Ge Hydrides Research Articles

Synthesis of group-IV ternary and binary semiconductors using epitaxy of GeH3Cl and SnH4

Ge1−x−ySixSny alloys were grown on Ge buffers via reactions of SnH4 and GeH3Cl. The latter is a new CVD source designed for epitaxial development of group-IV semiconductors under low thermal budgets and CMOS-compatible conditions. The Ge1−x−ySixSny films were produced at very low temperatures between 160 and 200 °C with 3%–5% Si and ∼5%–11% Sn. The films were characterized using an array of structural probes that include Rutherford backscattering, x-ray photoelectron spectroscopy, high-resolution x-ray diffraction, scanning transmission electron microscopy, and atomic force microscopy. These studies indicate that the films are strained to Ge and exhibit defect-free microstructures, flat surfaces, homogeneous compositions, and sharp interfaces. Raman was used to determine the compositional dependence of the vibrational modes indicating atomic distributions indistinguishable from those obtained when using high-order Ge hydrides. For a better understanding of the growth mechanisms, a parallel study was conducted to investigate the GeH3Cl applicability for synthesis of binary Ge1−ySny films. These grew strained to Ge, but with reduced Sn compositions and lower thicknesses relative to Ge1−x−ySixSny. Bypassing the Ge buffers led to Ge1−ySny-on-Si films with compositions and thicknesses comparable to Ge1−ySny-on-Ge; but their strains were mostly relaxed. Efforts to increase the concentration and thickness of Ge1−ySny-on-Si resulted in multiphase materials containing large amounts of interstitial Sn. These outcomes suggest that the incorporation of even small Si amounts in Ge1−x−ySixSny might compensate for the large Ge–Sn mismatch by lowering bond strains. Such an effect reduces strain energy, enhances stability, promotes higher Sn incorporation, and increases critical thickness.

Redox flexibility in a germanium hydride manifold: hydrogen shuttling via oxidative addition and reductive elimination.

We report the synthesis of a trimetallic mixed-valence Ge(I)/Ge(II)/Ge(III) trihydride, which presents a structural novel motif among systems of the type (XMH)n (M = group 14 metal). In terms of reactivity (ArNiPr2)GeGe(ArNiPr2)(H)Ge(ArNiPr2)(H)2 can act as a source of both the Ge(II) and Ge(IV) hydrides via Ge-H reductive elimination from the central metal centre involving two different regiochemistries.

Low Pressure Growth of Pseudomorphic Gesn with 16.7% Sn Incorporation

Alloys of GeSn offer promising optical advantages for high performance optoelectronic device applications monolithically integrated on Si operating in the near and mid-infrared spectrum. Investigations worldwide into the growth of GeSn alloys using various Ge and Sn precursors in conjunction with the chemical vapor deposition growth technique has been reported. The use of higher order Ge hydrides and/or higher growth pressures above 40 torr have been investigated to achieve relatively high incorporations of Sn. In this work, we successfully demonstrated the low pressure growth at 12 torr of GeSn alloy with 16.7% Sn composition. Instead of using a higher order Ge precursor, the alloy was grown via chemical vapor deposition using the commercially available percussors GeH4 and SnCl4. Material and optical characterizations were performed to study the crystalline quality and optical properties. The growth results demonstrate a novel growth window in the low pressure regime to achieve high Sn composition alloy material with high quality for the use in future devices and applications.

