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 makes use of a small bias voltage to pass through a conductive probe tip while simultaneously recording topographic height and local current flow. This dual-channel measurement makes C-AFM an ideal method for studying how electrical behaviour varies across a surface at resolutions down to 50 nm. Such resolutions are far beyond the resolution of the conventional four-point probe or spreading resistance methods.
C-AFM finds numerous applications in the semiconductor industry. For instance, 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 can be used to correlate processing conditions like deposition temperature, annealing atmosphere, doping level, etc., with device-relevant electrical performance. This is a serious advantage that comes with C-AFM as it records topography and current in a single scan pass, and every current feature is accurately registered to its structural point.
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 this floor |
Applied bias range | −10 V to +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?
C-AFM works in contact mode, i.e., the tip is in physical contact with the sample throughout the scan. Materials like platinum-irridium, diamond-like carbon, or doped diamond are coated on the tip. Such materials allow a controlled bias voltage to be applied between the tip and the grounded sample. Local variations in resistance cause the current to change as the tip scans across the surface. These changes are recorded pixel by pixel along with the standard height signal from the laser photodetector system.
Moreover, the method is also capable of holding the tip stationary at a pixel and sweeping the voltage to generate a local current-voltage (I-V) curve. This spectroscopic mode gives information about non-linear conduction behavior like tunnelling, Schottky emission, or resistive switching, which cannot be provided by a single-bias current map. This combination of spatial mapping and local spectroscopy makes C-AFM a comprehensive technique for linking nanoscale structure to electrical behavior.
C-AFM modes
Current imaging: Here, a fixed bias is applied as the tip scans the surface. This results in a spatially resolved map of local current. This method is suited for detecting conductive filaments, defect clusters, grain boundary leakages, and uniformity assessment across thin film surfaces.
I-V spectroscopy: In this mode, the tip is held stationary at given points, and voltage is swept to generate local I-V curves. This reveals tunelling currents, Schottky barriers, and non-linear conduction mechanisms that single bias mapping cannot resolve.
Resistance mapping: Here, the local resistance is calculated from the current map at a known applied voltage. This gives a quantitative nanoscale resistance image. This mode is used in process control for contact layer uniformity and in failure analysis of interconnected stacks.
Table 2: C-AFM vs. standard AFM - technical specifications
Parameter | C-AFM | Standard AFM |
Lateral Resolution | ~20 to 50 nm | ~5 to 20 nm |
Current Range | 1pA-10pA | NA |
Bias Range | -10V to 10V | NA |
Max Scan Area | 100 × 100 µm | 100 × 100 µm |
Max Feature Height | 20 µm | 20 µm |
Probe Type | Pt-Ir doped diamond | Si or Si3N4 |
Vacuum Required? | No | No |
Sample Preparation | Conductive substrate needed | Minimal |
Limitations and alternative techniques
C-AFM requires a conductive tip that needs to be in direct contact with the sample. Therefore, tip wear is an important consideration, especially on hard ceramic and metallic surfaces. Also, highly resistive materials, such as bulk insulators, fall outside the measurable current window, and contamination of native oxide layers can introduce artifacts due to contact resistance. Techniques like scanning spreading resistance microscopy (SSRM) or Kelvin probe force microscopy (KPFM) may be appropriate for such cases. Highly corrugated or rough surfaces (RMS roughness > ~50 nm) complicate stable contact and can generate artefacts in the current channel.
Table 3: Comparison of C-AFM with related scanning probe and electrical characterisation techniques
C-AFM | KPFM | SSRM | Four-point probe | |
Measured quantity | Local current / conductance | Surface potential/work function | Local resistivity (cross-section) | Sheet resistance |
Contact mode | Contact | Non-contact/lift | Contact (high force) | Contact (macro) |
Lateral resolution | 20-50 nm | 30-100nm | 10-30 nm | ~1mm |
Works on insulators? | No | Yes | Limited | No |
I-V spectroscopy | Yes, local | No | Yes, local | No |
Sample destructive technique? | Minimal due to tip contact | Non-destructive | Requires cross-sectioning | Contacts the surface |
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 shortly.
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, i.e., 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
Conductive AFM, also known as current-sensing AFM (CS-AFM) and conductive-probe AFM (CP-AFM), is a variant of atomic force microscopy that uses a conductive probe tip to simultaneously map surface topography and local electrical current at sub-50 nm resolution. It is the standard technique for nanoscale electrical characterization of thin films, 2D materials, and semiconductor surfaces.
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 and is governed by 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 by C-AFM.
A single sample is sufficient. The minimum practical sample size is approximately 5 × 5 mm, though smaller pieces can sometimes be mounted if they are discussed 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 out of the box. Films deposited on fully insulating substrates like bare glass or polymer need 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 absolute current flow through direct tip–sample contact and is best 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 surface potential or 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. The topography signal in C-AFM is identical in resolution and accuracy to standard contact-mode AFM. The electrical channel adds a complete picture of local conductance 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.