Germanene is a material made up of a single layer of

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...

atoms. The material is created in a process similar to that of

silicene Silicene is a two-dimensional allotrope of silicon, with a hexagonal honeycomb structure similar to that of graphene. Contrary to graphene, silicene is not flat, but has a periodically buckled topology; the coupling between layers in silicene is ...

and

graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.

, in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a substrate. High-quality thin films of germanene have revealed unusual two-dimensional structures with novel electronic properties suitable for semiconductor device applications and materials science research.

Preparation and structure

In September 2014, G. Le Lay and others reported the deposition of a single atom thickness, ordered and two-dimensional multi-phase film by

molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the devel ...

upon a

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...

surface in a

crystal lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by : \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...

with

Miller indices Miller indices form a notation system in crystallography for lattice planes in crystal (Bravais) lattices. In particular, a family of lattice planes of a given (direct) Bravais lattice is determined by three integers ''h'', ''k'', and ''� ...

(111). The structure was confirmed with

scanning tunneling microscopy A scanning tunneling microscope (STM) is a type of microscope used for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, then at IBM Zürich, the Nobel Prize in Physics in 1986. ...

(STM) revealing a nearly flat honeycomb structure. Additional confirmation was obtained by spectroscopic measurement and

density functional theory Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body ...

calculations. The development of high quality and nearly flat single atom films created speculation that germanene may replace

graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.

if not merely add an alternative to the novel properties of related nanomaterials. Bampoulis and others have reported the formation of germanene on the outermost layer of Ge₂Pt nanocrystals. Atomically resolved STM images of germanene on Ge₂Pt nanocrystals reveal a buckled honeycomb structure. This honeycomb lattice is composed of two hexagonal sublattices displaced by 0.2 Å in the vertical direction with respect to each other. The nearest-neighbor distance was found to be 2.5±0.1 Å, in close agreement with the Ge-Ge distance in germanene. Based on STM observations and density functional theory calculations, formation of an apparently more distorted form of germanene has been reported on

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...

. Epitaxial growth of germanene crystals on

GaAs Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circui ...

(0001) has also been demonstrated, and calculations suggest that the minimal interactions should allow germanene to be readily removed from this substrate. Germanene's structure is described as "a group-IV graphene-like two-dimensional buckled nanosheet". Adsorption of additional germanium onto the graphene-like sheet leads to formation of "

dumbbell The dumbbell, a type of free weight, is a piece of equipment used in weight training. It can be used individually or in pairs, with one in each hand. History The forerunner of the dumbbell, halteres, were used in ancient Greece as lifting w ...

" units, each with two out-of-plane atoms of germanium, one on either side of the plane. Dumbbells attract each other. Periodically repeating arrangements of dumbbell structures may lead to additional stable phases of germanene, with altered electronic and magnetic properties. In October 2018, Junji Yuhara and others reported that germanene is easily prepared by a segregation method, using a bare Ag thin film on a Ge substrate and achieved in situ its epitaxial growth. The growth of germanene, akin to graphene and silicene, by a segregation method, is considered to be technically very important for the easy synthesis and transfer of this highly promising 2D electronic material.

Properties

Germanene's electronic and optical properties have been determined from ''

ab initio ''Ab initio'' ( ) is a Latin term meaning "from the beginning" and is derived from the Latin ''ab'' ("from") + ''initio'', ablative singular of ''initium'' ("beginning"). Etymology Circa 1600, from Latin, literally "from the beginning", from ab ...

'' calculations, and structural and electronic properties from first principles. These properties make the material suitable for use in the channel of a high-performance

field-effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...

and have generated discussion regarding the use of elemental monolayers in other electronic devices. The electronic properties of germanene are unusual, and provide a rare opportunity to test the properties of

Dirac fermion In physics, a Dirac fermion is a spin-½ particle (a fermion) which is different from its antiparticle. The vast majority of fermions – perhaps all – fall under this category. Description In particle physics, all fermions in the standard model ...

s. Germanene has no

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...

, but attaching a hydrogen atom to each germanium atom creates one. These unusual properties are generally shared by

graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.

, germanene,

stanene Stanene is a topological insulator, theoretically predicted by Prof. Shoucheng Zhang's group at Stanford, which may display dissipationless currents at its edges near room temperature. It is composed of tin atoms arranged in a single layer, in a ...

, and plumbene.

References

External links

Meet Graphene's Sexy New Cousin Germanene
* ttp://www.newsledge.com/graphene-exciting-germanene-makes-appearance-9428 Graphene Family Tree? Germanene Makes Its Appearance* *{{Cite journal, title = Low-energy effective Hamiltonian involving spin-orbit coupling in silicene and two-dimensional germanium and tin, journal = Physical Review B, date = 1 January 2011, volume = 84, issue = 19, pages = 195430, doi = 10.1103/PhysRevB.84.195430, first = Cheng-Cheng, last = Liu, bibcode = 2011PhRvB..84s5430L, arxiv = 1108.2933, s2cid = 44216872
CNRS Website (2015)CNRS Website (2017)
Germanium Allotropes Group IV semiconductors Two-dimensional nanomaterials 2014 in science Substances discovered in the 2010s