A How can I understand 4-point-measurements?

Hello,

I've got some questions about a four-point measurement method. So first just consider we have a combination of 4 layers: on top an insulator like Slizium, than a heavy metal, that is conducting, than a ferromagnet that is also conducting and than another insulating sheet like glass or something:
1. How the hell can even, if you take your first 2 probes on top of the layer, a current go through the first Silizium layer? It is insulating...how is that possible?
2. If i have like here more than one sheet which is conducting, i can only say something about it if i know the other conducting properties of one layer from another experiement right?
3. Does somebody know where i can find a good describtion of the resistivity of more than one layer? With the correctionfactors and so on?
 

ZapperZ

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Hello,

I've got some questions about a four-point measurement method. So first just consider we have a combination of 4 layers: on top an insulator like Slizium, than a heavy metal, that is conducting, than a ferromagnet that is also conducting and than another insulating sheet like glass or something:
1. How the hell can even, if you take your first 2 probes on top of the layer, a current go through the first Silizium layer? It is insulating...how is that possible?
2. If i have like here more than one sheet which is conducting, i can only say something about it if i know the other conducting properties of one layer from another experiement right?
3. Does somebody know where i can find a good describtion of the resistivity of more than one layer? With the correctionfactors and so on?
First of all, you need to realize that you should have been using the word "then" rather than "than". It confused me in the beginning when I read your post on the first pass!

Secondly, you never explain whether you understand 4-point measurement under a general case in the first place. Do you?

Thirdly, what are you trying to measure here? The I-V characteristics of the entire layer?

Finally, what is this structure? I have made a similar measurement with an insulating layer in between, but this is to measure the tunneling current on a planar junction. So the fact that there is an insulating layer in between doesn't mean that there isn't a way in hell that current can't be measured through it. But I'll never know because you neglected to completely describe the nature of this structure.

Zz.
 
Hello

1. Sorry for that, i will see if i can change it haha.
2. I was thinking about to mention that but yes, in general (i think so) i understand the 4-point measurement technique. Its just a method, you put 2 probes on your surface, the outer ones and 2 inner ones, that measure the voltage drop. the current will flow through everything, more or less depends on the resistivity. What you mean with "the first case"?
3. I measured the resistance of the sample, but from which layer is a good question which i dont know either. Thats the reason im asking. i just put the four "nadles" on top and the Voltage-meter gives me a value, which i noted.
Im convinced or i think that the apperature gives the me total value of the resistance, so the sum of both. Because nothing else make sense for me.
4. I dont really know if that is important but sure i give you the structure: On top as i said is Silizium(2nanometers), oxidized for insulating. the second layer is tungsten (in bcc if that is important, vary in thickness), the third is a combination of Co, Fe and B(3nm), so its the ferromagnet layer. The last one is the substrate MgO(really thick), also insulating.

I though about tunneljunction but i dont really know if milli Ampere are able to give me a strong current flow.
Is there another way or why you asking about the structure?
 

ZapperZ

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Hello

1. Sorry for that, i will see if i can change it haha.
2. I was thinking about to mention that but yes, in general (i think so) i understand the 4-point measurement technique. Its just a method, you put 2 probes on your surface, the outer ones and 2 inner ones, that measure the voltage drop. the current will flow through everything, more or less depends on the resistivity. What you mean with "the first case"?
3. I measured the resistance of the sample, but from which layer is a good question which i dont know either. Thats the reason im asking. i just put the four "nadles" on top and the Voltage-meter gives me a value, which i noted.
Im convinced or i think that the apperature gives the me total value of the resistance, so the sum of both. Because nothing else make sense for me.
4. I dont really know if that is important but sure i give you the structure: On top as i said is Silizium(2nanometers), oxidized for insulating. the second layer is tungsten (in bcc if that is important, vary in thickness), the third is a combination of Co, Fe and B(3nm), so its the ferromagnet layer. The last one is the substrate MgO(really thick), also insulating.

