Liquid Germanium Research Articles

Visualising the structure of liquid germanium dioxide under compression

Visualising the structure of liquid germanium dioxide under compression

Examining the influence of turbulence on viscosity measurements of molten germanium under reduced gravity

The thermophysical properties of liquid germanium were recently measured both in parabolic flight experiments and on the ISS in the ISS-EML facility. The viscosity measurements differed between the reduced gravity experiments and the literature values. Since the oscillating drop method has been widely used in EML, further exploration into this phenomenon was of interest. Models of the magnetohydrodynamic flow indicated that turbulence was present during the measurement in the ISS-EML facility, which accounts for the observed difference.

Rapid quantitation of feed rotifer ( Brachionus plicatilis ) fatty acids by Raman spectroscopy

Improving the lipid composition of feed-rotifers enhances the survival and growth rates of juvenile fish in aquaculture, but monitoring enrichment profiles using gas chromatography (GC) is slow, labour-intensive and requires expensive instrumentation. Here, we describe the potential of Raman spectroscopy as an alternative, more rapid tool for quantitation of rotifer fatty acid composition in an aquaculture setting. A compositionally diverse sample set was prepared by periodically subsampling rotifers undergoing enrichment using three different feeding regimens. Sampled rotifers were freeze-dried and their fatty acid content and composition was measured by GC–MS (mass spectrometry). Raman spectra (1064 nm excitation) were acquired with two instruments: a state-of-the-art Fourier transform (FT)-Raman spectrometer equipped with a liquid nitrogen-cooled Germanium detector; and a smaller, portable spectrometer equipped with an InGaAs detector. Fatty acid reference data acquired by GC–MS were related to structured variance in each Raman spectral data set using partial least squares regression. The resultant models could accurately quantitate total fatty acids (TFA) and total polyunsaturated fatty acids (PUFA) using both FT-Raman spectra (Root Mean Square Error [RMSEV] = 5.0 mg g−1 TFA and 6.1 mg g−1 PUFA) and spectra generated using the portable instrument (RMSEV = 4.2 mg g−1 TFA and 5.3 mg g−1 PUFA). Analysis times with the portable instrument were approximately 3 min, compared to 16 min with the FT-Raman system. Portable Raman spectroscopy may be a useful tool for high throughput screening of rotifer lipid composition when testing and optimizing enrichment protocols and developing microdiets for aquaculture species.

Large Memory Window of van der Waals Heterostructure Devices Based on MOCVD-Grown 2D Layered Ge4 Se9.

Van der Waals (vdW) heterostructures have drawn much interest over the last decade owing to their absence of dangling bonds and their intriguing low-dimensional properties. The emergence of 2D materials has enabled the achievement of significant progress in both the discovery of physical phenomena and the realization of superior devices. In this work, the group IV metal chalcogenide 2D-layered Ge4 Se9 is introduced as a new selection of insulating vdW material. 2D-layered Ge4 Se9 is synthesized with a rectangular shape using the metalcorganic chemical vapor deposition system using a liquid germanium precursor at 240 °C. By stacking the Ge4 Se9 and MoS2 , vdW heterostructure devices are fabricated with a giant memory window of 129V by sweeping back gate range of ±80V. The gate-independent decay time reveals that the large hysteresis is induced by the interfacial charge transfer, which originates from the low band offset. Moreover, repeatable conductance changes are observed over the 2250 pulses with low non-linearity values of 0.26 and 0.95 for potentiation and depression curves, respectively. The energy consumption of the MoS2 /Ge4 Se9 device is about 15 fJ for operating energy and the learning accuracy of image classification reaches 88.3%, which further proves the great potential of artificial synapses.

Phase diagram, thermodynamic studies, and ab-initio calculations of the Ge-Li system

The limiting enthalpy of solution of liquid germanium in the liquid tin ΔsolH¯Ge(l)∞ was measured at 927 K and equals 3.24 ± 0.34 kJ/mol at. The standard enthalpy of formation of intermetallic phases from the Ge-Li system were calculated at 747 K with the use of the solution calorimetric method. These alloys and intermetallic phases were prepared from pure, metallic germanium and lithium, which were melted in a glove-box filled with high purity argon with a very low concentration of impurities. The X-ray diffraction measurements were conducted to verify the structure of the prepared alloys. The electromotive force studies were performed at three temperatures: 634 K, 807 K, and 841 K by the titration technique. Based on obtained results and other thermodynamic quantities available in the literature the thermodynamic properties of phases were optimized, and the Ge-Li phase diagram was determined.

