Defect-induced room-temperature modulation in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">NbSe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Ramšak, N.; Midden, H. J. P. van; Prodan, A.; Marinković, V.; Boswell, F.W.; Bennett, J.C.

doi:10.1103/physrevb.60.4513

Cited by 8 publications

(9 citation statements)

References 11 publications

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“…[11][12][13][14] In contrast to the intensively studied 2H-NbSe 2 , 15,16 the 1T counterpart has not yet been synthesized either in bulk or as an ultrathin film. Although a 1T-like phase has been observed locally around defects [17][18][19] in thermally treated bulk samples, 20 Ag x Nb 2 Se 3 (Koslowski et al 21 ) and Nb 1 − x Ti x Se 2 (Di Salvo et al 22 ), it has been difficult to selectively fabricate a pristine sample of a single phase for precise physical measurements as well as for device applications. It is thus of great importance to fabricate an ultrathin film of pristine 1T-NbSe 2 and to investigate its electronic states to reveal as-yet-unknown electronic properties.…”

Section: Introductionmentioning

confidence: 99%

Monolayer 1T-NbSe2 as a Mott insulator

et al. 2016

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The emergence of exotic quantum phenomena is often triggered by a subtle change in the crystal phase. Transition metal dichalcogenides (TMDs) exhibit a wide variety of novel properties, depending on their crystal phases, which can be trigonal prismatic (2H) or octahedral (1T). Bulk NbSe 2 crystallizes into the 2H phase, and the charge density wave and the superconductivity emerge simultaneously and interact with each other, thereby creating various anomalous properties. However, these properties and their interplay in another polymorph, 1T-NbSe 2 , have remained unclear because of the difficulty of synthesizing it. Here we report the first experimental realization of a monolayer 1T-NbSe 2 crystal grown epitaxially on bilayer graphene. In contrast with 2H-NbSe 2 , monolayer 1T-NbSe 2 was found to be a Mott insulator, with an energy gap of 0.4 eV. We also found that the insulating 1T and metallic 2H phases can be selectively fabricated by simply controlling the substrate temperature during epitaxy. The present results open a path to crystal-phase engineering based on TMDs.

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Section: Introductionmentioning

confidence: 99%

Monolayer 1T-NbSe2 as a Mott insulator

et al. 2016

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“…Low-temperature scanning tunneling microscopy (STM) is ideally suited for the engineering and investigation of the atomically sharp phase boundaries, because of its unique ability not only to image materials’ surfaces with atomic resolution but also to manipulate matter at the atomic scale. ,,,− Here, we demonstrate STM-based phase engineering in NbSe 2 to create atomically sharp metal–insulator 2H–1T phase boundaries, which we investigate at temperatures as low as 4.5 K. The creation of a 1T phase is particularly intriguing because it has been believed to be thermodynamically unstable in bulk form . More recently, however, is was reported that 1T-NbSe 2 can be stabilized in nanometer-scale regions of NbSe 2 monolayers …”

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Nanoscale Phase Engineering of Niobium Diselenide

et al. 2017

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With continuing miniaturization in semiconductor microelectronics, atomically thin materials are emerging as promising candidate materials for future ultra-scaled electronics. In particular, the layered transition metal dichalcogenides (TMDs) have attracted significant attention due to the variety of their electronic properties, depending on the type of transition metal and its coordination within the crystal. Here, we use low-temperature scanning tunneling microscopy (STM) for the structural and electronic phase-engineering of the group-V TMD niobium diselenide (NbSe 2 ). By applying voltage pulses with an STM tip, we can transform the material crystal phase locally from trigonal prismatic (2H) to octahedral (1T), as confirmed by the concomitant emergence of a characteristic (√13x√13)R13.9° charge density wave (CDW) order. At 77 K atomic-resolution STM images of the junction with sub-lattice detail confirm the successful phase-engineering of the material, as we resolve the difference in the Nb coordination evidenced by a slip of the top Se plane. Different 1T-CDW intensities suggest interlayer interactions to be present in 1T-NbSe 2 . Furthermore, a distinct voltage dependence suggests a complex CDW mechanism that does not just rely on a Star-of-David reconstruction as in the case of other 1T-TMDs. Additionally, bias pulses cause surface modifications inducing local lattice strain that favors a one-dimensional charge order (1D-CDW) over the intrinsic 3 x 3 CDW at 4.5 K for 2H-NbSe 2 , which can be reversibly manipulated by STM.

