Applications Of Silicene Research Articles

Electronic Properties and Electrocatalytic Water Splitting Activity for Precious-Metal-Adsorbed Silicene with Nonmetal Doping.

Since nonmetal (NM)-doped two-dimensional (2D) materials can effectively modulate their physical properties and chemical activities, they have received a lot of attention from researchers. Therefore, the stability, electronic properties, and electrocatalytic water splitting activity of precious-metal (PM)-adsorbed silicene doped with two NM atoms are investigated based on density functional theory (DFT) in this paper. The results show that NM doping can effectively improve the stability of PM-adsorbed silicene and exhibit rich electronic properties. Meanwhile, by comparing the free energies of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) intermediates of 15 more stable NM-doped systems, it can be concluded that the electrocatalytic water splitting activity of the NM-doped systems is more influenced by the temperature. Moreover, the Si–S2–Ir-doped system exhibits good HER performance when the temperature is 300 K, while the Si–N2–Pt-doped system shows excellent OER activity. Our theoretical study shows that NM doping can effectively promote the stability and electrocatalytic water splitting of PM-adsorbed silicene, which can help in the application of silicene in electrocatalytic water splitting.

Phonon Drag Thermopower in Silicene in Equipartition Regime at Room Temperature

Abstract: Similar to graphene, zero band gap limits the application of Silicene in nanoelectronics despite of its high carrier mobility. In this article we calculate the contribution of electron-phonon interaction to thermoelectric effects in silicene. One considers the case of free standing silicene taking into account interaction with intrinsic acoustic phonons. The temperature considered here is at room temperature. We noticed that the contribution to thermoelectromotive force due to electron drag by phonons is determined by the Fermi energy. The explicit temperature dependence of the contribution to thermoelectromotive force deriving from by phonons is weak in contrast to that due to diffusion, which is directly proportional to temperature. Thus a theoretical limit has been established for a possible increase of the thermoelectromotive force through electron drag by the intrinsic phonons of silicene. Keywords: Phonon-drag thermopower, electron-diffusion thermopower, silicene, fermi energy, zero band gap

Realizing n-type doping and high carrier mobility of silicene by decamethylcobaltocene molecular adsorption

In this work, the structural and electronic properties of silicene with decamethylcobaltocene (DMC) molecular doping are investigated by density functional theory to improve its semiconductor properties. DMC molecule with strong electron-donating ability is physisorbed on silicene. An interfacial charge transfer between silicene and DMC molecule occurs, then the location of Fermi energy is modulated lower than the Dirac point of silicene with 0.273 eV ‒ 0.282 eV. Consequently, n-type doped silicene is realized. Meanwhile, a band gap of 0.024 eV ‒ 0.032 eV opens in silicene. Moreover, silicene maintains a high carrier concentration (3.426 × 1013 ‒ 3.518 × 1013 cm−2) and carrier mobility (13.839 × 104 cm2 V−1 s−1 for electrons and 5.428 × 104 cm2 V−1 s−1 for holes) with anisotropy. This work opens possible applications of silicene in photonic and electronic devices.

Electronic and optical properties of silicene on GaAs(111) with hydrogen intercalation: a first-principles study.

In this paper, we investigated the electronic and optical properties of silicene on GaAs(111) substrates (silicene/HGaAs) on the basis of first-principles density functional theory. The hydrogen intercalation introduced substantially weakened the interaction between silicene and the GaAs(111) substrate and induced considerable bandgaps in silicene/HGaAs heterostructures. The effects of the interlayer spacing (L) between silicene and the substrate, silicene buckling height (h), biaxial strain (ε), and external electric field (F) on the electronic properties were also considered. Our results showed that the electronic properties of silicene/HGaAs heterostructures could be controlled by adjusting L and h and applying ε and an external F. Silicene/HGaAs heterostructures possessed the typical optical absorption properties of freestanding silicene and had high absorption coefficients. Besides, some strong peaks of absorption spectra and energy loss spectra existed in the ultraviolet light region, which showed that silicene/HGaAs heterostructures had evident enhancement in the ultraviolet light region. Results laid a theoretical foundation for the study of the electronic and optical properties and applications of silicene on semiconductor substrate devices.

