Germanium Nanowires Research Articles

DFT insight into the structural, vibrational, and electronic properties of thin [110] Ge nanowires as anodic material for Li batteries

Germanium nanowires could be used to improve as anodic materials since their charge rate is better than that of the current graphite electrodes. In this work, we present a Density Functional Theory study of the effect of interstitial Li atoms on the vibrational, electronic, and mechanical properties of ultrathin hydrogen-passivated Ge nanowires (HGeNWs) with diamond structure, grown along the [110] crystallographic direction, and with a diameter of ∼14.4 Å. The interstitial Li atoms were placed at the tetrahedral positions (Td) reported as the more favorable ones. The phonon band structure of the HGeNWs reveals the existence of high frequency vibrations due to the hydrogen atoms at the nanowire surface. The effect of one interstitial Li atom in the nanowire leads to the apparition of three flat phonon bands almost independent of the collective vibrational states of the nanowire, reflecting a weak interaction between the Li atom and the neighboring ones; and a shift of the high vibrational modes to lower frequencies that results in more dispersive states. The electronic band structure confirms a transition from semiconducting to metallic behavior by adding a single Li interstitial atom per unit cell. The formation energies indicate that the nanowires with interstitial Li atoms are stable, and the average binding energy per Li atom slightly increases as a function of the concentration of Li atoms. The insertion of Li atoms in the nanowire leads to a volumetric expansion, without fracture or broken bonds. Even more, the redistribution of the electronic charge due to the Li atoms give the Ge-Ge bonds more axial elasticity and the values of the modulus of Young are almost constant for all studied concentrations of Li atoms. These theoretical results indicate an improvement of mechanical and electronic properties of Ge nanowires through the addition of interstitial Li atoms that could be important for their use as anodes in rechargeable Li batteries.

Electrochemically deposited germanium nanowires: Structure and resistivity against high-temperature oxidation

Using photoluminescence and Raman spectroscopy, as well as high-resolution transmission microscopy and X-ray diffraction, germanium nanowires obtained by cathodic deposition from an aqueous solution of germanium dioxide were studied during their annealing by a laser at 720 °C under ambient conditions. It is established that the dynamics of Raman and photoluminescence spectra are related to the oxidation of wires during such annealing. The study showed that vacuum annealing of as-grown nanowires at 600 °C for 30 min suppresses laser high-temperature germanium oxidation. The observed effect is associated with the saturation of vacancies in the surface germanium suboxide with indium atoms used as a catalyst in the formation of nanowires.

Investigating Chain‐Like Core‐Shell Ge Nanowires Coated with Carbon Nanotubes Through Atomic Simulations: Implication for Improving Binding and Mechanical Properties

AbstractAtomic simulations within the classical mechanics' formalism are used to investigate the interfacial binding between carbon nanotubes (CNTs) and germanium nanowires (GeNWs) as well as the mechanical properties of the chain‐like coreshell germanium nanowires coated with CNTs. The simulations at the atomic scale provide the effect of temperature, systems’ cross–sectional diameter, interfacial distance, applied tension loading on their binding degree, and deformation behaviors. The simulation results reveal that the spacing between CNT and nanowires as well as the interfaces formed between them directly affect the thermal stability and the degree of interfacial bonding of the systems. The coreshell GeNWs coated with CNTs present significantly excellent mechanical properties. The Lode‐Nadai parameters and the atomic hydrostatic pressures on the atoms can be used to identify atoms’ bearing states in different regions and the stress‐transfer paths during different stages including elasticity, plasticity, and fracture of the confined systems.

Single-Crystal Silicon Nanotubes, Hollow Nanocones, and Branched Nanotube Networks.

We report a general approach for the synthesis of single-crystal silicon nanotubes, involving epitaxial deposition of silicon shells on germanium nanowire templates followed by removal of the germanium template by selective wet etching. By exploiting advances in the synthesis of germanium nanowires, we were able to rationally tune the nanotube internal diameters (5-80 nm), wall thicknesses (3-12 nm), and taper angles (0-9°) and additionally demonstrated branched silicon nanotube networks. Field effect transistors fabricated from p-type nanotubes exhibited a strong gate effect, and fluid transport experiments demonstrated that small molecules could be electrophoretically driven through the nanotubes. These results demonstrate the suitability of silicon nanotubes for the design of nanoelectrofluidic devices.

