Scanning Probe Microscopy (SPM)

Transcription

1 Scanning Probe Microscopy (FYST42 / FAFN30) Scanning Probe Microscopy (SPM) overview & general principles March 23 th, 2018 Jan Knudsen, room K522, jan.knudsen@sljus.lu.se Rainer Timm, room K516, rainer.timm@sljus.lu.se

2 Scanning Probe Microscopy: principle scanning a probe tip over a sample surface, measuring some kind of interaction, obtaining a magnified image analogy: record player figures: M. Dähne, TU Berlin

3 Scanning SPM tip video: STM tip scanning lead (Pb) particles on ruthenium (Ru), scan range 5 µm, imaged with a scanning electron microscope FZ Jülich,

4 What can we learn from an image?

5 What can we learn from an image?

6 What can we learn from an image? An image: presents information about an object depends on the imaging technique often needs interpretation is a projection (2-dimensional) is a snapshot (time) An SPM image: usually shows objects smaller than the wavelength of light is never a photographic picture, but converts information into a color scale figure

7 Tip-sample interaction in SPM local interaction microscope tunnel current scanning tunneling microscope / scanning tunneling spectroscopy STM STS force atomic force microscope AFM work function Kelvin probe force microscope KPFM electric field / light scanning near-field optical microscope SNOM magnetic field magnetic field microscope MFM capacitance scanning capacitance microscope scanning microwave microscope SCM SMM electric field effect scanning gate microscope SGM local mechanical stress, phonon interaction, chemical bond formation,

8 Scanning Probe Microscopes local interaction microscope samples & environment lateral resolution tunnel current scanning tunneling microscope / scanning tunneling spectroscopy STM STS force atomic force microscope AFM conductive samples with crystalline surfaces ultrahigh vacuum (typical) low temperatures ambient, liquid,... vacuum, clean surfaces atomic nm atomic work function Kelvin probe force microscope KPFM conductive samples electric field / light scanning near-field optical microscope SNOM magnetic field magnetic field microscope MFM capacitance electric field effect scanning capacitance microscope scanning microwave microscope scanning gate microscope SCM SMM SGM luminescent samples sensitive light detection larger samples processed devices electromagnetic shielding 10 nm several 10 nm local mechanical stress, phonon interaction, chemical bond formation,

9 Examples of SPM images STM images of Graphene on SiO 2 3D-rendered and color-coded STM image STM tip interacting with a Graphene membrane M. Morgenstern, Phys. Stat. Sol. B 248, 2423 (2011) T. Mashoff et al., Nano Lett. 10, 461 (2010) M. Pratzer, RWTH Aachen

10 Examples of SPM images GaAs nanowires STM images of different size E. Hilner et al., Nano Lett. 8, 3978 (2008) M. Hjort et al., Nano Lett. 13, 4492 (2013)

11 Examples of SPM images Fe atoms on Cu(111) electron density waves: STS images of artificially built quantum corrals atom manipulation Xe atoms on Ni(110) Don Eigler, IBM Almaden: vis/stm/gallery.html CO molecules on Pt(111)

12 Examples of SPM images STM images of Co atoms on a Pt(111) surface, imaged under external magnetic field and with magnetized STM tips Meier et al., Science 320, 82 (2008)

13 Examples of SPM images Science 319, 1066 (2008) AFM images and force/ potential measurements for single Co atoms and CO molecules on Cu(111)

14 Examples of SPM images AFM topography image infrared scattering-snom image nanophase separation in polymer films Raschke et al., ChemPhysChem 6, 2197 (2005) thin film consisting of two organic polymers: poly(styrene-b-2-vinylpyridine) and poly(styrene-b-ethyleneoxide

15 Examples of SPM images Scanning Capacitance Microsocpy (Scanning Microwave Microscopy): Imaging the capacitance (impedance) of n- and p-type semiconductor transistors on a SRAM memory chip topography dc / dv topography capacitance C dc / dv

16 Examples of SPM images conductance through the nanowire (colorscale) as a function of tip position, acting as local gate Scanning Gate Microscopy on an InAs nanowire with InP barriers: quantum-confined states in the central nanowire segment energy of these states is shifted by the electric field of the AFM tip resonances in conductance along the nanowire, through the barriers Boyd, Storm, Samuelson, and Westervelt, Nanotechnology 22, (2011)

17 Influence of the probe tip The lateral resolution depends on the probe tip and the kind of interaction: STM: 90% of the tunneling current through the topmost atom AFM: atomic resolution possible, but not standard SNOM: glas fibre of several nm diameter + diffusion of charge carriers inside sample The resulting image is always a convolution of the tip shape and the actual surface structure! Scanning Probe Microscopy: overview & general principles Rainer.Timm@sljus.lu.se 23 March 2018

18 Multiple tip artefact tip with 2 microtips surface STM image: GaAs surface step AFM image: top end of a GaN nanowire

19 Tip artefacts in STM images tip changes during imaging

20 History of SPM 1982 invention of STM by Binnig, Rohrer, Gerber & Weibel 1986 Nobel prize to Binnig & Rohrer 1986 invetion of AFM by Binnig, Quate & Gerber STM linescans on Au(110) Binnig et al., Phys. Rev. Lett. 49, 57 (2008)

21 Image acquisition The experimental setup: Two ways of forming the STM image: a) is almost always used! a) constant-current mode: I constant, feedback loop active, Z variation measured b) constant-height mode: Z constant, feedback loop idle, I variation measured

22 Image acquisition tip height determined by: sample topography (A) surface material properties (B/C) tip shape (A) G. Binnig et al., Phys. Rev. Lett. 49, 57 (1982)

23 Conclusion scanning probe microscopy scan a probe across a surface measuring physical interaction specific interaction between probe tip and sample tunneling current (STM) tip-sample force (AFM) electric field / light (SNOM) influence of the probe tip convolution of tip shape and sample topography double-tip effect advantages and limitations of SPM images nice, direct images of an object limited to a 2D snapshot footprint of the imaging technique not a photograph