Germanium Hydride Catalyzed Selective Hydroboration and Cyanosilylation of Ketones

AbstractTwo new examples of β‐diketiminate or NacNac analogues, i. e., conjugated bis‐guanidinate (CBG) stabilized low valent germanium chloride (1) and germanium hydride (2) complexes, are reported. Deprotonation of LH upon treatment with n‐BuLi and an in situ generated LLi further treated with GeCl2⋅dioxane afforded LGeCl in 79 % yield. Compound 1 reacted with hydride source NaHBEt3 in toluene, afforded Ge (II) hydride (2) in 76 % yield. Both compounds 1 and 2 were characterized by NMR and mass spectroscopic methods. Further, germanium hydride catalyzed hydroboration and cyanosilylation of a wide range of ketones have been investigated. Control reactions suggest hydroboration reactions occurred via insertion and Ge−O/B−H bond metathesis pathways. It is worthy of mentioning that, in the case of hydroboration of ketones, reducible groups such as alkene, alkyne, halide, ester, nitro, and heterocycles were untouched. Furthermore, compound 2 was employed for the reduction of carbonate, formate, and anhydride substrates via the hydroboration technique.

Optoelectronic and structural properties of Ge-rich narrow band gap nc-SixGe1-x absorber layer for tandem structure nc-Si solar cells

Germane (GeH4) and silane (SiH4) have grossly different dissociation behaviors. In the conventional preparation process, the inclusion of GeH4 in the gas mixture under nc-Si compatible growth conditions results in the spontaneous dissociation of GeH4 in the plasma into various lower hydrides of Ge with lower mobility than Si-hydrides. Ge-radicals exhibit a higher viscosity co-efficient and smaller surface diffusion length when compared to Si-radicals, which prompt the arbitrary and excess residence of Ge atoms at the growth sites, eventually destroying the development of nanocrystallinity in the film network. In the present work, the controlled inclusion of Si atoms during the growth of the network at ~220 °C under plasma conditions compatible for growing high-quality nc-Ge film has been pursued to produce nc-SiGe alloy material through which the dissociation of SiH4 becomes admissible for sustained nanocrystallinity. Systematic changes in the optoelectronic and structural characteristics of the intrinsic nc-SixGe1–x films from H2-diluted (SiH4 + GeH4)-plasma have been studied and correlated. The fabricated nc-SixGe1–x (x > 0) films belong to the Ge-nanocrystal dominated mixed-phase materials bearing a-SiGe matrix. The nc-SixGe1–x film sustaining significant crystallinity with an adequately widened optical band gap to Eg ~1.23 eV due to the incorporation of Si and its corresponding high dark conductivity (σD~4.72×10−4 S cm−1) appears appropriate for the absorber layer in the bottom sub-cell of nc-Si tandem solar cells.

(Invited) (Si)GeSn Semiconductors for Integrated Optoelectronics, Quantum Electronics, and More

