Nanoporous Ge Research Articles

Creation of an antireflection coating for the optical range based on a nanoporous germanium layer formed by implantation with indium ions

The possibility of using a nanoporous Ge layer formed by implantation with 115In+ ions on a monocrystal c-Ge substrate as an antireflection optical coating (In:PGe) was studied. For this purpose, ion implantation of c-Ge wafers was performed at an energy E=30 keV, current density in the ion beam J=5 μA/cm2, and dose D=1.8· 1016 ion/cm2. It was shown that the fabricated In:PGe spongy layer, which consists of intertwining Ge nanowires, is characterized by a low reflectivity (~ 5%) in a wide optical spectral range of 250-1050 nm. Keywords: nanoporous germanium, ion implantation, antireflection optical coating.

Создание антиотражающего покрытия для оптического диапазона на основе слоя нанопористого германия, сформированного имплантацией ионами индия

The possibility of using a nanoporous Ge layer formed by implantation with 115 In+ ions on a monocrystal c-Ge substrate as an antireflection optical coating (In:PGe) was studied. For this purpose, ion implantation of c-Ge wafers was performed at an energy E = 30 keV, current density in the ion beam J = 5 μA/cm2, and dose D = 1.8 × 1016 ion/cm2. It was shown that the obtained In:PGe spongy layer, which consists of intertwining Ge nanowires, is characterized by a low reflectivity (~5%) in a wide optical spectral range of 250–1050 nm.

Omnidirectional and broadband photon harvesting in self-organized Ge columnar nanovoids

Highly porous Germanium surfaces with uniformly distributed columnar nanovoid structures are fabricated over a large area (wafer scale) by large fluence Sn+ irradiation through a thin silicon nitride layer. The latter represents a one-step highly reproducible approach with no material loss to strongly increase photon harvesting into a semiconductor active layer by exploiting the moth-eye antireflection effect. The ion implantation through the nitride cap layer allows fabricating porous nanostructures with high aspect ratio, which can be tailored by varying ion fluence. By comparing the reflectivity of nanoporous Ge films with a flat reference we demonstrate a strong and omnidirectional reduction in the optical reflectivity by a factor of 96% in the selected spectral regions around 960 nm and by a factor of 67.1% averaged over the broad spectral range from 350 to 1800 nm. Such highly anti-reflective nanostructured Ge films prepared over large-areas with a self-organized maskless approach have the potential to impact real world applications aiming at energy harvesting.

Nanoporous germanium prepared by a mechanochemical reaction with enhanced lithium storage properties.

The cost-effective and facile fabrication of nanostructured germanium for lithium-ion batteries (LIBs) remains a grand challenge. Herein, nanoporous Z-Ge was generated via a facile two-step mechanochemical-etching reaction with Mg2Ge and ZnCl2. The prepared nanoporous Ge nanoparticles, as the anode for Li-Ge half cells, showed superior LIB performance, in terms of a high capacity, good rate capability, and good long-term stability of 700 cycles. Significantly, the mechanochemical reaction was extended to produce other nanoporous Ge or Si materials such as A-Ge, Z-Si, and A-Si via the mechanochemical reaction between Mg2Ge and AlCl3, Mg2Si and ZnCl2, and Mg2Si and AlCl3.

Hierarchical nanoporous Ge anodes for lithium-ion batteries via plasma-phase-fabricated Mg2Ge

Microwave-induced Mg plasma rapidly “deep reduces” GeO2 to Mg2Ge, a precursor to bespoke hierarchical nanoporous Ge, which acts as a high-performance anode in lithium-ion cells.

