Felling of individual freestanding nanoobjects using focused-ion-beam milling for investigations of structural and transport properties

Abstract

We report that, to enable studies of their compositional, structural and electrical properties, freestanding individual nanoobjects can be selectively felled in a controllable way by the technique of low-current focused-ion-beam (FIB) milling with the ion beam at a chosen angle of incidence to the nanoobject. To demonstrate the suitability of the technique, we report results zigzag/straight tungsten nanowires grown vertically on support substrates and then felled for characterization. We also describe a systematic investigation of the effect of the experimental geometry and parameters on the felling process and on the induced wire-bending phenomenon. The method of felling freestanding nanoobjects using FIB is an advantageous new technique for enabling investigations of the properties of selected individual nanoobjects.

Low-Current Focused Ion Beam Milling for Freestanding Nanomaterial Characterization

“…In the inset is the R -T curve for the low-temperature region, from which the superconducting transition temperature ( T c ) was derived to be of 5.2 K. Here T c is defi ned as the temperature at which the resistance falls to 50 % of its value at the onset of the transition. The room-temperature resistivity of the zigzag nanowire was calculated to be about 520 μΩ cm, a value similar to that of an air-bridge structure also grown by 1 pA ion beam current [ 19 ]. The results reveal that felling freestanding nanowires using 1 pA ion beam current does not affect their intrinsic electrical properties.…”

“…Alternatively, the ion beam may be raster-scanned repeatedly over a rectangular area, fi rst across the area in one direction and then back in the other direction; if the scan speed in one of the dimensions across the wire is slow, then a zigzag profi le results. The growth details can be found in [ 19 ]. Figure 3.1a shows the schematic confi guration of the relative position of the FIB and SEM columns, substrate, and GIS.…”

“…For measurements of transport properties, patterns for the electrical contacts can be fabricated by using electron beam lithography and/or photolithography [ 14 ] onto a selected individual nanowire and then metallic layers can be deposited by electron is an FIB image of the freestanding nanowire shown in ( a ) with the ion beam normal to its length and parallel to the support substrate surface; ( c ) the nanowire has been felled away from the incident ion beam and is lying on the substrate surface close to its base, with the top downwards [ 19 ] beam evaporation, thermal evaporation, or sputtering, followed by lift-off. FIB-induced deposition of Pt [ 7 , 20 ] and W [ 7 ] composites can be used to direct-write electrical connection and contact pads on individual nanowires.…”

“…3.4c that the shape and size of the wire are unchanged. After felling onto the substrate surface, FIB-induced deposition was used to fabricate contact pads and connectors for the measurement of electrical [ 19 ] properties. Figure 3.4d shows a typical such structure with a four-terminal confi guration.…”

“…W , T , and B denote, respectively, the center of mass, tip, and base of nanowire; the three arrows show the beam direction; and the one arrow shows the FIB cutting position. The scale bar is 2 μm [ 19 ] The bending effect could also affect the felling process and the fi nal felling direction of the nanoobject under investigation. To fell the nanowire, an FIB image was fi rst grabbed using a frame scanning time of 60 s, and then an area of 400 nm × 400 nm near the base of the nanowire was scanned with 30 pA for 30 s. An SEM image was taken at this point; this is shown in Fig.…”