Si Analogues Research Articles

Exchange Bias State at the Crossover to 2D Ferromagnetism.

The inherent malleability of 2D magnetism provides access to unconventional quantum phases, in particular those with coexisting magnetic orders. Incidentally, in a number of materials, the magnetic state in the bulk undergoes a fundamental change when the system is pushed to the monolayer limit. Therefore, a competition of magnetic states can be expected in the crossover region. Here, an exchange bias state is observed at the crossover from 3D antiferromagnetism to 2D ferromagnetism driven by the number of monolayers in the metalloxene GdSi2. The material constitutes a stack of alternating monolayers of Gd and silicene, the Si analogue of graphene. The exchange bias manifests itself as a shift of the hysteresis loop signifying coupling of magnetic systems, as evidenced by magnetization studies. Two features distinguish the phenomenon: (i) it is intrinsic, i.e. it is detected in an individual compound; (ii) the exchange bias field, 1.5 kOe, is unusually high, which is conducive to applications. The results suggest magnetic derivatives of 2D-Xenes to be prospective materials for ultracompact spintronics.

Nonthermal plasma synthesized silicon-silicon nitride core–shell nanocrystals with enhanced photoluminescence

Enhanced optical properties of silicon quantum dots (QDs) are pertinent for light-emitting applications including luminescent solar cell concentrators. Surface passivation plays a crucial role in improving photoluminescent quantum yield and effective carrier lifetimes of silicon nanocrystals and is often achieved by surface grafting of organic ligands. However, organically passivated silicon QDs often suffer from a deterioration of the optical properties when exposed to the environment. In this work, we explore the effect of an inorganic amorphous silicon nitride (SiN x ) shell on silicon QDs and their optical properties. Utilizing a dual plasma approach with dual injection ports, we synthesized Si/SiN x core–shell nanoparticles using SiH4, NH3, H2, and Ar. The core–shell nanocrystals were characterized using optical and structural methods, which revealed that higher nitridation plasma powers could lead to Si precipitation altering the composition of SiN x shell. While as-synthesized Si/SiN x core–shell nanocrystals did not exhibit photoluminescence, oxidized Si/SiN x core–shell nanocrystals show significantly higher quantum yield (35%) and longer carrier lifetime compared to their bare oxidized Si analogues even after an environmental exposure of six months.

Stabilization of group 14 elements E = C, Si, Ge by hetero-bileptic ligands cAAC, MCOn with push-pull mechanism.

The stability and bonding of a series of hetero-diatomic molecules with general formula (cAAC)EM(CO)n , where cAAC = cyclic alkyl(amino) carbene; E = group 14 elements (C, Si, and Ge); M = transition metal (Ni, Fe, and Cr) have been studied by quantum chemical calculations using density functional theory (DFT) and energy decomposition analysis-natural orbital chemical valence (EDA-NOCV). The equilibrium geometries were calculated at the BP86/def2-TZVPP level of theory. The tri-coordinated group 14 complex (1a, 4a, and 7a) in which one of the CO groups is migrated to the central group 14 element from adjacent metal is theoretically found to be more stable when the central atom (E) is carbon. On the other hand, the two-coordinate group 14 element containing metal-complexes (2, 5, 8, 3, 6, and 9) are found to be more stable with their corresponding heavier analogues. The electronic structures of all the molecules have been analyzed by molecular orbital, topological analysis of electron density and natural bond orbital (NBO) analysis at the M06/def2-TZVPP//BP86/def2-TZVPP level of theory. The nature of the cAACE and EM bonds has been studied by EDA-NOCV calculations at BP86-D3(BJ)/TZ2P level of theory. The EDA analysis suggests that the bonding of cAACC(CO) can be best represented by electron sharing σ and π interactions, whereas, C(CO)M(CO)n-1 by dative σ and π interactions. On the other hand, EDA-NOCV calculations suggests both dative σ and π interactions for cAACE and EM(CO)n bonds of the corresponding Si and Ge analogues having stronger σ- and relatively weaker π-bonds. The topological analysis of electron density supports the closed-shell interaction for the Si and Ge complexes and open-shell interaction for the carbon complexes. The calculated proton affinity and hydride affinity values corroborated well with the present bonding description. This class of complexes might act as efficient future catalysts for different organic transformations due to the presence of electron rich group 14 element and metal carbonyl.

