Silicon Atoms Research Articles

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

Intramolecular Ring Expansion of 3-Silaazetidine with Alkynes Enabled by Pd-Catalyzed Si-C Bond Activation.

An intramolecular ring expansion of in situ formed 3-silaazetidine with internal alkynes has been developed via Pd-catalyzed Si-C bond activation. The reaction gives rise to 6,5- and 6,6-fused bicyclic 1,3-azasilines, in which the silicon atom locates at the ring junction position.

Some Theoretical and Experimental Evidence for Particularities of the Siloxane Bond

The specific features of the siloxane bond unify the compounds based on it into a class with its own chemistry and unique combinations of chemical and physical properties. An illustration of their chemical peculiarity is the behavior of 1,3-bis(2-aminoethylaminomethyl)tetramethyldisiloxane (AEAMDS) in the reaction with carbonyl compounds and metal salts, by which we obtain the metal complexes of the corresponding Schiff bases formed in situ. Depending on the reaction conditions, the fragmentation of this compound takes place at the siloxane bond, but, in most cases, it is in the organic moieties in the β position with respect to the silicon atom. The main compounds that were formed based on the moieties resulting from the splitting of this diamine were isolated and characterized from a structural point of view. Depending on the presence or not of the metal salt in the reaction mixture, these are metal complexes with organic ligands (either dangling or not dangling silanol tails), or organic compounds. Through theoretical calculations, electrons that appear in the structure of the siloxane bond in different contexts and that lead to such fragmentations have been assessed.

Microstructural patterning of the reaction zone formed by solid-state interaction between iridium and SiC ceramics

The phenomena occurring within the Ir–SiC couple depending on temperature and time were studied. In the temperature range of 1300–1400°C, when all the components of the Ir–Si–C system are solids, the following sequence of phases is formed between Ir and SiC plates: Ir / Ir3Si / Eutectoid / Ir3Si2 / IrSi / IrSi + C/ SiC. The effect of exposure time on the morphology, phase composition, and thickness of the product layer was studied. The reaction between Ir and SiC was shown to obey the linear law, being indicative of the kinetic control. Iridium atoms diffuse faster across the product layer than silicon atoms do. The product thickness increases mainly due to growth of the IrSi layer with carbon inclusions. A periodic morphology of the IrSi layer composed of carbon-free IrSi layers and IrSi layers with carbon inclusions is observed with increasing exposure time. The thickness of carbon-free IrSi layers and sizes of carbon inclusions increases at greater distances from the reaction front. The process is accompanied by ordering and graphitization of carbon inclusions. The Vickers microhardness for the iridium silicide phases were measured. The microhardness of iridium silicides is ∼ 3 times less than that of SiC that can decrease the brittleness of SiC-based materials.

A silicene-based plasmonic electro-optical switch in THz range

The first design and simulation of a silicene-based optical switch in the frequency range of 20 to 50 THz are presented. Silicene is a monolayer of silicon atoms stacked together in the shape of a honeycomb that has outstanding features such as compatibility with current technology, strong spin-orbital coupling, and attractive optical properties. The proposed switch consists of a silicene waveguide encapsulated between layers of which transmits the input signal by emitting surface plasmon polaritons. To control the ON and OFF switching modes using impurities and DC voltage, we change the chemical potential of silicene. The main advantages of the proposed switch over similar graphene types are fewer losses, broadband frequency range, more compatibility with current technology, and also due to the encapsulation of silicene between the waveguide is isolated from the environment. Also, Q-factor, insertion loss, and extinction ratio for the proposed switch are 189, 0.39 dB, and 51 dB, respectively.