Control of Ge island coalescence for the formation of nanowires on silicon.

Germanium nanowires could be the building blocks of hole-spin qubit quantum computers. Selective area epitaxy enables the direct integration of Ge nanowires on a silicon chip while controlling the device design, density, and scalability. For this to become a reality, it is essential to understand and control the initial stages of the epitaxy process. In this work, we highlight the importance of surface treatment in the reactor prior to growth to achieve high crystal quality and connected Ge nanowire structures. In particular, we demonstrate that exposure to AsH3 during the high-temperature treatment enhances lateral growth of initial Ge islands and promotes faster formation of continuous Ge nanowires in trenches. The Kolmogorov-Johnson-Mehl-Avrami crystallization model supports our explanation of Ge coalescence. These results provide critical insight into the selective epitaxy of horizontal Ge nanowires on lattice-mismatched Si substrates, which can be translated to other material systems.

Enhanced Performances for Solid-State Lithium-Ion Batteries with Llzo Thin Electrolyte and Silicon-Nanowires Electrode

In the past decades, due to an always more electrification and the research of a greener environment, Li-ion Batteries (LIB) have taken an important place in worldwide research. Solid-state batteries (SSBs) have the potential to revolutionize the energy storage industry, offering superior safety and energy density in comparison to traditional LIBs[1, 2]. Our research aims to enhance the performance and safety of solid-state batteries at ambient temperature by incorporating electrodes with high specific capacity with a lithium lanthanum zirconate (LLZO) solid electrolyte.The integration of SiNW electrodes into the solid-state battery architecture offers several advantages. SiNWs are known for their large surface area and superior electrical conductivity and offer a strong platform for efficient lithium-ion transport and cell energy density optimization, theoretically almost 10 times the capacity of graphite[3, 4]. Furthermore, LLZO solid electrolytes are a stable and non-flammable alternative to conventional liquid electrolytes[2, 5], significantly improving battery safety.The main objectives of this study are to investigate the combined effects of silicon nanowires (SiNWs) electrodes and LLZO solid electrolyte and to determine the optimal amount of liquid electrolytes to improve cell safety.In this work, an LLZO thin solid electrolyte tape has been manufactured by casting technique. Precise volumes of liquid electrolyte have been added to the LLZO tape to improve surface contact and ion conductivity. Furthermore, the study will provide a view of the relationship between the quantity of liquid electrolytes introduced and their impact on cell stability and safety.Preliminary results show the preparation of a mechanically stable LLZO tape with high ionic conductivity (>10-4 S cm-1) through an easy and up-scalable procedure. Improvements have been reported in the electrochemical performance of SiNW-LLZO solid-state batteries compared to the relative Li-ion liquid cell.In conclusion, here we developed a new thin solid electrolyte tape with high ionic conductivity, used in solid-state LIBs with silicon nanowires as anode material. Moreover, we standardized a procedure to optimize the use of organic liquid electrolytes as an additive, without omitting the volume or using any excess that could lead to safety issues. This optimization process can contribute to the development of solid-state batteries that are not only high-performance but also safe and reliable for various applications, including electric vehicles and portable electronics. References Wu, F., J. Maier, and Y. Yu, Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries. Chem Soc Rev, 2020. 49(5): p. 1569-1614.Wang, C., et al., Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries. Chem Rev, 2020. 120(10): p. 4257-4300.Chan, C.K., et al., High-performance lithium battery anodes using silicon nanowires. Nat Nanotechnol, 2008. 3(1): p. 31-5.Kennedy, T., M. Brandon, and K.M. Ryan, Advances in the Application of Silicon and Germanium Nanowires for High-Performance Lithium-Ion Batteries. Adv Mater, 2016. 28(27): p. 5696-704.Xu, L., et al., Garnet Solid Electrolyte for Advanced All ‐Solid ‐State Li Batteries. Advanced Energy Materials, 2020. 11(2).