Adsorption of gas molecules on graphene, silicene, and germanene: A comparative first-principles study

Silicene and germanene, the Si and Ge analogs of graphene, have recently extended the list of existing two-dimensional atomic crystals. They have attracted great interest in various fields, ranging from electronics to energy, owing to their unique properties. In this work, we employed density functional theory to examine the dissociative adsorption of NH3, PH3, H2O, and H2S on graphene, silicene, and germanene two-dimensional materials. We found that the molecular adsorption energy is similar for all the molecules. However, the dissociative adsorption energy on silicene was significantly lower than that of germanene and graphene. Almost all the dissociative adsorptions on the silicene surface were exothermic, whereas those on the graphene and germanene surfaces were endothermic. The most stable dissociative adsorption was found at the para position. Overall, this study reveals that dissociative adsorption is more feasible on germanene and silicene compared to that on graphene.

Metal substitution effects of aluminophosphate AlPO4-5 as solid acid catalyst for esterification of acetic acid with ethanol

Metal substitution in aluminophosphates is known to induce unique structural and surface characteristics that can tune catalytic performance. Si, Co, Fe and Mg substituted AlPO4-5 (MeAPO-5) catalysts were hydrothermally prepared, characterized, and evaluated for ethanol - acetic acid esterification. Textural evaluation revealed that the Co and Si analogues possessed an order of magnitude higher mesopore volume compared to the rest of the studied materials. Divalent metal ions (i.e. Co, Fe, and Mg) substituted preferentially Al ions via the SM1 mechanism, as confirmed by the P/Al being greater than one, while Si ions substituted P ions (SM2) initially, followed by substitution of pairs of Al-P ions (SM3) at higher Si content. The esterification catalytic activity was found to follow the order SAPO-5 > > CoAPO-5 > MgAPO-5 ≈ FeAPO-5. The superior performance of SAPO-5 is ascribed to the higher concentration of Brønsted acid sites and faster mass transfer rates due to the relatively small crystal size and larger fraction of mesopores. Notably, the SAPO-5 with the optimal Si content demonstrated comparable stability against deactivation within the range of reaction conditions studied and sustained catalytic activity at prolonged reaction durations when compared to commercial Zeolite β, despite the significantly higher surface area, pore volume and density of acid sites of the latter, primarily attributed to less strong adsorption of the reaction products. The reported parametric results for various metal substitutions shed light towards optimizing aluminophosphate catalysts for esterification applications.

(Keynote) Sulfide Electrolytes Based on the LGPS Related Materials

All-solid-state is an ideal form of batteries. The solid electrolyte is a key issue for the development of all-solid-state batteries. Among the electrolytes proposed, the sulphide system is a candidate because of its high ionic conductivity. The LGPS (Li10GeP2S12) electrolyte exhibits a high bulk conductivity of over 10- 2 S cm-1 at room temperature and are promising for applications requiring batteries with high power and energy densities [1]. Moreover, material variations of the LGPS electrolytes provided suitable combinations of the electrodes and the electrolyte. For example, the LGPS-group materials, such as Li9.54Si1.74P1.44S11.7Cl0.3 and Li9.6P3S12, provided high power and high energy density to the all-solid-state cells [2]. These results clearly derive from the intrinsic nature of the solid electrolytes, indicating the advantages of the all-solid-state devices over conventional electrochemical devices.Systematic substitutions of the constituent elements were examined after the first report of Li10GeP2S12. The simplest substitution system was Si and Sn analogs. Solid solutions of the Ge-Si, Ge-Sn, and Si-Sn systems were examined. Among the substitution systems, the lithium tin-silicon system with Li10.35[Sn0.27Si1.08]P1.65S12 showed the high ionic conductivity which is comparable to the original LGPS material. On the other hand, the LGPS-type structre was also appered in the L-P-S ternary system. Li9.6P3S12 with the LGPS-type showed high electrochemical stability which might be used for low potential ranges such as Li and carbon anode.Partial substituteions of the anion-site were also studied for the halogen and oxygen systems. The oxygen and halogen substitution generally improved the electrochemical stabilities. Actually, the oxygen doped Li-P-S-O system showed higher electrochemical stability. Based on a wide composition range of the materials search, the LGPS materials were also found in the Li-A-P-S-X (A: Si, Ge, Sn, X:halogen) and Li-P-S-X (X: halogen) systems. For example, Li9.54Si1.74P1.44S11.7Cl0.3 showed the higest conductivity of 25 mScm-1 at room temperature. The halogen substitution systems of the L-P-S-X systems were also developed and this system had higher electrochemical stability.The present study summarizes the materials varieties and formation ranges of the LGPS materials in these ternary and quarternary sytems. In addition to the materials variety, the electrolyte-electrode combination which is another important parameter to achieve high battery characteristics is summarized. We also shows the properties of the all-solid-state cells using these LGPS-type solid electrolytes with various anode and cathode systems.

