Showing papers on "Germanane published in 2020"

Hydrogen Terminated Germanene for a Robust Self-Powered Flexible Photoelectrochemical Photodetector.

Abstract: As a rising star in the family of graphene analogues, germanene shows great potential for electronic and optical device applications due to its unique structure and electronic properties. It is revealed that the hydrogen terminated germanene not only maintains a high carrier mobility similar to that of germanene, but also exhibits strong light-matter interaction with a direct band gap, exhibiting great potential for photoelectronics. In this work, few-layer germanane (GeH) nanosheets with controllable thickness are successfully synthesized by a solution-based exfoliation-centrifugation route. Instead of complicated microfabrication techniques, a robust photoelectrochemical (PEC)-type photodetector, which can be extended to flexible device, is developed by simply using the GeH nanosheet film as an active electrode. The device exhibits an outstanding photocurrent density of 2.9 µA cm-2 with zero bias potential, excellent responsivity at around 22 µA W-1 under illumination with intensity ranging from 60 to 140 mW cm-2 , as well as short response time (with rise and decay times, tr = 0.24 s and td = 0.74 s). This efficient strategy for a constructing GeH-based PEC-type photodetector suggests a path to promising high-performance, self-powered, flexible photodetectors, and it also paves the way to a practical application of germanene.

Low thermal conductivity in single crystalline epitaxial germanane films

Abstract: We investigated thermal conductivity of epitaxial germanane films: stacked structure of hydrogenated germanenes. It was confirmed that single crystalline germanane films were epitaxially grown on Ge(111). The films exhibited low out-of-plane thermal conductivity of 1.1 ± 0.3 W m−1 K−1 which is lower than other layered materials composed of heavy atoms. This came from weak van der Waals interlayer interaction related to weak polarization in germanane composed of smaller atoms. This demonstrates that choice of small constituent atoms for weakening van der Waals interlayer interaction is a promising thermal conductivity reduction outline for developing ecofriendly high performance thermoelectric layered materials.

Chemistry of Germanene: Surface Modification of Germanane Using Alkyl Halides

Abstract: Two-dimensional materials attract enormous attention across several scientific fields. The current demands in nano- and optoelectronics, semiconductors, or in catalysis have been accelerating the research process in the field of 2D materials. Among the 14th group 2D materials besides graphene and silicene, layered germanium represents a promising candidate for another class of materials, and its functionalization represents a way to tune either its electronic or optical properties. Here, the exfoliation and functionalization of germanane surface is achieved via abstraction of hydrogen from Ge-H bond and its subsequent alkylation utilizing n-alkyl halides or trifluoromethyl (CF3) group containing benzyl halides. Composition of materials is confirmed by several methods including FT-IR, Raman, X-ray photoelectron, and energy-dispersive X-ray spectroscopy as well as X-ray powder diffraction. Scanning and transmission electron spectroscopy is used to reveal the layered morphology of functionalized germananes.

Towards Germanium Layered Materials as Superior Negative Electrodes for Li-, Na-, and K-Ion Batteries

Abstract: The germanium high theoretical capacity renders it as a promising anode material with 1384 mAh/g for Li (Li15Ge4) and 369 mAh/g for Na (NaGe) and K (KGe). Nevertheless, Ge suffers from volume variations due to alkali insertion, to mitigate this issue several strategies have been proposed. Among them the use of layered Ge-based phases, obtained from the CaGe2 Zintl phase by topotactic deintercalation of Ca to form the germanane (GeH)n. This last one has a particular morphology of Ge6 rings interconnected to form planes that buffers the volume changes and shortens the diffusion pathways. Here, we have studied the germanane alkali storage properties and 2150, 495 and 205 mAh/g of reversible capacity were obtained for Li, Na and K, respectively. These results indicate that germanane can store more alkali ions than the predicted phases, perform well at high rates and maintain a good

Influence of Surface Chemistry on Water Absorption in Functionalized Germanane

Abstract: The graphane analogues of group 14 are a unique family of 2D materials due to the necessity of a terminal ligand for stability. Here we highlight how changing the surface ligand can lead to nonobvi...

Structural, stability, electronic, optical and thermodynamic properties of hydrogenated germanene using first-principle calculations

Abstract: First-principle calculations are performed to study the structural, electronic, optical and thermodynamic properties of hydrogenated germanene (germanane) for most stable chair (C-), boat (B-) and tricycle (T-) structures. The band structure is studied under different hydrostatic pressures. The germanane shows metallic behavior at 30 GPa, 25 GPa and 12 GPa external pressures, respectively, for C-, B- and T-configurations. The calculated binding energy shows that germanane becomes unstable at 30 GPa, 25 GPa and 6 GPa for C-, B- and T-conformers, respectively. The thermodynamic properties of germanane are calculated in the temperature range of 5–1000 K and compared with germanene. The optical parameters such as dielectric constant, refractive index, birefringence, and plasmon energies ( ħ ωp) have been calculated for the first time. The calculated values are in good agreement with the experimental and reported values.

