Au Ge Research Articles

Morphology Control of Nanoporous Gold Through Selective Dissolution of Au–Ge Eutectic Microstructures

The synthesis of nanoporous gold (np‐Au) through the conventional method of dealloying a more reactive element from AuTherma alloys has been extensively studied and applied in various fields, particularly catalysis. Herein, a novel approach to creating droplet‐like np‐Au through the selective dissolution of Au–Ge eutectic microstructures is explored. This work reveals that adjusting the undercooling of the eutectic melt during solidification allows for the tuning of pore and ligament sizes. It is demonstrated that this undercooling can be modified, either directly or indirectly, by adjusting either the cooling rate or the heterogeneous nucleation site density of the eutectic melt. The findings, aligned with the model based on classical theory for eutectic solidification, elucidate the connection between the tuning of pore and ligament sizes in the eutectic microstructure and the undercooling of the eutectic melt. Importantly, it is established that this phenomenon is applicable across a variety of compositions, including hypereutectic, eutectic, and hypoeutectic. The ability to regulate pore and ligament size in single crystals of np‐Au droplets offers a novel approach to synthesizing catalytic np‐Au crystals with enhanced mechanical and thermal stability compared to conventional methods.

Synthesis, structure, and physical properties of a Y–Au-Ge 1/1 Tsai-type quasicrystal approximant and Y14(Au,Ge)51 with the Gd14Ag51 structure type

Exploration of the Au–Ge rich part of the pseudo-binary section Yx(Au0.70Ge0.30)100-x (3 < x < 18) in the Y–Au-Ge system afforded the intermetallic compounds Y3(Au0.7054Ge0.2946)19-x (x ≈ 0.38) and Y14(Au0.8313Ge0.1687)51, which are new representatives of the cubic 1/1 Tsai-type approximant crystal (YbCd6 parent type, space group Im3‾.) and the hexagonal Gd14Ag51 structure type (space group P6/m), respectively. Y3(Au0.7054Ge0.2946)19-x decomposes peritectically into Y14(Au,Ge)51 phase and melt at around 700 °C. In this respect the Y–Au-Ge system deviates from the Y–Au–Si system which firstly contains a second type of 1/1 approximant crystal phase with higher Y content, Y3.25(Au,Si)18-x (x ≈ 0.11) and, secondly, adjacent at higher Y composition there is a stoichiometric and ordered tetragonal phase YAu3Si. Y3(Au,Ge)19-x and Y14(Au,Ge)51 exhibit bulk superconductivity of conventional type-II BCS type albeit with very low transition temperatures (below 1 K), which is very similar to the corresponding compounds in the Y–Au–Si system.

Extraction of metals with analyzed new reagents foaming agents SK-1, SK-2 from coals

The article presents the results of studies of brown and black coals from the Angren and Shargun deposits of the Republic of Uzbekistan. According to the results of the research, a number of different non-ferrous and noble metals were revealed in their composition: Tungsten up to 2 wt.% Au, Ag as well as rare earth elements (REE). Methods and techniques have been developed for the extraction of precious metals from coals: Ag, Au and rare earth elements Ge and Sc. Scientists of the laboratory of the Institute of General and Inorganic Chemistry “ChT, PG and Surfactants” synthesized new reagents - blowing agents SK-1, SK-2, which are used in the enrichment and flotation of non-ferrous and noble metal-containing coals. The method developed by us allows the integrated use of natural coal and can solve the important problem of ash and slag waste disposal and significantly reduce emissions of toxic elements into the atmosphere.

