Xingxing Zhang

A second near‐infrared light (NIR II) mediated cancer theranostics based on 2D SnTe@MnO₂‐SP nanosheets (NSs) is developed by coupling ball‐milling, liquid exfoliating, and surface coating. The 2D SnTe@MnO₂‐SP NS platform exhibits multiple promising features including efficient photothermal conversion, multimodal and deep penetrative optical‐imaging in NIR II biowindow, tumor microenvironment–responsive biodegradability, and synergetic antitumor of the metabolite TeO₃ ²⁻.

Abstract

Near infrared light, especially the second near‐infrared light (NIR II) biowindows with deep penetration and high sensitivity are widely used for optical diagnosis and phototherapy. Here, a novel kind of 2D SnTe@MnO₂‐SP nanosheet (NS)‐based nanoplatform is developed for cancer theranostics with NIR II‐mediated precise optical imaging and effective photothermal ablation of mouse xenografted tumors. The 2D SnTe@MnO₂‐SP NSs are fabricated via a facile method combining ball‐milling and liquid exfoliation for synthesis of SnTe NSs, and surface coating MnO₂ shell and soybean phospholipid (SP). The ultrathin SnTe@MnO₂‐SP NSs reveal notably high photothermal conversion efficiency (38.2% in NIR I and 43.9% in NIR II). The SnTe@MnO₂‐SP NSs inherently feature tumor microenvironment (TME)‐responsive biodegradability, and the main metabolite TeO₃ ²⁻ shows great antitumor effect, coupling synergetic chemotherapy for cancer. Moreover, the SnTe@MnO₂‐SP NSs also exhibit great potential for fluorescence, photoacoustic (PA), and photothermal imaging agents in the NIR II biowindow with much higher resolution and sensitivity. This is the first report, as far as is known, with such an inorganic nanoagent setting fluorescence/PA/photothermal imaging and photothermal therapy in NIR II biowindow and TME‐responsive biodegradability rolled into one, which provide insight into the clinical potential for cancer theranostics.

Fundamental studies and technological advancements based on high quality epitaxially grown 2D tellurium are hampered due to strict substrate requirements, which compels to undergo undesirable and time consuming transfer procedures and prevents performing diverse substrate specific studies. Herein, we demonstrate a facile hot-pressing strategy to fabricate high quality sub-10 nm tellurium nanoflakes directly on the substrate of our choice. We further demonstrate that tellurium nanoflakes with thicknesses as low as ~2 nm can be achieved by this strategy. Compared with the peak positions of bulk crystal, peak shifts in Raman spectra for the flakes fabricated on different substrates is an indication of substrate induced strain. The strain-induced band gap variations are probed by the optical studies, which exhibit large photoluminescence from as-prepared tellurium nanoflakes as compared with bulk tellurium. As-prepared nanoflakes further exhibit substrate-dependent structural proper...

We carried out point contact (PC) investigation of WTe 2 single crystals. We measured Yanson PC spectra ( d 2 V / dI 2 ) of the electron–phonon interaction (EPI) in WTe 2 . The PC spectra demonstrate a main phonon peak around 8 meV and a shallow second maximum near 16 meV. Their position is in line with the calculation of the EPI spectra of WTe 2 in the literature, albeit phonons with higher energy are not resolved in our PC spectra. An additional contribution to the spectra is present above the phonon energy, what may be connected with the peculiar electronic band structure and need to be clarified. We detected tiny superconducting features in d 2 V / dI 2 close to zero bias, which broadens by increasing temperature and blurs above 6 K. Thus, (surface) superconductivity may exist in WTe 2 with a topologically nontrivial state. We found a broad maximum in dV

Two-dimensional (2D) layered materials have attracted intensive interests in the past decade. Their unique electronic, magnetic, optical, and mechanical properties render broad applications in various fields. Stability of these ultrathin materials has to be delicately considered because their structures and properties are subject to ambient conditions. In this work, we review the chemical and structural stabilities of versatile 2D layered materials, and summarize the ways to modify the materials for the enhancement of their stabilities. Our review not only provides deep understandings of the stability of 2D materials, but may inspire new ideas to improve the reliability and durability of related devices.

2D van der Waals (vdW) magnets, which present intrinsic ferromagnetic/antiferromagnetic ground states down to atomiclayer thicknesses, open a new horizon in materials science. Recent state‐of‐the‐art characterization and tuning of the magnetic properties of 2D vdW magnets are outlined. Future perspectives and emerging 2D vdW magnets are also discussed, to provide unprecedented opportunities in the fields of spintronics.

Abstract

2D van der Waals (vdW) magnets, which present intrinsic ferromagnetic/antiferromagnetic ground states at finite temperatures down to atomic‐layer thicknesses, open a new horizon in materials science and enable the potential development of new spin‐related applications. The layered structure of vdW magnets facilitates their atomic‐layer cleavability and magnetic anisotropy, which counteracts spin fluctuations, thereby providing an ideal platform for theoretically and experimentally exploring magnetic phase transitions in the 2D limit. With reduced dimensions, the susceptibility of 2D magnets to a large variety of external stimuli also makes them more promising than their bulk counterpart in various device applications. Here, the current status of characterization and tuning of the magnetic properties of 2D vdW magnets, particularly the atomic‐layer thickness, is presented. Various state‐of‐the‐art optical and electrical techniques have been applied to reveal the magnetic states of 2D vdW magnets. Other emerging 2D vdW magnets and future perspectives on the stacking strategy are also given; it is believed that they will excite more intensive research and provide unprecedented opportunities in the field of spintronics.