Sn-containing group IV semiconductors (Si)GeSn represent a versatile platform to implement a variety of Si-compatible photonic, optoelectronic, and photovoltaic devices. This class of semiconductors provides two degrees of freedom, strain and composition, to tailor the band structure and lattice parameter thus enabling a variety of heterostructures and low-dimensional systems on a Si substrate. In this presentation, we will discuss the recent progress in the growth of metastable (Si)GeSn semiconductors. We will highlight the current understanding of their fundamental properties and elucidate the effects of the atomistic-level structure on their optoelectronic performance. The relevance of these semiconductors for Si-compatible mid-infrared optoelectronics and quantum information will also be discussed form both materials and device perspectives. The (Si)GeSn multi-layer heterostructures discussed in this work have a Sn content reaching ~20at.% grown in a chemical vapor deposition (CVD) reactor on 4-inch Silicon wafers, using Monogermane (GeH4) and tin-tetrachloride (SnCl4) precursors, and disilane (Si2H6). By reducing the growth temperature, the Sn content in the alloy is increased, while preserving a high degree of crystal quality for the heterostructure in the topmost Sn-rich layer. No threading dislocations are observed in the upper layers, while misfit and edge dislocations remain mainly confined in the low Sn content layers underneath and in the proximity with the Ge-GeSn interface. By comparing multiple sample series with different strain and composition we demonstrate that the growth rate and the choice of the Ge hydride gas precursor play a limited role in enhancing the incorporation of Sn in the Ge lattice. However, strain minimization and the reduced growth temperature below 350 °C are of paramount importance to achieve Sn-rich GeSn semiconductors.[2,3] Atom probe tomography (APT) measurements will be discussed to address the abruptness of the interfaces in the GeSn multi-layer heterostructure and the composition uniformity.[2] The absence of short-range atomic ordering and Sn precipitates is estimated from the extended statistical APT analyses. Positron annihilation lifetime spectroscopy (PAS) and depth-profiled Doppler broadening measurements will be presented and discussed to elucidate the behavior of point defects in these semiconductors. Based on these analyses, we found that divacancies are the predominant type of point defects in GeSn.[4] Surprisingly, the increase in Sn content in the alloy yields an increase in the concentration of divacancies together with a small reduction in vacancy clusters. The interaction and possible pairing between Sn and vacancies have been proposed to explain the reduced formation of larger vacancy clusters in GeSn with higher Sn content. Photoluminescence (PL) emission studies will be described. In our GeSn with a Sn content of 18at.% the room temperature PL emission was found to be centered at 0.36 eV (i.e. 3.5 μm wavelength).[2] However, the compressive in-plane strain (-1.3 %) in these GeSn layers reduces the directness of the alloy, leading to a higher energy gap value. By releasing the strain down to -0.2% in the 18 at.% Sn layer using a fully-underetched micro-disk geometry, a 50 meV red-shift of the PL emission energy down to 0.31 eV (i.e. 4.0 μm wavelength) is obtained. Moreover, the strained and relaxed PL emission and reflectance measurements ranging from 300K down to 4K will be shown. These observations will be discussed in the light of photocurrent measurements and photodetector performance. Finally, we will also discuss the use of GeSn as a platform to develop highly tensile strained Ge quantum wells (QWs. These low-dimensional systems, made possible by the availability of GeSn templates, create a wealth of opportunities to design and fabricate new quantum devices. For instance, unlike the compressively strained QWs, the top of the valence band is of light hole (LH) type under tensile strain, thus corresponding to a much smaller effective mass and ½ spin. These characteristics, combined with high hole mobility and strong spin-orbit coupling in Ge, make tensile strained Ge QWs more attractive for hole spin qubits. Acknowledgements The authors thank J. Bouchard for the technical support with the CVD system. O.M. acknowledges support from NSERC Canada (Discovery, SPG, and CRD Grants), Canada Research Chairs, Canada Foundation for Innovation, Mitacs, PRIMA Québec, and Defence Canada (Innovation for Defence Excellence and Security, IDEaS).

Features of the Initial Stage of the Heteroepitaxy of Silicon Layers on Germanium When Grown from Silicon Hydrides

Data on the dependence of the growth rate of Si layers deposited onto Ge(111) by the hydride method on their thickness at the initial heteroepitaxy stage are reported. The effect of a Ge substrate within ten grown silicon single layers on the Si-film growth rate is demonstrated. Based on the data obtained, the kinetic coefficients responsible for the rate of the main physicochemical processes related to the interaction of hydride molecular beams with the growth surface are calculated. An analysis of the capture probability and rates of pyrolysis of the adsorbed Si(Ge) hydride molecules on the pure Ge(Si) surfaces reveals the dependence of their behavior on the growing-layer thickness. Comparison of the results obtained during Si-layer growth on Ge shows that the pure germanium surface has higher adsorption and catalytic abilities with respect to silane molecules than the pure Si surface. The unstrained pure Si surface has higher adsorption and catalytic characteristics with respect to Ge-hydride molecules.