Simulation and experimental study on limited cutting and heat effect of silicon carbide

As a typical third-generation semiconductor material, silicon carbide (SiC) presents outstanding properties in terms of the bandgap width, disruptive voltage strength, thermal conductivity and so on. However, there are still technical difficulties in acquiring the nondestructive surface with an optical quality, which seriously constrained the application and development of SiC functional devices. Therefore, in this paper, the material removal mechanism of SiC was firstly investigated according to the MD simulation results. Then, nanocutting experiments were conducted under the vacuum environment of the scanning electron microscope, where the transient behavior of material removal could be observed online with a high resolution, so that the simulation results can be effectively verified. From the simulated and experimental results, it was found that under the research range of parameters, the limited removal thickness (LRT) of SiC decreased with an increase in cutting speed, while the cutting depth had little effect on the LRT. Besides, the polycrystalline SiC presented a smaller LRT compared with the monocrystalline SiC. Therefore, it was advantageous to enhance the machined surface quality and improve the surface integrity with regard to polycrystalline SiC. The cutting temperature increased with an increase in cutting speed during the nanocutting, and a higher cutting speed can prolong the time for the workpiece temperature to stabilize. The findings of this study are able to provide a theoretical basis for the improvement of ultraprecision machining technology especially for hard–brittle and hard-to-process materials. • Material removal mechanism was studied both experimentally and numerically. • Limited removal thickness was studied by labeling and tracing the silicon atoms. • Nanocutting tests were performed with online observation via an SEM. • Experimental results are in good agreement with the MD simulation results.

Three-Input NPN Class Gate Library for Atomic Silicon Quantum Dots

This article proposes a complete three-input gate library using atomic silicon quantum dots made of silicon dangling bonds.

The Use of Exchange Coupled Atom Qubits as Atomic-Scale Magnetic Field Sensors.

Phosphorus atoms in silicon offer a rich quantum computing platform where both nuclear and electron spins can be used to store and process quantum information. While individual control of electron and nuclear spins has been demonstrated, the interplay between them during qubit operations has been largely unexplored. This study investigates the use of exchange-based operation between donor bound electron spins to probe the local magnetic fields experienced by the qubits with exquisite precision at the atomic scale. To achieve this, coherent exchange oscillations are performed between two electron spin qubits, where the left and right qubits are hosted by three and two phosphorus donors, respectively. The frequency spectrum of exchange oscillations shows quantized changes in the local magnetic fields at the qubit sites, corresponding to the different hyperfine coupling between the electron and each of the qubit-hosting nuclear spins. This ability to sense the hyperfine fields of individual nuclear spins using the exchange interaction constitutes a unique metrology technique, which reveals the exact crystallographic arrangements of the phosphorus atoms in the silicon crystal for each qubit. The detailed knowledge obtained of the local magnetic environment can then be used to engineer hyperfine fields in multi-donor qubits for high-fidelity two-qubitgates.

Structural and electronic properties of Ln2Si6q: (Sm, Eu, Yb; q = 0, −1) clusters

A systematic study on Ln2Si6q (Ln = Sm, Eu, Yb; q = 0, −1) clusters has been performed by density functional theory (DFT). Global minimum searches reveal that the two lanthanide atoms prefer to absorb on the surface of parent silicon-based clusters. Natural population analysis (NPA) is utilized to investigate the electronic and magnetic properties of Ln2Si6q, the electrons always transfer from the lanthanide atoms to parent silicon atoms. Most interestingly, the DFT calculations demonstrate that the magnetic moments of the doped rare earth atoms remain largely localized (13μB for Sm2Si6−/ Eu2Si6−, 12μB for Sm2Si6 and 14μB for Eu2Si6), and the atomic-like magnetism is maintained in the doped cluster. Combined with average binding energy, dissociation energy and HOMO-LUMO gap, Sm2Si6 is probed to the most stable cluster. The current work shows that lanthanide diatom doped silicon-based clusters could have potential utility in new rare earth nanomaterials with tunable magnetic properties.

