Nanoscale Infrared Spectroscopy

Frequently Asked Questions

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Understanding NanoIR/AFM-IR Spectroscopy and Technology

What is nanoscale IR spectroscopy and imaging?

Nanoscale IR spectroscopy and imaging is a family of chemical identification and material characterization techniques that achieve a lateral resolution far below the diffraction limit of light and beyond the limit of conventional infrared spectroscopy.

Like other infrared techniques, nanoscale IR spectroscopy provides the chemical "fingerprint" of a sample by detecting and measuring the interaction between infrared light and the sample surface. This allows identification and quantitation of its chemical composition, material properties, and structure.

Two key nanoscale IR techniques are photothermal AFM-IR and scattering scanning near-field optical microscopy (s-SNOM). Though they use different detection mechanisms (absorbed light and scattered light, respectively), both achieve a lateral resolution <10 nm — breaking the diffraction limit by more than 100x.

What is a nanoscale IR spectrometer?

A nanoscale IR spectrometer is a device that is capable of nanoscale IR spectroscopy. Nanoscale IR spectrometers combine an atomic force microscope (AFM), used to scan the sample, with IR optics and light sources designed to excite molecular absorption in a sample.

Bruker offers nanoscale IR spectrometers designed to meet the needs and measurement requirements of a diverse range of users and applications. Contact us to learn more about our nanoIR3nanoIR3-s, and IconIR systems.

What is AFM-IR spectroscopy?

Photothermal AFM-IR — sometimes called just AFM-IR, nano-IR, photothermal induced resonance (PTIR), infrared nanospectroscopy, or atomic force microscope-based infrared spectroscopy — is a nanoscale chemical and material characterization technique. It is performed using a nanoscale IR spectrometer, which works by applying the tip of an AFM probe to a sample surface to detect thermal expansion caused by the absorption of infrared radiation. In this way, photothermal AFM-IR provides both the spatial resolution of AFM and the chemical analysis and compositional imaging capabilities of infrared spectroscopy.

How does photothermal AFM-IR spectroscopy work?

Photothermal AFM-IR spectroscopy works by detecting thermal expansion caused by the absorption of infrared radiation.

The operating principle for photothermal AFM-IR can be explained in just three simple steps:

  1. An IR laser pulse arrives on the sample surface under the tip
  2. The sample absorbs the IR pulse, causing it to heat up and expand, thus applying a mechanical force on the AFM probe
  3. The magnitude of this force is proportional to the absorption coefficient and can be used to generate an IR spectrum

AFM-IR spectra can be interpreted just like Fourier-transform infrared spectroscopy (FTIR) spectra. Leveraging this ease of nanoscale chemical identification and combining it with correlated mechanical measurements on the AFM provides a valuable solution for researchers.

What is nanoscale IR spectroscopy used for?

Nanoscale IR spectroscopy is useful for any team that wants to perform infrared imaging and analysis below the diffraction limit. Nanoscale IR spectroscopy is not constrained in resolution by the diffraction limit and can be used for both organic and inorganic materials that are IR-absorbing, including polymers, biological materials, 2D materials, and semiconductors.

Moreover, Bruker’s exclusive photothermal AFM-IR technology allows for direct, model-free detection of materials down to individual monolayers, enabling rapid non-destructive chemical identification and characterization, simultaneous with mechanical property mapping.

Using NanoIR/AFM-IR Spectroscopy

What are the different types/modes of AFM-IR?

Bruker's photothermal AFM-IR technology is expanding the research possibilities for nanoprobe-based infrared measurements and chemical detection. Our Resonance Enhanced AFM-IR, Tapping AFM-IR, and Surface Sensitive AFM-IR modes all enable high-resolution, high-sensitivity chemical imaging with monolayer measurement sensitivity, extending the applications of nanoIR to an ever wider range of samples and applications.

How difficult is AFM-IR spectroscopy to use and analyze?

Bruker’s photothermal AFM-IR spectroscopy is easy to use and straightforward to analyze. After loading a sample, the operator’s role in the measurement process mostly consists of defining measurement locations and parameters. Data is interpreted just like a Fourier-transform infrared spectroscopy (FTIR) spectrum, using established spectral libraries like Wiley’s KnowItAll.

What is Resonance Enhanced AFM-IR?

Resonance Enhanced AFM-IR is a contact mode technique in which the pulse rate of the laser source is set to a resonance frequency of an AFM cantilever. Well-established as a fundamental nanoscale IR spectroscopy mode, it has continually demonstrated monolayer sensitivity to enable chemical analysis on the thinnest samples. This technique is simple, highly sensitive, and operates in a linear force regime, offering direct spectral correlation to FTIR.

Resonance Enhanced AFM-IR is best for: Situations in which spectral identification is the primary goal and ease-of-use is a primary concern. Resonance Enhanced AFM-IR also provides the foundation for Bruker's proprietary Tapping AFM-IR and Surface Sensitive AFM-IR modes, which enhance and extend the capabilities and sample compatibility of the photothermal AFM-IR technique.

What is Tapping AFM-IR?

Bruker's patented Tapping AFM-IR mode is a method of photothermal AFM-IR spectroscopy in which the nanoscale IR spectrometer operates in tapping mode. In Tapping AFM-IR mode, the pulse rate of the laser is the difference frequency of two AFM cantilever resonances.