The Effects of Ge Substrate Surface States and Au Catalyst Layer Thickness on the Growth of Different Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; Nanomaterials and Nanocrystals Configurations Using Vapor-Liquid-Solid Method with two Steps Temperature Mode

Recently the Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; nanomaterials have been studied intensively due to their interesting electronic materials, which have many particular properties and applications in nanotechnology and nano-devices fabrication. Much work has been done on many different synthesis methods and their properties of Ge and Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; nanomaterials. However, the effects of the different Ge substrate surface states and Au catalyst layer thicknesses on the formation of different forms/morphologies of nanomaterials (nanowires, nanorods, nanoparticles, and nanocrystals particularly) have yet to be discussed more in detail. This paper outlines the synthesis methods to grow the different Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; nanomaterials on the different Ge surface states at different Au catalyst layer thicknesses such as mechanically polished surface, deep Chemical etched surface, chemical polishing surface, and initial rough surface. The morphological, and structural properties of Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; nanomaterials have been investigated using SEM, EDX, and TEM techniques. The formation of different morphological, and structural properties of different Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; nanomaterials grown have been explained by the effects of the Au/Ge/O droplets/clusters formation situations and surface defects on the Ge substrate surface caused. The growth mechanisms have been explained by the model of the VLS growth method with the Oxide Assist Growth mechanism. The results showed that the effects of the different Ge substrate surface states and Au catalyst layers’ thickness strongly influence the formation of Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; materials in terms of the sizes, structures, and percentages of elements. The results of the controllable different Ge&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; nanomaterials have many significant meanings for both theoretical and practical applications in nanomaterials and nano-device fabrication.

High-efficiency GaInP/GaAs photoconverters of the 600 nm laser line

Optimized photoconverters for operation under high-power laser radiation in the green-red spectral range based on MOCVD-grown GaInP/GaAs heterostructures are fabricated. The Au(Ge)/Ni/Au and Pd/Ge/Au contact systems have been studied to form the front contact grid of devices. As a result, the laser photoconverter with a Pd/Ge/Au contact showed an efficiency of more than 50% up to an incident radiation power density of 30 W/cm2 with a maximum value of 54.4% under 7 W/cm2 for laser line with wavelength of 600 nm. Keywords: photoconverter, laser radiation, MOCVD, efficiency, spectral sensitivity.

Исследование технологии изготовления мощных ИК (850 nm) светодиодов, получаемых методом переноса AlGaAs-GaAs-гетероструктуры на подложку-носитель

Development of lift-off technique of AlGaAs/GaAs heterostructures, grown by the MOCVD technique, to GaAs carrier-substrate using silver-containing paste or Au-In compound has been carried out. Forming process of frontal ohmic contact to GaAs n-type conductivity based on contact systems Au(Ge)/Ni/Au and Pd/Ge/Au with specific contact resistivity 2-5·10-6 Ом·см2 has been investigated. Analyzed was the influence of heterostructure lift-off technique and forming process of frontal ohmic contact on the IR light-emitting diodes parameters: minimum light-emitting diodes (1mm2 square) series resistance was 0.16 Ohm. Optical power 270 mW at current 1.5A has been achieved.

Investigation of power IR (850 nm) light-emitting diodes manufacturing by lift-off technique of AlGaAs-GaAs- heterostructure to carrier-substrate

Development of lift-off technique of AlGaAs/GaAs- heterostructures, grown by the Metalorganic vapour-phase epitaxy, to GaAs carrier-substrate using silver-containing paste or Au-In compound has been carried out. Forming process of frontal ohmic contact to GaAs n-type conductivity based on contact systems Au(Ge)/Ni/Au and Pd/Ge/Au with specific contact resistance (2-5)·10-6 Ω·cm2 has been investigated. Analyzed was the influence of heterostructure lift-off technique and forming process of frontal ohmic contact on the IR light-emitting diodes parameters: minimum light-emitting diodes (1 mm2 square) series resistance was 0.16 Ω. Optical power 270 mW at current 1.5 A has been achieved. Keywords: AlGaAs/GaAs- heterostructure, light-emitting diode, transfer to carrier-substrate, Au--In- compound, ohmic contacts.

