Interfacial Force Microscope

Qunyang Li

Carpick Group

Interfacial Force Microscope (IFM)

Capable of measuring normal and lateral forces between a probe and

sample. Functions much like an AFM or a nano-indenter.

A few features make it different:

The force sensor has zero compliance (i.e. infinitely stiff), therefore

loading is through a displacement-controlled process

o The probe can (or has to) be made by users and mounted to the

force sensor

o The typical force sensor has a measuring range of 10 nN ~ 50 µN

(resolution better than 1nN), lying between conventional AFM and

nano-indenter; displacement resolution better than 1 Å

o Measurement environment (e.g. humidity) is potentially controllable

IFM System

Controller

Computer

Head & sample stage

IFM Probes and Sensors

sample

probe

Probe mounted ona sensor

Force sensor:

A novel electrostatically-driven & self-

balancing sensor, which ALWAYS

maintains at the same position Sample

Probe TipTorsion Bars

C2 C1

ZERO instrument compliance

Unique Feature

Because of zero machine compliance, there is no “snap-in” or “snap-out” of contact when we perform force-distance measurements.

Without feedback Without feedback

Joyce, S. A. and J. E. Houston (1991). Review ofScientific Instruments 62(3): 710-715

Typical Measurement of IFM

0 100 200 300 400 500 600 700-30

-20

-10

0

10

Fo

rce

( µN

)

Displacement (nm)

approaching retracting

Probe: Spherical silica tip (a few hundred microns in radius) made bypulling borosilicate glass capillary tube under H2 flame;

Substrate: Silica flat made by thermally oxidizing a silicon wafer.

Not accessibleby AFM

N2 environment with 20% relative humidity