Ge Bonds Research Articles

Structure of Glasses of the Li2O–K2O–GeO2 System: Raman Spectroscopic Data

Abstract—Glasses of the three-component Li2O–K2O–GeO2 system are studied by Raman spectroscopy. Spectra are curve-fitted and the main structural units formed in the system are established. Conditions of formation of highly coordinated germanium atoms are determined and non-statistic distribution of network-modifying cations is found. It is shown that lithium for potassium substitution is accompanied by a change of coordination number of germanium, which could cause the destruction of Ge–O–Ge bonds with formation of non-bridging oxygens.

Atomic layer deposition and tellurization of Ge-Sb film for phase-change memory applications.

We studied the atomic layer deposition (ALD) and the tellurization of Ge–Sb films to prepare conformal crystalline Ge–Sb–Te (GST) films and to achieve void-free gap filling for emerging phase-change memory applications. ALD Ge–Sb film was prepared by alternating exposures to GeCl2-dioxane and Sb(SiEt3)3 precursors at 100 °C. The growth rate was 0.021 nm per cycle, and the composition ratio of Ge to Sb was approximately 2.2. We annealed the ALD Ge–Sb films with a pulsed feeding of di(tert-butyl)tellurium. The ALD Ge–Sb films turned into GST films by the tellurization annealing. When the tellurization temperature was raised to 190 °C or higher temperatures, the Raman peaks corresponding to Ge–Sb bond and amorphous Ge–Ge bond disappeared. The Raman peaks corresponding to Ge–Te and Sb–Te bonds were evolved at 200 °C or higher temperatures, resulting in the phase transition temperature of 123 °C. At 230 °C or higher temperatures, the entire film was fully tellurized to form a GST film having a relatively uniform composition of Ge3Sb2Te6, and the carbon impurities in the as-deposited ALD Ge–Sb film were eliminated. As the tellurization temperature increases, the volume of the ALD film is expanded owing to the incorporation of tellurium, resulting in complete filling of a trench pattern by GST film after the tellurization at 230 °C.

Tuning Hydrogenated Silicon, Germanium, and SiGe Nanocluster Properties Using Theoretical Calculations and a Machine Learning Approach.

There are limited studies available that predict the properties of hydrogenated silicon-germanium (SiGe) clusters. For this purpose, we conducted a computational study of 46 hydrogenated SiGe clusters (Si xGe yH z, 1 < X + Y ≤ 6) to predict the structural, thermochemical, and electronic properties. The optimized geometries of the Si xGe yH z clusters were investigated using quantum chemical calculations and statistical thermodynamics. The clusters contained 6 to 9 fused Si-Si, Ge-Ge, or Si-Ge bonds, i.e., bonds participating in more than one 3- to 4-membered rings, and different degrees of hydrogenation, i.e., the ratio of hydrogen to Si/Ge atoms varied depending on cluster size and degree of multifunctionality. Our studies have established trends in standard enthalpy of formation, standard entropy, and constant pressure heat capacity as a function of cluster composition and structure. A novel bond additivity correction model for SiGe chemistry was regressed from experimental data on seven acyclic Si/Ge/SiGe species to improve the accuracy of the standard enthalpy of formation predictions. Electronic properties were investigated by analysis of the HOMO-LUMO energy gap to study the effect of elemental composition on the electronic stability of Si xGe yH z clusters. These properties will be discussed in the context of tailored nanomaterials design and generalized using a machine learning approach.

Nickel as a Lewis Base in a T‐Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand

AbstractFlexible, chelating bis(NHC) ligand 2, able to accommodate both cis‐ and trans‐coordination modes, was used to synthesize (2)Ni(η2‐cod), 3. In reaction with GeCl2, it produced (2)NiGeCl2, 4, featuring a T‐shaped Ni0 and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2, in a reaction that formally involved Ni–Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ‐donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2Ni(cod) complexes 9 and 10, as well as (NHC)2GeCl2 derivative 11, incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni–Ge complexes. The isolation of (2)Ni(η2‐Py), 12, provides further evidence for the reluctance of the (2)Ni0 fragment to act as a σ‐Lewis acid.

Nickel as a Lewis Base in a T-Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand.