Особенности начальной стадии гетероэпитаксии слоев кремния на германии при их выращивании из гидридов кремния

AbstractData on the dependence of the growth rate of Si layers deposited onto Ge(111) by the hydride method on their thickness at the initial heteroepitaxy stage are reported. The effect of a Ge substrate within ten grown silicon single layers on the Si-film growth rate is demonstrated. Based on the data obtained, the kinetic coefficients responsible for the rate of the main physicochemical processes related to the interaction of hydride molecular beams with the growth surface are calculated. An analysis of the capture probability and rates of pyrolysis of the adsorbed Si(Ge) hydride molecules on the pure Ge(Si) surfaces reveals the dependence of their behavior on the growing-layer thickness. Comparison of the results obtained during Si-layer growth on Ge shows that the pure germanium surface has higher adsorption and catalytic abilities with respect to silane molecules than the pure Si surface. The unstrained pure Si surface has higher adsorption and catalytic characteristics with respect to Ge-hydride molecules.

Alternating-Current-Driven Microplasma for Multielement Excitation and Determination by Optical-Emission Spectrometry.

Microplasma optical-emission spectrometry (OES) is a promising technique for developing portable analytical instrumentations for real-time and on-site measurement of trace elemental species. However, its analytical performance is far from satisfactory for multielement analysis. Herein, a miniature OES system is developed for simultaneous multielement analysis with alternating-current-driven microplasma generated on the nozzle of a pneumatic micronebulizer as the excitation source. Because of the strong excitation capability of the microplasma and its sufficient contact with solution, a series of elements, including Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, and Zn, is directly excited in the spray with solution nebulization at a flow rate of 8 μL s-1. The characteristic optical emissions are measured by a charge-coupled-device (CCD) spectrometer. In addition, hydride generation is compatible with the present system, which makes it feasible for the simultaneous excitation of hydrides of As, Ge, Hg, Sb, and Sn by reaction with 0.8% (m/v) NaBH4. The microplasma-OES system exhibits a powerful capability for multielement analysis with favorable limits of detection for the mentioned elements.

Simultaneous determination of As, Bi, Sb, Se and Sn by microwave induced plasma spectrometry using a quadruple-mode microflow ultrasonic nebulizer for in situ hydride generation with internal standardization

A method based on continuous-microflow ultrasonic nebulizer quadruple-mode micro-capillary system (μ-USN/QCS-HG) has been used for the efficient generation of As, Bi, Ge, Sb, Se and Sn hydrides directly formed at vibrating quartz plate before detection by microwave induced plasma-optical emission spectrometry (MIP-OES). The ultrasonic nebulizer incorporates four solution capillaries with independent liquid feeding and a common gas inlet. The μ-USN/QCS-HG allowed the hydride generation directly into the cyclonic spray chamber without using any additional device either for solution and gas control or for gas phase separation. The μ-USN/QCS-HG-MIP OES makes feasible the implementation of an on-line internal standard (IS) calibration strategy and Ge was suggested as internal standard. A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the μ-USN/QCS-HG-MIP OES observed at a 50μLmin−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 1, 5, 2, 3 and 2ngmL−1 for As, Bi, Sb, Se and Sn, respectively. The method offers good precision (RSD ranged from 2% to 3%) for micro-sampling analysis. The potential application of this system was demonstrated by successfully analyzing several certified reference environmental samples (CRM DOLT-2, SRM 2710 and SRM 1643e) with satisfactory results. The measured of contents of elements in certified reference materials were in good agreement with the certified values, according to the t-test, for a confidence level of 95%.

Enhanced Performance Designs of Group-IV Light Emitting Diodes for Mid IR Photonic Applications

This paper describes Ge1-y Sn y (y = 0.0-0.11) light emitting diodes (LEDs) with a broad range of compositions extending from pure Ge to Sn concentrations where the alloy becomes a direct gap material (y = 0.09) and beyond. The devices are grown on Si(100) platforms using ultra-low temperature depositions of highly reactive Ge and Sn hydrides. The device fabrication adopts two new photodiode designs. The first employs n-Ge/i-Ge1-y Sn y /p-Ge1-y ’ Sn y ’ hetero-structure stacks possessing a single defected interface between the n-Ge and i-Ge1-y Sn y layers. The second consists of a homo-structure n-Ge1-y Sn y /i-Ge1-y Sn y /p-Ge1- y Sn y design. The devices show low dark currents and the electroluminescence (EL) spectra show concomitant redshifts of the peak emission position and intensity increase near direct gap Sn compositions. The EL of the homo-structure design displays a large efficiency enhancement relative to the hetero-structure devices. The fabrication of ternary Ge1-x-y Si x Sn y diodes with ~9% Sn and 3-9% Si contents is also discussed.

