Structure Of Ge Research Articles

Effect of AFM ordering on thermoelectric responses of Mg3X2 (X: C, Si, Ge) monolayers : a DFT insight

Two-dimensional materials have gained a lot of attention in the last few decades due to their potential applications in thermoelectric and nano-electronic devices. This study systematically presents the mechanical, electronic and thermoelectric characteristics of two-dimensional honeycomb-kagomeMg3X2(X:C,Si,Ge) structures in the framework of density functional theory computations and by solving semiclassical Boltzmann transport equation. The geometrical stability of these structures is validated by phonon spectrum and molecular dynamics simulations. Following the elastic constants, we have inferred that all the systems are mechanically stable and brittle in nature. Lower values of Debye temperature of all structures suggest thatMg3X2monolayers should have lower values of lattice thermal conductivity compared to graphene. Electronic structure calculations indicate that these materials are semimetallic in their nonmagnetic phase. All the structures display remarkably low lattice thermal conductivity (0.9-1.5 W (mK)-1) due to a large scattering factor and higher anharmonicity. The presence of sharp density of states peaks close to the Fermi level, arising from nearly flat and dispersionless band in the antiferromagnetic (AFM) arrangement, is poised to enhance the Seebeck coefficient, thereby potentially boosting the thermoelectric performance. The estimated values of thermoelectric figure of merit (ZT) are around 0.78 and 0.67 forMg3Si2andMg3Ge2structure respectively in AFM phase atT= 700 K. These outcomes of our findings suggest thatMg3X2monolayers exhibit substantial promise for thermoelectric device application.

Structures of the Varicella Zoster Virus Glycoprotein E and Epitope Mapping of Vaccine-Elicited Antibodies.

Background: Varicella zoster virus (VZV) is the causative agent for chickenpox and herpes zoster (HZ, shingles). HZ is a debilitating disease affecting elderly and immunocompromised populations. Glycoprotein E (gE) is indispensable for viral replication and cell-to-cell spread and is the primary target for anti-VZV antibodies. Importantly, gE is the sole antigen in Shingrix, a highly efficacious, AS01B-adjuvanted vaccine approved in multiple countries for the prevention of HZ, yet the three-dimensional (3D) structure of gE remains elusive. Objectives: We sought to determine the structure of VZV gE and to understand in detail its interactions with neutralizing antibodies. Methods: We used X-ray crystallography and cryo-electron microscopy to elucidate structures of gE bound by recombinant Fabs of antibodies previously elicited through vaccination with Zostavax, a live, attenuated vaccine. Results: The 3D structures resolve distinct central and C-terminal antigenic domains, presenting an array of diverse conformational epitopes. The central domain has two beta-sheets and two alpha helices, including an IgG-like fold. The C-terminal domain exhibits 3 beta-sheets and an Ig-like fold and high structural similarity to HSV1 gE. Conclusions: gE from VZV-infected cells elicits a human antibody response with a preference for the gI binding domain of gE. These results yield insights to VZV gE structure and immunogenicity, provide a framework for future studies, and may guide the design of additional herpesvirus vaccine antigens. Teaser: Structures of varicella zoster virus glycoprotein E reveal distinct antigenic domains and define epitopes for vaccine-elicited human antibodies.

