarized, focusing on two strategies similar to other 2D nanomaterials, top-down and bottom-up methods. Then, the performance and evaluation of these 2D nanomaterials when applied to cancer therapy are discussed in detail. The specificity of metal-containing 2D nanomaterials in physics and optics makes them capable of killing cancer cells in a variety of ways, such as photodynamic therapy, photothermal therapy, sonodynamic therapy, chemodynamic therapy and so on. Besides, the integrated platform of diagnosis and treatment and the clinical translatability through metal-containing 2D nanomaterials is also introduced in this review. In the summary and perspective section, advanced rational design, challenges and promising clinical contributions to cancer therapy of these emerging metal-containing 2D nanomaterials are discussed.

Two-Dimensional Oxide Crystals for Device Applications: Challenges and Opportunities

Atomically thin two-dimensional (2D) oxide crystals have garnered considerable attention because of their remarkable physical properties and potential for versatile applications. In recent years, significant advancements have been made in the design, preparation, and application of ultrathin 2D oxides, providing many opportunities for new-generation advanced technologies. This review focuses on the controllable preparation of 2D oxide crystals and their applications in electronic and optoelectronic devices. Based on their bonding nature, the various types of 2D oxide crystals are first summarized, including both layered and nonlayered crystals, as well as their current top-down and bottom-up synthetic approaches. Subsequently, in terms of the unique physical and electrical properties of 2D oxides, recent advances in device applications are emphasized, including photodetectors, field-effect transistors, dielectric layers, magnetic and ferroelectric devices, memories, and gas sensors. Finally, conclusions and future prospects of 2D oxide crystals are presented. It is hoped that this review will provide comprehensive and insightful guidance for the development of 2D oxide crystals and their device applications.

Interface-induced enhanced room temperature ferromagnetism in hybrid transition metal dichalcogenides

Magnetic semiconductors with both electron charge and spin features exhibit tremendous potential in spintronics. Although defective transition-metal dichalcogenides are promising with induced room temperature (RT) magnetic moments, impacts of the defect type and underlying mechanisms remain unclear. Herein, two strategies involving elemental substitution and epitaxial growth have been explored to synthesize alloyed and hybrid MoSe2-xSx with lattice distortion and artificial interfaces respectively. Both experimental measurements and first-principle calculations demonstrate induced magnetism in the resultant MoSe2-xSx with the magnetization intensity closely associated to the atomic structure. The alloyed MoSe2-xSx exhibits satisfactory structural stability and atomic magnetic moments due to the Mo 4d orbital splitting induced by lattice distortion. Nevertheless, both enhanced RT ferromagnetism and thermomagnetic stability can be achieved for the hybrid MoSe2-xSx resulted from stronger localized spin polarization at the MoSe2/MoS2 interfaces. As such the work not only sheds light on the mechanisms underlying defect-induced ferromagnetism in transition-metal dichalcogenides, but also proposes an interface engineering strategy to induce significant ferromagnetism for multi-fields including spintronics, multiferroics and valleytronics.

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.

Controlled Growth and Size-Dependent Magnetic Domain States of 2D γ-Fe2O3

Nonlayered two-dimensional (2D) magnets have attracted special attention, as many of them possess magnetic order above room temperature and enhanced chemical stability compared to most existing vdW magnets, which offers remarkable opportunities for developing compact spintronic devices. However, the growth of these materials is quite challenging due to the inherent three-dimensionally bonded nature, which hampers the study of their magnetism. Here, we demonstrate the controllable growth of air-stable pure γ-Fe2O3 nanoflakes by a confined-vdW epitaxial approach. The lateral size of the nanoflakes could be adjusted from hundreds of nanometers to tens of micrometers by precisely controlling the annealing time. Interestingly, a lateral-size-dependent magnetic domain configuration was observed. As the sizes continuously increase, the magnetic domain evolves from single domain to vortex and finally to multidomain. This work provides guidance for the controllable synthesis of 2D inverse spinel-type crystals and expands the range of magnetic vortex materials into magnetic semiconductors.