Ge-Si Bond Research Articles

Unveiling the physical properties of RbCu3MSe4 (M = Si, Ge) direct band gap semiconductors: A systematic first-principles study

The Silicon and Germanium-based quaternary chalcogenides have remarkable features including their adjustable optical properties and outstanding thermal stability. We explored the complex interplay among the structural, electronic, optical, and thermoelectric characteristics of direct band gap novel RbCu3MSe4 (M = Si, Ge) quaternary chalcogenides by employing the well-known density functional theory. Direct type of band gap at high symmetry Г-point was noticed for both materials. The predicted band gaps of RbCu3SiSe4 and RbCu3GeSe4 are 1.32 eV and 0.73 eV, respectively. Due to the large size of germanium ions compared to silicon, the Ge–Se bonds in RbCu3GeSe4 are more wide-ranging than the Si–Se bonds in RbCu3SiSe4. The complex dielectric function along with other significant optical parameters are investigated and analyzed for their probable employment for optoelectronic applications. These examined materials are suitable to be employed in thermoelectric devices as observed from substantial and outstanding thermoelectric features. The present work could establish the potential employment of these complex systems and would open the way for advanced applications in various fields and technologies.

Activation of carbon disulfide by a hypersilyl germylene.

In this work, the insertion of CS2 into the Ge-Si bond of PhC(NtBu)2Ge-Si(SiMe3)3 (1) has been investigated, resulting in the formation of PhC(NtBu)2Ge-C(S)-S-Si(SiMe3)3 (2). Interestingly, the addition of NHC to 2 allows the release of NHC·CS2 with concomitant regeneration of 1. Addition of another equivalent of 1 or an analogous hypersilyl silylene, [PhC(NtBu)2Si-Si(SiMe3)3], to 2 led to the formation of compounds with a GeS (3) or a SiS (4) bond.

Current Status of Silicon Studies with GexSi1-x Binary Compounds and Possibilities of Their Applications in Electronics

The paper determines the technological regimes for obtaining GexSi1-x alloys by introducing germanium atoms into single-crystal silicon by the diffusion method. From the results of the study, it was found that the fundamental parameters of the formed GexSi1-x alloys differ from the fundamental parameters of the original silicon, in particular, the energy values of the silicon band gap change. Elemental analysis of the surface of the samples showed that the concentration of silicon (in atomic percent) was ~70.66%, germanium ~29.36%. It was assumed that on the silicon surface and in the front part, a thin layer of an alloy of a compound with a composition of approximately Ge0.3Si0.7 (0.5÷2 μm) would be formed. Analysis of the spectra (p shows that the spectrum contains peaks ~303 cm-1 and ~406 cm-1, corresponding to the Ge-Ge and Si-Ge bonds, respectively. It was also shown that GexSi1-x binary compounds are a new material for modern electronics, the possibility of creating properties on their basis in electronics was shown. It is proposed on their basis to create devices with new functionality and highly efficient solar cells.

In Situ Synthesis of Amorphous GeSe/CNT Composite via Defective-carbon-mediated Chemical Bonding for Ultrastable Na Ion Storage.

Herein, we report the in-situ synthesis of amorphous GeSe/CNT composite via defective-carbon-mediated chemical bonding for ultrastable Na-ion storage. Structural defects in CNTs play a crucial role in the chemical bonding and bonding strength in GeSe/CNTs composites. Specifically, the bonding strength tends to increase with increasing defect concentrations of CNTs. Remarkably, the strong chemical bonding between GeSe and CNTs significantly weakens Ge-Se bonds and promotes amorphization of GeSe, thus facilitating a reversible conversion reaction and enhancing Na-ion diffusion. Consequently, GeSe/CNTs composite exhibits outstanding cyclability of 87.9% even after 1000 cycles at 1 A g-1 and a high-rate capability of 288.3 mA h g-1 at 10 A g-1 . Our work presents a promising approach for the amorphization of electrode materials enabled by the defective-carbon-mediated strong chemical bonding for Li-, Na-, and K-ion batteries.

