Silicon Cages Research Articles

Extended X-ray Absorption Fine Structure (EXAFS) Measurements on Alkali Metal Superatoms of Ta-Atom-Encapsulated Si16 Cage.

The silicon cage nanoclusters encapsulating a tantalum atom, termed Ta@Si16, exhibit characteristics of alkali metal "superatoms (SAs)". Despite this conceptual framework, the precise structures of Ta@Si16 and Ta@Si16+ remain unclear in quantum calculations due to three energetically close structural isomers: C3v, Td, and D4d structures. To identify the geometrical structure of Ta@Si16 SAs, structural analysis was conducted using extended X-ray absorption fine structure (EXAFS) with a high-intensity monochromatic X-ray source, keeping anaerobic conditions. Focusing on "superordered" films, which constitute amorphous thin films composed solely of Ta@Si16 SAs, this analysis preserved locally ordered structures. Spectral comparisons between experimental and simulated Ta L3-edge EXAFS unveil that Ta@Si16 SAs on a substrate adopt a C3v-derived structure, while Si K-edge EXAFS introduces spectral ambiguity in structural identifications, attributed to both intracluster and intercluster scatterings. These findings underscore the significance of locally ordered structure analyses in understanding and characterizing novel nanoscale materials.

Alkaline Earth Metal Superatom of W@Si16: Characterization of Group 6 Metal Encapsulating Si16 Cage on Organic Substrates.

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si16) exhibit a superatomic nature, depending on the central M atom owing to the number of valence electrons and charge state on organic substrates. Since M@Si16 superatom featuring group 4 and 5 transition metal atoms exhibit rare-gas-like and alkali-like characteristics, respectively, group 6 transition metal atoms are expected to show alkaline earth-like behavior. In this study, M@Si16, comprising a central atom from group 6 (MVI = Cr, Mo, and W) were deposited on C60 substrates, and their electronic and chemical stabilities were investigated in terms of their charge state and chemical reactivity against oxygen exposures. In comparison to alkali-like Ta@Si16, the extent of charge transfer to the C60 substrate is approximately doubled, while the oxidative reactivity is subdued for MVI@Si16 on C60, especially for W@Si16. The results show that a divalent state of MVI@Si162+ appears on the C60 substrate, which is consistently calculated to be a symmetrical cage structure of W@Si162+ in C3v, revealing insights into the "periodic law" of M@Si16 superatoms pertaining to the characteristics of alkaline earth metals.

Low viscosity and low temperature curing reactive POSS/epoxy hybrid resin with enhanced toughness and comprehensive thermal performance.

The mechanical and high-temperature resistance properties of epoxy resins cured at low temperatures (Tcuring ≤ 100 °C) are often inferior, and the most toughening modification methods for epoxy resins tend to compromise thermal resistance, which significantly limit the practical applications of it. Therefore, this work reported a low viscosity and low-temperature curing epoxy hybrid resin system (OPEP), adopting E-51 as a resin matrix, liquid anhydride (MHHPA) as a curing agent, tertiary amine (DMBA) as a curing accelerator, and reactive octa-epoxy terminated polyhedral oligomeric silsesquioxane (OG-POSS) as a toughening modifier. Results demonstrated that the OPEP system has excellent processability with low viscosity and long processing window period and satisfies the practical requirements of low-temperature curing. The OG-POSS exhibits superior compatibility and reactivity with the resin matrix, and its addition slightly reduces the Eα of the curing reaction and has a certain promotive effect on the curing of epoxy resin. In addition, the curing reaction rate of the OPEP resin complies with the Šesták-Berggren autocatalytic kinetics model. The impact strength, flexural strength, tensile strength, and elongation at break of the OPEP resin reached a maximum of 15.55 kJ m-2, 121.65 MPa, 90.36 MPa, and 2.48%, representing increases of 55.97%, 3.1%, 64.68%, and 26.51% compared to those of the pure resin, respectively. Notably, due to the heat-resistant inorganic silicon cage structure of OG-POSS, the thermal decomposition temperature (Td5), glass transition temperature (Tg), and heat distortion temperature (THDT) of the OPEP0.02 resin were 313.2 °C, 123.7 °C, and 102.0 °C, showing increases of 13.0 °C, 2.3 °C, and 6.8 °C compared to the pure resin, respectively, which is difficult to achieve for the general thermosetting resin toughening modification method. This research utilized organic-inorganic nanohybrid materials (POSS) to optimize the toughness and thermal stability of the resin in a coordinated manner, providing guidance for the preparation of high-performance epoxy resins that cure at low temperatures.