Interrogating Gas-Borne Nanoparticles Using Laser-Based Diagnostics and Bayesian Data Fusion

We demonstrate how the evaporation properties of gas-borne nanoscale materials, here liquid silicon and germanium nanoparticles, can be obtained through a novel combination of in situ time-resolved...

Spatial distribution of gas-phase synthesized germanium nanoparticle volume-fraction and temperature using combined in situ line-of-sight emission and extinction spectroscopy.

In this study, emission and extinction spectroscopy were combined to in situ measure temperature and volume fraction distributions of liquid germanium nanoparticle gas-phase synthesized in an argon/hydrogen/germane flow through a microwave plasma. Emission of the hot particles and extinction against a continuous background were recorded by a spectrometer in the 380-703 nm and 230-556 nm ranges, respectively, selected based on the specific optical properties of the material. Absorption coefficients were deconvoluted from line-of-sight attenuation (LOSA) measurements by a least-square algorithm and then used to determine the local volume fraction distribution. The temperature field was derived from the line-of-sight emission (LOSE) spectra with the prior knowledge of absorption coefficients. A multi-wavelength reconstruction model was developed for the determination of the spatially-resolved distribution of the measured quantities assuming a stationary axisymmetric flow. Advantages of the method include experimental simplicity, low cost, and adaptability to up-scaled reactor sizes.

Comparative analysis of the short-range order in Al-Ge-Ni and Al-Ge-Fe melts

ABSTRACT The comparative analysis of structure in ternary Al-Ge-Fe and Al-Ge-Ni melts has been performed in a wide concentration range using results of X-ray diffraction experiment and RMC simulations. The analysis of total S(Q) and partial SGe-Ge(Q) structure factors has shown that germanium atoms are present in two structural states: in the local environment of Fe(Ni) atoms and as part of clusters with structure of liquid germanium. Formation of these clusters is a result of displacement of Ge atoms outside the nearest environment of Fe(Ni) atoms due to competition effect between Al and Ge atoms. It has been established that ratio between partial nearest neighbour distances R1(Al-Ni)<R1(Al-Fe)<R1(Ge-Ni)<R1(Ge-Fe) is valid for all investigated melts due to the energy non-equivalence of the interatomic interactions. The influence of an intensity of interatomic interactions (energy factor) and implementation of dense non-crystalline packing (packing factor) on the SRO in the investigated ternary melts are discussed.

Porous graphite fabricated by liquid metal dealloying of silicon carbide

Porous graphite was prepared by dealloying SiC in molten germanium, and then excavating the Ge phase. Dealloying is a technique whereby nanoporous materials are produced via the selective dissolution of one or more components from a homogeneous alloy. Here, the liquid metal dealloying (LMD) process was extended to non-metal precursors, demonstrating that carbide-derived carbons (CDCs) can be fabricated by this process. The dealloying depth, concentration profile and length scale of the dealloyed microstructure were examined as they varied with immersion times and temperatures. The dealloying depth h varied with time as h ∼ t1/2 and we also observed a build-up of Si concentration in the germanium near the dealloying interface. These observations are consistent with kinetics that are rate-limiting in the liquid germanium side of the moving interface. However, the measured activation barrier of 2.4–2.8 eV was too high to be consistent with diffusion in the liquid phase, so instead we propose a mechanism in which Si diffusion is impeded by unsaturated carbon bonds near the dealloying interface. The porous graphite exhibited three-dimensional connectivity and a high degree of crystallinity, with an I(D)/I(G) ratio of 0.3 for samples dealloyed at the highest temperatures.

Structure of liquid Al-Ge-Ni melts in a wide composition range

X-ray diffraction study of the Al-Ge-Ni melts along different sections of the ternary phase diagram has been discussed. The measurements were taken at 1000 °C or at temperatures on 50° above liquidus for compositions with high melting point. It has been shown that AlNi interactions play the most important role in the formation of the local atomic structure in the Al-Ge-Ni melts. The most significant decreasing of the nearest interatomic distance (R1) takes places with addition of Ni to binary AlGe alloys. There is a competition between Al and Ge atoms in the formation of local atomic structure around Ni atoms. For ternary melts with high Ge content the influence of GeGe pairs increases resulting in the formation of the clusters with structure similar to the liquid germanium. The ribbons of the Al79Ge15Ni6, Al61Ge29Ni10 and Al61Ge15Ni24 alloys have been obtained by rapid solidification from the liquid state. The phase analysis of the as-quenched and annealed ribbons has been discussed.