Germanium Nanowires (GeNW): Synthesis, Structural Properties, and Electrical Characterization for Advanced Nanoelectronic Devices

The exponential progress of nanoelectronic devices necessitates the development of novel materials and production methodologies to fulfill the escalating demands for enhanced performance. This research aims to answer the current need for high-performance materials by proposing a revolutionary approach known as Germanium Nanowires for Advanced Nanoelectronic Devices (GeNW-ANED). GeNW-ANED achieves the integration of GeNW growth with advanced nanoelectronic applications. The system has several distinctive attributes, such as meticulous regulation of nanowire fabrication, adjustable electrical characteristics, and improved thermal qualities. The GeNW-ANED method exhibits exceptional performance across multiple experimental metrics, encompassing Electrical Conductivity (1.70 S/cm), Carrier Mobility (1685.83 cm²/Vs), Dielectric Constant (4.73), Specific Capacity (325.00 mAh/g), Growth Rate (5.93 nm/s), and Thermal Conductivity (3.47 W/mK). The impressive results achieved by GeNW-ANED establish it as a prospective contender for advanced nanoelectronic devices, offering the potential for improved performance and increased adaptability. The presented approach exhibits promise in influencing the trajectory of nanoelectronics, as it provides a sturdy basis for advancing the creation of forthcoming devices that possess enhanced electrical, thermal, and energy storage properties.

Influence of Different Carrier Gases, Temperature, and Partial Pressure on Growth Dynamics of Ge and Si Nanowires.

The broad and fascinating properties of nanowires and their synthesis have attracted great attention as building blocks for functional devices at the nanoscale. Silicon and germanium are highly interesting materials due to their compatibility with standard CMOS technology. Their combination provides optimal templates for quantum applications, for which nanowires need to be of high quality, with carefully designed dimensions, crystal phase, and orientation. In this work, we present a detailed study on the growth kinetics of silicon (length 0.1-1 μm, diameter 10-60 nm) and germanium (length 0.06-1 μm, diameter 10-500 nm) nanowires grown by chemical vapor deposition applying the vapour-liquid-solid growth method catalysed by gold. The effects of temperature, partial pressure of the precursor gas, and different carrier gases are analysed via scanning electron microscopy. Argon as carrier gas enhances the growth rate at higher temperatures (120 nm/min for Ar and 48 nm/min H2), while hydrogen enhances it at lower temperatures (35 nm/min for H2 and 22 nm/min for Ar) due to lower heat capacity. Both materials exhibit two growth regimes as a function of the temperature. The tapering rate is about ten times lower for silicon nanowires than for germanium ones. Finally, we identify the optimal conditions for nucleation in the nanowire growth process.

Top-down fabrication of Ge nanowire arrays by nanoimprint lithography and hole gas accumulation in Ge/Si core–shell nanowires

Germanium (Ge) nanowire arrays are expected to be a promising channel material for high-performance field-effect transistors (FETs) due to their excellent electronic transport properties, silicon (Si) compatibility, and high integration. To produce highly ordered Ge nanowires with low contamination, nanoimprint lithography (NIL) and Bosch etching are used and the size of nanowires is reduced from 220 nm to ∼30 nm by adjusting the H2O2 etching time. Furthermore, Ge/Si core–shell nanowires are prepared by forming p-Si shells on Ge nanowires, and their good crystalline quality and sharp interfaces are confirmed by transmission electron microscope (TEM) observations. This structure is used as a high-mobility channel in HEMT-type devices, and the accumulation of hole gas inside the Ge nanowires, which is the most important, is demonstrated and investigated by Raman scattering.