Non-radiative recombination in Ge1−ySny light emitting diodes: The role of strain relaxation in tuned heterostructure designs

This paper describes the properties of Ge1−ySny light emitting diodes with a broad range of Sn concentrations (y = 0.0–0.11). The devices are grown upon Si(100) platforms using ultra-low temperature deposition of highly reactive Ge and Sn hydrides. The device fabrication adopts two new photodiode designs which lead to optimized performance and enables a systematic study of the effects of strain relaxation on emission efficiency. In contrast with n-Ge/i-Ge1−ySny/p-Ge analogs, which in most cases contain two defected interfaces, our designs include a p-layer with composition Ge1−zSnz chosen to be z < y to facilitate light extraction, but with z close enough to y to guarantee no strain relaxation at the i/p interface. In addition, a Ge1−xSnx alloy is also used for the n layer, with compositions in the 0 ≤ x ≤ y range, so that defected and non-defected n/i interfaces can be studied. The electroluminescence spectra vs the Sn content y in the intrinsic layer of the diodes exhibit a monotonic shift in the emission wavelength from 1550 nm to 2500 nm. On the other hand, the emission intensities show a complex dependence that cannot be explained solely on the basis of Sn concentrations. Detailed theoretical modeling of these intensities makes it possible to extract recombination lifetimes that are found to be more than three times longer in samples in which strain relaxation has not occurred at the n-i interface, demonstrating the existence of a large non-radiative contribution from the relaxation defects. This finding is particularly significant for direct gap diodes with y > 0.09, for which it is practically impossible to avoid strain relaxation in n-Ge/i-Ge1−ySny/p-Ge analogs. The new designs introduced here open the door to the fabrication of highly efficient electrically pumped systems for applications in future generations of integrated photonics.

Size Controlled Synthesis of Germanium Nanocrystals: Effect of Ge Precursor and Hydride Reducing Agent

Germanium nanocrystals (Ge NCs) have attracted increasing attention as a promising alternative to II–VI and IV–VI semiconductor materials as they are cheap, “green,” electrochemically stable, and compatible with existing CMOS processing methods. Germanium is a particularly attractive material for optoelectronic applications as it combines a narrow band gap with high carrier mobilities and a large exciton Bohr radius. Solution‐phase synthesis and characterisation of size monodisperse alkyl‐terminated Ge NCs are demonstrated. Ge NCs were synthesised under inert atmospheric conditions via the reduction of Ge halide salts (GeX4) by hydride reducing agents within inverse micelles. Regulation of NC size is achieved by variation of germanium precursor and the strength of hydride reducing agents used. UV‐Visible absorbance and photoluminescence spectroscopy showed strong significant quantum confinement effects, with moderate absorption in the UV spectral range, and strong emission in the violet with a marked dependence on excitation wavelength.

Theoretical Study of Reactivity of Ge(II)-hydride Compound: Comparison with Rh(I)-Hydride Complex and Prediction of Full Catalytic Cycle by Ge(II)-hydride