Evaluation of Drude parameters for liquid Germanium nanoparticles through aerosol-based line-of-sight attenuation measurements

The objective of this study is to infer Drude model parameters for liquid germanium nanoparticles from extinction measurements made across an aerosol within a microwave plasma reactor using a halogen lamp (410–700 nm) and a laser-driven light source (205–585 nm). The plasma frequency and relaxation time are inferred using Rayleigh theory, Mie theory, and a fourth-order Mie approximation. These parameters are compared with those found using the ellipsometry-derived complex dielectric function as well as the bulk density and electrical resistivity of liquid germanium. The analysis is carried out in a probabilistic context using Bayesian inference, which accounts for both the measurement noise and model error. While all the candidate models can reproduce the shape of the experimentally-derived extinction spectra, the Bayesian inference showed that extinction-derived parameters differed from those obtained from the density and electrical resistivity in a statistically-significant way. This highlights the limitations of the free-electron model that underpins Drude theory, and suggests potential opportunities for model refinement.

Formation of short-range order in Al–Ge–Fe melts: influence of composition

ABSTRACTThe short-range order in Al–Ge–Fe melts has been studied by X-ray diffraction and reverse Monte Carlo simulations in wide concentration range. Influence of the replacement of one component by another while the content of third component is constant on the formation of a local structure of ternary melts has been discussed. It has been shown that at Ge content less than 30 аt. % Ge atoms are uniformly distributed in the volume of the Al–Ge–Fe melts and atomic clusters with structure similar to the liquid germanium are formed at content more than 30 аt. % Ge. The addition of the third component (Ge or Al) to the binary Al–Fe or Fe–Ge melts, correspondingly, results in competition between Al and Ge atoms in formation of the local structure around Fe atoms. The obtained concentration dependences of the nearest neighbour distances point out that the ternary interactions take place in the Al–Fe–Ge melts.

X-ray Compton Scattering Study of Liquid Germanium and Tin

X-ray Compton scattering measurements have been carried out on germanium (Ge) and tin (Sn) in the solid and liquid states. While the shape of the Compton profiles (CPs) of Ge reflects the semiconductor-to-metal transition upon melting, it was found that even for Sn, which remains metallic during the solid–liquid phase transition, the shape of the CP in the liquid state exhibits more metallic characteristics than that in the solid state. The experimentally derived Fermi momenta of liquid Ge and Sn have systematically higher values than those of the electron gas at corresponding electron densities, which indicates a non-simple metallic nature of the group IV elements in the liquid state.

Germanium layers grown by zone thermal crystallization from a discrete liquid source

It is proposed and investigated a method for growing thin uniform germanium layers onto large silicon substrates. The technique uses the hexagonally arranged local sources filled with liquid germanium. Germanium evaporates on very close substrate and in these conditions the residual gases vapor pressure highly reduces. It is shown that to achieve uniformity of the deposited layer better than 97% the critical thickness of the vacuum zone must be equal to lcr = 1.2 mm for a hexagonal arranged system of round local sources with the radius of r = 0.75 mm and the distance between the sources of h = 0.5 mm.

Reference Correlations for the Thermal Conductivity of Liquid Bismuth, Cobalt, Germanium and Silicon.

The available experimental data for the thermal conductivity of liquid bismuth, cobalt, germanium and silicon have been critically examined with the intention of establishing thermal conductivity reference correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The proposed standard reference correlations for the thermal conductivity of liquid bismuth, cobalt, germanium, and silicon are respectively characterized by uncertainties of 10, 15, 16 and 9.5% at the 95% confidence level.