Flexible, chelating bis(NHC) ligand 2, able to accommodate both cis- and trans-coordination modes, was used to synthesize (2)Ni(η2 -cod), 3. In reaction with GeCl2 , it produced (2)NiGeCl2 , 4, featuring a T-shaped Ni0 and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2 , in a reaction that formally involved Ni-Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ-donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2 Ni(cod) complexes 9 and 10, as well as (NHC)2 GeCl2 derivative 11, incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni-Ge complexes. The isolation of (2)Ni(η2 -Py), 12, provides further evidence for the reluctance of the (2)Ni0 fragment to act as a σ-Lewis acid.

Effect of chemical composition on the structure, optical properties and femtosecond laser ablation performance of Ge-Sb-Se glasses

The effects of chemical composition on the physical and optical properties and femtosecond laser ablation performance of Ge–Sb–Se glasses with compositions of Ge18SbxSe82-x [x = 5, 10, 15, 17.5, 20, 21.5, 23, 25 (series A)] and GexSb25Se75-x [x = 10, 12.5, 15, 18, 20 (series B)] were systematically studied. With the increase in Sb and Ge in the series A and B glasses, respectively, the glass transition temperature increased at first and then decreased with increasing mean coordination number. The density and refractive index of the sample were mainly affected by Sb content. The third-order nonlinearity was measured at 3.5 μm by Z-scan technique. Raman spectra analysis showed that the proportion of Se–Se bonds declined and that of Sb–Sb and Ge–Ge bonds increased with the increase in Sb or Ge content. The enhancement of nonlinearity was associated with the presence of Sb–Sb homopolar bonds. Series A and B samples were irradiated by femtosecond laser (150 fs, 1 kHz) at 3 μm with different laser powers. The damaged area increased and ablation threshold fluence (Fth) was reduced gradually with the increase in Sb or Ge concentration. Thus, the addition of Sb or Ge can reduce the resistance of Ge–Sb–Se glasses from laser damage.

Insight into chemical bonding of the transition metal-doped cluster Ge2M (M = Sc–Zn) series using NBO and NRT theory

Chemical bonding of the 3d transition metal-doped germanium Ge2M (M = Sc–Zn) clusters is investigated by using quantum chemical calculations combined with the analyses of natural atomic orbital (NAO), natural bond orbital (NBO) and natural resonance theory (NRT). All of the clusters have ground state structure of isosceles triangle whose chemical bonding can be described by orbital overlaps and electron transfers between M atom and Ge2 unit. Among the series, Ge2Ti is found to be the most stable cluster due to the best electron pairing between AO-4s and AOs-3d of Ti atom and the three bonding orbitals of the Ge2 unit, whereas Ge2Zn is the least stable thanks to the only overlap between AO–4s(Zn) and MO-πy of the Ge2 unit. While the Ge–Ge bond is of most covalent character, the Ge–M bond is of half-half covalent and ionic character. The double Ge=Ge bond of Ge2 is either enhanced (M = Cr, Mn, Cu and Zn) or depleted (M = Sc–Ti, Fe–Ni) upon interacting with the transition metal atom due to the electron transfer between the metal atom and the Ge2 unit. Finally, the 3d shell of the dopant atoms remains most of their own character in these clusters, especially magnetic moment, which is very interesting for potential magnetic materials.

Lutetium Trigermanide LuGe3: High-Pressure Synthesis, Superconductivity, and Chemical Bonding

LuGe3 was obtained under high-pressure and high-temperature conditions at pressures between 8(1) and 14(2) GPa and at temperatures in the range from 1100(150) to 1500(150) K. The high-pressure phase is isotypic to DyGe3 and decomposes at ambient pressure and T = 690 K mainly into ( cF8)Ge and LuGe2- x. Chemical bonding analysis of LuGe3 reveals two-center electron-deficient Ge-Ge bonds, multicenter polar Lu-Ge interactions, and lone pairs on germanium. Magnetic susceptibility, specific heat, and electrical conductivity measurements indicate transition into a superconducting state below Tc = 3.3(3) K.

Iron Porphyrin Catalyzed Insertion Reaction of N-Tosylhydrazone-Derived Carbenes into X-H (X = Si, Sn, Ge) Bonds.

