Conductive atomic force microscopy
Conductive AFM (C-AFM) simultaneously maps surface topography and local electrical conductivity at the nanoscale. This enables direct correlation between structural and electronic properties in thin films, 2D materials, and nanodevices.
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What is C-AFM analysis used for?
C-AFM is a specialized contact mode AFM technique that applies a bias voltage between a conductive probe tip and the sample while simultaneously recording topographic height and the resulting local current. This dual-channel measurement makes C-AFM an ideal method for studying how electrical behavior varies across a surface at resolutions down to 20 nm, far beyond the resolution of the conventional four-point probe method. Because topography and current are recorded in a single scan pass, every current feature is accurately registered to its structural origin.
In the semiconductor industry, C-AFM is routinely used to identify leakage pathways in thin gate dielectrics, map grain boundary conductance in polycrystalline thin films, and assess the uniformity of contact layers. For energy materials, it provides quantitative data on local charge transport efficiency in organic photovoltaic blends, perovskite absorbers, and solid-state electrolytes. It is also very useful in detecting nanoscale defects like pinholes, conductive filaments, or resistive switching domains in oxide layers that are invisible to other structural characterization methods.
C-AFM is further used to correlate processing conditions like deposition temperature, annealing atmosphere, and doping level with device-relevant electrical performance.
Detection limits and measurement range
The measurable quantities in C-AFM span several orders of magnitude. The table below summarizes the practical operating ranges for current, voltage, and spatial resolution, along with the conditions that affect these limits.
Table 1: C-AFM operating ranges and detection limits
Parameter | Range/Limit | Notes |
Current detection range | ~1 pA – 10 µA | Depends on amplifier gain setting; lower gain extends the upper limit but sacrifices sensitivity at the pA end |
Current noise floor | ~0.5 – 2 pA | Limited by amplifier noise. Therefore, cleaner samples and stable environments lower the floor |
Applied bias range | −10 V – +10 V | Lower voltages (±1 V or less) are preferred for fragile films to avoid permanent tip or sample damage |
Lateral spatial resolution | 20 – 50 nm | Governed by the tip radius. Doped-diamond tips provide harder contact and finer resolution on rough surfaces |
Vertical (Z) resolution | < 0.1 nm | Topography channel identical to standard contact-mode AFM |
Maximum scan area | 100 × 100 µm | Larger areas can be tiled; data processing time increases |
Maximum feature height | ~20 µm | Highly stepped samples may shadow the tip during scanning |
Minimum measurable resistivity | ~10−3 Ω·cm | Highly resistive materials (>109 Ω·cm) fall below the pA noise floor and cannot be reliably mapped |
How does C-AFM work?
The probe tip used in C-AFM is coated with a hard conductive material such as platinum-iridium or doped diamond, which withstands the abrasion of contact-mode scanning. As the tip scans, local variations in resistance change the measured current, which is recorded pixel by pixel alongside the height signal from the laser photodetector.
The tip can also be held stationary at a single point while the voltage is swept, generating a local current-voltage (I-V) curve. This spectroscopic mode gives information about non-linear conduction behavior such as tunneling, Schottky emission, or resistive switching, which a single-bias current map cannot provide.
C-AFM modes
Current imaging applies a fixed bias during the scan, resulting in a spatially resolved current map. It is used to detect conductive filaments, defect clusters, and grain boundary leakage, and to assess uniformity across thin film surfaces.
I-V spectroscopy generates local current-voltage curves at selected points, identifying the conduction mechanism at a specific feature rather than its spatial distribution.
Resistance mapping converts a current map acquired at a known bias into a semi-quantitative resistance image that can be used in process control for contact layer uniformity and in failure analysis of interconnect stacks.
Limitations and alternative techniques
C-AFM requires a conductive tip in direct contact with the sample, making tip wear a significant consideration, particularly on hard ceramic and metallic surfaces. Surfaces with RMS roughness above ~50 nm make stable contact difficult and can generate artifacts in the current channel, as can contamination or native oxide layers that add variable contact resistance.
Highly resistive materials such as bulk insulators fall outside C-AFM's measurable current window. Kelvin probe force microscopy (KPFM) is the usual alternative for such samples, as it measures surface potential without requiring current flow. Scanning spreading resistance microscopy (SSRM) is better suited for projects where quantitative resistivity is required, although it requires a cross-sectioned sample.