Density functional theory study on the effect of germanium doping in sphalerite on the adsorption mechanism of butyl xanthate

In this study, density functional theory (DFT) was used to calculate the difference of adsorption between sphalerite (110) surfaces and butyl xanthate in the flotation process with and without Ge doping, and the effect of Ge doping on Cu (II) activation in the flotation process of sphalerite. The results show that there is covalent bonding between Zn-S and Cu-S bonds, the Cu-S bonds are more stable than Zn-S bonds, and Ge-S bonds cannot be bonded. The adsorption of sodium butyl xanthate (NaBX) on the surface of germanium-bearing sphalerite is weak, and the effect of Cu(II) activation on the adsorption of germanium-bearing sphalerite is less, that is, Cu is difficult to activate germanium-bearing sphalerite. Through the calculation and analysis of the adsorption model of NaBX on the (110) surface of sphalerite and germanium-bearing sphalerite in the absence and presence of Cu activation, it is proved that the existence of Ge doping will hinder the adsorption of sphalerite and NaBX, weaken the activation of Cu on sphalerite, reduce the flotability of sphalerite, and cause the loss of sphalerite and Ge elements in the froth flotation process.

Electrical and Structural Properties of Si1-xGex Nanowires Prepared from a Single-Source Precursor.

Si1-xGex nanowires (NWs) were prepared by gold-supported chemical vapor deposition (CVD) using a single-source precursor with preformed Si-Ge bonds. Besides the tamed reactivity of the precursor, the approach reduces the process parameters associated with the control of decomposition characteristics and the dosing of individual precursors. The group IV alloy NWs are single crystalline with a constant diameter along their axis. During the wire growth by low pressure CVD, an Au-containing surface layer on the NWs forms by surface diffusion from the substrate, which can be removed by a combination of oxidation and etching. The electrical properties of the Si1-xGex/Au core-shell NWs are compared to the Si1-xGex NWs after Au removal. Core-shell NWs show signatures of metal-like behavior, while the purely semiconducting NWs reveal typical signatures of intrinsic Si1-xGex. The synthesized materials should be of high interest for applications in nano- and quantum-electronics.

Effect of surface morphology and interfaces on longitudinal phonon thermal conductivity in Ge(001) and Si/Ge(001) thin-film structures

In this work the method of non-equilibrium molecular dynamics was used to study the longitudinal phonon thermal transport at 300 K in nanoscale homogenous Ge(001) and layered Si/Ge(001) thin films with p(2x1) surface reconstruction along different directions. The appearance of thermal transport anysotropy in the films under consideration, which is due to both the surface morphology and sharp Si/Ge interfaces, has been established. For the direction when the dimers and Si-Ge bonds at the interface lie in a plane parallel to the direction of the heat flow, the lowest thermal conductivity is observed (~5-18 W/(m·K) in the range from ~1 to 27 nm). It is shown that for films with thicknesses of more than 13 nm for all directions, layered films have a lower thermal conductivity compared to homogenous ones. In this case, the role of the surface morphology and interfaces is reduced to different degrees of phonon localization and compensation for more heat-conducting Si layers, respectively. Keywords: thermal conductivity, molecular dynamics, Si/Ge thin-film, surface, interfaces.

Short range order and topology of binary Ge-S glasses

Short range order and topology of GexS100-x glasses over a broad composition range (20 ≤ x ≤ 42 in at%) was investigated by neutron diffraction, X-ray diffraction, and Ge K-edge extended X-ray absorption fine structure (EXAFS) measurements. The experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo simulation method. It was found that both constituents (Ge and S) satisfy the Mott-rule in all investigated glasses: Ge and S atoms have 4 and 2 neighbours, respectively. The structure of these glasses can be described with the chemically ordered network model: Ge-S bonds are preferred; S-S bonds are present only in S-rich glasses. Dedicated simulations showed that Ge-Ge bonds are necessary in Ge-rich glasses. Connections between Ge atoms (such as edge-sharing GeS4/2 tetrahedra) in stoichiometric and S-rich glasses were analysed. The frequency of primitive rings was also calculated.

Mixed-Substituted Single-Source Precursors for Si1-xGex Thin Film Deposition.

A series of new mixed-substituted heteronuclear precursors with preformed Si-Ge bonds has been synthesized via a two-step synthesis protocol. The molecular sources combine convenient handling with sufficient thermal lability to provide access to group IV alloys with low carbon content. Differences in the molecule-material conversion by chemical vapor deposition (CVD) techniques are described and traced back to the molecular design. This study illustrates the possibility of tailoring the physical and chemical properties of single-source precursors for their application in the CVD of Si1-xGex coatings. Moreover, partial crystallization of the Si1-xGex has been achieved by Ga metal-supported CVD growth, which demonstrated the potential of the presented precursor class for the synthesis of crystalline group IV alloys.

Atomic mass dependency of a localized phonon mode in SiGe alloys

Using molecular dynamics, the effect of an atomic mass difference on a localized phonon mode in SiGe alloys was investigated. Phonon dispersion relations revealed that a change in atomic mass causes the optical and acoustic modes to shift frequency. The results indicate that the local mode is sensitive to both Si and Ge atomic mass changes; reducing the Si atomic mass shifts the local mode to higher frequencies, and increasing the Ge atomic mass shifts the local mode to lower frequencies. Furthermore, the results suggest that the local mode originates from the Si–Ge bond vibration. Although the Si–Si, Si–Ge, and Ge–Ge optical mode frequencies are well approximated by the two-body harmonic oscillator model, a much heavier effective mass than that of the Si–Ge pair must be assumed to reproduce the local mode frequency. A plausible interpretation of the local mode is a collective vibration of Ge clusters embedded within the Si lattice.

Alteration of structural, electronic, and vibrational properties of amorphous GeTe by selenium substitution: An experimentally constrained density functional study

The structural, vibrational and electronic properties of several compositions of amorphous Ge-Se-Te are studied from a combination of x-ray diffraction and density functional-based molecular dynamics. Different structural properties are considered such as structure factors, pair distribution functions, angular distributions, coordination numbers, and neighbor distributions. We compare results with experimental findings and a satisfying agreement is found for the structure functions in real and reciprocal spaces. The short range order is found to be more complex than in related binaries that result in mixed geometries ($\ensuremath{\simeq}65%--75%$ tetrahedral, and remaining defect octahedral) for a dominant fourfold Ge (80%). The chalcogen atoms are dominantly twofold, the former having furthermore an important fraction of threefold coordinated atoms (30%--40%). The obtained model structures indicate that Ge-Ge, Ge-Se, and Ge-Te bonds dominate with small fractions of Te-Te bonds remaining from the base system GeTe. The investigation of electronic properties indicates that the addition of Se atoms will lead to Te-related bands that are much more localized so that Ge-Te-Se can be regarded as having an increased covalent character with respect to GeTe.

Amorphization of germanium selenide driven by chemical interaction with carbon and realization of reversible conversion-alloying reaction for superior K-ion storage

Chemical interaction with carbon has been employed to establish electron conduction pathways through intimate contact with anode materials. It is highly plausible that the strong chemical interaction can change the crystallinity as well as bonding nature of anode materials. This highlights the importance of chemical interaction with carbon and its effects on the material and electrochemical properties of anode materials. However, this is not yet investigated. This study is the first report on the amorphization of layered structured GeSe induced by the chemical interaction and its implications on the electrochemical properties for K-ion batteries. The charge storage mechanism of GeSe/CNT composite, investigated using ex-situ X-ray diffraction, indicates that reversible conversion-alloying reaction of GeSe is realized by the amorphization, which is closely linked with weakening of Ge–Se bonds derived from the strong chemical interaction and a concomitant increase in K-ion diffusion. As a result, the GeSe/CNT composite exhibits excellent electrochemical properties. Similar amorphization driven by chemical interaction is also observed for other layered structured anode materials. This study provides new insights on the chemical interaction of layered anode materials with carbon. Our findings could effectively be used to realize reversible conversion reaction for other anode materials for advanced secondary batteries.

Dependency of a localized phonon mode intensity on compositional cluster size in SiGe alloys

Using molecular dynamics, we found that the localized phonon-mode spectrum in SiGe alloys, which was recently discovered by an inelastic x-ray scattering experiment, changes according to the size distribution of compositional clusters in alloys. By varying the spatial distributions of Si and Ge, alloy models with differing compositions of Si and Ge clusters were able to be produced. For a range of alloys comprising 20%–80% Ge, a mixture of small and intermediate sized clusters will give the highest intensities of the local mode. The Si–Ge optical mode intensity increases with the local mode intensity, but the Si–Ge bond alone is not sufficient to produce the local mode. Si rich alloys with small Ge clusters produce the highest local mode intensities, suggesting that this mode is caused by small Ge clusters surrounded by Si pairs.

Ovonic threshold switching induced local atomic displacements in amorphous Ge60Se40 film probed via in situ EXAFS under DC electric field

In an effort to verify whether the Ovonic threshold switching in amorphous chalcogenide film is concomitant with any noticeable atomic rearrangements, we analyze EXAFS spectra of amorphous chalcogenide Ge60Se40 (at%) film measured in situ under DC electric field. The in situ EXAFS measurements are performed with specifically prepared specimens, in which 100-nm-thick amorphous Ge60Se40 layer is sandwiched between two metallic electrode layers, all the while a constant DC electric bias being applied. Our EXAFS analysis indicates that only Debye-Waller factor undergoes a noticeable change upon the Ovonic threshold switching, keeping both coordination number and interatomic distance unaltered. The changes in Debye-Waller factors of Ge-Se and Ge-Ge pairs appear to be reversible during the ON/OFF cycle; however, heteropolar Ge-Se pair experiences a conspicuously greater change in its Debye-Waller factor than homopolar Ge-Ge counterpart. Increase of thermal disorder due to Joule heating is insufficient to support this observation, which instead is caused by a preferential increase of static disorder associated with heteropolar Ge-Se bonds in the ON state. The heteropolar Ge-Se pair is supposed to feel the electrical wind force (momentum transfer by conducting electrons) as well as the Coulombic force more strongly than the homopolar Ge-Ge pair.

Atomic Scale Structure of (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 Kesterite Thin Films

Kesterite based materials are being researched and developed as affordable, efficient, and mechanically flexible absorber materials for thin film photovoltaics. Both (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 based devices have shown great potential in overcoming some of the remaining challenges for further increasing the conversion efficiency of kesterite based solar cells. This study therefore investigates the long range crystallographic structure and the local atomic scale structure of technologically relevant thin films by means of grazing incidence X-ray diffraction and low temperature X-ray absorption spectroscopy. As expected, the unit cell dimensions change about an order of magnitude more than the element specific average bond lengths. In case of Cu2Zn(Sn,Ge)Se4, the thin film absorbers show a very similar behavior as Cu2Zn(Sn,Ge)Se4 powder samples previously studied. Small amounts of residual S in the thin films were taken into account in the analysis and the results imply a preferential formation of Sn-S bonds instead of Ge-S bonds. In (Ag,Cu)2ZnSnSe4, the dependence of the Ag-Se and Cu-Se bond lengths on Ag/(Ag+Cu) might indicate an energetic advantage in the formation of certain local configurations.

XPS analysis of [formula omitted] and its [formula omitted]-subsituted alloy

The investigation reported is the study of electronic structure of the intermetallic compound Gd5Ge2Si2 and its Co-substitution i.e. Gd5Ge1.9Si2Co0.1 with the help of X-ray photoelectron spectroscopy (XPS). The investigations reveal the crystallization of the compounds to be in a single phase with Orthorhombic structure. The XPS spectra disclose the signature peaks of the various orbitals of the constituent elements of the compounds. Though a subtle shift in the binding energy values is observed. The deconvoluted XPS spectra provides the interaction of the core of the compounds with different neighbours. Deconvolution shows that for Gd(3d) spectra the strongest bonding is for Gd-Ge bond with a binding energy value of ∼ 1190 eV for both the compounds. Also, for Si(2p) spectra this value is close to 102 eV for Si-Ge bond.

