2D Core/Shell-Structured Mesoporous Silicene@Silica for Targeted and Synergistic NIR-II-Induced Photothermal Ablation and Hypoxia-Activated Chemotherapy of Tumors

Silicene nanosheets, the emerging 2D nanomaterial, as the third topology of silicon-composed materials with distinct physicochemical properties, is a desirable candidate for photothermal-conversion nanoagent (PTA) and drug-delivery nanosystems. Inspired by the individual physiochemical properties and structure features of mesoporous silica and 2D silicene, a distinctive 2D core/shell-structured multifunctional silicon-composed theranostic nanoplatform (Silicene@Silica) is constructed by coating a mesoporous silica layer onto the surface of 2D silicene nanosheets. The well-defined mesopores originating from mesoporous silica shell provide the reservoirs for guest drug molecules and the core of silicene produces heat shock upon NIR-II laser irradiation, aiming to induce the synergistic cancer-therapeutic modality. Importantly, when AQ4N, hypoxia-activated prodrug, is introduced into this system, this nanoplatform (Silicene@Silica–AQ4N) exhibits tumor microenvironment (TME)-responsive and synergistic hyperthermia-augmented therapeutic bioactivity. Such a nanoplatform can amplify the hypoxia of TME by destroying the tumor microcirculation and then further efficiently activate AQ4N, a DNA affinity agent and topoisomerase II inhibitor. The results reveal that this multifunctional theranostic nanoplatform can efficiently eliminate tumors without recurrence.     

Recent Advances in Twisted Structures of Flatland Materials and Crafting Moiré Superlattices

The past decade has witnessed the occurrence of novel 2D moiré patterns in nanoflatland materials. These visually beautiful moiré superlattices have become a playground on which exotic quantum phenomena can be observed. The state‐of‐the‐art experimental techniques that have been developed for crafting moiré superlattices of flatland materials are reviewed. Graphene and its heterostructure with boron nitride have now sparked new interlayer twists as a new degree of freedom for tuning several angle‐dependent physical properties, e.g., the appearance of van Hove singularities, tunable Mott insulator states, and the Hofstadter butterfly pattern. Moreover, the interplay of correlated insulating states and superconductivity is recently observed for a so‐called magic‐angle twisted bilayer graphene. Furthermore, beyond graphene, other 2D materials, such as silicene, phosphorene, and the recent black phosphorus /MoS₂ heterojunctions, which are 2D allotropes of bismuth and antimony grown on highly ordered pyrolytic graphite and MoS₂, are considered. Finally, the optically important exciton phenomenon, which depends on the moiré potential and has been observed for a moiré superlattice of transition metal dichalcogenides, is discussed. This overview aims to cover all the fascinating prospects that depend on the moiré superlattice, ranging from electronic structure to optical exotics among flatland materials.     

Planar Silicene: A New Silicon Allotrope Epitaxially Grown by Segregation

2D sheets of graphene‐like silicon, namely planar silicene, are synthesized. This new silicon allotrope is prepared on Au(111) thin films grown on a Si(111) substrate in the process of surface segregation. Owing to its almost perfectly flat geometry it shares the atomic structure with graphene rather than with low‐buckled silicene. Scanning tunneling microscopy measurements clearly display an atomically resolved planar silicene honeycomb lattice. Ab initio density functional theory calculations fully support the experimental findings and predict a pure sp² atomic configuration of Si atoms. The present work is the first experimental evidence of epitaxial planar silicene.     

Siloxene,Germanane, and Methylgermanane: Functionalized 2D Materials of Group 14 for Electrochemical Applications