Thermally Induced Dehydrogenative Coupling of Organosilanes and H-Terminated Silicon Quantum Dots onto Germanane Surfaces

Abstract: Covalently bonded organic monolayers play important roles in defining the solution processability, ambient stability, and electronic properties of two-dimensional (2D) materials such as germanium n...

Hydrogen desorption from silicane and germanane crystals: Toward creation of free-standing monolayer silicene and germanene

Abstract: We investigate hydrogen desorptions from monolayer and multilayer graphane analogs, namely, silicane (SiH) and germanane (GeH), by the first-principles calculations. It is found from the calculated pressure–temperature diagrams of the monolayer and multilayer SiH and GeH crystals that the hydrogen atoms can be removed by heating and reducing hydrogen partial pressure. We also perform thermal-desorption-spectroscopy measurements for the multilayer crystals in order to demonstrate the validity of the theoretical calculations, and it turns out that the theoretical results are worth believing. Our theoretical results for monolayer SiH/GeH crystals indicate monolayer SiH and GeH crystals possess high potential to find their application as a precursor to free-standing monolayer silicene and germanene, respectively.

Properties of two-dimensional nanomaterials

Abstract: Materials having size between 1 and 100 nm, at least in one dimension, are known as nanomaterials. Two-dimensional (2D) materials are a special class of nanomaterials that are ultrathin, having only a single layer of atoms. Because of their large surface area, 2D layered nanomaterials exhibit special properties. The peculiar electronic properties of graphene drew a lot of attention toward the 2D structures. Other than graphene, 2D materials are hexagonal boron nitride (hBN), different transition metal chalcogenides, germanane, silicene, and phosphorene. The layered structures of 2D materials have properties to act as lubricants. These materials show a range of electronic properties and may be used in nanoelectronics, optoelectronics, catalysis, sensors, energy storage, and flexible devices in the future. In this chapter, some of the attributes, such as electronic, optoelectric, optical, electric, thermal, magnetic, and mechanical properties, have been discussed.

Tunable electronic structures of C2N/germanane van der waals heterostructures using an external electric field and normal strain

Abstract: Because the van der Waals (vdW) heterostructure offers unusual physical properties that can pave new ways toward design of nanoelectronic and optoelectronic devices, we have studied the electronic structures of C2N/germanane vdW heterostructures under vertical electric field and strain using density functional theory (DFT). It is found that metal-semiconductor phase transitions occurred at −0.4 and 0.8 V/A and band alignment transitions from type-Ⅱ to type-Ⅰ appeared at 0.1 and 0.4 V/A. Furthermore, we also found that band alignment transition from type-Ⅱ to type-Ⅰ emerged under in-plane biaxial strain of 3%. Our results indicated that C2N/germanane vdW heterostructures may offer a wide range of applications in new nanoelectronic and optoelectronic devices.

A Multi-Level Simulation Scheme for 2D Material-Based Nanoelectronics

Abstract: We present a scheme of multi-level simulation for 2D material-based nanodevices, which includes material parameterization, non-equilibrium Green's function (NEGF) device simulation, physics-based compact model, and circuit performance benchmark. A modified virtual source (VS) compact model is developed to capture unique carrier velocity and charge characteristics of 2D materials based on the quantum transport simulation results. HSPICE simulation is then performed for circuit analysis and device-circuit co-optimization. Using this framework, we achieve a minimum energy-delay product for germanane (GeH) field-effect transistor (FET) benchmark circuits by engineering power supply voltage and threshold voltage. The demonstrated multi-level process bridges the gap between device characteristics and circuit behaviors of 2D nanoelectronics, making it possible to evaluate 2D material-based electronic circuits on a solid foundation of unique 2D materials and their device physics.

Charge and spin transport in two-dimensional materials and their heterostructures

Abstract: Today, we live in a hi-tech world filled with electronic gadgets whose building blocks are field-effect transistors (FETs). FETs are made of semiconductors which are mostly silicon based. Over the past half-century, semiconductor industry has continually scaled down the semiconductor in FETs to make our electronic gadgets faster and smaller. However, we are nearing the physical scaling limit down to the size of individual atoms at which the semiconductor becomes unstable. To further continue scaling and increase performance of FETs, we need to explore new channel materials or new device concepts alternate to FETs, or a combination of these both. As part of my doctoral research, I have explored both the approaches: showcasing FETs of two-dimensional (2D) materials, and presenting an alternate device concept harnessing the spin property of electron. I report in my dissertation, for the first time, a FET fabricated of germanane – a new 2D semiconductor. Experimental results reveal unique electrical and optical properties for germanane with great potential for optoelectronics applications. To integrate the spin property of electron in the realm of FETs, I investigated heterostructures of 2D materials. In a heterostructure of WSe¬2 on single-layer graphene, the spins travelling in graphene along the in-plane direction were tuneable by applying an external electric field. And, in a heterostructure of WS2 and bi-layer graphene, the spins travelling in graphene along the in-plane and the out-of-plane directions showed different spin lifetimes. Both these observations are relevant in realising next generation of FETs, called Spin-FETs, to compute binary logic.