Design of Energy-Efficient RFET-Based Exact and Approximate 4:2 Compressors and Multipliers

The ever-increasing demand for low-power and area-efficient circuits for use in battery-powered devices and the CMOS scaling problems have attracted the attention of VLSI designers to beyond-CMOS technologies like Reconfigurable Field-Effect Transistors (RFETs). Improving the efficiency of multipliers is critical as the core component of many applications such as image processing and Machine Learning (ML). This paper proposes a compact and energy-efficient RFET-based architecture for the 4:2 compressor and Dadda multiplier, leveraging transistor-level reconfigurability and multi-input support of the RFET. Moreover, we propose a novel approximate 4:2 compressor based on efficient RFET logic cells to cater to the needs of error-resilient applications. Extensive circuit-level simulations with 14nm germanium nanowire (GeNW) RFET technology show that the proposed RFET-based exact multiplier improves the power consumption and power-delay product (PDP) by 65% and 45%, respectively, compared to the conventional CMOS-based counterpart in 14nm FinFET technology. Besides, we show that utilizing the proposed approximate compressor, the area and PDP of the multiplier reduce by 46% and 42%. The effectiveness of the approximate multiplier is evaluated in the image multiplication, and the average PSNR and SSIM values are 31.39 and 0.87, respectively.

Theoretical study of [111]-germanium nanowires as anode materials in rechargeable batteries: a density functional theory approach

In this work, we present a Density Functional Theory (DFT) study of hydrogen-passivated germanium nanowires grown along the [111] crystallographic direction. The study is performed within the local density approximation (LDA) and the supercell technique. Four different diameters of nanowires were considered and the surface hydrogen atoms were replaced by Li ones using a sequential process. The results indicate that the nanowires have a semiconductor behaviour and the energy band gap diminishes when the number of Li atoms per unit cell increases. The formation energy results reveal that the Li atoms increase the stability of the Ge nanowires, and there is a charge transfer from the Li atoms to the surface Ge atoms. The open circuit voltage values are almost independent of the concentration of Li atoms. On the other hand, the lithium storage capacity results reveal that the Ge nanowires could be good candidates to be incorporated as anodic materials in the new generation of rechargeable batteries.

NaFe0.5Mn0.5PO4–Ge electrochemical system for sodium-ion batteries

A new electrochemical system for sodium-ion batteries, sodium iron-manganese phosphate–germanium nanowires, has been developed and tested. The laboratory batteries possessed an average discharge voltage of ∼2.0 V and an energy density based on the weight of active materials to 210 Wh kg–1.

Cu Current Collector with Binder-Free Lithiophilic Nanowire Coating for High Energy Density Lithium Metal Batteries.

Despite significant efforts to fabricate high energy density (ED) lithium (Li) metal anodes, problems such as dendrite formation and the need for excess Li (leading to low N/P ratios) have hampered Li metal battery (LMB) development. Here, the use of germanium(Ge)nanowires (NWs) directly grown on copper(Cu) substrates (Cu-Ge) to induce lithiophilicity and subsequently guide Li ions for uniform Li metal deposition/stripping during electrochemical cycling is reported. The NW morphology along with the formation of the Li15 Ge4 phase promotes uniform Li-ion flux and fast charge kinetic, resulting in the Cu-Ge substrate demonstrating low nucleation overpotentials of 10mV (four times lower than planar Cu) and high Columbic efficiency (CE) efficiency during Li plating/stripping. Within a full-cell configuration, the Cu-Ge@Li - NMC cell delivered a 63.6% weight reduction at the anode level compared to a standard graphite-based anode, with impressive capacity retention and average CE of over 86.5% and 99.2% respectively. The Cu-Ge anodes are also paired with high specific capacity sulfur (S) cathodes, further demonstrating the benefits of developing surface-modified lithiophilic Cu current collectors, which can easily be integrated at the industrial scale.

Polarized emission from hexagonal-silicon–germanium nanowires

We present polarized emission from single hexagonal silicon–germanium (hex-SiGe) nanowires. To understand the nature of the band-to-band emission of hex-SiGe, we have performed photoluminescence spectroscopy to investigate the polarization properties of hex-SiGe core–shell nanowires. We observe a degree of polarization of 0.2 to 0.32 perpendicular to the nanowire c-axis. Finite-difference time-domain simulations were performed to investigate the influence of the dielectric contrast of nanowire structures. We find that the dielectric contrast significantly reduces the observable degree of polarization. Taking into account this reduction, the experimental data are in good agreement with polarized dipole emission perpendicular to the c-axis, as expected for the fundamental band-to-band transition, the lowest energy direct band-to-band transition in the hex-SiGe band structure.