2D monoelemental group 14 materials beyond graphene, such as silicene and germanene, have recently gained a lot of attention. Covalent functionalization of group 14 layered materials can lead to significant tuning of their properties. While optical and electronic properties of germanene, silicene, and their derivatives have been studied in detail previously, there is no information on their electrochemistry and toxicity. Herein, electrochemical applications of 2D siloxene, germanane, and methylgermanane, specifically for detection of an important biomarker, dopamine, as well as catalyzation of oxygen reduction and hydrogen evolution reactions, which are important in energy applications, are explored. Among the three materials, germanane portrays most superior properties for the electrochemical applications mentioned. All three materials possess fast heterogeneous electron transfer rates, relative to bare glassy carbon electrodes. In addition, toxicity studies of these materials are conducted to gain insights on their possible harmful effects toward human health. The results of this study show siloxene nontoxic while germanane and methylgermanane impose dose‐dependent toxicity. Interestingly, methylation successfully reduce the toxicity of methylgermanane at lower concentrations. These studies provide fundamental insights into electrochemical and toxic properties of functionalized group 14 layered materials for future electrochemical applications.     

Functional Nanomaterials on 2D Surfaces and in 3D Nanocomposite Hydrogels for Biomedical Applications

An emerging approach to improve the physicobiochemical properties and the multifunctionality of biomaterials is to incorporate functional nanomaterials (NMs) onto 2D surfaces and into 3D hydrogel networks. This approach is starting to generate promising advanced functional materials such as self‐assembled monolayers (SAMs) and nanocomposite (NC) hydrogels of NMs with remarkable properties and tailored functionalities that are beneficial for a variety of biomedical applications, including tissue engineering, drug delivery, and developing biosensors. A wide range of NMs, such as carbon‐, metal‐, and silica‐based NMs, can be integrated into 2D and 3D biomaterial formulations due to their unique characteristics, such as magnetic properties, electrical properties, stimuli responsiveness, hydrophobicity/hydrophilicity, and chemical composition. The highly ordered nano‐ or microscale assemblies of NMs on surfaces alter the original properties of the NMs and add enhanced and/or synergetic and novel features to the final SAMs of the NM constructs. Furthermore, the incorporation of NMs into polymeric hydrogel networks reinforces the (soft) polymer matrix such that the formed NC hydrogels show extraordinary mechanical properties with superior biological properties.     

激光辅助三维金属微打印（特邀）

当前微纳尺度的三维金属结构,由于其独特的物化性能和空间构型优势,在科学与工程领域的应用需求日益增多。由此应运而生的各种三维金属微尺度打印技术近年来相继被开发,并引起了广泛关注。在众多技术中,基于激光的三维微打印技术有着非接触加工、制造灵活性好等优势。文中综述了当前一些代表性的激光辅助三维金属微打印技术,总结了各种三维金属微打印的基本原理、技术优势及典型应用。针对高表面光滑度、高熔点、高电导率的三维金属微打印存在的挑战,介绍了超快激光制备玻璃微通道模具法辅助实现三维金属微制造的新技术。最后就三维金属微打印的未来方向和应用前景进行了探讨。     

Hindering the Oxidation of Silicene with Non‐Reactive Encapsulation

The chemical stability of buckled silicene, i.e., the silicon counterpart of graphene, is investigated then resulting in a low reactivity with O₂ when dosing up to 1000 L and in a progressive oxidation under ambient conditions. The latter drawback is addressed by engineering ad hoc Al‐ and Al₂O₃‐based encapsulations of the silicene layer. This encapsulation design can be generally applied to any silicene configuration, irrespective of the support substrate, and it leads to the fabrication of atomically sharp and chemically intact Al/silicene and Al₂O₃/silicene interfaces that can be functionally used for ex situ characterization as well as for gated device fabrication.     

The Metallic Nature of Epitaxial Silicene Monolayers on Ag(111)

Silicene is a two‐dimensional structure composed of a buckled hexagonal honeycomb lattice of silicon atoms. Freestanding silicene is yet to be synthesized, but epitaxial silicene monolayers have been directly observed or predicted to exist on a number of supporting substrates. Herein the atomic and electronic structures of five distinct epitaxial silicene morphologies on Ag(111) are examined through the complementary techniques of density functional theory and soft X‐ray spectroscopy at the Si L_2,3 edge. Hybridization with the Ag(111) substrate is shown to cause these silicene monolayers to become strongly metallic, and the specific electronic interactions that are responsible for this metallic nature are determined. The results imply that epitaxial silicene on Ag(111) does not possess the Dirac cone electronic structure that is characteristic of freestanding silicene and graphene sheets.     