Computer simulation of AlCoCuFeNi high-entropy alloy thin film deposition and crystallization

The processes of deposition and crystallization of high-entropy AlCoCuFeNi alloy thin film on a substrate of silicon (100) are studied by classical molecular dynamics simulation. Total simulation time reaches 50 ns. The embedded atom model is used to describe the interaction among Al–Co–Cu–Ni–Fe. Interaction between the atoms of Al, Co, Cu, Fe, Ni, and the Si substrate is described using the Lennard–Jones potential, and the interaction between the silicon atoms was modeled using the Stillinger–Weber potential. It is found that at the first stage of deposition small clusters are formed and the process of crystallization starts after ~ 5 ns of simulation, at the characteristic sizes of clusters of about 2 nm. At the end of the simulation, after the 50 ns of modeling, the simulated film contains a face-centered cubic phase, a body-centered cubic phase, a hexagonal close-packed phase, and an amorphous phase. An analysis of the radial distribution of atoms makes it possible to determine the distances between the nearest neighbors and estimate the lattice parameters of these phases.

Silicon Carbide Precursor: Structure Analysis and Thermal Behavior from Polymer Cross-Linking to Pyrolyzed Ceramics

The Silres H62C methyl-phenyl-vinyl-hydrogen polysiloxane is a promising candidate as a SiC precursor for 3D printing based on photopolymerization reaction. An in-depth nuclear magnetic resonance spectroscopy analysis allowed us to determine its structure and quantify its functional groups. The polysiloxane was found to have a highly branched ladder-like structure, with 21.9, 31.4 and 46.7% of mono-, di- and tri-functional silicon atoms. The polysiloxane cross-links from 180 °C using hydrosilylation between silyl groups (8.4% of the total functional groups) and vinyl groups (12.0%) and contains a non-negligible ethoxy content (2.4%), allowing cross-linking through a hydrolyze/condensation mechanism. After converting the polymer into ceramic and thus releasing mainly hydrogen and methane, the ceramic yield was 72.5%. An X-ray diffraction analysis on the cross-linked and pyrolyzed polysiloxane showed that the ceramic is amorphous at temperatures up to 1200 °C and starts to crystallize from 1200 °C, leading into 3C-SiC carbon-rich ceramic at 1700 °C in an argon atmosphere.

Effects of an epitaxial graphene layer for the growth of nickel silicides on a Ni(111) substrate

In this paper, we report on an in-depth study on the growth of nickel silicides, either on a clean Ni(111) substrate or in the presence of a previously-grown epitaxial single graphene (Gr) layer, by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). We demonstrate that two different nickel silicides, namely Ni3Si and Ni2Si, progressively form as the annealing temperature is increased from 450 °C to 600 °C. The presence of the Gr layer does not change the nature of the two silicide phases but rather affects the morphology of the silicide overlayer. Indeed, in the presence of Gr, the deposited silicon atoms intercalate by passing through the Gr defects or domain boundaries and accumulate on specific sample areas, resulting in the formation of multilayer silicide islands. In the absence of Gr, the deposited silicon atoms react uniformly with the nickel substrate, resulting in the formation of homogeneous large scale silicide layers.

N-Heterocyclic Carbene-Catalyzed Desymmetrization of Siladials To Access Silicon-Stereogenic Organosilanes.

An N-heterocyclic carbene (NHC)-catalyzed enantioselective monoesterification of silicon-centered dialdehydes with alcohols or phenols is accomplished, providing optically active organosilanes bearing a stereogenic center at the silicon atom. This desymmetrization protocol is suitable for scale-up synthesis and late-stage modifications of complex molecules, and the products can be further transformed to other enantiopure functionalized silanes.

Synthesis and Characterization of Cyclotri- and Tetrasiloxanes with Pyrenyl Groups.

Cyclosiloxanes directly bearing polyaromatic groups on silicon atoms have scarcely been reported. Herein, hexa(1-pyrenyl)cyclotrisiloxane (2) and octa(1-pyrenyl)cyclotetrasiloxane (3) were successfully prepared from di(1-pyrenyl)silanediol (1) in the presence of a weak base such as tetraethylammonium acetate and triethylamine in MeCN. The structure of the cyclosiloxanes bearing multiple pyrenyl groups in the solid and solution states was evaluated by NMR, X-ray crystallography, and density functional theory (DFT) calculations. All pyrenyl groups of 2 were oriented outward, and no π-π stacking of adjacent pyrenyl groups was observed. However, all pairs of adjacent pyrenyl groups at 1- and 3-positions in 3 are oriented in the same direction and were π-π stacked with respect to each other. The UV-vis spectra of 2 and 3 in organic solvents showed a slight broadening of the peaks, as observed for typical pyrene derivatives. Interestingly, the fluorescence spectra of 2 showed small monomer and strong excimer emissions; however, those of 3 showed only a strong excimer emission in all solvents. Partially pyrenylated cyclotri- and tetrasiloxanes (compounds 4 and 5) showed solvent-dependent monomer and excimer spectra as observed for di(1-pyrenyl)silane derivatives, implying that the excimer emissions of 2 and 3 arise from mainly geminal and vicinal pyrenyl groups, respectively.

