Atomic force microscopy cantilever, system and method

Abstract

The surface of the atomic force microscopy (AFM) cantilever is defined by a main cantilever body and an island. The island is partly separated from the main body by a separating space between facing edges of the main body and the island. At least one bridge connects the island to the main body, along a line around which the island is able to rotate through torsion of the at least one bridge. The island has a probe tip located on the island at a position offset from said line and a reflection area. In an AFM a light source directs light to the reflection area and a light spot position detector detects a displacement of a hght spot formed from light reflected by the reflection area, for measuring an effect of forces exerted on the probe tip.

1 . A cantilever for use in an atomic force microscopy (AFM) system, the cantilever comprising:
 a main body, the main body forming a part of a surface of the cantilever;   an island, the island forming a further part of the surface of the cantilever, the island being partly separated from the main body by a separating space between facing edges of the main body and the island;   at least one bridge connecting the island to the main body along a line around which the island is able to rotate through torsion of the at least one bridge;   a reflection area located on the island; and   a probe tip located on the island at a position offset from the line.   
     
     
         2 . The cantilever according to  claim 1 , wherein the at least one bridge consists of a first bridge and a second bridge, the first bridge and the second bridge connecting the island to the main body on opposite sides of the island, wherein the island lies within an outline of the main body. 
     
     
         3 . The cantilever according to  claim 1 , wherein the main body is mass balanced with respect to the line. 
     
     
         4 . The cantilever according to  claim 1 , wherein the line extends along a direction of a longest size of the cantilever. 
     
     
         5 . The cantilever according to  claim 1 , wherein the main body of the cantilever has an uneven mass distribution m(x) as function of position x between ends of the cantilever, an average of a product m(x)*u 2 (x) of the mass m(x) and a squared mode shape u 2 (x) as a function of position x along the cantilever divided by an average of u 2 (x) being larger for a contact vibration mode of order N, with N greater than one, than for a contact vibration mode of order one. 
     
     
         6 . The cantilever according to  claim 1 , wherein the main body of the cantilever has an uneven mass distribution m(x) as function of position x between ends of the cantilever the mass distribution having a maximum at a belly of a contact vibration mode of order N, with N greater than one. 
     
     
         7 . The cantilever according to  claim 1 , wherein the main body comprises: a main portion, a neck portion and a head portion,
 wherein the neck portion lies between the main portion and the head portion,   wherein the neck portion has a smaller width than the main portion and the head portion,   wherein the cantilever comprises a further reflection area located on the head portion,   wherein a difference between a contact resonance frequency of the main body and a resonance frequency of orientation changes of the head portion relative to the main portion due to bending of the neck portion being less than the quality factor of the resonance of said orientation changes of the head portion times the resonance frequency of the resonance of the orientation changes of the head portion.   
     
     
         8 . An atomic force microscopy (AFM) system comprising:
 a cantilever comprising:
 a main body, the main body forming a part of a surface of the cantilever; 
 an island, the island forming a further part of the surface of the cantilever, the island being partly separated from the main body by a separating space between facing edges of the main body and the island; 
 at least one bridge connecting the island to the main body along a line around which the island is able to rotate through torsion of the at least one bridge; 
 a reflection area located on the island; and 
 a probe tip located on the island at a position offset from the lien around which the island is able to rotate; 
   a light source positioned to direct a light to the reflection area; and   a light spot position detector positioned to detect a displacement of a light spot formed from light reflected by the reflection area, for using said displacement to measure an effect of forces exerted on the probe tip by a surface of a sample.   
     
     
         9 . The AFM system according to  claim 8 , further comprising:
 a sample platform;   a vibration generator coupled to the platform and/or the cantilever for generating vibration in the sample and/or the cantilever, a first end of the cantilever being fixed in said vibration;   an actuator for moving the cantilever and the platform relative to each other, at least in a height direction perpendicular to the surface of the sample and a scan direction parallel to the surface of the sample;   a control circuit configured to;
 control the actuator to move the cantilever and the platform relative to each other progressively in the scan direction; 
 activate the vibration generator to generate vibrations of the sample relative to the cantilever at a frequency of a contact resonance mode of the cantilever, 
 measure properties of vibration of the cantilever in the contact resonance mode from a first component of the displacement during movement of the cantilever and the platform relative to each other in the scan direction; and 
 control the actuator to move the cantilever and the platform relative to each other in the height direction in a feedback loop in response to a second component of the displacement during movement in the scan direction. 
   
     
     
         10 . The AFM system according to  claim 9 , wherein the light spot position detector is configured to distinguish light spot displacements in a first dimensional direction and a second dimensional direction that differs from the first dimensional direction,
 wherein the control circuit is configured to derive the first component of the displacement and the second component of the displacement from the light spot displacements in the first dimensional direction and the second dimensional direction, respectively.   
     
     
         11 . The AFM system according to  claim 9 , wherein the feedback loop comprises a low pass frequency filter to filter the second component of the displacement from an output of light spot position detector. 
     
     
         12 . A cantilever for use in an atomic force microscopy (AFM) system, the cantilever comprising:
 a main body, having an uneven mass distribution m(x) as function of position x between ends of the cantilever, an average of a product m(x)*u 2 (x), of the mass m(x) and a squared mode shape u 2 (x) as a function of position x along the cantilever, divided by an average of u 2 (x) being larger for a contact vibration mode of order N, with N greater than one, than for a contact vibration mode of order one;   a reflection area located on the cantilever; and   a probe tip on the cantilever at a node of the contact vibration modes.   
     
     
         13 . The cantilever according to  claim 12 , wherein the mass distribution has a maximum at a belly of the contact vibration mode of order N. 
     
     
         14 . A cantilever comprising a main portion, a neck portion and a head portion and a probe tip on the main portion, the neck portion lying between the main portion and the head portion, the neck portion having a smaller width than the main portion and the head portion,
 wherein the cantilever comprises a reflection area located on the head portion,   wherein a difference between a contact resonance frequency of the main portion and a resonance frequency of orientation changes of the head portion relative to the main portion due to bending of the neck portion is less than the quality factor of the resonance of said orientation changes of the head portion times the resonance frequency of the resonance of the orientation changes of the head portion.   
     
     
         15 . A method carried out by a cantilever for atomic force microscopy (AFM),
 wherein the cantilever comprises:
 a main body, the main body forming a part of a surface of the cantilever; 
 an island, the island forming a further part of the surface of the cantilever, the island being partly separated from the main body by a separating space between facing edges of the main body and the island; 
 at least one bridge connecting the island to the main body along a line around which the island is able to rotate through torsion of the at least one bridge; 
 a reflection area located on the island; and 
 a probe tip located on the island at a position offset from the line; and 
   wherein the method comprises:
 generating vibration of a sample relative to the cantilever at a frequency of a contact resonance mode of the cantilever; 
 moving the cantilever and the platform relative to each other, at least in a height direction perpendicular to the surface of the sample and a scan direction parallel to the surface of the sample; 
 directing light at the reflection area and measuring displacement of a light spot due to light reflected by the reflection area; 
 measuring properties of vibration of the cantilever in the contact resonance mode from a first component of the displacement during movement of the cantilever and the platform relative to each other in the scan direction; 
 controlling movement of the cantilever and the platform relative to each other in the height direction in a feedback loop in response to a second component of the displacement during movement in the scan direction.