Scanning Probe Microscopy. EMSE-515 F. Ernst

Transcription

1 Scanning Probe Microscopy EMSE-515 F. Ernst 1

2 Literature 2

3 3 Scanning Probe Microscopy: The Lab on a Tip by Ernst Meyer,Ans Josef Hug,Roland Bennewitz

4 4 Scanning Probe Microscopy and Spectroscopy : Theory, Techniques, and Applications by Dawn Bonnell (Editor)

5 5 High-Resolution Imaging and Spectrometry of Materials by Frank Ernst, M. Rühle (Editors)

6 Introduction 6

7 Scanning Probe Microscopy acronym: SPM group of surface characterization techniques scanning tunneling microscopy (STM) 1982, Binnig and Rohrer (IBM) Nobel Prize 1986 atomic force microscopy (AFM) 1986, Binnig, Quate, and Gerber advanced techniques based on STM and AFM new SPM techniques are still being developed 7

8 Principle of SPM sharp tip scanning over specimen surface motion controlled very precisely by piezoelectric actuators local tip surface interaction: measure local surface structure or properties or: manipulate 8

9 Tip Surface Interaction force electric fields magnetic fields energy transport electron current (tunneling or contact) heat current photon current elastic vibration 9

10 A Typical SPM Experiment move tip in three directions x, y, z by electrostatic actuator electronic controller: maintain tip specimen distance that yields preset tunneling current record required scanner voltage as a function of x, y display as two-dimensional image 10

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12 Families of SPM scanning tunneling microscopy (STM) and spectroscopy (STS) atomic force microscopy (AFM) scanning near-field microscopy (SNOM) related techniques nano-indentation, scratching, hardness, friction, wear conductive AFM electrochemical STM 12

13 Information Provided by SPM lateral range of imaging: 100µm to 10 pm surface topography structure of perfect crystal surfaces but also: defects (point defects, adsorbates, steps, ) local electronic structure magnetic and electrostatic domain structure local mechanical properties local electrochemical properties 13

14 Applications in Materials Science complimentary to RBS, XPS, SAM, XRD, LEED, SEM, TEM, does not require vacuum (although vacuum often beneficial) no irradiation damaging (but other kinds of damaging are possible) SPM provides complimentary information (e. g. topography and electronic structure) SPM can measure local properties (e. g. hardness, electrical conductivity) 14

15 Basic Concepts 15

16 Interaction interaction between scanning probe and sample near-field overcome resolution limits of far-field techniques resolution much better than e. g. photon or electron wavelength but: resolution limited by shape of probe (tip) lateral resolution depends on vertical amplitude of surface structure 16

17 Topography typical shape of probing tip: cone topography will not be imaged correctly sharp steps will be smeared out holes with diameter < tip radius will not be imaged mathematical description: convolution of surface structure with tip shape 17

18 Convolution P[x] = (S T )[x] = Z + S[x ] T [x x ] dx 18

19 Near-Field Interaction of STM most powerful near-field interaction: tunneling current reasons: very well localized decay length as small as the diameter of an atom no other electrical currents exist that could obscure tunneling current 19

20 Near-Field Interaction of AFM and SNOM near-field interaction: forces between atoms of tip and specimen some forces well localized comparable to tunneling current provide high spatial resolution but: also long-range forces e. g. AFM: van der Waals forces e. g. SNOM: optical far-field need to measure short-range forces on the background of long-range forces 20

21 Far-Field Interactions electrostatic forces isolated charge: force decays as r 2 with distance r not exactly near-field but: fields of multipoles decay more rapidly magnetic forces generally far-field but: decay length of magnetic forces from e. g. alternating magnetic domains domain size 21