CoreAFM application examples

Kelvin probe force microscopy (KPFM) on graphene

Graphene belongs to the category of 2D materials and is of interest in the research and development of new devices and materials. Besides atomic resolution imaging of graphene to learn more about crystal orientation, edges and defects, the functional properties of graphene are also of great interest.

In this application note, multilayer graphene was imaged with Kelvin probe force microscopy (KPFM) using a CoreAFM to study the contact potential difference variation on a single flake.

Optical image recorded on an upright microscope with a 50x NA0.9 objective. Inset: area where KPFM data and AFM images of graphene were recorded

Topview image of same area in CoreAFM

Multilayer graphene flakes were generated by mechanical exfoliation of graphite and subsequent transfer to a silicon-silicondioxide substrate. The KPFM measurement was carried out in single-run mode, recording the contact potential during the scanning of the topography.

Thin flakes were localized on the substrate with an upright microscope. Using markers on the substrate, the same flakes were placed under the cantilever using the topview camera of the CoreAFM, after which AFM images of graphene and KPFM data were recorded.

Overlay of contact potential difference on an AFM topography image of a multilayer graphene flake.

Sample courtesy: Hiske Overweg, Klaus Ensslin, ETH Zürich, Switzerland

All measurements were performed using a CoreAFM system equipped with a PPP-EFMR cantilever from Nanosensors. AFM images of graphene were processed using the MountainsMap SPM.

Out of plane piezoresponse force microscopy (PFM) on Lithium Niobate

Lithium Niobite (LiNbO₃) is an optically transparent, piezo responsive material used, for example, in piezo sensors or in mobile phones. We tested a LiNbO₃ sample (PFM03, obtained from TipsNano, Estonia) with CoreAFM. The sample has a regular domain structure with 10-µm period. The spontaneous polarization has the opposite direction in the neighboring domains.

To measure the piezoresponse during imaging, a 7.5 V AC voltage was applied to the cantilever while raster scanning the tip over the sample. In response to the applied voltage, the sample periodically expands and shrinks, either in phase with or in counter phase to the excitation frequency. Despite a small measured RMS roughness of 0.3 nm, the domains could not be recognized in the topography. The domains could however be readily identified in the out of plane piezoresponse.

Lithium Niobite (LiNbO₃) is an optically transparent, piezo responsive material used, for example, in piezo sensors or in mobile phones. We tested a LiNbO₃ sample (PFM03, obtained from TipsNano, Estonia) with CoreAFM. The sample has a regular domain structure with 10-µm period. The spontaneous polarization has the opposite direction in the neighboring domains.

3D representation of phase in color overlaid on topography of PFM03 showing domains with different phase. Image size: 20 µm

To measure the piezoresponse during imaging, a 7.5 V AC voltage was applied to the cantilever while raster scanning the tip over the sample. In response to the applied voltage, the sample periodically expands and shrinks, either in phase with or in counter phase to the excitation frequency. Despite a small measured RMS roughness of 0.3 nm, the domains could not be recognized in the topography. The domains could however be readily identified in the out of plane piezoresponse.

CoreAFM image gallery

Twisted graphene layers

Magnetic force microscopy of thin permalloy film with stripe domains

Topography of SrTiO3 in dynamic mode

Magnetic force microscopy of digital backup tape

Topography on multilayer graphene

KPFM on multilayer graphene

Topography of MoS2 monolayer

MoS2 monolayer: 3D topography overlaid with KPFM signal

Topography of locally deposited charges on an insulating oxide surface

KPFM of locally deposited charges on an insulating oxide surface

Topography of an integrated circuit structure with multiple transistor contacts

Conductive AFM of an integrated circuit structure with multiple transistor contacts

Out of plane PFM on Lithium Niobate

Electrostatic force (EFM) measurements on aluminum dots deposited on gold

Topography of polished stainless steel

KPFM on polished stainless steel

Digital Inverted Microscope Options

Enhanced viewing ability

Fluorescence measurements

The DIMO uses the internal illumination source for transmission optical microscopy. With the fluorescence option, light from an optical fiber can be easily guided into the CoreAFM for epi-illumination from the bottom.

AFM data can be overlaid with the optical data to colocalize information from each imaging mode. The image shows an overlay of AFM topography with fluorescence (green) and transmission light (gray) optical microscopy images. The overlay was created with MountainsMap image processing software.

High-powered microscope optics

0.8 μm resolution with 20× 0.4 NA objective shown on USAF 1951 Resolving Power Test Target

FluidFM^® on the CoreAFM using DIMO

Nanosurf has a long-standing collaboration with Cytosurge and has been developing FluidFM^® solutions for FlexAFM since 2011, offering powerful applications for single-cell analysis and manipulation.

The DIMO upgrades the CoreAFM to be capable of performing FluidFM^® on biological samples too.

Below is an example of FluidFM^® colloidal spectroscopy on HeLa cells: the powerful digital microscope allows you to easily view cells, maneuver the cantilever, and carry out your single-cell manipulations.

Motorized function for cantilever centering and focus

Scanning Microwave Microscopy (SMM)

Scanning microwave microscopy (SMM) is a scanning probe technique, that measures the interactions of a microwave from a sharp tip with the sample. The microwave reflection coefficient (S11 parameter), which is the ratio between the microwave power sent to the tip and the one received back after being reflected at the tip-sample contact, is used to deduce the local tip-sample microwave impedance. The microwave impedance yields information about the local capacitance from which one can deduce the dielectric constant and the dopant density. In terms of the dopant density measurement, the SMM is similar to the scanning capacitance microscopy (SCM), but offers wider range of measurements. SMM can be used for measurements of not only semiconductors, but also dielectric materials and metals, since it is not solely relying of the modulation of the depletion capacitance in the sample.