An efficient Fe(TPP)Cl catalyzed insertion reaction of in situ generated benzylic carbenes from N-tosylhydrazones into X-H (X = Si, Sn, Ge) was developed. Silanes bearing tertiary, secondary, and primary (3°, 2°, and 1°) Si-H bonds all reacted well to afford insertion products in moderate to high yields (up to 97%), and the reaction time could be significantly shortened to 1 h under microwave irradiation. A programmable stepwise double insertion strategy was developed for the synthesis of unsymmetrical tetrasubstituted silanes.

Physics of Fermi-Level “Unpinning” at Metal/Ge Interfaces; First-Principles View

The control of Fermi-energy position at metal/Ge interface is one of issues to be overcome for developing next-generation Ge devices. In this work, at first, we study the Schottky barrier at various TiN/Ge interfaces by the first-principles calculation and show that the Fermi-level pinning occurs at clean TiN/Ge interface, while the pinning is broken, i.e., the depinning occurs, at N-rich TiN/Ge interface, in agreement with experiments. By analyzing electronic structures, we show that the appearance of N-rich interface layers such as TiN2 and Ge3N4 layers realizes the depinning. Next, we compare the depinning features at various metal/Ge interfaces and show that the termination of interface bonds of Ge eliminates the electronic freedom of gap states in interface Ge layers and promotes the depinning.

SiC‐Doped Ge2Sb2Te5 Phase‐Change Material: A Candidate for High‐Density Embedded Memory Application

AbstractPhase‐change memory is one of the most attractive solutions for embedded applications, thanks to the low cost of integration with current manufacturing processes and the good scaling behavior. Despite intensive research efforts that are devoted to the modification of Ge2Sb2Te5 (GST) phase‐change material, the obtained improvements are still unsatisfactory for high‐performance applications. In this paper, SiC‐modification is first introduced to enhance the amorphous stability of GST without sacrificing its transition speed. Several enhancements can be demonstrated, including better thermal stability (10‐year data retention above 120 °C), lower RESET voltage (about 3.0 V at 20 ns pulse width), reduced volume change (smaller than 3.0%), and expected operation cycles (more than 1.0 × 105). According to the findings, the local bonding nature of Ge/Te atoms can be tuned by C/Si dopants through forming CGe and SiTe bonds. Apart from strengthening the atomic binding network for desirable data retention, the element interdiffusion is also effectively controlled and suppressed. Together with finer grains, smaller density change, and more uniform morphology, the modified structure transition finally contributes to the reduced switching voltage and long‐term endurance. Hence, it is envisaged that SiC‐doped GST with such advantages will give a competitive option for high‐density and high‐performance embedded memory.

Synthesis of the Elusive Branched Fluoro-oligogermane (Ph3Ge)3GeF: A Structural, Spectroscopic, Electrochemical, and Computational Study

The fluorine-substituted branched oligogermane (Ph3Ge)3GeF was successfully synthesized from (Ph3Ge)3GeH and [Ph3C][BF4] after several unfruitful attempts using other synthetic methods and was formed as a mixture with Ph3GeF. Pure (Ph3Ge)3GeF could be obtained from the reaction mixture by successive recrystallizations and was characterized by elemental analysis and NMR (1H, 13C, and 19F) spectroscopy, including a variable-temperature 19F NMR study to investigate the presence or absence of hydrogen bonding in this species. The oligogermane (Ph3Ge)3GeF is indefinitely stable in the solid state under an inert atmosphere, but gradually decomposes to Ph3GeF and other unidentified products in solution. The X-ray crystal structure of (Ph3Ge)3GeF was obtained and represents the only crystallographically characterized germanium–fluorine compound having unsupported Ge–Ge bonds. The Ge4 framework of the oligogermane (Ph3Ge)3GeF is isostructural with the other previously prepared halogen-substituted analogues (Ph3Ge)...

