14.2 Advanced characterization and imaging techniques
3 min read•august 7, 2024
Advanced characterization and imaging techniques are crucial for understanding molecular electronics at the nanoscale. From scanning probe microscopy to electron microscopy and spectroscopy, these methods offer unprecedented insights into material properties and behaviors.
Optical spectroscopy methods like Raman and provide valuable information about molecular structures and dynamics. Single-molecule techniques push the boundaries of detection, enabling researchers to study individual molecules and their interactions.
Scanning Probe Microscopy Techniques
Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM)
STM utilizes quantum tunneling of electrons between a sharp probe tip and a conductive sample surface to create high-resolution images of the surface topography and electronic structure
Provides atomic-scale resolution, enabling the visualization of individual atoms and molecules on surfaces (graphene, carbon nanotubes)
AFM uses a cantilever with a sharp tip to scan the sample surface, measuring the force interactions between the tip and the surface
Offers and can be used on both conductive and non-conductive samples (polymers, biological samples)
AFM has various modes of operation, including contact mode, non-contact mode, and tapping mode, each suited for different types of samples and measurements
Kelvin Probe Force Microscopy (KPFM) and Conductive Atomic Force Microscopy (C-AFM)
KPFM is a variant of AFM that measures the local work function and surface potential of a sample
Enables mapping of the with nanometer-scale resolution (solar cells, semiconductor devices)
Provides insights into the electronic properties, such as the local work function, band bending, and
C-AFM is another AFM-based technique that measures the local electrical conductivity of a sample
Uses a conductive probe tip to apply a bias voltage and measure the resulting current flow through the sample
Allows mapping of the local electrical properties, such as conductivity, resistivity, and (nanowires, thin films)
Electron Microscopy and Spectroscopy
Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS)
TEM uses a high-energy electron beam transmitted through an ultra-thin sample to create high-resolution images
Provides atomic-scale resolution, enabling the visualization of crystal structures, defects, and interfaces (nanoparticles, 2D materials)
Offers various imaging modes, such as bright-field, dark-field, and high-resolution TEM, as well as analytical capabilities like electron diffraction and energy-dispersive X-ray spectroscopy
XPS is a surface-sensitive spectroscopic technique that measures the elemental composition and chemical state of a sample
Uses X-rays to excite photoelectrons from the sample surface, which are then analyzed based on their kinetic energy
Provides quantitative information about the elemental composition, oxidation states, and chemical bonding (thin films, functionalized surfaces)
Advanced Optical Spectroscopy Methods
Raman Spectroscopy and Ultrafast Spectroscopy
is a vibrational spectroscopy technique that probes the inelastic scattering of monochromatic light by molecules or materials
Provides information about the , chemical structure, and (carbon nanomaterials, semiconductors)
Enables non-destructive and label-free characterization of samples, with high sensitivity and spatial resolution
Ultrafast spectroscopy encompasses a range of techniques that use ultrashort laser pulses to study dynamic processes on femtosecond to picosecond timescales
Includes techniques such as pump-probe spectroscopy, time-resolved fluorescence, and transient absorption spectroscopy
Allows the investigation of fast processes, such as , , and (photovoltaic materials, molecular switches)
Single-Molecule Spectroscopy
techniques enable the detection and analysis of individual molecules, providing insights into their properties and behavior
Includes techniques such as single-molecule fluorescence spectroscopy, scanning probe microscopy-based methods, and
Offers the ability to study heterogeneity, conformational dynamics, and intermolecular interactions at the single-molecule level (fluorescent proteins, DNA-protein interactions)
Requires highly sensitive detection methods, such as confocal microscopy, total internal reflection fluorescence (TIRF) microscopy, or near-field scanning optical microscopy (NSOM)
Provides fundamental understanding of molecular processes and enables the development of novel sensing and imaging applications (single-molecule biosensors, super-resolution imaging)