Direct Observation of Dirac Cone in Multilayer Silicene Intercalation Compound CaSi<sub>2</sub>

Noguchi, Eiichi; Sugawara, Kazuo; Yaokawa, Ritsuko; Hitosugi, Taro; Nakano, Hideyuki; Takahashi, Takashi

doi:10.1002/adma.201403077

Cited by 81 publications

(47 citation statements)

References 26 publications

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“…In order to form the single crystal CaSi 2 , the polycrystalline material in the Ta crucible is enclosed in an quartz tube and sintered at 1080 °C for 1 h, and then slowly cooled to 500 °C at the rate of 10 °C h −1 . After that, the furnace is shut down and the sample is cooled down to room temperature . The silicene layers and Ca layers stack alternatively along the [0001] crystal axis, with the ABC stacking sequence per unit cell in the CaSi 2 single crystal.…”

Section: Fabrication Of Silicene Nanosheetsmentioning

confidence: 99%

Silicene: A Promising Anode for Lithium‐Ion Batteries

et al. 2017

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Silicene, a single-layer-thick silicon nanosheet with a honeycomb structure, is successfully fabricated by the molecular-beam-epitaxy (MBE) deposition method on metallic substrates and by the solid-state reaction method. Here, recent progress on the features of silicene that make it a prospective anode for lithium-ion batteries (LIBs) are discussed, including its charge-carrier mobility, chemical stability, and metal-silicene interactions. The electrochemical performance of silicene is reviewed in terms of both theoretical predictions and experimental measurements, and finally, its challenges and outlook are considered.

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Section: Fabrication Of Silicene Nanosheetsmentioning

confidence: 99%

Silicene: A Promising Anode for Lithium‐Ion Batteries

et al. 2017

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“…This finding encouraged us to design the present flat silicene building blocks using electron-donating substituents. A pioneering work recently reported the formation of flat silicene via doping with calcium as an electron donor 27 , and attempts to make flat hexasilabenzene and Si 6 clusters were carried out earlier with Zintl anions 28, 29 . In either case, the Si 6 hexagon is surrounded by an electron donor, creating a three-dimensional crystal but not a pure 2D crystal.…”

Section: Introductionmentioning

confidence: 99%

Flat building blocks for flat silicene

Takahashi

2017

Sci Rep

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Silicene is the silicon equivalent of graphene, which is composed of a honeycomb carbon structure with one atom thickness and has attractive characteristics of a perfect two-dimensional π-conjugated sheet. However, unlike flat and highly stable graphene, silicene is relatively sticky and thus unstable due to its puckered or crinkled structure. Flatness is important for stability, and to obtain perfect π-conjugation, electron-donating atoms and molecules should not interact with the π electrons. The structural differences between silicene and graphene result from the differences in their building blocks, flat benzene and chair-form hexasilabenzene. It is crucial to design flat building blocks for silicene with no interactions between the electron donor and π-orbitals. Here, we report the successful design of such building blocks with the aid of density functional theory calculations. Our fundamental concept is to attach substituents that have sp-hybrid orbitals and act as electron donors in a manner that it does not interact with the π orbitals. The honeycomb silicon molecule with BeH at the edge designed according to our concept, clearly shows the same structural, charge distribution and molecular orbital characteristics as the corresponding carbon-based molecule.

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“…Clearly, the inherent buckling in silicene and germanene results in strong covalent bonding interaction with the underlying metal surface, resulting in solitonic kinks that reduce mobility of the charge carriers 13. Recently, Takahashi and co‐workers overcame this bottleneck for crystalline CaSi 2 consisting of silicene layers intercalated with Ca II ions and effectively restored the massless Dirac cone state, albeit below the Fermi level ( E F ), owing to charge transfer (CT) from the Si layer to Ca II 14. Calculations show that buckling distortions in the silicene layers result in momentum shift of the Dirac cones away from the high symmetry points K and H of the hexagonal Brillouin zone 15…”

Section: Introductionmentioning

confidence: 99%

“…[13] Recently,T akahashi and co-workers overcamethis bottleneck for crystalline CaSi 2 consisting of silicene layers intercalated with Ca II ions and effectively restored the massless Dirac cone state, albeit below the Fermi level (E F ), owing to charge transfer (CT) from the Si layer to Ca II . [14] Calculations show that bucklingd istortions in the silicenel ayers result in momentum shift of the Dirac cones away from the high symmetry points K and H of the hexagonal Brillouin zone. [15] Therefore, the ideal systemst or ealize the exotic properties of low-dimensional systems would to fabricate free-standing layerso fsilicon and germanium that might be well separated by alkyl chains yet stabilized by alkyl-alkyl van der Waals forces.…”

Section: Introductionmentioning

confidence: 99%

Topochemical Transformations of CaX₂ (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

Pratik

Nijamudheen

Datta

2015

Chemistry A European J

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Topochemical transformations of layered materials CaX2 (X=Si, Ge) are the method of choice for the high-yield synthesis of pristine, defect-free two-dimensional systems silicane and germanane, which have advanced electronic properties. Based on solid-state dispersion-corrected calculations, mechanisms for such transformations are elucidated that provide an in-depth understanding of phase transition in these layered materials. While formation of such layered materials is highly favorable for silicane and germanane, a barrier of 1.2 eV in the case of graphane precludes its synthesis from CaC2 topochemically. The energy penalty required for distorting linear acetylene into a trans-bent geometry accounts for this barrier. In contrast it is highly favorable in the heavier analogues, resulting in barrierless topochemical generation of silicane and germanane. Photochemical generation of the trans-bent structure of acetylene in its first excited state (S1 ) can directly generate graphane through a barrierless condensation. Unlike the buckled structure of silicene, the phase-h of CaSi2 with perfectly planar silicene layers exhibits the Dirac cones at the high symmetry points K and H. Interestingly, topochemical acidification of the cubic phase of calcium carbide is predicted to generate the previously elusive platonic hydrocarbon, tetrahedrane.

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Direct Observation of Dirac Cone in Multilayer Silicene Intercalation Compound CaSi₂

Cited by 81 publications

References 26 publications

Silicene: A Promising Anode for Lithium‐Ion Batteries

Silicene: A Promising Anode for Lithium‐Ion Batteries

Flat building blocks for flat silicene

Topochemical Transformations of CaX₂ (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

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Direct Observation of Dirac Cone in Multilayer Silicene Intercalation Compound CaSi2

Cited by 81 publications

References 26 publications

Silicene: A Promising Anode for Lithium‐Ion Batteries

Silicene: A Promising Anode for Lithium‐Ion Batteries

Flat building blocks for flat silicene

Topochemical Transformations of CaX2 (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

Contact Info

Product

Resources

About

Direct Observation of Dirac Cone in Multilayer Silicene Intercalation Compound CaSi₂

Topochemical Transformations of CaX₂ (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials