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Nanonics combine AFM-Raman systems are ideal for obaining combined topogrpahical and chemical data of solid state semiconductor devices. These systems have the ability to obtain complementary information simultaneonsly and their unique design gives rise to true intensity comparisons for the first time
A Problem inherent in all confocal microscopes, including Raman, is that of intensity comparisons. Typically when running a scan one begins by focusing the objective on the sample. As the scan proceeds differences in topography of the sample lead to differences in intensity of the Raman signal due to the imaging of air. This is particularly important when the sample is one that has a rough topography. However even if the sample is completely flat it still cannot be mounted without some angle relative to the lens. Nanonics systems use SPM technology to keep the sample stationary relative to the focal point of the Raman beam through Z adjustment.
When an AFM probe is on-line, pixel-by-pixel AFM feedback alters the Z position of the sample surface (sitting on a piezoelectric device or PZT) to the same position no matter what the surface topography is. Thus, the position of the surface of the sample is rigidly controlled relative to the lens within a single nanometer. This leads to “true” Raman intensities, i.e. removes topographical differences and thus allows for the correction of the problem in all confocal microscopes
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Surface topography contributes to out-of-focus effects on resolution
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Online AFM pixel by Pixel adjustment leads to the first true Raman Intensity Imaging by correction of differences due to surface topography. The AFM probe is represented by the green tip |
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AFM topography with Raman mapping at 1525cm-1 (carbon band). Without online AFM, the green arrow areas in the above images bellow would appear as a 2D image without the topographical data. |
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AFM topography with Raman mapping at 1334cm-1 (diamond band). Without online AFM, the green arrow areas in the above images would appear as a 2D image without the topographical data. |
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The Nanonics system uses this set-up to achieve, online- AFM pixel by pixel adjustments yielding true Raman intensity imaging
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Figure.9 shows Raman intensity obtained with AFM feedback (top graph) and without (bottom graph). Intensity of a Raman band, in this case the vibrational mode of diamond at 1334 cm-1 in a carbon film, is entirely different with and without AFM feedback. Rigorous Z feedback is essential for accurate comparisons of Raman intensities
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Diamond film Raman intensities with (top) and without (bottom) AFM feedback. |
Imaging Micro-electronic Devices/Transistors
When silicon is deposited on top of a different substrate where the atoms are spaced farther apart, the atoms in silicon stretch in order to line up with the atoms of the substrate beneath, “stretching” -- or "straining" -- the silicon. In the strained silicon, electrons experience less resistance and flow up to 70 percent faster, which can lead to microchips that are up to 35 percent faster -- without having to shrink the size of the transistors used. Below is a 3D AFM image of a Transistor device. AFM alone does not answer the question of where is the strained silicon and where is the regular silicon in the device?
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| 3D AFM image of Transistor |
Simultaneous AFM and Raman micrscopies allow the introduction of “chemical” mapping to topographic data obtained with AFM. The image below (fig. 19) shows simultaneous Raman and AFM measurements on the above transistor (taken at 520cm-1 and 503 cm-1 respectively), with differences in the shading corresponding to differences between strained and non-strained silicon.
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| Simultaneous AFM and Raman mapping of a transistor. Differences in shade due to Si strain. |
Below are representations of topography and Raman images of silicon wire on a silicon substrate, with an imperfect 8 nm gold film on the substrate. The images were simultaneously obtained using a Nanonics-Renishaw system.
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Left image shows a 3D representation of the topography of a Si wire
on Si substrate, with Au film 8nm thick, while the righthand image
shows Raman mapping of same sample. |
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