Material Property Measurements Using Multiple Frequency Atomic Fore Microscopy

Abstract

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.

What is claimed is: 
     
         1 . An atomic force microscope which processes a sample, comprising:
 a atomic force microscope cantilever which has a probe tip which moves relative to a surface of the sample;   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;   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. 
     
     
         3 . The microscope as in  claim 1 , wherein said controller includes an RMS measurement circuit. 
     
     
         4 . 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. 
     
     
         5 . The microscope as in  claim 1 , further comprising a mechanical actuator for moving said cantilever under control of said controller, said mechanical actuator driven by said first frequency. 
     
     
         6 . The microscope as in  claim 5 , wherein said second frequency is used to vary a potential of the cantilever probe relative to the sample. 
     
     
         7 . The microscope as in  claim 6 , wherein said controller measures amplitude and phase of the second frequency to determine said information about the sample. 
     
     
         8 . The microscope as in  claim 5 , wherein said second frequency is used to vary a property of a surface of the sample. 
     
     
         9 . The microscope as in  claim 1 , wherein said second frequency is used to vary a magnetic state of a surface of the sample. 
     
     
         10 . 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;   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;   a mechanical actuator, driven by said controller for moving said cantilever, said mechanical actuator driven by said first frequency;   said controller using said second frequency to vary a property of a surface of the sample;   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.   
     
     
         11 . The microscope as in  claim 10 , wherein said controller includes a lock in amplifier. 
     
     
         12 . The microscope as in  claim 10 , wherein said controller includes an RMS measurement circuit. 
     
     
         13 . The microscope as in  claim 10 , wherein said property is a potential of the cantilever probe relative to the sample. 
     
     
         14 . The microscope as in  claim 13 , wherein said controller measures amplitude and phase of the second frequency to determine information about the sample. 
     
     
         15 . The microscope as in  claim 10 , wherein said property is a magnetic state of a surface of the sample. 
     
     
         16 . The microscope as in  claim 10 , wherein said controller uses a feedback loop to control a distance between the cantilever of the atomic force microscope and said surface, to maintain the probe tip of the cantilever in a pre-established relationship with respect to the surface of the sample while scanning the sample by creating relative movement between the probe tip of the cantilever and the sample, said using a phase of the cantilever movement in the feedback loop, and using a frequency of the cantilever movement to maintain the phase substantially constant in the feedback loop. 
     
     
         17 . A method of processing a sample using an atomic force microscope, comprising:
 changing a relationship between an atomic force microscope cantilever which has a probe tip and a surface of the sample by creating relative movement between the probe tip of the cantilever and the sample using both first and second frequencies to cause said relative movement of the cantilever;   said changing comprising controlling a mechanical actuator for moving said cantilever, driven by said first frequency;   said changing also comprising using said second frequency to vary a property of a surface of the sample; and   measuring values used to control said cantilever during said changing, to determine information about said first and second frequencies and a measured value indicative of said relative movement, to provide information indicative of a surface of the sample.   
     
     
         18 . The method as in  claim 17 , wherein said property is a potential of the cantilever probe relative to the sample. 
     
     
         19 . The method as in  claim 18 , wherein said measuring measures amplitude and phase of the second frequency to determine information about the sample. 
     
     
         20 . The method as in  claim 17 , wherein said property is a magnetic state of a surface of the sample.