Sustainable Production of Ultrathin Ge Freestanding Membranes

Germanium (Ge) is a critical material for applications in space solar cells, integrated photonics, infrared imaging, sensing, and photodetectors. However, the corresponding cost and limited availability hinder its potential for widespread applications. However, using Ge freestanding membranes (FSMs) allows for a significant reduction in the material consumption during device fabrication while offering additional advantages such as lightweight and flexible form factor for novel applications. In this work, we present the Ge FSM production process involving sequential porous Ge (PGe) structure formation, Ge membrane epitaxial growth, detachment, substrate cleaning, and subsequent reuse. This process enables the fabrication of multiple high-quality monocrystalline Ge FSMs from the same substrate through efficient substrate reuse at a 100 mm wafer scale by a simple and low-cost chemical cleaning process. A uniform, high-quality PGe layer is produced on the entire recovered substrate. By circumventing the use of conventional high-cost chemical–mechanical polishing or even substantial chemical wet-etching, and by using an optimized PGe structure with reduced thickness, the developed process allows for both cost and an environmental impact reduction in Ge FSMs production, lowering the amount of Ge used per membrane fabrication. Moreover, this process employs large-scale compatible techniques paving the way for the sustainable production of group IV FSMs for next-generation flexible optoelectronics.

Noncentrosymmetric two-dimensional Weyl semimetals in porous Si/Ge structures.

In this work we predict a family of noncentrosymmetric two-dimensional (2D) Weyl semimetals (WSMs) composed by porous Ge and SiGe structures. These systems are energetically stable graphenylene-like structures with a buckling, spontaneously breaking the inversion symmetry. The nontrivial topological phase for these 2D systems occurs just below the Fermi level, resulting in nonvanishing Berry curvature around the Weyl nodes. The emerged WSMs are protected byC3symmetry, presenting one-dimensional edge Fermi-arcs connecting Weyl points with opposite chiralities. Our findings complete the family of Weyl in condensed-matter physics, by predicting the first noncentrosymmetric class of 2D WSMs.

Pressure-induced superconductivity in a novel germanium allotrope

High-pressure studies on elements play an essential role in superconductivity research, with implications for both fundamental science and applications. Here we report the experimental discovery of surprisingly low pressure driving a novel germanium allotrope into a superconducting state in comparison to that for α-Ge. Raman measurements revealed structural phase transitions and possible electronic topological transitions under pressure up to 58 GPa. Based on pressure-dependent resistivity measurements, superconductivity was induced above 2 GPa and the maximum Tc of 6.8 K was observed under 4.6 GPa. Interestingly, a superconductivity enhancement was discovered during decompression, indicating the possibility of maintaining pressure-induced superconductivity at ambient pressure with better superconducting performance. Density functional theory analysis further suggested that the electronic structure of Ge (oP32) is sensitive to its detailed geometry and revealed that disorder in the β-tin structure leads to a higher Tc in comparison to the perfect β-tin Ge.

Enhanced second-harmonic generation in strained germanium-on-insulator microdisks for integrated quantum photonic technologies.

Quantum photonic circuits have recently attracted much attention owing to the potential to achieve exceptional performance improvements over conventional classical electronic circuits. Second-order χ(2) nonlinear processes play an important role in the realization of several key quantum photonic components. However, owing to their centrosymmetric nature, CMOS-compatible materials including silicon (Si) and germanium (Ge) traditionally do not possess the χ(2) response. Recently, second-harmonic generation (SHG) that requires the χ(2) response was reported in Ge, but no attempts at enhancing the SHG signal have been conducted and proven experimentally. Herein, we demonstrate the effect of strain on SHG from Ge by depositing a silicon nitride (Si3N4) stressor layer on Ge-on-insulator (GOI) microdisks. This approach allows the deformation of the centrosymmetric unit cell structure of Ge, which can further enhance the χ(2) nonlinear susceptibility for SHG emission. The experimental observation of SHG under femtosecond optical pumping indicates a clear trend of enhancement in SHG signals with increasing strain. Such improvements boost conversion efficiencies by 300% when compared to the control counterpart. This technique paves the way toward realizing a CMOS-compatible material with nonlinear characteristics, presenting unforeseen opportunities for its integration in the semiconductor industry.

Atomic-scale in situ observation of electron beam and heat induced crystallization of Ge nanoparticles and transformation of Ag@Ge core-shell nanocrystals.

