Unusual Angular Dependence of the Raman Response in Black Phosphorus

Ribeiro, Henrique B.; Pimenta, M. A.; Matos, Christiano J. S. de; Moreira, R. L.; Родин, Александр; Zapata, Juan D.; Souza, E. A. Thoroh de; Neto, A. H. Castro

doi:10.1021/acsnano.5b00698

Cited by 313 publications

(434 citation statements)

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“…Measurement of bulk flakes has the added advantage of minimizing the well-known degrading oxidation effects of Te-based TMDs [35]. XRD [18,36] as well as studies of other layered TMD materials [37]. The Raman peaks for certain phonon modes show particular sensitivity to x and lattice symmetry.…”

Section: Introductionmentioning

confidence: 99%

The structural phases and vibrational properties of Mo _1−x W _x Te ₂ alloys

Oliver¹,

Beams²,

Krylyuk³

et al. 2017

2D Mater.

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The structural polymorphism in transition metal dichalcogenides (TMDs) provides exciting opportunities for developing advanced electronics. For example, MoTe 2 crystallizes in the 2H semiconducting phase at ambient temperature and pressure, but transitions into the 1T′ semimetallic phase at high temperatures. Alloying MoTe 2 with WTe 2 reduces the energy barrier between these two phases, while also allowing access to the T d Weyl semimetal phase. The −RECEIVED

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Section: Introductionmentioning

confidence: 99%

The structural phases and vibrational properties of Mo _1−x W _x Te ₂ alloys

Oliver¹,

Beams²,

Krylyuk³

et al. 2017

2D Mater.

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“…1c, corresponding to the A g 1 , B 2g and A g 2 modes 24 . Following similar analysis done by Riberio et al, 24 we confirm that the long straight edges of the crystal is indeed along the zigzag direction consistent with recent transmission electron microscopy analysis 25 .…”

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confidence: 99%

Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

et al. 2017

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Two-dimensional materials offer new opportunities for both fundamental science and technological applications, by exploiting the electron's spin 1 . While graphene is very promising for spin communication due to its extraordinary electron mobility, the lack of a band gap restricts its prospects for semiconducting spin devices such as spin diodes and bipolar spin transistors 2 . The recent emergence of 2D semiconductors could help overcome this basic challenge. In this letter we report the first important step towards making 2D semiconductor spin devices. We have fabricated a spin valve based on ultra-thin (~ 5 nm) semiconducting black phosphorus (bP), and established fundamental spin properties of this spin channel material which supports all electrical spin injection, transport, precession and detection up to room temperature (RT). Inserting a few layers of boron nitride between the ferromagnetic electrodes and bP alleviates the notorious conductivity mismatch problem and allows efficient electrical spin injection into an n-type bP. In the non-local spin valve geometry we measure Hanle spin precession and observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 µm. Our experimental results are in a very good agreement with first-principles calculations and demonstrate that Elliott-Yafet spin relaxation mechanism is dominant. We also demonstrate that spin transport in ultra-thin bP depends strongly on the charge carrier concentration, and can be manipulated by the electric field effect. 2 Electron spin is an important degree of freedom which can complement or even replace charge in information storage and logic devices 3 . For spin-based electronics, it is essential to have materials with long spin relaxation times at RT 1 . With respect to the material selection, semiconductors in particular offer new opportunities that are unfeasible in metal-based spintronics devices. These include doping by the electric field effect and gate controlled amplification/switching actions 4 . The boom of semiconductor spintronics started with the demonstration of the electrical spin injection into GaAs by R. Fiederling et al., also later by H.Ohno et al. 5,6 . I. Appelbaum and his colleagues further fostered this by adding silicon into the spintronics materials family 7 . More recently 2D materials such as graphene have captured the interest of engineers and scientists on the grounds of their high electronic mobility and the simultaneous ability to tune their charge carrier concentrations by the electric field effect 8 .Graphene has already been investigated very extensively in the spintronics community since the first unequivocal demonstration of RT spin injection by N. Tombros et al., 1,9 . While the first devices showed spin lifetimes of only 0.1 ns 9 , the new generation of graphene devices that have surfaces within the last year show remarkable spin lifetimes of ~ 10 ns, making graphene suitable for spin communication channels 10 .Conversely, the zero-band gap nature of graphene does not al...

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“…One of them is Raman active (labeled as A g 2 ) with its measured frequency in the range from 463 to 470 cm −1 and the other one (label as B 2u ) is infrared (IR) active with its frequency from 468 to 470 cm −1 . 4,5,[9][10][11][12] The two modes also exist in monolayer phosphorene, as illustrated in the inset of Figure 1. Raman experiments on few-layer phosphorenes have shown that the frequency shift of the A g 2 mode from that of bulk is about 2-3 cm −1 or smaller.…”

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confidence: 88%

“…Raman experiments on few-layer phosphorenes have shown that the frequency shift of the A g 2 mode from that of bulk is about 2-3 cm −1 or smaller. 4,5,[9][10][11]13 While there has been no IR measurement on monolayer phosphorene, it is reasonable to expect that the two modes remain nearly degenerate (possibly within a couple of wavenumbers). A recent experiment 9 has observed the splitting of the A g 2 mode in bilayer graphene and proposed that it could be caused by such accidental degeneracy, while other experiments did not report such splitting.…”

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Communication: Effect of accidental mode degeneracy on Raman intensity in 2D materials: Hybrid functional study of bilayer phosphorene

Sun

Zhang

2016

The Journal of Chemical Physics

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Bulk black phosphorus has two optical phonon modes labeled as Ag2 and B2u, respectively, that are nearly degenerate in frequency. However, density functional theory calculations using local or semi-local functionals cannot reproduce this degeneracy. Here, we propose a hybrid functional approach aided by van der Waals (vdW) force fields, which can accurately describe the lattice dynamic and electronic properties of both bulk and few-layer black phosphorus (phosphorene). Using this approach we show that in bilayer phosphorene, the two Raman modes derived from the B2u and Ag2 modes could exhibit strong resonance as a result of the accidental degeneracy so that both modes could be observed in Raman experiment. Without the mode degeneracy, however, the Raman intensity of the B2u-derived mode would be too weak to be observed. We further show that the accidental degeneracy is correlated to the applied strain, which enables Raman spectroscopy to be a powerful tool for characterizing built-in strains in 2D materials, e.g., due to the interaction with substrates, which has emerged as an important issue in vdW epitaxy.

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Unusual Angular Dependence of the Raman Response in Black Phosphorus

Cited by 313 publications

References 34 publications

The structural phases and vibrational properties of Mo _1−x W _x Te ₂ alloys

The structural phases and vibrational properties of Mo _1−x W _x Te ₂ alloys

Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

Communication: Effect of accidental mode degeneracy on Raman intensity in 2D materials: Hybrid functional study of bilayer phosphorene

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Unusual Angular Dependence of the Raman Response in Black Phosphorus

Cited by 313 publications

References 34 publications

The structural phases and vibrational properties of Mo 1−x W x Te 2 alloys

The structural phases and vibrational properties of Mo 1−x W x Te 2 alloys

Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

Communication: Effect of accidental mode degeneracy on Raman intensity in 2D materials: Hybrid functional study of bilayer phosphorene

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Product

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The structural phases and vibrational properties of Mo _1−x W _x Te ₂ alloys

The structural phases and vibrational properties of Mo _1−x W _x Te ₂ alloys