Material property measurements using multiple frequency atomic force microscopy
View Patent ↗Apparatus and techniques for extracting information carried in higher eigenmodes or harmonics of an oscillating cantilever or other oscillating sensors in atomic force microscopy and related MEMs work are described. Similar apparatus and techniques for extracting information using contact resonance with multiple excitation signals are also described.
1. An atomic force microscope which processes a sample, comprising:
an atomic force microscope cantilever which has a probe tip which moves relative to a surface of the sample;
an actuator for the cantilever which actuates the probe tip;
a magnetic connection to the probe tip which modulates a magnetic state of a circuit part adjacent to the probe tip;
a controller, controlling said cantilever by creating relative movement between the probe tip of the cantilever and the sample and measuring values used to control said cantilever, said controller using both first and second frequencies to cause said relative movement of the cantilever, where said first and second frequencies are different frequencies,
and said controller including a first frequency source that creates said first frequency and a second frequency source that creates said second frequency,
said controller coupling said first frequency to the actuator to drive actuation of the probe tip,
said controller coupling said second frequency to change the magnetic state of the circuit part adjacent to the probe tip connection to vary a characteristic of the surface of the cantilever probe using said second frequency; and
said controller using said first and second frequencies and a measured value indicative of said relative movement, to provide information indicative of a surface of the sample.
2. The microscope as in claim 1 , wherein said controller includes a lock-in amplifier locking in the first and second frequencies.
3. The microscope as in claim 1 , wherein said cantilever is controlled using both amplitude and phase of the cantilever at both of said first and second frequencies.
4. The microscope as in claim 1 , wherein the measured value includes a value indicative of motion measured at a first eigenvalue excited by the first frequency source, and also includes another value indicative of surface-state dependent properties at a second eigenvalue excited by the second frequency source.
5. The microscope as in claim 4 , wherein the measured value is based on amplitude of the cantilever.
6. The microscope as in claim 1 , wherein the circuit part is a surface near the sample being measured.