Adsorption Of Alkali Metal Atoms Research Articles

Electronic structure and optical properties of alkali metal X (X=Li, Na, K, Rb, Cs) adsorbed in the Te vacancy-deficient molybdenum ditelluride system: A first-principles study

In the framework of density functional theory, based on first principles, the plane wave pseudopotential technique was utilized to investigate the electrical and optical properties of MoTe2 adjusted by alkali metal X adsorption on Te vacancy defects (X[Formula: see text]=[Formula: see text]Li, Na, K, Rb, Cs). The adsorption of alkali metals on Te vacancy-deficient MoTe2 monolayers has been computationally analyzed. Charge transfer, electronic structure, and optical properties of alkali metal adsorption were systematically studied. It is shown that the MoTe2 bandgap is significantly reduced under Te vacancies. Te vacancies are frequently active sites in TMDs materials. With the adsorption of alkali metal atoms X (X = Li, Na, K, Rb, Cs) in the Te vacancy MoTe2 system, Li atoms have the most substantial geometrical deformation and the minor adsorption energy and can improve the adsorption properties more effectively. The MoTe2 system undergoes a change from semiconductor to metal after adsorption. Regarding optical properties, firm absorption and reflection peaks appeared, and a blueshift phenomenon was observed in the mountains. It is expected that these discoveries are likely to guide the use of molybdenum ditelluride in optoelectronics.

Alkali-metal(Li, Na, and K)-adsorbed MoSi2N4 monolayer: an investigation of its outstanding electronic, optical, and photocatalytic properties

Single-layer MoSi2N4, a high-quality two-dimensional material, has recently been fabricated by chemical vapor deposition. Motivated by this latest experimental work, herein, we apply first principles calculations to investigate the electronic, optical, and photocatalytic properties of alkali-metal(Li, Na, and K)-adsorbed MoSi2N4 monolayer. The electronic structure analysis shows that pristine MoSi2N4 monolayer exhibits an indirect bandgap (E g = 1.89 eV). By contrast, the bandgaps of one Li-, Na-, and K-adsorbed MoSi2N4 monolayer are 1.73 eV, 1.61 eV, and 1.75 eV, respectively. Moreover, the work function of MoSi2N4 monolayer (4.80 eV) is significantly reduced after the adsorption of alkali metal atoms. The work functions of one Li-, Na-, and K-adsorbed MoSi2N4 monolayer are 1.50 eV, 1.43 eV, and 2.03 eV, respectively. Then, optical investigations indicate that alkali metal adsorption processes substantially increase the visible light absorption range and coefficient of MoSi2N4 monolayer. Furthermore, based on redox potential variations after alkali metals are adsorbed, Li- and Na-adsorbed MoSi2N4 monolayers are more suitable for the water splitting photocatalytic process, and the Li-adsorbed case shows the highest potential application for CO2 reduction. In conclusion, alkali-metal-adsorbed MoSi2N4 monolayer exhibits promising applications as novel optoelectronic devices and photocatalytic materials due to its unique physical and chemical properties.

Adsorption of alkali metal atoms on predicted C3N2 sheet

Two-dimensional C3N2 was predicted to become stable using structure searching simulations. In view of the planar porous structure, two-dimensional C3N2 is likely to absorb alkali metal such as Li, Na and K, and the electronic properties of two-dimensional C3N2 could be modified by atomic adsorption. In this work, the effects of adsorption of alkali metal atoms on the monolayer C3N2 structure were systematically investigated. Our current results uncovered that the adsorbing ability of Li is stronger than that of Na as evidenced by the lower negative formation energy. Moreover, the adsorption of alkali metal atoms can efficiently influence the electronic properties of monolayer C3N2 with the modification from semiconductor to metal.

