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Infrared-spectroscopic nanoimaging with a thermal source


Fourier-transform infrared (FTIR) spectroscopy1 is a widely used analytical tool for chemical identification of inorganic, organic and biomedical materials2, as well as for exploring conduction phenomena3. Because of the diffraction limit, however, conventional FTIR cannot be applied for nanoscale imaging. Here we demonstrate a novel FTIR system that allows for infrared-spectroscopic nanoimaging of dielectric properties (nano-FTIR). Based on superfocusing4,5 of thermal radiation with an infrared antenna4,6, detection of the scattered light, and strong signal enhancement employing an asymmetric7 FTIR spectrometer, we improve the spatial resolution of conventional infrared spectroscopy by more than two orders of magnitude. By mapping a semiconductor device, we demonstrate spectroscopic identification of silicon oxides and quantification of the free-carrier concentration in doped Si regions with a spatial resolution better than 100 nm. We envisage nano-FTIR becoming a powerful tool for chemical identification of nanomaterials, as well as for quantitative and contact-free measurement of the local free-carrier concentration and mobility in doped nanostructures.

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Figure 1: Near-field spectroscopy with a thermal source.
Figure 2: Nanoimaging and spectroscopy of a polished cross-section of a semiconductor device with a thermal source.
Figure 3: Spectroscopic nanoimaging with a thermal source.
Figure 4: Application of nano-FTIR for detection of chemically different silicon oxides and for determination of the local free-carrier concentration in doping gradients.


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We thank A. Huber (Neaspec GmbH, Martinsried) for discussions. The work has been supported by the ERC within the programme ‘Ideas’ under grant agreement no. ERC-2010-StG-258461 and the National Project MAT2009-08393 from the Spanish Ministerio de Ciencia e Innovacion. M.S. acknowledges financial support from ‘Programa de Formación de Personal Investigador’ promoted by the Department of Education, Universities and Research of the Basque Government.

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F.H., N.O. and R.H. designed the experiments. F.H. implemented and performed the experiments, analysed the data and performed calculations. N.O. performed calculations and contributed to the data analysis. F.H., N.O. and R.H. discussed the results. M.S. contributed to the experiments and the data analysis. J.W. prepared the sample. F.H. and R.H. wrote the paper with the support of M.S. and N.O.

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Correspondence to R. Hillenbrand.

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The authors declare no competing financial interests.

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Huth, F., Schnell, M., Wittborn, J. et al. Infrared-spectroscopic nanoimaging with a thermal source. Nature Mater 10, 352–356 (2011).

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