Mn2 Dimers Encapsulated in Silicon Cages: A Complex Challenge to MC-SCF Theory.

MC-SCF wavefunctions for three endohedral Mn/Si clusters, Mn2Si10, Mn2Si12, and [Mn2Si13]+, show evidence for strong static correlation, both in the Mn-Si bonds ('in-out correlation') and between the two Mn centers ('up-down correlation'). We use both Restricted and Generalized Active Spaces (RAS and GAS) to place constraints on the configurations included in the trial wavefunction, showing that, particularly in the high-symmetry cases, the GAS approach captures more of the static correlation. The important correlating pairs are similar across the series, indicating that the electronic structure of the endohedral Mn2 unit is, to a first approximation, independent of the size of the silicon cage in which it is embedded.

Two Complementary Approaches to Silicon-Supported Soluble [FeFe]-Hydrogenase Mimics

Two series of silicon-supported [(μ-SCH2)2NRFe2(CO)6] (R = p-OHC6H4, 3, and (CH2)2OH, 4a, and (CH2)5OH, 4b) hydrogenase mimics, as well as octamethylsilsesquioxane (POSS)-based nanostructures containing eight [(μ-SCH2)2NRFe2(CO)6] moieties, have been prepared either by reaction of the corresponding silyl and silyloxy chlorides and compounds 3 and 4 or by CuAAC between propargyl derivatives of silyl and silyloxy chlorides and azide 14. Cycloaddition between POSS-derived azide 23b and [(μ-SCH2)2NRFe2(CO)6] (R = alkyne) complexes 24 and 26 is efficient, leading to POSS-based nanostructures containing eight [(μ-SCH2)2NRFe2(CO)6] units. All of the complexes prepared through this work were soluble in organic solvents and hence fully characterizable by spectroscopic media. The electrochemistry of the linear siloxanes 6a and 10 is similar, with a reduction wave around −1.7 V, which is characteristic of these [(μ-SCH2)2NRFe2(CO)6] entities. Complexes 6a and 6b lacking 1,2,3-triazole moieties were electrochemically stable in the presence of AcOH, showing a strong electrocatalytic wave at −2.2 V, while complexes 16 and 18 having the 1,2,3-triazole ring decomposed but were electrocatalytically active in the wave at −2.2 V. POSS-[(μ-SCH2)2NRFe2(CO)6] derivatives 25 and 27 show a strong irreversible reduction event and are deposited in the electrode either when adding AcOH or over time (successive voltammograms). 29Si NMR shows that the integrity of the silicon cage is not affected by time or AcOH addition. These synthetic protocols and electrochemical studies will be applied in the design of silicon-supported [(μ-SCH2)2NRFe2(CO)6] mimics.

Molecularly Designed Cluster–Surface Interaction for Halogen-like and Alkali-like Metal-Encapsulating Silicon Cage Superatoms on n- and p-Type Organic Substrates

Molecularly Designed Cluster–Surface Interaction for Halogen-like and Alkali-like Metal-Encapsulating Silicon Cage Superatoms on n- and p-Type Organic Substrates

Size-Dependent Oxidative Stability of Silicon Nanoclusters Mixed with a Tantalum Atom

Metal-encapsulating silicon cage (M@Si16) nanoclusters (NCs) are promising superatoms (SAs) as function-tunable nanomaterials, which exhibit a superior chemical stability owing to electronic and geometric closures. Here, we examine how the superatomic nature of an alkali-like Ta@Si16 SA is staggered by the variation of the number of Si atoms in TaSin NCs (n = 6, 8, 12, 15, 17, and 18) and subsequent immobilization on a C60 fullerene substrate. Using X-ray photoelectron spectroscopy, the size dependence of chemical robustness of TaSin NCs on C60 against O2 exposures is quantitatively evaluated: In addition to the most outstanding stability of a Ta@Si16 SA as compared to TaSi15, some enhanced stability is also observed at Ta@Si17, which couples in a Si-adatom structure of (Ta@Si16)-Si to the support. While oxidative reactivities of TaSin are gradually suppressed from small NCs (n = 6) to larger ones (n = 18) with increasing number of Si atoms, the results show that (1) an enclosing Si cage around a Ta atom is completed at Ta@Si16 on C60 and (2) Ta@Si17 NCs are robust against O2 oxidation with assistance from the stability of Ta@Si16 SA despite the Si-adatom.