Higher Carbon Analogues of 1,4‐Dihydropyridines as Potent TGFβ/Smad Inhibitors

The C to Si and Ge exchange in bioactive compounds has often led to positive changes in the molecular properties, whereby Ge analogues are underrepresented. This is only possible at tetrahedral positions, and it is necessary for the analogue building blocks to withstand the synthetic conditions. Here, we present the synthesis of Si and Ge analogues of a TGFβ inhibiting 1,4‐dihydropyridine, which has a tetrahedral carbon in an important position for its activity. The molecular properties are compared by the discussion of the single X‐ray crystal structures and the electrostatic potential on the molecule surface which could play a role in the target interaction. Biological activities show that the C to Si and Ge exchange goes with full preservation of the potency, thus representing good starting points to modify physicochemical features and pharmacokinetics of these TGFβ inhibitors.

Cyclonona‐3,5,7‐trienylidene and its Si, Ge, Sn, and Pb analogs versus their α‐halogenated derivatives at B3LYP and MP2 methods

AbstractFive sets of group 14 sextet cyclic unsaturated divalent species including carbenes (1X), silylenes (2X), germylenes (3X), stannylenes (4X), and plumbylenes (5X) are compared and contrasted at B3LYP/AUG‐cc‐pVTZ//B3LYP/6‐311 + G* and MP2/AUG‐cc‐pVTZ//MP2/6‐311 + G* levels of theory, where X = H, F, Cl, and Br. The scrutinized carbenes consisting of cyclonona‐3,5,7‐trienylidene (1H) and its 2,2,9,9‐tetrahalo derivatives (1Cl, 1Br) appear as boat shaped minima except for 1H which turns out as a boat shaped transition state for having a negative force constant. All of carbenes (1H, 1Cl, and 1Br) have triplet ground states except for 1F. In contrast, all of the corresponding 2X‐ 5X metallylenes appear as singlet boat shaped minima on their potential energy surfaces. Stability (estimated by ΔEs‐t, ie, energy gap between singlet [s] and triplet states) appear as a function of size and decreases by going down in group 14 column: 5X > 4X > 3X > 2X > 1X. Exclusive of carbene set, within other four sets stability decreases by going down in group 17 column: Br > Cl > F > H. Hence, singlet 2,2,9,9‐tetrabromocyclonona‐3,5,7‐trienplumbylene, 5Br, appears as the most stable sextet divalent with no tendency for dimerization. Comparison is extended to the structural parameters, band gap, nucleophilicity, electrophilicity, isodesmic reactions, and dimerization.