Crystallization of amorphous materials by thermal annealing has been investigated for numerous applications in the fields of nanotechnology, such as thin-film transistors and thermoelectric devices. The phase transition and shape evolution of amorphous germanium (Ge) and Ag@Ge core-shell nanoparticles with average diameters of 10 and 12nm, respectively, were investigated by high-energy electron beam irradiation and in situ heating within a transmission electron microscope. The transition of a single Ge amorphous nanoparticle to the crystalline diamond cubic structure at the atomic scale was clearly demonstrated. Depending on the heating temperature, a hollow Ge structure can be maintained or transformed into a solid Ge nanocrystal through a diffusive process during the amorphous to crystalline phase transition. Selected area diffraction patterns were obtained to confirm the crystallization process. In addition, the thermal stability of Ag@Ge core-shell nanoparticles with an average core of 7.4 and a 2.1nm Ge shell was studied by applying the same beam conditions and temperatures. The results show that at a moderate temperature (e.g., 385°C), the amorphous Ge shell can completely crystallize while maintaining the well-defined core-shell structure, while at a high temperature (e.g., 545°C), the high thermal energy enables a freely diffusive process of both Ag and Ge atoms on the carbon support film and leads to transformation into a phase segregated Ag-Ge Janus nanoparticle with a clear interface between the Ag and Ge domains. This study provides a protocol as well as insight into the thermal stability and strain relief mechanism of complex nanostructures at the single nanoparticle level with atomic resolution.

Molecular Adsorption of Silane on Ge, Ga and Al-doped CNT Structures: A Density Functional Theory Study

Molecular Adsorption of Silane on Ge, Ga and Al-doped CNT Structures: A Density Functional Theory Study

Role of Metallic Adlayer in Limiting Ge Incorporation into GaN.

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled up with available Si atomic flux in a wide range of dopant concentrations. However, a surprisingly different behavior of the Ge dopant is observed, and the presence of atomically thin gallium or an indium layer dramatically affects Ge incorporation, hindering the fabrication of GaN:Ge structures with abrupt doping profiles. Here, we show an experimental study presenting a striking improvement in sharpness of the Ge doping profile obtained for indium as compared to the gallium surfactant layer during GaN-plasma-assisted molecular beam epitaxy. We show that the atomically thin indium surfactant layer promotes the incorporation of Ge in contrast to the gallium surfactant layer, which promotes segregation of Ge to the surface and Ge crystallite formation. Understanding the role of the surfactant is essential to control GaN doping and to obtain extremely high n-type doped III-nitride layers using Ge, because doping levels >1020 cm−3 are not easily available with Si.

Alphaherpesvirus glycoprotein E: A review of its interactions with other proteins of the virus and its application in vaccinology.

The viral envelope glycoprotein E (gE) is required for cell-to-cell transmission, anterograde and retrograde neurotransmission, and immune evasion of alphaherpesviruses. gE can also interact with other proteins of the virus and perform various functions in the virus life cycle. In addition, the gE gene is often the target gene for the construction of gene-deleted attenuated marker vaccines. In recent years, new progress has been made in the research and vaccine application of gE with other proteins of the virus. This article reviews the structure of gE, the relationship between gE and other proteins of the virus, and the application of gE in vaccinology, which provides useful information for further research on gE.

DFT Analysis of Hole Qubits Spin State in Germanium Thin Layer.

Due to the presence of a strong spin–orbit interaction, hole qubits in germanium are increasingly being considered as candidates for quantum computing. These objects make it possible to create electrically controlled logic gates with the basic properties of scalability, a reasonable quantum error correction, and the necessary speed of operation. In this paper, using the methods of quantum-mechanical calculations and considering the non-collinear magnetic interactions, the quantum states of the system 2D structure of Ge in the presence of even and odd numbers of holes were investigated. The spatial localizations of hole states were calculated, favorable quantum states were revealed, and the magnetic structural characteristics of the system were analyzed.

