Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron microscopy

Alem, Nasim; Erni, Rolf; Kisielowski, Christian; Rossell, Marta D.; Gannett, Will; Zettl, A.

doi:10.1103/physrevb.80.155425

Cited by 493 publications

(401 citation statements)

References 28 publications

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“…Atomically thin flakes of TMDCs can be peeled from their parent bulk crystals by micromechanical cleavage using adhesive tape 1,[29][30][31][32][33][34][35] , applied to substrates and optically identified by light interference 36,37 , using the same techniques that were developed for graphene. A bulk crystal of MoS 2 is shown in Fig.…”

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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699M any two-dimensional (2D) materials exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction, allowing exfoliation into individual, atomically thin layers 1 . The form receiving the most attention today is graphene, the monolayer counterpart of graphite. The electronic band structure of graphene has a linear dispersion near the K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics 2,3 . Graphene is a unique example of an extremely thin electrical and thermal conductor 4 , with high carrier mobility 5 , and surprising molecular barrier properties 6,7 .Many other 2D materials are known, such as the TMDCs 8,9 , transition metal oxides including titania-and perovskite-based oxides 10,11 , and graphene analogues such as boron nitride (BN) 12,13 . In particular, TMDCs show a wide range of electronic, optical, mechanical, chemical and thermal properties that have been studied by researchers for decades 9,14,15 . There is at present a resurgence of scientific and engineering interest in TMDCs in their atomically thin 2D forms because of recent advances in sample preparation, optical detection, transfer and manipulation of 2D materials, and physical understanding of 2D materials learned from graphene.The 2D exfoliated versions of TMDCs offer properties that are complementary to yet distinct from those in graphene. Graphene displays an exceptionally high carrier mobility exceeding 10 6 cm 2 V -1 s -1 at 2 K (ref. 16) and exceeding 10 5 cm 2 V -1 s -1 at room temperature for devices encapsulated in BN dielectric layers 5 ; because pristine graphene lacks a bandgap, however, fieldeffect transistors (FETs) made from graphene cannot be effectively switched off and have low on/off switching ratios. Bandgaps can be engineered in graphene using nanostructuring [17][18][19] , chemical functionalization 20 and applying a high electric field to bilayer graphene 21 , but these methods add complexity and diminish mobility. In contrast, several 2D TMDCs possess sizable bandgaps around 1-2 eV (refs 9,14), promising interesting new FET and optoelectronic devices.TMDCs are a class of materials with the formula MX 2 , where M is a transition metal element from group IV (Ti, Zr, Hf and so on), group V (for instance V, Nb or Ta) or group VI (Mo, W and so on), and X is a chalcogen (S, Se or Te). These materials form layered structures of the form X-M-X, with the chalcogen atoms in two hexagonal planes separated by a plane of metal atoms, as shown in Fig. 1a. Adjacent layers are weakly held together to form the bulk crystal in a variety of polytypes, which vary in stacking orders and metal atom coordination, as shown in Fig. 1e. The overall symmetry of TMDCs is hexagonal or rhombohedral, and the metal atoms have octahedral or trigonal prismatic coordination. The electronic properties of TMDCs range from metallic to semiconducting, as summarized in Table 1. There are also TMDCs that exhibit exotic behaviours such as charge density waves ...

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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“…Supporting this observation, theoretical calculations predict a higher formation energy for B monovacancies compared to N. 48,49 In contrast, high-resolution transmission electron microscopy (HRTEM) studies have reported recently the formation of point defects in h-BN single-layers, thinned down with a high-energy electron beam. 29,30,50,51 Strikingly, it seems that B vacancies are preferentially formed to N vacancies. It is obvious that, at present, the nature and formation of point defects in h-BN structures is an open unresolved subject on which rely many of its promising properties.…”

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Point defects in hexagonal BN, BC3 and BCxN compounds studied by x-ray absorption near-edge structure

Caretti

Jiménez

2011

Journal of Applied Physics

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The generation of point defects in highly oriented pyrolytic boron nitride (HOPBN) after Ar þ ion bombardment in ultrahigh vacuum and subsequent exposure to air was studied by angle-resolved x-ray absorption near edge structure (XANES). The pristine HOPBN showed well-oriented boron nitride (BN) basal planes parallel to the surface, with a negligible amount of defects. Amorphization of the BN structure took place after Ar þ sputtering, as indicated by the broadening of the XANES spectra and significant decrease of the characteristic p* states. Following air exposure, the XANES analysis revealed a spontaneous reorganization of the sample structure. The appearance of four new B1s p* excitonic peaks indicates an oxygen decoration process of the nitrogen vacancies created by ion bombardment. A core-level shift model is presented to support this statement. This model is successfully extended to the case of oxygen substitutional defects in hexagonal BC 3 and BC x N (0 < x < 4) materials, which can be applied to any B-based sp 2 -bonded honeycomb structure.

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“…C urrent research in layered materials primarily focuses on graphene [1][2][3][4][5][6][7][8][9][10] , insulating hexagonal boron nitride [11][12][13] , and members from the transition metal dichalcogenides (TMDCs) [14][15][16][17][18][19][20][21] family, such as molybdenum disulphide (MoS 2 ) and tungsten diselenide (WSe 2 ). Graphene transistors suffer from a low on-off current ratio because of its zero-bandgap nature.…”

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Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics

2014

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Graphene and transition metal dichalcogenides (TMDCs) are the two major types of layered materials under intensive investigation. However, the zero-bandgap nature of graphene and the relatively low mobility in TMDCs limit their applications. Here we reintroduce black phosphorus (BP), the most stable allotrope of phosphorus with strong intrinsic in-plane anisotropy, to the layered-material family. For 15-nm-thick BP, we measure a Hall mobility of 1,000 and 600 cm 2 V À 1 s À 1 for holes along the light (x) and heavy (y) effective mass directions at 120 K. BP thin films also exhibit large and anisotropic in-plane optical conductivity from 2 to 5 mm. Field-effect transistors using 5 nm BP along x direction exhibit an on-off current ratio exceeding 10 5 , a field-effect mobility of 205 cm 2 V À 1 s À 1 , and good current saturation characteristics all at room temperature. BP shows great potential for thin-film electronics, infrared optoelectronics and novel devices in which anisotropic properties are desirable.

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Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron microscopy

Cited by 493 publications

References 28 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Point defects in hexagonal BN, BC3 and BCxN compounds studied by x-ray absorption near-edge structure

Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics

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