Expanding Characterization of Materials with Kelvin Force Microscopy

Transcription

1 Expanding Characterization of Materials with Kelvin Force Microscopy Sergei Magonov Page 1

2 Outline Introduction to Kelvin Force Microscopy Different KFM Modes and Their Practical Evaluation Applications of Kelvin Force Microscopy Metals and Semiconductors Molecular Self-Assemblies Conclusions Page Group/Presentation Title Agilent Restricted Month ##, X

3 Atomic Force Microscopy/Scanning Force Microscopy High-Resolution/Low- i Local Mechanical Local Electromagnetic Other Properties: Force Profilometry Properties Properties Optical, Thermal, Air Vapors Liquid Vacuum High/Low Temperatures Local Electromagnetic Properties Force sensing Magnetic Force Microscopy, MFM Electric Force Microscopy, EFM: df/dz Kelvin Force Microscopy, KFM (SKPM) : surface potential, dc/dz Piezoresponse Force Microscopy, PFM Current sensing Conducting AFM, c-afm Scanning spreading resistance microscopy, SSRM Capacitance/Impedance sensing Scanning capacitance microscopy Scanning microwave microscopy Page 3 Group/Presentation Title Agilent Restricted Month ##, X

4 Kelvin Probe Technique (macroscopic method) Surface potential of semiconductor V s = ΔW f + V ox + φ s B. Laegel, M. D. Ayala, R. Schlaf APL, 5, 1. Page Group/Presentation Title Agilent Restricted Month ##, X

5 Metalized Probe Historical Pathway of AFM-based Electrostatic modes Electric force microscopy Contours of constant force gradient Back electrode Contours of constant force gradient An example of a cross-talk Y. Martin, D. A. Abraham, H. K. Wickramasinghe, Appl. Phys. Lett. 5, 113,19. J.E. Stern, B.D. Terris, H.J. Mamin, and D. Rugar, Appl. Phys. Lett. 53, 717, 19.

6 Electrostatic Force in Atomic Force Microscopy Metalized Probe Back electrode Responses at ω and ω can be used for detection of surface charge and capacitance/dielectric constant. KFM feedback is the nullifying the electrostatic t ti force at ω. J. M. R. Weaver and D. W. Abraham, J. Vac. Sci. Techn. 1991, B9, 1559 M. Nonnenmacher, M. P. O Boyle, H. K. Wickramasinghe, Appl. Phys. Lett. 5, 91, Electrostatic force at ω is proportional to dc/dz Solution: Problem: the AFM probe responds to all tip-sample forces! Single Pass the use of frequencies(ω mech, ω elec ) for probing mechanical and electrostatic tip-sample forces + operation in non-contact mode Y. Martin, D. A. Abraham, H. K. Wickramasinghe, Appl. Phys. Lett. 5, 113,19 Path Lift technique - the use of single frequency (ω mech ) with probing the electrostatic force in non-contact mode V. B. Elings, J. A. Gurley US Patent 5,3,97, 199. Page Month ##, X

7 Advanced Consideration of Electric Force Measurements with AFM Electrostatic energy and force J. Colchero, A. Gil, and A. M. Baro Phys Rev B (1) 53 Total force F Spatial Resolution in KFM Cantilever Metal Surface Cone Metal Surface Apex Metal Surface Force gradient vs. Force!? S. Kitamura et al Appl. Surf. Sci., 157, Atomic-scale KFM resolution on crystals in UHV KFM-FM InSb KFM-FM KCl 15 nm U. Zerweck et al Phys. Rev. B 5, 71, 15 UHV KFM-Lift BR M. Zhao et al Nanotechnology, 19, 357 UHV FK F. Krok et al lphys. Rev. B, 77, nm KCl Au nm KFM-AM Page 7 Group/Presentation Title Agilent Restricted Month ##, X

8 Kelvin Force Microscopy in AM-AM and AM-FM modes AM-AM AM-AM: the amplitude changes at ω elec reflect the electrostatic force variations. AM-FM: the electrostatic force gradient causes the phase shift at ω mech which is reflected in the amplitude of satellites. Amplitude-versus-Frequency (sketch) ω elec ω mech Heterodyne procedure ω mech ω elec ω mech + ω elec AM-FM Imaging in the intermittent contact! A Non-contact Intermittent contact UHV: L.Eng et al Phys. Rev. B 71 (5) 15 Z Page

9 Conducting Probes for AFM-Based Electrical Modes SEM TEM Pt-coated Olympus probes 5 N/m, ~ 7 khz SEM SEM SEM images- courtesy of Maozi Liu (Agilent Labs) TEM image courtesy of Bernard Mesa (MicroStar Technologies) Page 9 Group/Presentation Title Agilent Restricted Month ##, X

10 . nm Semifluorinated Alkanes: Self-Assembly in Thin Films F(CF ) 1 -(CH ) H F 1 H F(CF ) 1 -(CH ) H F 1 H nm -CF -δ δ CH +δ -. nm nm 9.9 nm. nm F 1 H F 1 H F 1 H F 1 H 1 μm nm F1H: Perfluorodecalin li vapor 5 nm 1 μm Substrates: Si, mica, graphite Solvent: perfluorodecalin A. Mourran et al Langmuir 5, 1, 3

11 Self-Assemblies of Semifluorinated Alkane F 1 H on Si: EFM, KFM and dc/dz Topography X-component (5kHz), KFM servo off AM-FM Electric Force Microscopy, EFM 1. μm Surface Potential (5kHz) KFM servo on 1. μm dc/dz (1kHz) Surface Potential (5kHz) Page μm 1. μm

12 Comparison of AM-AM and AM-FM modes in study of F 1 H self-assemblies Topography Surface Potential, AM-FM (Phase) Surface Potential, AM-AM Surface Potential, AM-FM (Phase) Surface Potential, AM-AM Surface Potential, AM-FM (Y) Surface Potential, AM-FM (Y)