Epitaxial Growth of 2D Materials on High-Index Substrate Surfaces

Recently, the successful synthesis of wafer-scale single-crystal graphene, hexagonal boron nitride (hBN), and MoS₂ on transition metal surfaces with step edges boosted the research interests in synthesizing wafer-scale 2D single crystals on high-index substrate surfaces. Here, using hBN growth on high-index Cu surfaces as an example, a systematic theoretical study to understand the epitaxial growth of 2D materials on various high-index surfaces is performed. It is revealed that hBN orientation on a high-index surface is highly dependent on the alignment of the step edges of the surface as well as the surface roughness. On an ideal high-index surface, well-aligned hBN islands can be easily achieved, whereas curved step edges on a rough surface can lead to the alignment of hBN along with different directions. This study shows that high-index surfaces with a large step density are robust for templating the epitaxial growth of 2D single crystals due to their large tolerance for surface roughness and provides a general guideline for the epitaxial growth of various 2D single crystals.     

Probing Spintronic Features in Conduction through Silicene and Graphene Barriers

The Dirac electrons in silicene experience stronger spin-orbit interaction (SOI) than in graphene due to silicene's band buckled two-dimensional (2D) structure. In this work we theoretically probe the main effects of the SOI in silicene, provided this interaction can be controlled by an external electrical field. Attention is paid to how silicene's SOI effects can turn into graphene’s once external parameters can be regulated. By comparing the electronic transmission through silicene and graphene structures we are able to fit the external electrical field to obtain similar results for both materials. We study the conductance through silicene barriers and also show how to straightforwardly probe spin polarization and spin-resolved transmission using as few parameters as possible. We first calculate the electronic transmission through single and double barriers as a function of the electron’s angle of incidence \(\theta \), the electron energy E, and the strength of the external electrical field \(E_{z}.\) We then found that the polarization P versus \(\theta \) in double-barrier structures exhibits quasi-periodic resonances. We finally study asymmetric structures that allow the presence of more transmission channels in the conductance.     

Terahertz Surface Waves Propagating on Metals with Sub-wavelength Structure and Grating Reliefs

Due to their long propagation length at a metal surface in the far infrared, surface plasmons make potentially feasible the design and realization of 2D integrated terahertz systems over a metallic substrate. In this article, we present a review of recent works dedicated to surface plasmon properties on structured metallic surfaces. We study excitation, propagation, diffraction and reflection of terahertz surface plasmon on shallow gratings and of spoof plasmons on deep sub-wavelength structures. The analysis of the experimental data supplied by terahertz time-domain spectroscopy allows us to point out the main parameters that govern this diffraction process and the propagation of a surface plasmon over a flat or corrugated metal surface.     

Versatile Crystal Structures and (Opto)electronic Applications of the 2D Metal Mono‐, Di‐, and Tri‐Chalcogenide Nanosheets

Emerging 2D metal chalcogenides present excellent performance for electronic and optoelectronic applications. In contrast to graphene and other 2D materials, 2D metal chalcogenides possess intrinsic bandgaps, versatile band structures, and superior atmospheric stability. The many categories of 2D metal chalcogenides ensure that they can be applied to various practical scenarios. 2D metal monochalcogenides, dichalcogenides, and trichalcogenides are the three main categories of these materials. They have distinct crystal structures resulting in different characteristics. Some basic device characteristics, such as the charge carrier characteristics, scattering mechanisms, interfacial contacts, and band alignments of heterojunctions, are vital factors for practical device applications that ensure that the desired properties can be achieved. Various electronic, optoelectronic, and photonic applications based on 2D metal chalcogenides have been extensively investigated. 2D metal chalcogenides are considered as competitive candidates for future electronic and optoelectronic applications.     

