Germanium Nanotubes Research Articles

A detailed study of the electronic and optical properties of germanium nanotubes.

We employed first-principles calculations to investigate the electronic and optical properties of germanene nanotubes (GeNTs). Significant multi-orbital hybridizations lead to metallic and semiconducting behaviors in small-sized armchair and zigzag GeNTs, respectively. The changes in band gaps and subband dispersions with increasing diameter have been thoroughly understood by analyzing spatial charge densities and projected density of states. The optical absorption spectra exhibit diameter-dependent anisotropy and suggest a dimensional transition beyond a critical diameter. This comprehensive study not only deepens our understanding of GeNTs but also reveals new possibilities for various nanotechnology applications.

Intercalation of Lithium Atom/Ion in carbon, Silicon and Germanium Nanotubes

In this paper, we have studied the impact of Li atom/ion intercalation in C, Si and Ge nanotubes. The bond lengths for the optimized structures of the Li atoms/ions intercalation are similar and consistent with the bond lengths of pristine nanotubes. Based on Mulliken population and charge density analysis,there is a net transfer of charge from Lithium atoms to nanotube atoms. However, it is opposite in case of ion intercalation. The intercalation of Li atom/ion alters the electronic structure of the SWNTs, resulting in a shift from semiconducting to metallic. Our study also reveals that the conductance is 5G 0 for GeNT on Li atom/ion intercalation, which is 2G 0 for pristine GeNT. Due to their enhanced conductance as compared to pristine nanotubes, Li atom/ion intercalated systems can also be expected as materials for nano scale electronic devices, perfect for ballistic transport.

Synthesis of Microdiamonds and Germanium Nanotubes In the Argon-Germanium Arc

The paper describes a technique for the synthesis of microdiamonds, germanium nanoballs and nanotubes in an argon-germanium arc. The evaporation of germanium atoms was carried out from the surface of a graphite rod, which served as the anode of the arc discharge. The synthesis of microdiamonds was observed on graphite substrates near the anode; germanium nanotubes and germanium nanoballs were also found nearby. It has been established that germanium promotes the synthesis of nano and microdiamonds. Synthesized diamonds have a classic structure with rectangle faces and four hexagons adjacent to the edges of this rectangle. The sizes of microdiamonds reach tens of microns. The diameters of germanium nanotubes are of the order of 50-100 nm, and the length is of the order of 10 μm.

Mechanical properties of group IV single-walled nanotubes: a finite element approach based on the density functional theory.

In this article, the density functional theory is applied to characterize the mechanical properties of single-walled nanotubes of group IV of the periodic table. These materials include carbon nanotube, silicon nanotube, germanium nanotube, and stanene nanotube. (10,10) armchair nanotube is selected for the investigation. By establishing a link between potential energy expressions in molecular and structural mechanics, a finite element approach is proposed for modeling nanotubes. In the proposed model, the nanotubes are considered as an assemblage of beam elements. Young's modulus of the nanotubes is computed by the proposed finite element model. Young's modulus of carbon, silicon, germanium, and tin nanotubes are obtained as 1029, 159.82, 83.23, and 83.15GPa, respectively, using the density functional theory. Also, the finite element approach gives the values as 1090, 154.67, 85.2, and 82.6GPa, respectively. It is shown that the finite element model can predict the results of the density functional theory with good accuracy.

Plasma-chemical synthesis of germanium nanotubes

The paper describes the synthesis of germanium nanotubes in an argon microarc. The article presents the results of two experiments. The evaporation of germanium atoms was carried out from the surface of single-crystal germanium, which served as the anode of the microarc discharge. The synthesis of nanotubes was observed on the surface of a molybdenum cathode in the first experiment and on the surface of a graphite rod in the second experiment. The diameters of the obtained germanium nanotubes reach 800-900nm.

A theoretical study on the electronic, structural and optical properties of armchair, zigzag and chiral silicon-germanium nanotubes.

