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  • Instrument Improves IR Spectroscopy by Factor of 100
May 2011
SAN SEBASTIÁN, Spain, May 11, 2011 — A novel instrument records infrared spectra using a thermal source to gain a resolution 100 times better than conventional IR spectroscopy. The technique could be used to analyze the chemical compositions and structures of nanoscale materials in polymer composites, semiconductor devices, minerals or biological tissue.

An IR spectrum commonly is used as a material’s “fingerprint,” and IR spectroscopy thus has become an important tool for characterizing and identifying materials. However, with conventional optical instruments such as Fourier-transform IR spectrometers, the light cannot be focused to spot sizes below several micrometers. This fundamental limitation prevents IR-spectroscopic mapping of single nanoparticles, molecules or modern semiconductor devices.

Using the setup shown here, IR nanospectroscopy uses a thermal source to gain highly localized IR spectra with a spatial resolution >100 nm. The displayed graph shows IR spectra of differently processed oxides in an industrial semiconductor device. (Image: Florian Huth, CIC nanoGUNE)

Researchers from the Basque nanoscience research center CIC nanoGUNE and from Neaspec GmbH in Martinsried, Germany, developed the new IR spectrometer, which allows nanoscale imaging with thermal radiation. The setup is based on a scattering-type near-field microscope that uses a sharp metallic tip to scan the topography of a sample surface. While scanning the surface, the tip is illuminated with the IR light from a thermal source. Acting like an antenna, the tip converts the incident light into a nanoscale IR spot (nanofocus) at the tip apex. By analyzing the scattered IR light with a specially designed FTIR spectrometer, the researchers recorded IR spectra from ultrasmall sample volumes.

In their experiments, the investigators managed to record IR images of a semiconductor device from Munich-based Infineon Technologies AG. “We achieved a spatial resolution better than 100 nm. This directly shows that thermal radiation can be focused to a spot size that is hundred times smaller than in conventional infrared spectroscopy,” said Florian Huth, who performed the experiments. The researcher demonstrated that nano-FTIR can be applied for recognizing differently processed silicon oxides or for measuring the local electron density within complex industrial electronic devices.

“Our technique allows for recording spectra in the near- to far-infrared spectral range. This is an essential feature for analyzing the chemical composition of unknown nanomaterials,” said Rainer Hillenbrand, leader of the nano-optics group at nanoGUNE.

Nano-FTIR has application potential in widely different sciences and technologies, ranging from the semiconductor industry to nanogeochemistry and astrophysics.

“Based on vibrational fingerprint spectroscopy, it could be applied for nanoscale mapping of chemical composition and structural properties of organic and inorganic nanosystems, including organic semiconductors, solar cells, nanowires, ceramics and minerals,” Huth said.

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infrared spectroscopy
The measurement of the ability of matter to absorb, transmit or reflect infrared radiation and the relating of the resultant data to chemical structure.
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