Ultrasensitive, universal single-ion nanodetector

Abstract

In this paper, a carbon nanotube (CNT) based single-ion detector is proposed and its performance is evaluated with atomistic quantum transport models. The sensor can detect any ion type without molecule-specific functionalization and allows for continuous real-time ion monitoring. A single ion temporarily changes the operating principle of the sensor's CNT field-effect transistor into a resonant tunneling diode. The concrete device example of this paper showed a source-drain current increase of 5 orders of magnitude induced by a single ion.

Figures (5)

• Figure 1: Schematic of the CNT based single-ion detector: The side view in (a) shows the dimensions of the specific CNT FET structure considered in the main text. Ions within the CNT channel get detected when they enter the gate region as illustrated in (b).
• Figure 2: Drain-source current density of the single ion detector of Fig. \ref{['fig1']} with (red solid lines) and without (black dashed lines) a positive ion in the CNT channel under the gate. An ion with a charge of 1 e under the gate switches the device's performance from a standard FET characteristics to the one of a resonant tunneling diode. The negative differential resistance of the diode is highlighted in the linear-scale inset. The sensor's highest sensitivity is around the diode's current density peak at a gate bias of -0.2 V in the considered device.
• Figure 3: Conduction band energy (line) and contour graph of the spatially and energy resolved electron density along the surface of the CNT of Fig. \ref{['fig1']} at the resonant gate voltage of -0.2 V for (a) no ion in the CNT and (b) a positive ion centered in the CNT channel under the gate at 7.5 nm. The gate extends from 4.2 nm to 12.2 nm.
• Figure 4: Source-drain current density of the CNT sensor of Fig. \ref{['fig1']} as a function of the ion position centered in the channel along the CNT axis for a gate voltage of -0.2 V. The solid line is only meant to guide the eye. The dashed horizontal line shows the drain current without an ion in the channel. The dashed vertical lines indicate the gate region.
• Figure 5: Contour graph of the electron density of the first ion-induced quantum confined state at $E=0.059~\textit{eV}$ of Fig. \ref{['fig3']}(b) projected on the CNT surface. The positive ion is placed at the CNT center axis at x=7.5 nm.