He is an outstanding student who made a lot of impressive work.
One of his previous work named "Surface Potentials and Layer Charge Distributions in Few-Layer Graphene Films" is an important reference for my KPM study.
When I found his website and blog, I am so excited because he also shared the idea and comments about scientific research just like me.
And I asked him some questions about the article I just mentioned, and I listed them as follows:
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(1) You mentioned that the surface potential of few layer graphene(FLGs) on SiO2 substrate is always positive, indicating hole doping in ambient.
But what about single layer graphene?
In our experiments, they sometimes exhibit higher potential than surrounding silica but sometimes lower than that. Could such variation be an evidence for doping tendency?
(2) The surface potential of FLGs increases with film thickness and approach to a finite value is resulted from "interlayer screening".
Is that means each graphene layer can "feel" positive charges on the bottom layer which is strongly doped by holes from silica?
And will each layer redistribute the electron density to adapt the positive surface charges of the bottom layer?
If the bottom layer is doped by negative electrons, instead of holes. Would it be possible that the potential of FLGs may decrease with layer thickness, or it still increases with film thickness?
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Surprisingly, he replied me very fast !
In spite of some unanswered questions, I’m so grateful to him!
Showing posts with label Notes. Show all posts
Showing posts with label Notes. Show all posts
Can we exfoliate graphene with the aid of solution?
The most common preparation of graphene is to exfoliate the graphite with scotch tape.
On the other hand, the researchers try to seek an alternative way to exfoliate the graphite stacks, that is, using various kinds of solvent to intercalate the graphite and exfoliate the stacks.
The most representational work is
Since the experiments in this paper seems to be relatively simple. I made a test immediately.
The solvent I chose is NMP (N-Methyl-2-pyrrolidone) which is the best solvent they concluded.
The mechanism is easily comprehended by the solvent-graphene interaction, but the main problem is that NMP is hard to evaporate in ambient condition. It can only be removed in vacuum with heat assistance.
After drying the solvent, the graphene flakes is so small to the extent that are difficult to process.
Meanwhile, something came to my mind, can we exfoliate the graphene sheets by similar technique used for dispersing CNT bundle?
So I test this idea with a surfactant called NaDDBS (sodium dodecylbenzenesulfonate) which were used in our previous study of CNT-FET biosensor. The results is better, I was so happy with that !
Immediately, I searched the literature to see whether it has been published or not....
And then.......I found this one.....
I was so depressed about it..............
It was too late, they already published their work in Feb, 2009.
The early bird catches the worm.......
Raman spectroscopy in our lab again !!
In fact, we have a confocal Raman system in the lab already, but the alignment is completely lost...
In order to dealing with our new baby--graphene, I told to my boss that I want to refurbish the previous Raman system in the lab. Since it is has long fallen into disuse. And once again, I gave myself a challenge, just like the previous work in redesigning the CVD system.
But I have to say this is definitely a wearing job to save this old Raman system.
The confocal Raman system has several parts, laser, confocal microscope, spectrometer, CCD, the most difficult task is how to adjust the laser spot and make it align to the identical light path of signal from sample. I spent almost two weeks adjusting a small piece of filter, namely "notch filter" which is an essential part of confocal Raman system. This small filter is responsible for filtering out the original laser signal from the reflected Raman signal of sample. Even the most subtle adjustment of this filter could lead to significant change in the position of light spot. That's why no one in the lab want to solve this thorny problem!
Anyway, through this experience of refurbishing our old Raman system, I have learned the alignment of optical path, and the basic sense of the optical component as well. After about 1 month wearing job of alignment, the Raman started to work normally with graphene.
Graphene Times !?
Incredibly, I found a website named "Graphene Times"!!
The guy who built this website is almost doing the same thing as me!!
But, the difference is that I catch the RSS feeds with a software called "Newsfire" (Mac only). NewFire is the best RSS reader I ever used, since it has the major and most important function -- filter. The filter just as the name implies, it filters out the unwanted and huge amount of RSS feeds except the keyword I set, for example, graphene as a keyword. With the help of filter in NewsFire, I can easily follow the newest publication related to graphene which were just updated in each journal website all around the world.
In comparison with "Graphene Times", my solution is even better, because the number of journal I monitored is more than he did, in addition, I could set more keywords to seek more research combination with graphene.
Substrate engineering of graphene?
I always think that the substrate has enormous effect on the graphene.
It is not difficult to imagine because the vast area of graphene have contacted with substrate, and the substrate has long been considered as major source of charge impurities. (though no one knows where they came from)The clues can be found from the previous work done by Andrei group in Rutgers, they reported that they could approach ballistic transport by suspending the graphene and measured the highest mobility ever in low-temperature about 200,000 cm2/ Vs.
http://www.nature.com/nnano/journal/v3/n8/full/nnano.2008.199.html
And the work related to Raman Spectroscopy
http://pubs.acs.org/doi/abs/10.1021/nn900130g
And the work that focus on the doping effect of the substrate
http://prb.aps.org/abstract/PRB/v79/i11/e115402
Since the previous work I focused is the surface modification of silica surface.
One of the various kinds modification I did is that I capped the silanol groups with HMDS which make silica to be hydrophobic.
And I analyzed the sensing signal change when I injected the buffer with stepwise concentration.
I found that the influence of surface silanol groups is quite important, since they are greatly responsible for the surface potential change in SiNW-FET biosensor. Moreover, I think the ionic behavior is quite different when we replaced the surface groups or capped them.
So, a question has now appeared--
If the so called "charge impurity" mainly came from the ions or ion-like molecules that associated with substrate, what would happen if I capped the surface silanol groups of SiO2 substrate with trimethylsilane?
I think it would be better, at least the mobility should increase, since the ion-like charge impurities would reduce the amount of them which associated with silica prior to the graphene attaching.
Can graphene quench the light from FITC?
I found that when I try to excite an FITC-tag protein linked to graphene with blue light, it seems graphene quench the light every time. No matter how many times I tried, it still became the darkest one on the screen. In order to find the answers, I've searched the literature and only found these two.
http://link.aip.org/link/JCPSA6/v130/i8/p086101/s1http://link.aip.org/link/JCPSA6/v129/i5/p054703/s1
I also repeated this experiment with almost identical condition simply by replacing graphene with CNT.
The results is quite different from graphene, it emitted green light normally.
But I think this may be due to some of CNTs are semiconductor which would not quench the light so effectly whereas the metallic one would do.
Maybe graphene behaves just like a metal, since the metal marks in the surrounding area were able to quench all the light as well.
But, what would happen if we put the FITC-tag protein on the top of the GO?
GO should have a band gap due the disruption of the π network, but it seems to depend on some specially distributed oxidized sites to open the "gap". I believe that one day the GO will be a band gap controllable materials in the future, but now, still long way to go.