Scanning Probe Microscopy

NREL uses scanning probe microscopy (SPM) tools and techniques, which scan very sharp tips extremely close to (several nanometers) or in contact with the material being analyzed.

The interaction between the tip and the sample surface is monitored and controlled to generate the output, which defines the SPM technique being used. A large number of interactions can be measured, including force, current, and capacitance. This makes SPM flexible and capable of providing information on different properties of materials down to nanoscale spatial resolutions.

Techniques

Atomic force microscopy (AFM) can be used to measure sample topography down to the nanoscale.
Conductive AFM (C-AFM) scans a conductive tip while applying a voltage between the sample and tip to measure current and map out sample conductivity with high spatial resolution.
Kelvin probe force microscopy (KPFM) measures the contact potential between the tip and sample to calculate and map out the work function or electrical potential of the sample with high spatial resolution.
Scanning capacitance microscopy (SCM) provides qualitative information on the doping of semiconductor materials using an atomic force microscope.
Scanning tunneling microscopy (STM) uses tunneling current between the tip and sample surface to measure topography with extremely fine resolution.
Scanning spreading resistance microscopy (SSRM) measures electrical resistivity across a broad range from conductors to insulators.
Scanning thermal ionic microscopy (STIM) measures ionic motion.
Piezo force microscopy (PFM) measures piezo effect.
Magnetic force microscopy (MFM) measures magnetic structure.
Contact resonance and force volume (CR-FV) measures mechanical properties.
Scanning electrochemical microscopy (SECM) measures electrochemical reactions.
Scanning microwave impedance microscopy (SMIM) simultaneously measures conductance and capacitance.

Tools

Scanning Probe Microscopy Instruments and Capabilities
Instrument	Description	Technique Capabilities
Bruker D3100 and D5000	D3100: User AFM with a variety of capabilities D5000: Similar to D3100, but housed inside an Ar glovebox	AFM, KPFM, SSRM, C-AFM, STIM, SCM, PFM, MFM
Operating modes: Atomic force microscopy (AFM) for surface morphology Kelvin probe force microscopy (KPFM) for surface potential Scanning spreading resistance microscopy (SSRM) for electrical resistivity Conductive AFM (C-AFM) for electrical current conduction Scanning thermal ionic microscopy (STIM) for ionic motion Scanning capacitance microscopy (SCM) for charge carrier concentration Piezo force microscopy (PFM) for piezo effect Magnetic force microscopy (MFM) for magnetic structure Spatial resolution(s): AFM: <10 nm lateral and <1 nm vertical resolutions KPFM: 30 nm resolution and 10 mV voltage sensitivity SSRM: 40 nm resolution and a factor of 2 resistance sensitivity C-AFM: 30 nm resolution and 5 pA current sensitivity STIM: 20 nm resolution SCM: 50 nm resolution PFM: 50 nm resolution MFM: 100 nm resolution Max field of view: 100 μm (all operating modes) Unique capabilities: D5000 is housed in Ar glove box to allow measurement of air-sensitive samples KPFM is home-built (second harmonic oscillation) with the state of art combination of artifact-free and spatial/voltage resolutions
Bruker Dimension Icon	Specialty AFM housed inside an Ar glovebox	AFM, SSRM, C-AFM, SCM, CR-FV, SECM, SMIM, PFM, MFM
Operating modes: Atomic force microscopy (AFM) for surface morphology Scanning spreading resistance microscopy (SSRM) for electrical resistivity Conductive AFM (C-AFM) for electrical current conduction Scanning capacitance microscopy (SCM) for charge carrier concentration Contact resonance and force volume microscopy (CR-FV) for mechanical properties Scanning electrochemical microscopy (SECM) for electrochemical reaction Scanning microwave impedance microscopy (SMIM) for simultaneous conductance and capacitance Piezo force microscopy (PFM) for piezo effect Magnetic force microscopy (MFM) for magnetic structure Spatial resolution(s): AFM: <10 nm lateral and <1 nm vertical resolutions SSRM: 40 nm resolution and a factor of 2 resistance sensitivity C-AFM: 30 nm resolution and 5 pA current sensitivity SCM: 50 nm resolution CR-FV: 100 nm resolution SECM: 200 nm resolution and 5 pA electrochemical current sensitivity SMIM: 100 nm resolution PFM: 50 nm resolution MFM: 100 nm resolution Max field of view: 100 μm (all operating modes) Unique capabilities: Housed in Ar glove box to allow measurement of air-sensitive samples
Nanonics MultiView 4000	Dual probe AFM for optoelectronic SPM measurements	AFM, NSOM, DOPB, DECM
Operation modes: Dual probe atomic force microscopy Near-field scanning optical microscopy (NSOM) for near-field optical signal Dual configuration for optical pump/probe (DOPB) Dual probe for electrical conduction measurement (DECM) Spatial resolution(s): AFM: 10 nm lateral and 1 nm vertical resolutions NSOM: 100 nm resolution DOPB: 100 nm resolution DECM: 50 nm resolution Max field of view: Sample scan range of 100 μm and probe scan range of 30 μm (all operating modes) Unique capability: Dual probe distance is only limited by probe size and can be up to 4.5 mm
Omicron UHV VT-STM/AFM	Ultra-high vacuum STM and AFM for high image quality	AFM, STM, KPFM, C-AFM
Operation modes: Ultra-high vacuum scanning tunneling microscopy (STM) with variable temperature of 50 K — 650 K Ultra-high vacuum atomic force microscopy (AFM) with variable temperature of 50 K — 650 K Kelvin probe force microscopy (KPFM) for surface potential Conductive AFM (C-AFM) for electrical current conduction Spatial resolution(s): STM: 0.1 nm lateral and 0.01 nm vertical resolutions AFM: 10 nm lateral and 1 nm vertical resolutions KPFM: 30 nm resolution and 10 mV voltage sensitivity C-AFM: 30 nm resolution and 2 pA current sensitivity Max field of view: 12 μm (all operating modes) Unique capability: Beam reflection type AFM in UHV assures high image quality

Three-dimensional AFM image of gallium phosphide grown on a silicon substrate showing atomic-scale terraces and step ledges. AFM produces real 3D representations of sample surface which can be rotated to reveal morphological and topographical features.

AFM (top) and C-AFM (bottom) images of a cadmium telluride film showing enhanced conductivity at grain boundaries.

SSRM (top) and corresponding AFM (bottom) images showing significant increases in electrical resistance across a degraded interface between a silver grid finger and silicon solar cell.

Probing spatial distribution of minority carrier transport in photovoltaic materials by dual probe of e-beam excitation and near-field scanning optical microscopy (NSOM)-probe light collection.

Contact

Senior Scientist, Materials Science

Chun.Sheng.Jiang@nrel.gov
303-384-6687