(Color online) Conceptual illustration of electrode fabrication sequence. First, a carbon fiber is placed perpendicular to the nanofibers (a) to define the electrode gaps, and a TEM grid is placed to define the electrodes (b). The first electrode material is deposited at −18° relative to the sample normal (c) followed by the second electrode material deposited at (d). When both shadow masks are removed, electrode gaps between two different contact materials have been defined (e). The device width is approximately .
Close-up SEM image of nanofibers contacted with Au (left) and Sm (right) electrodes. The device length is , and the broadening of the Au edge is .
(Color online) Semilog plot of the measured current vs applied voltage characteristics of six representative devices. The measured data are shown as red circles, while the full curve is a model fit to the measured data. The labels on the curves are device lengths in units of . The characteristics of the two longest devices may deviate due to variation in effective cross sectional area.
Schematic energy diagram of a forward biased device. An energy barrier of height , a small distance from the Sm cathode, is formed. The distance between cathode and energy barrier peak, , is exaggerated for clarity. A small negative Sm contact barrier is assumed. The current is due to electrons emitted above this barrier and drifted across the anode region of length .
(Color online) Measured voltage times measured current vs measured current times device length for seven different devices with lengths from 0.36 to . The data (●) are corrected for the estimated relative cross-sectional area , for all devices is of the order 1. Also shown as a full line is the model of Eq. (3) and as seen the agreement is excellent.
(Color online) Characteristic voltage as a function of device length (black dots) extracted from the characteristic of all devices. The horizontal error bars represent the range from minimum to maximum measured device length. Vertical error bars are drawn but are too small to be visible. Every device is measured several times, and the blue triangles represent the mean extracted value for every device. The full line is a linear fit to the data.
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