UNIMO Technology UDR-204 Manual de instrucciones descargar pdf (Pagina 46)

SPM Fundamentals for the MultiMode

Hardware

26 MultiMode SPM Instruction Manual Rev. B

Cantilevered Probes

Most SPM work is done using cantilevered probes. These consist of a ﬂexible cantilever extending

from a rigid substrate, to which a tip has been attached. In contact AFM, the cantilever ﬂexibility

acts as a nanometric spring, allowing the tip to measure surface forces. In TappingMode, the probe

is oscillated up and down at its resonant frequency while its amplitude and phase are monitored.

Figure 2.1j Two Types of Cantilevered Probes

Cantilevered Probes—silicon nitride

Most contact AFM is conducted with silicon nitride tips. These tips exhibit excellent ﬂexibility,

making them easier to use and more “forgiving” than stiffer crystal silicon cantilevers. They are

offered in a variety of sizes and coatings, allowing the user to match them to the sample being

imaged. One characteristic of silicon nitride tips is that they are easily captured by the sample’s

surface tension (capillary) properties; that is, trapped within a microscopic layer of condensed

atmospheric water vapor on the sample surface. This surface tension effect exerts considerable

force at the probe’s atomically sharp tip. Although this may prove unproblematic on harder

samples, it is frequently enough to deform softer samples. Adjustment to the Setpoint parameter

can offset much of this force; however, it may still prove troublesome on delicate samples. Silicon

nitride tips may also be operated in TappingMode, although they are not optimal for this purpose.

Cantilevered Probes—TappingMode

Veeco’s answer to minimizing contact AFM forces is TappingMode, a proprietary form of AFM. In

this instance, a stiff crystal silicon probe is oscillated to its resonant frequency. Because the tip

describes a high-frequency (e.g., 100-plus kHz), oscillating arc, it possesses sufﬁcient energy to

break free of surface tension forces. The probe is considerably stiffer than silicon nitride, making it

more brittle and less forgiving. Thus, the operator must be more cautious while setting up the tip

and sample.

Siliscon Nitride Crystal Silicon

1 2 ... 41 42 43 44 45 46 47 48 49 50 51 ... 357 358

Sin comentarios

UNIMO Technology UDR-204 Manual de instrucciones Pagina 46