In this work we have studied infinite size silicon-germanium alloy nanotubes of several types, armchair, zigzag and chiral, by theoretical analysis based on density functional theory as implemented in the SIESTA code, which utilizes a linear combination of atomic orbitals and a generalized gradient approximation proposed by Perdew, Burke and Ernzerhof (GGA-PBE) for the exchange and correlation energy. The structures were relaxed until the atomic forces were less than 0.0001 eV Å-1. The electronic band structure, density of states and cohesive energy were then computed; the optical calculation was run in between 0 and 6 eV, with a broadening of 0.05 eV. The obtained results exhibit the deformation of the structure on the surface, which seems to be related to its stability. The armchair and zigzag tubes are direct band gap semiconductor materials, while chiral nanotubes shift from indirect to direct bandgap semiconductors, depending on their diameter size. Likewise, the bandgap depends on the diameter of the SiGe nanotubes (SiGeNTs). We have associated the absorption curves and the density of states through Van Hove singularities. In summary, our results on the structural and electronic properties of SiGeNTs elucidate their possible applications in thermoelectrics, photovoltaics and nanoelectronics, while the possibility of associating the absorption curves with the density of states provides a method of characterization.

Synthesizing Germanium Nanotubes in an Electric Arc Plasma

An original technique for the synthesis of germanium nanostructures in an electric arc argon plasma is described. The plasma–chemical synthesis of germanium nanotubes up to 100 μm long and up to 1 μm in diameter is performed by selecting the strength of the electric current, the pressure of the buffer gas, and the interelectrode distance. Individual nanotubes reach lengths of several mm. Unlike germanium nanotubes grown via CVD, the germanium nanotubes synthesized in this work have distinct shapes and sizes. They are separated from each other and can be easily manipulated. It is shown that this technique allows both germanium nanotubes and germanene to be grown.

Electric arc synthesis of germanium nanotubes

This paper describes the experimental setup and outlines the original methodology for conducting an experiment on growing germanium nanostructures. The obtained samples were examined with an electron microscope. It is shown that this technique allows one to grow both germanium nanotubes and germanium.

H2 storage by confinement inside germanium nanotubes

This work enabled us to compare the behaviour of different types of CNTs and BNNTs with that of various germanium nanotubes with a hydrogen molecule introduced perpendicularly or parallel to their axis. The confinement of the H2 molecule in GeNTs in both cases showed that the confinement energy is large for the smallest diameter, but it becomes close to zero for larger diameters. The main difference with respect to carbon nanotubes is the disappearance of H-H bond activation due to the absence of interactions between the π electrons and the hydrogen atoms. Compared to the BNNTs, we noted elongation of the H-H bond in both orientations for small diameters instead of breaking or shortening. This elongation is due to the strong interaction between the van der Waals radius of hydrogen and the atomic radius of germanium. This leads to a strong attraction between germanium and hydrogen for both orientations. This situation engenders a significant polarization. The most important consequence of the existence of this induced dipole moment is the IR activation of the H-H stretching vibration, which becomes very intense and whose value depends on the diameter of the nanotube. As an application, this vibration frequency can be used to detect and assay H2 contained in nanotubes or deduce the diameter of the host tube. This result shows that it is possible to detect H2 molecules inside GeNTs as well as in CNTs and BNNTs. However, in the germanium nanotubes, the most remarkable result that emerges from this study is that it is possible to detect and clearly differentiate the orientation of the H2 molecule inside the nanotubes, in contrast to other types of nanotubes.

Benchmarking Performance of a Gate-All-Around Germanium Nanotube Field Effect Transistor (GAA-GeNTFET) against GAA-CNTFET

Two gate-all-around field effect transistors (GAA-FETs) based on carbon and germanium nanotubes are proposed. The electronic properties and analog performance of the FETs are theoretically calculated and compared with each other. Also, by adding 5 × 1019 dopant/cm2 doping concentration in the source and drain regions, the results are re-obtained. Non-equilibrium Green's function method within the tight-binding Hamiltonian, which is extracted from density functional theory through the Wannier function, are used to calculate the output results. From the transfer characteristics analysis for nanotubes with the same chirality, it can be found that the ON- and OFF-currents for GeNTFET is about ten times smaller than that of CNTFET. Moreover, by adding dopants in the source and drain regions, the ION increases for both devices. The ION/IOFF ratio for all proposed FETs is almost the same and it is of order 104. We also found that the subthreshold swing for doped CNTFET is smaller than the other examined devices. The output characteristic of the CNTFET shown a saturation current when the drain voltage reached to 0.4 V, while this value for GeNTFET is equal to 0.6 V. Comparison between CNTFET and GeNTFET with the same chirality shows that the CNTFET has a better transistor performance but when comparing is performed on the same diameter of CNT and GeNT FETs, results show better transistor performance of GeNTFET compared to the CNTFET.