Photoelectron Spectroscopy and Density Functional Investigation of the Structural Evolution, Electronic, and Magnetic Properties of CrSin- (n = 14-18) Clusters.

CrSin- (n = 14-18) cluster anions have been investigated by a combination of photoelectron spectroscopy (PES) and first-principles calculations. The lowest-lying structures of the clusters have been determined by a global minimum search based on the genetic algorithm, combined with density functional theory (DFT) calculations. The simulated PES spectra of the lowest-energy isomers are in agreement with the experimental results, which gives strong evidence that the correct structures have been found. While sizes n = 14 and n = 15 prefer cage-like structures based on multi-center bonding within the cage, the larger sizes adopt structures based on fullerene-type cages around the Cr atom, with the additional atoms attached to the cage surface. A Hirshfeld analysis shows that the Cr atoms act as electron donors in all clusters, thus enhancing the electron count in the cage. It also reveals that the magnetic moment of 1μB shown by all clusters is mainly contributed by the Cr atom. One interesting exception is size 17, where the Cr atom contributes a small moment antiparallel to that of the silicon cage.

Cl@Si20H20]-: Parent Siladodecahedrane with Endohedral Chloride Ion.

Fullerenes and diamondoids are at the core of nanoscience. Comparable monodisperse silicon analogues are scarce. Herein, we report the synthesis of the parent siladodecahedrane, which represents the largest Platonic solid. It shares its pattern of pentagonal faces with the smallest fullerene, C20, and its saturated, H-terminated skeleton with diamondoids. Similar to endofullerenes, the silicon cage encapsulates a chloride ion ([Cl@Si20H20]-); similar to diamondoids, its Si-H termini offer a wealth of opportunities for further functionalization. Mere treatment with chloromethanes leads to the perchlorinated cluster [Cl@Si20Cl20]-. Both compounds were characterized by mass spectrometry, X-ray crystallography, NMR spectroscopy, and quantum-chemical calculations. The experimentally determined 35Cl resonances of the endohedral chloride ions are particularly diagnostic to probe the Cl- → Si20 interaction strength as a function of the different surface substituents, as we have proven by high-level computational analyses.

Silicon cages with tailored mesopores as anodes for high rate performance lithium ion batteries

Silicon (Si) with high energy density is identified as the most promising candidate for commercial lithium-ion batteries anodes. Unfortunately, the volume expansion severely damages the battery cycle life during cycling, resulting in fast capacity fading during the battery operation. Herein, a facile design was proposed for the preparation of novel tailored mesoporous Si cages (TMSC) to mitigate this issue. The TMSC material, with mesoporous anamorphic spherical shells and nano-sized Si cores, consists of numerous interconnected channels and forms a half open three-dimensional network. When evaluated as electrode material for lithium-ion batteries, it exhibits the reversible capacity of 931.1 mAh/g after 200 cycles at 1 A/g, which is more stable than that of Si pomegranates with intact shells. Moreover, it displays a high rechargeable capacity of 552.3 mA h/g over 500 cycles at 4 A/g and the capacity decay ratio is only 0.11% for each cycle.

Electronic and geometric stability of double titanium-doped silicon clusters

We performed the genetic algorithm (GA) incorporated with density functional theory (DFT) calculations to investigate the atomic and electronic properties of a series of Ti2Si n (n = 3 = –24) clusters. Comprehensive consideration on the formation energy, the second difference in cluster energy and the addition energy of Si to a Ti2Si n−1 cluster as well as the HOMO-LUMO gap, our results show that Ti2Si4 cluster is the most stable one in the series of clusters, followed by the Ti2Si13, Ti2Si21,Ti2Si15 and Ti2Si7 clusters, which can be understood by the combination of symmetry and electron shell filling rule. The silicon cage could be obviously enhanced by doping double Ti atoms making them promising nanoscale materials.