Phase Transitions in Amorphous Germanium under Non-Hydrostatic Compression

As the pioneer semiconductor in transistor, germanium (Ge) has been widely applied in information technology for over half a century. Although many phase transitions in Ge have been reported, the complicated phenomena of the phase structures in amorphous Ge under extreme conditions are still not fully investigated. Here, we report the different routes of phase transition in amorphous Ge under different compression conditions utilizing diamond anvil cell (DAC) combined with synchrotron-based X-ray diffraction (XRD) and Raman spectroscopy techniques. Upon non-hydrostatic compression of amorphous Ge, we observed that shear stress facilitates a reversible pressure-induced phase transformation, in contrast to the pressure-quenchable structure under a hydrostatic compression. These findings afford better understanding of the structural behaviors of Ge under extreme conditions, which contributes to more potential applications in the semiconductor field.

Modification of the Ge(0 0 1) subsurface electronic structure after adsorption of Sn

In this work, we investigate how the electronic structure of the Ge(001) surface is modified by the adsorption of Sn atoms. We extend a previously established growth model of the Sn layer formation on Ge(001) with a detailed analysis of surface core-level shifts, observing a prevalence of symmetric Sn ad-dimers at a Sn coverage above onemonolayer. The valence band structure of Ge(001) reveals the appearance of a non-dispersive electronic state after the adsorption of Sn. We correlate the presence of this state to the interaction of electronic states from a Sn ad-dimer configuration with the surface resonances of the Ge up-dimer. Post-deposition annealing leads to full incorporation of Sn and, consequently, to the disappearance of valence band state attributable to Sn ad-atoms. Notably, the adsorption and/or incorporation of Sn removes a Ge(001) surface state above the valence band maximum. The Fermi-level remains pinned close to the valence band maximum, indicating the initial stages of a Schottky barrier formation. Overall, these results provide new fundamental insights into the electronic structure of Sn on Ge(001), crucial for the development of SnGe electronics devices, and more generally of use for understanding the controlled alloying of isoelectronic layered materials.

Conformal atomic layer etching for Ge based on sacrificial oxide with higher Gibbs free energy of formation

Layer-by-layer conformal atomic layer etching (cALE) for Ge is demonstrated by alternating processes consisting of the self-limiting deposition of a sacrificial oxide and the self-stop etching of the sacrificial oxide and interfacial layer (IL). The critical point of cALE is the formation of the GeOx IL between Ge and the sacrificial oxide. Accordingly, a sacrificial oxide with higher Gibbs free energy of formation was selected and investigated in the cALE process for the formation of more GeOx to increase the Ge etching rate. The cALE process presents a linear dependence of the etching depth on the cALE cycles, along with an accurate etching rate (several Å per cALE cycle) and a low surface roughness of Ge. In addition, the transmission electron microscopy images of three-dimensional fin structures of Ge demonstrate the damage-free Ge surface as well as the conformal etching of cALE. The result shows that the cALE technique can achieve precise etching of Ge accompanied with the self-limiting, self-stop, damage-free, layer-by-layer, and conformal characteristics, which is highly favorable to Ge-based nanoelectronic devices in advanced semiconductor technology nodes.

Electronic structure, optical and thermoelectric properties of Ge2SeS monolayer via first-principles study

The electronic, optical and thermoelectric properties of the Ge 2 SeS monolayer were detailed using the first-principle calculations. The dynamic stability of the Ge 2 SeS structure monolayer has been confirmed by the phonon dispersion curve. Our electronic calculations indicate that the Ge 2 SeS monolayer is a semiconductor at equilibrium state with an indirect bandgap lower/larger than that of the GeS/GeSe monolayer calculated by generalized gradient approximation (GGA) of Perdew Burke Ernzerhof (PBE) functional. The optical properties such as dielectric constant, reflectivity , extinction coefficient, and absorption coefficient versus the energy were investigated. In addition, the thermoelectric properties are obtained using the semi-classical Boltzmann transport theory. The results show a large Seebeck coefficient of 2470 μV/K at 300K, the electronic figure of merit ( ZT e ) is 0.91 in Ge 2 SeS monolayer at 300 K. The predicted optical and thermoelectric properties could make the Ge 2 SeS monolayer a potential candidate for applications in optoelectronic and energy conversion technologies at room temperature. • First-principles calculations on electronic structure, optical and thermoelectric properties of Ge 2 SeS monolayer. • Dynamic stability of the Ge 2 SeS structure monolayer has been confirmed by the phonon dispersion curve. • Ge 2 SeS monolayer is a semiconductor with an indirect bandgap of 1.47 eV. • A high electronic figure of merit (ZT e ) of 0.91 have been predicted in Ge 2 SeS monolayer at 300 K. • Optical properties of the Ge 2 SeS monolayer have been investigated in agreement with reported experimental results.

