Measuring the electron mobility of a molecule

[warfreak131]

Hello PF

Let's say I have a device with three layers, A, B, and C, where layers A and C are the anode and cathode.

I can measure the IV curves from that device easily. Now let's say I added a fourth layer, D, in between A and B. Layer D interacts with layer B such that it increases it's conductivity.

So if I measure the IV curves again, I should get an increase in I for a given V. From looking up some equations on mobility, I know I can characterize the mobility as *sigma* = n e *mu*.

Now I would normally say that if I get a doubling of conductivity, I would get a doubling of mobility, but the charge carrier density, n, is different since I added the fourth layer D. So how could I figure out my exact increase in mobility?

 

[rigetFrog]

Is this STM stuff?

Go back to ohms law here. Convert the conductivity (sigma) to resistivity (R) and then add up all the resistivities. You might have to solve a set of 2 or more equations here.

 

[warfreak131]

What I have is a layer of Indium Tin Oxide as the anode, a molecule in between, and gold as the cathode. When I run the IV curve of it, it isn't a linear relationship. The closest way I can approximate the behavior is like sqrt(x) or 1-e^(-x). the slope is constantly changing, so I don't know if I can apply ohms law.

 

[rigetFrog]

Good point. You can't directly apply ohms law. The IV curves you're studying intimately depend on the electronic structure and material interface, so you might have to dive down the rabbit hole here, and really develop an understanding of electronic structure.

You may still be able to apply ohms law at specific points along the IV curve by Taylor expanding the resistances about a specific voltage there. Doing this for all voltages will give you a hodge podge of approximations as opposed to one nice equation, though.

 

[sardar]

I would approach this problem by first understanding the concept of electron mobility. Electron mobility is a measure of how quickly an electron can move through a material under the influence of an electric field. It is affected by various factors such as the structure of the molecule, temperature, and the presence of impurities.

In this scenario, the addition of layer D has increased the conductivity of the device, which suggests that the mobility of electrons has also increased. To accurately measure the electron mobility, we need to first determine the charge carrier density (n) in the device. This can be done by measuring the current (I) and voltage (V) in the device and using the equation n=eI/AV, where e is the charge of an electron and A is the area of the device.

Once we have determined the charge carrier density, we can use the equation *sigma* = n e *mu* to calculate the electron mobility (*mu*) of the molecule. By comparing the IV curves before and after adding layer D, we can determine the increase in conductivity and use that to calculate the increase in electron mobility.

It is important to note that electron mobility is not a fixed value and can vary depending on the conditions. Therefore, it is essential to carefully control and measure all the factors that can affect it, such as temperature and impurities, to accurately determine the electron mobility of a molecule.

In conclusion, to measure the electron mobility of a molecule in this scenario, we would need to measure the IV curves, determine the charge carrier density, and use the equation *sigma* = n e *mu* to calculate the electron mobility. Additionally, we would need to carefully control and measure all the factors that can affect the mobility to get an accurate measurement.