A first-principles study of Janus monolayer TiSSe and VSSe as anode materials in alkali metal ion batteries

Anode materials play an important role in the performance of rechargeable batteries and have been attracting much research interest. In this work, we have investigated the electrochemical properties of two-dimensional (2D) Janus MSSe (M = Ti or V) for potential applications as anode materials in alkali metal ion batteries from density functional theory (DFT), following the recent successful synthesis of 2D Janus MoSSe. Our DFT calculations suggest that 2D Janus TiSSe and VSSe are stable in the 1T phase and 1H phase, respectively. It is found that alkali metal atoms X (X = Li, Na or K) can be stably adsorbed on the surfaces of Janus MSSe, and have low diffusion energy barriers. Additionally, small volume changes are observed in Janus MSSe after the adsorption of alkali metal atoms. It is predicted that the MSSe-2X systems have low open circuit voltages and high capacities. Our results suggest that 2D Janus TiSSe and VSSe are potential anode materials for alkali metal ion batteries.

2D SiC/Si Structure: Electron States and Adsorbability

A model of a heterostructure consisting of a silicon-carbide single layer formed on a massive silicon substrate is proposed. The problem of the adsorption of alkali metal atoms and halogen atoms on the carbon and silicon surface atoms of a 2D SiC/Si heterostructure is considered. Analytical estimates for charge transfer and the adsorption energy are reported.

Surface Electronic Properties of Si‐Doped AlGaN and Thermionic Emission Characteristics with Adsorption of Alkali Metal Atoms

Surface Electronic Properties of Si‐Doped AlGaN and Thermionic Emission Characteristics with Adsorption of Alkali Metal Atoms

Performance effects of doping engineering on graphene-like C3N as an anode material for alkali metal ion batteries

Growing demands for rechargeable batteries have promoted the design of high-performance electrode materials. Based on first-principles calculations, we investigate the selected B-doping C3N monolayer as an alternative anode material for Li-, Na-, and K-ion batteries. Doping substrates have provided higher adsorption energy for alkali metal atoms than that of pristine substrate. The electron loss of C3N monolayer caused by B-doping will strengthen the adsorption of alkali metal atoms on the system, and prevent the cluster formation of alkali metal atoms. Therefore, it can improve the recycle stability of alkali metal ion batteries. More interestingly, compared with the pristine C3N monolayer, the B4-doped C3N systems have an enhanced specific capacity for these alkali metal atoms. Furthermore, the B4-doped C3N substrates with the adsorption of alkali metal atoms have highly thermal stabilities verified by ab-initio molecular dynamics simulations. The diffusion barriers of Li, Na and K atoms on the B4-doped C3N systems have slightly increase, which are still smaller than the threshold (0.5 eV) for metal migration at room temperature. These above analysis indicate that the B-doping in the C3N monolayer can improve its performance as an anode material for alkali metal ion batteries.

Гетероструктура 2D SiC/Si: электронные состояния и адсорбционная способность

Abstract A model of a heterostructure consisting of a silicon-carbide single layer formed on a massive silicon substrate is proposed. The problem of the adsorption of alkali metal atoms and halogen atoms on the carbon and silicon surface atoms of a 2D SiC/Si heterostructure is considered. Analytical estimates for charge transfer and the adsorption energy are reported.

Lithium adsorption on 2D transition metal dichalcogenides: towards a descriptor for machine learned materials design

Adsorption energy: an efficient descriptor for prediction of single-atom adsorption on 2D TMDs.

Surface Electronic Properties of Si‐Doped AlGaN and Thermionic Emission Characteristics with Adsorption of Alkali Metal Atoms

A thermionic energy converter (TEC) is a heat engine with a high theoretical efficiency, but a reduction in operating temperature is required for practical applications. Herein, the experimentally determined thermionic conversion characteristics of Si‐doped GaN films with Cs adsorption at 600 °C are reported. Low‐temperature thermionic emission around 300 °C is also reported for Si‐doped AlGaN surfaces with Cs adsorption. This emission temperature is considerably lower than the operating temperatures of conventional systems with a metal emitter. The AlGaN thin films are grown on n‐type 6H‐SiC substrates, and it is confirmed by ultraviolet photoelectron spectroscopy that the work function decreases as the AlN mole fraction x in the AlGaN samples is increased. Threshold temperatures of thermionic emission decrease with increasing AlN mole fraction and a corresponding reduction in the work function.