Identification and characterization of selected silyl substituted silyl anions by liquid injection field desorption ionization mass spectrometry.

Silyl anions are crucial building blocks in silicon chemistry and are frequently used in organosilicon chemistry. These so-called silanides are negatively charged three-coordinate species, isoelectronic to carbanions. In this contribution, we synthesized already literature known and unknown anionic silicon species. Here we focused on silyl substituted silyl anions with different substituted silicon atoms like hydrogen, methyl, and methoxy groups. Furthermore, we investigated these species with liquid injection field desorption ionization mass spectrometry.

TG/MS/FTIR study on thermal degradation process of clay mineral–polysiloxane nanocomposites

Clay-polymer nanocomposites (CPNs) are an important group of materials that are currently receiving increasing attention. The study of the properties of new CPNs is vital, as it facilitates a deeper understanding of their applicability. This study assessed for the first time the thermal stability of clay-polysiloxane nanocomposite as well as their degradation mechanism under an inert atmosphere with the use of the TG/MS/FTIR (simultaneous mass spectrometry and Fourier transform infrared spectroscopy of off-gases from a thermogravimetric analyzer) technique. Organo-montmorillonite (organo-Mt) nanofiller was introduced at different amounts (0, 1, 2, 4, and 8 wt% in relation to the weight of the polymer matrix) into the structure-controlled polysiloxane network. The polysiloxane matrix was obtained by cross-linking poly(methylhydrosiloxane) with poly(dimethylsiloxane) terminated by vinyldimethylsiloxy groups at both ends. This cross-linking was carried out through a hydrosilylation reaction with an equimolar ratio of Si–H and Si-CH=CH2 groups, in the presence of Karstedt's catalyst. Along with an increased amount of organo-Mt, a deterioration in nanocomposites thermal stability, with an increase in the number of thermal decomposition steps, and changes in the degradation mechanism of polysiloxane matrix were observed. The presence of organo-Mt mainly affected the redistribution of bonds at the silicon atoms during the thermolysis of the studied materials. Regardless of the amount of the mineral nanofiller added, the nanocomposites had a similar residual mass remaining after pyrolysis of the studied CPNs at 1000 °C, which was much lower than that of the initial polysiloxane network.

The millimeter-wave spectrum of the SiP radical (X2Πi): Rotational perturbations and hyperfine structure.

The millimeter/submillimeter-wave spectrum of the SiP radical (X2Πi) has been recorded using direct absorption spectroscopy in the frequency range of 151-532GHz. SiP was synthesized in an AC discharge from the reaction of SiH4 and gas-phase phosphorus, in argon carrier gas. Both spin-orbit ladders were observed. Fifteen rotational transitions were measured originating in the Ω = 3/2 ladder, and twelve in the Ω = 1/2 substate, each exhibiting lambda doubling and, at lower frequencies, hyperfine interactions from the phosphorus nuclear spin of I = 1/2. The lambda-doublets in the Ω = 1/2 levels appeared to be perturbed at higher J, with the f component deviating from the predicted pattern, likely due to interactions with the nearby excited A2Σ+ electronic state, where ΔEΠ-Σ ∼ 430cm-1. The data were analyzed using a Hund's case aβ Hamiltonian and rotational, spin-orbit, lambda-doubling, and hyperfine parameters were determined. A 2Π/2Σ deperturbation analysis was also performed, considering spin-orbit, spin-electronic, and L-uncoupling interactions. Although SiP is clearly not a hydride, the deperturbed parameters derived suggest that the pure precession hypothesis may be useful in assessing the 2Π/2Σ interaction. Interpretation of the Fermi contact term, bF, the spin-dipolar constant, c, and the nuclear spin-orbital parameter, a, indicates that the orbital of the unpaired electron is chiefly pπ in character. The bond length in the v = 0 level was found to be r0 = 2.076 Å, suggestive of a double bond between the silicon and phosphorus atoms.

