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Scanning Probe Microscopy (SPM) Overview & General Principles

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Scanning Probe Microscopy (SPM) Overview & General Principles Scanning Probe Microscopy (FYST42 / FAFN30) Scanning Probe Microscopy (SPM) overview & general principles March 25th, 2020 Jan Knudsen, [email protected] Rainer Timm, [email protected] join via Zoom: https://lu-se.zoom.us/j/204464585 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 Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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, www.fz-juelich.de/jsc/cv/vislab/video/examples/a_emundts Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 What can we learn from an image? Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 What can we learn from an image? Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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 Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 Scanning Probe Microscopes local interaction microscope samples & environment lateral resolution tunnel current scanning tunneling microscope / STM conductive samples with scanning tunneling spectroscopy STS crystalline surfaces atomic ultrahigh vacuum (typical) low temperatures ambient, liquid, ... nm force atomic force microscope AFM vacuum, clean surfaces atomic work function Kelvin probe force microscope KPFM conductive samples electric field / scanning near-field optical SNOM luminescent samples 10 nm light microscope sensitive light detection magnetic field magnetic field microscope MFM larger samples capacitance scanning capacitance microscope SCM processed devices several 10 nm electric field scanning gate microscope SGM electromagnetic shielding effect local mechanical stress, phonon interaction, chemical bond formation, … Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 SPM quiz 1 2 A STM image of graphene B STM image of a GaAs nanowire 3 4 C STS image of Fe atoms on Cu(111) D spin-resolved STM image of Co atoms on Pt(111) E AFM image of a Cu(111) surface F infrared SNOM image of organic 5 6 polymers G Scanning Capacitance Microscopy image of a memory chip H Scanning Gate Microscopy 7 conductance image of a InAs 8 nanowire with InP barriers Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 Examples of SPM images STM images of Graphene on SiO2 STM 3D-rendered and color-coded STM image tip inter- acting 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 Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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: www.almaden.ibm.com/ CO molecules vis/stm/gallery.html on Pt(111) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 Examples of SPM images Science 319, 1066 (2008) AFM images and force/ potential measurements for single Co atoms and CO molecules on Cu(111) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 Examples of SPM images AFM topography image infrared scattering-SNOM image Raschke et al., ChemPhysChem , 2197 (2005) nanophase separation in polymer films 6 thin film consisting of two organic polymers: poly(styrene-b-2-vinylpyridine) and poly(styrene-b-ethyleneoxide) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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 Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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 Boyd, Storm, Samuelson, and Westervelt, the nanowire, through the barriers Nanotechnology 22, 185201 (2011) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 SPM quiz A 2 STM image of graphene B 7 STM image of a GaAs nanowire C 3 STS image of Fe atoms on Cu(111) D 8 spin-resolved STM image of Co atoms on Pt(111) E 6 AFM image of a Cu(111) surface F 5 infrared SNOM image of organic polymers G 1 Scanning Capacitance Microscopy image of a memory chip H 4 Scanning Gate Microscopy conductance image of an InAs nanowire with InP barriers Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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 [email protected] 25 March 2020 Multiple tip artefact tip with 2 microtips surface STM image: GaAs surface step AFM image: top end of a GaN nanowire Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 Tip artefacts in STM images tip changes during imaging Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 Image acquisition Two ways of forming the STM image: The experimental setup: 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 Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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) Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020 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 Scanning Probe Microscopy: overview & general principles [email protected] 25 March 2020.
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