Silicon Intercalation Research Articles

Silicon intercalation on MXene nanosheets towards new insights into a superior electrode material for high-performance Zn-ion supercapacitor

MXenes seem promising as a new two-dimensional (2D) material for energy storage and conversion applications due to their excellent conductivity, efficient accordion-like layered structure, surface chemistry, and many organized nanochannels. Nevertheless, the demonstration of MXenes' superiority is impeded by an accumulation of interlayers and the chemical sluggishness of structural components. With silicon (Si) pre intercalation techniques on V2CTx, MXene is able to increase its interlayer spacing and excite the outermost vanadium atoms, resulting in a frequent transfer and high storage capability of Zn-ions in supercapacitors (SCs). Motivated by the distinctive properties of Si and MXene, we have reported the V2CTx@Si nanocomposite electrode material for SC in this work. Si nanospheres act as spacers to intercalate into the MXene interlayers, increasing the ion transport channels while simultaneously lowering the ion transport resistance. The V2CTx@Si nanocomposite electrode delivers a maximum specific capacitance of 557.7 F/g at 1 A/g. The outstanding performance of the V2CTx@Si electrode material is demonstrated by DFT simulations, thanks to its electronic characteristics. These findings indicate that the V2CTx@Si possesses enhanced conductivities than the pristine MXene, which is beneficial for the rate performance of V2CTx@Si. The obtained Eads value of the V2CTx@Si is −0.845 eV, higher than the pristine material (−0.652 eV), indicating energetically favorable. A zinc–ion supercapacitor (ZISC) is constructed via coupling V2CTx@Si as a cathode and Zn foil as an anode (denoted as V2CTx@Si//Zn). The V2CTx@Si//Zn can function at a wide potential range of 1.8 V and provide a high capacitance of 318.25 F/g at 1 A/g with a consistent cyclic life (96.4 %) up to 10,000 cycles. Furthermore, the V2CTx@Si//Zn possessed a maximum energy density of 143.33 Wh/kg at a power density of 900.72 W/kg, outperforming previously reported similar work.

Synthesis of Monolayer Blue Phosphorus Enabled by Silicon Intercalation.

The growth of entirely synthetic two-dimensional (2D) materials could further expand the library of naturally occurring layered solids and provide opportunities to design materials with finely tunable properties. Among them, the synthesis of elemental 2D materials is of particular interest as they represent the chemically simplest case and serve as a model system for exploring the on-surface synthesis mechanism. Here, a pure atomically thin blue phosphorus (BlueP) monolayer is synthesized via silicon intercalation of the BlueP-Au alloy on Au(111). The intercalation process is characterized at the atomic scale by low-temperature scanning probe microscopy and further corroborated by synchrotron radiation-based X-ray photoelectron spectroscopy measurements. The evolution of the band structures from the BlueP-Au alloy into Si-intercalated BlueP are clearly revealed by angle-resolved photoemission spectroscopy and further verified by density functional theory calculations.

Interaction of two symmetric monovacancy defects in graphene**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0202300 and 2018YFA0305800), the National Natural Science Foundation of China (Grant Nos. 61622116, 61474141, 61390501, and 11604373), and the Pioneer Hundred Talents Program, Chinese Academy of Sciences.

We investigate the interactions between two symmetric monovacancy defects in graphene grown on Ru (0001) after silicon intercalation by combining first-principles calculations with scanning tunneling microscopy (STM). First-principles calculations based on free-standing graphene show that the interaction is weak and no scattering pattern is observed when the two vacancies are located in the same sublattice of graphene, no matter how close they are, except that they are next to each other. For the two vacancies in different sublattices of graphene, the interaction strongly influences the scattering and new patterns’ emerge, which are determined by the distance between two vacancies. Further experiments on silicon intercalated graphene epitaxially grown on Ru (0001) shows that the experiment results are consistent with the simulated STM images based on free-standing graphene, suggesting that a single layer of silicon is good enough to decouple the strong interaction between graphene and the Ru (0001) substrate.

Stable Silicene in Graphene/Silicene Van der Waals Heterostructures.

Silicene-based van der Waals heterostructures are theoretically predicted to have interesting physical properties, but their experimental fabrication has remained a challenge because of the easy oxidation of silicene in air. Here, the fabrication of graphene/silicene van der Waals heterostructures by silicon intercalation is reported. Density functional theory calculations show weak interactions between graphene and silicene layers, confirming the formation of van der Waals heterostructures. The heterostructures show no observable damage after air exposure for extended periods, indicating good air stability. The I-V characteristics of the vertical graphene/silicene/Ru heterostructures show rectification behavior.

Recovery of edge states of graphene nanoislands on an iridium substrate by silicon intercalation

Finite-sized graphene sheets, such as graphene nanoislands (GNIs), are promising candidates for practical applications in graphene-based nanoelectronics. GNIs with well-defined zigzag edges are predicted to have spin-polarized edge-states similar to those of zigzag-edged graphene nanoribbons, which can achieve graphene spintronics. However, it has been reported that GNIs on metal substrates have no edge states because of interactions with the substrate.We used a combination of scanning tunneling microscopy, spectroscopy, and density functional theory calculations to demonstrate that the edge states of GNIs on an Ir substrate can be recovered by intercalating a layer of Si atoms between the GNIs and the substrate. We also found that the edge states gradually shift to the Fermi level with increasing island size. This work provides a method to investigate spin-polarized edge states in high-quality graphene nanostructures on a metal substrate.