Table 2: Comparison of C-AFM with related scanning probe and electrical characterization techniques
C-AFM | KPFM | SSRM | ||
Measured quantity | Local current/conductance | Surface potential/work function | Local resistivity (cross-section) | Sheet resistance |
Sample preparation | As-received surface | As-received surface | Polished cross-section required | As-received surface |
Lateral resolution | 20–50 nm | 30–100 nm | 10–30 nm | ~1 mm |
Works on insulators? | No | Yes | Limited | No |
I-V spectroscopy | Yes, local | No | Yes, local | No |
Destructive technique? | Largely non-destructive; possible surface modification from tip contact | Non-destructive | Destructive; requires cross-sectioning | Non-destructive; may leave probe marks |
Best for | Thin films, 2D materials, organics | Work function/band alignment | Doped Si cross sections | Sheet resistance QC |
Our C-AFM analysis services
Measurlabs provides C-AFM measurements for clients in the semiconductor industry and related fields, including energy materials research and 2D materials characterization. For surface topography determination without the electrical channel, we also offer conventional AFM and optical profilometry measurements, and can advise on the most suitable technique for your application.
We offer a full set of advanced techniques for thin film and semiconductor characterization, allowing you to get all the analyses you need through a single point of contact. Use the form below to tell us about your samples and measurement goals, and we will get back to you in one business day.
Method Expert
Suitable sample matrices
- Silicon (Si), SiO2, SiC, GaN, and GaAs wafers with thin film stacks
- Thin films of ALD and CVD oxides, nitrides, and oxynitrides
- Organic semiconductor films and photovoltaic blends
- Perovskite absorber and transport layers
- Graphene, MoS2, and other van der Waals materials
- Metal and alloy thin films on conductive substrates
- Solid-state electrolyte and battery electrode materials
- Resistive switching oxide stacks (HfO2, TiO2, NiO)
Ideal uses of C-AFM
- Leakage detection through nanoscale conductance mapping of gate dielectrics and tunnel oxides
- Grain boundary and domain wall conductance in polycrystalline and multiferroic films
- Local I-V characterization of resistive switching layers in memory devices
- Charge-transport mapping in organic and perovskite photovoltaic absorbers
- Defect density and pinhole detection in ALD and CVD barrier layers
- Electrical uniformity assessment in 2D materials like graphene and MoS2
- Process optimization and quality control for thin film deposition, e.g., correlating deposition temperature, pressure, or precursor with electrical uniformity
- Failure analysis of interconnects, contacts, and barrier layers in microelectronic devices
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Frequently asked questions
The current detection range is approximately 1 pA to 10 µA, depending on the amplifier gain setting. Lateral spatial resolution is typically 20–50 nm, depending on the tip radius. Applied bias can range from −10 V to +10 V. Materials with resistivity above ~10⁹ Ω·cm fall below the noise floor and cannot be reliably characterized.
A single sample is sufficient. The minimum practical sample size is approximately 5 × 5 mm, though smaller pieces can sometimes be mounted if agreed in advance. We recommend sending at least two samples for comparative or process optimization studies. C-AFM is non-destructive, so samples can be returned after measurement at an extra cost.
Yes. C-AFM requires an electrical circuit from the tip through the film to a grounded substrate. Silicon, metal foils, and ITO glass work as is. Films deposited on fully insulating substrates such as bare glass or polymer require a thin conductive back-contact layer, such as 10–20 nm of sputtered Ti or Cr added before film deposition. Contact our team before sending samples, and we will advise you on the simplest preparation route.
C-AFM measures the absolute current flow via direct tip–sample contact and is best suited for conductance mapping, leakage detection, and local I–V spectroscopy on thin films and surfaces. KPFM (Kelvin probe force microscopy) operates in non-contact mode and maps the surface potential (work function) without passing current. This is ideal when tip wear is a concern or when you need band alignment information. SSRM (scanning spreading resistance microscopy) uses a very high contact force with a diamond tip and is optimized for resistivity profiling of cross-sectioned silicon device structures, with a wider dynamic range than C-AFM but requiring sample cross-sectioning. We offer all three techniques and can recommend the right combination for your measurement goal.
Standard AFM measures only the mechanical deflection of the cantilever to reconstruct surface topography. C-AFM adds a conductive probe coating and a current amplifier in series with the tip–sample junction, enabling simultaneous measurement of electrical current alongside height, with identical resolution and accuracy, and without any additional scan or sample preparation steps.
Measurlabs offers a variety of laboratory analyses for product developers and quality managers. We perform some of the analyses in our own lab, but mostly we outsource them to carefully selected partner laboratories. This way we can send each sample to the lab that is best suited for the purpose, and offer high-quality analyses with more than a thousand different methods to our clients.
When you contact us through our contact form or by email, one of our specialists will take ownership of your case and answer your query. You get an offer with all the necessary details about the analysis, and can send your samples to the indicated address. We will then take care of sending your samples to the correct laboratories and write a clear report on the results for you.
Samples are usually delivered to our laboratory via courier. Contact us for further details before sending samples.