2D Honeycomb Silicon: A Review on Theoretical Advances for Silicene Field-Effect Transistors

Catalysed by the success of mechanical exfoliated free-standing graphene, two dimensional (2D) semiconductor materials are successively an active area of research. Silicene is a monolayer of silicon (Si) atoms with a low-buckled honeycomb lattice possessing a Dirac cone and massless fermions in the band structure. Another advantage of silicene is its compatibility with the Silicon wafer fabrication technology. To effectively apply this 2D material in the semiconductor industry, it is important to carry out theoretical studies before proceeding to the next step. In this paper, an overview of silicene and silicene nanoribbons (SiNRs) is described. After that, the theoretical studies to engineer the bandgap of silicene are reviewed. Recent theoretical advancement on the applications of silicene for various field-effect transistor (FET) structures is also discussed. Theoretical studies of silicene have shown promising results for their application as FETs and the efforts to study the performance of bandgap-engineered silicene FET should continue to improve the device performance.

Intervalley scattering in GaAs(111)-supported silicene.

In this paper, we investigated the valley transport properties of silicene on a GaAs(111) substrate. Hydrogen atoms as intercalation substantially weaken the interaction between silicene and GaAs(111) substrate. Thus, the equivalent intervalley scattering between K valleys and the non-equivalent intervalley scattering between Γ and K valleys were studied. The effects of external temperature, the distance Lz between silicene and the substrate, and the buckling height d of silicene on intervalley scattering were also considered. Our results showed that the intervalley scattering rates of silicene on GaAs(111) were about 1011-1012 s-1, which indicate that the weakened interaction between silicene and the substrate can effectively reduce intervalley scattering rates. The equivalent intervalley scattering of silicene was insensitive to changes of the distance Lz between silicene and the substrate and the buckling height d of silicene, but the non-equivalent intervalley scattering was greatly affected by these changes. The research results have laid a theoretical foundation for the study of the transport properties and application of silicene on semiconductor substrates.

Few-Layer Silicene Nanosheets with Superior Lithium-Storage Properties.

Silicene, a 2D silicon allotrope with unique low-buckled structure, has attracted increasing attention in recent years due to its many superior properties. So far, epitaxial growth is one of the very limited ways to obtain high-quality silicene, which severely impedes the research and application of silicene. Therefore, large-scale synthesis of silicene is a great challenge, yet urgently desired. Herein, the first scalable preparation of free-standing high-quality silicene nanosheets via liquid oxidation and exfoliation of CaSi2 is reported. This new synthesis strategy successfully induces mild oxidation of the (Si2n )2n- layers in CaSi2 into neutral Si2n layers without damage of pristine silicene structure and promotes the exfoliation of stacked silicene layers. The obtained silicene sheets are dispersible and ultrathin ones with monolayer or few-layer thickness and exhibit excellent crystallinity. As a unique 2D layered silicon allotrope, the silicene nanosheets are further explored as new anodes for lithium-ion batteries and exhibit a nearly theoretical capacity of 721 mAh g-1 at 0.1 A g-1 and an extraordinary cycling stability with no capacity decay after 1800 cycles in contrast to previous most silicon anodes showing rapid capacity decay, thus holding great promise for energy storage and beyond.

Tuning the Electronic Structure of Hydrogen-Decorated Silicene

The effects of strain, charge doping, and external electric field on the electronic structure of a free-standing silicene layer decorated by hydrogen atoms are studied by first-principles density functional theory. Various phases, including insulating, metallic, spin-polarized, and half-metallic have been found, depending on these external factors. The most efficient way of switching the system between these phases is charge doping. The character of the energy gap of the H/silicene system can also be modified, and for charged or for strained systems, the originally indirect gap can be tuned to become direct. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in the fields of spintronics and optoelectronics.

