Ge-C Bond Research Articles

Frustrated Lewis Pairs from Al-E{14} Bonds (E{14}=Ge, Sn, Pb).

The potassium aluminyl K[Al(NON)] ([NON]2-=[O(SiMe2NDipp)2]2-, Dipp=2,6-iPr2C6H3) reacts with group 14 chloroamidinates E{14}(Am)Cl (E{14}=Ge, Sn, Pb. [Am]-=[tBuC(NDipp)2]-) to form (NON)Al-E{14}(Am) Lewis pairs with unsupported Al-E{14} bonds, including the first structurally authenticated Al-Pb bond. Analysis using spectroscopic (NMR, UV-vis and Mössbauer for E{14}=Sn), X-ray diffraction and computational (DFT, QTAIM, TD-DFT) methods conclude an Al-E{14} σ-bond derived from a Lewis basic Al and a Lewis acidic tetrylene, with back-donation from the E{14} s-orbital lone pair donor NBO to acceptor NBOs on Al that are derived from s/p-orbitals. The reaction of the Al-Ge compound with CO2 forms the dioxocarbene (NON)Al(μ-O2C)Ge(Am), whilst under the same conditions the Al-Sn compound reacts with additional CO2 to form the carbonate, (NON)Al(μ-CO3)Sn(Am). Addition of ethene to the Al-E{14} (E{14}=Ge, Sn) compounds introduces an ethylene bridge between the aluminium and group 14 atoms forming a frustrated Lewis pair (FLP). Reaction of the (Al/Ge) FLP with CO2 forms an activation product with new Al-O and Ge-C bonds, whilst reaction with iPrN=C=NiPr proceeds with insertion into the Al-C bond to form an aluminium amidinate.

Enhancing minority carrier lifetime in Ge: Insights from HF and HCl cleaning procedures

Efficiently passivating germanium (Ge) surfaces is crucial to reduce the unwanted recombination current in high-performance devices. Chemical surface cleaning is critical to remove surface contaminants and Ge oxides, ensuring effective surface passivation after dielectric deposition. However, Ge oxides can rapidly regrow upon air exposure. To understand the surface evolution after wet cleaning, we present a comprehensive study comparing HF and HCl deoxidation steps on p-type Ge surfaces and monitor the surface as a function of air exposure time. Distinct oxide regrowth dynamics are observed: HF-treated samples exhibit swift regrowth of all Ge oxide states, whereas HCl-treated Ge surfaces exhibit a lower concentration of low degrees of oxidation and slower or no regrowth of high oxide states even after 110 min of air exposure. In addition, the presence of Ge–Cl bonds induces different oxidation dynamics compared to the Ge–OH bonds resulting from HF cleaning. This leads to varying surface electronic band structures, with HF-treated Ge exhibiting a strong positive band bending (+0.20 eV). Conversely, HCl-treated samples display a lower band curvature (+0.07 eV), mostly due to the presence of Ge–Cl bonds on the Ge surface. During air exposure, the increased GeOx coverage significantly reduces the band bending after HF, while a constant band bending is observed after HCl. Finally, these factors induce a reduction in the surface recombination velocity after wet etching. Combining both chemical and field-induced passivation, HF-treated Ge without rinsing exceeds 800 μs.

Evaluating the Ge: C ratio on the bonding structure, hardness, and residual stress of Ge1-x-Cx coatings fabricated by the PE-CVD method

In the present research, the effect of the Ge: C ratio was evaluated and explained on the bonding structure, the hardness, and residual stress of germanium-carbon (Ge1-x-Cx) coatings fabricated by plasma-enhanced chemical vapor deposition (PECVD) method. For characterizing the coatings, a field emission scanning electron microscope (FE-SEM) equipped with an energy dispersive spectrometer (EDS), transmission electron microscope (TEM), Raman spectrometer, Rutherford backscattering spectrometer (RBS), elastic recoil detection (ERD) analysis, X-ray photoelectron spectrometer (XPS), nanoindentation test, and cohesion test were used. by increasing the flow rate ratio of CH4:GeH4 and as a result of decreasing the ratio of Ge: C, the fraction of sp2 C-C and sp3 Ge-C bonds were increased and the fraction of Ge-Ge bonds was decreased. The hardness of the Ge1-x-Cx coatings was heavily reliant on changes in the Ge: C ratio and, consequently, the fraction of the bonds incorporated within the coating structure. To achieve a hard coating, the selection of a moderate carbon content is very important such that it would lead to the formation of maximum sp3 Ge-C bonds alongside slight amounts of sp2 C-C and hydrogen bonds. For very low carbon concentrations, the existence of dominant Ge-Ge bonds would create the coating structure as germanium-like; the excessive rise of the carbon concentration promotes the undesirable graphite-like structures. In the optimum conditions, the hardness of the coating was obtained at 10.1 GPa. The coatings presented a very low residual stress (∼98-240 MPa) despite having suitable hardness.