Cycle-dependent morphology and surface potential of germanium nanowire anode electrodes.

Germanium nanowire (GeNW) electrodes have shown great promise as high-power, fast-charging alternatives to silicon-based electrodes, owing to their vastly improved Li ion diffusion, electron mobility and ionic conductivity. Formation of the solid electrolyte interphase (SEI) on the anode surface is critical to electrode performance and stability but is not completely understood for NW anodes. Here, a systematic study characterizing pristine and cycled GeNWs in charged and discharged states with SEI layer present and removed is performed using Kelvin probe force microscopy in air. Correlating changes in the morphology of the GeNW anodes with contact potential difference mapping at different cycles provides insight into SEI layer formation and growth, and the effect of the SEI on battery performance.

Electrodes of Germanium and Germanium Phosphide Nanowires in Lithium-Ion and Sodium-Ion Batteries (A Review)

Electrodes of Germanium and Germanium Phosphide Nanowires in Lithium-Ion and Sodium-Ion Batteries (A Review)

Selection and Functionalization of Germanium Nanowires for Bio-Sensing.

In this paper, we investigate the use of dielectrophoresis to align germanium nanowire arrays to realize nanowire-based diodes and their subsequent use for bio-sensing. After establishing that dielectrophoresis is a controllable and repeatable fabrication method to create devices from germanium nanowires, we use the optimum process conditions to form a series of diodes. These are subsequently functionalized with an aptamer, which is able to bind specifically to the spike protein of SARS-Cov2 and investigated as a potential sensor. We observe a linear increase in the source to drain current as the concentration of spike protein is increased from 100 fM/L to 1 nM/L.

Design and Simulation Analysis of Silicon Germanium Nanowire FET for Low Power Applications

Design and Simulation Analysis of Silicon Germanium Nanowire FET for Low Power Applications

Effect of Vinylene Carbonate Electrolyte Additive on the Process of Insertion/Extraction of Na into Ge Microrods Formed by Electrodeposition

Layers of germanium (Ge) microrods with a core–shell structure on titanium foils were grown by a metal-assisted electrochemical reduction of germanium oxide in aqueous electrolytes. The structural properties and composition of the germanium microrods were studied by means of scanning and transmission electron microscopy. Electrochemical studies of germanium nanowires were carried out by impedance spectroscopy and cyclic voltammetry. The results showed that the addition of vinylene carbonate (VC) in the electrolyte significantly reduced the irreversible capacity during the first charge/discharge cycles and increased the long-term cycling stability of the Ge microrods. The obtained results will benefit the further design of Ge microrods-based anodes that are formed by simple electrochemical deposition.

Effect of Silicate Additive on Structural and Electrical Properties of Germanium Nanowires Formed by Electrochemical Reduction from Aqueous Solutions.

Layers of germanium (Ge) nanowires (NWs) on titanium foils were grown by metal-assisted electrochemical reduction of germanium oxide in aqueous electrolytes based on germanium oxide without and with addition of sodium silicate. Structural properties and composition of Ge NWs were studied by means of the scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. When sodium silicate was added to the electrolyte, Ge NWs consisted of 1–2 at.% of silicon (Si) and exhibited smaller mean diameter and improved crystallinity. Additionally, samples of Ge NW films were prepared by ultrasonic removal of Ge NWs from titanium foils followed with redeposition on corundum substrates with platinum electrodes. The electrical conductivity of Ge NW films was studied at different temperatures from 25 to 300 °C and an effect of the silicon impurity on the thermally activated electrical conductivity was revealed. Furthermore, the electrical conductivity of Ge NW films on corundum substrates exhibited a strong sensor response on the presence of saturated vapors of different liquids (water, acetone, ethanol, and isopropanol) in air and the response was dependent on the presence of Si impurities in the nanowires. The results obtained indicate the possibility of controlling the structure and electrical properties of Ge NWs by introducing silicate additives during their formation, which is of interest for applications in printed electronics and molecular sensorics.