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Scanning Probe Microscopy Overview


Description:

In scanning probe microscopy (SPM), commonly termed atomic force microscopy (AFM), the interaction of a stylus probe and sample surface is quantified and mapped across the sample.  The probe or "tip" is of nanometer-scale sharpness, and the standard image is 3D surface topography at a resolution approaching the atomic or molecular scale.  The tip is attached to a microfabricated cantilever of low spring constant.  Property-sensitive imaging modes are performed simultaneous to topographic imaging.  Gaseous or liquid media, plus sample temperature, can be controlled.  Tip chemistry can be modified for controlled studies of probe-sample interaction.

The Characterization Facility has four scanning probe microscopes:


Accessories and special features (all SPM's except where indicated):

  • Optical access.  Ability to acquire digital video image.  Optional inverted light microscope on SPM 3.
  • BNC breakout box; may interface with the following four items as well as temperature and humidity signals
  • SRS external lock-in amplifier (only SPM 1-2; e.g., to provide true phase measurement in place of extender electronics)
  • Custom adder circuit box for signal manipulation, for example to ramp set point during imaging (e.g., for friction-load characterization; only SPM 3-4)
  • LabView station with virtual instruments: oscilloscope, digital signal analyzer, function generator (only SPM 3-4)
  • Witec pulsed force mode for adhesion and stiffness imaging (digital version only on SPM 4, to capture entire force curves with second computer).
  • Optional closed-loop scanners (nPoint on SPM 1-2; Agilent on SPM 4)
  • MAC III box for multifrequency excitation, three lock-in amplifiers, Q control, contact resonance, and single-pass EFM/KFM (only on SPM 4)
  • Magnetic AC mode (only on SPM 3-4 and requires magnetically coated maclevers)
  • Closed (SPM 1-2) and open (SPM 3-4) liquid cells
  • Sample heating (to 250° C) and Peltier (-30 to +35° C) stages (only SPM 4)
  • Humidity control (1-95% on SPM 3, 0.1-95% on SPM 4)
  • Cryo-microtome for cross sectioning samples.  Double-D clamp for mounting cross-sectioned samples for AFM.
  • XYZ manipulator to attach SiO2 or polystyrene microspheres to tipless cantilevers
  • Plasma chamber and metal evaporator for chemical modification of tips by users.  Tip modification using silane linkage or gold coating/thiolate chemistry
  • Special software:
    • - Mathematica and ICAdams for quantitative analysis and modeling of force-distance data and dynamic tip-sample interactions, in order to extract sample storage/loss moduli, surface energy, etc.

    - SPIP for broad suite of image (e.g. grain size) and force curve (e.g. freely jointed chain model) analysis applications.  Also freeware programs WSXM and Gwyddion.

    - SPManalysis for custom histogram generation (multiregion, variable bin size), X-offsetted image subtraction (e.g., friction loop), ramped-signal image analysis (average each image over X lines, plot vs. Y meaning time), and myriad image and histogram generation from "force volume" data (Bruker data type).

Applications:

  • Sensitive to the following properties: surface chemistry, storage/loss modulus, hardness, interfacial energy (Hamaker constant), crystallinity, polarization, magnetization, surface charge, and local work function (surface potential).
  • Samples can be imaged in air or in liquid media in all modes of operation.
  • Can measure tribological response versus load, scan velocity, temperature, relative humidity.

Capabilities:

  • No sample pre-treatment needed and imaging can be performed in air.
  • Sample can be conductive or nonconductive, hard or soft.
  • Positioning resolution is 0.1 nm laterally and 0.01 nm vertically; imaging lateral resolution depends on sample/tip characteristics (adhesive contact mechanics) and typically is of order 1-10 nm.

Basic Training:

  • Please visit our General Policies web page, which is confirmed during user registration.
  • Training is suitable for those who will engage in a significant amount of usage, typically months or years of frequent use.  Short-term analysis of a small to moderate number of samples should be done by the CharFac staff instead as an analytical service.
  • Beyond the mandatory three training sessions, additional assisted session(s) may be needed even for basic AFM methods (especially if your sample is difficult), and should be sought without hesitation.  -- Our mission statement mandates that we train people to do goodanalytical research.
  • Beyond basic training there is much more that one can learn to do with AFM (i.e., more advanced, research-intensive methods) and thus we encourage further training.  Literature can be provided, and experts can advise on higher methods in the context of your research problem.

Training Description:

The scheduled sessions are located at:

    (I, all trainees) 201-202 Shepherd
    (II, those training on spm1-2 OR spm3-4) 87 Shepherd OR 1-214 Nils Hasselmo
    (III, as individuals) 87 Shepherd OR 1-214 Nils Hasselmo


The three mandatory sessions are, briefly:

    (I) overview presentation/consultation as a group (2 hours)
    (II) demo; intro to hardware/software (3 hours)
    (III) one-one-one, hands-on with trainee’s sample (2 hours)


In detail:

    (I) Principles of the technique: tip/cantilever, force measurement, Z dependence of forces, XY scanning, topographic imaging under feedback, contact versus tapping/AC modes, compositional imaging via friction force and phase, attractive/repulsive regimes of dynamic ("tapping"/"AC") mode, complications due to complexities of tip-sample interaction, artifacts.  Brief concepts of force curve mapping / pulsed force mode (similar to “peak force tapping”); full training in force-curve mapping modes is an additional session.

    (II) Cantilever/sample/optics setup, software setup, approach to engagement (optical and thermal artifacts), set point adjustment and tip state diagnostics in approach-retract (force curve) mode, image acquisition details in multiple modes, zooming/translation (piezocreep artifacts), core software procedures for post processing (issues of raw versus modified data, nonlinearity artifacts), image rendering, quantitative analysis and file exporting.

    (III) Step-by-step hands-on sessions using trainee sample, focusing on contact or dynamic (“tapping”/”AC”) mode depending on the nature of the trainee's sample and research questions.


Document downloads:

Full introduction to AFM (18pp)  [  PDF 1.3MB]
Brief SPM training overview  [  PDF 24kB]
Clarification of "tapping" and non-contact  [  PDF 17kB]
Dissipation interpretation of phase  [  PDF 53kB]
Post-training self-test  [  PDF 33kB]


Documents specifically for SPM1-2:
   SPM1-2 setup document  [  PDF 456kB]
   Clarification of Extender phase on SPM1-2  [  PDF 18kB]


Documents specifically for SPM3-4:
   SPM3-4 hardware  [  PDF 11MB]