PHOTOBLEACHING IN GeSe2 AND SiO2/GeSe2 THIN FILMS

We prepared GeSe2 film and GeSe2 covered by a layer of thin SiO2 (SiO2/GeSe2) to examine photo-induced effects. We found, upon sub-gap light illumination, transmission edge of both the films exhibit a blue shift, but the amount of the shift in SiO2/GeSe2 is less than that in GeSe2. Kinetics measurements of the photo-induced effects indicate that the both films exhibit PB behavior after more than few hundreds seconds illumination. Raman scattering measurements show that some of Ge-Ge and Se-Se bonds are broken and convert to Ge-Se bonds. All the results indicate that the change of the intrinsic structure upon illumination is dominated in the PB process.

Ge30AsxSe70-x bulk glasses from the point of view of chemistry

To elucidate the chemical structure of Ge-As-Se based glasses with selenium substoichiometry, Ge30AsxSe70-x homogeneous bulk glasses were prepared and the glass-forming region was found from x ​= ​0 up to 40. The chemical structure of these glasses was characterized by basic structural units. The structure of Ge30Se70 (x ​= ​0) glass is based on GeSe4/2 and GeSe4 structural units and traces of selenium. When selenium is gradually replaced with arsenic AsSe3/2 and GeIIAs2/3 structural units appear in the equimolar ratio with gradually increasing concentrations at the expense of the units with Ge–Se bonds. Finally, for x ​= ​40 the glass is formed exclusively by structural units AsSe3/2 and GeAs2/3. Thus, the structure of both border glasses is based only on two structural units whereas other glasses are based on four units. For this reason, the undercooled melts of both border glasses are less stable and undergo crystallization when heated. In terms of the geometry of the basic structures, the structure for x ​= ​0 is formed solely by tetrahedral units with germanium as the central atom, and then is gradually transformed with increasing concentration of arsenic to a structure consisting only of trigonal pyramids with arsenic as a central atom.

The effect of edge functionalization on the device performance of monolayer Si0.5Ge0.5 nanoribbon transistors

Monolayer silicene and germanene have received intensive attention due to their good compatibility with current Si-based electronics. However, the lack of a bandgap severely limits their applications in complex electronic circuits. To overcome this obstacle, we build Si1−xGex superlattices (SLs) and further cleave them into nanoribbons to tune the electrical properties of silicene and germanene, and analyze their transport behavior by means of density functional theory combined with the nonequilibrium Green’s function formalism. Among all the designed Si1−xGex SLs, Si0.5Ge0.5 possesses the widest bandgap of 0.53 eV, as its larger amount of Ge–Si bonds can result in strong absorption of light towards short wavelengths. By edge functionalization with Li, H, and F atoms, the conduction type of the monolayer Si0.5Ge0.5 nanoribbons can be rationally tuned from n-type to ambipolar to p-type. These tunable electronic properties can be attributed to the internal and interfacial charge transfer. The simulated transport behavior of field-effect transistors based on monolayer Si0.5Ge0.5 nanoribbons demonstrates that such edge functionalization could be applied to modulate the conductivity, conduction type, on/off ratio, and carrier concentration effectively. The results of this work reveal the great potential of edge functionalization for tuning the electrical properties of two-dimensional (2D) semiconductors.

A Silylene-Germylene Molecule Containing a SiI -GeI Single Bond.

The first isolable silylene-germylene complex 5 was assembled by a salt metathesis reaction between the germylene anion 3 and the N-heterocyclic chlorosilylene 4, and structurally characterized. The central structure of 5 demonstrates a remarkable gauche-bent geometry with the silylene and germylene units, which are interconnected by a Si-Ge bond with a length of 2.4498(9) Å. This value is not only perceptibly longer than the distances known in doubly bonded germasilenes, and also slightly longer than those in germylsilanes. The DFT calculations on 5 confirmed a nearly nonpolar SiI -GeI single-bond nature and its bonding orbital, as well as the aromaticity of the C3 NGe-rings in 3 and 5. The latter increases the molecular stability of 3 and 5, and makes the preparation of silylene-germylene complex 5 a reality.