Identification of novel mutations in genes involved in silicon and arsenic uptake and accumulation in rice

Novel mutations in rice genes involved in silicon (Si) and arsenic (As) transport (Lsi1, Lsi2) and vacuolar sequestration of As (OsABCC1) were identified using reverse genetics. TILLING by sequencing of a population of chemically-induced mutants (n = 2048) detected 61 putative mutations. Following removal of mutations predicted to be synonymous or residing in introns, Sanger sequencing confirmed 21 of 23 nonsynonymous mutations and 13 M3 lines harboring homozygous mutant alleles (three lsi1, nine lsi2, and one Osabcc1) were identified for phenotyping. Altered sensitivity to germanium (Ge), a phytotoxic analog of Si, was observed in three lines. NM-E1746 and NM-3403 (both lsi1) had increased tolerance whereas NM-3036 (lsi2) was more sensitive, however, this appears unrelated to the mutation. Analysis of the straw from field grown plants revealed that NM-E1746 and NM-3403 were the only lines with significant reductions in total Si. Both mutants also had significant increases in total As and NM-3403 exhibited higher grain total As. The third lsi1 mutant (NM-3380) and two lsi2 mutants (NM-2902 and NM-2249) had increased straw total As. Increased grain total As was observed in NM-2902, NM-2249, and a third lsi2 mutant NM-E2244. Interestingly, NM-4903 (Osabcc1) had the highest total Si and was also the only line to have significantly less straw and grain total As. These novel mutant alleles represent useful genetic resources for further dissection of Si, As, and Ge transport in rice and the corresponding germplasm has potential for enhancing rice productivity and quality.

Thermal evolution of hydrates in carbonation-cured Portland cement

The present study investigates the thermal evolution of hydrates in carbonation-cured Portland cement. Paste samples were placed in a carbonation chamber after the 24 h of initial curing, while reference samples were cured in a sealed condition until 28 days. Thermogravimetry, unconfined strength tests, X-ray diffractometry, and solid-state 29Si and 27Al MAS NMR spectroscopy were conducted. The results showed that the binder gel in carbonation-cured cement shares some structural similarities with aluminosilicate glass in terms of Si and Al analogues. This characteristic was also reflected by its thermogravimetric behavior, presenting much less weight loss associated with dehydration in comparison with hydrated cement. However, the binder gel in carbonation-cured cement underwent depolymerization into monomeric Si at 800 °C, similar to hydrated cement. Moreover, carbonation-cured cement underwent crystallization pathway identical to that of hydrated cement, displaying a hydrate-like thermal behavior.

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Engineering of Magnetically Intercalated Silicene Compound: An Overlooked Polymorph of EuSi2

Silicene, a Si analogue of graphene, is suggested to become a versatile material for nanoelectronics. Being coupled with magnetism, it is predicted to be particularly suitable for spintronic applications. However, experimental realization of free‐standing silicene and its magnetic derivatives is lacking. Fortunately, magnetism can be induced into silicene layers, in particular, by intercalation. Here, a successful synthesis of multilayer silicene intercalated by inherently magnetic Eu ions – a compound expected to exhibit both massless Dirac‐cone states, as its Ca analogue, and a nontrivial magnetic structure – is reported. This new polymorph with EuSi2 stoichiometry is epitaxially stabilized by continual replication of silicene layers employing Sr‐intercalated multilayer silicene as a template. The atomic structure of the new compound and its sharp interface with the template are confirmed using electron diffraction, X‐ray diffraction, and electron microscopy techniques. Below 80 K, the material demonstrates anisotropic antiferromagnetism coexisting with weak ferromagnetism. The magnetic state is accompanied by an anomalous behavior of magnetoresistivity.

Aromatization of triafulvene and its exocyclic Si, Ge, and Sn derivations by complexation with halogen atoms

GRAPHICAL ABSTRACT

Silicene and graphene nano materials in gas sensing mechanism

Silicene, the Si analogue of graphene, has recently extended the short list of existing two-dimensional (2D) atomic crystals.

Theoretical Study of Pd11 Si6 Nanosheet Compounds Including Seven-Coordinated Si Species and Its Ge Analogues.