Inverting the Electronic Structure of Diylidylgermylenes by Backbone Modification.

Owing to the strong electron-donating ability of ylide substituents, diylidyltetrylenes are usually highly nucleophilic species with strong donor capacities. Here, we demonstrate that their electronic properties are in fact highly flexible and can be effectively tuned through variation of the substituent in the ylide backbone. Initial density functional theory studies showed that cyano groups are particularly capable in lowering the LUMO energy of diylidyl germylenes thus turning these usually highly nucleophilic species into electrophilic compounds. This was confirmed by experimental studies. Attempts to synthesize the germylene (YCN)2Ge [with YCN = Ph3P-(C)-CN] from the corresponding metalated ylides YCNK selectively led to germanide [(YCN)3Ge)K]2 thus reflecting the electrophilic nature of the intermediate formed germylene. XRD analysis of single crystals of (YCN)2Ge - serendipitously obtained through protonative cleavage of one ylide from the germanide - revealed a monomeric structure with rather long Ge-ylide linkages, which corroborates well with a pure single bond and no stabilization of the empty pπ orbital at germanium through pi bonding. The germanide exhibits methanide-like reactivity towards chalcogens but a likewise weak Ge-C bond as demonstrated by the insertion of carbon dioxide.

Growth and analysis of the tetragonal (ST12) germanium nanowires.

New semiconducting materials, such as state-of-the-art alloys, engineered composites and allotropes of well-established materials can demonstrate unique physical properties and generate wide possibilities for a vast range of applications. Here we demonstrate, for the first time, the fabrication of a metastable allotrope of Ge, tetragonal germanium (ST12-Ge), in nanowire form. Nanowires were grown in a solvothermal-like single-pot method using supercritical toluene as a solvent, at moderate temperatures (290-330 °C) and a pressure of ∼48 bar. One-dimensional (1D) nanostructures of ST12-Ge were achieved via a self-seeded vapour-liquid-solid (VLS)-like paradigm, with the aid of an in situ formed amorphous carbonaceous layer. The ST12 phase of Ge nanowires is governed by the formation of this carbonaceous structure on the surface of the nanowires and the creation of Ge-C bonds. The crystalline phase and structure of the ST12-Ge nanowires were confirmed by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The nanowires produced displayed a high aspect ratio, with a very narrow mean diameter of 9.0 ± 1.4 nm, and lengths beyond 4 μm. The ST12-Ge nanowire allotrope was found to have a profound effect on the intensity of the light emission and the directness of the bandgap, as confirmed by a temperature-dependent photoluminescence study.

N→Ge Coordinated Germylenes as Ligands for Monomeric Cu Complexes

AbstractSynthesis of monomeric Cu complexes stabilized by the N→Ge coordinated germylene L(Cl)Ge (L=2‐Et2NCH2‐4,6‐tBu2‐C6H2) is reported. The reactions of the [L(Cl)Ge]2CuI (1) with AgX provided the complexes [L(Cl)Ge]2CuX (X=2: X=OAc, 3: X=OTf) by selective substitution of the CuI bond. In contrast, the reaction of 1 with K[BEt3H] provided [L(H)Ge]2CuI (4), the product of selective substitution of the GeCl bonds. The 4 represents the first example of Cu complex stabilized by two organogermaniun hydrides [L(H)Ge].

1,2- and 1,1-Migratory Insertion Reactions of Silylated Germylene Adducts.

The reactions of the PMe3 adduct of the silylated germylene [(Me3Si)3Si]2Ge: with GeCl2·dioxane were found to yield 1,1-migratory insertion products of GeCl2 into one or two Ge–Si bonds. In a related reaction, a germylene was inserted with tris(trimethylsilyl)silyl and vinyl substituents into a Ge–Cl bond of GeCl2. This was followed by intramolecular trimethylsilyl chloride elimination to another cyclic germylene PMe3 adduct. The reaction of the GeCl2 mono-insertion product (Me3Si)3SiGe:GeCl2Si(SiMe3)3 with Me3SiC≡CH gave a mixture of alkyne mono- and diinsertion products. While the reaction of a divinylgermylene with GeCl2·dioxane only results in the exchange of the dioxane of GeCl2 against the divinylgermylene as base, the reaction of [(Me3Si)3Si]2Ge: with one GeCl2·dioxane and three phenylacetylenes gives a trivinylated germane with a chlorogermylene attached to one of the vinyl units.