13 Spatial resolution of KFM (AM-FM) in the Intermittent Contact: F 1 H on HOPG Topography Surface Potential Surface Potential Topography F 1 H F 1 H 1 nm F 1 H 1 μm 1 μm 5 nm 3 μm Topography Surface Potential Surface Potential Surface Potential.1V nm 1 μm 1 μm nm 3 μm

14 HOPG Topography Kelvin Force Microscopy of Substrates: Au (111) & HOPG µm Topography Au (111) µm Phase µm Surface Potential µ h hours after cleavage +15 min 1 1 µm +3 min +5 min µ + min +75 min Surface Potential ti µm Phase m Page 1 Group/Presentation Title Agilent Restricted Month ##, X

15 Kelvin Force Microscopy & Compositional Imaging of Material Heterogeneities SiGe PMMA topography surface potential topography surface potential 5 μm 5 μm μm μm TPV (polypropylene, EPDM, carbon black) C H 1 topography surface potential topography surface potential 5 μm 5 μm μm μm Page 15 Month ##, X

16 Monitoring Changes of Soldering Materials: 5%Bi-%Sn Alloy 1 hr after preparation Bi.eV Sn. ev topography surface potential μm μm 15 hr after preparation topography surface potential μm μm Page 1

17 KFM of Semifluorinated Alkane F 1 H Assemblies on Si Substrate Topography Surface Potential Zmean() Zmean(1).73 V Zmean() Zmean(1).757 V F(CF ) 1 -(CH ) H -CF -δ +δ CH nm. nm A. El Abed et al PRE, 5, 513

18 KFM of Semifluorinated Alkane F 1 H Assemblies on Mica Substrate Topography Surface Potential Zmean() Zmean(1) 1.51 V μ=3.1d μm 3 μm Topography Surface Potential A. Mourran et al Langmuir 5, 1, 3 ( ϕ si ϕtip ) μ V = + Zmean() Zmean(1)1. V e A ε ε ( ϕ si ϕtip ) CPD = e V = CPD Volts 1.5 μm 1.5 μm

19 KFM of Semifluorinated Alkane F 1 H Assemblies on HOPG substrate Topography Phase Surface Potential Zmean() Zmean(1).73 V 1 7 nm 7 nm Topography nm Surface Potential 1 9. nm nm nm

20 KFM of Semifluorinated Alkane F 1 H Assemblies on Si substrate: Humid Air Spreading of self-assemblies and conversion from spirals to toroids Topography Topography Topography Topography 1 μm 1 μm 3 μm 1 μm 1 1 Topography Topography Surface Potential Zmean() Zmean(1) V. nm nm nm

21 Monitoring of Sublimation of F 1 H Self-Assemblies on Mica Topography 115 min Topography 1 min Topography min Topography min nm nm nm nm Topography 55 min Surface Potential Topography Surface Potential nm nm Page 1 Month ##, X

22 Monitoring of Sublimation of F 1 H Self-Assemblies on Graphite Topography Surface Potential Topography Surface Potential μm 1. μm 1 μm 1 μm Topography Surface Potential Topography Surface Potential 1. μm 1. μm 1 μm 1 μm Page Group/Presentation Title Agilent Restricted Month ##, X

23 Monitoring of Sublimation of F 1 H Self-Assemblies on Graphite Topography Surface Potential Topography Surface Potential 7 nm 7 nm Topography Surface Potential 5 nm 5 nm Surface potential of FnHm (n=1, 1; m =, 1, 1, ) self-assemblies does not depend on the molecular length being determined primarily by molecular dipoles of -CF -δ CH +δ -, -CF 3 and CH 3 groups and their orientation. Page 3 Group/Presentation Title Agilent Restricted Month ##, X

24 Z. Tang, N. A. Kotov, M. Giersig Science, 97, 37 Self-Assembly of CdTe Nanoparticles into Nanowires After spincast in 9% humidity topography phase surface potential 5 μm 5 μm 5 μm topography phase surface potential Sample in 9% humidity after night 5 μm 5 μm 5 μm topography phase surface potential High luminescence quantum yields Dried Page

25 Self-Assembly of CdTe Nanoparticles into Nanowires topography surface potential topography surface potential 3 nm 3 nm. μm topography (1 min later). μm surface potential S. Shanbhag, N. Kotov, J. Phys. Chem. B, Let, 11, 111 Cubic NCs: ZnS, CdS, ZnSe, PbSe, and CdTe μ Page 5 1. μm 1. μm

26 Conclusions Expansion of AFM applications strongly depends on practical implementation of a combination of high-resolution capabilities with mapping of local properties in broad range of environments. Here the unique capabilities of KFM as the characterization technique down to the sub-1 nm scale were demonstrated on a number of materials. The progress of AFM-based local electric (as well as mechanical) studies is based on use of multiple frequencies and a broader frequency range. Analysis of multifrequency responses leads to more sensitive and high-resolution mapping of these properties. Nanotechnology 1 (7) 55 R W Stark, N Naujoks and A Stemmer The multifrequency approach in AFM and related techniques requires definite efforts towards optimization of experiments, which include a choice of rational detection schemes, an appropriate choice of probes and imaging conditions. There is no doubts that the payoff will be quite valuable and unique information about materials, their properties and behavior will be discovered. Page Group/Presentation Title Agilent Restricted Month ##, X

27 Acknowledgements John Alexander (Agilent Technologies) - for everyday cooperation on AFM developments and applications Martin Moeller (RWTH--DWI, Aachen, Germany) Nicholas Kotov (University of Michigan, Ann Arbor, MI) Page 7 Group/Presentation Title Agilent Restricted Month ##, X