Enhancing the shear strength of the Au–Ge solder joint via forming a ductile face-centered cubic solid solution layer at the interface

The Au-28Ge (at%) eutectic alloy is a high-performance solder with a melting point of 361 °C. However, the brittle interfacial reaction products layer formed between the Au–Ge solder and substrate (Cu or Ni) is always the weak region. Hence, the joint fails at a relatively low shear strength (∼53 MPa). Here, the Cu–Ni alloys (Ni content is 20, 50, or 70 at%) are designed as the substrates to connect with the Au–Ge eutectic at 400 °C. A classic example is represented by the Au–Ge/Cu20Ni joint, which achieves a shear strength of above 100 MPa after soldering at 400 °C for 10–20 min. Microstructure characterization reveals that a face-centered cubic structured solid solution (FCC) layer forms at the Au–Ge/Cu20Ni joint. In contrast, it is mainly the NiGe or Ni2Ge layer in the Au–Ge/Cu50Ni and Au–Ge/Cu70Ni joints. On the one hand, compared to the brittle intermetallic compound products layer, the FCC layer shows adequate ductility, releasing the local strain incompatibility via pronounced local plastic deformation. On the other hand, the fine NiGe and Ni2Ge precipitation and fine grains make the FCC layer stronger than the solder matrix. Therefore, this products layer is no longer the weak region in the solder joint. As a result, the Au–Ge/Cu20Ni joint achieves outstanding shear strength. This study enriches our fundamental understanding of producing ductile phases to enhance the shear strength of the solder joints by designing alloy substrates.

Capacitor-type thin-film heat flow switching device

We developed a capacitor-type heat flow switching device, in which electron thermal conductivity of the electrodes is actively controlled through the carrier concentration varied by an applied bias voltage. The device consisted of an amorphous p-type Si–Ge–Au alloy layer, an amorphous SiO2 as the dielectric layer, and an n-type Si substrate. Both amorphous materials are characterized by very low lattice thermal conductivity, ≤1 W m–1 K–1. The Si–Ge–Au amorphous layer with 40 nm in thickness was deposited by means of molecular beam deposition technique on the 100 nm thick SiO2 layer formed at the top surface of Si substrate. Bias voltage-dependent heat flow density through the fabricated device was evaluated by a time-domain thermoreflectance method at room temperature. Consequently, we observed a 55% increase in the heat flow density at the maximum.

High-performance infrared Ge-based plasmonic photodetector enhanced by dual absorption mechanism

A sub-wavelength plasmonic Au–Ge grating was used to enhance the responsivity of Ge-based metal–semiconductor–metal photodetectors at infrared communication wavelengths. Furthermore, a finite-difference time-domain simulation was performed to optimize absorption of light by the detectors. Characterizations of the photoelectronic properties of the optimized device revealed high-performance photodetection with a responsivity of 0.38 A/W and an external quantum efficiency of 30% for 1.55 μm wavelength incident light. Moreover, an enhancement peak across three infrared telecommunication bands (C-band, L-band, and U-band) was achieved in the plasmon-enhanced photodetector. According to the simulation results of the optical absorption spectra, the distributions of electric field, and absorbed power, the enhancements of responsivity and quantum efficiency could be ascribed to the surface plasmons at the Au/Ge interface. These plasmons boosted inter-band transition and internal photoemission effect simultaneously, enabling high efficient photodetection around the C-band. The results of the fabricated devices demonstrated the potential of this approach for achieving high-performance Ge-based photodetectors.

Periodical distribution of Au nanoparticles through dewetting on patterned substrates

Metal nanoparticles (NPs) are widely applied in many fields, such as optics, electronics, and sensor platforms. The size and density of the NPs play important roles in device performance and nanostructure distribution. In this paper, the periodically distributed Au NPs are obtained by dewetting the Au film or Au–Ge film on a patterned SiO2 substrate. The influence of the substrate morphology and the Ge film on the dewetting process is investigated. The former modifies the crucial dewetting parameters periodically, i.e., the surface curvature, while the latter provides energy for Au atoms' surface diffusion. The extinction spectrum shows a prominent enhancement in local surface plasmon resonance, over 5 times in the visible region, which is due to the periodicity and high-density in NP distribution. This study provides a simple and regulable method to prepare periodically distributed metal NPs.