The reaction of a Ge(II) hydride compound HC{CMeArN}2GeH (Ar = 2,6-iPr2C6H3) 1 with 2,2,2-trifluoroacetophenone (CF3PhCO) is theoretically investigated with density functional theory and spin-component-scaled second-order Møller-Plesset methods. This reaction easily occurs with moderate activation barrier and considerably large exothermicity, to afford a Ge(II) alkoxide 2 through a four-membered transition state. In the transition state, the charge transfer from the Ge-H σ-bonding molecular orbital (MO) to the C═O π*-antibonding MO of CF3PhCO plays an important role. Acetone ((CH3)2CO) and benzophenone (Ph2CO) are not reactive for 1, because their π*-antibonding MOs exist at higher energy than that of CF3PhCO. Though 2 is easily formed, the catalytic hydrogenation of CF3PhCO by 1 is difficult because the reaction of 2 with a dihydrogen molecule needs a large activation energy. On the other hand, our calculations clearly show that the catalytic hydrogenation of ketone by cis-RhH(PPh3)24 easily occurs, as expected. The comparison of catalytic cycle between 1 and 4 suggests that the strong Ge-O bond of 2 is the reason of the very large activation energy for the hydrogenation by 1. To overcome this defect, we investigated various reagents and found that the catalytic cycle can be completed with the use of SiF3H. The product is silylether CF3PhCHOSiF3, which is equivalent to alcohol because it easily undergoes hydrolysis to afford CF3PhCHOH. The similar catalytic cycles are also theoretically predicted for hydrosilylations of CO2 and imine. This is the first theoretical prediction of the full catalytic cycle with a heavier main-group element compound.

Tetragermacyclobutadiene: Energetically Disfavored with Respect to Its Structural Isomers

Germanium has been a central feature in the renaissance of main-group inorganic chemistry. Herein, we present the stationary-point geometries of tetragermacyclobutadiene and its related isomers on the singlet potential energy surface at the CCSD(T)/cc-pVTZ level of theory. Three of these 12 structures are reported for the first time and one of them is predicted to lie only 0.4 kcal mol(-1) above the previously reported global minimum. Focal-point analyses has provided electronic energies at the CCSD(T) level of theory, which are extrapolated to the complete basis-set limit and demonstrate the convergence behavior of the electronic energies with improving levels of theory and increasing basis-set size. The lowest-energy structure is the bicyclic structure, which lies 35 kcal mol(-1) below the "all-Ge" cyclobutadiene structure. The reaction energies for the association of known Ge hydrides (e.g., digermene) to form Ge4H4 indicate that Ge4H4 could be observed experimentally. We investigate the bonding patterns by examining the frontier molecular orbitals. Our results demonstrate that: 1) the cyclic isomers of (GeH)4 distort to maximize the mixing of the p orbitals that are involved in the π system of tetragermacyclobutadiene and 2) the lowest-energy isomers exhibit unusual bonding arrangements (e.g., bridging H bonds) that maximize the nonbonding electron density at the Ge centers.

Why the Mechanisms of Digermyne and Distannyne Reactions with H2 Differ So Greatly