I though about tunneljunction but i dont really know if milli Ampere are able to give me a strong current flow.
Is there another way or why you asking about the structure?
I'm asking about the structure because it tells me the thickness and the quality of the layers. How certain are you that you have a uniform layer without any pits or holes? 2 nm and 3 nm are very thin. Have you looked at the SEM image of each of the layer to figure out not just the morphology but also uniformity of the thickness?

I too, have made an oxide layer as my insulating layer. In fact, that was how I made my NbO insulating layer, but exposing it to oxygen for a short period of time. So such thicknesses can exhibit tunneling effects.

Next, where exactly are you placing all the electrodes? How are the edges of this structure made? In cuprate superconductors, one of the most tedious thing to do is to measure the c-axis resistivity of the sample, because depending on how the material was made and prepared, the edges of the crystal can affect the measurement.

There are a lot of things still unknown here.

Zz.
 
I'm asking about the structure because it tells me the thickness and the quality of the layers. How certain are you that you have a uniform layer without any pits or holes? 2 nm and 3 nm are very thin. Have you looked at the SEM image of each of the layer to figure out not just the morphology but also uniformity of the thickness?
Eeeehhhmmm you meant an electronic picture??? Ehm no i just made some diffraction pictures, for example i take a view on the layer thickness a XRR measurement. For me and the professor that image looks normal, meaning its quiet uniform.

Next, where exactly are you placing all the electrodes? How are the edges of this structure made? In cuprate superconductors, one of the most tedious thing to do is to measure the c-axis resistivity of the sample, because depending on how the material was made and prepared, the edges of the crystal can affect the measurement.
First i should say that my aim has nothing to do with superconducting, its something about the spin hall conductivity in tungsten, but i think you just said that cause its a nice background information.
Puhh, as long as i can renember it was an in-line position of the probes, the sample was fixed and the four in-lie probes just got on top of the silizium layer and then you saw a value...im not so sure if i used a multimeter to see the value but i think im not.
About the edges i have no information, it was just like a square formation of the sample with a very thin z component, the thickness of the whole thing i meant. Im sure i shoudnt really care about the edges.
 

ZapperZ

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Eeeehhhmmm you meant an electronic picture??? Ehm no i just made some diffraction pictures, for example i take a view on the layer thickness a XRR measurement. For me and the professor that image looks normal, meaning its quiet uniform.
No. SEM image doesn't give you an "electronic picture". It does, however, tells you if your film is rough, flat, have holes, etc... Does "XXR" measurement tell you those?

First i should say that my aim has nothing to do with superconducting, its something about the spin hall conductivity in tungsten, but i think you just said that cause its a nice background information.
It wasn't meant as background information. It was meant to tell you that at such insulator thicknesses, tunneling is possible!

Puhh, as long as i can renember it was an in-line position of the probes, the sample was fixed and the four in-lie probes just got on top of the silizium layer and then you saw a value...im not so sure if i used a multimeter to see the value but i think im not.
About the edges i have no information, it was just like a square formation of the sample with a very thin z component, the thickness of the whole thing i meant. Im sure i shoudnt really care about the edges.
In other words, you can't do an I-V scan, which is too bad. This might tell you if the current is ohmic or that it is a tunnel currrent.

Have you ever considered that a picture of it might help me understand MORE of what this looks like?

Zz.
 
No. SEM image doesn't give you an "electronic picture". It does, however, tells you if your film is rough, flat, have holes, etc... Does "XXR" measurement tell you those?
Yeah, XRR tells you something about roughness, i dont know what you meant with SEM or what does it gives you more or less an information, but XRR is way to see how unity is the structure.
In other words, you can't do an I-V scan, which is too bad. This might tell you if the current is ohmic or that it is a tunnel currrent.
What is an I-V Scan?
Have you ever considered that a picture of it might help me understand MORE of what this looks like?
You meant a picture of the sample structure or of the measurement technique? Well i dont really have one (yet) of both, i can try to make one of the sample, i will put one of the sample with the 4-point technique (on the picture is the a thin wafer instead of an insulator layer, but dont mind that).
 

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