Lattice contraction with boron doping in fully strained SiGe epitaxial layers

Changes in lattice constants of epitaxial SiGe layers by boron (B) doping were studied by using high resolution X-ray diffraction (HRXRD) by using SiGe:B with Ge and B concentrations in the range of 11–23% and (1.5–4.2) × 1019 cm−3, respectively. The lattice contraction coefficient (β) of B in SiGe was measured to be (9.6 ± 0.6) × 10−24 cm3, which was approximately twice as large as that of B in Si. The ab initio calculation of β, 9.35 × 10−24 cm3, was in excellent agreement with the experiment. From the ab initio calculation, it is found that the large lattice contraction is due to the favorability of Si–B bond than Si–Ge bond.

X‐ray photoelectron spectroscopy analysis of Ge–Sb–Se pulsed laser deposited thin films

AbstractPulsed laser deposition was used to prepare amorphous thin films from (GeSe2)100−x(Sb2Se3)x system (x = 0, 5, 10, 20, 30, 40, 50, and 60). From a wide variety of chalcogenide glass‐forming systems, Ge–Sb–Se one, especially in thin films form, already proved to offer a great potential for photonic devices such as chemical sensors. This system has a large glass‐forming region which gives the possibility to adjust the chemical composition of the glasses according to required physical characteristics. The chemical composition of fabricated thin films was analyzed via X‐ray photoelectron spectroscopy (XPS) and compared to energy dispersive spectroscopy (EDS) data. The results of both techniques agree well: a small deficiency in chalcogen element and an excess of antimony was found. The structure of as‐deposited thin films has been investigated by XPS. The presence of the two main structural units, [GeSe4] and [SbSe3] proposed by Raman scattering spectroscopy data analysis, was confirmed by XPS. Moreover, XPS core level spectra analysis revealed the presence of M–M bonds (M = Ge, Sb) in (Ge,Sb)–Ge–(Se)3 and (Ge,Sb)–Sb–(Se)2 entities that could correspond to Ge‐based tetrahedra and Sb‐based pyramids where one of its Se atoms at corners is substituted by Ge or Sb ones. The content of depicted M–M bonds tends to increase with introduction of antimony in the amorphous network of as‐deposited thin films from x = 0 to x = 40 and then it decreases. XPS analysis of as‐deposited thin films shows also the presence of the (Ge,Sb)–Se–(Ge,Sb) and Se–Se–(Ge,Sb) entities.

Magnetic behavior of Si-Ge bond in SixGe4-x nano-clusters

The structure of SixGe4-x nano-clusters were optimized by MPW1B95 level of theory using MG3S and SDB-aug-cc-PVTZ basis set. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. Since the Si–Si bond is stronger than Si–Ge and Ge–Ge bonds, the Si–Si, Si–Ge, and Ge–Ge diagonal bonds determine the precedence of the stability in these nano-clusters. The hybrid meta density functional calculations were carried out to investigate the adsorption of CO on all possible SixGe4-x nano-clusters. It was found that the silicon atom generally makes a stronger bond with CO than germanium and thereby preferentially affects the shape of structures having higher multiplicity. In Si-Ge structures with higher spin more than 95% of spins accumulate on positions with less bonds to other atoms of the cluster. Through CO adsorption on these clusters bridge structures are made that behave as spin bridge which conduct the spin from the nano-cluster surface to the adsorbate atoms. A better understanding of bridged structures was achieved upon introducing the ‘spin bridge’ concept. Based on exhaustive spin density analysis, it was found that the reason for the extra negative charge on oxygen in the bridged structures is the relocation of spin from the surface through the bridge.

Regioselective Cyclotrimerization of Terminal Alkynes Using a Digermyne.

The catalytic activation of small neutral molecules followed by the formation of C-C bonds is a highly important method to increase the complexity and/or value of simple starting materials. Reported is an isolable digermyne, a compound with a Ge≡Ge bond, which acts as a precatalyst for the cyclotrimerization of terminal arylacetylenes to afford the corresponding 1,2,4-triarylbenzenes with absolute regioselectivity. The results demonstrate that bespoke main-group-element compounds can catalytically activate and transform small neutral organic molecules and induce the formation of C-C bonds.