Development of the anode for a lithium-ion battery based on nanoporous germanium formed by the implantation with silver ions

In this work, the possibility of using a nanoporous Ge layer (p-Ge), formed by implantation with Ag+ ions on a single crystal c-Ge substrate, as an anode electrode for a lithium-ion battery was studied. For this, the ion implantation of c-Ge substrutes was carried out at an energy of E=30 keV, a current density of J=5 μA/cm2, and a dose of D=1.3·1016 ion/cm2. It was shown that the obtained spongy Ag:p-Ge layers, consisting of intertwining Ge nanowires, demonstrate a high Coulomb efficiency (>97%) after the first cycle and show up to 79.5% of reversible capacity after 1000 cycles. Keywords: nanoporous germanium, ion implantation, anod, lithium-ion battery.

Создание анода литий-ионного аккумулятора на основе нанопористого германия, сформированного имплантацией ионами серебра

In this work, we investigated the possibility of using a nanoporous Ge layer (p-Ge) formed by implantation with Ag+ ions on a single crystal c-Ge substrate as an anode electrode for a lithium-ion battery. For this, ion implantation of c-Ge plates was carried out at an energy of E = 30 keV, a current density in the ion beam of J=5 μA/cm2, and a dose of D=1.3·1016 ion/cm2. It is shown that the obtained spongy Ag:p-Ge layers, consisting of intertwining Ge nanowires, demonstrate a high Coulomb efficiency (> 97%) after the first cycle and show up to 79.5% of reversible capacity after 1000 cycles.

Formation, lithium storage properties, and mechanism of nanoporous germanium fabricated by dealloying

Germanium (Ge) has become a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and decent electron/ion conductivity, but it exhibits inferior lifespan caused by dramatic volume variations during the (de)lithiation process. Herein, hierarchically, nanoporous Ge (np-Ge) was fabricated by the combination of selective phase corrosion with chemical dealloying. As an anode for LIBs, the np-Ge electrode exhibits marvelous cycling stability with capacity retentions of 1060.0 mA h g-1 at 0.2Ag-1 and 767.1 mA h g-1 at 1Ag-1 after 100 cycles. Moreover, the electrode shows excellent rate capability with a capacity retention of 844.2 mA h g-1 at 5Ag-1. Noticeably, the (de)lithiation mechanisms of np-Ge and porous Si-Ge (p-Si6Ge4) were unveiled by operando X-ray diffraction.

Formation of nanoporous Ge layers by ion implantation at different temperatures of c-Ge substrate

The flat monocrystalline c-Ge wafers implanted by 108Ag + ions with the energy E = 30 keV, dose D = 1.3·1016 ion/cm2 and at current density J = 5 μA/cm2 for various substrate temperatures from 25 to 400 °C were studied. By scanning electron microscopy and optical reflection spectroscopy it was found that as a result of ion implantation in the temperature range from 25 to 300 °C an amorphous porous Ag:PGe layers of a spongy structure consisting of Ge nanowires on the c-Ge substrate surface are formed. The diameter of Ge nanowires increases from 16 to 24 nm with a rising of substrate temperature. It is shown that at the highest temperature of 400 °C, the porous structure does not form and the Ge surface remains flat on which the formation of Ag nanoparticles can be observed. A change in the level of the sample surface in dependence on substrate temperature due to swelling up to 280 °C was replaced by effective ion sputtering at higher temperatures.

Ag Nanoparticles Anchored on Nanoporous Ge Skeleton as High‐Performance Anode for Lithium‐ion Batteries

Main observation and conclusionNanoporous (NP) Ge/Ag composite is controllably fabricated via one simple dealloying method under mild conditions. After corroding the well‐designed Ge9Ag1Al90 source alloy, the resulting Ge/Ag consists of the three dimensional (3D) interconnected Ge network skeleton with Ag nanoparticles uniformly dispersed onto the surface. Benefitting from unique 3D porous nanostructure and introduction of high‐conductive Ag, the NP Ge/Ag composite exhibits much enhanced lithium storage performances by comparison with pure Ge material, including higher reversible capacitance, optimized rate capability as well as superior cycling performances. Besides, the NP Ge/Ag holds high cycling stability with large reversible capacity of 500 mA·h·g–1 remained under high current rate of 3200 mA·g–1 for an extended period of 300 loops. The Ge/Ag composite presents great potential in applications as an advanced anode candidate for lithium ion batteries in virtue of its excellent performances and green fabrication.

