Owing to its high spatial resolution, near-field spectroscopy is a useful method for sensing the stress in a narrow region of submicron order. Here, on the basis of the highly resolved images obtained by near-field luminescence spectroscopy, we propose a statistical method of analyzing grain anisotropy-induced stress in polycrystalline Al 2 O 3 . We focus on two characteristics of a spectra: the intensity ratio and peak shift of luminescence of two lines (R 1 and R 2 ) from Al 2 O 3 to discuss crystal orientation and stress, respectively. By incorporating the concept of the crystal misorientation parameter using intensity ratio, an apparent correlation between the magnitude of stress and the misorientation is found. This correlation analysis provides an important insight for the investigation of local thermal stress in Al 2 O 3 .
To increase the intensity of Raman scattering with surface enhanced Raman scattering (SERS) effect, the authors proposed the triple-walled gold (Au) structures on silicon (Si) substrate. High aspect ratio Au nanowalls with nanogaps were realized by two different techniques. One is layer by layer technique. The other is standing high aspect ratio Au wall fabrication technique. Finally, 50 nm-thick Au standing walls and 50 nm gaps were obtained. Through the comparison of bare Si substrate, Au film, single-walled Au structures, and triple-walled Au structures in SERS intensity with 0.020 wt. % rhodamine 6G molecules, it was revealed that the SERS intensity from triple-walled Au structure was 50 times higher than that from Au film. The enhancement factor (EF) of our proposed SERS chip was estimated as 4.7 × 106. The proposed method will allow us to realize multiwalled Au structure, which can increase EF efficiently.
Raman scattering spectroscopy is one of the method to detect vibrational modes of molecules. These detected modes are applied to determine the chemical bonds and crystal orientations. For over years, surface enhanced Raman scattering (SERS) spectroscopy with strong electromagnetic enhancement has been studied to increase the sensitivity to the vibrational modes. To enhance the SERS effect, we propose the small nano-gaps between noble metals from two-dimensional surface to three-dimensional structure to increase the effective SERS surface area. To realize the small nano-gaps in three-dimensional structure, two types of techniques were applied. One was layer by layer (LbL) fabrication technique and the other was high aspect ratio metallic nano-fin fabrication technique. Through the experimental study with Rhodamine 6G (0.020 wt%), our lamellar-like metallic structures showed 50 times stronger SERS intensity compared to a bare gold film.
The luminescence spectroscopy of Al 2 O 3 is widely used for sensing the stress in Al 2 O 3based materials. One promising approach that improves the spatial resolution of luminescence spectroscopy is the use of a near-field optical system, which is effective for assessing the localized stress in nano/microsize structural components. Here, we perform the spectral analysis of near-field excited luminescence for stressed Al 2 O 3 , which shows an abnormal asymmetry in line shape, which is not observed in a conventional far-field measurement. For analysis, we employ two models that include different effects. The model of stress-gradientbased spectrum broadening fails to account for the asymmetry of the luminescence spectrum. In contrast, the model including vibronic state transition yields good matching of the measured spectrum line shape, indicating that the electron-phonon coupling in Al 2 O 3 affects the appearance of the asymmetric line shape. The magnitude of electron-phonon interaction as well as the effect of the excitation method on the line shape are discussed.
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