The aromatic fullerene-like silicon cage with 12 Si5 pentagons stabilized by a V3 unit

Silicon clusters doped with transition-metal (TM) atoms not only can hold stable fullerene-like structures, but also can exhibit unique electronic properties. Multiple TM doped silicon clusters are ideal models for investigating semiconductor nanomaterials and localized effects of condensed states. In this work, the geometrical and electronic properties of three V atoms doped anionic, neutral, and cationic Si20 clusters were investigated using quantum chemical calculations and a DFT-based unbiased search based on the particle swarm optimization (CALYPSO) software. The global minima of anionic, neutral, and cationic V3Si20 clusters were found to all hold a fullerene-like silicon cage with 12 Si5 pentagons stabilized by a V3 unit. The three V atoms exhibit strong interactions based on the bonding length, Wiberg bond orders, electronic charge density surfaces, and MOs. Moreover, the V atoms act as the electron acceptors on the basis of the natural population analysis (NPA), atomic dipole moment corrected Hirshfeld (ADCH) population, and atoms in molecules (AIM) population. Furthermore, V3Si20ˉ, V3Si20, and V3Si20+ show significant aromaticity according to the nucleus-independent chemical shift (NICS), aromatic stabilization energy (ASE), and multicenter bond index calculations.

Structures, stabilities and electronic properties of the bimetal V2-doped Sin (n = 1–10) clusters: a density functional investigation

Structures, stabilities and electronic properties of mixed silicon/vanadium clusters (V2Sin; n = 1–10) have been investigated systematically using the CALYPSO structural searching approach and density functional theory calculations. Results indicate two vanadium atoms tend to form V2 bond encapsulated gradually into silicon cages with the increasing number of silicon atoms. Analyses of stabilities reveal that V2Si6 has the highest stability and the doping of two vanadium atoms makes the stabilities of silicon clusters decrease. At last, charge transfer, Mayer bond order, electron localization function, IR and Raman spectrum are operative for characterizing and rationalizing the electronic properties of doped clusters.

A Novel Polystyrene Nanocomposite with Fully Phenyl POSSs Functionalized

AbstractTwo novel polyhedral oligomeric silsesquioxanes/polystyrene (POSS/PS) nanocomposites are synthesized by in situ polymerization of styrene, in the presence of 5% w/w of POSS in which two identical silicon cages Ar7(SiO1.5)8 (with Ar═Phenyl) are linked to different rigid molecular bridges. The obtained nanocomposites are characterized by 1H‐NMR spectroscopy, thermogravimetric analysis, and by scanning electron microscopy (SEM). The resistance to the thermal degradation is evaluated by measuring the temperature at 5% mass loss (T5%), whose values for the prepared nanocomposites are largely higher than those found for PS, in the same experimental conditions. SEM analysis showed a good dispersion of the molecular filler within the matrix, thus providing a justification for the increasing in PS/POSSs thermal stability.

Solar Driven CO2 Hydrogenation on Ti-Doped Silicon Nanocages

Hydrogenation of carbon dioxide (CO2) to produce fuels and value-added chemicals is a critical reaction to solve both energy and environment issues. Developing efficient catalysts composed of earth-abundant, cost-effective and eco-friendly elements is highly desired but remains challenging. Here, we exploit titanium-doped silicon cage nanoclusters (TiSin, n = 12–16) for CO2 hydrogenation. Our first-principles calculations show that the activity and product selectivity of TiSin clusters exhibit remarkable size-dependences, and they can also absorb a large portion of sun light from visible to ultraviolet regimes to drive the catalysis. Their activity origins from the unsaturated electronic states on the silicon cage, mediated by the strong covalent bonding between Si and Ti atoms. More importantly, we establish a relationship between binding capability of TiSin clusters and the p orbital center of silicon cage, which provide general guidelines for atomically precise design of not only silicon-based clusters but also other non-metal catalysts for highly active and selective CO2 conversion.

Polystyrene Nanocomposites Reinforced with Novel Dumbbell-Shaped Phenyl-POSSs: Synthesis and Thermal Characterization.