Nanosheet compounds Pd11 (SiiPr)2 (SiiPr2 )4 (CNtBu)10 (1) and Pd11 (SiiPr)2 (SiiPr2 )4 (CNMes)10 (2), containing two Pd7 (SiiPr)(SiiPr2 )2 (CNR)4 plates (R=tBu or Mes) connected with three common Pd atoms, were investigated with DFT method. All Pd atoms are somewhat positively charged and the electron density is accumulated between the Pd and Si atoms, indicating that a charge transfer (CT) occurs from the Pd to the Si atoms of the SiMe2 and SiMe groups. Negative regions of the Laplacian of the electron density were found between the Pd and Si atoms. A model of a seven-coordinated Si species, that is, Pd5 (Pd-SiMe), is predicted to be a stable pentagonal bipyramidal molecule. Five Pd atoms in the equatorial plane form bonding overlaps with two 3p orbitals of the Si atom. This is a new type of hypervalency. The Ge analogues have geometry and an electronic structure similar to those of the Si compounds. But their formation energies are smaller than those of the Si analogues. The use of the element Si is crucial to synthesize these nanoplate compounds.

Crystal structure of 4-(tri-methyl-germ-yl)benzoic acid.

The title compound, [Ge(CH3)3(C7H5O2)], was obtained as a by-product in the synthesis of the corresponding aldehyde. Two slightly different mol-ecules are present in the asymmetric unit. In both mol-ecules, the geometry of the aromatic ring plane is distorted by varying intensities. Additionally, the Ge atoms deviate from the mean aromatic ring planes. Whereas the distance of the Ge atom to the ring plane is only 0.101 (4) Å in the first mol-ecule, this distance is increased to 0.210 (4) Å in the second. In the crystal structure, centrosymmetric O-H⋯O hydrogen-bonded dimers are formed. The title compound is isostructural with the Si analogue [Haberecht et al. (2004 ▶). Acta Cryst. E60, o329-0330].

(Invited) Synthesis, Properties and Applications of Group IV Graphane Analogues

In this talk, we will summarize our recent work on the synthesis, properties, and applications of a new family of two-dimensional materials based on sp3-hybridized Group IV elements. Ligand-terminated Si, Ge, and Sn graphane analogues are an emerging and unique class of two-dimensional materials that offer the potential to tailor the structure, stability, and properties via covalent chemistry. The presence of a fourth bond on the surface of the layers allows these materials to have the surface terminating ligand to be exchanged with a variety of organic functional groups. These materials feature a direct band gap which can be tuned with the surface ligand and the main group element. These materials can be synthesized as robust single crystals in gram-scale quantities, exfoliated into single layers, and prepared on conventional VLSI substrates as few-layer thin films. Furthermore, these graphane analogues are resilient towards oxidation and thermal degradation. Additionally, we will describe our recent studies on the electronic and thermal properties of these systems. Overall, this class of two-dimensional materials are not only promising building blocks for a variety of conventional semiconductor applications, but also provides a pioneering platform to systematically and rationally control material properties using covalent chemistry.