Effect of Alkali Metal Elements on Nitric Oxide Chemisorption at the edge of Char: A DFT study

The effect of alkali metal elements on nitric oxide (NO) heterogeneous adsorption on the surface of char was investigated by density functional theory (DFT) calculations. Geometries of reactants and products are optimized at B3LYP/6-31G(d) level. Adsorptions of alkali metal atoms on the "defective" activate sites of char is chemical adsorption with lots of energies released. Energies released from adsorption of alkali metal atoms on char is Li>K>Na. It is found that chemisorption of NO could be enhanced by loading alkali metal atoms on char as the absolute value of adsorption energy increases. The catalytic activity for NO chemisorption is K>Na>Li.

Rational Design of Two-dimensional Anode Materials: B2S as a Strained Graphene.

Alkali metal atom adsorption energy is an important descriptor for anode material design. In this study, an energy decomposition model is developed to provide valuable insights in understanding how the adsorption behavior can be tuned. As an example, Li adsorption on graphene enhanced by a tensile strain is analyzed based on this model. Such an analysis then motivates us to find a system with similar electronic structure but larger lattice parameter compared to graphene as an anode material. Our first-principles calculations indicate that B2S, as an isoelectronic system of graphene, is a good candidate. Its capacity is as high as 1498 mA h g-1 for both Li and Na ion batteries. Li and Na diffusion barriers on B2S are 0.45 and 0.23 eV, respectively. This study opens a new avenue for adsorption-behavior-guided two-dimensional material design.

Study on electronic and optical properties of alkali metal atoms adsorbed GaAs nanowires by first-principles calculations

This study presents a systematic investigation on the electronic and optical properties of GaAs nanowire surfaces by adsorption of alkali metal atoms (Li, Na, K, Cs) using a first-principles approach. Calculated adsorption energies show that all alkali metal atoms prefer to adsorb on the GaAs bridge site of GaAs nanowire surface, and Na adsorbed GaAs nanowire structure is the most stable. Under the joint action of surface dipole moment and band bending region, alkali metal atoms adsorption can obviously reduce the work function of GaAs nanowire surface. All alkali metal atoms carry positive charge due to the electron transfer from adatoms to nanowire surface atoms. After alkali metal atoms adsorption, the band gap of GaAs nanowire surface is narrowed and the Fermi level enters into the conduction band, which makes nanowire surfaces exhibit n-type conductivity. The absorption coefficient curves occur red-shifted phenomenon and the highest absorption peaks are slightly decreased due to alkali metal adsorption. We believe that these calculations are suitable for experimental exploration and useful for preparing alkali metal adsorbed GaAs-based nano-optoelectronic devices.

Effect of charging on silicene with alkali metal atom adsorption

Based on first-principles calculations, we studied the effects of charging on the structure, binding energy and electronic properties of silicene with alkali metal (AM) atom (Li, Na or K) adsorption. In AMSi2, electron doping enlarges the lattice constant of silicene, while the influence of hole doping is non-monotonic. In AMSi8, the lattice constant increases/decreases almost linearly with the increase in electron/hole doping. In addition, the AM–Si vertical distance can be greatly enlarged by excessive hole doping in both AMSi2 and AMSi8 systems. When the hole doping is as large as +e per unit cell, both AMSi2 and AMSi8 can be transformed from metal to semiconductor. However, the binding energy would be negative in the AM+ Si2 semiconductor. It suggests AM+ Si2 is unstable in this case. In addition, the electron doping and the AM–Si vertical distance would greatly influence the band gap of silicene in LiSi8 and NaSi8, while the band gap in KSi8 is relatively stable. Therefore, KSi8 may be a more practicable material in nanotechnology.