1,2-Insertion reactions of alkynes into Ge-C bonds of arylbromogermylene.

1,2-Insertion reactions of alkynes into the Ge-C bonds in dibromodigermenes afford stable crystalline bromovinylgermylenes. In contrast to previously reported Lewis-base-supported vinylgermylenes, the bromovinylgermylene obtained from reaction of the bromogermylene with 3-hexyne via such an 1,2-insertion is a donor-free monomer. A feasible reaction mechanism, proposed on the basis of the observed experimental results in combination with theoretical calculations, suggests that the [1+2]-cycloadduct and the insertion product are the kinetic and thermodynamic product, respectively.

Characteristics of films deposited by the irradiation of GeCHx+ ions produced from hexamethyldigermane and their dependence on the injected ion energy

The characteristics of films deposited by the irradiation of GeCHx+ ions and their dependence on the injected ion energy were investigated. GeCHx+ ion beams were produced by the decomposition of hexamethyldigermane in a Freeman-type ion source. GeCHx+ ions were then mass-selected and irradiated for film deposition on Si substrates at room temperature. The GeCHx+ ion energy was set at about 100, 30, 20, and 10 eV. The Fourier transform infrared spectroscopy (FTIR) analyses of the deposited films suggested that Ge-C bonds of GeCHx+ ions were broken due to the collision between GeCHx+ ions and the substrate surface in the cases of 100 and 30 eV. In contrast, Ge-C bonds remained in the film at the ion energy of 20 or 10 eV. Subsequently, the GeCHx+ ion energy was set at 20 eV, whereas the Si substrate temperature was set at 300 °C. FTIR and X-ray diffraction analyses of the films obtained suggested that the Ge-C bonds were broken at 300 °C and the resulting Ge atoms recombined with each other to form a metallic Ge film.

Electron Density Redistribution in the System GeCl4←O=C[N(CH3)2]2 upon Coordination Bond Formation

Quantum-chemical calculations of the system Cl4Ge←O=C[N(CH3)2]2 with full geometry optimization were performed by RHF/6-31G(d) and MP2/6-31G(d) methods. The calculations took into account that the Ge–Cl axial bond and the O=C bond are not at one line, as opposed to the previous belief. The MP2/6-31G(d) calculations of this system were also performed for various distances between coordination centers, and for GeCl4 and O=C[N(CH3)2]2 molecules, with full geometry optimization. The results of the calculations were used to quantify electron density redistribution in the system upon coordination bond formation. The electron density of chlorine atoms, especially, of the axial chlorine atom, was shown to increase upon coordination bond formation due to its transfer from the ligand hydrogen atoms and Ge–Cl bond polarization. The partial negative charge of the oxygen atom and the positive charge of the carbonyl carbon atom increase in association.

Photoelectrochemical Pyramid Texturization of n-Type Ge (100) Probed By Integrated Electrochemical Chamber/X-Ray Photoelectron Spectroscopy

Recently, Germanium (Ge) has gained a massive attention from different research fields like energy1-2, photonics3-4, biomedicine5, and most importantly, nanoelectronics6. Historically, Ge was the very first semiconductor utilized as a key material for transistors by John Bardeen, William B. Shockley and Walter H. Brattain but was abandoned because of its low purity, narrow band gap and chemically unstable oxide.7 From being left behind, after silicon (Si) found its way to fame, Ge is now enjoying resurgence in the world of CMOS devices.8 Due to the extreme size scaling of Si-based complementary metal-oxide semiconductor (CMOS) devices, performance enhancement can no longer be achieved due to intrinsic mobility issues, which can be compensated by the higher carrier mobility of Ge.9 In this context, Ge is a promising candidate to replace Si. Hence, central understanding in Ge surface and interface chemistry is currently indispensable for the development of novel nanodevice applications. In this work, we report the very first formation of Ge pyramids through electrochemical etching and its surface chemistry in HCl solutions under applied potential conditions. As a starting point, voltammetric (j-V) measurements were performed for a large concentration range of the acid (Figure 1a). In all cases in the plateau region (at 0.8V), a linear increase in photocurrent density with increasing light intensity was measured (Figure 1a inset). These results are attributed to a high oxide solubility and, consequently, low oxide coverage (supported by XPS results). No characteristic oxide passivation is observed during anodic etching of n-type Ge, even in the case of a very dilute 0.05 M HCl solution and current densities as high as ~6.0 mA cm-2. Morphological studies (AFM and SEM) revealed a striking and unexpected anisotropy in the surface chemistry of etching for high HCl concentrations, evidenced by the formation of random pyramids with characteristic (111) facets (Figure 1b). For Si, patterning can be used to further lower reflectance and hence improve light coupling effects. In order to scrutinize if similar effects can be observed for Ge, we fabricated a honeycomb template with circular openings of 1 mm to expose the Ge via photolithography. After photoanodic etching of the patterned Ge sample at 0.8 V in 8 M HCl solution, highly ordered pyramidal structures were obtained which lowered the reflectance further by 6% as presented in Figure 1c. This shows that light coupling effects are very likely vital. Integrated electrochemical etching chamber connected to X-ray photoelectron spectroscopy (XPS) instrument as displayed in Figure 1d, which excludes the effect of O2 and H2O vapor from the atmosphere, was utilized. Core-level Ge3d spectra suggest that the process of pyramid texturization is induced by the presence of Ge-Cl bonds on the Ge (100) surface during photoanodic dissolution (Figure 1e). A strong decrease in Ge-OH upon increasing the HCl concentration from 1 M to 8 M is accompanied by an increase in chemically bonded Cl, supported by the chemical shift of 0.6 eV. As the Cl content is similar based in Cl 2p (data not shown), it is very likely that for lower HCl concentration, with less Ge-Cl, physisorption of the halide ion is more important. While, at high HCl concentration, chemisorption governs. Based on these results, we propose surface electrochemical reaction schemes that relate the observed anisotropy in etching to surface chemistry. We believe that these findings are of fundamental interest and of technological importance for new developments in the fields of energy, photonics, biomedicine, and nanoelectronics.