Sn modified nanoporous Ge for improved lithium storage performance

Although high-capacity germanium (Ge) has been regarded as the promising anode material for lithium ion batteries (LIBs), its actual performance is far from expectation because of low electrical conductivity and rapid capacity decay during cycling. In this work, Sn modified nanoporous Ge materials with different Ge/Sn atomic ratios in precursors were synthesized by a simple melt-spinning and dealloying strategy. As the anodes of LIBs, Sn modified nanoporous Ge materials display improved cycling stability compared with Sn-free nanoporous Ge, revealing a potential role of Sn in improving electrochemical properties of Ge-based anodes. In particular, Sn modified nanoporous Ge with Ge/Sn atomic ratio of 3:1 presents the best Li storage performance among measured electrodes, delivering a reversible capacity of 974 mA h g−1 after 500 cycles at 200 mA g−1. It is found that the introduction of appropriate amount of Sn can not only regulate the nanoporous structure of Ge to better alleviate volume expansion, but also improves the conductivity and activity of the electrode material. This improvement is demonstrated by density functional theory calculations. The study uncovers a route to improve Li storage properties by rationally modify Ge-based anodes with Sn, which may facilitate the development of high-performance LIBs.

Improving the cycling stability of three-dimensional nanoporous Ge anode by embedding Ag nanoparticles for high-performance lithium-ion battery

Due to huge volume expansion and poor electrical conductivity, the commercial application of the promising Germanium (Ge) anode is restrained in lithium ion battery (LIB) field. Generally, conductive metals can improve the electron mobility in Ge. In that way, whether active materials or conductive metals account for a higher proportion in the anode is controversial in this field and needs to be clarified urgently. Herein, three Ge-based anodes with different ratios in conductive Ag are fabricated by a facile melt spinning and one-step dealloying method. It is found that Ag nanoparticles embedded three-dimensional nanoporous Ge (Ag/np-Ge) electrode with high active material ratio exhibits the best cycling stability among tested samples, delivering a high capacity of 953 mAh g−1 after 100 cycles at a current density of 100 mA g−1 and an excellent reversible capacity of 522 mAh g−1 after 200 cycles even at the high current density of 1000 mA g−1. The enhanced cycling stability can be attributed to the synergistic effect of nanoporous network-like structure and embedded Ag nanoparticles. A dramatical increase in electrical conductivity and activity of Ge by doping of Ag is confirmed by density functional theory (DFT) calculations. The work provides us an idea to rationally design the three-dimensional structure of active materials assisting with a proper ratio of conductive metals, which may promote the development of promising Ge anodes for LIBs with excellent cycling stability.

Formation of porous germanium layers with various surface morphology in dependence on mass of implanted ions

The surface morphology of nanoporous Ge (PGe) layers formed by low-energy high-dose implantation with transition metal ions depending on their mass ( 52 Cr + , 55 Mn + , 56 Fe + , 59 Co + , 59 Ni + and 63 Cu + ) was studied by high-resolution scanning electron microscopy. Ion implantation of single-crystal c -Ge substrates was carried out using similar conditions with an energy of E = 40 keV and a dose of D = 5.0·10 16 ion/cm 2 . Additionally, c -Ge was also implanted with heavier ions 108 Ag + and 122 Sb + at E = 30 keV for comparative experiments on the surface PGe morphology. It was observed that the morphology of the PGe layers changed with increasing mass of the irradiated ion from a labyrinth, hole type, three-dimensional network to spongy structure. • Various surface morphology of porous Ge layer formed by implantation with metal ions depending on their mass. • Detected morphology PGe structures from a labyrinth, hole type, 3D network to spongy structure. • SEM image observed at angle 70° to the sample surface gives a false view for Co:PGe layer.