Optoelectronic optimization of graded-bandgap thin-film AlGaAs solar cells.

An optoelectronic optimization was carried out for an $ {{\rm Al}_\xi }{{\rm Ga}_{1 - \xi }}{\rm As} $AlξGa1-ξAs (AlGaAs) solar cell containing (i) an $ n $n-AlGaAs absorber layer with a graded bandgap and (ii) a periodically corrugated Ag backreflector combined with localized ohmic Pd-Ge-Au backcontacts. The bandgap of the absorber layer was varied either sinusoidally or linearly. An efficiency of 33.1% with the 2000-nm-thick $ n $n-AlGaAs absorber layer is predicted with linearly graded bandgap along with silver backreflector and localized ohmic backcontacts, in comparison to 27.4% efficiency obtained with homogeneous bandgap and a continuous ohmic backcontact. Sinusoidal grading of the bandgap is predicted to enhance the maximum efficiency to 34.5%. Thus, grading the bandgap of the absorber layer, along with a periodically corrugated Ag backreflector and localized ohmic Pd-Ge-Au backcontacts, can help realize ultrathin and high-efficient AlGaAs solar cells for terrestrial applications.

Chemically Modulating the Twist Rate of Helical van der Waals Crystals

Twisted van der Waals (vdW) materials with a controllable twist are of great interest because the twist offers new opportunities to modify the optoelectronic properties of the materials, giving rise to exotic phenomena, such as superconductivity, moiré excitons, and chiroptical response. Recently, we have synthesized helical vdW crystals with a periodic twist via the vapor–liquid–solid (VLS) growth of dislocated germanium sulfide nanowires with an Eshelby twist. The twist rates and periods of these structures are determined by the radii of the dislocated nanowires, which are defined by the size of the droplets catalyzing the VLS process. In this work, we tailor the twist rates and periods of the structures via chemically modulating the droplet size and the diameter of dislocated vdW nanowires. Our chemical analysis reveals that the growth of twisted GeS nanowires is catalyzed by droplets of an Au–Ge alloy. The size of the catalyst droplets was tailored by introducing GeSe into the growth. The addition of GeSe significantly increases the surface energy of the droplets, increasing the size of the droplets. This results in the growth of GeS1–xSex with decreased twist rates. The chemical modulation of the droplet size is correlated with the change of germanium concentration (supersaturation) in the alloy droplets, consistent with the Gibbs–Thomson effect. Increasing the selenium concentration in the GeS1–xSex from x = 0 to x = 0.11 decreases the twist rate from 0.59 to 0.22 rad/μm, increasing the period from 8 to 15 μm. The chemical modulation demonstrates good potential to tailor the twist rate and period of helical vdW crystals, providing more flexibility to modulate the optoelectronic properties and chiral light–matter interactions. Moreover, adding GeS into the source powder provides a means to tune the composition of the nanowires and mesoscale twisted crystals as GeS1-xSex alloy structures are produced. Our Raman spectroscopy and photoluminescence spectroscopy studies suggest that the compositional engineering in GeS1–xSex has good potential to tune the optoelectronic property.

