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Figure 1: #1 Hard Disk (A) Topography; (B) MFM image acquired by raising the
magnetic tip ~ 80 nm above the surface.

Figure 2: Variable topography of the sample #112 in air. (A) and (B) are collected in two different localities,
which are also different from where the Figure 1 was collected.

To analyze the topography of the sample in a wet environment, these two sample wires were immersed in warm water during scanning. The Environmental Cell (EC) and MicroCell options for the Nano-R™ AFM are designed to allow users to study samples in liquid and gas phases. In the Close-Contact mode, because the damping of the cantilever induced by surrounding media would decrease the mechanic Q-factor of vibrating probes, the soft triangular silicon nitride probe was used to obtain optimal results. Those commercially available nitride probes have resonance frequency of ~50 KHz, tip radius of 60 nm, and Au back coating layer. The frequency sweep was performed by putting probes very close to the samples (a few of hundreds microns) to avoid variable peaks during sweeping. Due to damped Q and greater tip radius, images scanned in liquid are generally less crisp than in air. Silicon probes used in air scan have a Q factor of ~600 and radius of < 10 nm.

Figure 3 shows liquid scan of the sample #112. No apparent morphology change or deformation was observed in the present samples. However, the peak-to-peak height and surface roughness increase slightly in general. The roughness of the sample #112, for example, increases from 5.91 nm to 11.33 nm (Figure 3). The imaging scan for the sample #163 in liquid was similar to the sample #112. The observed data changes in the acquired images are listed in Table 1.

Figure 4 shows three topography images of the sample #163 in air. This sample is much less uniform than the sample #112. The peak-to-peak height in Figure 4A (20 × 20 μm) is about 1.79 μm, comparing to about 293 nm in Figure 1A (30 × 30 μm). This results from polymer aggregation without uniformity. One can see some where the surface is smooth, but others are rough. In some other localities, the peak-to-peak height is more than 5-6 μm (not shown). The peak-to-peak height is as large as 2.3 μm in Figure 4C.

Figure 3: Liquid scan (5 × 5 μm) of the sample #112. The wire was immersed into warm water during scanning. There is no apparent morphology change after soaking (see Figure 1B-C for dry images), although the peak-to-peak height increases from
55 nm (Figure 1B) to 102 nm and the roughness increases from 5.91 nm (Figure 1B) to 11.33 nm.

Figure 4: Topography of the sample #163 in air. (A) and (B) were collected in same locality. (C) was collected
from a different locality. This sample is much rougher and less uniform than the sample #112 in terms of
peak-to-peak height and roughness.

Figure 5: Liquid scan (5 × 5 μm) of the sample #163. The wire was immersed into warm water during
scanning. (A) and (B) were from different localities.

and pushed the tip upward during scanning because of magnetic coupling between tip and the sample; this results in the bit appearing higher than the surface. The pair 3 represents the bit-to-bit spacing of 362 nm. Another line analysis shows a bit is about 1.45 μm long (not shown). The measurement method was similar to Figure 4.

In order to verify the degaussering process, a PNI reference hard disk (4GB) full of data was analyzed by MFM. Figure 5 shows a typical MFM image. Similar to the #1 hard disk, the regular bit tracks were found uniformly on the disk surface.

Conclusion

Table 1: Comparison of dry and wet samples
	Peak-to-Peak Height (nm)	Roughness (nm)	Reference Figure
#112 (dry)	54.89	5.91	Figure 1B
#112 (in water)	101.79	11.33	Figure 3
#163 (dry)	241.04	28.17	Figure 4B
#163 (in water)	372.99	44.45	Figure 5A

This measurement shows example results of scanned topographies for two polymer-coated wires. The sample #112 is smoother than the sample #163 in terms of peak-to-peak height and roughness (see Table). It is clear that an AFM can provide very detailed quantitative information on wire surface. EC or MicroCell provides easy operation in liquid scan.

Pacific Nanotechnology’s Nano-R2™ AFM is shown fully capable for analysis and study of coating microstructures both in air and liquid.

AFM Metrology for Polymer-Coated Wires

AFM Metrology for Polymer-Coated Wires

Introduction