Figure 1

An intentional misalignment of the two Pyrex slides (a) results in asymmetric nanoslot entrances to the microchambers, as seen in the optical microscope image (b) (top view—normal to the uniform nanoslot depth $h=190\mathrm{nm}$). On the right side, the separate nanoslots exit directly into the microchamber, while on the left side, they first merge into a wide slot which in turn exits into the microchamber. The influx direction associated with the different voltage biases represents the flow direction of the counterions into the nanoslot. The geometric parameters of the slot are $d_1=50\mu \mathrm{m}$, $d_2=450\mu \mathrm{m}$, $w_1=350\mu \mathrm{m}$, $w_2=100\mu \mathrm{m}$, based on the simplified theoretical model depicted in (c) (top view) which represents one cell of a periodic array (in the $y$-direction) of the actual asymmetric (in the $x$ direction) nanoslot array (b).Reuse & Permissions

Figure 2

Numerical computation results for the concentration and voltage profiles across the asymmetric periodic cell [Fig. 1c] below (a) and beyond (b) the limiting current $I_L$. The electric resistance clearly shifts from the nanoslot in (a) to a small polarized layer at the left anodic entrance in (b), which is blown up in (c). Note that $c^{-}$ and $c^{+}$ are identical outside the nanoslot (electroneutrality condition) except for the small polarized layer (c). Increase of the rectification factor with the voltage is depicted in part (d) of the figure. Reverse bias profiles are qualitatively similar but of opposite concentration and voltage trends. The normalized values of $\Sigma /c_0=2$, $(d_1+d_2)/L=1$, $\delta =\lambda /L=2\times {10}^{-5}$, and $h/L=3.8\times {10}^{-4}$ have been used.Reuse & Permissions

Figure 3

(a) I–V measurements of the device in Fig. 1 for varying ionic strengths and applied voltages (continuous lines: reverse bias; dashed lines: forward bias). Upper (1–3) and lower (4–6) insets of part (a) of the figure depict the evolution (at three time instances) of the depletion-enrichment phenomenon under forward and reverse 30 V bias, respectively. In the former, the depletion layer evolves at the left hand side of the nanoslot, while the opposite in the latter. (b) The measured rectification factor versus voltage for the data in part (a) of the figure. Inset depicts the conductance of the nanoslot array as a function of solution concentration [symbols—experiment; continuous line—model (Eq. 13, 13); dashed line—bulk conductivity {model (Eq. 13, 13) with $\Sigma =0$}]. A fitted value of $|\sigma |=21.7\mathrm{mC}/{\mathrm{m}}^2$ (corresponding to a fixed volume charge density $zF\Sigma =-2\sigma /h$ of about $\sim 229\mathrm{KC}/{\mathrm{m}}^3$, wherein $z$ denotes the ion valency and $F$ the Faraday number) was obtained for the surface charge density.Reuse & Permissions

Figure 4

Comparison of I–V measurements under reverse bias of the seven-nanoslot array (solid line) versus seven times the current measured across an isolated single nanoslot device (dotted line). The upper (1) and lower (2) insets depict the depletion-enrichment phenomenon under reverse 40 V bias for a single versus a nanoslot periodic array, respectively.Reuse & Permissions