Off-Eutectic Au–Ge Die-Attach—Microstructure, Mechanical Strength, and Electrical Resistivity

In this paper, off-eutectic Au–Ge joints were formed between Si substrates to investigate their high-temperature compatibility. High-quality joints made with small bond pressure, 53 kPa, were fabricated. The joints comprised three different types of morphologies: 1) a layered structure of Au/Au–Ge/Au; 2) a layered structure of Au/Au–Ge/Au where some sections of the central Au–Ge band have been replaced by an Au section that extended across the entire section; and 3) a roughly homogenous Au layer comprising the primary $\alpha $ phase. The average Ge concentration was 10 ± 2 at%. Joints formed with a higher bond line pressure, 7.6 MPa, were of a reduced quality with voids and cracks at the original bond line. Annealing at 400 °C for 1000 h transformed the microstructure into an Au–Ge–Si compound with Au precipitates. The shear strength of the fabricated joints was found to be at least 50 MPa, and the fracture mode was an adhesive fracture between the adhesion layer and the die or substrate. Heated dies detached from the substrates at 460 °C, i.e., more than 100 °C above the eutectic melting point of the binary Au–Ge system. Electrical resistivity measurements confirmed a melting process at the eutectic melting point by an abrupt increase in resistivity.

Self- and interdiffusion in dilute liquid germanium-based alloys

Self- and inter-diffusion coefficients in liquid Ge and dilute Ge-based Ge–Si, Ge–Au, Ge–In, Ge–Ce and Ge–Gd alloys-containing 2 at% additions, respectively, are measured using a comprehensive approach of measuring techniques: quasi-elastic neutron scattering, in situ long-capillary experiments combined with x-ray radiography, and a long-capillary experiment under microgravity conditions. Resulting inter- and Ge self-diffusion coefficients are equal within error bars for each investigated alloy. The interdiffusion coefficients are smaller for the alloys containing Ce and Gd, However, no dependence of the atomic mass of the minor additions, that varies by about a factor of seven between Si and Au, on the diffusion coefficients could be observed. This demonstrates that in a loosely-packed metallic liquid with fast diffusive dynamics the diffusion mechanism is highly collective in nature.

Improved barrier parameters and working stability of Au/p-GO/n-lnP/Au–Ge Schottky barrier diode with GO interlayer showing resistive switching effect

In this study, Au/p-GO/n-lnP/Au–Ge device structure for possible micro- and opto-electronic applications has been investigated. Firstly, the graphene oxide (GO) interlayer has been characterized before device fabrication. The GO interlayer has band gap energy of 2.4 eV and large contact area. In the Raman spectrum, ID/IG ratio was determined as 0.78. According to the Thermionic, Norde and Cheung methods, ideality factor, Schottky barrier height, series resistance and distribution of interface states have been investigated for the devices. The presence of GO interlayer has caused to both the barrier height increased from 0.44 to 0.71 eV and the significant increase in rectification ratio from 102 to 105 at ±1 V. Additionally, the ideality factor has improved from 1.32 to 1.23 at 300 K. The device working stability at high temperatures (400 K) has been observed in the Au/p-GO/n-lnP/Au–Ge device. Furthermore, the resistive switching effect of the GO interlayer has been observed as temperature-dependent metallic character of series resistance in high voltage region.

Growth of heterojunctions in Si–Ge alloy nanowires by altering AuGeSi eutectic composition using an approach based on thermal oxidation

Understanding the growth mechanism of heterojunctions in silicon–germanium alloy (Si–Ge) nanowires is helpful for designing adequate physical properties in the material for device applications. We examine the formation of the heterojunction in low Ge-content Si–Ge nanowires by an approach of thermal oxidation, which produces an atomically abrupt interface with an obvious concentration change. Forming heterojunctions in Si–Ge nanowires by this approach involves more complicated reaction routes than direct growth of heterojunction nanowires using the vapor–liquid–solid method. At the beginning of the oxidation process, the AuGeSi eutectic liquid at the nanowire tip significantly etches the Si–Ge alloy nanowires. Selective oxidation of Si results in a change of the relative amount of Ge to Si in the eutectic liquid, which further modulates the solubility of Ge and Si atoms. The compositional variation in the Au–Ge–Si ternary alloy system during the oxidation process accounts for the observed concentration profile in the heterojunction nanowire. The thermal oxidation approach is applied on a low Ge-content Si–Ge thin film that is coated with Au nanoparticles. Si–Ge nanodots, which exhibit a higher Ge concentration, are precipitated epitaxially in the film, as a result of compositional modulation in the AuGeSi eutectic liquid.

