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25 September 2007 Characterization of localized strain of crystals in nano-scale by tip-enhanced Raman spectroscope and microscope
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Strained silicon (ε-Si), the fundamental material of integrated circuit, is finding tremendous attention not only because it boosts the speed but also reduces the power consumptions of electronic devices. Carrier mobility in a ε-Si thin layer is enhanced compared to unstrained layers. However, strain distribution in ε-Si layers is inhomogeneous in the nano-scale, which can degrade performance of electronic devices. Raman spectroscopy can be used to study strain fluctuations in silicon because the optical phonons in Raman spectra are strongly influenced by strain. Though silicon are Raman active devices, the Raman efficiency of a nanometer layer of strained silicon is extremely weak and is often eclipsed under the Raman scattering of underlying buffer substrates. Here, we utilized surface enhancement in Raman scattering to overcome weak emission problems and to suppress averaging effect. Thin ε-Si layers were covered with thin silver layer to invoke surface enhanced Raman spectroscopy. This technique is promising but it lacks the spatial resolution in the nano-scale due to diffraction limit from the probing light. In order to achieve nano-scale spectroscopy, point-surface-enhancement was used, rather than a large surface enhancement. We used a silver-coated sharp tip, just like SERS, but only the sample region very close to the tip apex is characterized. This technique, known as the tipenhanced Raman spectroscopy, provides nanometric resolution in our measurement. For further improvement of SNR, we introduce several approaches mainly for the suppression of background signals arising from crystalline bulk materials. The characterization techniques describe above is applicable to other nano-materials.
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Norihiko Hayazawa, Masashi Motohashi, Yuika Saito, and Satoshi Kawata "Characterization of localized strain of crystals in nano-scale by tip-enhanced Raman spectroscope and microscope", Proc. SPIE 6769, Nanosensing: Materials, Devices, and Systems III, 67690P (25 September 2007);


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