AC Mode AFM in Air

Three Different Operating Conditions

(From H. Ho Ph.D. Thesis)

"Near Contact", a new ultra high resolution operating mode, is compared to the IBM-patented AC modes of Non-Contact and Periodic Contact.

General: The sample is polished hardened glass. It is an insulator and is very hard. The near contact image was acquired prior to the other images and the tip imaged with an SEM before and after imaging. The images are not filtered.

Traditional Non-Contact Condition.

Atomic Force Microscope-force mapping and profiling on a sub 100-Å scale

Y. Martin, C. C. Williams, and H. K. Wickramasinghe

J. Appl. Phys. 61 (10), 15 May 1987 (see section V. Material Sensing and Imaging)

[non-contact] [non-contact] click each image for full view

A single crystal silicon cantilever is vibrated with an amplitude of about 2 nm, near to the surface of the inherent contamination layer on the surface of a sample. In this operating mode, the tip can last indefinitely, but may image the surface of the contamination layer itself. At high magnification this may or may not accurately represent the surface of the sample. A sensitive low noise AC detection circuit is required, but even then, tracking may be somewhat unstable.

Periodic Contact Condition.

[periodic contact] [periodic contact] click each image for full view
In a Periodic Contact condition, the cantilever is vibrating at an amplitude of 20 to 100 nm, and moves in and out of the contamination layer on the surface of a sample. The tip contacts the sample on every oscillation, however, in this mode either the tip is quickly damaged on a hard sample surface, or a soft sample is damaged. Note that the image may have slightly higher resolution than the True Non-Contact image. This mode does not require sensitive low noise AC detection circuitry to operate.
Silicon probe before (left) and after (right) use in Periodic Contact mode on a hard disk surface.

NearContact(tm) Condition.

[near contact] [near contact] click each image for full view
In Near Contact mode, the probe is vibrated at an amplitude of about 2 nm within the contamination layer on the surface of a sample and extremely close to the sample surface. In this mode there is no damage to the tip or the sample and extremely high resolution is obtained. . Sensitive low noise AC detection circuitry is required (such as ECU-plus) but feedback is very stable. Note that this mode provides the highest overall image resolution.

[near contact] [near contact] [near contact] [near contact] [near contact]

Line profile resolution comparison of 2 different lines (A and B - left to right) from a 100nm zoom of the above images. Click profiles for full view of the line profile analysis screen.

Other User [Applications] Home - Top