Regioselective Cyclotrimerization of Terminal Alkynes Using a Digermyne

AbstractThe catalytic activation of small neutral molecules followed by the formation of C−C bonds is a highly important method to increase the complexity and/or value of simple starting materials. Reported is an isolable digermyne, a compound with a Ge≡Ge bond, which acts as a precatalyst for the cyclotrimerization of terminal arylacetylenes to afford the corresponding 1,2,4‐triarylbenzenes with absolute regioselectivity. The results demonstrate that bespoke main‐group‐element compounds can catalytically activate and transform small neutral organic molecules and induce the formation of C−C bonds.

Isolation and Reactivity of a Chlorogermyliumylidene Featuring Two Ge–Cl Units

Deprotonation of 1‐mesityl‐4,5‐diphenyl‐2‐imidazole 1 with nBuLi, followed by salt metathesis reaction with GeCl2·dioxane complex, led to the formation of the chlorogermyliumylidene 2 bearing two Ge–Cl units, which has been isolated and fully characterized by standard spectroscopic and X‐ray diffraction analysis. Structural and NMR spectroscopic data as well as computational studies revealed that the positive charge mainly resides on the Ge atom between two nitrogen atoms. Reduction of 2 with an excess amount of lithium metal resulted in Ge–Ge bond formation concomitant with elimination of one of the Ge atoms of 2, to give rise to the digermylenedilithium compound 3 involving intramolecular coordination of the imines and the lone pairs to the Li atoms.

Growth model and structure evolution of Ag layers deposited on Ge films.

We investigated the crystallinity and optical parameters of silver layers of 10–35 nm thickness as a function 2–10 nm thick Ge wetting films deposited on SiO2 substrates. X-ray reflectometry (XRR) and X-ray diffraction (XRD) measurements proved that segregation of germanium into the surface of the silver film is a result of the gradient growth of silver crystals. The free energy of Ge atoms is reduced by their migration from boundaries of larger grains at the Ag/SiO2 interface to boundaries of smaller grains near the Ag surface. Annealing at different temperatures and various durations allowed for a controlled distribution of crystal dimensions, thus influencing the segregation rate. Furthermore, using ellipsometric and optical transmission measurements we determined the time-dependent evolution of the film structure. If stored under ambient conditions for the first week after deposition, the changes in the transmission spectra are smaller than the measurement accuracy. Over the course of the following three weeks, the segregation-induced effects result in considerably modified transmission spectra. Two months after deposition, the slope of the silver layer density profile derived from the XRR spectra was found to be inverted due to the completed segregation process, and the optical transmission spectra increased uniformly due to the roughened surfaces, corrosion of silver and ongoing recrystallization. The Raman spectra of the Ge wetted Ag films were measured immediately after deposition and ten days later and demonstrated that the Ge atoms at the Ag grain boundaries form clusters of a few atoms where the Ge–Ge bonds are still present.

Characterization of C20 fullerene and its isolated C20‐nGen derivatives (n = 1‐5) by alternating germanium atom(s) in equatorial position: A DFT survey

AbstractDFT calculations are applied to compare and contrast germanium atom(s) substituted C20‐nGen heterofullerenes with n = 1‐5, where the substitution is completely isolated from each other by means of one carbon atom in equatorial position. The structural stabilities, geometry, and electronic properties of C20 and its heterofullerene derivatives are compared and contrasted at M062X/6‐311++G**, B3LYP/AUG‐cc‐pVTZ, B3LYP/6‐311++G**, B3LYP/6‐311+G*, and B3PW91/6‐311++G** levels of theory. Vibrational frequency analysis shows that all of the heterofullerenes are real minima. Contrary to identical bonds in C20, contractions of C=C double bonds are encountered at the expense of longer C―Ge bonds in C20‐nGen. In contrast to previous reports on silicon doped heterofullerenes, none of the computed heterofullerenes collapses to open cage structures. Successive Ge doping on C20 induces more positive atomic charge on Ge atoms and more negative charge on C atoms. High charge transfer on the surfaces of our stable heterofullerenes provokes further investigations on their possible application for hydrogen storage. As to band gap, binding energy, heat of atomization per carbon, nucleus‐independent chemical shift, aromaticity, and the smallest vibrational frequency C19Ge immerges with the highest value. The reactivity in terms of ionization potential, nucleophilicity, electrophilicity, hardness, softness, maximum electronic charge, and proton affinity issues predicts C19Ge as the most stable heterofullerene against electronic excitation.