Disilicon Dicarbonyl Complex: Synthesis and Protonation of CO with O-H Bond.

Reaction of solid NHB-stabilized disilyne (NHB)Si≡Si(NHB) (1, NHB = [ArN(CMe)2NAr]B, Ar = 2,6-iPr2C6H3) with 1 atm of carbon monoxide yielded the first 1,2-disilicon dicarbonyl complex (NHB)(OC)SiSi(CO)(NHB) (2). Hydrolysis and methanolysis of 2 led to the C-C coupling and protonation of two CO oxygen atoms giving disilacyclobutene derivatives 3 and 4. In contrast, reaction of 2 with iodomethane resulted in the oxidative addition to the silicon atoms with the formation of 1,2-diiodo-disilane 5 with the liberation of CO molecules. Single-crystal X-ray diffraction analysis of 2 disclosed the coordination of CO to the two silicon atoms with a unique 1,2-dicarbonyl-disilane skeleton, in which the pronounced backbonding from the lone pairs of silicon p orbitals to CO π* orbitals was elucidated by DFT calculations.

On-surface synthesis of disilabenzene-bridged covalent organic frameworks

Substituting carbon with silicon in organic molecules and materials has long been an attractive way to modify their electronic structure and properties. Silicon-doped graphene-based materials are known to exhibit exotic properties, yet conjugated organic materials with atomically precise Si substitution have remained difficult to prepare. Here we present the on-surface synthesis of one- and two-dimensional covalent organic frameworks whose backbones contain 1,4-disilabenzene (C4Si2) linkers. Silicon atoms were first deposited on a Au(111) surface, forming a AuSix film on annealing. The subsequent deposition and annealing of a bromo-substituted polyaromatic hydrocarbon precursor (triphenylene or pyrene) on this surface led to the formation of the C4Si2-bridged networks, which were characterized by a combination of high-resolution scanning tunnelling microscopy and photoelectron spectroscopy supported by density functional theory calculations. Each Si in a hexagonal C4Si2 ring was found to be covalently linked to one terminal Br atom. For the linear structure obtained with the pyrene-based precursor, the C4Si2 rings were converted into C4Si pentagonal siloles by further annealing.

A computational insight into the intrinsic, Si-decorated and vacancy-defected γ-graphyne nanoribbon towards adsorption of CO2 and O2 molecules

In this study, the effects of decorating a silicon (Si) atom and applying a single vacancy defect on an armchair γ-graphyne nanoribbon (A-γ-GyNR) are investigated toward CO2 and O2 molecules adsorption. The magnetic and electronic transport properties, including the calculation of adsorption energy, charge transfer, magnetic moment, band structure, phonon dispersion and density of state (DOS), have been studied using the spin-polarized density functional theory (DFT) method. The stability of the proposed substrates is measured and different positions for gas molecules are considered. The results reveal that the highest amounts of adsorption energy of CO2 (0.63 eV) and O2 (2.2 eV) molecules belong to the substrate decorated with the Si atom in the 12-membered ring (H1) and acetylene linkage (B3), respectively. In addition, the removal of a carbon atom with sp hybridization improves the O2 molecule adsorption by 3.34 times compared to the primary substrate (P-GyNR). According to the recovery time calculations, the most appropriate desorption time is related to T1-M1 model. The current–voltage characteristic confirms that the resistance of the introduced sensors fully changed after sensing. This work can be considered as an effective step toward understanding and developing A-γ-GyNR-based gas sensors.