Engineering of Magnetically Intercalated Silicene Compound: An Overlooked Polymorph of EuSi2

Silicene, a Si analogue of graphene, is suggested to become a versatile material for nanoelectronics. Being coupled with magnetism, it is predicted to be particularly suitable for spintronic applications. However, experimental realization of free‐standing silicene and its magnetic derivatives is lacking. Fortunately, magnetism can be induced into silicene layers, in particular, by intercalation. Here, a successful synthesis of multilayer silicene intercalated by inherently magnetic Eu ions – a compound expected to exhibit both massless Dirac‐cone states, as its Ca analogue, and a nontrivial magnetic structure – is reported. This new polymorph with EuSi₂ stoichiometry is epitaxially stabilized by continual replication of silicene layers employing Sr‐intercalated multilayer silicene as a template. The atomic structure of the new compound and its sharp interface with the template are confirmed using electron diffraction, X‐ray diffraction, and electron microscopy techniques. Below 80 K, the material demonstrates anisotropic antiferromagnetism coexisting with weak ferromagnetism. The magnetic state is accompanied by an anomalous behavior of magnetoresistivity.     

Band structure of monolayer of graphene,silicene and silicon-carbide including a lattice of empty or filled holes

We have developed a π-orbital tight-binding Hamiltonian model taking into account the nearest neighbors to study the effect of antidot lattices (two dimensional honeycomb lattice of atoms including holes) on the band structure of silicene and silicon carbide (SiC) sheets.We obtained that the band structure of the silicene antidot superlattice strongly depends on the size of embedded holes,and the band gap of the silicene antidot lattice increases by increasing of holes diameter.The band gap of SiC antidot lattice,except for the lattice of the small unit cell,is independent of the holes diameter and also depends on the distance between holes.We obtained that,the band gap of the SiC antidot lattice is the same as the band gap of the corresponding sheet without hole.Also,the electronic properties of the SiC antidot superlattice occupied either by carbon or by silicon atoms are investigated,numerically.Furthermore,we study the effect of occupation of graphene antidot by Si atoms and vice versa.Also,we have calculated the band structure of graphene and silicene antidot lattice filled by Si + C atoms.Finally,we compute the band structure of the SiC antidot lattice including the holes which are filled by C or by Si atoms.Really,in this paper we have generalized the method of paper[38] about graphene antidot with empty holes to the cases of filled holes by different atoms and also to the case of silicene and silicon carbide antidot lattices.     

Low‐Dimensional Transition Metal Dichalcogenide Nanostructures Based Sensors

Two‐dimensional (2D) transition metal dichalcogenides (TMDs) nanostructures have been widely applied in environmental and biological analysis, biomedicine, electronic devices, and hydrogen evolution catalysis. Meanwhile, this excitement in 2D TMDs has spilled over to their counterparts of different dimensionalities like one‐dimensional (1D) and zero‐dimensional (0D) TMDs nanostructures. Eventual physical and chemical properties of TMDs nanostructures still remain to be highly dependent on their dimensionalities and size scale, and recently creatively exploring these physical and chemical properties is extremely impactful for the sensing field of TMD nanomaterials. Herein, we review a wide range of sensing applications based on not only graphene‐like 2D TMDs nanostructures but also the rapidly emerging subclasses of 1D, and 0D TMDs nanostructures. Their unique and interesting structures, excellent properties, and valid preparation methods are also included and the analytical objectives, ranging from heavy metal ions to small molecules, from DNA to proteins, from liquids to even vapors, can be met with extremely high selectivity and sensitivity. We have also analyzed our current understanding of 0D and 1D TMDs nanostructures and learning from graphene with the goal of contributing fresh ideas to the overall development of more advanced future TMDs based sensors.     

Electronic band structures and optical properties of atomically thin AuSe: first-principle calculations

As a large family of 2D materials, transition metal dichalcogenides(TMDs) have stimulated numerous works owing to their attractive properties. The replacement of constituent elements could promote the discovery and fabrication of new nanofilm in this family. Using precious metals, such as platinum and palladium, to serve as transition metals combined with chalcogen is a new approach to explore novel TMDs. Also, the proportion between transition metal and chalcogen atoms is found not only to exist in conventional form of 1 : 2. Herein, we reported a comprehensive study of a new 2D precious metal selenide, namely AuSe monolayer. Based on density functional theory, our result indicated that AuSe monolayer is a semiconductor with indirect band-gap of 2.0 eV, which possesses superior dynamic stability and thermodynamic stability with cohesive energy up to–7.87 eV/atom. Moreover, it has been confirmed that ionic bonding predominates in Au–Se bonds and absorption peaks in all directions distribute in the deep ultraviolet region. In addition, both vibration modes dominating marked Raman peaks are parallel to the 2D plane.     