Despite their formal relationship to alkynes, Ar'GeGeAr', Ar'SnSnAr', and Ar*SnSnAr* [Ar' = 2,6-(2,6-iPr(2)C(6)H(3))(2)C(6)H(3); Ar* = 2,6-(2,4,6-iPr(3)C(6)H(2))(2)-3,5-iPr(2)C(6)H] exhibit high reactivity toward H(2), quite unlike acetylenes. Remarkably, the products are totally different. Ar'GeGeAr' can react with 1-3 equiv of H(2) to give mixtures of Ar'HGeGeHAr', Ar'H(2)GeGeH(2)Ar', and Ar'GeH(3). In contrast, Ar'SnSnAr' and Ar*SnSnAr* react with only 1 equiv of H(2) but give different types of products, Ar'Sn(μ-H)(2)SnAr' and Ar*SnSnH(2)Ar*, respectively. In this work, this disparate behavior toward H(2) has been elucidated by TPSSTPSS DFT computations of the detailed reaction mechanisms, which provide insight into the different pathways involved. Ar'GeGeAr' reacts with H(2) via three sequential steps: H(2) addition to Ar'GeGeAr' to give singly H-bridged Ar'Ge(μ-H)GeHAr'; isomerization of the latter to the more reactive Ge(II) hydride Ar'GeGeH(2)Ar'; and finally, addition of another H(2) to the hydride, either at a single Ge site, giving Ar'H(2)GeGeH(2)Ar', or at a Ge-Ge joint site, affording Ar'GeH(3) + Ar'HGe:. Alternatively, Ar'Ge(μ-H)GeHAr' also can isomerize into the kinetically stable Ar'HGeGeHAr', which cannot react with H(2) directly but can be transformed to the reactive Ar'GeGeH(2)Ar'. The activation of H(2) by Ar'SnSnAr' is similar to that by Ar'GeGeAr'. The resulting singly H-bridged Ar'Sn(μ-H)SnHAr' then isomerizes into Ar'HSnSnHAr'. The subsequent facile dissociation of the latter gives two Ar'HSn: species, which then reassemble into the experimental product Ar'Sn(μ-H)(2)SnAr'. The reaction of Ar*SnSnAr* with H(2) forms in the kinetically and thermodynamically more stable Ar*SnSnH(2)Ar* product rather than Ar*Sn(μ-H)(2)SnAr*. The computed mechanisms successfully rationalize all of the known experimental differences among these reactions and yield the following insights into the behavior of the Ge and Sn species: (I) The active sites of Ar'EEAr' (E = Ge, Sn) involve both E atoms, and the products with H(2) are the singly H-bridged Ar'E(μ-H)EHAr' species rather than Ar'HEEHAr' or Ar'EEH(2)Ar'. (II) The heavier alkene congeners Ar'HEEHAr' (E = Ge, Sn) cannot activate H(2) directly. Instead, Ar'HGeGeHAr' must first isomerize into the more reactive Ar'GeGeH(2)Ar'. Interestingly, the subsequent H(2) activation by Ar'GeGeH(2)Ar' can take place on either a single Ge site or a joint Ge-Ge site, but Ar'SnSnH(2)Ar' is not reactive toward H(2). The higher reactivity of Ar'GeGeH(2)Ar' in comparison with Ar'SnSnH(2)Ar' is due to the tendency of group 14 elements lower in the periodic table to have more stable lone pairs (i.e., the inert pair effect) and is responsible for the differences between the reactions of Ar'EEAr' (E = Ge, Sn) with H(2). Similarly, the carbene-like Ar'HGe: is more reactive toward H(2) than is Ar'HSn:. (III) The doubly H-bridged Ar'E(μ-H)(2)EAr' (E = Ge, Sn) species are not reactive toward H(2).

Monomeric Sn(ii) and Ge(ii) hydrides supported by a tridentate pincer-based ligand

Herein we report the syntheses of terminal Sn(II) (3) and Ge(II) (4) hydrides from the corresponding chloride precursors [{2,6-iPr(2)C(6)H(3)NCMe}(2)C(6)H(3)MCl] (M = Sn (1), Ge (2)) using [K{B(sec-Bu)(3)}H] as a hydrogenating agent. Combination of steric shielding and intramolecular N → M interactions resulted in the protection of M(II)-H bonds.

Hydrosilylation of Alkynes by Ni(CO)3‐Stabilized Silicon(II) Hydride

Not copy and paste: Although β-diketiminato ligands have been employed for the stabilization of Ge(II) and Sn(II) hydrides, the corresponding Si(II) hydride is not accessible. However, coordination of silicon(II) to a {Ni(CO)(3)} fragment allowed the isolation of the first Si(II) hydride metal complex 1. This complex was used for the first silicon(II)-based and Ni(0)-mediated, stereoselective hydrosilylation of alkynes. R = phenyl, tolyl.