Thermoelectric Properties of Thin Films of Germanium-Gold Alloy Obtained by Magnetron Sputtering

In this paper, the electric and thermoelectric properties of thin films of germanium–gold alloy (Ge–Au) are discussed in terms of choosing the optimal deposition process and post-processing conditions to obtain Ge–Au layers with the best thermoelectric parameters. Thin films were fabricated by magnetron sputtering using the Ge–Au alloy target onto glass substrates at two various conditions; during one of the sputtering processes, the external substrate bias voltage (Ub = −150 V) was used. After deposition thin films were annealed in the atmosphere of N2 at various temperatures (473, 523 and 573 K) to investigate the influence of annealing temperature on the electric and thermoelectric properties of films. Afterwards, the thermocouples were created by deposition of the NiCrSi/Ag contact pads onto Ge–Au films. In this work, particular attention has been paid to thermoelectric properties of fabricated thin films—the thermoelectric voltage, Seebeck coefficient, power factor PF and dimensionless figure of merit ZT were determined.

Growth dynamics of SiGe nanowires by the vapour–liquid–solid method and its impact on SiGe/Si axial heterojunction abruptness

The vapour–liquid–solid (VLS) method is by far the most extended procedure for bottom-up nanowire growth. This method also allows for the manufacture of nanowire axial heterojunctions in a straightforward way. To do this, during the growth process, precursor gases are switched on/off to obtain the desired change in the nanowire composition. Using this technique, axially heterostructured nanowires can be grown, which are crucial for the fabrication of electronic and optoelectronic devices. SiGe/Si nanowires are compatible with complementary metal oxide semiconductor (CMOS) technology, which improves their versatility and the possibility of integration with current electronic technologies. Abrupt heterointerfaces are fundamental for the development and correct operation of electronic and optoelectronic devices. Unfortunately, the VLS growth of SiGe/Si heterojunctions does not provide abrupt transitions because of the high solubility of group IV semiconductors in Au, with the corresponding reservoir effect that precludes the growth of sharp interfaces. In this work, we studied the growth dynamics of SiGe/Si heterojunctions based on already developed models for VLS growth. A composition map of the Si–Ge–Au liquid alloy is proposed to better understand the impact of the growing conditions on the nanowire growth process and the heterojunction formation. The solution of our model provides heterojunction profiles that are in good agreement with the experimental measurements. Finally, an in-depth study of the composition map provides a practical approach to the drastic reduction of heterojunction abruptness by reducing the Si and Ge concentrations in the catalyst droplet. This converges with previous approaches, which use catalysts aiming to reduce the solubility of the atomic species. This analysis opens new paths to the reduction of heterojunction abruptness using Au catalysts, but the model can be naturally extended to other catalysts and semiconductors.

Necessary conditions for superior thermoelectric power of Si/Au artificial superlattice thin-film

The Si–Ge–Au ternary artificial superlattice thin-films showed superior thermoelectric power with low reproducibility. Superior thermoelectric power was only generated, when nanocrystals existed. Therefore, the origin of superior thermoelectric power was considered to be the quantum size effect of nanocrystals. However, even with the presence of nanocrystals, superior thermoelectric power was often not generated. In order to investigate the generation conditions of superior thermoelectric power in more detail, the samples were simplified to Si–Au binary artificial superlattice samples. Furthermore, annealings were carried out under conditions where nanocrystals were likely to be formed. From the results of Raman scattering spectroscopy and X-ray diffraction (XRD) analysis, the diameter of nanocrystals and the spacing between nanocrystals were calculated with an isotropic three-dimensional mosaic model. It was found that superior thermoelectric power was generated only when the diameter of nanocrystals was 11 nm or less and the spacing between nanocrystals was 3 nm or less.