The small vertical and lateral forces of tapping mode allow this technique to be used for soft and loosely bound materials. The intermittent response also improves the lateral resolution to <10 nm.

Tapping AFM-IR is ideal for: Samples with the smallest domains, hydrogels, and the most difficult samples.

What is Surface Sensitive AFM-IR?

Surface Sensitive AFM-IR is a contact mode technique that makes it possible to distinguish top surface data from that of layers and bulk material beyond the probing depth.

As in Tapping AFM-IR — which Surface Sensitive AFM-IR is based on — the pulse rate of the laser is the difference frequency of two AFM cantilever resonances. To further extend measurement capabilities, Surface Sensitive AFM-IR uses high laser pulse rates and a heterodyne detection mechanism. These confine the detected signal to the top surface of the material and eliminate the need for microtoming/cross-sectioning of multilayer samples.

Surface Sensitive AFM-IR is best for: Multilayered samples with multiple absorbing species layered on top of each other and large IR absorbers that would otherwise cause spectral saturation when measured by other IR techniques.

What AFM probes should I use for nanoscale IR spectroscopy?

Bruker is the only major AFM/SPM equipment manufacturer that also owns and operates a probes nanofabrication facility. Find out more about our AFM-IR probes or see our reference guide for probe selection.

Selecting a Nanoscale IR Spectrometer

What are some general considerations?

An instrument's utility for any application depends on factors including sample type and size, material thickness, and need for correlative electrical and mechanical microscopy. The following segments provide some guidelines for choosing the right Bruker nanoscale infrared spectrometer for some common applications.

Contact us to discuss your specific sample and measurement requirements. We will be happy to provide instrument and configuration recommendations tailored to your needs.

What makes Bruker’s nanoscale IR spectroscopy technology unique?

At the core of Bruker’s nanoscale IR spectroscopy (nanoIR) systems is our patented photothermal AFM-IR technique. Photothermal AFM-IR uniquely provides non-destructive, model-free chemical spectroscopy and imaging, minimizing complex sample preparation and system set-up and allowing for direct data interpretation over the broadest range of material types.

Photothermal AFM-IR produces spectra that are directly comparable to FTIR spectra, making data analysis and interpretation easy and accessible. Data acquisition is done by coupling IR optics to an AFM, leading to a lateral resolution that is on the order of an AFM tip radius — far smaller than the IR diffraction limit. Providing easy-to-interpret chemical information at the nano-scale has enabled breakthrough research and discovery across many fields, including life sciences, polymer sciences, and semiconductors.

For decades, Bruker has been the leading manufacturer of FTIR and AFM platforms. We released our first FTIR in 1974 and our first AFM in 1989. Leveraging the expertise gained over these many years, Bruker has consistently developed high-performance and robust photothermal AFM-IR platforms with capabilities that extend and break the boundaries of what is achievable by traditional infrared spectroscopy.

Which nanoIR system should I choose for working with wafers or wafer-sized samples?

The Dimension IconIR300 is the ideal platform for analyzing wafer-sized samples. This system provides the high performance and advanced correlative imaging capabilities of the Dimension IconIR system with 300 mm of sample access.

Which nanoIR system should I choose to perform correlative imaging with other AFM modes?

The Dimension IconIR platform offers correlative imaging modes for ultimate versatility in materials research and industrial R&D. The system enables correlative microscopy and chemical imaging with enhanced resolution and monolayer sensitivity, while its unique large-sample architecture provides ultimate sample flexibility for the broadest range of applications.

The flagship Dimension IconIR has 150 mm of sample access. For correlative imaging of wafer-sized samples, the Dimension IconIR300 provides full-wafer, 300 mm sample access.

Which nanoIR system should I choose for a multi-user facility?

To accommodate the needs of a large number of users, we recommend the Dimension IconIR system.

Bruker nanoscale IR spectrometers offer the world’s easiest to use and most productive nanoscale chemical analysis capabilities. The Dimension IconIR also offers the broadest range of operational capabilities; it can access a variety of standard AFM imaging modes, enabling correlative imaging and analysis of a wide range of sample types in addition to sub-10nm photothermal AFM-IR imaging.

Which system should I choose for routine photothermal AFM-IR analysis on small samples?

The nanoIR3 offers a streamlined solution for performing routine chemical analyses on small samples. This platform provides easy-to-use functionality and direct, interpretable chemical identification on organic and inorganic materials.

Which Bruker nanoIR systems enable s-SNOM analysis along with photothermal AFM-IR?

The nanoIR3-s can be used to perform both s-SNOM and photothermal AFM-IR. The system is configured to support both techniques depending on sample and measurement needs.

Configurations that include s-SNOM capabilities enable nanoscale electrical and optical characterization of plasmonics and photonics, and are ideal for use with materials with large dielectric functions that interact strongly with light. The nanoIR3-s system is optionally available with a broadband laser to further extend the accessible spectral range (670 to 4000 cm⁻¹).

Which nanoIR system should I choose for polymer research?

Bruker has designed the IconIR polymer, an IconIR solution specifically to address key needs in polymer research and engineering, offering turn-key correlative mechanical and viscoelastic mapping and photothermal AFM-IR on a 150 mm sample stage.

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