Experimental setup. The etched anode tip is biased at a positive bias by a high-voltage source-measurement unit (SMU). Series resistor is positioned near the tip and limits the current flow to prevent fast transients from destroying the nanowire.
(a) Dark-field TEM image showing typical iron nanowire with a core diameter of about . (b) SEM micrograph of a carbon nanowire with corrugated surface grown from acetylene.
Schematic of dissociation processes near the growing nanowire tip. The dashed line illustrates the cone of electrons emitted from the tip. Neutral carbon atoms intercepted by the wire form the amorphous overcoat.
Multiply forked tungsten nanowires. (a) After step 1, and (b) after step 4 (see text). The thicker portions result from overcoating using tetramethyl silane precursor. The point labeled “X” refers to the same point in (a) and (b).
Schematic of experiment. (a) After step 1, (b) step 2, (c) step 3, and (d) step 4. The gray shaded areas represent material deposited using a tetramethyl silane precursor.
Typical selective-area diffraction pattern of nanowires grown from precursor, indexed with most probably planes.
Energy-loss images of nanowires grown from precursor, depicting the spatial distributions of (a) carbon, and (b) oxygen.
(a) Image of a nanowire at a branch junction. The overcoat is thickest on the side facing the growing tip front that is located beyond the top of the image. The underside of the branch has almost no overcoat. (b) Typical dark-field image of tungsten nanowire. Regions of strong diffraction contrast are observed in all portions of the nanowire, while the carbonaceous overcoat exhibits diffused scattering.
High-resolution image at the interface between the tungsten core and amorphous overcoat showing the lattice spacing and its corresponding bulk Miller index.
Average tungsten core diameter and thickness of carbonaceous overcoat of as-grown nanowires vs growth current.
Average grain size at different growth currents determined via dark-field imaging.
Nanowire length vs growth current for growth at 1 and chamber pressures.
Schematic showing the relative contributions to axial and radial growth for ions generated close to the emission tip, and those generated further away from the tip.
Plot of reciprocal length vs reciprocal growth current using the data from Fig. 13 for growth at chamber pressure.
Growth volume for growth, normalized by the growth current. Error in estimation primarily arises from the uncertainty in the overcoat thickness.
Illustration of electron impact ionization cross section along the space between the cathode and the anode for anode voltages of 50 and .
Number of tips observed to initiate and grow at different currents for a series of repeated experiments.
TEM images showing typical branching morphology of nanowires grown at (a) currents greater than , and (b) currents below with little evidence of branching.
Nanowire grown from at shows a thin wire at the base growing to a thick bulge toward the tip.
Precursors for nanowire growth.
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