Silicon and other silicide’s great optical character provide a new method to integrate optical component on the chip, which is compatible with CMOS. With advanced CMOS process, the waveguide, microdisk, microring and other optical compenent can be reduced to micrometer level.
Microdisk is component that I will focus with in this project. There are two different material disk in my project. One is silicon-based and another is based on silicon nitride which is nonconducting. I will apply several different tech learn in opt 407. Coating process will be applied with silicon nitride mircodisk and SEM, AFM are two microscope I will use to view my sample. Photoshop is the main software to do image process work.
The type of the SEM we used is Zeiss-Leo Dsm982 SEM which is located at Institute of Optics. There are three main steps for this SEM lab(1) prepare for the sample and place it on the stage (2) coat part of the sample with sputter(3)viewing the image of coating and uncoating part under SEM.to view the influence of the charge on the sample, we need to coat part of the sample. First we need to cut the paper into strip which fits with the stage. Then we should affix carefully the strip on the stage to prevent the fingerprints. To prevent the sputter coating the selected area, we should put a strip of copper tape to cover the sample.
During Sputter coating procedure we will apply gold to be the coating material. The stage with the sample is placed at the center of the sputter’s chamber. Before coating procedure, we should pump down the chamber to 1 mTorr and then filled with argon gas for three times. After all those steps, pumping down to 50 mTorr again and increase the cathode current to 15 mA for 60 seconds, which enable the sputter to coat a gold layer of 6 nm on the top of the sample. When the coating process is finished, take out the sample and take off the copper tape. The final step is to smear the nanotube on the edge of the sample which could ground the sample. After preparation above, we will view the sample in SEM under different condition. Different voltage, 3KeV, 10KeV, 20KeV, of electron gun will be applied to view the sample. The compare among images under different voltage will show the impact of the voltage on the image. Sample with coating and uncoating will both be imaged under same voltage and aperture, which to see the influence of the charging.
All Samples are collected from Prof. Qiang’s group. The main preparation work is coating the sample. silicon nitride is nonconducting which make it difficult to observe under SEM compared with silicon sample. I collect two silicon nitride sample, and coat one of them. Comparing the image with those two sample clearly shows the coating process really increase the spatial resolution.
The signal AFM get is the resonant frequency between the can scanning tip and sample. the frequency will directly connect with the distance between the sample and scanning tip. Short distance will induce low frequency. There are two main mode for AFM to operation, contact mode and semi-contact (tapping) mode. Contact mode is keep the scanning tip in one plain and detect the change in frequency. And the tapping mode is to control the height of cantilever to keep the frequency stable. Compared with contact mode, tapping mode is safer for the cantilever, since it will have less opportunity to touch the bump on the sample. in out lab, we will apply the tapping mode. There are another signal that AFM can catch, tunnel current, whose name is STM. STM count the tunnel current to measure the distance the scanning tip and sample. However STM always not performs as well as AFM. We will apply AFM and tapping mode in our lab.
1. scanning electron microscope
The most part of image are captured by the SEM. I have utilize different operation mode to capture the image. in additon, with the help of photoshop, I have made several image processing work, colorization, adjustment in contrast and brightness. Since due to the postion of different detector, the dittribution of brightness are different.
with short working distance, the contrast caused by the height of the sample would be much higher for inlens detector. photoshop is also a powerful tool to reduce the noise, however it will not increase the signal- noise ratio.
light mircoscope is useful microscope, which has much less requirement for the sample than SEM and AFM. Compared with SEM, light microscope could caputre colorful image, which is the most advantage for light microscope. but due to diffreaction limitation, light microscope couldn't reach very high magnification.
3 atomic force microscope
AFM is a powerful microscopy to capture nanostructure image. with the help of the software, we could get different type image which is more convenient for view the surface structure of the sample. However, AFM could not really 3D image for microdisk. since AFM could get the image from the top of the sample.
4 3D image
I capture two image with SEM and then combine those two to be a 3D image
4 Sputter coating procedure
The iamge clear shows that the coating really increase the image's resolution. There are more detail and micro structure showing on the image for the coating sample