Adsorption of alkali-metal atoms on GaN nanowires photocathode

The adsorption of alkali-metal atoms on GaN nanowires photocathode was investigated by using first principles with density functional theory. The calculation of electronic and optical properties indicates that alkali metal adsorbed GaN nanowires are direct band gap semiconductor, and the band gap of GaN nanowires could be decreased by alkali metal adsorption. A new surface state near the Fermi level results from the Ga, N and alkali metal hybridization, which leads to form a metal electrical conductivity for GaN nanowires. More importantly, alkali metal adsorption can decrease the work function of GaN nanowires. Furthermore, the absorption spectrum of GaN nanowires is red shifted and moves to lower energy side because of alkali metal adsorption. Accordingly, this study will provide the theoretical basis for producing the alkali metal adsorbed GaN photoelectric devices.

The electronic properties of bare and alkali metal adsorbed two-dimensional GeSi alloy sheet

In this paper, the structural and electronic properties of both bare and alkali metal (AM) atoms adsorbed two-dimensional GeSi alloy sheet (GeSiAS) are investigated by means of first-principles calculations. The band gaps of bare GeSiAS are shown slightly opened at Dirac point with the energy dispersion remain linear due to the spin-orbit coupling effect at all concentrations of Ge atoms. For metal adsorption, AM atoms (including Li, Na and K) prefer to occupy the hexagonal hollow site of GeSiAS and the primary chemical bond between AM adatom and GeSiAS is ionic. The adsorption energy has an increase tendency with the increase of the Ge concentration in supercell. Besides, single-side adsorption of AM atoms introduces band gap at Dirac point, which can be tuned by the Ge concentration and the species of AM atoms. The strong relation between the band gaps and the distribution of Si and Ge atoms inside GeSiAS are also demonstrated. The opened band gaps of AM covered GeSiAS range from 14.8 to 269.1 meV along with the effective masses of electrons ranging from 0.013 to 0.109 me, indicating the high tunability of band gap as well as high mobility of carriers. These results provide a development in two-dimensional alloys and show potential applications in novel micro/nano-electronic devices.

Improvement of n-type conductivity in hexagonal boron nitride monolayers by doping, strain and adsorption

The n-type conductivity of h-BN monolayers is improved significantly via doping, applying strain and alkali-metal atom adsorption.

First-principles study on saturated adsorption of alkali metal atoms on silicene

Based on density functional first-principles calculations, we study the stability, micro-geometry, and electronic properties of alkali metal atoms adsorbed on silicene, and perform the comparison between pure and hydrogen-saturated silicenes. We found that all the formation energies of SiX(X=Li, Na, K and Rb) are negative, indicating that the relative structural stability of these new compounds is higher than silicene. Bader charge analysis shows that electric charge is transferred from Si atoms to H atoms in SiH compound, but in SiX the direction of charge transfer is opposite, i.e., the charge is transferred from alkali metal atoms to Si atoms. From the viewpoint of chemical bonding, it can be regarded that valence bond is formed between Si atoms and H atoms, and the bonds between Si and alkali metal atoms are mainly ionic, but there exists covalent contribution. From the band structure calculations, it is also found that the new type compound SiLi is a semiconductor with a direct band gap of 0.34 eV; however, all the other compounds of SiX(X=Na, K and Rb) exhibit metallic property.

Field emission properties of capped carbon nanotubes doped by alkali metals: a theoretical investigation

The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation. The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable. In addition, the adsorption energies increase with the introduction of the electric field. The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function. Furthermore, the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.

Anomalous changes in electron emission during adsorption of alkali metals on a carbon film

An anomalous change was discovered in the field of electron emission during the adsorption of alkali metal atoms on the surface of an amorphous carbon film. The phenomenon involves the disappearance of electron emission from graphite nanoclusters that were local emission sources before the deposition of cesium. The observed effect is explained on the basis of surface diffusion processes of cesium atoms in a nonuniform electric field and intercalation graphite nanostructures by cesium.