Atomic and electronic structures of silicene and germanene on GaAs(111)

By using first-principles method in the density-functional theory, we clarify the atomic and electronic structures of silicene and germanene on 1×1 GaAs(111). We find stable structures for silicene and germanene on both the As-terminated and Ga-terminated GaAs surfaces. The structures of silicene and germanene are similar to those of the free-standing ones, which present a honeycomb-hexagonal geometry. The cohesive energies of silicene and germanene on both As and Ga sides of GaAs surfaces are comparable to those of their bulk structures and/or those on Ag(111) substrates which have been widely observed in experiment, showing the possibility of synthesizing them on both sides of GaAs surfaces in experiment. The corresponding binding energies are in a range of 0.56-1.37 eV per Si (Ge) atom, 10 times larger than the usual van der Waals interaction, showing the covalent interaction between silicene (germanene) and GaAs surfaces. The band structure calculations show that such a covalent interaction induces the absence of Dirac electrons for silicene and germanene on GaAs surfaces. We then explore the method of recovering the Dirac electrons by using hydrogen (H) intercalation. It is found that the intercalated H atoms are chemically bonded to GaAs surface, and the silicene (germanene) shifts upward distance from GaAs surface increasing from 2.50-2.58 Å to 3.49-3.86 Å, where a covalent van-der-Waals interaction transition happens between silicene (germanene) and GaAs surface. Moreover, the distances between silicene (germanene) and H atoms are 30% and 8% larger than the atomic-radius sum of Si (Ge) and H on As-terminated and Ga-terminated GaAs surfaces, respectively. This shows that the interaction between silicene (germanene) and H on the As-terminated GaAs surface is obviously weaker than the typical covalent interaction, while on the Ga-terminated GaAs surface, it is comparable to the typical covalent interaction. This difference is induced by the difference in electronegativity between As and Ga atoms. We further find that the H intercalation recovers the Dirac electrons well on the As-terminated GaAs(111) due to the weaker Si (Ge)-H interaction, while it does not on the Ga-terminated GaAs(111) due to the stronger Si (Ge)-H interaction. The results are confirmed by performing calculations for silicene (germanene) on larger GaAs(111) surfaces, i.e., the 3×3 GaAs surface. Our study provides the theoretical basis for the preparation and application of silicene and germanene on semiconductor surfaces.

Structures and Chemical Properties of Silicene: Unlike Graphene

The discovery of graphene and its remarkable and exotic properties have aroused interest in other elements and molecules that form 2D atomic layers, such as metal chalcogenides, transition metal oxides, boron nitride, silicon, and germanium. Silicene and germanene, the Si and Ge counterparts of graphene, have interesting fundamental physical properties with potential applications in technology. For example, researchers expect that silicene will be relatively easy to incorporate within existing silicon-based electronics. In this Account, we summarize the challenges and progress in the field of silicene research. Theoretical calculations have predicted that silicene possesses graphene-like properties such as massless Dirac fermions that carry charge and the quantum spin Hall effect. Researchers are actively exploring the physical and chemical properties of silicene and tailoring it for wide variety of applications. The symmetric buckling in each of the six-membered rings of silicene differentiates it from graphene and imparts a variety of interesting properties with potential technological applications. The pseudo-Jahn-Teller (PJT) distortion breaks the symmetry and leads to the buckling in silicenes. In graphene, the two sublattice structures are equivalent, which does not allow for the opening of the band gap by an external electric field. However, in silicene where the neighboring Si atoms are displaced alternatively perpendicular to the plane, the intrinsic buckling permits a band gap opening in silicene in the presence of external electric field. Silicene's stronger spin orbit coupling than graphene has far reaching applications in spintronic devices. Because silicon prefers sp(3) hybridization over sp(2), hydrogenation is much easier in silicene. The hydrogenation of silicene to form silicane opens the band gap and increases the puckering angle. Lithiation can suppress the pseudo-Jahn-Teller distortion in silicene and hence can flatten silicene's structure while opening the band gap. So far, chemists have not successfully synthesized and characterized a free-standing silicene. But recently chemists have successfully produced silicene sheets and nanoribbons over various substrates such as silver, diboride thin films, and iridium. The supporting substrate critically controls the electronic properties of silicene, and the match of the appropriate support and its use is critical in applications of silicene.