Comparison of wear characteristics of etched-silicon and carbon nanotube atomic-force microscopy probes

Abstract

The resolution and wear properties of carbon nanotube and etched-silicon atomic force microscopy probes are compared in intermittent-contact mode. Carbon nanotube probes have at least 20 times the life of etched-silicon probes and provide better resolution at all stages. Sample wear is minimized with carbon nanotube probes. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1452782͔Since the discovery of carbon nanotubes ͑CNTs͒ in 1991, 1 much has been done to characterize their properties and explore their potential applications. Although many of these potential uses are still in the nascent stage, it has become clear that CNTs, because of their geometry and unique mechanical properties, are very well suited for scannedprobe microscopy probes, 2 in particular atomic-force microscopy ͑AFM͒, 3 but also magnetic-force microscopy 4 and electric-force microscopy. 5 CNTs are preferred probes for topographic imaging because they ͑1͒ provide improved resolution ͑uniformly good end form͒, ͑2͒ allow investigating deep and/or narrow surface features ͑very high aspect ratio and long length͒, ͑3͒ enable probing sensitive and/or easily damaged surface features ͑mechanical properties of the CNT͒, ͑4͒ have long life ͑anecdotal evidence of a factor of 10 increased life without degradation of resolution͒, and ͑5͒ provide enhanced capabilities for scanning in water ͑hydro-phobicity of the CNT͒. 6 In this letter we quantify the improved resolution, the long life and the superior imaging properties of CNT probes on fragile samples. We compare the wear and degradation of conventional commercial etched-silicon ͑ES͒ probes with those of multiwall CNTs during intermittent-contact imaging. We confirm at least an order of magnitude longer life of the CNT without degradation of resolution; in fact we are not able to find a reduction of resolution or any wear of the CNT even after more than two meters of scanning ͑over 1000 2 mϫ2 m images͒. Samples imaged with CNT probes also show negligible wear compared with those imaged with ES probes. Figure 1 shows a comparison of the resolution achievable with CNT ͑a͒ and ES ͑b͒ tips, using 10 nm Co spheres on Si͑111͒. The end form of tips made from multiwall CNTs or CNT bundles is invariably better than 20 nm in diameter, and can be made as small as 3 nm, providing resolution of this order. Although new ES tips can sometimes achieve the resolution of a CNT ͑we have never observed it to be better than that of a CNT͒, their resolution begins to degrade within two or three scans in most cases. Figure 1 also shows a comparison of the ability of the CNT tips to probe deep features ͑c͒ versus that of an ES tip ͑d͒. Because they are long, narrow tubes, CNTs have a high aspect ratio ͑tubes with lengths from nanometers to several micrometers can be fabricated as metrology probes͒. Conventional ͑ES͒ probes have a pyramidal shape, which is apparent in the AFM image of a deep trench. Thus, CNT probes can profile morphologies that are inaccessible to ES probes.The wear characteristics of conventional ES tips ...

Comparison of magnetic- and chemical-boundary roughness in magnetic films and multilayers

“…24 We measure surface roughness of exterior surfaces ͑i.e., for the bare Co film and the Fe surface of the Fe-capped Co film͒ with atomic-force microscopy ͑AFM͒ in the intermittent-contact mode, using carbon nanotube ͑CNT͒ probes for enhanced resolution. 25 Measurements made with CNTs show a larger rms roughness than those made with regular Si etched tips; nevertheless we expect AFM to produce slightly lower rms roughness values than do x rays because of the wider range of frequencies that the x rays can see. Additionally, because these measurements are ex situ, the surfaces will be slightly oxidized.…”

Imaging artefacts in atomic force microscopy with carbon nanotube tips

“…Compared to those taken with conventional AFM tips, dynamic AFM images obtained with multi-walled carbon nanotube (MWCNT) tips (an AFM microcantilever with a CNT tip is henceforth referred to as a 'CNT AFM probe') have demonstrated improved lateral resolution of polymeric photoresist trenches on silicon [1], etched polyvinyl alcohol on silicon [2], and silacatein protein filaments [3]. MWCNT tips also offer excellent wear resistance [4,5], and possess the ability to image high aspect ratio structures such as semiconductor trenches [6]. The low bending stiffness of multi-walled and single-walled carbon nanotubes allows the imaging of soft surfaces, such as biomolecules, with reduced contact forces [7,8].…”

The Moving Finger Writes: Carbon Nanotubes as AFM Probe Tips

“…Similar results were found in the degredation studies performed by Larsenetal. [5]. Advanced Lithography Semiconductor structures start out as a photoresist pattern on a thin film that will be subsequently patterned by a plasma etching process.…”