Effect of reactive sputter etching of SiO2 on the properties of subsequently formed MOS systems

We investigated the effects of reactive sputter etching (RSE) of SiO₂ on the electrical properties of the SiSiO₂ system using CHF₃ in a commercial apparatus. SIMS and Auger spectrometry revealed contamination of RSE-exposed Si surfaces with carbon and heavy metals. The generation of crystal defects during thermal reoxidation was observed to be closely related to the level of metal contamination. C-V, C-t and I-V measurements on subsequently formed MOS structures showed, that oxide charge, interface state and mobile ion densities are nearly unaffected by the RSE process. However, minority carrier lifetime in the Si substrate and isolation behavior of the oxide layer are strongly degraded; our results suggest, that both effects are mainly due to metallic impurities. The use of inert cathode materials like quartz reduces metal contamination, but a non-negligible contribution from the grounded metal surfaces of the reactor remains. Carrier lifetime and insulating properties reach the values obtained on wet chemically etched samples only after extended times of plasma excitation in the apparatus. This is attributed to a passivation of the grounded surfaces by the formation of polymer films. Taking advantage of this effect MOSFETs were fabricated by the use of RSE without deterioration of their electrical performance.     

Facile and Versatile Functionalization of Two‐Dimensional Carbon Nitrides by Design: Magnetism/Multiferroicity,Valleytronics, and Photovoltaics

Ab initio calculation evidence has shown that two‐dimensional (2D) carbon nitrides may enable “facile functionalization” when a domain of carbon nitride is wetted by a solution of metal halides with mobile cations/anions. During the wetting process, each cavity can be functionalized by a unit of metal halide. Compared with prevailing functionalization or doping strategies through either high‐temperature diffusion of source ions or ion implantation by using accelerators, such a room‐temperature “wet‐lab” functionalization approach is more facile and efficient. The wet‐lab functionalization not only can facilitate isolation of the 2D monolayer, but also, with applying different metal halides, enable various new and desirable properties for broad applications, e.g., 2D magnetism and 2D ferroelectricity with high piezoelectric coefficient. The latter can be implemented in spin‐independent valleytronics for non‐volatile electrical manipulations. Notably, tunable bandgaps, ranging from 1.0 to 2.5 eV, can be realized by controlling the metal‐halide functionalization density, while the separation of electrons/holes can be facilitated by the ferroelectric polarizations and heterostructure band alignments. Moreover, multifunctional domains like P/N doped or magnetic/ferroelectric domains can be selectively constructed through such solution‐processed functionalization with different halides, followed by seamless integration into a single sheet of carbon nitride, akin to the P/N channels in silicon wafers.     

Enhanced Performance of Planar Perovskite Solar Cells Induced by Van Der Waals Epitaxial Growth of Mixed Perovskite Films on WS2 Flakes

Organic–inorganic metal halide perovskite solar cells (PSCs) have attracted much research interest owing to their high power conversion efficiency (PCE), solution processability, and the great potential for commercialization. However, the device performance is closely related to the quality of the perovskite film and the interface properties, which cannot be easily controlled by solution processes. Here, 2D WS₂ flakes with defect‐free surfaces are introduced as a template for van der Waals epitaxial growth of mixed perovskite films by solution process for the first time. The mixed perovskite films demonstrate a preferable growth along (001) direction on WS₂ surfaces. In addition, the WS₂/perovskite heterojunction forms a cascade energy alignment for efficient charge extraction and reduced interfacial recombination. The inverted PSCs with WS₂ interlayers show high PCEs up to 21.1%, which is among the highest efficiency of inverted planar PSCs. This work demonstrates that high‐mobility 2D materials can find important applications in PSCs as well as other perovskite‐based optoelectronic devices.