Atomic Force Microscopy (AFM)

On Monday we worked with the Atomic Force Microscope (AFM). This microscope (seen with the beautiful model to the right) has the ability to create a topographic map (in both 2-D & 3-D) of two of the ZnO thin film samples Jennifer and I created. It does the measurements by running the tip over the sample. The area that is actually measure is 15nmx15nm (for those of you that are not scientists, 15nm=0.000000015mm (remember that 1mm is the thickness of your fingernail), so basically it is really, really, really small...how about that!?!?!). The tip that does the readings is, in a perfect world, only 1 atom thick (Yeah, try and wrap your head around that!...Not literally!)

To the left is an example of what our ZnO deposition looks like (it's the orange part of the screen). The samples which we did reading on were created at -0.9V and -1.0V. The roughness and the mean grain size measurements were the pieces of data used to make a comparison. The roughness of the sample is relevant to the conductivity of the sample (i.e. the smoother the sample=better conduction). The mean grain size measurement is used to determine the average diameter of the grains, also for the conductivity of the sample (i.e. larger grain size= better conductivity).

After using the AFM, we proceeded to place the samples into a "oven" (seen above) to cook at 350 degrees Celcius for 2 hours (remember, water boils at 100 degrees celcius). This process is called aneiling. The purpose of doing this is to remove any water gas that could be trapped in the sample.

Today, we used the AFM on those same sample (seen me to the left removing the sample after testing). The -0.9V sample's roughness remained the same and the mean grain size decreased. This is possibly due to the large grains reducing to two particles. The -1.0V sample, which had many cracks in it due to the aneiling, had a more homogenous roughness and the mean grain size doubled. This is possibly due to the tall grains flattening out due to the aneiling process. Tomorrow we are going to test the semi-conductive properties of the thin films.