Electronic properties of two-dimensional hexagonal germanium

Houssa, Michel; Pourtois, Geoffrey; Afanas’ev, Valery V.; Stesmans, André

doi:10.1063/1.3332588

Cited by 126 publications

(84 citation statements)

References 17 publications

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“…The synthesis of monolayer graphene [1][2][3] not only gave researchers, for the first time, access to a quasi-twodimensional (2D) crystal, but it also drew significant attention to similar single-atomic-layer structures such as silicene [4,5], germanene [5][6][7], and transition-metal dichalcogenides (TMDCs) [8,9]. Following advances in delamination, techniques of bulk materials opened the possibility of the synthesis of novel monolayer structures having new functionalities and their use in various fields of nanotechnology.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast to the abundant literature on graphene-like ultrathin structures, few-layer alkaline-earth-metal hydroxides (AEMHs) have not been investigated so far. Bulk forms of AEMHs are layered structures belonging to the P 3m1 space group [10] and the crystal structure of a layered AEMHs comprises stacked sheets of MO 6 (M = alkaline-earth metals) edge-sharing octahedra (see Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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Portlandite crystal: Bulk, bilayer, and monolayer structures

et al. 2015

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Ca(OH) 2 crystals, well known as portlandite, are grown in layered form, and we found that they can be exfoliated on different substrates. We performed first principles calculations to investigate the structural, electronic, vibrational, and mechanical properties of bulk, bilayer, and monolayer structures of this material. Different from other lamellar structures such as graphite and transition-metal dichalcogenides, intralayer bonding in Ca(OH) 2 is mainly ionic, while the interlayer interaction remains a weak dispersion-type force. Unlike well-known transition-metal dichalcogenides that exhibit an indirect-to-direct band gap crossover when going from bulk to a single layer, Ca(OH) 2 is a direct band gap semiconductor independent of the number layers. The in-plane Young's modulus and the in-plane shear modulus of monolayer Ca(OH) 2 are predicted to be quite low while the in-plane Poisson ratio is larger in comparison to those in the monolayer of ionic crystal BN. We measured the Raman spectrum of bulk Ca(OH) 2 and identified the high-frequency OH stretching mode A 1g at 3620 cm −1 . In this study, bilayer and monolayer portlandite [Ca(OH) 2 ] are predicted to be stable and their characteristics are analyzed in detail. Our results can guide further research on ultrathin hydroxites.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Portlandite crystal: Bulk, bilayer, and monolayer structures

et al. 2015

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“…[1][2][3] Due to this remarkable achievement, a new field of quasi-two-dimensional (2D) materials has emerged which changed the perspective of materials research. Since then, the attention of material science and condensed matter physics has been widened towards new single layer structures such as silicene 4,5 , germanene [5][6][7] , transition-metal dichalcogenides (TMDs) [8][9][10][11] , alkaline-earth-metal hydroxide (AEMHs) 12 and post-transition metal chalcogenides (PTMCs).…”

Section: Introductionmentioning

confidence: 99%

Optical properties of GaS-Ca(OH)2bilayer heterostructure

2016

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Finding novel atomically-thin heterostructures and understanding their characteristic properties are critical for developing better nanoscale optoelectronic devices. In this study, we investigate the electronic and optical properties of GaS-Ca(OH) 2 heterostructure using first-principle calculations.The band gap of the GaS-Ca(OH) 2 heterostructure is significantly reduced when compared with those of the isolated constituent layers. Our calculations show that the GaS-Ca(OH) 2 heterostructure is a type-II heterojunction which can be used to separate photoinduced charge carriers where electrons are localized in GaS and holes in the Ca(OH) 2 layer. This leads to spatially indirect excitons which are important for solar energy and optoelectronic applications due to their long lifetime. By solving the Bethe-Salpeter equation on top of single shot GW calculation (G 0 W 0 ) the dielectric function and optical oscillator strength of the constituent monolayers and the heterostructure are obtained. The oscillator strength of the optical transition for GaS monolayer is an order of magnitude larger than Ca(OH) 2 monolayer. We also found that the calculated optical spectra of different stacking types of the heterostructure show dissimilarities, although their electronic structures are rather similar. This prediction can be used to determine the stacking type of ultra-thin heterostructures.

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“…18 A Raman shift of about 290 cm −1 has been predicted from ab initio studies. [19][20][21][22][23][24] Germanene appears to be a unique material that does not exist in nature. However, due to the possibility of germanene being more facilely integrated into Si nanotechnology than graphene, 16,25 development of synthetic methods for its formation are of interest.…”

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confidence: 99%

Electrochemical Formation of Germanene: pH 4.5

Ledina

Bui

Liang

et al. 2017

J. Electrochem. Soc.

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Germanene is a single layer allotrope of Ge, with a honeycomb structure similar to graphene. This report concerns the electrochemical formation of germanene in a pH 4.5 solution. The studies were performed using in situ Electrochemical Scanning Tunneling Microscopy (EC-STM), voltammetry, coulometry, surface X-ray diffraction (SXRD) and Raman spectroscopy to study germanene electrodeposition on Au(111) terraces. The deposition of Ge is kinetically slow and stops after 2–3 monolayers. EC-STM revealed a honeycomb (HC) structure with a rhombic unit cell, 0.44 ± 0.02 nm on a side, very close to that predicted for germanene in the literature. Ideally the HC structure is a continuous sheet, with six Ge atoms around each hole. However, only small domains, surrounded by defects, of this structure were observed in this study. The small coherence length and multiple rotations domains made direct observation with surface X-ray diffraction difficult. Raman spectroscopy was used to investigate the multi-layer Ge deposits. A peak near 290 cm−1, predicted to correspond to germanene, was observed on one particular area of the sample, while the rest resembled amorphous germanium. Electrochemical studies of germanene showed limited stability when exposed to oxygen.

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Electronic properties of two-dimensional hexagonal germanium

Cited by 126 publications

References 17 publications

Portlandite crystal: Bulk, bilayer, and monolayer structures

Portlandite crystal: Bulk, bilayer, and monolayer structures

Optical properties of GaS-Ca(OH)2bilayer heterostructure

Electrochemical Formation of Germanene: pH 4.5

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