Identification of fragment ions produced from hexamethyldigermane and the production of low-energy beam of fragment ion possessing Ge-C bond

Fragment ions produced from hexamethyldigermane (HMDG) were identified using an ion beam system. The possible chemical formulae for these ions are CH3+, C2H4+, Ge+, GeCHx+, and GeC3Hx+. Among the fragment ions, GeCHx+ ions were mass-selected and irradiated to a Si substrate at room temperature. The ion energy was set at approximately 10 eV. The analyses of the film deposited on the substrate suggested that GeCHx+ ion beam produced from HMDG was useful for germanium-carbon film formation.

Stereocontrolled Synthesis of Triols Containing Four Asymmetric Centers: Application of C, O-Chelated Germyl Enolates to a Diastereoselective Aldol Reaction.

The treatment of α,β-unsaturated ketones with divalent germanium salts cleanly generated C, O-chelated germyl enolates. The aldol reactions of the chelated enolates with the aldehydes achieved a high diastereoselectivity in the construction of the five-membered aldol adducts. Furthermore, the subsequent transformation of the Ge-C bond in the aldol adduct enabled the stereocontrolled synthesis of triols bearing four asymmetric centers.

Carbon doping induced Ge local structure change in as-deposited Ge2Sb2Te5 film by EXAFS and Raman spectrum

The local structure change of Ge induced by carbon doping in as-deposited Ge2Sb2Te5 films were studied by extended X-ray absorption fine structure and Raman spectrum. Ge-C bonds are formed at the expense of reducing the coordination of Ge-Ge and Ge-Te bonds, and make the local structure of Ge to be a well-defined tetrahedral geometry, which increases the rigidity of amorphous network and reduces the number of ABAB rings, thus the crystallization temperature of carbon-doped Ge2Sb2Te5 (CGST) films are enhanced. The reduced proportion of the tetrahedral units GeTe4−nGen (n = 1, 2) caused by carbon doping accounts for the weaker Raman peak intensity at ∼124 cm−1 in CGST films. Meanwhile, the impact of doping carbon on the crystalline structure of CGST films were investigated by high resolution transmission electron microscope.

Synthesis and Photodynamics of Tetragermatetrathia[8]circulene.

Tetragermatetrathia[8]circulene has successfully been synthesized from tetraiodotetrathienylene through palladium-catalyzed germylation and rhodium-catalyzed intramolecular dehydrogenative cyclization. A single-crystal X-ray diffraction analysis elucidated that tetragermatetrathia[8]circulene has a highly symmetric, planar, and rigid structure. DFT calculations suggested that LUMO of tetragermatetrathia[8]circulene is stabilized due to σ*-π* interactions between σ* orbitals of the Ge-C bonds and π* orbitals of the thiophene rings. The excited dynamics of tetragermatetrathia[8]circulene have also been found to be significantly affected by the heavy-atom effect of the germanium atom.

Germanium Dicarbide: Evidence for a T-Shaped Ground State Structure.