Silver Nanoparticles in Porous Germanium

Recent experiments on fabrication of nanoporous Si and Ge layers with Ag nanoparticles by low-energy high-dose ion implantation are discussed. Ag+-ion implantation of single-crystal c-Si and c-Ge at low-energy (E = 30 keV) highdoses (D = 1.25·1015 - 1.5·1017 ion/cm2 ) and current density (J = 2-15 μA/cm2 ) was carried out for this purpose. The changes of Si and Ge surface morphology after ion implantation were studied by scanning electron and atom-force microscopy. The near surface area of samples was also analyzed by diffraction of the backscattered electrons and energydispersive X-ray microanalysis. Amorphization of near-surface layer was observed at the lowest implantation doses of c-Si. Ag nanoparticles were synthesized and uniformly distributed over the near Si surface when the threshold dose of 3.1·1015 ion/cm2 exceeded. At a dose of more than 1017 ion/cm2 , the formation of a surface nanoporous PSi structure was detected. Ag nanoparticle size distribution function became bimodal and the largest particles were localized along Si-pore walls. In the case of Ge substrates, as a result of the implantation on the c-Ge surface, a porous amorphous PGe layer of a spongy structure was formed consisting of a network of intersecting Ge nanowires with an average diameter of ~ 10-20 nm. At the ends of the nanowires, the synthesis of Ag nanoparticles was observed. It was found that the formation of pores during Ag+-ion implantation was accompanied by efficient spattering of the Si and Ge surface. Thus, ion implantation is suggested to be used for the formation of nanoporous semiconductor thin layers for industry, which could be easily combined with the crystalline matrix for various applications.

In situ electrochemical dilatometry study of capacity fading in nanoporous Ge-based Na-ion battery anodes

It is found that crystalline nanoporous Ge can only partially store sodium, with amorphous NaxGe as the sodiation product. Electrochemical dilatometry techniques were used to measure the corresponding (de)sodiation-induced strains. The capacity and strain amplitude were found to exhibit the same decay trend during long-term cycling, which is expected since the capacity fades because of the volume changes arising during cycling. However, viewed from a different perspective, the similarity between capacity fading and strain decay suggests that one way to mitigate this capacity fading might be by preventing the initial strain from decaying, instead of getting rid of this strain.

Easy preparation of nanoporous Ge/Cu3Ge composite and its high performances towards lithium storage

Nanoporous Ge/Cu3Ge composite is fabricated simply through selective dealloying of GeCuAl precursor alloy in dilute alkaline solution. The as-made Ge/Cu3Ge is characterized by three dimensional (3D) bicontinuous network nanostructure which comprises of substantial nanoscale pore voids and ligaments. Owing to the 3D porous architecture and the introduction of well-conductive Cu3Ge, the lithium storage performances of Ge are dramatically enhanced in terms of higher cycling stability and superior rate performance. Nanoporous Ge/Cu3Ge anode delivers steady capacities above 1000 mA h g−1 upon cycling for 70 loops at 400 mA g−1. In particular, after 300 cycles at the high rate of 3200 mA g−1 the capacity retention for Ge/Cu3Ge is able to reach a maximum of 99.3%. On the contrary, the pure nanoporous Ge encounters severe capacity decay. In view of the outstanding energy storage performances and easy preparation, nanoporous Ge/Cu3Ge exhibits great application potential as an advanced anode in lithium storage related technologies.

Stress-Tolerant Nanoporous Germanium Nanofibers for Long Cycle Life Lithium Storage with High Structural Stability.

