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AFM Workshop

Cleaning Microscopic Contamination for AFM Calibration

Although the New Skin® method is successful in removing large contaminants such as dust and fibers, you will need a technique that can remove microscopic contaminants and organic layers, such as airborne hydrocarbons, if the sample is to be used for calibrating the AFM.

When operated in air, short wavelength UV light produces ozone, an extremely strong oxidising agent. The combination of UV irradiation (<300nm) and ozone can rapidly decompose a wide variety of organic contaminants. This is a quick and effective procedure for removing organic matter from sensitive surfaces. Devices to safely expose small surfaces to a combination of UV and ozone can be constructed fairly simply**, since all that is required is a small light-proof chamber, a power supply and an appropriate UV lamp. Commercial UV/ozone devices are also available.

Samples can be cleaned by UV irradiation consistently only if macroscopic contamination is removed first. Typically, pre-cleaning involves a sequence of actions that include swabbing, rinsing and ultrasonic agitation, and utilizes multiple solvents. However, some samples are not resistant to the usual pre-cleaning procedures. In the case of cleaning AFM reference samples, the surfaces are very sensitive to mechanical damage. Swabbing with even the softest materials is not appropriate for AFM calibration/reference specimens, and will irreparably damage the sample. Additionally, while UV/ozone is highly effective for removing organic contaminants, it is ineffective against nearly all inorganic contamination.

The New Skin® method addresses both the potential risk of mechanically damaging AFM calibration specimens and the need for a low-cost and simple mechanism to remove large-scale contamination from surfaces. This New Skin® technique can be used in combination with more advanced techniques, such as the UV/ozone method, to achieve near-perfect cleaning for AFM reference artifacts.

* * Note that in the UV/ozone technique, short wavelength UV and ozone are both very dangerous, and the chamber should only be operated closed, in a well-ventilated space.

UV/ozone Cleaning Reference: J. Vig, J. Vac. Sci. Technol. A3 (1985)

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