The equilibrium structure of germanium dicarbide GeC2 has been an open question since the late 1950s. Although most high-level quantum calculations predict an L-shaped geometry, a T-shaped or even a linear geometry cannot be ruled out because of the very flat potential energy surface. By recording the rotational spectrum of this dicarbide using sensitive microwave and millimeter techniques, we unambiguously establish that GeC2 adopts a vibrationally averaged T-shaped structure in its ground state. From analysis of 14 isotopologues, a precise r0 structure has been derived, yielding a Ge-C bond length of 1.952(1) Å and an apex angle of 38.7(2)°.

Thermal conductivity of carbon doped GeTe thin films in amorphous and crystalline state measured by modulated photo thermal radiometry

The thermal conductivity and thermal boundary resistance of GeTe and carbon doped GeTe thin films, designed for phase change memory (PCM) applications, were investigated by modulated photo thermal radiometry. It was found that C doping has no significant effect on the thermal conductivity of these chalcogenides in amorphous state. The thermal boundary resistance between the amorphous films and SiO2 substrate is also not affected by C doping. The films were then crystallized by an annealing at 450°C as confirmed by optical reflectivity analysis. The thermal conductivity of non-doped GeTe significantly increases after crystallization annealing. But, surprisingly the thermal conductivity of the crystallized C doped GeTe was found to be similar from that of the amorphous state and independent of C concentration. As for the amorphous phase, C doping does not affect the thermal boundary resistance between the crystalline GeTe films and SiO2 substrate. This behaviour is discussed thanks to XRD and FTIR analysis. In particular, XRD shows a decrease of crystalline grain size in crystalline films as C concentration is increased. FTIR analysis of the film before and after crystallization evidenced that this evolution could be attributed to the disappearing of Ge-C bonds and migration of C atoms out of the GeTe phase upon crystallization, limiting then the growth of GeTe crystallites in C-doped films.

σ‐Bond Activation in Aluminium‐Functionalized Alkynylchlorogermanes: Facile Insertion of Isocyanate and Azide into Al–C and Ge–Cl Bonds

Hydroalumination of Cl‐functionalized alkynylgermanes yielded mixed Al/Ge compounds (1). The Cl atoms adopted bridging positions between the Ge and Al atoms to form four‐membered GeCAlCl heterocycles with relatively long endocyclic Ge–Cl and Al–C bonds. Reactions with isocyanates resulted in the insertion of the heterocumulenes into both activated bonds and the formation of four‐membered GeC2N heterocycles, which featured exocyclic C–C and C–O double bonds with C–O oxygen atoms coordinated to ClAltBu2 molcules (2). An intermediate (3) was isolated with Ad‐NCO (Ad = 1‐adamantyl) from the insertion of isocyanate into the endocyclic Al–C bond. These products are characterized by intact Ge–Cl bonds and a chelating coordination of the Al atoms by the OCN groups. They rearranged at elevated temperature to yield compounds of type 2. Quantum‐chemical calculations were applied to evaluate the thermodynamics of these isocyanate insertion reactions. An azide reacted similarly by insertion into the Al–C and Ge–Cl bonds and afforded a GeCN3 heterocycle with an intact N3 group.

Basic Reactivity Pattern of a Cyclic Disilylated Germylene.

In order to estimate the reactivity of disilylated germylene phosphine adducts, a cyclic version of this compound class was reacted with a number of different reagents. Reactions with the chalcogens sulfur, selenium, and tellurium led to dimers of the heavy ketone analogues. Reactions with water and ethyl bromide proceeded to give the respective oxidized germanol and germyl bromide. Two different reactions with alkynes were observed which led either to a germacyclopropene, by addition of tolane to the germylene, or to a silagermacyclobutene, likely formed by addition of the alkyne across a silagermene. Reaction via the silagermene was also observed in the reaction with benzophenone. Reaction of a germylene phosphine adduct with GeCl2·(dioxane) provided insertion of the silylated germylene into a Ge–Cl bond, leading to a germylated chlorogermylene phosphine adduct.

Dual doped monolayer and bilayer graphene: The case of 4p and 2p elements

4p/2p dual-doped monolayer and bilayer graphene were studied via first principle calculations. Generally, dopants prefer to be agglomerated. A second dopant significantly reduces formation energies. Thus, partially reduced graphene oxide would favor substitutional doping by facilitating the introduction of the 4p dopants. Dual-doping can tune the band gap from 0.1 to 0.8eV. For bilayer graphene, large atomic radii elements (Gallium and Germanium) form interlayer bonds with the undoped sheet. For some dual-doped graphenes, interlayer GaC and GeC bonds were formed, increasing the chemical reactivity of the undoped layer and affecting its electronic structure, with metallic or semiconducting characters observed.