1 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Laurens Pluimers Supervisors: Dr.ir. W.M. van Spengen Prof.dr.ir. A. van Keulen

2 Challenge the future Micrometer(µm) Nanometer(nm) Picometer(pm) Millimeter(mm) Meter(m ) Kilometer(km ) Scaling

3 Challenge the future Microscopes Hair: µm DNA: nm Atoms: pm Optical microscope Resolution: 200nm Resolution: 100pm Source: andrew.cmu.edu Atomic force microscope (AFM)

4 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability

5 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability

6 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability

7 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Outline  Introduction Atomic Force Microscope (AFM)

8 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Outline  Introduction Atomic Force Microscope (AFM)  Probe calibration

9 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Outline  Introduction Atomic Force Microscope (AFM)  Probe calibration  Electrostatic pull-in instability

10 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Outline  Introduction Atomic Force Microscope (AFM)  Probe calibration  Electrostatic pull-in instability  Results of feasibility study

11 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Outline  Introduction Atomic Force Microscope (AFM)  Probe calibration  Electrostatic pull-in instability  Results of feasibility study  Conclusions & Recommendations

12 Challenge the future Atomic Force Microscope Working principle Quadrant detector Laser Cantilever beam(probe) Sample Source:

13 Challenge the future Atomic Force Microscope Working principle Source:

14 Challenge the future Atomic Force Microscope Setup: Optical beam deflection system

15 Challenge the future Atomic Force Microscope AFM probe 20μm Source:

16 Challenge the future Atomic Force Microscope Images Topography image of metallic nanoparticles deposited on graphite Source:

17 Challenge the future Recap What is an Atomic Force Microscope (AFM)?  “Feeling” the sample surface with probe  Optical beam deflection system  Resolution ~100pm √

18 Challenge the future Atomic Force Microscope Modes of operation  Imaging  Topography scan  Force measurements  Material properties

19 Challenge the future Atomic Force Microscope Mode of operation: Force measurements Measurement tip / sample interaction forces:  Atomic bonding  Van der Waals forces  Magnetic forces  Chemical bonding Probe Sample h Source:

20 Challenge the future Atomic Force Microscope Interaction forces Material A Material B Quadrant detector Laser Probe F int

21 Challenge the future Atomic Force Microscope Interaction forces x y “Force” image Material A Material B

22 Challenge the future Atomic Force Microscope Probe calibration k F int x Hooke’s law F int =k ·x Probe Laser Quadrant detector k=spring constant

23 Challenge the future Probe calibration Added mass M x Hooke’s law k

24 Challenge the future Probe calibration Euler-Bernoulli beam theory t L b Cantilever base

25 Challenge the future Probe calibration Other calibration methods MethodAccuracyDisadvantages Added mass15-25%Destructive, slow Euler-Bernoulli beam theory 20-40%Inaccurate, slow Nano-Force Balance0.4%External equipment, expensive Thermal tune20%Only compliant beams

26 Challenge the future Recap Why do you need to calibrate the probe?  To determine the exact interaction forces between tip and sample  Bonding forces  Material properties Disadvantages other methods  Need for new method √

27 Challenge the future Probe calibration New calibration method Based on probe’s Electrostatic Pull-in Instability (EPI) Inventor: Prof.dr.ir. F. van Keulen Improvements:  Wide range of cantilever beams (k= 0.1 – 50 N/m)  Non-destructive  Integrated system in AFM  Fast and easy to use

28 Challenge the future Probe calibration New calibration method Based on probe’s Electrostatic Pull-in Instability (EPI)  EPI  Probe calibration using EPI  Experimental setup

29 Challenge the future Electrostatic Pull-in Instability V u=d 0 u Probe Counter electrode DC voltage source Pull-in point

30 Challenge the future Electrostatic Pull-in Instability Top view cantilever beam

31 Challenge the future  Non-linear behaviour of the cantilever beam  Elastic restoring forces are linear  Electrostatic forces are quadratic  Main advantage: well defined instability point(pull-in)  measurement Electrostatic Pull-in Instability

32 Challenge the future Probe calibration Electrostatic pull-in instability L b d0d0

33 Challenge the future Probe calibration EPI: differential gap method V p1 V V V p2 Δd Δd

34 Challenge the future EPI probe calibration Experimental setup Variables:  Differential gap ( Δd )  Pull-in voltage (V pi )  Length (L)  Width (b) Accuracy: % Model Source: AFM system

35 Challenge the future EPI probe calibration Experimental setup XYZ stage Variables:  Differential gap ( Δd ) XYZ stage Source:

36 Challenge the future EPI probe calibration Experimental setup Variables:  Differential gap ( Δd )  Pull-in voltage (V pi ) Source: XYZ stage Counter electrode XYZ stage

37 Challenge the future EPI probe calibration Experimental setup Variables:  Differential gap ( Δd )  Pull-in voltage (V pi ) Source: Counter electrode XYZ stage

38 Challenge the future EPI probe calibration Experimental setup Variables:  Differential gap ( Δd )  Pull-in voltage (V pi )  Length (L)  Width (b) Source: Counter electrode XYZ stage Aspheric lens

39 Challenge the future EPI probe calibration Calibration mode Source: Variable:  Pull-in voltage (V pi ) Source:

40 Challenge the future EPI probe calibration Width scan x Source: Variable:  Width (b) Source:

41 Challenge the future EPI probe calibration Length scan y Source: Variable:  Length (L) Source:

42 Challenge the future EPI probe calibration Experimental setup Source:

43 Challenge the future Probe calibration Experimental setup Optical path Laser Aspheric lens Quadrant detector

44 Challenge the future Probe calibration Experimental setup

45 Challenge the future Probe calibration Experimental setup

46 Challenge the future Probe calibration Experimental setup

47 Challenge the future Probe calibration Experimental setup

48 Challenge the future Probe calibration Experimental setup

49 Challenge the future Results Performance check:  Differential gap ( Δd )  Pull-in voltage (V pi )  Length (L)  Width (w) Calibration test probe

50 Challenge the future Results Width scan Width Position stage [µm] QD output [V] Width scan EPI

51 Challenge the future Results Length scan Length Position stage [µm] QD output [V] Length scan EPI

52 Challenge the future Results Length/Width scan Width [µm]Length[µm] EPI50.59 ± ±0.40 Bruker WL50.71 ± ±0.3 Error [µm] 0.12 ± ±0.5 Error [%]

53 Challenge the future Results Calibration test probe ProbeSpring constant k [N/m]Δk [%] NanoWorldEPI 1 (compliant) (stiff) Requirement: Accuracy %

54 Challenge the future Conclusions Performance check:  EPI method can be implemented as integrated system Calibration test probe:  EPI calibration method is able to determine the spring constant of AFM probes  Accuracy system not within requirements

55 Challenge the future Recomendations Increase accuracy by improving model  Include fringing field effects  Tapered end beam My model Reality

56 Challenge the future Recommendations Increase accuracy by improving model  Include fringing field effects  Tapered end

57 Challenge the future Recommendations Increase accuracy by improving model  Include fringing field effects  Tapered end Cantilever beam

58 Challenge the future Recommendations Increase accuracy by improving model  Include fringing field effects  Tapered end New model in progress

59 Challenge the future Feasibility study for AFM probe calibration using the probe’s electrostatic pull-in instability Questions?

60 Challenge the future Extra sheet Width scan Width Position stage [µm] QD output [V] Width scan EPI

61 Challenge the future Extra sheet Width scan

62 Challenge the future Laser + Lens Quadrant detector Laser beam Width cantilever beam Extra sheet Width scan

63 Challenge the future Extra sheet Extended model