Understanding the S11 Parameter

The S11 parameter is defined as a function of the complex impedances of reference impedance (Z₀) and load (Z_L) – Eq.1. Impedance is a complex value and can be represented as a sum of real and imaginary parts – Eq.2. The real part of Z is resistance (R) and the imaginary part can be considered as capacitance (C) -Eq.3. Depending on the sample, resistance and capacitance are functions of conductivity, dielectric constant and carrier density.

Key benefits

• Electrical characterization of materials – dielectrics, semiconductors and metals
• High sensitivity to changes of dopant density in semiconductors
• High sensitivity to DC capacitance
• Minimal sample preparation
• Imaging of buried structures

Application examples

SMM provides ultra-sensitive measurements of local capacitances. A capacitance measurement can yield material or device parameters, and it is indispensable for characterization of semiconductor materials, and electronic structures. Read in more detail about application examples in our SMM technical note and application note on Studies of MC2 capacitance standard sample by scanning microwave microscopy (SMM)

Nanosurf SMM Option

The Nanosurf SMM option is currently available for the Nanosurf CoreAFM and FlexAFM and DriveAFM.

CoreAFM options and accessories

Standard sample holder

Samples up to 100 mm in diameter, central magnet to hold small samples on pucks, clips to hold larger samples.

Petri dish holder

Holds petri dishes of 35 or 50 mm diameter and height up to 10 mm.

Heater sample holder

Heats samples up to 250 °C. Needs TEC controller CH1.

Cooling & heating sample holder

Temperature range of -35 °C to 180 °C. Needs TEC controller CH1, pump and temperature reference unit.

TEC contoller CH1

Temperature monitoring and control, temperature stability < 0.05 °C.

Pump and temperature control unit

Used with cooling & heating sample holder. Includes a pump and temperature control unit for the circulating coolant.

C-AFM sample holder

Sample holder for advanced conductive AFM option. Current range of ± 25 nA with a sensitivity of 10⁸ V/A. Current noise 1.5 pA at 2 kHz bandwidth.

150 µm z-stage

Z-range extension of up to 150 µm for long range force spectroscopy experiments. For petri dishes of 35 mm diameter and 50 mm diameter.

Variable magnetic field sample holder

Variable in-plane magnetic field, integrated Hall sensor, Max. field – 720 mT (2 mm gap), Field resolution – 0.1 mT, Sample size - up to 10 x 10 mm².

Digital inverted microscope option

The DIMO can be integrated with Isostage 300, SMA optical port for illumination, Motorized centering and focus, Nikon objective, Fluorescence option with a fiber coupled light source.

EC cell

For electrochemical experiments, PEEK or PVDF EC cell in a stainless-steel frame. Built-in electrode and tubing feedthroughs.

Environmental control chamber

For sample measurements under controlled environments. Expanding sealing membrane. Gas inlet and outlet.

AE 350

Acoustic enclosure for the stand-alone setup

Samples & mode kits

Mode Kits

• CoreAFM standard conductive AFM mode option
• Dynamic force mode kit
• EFM mode kit
• Force modulation mode kit
• Lateral force mode kit
• Phase imaging mode kit
• Standard liquid mode kit
• Standard lithography kit
• Standard MFM mode kit
• Standard spectroscopy mode kit
• Static force mode kit

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Cantilever holders

• Cantilever holder liquid/air flat
• Cantilever holder liquid/air flat conductive
• Cantilever holder liquid/air flat grooveless 0.3 mm
• Cantilever holder liquid/air flat grooveless 0.6 mm

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Control software

The control software for Nanosurf AFMs is an intuitive platform made for performing your AFM measurements efficiently and easily. Our Service team and software engineers are constantly developing and implementing new features and enhancements to further improve the user experience. We regularly publish new and improved versions, which you can download for free. You can install the software on as many computers as you wish to analyze your data.

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Free lifetime updates: download all software updates for free

All software updates for Nanosurf control software are free of charge. Our software team is constantly working on new features and improvements to make the user experience better, more intuitive and more efficient.

Software features

Scripting interface: Python package for COM interface

Python API for data acquisition and control of Nanosurf atomic force microscopes

At Nanosurf we realize that leading researchers are often interested in modifying the standard routines of an instrument, or else everyone would be doing the same thing with the same hardware.

Sometimes there are also application-specific routines, the scope of which we cannot predict and program ourselves. This is why we developed the Nanosurf Scripting Interface.

This interface can be used for automation of routine tasks and for creating new experiments. It gives the users full control over our user interface, and some control over the hardware functionality.

The Nanosurf control software publishes its functionality via the COM interface, by running an instance of COM Automation Server. COM Automation Clients can ask the server during the runtime about its functions and access them. These functions can be accessed through most modern programming languages: Python, C++, C#, VBS, Matlab, JS, LabView, etc.

For ease of use, Nanosurf has created a Python API for its COM interface. We chose Python as our API language, because of its ease of use and learning, popularity and universality, and because of number of data and image processing libraries used in academia and industry.

The Nanosurf Python package can be downloaded and installed from PyPI using pip:

pip install nanosurf

Additional usability features

• Spectroscopy wizard: follow easy steps to set up spectroscopy measurements
• One software UI for all scan heads: no additional learning curve if you use multiple Nanosurf AFM systems
• Automated deflection calibration
• UI layouts for beginners and advanced users
• Highly configurable graph area with mode-dependent auto-layout: the software automatically shows the relevant graphs and information
• Easy file handling with comfort features: auto apply naming conventions, Windows Explorer integration, image gallery, bulk renaming.