Observation of interlayer phonon modes in van der Waals heterostructures

Lui, Chun Hung; Ye, Zhipeng; Ji, Chao; Chiu, Kuan Chang; Chou, Cheng Tse; Andersen, Trond I.; Means-Shively, Casie; Anderson, Heidi; Wu, Jiayi; Kidd, Tim; Lee, Yi Hsien; He, Rui

doi:10.1103/physrevb.91.165403

Cited by 191 publications

(223 citation statements)

References 58 publications

(88 reference statements)

Supporting

Mentioning

200

Contrasting

Order By: Relevance

“…In order to maintain a sufficient interlayer coupling, careful cleaning of the interface with suitable solvents, annealing procedures or performing the transfer process in inert atmosphere are possible routes. Interlayer coupling in vertical van der Waals heterostructures has been investigated by means of optical spectroscopy with reflectance [162] , photo-luminescence [161,[163][164][165] , electroluminescence [58] , and Raman-experiments [155] , by measurements of the photovoltaic effect [57,60] or by scanning tunneling spectroscopy [166,167] . bound bosonic quasiparticles called interlayer excitons (IX) can form.…”

Section: Optical Properties Of Tmdc Heterostructuresmentioning

confidence: 99%

Light–matter interaction in transition metal dichalcogenides and their heterostructures

Wurstbauer¹,

Miller²,

Parzinger³

et al. 2017

J. Phys. D: Appl. Phys.

104

View full text Add to dashboard Cite

Abstract:The investigation of two-dimensional van der Waals materials is a vibrant, fast moving and still growing interdisciplinary area of research. Two-dimensional van der Waals materials are truly two-dimensional crystals with strong covalent in-plane bonds and weak van der Waals interaction between the layers with a variety of different electronic, optical and mechanical properties. A very prominent class of twodimensional materials are transition metal dichalcogenides and amongst them particularly the semiconducting subclass. Their properties include bandgaps in the near-infrared to the visible range, decent charge carrier mobility together with high (photo-)catalytic and mechanical stability and exotic many body phenomena. These characteristics make the materials highly attractive for both fundamental research as well as innovative device applications. Furthermore, the materials exhibit a strong light matter interaction providing a high sun light absorbance of up to 15% in the monolayer limit, strong scattering cross section in Raman experiments and access to excitonic phenomena in van der Waals heterostructures. This review focuses on the light matter interaction in MoS2, WS2, MoSe2, and WSe2 that is dictated by the materials complex dielectric functions and on the multiplicity of studying the first order phonon modes by Raman spectroscopy to gain access to several material properties such as doping, strain, defects and temperature. Two-dimensional materials provide an interesting platform to stack them into van der Waals heterostructures without the limitation of lattice mismatch resulting in novel devices for application but also to study exotic many body interaction phenomena such as interlayer excitons. Future perspectives of semiconducting transition metal dichalcogenides and their heterostructures for applications in optoelectronic devices will be examined and routes to study emergent fundamental problems and manybody quantum phenomena under excitations with photons will be discussed.

show abstract

Section: Optical Properties Of Tmdc Heterostructuresmentioning

confidence: 99%

Light–matter interaction in transition metal dichalcogenides and their heterostructures

Wurstbauer¹,

Miller²,

Parzinger³

et al. 2017

J. Phys. D: Appl. Phys.

104

View full text Add to dashboard Cite

show abstract

“…[27][28][29] Meanwhile, the manually assembled bilayer generally has an incommensurate lattice structure due to the inevitable interlayer twist and/or lattice constant mismatch. This brings anomalous interlayer couplings which have profound effects on the transport, [14][15][16]30,31 optical 32-36 and Raman 37,38 properties of the bilayers. Moreover, recent theoretical studies have shown that the interlayer coupling together with the formation of a large scale moiré superlattice pattern can lead to the emergence of topological orders in a TMD heterobilayer.…”

Section: 13mentioning

confidence: 99%

Interlayer coupling in commensurate and incommensurate bilayer structures of transition-metal dichalcogenides

et al. 2017

View full text Add to dashboard Cite

The interlayer couplings in commensurate and incommensurate bilayer structures of transition metal dichalcogenides are investigated with perturbative treatment. The interlayer coupling in ±K valleys can be decomposed into a series of hopping terms with distinct phase factors. In H-type and R-type commensurate bilayers, the interference between the three main hopping terms leads to a sensitive dependence of the interlayer coupling strength on the translation, that can explain the position dependent local band gap modulation in a heterobilayer moiré superlattice. The interlayer couplings in the Γ valley of valence band and Q valley of conduction band are also studied, where the strong coupling strengths of several hundred meV can play important roles in mediating the ultrafast interlayer charge transfer in heterobilayers of transition metal dichalcogenides.