Electronic characterization of silicon intercalated chevron graphene nanoribbons on Au(111).

Electronic and thermal properties of chevron-type graphene nanoribbons can be widely tuned, making them interesting candidates for electronic and thermoelectric applications. Here, we use post-growth silicon intercalation to unambiguously access nanoribbons' energy position of their electronic frontier states. These are otherwise obscured by substrate effects when investigated directly on the growth substrate. In agreement with first-principles calculations we find a band gap of 2.4 eV.

Graphene modification via cobalt and silicon intercalation

Cobalt and silicon intercalation under graphene formed on the Co(111) surface has been investigated. The thickness of deposited films was varied within the range of up to 2 nm and the temperature of their annealing was 400-450°C. The evolution of atomic and electronic structure of the surface due to intercalation was studied by low-energy electron diffraction and high-resolution photoelectron spectroscopy with synchrotron radiation. It is shown that annealing of deposited Si layer leads to formation on the sample surface of both intercalated and nonintercalated areas. On the intercalated areas, the Co-Si solid solution is formed covered with segregated Si. The presence of a silicon phase strongly affects the electronic structure of graphene and substantially weakens its interaction with the substrate. Subsequent intercallation of Co leads to the restoration of strong coupling between graphene and the substrate.

Intercalation synthesis of cobalt silicide under a graphene layer

The silicon intercalation under single-layer graphene formed on the surface of an epitaxial Co(0001) film was investigated. The experiments were performed under conditions of ultra-high vacuum. The thickness of silicon films was varied within the range of up to 1 nm, and the temperature of their annealing was 500°C. The characterization of the samples was carried out in situ by the methods of low-energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and magnetic linear dichroism in photoemission of Co 3p electrons. New data were obtained on the evolution of the atomic and electronic structure, as well as on the magnetic properties of the system with an increase in the amount of intercalated silicon. It was shown that the intercalation under a graphene layer is accompanied by the synthesis of surface silicide Co2Si and a solid solution of silicon in cobalt.

Electronic properties of zero‐layer graphene on 6H‐SiC(0001) substrate decoupled by silicon intercalation

Graphene exhibits electronic properties that are very sensitive not only to defects but also to the interaction with extra molecules or atoms and underlying substrate. To overcome this limitation for application and mass device production, various methods have been investigated to decouple graphene from substrate and to form quasi‐free standing layer. Silicon has shown to be able to softly decouple the zero‐layer graphene from the substrate. However, the electronic properties of decoupled zero‐layer graphene (ZLG) by silicon intercalation on 6H‐SiC(0001) stay unknown. The decoupling process of the ZLG terminated surface happens at lower temperature compared with ZLG covered by 1 monolayer graphene. The presence of extra graphene layer appears to be of an impediment to silicon intercalation. The decoupled ZLG exhibits electronic properties of a quasi‐free‐standing monolayer graphene. Ab initio calculation corroborates the experimental data and confirms the evolution of the ZLG band structure with silicon intercalation. Copyright © 2014 John Wiley & Sons, Ltd.

Electronic and structural properties of graphene-based metal-semiconducting heterostructures engineered by silicon intercalation

The initial decoupling of the (6√3×6√3)R30° buffer layer also called zero layer graphene (ZLG) on 6H-SiC(0001) by Si intercalation has been investigated by means of high resolution photoemission spectroscopy (HRPES) and microscopy imaging techniques. A combination of complementary techniques has shown that the annealing above 700°C of amorphous Si deposited on ZLG leads to the diffusion of the silicon over the surface. Two competing processes are then observed. Part of the silicon contributes to a progressive decoupling of the ZLG from the substrate (partial decoupling) while the rest agglomerates at the surface to form oriented silicon clusters. After sequences of Si deposition, followed by annealing at 750°C, complete decoupling is observed into quasi-free standing monolayer (ML) graphene. Investigation of the evolution of the C1s and Si2p core levels during the intermediate states shows that the appearance of the graphene contribution coincides with the creation of an extra SiC bulk component, indicating their electronic decoupling. At partial decoupling of the ZLG, we have the coexistence of structurally linked metal-semiconducting materials presenting mutual electronic interactions and composed of nanometric metal-semiconducting heterojunctions.

Silicon intercalation into the graphene-SiC interface

In this work we use low-energy electron microscopy, x-ray photoemission electron microscopy, and x-ray photoelectron spectroscopy to study how the excess Si at the graphene-vacuum interface reorders itself at high temperatures. We show that silicon deposited at room temperature onto multilayer graphene films grown on the SiC$(000\overline{1})$ rapidly diffuses to the graphene-SiC interface when heated to temperatures above 1020${\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. In a sequence of depositions, we have been able to intercalate $\ensuremath{\sim}$6 ML of Si into the graphene-SiC interface.

Silicon intercalation at the interface of graphene and Ir(111)

We report on the structural and electronic properties in the heterostructure of graphene/silicon/Ir(111). A (√19 × √19)R23.41° superstructure is confirmed by low energy electron diffraction and scanning tunneling microscopy and its formation is ascribed to silicon intercalation at the interface between the graphene and the Ir(111) substrate. The dI/dV measurements indicate that the interaction between graphene and Ir is effectively decoupled after silicon intercalation. Raman spectroscopy also reveals the vibrational states of graphene, G peak and 2D peak, which further demonstrates that the silicon-buffered graphene behaves more like intrinsic graphene.