Few‐layer (2D) intercalation compounds present an attractive pathway to tune the structure, as well as the electronic, optical, and energy‐storage properties near the atomic limit. Recent advances in 2D intercalation are summarized in the historical context of bulk intercalation as well as scaling relationships to motivate research in synthesizing and characterizing 2D materials for optoelectronic and energy‐storage devices.

Abstract

Intercalation in few‐layer (2D) materials is a rapidly growing area of research to develop next‐generation energy‐storage and optoelectronic devices, including batteries, sensors, transistors, and electrically tunable displays. Identifying fundamental differences between intercalation in bulk and 2D materials will play a key role in developing functional devices. Herein, advances in few‐layer intercalation are addressed in the historical context of bulk intercalation. First, synthesis methods and structural properties are discussed, emphasizing electrochemical techniques, the mechanism of intercalation, and the formation of a solid‐electrolyte interphase. To address fundamental differences between bulk and 2D materials, scaling relationships describe how intercalation kinetics, structure, and electronic and optical properties depend on material thickness and lateral dimension. Here, diffusion rates, pseudocapacity, limits of staging, and electronic structure are compared for bulk and 2D materials. Next, the optoelectronic properties are summarized, focusing on charge transfer, conductivity, and electronic structure. For energy devices, opportunities also emerge to design van der Waals heterostructures with high capacities and excellent cycling performance. Initial studies of heterostructured electrodes are compared to state‐of‐the‐art battery materials. Finally, challenges and opportunities are presented for 2D materials in energy and optoelectronic applications, along with promising research directions in synthesis and characterization to engineer 2D materials for superior devices.

Epitaxial growth of large‐area plumbene sheets on the (111) surface of Pd_{(1− x )}Pb _x dilute alloy thin film, using a segregation method, is reported. The alloy surface exhibits a striking structure in large‐scale scanning tunneling microscopy (STM) images, looking like a nanoarchitectonics “WaterCube.” Atomic‐scale STM images clearly show a basically flat honeycomb structure, which covers all the “bubbles,” regardless of their sizes and locations.

Abstract

While theoretical studies predicted the stability and exotic properties of plumbene, the last group‐14 cousin of graphene, its realization has remained a challenging quest. Here, it is shown with compelling evidence that plumbene is epitaxially grown by segregation on a Pd_{1− x} Pb _x (111) alloy surface. In scanning tunneling microscopy (STM), it exhibits a unique surface morphology resembling the famous Weaire–Phelan bubble structure of the Olympic “WaterCube” in Beijing. The “soap bubbles” of this “Nano WaterCube” are adjustable with their average sizes (in‐between 15 and 80 nm) related to the Pb concentration (x < 0.2) dependence of the lattice parameter of the Pd_{1− x} Pb _x (111) alloy surface. Angle‐resolved core‐level measurements demonstrate that a lead sheet overlays the Pd_{1− x} Pb _x (111) alloy. Atomic‐scale STM images of this Pb sheet show a planar honeycomb structure with a unit cell ranging from 0.48 to 0.49 nm corresponding to that of the standalone 2D topological insulator plumbene.

The existence of a fractal‐growth‐based mechanism in 2D‐material chemical vapor deposition (CVD) synthesis is revealed. Based on fractal theory and CVD‐grown mechanisms, a 2D diffusion‐limited aggregation model is built up. Perfect correlations between theoretically simulated data and CVD experimental results are obtained. Precise control of 2D‐material shape and quality is achieved by adjusting single‐domain net growth rates in the CVD‐growth process.

Abstract

The precise control of the shape and quality of 2D materials during chemical vapor deposition (CVD) processes remains a challenging task, due to a lack of understanding of their underlying growth mechanisms. The existence of a fractal‐growth‐based mechanism in the CVD synthesis of several 2D materials is revealed, to which a modified traditional fractal theory is applied in order to build a 2D diffusion‐limited aggregation (2D‐DLA) model based on an atomic‐scale growth mechanism. The strength of this model is validated by the perfect correlation between theoretically simulated data, predicted by 2D‐DLA, and experimental results obtained from the CVD synthesis of graphene, hexagonal boron nitride, and transition metal dichalcogenides. By applying the 2D‐DLA model, it is also discovered that the single‐domain net growth rate (SD‐NGR) plays a crucial factor in governing the shape and quality of 2D‐material crystals. By carefully tuning SD‐NGR, various fractal‐morphology high‐quality single‐crystal 2D materials are synthesized, achieving, for the first time, the precise control of 2D‐material CVD growth. This work lays the theoretical foundation for the precise adjustment of the morphologies and physical properties of 2D materials, which is essential to the use of fractal‐shaped nanomaterials for the fabrication of new‐generation neural‐network nanodevices.