Germanium Nanotube as the Catalyst for Oxygen Reduction Reaction: Performance and Mechanism

Germanium Nanotube as the Catalyst for Oxygen Reduction Reaction: Performance and Mechanism

A simple and fast technique to grow free-standing germanium nanotubes and core-shell structures from room temperature ionic liquids

A simple and fast technique to grow free standing, open ended germanium nanotubes is demonstrated using template assisted electrodeposition from a room temperature ionic liquid. Germanium nanotubes as long as 2μm could be grown using this technique. We also show the possibility for the growth of core-shell structures. The technique demonstrated is not limited to the growth of Ge, but can be extended to grow other semiconductor nanotubes and core-shell structures.

Using Si and Ge Nanostructures as Substrates for Surface-Enhanced Raman Scattering Based on Photoinduced Charge Transfer Mechanism

The possibility of utilizing the Si and Ge nanostructures to promote surface-enhanced Raman scattering (SERS) is discussed. The vibronic coupling of the conduction band and valence band states of Si or Ge with the excited and ground states of the target molecule during the charge transfer (CT) process could enhance the molecular polarizability tensor. Using H-terminated silicon nanowire (H-SiNW) and germanium nanotube (H-GeNT) arrays as substrates, significant Raman enhancement of the standard probes, Rodamine 6G (R6G), dye (Bu(4)N)(2)[Ru(dcbpyH)(2)-(NCS)(2)] (N719), and 4-aminothiophenol (PATP), are demonstrated. The abundant hydrogen atoms terminated on the surface of SiNW and GeNT arrays play a critical role in promoting efficient CT and enable the SERS effect.

Germanium Nanotubes Prepared by Using the Kirkendall Effect as Anodes for High‐Rate Lithium Batteries

Ultralong germanium nanotubes (Ge NTs; see picture) are synthesized in high yield from core–shell Ge–Sb nanowires by utilizing the Kirkendall effect at 700 °C. The Ge NTs have an exceptionally high rate capability (40 Ag−1) while maintaining a reversible capacity of more than 1000 mAhg−1 over 400 cycles, with minimal capacity fading when paired with a LiCoO2 cathode in a lithium-ion cell.

Germanium Nanotubes Prepared by Using the Kirkendall Effect as Anodes for High‐Rate Lithium Batteries

Germanium Nanotubes Prepared by Using the Kirkendall Effect as Anodes for High‐Rate Lithium Batteries

Geometries, Stabilities, and Vibrational Properties of Bimetallic Mo2-Doped Gen (n = 9−15) Clusters: A Density Functional Investigation

Geometries of the bimetallic Mo2Gen (n = 9-15) clusters have been investigated systematically with the density functional approach. The relative stabilities and charge-transfer and vibrational properties of these clusters are presented and discussed. The dominant geometries of Mo2Gen (n = 9-12) clusters can be described as one Mo atom inside a Ge cage and another Mo atom on the surface at smaller sizes with n = 9-12. Interestingly, the stable geometry of Mo2Ge9 cluster has the framework which is analogous to a recent experimental observation (Goicoechea, J. M.; Sevov, S. C. J. Am Chem. Soc. 2006, 128, 4155). The calculated fragmentation energies and the obtained relative stabilities demonstrate that the remarkable Mo2-doped Ge12 is the most stable species of all different sized clusters. The critical size of Mo2-encapsulated cagelike germanium clusters appears at n = 15. The largest energy gap and strongest stability of Mo2Ge12 enable this species to be a unit of multiple metal Mo-doped germanium nanotubes. Vibrational mode analyses of Mo2Gen clusters demonstrate that the Mo-Mo stretching vibrations are sensitive to the geometries of the germanium frame, and that the point-group symmetry of germanium clusters can vary the Mo-Mo stretching vibration relative to the IR inactive vibration.

Ferromagnetism and piezomagnetic behavior in Mn-doped germanium nanotubes

Using ab initio density functional calculations, we show that pentagonal and hexagonal nanotubes of Ge can be stabilized in the antiprism structure by doping with Mn atoms. In both cases the infinite nanotubes are metallic and ferromagnetic. Hexagonal nanotubes have the highest average magnetic moments of $3.06\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ per Mn atom found so far in metal doped nanotubes of semiconductors, while the pentagonal nanotubes show a transition from a ferromagnetic to a ferrimagnetic state upon compression with an abrupt change in the magnetic moments, leading to the possibility of these nanotubes to act as a nano-piezomagnet.