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“…In another trichalcogenide, ZrTe 3 , a surface compositional modulation [6] was shown to be a result of ordered, surplus tellurium atoms, which occupied the interstitial positions on the (001) ZrTe 3 surface. Calculations within the extended Hückel tight binding (EHTB) approximation show that these tellurium atoms also account for the relatively high metallic conductivity of this compound.CDW domains of two orientational variants were detected at the edges of disk-like surface defects in NbSe 2 , which was an indication that the deformed regions of the Se-Nb-Se sandwiches assumed an octahedral rather than trigonal-prismatic coordination [7]. It was further shown that surface domain boundaries between orientational variants in the monoclinic NbTe 2 were often strongly modulated (Fig.2) with periodicities identical to those of the adjacent domains [8].…”

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confidence: 88%

“…CDW domains of two orientational variants were detected at the edges of disk-like surface defects in NbSe 2 , which was an indication that the deformed regions of the Se-Nb-Se sandwiches assumed an octahedral rather than trigonal-prismatic coordination [7]. It was further shown that surface domain boundaries between orientational variants in the monoclinic NbTe 2 were often strongly modulated (Fig.2) with periodicities identical to those of the adjacent domains [8].…”

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Scanning Tunneling Microscopy of Modulated Surface Structures

et al. 2002

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Modulated structures are commonly found in transition-metal chalcogenides with compositions between MX 4 and M 3 X 4 . Their origin is in the low-dimensional character of these compounds, which supports phenomena like charge density waves (CDW). These can be further stabilized at surfaces, where the bulk dimensionality is additionally reduced. Modern surface methods, combined with calculations of the electronic properties, can give a new insight into such phenomena.Two weak incommensurate modes, superimposed onto the main breathing mode, were discovered during the initial TEM studies of Nb 1-x Ta x Te 4 . They were detected at the NbTe 4 side of the phase diagram as weak and diffuse satellites in overexposed electron diffraction patterns [1]. Although a bulk phenomenon, these modes were for the first time successfully resolved by STM [2]. This was possible due to the preferential cleavage of the NbTe 4 crystals, which exposed complete tetragonal anti-prismatic columns. The weak transversal modes were observed as a surface phenomenon, superimposed onto the much stronger breathing mode (Fig.1).The observed sliding of two apparently independent low-temperature CDWs in NbSe 3 was recently explained on basis of a new model [3], which took into account statistically distributed nanodomains of both CDW modes. The results of earlier low-temperature STM [4] and satellite dark field TEM studies [5] were shown to be in a good accord with the model. It was further shown that sub-monolayer gold deposits on the NbSe 3 van der Waals surface exhibit poorly correlated modulated regions, whose periodicities are comparable to those of the two CDWs in pure NbSe 3 . In another trichalcogenide, ZrTe 3 , a surface compositional modulation [6] was shown to be a result of ordered, surplus tellurium atoms, which occupied the interstitial positions on the (001) ZrTe 3 surface. Calculations within the extended Hückel tight binding (EHTB) approximation show that these tellurium atoms also account for the relatively high metallic conductivity of this compound.CDW domains of two orientational variants were detected at the edges of disk-like surface defects in NbSe 2 , which was an indication that the deformed regions of the Se-Nb-Se sandwiches assumed an octahedral rather than trigonal-prismatic coordination [7]. It was further shown that surface domain boundaries between orientational variants in the monoclinic NbTe 2 were often strongly modulated (Fig.2) with periodicities identical to those of the adjacent domains [8]. In contrast to the modulation in NbSe 2 , the NbTe 2 modulation was interpreted on basis of a misfit between the domain boundaries across the van der Waals gaps. Finally, the Nb 3 X 4 (X = S, Se, Te) compounds, characterized by large hexagonal tunnels [9], were studied by means of TEM and STM. From the three compounds forming the family only Nb 3 Te 4 shows bulk conductivity anomalies at 95 K, which were attributed to a CDW with a modulation vector q = ±(1/3a* + 1/3b* + 3/7c*). Intercalation with indium and thallium raises th...

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Defect-induced room-temperature modulation inNbSe2

Cited by 8 publications

References 11 publications

Monolayer 1T-NbSe2 as a Mott insulator

Monolayer 1T-NbSe2 as a Mott insulator

Nanoscale Phase Engineering of Niobium Diselenide

Scanning Tunneling Microscopy of Modulated Surface Structures

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