show abstract

“…1c, allows an estimation of the twist angle θ [5,7,[19][20][21][22]. For optical transitions in the parallel band model [19,20], the blue shift, intensity enhancement and width reduction of Raman peaks is attributed to van Hove singularities in the presence of weak interlayer interaction.…”

mentioning

confidence: 99%

“…In spite of subnanometer separation of the van der Waals gap (∼ 0.5 nm), the coupling of the two graphene layers in twisted bilayer graphene (tBLG) varies strongly with temperature (T ), and the twist or misorientation angle θ between the hexagonal lattices of participating graphene layers [1][2][3][4][5][6][7][8][9]. At T Θ BG , where Θ BG is the Bloch-Grüneisen temperature, the layers are coherently coupled either for θ 10…”

mentioning

confidence: 99%

“…The cross-plane thermovoltage which is nonmonotonic in both temperature and density, is generated through scattering of electrons by the out-of-plane layer breathing (ZO /ZA2) phonon modes and differs dramatically from the expected LandauerButtiker formalism in conventional tunnel junctions. The Tunability of cross-plane seebeck effect in van der Waals junctions may be valuable in creating a new genre of versatile thermoelectric systems with layered solidsIn spite of subnanometer separation of the van der Waals gap (∼ 0.5 nm), the coupling of the two graphene layers in twisted bilayer graphene (tBLG) varies strongly with temperature (T ), and the twist or misorientation angle θ between the hexagonal lattices of participating graphene layers [1][2][3][4][5][6][7][8][9]. At T Θ BG , where Θ BG is the Bloch-Grüneisen temperature, the layers are coherently coupled either for θ 10…”

mentioning

confidence: 99%

See 1 more Smart Citation

Seebeck Coefficient of a Single van der Waals Junction in Twisted Bilayer Graphene

et al. 2017

View full text Add to dashboard Cite

When two planar atomic membranes are placed within the van der Waals distance, the charge and heat transport across the interface are coupled by the rules of momentum conservation and structural commensurability, lead to outstanding thermoelectric properties. Here we show that an effective 'inter-layer phonon drag' determines the Seebeck coefficient (S) across the van der Waals gap formed in twisted bilayer graphene (tBLG). The cross-plane thermovoltage which is nonmonotonic in both temperature and density, is generated through scattering of electrons by the out-of-plane layer breathing (ZO /ZA2) phonon modes and differs dramatically from the expected LandauerButtiker formalism in conventional tunnel junctions. The Tunability of cross-plane seebeck effect in van der Waals junctions may be valuable in creating a new genre of versatile thermoelectric systems with layered solidsIn spite of subnanometer separation of the van der Waals gap (∼ 0.5 nm), the coupling of the two graphene layers in twisted bilayer graphene (tBLG) varies strongly with temperature (T ), and the twist or misorientation angle θ between the hexagonal lattices of participating graphene layers [1][2][3][4][5][6][7][8][9]. At T Θ BG , where Θ BG is the Bloch-Grüneisen temperature, the layers are coherently coupled either for θ 10• with a renormalized Fermi velocity [4,8], or at specific values of θ, such as θ = 30• ± 8.21• , when the hexagonal crystal structures become commensurate [1]. For θ > 10• (and away from the 'magic' angles), the layers are essentially decoupled at low T , but get effectively re-coupled at higher T (> Θ BG ), when the interlayer phonons drive cross-plane electrical transport through strong electron-phonon scattering [2,3]. These phonons are also expected to determine thermal and thermoelectric transport across the interface [10][11][12][13][14][15]. In fact, since the in-plane transverse and longitudinal phonons are effectively filtered out from contributing to cross-plane transport because they do not substantially alter the tunneling matrix elements, theoretical calculations predict enhanced cross-plane thermoelectric properties in van der Waals heterojunctions, including high ZT factors at room temperature [12]. However, although the impact of interlayer coherence and electron-phonon interaction on electrical conductance has been studied in detail [1,3], their relevance to the thermal and thermoelectric properties of tBLG remains unexplored.We assembled the tBLG devices with layer-by-layer mechanical transfer method, which is common in van der Waals epitaxy [16][17][18]. Three devices were constructed which show very similar behavior, and we present the results from one of the devices here. The device consists of two graphene layers oriented in a "cross" configuration (inset of Fig. 1a and an optical micrograph in Fig. 1b), and entirely encapsulated within two layers of hexagonal boron nitride (hBN). The carrier mobilities in the upper and lower layers are ≈ 25000 cm 2 V −1 s −1 and ≈ 60000 cm 2 V −1 s −1 , at room tem...

show abstract

Observation of interlayer phonon modes in van der Waals heterostructures

Cited by 191 publications

References 58 publications

Light–matter interaction in transition metal dichalcogenides and their heterostructures

Light–matter interaction in transition metal dichalcogenides and their heterostructures

Interlayer coupling in commensurate and incommensurate bilayer structures of transition-metal dichalcogenides

Seebeck Coefficient of a Single van der Waals Junction in Twisted Bilayer Graphene

Contact Info

Product

Resources

About