Two series of novel dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), fully functionalized with phenyl groups at the corner of the silicon cages, were used to prepare polystyrene (PS) nanocomposites through the method of in situ polymerization. The percentage of the molecular filler reinforcement was set as 5% w/w of POSS and was checked by 1H-NMR spectroscopy. The obtained nanocomposites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermal and morphological properties were evaluated and compared among the nanocomposites obtained using the two different series of dumbbell-shaped POSSs and with the net PS. The thermal parameters for the prepared nanocomposites were very high when compared with those of neat PS, and they evidenced significant differences when an aliphatic or aromatic bridge was used to link the silicon cages. SEM analysis results allow us to hypothesize a justification for the different resistance to thermal degradation showed by the two series of molecular reinforcement.

Largely Improved Battery Performance Using a Microsized Silicon Skeleton Caged by Polypyrrole as Anode.

Various architectures with nanostructured silicon have demonstrated promising battery performance while posing a challenge in industrial production. The current ratio of silicon in graphite as anode is less than 5 wt %, which greatly limits the battery energy density. In this article, we report a scalable synthesis of a large silicon cage composite (micrometers) that is composed of a silicon skeleton and an ultrathin (<5 nm) mesoporous polypyrrole (PPy) skin via a facile wet-chemical method. The industry available, microsized AlSi alloy was used as precursor. The hollow skeleton configuration provides sufficient space to accommodate the drastic volume expansion/shrinkage upon charging/discharging, while the conductive polymer serves as a protective layer and fast channel for Li+/e- transport. The battery with the microsilicon (μ-Si) cage as anode displays an excellent capacity retention upon long cycling at high charge/discharge rates and high material loadings. At 0.2 C, a specific capacity of ∼1660 mAh/g with a Coulombic efficiency (CE) of ∼99.8% and 99.4% was achieved after 500 cycles at 3 mg/cm2 loading and 400 cycles at 4.4 mg/cm2 loading, respectively. At 1.0 C, a capacity as high as 1149 mAh/g was retained after 500 cycles with such high silicon loading. The areal capacity of as high as 6.4 mAh/cm2 with 4.4 mg/cm2 loading was obtained, which ensures a high battery energy density in powering large devices such as electric vehicles.

Trapped in a Silicon Cage

Almost fifty years ago, in April 1970, there was a rebellion at the annual conference of the American Society for Public Administration in Philadelphia. A group of young professors boycotted the of...

Theoretical Study on the Growth Behavior and Photoelectron Spectroscopy of Lanthanum-Doped Silicon Clusters LaSi n 0/− (n = 6–20)

The growth behavior and electronic properties of the lowest energy structures of neutral LaSin (n = 6–20) and their anions were explored by means of the ABCluster global structure searching strategy combined with the mPW2PLYP double-hybrid density functional. The results revealed that the growth behavior of the lowest energy structures of anionic LaSi − (n = 10–20) clusters choose La-linked two silicon subclusters to La-encapsulated in silicon cages. For neutral LaSin (n = 6–20), the growth behavior of the lowest energy structures from substitutional structure to linked motifs and finally to encapsulated configurations occurs at n = 14 and 20, respectively. The simulated photoelectron spectroscopy, adiabatic electron affinities, vertical detachment energies, relative stability and HOMO–LUMO energy gaps were presented. Analyses of HOMO–LUMO energy gaps, relative stability, and chemical bonding reveal that the LaSi20− possesses ideal thermodynamic and chemical stability in a high Ih-symmetry endohedral motif, which can turn it into suitable constitutional units for cluster-assembled nanomaterials.

Probing the structures and properties of Ti2Si20−/0 clusters by density functional theory calculations

We present a theoretical investigation on the structures and properties of Ti2Si20−/0 clusters using density functional theory calculations. The results showed that the global minima of both anionic and neutral Ti2Si20 adopt a C2h symmetric double hexagonal prisms stacked structure with the two Ti atoms encapsulated inside the silicon cage. Bond length, Wiberg bond order, constant electronic charge density, and molecular orbital analyses suggest that the TiTi interactions in Ti2Si20−/0 are weak. Interestingly, Ti2Si20−/0 exhibit significant 3D aromaticity, which play important roles in their structural stability.