Group 14 Hydrides with Low Valent Elements for Activation of Small Molecules

Transition metal compounds are well known as activators of small molecules, and they serve as efficient catalysts for a variety of homogeneous and heterogeneous transformations. In contrast, there is a general feeling that main group compounds cannot act as efficient catalysts because of their inability to activate small molecules. Traditionally, the activation of small molecules is considered one of the key steps during a catalytic cycle with transition metals. As a consequence, researchers have long neglected the full range of possibilities in harnessing main group elements for the design of efficient catalysts. Recent developments, however, have made it possible to synthesize main group compounds with low-valent elements capable of activating small molecules. In particular, the judicious use of sterically appropriate ligands has been successful in preparing and stabilizing a variety of Group 14 hydrides with low-valent elements. In this Account, we discuss recent advances in the synthesis of Group 14 hydrides with low-valent elements and assess their potential as small-molecule activators. Group 14, which comprises the nonmetal C, the semimetals Si and Ge, and the metals Sn and Pb, was for years a source of hydrides with the Group 14 element almost exclusively in tetravalent form. Synthetic difficulties and the low stability of Group 14 hydrides in lower oxidation states were difficult to overcome. But in 2000, a divalent Sn(II) hydride was prepared as a stable compound through the incorporation of sterically encumbered aromatic ligands. More recently, the stabilization of GeH(2) and SnH(2) complexes using an N-heterocyclic carbene (NHC) as a donor and BH(3) or a metal carbonyl complex as an acceptor was reported. A similar strategy was also employed to synthesize the Si(II) hydride. This class of hydrides may be considered coordinatively saturated, with the lone pair of electrons on the Group 14 elements taking part in coordination. We discuss the large-scale synthesis of hydrides of the form LMH (where M is Ge or Sn, L is CH(N(Ar)(CMe))(2), and Ar is 2,6-iPr(2)C(6)H(3)), which has made it possible to test their reactivity in the activation of small molecules. Unlike the tetravalent Group 14 hydrides, the Ge(II) and Sn(II) hydrides were found to be able to activate a number of small molecules in the absence of any externally added catalyst. For example, the Ge(II) hydride and Sn(II) hydride can activate CO(2), and the reaction results in the formation of Ge(II) and Sn(II) esters of formic acid. This product represents a prototype of a new class of compounds of Group 14 elements. Moreover, we examined the activation of carbonyl compounds, alkynes, diazo and azo compounds, azides, and compounds containing the C═N bond. These Group 14 hydrides with low-valent elements are shown to be able to activate a number of important small molecules with C≡C, C═O, N═N, and C═N bonds. The activation of small molecules is an important step forward in the realization of main group catalyst development. Although it is not yet customary to assay the potential of newly synthesized main group compounds for small-molecule activation, our results offer good reason to do so.

Overlayer Surface-Enhanced Raman Spectroscopy for Studying the Electrodeposition and Interfacial Chemistry of Ultrathin Ge on a Nanostructured Support

Ultrathin films of germanium (Ge) have been electrodeposited onto surface-enhanced raman spectroscopy (SERS)-active, polycrystalline gold (Au) nanoparticle film electrodes from aqueous solutions containing dissolved GeO2. An overlayer SERS strategy was employed to use the SERS-activity of the underlying Au electrode to enhance the Raman signatures separately for the Ge phonon mode and vibrational modes of surface groups. Electrochemical and spectroscopic data are presented that demonstrate monolayer-level detection of the electrodeposited material and the preparation of crystalline Ge films exhibiting quantum-confinement effects. Potential-dependent Raman spectra are shown that identify electrodeposition conditions where Ge films can be deposited with either long- or short-range crystalline order. Raman spectra collected with electrodeposited Ge films immersed in solutions containing CN-(aq) did not indicate a significant presence of pinholes that exposed the underlying Au(s) substrate. Raman spectra were also collected that identified a potential-dependence for Ge hydride formation at the interface of these films. Separate spectra were collected for the oxidative dissolution of Ge in solution and the complete dry oxidation of Ge to GeOx in air. These data sets cumulatively represent the first demonstration of the overlayer SERS strategy to follow surface chemical processes at crystalline, nanostructured, Ge materials in situ and in real time.