“Breathing” organic cation to stabilize multiple structures in low-dimensional Ge-, Sn-, and Pb-based hybrid iodide perovskites

By using S-(2-aminoethyl)isothiouronium (ETU) as the templating cation, five new metal iodide hybrids, (ETU)GeI4, (ETU)4Ge5I18, (ETU)PbI4 and (ETU)3Pb2I10 are reported with varied C–S–C angles in the organic cation.

Structure of Ge<sub><i>x</i></sub>Ga<sub>8</sub>S<sub>92–<i>x</i></sub> glasses studied by high-resolution X-ray photoelectron spectroscopy and Raman scattering

In this paper, the structures of chalcogenide glasses Ge<sub><i>x</i></sub>Ga<sub>8</sub>S<sub>92–<i>x</i></sub> (<i>x</i> = 24%, 26.67%, 29.6%, 32% and 36%) at a fixed Ga atomic content of 8% are studied by high-resolution X-ray photoelectron spectroscopy and Raman scattering spectra. In order to quantify the evolutions of the different structural units in Ge<sub><i>x</i></sub>Ga<sub>8</sub>S<sub>92–<i>x</i></sub> glasses, the number of double peaks in the Ge 3d, Ga 3d and S 2p spectra are determined by iterative fitting method, the binding energy and the full width at half maximum of each peak, and the relative ratio of the integral area of each decomposed peak to that of the whole area of the X-ray photoelectron spectroscopy are thus achieved. On the other hand, the Raman scattering spectra of Ge<sub><i>x</i></sub>Ga<sub>8</sub>S<sub>92–<i>x</i></sub> glass are decomposed into multiple Gaussians based on the structural units. We use the iterative method to simulate the position of peak center, full width at half maximum, and height of each Raman peak. By analyzing the evolution of each unit structure in the glasses, it is found that the network structure of glass network is mainly formed by S atom bridging the tetrahedral structure of GeS<sub>4</sub> and GaS<sub>4</sub>. The S chains or rings structural units are formed in Ge<sub>24</sub>Ga<sub>8</sub>S<sub>68</sub> glass, indicating that S atoms are in excess in the chemical composition of the glass, so there are enough S atoms around Ge and Ga atoms, forming heteropolar Ge—S and Ga—S bonds. With the gradual increase of Ge content, S chains or rings structure units rapidly disappear in Ge<sub>26.67</sub>Ga<sub>8</sub>S<sub>65.33</sub> glass. The Ge—Ge homopolar bonds in the ethane-like structure S<sub>3</sub>Ge—GeS<sub>3</sub> and the <i>M</i>—<i>M</i> (Ge—Ge, Ga—Ga or Ge—Ga) homopolar bonds in the S<sub>3</sub>Ge/Ga—Ga/GeS<sub>3</sub> structure simultaneous appear in the Ge<sub>29.6</sub>Ga<sub>8</sub>S<sub>62.4</sub> glass, and the number of structures increases gradually with the increase of Ge content. This is mainly due to the insufficient number of S atoms in the Ge-Ga-S glass. Once S atoms are lacking, the excess Ge and Ga atoms can only combine with themselves to form the homopolar bond <i>M</i>—<i>M</i>. It can be concluded below. Firstly, Ge and Ga atoms appear mainly in the form of 4-coordination, while S atoms occur mainly in the form of 2-coordination in the chalcogenide glasses of Ge<sub><i>x</i></sub>Ga<sub>8</sub>S<sub>92–<i>x</i></sub>. Secondly, the existence of <i>M</i>—<i>M</i> bond leads the nanophase to separate, and the ordering degree of glass network structure to decrease .

