Electrostatic and Kelvin Probe Force Microscopy

Kelvin Probe Force Microscopy (KPFM) is a non-contact technique with nanoscale resolution that measures the contact potential difference (CPD) between a conductive AFM tip and a sample, unveiling work function variations or surface potentials in non-metals. When operated in open loop, namely electrostatic force microscopy (EFM), it can provide insights into charge density and local dielectric properties. KPFM/EFM are essential for exploring electrical, ionic and electrochemical properties in various research fields, including semiconductors, ferroelectrics, batteries, and photovoltaics.

While traditional KPFM offers excellent spatial resolution, its slow detection speeds, compared to other microscopy techniques like optical or scanning electron microscopy, limit its application to static or quasi-static processes. This restriction is inadequate for analyzing electroactive materials or devices with fast ionic processes. At the CNMS, we have addressed this, by developing a suite of high-speed and time-resolved capabilities, enabling the study of faster phenomena across a broad range of timescales (microseconds to seconds), with the time resolved Kelvin Probe Force Microscopy (tr-KPFM).

Features:

Available modes:

• Amplitude Modulated-KPFM & EFM 
• Frequency Modulated-KPFM                      
• Heterodyne-KPFM                                          
• Band Excitation-KPFM                   (Force and Force Gradient Sensitivity)                     
• Dual Harmonic-KPFM                     (Specialized mode for Liquid Operation)
• 3Dimensional KPFM                       (Rough samples or sub-surface imaging)

Time resolved KPFM:

• G-Mode KPFM                                 (G-Mode Based à microseconds to milliseconds)
• Time resolved-KPFM                      (Lockin Based à ms-100s milliseconds)
• Spiral Scan KPFM                            (PyAE based à 100s milliseconds to minutes) 

Specifications:

• Sample size 12x12 mm
• Requires a back electrode
• Scan range (30x30 um, 80x80 um) 
• Z height limit (< µm)
• Environmental Control 
• Glove box (Ar filled) 
• Environmental cells for gases: humidity, nonreactive 
• Non-polar or Low molarity liquids possible
• Temperature stage (sample heating 0-250 C) 
• In-situ photoexcitation
• In-situ gating of devices

Applications:

Metals, Energy Materials, Oxides and ferroelectrics, Photovoltaics, Ionic conductors, 2D Materials, Biological systems, Polymers and soft mater.

Equipment:  

Cypher AFM, MFP 3D AFM (Asylum Research) in ambient and liquid

Icon Dimension AFM, (Bruker) in ambient and glove box

Nanosurf (Drive AFM)     

References:

(Book chapter) Checa, Martí, et al. "Advanced Modes of Electrostatic and Kelvin Probe Force Microscopy for Energy Applications." Atomic Force Microscopy for Energy Research. CRC Press, 2022. 45-104.

(Review) Collins, Liam, et al. "Towards nanoscale electrical measurements in liquid by advanced KPFM techniques: a review." Reports on Progress in Physics 81.8 (2018): 086101. DOI 10.1088/1361-6633/aab560

Collins, Liam, et al. "Open loop Kelvin probe force microscopy with single and multi-frequency excitation." Nanotechnology 24.47 (2013): 475702. DOI 10.1088/0957-4484/24/47/475702

Collins, L., et al. "Quantitative 3D-KPFM imaging with simultaneous electrostatic force and force gradient detection." Nanotechnology 26.17 (2015): 175707. DOI 10.1088/0957-4484/26/17/175707

Collins, Liam, et al. "Breaking the time barrier in Kelvin probe force microscopy: fast free force reconstruction using the G-mode platform." ACS nano 11.9 (2017): 8717-8729. DOI 10.1021/acsnano.7b02114

Collins, Liam, Rama K. Vasudevan, and Alp Sehirlioglu. "Visualizing charge transport and nanoscale electrochemistry by hyperspectral kelvin probe force microscopy." ACS applied materials & interfaces 12.29 (2020): 33361-33369. DOI 10.1021/acsami.0c06426

Giridharagopal, Rajiv, et al. "Time-resolved electrical scanning probe microscopy of layered perovskites reveals spatial variations in photoinduced ionic and electronic carrier motion." ACS nano 13.3 (2019): 2812-2821. DOI 10.1021/acsnano.8b08390

Checa, Marti, et al. "High-speed mapping of surface charge dynamics using sparse scanning Kelvin probe force microscopy." Nature Communications 14.1 (2023): 7196. DOI 10.1038/s41467-023-42583-x