Interfacial kinetics in nanosized Au/Ge films: An in situ TEM study

We investigate the morphology and crystalline structure of Au/Ge films in a wide range of temperatures by in situ TEM heating. Au/Ge films with Au mass thickness of 0.2–0.3nm and Ge thickness of 5nm were produced in vacuum by the sequential deposition of components on a carbon substrate at room temperature. It has been shown that particles with an average size of 4nm, formed by Au film de-wetting, melt on the germanium substrate at temperatures 110–160°C, which are below the eutectic temperature for the bulk. The effect of crystallization-induced capillary motion of liquid eutectic particles over Ge surface has been found in this work. Formation of metastable fcc phase of Ge has been observed at the liquid–germanium interface and behind the moving particle. Formation of a liquid phase with its subsequent crystallization at the metal–semiconductor interface seems to play a key role in the metal-induced crystallization effect.

Graphene-like monolayer low-buckled honeycomb germanium film

Molecular dynamics simulations have been performed to study the cooling process of two-dimensional liquid germanium under nanoslit confinement. The results clearly indicates that the liquid germanium undergoes an obvious liquid-solid phase transition to a monolayer honeycomb film with the decrease of temperature, accompanying the rapid change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the solidification process, some hexagonal atomic islands first randomly emerge in the disordered liquid film and then grow up to stable crystal grains which keep growing and finally connect together to form a honeycomb polycrystalline film. It is worth noting that the honeycomb germanium film is low-buckled, quite different from the planar graphene.

Polymorphic germanium films forming in slit nanopore

The solidification of two-dimensional liquid germanium confined to slit nanopores with different sizes has been studied using molecular dynamics simulations. The results clearly show that the system undergoes an obvious liquid-solid phase transition to polymorphic ordered germanium films with the decrease of temperature, accompanied by dramatic change in potential energy and coordination number. Moreover, it is found that the slit size is of vital importance to the transition point and the structure of the germanium films. The results of radial distribution functions, density distribution functions and angular distribution functions suggest the obtained germanium films have various novel structures different from the graphene.

Structure of the Al–Ge–Fe alloys in the liquid and solid state

X-ray diffraction study of liquid and solid Al–Ge–Fe alloys along the sections Al-Fe33.3Ge66.7, Fe-Al65Ge35 и Ge-Al78Fe22 has been discussed. It has been shown that addition of third component to the corresponding binary melt leads to the atomic clusters with structure similar to liquid germanium due to energy inequality of interactions in Al–Fe and Fe–Ge pairs and competition between Al and Ge atoms in formation of local structure around Fe atoms in the ternary melts. The Al88Ge8Fe4, Al68Ge21Fe11, Al64Ge18Fe18, Al55Ge30Fe15 melts have been quenched by melt spinning technique. The fully amorphous state was obtained only for the Al55Ge30Fe15 ribbon, the one with composition Al68Ge21Fe11 is amorphous-crystalline and Al88Ge8Fe4 и Al64Ge18Fe18 ribbons are microcrystalline. A new hexagonal τ1 phase (a=9.75(1)Å, c=8.80(1)Å) in the ingot Al55Ge30Fe15 and Al41Ge39Fe20 alloys and a new tetragonal phase τ2 (a=5.11(3)Å, c=4.60(2)Å) in the ingot Al20Ge53Fe27 alloy have been found. The annealed at 623K ribbons with composition Al88Ge8Fe4 and Al68Ge21Fe11 contain a new hexagonal phase τ3 (a=6.709(5)Å, c=9.07(1)Å), which is missing in the ingot.

RMC simulations of the liquid Al[sbnd]Ge alloys

The structure of AlGe melts has been studied in a wide temperature-concentration range by Reverse Monte Carlo simulations and Voronoi-Delaunay diagrams. The experimental structure factors of the AlGe melts with ≥20at.% Ge have a shoulder on high-Q side of the first peak that coincides with the one on the S(Q) of liquid Ge. There is the same shoulder on partial SGeGe(Q) that indicates the primary role of Ge in formation of the structure of binary melts near liquidus temperatures. The obtained data point out the quasi-eutectic structure of AlGe melts, which consist of atomic clusters with structure of homogeneous solution of Ge atoms in aluminium matrix and clusters with local structure like liquid Ge. The latter exist due to incomplete metallization of covalent Ge bonds during melting. An increase in temperature causes a metallization of Ge bonds resulting in disappearance of signs of pure liquid germanium's structure on experimental S(Q) and g(r) curves. Formation of the homogeneous solution with the increase in temperature promotes the process of metallization of residual covalent bonds in AlGe melts till complete conversion at ≈1800K.