Linear Oligostannanes: A Synthetic and TD-DFT Study

A series of model linear tristannanes [((1R)3Sn)2(2R)2Sn (1: 1R = 2R = n-Bu, 2: 1R = Ph, 2R = n-Bu, 3: 1R = Me, 2R = n-Bu, 4: 1R = n-Bu, 2R = Ph, 5: 1R = Me, 2R = Ph, 6: 1R = n-Bu, 2R = Me, 7: 1R = Ph, 2R = Me)] were prepared by condensation reactions of one equivalent of a dialkyl or diaryl tin diamide or dihydride and two equivalents of a trialkyl or triaryl tin hydride or amide respectively, and characterized by NMR (1H, 13C, 119Sn) and UV–Vis spectroscopy, and elemental analysis. An LSDA/SDD level of DFT and TD-DFT for trimers 1–7 predicts significant structural differences as a function and nature of the substituents bound to tin and calculated electronic transitions for these compounds in fair relative agreement with experimental results. Calculated electronic spectra obtained from equivalent DFT studies of the sequentially lengthened oligomers Ph3Sn[t-Bu2Sn]nSnPh3 (8–11 where n = 1–4) previously prepared by Drager are in good agreement with the reported experimental UV–Visible spectroscopic and X-ray diffraction data which show a red shift of the σ–σ* absorption transition (λmax) and bond lengthening and bond angle widening of the central tin atoms as the oligostannane is extended. TD-DFT studies of the alkoxy terminated di(n-butyl) oligostannanes 12a–m (CH3CH2OCH2CH2[Sn(n-Bu)2]nCH2CH2OCH2CH3); n = 3–15) indicate lower limiting energy gaps as the polymer chain size is increased. The calculated data deviates significantly from results found experimentally by Sita and suggests that even smaller energy gaps are possible if the polymer (13) resides in an all trans configuration. TD-DFT studies at the LSDA/SDD level were also carried out on a model polystannane 16 (H[SnH2]nH, n = 1–40) to investigate the impact of Sn catenation on the intrinsic band gap of the material and compared to both the Si and Ge analogues 14 and 15 (H[MH2]nH, M = Si, Ge: n = 1–40). The modelling of the polymetallanes reveals the expected limiting energy gap of the σ–σ* transition in a trans-planar configuration with Sn (2.681 eV) < Ge (3.096 eV) < Si (3.719 eV) in good agreement with previous studies by Takeda. Finally, comparison of the TD-DFT calculated data for model alternating oligostannanes (17–19) with the UV–Vis spectroscopic data for alternating polystannanes (20–22) recently prepared by polycondensation is made.

Unusual structural and electronic properties of porous silicene and germanene: insights from first-principles calculations.

Using first-principles calculations, we investigate the geometric structures and electronic properties of porous silicene and germanene nanosheets, which are the Si and Ge analogues of α−graphyne (referred to as silicyne and germanyne). It is found that the elemental silicyne and germanyne sheets are energetically unfavourable. However, after the C-substitution, the hybrid graphyne-like sheets (c-silicyne/c-germanyne) possess robust energetic and dynamical stabilities. Different from silicene and germanene, c-silicyne is a flat sheet, and c-germanyne is buckled with a distinct half-hilled conformation. Such asymmetric buckling structure causes the semiconducting behaviour into c-germanyne. While in c-silicyne, the semimetallic Dirac-like property is kept at the nonmagnetic state, but a spontaneous antiferromagnetism produces the massive Dirac fermions and opens a sizeable gap between Dirac cones. A tensile strain can further enhance the antiferromagnetism, which also linearly modulates the gap value without altering the direct-bandgap feature. Through strain engineering, c-silicyne can form a type-II band alignment with the MoS 2 sheet. The combined c-silicyne/MoS 2 nanostructure has a high power conversion efficiency beyond 20% for photovoltaic solar cells, enabling a fascinating utilization in the fields of solar energy and nano-devices.

Dithienogermole‐Containing Small‐Molecule Solar Cells with 7.3% Efficiency: In‐Depth Study on the Effects of Heteroatom Substitution of Si with Ge

Two small molecule donor materials (DTGe(FBTTh2)2 and DTGe(FBTBFu)2) incorporating the dithienogermole (DTGe) moiety with fluorobenzothiadiazole (FBT) and bithiophene (Th2) or benzofuran (BFu) end‐capping groups are synthesized and their properties as donor materials in small molecule bulk heterojunction type (BHJ) solar cells are investigated. The DTGe(FBTTh2)2 with Th2 end groups shows outstanding solar cell characteristics with efficiencies up to 6.4% using a standard BHJ architecture and 7.3% using a ZnO optical spacer, while the BFu end‐capped DTGe(FBTBFu)2 has slightly wider band gaps and yields slightly higher open circuit voltage (VOC) at the expense of short circuit current (JSC) and fill factor (FF). In this study, the DTGe‐based molecules are systematically compared to the dithienosilole (DTSi)‐based analogues, which are currently among the highest power conversion efficiency (PCE) small molecule solar cell donor materials known. The JSC produced by the DTGe molecule is found to be similar to, or slightly higher than the Si analogue, despite similar absorption characteristics, however, the PCE is similar to the Si analogues due to small decreases in VOC and FF. This report marks the first small molecule BHJ based on a Ge‐containing heterocycle with PCE over 7%.