Infuence of Ba atov adsorption and implanation of Ba-=SUP=-+-=/SUP=- ions on the electronic structure of single crystalline Ge

The effect of the adsorption of Ba atoms with a thickness of theta≤3-4 monolayers and the implantation of Ba+ ions with an energy of E0=0.5-2 keV on the density of states of electrons in the valence band, the parameters of the energy bands, and the emission and optical properties of Ge(111) has been studied for the first time. It is shown that during the adsorption of Ba atoms with theta=1 monolayer, the value of the thermoelectric work function φ decreases by ~ 1.9 eV, and the value of the secondary electron emission coefficient and the quantum yield of photoelectrons Y increases by 1.5-2 times. In the case of implantation of Ba+ ions with E0=0.5 keV at an irradiation dose D=6·1016 cm-2, the density of state of valence electrons and the parameters of the energy bands change sharply; the quantum yield of photoelectrons increases by a factor of 2 or more. The observed changes are explained by the formation on the surface of a thin (~25-30 Angstrem) amorphous doped layer consisting of nanoscale phases of the Ba-Ge type (~60-65 at.%). And excess (unbound) Ba and Ge atoms. In this case, the band gap Eg decreases by ~ 0.3 eV. Keywords: Ion implantation, quantum yield of photoelectrons, emission efficiency, heating, band gap, amorphous layer.

Short-range order and atomic diffusion in liquid Ge and Si20Ge80 investigated by neutron scattering and x-ray diffraction

We studied structure and dynamics in liquid Ge and ${\text{Si}}_{20}{\text{Ge}}_{80}$. Quasielastic neutron scattering (QNS) was employed to accurately determine the Ge self-diffusion coefficient. Static structure factors were measured using neutron and x-ray diffraction. Containerless processing via electromagnetic levitation (EML) enabled to obtain structure factors over a broad temperature range from the metastable regime of the undercooled melt to several hundred Kelvin above the melting point. Moreover, isotopic substitution and combination with x-ray diffraction allowed to determine the partial structure factors ${S}_{\mathrm{NN}}(q), {S}_{\mathrm{NC}}(q), {S}_{\mathrm{GeGe}}(q)$, and ${S}_{\mathrm{GeSi}}(q)$ for liquid ${\text{Si}}_{20}{\text{Ge}}_{80}$. The topological structures of liquid Ge and ${\text{Si}}_{20}{\text{Ge}}_{80}$ are very similar. In addition, the Ge self-diffusion coefficients in liquid Ge and ${\text{Si}}_{20}{\text{Ge}}_{80}$ are equal within error limits.

(Invited) Selective Epitaxy of Submicron Ge Wire Structures for Photodetectors and Optical Modulators in Si Photonics

A selective-area epitaxial growth of Ge on the submicron scale is studied using chemical vapor deposition (CVD) on Si in terms of the fabrication of integrated photonic devices operating at the optical communication wavelengths of around 1.55 μm. A mesa structure of Ge on the micron scale, having a vertical pin junction, is effective for fabricating a waveguide-integrated photodetector in the optical receiver. A 3-dB cutoff frequency is obtained up to approximately 50 GHz. For a higher frequency operation, a narrower structure of submicron-wide Ge wire, having a lateral pin junction, is required. Such a wire structure is also important for the application to an electro-absorption optical intensity modulator in the optical transmitter. Structural and optical properties are investigated for a submicron-wide Ge wire on Si selectively grown by CVD.