Fast and reliable identification of atomically thin layers of TaSe2 crystals

Abstract

Deposition of clean and defect-free atomically thin two-dimensional crystalline flakes on surfaces by mechanical exfoliation of layered bulk materials has proven to be a powerful technique, but it requires a fast, reliable and non-destructive way to identify the atomically thin flakes among a crowd of thick flakes. In this work, we provide general guidelines to identify ultrathin flakes of TaSe 2 by means of optical microscopy and Raman spectroscopy. Additionally, we determine the optimal substrates to facilitate the optical identification of atomically thin TaSe 2 crystals. Experimental realization and isolation of ultrathin layers of TaSe 2 enables future studies on the role of the dimensionality in interesting phenomena such as superconductivity and charge density waves. KEYWORDSatomically thin layer, metal dichalcogenide, layered superconductor, TaSe 2 , optical microscopy, Raman spectroscopy This is the post-peer reviewed version of the following article: A.Castellanos-Gomez et al. "Fast and reliable identification of atomically thin layers of TaSe 2 crystals".2 thoroughly characterized, [16][17][18][19][20] most of other possible two-dimensional (2D) crystals with attractive properties remain barely explored. For instance, layered transition metal dichalcogenides with the formula MX 2 (M = Mo, W, Nb, Ta or Ti and X = Se, S or Te) present a broad variety of electrical properties ranging from wide band-gap semiconductors to superconductors. As in the case of graphene, while fabrication by mechanical exfoliation from bulk crystals of these layered materials is rather simple,[2] identification of atomically thin flakes requires fast, reliable and non-destructive characterization techniques. [21][22][23][24][25][26][27] The realization of ultrathin superconducting layers would enable one to employ the electric field effect to control physical properties such as the superconducting transition temperature or to study the interplay between the superconductivity and the sample dimensionality. However, among the family of transition metal dichalcogenides, the studies on atomically thin superconducting layers are scarce and mainly focused on NbSe 2 and TaS 2 crystals. [3, 4,28] TaSe 2 is a good example of a layered material which has not been studied in its This is the post-peer reviewed version of the following article: A.Castellanos-Gomez et al. "Fast and reliable identification of atomically thin layers of TaSe 2 crystals".3 one end of the ampoule and the latter was exhaustively evacuated and flame-sealed. The quartz tube was finally placed inside a three-zone split muffle where a gradient of 25 ºC was established between the leftmost load (725 ºC) and central growth (700 ºC) zones. A gradient of 25 ºC was also set between the rightmost and central regions. The temperature gradient was maintained constant during 15 days and the muffle was eventually switched off and left to cool down at ambient conditions. Millimetric TaSe 2 crystals were recovered from the ampoule's central zone, exhaustively rinsed with diethyl e...

Phonon and thermal properties of exfoliated TaSe2 thin films

“…Comparison of our data with that in Ref. [33] indicates that the peak positions and mode assignments are consistent.…”

Fast and Broadband Photoresponse of Few-Layer Black Phosphorus Field-Effect Transistors

“…The metallic leads were patterned after selection of thin regions in the flake by optical contrast. 19 The topography of the fabricated devices is studied by atomic force microscopy ( Figure 1b). The measured height of the flake shown in Figure 1b is 8 nm, corresponding to 15 layers of b-P. Figure 1c shows a Raman spectrum of the flake in which the three peaks characteristic for pristine black phosphorus can clearly be identified.…”

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

“…Deposition of products in the form of single crystals is driven by a temperature gradient between the source and the growth regions [49]. Bulk CDW materials such as 1T-VSe2 [50], 1T-TaSe2 [28], 2H-TaSe2 [5,51] and 2H-NbSe2 [52] have been reported by the CVT method in recent years. For synthesis of 2D CDW materials, recently, J. Wang et al reported controlled synthesis of two-dimensional 1T-TiSe2 on sapphire substrates with sub-10-nm thickness [53] (Figure 5).…”

“…Transition metal dichalcogenides (TMDs) are a group of layered materials that has renewed interest due to their 2D confined structures [4,5]. TMDs disclose a variety of fascinating properties including semiconducting [6][7][8], superconducting [9], charge density waves (CDWs) [10,11], and so on.…”