Force Measurement with Real-Time Baseline Determination

Abstract

An atomic force microscope (AFM) and corresponding method to provide low force (sub-20 pN) AFM control and mechanical property measurement is provided. The preferred embodiments employ real-time false deflection correction/discrimination by adaptively modifying the drive ramp to accommodate to deflection artifacts.

1 . A method of detecting a force between a sample and a probe of an AFM, the method comprising:
 positioning at least one of the probe and the sample at a location of interest of the sample;   moving at least one of the probe and the sample to lessen a separation therebetween and cause the two to interact;   measuring a deflection of the probe based on the moving step;   discriminating a deflection artifact from a deflection due to probe-sample interaction from the measured deflection data without making any assumptions regarding a background responsible for deflection artifact; and   determining, based on the discriminating step, the force between the sample and the probe, wherein the force is less than 20 pN.   
     
     
         2 . The method of  claim 1 , further comprising:
 using the measured deflection, in real time during the moving step, to determine an instantaneous baseline, and wherein the discriminating step uses the instantaneous baseline.   
     
     
         3 . A method of detecting a force between a sample and a probe of an AFM, the method comprising:
 positioning at least one of the probe and the sample at a location of interest of the sample;   moving at least one of the probe and the sample to lessen a separation therebetween and cause the two to interact;   measuring a deflection of the probe based on the moving step;   discriminating, in real-time, a deflection artifact from a deflection due to probe-sample interaction from the measured deflection data; and   observing a first contact between the tip and the sample based on the discriminating step.   
     
     
         4 . The method of  claim 1 , further comprising:
 determining, based on the discriminating step, the force between the sample and the probe; and   performing, once the force corresponds to a specific user-selected force, at least one of a group including a scratch of the sample, a hold of the tip-sample separation and a change of direction of a scan.