Abstract
Various intriguing quantum transport measurements for carbon nanotubes (CNTs) based on their unique electronic band structures have been performed adopting a field-effect transistor (FET), where the contact resistance represents the interaction between the one-dimensional and three-dimensional systems. Recently, van der Waals (vdW) gap tunneling spectroscopy for single-walled CNTs with indium–metal contacts was performed adopting an FET device, providing the direct assignment of the subband location in terms of the current–voltage characteristic. Here, we extend the vdW gap tunneling spectroscopy to multi-walled CNTs, which provides transport spectroscopy in a tunneling regime of ~1 eV, directly reflecting the electronic density of states. This new quantum transport regime may allow the development of novel quantum devices by selective electron (or hole) injection to specific subbands.
Highlights
The main difference from a conventional field-effect transistor (FET) with Ohmic contacts is the existence of the van der Waals (vdW) gap between the source and multi-walled CNTs (MWCNTs)
Electrons in the source electrode start to tunnel into the MWCNT though the vdW gap, resulting in a current (I) flow, and the differential conductance at a given V sd is proportional to the density of states (DOS) in the MWCNT
Contact forms a vdW interface, i.e., the electronic DOS of an MWCNT is conserved at the interface, with a vdW vacuum gap
Summary
For the vdW metal–semiconducting transition metal chalcogenide (TMDC) junctions, the non-perturbed interface allows a tunable Schottky barrier height with various metals having different work functions, following the Schottky–Mott rule [1]. In this case, to achieve vdW contacts between metals and TMDC, metals are mechanically transferred to the TMDC flakes. It has been revealed that thermally evaporated In metal on TMDCs can provide the vdW interface with good contact resistance, contrary to other metals evaporated with high evaporation energy, inducing atomic defects in the TMDC layers [2,3,4,5]. For single-walled carbon nanotubes (SWCNTs), the In/SWCNT vdW interface functions as a vacuum gap, allowing vdW gap tunneling spectroscopy for the electronic band in SWCNTs [6]
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