Nanowires (NWs) synthesized via chemical vapor deposition (CVD) have demonstrated significant improvement in lithium storage performance along with their outstanding accommodation of large volume changes during the charge/discharge process. Nevertheless, NW electrodes have been confined to the research level due to the lack of scalability and severe side reactions by their high surface area. Here, we present nanoporous Ge nanofibers (NPGeNFs) having moderate nanoporosity via a combination of simple electrospinning and a low-energetic zincothermic reduction reaction. In contrast with the CVD-assisted NW growth, our method provides high tunability of macro/microscopic morphologies such as a porosity, length, and diameter of the nanoscale 1D structures. Significantly, the customized NPGeNFs showed a highly suppressed volume expansion of less than 15% (for electrodes) after full lithation and excellent durability with high lithium storage performance over 500 cycles. Our approach offers effective 1D nanostructuring with highly customized geometries and can be extended to other applications including optoelectronics, catalysis, and energy conversion.

Nanoporous amorphous Ge–Si alloys – unraveling the physics behind ion beam induced morphogenesis

Despite a high technical relevance and 35 years of observation, self-organized morphogenesis of nanoporous sponge-like amorphous structures during exposure of selected covalent materials to energetic ions is still insufficiently understood. Due to the presence and absence of these effects in amorphous Ge and Si, respectively, the Ge-Si alloy system constitutes an ideal testbed to track down the underlying physics at the atomic scale. This is realized within the present study by a combination of tailored experiments and extensive molecular dynamics computer modeling. The swelling capabilities of a variety of interaction potentials for the Ge-Si system and its elemental constituents are scrutinized with respect to the experimental observations and related to relevant physical properties of the model systems. This allows to identify defect kinetics in combination with a moderate radiation induced fluidity as key ingredients for nanopore morphogenesis. Cast in a simple quantitative model, it enables to account for both experimental as well as computational results, thus paving the way for a design by understanding approach in synthesis.

Analytical model for phonon transport analysis of periodic bulk nanoporous structures

Phonon transport analysis in nano- and micro-porous materials is critical to their energy-related applications. Assuming diffusive phonon scattering by pore edges, the lattice thermal conductivity can be predicted by modifying the bulk phonon mean free paths with the characteristic length of the nanoporous structure, i.e., the phonon mean free path (ΛPore) for the pore-edge scattering of phonons. In previous studies (Jean et al., 2014), a Monte Carlo (MC) technique have been employed to extract geometry-determined ΛPore for nanoporous bulk materials with selected periods and porosities. In other studies (Minnich and Chen, 2007; Machrafi and Lebon, 2015), simple expressions have been proposed to compute ΛPore. However, some divergence can often be found between lattice thermal conductivities predicted by phonon MC simulations and by analytical models using ΛPore. In this work, the effective ΛPore values are extracted by matching the frequency-dependent phonon MC simulations with the analytical model for nanoporous bulk Si. The obtained ΛPore values are usually smaller than their analytical expressions. These new values are further confirmed by frequency-dependent phonon MC simulations on nanoporous bulk Ge. By normalizing the volumetric surface area A and ΛPore with the period length p, the same curve can be used for bulk materials with aligned cubic or spherical pores up to dimensionless p·A of 1.5. Available experimental data for nanoporous Si materials are further analyzed with new ΛPore values. In practice, the proposed model can be employed for the thermal analysis of various nanoporous materials and thus replace the time-consuming phonon MC simulations.

Optical Properties of Nanoporous Germanium Thin Films.

In the present article we report enhanced light absorption, tunable size-dependent blue shift, and efficient electron-hole pairs generation in Ge nanoporous films (np-Ge) grown on Si. The Ge films are grown by sputtering and molecular beam epitaxy; subsequently, the nanoporous structure is obtained by Ge+ self-implantation. We show, by surface photovoltage spectroscopy measurements, blue shift of the optical energy gap and strong signal enhancement effects in the np-Ge films. The blue shift is related to quantum confinement effects at the wall separating the pore in the structure, the signal enhancement to multiple light-scattering events, which result in enhanced absorption. All these characteristics are highly stable with time. These findings demonstrate that nanoporous Ge films can be very promising for photovoltaic applications.